Because high-index facets (HIFs) possess high surface energy, the metal nanoparticles enclosed with HIFs are eliminated during their growth in a conventional shape-controlled synthesis due to the thermodynamics that drives the particles minimizing their total surface energy. This study develops a double-step potential method to prepare an unprecedentedly stellated Au nanocrystals (NCs) bounded by high-index {711} and {331} facets in deep eutectic solvent (DES) medium. The formation of Au NCs bounded by HIFs was systematically studied. It has demonstrated that the shapes of Au NCs are strongly dependent on the size of seeds and the growth potentials as well as the urea adsorbates in the DES. By adjusting the size of seeds and the growth potentials, the stellated Au NCs can be transformed into concave hexoctahedra (HOH) with high-index {421} facets and concave trisoctahedra (TOH) with high-index {991} facets. The electrocatalytic activities of the as-prepared Au NCs are evaluated by glucose oxidation. Thanks to HIFs having high density of atomic steps and kinks, the stellated, TOH, and HOH Au NCs exhibit higher electrocatalytic activity than that of the polycrystalline Au electrode, demonstrating that the steps and kinks serve as the active sites and play an important role in glucose electro-oxidation.

In order to maximize the Pt utilization in catalysts and improve catalytic processes, we report a convenient strategy for preparation of Pt3Co with Pt-skin structured bimetallic nanocatalysts directly supported on porous graphitic carbon. Notably, the thickness of the Pt-skin is only 1–2 atomic layers, about 0.5 nm. Surprisingly, the bimetallic nanocatalysts composed of Pt3Co with Pt-skin are first used as ethanol electro-catalysts, with the mass activity of 0.79 mA μgPt–1, which is a 250% enhancement compared with commercial Pt/C (0.32 mA μgPt–1). On the basis of the results of electrochemical in situ Fourier transform infrared spectroscopy (FTIRS) and density functional theory (DFT), a new ethanol electro-oxidation enhancement mechanism is proposed in which Pt3Co with Pt-skin promotes partial oxidation of ethanol over C–C bond cleavage, thereby resulting in higher CH3COOH production than CO2 production.Keywords: DFT; ethanol electro-oxidation; in situ FTIRS; Pt-skin; Pt3Co bimetallic;

Pyrolyzed Fe/N/C is one of the most promising non-precious-metal catalysts for the oxygen reduction reaction (ORR), which is supposed to boost the commercialization of proton exchange membrane fuel cells (PEMFC). However, the nature of the active sites of Fe/N/C is not clear and has long been debated. The challenges mainly come from highly heterogeneous structures formed during the pyrolysis process as well as no suitable surface probes. To elucidate the active sites, the most effective approach is building well-defined model catalysts as single-crystal planes in surface sciences. Herein, we designed a single-atomic-layer Fe/N/C model catalyst based on monolayer graphene (FeN-MLG) to explore the active sites. The model catalyst was prepared by 950 °C heat treatment of graphene with controlled defects under an FeCl3(g)/NH3 atmosphere. The as-prepared model catalyst exhibits ORR activity and SCN– suppressive effect comparable to those of normal nanoparticle-like Fe/N/C catalysts, indicating that active sites are successfully created in the model catalyst. The effect of defect density, the layer number of graphene, and nitrogen species on the ORR activity has been investigated. The main content of nitrogen species on FeN-MLG is Nx-Fe, and quantitative correlation between Nx-Fe and ORR activity demonstrates that Nx-Fe species are the active site of Fe/N/C catalysts. The proposed model catalyst serves to simplify the catalyst structures and to simulate the topmost atomic layer of normal Fe/N/C, where ORR is catalyzed. This model system opens an opportunity to further understand the highly heterogeneous Fe/N/C catalysts.Keywords: active site; iron-based catalysts; model catalysts; monolayer graphene; oxygen reduction reaction;

LiNi0.5Co0.2Mn0.3O2 positive electrode materials of lithium ion battery can release a discharge capacity larger than 200 mAh/g at high potential (>4.30 V). However, its inevitable capacity fading, which is greatly related to the structural evolution, reduces the cycling performance. The origin of this capacity fading is investigated by coupled in situ XRD-PITT-EIS. A new phase of NiMn2O4 is discovered on the surface of the LiNi0.5Co0.2Mn0.3O2 upon charging to high voltage, which blocks Li+ diffusion pathways. Theoretical calculations predict the formation of cubic NiMn2O4. Moreover, corrosion, cracks, and microstress appear to increase the difficulty of Li+ transportation, which are attributed to the protection degradation of the interfacial film on the positive electrode material at high voltage. After 50 electrochemical cycles, the increase in degree of crystal defects by low-angle grain boundary, evidenced through HR-TEM, leads to poor Li+ kinetics, which in turn causes capacity loss. The in situ XRD-PITT-EIS technique can bring multiperspective insights into fading mechanism of the high-voltage positive electrode materials and provide a solution to control or suppress the problem on the basis of structural, kinetic, and electrochemical interfacial understandings.Keywords: capacity fade; high voltage; in situ XRD-PITT-EIS; LiNi0.5Co0.2Mn0.3O2; NiMn2O4;

The reactivity of an electrocatalyst depends strongly on its surface structure. Pt-based electrocatalysts of nanocrystals (NCs) enclosed with high-index facets contain a large density of catalytically active sites formed from step and kink atoms on the facets and exhibit intrinsically superior activity. However, the Pt-based NCs of high-index facets do possess a high surface energy and are thermodynamically metastable, leading to a big challenge in their shape-controlled synthesis. To overcome the challenge, kinetic–thermodynamic control of crystal growth is indispensable and is currently realized mainly by electrochemical methods and surfactant-based wet chemical approaches. This Perspective reviews recent progresses in Pt-based electrocatalysts of monometallic and bimetallic NCs of high surface energy with different morphologies of convex or concave tetrahexahedron, trapezohedron, trisoctahedron, hexoctahedron, etc. Remarkable electrocatalytic performance of these NCs has been demonstrated. Despite the considerable progress already made, the electrocatalysts of NCs with high surface energy still hold significant future opportunities in both fundamental understanding and practical applications.

We have reported, for the first time, in situ growth of high-index {hk0} faceted concave Pt nanocubes on multi-walled carbon nanotubes (CNTs) via an electrochemical method in choline chloride–urea (ChCl–U) based deep eutectic solvents (DESs). Mechanistic studies indicate that a urea hydrogen bond donor (HBD) plays a key role in the formation of concave Pt nanocubes, in which the urea HBD preferentially adsorbs onto the {100} faces and blocks the growth of nanocrystals along the 〈100〉 axis. The as-prepared concave Pt nanocubes are characterized to be enclosed mainly with high-index {710}, {610} and {510} facets. It has been determined that the concave cubic Pt/CNT exhibits higher catalytic activity and stability than the flower-like Pt/CNT and commercial Pt/C catalysts, and this is ascribed to its high density of surface atomic steps and the synergistic effect between the CNT and Pt nanocubes.

Shape transformation of Pt nanocrystals from a {730}-bounded tetrahexahedron into a {310}-bounded truncated ditetragonal prism was achieved using the electrochemical square-wave potential method. The transformation process and mechanism were revealed. This study provides new insight into the nanocrystal growth habit.

Pyrolyzed Fe/N/C, a promising nonprecious-metal catalyst for oxygen reduction reaction (ORR), usually relies on abundant micropores, which can host a large amount of active sites. However, microporous structure suffers from severe water flooding to break the triple-phase interface where ORR occurs, especially in a direct methanol fuel cell (DMFC) fed with liquid fuel. Current studies about the fabrication of a triple-phase interface are mainly limited on a Pt/C catalyst layer, where mesopores and macropores are concerned. Here, we successfully constructed a triple-phase interface in micropores of Fe/N/C catalysts by controlling the distribution of a hydrophobic additive, dimethyl silicon oil (DMS), just partially penetrating into the micropores. The elaborately constructed Fe/N/C-based DMFC can deliver high power density (102 and 130 mW cm–2 at 60 and 80 °C, respectively) and durability comparable to that of Pt/C-based DMFC. This study presents a new avenue to engineer catalyst microporous channels to boost the performance of nonprecious-metal catalysts for fuel cells.

•Facile synthesis of 2D-Co-Ni mixed MOFs by electrodeposition.•In-situ growth of metal oxide anchored carbon matrix on Ni foam.•The achieved 2D-CMO electrode exhibits excellent rate performance with high mass loading.•This approach is expected to be a universal strategy for in-situ growth of metal oxide anchored carbon matrix electrodes.Despite the significant advances in preparing carbon-metal oxide composite electrodes, strategies for seamless interconnecting of these two materials without using binders are still scarce. Herein we design a novel method for in situ synthesis of porous 2D-layered carbon–metal oxide composite electrode. Firstly, 2D-layered Ni-Co mixed metal-organic frameworks (MOFs) are deposited directly on nickel foam by anodic electrodeposition. Subsequent pyrolysis and activation procedure lead to the formation of carbon–metal oxides composite electrodes. Even with an ultrahigh mass loading of 13.4 mg cm−2, the as-prepared electrodes exhibit a superior rate performance of 93% (from 1 to 20 mA cm−2), high capacitance (2098 mF cm−2 at a current density of 1 mA cm−2), low resistance and excellent cycling stability, making them promising candidates for practical supercapacitor application. As a proof of concept, several MOF derived electrodes with different metal sources have also been prepared successfully via the same route, demonstrating the versatility of the proposed method for the preparation of binder-free carbon–metal oxide composite electrodes for electrochemical devices.A novel 2D carbon−metal oxide composite electrode was prepared by four steps and demonstrated as promising binder-free electrode materials for supercapacitors with ultrahigh rate performance of 93% (from 1 to 20 mA cm−2) and high mass loading (13.4 mg cm−2). Moreover, this new general strategy is also expected to facilitate the synthesis of carbon–metal oxide composite electrodes for other electrochemical devices.

Doped nanocarbon materials (e.g., carbon nanotubes, graphene) are considered as effective electrocatalyst supports for fuel cells, and their electrochemical properties are closely related to the synthetic methods and the types of doping elements. In the current paper, we report a novel approach to synthesize sulfur-doped multi-walled carbon nanotubes (S-MWCNTs) as a highly efficient support material for Pt nanoparticle catalysts. The S-MWCNTs are obtained by annealing poly(3,4-ethylenedioxythiophene) (PEDOT) functionalized multi-walled carbon nanotubes at 800 °C. The prepared nanohybrids were physically characterized by Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). It has been found that the doping of sulfur into MWCNTs could significantly improve the dispersion of supported Pt nanoparticles of 2.37 nm in size and increase the electrochemically active surface area (ECSA, 161.4 m2 g−1). The doped sulfur atoms not only provide uniformly dispersed anchoring sites for the deposition of Pt nanoparticles on the surface of MWCNTs but also enhance the electron transfer interaction between Pt nanoparticles and the S-MWCNT support. The electrochemical properties of the catalysts were evaluated by using cyclic voltammetry (CV) and chronoamperometry (CA) techniques. The results demonstrate that the as-prepared Pt/S-MWCNTs exhibit much higher electrocatalytic activity, long-term durability and CO-tolerance ability for the methanol oxidation reaction (MOR) compared to the undoped MWCNT supported Pt and commercial Pt/C catalysts.

In this work, we have studied methanol oxidation mechanisms on RuO2(100) by using density functional theory (DFT) calculations and ab initio molecular dynamics (MD) simulations with some explicit interfacial water molecules. The overall mechanisms are identified as: CH3OH* → CH3O* → HCHO* → HCH(OH)2* → HCHOOH* → HCOOH* → mono-HCOO* → CO2*, without CO formation. This study provides a theoretical insight into C1 molecule oxidation mechanisms at atomic levels on metal oxide surfaces under an aqueous environment.

•CO2 electroreduction mechanisms on a porphyrin-like FeN4 site were investigated.•CO2 adsorption through one electron transfer was the initial step.•CO desorption is the rate-limiting step.•Decreasing the CO adsorption energy may boost the catalytic performance.Experiments have found that the porphyrin-like FeN4 site in Fe-N-C materials is highly efficient for the electrochemical reduction of CO2 into CO. In this work, we investigated the reduction mechanisms on FeN4 embedded graphene layer catalyst with some explicit water molecules by combining the constrained ab initio molecular dynamics simulations and thermodynamic integrations. The reaction free energy and electron transfer in each elementary step were identified. The initial CO2 activation was identified to go through the first electron transfer to form adsorbed CO2− anion and the CO desorption was the rate limiting step in the overall catalytic cycle.Download high-res image (70KB)Download full-size image

•Free energy profiles for CH4 production via the proton-electron transfer were presented.•C atoms in CHx* were negatively charged, allowing to react with protons directly.•CH4 production in CO2 electroreduction differs from that in heterogeneous catalysis.In electrocatalysis, there are two mechanisms for hydrogenation reactions: Heyrovsky mechanism via the proton-electron transfer and Tafel mechanism via surface coupling with adsorbed hydrogen. In CO/CO2 electroreduction over copper catalysts, CH4 is a final product from the subsequent hydrogenation of carbon. In this work, by performing the constrained ab initio molecular dynamics simulations, we firstly identify that CH4 production on Cu(100) via the proton-electron transfer is more kinetically favored than via surface coupling, due to the negatively charged C atoms in CHx*. Our findings highlight the significance of proton-electron transfer in CO2 electroreduction, and help understand the essential difference between electrocatalysis and heterogeneous catalysis.Download high-res image (134KB)Download full-size image

•Microsphere, microrod, nanoplate, and irregular structured Li1.2Mn0.56Co0.12Ni0.12O2 (LLO) are synthesized.•The relationship between the morphologies and electrochemical properties of LLO are investigated.•Porous LLO microrods exhibit the best performance.•The prominent performance of LLO microrods arises from the synergistic effect of 1D shape and porous hierarchical structure.Rational and precise control of the structure and dimension of electrode materials is an efficient way to improve their electrochemical performance. In this work, solvothermal or co-precipitation method is used to synthesize lithium-rich layered oxide materials of Li1.2Mn0.56Co0.12Ni0.12O2 (LLO) with various morphologies and structures, including microspheres, microrods, nanoplates, and irregular nanoparticles. These materials exhibit strong structure-dependent electrochemical properties. The porous hierarchical structured LLO microrods exhibit the best performance, delivering a discharge capacity of 264.6 mAh g−1 at 0.5 C with over 91% retention after 100 cycles. At a high rate of 5 C, a high discharge capacity of 173.6 mAh g−1 can be achieved. This work reveals the relationship between the morphologies and electrochemical properties of LLO cathode materials, and provides a feasible approach to fabricating robust and high-performance electrode materials for lithium-ion batteries.Download high-res image (307KB)Download full-size image

•Typical extended Pt-based surface for ORR is overviewed.•The improvement of ORR activity and corresponding origin are discussed.•The strategies of enhanced stability of Pt-based catalysts are summarized.The structural sensitivity is one of the major themes in electrocatalysis, and it is now well established that the reaction rate of oxygen reduction reaction (ORR) on Pt-based catalysts depends strongly on the surface structure. This paper presents a brief overview of insights of surface structure effects of Pt-based catalysts for ORR. We first introduce some typical extended Pt-based surface and then focus on Pt-based nanoparticles in both ORR activity and stability.

The performance of nanomaterials in electrochemical energy conversion (fuel cells) and storage (secondary batteries) strongly depends on the nature of their surfaces. Designing the structure of electrode materials is the key approach to achieving better performance. Metal or metal oxide nanocrystals (NCs) with high-energy surfaces and open surface structures have attained significant attention in the past decade since such features possess intrinsically exceptional properties. However, they are thermodynamically metastable, resulting in a huge challenge in their shape-controlled synthesis. The tuning of material structure, design, and performance on the nanoscale for electrochemical energy conversion and storage has attracted extended attention over the past few years. In this Account, recent progress made in shape-controlled synthesis of nanomaterials with high-energy surfaces and open surface structures using both electrochemical methods and surfactant-based wet chemical route are reviewed.In fuel cells, the most important catalytic materials are Pt and Pd and their NCs with high-energy surfaces of convex or concave morphology. These exhibit remarkable activity toward electrooxidation of small organic molecules, such as formic acid, methanol, and ethanol and so on. In practical applications, the successful synthesis of Pt NCs with high-energy surfaces of small sizes (sub-10 nm) realized a superior high mass activity. The electrocatalytic performances have been further boosted by synergetic effects in bimetallic systems, either through surface decoration using foreign metal atoms or by alloying in which the high-index facet structure is preserved and the electronic structure of the NCs is altered.The intrinsic relationship of high electrocatalytic performance dependent on open structure and high-energy surface is also valid for (metal) oxide nanomaterials used in Li ion batteries (LIB). It is essential for the anode nanomaterials to have optimized structures to keep them more stable during the charge/discharge processes for reducing damaging volume expansion via intercalation and subsequent reduced battery lifetime. In the case of cathodes, tuning the surface structure of nanomaterials should be one of the most beneficial strategies to enhance the capacity and rate performance. In addition, metal oxides with unique defective structure of high catalytic activity and carbon materials of porous structure for facilitating fast Li+ diffusion paths and efficiently trapping polysulfide are most important approached and employed in Li–O2 battery and Li–S battery, respectively.In summary, significant progress has already been made in the electrocatalytic field, and likely emerging techniques based on NCs enclosed with high-energy surfaces and high-index facets could provide a promising platform to investigate the surface structure–catalytic functionality at nanoscale, thus shedding light on the rational design of practical catalysts with high activity, selectivity, and durability for energy conversion and storage.

Controlling the surface structure of Pt nanocrystals (NCs), especially creating high-index facets with abundant active step sites, is an effective approach to enhance catalytic performances. However, the available high-index faceted Pt NCs have large particle sizes, which severely impedes their practical applications. In this study, we reported a new electrochemically seed-mediated method, by which sub-10 nm tetrahexahedral Pt NCs (THH Pt NCs) enclosed with {210} high-index facets supported on graphene were synthesized. Pt nanoparticles of ∼3 nm in size as high-density crystal seeds play a key role in the small-sized control. The obtained THH Pt NCs exhibited a higher mass activity than commercial Pt/C catalyst for ethanol electrooxidation. We further demonstrated that this method is also valid for reshaping commercial Pt/C, to create high-index facets on surfaces and thus to improve both mass activity and stability.

Glycerol, a byproduct of biodiesel production, is an industrial waste because of its excess yield. Electrooxidation of glycerol is a promising way to utilize glycerol—through harvesting electric energy as fuels in a fuel cell or hydrogen as sacrificial agent in electrolysis cell—while generating valuable chemicals. Here, we report a detailed mechanistic study of the glycerol electrooxidation reaction (GOR) on a series of Pt/C, PtxRuy/C, and PtxRhy/C nanocatalysts synthesized by NaBH4 reduction. The EC cyclic voltammetry characterization indicates that alloying Ru with Pt greatly enhanced the GOR activity, especially at low potential, but not as much with alloying Rh, as compared with Pt/C. In situ FTIR and 13C NMR spectroscopies were used to investigate the GOR mechanism at a molecular level. The results demonstrate that the selectivity of products depends on the type of catalysts and the oxidation potential. Although both PtRu/C and PtRh/C could accelerate the oxygen insertion reactions that led to higher selectivity of carboxylic acids, tartronic acid was more favored at high potential on the PtRh/C surface.Keywords: electrocatalysis; glycerol electrooxidation; in situ 13C NMR; in situ FTIR; nanocatalyst

Li-rich materials, Li1.140Mn0.622Ni0.114Co0.124O2, of a layered/spinel heterostructure were synthesized by a one-step solvothermal route with subsequent moderate heat treatment. The as-prepared materials consist of hierarchical microspheres and an integral layered/spinel heterostructure. The effects of calcination time on both the structure and electrochemical performance of materials have been studied systematically. It has been found that the formation of the spinel structure could be controlled by adjusting the calcination time at 650 °C, and the materials calcined at this temperature for 24 hours present the optimal electrochemical performance. High initial efficiencies of 101% at 0.2C and 92% at 2C, as well as high discharge capacities of 280, 256, 234 and 206 mA h g−1 respectively at 1C, 2C, 5C and 10C have been achieved. The empty 16c octahedral site and 3D Li+ diffusion channel provided by the spinel have been regarded as the key to the improvement of electrochemical performances.

Li3VO4 has been regarded as a new-type anode of lithium-ion batteries in recent years, which has a high theoretical specific capacity of 394 mAh g–1, a proper potential for Li+ insertion/deinsertion (∼1 V), and a good rate capacity. However, its low initial Coulombic efficiency, poor conductivity, and poor cycle performance restricts its development. In order to figure out the cause of the low initial Coulombic efficiency of Li3VO4 material, the nanosized Li3VO4 material was synthesized by citric acid-assisted sol–gel method. The lithium storage behaviors of the prepared Li3VO4 material were studied by in-situ XRD and in-situ EIS techniques. In-situ XRD results indicated that there was irreversible phase transformation of Li3VO4 during the initial charging/discharging process. In-situ EIS experiment was performed during the potentiostatic intermittent titration technique (PITT) process to discuss the formation of the solid electrolyte interface (SEI) on the Li3VO4 and the kinetics of lithium-ion diffusion. It is worth pointing out that this is the first time to prove the existence of SEI on Li3VO4 during the initial charging/discharging process by in-situ EIS experiment. It turned out that the irreversible phase transformation and the formation of SEI on Li3VO4 were the two important reasons causing the low initial Coulombic efficiency of Li3VO4 material.Keywords: in-situ EIS; in-situ XRD; low initial Coulombic efficiency; nanosized Li3VO4; PITT

Bimetallic PtPb nanodendrites with a single-crystalline structure were obtained by a facile one-pot strategy. The as-synthesized dendritic structure was well characterized and the growth mechanism was investigated. PtPb nanodendrites exhibited superior activity (5.1 times higher than commercial Pd black) and strong anti-poisoning ability for electrooxidation of formic acid.

•Densely packed submicron polyhedral LiNi0.5Mn1.5O4 was synthesized.•LiNi0.5Mn1.5O4/Li half-cell exhibits superior cycle stability and rate capability.•LiNi0.5Mn1.5O4/graphite full-cell delivers stable high discharge capacity.Densely packed submicron polyhedral LiNi0.5Mn1.5O4 material with disordered Fd  3¯m structure was synthesized via a modified sol–gel method. The as-synthesized material has a high tap density of 2.15 g cm−3, guaranteeing a high volumetric energy density for high power batteries. Electrochemical properties were investigated in both a LiNi0.5Mn1.5O4/Li half-cell and a LiNi0.5Mn1.5O4/graphite full-cell. The LiNi0.5Mn1.5O4/Li half-cell exhibits a superior cycle stability and rate capability. Here the LiNi0.5Mn1.5O4 material can deliver capacity retentions of 86% at 25 °C and 75% at 55 °C within 1000 cycles for a charge–discharge rate of 1 C. At a much higher rate of 10 C, a discharge capacity of 95 mAh g−1 can be still obtained. The LiNi0.5Mn1.5O4/graphite full-cell delivers a stable discharge capacity of 130.2 mAh g−1 at 0.2 C, corresponding to a discharge energy density as high as 576.2 Wh kg−1. After 100 cycles, the full cell can maintain a working voltage of 4.55 V and capacity retention of 84.6%. The excellent cycle stability is attributed to the dense structure, large particle size, low specific surface area and less exposed (110) facets, which dramatically reduce irreversible surface chemical reactions and manganese dissolution.

By doping iron into isoreticular metal organic framework-3 (IRMOF-3) as a precursor and then annealing at 900 °C under inert gas atmosphere, we have successfully prepared high efficient electrocatalyst of x%Fe/IRMOF-3-900 (x ranges from 1% to 10%) with porous carbon sphere structure. The electrocatalytic properties of the x%Fe/IRMOF-3-900 towards oxygen reduction reaction (ORR) are investigated by using rotating ring disk electrode (RRDE). The results demonstrate that the 1%Fe/IRMOF-3-900 exhibits the highest ORR activity: the onset and half-wave potentials are measured at 1.02 V and 0.88 V vs. RHE, respectively, together with electron transfer number of 3.90 at 0.4 V, kinetic current density of 4.5 mA cm−2 at 0.88 V, and excellent longtime stability in alkaline solution. Such high ORR activity is is superior to many MOFs derived noble metal free electrocatalysts reported so far, and attributed to that the 1%Fe doped could retain the well-defined cubic morphology of the IRMOF-3, resulting in high surface area and large total pore volume, high nitrogen content and high density of electrocatalytic active N-species. This study provides a new strategy for preparation of non-precious metal ORR catalysts using the MOF as a precursor.A novel 1%Fe/IRMOF-3-900 catalyst was prepared by doping Fe into IRMOF-3 and annealing at 900 °C under N2 flow, which showed the excellent ORR activity and excellent longtime stability.

Electroreduction of CO2 to hydrocarbons on a copper surface has attracted much attention in the last few decades for providing a sustainable way for energy storage. During the CO2 and further CO electroreduction processes, deoxygenation that is C–O bond dissociation, and hydrogenation that is C–H bond formation, are two main types of surface reactions catalyzed by the copper electrode. In this work, by performing the state-of-the-art constrained ab initio molecular dynamics simulations, we have systematically investigated deoxygenation and hydrogenation reactions involving two important intermediates, COHads and CHOads, under various conditions of (i) on a Cu(100) surface without water molecules, (ii) at the water/Cu(100) interface and (iii) at the charged water/Cu(100) interface, in order to elucidate the electrochemical interfacial influences. It has been found that the electrochemical interface can facilitate considerably the C–O bond dissociation via changing the reaction mechanisms. However, C–H bond formation has not been affected by the presence of water or electrical charge. Furthermore, the promotional roles of an aqueous environment and negative electrode potential in deoxygenation have been clarified, respectively. This fundamental study provides an atomic level insight into the significance of the electrochemical interface towards electrocatalysis, which is of general importance for understanding electrochemistry.

We have successfully built a general framework to comprehend the structure–selectivity relationship in ethanol electrooxidation on platinum by density functional theory calculations. Based on the reaction mechanisms on three basal planes and five stepped surfaces, it was found that only (110) and n(111) × (110) sites can enhance CO2 selectivity but other non-selective step sites are more beneficial to activity.

Deep eutectic solvents (DESs) are being increasingly used in electrochemically controllable synthesis of functional nanomaterials because of their unique merits (e.g., high conductivity, wide electrochemical windows and environmental friendship). Herein, we report a novel strategy in DESs for the fabrication of multi-walled carbon nanotubes (MWCNTs)-supported Pd-based alloy nanostructures. Using a NaBH4 solvothermal reduction process in DESs, highly active PdSn alloy nanocatalysts supported on MWCNTs towards the formic acid oxidation (FAO) reaction were synthesized for the first time. The as-synthesized materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS) and electrochemical tests. The results demonstrate that the PdSn nanocluster structure with a rough surface provides a high density of catalytically active sites and thereby increases the electrochemically active surface area. There is a strong charge transfer interaction between Pd and Sn in the PdSn/MWCNT catalyst due to its high degree of alloying. The electrochemical studies indicate that the PdSn/MWCNT shows remarkably improved electrocatalytic performance towards FAO compared to Pd/MWCNT and commercial Pd/C catalysts. This study suggests an effective synthesis strategy for Pd-based electrocatalysts with high performance for DFAFCs applications.

•Methanol electrooxidation mechanism is investigated on Rh/Pt(111).•Rh sites are more active for dehydrogenation and the origin of the promoting effect is revealed.•Rh sites also facilitate OH formation at low potentials and accelerate CO oxidation.•A moderate Rh coverage on Pt would be expected.The bi-functional mechanism has been widely accepted for describing the binary catalysts in methanol electrooxidation, in which Pt sites can catalyze the methanol dehydrogenation and the second elements (e.g. Ru, Sn) can activate water to oxidants. However, in terms of binary PtRh, the surface Rh sites being identified not to be oxidized as easily as Ru, may participate in the dehydrogenation reaction at low potentials rather than just activate water. In this work, we investigate the roles of doped Rh on Pt(111) in methanol electrooxidation by density functional theory (DFT) calculations for the first time. We find that the methanol dehydrogenation activity is enhanced on Rh/Pt(111) because Rh can eliminate significantly the repulsive interaction between carbon fragment and H at the transition state. The formation potential of OH* on Rh/Pt(111) is 0.36 V (vs SHE) which is lower than 0.64 V (vs SHE) on Pt(111). Meantime, the coupling barrier between CO* and OH* is also decreased from 0.47 eV to 0.24 eV. By considering coverage, the individual Rh atom on surface is identified to be more effective than the neighbouring atoms for methanol electrooxidation, and thus a moderate Rh coverage is suggested. This work provides some insight into the binary catalysts for methanol electrooxidation.

•3D nanostructured multilayer Si/Al film of 1 μm in total Si thickness is prepared.•The 3D nanostructured multilayer Si/Al film exhibits excellent cycle performance and rate capability.•The 3D multilayer structure can effectively enhance the electrochemical performance of Si film with increasing thickness.The practical application of Si film anode is hindered severely, due to the very low active material loading. In current study, 3-dimensional nanostructured multilayer Si/Al film (3D-MSAF) of 1 μm in total Si thickness was prepared through chemical etching, electrochemical reduction and magnetron sputtering method and served as anode material of lithium-ion battery. This 3D-MSAF anode exhibits excellent cycle performance evidenced by a capacity as high as 1015 mAh g−1 after 120 charge–discharge cycles at the current density of 4.2 A g−1. Even at a much higher current density of 10.0 A g−1, the 3D-MSAF anode can still provide a capacity of 919 mAh g−1. However, the planar multilayer Si/Al film (P-MSAF) with the same Si thickness delivers only a capacity of 336 mAh g−1 after 55 cycles at 4.2 A g−1. The enhanced electrochemical performance is mainly attributed to the unique structure of the 3D-MSAF electrode, which could effectively accommodate the volume variation and improve the electronic conductivity.

•Porous MnO/C with composite nanostructure was prepared by hydrothermal reaction.•The composite nanostructure is consisting of nanorods and nano-octahedra.•The nRO-MnO/C delivers a charge capacity of 628.9 mAh g−1 after 300 cycles at 1.32 C.•The superior electrochemical performance should be owed to composite structure.Porous MnO/C materials of composite nanostructure consisting of nanorods and nano-octahedra (denoted as nRO-MnO/C) were synthesized for the first time through a one-pot hydrothermal procedure followed by thermal annealing using PEG6000 as a soft template. When served as anode of LIBs, the nRO-MnO/C materials could maintain a reversible capacity as high as 861.3 mAh g−1 after 120 cycles at a rate of 0.13 C (1 C = 755.6 mA g−1), and a stable capacity of 313.5 mAh g−1 at a much higher rate of 4.16 C. Moreover, excellent long cycleability at high rate has been also evidenced by a capacity of 628.9 mAh g−1 measured after 300 cycles at 1.32 C. In comparison with mono-form porous nanorods (nR-MnO/C) and mono-form porous nano-octahedra (nO-MnO/C), the enhanced electrochemical performances of the nRO-MnO/C materials are attributed to the composite nanostructure, in which the nano-octahedra contact effectively with nanorods by laying in the space between them yielding synergy effect that facilitates the electronic transportation on electrode.

•Fundamental of in-situ FTIR spectroscopy.•The application of in-situ FTIRS in the investigation of electrocatalytic reactions and processes.•An insightful perspective for the future research.Investigation of electrocatalytic reactions and processes at molecule level is of essential importance in the successful development of electrocatalyst. It is critical to understand the detail pathways and mechanism of complex electrocatalytic processes in order to control the reaction and suppress the formation of byproducts. Based on its fingerprint and surface selection rules, electrochemical in-situ FTIR spectroscopy (in-situ FTIRS) is a powerful method to acquire real-time information about the chemical nature of adsorbates and the solution species involved in electrochemical reactions. These unique features make this technique well-suitable and widely applicable in electrocatalytic reactions.In this paper, we review recent progresses of in-situ FTIRS and its application in the investigation of electrocatalytic reactions and processes. First, we focus on the in-situ FTIR studies of electrocatalytic oxidation of small organic molecules. Next, in-situ FTIR characterization of electrocatalysts through employing a probe molecule, i.e. CO, is reviewed. Finally, the application of in-situ FTIRS to analyze some important electrochemical processes such as CO2 electroreduction, biomolecule reaction and Lithium ion battery is reviewed. The body of work has advanced the knowledge of electrode process and summarized the frontier in study of electrocatalytic reactions and processes at molecular level.

•The np-RuO2/nr-MnO2 were firstly synthesized via a two-step hydrothermal reaction.•The np-RuO2/nr-MnO2 as cathode of Li–O2 battery exhibits high bifunctional electrocatalytic activity.•In-situ synchrotron HEXRD illustrated the formation process of Li2O2.RuO2 nanoparticles supported on MnO2 nanorods (denoted as np-RuO2/nr-MnO2) were synthesized via a two-step hydrothermal reaction. SEM and TEM images both illustrated that RuO2 nanoparticles are well dispersed on the surface of MnO2 nanorods in the as-prepared np-RuO2/nr-MnO2 material. Electrochemical results demonstrated that the np-RuO2/nr-MnO2 as oxygen cathode of Li–O2 batteries could maintain a reversible capacity of 500 mA h g−1 within 75 cycles at a rate of 50 mA g−1, and a higher capacity of 4000 mA h g−1 within 20 cycles at a rate as high as 200 mA g−1. Moreover, the cell with the np-RuO2/nr-MnO2 catalyst presented much lower voltage polarization (about 0.58 V at a rate of 50 mA g−1) than that measured with only MnO2 nanorods during charge/discharge processes. The catalytic property of the np-RuO2/nr-MnO2 and MnO2 nanorods were further compared by conducting studies of using rotating disk electrode (RDE), chronoamperommetry and linear sweep voltammetry. The results illustrated that the np-RuO2/nr-MnO2 exhibited excellent bifunctional electrocatalytic activities towards both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Furthermore, in-situ high-energy X-ray diffraction was employed to trace evolution of species on the np-RuO2/nr-MnO2 cathode during the discharge processes. In-situ XRD patterns demonstrated the formation process of the discharge products that consisted of mainly Li2O2. Ex-situ SEM images were recorded to investigate the morphology and decomposition of the sphere-like Li2O2, which could be observed clearly after discharge process, while are decomposed almost after charge process. The excellent electrochemical performances of the np-RuO2/nr-MnO2 as cathode of Li–O2 battery could be contributed to the excellent bifunctional electrocatalytic activities for both the ORR and OER, and to the one-dimensional structure which would benefit the diffusion of oxygen and the storage of Li2O2 in the discharge process of Li–O2 battery.

Concave-disdyakis triacontahedral palladium nanocrystals (C-DTH Pd NCs) bound with 120 {631} high-index facets were prepared by electrochemically shape-controlled method in deep eutectic solvent (DES). It has found that both the adsorption of urea derived from EDS and the upper (EU) and lower (EL) limit potentials of the square-wave potential applied in the synthesis are contributed synergetically in controlling the shape of Pd NCs. The formation of C-DTH Pd NCs with well-defined shape was achieved by the dynamic interaction between urea adsorption at EU and growth at EL. In situ FTIR spectroscopic studies revealed that the urea adsorbates at EU play a crucial role in shape evolution, especially in the formation of C-DTH Pd NCs. It has demonstrated that the as-synthesized C-DTH Pd NCs enclosed by {631} high-index facets exhibit higher electrocatalytic activity than Pd NCs with other shapes bound by {111} low-index facets (octahedral (OH) and icosahedral (IH)) toward ethanol electrooxidation in alkaline medium.

The irreversible adsorption of polyvinylpyrrolidone (PVP) on a series of well-defined platinum single crystal electrode surfaces has been investigated using voltammetry, ex situ XPS and DFT calculations. It is found that the adsorption of PVP is highly structure sensitive with strong adsorption exhibited by step and {100} terrace sites with only weak interactions observed between PVP and Pt{111} terraces, at least at low PVP surface concentrations. Subsequent investigations using CO electrooxidation confirmed that blocking of platinum surface sites by PVP toward CO chemisorption was marked for Pt{100} terraces but hardly occurred at all at Pt{111} terraces. Density Functional Theory calculations also confirmed that the monomer of PVP interacts more strongly with Pt{100} compared to Pt{111} sites (−142 and −125 kJ mol–1 respectively). Ex situ XPS studies suggested that the main PVP–Pt interaction is associated with charge transfer from the carbonyl substituent of PVP toward the metal surface in accordance with earlier studies of PVP adsorbed on polycrystalline platinum surfaces. Irreversible adsorption of Pt adatoms onto Pt{hkl} surfaces with and without PVP–surface modification demonstrated a marked preference for {100} facet formation on Pt{100} surfaces but no corresponding preferential {111} facet growth on Pt{111} when PVP was present. Hence, the shape control exhibited by PVP in expediting the formation of cubic Pt nanoparticles is explicitly confirmed as arising from relatively weak PVP chemisorption on Pt{111} facets at low PVP surface loading.

In this work, a composite consisting of layered Li[Li0.2Ni0.12 Mn0.56Co0.12]O2 (LNMC) and spinel Li[Ni0.5Mn1.5]O4 (LNMO) was synthesized by a modified Pechini method. Extensive analysis was carried out to investigate the synergistic effect between the layered oxide and spinels in the composite by comparing its properties with baseline individual compounds, as well as a physical mixture of LMNC and LNMO. Comparing to the LNMC, the compsoite cathode exhibited a similar initial capacity of ∼250 mA·h/g at 0.1 C, but a much higher first-cycle effeciency, better cyclability and rate capability, attributed to the presence of spinel. The synertistic effect of integrated spinel on the microstructure, crystal strucutre, Mn oxidation states, and Li+/Ni2+ disordering of the composite was studied by X-ray absorption near edge structure (XANES), electron microscopy, and X-ray diffraction (XRD). The presence of a spinel component in the composite cathode is the origin for the improvement of cyclability and rate capability, largely due to a lower Li+/Ni2+ disordering, milder redox reaction of manganese ions, and suppressed converting reaction to form LixMn2O4-like spinel.

•A well-defined non-precious metal and N dual-doped mesoporous carbon is developed.•Superior catalytic activity for ORR than Pt is demonstrated.•A novel sublimation and capillary assisted nanocasting method is developed for nano synthesis.Fe and N dual-doped mesoporous carbon catalyst demonstrated superior catalytic activity than Pt catalyst for both oxygen reduction and oxidation reactions in alkaline electrolyte. The catalyst was synthesized through a novel simple sublimation and capillary assisted nanocasting method. Using the method, multiple transition metal and nitrogen dual-doped mesoporous carbon electrocatalysts were also successfully made. It was believed that the excellent catalytic activity was resulted from the synergistic effects of highly active metal-nitrogen species, mesoporous structure, large interfacial surface and excellent conductivity. The present synthetic strategy offers a new insight into preparation of heteroatom-doped electrocatalysts with promising applications in metal-air batteries, fuel cells, and supercapacitors as well.

•We describe the origin of degradation of tin electrode for electro-reduction of CO2.•We implement a stable and active electrode materials.•Pulverization of the electrode resulted in an increase in cell Ohmic resistance.•The apparent cathode potential then decreases, resulting in performance degradation.Mastery of the electrochemical conversion of carbon dioxide and water to fuels using renewable electricity can shed light on understanding the nature of artificial photosynthesis and offer an approach to mitigate the negative impact of anthropogenic carbon dioxide emissions on the planet. Presently, copper, silver and tin are the most extensively scrutinized electrocatalysts, which can convert CO2 to CH4, C2H4 and alcohols, CO, and carbolic acid in aqueous electrolytes, respectively. A long-lasting challenge in the electrosynthesis of fuels from CO2 is to achieve durable electrochemical performance, an equally important characteristic of an electrode as the activity and selectivity, but it has not yet been reported in open literature. Here, we describe the origin of degradation of an active electrode for the electrochemical reduction of CO2 to liquid fuels and an approach to implement stable and active electrode materials. Pulverization was observed in tin-based electrocatalyst particles, resulting in an increase in cell Ohmic resistance and subsequently decreasing the apparent potential at the cathode. As a consequence, the selectivity towards the formation of formate was decreased during a long-term operation. The pulverization was attributed to hydrogen diffusion-induced stress with a calculated critical size of ~3 nm. Nanosized particles below this size were capable of suppressing pulverization in electrocatalysts and resulted in a stable and active performance.

We have developed a facile procedure that can create asymmetrical building blocks by uniformly deforming nanospheres into C∞v symmetry at low cost and high quality. Concave polystyrene@carbon (PS@C) core–shell nanospheres were produced by a very simple microwave-assisted alcohol thermal treatment of spherical PS@C nanoparticles. The dimensions and ratio of the concave part can be precisely controlled by temperature and solvents. The concavity is created by varying the alcohol-thermal treatment to tune the swelling properties that lead to the mechanical deformation of the PS@C core–shell structure. The driving force is attributed to the significant volume increase that occurs upon polystyrene core swelling with the incorporation of solvent. We propose a mechanism adapted from published models for the depression of soft capsules. An extrapolation from this model predicts that the rigid shell is used to generate a cavity in the unbuckled shell, which is experimentally confirmed. This swelling and deformation route is flexible and should be applicable to other polymeric nanoparticles to produce asymmetrical nanoparticles.

Different morphologies and compositions of Li-rich layered Li1.2Mn0.56Ni0.12Co0.12O2 (LMNCO) materials are successfully synthesized by solvothermal and coprecipitation methods. The samples synthesized by the solvothermal method possess a 3D porous hierarchical microstructure and designed chemical components, while those prepared through the coprecipitation method present partially agglomerated nanoplates and Mn-deficiency. When used as a cathode for lithium ion batteries (LIBs), the LMNCO synthesized by the solvothermal method exhibits superior performances to that prepared by the coprecipitation method, especially in terms of discharge capacity and rate capability: it delivers a discharge capacity of 292.3 mA h g−1 at 0.2 C and 131.1 mA h g−1 even at a rate as high as 10 C. The excellent electrochemical performances of the LMNCO synthesized by the solvothermal method are associated with a synergistic effect of the well-defined morphology and well-ordered structure with good homogeneity and designed stoichiometry. The results demonstrate that the facile solvothermal method may offer an attractive alternative approach for the preparation of Li-rich layered cathode materials with high rate capability.

Identifying and quantifying electrocatalytic-reaction-generated solution species, be they reaction intermediates or products, are highly desirable in terms of understanding the associated reaction mechanisms. We report herein a straightforward implementation of in situ solution electrochemical 13C NMR spectroscopy for the first time that enables in situ studies of reactions on commercial fuel-cell electrocatalysts (Pt and PtRu blacks). Using ethanol oxidation reaction (EOR) as a working example, we discovered that (1) the complete oxidation of ethanol to CO2 only took place dominantly at the very beginning of a potentiostatic chronoamperometric (CA) measurement and (2) the PtRu had a much higher activity in catalysing oxygen insertion reaction that leads to acetic acid.

N,S,Fe-doped graphene nanosheets were directly synthesized from aminothiazole, a precursor molecule that contains N and S atoms, through Fe catalysis under heat treatment. The graphene nanosheets exhibited high electrocatalytic activity toward oxygen reduction reaction in both acidic and alkaline media during rotating disk electrode half-cell and fuel cell tests.

Hierarchical Mn2O3 hollow microspheres of diameter about 6–10 μm were synthesized by solvent-thermal method. When serving as anode materials of LIBs, the hierarchical Mn2O3 hollow microspheres could deliver a reversible capacity of 580 mAh g–1 at 500 mA g–1 after 140 cycles, and a specific capacity of 422 mAh g–1 at a current density as high as 1600 mA g–1, demonstrating a good rate capability. Ex situ X-ray absorption near edge structure (XANES) spectrum reveals that, for the first time, the pristine Mn2O3 was reduced to metallic Mn when it discharged to 0.01 V, and oxidized to MnO as it charged to 3 V in the first cycle. Furthermore, the XANES data demonstrated also that the average valence of Mn in the sample at charged state has decreased slowly with cycling number, which signifies an incomplete lithiation process and interprets the capacity loss of the Mn2O3 during cycling.Keywords: conversion reaction mechanism; hierarchical hollow microspheres; lithium ion battery; Mn2O3; XANES;

•A new Pt-based catalyst using PIn-functionalized MWCNTs as support is reported.•There is strong electron interaction between Pt nanoparticles and PIn-MWCNTs.•Pt nanoparticles with small sizes are evenly deposited on the PIn-MWCNT surface.•The Pt/PIn-MWCNTs exhibit much higher electrocatalytic performance for MOR.Herein, we report a novel electrocatalyst consisting of Pt nanoparticles supported on a polyindole (PIn)-functionalized multi-walled carbon nanotube (MWCNT) composite (Pt/PIn-MWCNT) for use in the methanol oxidation reaction (MOR). The PIn-MWCNT support is synthesized via in situ chemical polymerization of indole on the MWCNT surface. The transmission electron microscopy (TEM) images indicated that the Pt nanoparticles were approximately 3.0 nm in size and were uniformly deposited on the surface of PIn-MWCNTs with no aggregation into larger clusters. X-ray photoelectron spectroscopy (XPS) measurements confirm the strong electron interaction between the Pt nanoparticles and the PIn-MWCNT support as well as the formation of the Pt–N bond. The electrochemical tests demonstrate that the Pt/PIn-MWCNT composite exhibits much higher electrocatalytic activity, durability and CO tolerance than the Pt/MWCNT and commercial Pt/C catalysts toward MOR. The results indicate that the as-prepared Pt/PIn-MWCNTs are promising for use as an anode electrocatalyst in direct methanol fuel cells (DMFCs).

•Adsorption of CTAB and HBr on Pt(100) was studied by cyclic voltammetry.•Both HBr and CTAB can prevent the long-range ordered structure of Pt(100) from perturbation by inhibiting oxygen adsorption, and the ability order is CTAB > HBr.•The irreversibly adsorbed CTAB on Pt(100) can be removed mostly by CO adsorption/stripping.Adsorption of CTAB and HBr on Pt(100) in acid solutions were studied by using cyclic voltammetry (CV). The effects of bromide anion (Br−), and cetyltrimethylammonium cation (CTA+) together with Br− (CTAB) on the long-range ordered structure of Pt(100) were investigated systematically and analyzed quantitatively. It has demonstrated that adsorption of both CTA+ and Br− can protect the long-range ordered structure of Pt(100). The upper limit potential of CV below which the long-range ordered structure of Pt(100) is starting to be disturbed was measured at 0.6 V in 0.1 M H2SO4, and it was shifted positively to 0.9 V in 0.1 M H2SO4 + 1 mM HBr; this potential has been further postponed to even a higher potential of 1.1 V in 0.1 M H2SO4 + 1 mM CTAB solution, demonstrating that the ability of protecting the long-range ordered structure of Pt(100) is CTAB > HBr. The adsorbed Br− can desorb simultaneously with proton adsorption, while the CTA+ has adsorbed firmly on Pt(100). It has demonstrated that the irreversibly adsorbed CTA+ could be mostly removed by CO adsorption/stripping. The results revealed that the origin of protecting the long-range ordered (100) structure by HBr is mainly through the inhibition of oxygen adsorption, while that by CTAB comes from both the inhibition of oxygen adsorption and the CTA+ irreversible adsorption. The study has thrown insights in understanding the interaction of Br− and CTA+ with Pt(100), and interpreted that using CTAB as shape-tuning agent is more favorable to yield Pt nanomaterials with long-range ordered (100) surface structure.

High-temperature pyrolyzed FeNx/C catalyst is one of the most promising nonprecious metal electrocatalysts for oxygen reduction reaction (ORR). However, it suffers from two challenging problems: insufficient ORR activity and unclear active site structure. Herein, we report a FeNx/C catalyst derived from poly-m-phenylenediamine (PmPDA-FeNx/C) that possesses high ORR activity (11.5 A g–1 at 0.80 V vs RHE) and low H2O2 yield (<1%) in acid medium. The PmPDA-FeNx/C also exhibits high catalytic activity for both reduction and oxidation of H2O2. We further find that the ORR activity of PmPDA-FeNx/C is not sensitive to CO and NOx but can be suppressed significantly by halide ions (e.g., Cl–, F–, and Br–) and low valence state sulfur-containing species (e.g., SCN–, SO2, and H2S). This result reveals that the active sites of the FeNx/C catalyst contains Fe element (mainly as FeIII at high potentials) in acid medium.

Aimed at developing a highly active and stable non-precious metal catalyst (NPMC) for oxygen reduction reaction (ORR) in acidic proton-exchange membrane fuel cells (PEMFCs), a novel NPMC was prepared by pyrolyzing a composite of carbon-supported Fe-doped graphitic carbon nitride (Fe–g-C3N4@C) above 700 °C. In this paper, the influence of the pyrolysis temperature and Fe content on ORR performance was investigated. Rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) studies reveal that, with a half-wave potential of 0.75 V [versus reversible hydrogen electrode (RHE)] and a H2O2 yield of 2.6% at 0.4 V, the as-synthesized catalyst heat-treated at 750 °C with a Fe salt/dicyandiamide (DCD) mass ratio of 10% displays the optimal ORR activity and selectivity. Furthermore, the pyrolyzed Fe–N–C composite exhibits superior durability in comparison to that of commercial 20 wt % Pt/C in acidic medium, making it a good candidate for an ORR electrocatalyst in PEMFCs.Keywords: carbon-supported Fe-doped g-C3N4 (Fe−g-C3N4@C); Fe−N−C composite; non-precious metal catalyst (NPMC); oxygen reduction reaction (ORR); proton-exchange membrane fuel cell (PEMFC); pyrolysis

A novel nanostructured catalyst of platinum nanoparticles supported on 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin tetra(p-toluenesulfonate) (TMPyP) functionalized graphene (TMPyP-graphene) is synthesized by the hydrothermal polyol process. The as-synthesized nanocomposites are characterized by Fourier transform infrared (FTIR) spectroscopy, UV-vis absorption spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and electrochemical tests. It has been found that Pt nanoparticles of ca. 3.4 nm are uniformly dispersed on the surface of TMPyP-graphene, and hold a high electrochemical active surface area (ECSA) of 126.2 m2 g−1. The results demonstrate that the Pt/TMPyP-graphene catalyst exhibits a much higher electrocatalytic activity and stability than the Pt/graphene and commercial Pt/C catalysts for methanol oxidation, which is of significant importance in improving the efficiency of Pt-based electrocatalysts for DMFCs applications.

An alginate hydrogel binder is prepared through the cross linking effect of Na alginate with Ca2+ ions, which leads to a remarkable improvement in the electrochemical performance of the Si/C anode of a Li-ion battery.

In this work, the Li-rich oxide Li1.23Ni0.09Co0.12Mn0.56O2 was synthesized through a facile route called aqueous solution-evaporation route that is simple and without waste water. The as-prepared Li1.23Ni0.09Co0.12Mn0.56O2 oxide was confirmed to be a layered LiMO2–Li2MnO3 solid solution through ex situ X-ray diffraction (ex situ XRD) and transmission electron microscopy (TEM). Electrochemical results showed that the Li-rich oxide Li1.23Ni0.09Co0.12Mn0.56O2 material can deliver a discharge capacity of 250.8 mAhg–1 in the 1st cycle at 0.1 C and capacity retention of 86.0% in 81 cycles. In situ X-ray diffraction technique (in situ XRD) and ex situ TEM were applied to study structural changes of the Li-rich oxide Li1.23Ni0.09Co0.12Mn0.56O2 material during charge–discharge cycles. The study allowed observing experimentally, for the first time, the existence of β-MnO2 phase that is appeared near 4.54 V in the first charge process, and a phase transformation of the β-MnO2 to layered Li0.9MnO2 is occurred in the initial discharge process by evidence of in situ XRD pattrens and selected area electron diffraction (SAED) patterns at different states of the initial charge and discharge process. The results illustrated also that the variation of the in situ X-ray reflections during charge–discharge cycling are clearly related to the changes of lattice parameters of the as-prepared Li-rich oxide during the charge–discharge cycles.Keywords: aqueous solution evaporation; in situ XRD; layered Li0.9MnO2; Li-rich layered oxide; β-MnO2;

A facile and scalable single-step approach is employed to synthesize a bulk germanium electrode, which consists of nanoscale Ge-grains in ∼5 μm porous powders. This three-dimensional Ge electrode exhibits superior specific capacity (∼1500 mA h g−1) and cyclic performance, attributed to its unique lithiation/delithiation processes.

A hierarchical micro/nanostructured Li-rich layered 0.5Li2MnO3·0.5LiMn0.4Ni0.3Co0.3O2 (H-LMNCO) material is prepared for the first time through the development of a solvothermal method, and served as cathode of lithium ion batteries. Electrochemical tests indicate that the H-LMNCO exhibits both a high reversible capacity and an excellent rate capability. The reversible discharge capacity of the H-LMNCO has been measured as high as 300.1 mAh·g− 1 at 0.2 C rate. When the rate is increased to 10 C, the discharge capacity could still maintain a high value of 163.3 mAh·g− 1. The results demonstrate that the developed solvothermal route is a novel synthesis strategy of preparing high rate performance Li-rich layered cathode material for lithium ion batteries.

•We imaged nanocrystals in eutectic based ionic liquid.•We studied the growth of nanocrystal by in situ TEM.•Observation indicates possible growth mechanisms for five-fold twinned nanoparticles.Nanocrystals play a key role in modern science and technology, and there has been much effort in recent years in tailoring the size, shape, and properties of nanocrystals. The capability to monitor the colloidal nanocrystal growth in liquid is essential for fully understanding the growth and shape control mechanisms. In current study, we imaged nanocrystals in a eutectic-based ionic liquid and studied the growth of five-fold twined gold nanocrystal with in situ transmission electron microscopy (TEM). Our studies suggest that the coalescence-based growth may be also an important mechanism for the formation of twinned nanocrystals in solution in addition to nucleation-based layer-by-layer growth and successive growth twinning mechanisms. This observation reveals much important information about colloidal nanocrystal growth, and is very beneficial in a detailed understanding of growth mechanisms and precise shape controlling synthesis of nanoparticles.

The methanol oxidation reaction (MOR) and related carbon monoxide (CO) oxidation reaction (COR) activities on the synthesized cubic and octahedral/tetrahedral (O/T) Pt nanoparticles (NPs) still having residual polyvinylpyrrolidone (PVP) were investigated using electrochemical (EC) and in situ Fourier transform infrared (FT-IR) spectroscopic measurements in both 0.1 M HClO4 and 0.1 M H2SO4. While EC measurements confirmed the enhanced MOR activity on the O/T Pt NPs as observed previously (Susut et al., Phys. Chem. Chem. Phys. 10:3712, 6), the in situ IR measurements showed much improved data quality as compared to the previous studies and provided strong indications that the underlying reason for the observed MOR enhancement on the O/T Pt NPs was highly likely related to the enhanced no-CO-generating reaction pathway(s), as evidenced by much lower CO generation during the MOR on these Pt NPs.

•Active Fe3O4 was deposited onto Cu nanowires with the mass ratio of Fe3O4 to Cu ~ 8.6, which exhibited excellent performance as the anode for lithium ion batteries.•After 135 cycles, the capacity was 735 mAh g− 1, corresponding to capacity retention of 98%.•The improved cycleability is attributed to an intimate contact between Fe3O4 nanoparticles and Cu nanowire substrates.Magnetite (Fe3O4) is a candidate anode material for Li ion batteries due to its low cost, high theoretical capacity, environmental benignity, and relative safety. Challenges that limit its realization as a suitable material include the low electrical conductivity and volume changes during charge and discharge processes, leading to poor cycleability. To overcome these challenges, we carried out research to electrodeposit Fe3O4 nanoparticles onto a network-like structure of Cu nanowires for use as an active anode component. Structural characterization showed that the Cu nanowires exhibited a strong contact with the Cu substrate, resulting in an excellent current collector. In addition, the electrodeposition process enables intimate adhesion between Fe3O4 and Cu nanowires. Galvanostatic cycling measurements revealed the initial discharge and charge capacities of 967.0 and 750.0 mAh g− 1, respectively. Further cycling showed a charge capacity of 735 mAh g− 1 up to 135 cycles with capacity retention of 98%. The exceptional electrochemical properties of the Fe3O4-Cu composite electrode make it an excellent candidate for anode material.

Systematic manipulation of nanocrystal shapes is prerequisite for revealing their shape-dependent physical and chemical properties. Here we successfully prepared a complex shape of Pt micro/nanocrystals: convex hexoctahedron (HOH) enclosed with 48 {15 5 3} high-index facets by electrochemical square-wave-potential (SWP) method. This shape is the last crystal single form that had not been achieved previously for face-centered-cubic (fcc) metals. We further realized the shape evolution of Pt nanocrystals with high-index facets from tetrahexahedron (THH) to the HOH, and finally to trapezohedron (TPH) by increasing either the upper (EU) or lower potential (EL). The shape evolution, accompanied by the decrease of low-coordinated kink atoms, can be correlated with the competitive interactions between preferentially oxidative dissolution of kink atoms at high EU and the redeposition of Pt atoms at the EL.

Single crystalline LiNi1/3Co1/3Mn1/3O2 (LNCM) hexagonal nanobricks with a high percentage of exposed {010} facets are synthesized by using Ni1/3Co1/3Mn1/3(OH)2 hexagonal nanosheets as both template and precursor, and exhibit excellent high rate performance as a cathode of lithium ion batteries.

Hierarchical micro/nanostructured MnO material is synthesized from a precursor of MnCO3 with olive shape that is obtained through a facile one-pot hydrothermal procedure. The hierarchical micro/nanostructured MnO is served as anode of lithium ion battery together with a cathode of spinel LiNi0.5Mn1.5O4-δ material, which is synthesized also from the precursor of MnCO3 with olive shape through a different calcination process. The structures and compositions of the as-prepared materials are characterized by TGA, XRD, BET, SEM, and TEM. Electrochemical tests of the MnO materials demonstrate that it exhibit excellent lithium storage property. The MnO material in a MnO/Li half cell can deliver a reversible capacity of 782.8 mAh g–1 after 200 cycles at a rate of 0.13 C, and a stable discharge capacity of 350 mAh g–1 at a high rate of 2.08 C. Based on the outstanding electrochemical property of the MnO material and the LiNi0.5Mn1.5O4-δ as well, the MnO/LiNi0.5Mn1.5O4-δ full cell has demonstrated a high discharge specific energy ca. 350 Wh kg–1 after 30 cycles at 0.1 C with an average high working voltage at 3.5 V and a long cycle stability. It can release a discharge specific energy of 227 Wh kg–1 after 300 cycles at a higher rate of 0.5 C. Even at a much higher rate of 20 C, the MnO/LiNi0.5Mn1.5O4-δ full cell can still deliver a discharge specific energy of 145.5 Wh kg–1. The excellent lithium storage property of the MnO material and its high performance as anode in the MnO/LiNi0.5Mn1.5O4-δ lithium ion battery is mainly attributed to its hierarchical micro/nanostructure, which could buffer the volume change and shorten the diffusion length of Li+ during the charge/discharge processes.Keywords: full cell; hierarchical micro/nanostructured; lithium ion batteries; MnO; olive shape; spinel LiNi0.5Mn1.5O4-δ;

Porous graphitic carbon of high specific surface area of 1416 m2 g–1 and high pore volume of 1.11 cm3 g–1 is prepared by using commercial CaCO3 nanoparticles as template and sucrose as carbon source followed by 1200 °C high-temperature calcination. Sulfur/porous graphitic carbon composites with ultra high sulfur loading of 88.9 wt % (88.9%S/PC) and lower sulfur loading of 60.8 wt % (60.8%S/PC) are both synthesized by a simple melt-diffusion strategy, and served as cathode of rechargeable lithium–sulfur batteries. In comparison with the 60.8%S/PC, the 88.9%S/PC exhibits higher overall discharge capacity of 649.4 mAh g–1(S–C), higher capacity retention of 84.6% and better coulombic efficiency of 97.4% after 50 cycles at a rate of 0.1C, which benefits from its remarkable specific capacity with such a high sulfur loading. Moreover, by using BP2000 to replace the conventional acetylene black conductive agent, the 88.9% S/PC can further improve its overall discharge capacity and high rate property. At a high rate of 4C, it can still deliver an overall discharge capacity of 387.2 mAh g–1(S–C). The porous structure, high specific surface area, high pore volume and high electronic conductivity that is originated from increased graphitization of the porous graphitic carbon can provide stable electronic and ionic transfer channel for sulfur/porous graphitic carbon composite with ultra high sulfur loading, and are ascribed to the excellent electrochemical performance of the 88.9%S/PC.Keywords: BP2000; high sulfur loading; Li−S batteries; ovreall capacity; porous graphitic carbon; sulfur/carbon composite;

Carbon coated LiMn0.5Fe0.5PO4 solid solution materials (LiMn0.5Fe0.5PO4/C) are synthesized by rheological phase reaction with stearic acid as carbon source, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), BET and TG/DTG. The results show that well-crystallized olivine structure LiMn0.5Fe0.5PO4 nanoplatelets with no obvious impurity phase are obtained. The as-synthesized materials are served as cathode of lithium ion battery and investigated by galvanostatic charge/discharge tests. The results demonstrate that, in comparison with the LMFP materials of different Mn:Fe ratio (LiMn0.2Fe0.8PO4/C and LiMn0.8Fe0.2PO4/C) synthesized by the same route of rheological phase reaction, the LiMn0.5Fe0.5PO4/C exhibit excellent rate specific capability, and can deliver discharge capacity of 138, 99, 80, 72, 67 and 55 mAh g−1 at respectively 0.1, 1, 5, 10, 15 and 20C rates. Moreover, the electrode possesses good cycle stability. A specific capacity of 100 mAh g−1 at 1C after 300 cycles of charge–discharge at room temperature is reached, which represents 95% of capacity retention. The significantly improved electrochemical performances of the LiMn0.5Fe0.5PO4/C cathode are attributed to the uniformly distributed particles and the enhancement of conductivity that is originated from the surface coating of carbon on primary particles.Highlights► Carbon coated LiMn0.5Fe0.5PO4 solid solution is synthesized by rheological phase reaction. ► This process possesses simple technology, low energy consumption. ► Nanoplatelet particles are coated uniformly with carbon layer. ► The obtained LiMn0.5Fe0.5PO4/C exhibit excellent rate capability and cycling performance. ► LiMn0.2Fe0.8PO4/C and LiMn0.8Fe0.2PO4/C are synthesized by the same route for the comparison.

Different composition, thickness and structure of CoNi thin films supported on glassy carbon were prepared by electrochemical codeposition. Potential step method was applied to prepare CoNi thin films with different composition which was controlled by varying the concentration ratio of Co2+/Ni2+ (x:y) in the deposition solution, thus this type of CoNi thin film was defined as CoNi(x:y). Nevertheless, CoNi thin films with different thickness and structure (denoted as CoNi(n)) were synthesized in a fixed Co2+/Ni2+ solution under cyclic voltammetric conditions by varying the cyclic numbers (n) within a defined potential range. AES and EDS analysis revealed that the atomic ratio of Co/Ni in the film (including both outer and inner layer) was in good accordance with the initial Co2+/Ni2+ ratio. XRD investigation indicated that the CoNi(20:0) and CoNi(15:5) thin films were hexagonal closed-packed (hcp) structure, however, the CoNi(10:10), CoNi(5:15) and CoNi(0:20) thin films were face centered cubic (fcc) structure. SEM studies demonstrated that the CoNi(x:y) thin films were uniformly composed of irregular nanoparticles. In the case of CoNi(n), with n increasing, the structure of nanoparticles inside the CoNi thin films underwent a transition from imperfectly spherical particles to multiform particles, and finally to irregular polyhedral particles, accompany with an increase of average size. In situ FTIR reflection spectroscopic studies demonstrated that the mainly chemisorbed CO species (COad) on CoNi(x:y) surfaces were transferred from linearly bonded CO (COL) to bridge bonded CO (COB) as a function of the content of Ni and the crystal phase structure of CoNi thin films. CoNi(x:y) and CoNi(n) thin films all exhibited anomalous IR properties, corresponding respectively to abnormal IR effects (AIREs), Fano-like IR effects and surface-enhanced IR absorption effects. AIREs characterized mostly with inversion of IR band was found on CoNi(x:y), CoNi(4), CoNi(8) thin films which were dominated by irregular or imperfectly spherical particles. Fano-like IR bands with positive-going peak on the lower wavenumbers side were observed in cases of CO adsorbed on CoNi thin films composed mainly of multiform nanoparticles, typically on CoNi(25) thin film. IR features were finally changed into surface-enhanced IR absorption as CO adsorbed on the CoNi(50) thin film, i.e., the CoNi thin film was dominated by smooth irregular polyhedral particles.

The present study applies electrochemical impedance spectra (EIS) to study the interfacial processes of lithium ion batteries (LIBs) and determine the corresponding kinetic parameters. The EIS of the insertion and extraction of lithium ions in layered LiNi1/3Co1/3Mn1/3O2 materials as cathode of LIBs are obtained at different potentials during the first charge/discharge cycle and at different temperatures after 10 charge/discharge cycles. The EIS spectra exhibit three semicircles and a slightly inclined line that appear successively along with decrease in frequency. The high-frequency, the middle-frequency, and the low-frequency semicircles can be attributed respectively to the migration of the lithium ions through the SEI film, the electronic properties of the material and the charge transfer step. The slightly inclined line arises from the solid state diffusion process. The electrical conductivity of the layered LiNi1/3Mn1/3Co1/3O2 changes dramatically at early delithiation as a result of an insulator-to-metal transition. In an electrolyte solution of 1 mol L−1 LiPF6–EC(ethylene carbonate): DEC(diethyl carbonate): DMC(dimethyl carbonate), the activation energy of the ion jump which is related to the migration of the lithium ions through the SEI film, the thermal activation energy of the electrical conductivity and the activation energy of the intercalation/deintercalation reaction are determined 23.1, 44.0 and 66.5 kJ mol−1, respectively.Highlights► We obtained exhaustive electrochemical properties of LiNi1/3Co1/3Mn1/3O2 by EIS. ► We first observed three semicircles via a three-electrode glass cell by EIS. ► The drastic change of electronic conductivity of LiNi1/3Co1/3Mn1/3O2 was observed. ► We proved the presence of an insulator to metal transition in LiNi1/3Co1/3Mn1/3O2. ► Kinetic parameters were calculated in 1 mol L−1 LiPF6–EC: DEC: DMC.

Nano-sized (nO-Co3O4, 387 nm) and micron-sized (mO-Co3O4, 6.65 μm) Co3O4 octahedra enclosed by {111} facets have been both synthesized through a wet chemical method followed by thermal treatment, and served as anode material of lithium ion batteries (LIBs). Electrochemical results demonstrate that the nO-Co3O4 shows excellent long cyclability and rate capability. The nO-Co3O4 can deliver a stable charge capacity as high as 955.5 mAh g−1 up to 200 cycles without noticeable capacity fading at a charge/discharge current density of 0.1 A g−1 (ca. 0.11C). The excellent electrochemical performance is ascribed to the nano-size and the {111} facets that enclose the octahedra. While the mO-Co3O4 could only maintain 288.5 mAh g−1 after 200 cycles, illustrating very poor cycling performance, which is ascribed to the large particle size that may cause huge volume change during repeated charging/discharging process. The results reveal that the Co3O4 nano-octahedra would be a promising anode material for the next-generation of LIBs.Graphical abstractCo3O4 nano-octahedra (387 nm) enclosed by {111} facets are synthesized and served as anode of lithium ion battery. The Co3O4 nano-octahedra can deliver a capacity of 955.5 mAh g−1 at 0.1 A g−1 after 200 cycles of charge/discharge, which is ascribed to both the nano-size and the {111} facets that enclose the octahedra.Highlights► Nano-sized and micron-sized Co3O4 octahedra are both synthesized. ► High reversible capacity, excellent long cyclability and rate capability are determined. ► Excellent electrochemical performance is ascribed to the nano-size and {111} facets. ► Co3O4 nano-octahedra are promising anode materials of the next-generation lithium ion batteries.

•Three dimensional porous copper matrix was prepared by an electroless deposition.•Sn-based intermetallic electrode was electrodeposited in the 3D porous Cu matrix.•Porous Sn50Sb44Co6 exhibits simultaneous high-rate and long-life performances.•Mechanistic studies of the function of porous structure during discharge/charge.The rate capacity and cycleability of a battery electrode are strongly determined by their chemistry and nano/microstructures. This is particularly true in developing next-generation lithium-ion batteries for electric vehicles. In this article, we report synthesis of nanometer tin based negative electrodes encapsulated in microporous copper substrates, which exhibit simultaneously high-rate and long-life performances. This intermetallic compound consists of an amorphous phase rich in Co, located at the boundaries of nanoscale crystalline Sn–Sb grains. The rate capacity retention is ~71.5% while increasing charge rate from 0.15 C (698.9 mAh g−1) to 25.0 C (500 mAh g−1 at ~16 A g−1). Such a high rate performance is a result of novel chemistry (Sn50Sb44Co6) and high electrical conductivity of Cu framework. The cycling capacity is 549 mAh g−1 at 0.2 C (1 C=650 mA g−1) after 300 cycles, and 493.6 mAh g−1 at 0.4 C after 600 cycles. The Co-rich amorphous phase, along with the three dimensional porous structure, contributes to mitigating volume expansion/shrinkage during discharge/charge of the electrode. Our results suggest that the ternary Sn–Sb–Co intermetallic compound with the desirable chemistry and structure is a promising candidate as a high-rate and long-life negative electrode for lithium-ion batteries.The morphology of 3D porous Sn50Sb44Co6 intermetallic compound electrode and the super high-rate performance.

We studied clean and oxygen-covered surfaces of unreconstructed and reconstructed Pt(110) by density functional theory (DFT) calculations and used these data in thermodynamic considerations to establish the stabilities of these surfaces as a function of the oxygen surface coverage. The clean Pt(110) prefers to reconstruct into a (1 × n) missing-row structure with n = 2–4. The surface free energies of the three reconstructed surfaces are very similar within the accuracy of our calculations. Upon oxygen adsorption, the c(2 × 2) with 0.5 monolayer (ML) coverage on the unreconstructed surface is equally stable as the 0.5 ML coverage on the Pt(110)-(1 × 2) reconstructed surface. There is no clear transition between (1 × 1) and (1 × 2). With increasing oxygen pressure, the fully oxygen-covered (1 ML) Pt(110)-(1 × 2) becomes the most stable structure. We assume that this structure is relevant in the onset of the formation of bulk Pt-oxide. Compared to Au, we found that the Pt(110)-(1 × 2) surface is very stable even under very positive electro potential, and the (1 × 3) structure is not stabilized by impurities (e.g., oxygen).

With their ability to convert chemical energy of fuels directly into electrical power or reversibly store electrical energy, systems such as fuel cells and lithium ion batteries are of great importance in managing energy use. In these electrochemical energy conversion and storage (EECS) systems, controlled electrochemical redox reactions generate or store the electrical energy, ideally under conditions that avoid or kinetically suppress side reactions. A comprehensive understanding of electrode reactions is critical for the exploration and optimization of electrode materials and is therefore the key issue for developing advanced EECS systems. Based on its fingerprint and surface selection rules, electrochemical in-situ FTIR spectroscopy (in-situ FTIRS) can provide real-time information about the chemical nature of adsorbates and solution species as well as intermediate/product species involved in the electrochemical reactions. These unique features make this technique well-suited for insitu studies of EECS.In this Account, we review the characterization of electrode materials and the investigation of interfacial reaction processes involved in EECS systems by using state-of-the-art in-situ FTIR reflection technologies, primarily with an external configuration. We introduce the application of in-situ FTIRS to EECS systems and describe relevant technologies including in-situ microscope FTIRS, in-situ time-resolved FTIRS, and the combinatorial FTIRS approach. We focus first on the in-situ steady-state and time-resolved FTIRS studies on the electrooxidation of small organic molecules. Next, we review the characterization of electrocatalysts through the IR properties of nanomaterials, such as abnormal IR effects (AIREs) and surface enhanced infrared absorption (SEIRA). Finally, we introduce the application of in-situ FTIRS to demonstrate the decomposition of electrolyte and (de)lithiation processes involved in lithium ion batteries. The body of work summarized here has substantially advanced the knowledge of electrode processes and represents the forefront in studies of EECS at the molecular level.

Tetrahexahedral Pt nanocrystals (THH Pt NCs) bound by well-defined high index crystal planes offer exceptional electrocatalytic activity, owing to a high density of low-coordination surface Pt sites. We report, herein, on methanol electrooxidation at THH Pt NC electrodes studied by a combination of electrochemical techniques and in situ FTIR spectroscopy. Pure THH Pt NC surfaces readily facilitate the dissociative chemisorption of methanol leading to poisoning by strongly adsorbed CO. Decoration of the stepped surfaces by Ru adatoms increases the tolerance to poisoning and thereby reduces the onset potential for methanol oxidation by over 100 mV. The Ru modified THH Pt NCs exhibit greatly superior catalytic currents and CO2 yields in the low potential range, when compared with a commercial PtRu alloy nanoparticle catalyst. These results are of fundamental importance in terms of model nanoparticle electrocatalytic systems of stepped surfaces and also have practical significance in the development of surface tailored, direct methanol fuel cell catalysts.Keywords: electrocatalysis; fuel cells; high index facets; methanol electrooxidation; Ru adatoms; tetrahexahedral platinum;

Alloy tetrahexahedral Pd–Pt nanocrystals (THH Pd–Pt NCs) mainly enclosed by {10 3 0} high-index facets were prepared by electrochemistry. The as-prepared THH Pd–Pt NCs exhibit a catalytic activity that is at least three times higher than the tetrahexahedral Pd catalysts, and six times higher than commercial Pd black catalysts for the electrooxidation of formic acid. The significant enhancement in catalytic activity has been attributed to the synergy effect of high-index facets and electronic structure of the alloy.

In the present paper, preferentially oriented (111) Pt nanoparticles (mostly octahedral and tetrahedral, namely {111}Pt nanoparticles) have been characterized and compared with a Pt(554) single-crystal electrode as their voltammetric features are quite similar in 0.5 M H2SO4. The anion and Bi adsorption behaviours suggest that the {111}Pt nanoparticles contain relatively wide hexagonal domains and also isolated sites which could adsorb solely hydrogen. Bi step decoration has been successfully extended to modify the defects of {111}Pt nanoparticles without blocking terrace sites. CO charge displacement has been applied to determine the potential of zero total charge (pztc) of non-decorated and Bi decorated surfaces. It has found that the positive shift of pztc on defect-decorated {111}Pt nanoparticles is not so significant in comparison with that of Pt(554) due to the relative short mean length of (111) domains on the {111}Pt nanoparticles. CO stripping demonstrates that {111}Pt nanoparticles exhibit higher reactivity toward CO oxidation. This reflects the role of the defect sites in nanoparticles, evidenced by the disappearance of the “pre-wave” in the stripping voltammogram once the defects were blocked by Bi. The stripping peaks shift to higher potential on Bi decorated surfaces, indicating the active role of both steps and defects for CO oxidation. By comparing the CO stripping charge and the change in hydrogen adsorption charge of surfaces with and without Bi decoration, including reasonable deconvolution, the local CO coverage on defect and terrace sites were obtained for the first time for the {111}Pt nanoparticles, and the results are in good agreement with those obtained on Pt(554). Chronoamperometry studies show tailing in all current–time transients of CO oxidation on all surfaces studied. The kinetics of CO oxidation can be satisfactorily simulated by a modified Langmuir–Hinshelwood model, demonstrating that CO oxidation on all studied surfaces follows the same mechanism.

This paper reports the facile synthesis of a unique interleaved expanded graphite-embedded sulphur nanocomposite (S-EG) by melt-diffusion strategy. The SEM images of the S-EG materials indicate the nanocomposites consist of nanosheets with a layer-by-layer structure. Electrochemical tests reveal that the nanocomposite with a sulphur content of 60% (0.6S-EG) can deliver the highest discharge capacity of 1210.4 mAh g−1 at a charge–discharge rate of 280 mA g−1 in the first cycle, the discharge capacity of the 0.6S-EG remains as high as 957.9 mAh g−1 after 50 cycles of charge–discharge. Furthermore, at a much higher charge–discharge rate of 28 A g−1, the 0.6S-EG cathode can still deliver a high reversible capacity of 337.5 mAh g−1. The high sulphur utilization, excellent rate capability and reduced over-discharge phenomenon of the 0.6S-EG material are exclusively attributed to the particular microstructure and composition of the cathode.

Development of core–shell bimetallic nanoparticles with bifunctional catalytic activity and excellent stability is a challenging issue in nanocatalyst synthesis. Here we present a detailed study of thermal stabilities of Au-core/Pt-shell nanoparticles with different core sizes and shell thicknesses. Molecular dynamics simulations are used to provide insights into the melting and diffusive behavior at atomic-level. It is found that the thermal stabilities of core-shell nanoparticles are significantly enhanced with increasing thickness of Pt shell. Meanwhile, the melting mechanism is strongly dependent on the shell thickness. When the core size or shell thickness is very small, the melting is initiated in the shell and gradually spreads into the core, similar to that of monometallic nanoparticles. As the core increases up to moderate size, an inhomogeneous melting has been observed. Due to the relatively weak confinement of thin shell, local lattice instability preferentially takes place in the core, leading to the inhomogeneous premelting of Au core ahead of the overall melting of Pt shell. The diffusion coefficients of both Au and Pt are decreased with the increasing thickness of shell, and the difference in their diffusions favors the formation of inhomogeneous atomic distributions of Au and Pt. The study is of considerable importance for improving the stability of Pt-based nanocatalysts by tuning the shell thickness and core size.

A novel nanoarchitectured Sn–Sb–Co alloy electrode is reported, which was prepared by direct electrodeposition on a Cu nanoribbon array in order to target the rapidly fading capacity and the poor rate-capability issues of Sn based materials for Li-ion batteries. The SEM images indicate a three-dimensional (3D) nanoarchitectured Sn–Sb–Co alloy with an array structure. Electrochemical measurements show that the 3D nanoarchitectured Sn54Sb41Co5 alloy electrode exhibits a reversible capacity as high as 512.8 mA h g−1 at 0.2 C (1 C = 650 mA g−1) after 150 cycles. Furthermore, the 3D nanoarchitectured Sn54Sb41Co5 anode can deliver a high reversible capacity (275 mA h g−1) up to the 80th cycle at a high discharge–charge rate of 23 C (∼15 A g−1). These outstanding electrochemical properties are attributed to the unique nanoarchitectures of the Sn54Sb41Co5 electrodes, making them an excellent anode material.

A novel dicranopteris-like Fe–Sn–Sb–P composite was prepared, for the first time, by electrodeposition. The quaternary Fe–Sn–Sb–P alloy of multiphase displayed an excellent cycling performance as an anode of Li ion secondary batteries.

Porous MnO/C nanotubes are synthesized by a facile hydrothermal method followed by thermal annealing, and possess excellent cyclability and high rate capability as an anode for lithium ion batteries.

Trapezohedral Pt nanocrystals enclosed by 24 high-index {522} facets have been successfully prepared for the first time in high yield by a direct square wave electrodeposition method. They exhibit a significantly enhanced catalytic activity for C-1 molecules (CO, CH3OH, HCOOH).

The electrochemically shape-controlled synthesis in deep eutectic solvents (DESs) has been applied to produce the electrocatalyst of Pt nanoflowers. The uniform Pt nanoflowers with sharp single crystal petals and high density of atomic steps were characterized by SEM, TEM, XRD, XPS and electrochemical tests. The results illustrated that the as-prepared Pt nanoflowers exhibit higher electrocatalytic activity and stability than commercial Pt black catalyst toward ethanol electrooxidation. The growth of Pt nanoflowers in DESs by the simple electrochemical route is straightforward and controllable in terms of nanoflowers’ shape and size, which can be applied in shape-controlled synthesis of other noble metal nanoparticles with high catalytic activity.Highlights► The electrochemically shape-controlled synthesis in deep eutectic solvents (DESs) has been applied to produce the uniform Pt nanoflowers with sharp single crystal petals and high density of atomic steps. ► The as-prepared Pt nanoflowers exhibit higher electrocatalytic activity and stability than commercial Pt black catalyst toward ethanol electrooxidation. ► The growth of Pt nanoflowers in DESs by the simple electrochemical route is straightforward and controllable in terms of nanoflowers’ shape and size.

Tetrahexahedral Pt nanocrystals (THH Pt NCs), bound by high index facets, belong to an emerging class of nanomaterials that promise to bridge the gap between model and practical electrocatalysts. The atomically stepped surfaces of THH Pt NCs are extremely active for the electrooxidation of small organic molecules but they also readily accommodate the dissociative chemisorption of such species, resulting in poisoning by strongly adsorbed CO. Formic acid oxidation is an ideal reaction for studying the balance between these competing catalyst characteristics, since it can proceed by either a direct or a CO mediated pathway. Herein, we describe electrochemical and in situ FTIR spectroscopic investigations of formic acid electrooxidation at both clean and Au adatom decorated THH Pt NC surfaces. The Au decoration leads to higher catalytic currents and enhanced CO2 production in the low potential range. As the CO oxidation behaviour of the catalyst is not improved by the presence of the Au, it is likely that the role of the Au is to promote the direct pathway. Beyond their fundamental importance, these results are significant in the development of stable, poison resistant anodic electrocatalysts for direct formic acid fuel cells.

Aimed at searching for highly active and stable nano-scale Pt-based catalysts that can improve significantly the energy conversion efficiency of direct ethanol fuel cells (DEFCs), a novel Pt–PbOx nanocomposite (Pt–PbOx NC) catalyst with a mean size of 3.23 nm was synthesized through a simple wet chemistry method without using a surfactant, organometallic precursors and high temperature. Electrocatalytic tests demonstrated that the as-prepared Pt–PbOx NC catalyst possesses a much higher catalytic activity and a longer durability than Pt nanoparticles (nm-Pt) and commercial Pt black catalysts for ethanol electrooxidation. For instance, Pt–PbOx NC showed an onset potential that was 30 mV and 44 mV less positive, together with a peak current density 1.7 and 2.6 times higher than those observed for nm-Pt and Pt black catalysts in the cyclic voltammogram tests. The ratio of current densities per unit Pt mass on Pt–PbOx NC, nm-Pt and Pt black catalysts is 27.3:3.4:1 for the long-term (2 hours) chronoamperometric experiments measured at −0.4 V (vs. SCE). In situ FTIR spectroscopic studies revealed that the activity of breaking C–C bonds of ethanol of the Pt–PbOx NC is as high as 5.17 times that of the nm-Pt, which illustrates a high efficiency of ethanol oxidation to CO2 on the as-prepared Pt–PbOx NC catalyst.

The processes of extraction and insertion of lithium ions in LiCoO2 cathode are investigated by galvanostatic cycling and electrochemical impedance spectroscopy (EIS) at different potentials during the first charge/discharge cycle and at different temperatures after 10 charge/discharge cycles. The spectra exhibit three semicircles and a slightly inclined line that appear successively as the frequency decreases. An appropriate equivalent circuit is proposed to fit the experimental EIS data. Based on detailed analysis of the change in kinetic parameters obtained from simulating the experimental EIS data as functions of potential and temperature, the high-frequency, the middle-frequency, and the low-frequency semicircles can be attributed to the migration of the lithium ions through the SEI film, the electronic properties of the material and the charge transfer step, respectively. The slightly inclined line arises from the solid state diffusion process. The electrical conductivity of the layered LiCoO2 changes dramatically at early delithiation as a result of a polaron-to-metal transition. In an electrolyte solution of 1 mol L−1LiPF6–EC (ethylene carbonate)∶DMC (dimethyl carbonate), the activation energy of the ion jump (which is related to the migration of the lithium ions through the SEI film), the thermal activation energy of the electrical conductivity and the activation energy of the intercalation/deintercalation reaction are 37.7, 39.1 and 69.0 kJ mol−1, respectively.

The present study applies electrochemical impedance spectra (EIS) to study the interfacial processes of lithium ion batteries (LIBs) and determine the corresponding kinetic parameters. The EIS of the insertion and extraction of lithium ions in layered LiNi1/3Co1/3Mn1/3O2 materials as cathode of LIBs are obtained at different potentials during the first charge/discharge cycle and at different temperatures after 10 charge/discharge cycles. The EIS spectra exhibit three semicircles and a slightly inclined line that appear successively along with decrease in frequency. The high-frequency, the middle-frequency, and the low-frequency semicircles can be attributed respectively to the migration of the lithium ions through the SEI film, the electronic properties of the material and the charge transfer step. The slightly inclined line arises from the solid state diffusion process. The electrical conductivity of the layered LiNi1/3Mn1/3Co1/3O2 changes dramatically at early delithiation as a result of an insulator-to-metal transition. In an electrolyte solution of 1 mol L−1 LiPF6–EC(ethylene carbonate): DEC(diethyl carbonate): DMC(dimethyl carbonate), the activation energy of the ion jump which is related to the migration of the lithium ions through the SEI film, the thermal activation energy of the electrical conductivity and the activation energy of the intercalation/deintercalation reaction are determined 23.1, 44.0 and 66.5 kJ mol−1, respectively.Highlights► We obtained exhaustive electrochemical properties of LiNi1/3Co1/3Mn1/3O2 by EIS. ► We first observed three semicircles via a three-electrode glass cell by EIS. ► The drastic change of electronic conductivity of LiNi1/3Co1/3Mn1/3O2 was observed. ► We proved the presence of an insulator to metal transition in LiNi1/3Co1/3Mn1/3O2. ► Kinetic parameters were calculated in 1 mol L−1 LiPF6–EC: DEC: DMC.

Atomic-level understanding of structural characteristics and thermal behaviors of nanocatalysts is important for their syntheses and applications. In this article, we present a systematic study on structural and thermal stabilities of Pt–Pd bimetallic nanoparticles with core–shell and alloyed structures by using atomistic simulations. It was revealed that the Pd-core/Pt-shell structures are the least structurally stable, while the inverted Pt-core/Pd-shell nanoparticles are more stable than the alloyed ones when the Pt percentage exceeds 42% or so. The origin for this order was clarified through analysis of atomic energy distribution in these structures. Furthermore, the core–shell structures exhibit enhanced thermal stability as compared to the alloyed ones for Pt composition more than about 30%. The diverse melting behaviors of bimetallic nanoparticles, associating with their thermally driven structural evolutions under the heating process, were characterized by the measurement of the Lindemann index. In addition, the analyses of diffusion behavior and atomic distribution suggest that the minimization of surface energy tends to form Pd surface segregation. This study is of considerable importance not only to experimental preparation of Pt–Pd nanocatalysts but also to design of bimetallic (even multimetallic) nanostructures of high catalytic activity and excellent stability.

In the present paper, we have developed for the first time the electrochemically shape-controlled synthesis in deep eutectic solvents (DESs) for the preparation of Pt nanocrystals enclosed by high-index facets. Monodispersed concave tetrahexahedral Pt nanocrystals (THH Pt NCs) have been prepared through this new route. The concave THH Pt NCs were characterized by SEM, TEM, and AFM. The as-prepared concave Pt NCs are bounded with {910} and vicinal high-index facets, which exhibit superior catalytic activity and stability to those of the commercial Pt black catalyst for ethanol electrooxidation. We have demonstrated also that the electrochemically shape-controlled synthesis in DESs proves advantageous in controlling the size and shape of Pt NCs without the addition of seeds, surfactants, or other chemicals and could be applied in the synthesis of other noble metal NCs with high surface energy and high catalytic activity.

This study aims to understand the effects of functional agents such as capping agents, stabilizers, surfactants and additives in shape-controlled synthesis of nanomaterials. The well-defined Pt(100) single crystal surface was used as a model to investigate its interaction with citrate, a capping agent that is often used in shape-controlled synthesis of nanomaterials. It demonstrated that, through a systematic study of electrochemical cyclic voltammetry, the presence of citrate in solution could increase the current peak density of hydrogen adsorption at high potential (jp,L), while decrease proportionally the current peak density of hydrogen adsorption at low potential (jp,S). Furthermore, the increase of citrate concentration shifted negatively the peak potentials (Ep,L and Ep,S) of both jp,L and jp,S. The results indicated that the interaction of citrate with Pt(100) surface could induce increasing the (100) surface domains of two-dimensional long range order (2D-(100)), and decreasing the (100) surface domains of one-dimensional short range order (1D-(100)). It also revealed that the interaction of citrate with Pt(100) surface could stabilize the 2D-(100) structure. The findings gained in this study implied that the citrate may lead to form stable 2D-(100) domains on Pt nanoparticles upon the shape-controlled synthesis of Pt nanomaterials.

The properties of nanomaterials for use in catalytic and energy storage applications strongly depends on the nature of their surfaces. Nanocrystals with high surface energy have an open surface structure and possess a high density of low-coordinated step and kink atoms. Possession of such features can lead to exceptional catalytic properties. The current barrier for widespread industrial use is found in the difficulty to synthesise nanocrystals with high-energy surfaces. In this critical review we present a review of the progress made for producing shape-controlled synthesis of nanomaterials of high surface energy using electrochemical and wet chemistry techniques. Important nanomaterials such as nanocrystal catalysts based on Pt, Pd, Au and Fe, metal oxides TiO2 and SnO2, as well as lithium Mn-rich metal oxides are covered. Emphasis of current applications in electrocatalysis, photocatalysis, gas sensor and lithium ion batteries are extensively discussed. Finally, a future synopsis about emerging applications is given (139 references).

Tetrahexahedral Pt nanocrystals (THH Pt NCs) bounded by high-index facets possess a high density of active sites and display therefore a higher catalytic activity in comparison with those enclosed by low-index facets. In the current communication, we report, for the first time, the decoration of THH Pt NC surfaces by using Bi adatoms and have demonstrated that the catalytic activity of the Bi decorated THH Pt NCs toward HCOOH electrooxidation has been drastically enhanced in comparison with bare THH Pt NCs. It has also been revealed that the catalytic activity of Bi decorated THH Pt NCs for all coverages investigated always exhibits a higher catalytic activity that is about double that of Bi decorated Pt nanospheres. The study is of great importance regarding both fundamentals and applications.

Nanostructured Cu2Sb @C material was prepared through a simple polyol approach. Hollow Cu2Sb@C core–shell nanoparticles were obtained by controlling the amount of CuCl2 and time of replacement reaction. The hollow Cu2Sb@C nanoparticle electrode showed excellent cycling performance.

Platinum is the most active and one of most commonly used catalytic metals. In this article, atomistic simulations have been employed to systematically investigate the thermal stability of platinum nanowires with single-crystalline and fivefold twinned structures. It has been revealed that the single-crystalline nanowires possess better structural stabilities than the twinned ones. Furthermore, when subjected to continuous heating, the twinned nanowires exhibit an inhomogeneous melting, essentially different from what happens in the single-crystalline ones, and hence the lower melting point. By analyses of the microstructural evolution and dynamics behavior during the heating process, the structural transition of the nanowire is discussed and the inhomogeneity in the twinned nanowire is identified to originate from the dislocation-induced destruction of twin boundaries.

High index surfaces are introduced into Pt nanocrystals because they are expected to exhibit higher catalytic activity than low index planes such as {111}, {100}, and even {110}. This article presents a systematic investigation on the structure and stability of polyhedral Pt nanocrystals with both low-index and high-index facets by means of atomistic simulations. It has been found that the stability of Pt nanocrystals depends strongly on the particle shape and surface structures. Those nanocrystals, enclosed by high-index facets of {310}, {311}, and {331}, possess better stability and higher dangling bond density of surface compared with those ones with low-index facets, such as {100} and {110}, suggesting that they should become preferential candidates for nanocatalysts. The octahedral nanocrystals with {111} facets, though they have excellent structural and thermal stabilities, present the lowest dangling bond density of surface.

A Pt nanoparticle netlike-assembly (Pt-NNA) synthesized through a facile hydrothermal method, with high specific surface area and large overall size, exhibits much higher durability and 2.9 times higher mass activity for oxygen reduction reaction than commercial Pt black catalyst.

We report the synthesis and characterization of hollow PtNi nanospheres by chemical successive-reduction method. The results of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) account for the alloy formation between Pt and Ni and electronic structure change of Pt in the alloy. The prepared nanospheres show a high activity and stability for electrocatalytic oxidation of methanol as compared to the commercial Pt/C catalyst and the co-reduced PtNi nanoparticles. The reasons of the high electrocatalytic activity of the hollow PtNi nanospheres were discussed.

The dissociative adsorption of ethylene glycol (EG) on stepped surfaces of Pt single crystal (Pt(s) − [n(100) × (111)]) was investigated. Different surface structures of these platinum single crystal electrodes were obtained by various treatment conditions. The results illustrated that the electrocatalytic activity of Pt single crystal electrodes towards EG dissociative adsorption is increased with the increase of (100) terrace length on the surfaces. It has been found that the different pretreatment hardly influences the reactivity of stepped Pt(s) − [n(100) × (111)] surfaces towards EG dissociative adsorption. The results indicated that all studied surfaces are more active in perchloric acid than in sulfuric acid, and this effect is decreased with the increase of (100) terrace length on the surfaces, demonstrating the strong adsorption of (bi)sulfate anions on (111) sites and their weak adsorption on (100) sites. This study has gained knowledge on the interaction between EG and Pt single crystal electrodes, and thrown a new insight into understanding the fundamental of electrocatalysis and surface processes of EG dissociative adsorption.► The electrocatalytic activity of Pt single crystal electrodes towards EG dissociative adsorption is increased with the increase of (100) terrace length on the stepped surfaces. ► Different pretreatments could hardly influence the reactivity of stepped Pt(s)–[n(100)×(111)] surfaces. ► The effect of specific adsorption of (bi)sulfate anions on EG dissociative adsorption is decreased with the increase of (100) terrace length on the surfaces, demonstrating the strong adsorption of (bi)sulfate anions on (111) sites and their weak adsorption on (100) sites.

In this work, surface modification at atomic level was applied to study the reactivity of step sites on platinum single crystal surfaces. Stepped platinum single crystal electrodes with (1 1 1) terraces separated by monoatomic step sites with different symmetry were decorated with irreversibly adsorbed adatoms, without blocking the terrace sites, and characterized in 0.1 M HClO4 solution. The kinetics of CO oxidation on the different platinum single crystal planes as well as on the step decorated surfaces has been studied using chronoamperometry. The apparent rate constants, which were determined by fitting the experimental data to a mean-field model, decrease after the steps of platinum single crystal electrodes have been blocked by the adatoms. This behavior indicates that steps are active sites for CO oxidation. Tafel slopes measured from the potential dependence of the apparent rate constants of CO oxidation were similar in all cases. This result demonstrates that the electrochemical oxidation of the CO adlayer on all the surfaces follows the same Langmuir–Hinshelwood model, irrespectively of step modification.Highlights► Chronoamperometry has been used to study CO oxidation on Pt stepped surfaces. ► Adatoms step decoration allows determination of the role of steps on CO oxidation. ► Rate constant decreases after step decoration with adatoms. ► Tafel slopes are around 60–90 mV/dec, suggesting a Langmuir–Hinshelwood mechanism.

Three-dimensional porous Cu film is prepared for the first time by electroless plating. Sn–Co alloy is electrodeposited on the porous Cu film to fabricate porous Sn–Co alloy electrode. SEM images evidence that porous Sn–Co alloy electrode presents a three-dimensional porous structure. XRD results show that the Sn–Co alloy electrode comprises pure Sn and CoSn2 phases. Electrochemical discharge/charge results show that the three-dimensional porous Sn–Co alloy electrode exhibits much better cycleability than planar Sn–Co alloy electrode, with first discharge capacity and charge capacity of 636.3 and 528.7 mAh g−1, respectively. After 70th cycling, capacity retention is 83.1% with 529.5 mAh g−1. The lithiation and delithiation processes during first discharge and charge were investigated by electrochemical impedance spectroscopy (EIS). EIS results together with differential capacity curves describe the process of SEI formation, charge transfer and phase transformation in the alloy electrode in the first discharge, and phase transformation during charge at delithiation potential.Highlights► An electroless plating method is applied for the first time to prepare three-dimensional (3D) porous copper film with pore size ranging from several hundred nanometers to several micrometers, and good adhesion to the substrate. ► The porous copper film is directly used as current collector of Sn–Co alloy anode for lithium ion batteries. ► Electrochemical discharge/charge results show that the three-dimensional porous Sn–Co alloy electrode exhibits much better cycleability than planar Sn–Co alloy electrode.

Ordered mesoporous carbon/sulfur (OMC/S) nanocomposites with hierarchically structured sulfur loading, ranging from 50 to 75 wt%, were synthesized via a simple melt-diffusion strategy. The OMC with a BET surface area of 2102 m2 g−1, a pore volume of 2.0 cm3 g−1 and unique bimodal mesoporous (5.6/2.3 nm) structure, was prepared from a triconstituent co-assembly method. The resulting OMC/S nanocomposite material served as cathode of rechargeable lithium–sulfur (Li–S) battery. It has been tested that the novel OMC/S cathode can deliver a superior reversible capacity and cyclability. In particular, the nanocomposite with a loading of 60 wt% sulfur (OMC/S-60) presents the highest sulfur utilization ca. 70%, an excellent high rate capability ca. 6 C and a good cycling stability for up to 400 full charge–discharge cycles. The exceptional electrochemical performances are exclusively attributed to the large internal surface area and high porosity of the ordered mesoporous carbon, which favorites both electron and Li-ion transportations.

Unexpected yet highly remarkable and intriguing observations of the polymer-enhanced electro-catalytic activity of the Pt nanoparticles for electro-oxidations of both methanol and formic acid were reported. In situFTIR investigation suggests strongly that the observed activity enhancements are highly likely due to the PVP-induced additional reaction pathways. These observations may open up a new paradigm of research in which the protecting/stabilizing organic ligands can now be incorporated as an advantageous part and/or a finer catalytic activity tuner of a nanocatalytic system.

A novel composite material of SnO2/ordered mesoporous carbon (SnO2/OMC) was prepared through a hydrolysis process. The morphology, structure and composition of the SnO2/OMC was characterized by using powder X-ray diffraction (low-angle and wide-angle diffraction patterns), transmission electron microscopy (TEM), thermogravimetric analysis (TG-DTA) and nitrogen-adsorption measurement. Cyclic voltammetry (CV) and galvanostatic discharge–charge measurements were used to test the electrochemical performance of the SnO2/OMC. It has found that the SnO2/OMC composite could deliver a reversible capacity as high as 395.6 mAh g−1 up to 50 cycles of discharge/charge. The results demonstrated also a good rate capability. When the charge current density was increased gradually from 200 to 1000 mA g−1 and then returned immediately to 200 mA g−1, 75% of the initial capacity at 200 mA g−1 has been recovered. Therefore, the SnO2/OMC is revealed as a promising candidate of anode material for high energy and high power lithium ion batteries (LIBs).

The coadsorption of CN− and CO on Pt(1 1 0) electrode in acid solutions was investigated by using cyclic voltammetry and in situ FTIR spectroscopy. In comparison with individual adsorption of CO or CN−, the onset oxidation potential of CO (COad) coadsorbed with CN− is positively shifted ca. 100 mV, and its oxidation peak is postponed ca. 260 mV together with a significant decrease in current density. When the coadsorbed CO has been stripped completely, the CV recovers the feature of Pt(1 1 0)/CN− surface, which signifies that the coadsorption of CO does not affect the oxidation behavior of the coadsorbed CN− (CNad-). In comparison of CN− and CO adsorbed alone, the CNad- band is blue shifted from 2090 to 2108 cm−1 at 0.0 V, and the stark tuning rate is decreased dramatically from 53 to 4 cm−1 V−1; while the COad band is red shifted from 2075 to 2064 cm−1 at 0.0 V, and the stark tuning rate is slightly decreased from 24 to 19 cm−1 V−1, The result revealed the strong interaction between CNad- and COad at Pt(1 1 0) surface in the coadsorption system.Highlights► CN− and CO coadsorption on Pt(1 1 0) was studied by in situ FTIR spectroscopy for the first time, and important results were reported. ► It has demonstrated that CN−ad has an inhibition effect for COad oxidation, while the anodic stripping of COad do not affect on previously adsorbed CN−. ► The results revealed the strong interaction between CN−ad and COad at Pt(1 1 0) surface in the coadsorption system.

The energetic and structural evolutions of fcc Fe nanoparticles under heating process have been investigated by molecular dynamics simulations, and the phase transition between fcc and bcc phases is addressed. It is found that the solid–solid transition from fcc to bcc phase happens prior to the melting, accompanied with the particle shape from initial sphere into ellipsoid. The critical temperatures of phase transition and melting are inversely proportional to the particle diameters. It is demonstrated that high percentage of surface atoms may be beneficial to the phase transition of fcc Fe nanoparticles.Graphical abstractSnapshots of Fe nanocrystal taken at five temperatures during continuous heating.Research highlights► The solid–solid phase transition happens in fcc Fe nanoparticles prior to the melting. ► The temperatures of phase transition and melting are inversely proportional to the particle size.

This paper reports a detailed electrochemical in situ surface-enhanced infrared reflection absorption spectroscopic (SEIRAS) investigation of two different core−shell, Ru@Pt and Au@Pt/C, metal nanoparticles (NPs). We were able to identify the most active sites and surface water species involved in the carbon monoxide oxidation reaction (COR) and methanol oxidation reaction (MOR) on these NPs. We discovered that exposing the as-synthesized Ru@Pt NPs to air could turn them into largely surface-ruthenated NPs whose structure was rather stable under multiple potential cyclings between −0.2 and 0.7 V (vs Ag/AgCl, 3 M) and reduction at −0.3 V but could be annealed by the COR. The SEIRAS data enabled the identification of the Ru-coordinated-to-Ru, Ru-coordinated-to-Pt, and Pt-islands-on-Ru-core sites on the COR-annealed Ru@Pt NPs among which the most active sites were the Pt-islands-on-Ru-core sites for the COR and MOR, as evidenced by an onset potential as low as −0.1 V for the COR. For the Au@Pt/C NPs, the SEIRAS data showed a much higher onset potential (0.45 V) for the COR that accounted for their much lower activity observed as compared to that of the Ru@Pt in terms of COR and MOR. Among the three different surface water species, namely the water monomer, the weakly hydrogen-bonded water, and the strongly hydrogen-bonded water, the SEIRAS data pointed to the weakly hydrogen-bonded water as the dominant source that provided oxygen for the COR and MOR. Furthermore, the SEIRAS data showed that the surface water structure was very different in reaction media, i.e., with preadsorbed CO or methanol, from that in pure supporting electrolyte, an observation that strongly cautions the practice of using the latter to identify the active water species.

The characterization of electrode processes induced by lithiation/delithiation of Sn−Ni alloy films electroplated on a copper substrate is presented. Galvanostatic discharge/charge measurements were combined with X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). XPS shows the buildup of a solid electrolyte interphase (SEI) layer formed by reductive decomposition of the electrolyte at the surface of the Sn−Ni anode during the first discharge. The SEI layer is constituted of a mixture of Li2CO3, ROCO2Li, Li2C2O4, and/or ROLi whose balance is not markedly modified upon cycling. ToF-SIMS depth profiling evidences an incomplete initial alloying process of lithium ion with Sn and the resulting partition of the Sn−Ni layer alloy into a fully lithiated outer part and a partially lithiated inner layer during the first discharge. After the first cycle, the volume expansion/shrink associated with the alloying/dealloying reaction, also evidenced by ToF-SIMS, irreversibly cracks and divides the Sn−Ni alloy into island-like morphology with gaps filled by the SEI layer. Multicycling (tested up to 9 cycles) amplifies the division of the Sn−Ni alloy layer and the related penetration of the SEI layer as indicated by the increase of trapped lithium and chlorine but with no apparent loss of active material or drop of capacity.

Tetrahexahedral Pd nanocrystals (THH Pd NCs) with {730} high-index facets were directly produced on a glassy carbon substrate in a dilute PdCl2 solution by a newly developed programmed electrodeposition method. The THH Pd NCs, thanks to their high density of surface atomic steps, exhibit 4−6 times higher catalytic activity than commercial Pd black catalyst toward ethanol electrooxidation in alkaline solutions. This straightforward method provides a promising route to facile preparation of high-index-faceted metal nanocatalysts with high catalytic activity.

A non-intermetallic PtPb/C catalyst of hollow structure is synthesized through a simple reduction method, and exhibits an activity as high as 3.6 times that of commercial Pd black and a much higher stability for electrooxidation of formic acid.

Sn–Co alloy films were prepared by electroplating on copper and used as anode material of lithium ion battery. Cyclic voltammetry and galvanostatic discharge/charge measurements were combined with surface analysis by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The results show the buildup of a solid electrolyte interphase (SEI) layer formed by reductive decomposition of electrolyte during the first Li–Sn alloying cycle. The layer is constituted of a mixture of Li2CO3, ROCO2Li, lithium oxalates, and/or ROLi, and its chemical composition is modified during the electrochemical multi-cycling process with increase of the Li2CO3 content. Multi-cycling also fractures the SEI layer. ToF-SIMS results revealed an incomplete initial alloying process of lithium ion with Sn, limited by mass transport through a Co layer and dividing the Sn–Co layer alloy into a fully lithiated outer part and an essentially non-lithiated inner layer during the first discharge. The volume expansion/shrink associated with the alloying/dealloying reaction irreversibly cracks and splits up the Sn–Co alloy into particles with interstitials voids filled by the SEI layer. Multi-cycling amplifies this division of the Sn–Co layer without material loss and stabilizes discharge/charge capacity.

Polyvinyl alcohol (PVA) was used as a hydrogen bond functionalizing agent to modify multi-walled carbon nanotubes (CNTs). Nanoparticles of Fe3O4 were then formed along the sidewalls of the as-modified CNTs by the chemical coprecipitation of Fe2+ and Fe3+ in the presence of CNTs in an alkaline solution. The structure and electrochemical performance of the Fe3O4/CNTs nanocomposite electrodes have been investigated in detail. Electrochemical tests indicated that at the 145th cycle, the CNTs–66.7 wt.%Fe3O4 nanocomposite electrode can deliver a high discharge capacity of 656 mAh g−1 and stable cyclic retention. The improvement of reversible capacity and cyclic performance of the Fe3O4/CNTs nanocomposite could be attributed to the nanosized Fe3O4 particles and the network of CNTs.

A new ternary Sn–Ni–P alloy rods array electrode for lithium-ion batteries is synthesized by electrodeposition with a Cu nanorods array structured foil as current collector. The Cu nanorods array foil is fabricated by heat treatment and electrochemical reduction of Cu(OH)2 nanorods film, which is grown directly on Cu substrate through an oxidation method. The Sn–Ni–P alloy rods array electrode is mainly composed of pure Sn, Ni3Sn4 and Ni–P phases. The electrochemical experimental results illustrate that the Sn–Ni–P alloy rods array electrode has high reversible capacity and excellent coulombic efficiency, with an initial discharge capacity and charge capacity of 785.0 mAh g−1 and 567.8 mAh g−1, respectively. After the 100th discharge–charge cycling, capacity retention is 94.2% with a value of 534.8 mAh g−1. The electrode also performs with an excellent rate capacity.

In this work, surface modification at an atomic level, coupled with CO as molecular probe, was applied to study the step-site reactivity of platinum single crystals. Stepped platinum single crystal electrodes with (111) terraces and step sites of different symmetry were modified by irreversible adsorption of Bi and Te adatoms selectively deposited on steps, and characterized in 0.1 M HClO4 solution. CO charge-displacement and oxidative stripping were employed to investigate the reactivity changes before and after modification of the electrode surfaces. The values of potential of zero total charge (pztc) determined from CO displacement experiments were found to shift positively on all decorated electrodes. The CO oxidation peaks also shifted to higher potential once the step sites were blocked by the adatoms, indicating a catalytic effect of the step sites for this reaction. The CO coverage values on the step sites were determined by comparing the stripping charges and the change in the hydrogen de/adsorption charge, using the pztc's for double layer correction. The CO coverage was determined to be ca. 0.7 for (110) step sites while only 0.4 for (100) step sites, which suggests a different bond of CO adsorbed on the different step sites. This was confirmed by in situ infrared reflection–absorption spectroscopy (IRAS) studies, showing that the (110) step sites are dominated by atop CO while bridged bonded CO are prevalent on (100) step sites. The comparison of CO stripping and hydrogen adsorption charges before and after adatom modification allows the separation of step and terrace contributions to the overall CO coverage.

Sn–Co alloy thin films with high IR reflectivity were prepared by electroplating on a copper substrate and served as anodes of lithium ion battery. The interfacial properties of the Sn–Co alloy anode in an electrolyte of 1 M LiPF6/EC + DMC (1:1, vol.%) during discharge/charge (or lithiation/delithiation) processes were investigated by using in situ microscope Fourier transform infrared reflection spectroscopy (in situ MFTIRS). The results demonstrated that the solvation/desolvation reactions of lithium ions with solvent molecules in discharge/charge processes vary with the concentration of both solvated and free solvent molecules, leading to the shift of CO, C–O and C–H IR bands. The effect of solvation/desolvation, which provides a possibility to probe the lithiation/delithiation processes by in situ MFTIRS, is observed and analyzed clearly. The solid electrolyte interphase (SEI) layer on a cycled Sn–Co alloy anode has also been investigated by ex situ MFTIRS, which determined that the main chemical composition of the SEI layer is ROCO2Li. The current studies are of significance in understanding the interfacial reactions involving in lithium ion battery at molecular level.

One-dimensional (1D) CoPt nanorods were synthesized by a galvanic displacement reaction. The morphology of the nanomaterials was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). Energy-dispersive X-ray spectroscopy (EDS) analysis confirmed the coexistence of Co and Pt in the 1D nanorods. Studies of cyclic voltammetry (CV) demonstrated that the 1D CoPt nanorods exhibit a better electrocatalytic property for CO oxidation than that of bulk Pt electrode does. In situ electrochemical FTIRS illustrated, for the first time, that the 1D CoPt nanorods display abnormal infrared effects (AIREs), which was previously revealed mainly on 2D film nanomaterials.It has revealed, for the first time, that the 1D CoPt nanorods present abnormal infrared effects (AIREs). The substrate materials do not affect significantly the anomalous IR features.

Electrochemical impedance spectra (EIS) for lithium ion insertion and deinsertion in spinel LiMn2O4 were obtained at different potentials and different temperatures during initial charge−discharge cycle. The results revealed that, at intermediate degrees of intercalation, three semicircles appeared in the Nyquist diagram. This new phenomenon has been investigated through EIS measurements as a function of temperature. It has found that the high frequency semicircle and the middle to high frequency semicircle begin to overlap each other above 20 °C, which indicates that the high frequency compressed semicircle commonly obtained at room temperature in the literature may consist of two semicircles. This signifies that the effects of the electronic and ionic transport properties of lithium intercalation materials clearly appear as separate features in the EIS spectra at low temperatures. A new equivalent circuit that includes elements related to the electronic and ionic transport, in addition to the charge transfer process, is proposed to simulate the experimental EIS data. The change of kinetic parameters for lithium ion insertion and deinsertion in spinel LiMn2O4 as a function of potential in the first charge−discharge cycle is discussed in detail, and a modified model is proposed to explain the impedance response of the insertion materials for lithium ion batteries.

By means of atomistic simulations, we have investigated the energetics and stability of Fe nanocrystals with different crystal structures and shapes. It has been found that structural stability of Fe nanocrystals depends strongly on the size of nanocrystals. Furthermore, twinned fcc nanocrystals are energetically more stable than bcc single nanocrystals at very small sizes. Investigation on dynamics evolution of fcc Fe nanocrystals under heating reveals that the solid−solid phase transition from fcc to bcc occurs prior to the melting. The temperature of phase transformation depends on the shape of Fe nanocrystals. The bcc phase preferentially nucleates in apes of fcc Fe nanocrystals and spreads through entire ones with increased temperature. Twin structures suppress the propagation of the nucleated bcc phase, thereby, enhancing the thermal stability of twinned fcc Fe nanocrystals.

In this work, we develop a novel method to prepare a well-dispersed platinum precursor in the modified mesoporous carbon-46 (MPC) by using a simple melt−diffusion strategy. After the Pt precursor was reduced by hydrogen gas, almost 100% platinum nanoparticle catalysts (Pt/MPC) were confined in the pores of MPC. Physical (XRD, HRTEM, and BET), electrochemical, and in situ FTIR spectroscopic methods were used to investigate the properties of the Pt/MPC. The HRTEM image illustrates that Pt nanoparticles (NPs) of ca. 2−3 nm are loaded inside the small mesopores of the pore walls and NPs of ca. 5−6 nm are in the mesochannels of the MPC, and the Pt loading in Pt/MPC is 35 wt %. In comparison with the commercial Pt/C catalysts (40 wt %, Johnson Matthey), the Pt/MPC displays a high activity toward ethanol oxidation. The Pt/MPC exhibits also a high durability after a long-time potential scan: the loss of catalytic surface area is only 4.73% for Pt/MPC, whereas it is 14.75% for Pt/C. Moreover, in situ FTIR studies demonstrate that the Pt/MPC can promote the cleavage of the C−C bond of ethanol.

Fe nanocrystal catalysts were synthesized by electrochemistry. Shape transformations of Fe nanocrystals from rhombic dodecahedra and tetragonal bipyramids, both bounded by {110} facets, to 18-facet polyhedra enclosed by different combinations of {110} and {100} facets and finally to cubes exclusively covered by {100} facets have been achieved. A study of the surface-structure functionality of the Fe nanocrystals toward electroreduction of nitrite revealed that the electrocatalytic activity of the Fe nanocrystals increases as the fraction of {100} facets on the surface of the Fe NCs increases.

Fivefold twinned Pd nanorods bounded by high-index facets of {hk0} or {hkk} were prepared by an electrochemical method and tested as electrocatalysts of high activity for ethanol oxidation.

CuO nanoribbons array (NRA) electrode was fabricated by developing a one-step synthesis route, which consists of advantages of large-scale, fast, and without using any surfactant or template. The structure and electrochemical properties of the CuO NRA electrode were examined by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV) and galvanostatic cycling. The results demonstrated that the CuO NRA electrode can deliver a reversible capacity as high as 608 mAh g−1 up to 275th cycle. The excellent cycleability, the high capacity retention and the high rate-capability of the CuO NRA electrode is attributed to its peculiar nanostructure with large surface area, numerous interspaces of the CuO nanoribbons, and the solid adhesion of the active material to Cu current collector.

The three-dimensional porous Fe–Sb–P amorphous alloy electrodes were prepared by electroplating on porous copper current collector. The structure and electrochemical performance of the electroplated Fe–Sb–P amorphous alloy electrodes have been investigated in detail. XRD results showed that the as-deposited Fe–Sb–P alloy electrode exhibits an amorphous nature. Electrochemical tests indicated that at the 50th cycle, the Fe–Sb–P amorphous alloy electrodes can deliver a discharge capacity of 448 mAh g−1. The porous and amorphous structure of electrode of Fe–Sb–P alloy was beneficial in relaxing the volume expansion during cycling, which improved the cycle ability of Fe–Sb–P alloy electrode.

Porous Sn–Co–P alloy with reticular structure were prepared by electroplating using copper foam as current collector. The structure and electrochemical performance of the electroplated porous Sn–Co–P alloy electrodes were investigated in detail. Experimental results illustrated that the porous Sn–Co–P alloy consists of mainly SnP0.94 phase with a minor quantity of Sn and Co3Sn2. Galvanostatic charge–discharge tests of porous Sn–Co–P alloy electrodes confirmed its excellent performances: at 50th charge–discharge cycle, the discharge specific capacity is 503 mAh g−1 and the columbic efficiency is as high as 99%. It has revealed that the porous and multi-phase composite structure of the alloy can restrain the pulverization of electrode in charge/discharge cycles, and accommodate partly the volume expansion and phase transition, resulting in good cycleability of the electrode.

Nanoparticles of Sn–Co alloy were deposited on the surface of multi-walled carbon nanotubes (CNTs) by reductive precipitation of solution of chelating metal salts within a CNTs suspension. The Sn–Co/CNTs nano-composite revealed a high reversible capacity of 424 mA h g−1 and stable cyclic retention at 30th cycle. The improvement of reversible capacity and cyclic performance of the Sn–Co/CNTs composite is attributed to the nanoscale dimension of the Sn–Co alloy particles and the network of CNTs. Inactive Co as glue matrix of Sn prevents the possible pulverization of nanosized alloy particles. The CNTs could be pinning the Sn–Co alloy particles on their surfaces so as to hinder the agglomeration of Sn–Co alloy particles, while maintaining electronic conduction as well as accommodating drastic volume change during Li insertion and extraction reactions.

A novel ternary Sb–Co–P alloy electrode was prepared by electroplating on copper current collector as a promising negative electrode material for lithium-ion batteries. The structural and morphological features of the Sb–Co–P alloy were characterized by powder X-ray diffraction (XRD) and scanning electron microscope (SEM). The as-prepared alloy electrode exhibits a high specific capacity and an excellent cycleability. The initial discharge and charge capacities of the Sb–Co–P alloy anode were measured 700 and 539 mA h g−1, respectively. The results suggest that the Sb–Co–P alloy material obtained by the electrodeposition shows a good candidate anode material for lithium-ion batteries.

Ultra-thin Cr2O3 films (12.0, 17.3 and 29.6 nm thick) were produced on Cr metal by thermal oxidation, and their electrochemical properties in 1 M LiClO4 in propylene carbonate (PC) were investigated by cyclic voltammetry and chronopotentiometry. The reductive electrolyte decomposition and the conversion/deconversion process were observed and analyzed by X-ray photoelectron spectroscopy (XPS), polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The initial irreversible capacity due to the reduction of electrolyte and the incomplete deconversion process during the first cycle is 70% of the first discharge capacity. A stable charge/discharge capacity of 460 mAh g−1 was obtained in the 3rd to 10th cycles. XPS and PM-IRRAS evidenced the growth of a solid electrolyte interphase (SEI) layer that is constituted of Li2CO3 formed by reductive decomposition of the electrolyte. The SEI layer thickness and/or density is modified by the conversion/deconversion reaction. ToF-SIMS evidenced the volume expansion/shrink resulting from the conversion/deconversion reaction. ToF-SIMS also revealed an incomplete conversion process limited by mass transport, which partitions the oxide into a converted outer part assigned to Li2O containing Cr traces and an unconverted inner part ascribed to Cr2O3 or lower Cr oxide containing Li. It was found that the deconversion re-homogenizes the oxide film in a single layer but with lithium trapped in it. The present study provides a detailed understanding of the interfacial reaction on the oxide anode undergoing a conversion/deconversion reaction.

Three-dimensional (3D) porous materials of Sn–Ni alloy with reticular structure were prepared by electroplating using copper foam as current collector. The structure and electrochemical performance of the electroplated 3D porous Sn–Ni alloys were investigated in detail. Experimental results illustrated that the 3D porous Sn–Ni alloy consists of mainly Ni3Sn4 phase with a hexagonal structure. Galvonostatic charging/discharging of annealed 3D porous Sn–Ni alloy confirmed its excellent performances: at 50th charge–discharge cycle, the discharge specific capacity is 505 mAh g−1 and the corresponding charge (delithiation) specific capacity is 501 mAh g−1, yielding columbic efficiency as high as 99%. It has revealed that the porous structure of the alloy can restrain the pulverization of electrode in charge/discharge cycles, and accommodate partly the volume expansion and phase transition, resulting in a significant improvement of cycle life of the Sn–Ni electrode.

Porous Cu was prepared by electrodepositing Cu on a Cu foil using hydrogen bubbles as dynamic template, followed annealing at appropriate conditions to strengthen the adhesion between the porous Cu layer and the Cu foil substrate. Sn–Co alloy was then electrodeposited on the porous Cu substrate which served as current collector to be used as anode of lithium ion battery. X-ray diffraction (XRD) and EDS analysis indicated that the Sn–Co alloy was an intermetallic compound of CoSn3, whose surface structure is stable as illustrated by scanning electronic microscopy (SEM) images obtained before and after electrochemical cycles. It has also revealed that the Sn–Co alloy anode on the porous Cu substrate possessed a relative large capacity and a superior cycleability than that of the Sn–Co alloy anode on the smooth Cu sheet. The first discharge and charge capacities were measured respectively at 726 and 563 mAh g−1, and its capacity in the 50th cycle was retained at ca. 71% of that in the second cycle, which has been improved more than 3 times higher of that of the Sn–Co alloy anode on the smooth Cu sheet under the same conditions.

Sn–Co alloys were electrodeposited on the rough Cu foil and smooth Cu sheet, respectively. The capacity retention of the Sn–Co alloy electrode electrodeposited on the rough Cu foil in the 70th cycle was found to be 80.0% compared with the maximal capacity, which was much better than that of the Sn–Co alloy electrode on the smooth Cu sheet. The revolution of the surface morphology of the Sn–Co alloy electrode during cycling was investigated by scanning electron microscopy. The result indicated that the reversibility of the expansion and contraction of the Sn–Co alloy electrode on the rough Cu foil during charging/discharging assisted by the unique rough surface was one main reason of improving the cycleability. Solid electrolyte interphase (SEI) film was detected on the Sn–Co alloy electrode surface by electrochemical impedance spectroscopy (EIS) during lithiation/delithiation, and the result demonstrated that the SEI film suffered breaking and repairing at different lithiation status. In addition, the unique phase transformation process for the Sn–Co alloy electrode during first lithiation was also investigated by EIS.

In the present paper we study the kinetics of dissociative adsorption of formic acid on the electrode of tetrahexahedral platinum nanocrystals (THH Pt NCs). In situ FTIR spectroscopic results demonstrate that HCOOH can be oxidized to CO2 at a low potential (−0.2 V(SCE)) on the THH Pt NCs electrode, and the chemical bonds inside formic acid molecule are broken to form adsorbed COL species. The kinetics of the dissociative adsorption of HCOOH was quantitatively investigated by employing programmed potential step technique. It has been determined that, in 5 × 10−3 mol·L−1 HCOOH + 0.1 mol·L−1 H2SO4 solution, the maximal value of the average rate (υamax) of dissociative adsorption of HCOOH on a commercial Pt/C catalyst electrode is 8.58 × 10−10 mol·cm−2·s−1, while on the THH Pt NCs the υamax is 1.5 times larger than the υamax measured on Pt/C and reaches 13.19 × 10−10 mol·cm−2·s−1. The results have revealed that the reactivity of the THH Pt NCs is much higher than that of the Pt/C catalysts.

The first lithiation of graphite electrode was investigated by electrochemical impedance spectroscopy (EIS) and scanning electron microscope (SEM) in a two-electrode button cell and a three-electrode glass cell. The results demonstrate that the study of the variation of EIS feature of the graphite electrode in the two-electrode button cell with electrode polarization potential decreasing in the first lithiation cannot be used to investigate the formation mechanism of the solid electrolyte interphase (SEI) film. However, the formation and growth process of the SEI film can be acquired by investigating the variation of EIS features of the graphite electrode in the three-electrode glass cell with the decrease of electrode polarization potential in the first lithiation. Moreover, the results also point out that the SEI film on graphite electrode is mainly formed between 1.0 and 0.6 V in the first lithiation.

CoPt nanoparticles supported on a glassy carbon electrode (denoted as CoPt/GC) were prepared by galvanic replacement reaction between electrodeposited Co nanoparticles and K2PtCl6 solution. Scanning electron microscope (SEM) and transmission electron microscope (TEM) were both employed to characterize the CoPt nanoparticles. It was shown that the CoPt nanoparticles have irregular shapes and most of them exhibit a core-shell structure with a porous Co core and a shell of Pt tiny particles. The composition of the CoPt nanoparticles was analyzed by energy-dispersive X-ray spectroscopy (EDX), which depicts a Co:Pt ratio of ca. 21:79. Studies of cyclic voltammetry (CV) demonstrated that CoPt/GC possesses a much higher catalytic activity towards CO and methanol electrooxidation than a nanoscale Pt thin film electrode. In situ FTIR spectroscopic studies have revealed for the first time, that a CoPt nanoparticles electrode exhibits abnormal IR effects (AIREs) for IR absorption of CO adsorbed on it. In comparison with the IR features of CO adsorbed on a bulk Pt electrode, the direction of the IR bands of CO adsorbed on the CoPt/GC electrode is inverted completely, and the intensity of the IR bands has been enhanced up to 15.4 times. The AIREs is significant in detecting the adsorbed intermediate species involved in electrocatalytic reactions. The results demonstrated a reaction mechanism of CH3OH oxidation on CoPt/GC in alkaline solutions through evidencing COL, COM, HCOO−, CO32−, HCO3− and CO2 as intermediate and product species by in situ FTIRS.

Dissociative adsorption and electrooxidation of dimethyl ether (DME) on a platinum electrode in different pH solutions were studied using cyclic voltammetry (CV) and in situ FTIR reflection spectroscopy. The coverage of the dissociative adsorbed species was measured about 70% from hydrogen adsorption-desorption region (0.05-0.35 V (vs RHE)) of steady-state voltammogram recorded in 0.1 mol·L−1 H2SO4 solution. It was found that the electrochemical reactivity of DME was pH dependent, i.e., the larger the pH value was, the less the reactivity of DME would be. No perceptible reactivity of DME in 0.1 mol·L−1 NaOH solution could be detected. It was revealed that the protonation of the oxygen atom in the C-O-C bond played a key role in the electrooxidation of DME. In situ FTIR spectroscopic results illustrated that linearly bonded CO (COL) species determined at low potential region were derived from the dissociative adsorption of DME and behaved as ‘poisoning’ intermediate. The COL species could be oxidized to CO2 at potential higher than 0.55 V (vs RHE) and in the potential range from 0.75 to 1.00 V (vs RHE) DME was oxidized simultaneously via HCOOH species that were identified as the reactive intermediates.

The electrochemical processes of irreversibly adsorbed antimony (Sbad) on Au electrode were investigated by cyclic voltammetry (CV) and electrochemical quartz crystal microbalance (EQCM). CV data showed that Sbad on Au electrode yielded oxidation and reduction features at about 0.15 V (vs saturated calomel electrode, SCE). EQCM data indicated that Sbad species were stable on Au electrode in the potential region from −0.25 to 0.18 V (vs SCE); the adsorption of Sb inhibited the adsorption of water and anion on Au electrode at low electrode potentials. Sb2O3 species was suggested to form on the Au electrode at 0.18 V. At a potential higher than 0.20 V the Sb2O3 species could be further oxidized to Sb(V) oxidation state and then desorbed from Au electrode.

Nanoparticles of platinum group metals (PGM) supported on diverse substrate materials are widely used catalysts in many important fields such as modern chemical industry, petrochemical industry, automobile exhaust purification, and fuel cells. Due to the extremely high cost and rare reserve of the PGM on the earth, to further improve the catalytic activity, stability, and utility efficiency of PGM nanoparticles is the key issue in relevant industrial development as well as the challenge of basic research of science and technology. This feature article summarizes at first the relationship between surface structure and catalytic functionality gained by using metal single-crystal planes as model electrocatalysts, which reveals that high-index planes, i.e., the planes denoted by a set of Miller indices (hkl) with at least one index being larger than unit, with high density of atomic steps and kinks, exhibit generally high catalytic reactivity and stability. Next, guided by the knowledge acquired in model electrocatalysis, we put emphasis upon the electrochemically shape-controlled synthesis of Pt and Pd nanocrystals (NCs) bounded by high-index facets, including tetrahexahedral NCs with 24 {hk0} facets, trapezohedral NCs with 24 {hkk} facets, concave hexoctahedral NCs with 48 {hkl} facets, and multiple twinned nanorods with {hk0} facets. Finally, challenging issues and future prospects in this exciting field are outlined.

Electrooxidation of dimethoxymethane (DMM, H2C(OCH3)2), a promising alternative fuel to methanol in direct fuel cells, on a Pt electrode in acidic solutions was studied by in situ Fourier transform infrared (FTIR) reflection spectroscopy. The study revealed that the dissolved products of DMM oxidation are mainly methyl formate (MF, HCOOCH3), methanol and CO2, and the adsorbed species are linearly bonded CO (COL) that are derived from the further dissociative adsorption of methanol. The variation of products involved in DMM oxidation at different electrode potentials was analyzed quantitatively from in situ FTIR spectra. The results demonstrated that the MF and methanol are preferentially generated at low potentials or in the initial stage of DMM oxidation, while CO2 dominates at high potentials or in the final oxidation step. On the basis of experimental results, a reaction mechanism of DMM oxidation on Pt electrode was suggested at molecular level.

Functionalized molecular sieve SBA-15 with trimethylchlorosilane was used as an inorganic filler in a poly(ethyleneoxide) (PEO) polymer matrix to synthesize a composite solid-state polymer electrolyte (CSPE) using LiClO4 as the doping salts, which is designated to be used for rechargeable lithium batteries. The methyl group-functionalized SBA-15 (fSBA-15) powder possesses more hydrophobic characters than SBA-15, which improves the miscibility between the fSBA-15 filler and the PEO matrix. The interaction between the fSBA-15 and PEO polymer matrix was investigated by scanning electron microscopy, X-ray diffraction, and differential scanning calorimetry. Linear sweep voltammetry and electrochemical impedance spectroscopy were employed to study the electrochemical stability windows, ionic conductivity, and interfacial stability of the CSPE. The temperature dependence of the change of the PEO polymer matrix in the CSPE from crystallization to amorphous phase was surveyed, for the first time, at different temperature by Fourier transform infrared emission spectroscopy. It has demonstrated that the addition of the fSBA-15 filler has improved significantly the electrochemical compatibility of the CSPE with a lithium metal electrode and enhanced effectively the ion conductivity of the CSPE.

The interaction of colloid-based, carbon supported Pt/C (40 wt%), PtRu/C (45 wt%) and Pt3Sn/C (24 wt%) catalysts with ethanol and their performance for ethanol electrooxidation were investigated in model studies by electrochemical, in situ infrared spectroscopy and on-line differential electrochemical mass spectrometry measurements. The combined application of in situ spectroscopic techniques on realistic catalysts and under realistic reaction (DEMS, IR) and transport conditions (DEMS) yields new insight on mechanistic details of the reaction on these catalysts under the above reaction and transport conditions. Based on these results, the addition of Sn or Ru, though beneficial for the overall activity for ethanol oxidation, does not enhance the activity for C–C bond breaking. Dissociative adsorption of ethanol to form CO2 is more facile on the Pt/C catalyst than on PtRu/C and Pt3Sn/C catalysts within the potential range of technical interests (<0.6 V), but Pt/C is rapidly blocked by an inhibiting CO adlayer. In all cases acetaldehyde and acetic acid are dominant products, CO2 formation contributes less than 2% to the total current. The higher ethanol oxidation current density on the Pt3Sn/C catalyst at these potentials results from higher yields of C2 products, not from an improved complete ethanol oxidation to CO2.

Three-dimensional porous Cu6Sn5 alloy electrodes were prepared by electroplating using copper foam as the current collector. The micro-holes and small islands on surface of the Cu6Sn5 alloy largely increased the surface area of the electrode, and significantly improved the ability of the electrode in buffering the volume change in the process of charge/discharge when the Cu6Sn5 alloy was employed as the anode in a lithium-ion battery. Galvonostatic charging/discharging results demonstrated that the initial discharge (lithiation) and charge (delithiation) specific capacities of the Cu6Sn5 alloy electrode were 620 mAh·g−1 and 560 mAh·g−1, respectively. It demonstrated that the Cu6Sn5 alloy electrode exhibited a large initial coulomb efficiency (90.3%) and good capacity retention. Scanning electron microscopy (SEM) results illustrated that the Cu6Sn5 alloy deposited on copper foam substrate was more stable than that on a conventional copper substrate, and displayed no obvious exfoliation after 50 charge/discharge cycles.

The storage behavior and the first delithiation of LiCoO2 electrode in 1 mol/L LiPF6-EC:DMC:DEC electrolyte were investigated by electrochemical impedance spectroscopy (EIS). It has found that, along with the increase of storage time, the thickness of SEI film increases, and some organic carbonate lithium compounds are formed due to spontaneous reactions occurring between the LiCoO2 electrode and the electrolyte. When electrode potential is changed from 3.8 to 3.95 V, the reversible breakdown of the resistive SEI film occurs, which is attributed to the reversible dissolution of the SEI film component. With the increase of electrode potential, the thickness of SEI film increases rapidly above 4.2 V, due to overcharge reactions. The inductive loop observed in impedance spectra of the LiCoO2 electrode in Li/LiCoO2 cells is attributed to the formation of a Li1−xCoO2/LiCoO2 concentration cell. Moreover, it has been demonstrated that the lithium-ion insertion-deinsertion in LiCoO2 hosts can be well described by both Langmuir and Frumkin insertion isotherms, and the symmetry factor of charge transfer has been evaluated at 0.5.

Surface processes of CO2 reduction on Pt(210), Pt(310), and Pt(510) electrodes were studied by cyclic voltammetry. Different surface structures of these platinum single crystal electrodes were obtained by various treatment conditions. The experimental results illustrated that the electrocatalytic activity of Pt single crystal electrodes towards CO2 reduction is decreased in an order of Pt(210)>Pt(310)>Pt(510), i.e., with the decrease of (110) step density on well-defined surfaces. When the surfaces were reconstructed due to oxygen adsorption, the catalytic activity of all the three electrodes has been enhanced to a certain extent. Although the activity order remains unchanged, the electrocatalytic activity has been enhanced more significantly as the density of (110) step sites is more intensive on the Pt single crystal surface. It has revealed that the more open the surface structure is, the more active the Pt single crystal electrode will be, and the easier for the electrode to be transformed into a surface structure that exhibits higher activity under external inductions. However, the relatively ordered surfaces of Pt single crystal electrode are comparatively stable under the same external inductions. The present study has gained knowledge on the interaction between CO2 and Pt single crystal electrode surfaces at a microscopic level, and thrown new insight into understanding the surface processes of electrocatalytic reduction of CO2.

Abstract

The shapes of noble metal nanocrystals (NCs) are usually defined by polyhedra that are enclosed by {111} and {100} facets, such as cubes, tetrahedra, and octahedra. Platinum NCs of unusual tetrahexahedral (THH) shape were prepared at high yield by an electrochemical treatment of Pt nanospheres supported on glassy carbon by a square-wave potential. The single-crystal THH NC is enclosed by 24 high-index facets such as {730}, {210}, and/or {520} surfaces that have a large density of atomic steps and dangling bonds. These high-energy surfaces are stable thermally (to 800°C) and chemically and exhibit much enhanced (up to 400%) catalytic activity for equivalent Pt surface areas for electro-oxidation of small organic fuels such as formic acid and ethanol.

The storage behavior and process of the first delithiation-lithiation of LiCoO2 cathode were investigated by electrochemical impedance spectroscopy (EIS). The electronic and ionic transport properties of LiCoO2 cathode along with variation of electrode potential were obtained in 1 mol·L−1 LiPF6-EC:DMC: DEC electrolyte solution. It was found that after 9 h storage of the LiCoO2 cathode in electrolyte solutions, a new arc appears in the medium frequency range in Nyquist plots of EIS, which increases with increasing the storage time. In the charge/discharge processes, the diameter of the new arc is reversibly changed with electrode potential. Such variation coincides well with the electrode potential dependence of electronic conductivity of the LiCoO2. Thus this new EIS feature is attributed to the change of electronic conductivity of LixCoO2 during storage of the LiCoO2 cathode in electrolyte solutions, as well as in processes of intercalation-deintercalationtion of lithium ions. It has been revealed that the reversible increase and decrease of the resistance of SEI film in charge-discharge processes can be also ascribed to the variation of electronic conductance of active materials of the LiCoO2 cathode

The reduction of CO2 on a Pt(100) electrode in CO2 saturated 0.5 M H2SO4 solutions was studied by in situ FTIR reflection spectroscopy and a programmed potential step technique. Different surface structures of Pt(100) electrode were prepared by different treatments including fast potential cycling (200 V s−1) for a known time. The Pt(100) surface was characterized by a parameter γ that designates the relative amplitude of the current peak of hydrogen adsorption on (100) sites distributed on the one-dimensional surface domains to that on the two-dimensional surface domains. The in situ FTIR spectroscopic results demonstrated that the reduction of CO2 on the Pt(100) dominated by two-dimensional surface domains produced only bridge-bonded CO (COB) species, which give rise to IR absorption near 1840 cm−1. However both bridge- and linear-bonded CO (COL, yielding IR absorption at around 2010 cm−1) species are found for CO2 reduction on the Pt(100) dominated by one–dimensional surface domains. The small intensity of the COL and COB bands indicates that coverage by reduced CO2 species (r-CO2, or COL and COB species) is low. The cyclic voltammetric (CV) studies confirmed quantitatively the in situ FTIRS results, and revealed that the r-CO2 species adsorb preferentially on (100) sites distributed on the two-dimensional surface domains. The initial rate of CO2 reduction υi, i.e., the rate of CO2 reduction on a clean Pt(100) surface, has been determined quantitatively from studies using a programmed potential step technique. It has been demonstrated that the maximum values of υi (υim) measured on Pt(100) electrodes with different surface structures all appeared at − 0.19 V. From analysis of the relationship between υim and γ we have determined that the υim of CO2 reduction on (100) sites distributed on the two-dimensional surface domains is 0.53 × 10−11 mol cm−2 s−1 and that on (100) sites distributed on the one-dimensional surface domains is approximately 2.66 × 10−11 mol cm−2 s−1. Based on in situ FTIRS and electrochemical studies a migration process of the r-CO2 from the one-dimensional surface domains to the two-dimensional surface domains has been proposed to be involved in CO2 reduction. The present study has thrown new light on the electrocatalytic activity of different surface structures of a Pt(100) electrode and the surface processes and kinetics of CO2 reduction.

•Octahedral PtCu nanocrystals have been synthesized by a developed facile strategy for the one-pot synthesis without using surfactants.•The area specific activity and mass activity of the synthesized octahedral PtCu/C reach 4.25 mA cm−2 and 1.20 mA µgPt−1 at 0.90 V (vs RHE), respectively, which are 21.3 and 8.6 times higher than those of commercial Pt/C catalyst.•A tiny amount of gold doping, without much compromising ORR activity, can suppress diffusion/dissolution of low-coordinated Pt atoms and greatly enhance the stability of octahedral PtCu alloy.In fuel cell technologies, the sluggish kinetics of oxygen reduction reaction (ORR) on the cathode is the main obstacle, and it is thus urgent to develop high-performance catalysts. In this work, we have synthesized 10 nm-sized octahedral PtCu alloy nanocrystals by a simple one-pot strategy using I- as shape-directing agent instead of using large surfactants. The area specific activity and mass activity of the synthesized octahedral PtCu/C reach 4.25 mA cm−2 and 1.20 mA μgPt−1 at 0.90 V (vs RHE), respectively, which are 21.3 and 8.6 times higher than those of commercial Pt/C catalysts. Unexpectedly, we found that the stability of PtCu/C can be enhanced dramatically by doping trace Au (Au/Pt =0.0005). The mass activity loss of PtCuAu0.0005/C was only 8%, much smaller than those of PtCu/C (32%), and Pt/C (52%) after 10,000 potential cycles. This study provides a strategic design of Pt-based efficient ORR catalysts for fuel cells.Compared with their high ORR activity, the stability of PtCu octahedral nanoparticles is not satisfied, which is hindered by the diffusion/ dissolution of low-coordinated Pt atoms at the defect sites. The trace Au atoms preferentially protects these Pt atoms and inhibits the diffusion/dissolution of these Pt atoms, which is helpful for the maintenance of the shape and thus might promise a high stability.

The processes of extraction and insertion of lithium ions in LiCoO2 cathode are investigated by galvanostatic cycling and electrochemical impedance spectroscopy (EIS) at different potentials during the first charge/discharge cycle and at different temperatures after 10 charge/discharge cycles. The spectra exhibit three semicircles and a slightly inclined line that appear successively as the frequency decreases. An appropriate equivalent circuit is proposed to fit the experimental EIS data. Based on detailed analysis of the change in kinetic parameters obtained from simulating the experimental EIS data as functions of potential and temperature, the high-frequency, the middle-frequency, and the low-frequency semicircles can be attributed to the migration of the lithium ions through the SEI film, the electronic properties of the material and the charge transfer step, respectively. The slightly inclined line arises from the solid state diffusion process. The electrical conductivity of the layered LiCoO2 changes dramatically at early delithiation as a result of a polaron-to-metal transition. In an electrolyte solution of 1 mol L−1LiPF6–EC (ethylene carbonate)∶DMC (dimethyl carbonate), the activation energy of the ion jump (which is related to the migration of the lithium ions through the SEI film), the thermal activation energy of the electrical conductivity and the activation energy of the intercalation/deintercalation reaction are 37.7, 39.1 and 69.0 kJ mol−1, respectively.

Electroreduction of CO2 to hydrocarbons on a copper surface has attracted much attention in the last few decades for providing a sustainable way for energy storage. During the CO2 and further CO electroreduction processes, deoxygenation that is C–O bond dissociation, and hydrogenation that is C–H bond formation, are two main types of surface reactions catalyzed by the copper electrode. In this work, by performing the state-of-the-art constrained ab initio molecular dynamics simulations, we have systematically investigated deoxygenation and hydrogenation reactions involving two important intermediates, COHads and CHOads, under various conditions of (i) on a Cu(100) surface without water molecules, (ii) at the water/Cu(100) interface and (iii) at the charged water/Cu(100) interface, in order to elucidate the electrochemical interfacial influences. It has been found that the electrochemical interface can facilitate considerably the C–O bond dissociation via changing the reaction mechanisms. However, C–H bond formation has not been affected by the presence of water or electrical charge. Furthermore, the promotional roles of an aqueous environment and negative electrode potential in deoxygenation have been clarified, respectively. This fundamental study provides an atomic level insight into the significance of the electrochemical interface towards electrocatalysis, which is of general importance for understanding electrochemistry.

High index surfaces are introduced into Pt nanocrystals because they are expected to exhibit higher catalytic activity than low index planes such as {111}, {100}, and even {110}. This article presents a systematic investigation on the structure and stability of polyhedral Pt nanocrystals with both low-index and high-index facets by means of atomistic simulations. It has been found that the stability of Pt nanocrystals depends strongly on the particle shape and surface structures. Those nanocrystals, enclosed by high-index facets of {310}, {311}, and {331}, possess better stability and higher dangling bond density of surface compared with those ones with low-index facets, such as {100} and {110}, suggesting that they should become preferential candidates for nanocatalysts. The octahedral nanocrystals with {111} facets, though they have excellent structural and thermal stabilities, present the lowest dangling bond density of surface.

A novel nanoarchitectured Sn–Sb–Co alloy electrode is reported, which was prepared by direct electrodeposition on a Cu nanoribbon array in order to target the rapidly fading capacity and the poor rate-capability issues of Sn based materials for Li-ion batteries. The SEM images indicate a three-dimensional (3D) nanoarchitectured Sn–Sb–Co alloy with an array structure. Electrochemical measurements show that the 3D nanoarchitectured Sn54Sb41Co5 alloy electrode exhibits a reversible capacity as high as 512.8 mA h g−1 at 0.2 C (1 C = 650 mA g−1) after 150 cycles. Furthermore, the 3D nanoarchitectured Sn54Sb41Co5 anode can deliver a high reversible capacity (275 mA h g−1) up to the 80th cycle at a high discharge–charge rate of 23 C (∼15 A g−1). These outstanding electrochemical properties are attributed to the unique nanoarchitectures of the Sn54Sb41Co5 electrodes, making them an excellent anode material.

In this work, we have studied methanol oxidation mechanisms on RuO2(100) by using density functional theory (DFT) calculations and ab initio molecular dynamics (MD) simulations with some explicit interfacial water molecules. The overall mechanisms are identified as: CH3OH* → CH3O* → HCHO* → HCH(OH)2* → HCHOOH* → HCOOH* → mono-HCOO* → CO2*, without CO formation. This study provides a theoretical insight into C1 molecule oxidation mechanisms at atomic levels on metal oxide surfaces under an aqueous environment.

Shape transformation of Pt nanocrystals from a {730}-bounded tetrahexahedron into a {310}-bounded truncated ditetragonal prism was achieved using the electrochemical square-wave potential method. The transformation process and mechanism were revealed. This study provides new insight into the nanocrystal growth habit.

CoPt nanoparticles supported on a glassy carbon electrode (denoted as CoPt/GC) were prepared by galvanic replacement reaction between electrodeposited Co nanoparticles and K2PtCl6 solution. Scanning electron microscope (SEM) and transmission electron microscope (TEM) were both employed to characterize the CoPt nanoparticles. It was shown that the CoPt nanoparticles have irregular shapes and most of them exhibit a core-shell structure with a porous Co core and a shell of Pt tiny particles. The composition of the CoPt nanoparticles was analyzed by energy-dispersive X-ray spectroscopy (EDX), which depicts a Co:Pt ratio of ca. 21:79. Studies of cyclic voltammetry (CV) demonstrated that CoPt/GC possesses a much higher catalytic activity towards CO and methanol electrooxidation than a nanoscale Pt thin film electrode. In situ FTIR spectroscopic studies have revealed for the first time, that a CoPt nanoparticles electrode exhibits abnormal IR effects (AIREs) for IR absorption of CO adsorbed on it. In comparison with the IR features of CO adsorbed on a bulk Pt electrode, the direction of the IR bands of CO adsorbed on the CoPt/GC electrode is inverted completely, and the intensity of the IR bands has been enhanced up to 15.4 times. The AIREs is significant in detecting the adsorbed intermediate species involved in electrocatalytic reactions. The results demonstrated a reaction mechanism of CH3OH oxidation on CoPt/GC in alkaline solutions through evidencing COL, COM, HCOO−, CO32−, HCO3− and CO2 as intermediate and product species by in situ FTIRS.

Nanostructured Cu2Sb @C material was prepared through a simple polyol approach. Hollow Cu2Sb@C core–shell nanoparticles were obtained by controlling the amount of CuCl2 and time of replacement reaction. The hollow Cu2Sb@C nanoparticle electrode showed excellent cycling performance.

Single crystalline LiNi1/3Co1/3Mn1/3O2 (LNCM) hexagonal nanobricks with a high percentage of exposed {010} facets are synthesized by using Ni1/3Co1/3Mn1/3(OH)2 hexagonal nanosheets as both template and precursor, and exhibit excellent high rate performance as a cathode of lithium ion batteries.

Different morphologies and compositions of Li-rich layered Li1.2Mn0.56Ni0.12Co0.12O2 (LMNCO) materials are successfully synthesized by solvothermal and coprecipitation methods. The samples synthesized by the solvothermal method possess a 3D porous hierarchical microstructure and designed chemical components, while those prepared through the coprecipitation method present partially agglomerated nanoplates and Mn-deficiency. When used as a cathode for lithium ion batteries (LIBs), the LMNCO synthesized by the solvothermal method exhibits superior performances to that prepared by the coprecipitation method, especially in terms of discharge capacity and rate capability: it delivers a discharge capacity of 292.3 mA h g−1 at 0.2 C and 131.1 mA h g−1 even at a rate as high as 10 C. The excellent electrochemical performances of the LMNCO synthesized by the solvothermal method are associated with a synergistic effect of the well-defined morphology and well-ordered structure with good homogeneity and designed stoichiometry. The results demonstrate that the facile solvothermal method may offer an attractive alternative approach for the preparation of Li-rich layered cathode materials with high rate capability.

In the present paper, preferentially oriented (111) Pt nanoparticles (mostly octahedral and tetrahedral, namely {111}Pt nanoparticles) have been characterized and compared with a Pt(554) single-crystal electrode as their voltammetric features are quite similar in 0.5 M H2SO4. The anion and Bi adsorption behaviours suggest that the {111}Pt nanoparticles contain relatively wide hexagonal domains and also isolated sites which could adsorb solely hydrogen. Bi step decoration has been successfully extended to modify the defects of {111}Pt nanoparticles without blocking terrace sites. CO charge displacement has been applied to determine the potential of zero total charge (pztc) of non-decorated and Bi decorated surfaces. It has found that the positive shift of pztc on defect-decorated {111}Pt nanoparticles is not so significant in comparison with that of Pt(554) due to the relative short mean length of (111) domains on the {111}Pt nanoparticles. CO stripping demonstrates that {111}Pt nanoparticles exhibit higher reactivity toward CO oxidation. This reflects the role of the defect sites in nanoparticles, evidenced by the disappearance of the “pre-wave” in the stripping voltammogram once the defects were blocked by Bi. The stripping peaks shift to higher potential on Bi decorated surfaces, indicating the active role of both steps and defects for CO oxidation. By comparing the CO stripping charge and the change in hydrogen adsorption charge of surfaces with and without Bi decoration, including reasonable deconvolution, the local CO coverage on defect and terrace sites were obtained for the first time for the {111}Pt nanoparticles, and the results are in good agreement with those obtained on Pt(554). Chronoamperometry studies show tailing in all current–time transients of CO oxidation on all surfaces studied. The kinetics of CO oxidation can be satisfactorily simulated by a modified Langmuir–Hinshelwood model, demonstrating that CO oxidation on all studied surfaces follows the same mechanism.

Alloy tetrahexahedral Pd–Pt nanocrystals (THH Pd–Pt NCs) mainly enclosed by {10 3 0} high-index facets were prepared by electrochemistry. The as-prepared THH Pd–Pt NCs exhibit a catalytic activity that is at least three times higher than the tetrahexahedral Pd catalysts, and six times higher than commercial Pd black catalysts for the electrooxidation of formic acid. The significant enhancement in catalytic activity has been attributed to the synergy effect of high-index facets and electronic structure of the alloy.

Fivefold twinned Pd nanorods bounded by high-index facets of {hk0} or {hkk} were prepared by an electrochemical method and tested as electrocatalysts of high activity for ethanol oxidation.

A Pt nanoparticle netlike-assembly (Pt-NNA) synthesized through a facile hydrothermal method, with high specific surface area and large overall size, exhibits much higher durability and 2.9 times higher mass activity for oxygen reduction reaction than commercial Pt black catalyst.

An alginate hydrogel binder is prepared through the cross linking effect of Na alginate with Ca2+ ions, which leads to a remarkable improvement in the electrochemical performance of the Si/C anode of a Li-ion battery.

A facile and scalable single-step approach is employed to synthesize a bulk germanium electrode, which consists of nanoscale Ge-grains in ∼5 μm porous powders. This three-dimensional Ge electrode exhibits superior specific capacity (∼1500 mA h g−1) and cyclic performance, attributed to its unique lithiation/delithiation processes.

Identifying and quantifying electrocatalytic-reaction-generated solution species, be they reaction intermediates or products, are highly desirable in terms of understanding the associated reaction mechanisms. We report herein a straightforward implementation of in situ solution electrochemical 13C NMR spectroscopy for the first time that enables in situ studies of reactions on commercial fuel-cell electrocatalysts (Pt and PtRu blacks). Using ethanol oxidation reaction (EOR) as a working example, we discovered that (1) the complete oxidation of ethanol to CO2 only took place dominantly at the very beginning of a potentiostatic chronoamperometric (CA) measurement and (2) the PtRu had a much higher activity in catalysing oxygen insertion reaction that leads to acetic acid.

N,S,Fe-doped graphene nanosheets were directly synthesized from aminothiazole, a precursor molecule that contains N and S atoms, through Fe catalysis under heat treatment. The graphene nanosheets exhibited high electrocatalytic activity toward oxygen reduction reaction in both acidic and alkaline media during rotating disk electrode half-cell and fuel cell tests.

Bimetallic PtPb nanodendrites with a single-crystalline structure were obtained by a facile one-pot strategy. The as-synthesized dendritic structure was well characterized and the growth mechanism was investigated. PtPb nanodendrites exhibited superior activity (5.1 times higher than commercial Pd black) and strong anti-poisoning ability for electrooxidation of formic acid.

A novel dicranopteris-like Fe–Sn–Sb–P composite was prepared, for the first time, by electrodeposition. The quaternary Fe–Sn–Sb–P alloy of multiphase displayed an excellent cycling performance as an anode of Li ion secondary batteries.

Porous MnO/C nanotubes are synthesized by a facile hydrothermal method followed by thermal annealing, and possess excellent cyclability and high rate capability as an anode for lithium ion batteries.

Trapezohedral Pt nanocrystals enclosed by 24 high-index {522} facets have been successfully prepared for the first time in high yield by a direct square wave electrodeposition method. They exhibit a significantly enhanced catalytic activity for C-1 molecules (CO, CH3OH, HCOOH).

A non-intermetallic PtPb/C catalyst of hollow structure is synthesized through a simple reduction method, and exhibits an activity as high as 3.6 times that of commercial Pd black and a much higher stability for electrooxidation of formic acid.

The properties of nanomaterials for use in catalytic and energy storage applications strongly depends on the nature of their surfaces. Nanocrystals with high surface energy have an open surface structure and possess a high density of low-coordinated step and kink atoms. Possession of such features can lead to exceptional catalytic properties. The current barrier for widespread industrial use is found in the difficulty to synthesise nanocrystals with high-energy surfaces. In this critical review we present a review of the progress made for producing shape-controlled synthesis of nanomaterials of high surface energy using electrochemical and wet chemistry techniques. Important nanomaterials such as nanocrystal catalysts based on Pt, Pd, Au and Fe, metal oxides TiO2 and SnO2, as well as lithium Mn-rich metal oxides are covered. Emphasis of current applications in electrocatalysis, photocatalysis, gas sensor and lithium ion batteries are extensively discussed. Finally, a future synopsis about emerging applications is given (139 references).

Li-rich materials, Li1.140Mn0.622Ni0.114Co0.124O2, of a layered/spinel heterostructure were synthesized by a one-step solvothermal route with subsequent moderate heat treatment. The as-prepared materials consist of hierarchical microspheres and an integral layered/spinel heterostructure. The effects of calcination time on both the structure and electrochemical performance of materials have been studied systematically. It has been found that the formation of the spinel structure could be controlled by adjusting the calcination time at 650 °C, and the materials calcined at this temperature for 24 hours present the optimal electrochemical performance. High initial efficiencies of 101% at 0.2C and 92% at 2C, as well as high discharge capacities of 280, 256, 234 and 206 mA h g−1 respectively at 1C, 2C, 5C and 10C have been achieved. The empty 16c octahedral site and 3D Li+ diffusion channel provided by the spinel have been regarded as the key to the improvement of electrochemical performances.

This paper reports the facile synthesis of a unique interleaved expanded graphite-embedded sulphur nanocomposite (S-EG) by melt-diffusion strategy. The SEM images of the S-EG materials indicate the nanocomposites consist of nanosheets with a layer-by-layer structure. Electrochemical tests reveal that the nanocomposite with a sulphur content of 60% (0.6S-EG) can deliver the highest discharge capacity of 1210.4 mAh g−1 at a charge–discharge rate of 280 mA g−1 in the first cycle, the discharge capacity of the 0.6S-EG remains as high as 957.9 mAh g−1 after 50 cycles of charge–discharge. Furthermore, at a much higher charge–discharge rate of 28 A g−1, the 0.6S-EG cathode can still deliver a high reversible capacity of 337.5 mAh g−1. The high sulphur utilization, excellent rate capability and reduced over-discharge phenomenon of the 0.6S-EG material are exclusively attributed to the particular microstructure and composition of the cathode.

Development of core–shell bimetallic nanoparticles with bifunctional catalytic activity and excellent stability is a challenging issue in nanocatalyst synthesis. Here we present a detailed study of thermal stabilities of Au-core/Pt-shell nanoparticles with different core sizes and shell thicknesses. Molecular dynamics simulations are used to provide insights into the melting and diffusive behavior at atomic-level. It is found that the thermal stabilities of core-shell nanoparticles are significantly enhanced with increasing thickness of Pt shell. Meanwhile, the melting mechanism is strongly dependent on the shell thickness. When the core size or shell thickness is very small, the melting is initiated in the shell and gradually spreads into the core, similar to that of monometallic nanoparticles. As the core increases up to moderate size, an inhomogeneous melting has been observed. Due to the relatively weak confinement of thin shell, local lattice instability preferentially takes place in the core, leading to the inhomogeneous premelting of Au core ahead of the overall melting of Pt shell. The diffusion coefficients of both Au and Pt are decreased with the increasing thickness of shell, and the difference in their diffusions favors the formation of inhomogeneous atomic distributions of Au and Pt. The study is of considerable importance for improving the stability of Pt-based nanocatalysts by tuning the shell thickness and core size.

Platinum is the most active and one of most commonly used catalytic metals. In this article, atomistic simulations have been employed to systematically investigate the thermal stability of platinum nanowires with single-crystalline and fivefold twinned structures. It has been revealed that the single-crystalline nanowires possess better structural stabilities than the twinned ones. Furthermore, when subjected to continuous heating, the twinned nanowires exhibit an inhomogeneous melting, essentially different from what happens in the single-crystalline ones, and hence the lower melting point. By analyses of the microstructural evolution and dynamics behavior during the heating process, the structural transition of the nanowire is discussed and the inhomogeneity in the twinned nanowire is identified to originate from the dislocation-induced destruction of twin boundaries.

We have successfully built a general framework to comprehend the structure–selectivity relationship in ethanol electrooxidation on platinum by density functional theory calculations. Based on the reaction mechanisms on three basal planes and five stepped surfaces, it was found that only (110) and n(111) × (110) sites can enhance CO2 selectivity but other non-selective step sites are more beneficial to activity.

Tetrahexahedral Pt nanocrystals (THH Pt NCs), bound by high index facets, belong to an emerging class of nanomaterials that promise to bridge the gap between model and practical electrocatalysts. The atomically stepped surfaces of THH Pt NCs are extremely active for the electrooxidation of small organic molecules but they also readily accommodate the dissociative chemisorption of such species, resulting in poisoning by strongly adsorbed CO. Formic acid oxidation is an ideal reaction for studying the balance between these competing catalyst characteristics, since it can proceed by either a direct or a CO mediated pathway. Herein, we describe electrochemical and in situ FTIR spectroscopic investigations of formic acid electrooxidation at both clean and Au adatom decorated THH Pt NC surfaces. The Au decoration leads to higher catalytic currents and enhanced CO2 production in the low potential range. As the CO oxidation behaviour of the catalyst is not improved by the presence of the Au, it is likely that the role of the Au is to promote the direct pathway. Beyond their fundamental importance, these results are significant in the development of stable, poison resistant anodic electrocatalysts for direct formic acid fuel cells.

Aimed at searching for highly active and stable nano-scale Pt-based catalysts that can improve significantly the energy conversion efficiency of direct ethanol fuel cells (DEFCs), a novel Pt–PbOx nanocomposite (Pt–PbOx NC) catalyst with a mean size of 3.23 nm was synthesized through a simple wet chemistry method without using a surfactant, organometallic precursors and high temperature. Electrocatalytic tests demonstrated that the as-prepared Pt–PbOx NC catalyst possesses a much higher catalytic activity and a longer durability than Pt nanoparticles (nm-Pt) and commercial Pt black catalysts for ethanol electrooxidation. For instance, Pt–PbOx NC showed an onset potential that was 30 mV and 44 mV less positive, together with a peak current density 1.7 and 2.6 times higher than those observed for nm-Pt and Pt black catalysts in the cyclic voltammogram tests. The ratio of current densities per unit Pt mass on Pt–PbOx NC, nm-Pt and Pt black catalysts is 27.3:3.4:1 for the long-term (2 hours) chronoamperometric experiments measured at −0.4 V (vs. SCE). In situ FTIR spectroscopic studies revealed that the activity of breaking C–C bonds of ethanol of the Pt–PbOx NC is as high as 5.17 times that of the nm-Pt, which illustrates a high efficiency of ethanol oxidation to CO2 on the as-prepared Pt–PbOx NC catalyst.

Unexpected yet highly remarkable and intriguing observations of the polymer-enhanced electro-catalytic activity of the Pt nanoparticles for electro-oxidations of both methanol and formic acid were reported. In situFTIR investigation suggests strongly that the observed activity enhancements are highly likely due to the PVP-induced additional reaction pathways. These observations may open up a new paradigm of research in which the protecting/stabilizing organic ligands can now be incorporated as an advantageous part and/or a finer catalytic activity tuner of a nanocatalytic system.

In this work, surface modification at an atomic level, coupled with CO as molecular probe, was applied to study the step-site reactivity of platinum single crystals. Stepped platinum single crystal electrodes with (111) terraces and step sites of different symmetry were modified by irreversible adsorption of Bi and Te adatoms selectively deposited on steps, and characterized in 0.1 M HClO4 solution. CO charge-displacement and oxidative stripping were employed to investigate the reactivity changes before and after modification of the electrode surfaces. The values of potential of zero total charge (pztc) determined from CO displacement experiments were found to shift positively on all decorated electrodes. The CO oxidation peaks also shifted to higher potential once the step sites were blocked by the adatoms, indicating a catalytic effect of the step sites for this reaction. The CO coverage values on the step sites were determined by comparing the stripping charges and the change in the hydrogen de/adsorption charge, using the pztc's for double layer correction. The CO coverage was determined to be ca. 0.7 for (110) step sites while only 0.4 for (100) step sites, which suggests a different bond of CO adsorbed on the different step sites. This was confirmed by in situ infrared reflection–absorption spectroscopy (IRAS) studies, showing that the (110) step sites are dominated by atop CO while bridged bonded CO are prevalent on (100) step sites. The comparison of CO stripping and hydrogen adsorption charges before and after adatom modification allows the separation of step and terrace contributions to the overall CO coverage.

The interaction of colloid-based, carbon supported Pt/C (40 wt%), PtRu/C (45 wt%) and Pt3Sn/C (24 wt%) catalysts with ethanol and their performance for ethanol electrooxidation were investigated in model studies by electrochemical, in situ infrared spectroscopy and on-line differential electrochemical mass spectrometry measurements. The combined application of in situ spectroscopic techniques on realistic catalysts and under realistic reaction (DEMS, IR) and transport conditions (DEMS) yields new insight on mechanistic details of the reaction on these catalysts under the above reaction and transport conditions. Based on these results, the addition of Sn or Ru, though beneficial for the overall activity for ethanol oxidation, does not enhance the activity for C–C bond breaking. Dissociative adsorption of ethanol to form CO2 is more facile on the Pt/C catalyst than on PtRu/C and Pt3Sn/C catalysts within the potential range of technical interests (<0.6 V), but Pt/C is rapidly blocked by an inhibiting CO adlayer. In all cases acetaldehyde and acetic acid are dominant products, CO2 formation contributes less than 2% to the total current. The higher ethanol oxidation current density on the Pt3Sn/C catalyst at these potentials results from higher yields of C2 products, not from an improved complete ethanol oxidation to CO2.