Heterogeneous nanostructures hold substantial promise in many fields including energy conversion and catalysis, and their functionality is largely determined by the interactive surface features of respective architectural components. Herein, we report the facile preparation of a Pt–Au heterogeneous nanostructure, which as a model exhibits not only the enhanced electrocatalysis for oxygen reduction reaction (ORR) and ethanol oxidation reaction (EOR), but also an unprecedented activity for formic acid oxidation (FAO). Further, selective under-potential deposition coupled with CO adsorption is employed to probe the electrocatalytic mechanism of the Pt–Au heterogeneous nanostructure. The electronic effect is clarified for the ORR and EOR mechanisms on the Pt–Au nanostructure. A synergetic mechanism in that Pt ruptures the C–H bond of HCOOH and Au converts the resulted −COOH into CO2 is revealed for FAO. This strategy provides a versatile and powerful tool for the selective surface engineering and in-depth analysis of the functionalizing mechanism of heterogeneous nanostructures.Keywords: electrocatalysis; formic acid oxidation; nanostructure; selective under-potential deposition; synergy effect;

•Open circuit voltage evolution over ageing of lithium ion batteries is deciphered.•The mechanism responsible for the end-of-life (EOL) threshold is elaborated.•A new prediction model of EOL threshold with improved accuracy is developed.•This EOL prediction model is promising for the applications in electric vehicles.The end-of-life (EOL) of a lithium ion battery (LIB) is defined as the time point when the LIB can no longer provide sufficient power or energy to accomplish its intended function. Generally, the EOL occurs abruptly when the degradation of a LIB reaches the threshold. Therefore, current prediction methods of EOL by extrapolating the early degradation behavior often result in significant errors. To address this problem, this paper analyzes the reason for the EOL threshold of a LIB with shallow depth of discharge. It is found that the sudden appearance of EOL threshold results from the drift of open circuit voltage (OCV) at the end of both shallow depth and full discharges. Further, a new EOL threshold prediction model with highly improved accuracy is developed based on the OCV drifts and their evolution mechanism, which can effectively avoid the misjudgment of EOL threshold. The accuracy of this EOL threshold prediction model is verified by comparing with experimental results. The EOL threshold prediction model can be applied to other battery chemistry systems and its possible application in electric vehicles is finally discussed.Download high-res image (164KB)Download full-size image

The inferior CO-like intermediates tolerance of Pt nanoparticle greatly hampered the MOR activity and durability. To alleviate this issue, tremendous efforts have been made to create oxygen-containing groups on neighbouring Pt site for oxidizing the poisonous carbonaceous species. Given this, two-dimensional FeP nanosheet with excellent HER activity was utilized as support and cocatalyst. FeP nanosheet with special Feδ+ and Pδ− active sites was conductive to mass transfer, fast charge transfer and facilitating water dissociation for generating OH species to removal CO-like intermediates on Pt sites. The XRD, XPS, SEM and TEM analysis demonstrated that the Pt nanoparticle with an average size of 3.68 nm was successfully deposited on the FeP nanosheet surface. The methanol oxidation experiments in acidic medium revealed that the as-prepared binary Pt/FeP nanosheet hybrid exhibited superior MOR activity with enhanced anodic peak current density of 0.994 mA/cm2, which was 2.74-fold greater than that of commercial Pt/C, and the intensive CO oxidation peak potential was negatively shifted about 100 mV with respect to that of Pt/C. The better CO tolerance of Pt/FeP nanosheet hybrid might be attributed to cooperative effect from down-shifted d-band center of Pt, abundant hydroxyls on the Pt/FeP and special activity of Feδ+ and Pδ−. In addition, this hybrid electrocatalyst also showed relatively higher HER activity compared with that of Pt/C. This study provides a promising application of metal phosphide in methanol oxidation for enhancing CO resistance capability of Pt-based catalyst.

•The residual lithium compounds are significantly reduced by polyaniline washing.•The capacity and cyclability of washed LiNi0.8Co0.1Mn0.1O2 material are increased.•The polyaniline washing process has no harmful effect on the surface structure.•The Li+ diffusion and electronic conductivity are improved.The residual lithium compounds on the surface of Ni-rich layered LiNixCoyMn1-x-yO2 materials are detrimental to their electrochemical properties. This study reports a mild polyaniline (PANI) washing method to effectively reduce the residual lithium compounds on the surface of LiNi0.8Co0.1Mn0.1O2 material without any harmful effects on its structural integrity. After the PANI washing process, the rate and cycling performance of LiNi0.8Co0.1Mn0.1O2 material are significantly enhanced. The as-obtained LiNi0.8Co0.1Mn0.1O2 material exhibits a discharge capacity of 160.65 mAh g−1 and a capacity retention of 86.95% after 100 cycles at 55 °C and the current rate of 2C, which are much higher than those of pristine material (131.57 mAh g−1 and 74.90%). The performance enhancement mechanism is the reduction of surface residual lithium compounds due to the PANI washing process, leading to the improvement of lithium ions diffusion and electron transport. Furthermore, some PANI can be left and coated on the surface of LiNi0.8Co0.1Mn0.1O2 material via the washing process, which forms more stable interface film, resulting in even better cycling capability. This study provides a promising strategy for the surface modification of Ni-rich layered oxide materials for lithium ion batteries.Download high-res image (72KB)Download full-size image

•P atoms are successfully incorporated into graphene matrix (PG).•Pt/PG presents excellent methanol oxidation activity and stability.•Defects on PG provide anchoring sites to improve both Pt dispersion and stability.•The tuned d-band center of Pt weakens the poisonous CO absorption.Phosphorus is incorporated into graphene (PG) by thermal treating method, which is further employed as supports for Pt nanoparticles. The as-obtained Pt/PG catalyst exhibits over 2.4 times enhanced methanol electrooxidation activity compared with Pt/C, as well as desirable stability and remarkably improved CO-tolerance. These improvements are attributed to not only uniformly dispersed Pt nanoparticles that are anchored by introduced defects in PG, but also negative d-band center shift and weakened CO adsorption on Pt caused by strong interactions between Pt and PG. Consequently, PG is a promising support material for Pt-based catalysts towards methanol electrooxidation.Download high-res image (70KB)Download full-size image

In spite of the ultrahigh theoretical energy density, non-aqueous Li-O2 batteries are still constrained by their inefficient cathodes. Here, we report the synthesis of a distinctive hierarchical carbon architecture (HOM-AMUW) for Li-O2 batteries, which consists of highly ordered macropores (250 nm) with abundant mesopores on their ultrathin walls (4–5 nm). This carbon architecture exhibits unprecedented discharge capacity of 37523 mAh g−1 and 12686 mAh g−1 at the current density of 500 mA g−1 and even 2000 mA g−1, respectively. After further functionalization by low crystalline Ru nanoclusters, the resulted Ru-HOM-AMUW architecture presents a much low charge polarization and outstanding cycling stability. The significant performance enhancement is mainly attributed to the unique hierarchical porous structure, wherein the ordered macropores and ultrathin mesoporous walls remarkably enhance the access capability of O2 or Li+ to the numerous active sites, and the large pore volume easily accommodates the discharge products. Moreover, the hierarchical porous structure modulates the morphology of discharge products to three-dimensional porous structure with high charge transport, which also contributes to the striking rate capability. This HOM-AMUW architecture is a promising scaffold to design the gas electrodes with ultrahigh rate performance not only for Li-O2 batteries but also for other metal-air batteries.Download high-res image (325KB)Download full-size image

•Conductive Sb-doped SnO2 (ATO) is coated on LiNi0.8Co0.15Al0.05O2 material.•The wet chemical process leads to homogeneous ATO coating layer.•The coated sample exhibits excellent rate capability and cyclic stability.•The capacity retention after 200 cycles at 60 °C increases by 20.81%.•The ATO coating restrains the cation disordering and SEI growth during cycling.The LiNi0.8Co0.15Al0.05O2 (NCA) cathode material is modified by electronically conductive antimony-doped tin oxide (ATO) nanoparticles via a facile wet chemical process. As observed by scanning and transmission electron microscopy, the ATO nanoparticles are homogeneously coated on the surface of NCA material. Thus-obtained ATO-coated NCA (ATO-NCA) material delivers a high discharge capacity of 145 mAh g−1 at the current rate of 5C, which is significantly higher than that of pristine NCA material (135 mAh g−1). Moreover, the capacity retention of ATO-NCA material is 91.70% after 200 cycles at the current rate of 1C and 60 °C. In contrast, the pristine NCA only maintains 70.89% of its initial capacity after the same cycles. The substantially improved cyclability and rate capability are mainly attributed to the ATO coating layer, which can not only enhance the electron transport but also effectively restrain the side reactions between the NCA material and the electrolyte. More specifically, X-ray diffraction and photoelectron spectroscopy reveal that the ATO coating layer can restrain the Li+/Ni2+ disordering and the growth of SEI layer of NCA material, which are responsible for the improved cycling stability, especially at elevated temperatures.

Performance degradation of prismatic lithium ion batteries (LIBs) with LiCoO2 and mesocarbon microbead as active materials is investigated at an elevated temperature for shallow depth of discharge. Aged LIBs are disassembled to characterize the interface morphology, bulk structure, and reversible capacity of an individual electrode. It is found that the formation of interfacial blocking layer (IBL) on the anode results in the cathode state of charge (SOC) offset, which is the primary reason for the cathode degradation. The main capacity degradation of the anode is attributed to the IBL on the anode surface that impedes the intercalation and deintercalation of lithium ions. Because the full battery capacity is limited by the cathode during aging, the cathode SOC offset is the most important reason for the full battery capacity loss. Interestingly, the capacity of aged LIBs can be recovered to a relative high level after adding the electrolyte, rather than the solvent. This recovery is attributed to the relief of the cathode SOC offset and the dissolution of the anode IBL, which reopens the intercalation and deintercalation paths of lithium ions on the anode. Moreover, it is revealed that the relief of cathode SOC offset and the dissolution of anode IBL trigger and promote mutually to drive the recovery of LIBs.Keywords: capacity recovery; degradation; elevated temperature; interfacial blocking layer; shallow depth of discharge; state of charge offset

Oxygen reduction reaction (ORR) is the cornerstone in the electrochemical energy conversion devices such as fuel cells and metal–air batteries. It remains a great challenge to develop the ORR electrocatalysts with fast kinetics and high durability. Herein, we report the synthesis of a novel metal–organic coordination networks material, prussian blue crystalline nanograins mosaicked within amorphous membrane (PB CNG-M-AM). Such unique PB CNG-M-AM is designed to enhance the electrocatalysis of Pt toward the ORR by the electrostatic self-assembly. Thus, obtained Pt-PB/C catalysts form numerous Pt-PB-gas three-phase boundaries and present rather high intrinsic activity, four-electron selectivity and superior stability. Moreover, a completely new synergetic mechanism between PB and Pt is discovered, which delicately alters the ORR route and significantly enhances the ORR kinetics. This work provides not only a new strategy and mechanism for developing highly efficient ORR electrocatalysts, but also an alternative way to utilize metal–organic coordination networks materials.

•LiPON is coated on Li[Ni0.73Co0.12Mn0.15]O2 by a facile solid phase method.•LiPON-coated material shows 36.1% higher cycling stability than pristine material.•LiPON layer provides a reliable interface protection on Li[Ni0.73Co0.12Mn0.15]O2.•LiPON coating increases Li+ conductivity and is good to rate capability.A facile high-temperature solid phase approach is employed to coat lithium phosphorus oxynitride (LiPON) layer on the concentration gradient Li[Ni0.73Co0.12Mn0.15]O2 material with Ni-rich core and Ni-poor surface. X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy demonstrate that LiPON forms an even coating with ∼4 nm of thickness on the surface without destroying the bulk structure of Li[Ni0.73Co0.12Mn0.15]O2 material. The LiPON-coated concentration gradient Li[Ni0.73Co0.12Mn0.15]O2 material exhibits a capacity retention of 87.3% at 25 °C after 1000 cycles and 89.9% at 55 °C after 250 cycles, which is 36.1% and 17.2% higher than that of pristine Li[Ni0.73Co0.12Mn0.15]O2 material, respectively, under the same operating conditions. This significantly improved cycling performance is ascribed to the noncrystalline LiPON layer on the surface, which provides a reliable interface protection. The LiPON coating is an effective approach to enhancing the electrochemical performance of electrode materials for lithium ion batteries.

•A cost-efficient way is used to prepare transition-noble metal alloy nanoparticles.•The Pd50Fe50/C catalyst shows excellent activity for formic acid oxidation (FAO).•Much activity enhancement of FAO is acquired by ultra-low Pt decorated Pd50Fe50.•A synergistic mechanism between Pt clusters and PdFe is proposed during the FAO.Palladium (Pd), has demonstrated promising electro-catalytic activity for formic acid oxidation, but suffers from extremely low abundance. Recently alloying with a transition metal has been considered as an effective approach to reducing the loading of Pd and enhancing the activity of Pd-based catalysts simultaneously. Herein, carbon supported PdFe nanoparticles (NPs) are synthesized at room temperature by using sodium borohydride as reducing agent and potassium ferrocyanide as Fe precursor. The Pd50Fe50 alloy sample annealed at 900 °C for 1 h shows the best catalytic activity among PdxFe1-x (x = 0.2, 0.4, 0.5, 0.6, and 0.8) towards formic acid oxidation. To further improve both catalytic activity and stability, the ultra-low Pt (0.09 wt %) decorated Pd50Fe50 NPs (PtPd/PdFe) are prepared via the galvanic replacement reaction. Compared with Pd50Fe50/C, the PtPd/PdFe/C Exhibits 1.52 times higher catalytic activity and lower onset potential (−0.12 V). The significant enhancements of formic acid oxidation can be attributed to the accelerated dehydrogenation reaction of formic acid by Pt atomic clusters. Moreover, the PtPd/PdFe/C also demonstrates better tolerance to poisons during formic acid oxidation.

•A concentration gradient core-shell Pd-Ir-Ni/C electrocatalyst is facilely synthesized.•The Pd-Ir-Ni/C catalyst exhibits high activity for oxygen reduction reaction (ORR).•This catalyst possesses excellent ORR selectivity in the presence of methanol.•The enhanced ORR activity is ascribed to the optimal compressive lattice strain.•The underlying alloy core induces the lattice strain on the outer surface.This study demonstrates a concept of concentration gradient (CG) Pd-Ir-Ni/C electrocatalyst consisting of IrNi alloy core, concentration gradient IrPd layer and Pd surface for the oxygen reduction reaction (ORR), which is synthesized by a facile sequential polyol method without any additional surfactant. The CG Pd-Ir-Ni/C electrocatalyst is characterized by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. It is found that the Pd-Ir-Ni nanoparticles with a mean diameter of 5.8 ± 1.5 nm are uniformly distributed on the carbon support. These Pd-Ir-Ni nanoparticles possess a certain degree of Pd alloying through the spontaneous replacement reaction, and concentration gradient IrPd shell with Pd-rich surface. The ORR polarization measurement of the CG Pd-Ir-Ni/C catalyst illustrates a mass activity of 5.6 and 9.9 times that of Pd/C catalyst at 0.80 V and 0.7 V, respectively. Moreover, this catalyst exhibits a better ORR selectivity than commercial Pt/C catalyst in the presence of methanol. The enhanced electrocatalytic activity is mainly attributed to the optimal compressive lattice strain of surface Pd induced by the underlying concentration gradient layer. Our work provides a highly potential strategy to develop high performance and low cost electrocatalytic materials for fuel cells.

•Boron, nitrogen co-doped graphene was synthesized through simple thermal annealing.•Pt/BNG catalyst exhibits high catalytic activity towards the MOR.•The synergetic effects of support accelerate the methanol oxidation for Pt/BNG.•The low CO adsorption energy promotes CO oxidation for Pt/BNG.•Boron with lower electronegtivity doped graphene weakens the d-band center of Pt.Boron, nitrogen co-doped graphene (BNG) is facilely synthesized by the two-step thermal annealing of graphene in the presence of melamine and boric acid, which is served as a novel support to enhance the catalytic properties of noble metal catalysts for the methanol oxidation reaction (MOR). It is revealed that the BNG support has more defect sites due to the co-doping of boron and nitrogen, so that uniformly dispersed Pt nanoparticles with average size of 2.3 nm are anchored on the surface of BNG support. The BNG supported Pt (Pt/BNG) catalyst exhibits excellent activity and improved stability towards the MOR, which is mainly attributed to the synergetic effects of boron and nitrogen co-doping into graphene support. It is revealed that nitrogen and boron co-doping produces more oxygen-containing species, which accelerates the methanol oxidation by the so-called bifunctional mechanism. Moreover, the boron doping weakens the adsorption energy of poisoning intermediates on Pt surface by lowering the d-band center of Pt, facilitating the oxidative removal of poisoning intermediates and methanol oxidation. The boron and nitrogen co-doping of graphene opens up a new strategy for the catalyst performance optimization.

This paper reports the surface fluorine modification of the nickel-rich concentration gradient Li[Ni0.73Co0.12Mn0.15]O2 material by facile high temperature annealing, and its influence on the electrochemical performance. The samples are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, galvanostatic charge–discharge behaviour and electrochemical impedance spectroscopy. It is found that the fluorine surface modification induces a partial phase transformation from a layered structure to a cubic rock structure (NiO-like phase) on the surface region. Meanwhile, the lithium residues on the surface of the pristine material are remarkably reduced and transformed into fluorides after the fluorine modification. The fluorine-modified concentration gradient Li[Ni0.73Co0.12Mn0.15]O2−xFx (x = 0.02) material exhibits a remarkably enhanced capacity retention of 97.5% after 200 cycles, which is significantly higher than that of the pristine material (87.4%). The superior electrochemical stability of the fluorine-modified Li[Ni0.73Co0.12Mn0.15]O2−xFx samples is attributed to the synergistic protection of the NiO-like phase and the surface fluoride layer, which can effectively restrain the side reactions between the active material and electrolyte. The fluorine-modified concentration gradient Li[Ni0.73Co0.12Mn0.15]O2−xFx materials present a promising type of cathode material for lithium-ion batteries.

A series of ternary PdxIrFe/C alloy catalysts with Pd:Ir:Fe atomic ratios of 1:1:1 (denoted as PdIrFe/C), 2:1:1 (denoted as Pd2IrFe/C) and 3:1:1 (denoted as Pd3IrFe/C) have been prepared through a microwave polyol reduction method for oxygen reduction reaction in acid medium. The morphology, structure, composition and electrochemical properties of the catalysts are analyzed by X-ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM) equipped with electron diffraction spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and rotating disc electrode (RDE) measurements. It is clearly shown that PdxIrFe alloy nanoparticles are uniformly distributed on carbon support and Pd is enriched in the surface region of the Pd3IrFe/C catalyst. Among the PdxIrFe/C catalysts, the ternary Pd3IrFe/C alloy catalyst exhibits a rather high Pd mass activity that is 11-fold and 5.7-fold higher than that of Pd/C and Pd3Fe/C catalysts, respectively, at 0.72 V. This activity enhancement is believed to result from the surface segregation of Pd and the modification of electronic structure induced by subsurface Ir, which weakens the binding strength of oxygen-containing intermediates and further enhances their removal from the catalyst surface. Furthermore, the ternary Pd3IrFe/C alloy catalyst possesses higher methanol tolerance than the Pt/C catalyst. The ternary Pd3IrFe/C alloy electrocatalyst is a promising ORR catalytic material, especially for DMFCs.

•Hierarchical LiCoPO4@C/G nanocomposite is prepared by a facile solid state method.•The LiCoPO4@C/G material shows excellent discharge capacity and rate capability.•Synergy of graphene and carbon coating enhances the electrochemical properties.•LiCoPO4@C/G is a promising cathode for high-energy-density Li-ion batteries.We report the design and synthesis of a novel hierarchical LiCoPO4@C/G cathode material, consisting of carbon coated LiCoPO4 nanoparticles crosslinked by wrinkled graphene, for high-energy-density lithium ion batteries. This material is facilely prepared by a solid-state milling process followed by heat annealing. Its morphology and structure are characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and X-ray diffraction. It is revealed that the LiCoPO4 nanoparticles are coated by an amorphous carbon layer with ∼3 nm thickness and further crosslinked by wrinkled graphene. The LiCoPO4@C/G material delivers a high discharge capacity of 146.1 mAh g−1 at 0.1 C rate and 93.0 mAh g−1 at 2 C rate. The enhanced electrochemical properties are attributed to the nanosized LiCoPO4 particles and the high electronic conductivity resulted from the synergistic carbon coating and graphene crosslinking. Our work provides a facile approach to prepare high performance LiCoPO4 cathode materials for lithium ion batteries.

A novel palladium-doped ceria and carbon core–sheath nanowire network (Pd–CeO2@C CSNWN) is synthesized by a template-free and surfactant-free solvothermal process, followed by high temperature carbonization. This hierarchical network serves as a new class of catalyst support to enhance the activity and durability of noble metal catalysts for alcohol oxidation reactions. Its supported Pd nanoparticles, Pd/(Pd–CeO2@C CSNWN), exhibit >9 fold increase in activity toward the ethanol oxidation over the state-of-the-art Pd/C catalyst, which is the highest among the reported Pd systems. Moreover, stability tests show a virtually unchanged activity after 1000 cycles. The high activity is mainly attributed to the superior oxygen-species releasing capability of Pd-doped CeO2 nanowires by accelerating the removal of the poisoning intermediate. The unique interconnected one-dimensional core–sheath structure is revealed to facilitate immobilization of the metal catalysts, leading to the improved durability. This core–sheath nanowire network opens up a new strategy for catalyst performance optimization for next-generation fuel cells.

Lithium-rich layered oxide Li1.2Ni0.13Co0.13Mn0.54O2 (LNCMO) coated with a nanocomposite layer of Li3PO4 and carbon (LNCMO@Li3PO4/C) is designed and facilely prepared as the cathode material for rechargeable lithium ion batteries. The structure and morphology of the LNCMO@Li3PO4/C material are characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy, and its electrochemical performance is measured by the constant current charge and discharge, electrochemical impedance spectroscopy and cyclic voltammetry. It is clearly revealed that the LNCMO surface is uniformly coated by the Li3PO4/C nanocomposite layer. Moreover, the coating process induces the layer-to-spinel phase transformation, leading to the formation of a spinel nanophase in the LNCMO@Li3PO4/C material. The presence of Li3PO4/C composite coating with high ionic and electronic conductivity and the spinel nanophase synergistically contribute to the electrochemical properties. Therefore, the LNCMO@Li3PO4/C material shows a high discharge capacity of 124.4 mA h g−1 even at a current density of 1000 mA g−1, a remarkable capacity retention of 87.3% after 200 cycles, and a desirable initial coulombic efficiency of 87.0%. The LNCMO@Li3PO4/C material represents an attractive alternative to high-rate and long-life electrode materials for lithium-ion batteries.

•PtNi alloy nanourchins are facilely synthesized by modulating temperature ramping.•The nanourchins exhibit high activity for methanol oxidation and oxygen reduction.•The PtNi alloy nanourchins are rather stable during the long-term operation.•Anistropic structure and alloying synergistically lead to the improved properties.The controlled synthesis of noble metal alloy nanocrystals with anistropic structures is significant for their applications in catalysis, sensing, imaging and biomedicine. This article reports the facile and high-yield synthesis of multi-branched PtNi alloy nanourchins. The synthesis is achieved by the co-reduction of Pt and Ni acetylacetonates through modulating the heating rate of reduction process, which can completely tune the growth kinetics of Pt alloy nanocrystals. Thus obtained PtNi alloy nanourchins exhibit excellent catalytic performance for methanol oxidation and oxygen reduction reactions, which is over 10 times higher than a conventional Pt/C catalyst. In addition, the PtNi alloy nanourchins are highly stable during the long-term operation. It is proposed that the anistropic structure and the alloying effect contribute synergistically to the improvement of catalytic properties. The synthetic strategy is simple, low cost, high yield and up-scalable, which offer a valuable approach to synthesizing metal alloynanocrystals with structural anisotropies, and is promising in designing novel materials for both electrocatalytic and other applications.Figure optionsDownload full-size imageDownload as PowerPoint slide

Lithium-rich layered oxides are considered to be one of the most promising cathode materials for lithium ion batteries due to their extremely high reversible capacity. Here, we report the design of a novel heterostructured Li1.2Ni0.13Co0.13Mn0.54O2 material with mosaic spinel nanograins and a surface coating, which is synthesized by a facile and green one-step solid-phase surface-modification process. We propose that the chemical Li leaching from Li2MnO3 simultaneously induces the formation of a fluorite coating and the layer-to-spinel phase transformation at high temperatures. The fluorite coating protects the lithium-rich oxides from direct exposure to the highly active electrolyte. The spinel phase provides an efficient path for Li+ mobility and also facilitates the suppression of the initial irreversible capacity loss. This unique heterostructured Li1.2Ni0.13Co0.13Mn0.54O2 material thus exhibits an outstanding initial Coulombic efficiency, superior rate capability and excellent cyclability. The design concept and facile synthetic strategy can be applied to both advanced lithium ion batteries and other high-performance energy storage devices.

In this work, we report a Pd-around-CeO2−x hybrid nanostructure catalyst for direct ethanol fuel cells, which is synthesized via a facile three-phase-transfer approach. The obtained nanostructure catalyst is characterized by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. In this nanostructure, Pd nanoparticles (NPs) are closely attached onto the surface of the CeO2−x NPs, leading to an intense interfacial interaction between Pd and CeO2−x. The electrocatalytic properties of the Pd-around-CeO2−x hybrid nanostructure catalyst for ethanol electrooxidation is investigated by cyclic voltammetry and chronoamperometry. This Pd-around-CeO2−x hybrid nanostructure catalyst shows a superior catalytic performance for ethanol electrooxidation, which can be attributed to a novel dual promoting mechanism.

The shape control of platinum nanocrystals is significant to the enhancement of their catalytic performance in terms of activity and selectivity. However, it still remains a major challenge to prepare Pt nanocrystals with tunable shape and clean surface in an eco-friendly way. This article develops a facile and green strategy to prepare well tuned platinum nanocrystals employing poly(diallyldimethylammonium chloride) (PDDA) as the capping agent, reductant, and stabilizer simultaneously in a facile hydrothermal process. It is identified that the variation of PDDA concentration is crucial to control the growth of crystalline facets, leading to the formation of cubic, truncated cubic, and octahedral Pt nanocrystals with sizes tunable from ca. 17 nm to ca. 50 nm. The resultant Pt nanocrystals exhibit excellent electrocatalytic activity and stability toward the oxygen reduction reaction (ORR) in acidic media compared with those of commercial Pt black and the state-of-the-art Pt/C catalyst. It is proposed that the preferential Pt surface and the decoration of PDDA, which modulates the electronic structures and electrooxidation of Pt nanocrystals, synergistically contribute to the enhanced catalytic performance.Keywords: electrocatalysts; oxygen reduction reactions; platinum nanocrystals; polyelectrolyte; shape control

•Ni-doped CeO2 nanoparticles were synthesized by a thermal decomposition method.•Ni-doped CeO2 nanoparticles enhance the activity of Pt/C for ethanol electrooxidation.•Oxygen releasing capacity and interaction with Pt of Ni-doped CeO2 contribute to the activity.This paper reports the facile synthesis of monodispersed nickel-doped ceria nanoparticles by a thermal decomposition method, which is used to promote catalytic properties of Pt/C. The Pt/Ni-doped CeO2/C catalyst obtained exhibits remarkably high activity and stability towards the ethanol electrooxidation in acidic media. This is attributed to higher oxygen releasing capacity and stronger interaction of Ni-doped CeO2 with Pt than pure CeO2 nanoparticles that contribute positively to the removal of poisoning intermediates. We believe that the design concept and synthetic strategy of metal doped oxides used for fuel cell catalysts can be potentially extended to other catalytic fields.

This paper reports a facile approach to prepare FePO4 microspheres with carbon nanotube embedded (FePO4/CNT) by a hydrothermal process, from which LiFePO4/CNT microspheres were further obtained by chemical lithiation. The preparation procedure is simple, well reproducible, and easy to be scaled up. In addition to the desirable spherical morphology that leads to high tap density, these microspheres contain uniform and well-connected CNT networks, which remarkably enhances their electronic conductivity. Meanwhile, these materials develop a large amount of nanopores during the synthesis, giving rise to both large surface area and good electrolyte infiltration. The LiFePO4/CNT material displays both excellent volumetric Li storage properties at high current rates (>155 mAh cm−3 at 5C), and stable charge/discharge cyclability (>90% capacity retention after 1000 charge/discharge cycles). The LiFePO4/CNT microspheres are rather promising for high-power lithium ion batteries, and such an approach can be extended to prepare other high-performance electrode materials.Graphical abstractHighlights► Porous FePO4 microspheres with uniform carbon nanotube (CNT) embedded are prepared by a hydrothermal process. ► LiFePO4 microspheres with CNT networks (LiFePO4/CNT) are obtained and tested as the cathode material for lithium ion batteries. ► Our LiFePO4/CNT material displays both excellent volumetric Li storage properties and stable charge/discharge cyclability.

In this paper, we demonstrate that a novel silicon electrode with a large amount of nanopores can be fabricated by an in-situ thermal generating approach using triethanolamine as a sacrificing template. The fabrication process is simple, green, low cost, and easy to be scaled up. This electrode achieves high reversible capacities (2500 mAh g−1) with excellent cycling stability (∼90% capacity retention after 100 charge–discharge cycles), showing great potential as a high-performance anode for lithium-ion batteries. It is revealed that the high void volume with pore size of <200 nm can both enlarge the interface between active silicon particles and the electrolyte, and accommodate the severe volume change of silicon, thus leading to remarkably improved reversible capacity and cycling stability. The design concept and the fabrication approach used in the nanoporous silicon electrode may also be extended to other electrodes for electrochemical applications.

This paper reports the facile fabrication of Si@C core–shell nanocomposites by covalently grafting aniline monomer onto the surface of silicon nanoparticles, followed by a carbonizing process. Our covalently-functionalizing approach can lead to a uniform carbon coating with a tunable thickness and is low cost, environmentally friendly and easily scaled up. The Si@C nanocomposite was employed as an anode material for lithium-ion batteries (LIBs), showing a high initial reversible capacity of >1300 mA h g−1 as well as a good cycling stability. The enhanced performance is attributed to the fact that the uniform and elastic carbon coating can efficiently increase the electronic conductivity and accommodate severe volume changes of the Si particles. This Si@C nanocomposite exhibits great potential as an anode material in LIBs, and the fabrication strategy can be extended to prepare other carbon-coated core–shell nanocomposites.

Highly active and durable catalysts for formic acid oxidation are crucial to the development of direct formic acid fuel cell. In this letter, we report the synthesis, characterization, and electrochemical testing of nanoporous Pd57Ni43 alloy nanowires for use as the electrocatalyst towards formic acid oxidation (FAO). These nanowires are prepared by chemically dealloying of Ni from Ni-rich PdNi alloy nanowires, and have high surface area. X-ray diffraction data show that the Pd57Ni43 nanowires have the face-centered cubic crystalline structure of pure Pd, whereas X-ray photoelectron spectroscopy confirm the modification of electronic structure of Pd by electron transfer from Ni to Pd. Electrocatalytic activity of the nanowires towards FAO exceeds that of the state-of-the-art Pd/C. More importantly, the nanowires are highly resistant to deactivation. It is proposed that the high active surface area and modulated surface properties by Ni are responsible for the improvement of activity and durability. Dealloyed nanoporous Pd57Ni43 alloy nanowires are thus proposed as a promising catalyst towards FAO.Keywords (keywords): dealloying; electrocatalyst; formic acid oxidation; nanowires; palladium−nickel alloy

The poisoning of nitrogen oxides (NOx) on the oxygen reduction reaction (ORR) at the Pt/C catalyst has been studied for proton exchange membrane fuel cells by a three-electrode method in liquid electrolyte solution. The cyclic voltammetry (CV) results reveal that the absorption of NOx on metallic Pt is more significant than on Pt oxides, and this absorption is probably a chemical rather than an electrochemical process. Linear sweeping voltammetry (LSV) curves for the ORR show that it is the absorption of NOx on the Pt surface that results in significant performance degradation of Pt/C catalysts. This degradation is mainly due to the reduction of electrochemically active surface area, since the ORR mechanism remains almost the same after the NOx poisoning as revealed by similar Tafel slopes. Because lower potentials facilitate the reduction of NOx to water soluble NH4+, reducing the working potential can mitigate the poisoning of NOx. However, to completely recover the performance loss due to NOx poisoning through the potential sweeping, it is found that the oxidation removal is more efficient than the reduction removal.

Bimetallic palladium–nickel (PdNi2) alloy catalyst has been prepared for the electrooxidation of formic acid through a simple electrodepositing approach. Scanning Electron Microscopy and X-ray Diffraction revealed that the particle morphology and the crystalline lattice of PdNi2 alloy were highly different from those of Pd. Although the PdNi2 catalyst had less noble Pd content, the cyclic voltammetry and chronoamperometry results clearly demonstrated that its catalytic activity was significantly higher than that of Pd. The novel enhancement of catalytic activity was mainly ascribed to the weak absorption strength of intermediates on Pd through the interaction between Pd and additive Ni, which facilitated the formic acid oxidation through direct pathway.

This communication described the fabrication of a hierarchy carbon paper, and its application to the gas diffusion layer (GDL) of proton exchange membrane (PEM) fuel cells. The carbon paper was fabricated by growing carbon nanotubes (CNTs) on carbon fibers via covalently assembling metal nanocatalysts. Surface morphology observation revealed a highly uniform distribution of hydrophobic materials within the carbon paper. The contact angle to water of this carbon paper was not only very large but also particularly even. Polarization measurements verified that the hierarchy carbon paper facilitated the self-humidifying of PEM fuel cells, which could be mainly attributed to its higher hydrophobic property as diagnosed by electrochemical impedance spectroscopy (EIS).

Mesoporous SnO2 coated carbon nanotube (CNT) core–sheath nanocomposite, CNT@SnO2, was prepared by a hydrothermal method and proposed as a catalyst support for proton exchange membrane fuel cells (PEMFCs). The CNT@SnO2 and its supported Pt catalyst, Pt/(CNT@SnO2), were characterized by TEM, XRD, cyclic voltammetry, and polarization curves. The CNT@SnO2 composite showed a much lower anodic current than the CNT, especially at high potentials, indicating the CNT@SnO2 was more corrosion resistant. The Pt/(CNT@SnO2) catalyst was electrochemically active and exhibited comparable activity for the oxygen reduction reaction to the CNT supported catalyst (Pt/CNT). More importantly, the long-term stability of the Pt/(CNT@SnO2) catalyst was significantly higher than that of the Pt/CNT catalyst, which might be mainly due to the fact that the CNT@SnO2 was more corrosion resistant and mesoporous SnO2 was beneficial to restrict the Pt migration and aggregation. Consequently, the CNT@SnO2 would be a promising durable catalyst support for PEMFCs.

A mathematical model is developed to simulate the electrochemical impedance spectra (EIS) of the cathode of a direct methanol fuel cell (DMFC) based on the electrode kinetics and mass transports. Successful simulation of the impedance spectra confirms the usefulness of the model as a diagnostic tool for interpreting the impedance characteristics of the cathode. Numerically, the capacitive semicircle in the impedance pattern is ascribed to the charge transfer process and the inductive semicircle is mainly due to the CO adsorption relaxation. Results show that the impedance pattern is strongly dependent on the electrode potential, which can be used as a criterion for judging the relative effect of the methanol permeation on the cathode. Another capacitive semicircle appears and the charge transfer resistance is changed when the oxygen transport is limited. The effects of the methanol permeation on the impedance pattern are also delineated, indicating that the methanol permeation often leads to larger oxygen transport impedance and the charge transfer resistance of the DMFC cathode depends on the methanol permeation rate.

This paper reports the easy synthesis of Au@Pd core–shell nanoparticles (NPs) with uniform shell thickness and demonstrates their viability as a nonplatinum catalyst for the electrooxidation of methanol in alkaline anion-exchange membrane fuel cells. The synthesis involves the first preparation of Au core NPs, followed by a three-phase-transfer procedure to coat Pd shells, through which homogeneous Pd shell growth on Au cores can be achieved. The as-prepared Au@Pd NPs have an activity more than 40 times higher than that of the Pd catalyst for the methanol oxidation. Moreover, these Au@Pd NPs possess excellent stability (over seven times more stable than Pd catalysts). The remarkable performance enhancement is mainly attributed to the finely tailored electronic structure of the Pd shell achieved by the underlying Au core. The easily synthesized Au@Pd core–shell NPs represent a promising class of nonplatinum anode catalysts with high activity and durability for alkaline fuel cell applications.Graphical abstractAu@Pd core-shell nanoparticles (NPs) were synthesized by a three-phase-transfer approach. These NPs as a non-platinum catalyst exhibited rather high activity and excellent durability towards the methanol electrooxidation in alkaline media: over 40 times more active and 7 times more durable than the Pd catalyst.Download high-res image (128KB)Download full-size imageHighlights► Au@Pd core-shell nanoparticles (NPs) synthesized by a three-phase-transfer approach. ► Pd shell is uniformly coated on the monodispersed Au cores. ► Au@Pd NPs are highly active and durable for the methanol oxidation in alkaline media. ► Superior activity and durability mainly determined by the upshift of d-band center.

This paper reports the facile fabrication of Si@C core–shell nanocomposites by covalently grafting aniline monomer onto the surface of silicon nanoparticles, followed by a carbonizing process. Our covalently-functionalizing approach can lead to a uniform carbon coating with a tunable thickness and is low cost, environmentally friendly and easily scaled up. The Si@C nanocomposite was employed as an anode material for lithium-ion batteries (LIBs), showing a high initial reversible capacity of >1300 mA h g−1 as well as a good cycling stability. The enhanced performance is attributed to the fact that the uniform and elastic carbon coating can efficiently increase the electronic conductivity and accommodate severe volume changes of the Si particles. This Si@C nanocomposite exhibits great potential as an anode material in LIBs, and the fabrication strategy can be extended to prepare other carbon-coated core–shell nanocomposites.

Lithium-rich layered oxides are considered to be one of the most promising cathode materials for lithium ion batteries due to their extremely high reversible capacity. Here, we report the design of a novel heterostructured Li1.2Ni0.13Co0.13Mn0.54O2 material with mosaic spinel nanograins and a surface coating, which is synthesized by a facile and green one-step solid-phase surface-modification process. We propose that the chemical Li leaching from Li2MnO3 simultaneously induces the formation of a fluorite coating and the layer-to-spinel phase transformation at high temperatures. The fluorite coating protects the lithium-rich oxides from direct exposure to the highly active electrolyte. The spinel phase provides an efficient path for Li+ mobility and also facilitates the suppression of the initial irreversible capacity loss. This unique heterostructured Li1.2Ni0.13Co0.13Mn0.54O2 material thus exhibits an outstanding initial Coulombic efficiency, superior rate capability and excellent cyclability. The design concept and facile synthetic strategy can be applied to both advanced lithium ion batteries and other high-performance energy storage devices.

In this work, we report a Pd-around-CeO2−x hybrid nanostructure catalyst for direct ethanol fuel cells, which is synthesized via a facile three-phase-transfer approach. The obtained nanostructure catalyst is characterized by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. In this nanostructure, Pd nanoparticles (NPs) are closely attached onto the surface of the CeO2−x NPs, leading to an intense interfacial interaction between Pd and CeO2−x. The electrocatalytic properties of the Pd-around-CeO2−x hybrid nanostructure catalyst for ethanol electrooxidation is investigated by cyclic voltammetry and chronoamperometry. This Pd-around-CeO2−x hybrid nanostructure catalyst shows a superior catalytic performance for ethanol electrooxidation, which can be attributed to a novel dual promoting mechanism.

Lithium-rich layered oxide Li1.2Ni0.13Co0.13Mn0.54O2 (LNCMO) coated with a nanocomposite layer of Li3PO4 and carbon (LNCMO@Li3PO4/C) is designed and facilely prepared as the cathode material for rechargeable lithium ion batteries. The structure and morphology of the LNCMO@Li3PO4/C material are characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy, and its electrochemical performance is measured by the constant current charge and discharge, electrochemical impedance spectroscopy and cyclic voltammetry. It is clearly revealed that the LNCMO surface is uniformly coated by the Li3PO4/C nanocomposite layer. Moreover, the coating process induces the layer-to-spinel phase transformation, leading to the formation of a spinel nanophase in the LNCMO@Li3PO4/C material. The presence of Li3PO4/C composite coating with high ionic and electronic conductivity and the spinel nanophase synergistically contribute to the electrochemical properties. Therefore, the LNCMO@Li3PO4/C material shows a high discharge capacity of 124.4 mA h g−1 even at a current density of 1000 mA g−1, a remarkable capacity retention of 87.3% after 200 cycles, and a desirable initial coulombic efficiency of 87.0%. The LNCMO@Li3PO4/C material represents an attractive alternative to high-rate and long-life electrode materials for lithium-ion batteries.