In this study, a series of activated N-doped porous carbon spheres (ANCSs) have been prepared from biomass as the carbon source to be used as highly active and stable electrocatalysts toward the electrocatalytic oxygen reduction reaction (ORR). Hydrothermal carbonization of biomass glucose, which obtains uniform carbon nanopsheres, is followed by doping N atoms by treatment in ammonia and subsequent activation treatment to form ANCSs. The resultant ANCSs possess a large specific surface area of up to 2813 m2/g and pore volume of up to 1.384 cm3/g, and adjustable N contents (2.38–4.53 atom %) with increasing activation temperature. The graphitic and pyridinic-N groups dominate in various N functional groups in the ANCSs. Remarkably, the 1000 °C-activated sample demonstrates competitive activity and outstanding stability and methanol crossover toward the ORR with a four-electron transfer pathway in alkaline media compared to commercial Pt/C catalyst. This excellent performance should be mainly due to effective N-doping and high porosity which can boost the mass transfer and charge transfer and provide a larger number of active sites for the ORR. The unique spherical morphologies with improved porosity as well as excellent stability and recyclability make these ANCSs among the most promising ORR electrocatalysts in practical applications.Keywords: Carbon nanospheres; Electrocatalysis; N-Doping; Oxygen reduction reaction; Porosity;

•Ultrathin N-doped defective carbon layers-encapsulated W2C hybrid (W2C@NC) was prepared by an in-situ pyrolysis and reduction of WO3@g-C3N4.•W2C@NC improves the electrical and Li+ conductivity and provides more active sites.•W2C@NC shows a high catalytic activity on oxygen reduction, oxygen evolution and the decomposition of undesired Li2CO3.•W2C@NC as cathode catalyst for Li-O2 battery shows a lower overpotential and longer cycle life.The sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) restricts the practical application of Li-O2 batteries. The design and facile synthesis of cathode catalysts with high activity on both ORR and OER are desired. In this study, an ultrathin N-doped defective carbon layer-encapsulated W2C hybrid (W2C@NC) which has been successfully synthesized through a facile in-situ pyrolysis and reduction of WO3@g-C3N4 shows a high activity on ORR, OER and even the decomposition of the undesired Li2CO3 as a multifunctional cathode catalyst for Li-O2 batteries. The cells catalyzed by W2C@NC show a much higher initial capacity of 10976 mAh g−1, lower overpotential and longer cycle life, which can be largely attributed to the synergistic effect of W2C nanoparticles and the ultrathin defective N-doped carbon layers. The unique architecture not only accelerates the electron and Li+ conduction but also provides more active sites, which lead to the large enhancement of the electrocatalytic performance. In addition to the high activity on both ORR and OER, W2C@NC also shows a high catalytic function on the decomposition of the undesired side product of Li2CO3. This study offers some new insights into the design and synthesis of novel high performance cathode catalyst for Li-O2 battery.Download high-res image (342KB)Download full-size image

The replacement of platinum (Pt) by nonprecious catalysts with superior activity and stability for the oxygen reduction reaction (ORR) remains challenging for fuel cell devices. Herein, we describe a controllable strategy to prepare hollow graphitic carbon spheres with Fe–N-doped mesoporous shells via in situ polymerization and functionalization. The optimized catalyst exhibits very superior ORR activity with a half-wave potential (E1/2) of 0.886 V in 0.1 M KOH, 15 mV more positive than that of commercial Pt/C catalysts. Even in acidic solution, it also shows a competitive 4e− ORR activity compared to Pt/C. Most importantly, it demonstrates much better long-term stability and resistance to methanol crossover than Pt/C in both alkaline and acidic media. The outstanding activity is contributed by the synergy of chemical functions (Fe–Nx-coordinated moieties) and excellent structural properties (hollow large cores (∼91 nm), open mesopores (∼2.1 nm) throughout the shells, and highly graphitic microstructures), ensuring rapid mass-diffusion and electron-transfer kinetics and full accessibility of catalytic sites.

•N-doped carbon nanotubes (NCNTs) are prepared by pyrolysis of Co2+@g-C3N4.•Ultrafine Pt nanoparticles grow onto the NCNTs.•Pt/NCNTs with ultralow-Pt-loading show high hydrogen evolution activity.•Addition of mesoporous silica to the electrode could improve the activity.The highly effective catalysts for the electrochemical hydrogen generation with substantially reduced cost are strongly desirable, but difficult to achieve. The reduction of Pt-loading by downsizing the Pt nanoparticles is an efficient strategy for obtaining low-cost and high-activity HER electrocatalysts. Herein, we describe a facile strategy to the formation of ultrafine Pt nanoparticles (NPs) bonding to N-doped bamboo-like carbon nanotubes, serving as a highly active and durable catalyst with ultra-low Pt loading for the electrochemical hydrogen generation. With the addition of mesoporous silica to change the wettability of the electrode from hydrophobicity to hydrophilicity of the electrode, the optimized nanocomposite catalyst with ultra-low Pt loading (0.74 wt%) shows a near-zero onset potential (Uonset), an extremely low overpotential of 40 mV to reach 10 mA cm−2 (η10), a small Tafel slope of 33 mV dec−1, and excellent long-term stability, which are comparable to those of 20 wt% Pt/C catalyst. The outstanding properties ensure this promising nanocomposite with significantly reduced Pt loading to become one of the most active catalysts towards the electrochemical hydrogen generation in acid medium.The facile formation of ultrafine Pt nanoparticles bonding to bamboo-like CNTs with structural defects and N-dopants can bring a new class of ultra-low Pt-loading nanocomposites, functioning as highly active and stable hydrogen-evolving electrocatalysts in acidic electrolyte compared to commercial 20 wt% Pt/C catalyst.Download high-res image (337KB)Download full-size image

The development of efficient non-precious-metal electrocatalysts towards the hydrogen evolution reaction (HER), with superior activity and stability, remains a great challenge in the area of renewable energy. In this work, we demonstrated a facile, one-step protocol to synthesize ultrathin graphitic layer (GL)-encapsulated ultrafine ditungsten carbide (W2C) nanoparticles (W2C@GL) with sizes smaller than 10 nm, exhibiting a superior HER activity in acidic solution. An efficient W2C phase, along with an improved electron transfer process by GL wrapping, cooperatively leads to a small Tafel slope of 68 mV dec−1 and a large exchange current density of 0.24 mA cm−2 for W2C@GL, which exceeds the previous W2C materials by far. Over 91% of the current density is maintained after over 8 h of operation, which indicates a good stability of this hybrid catalyst. Thus, W2C@GL with these excellent properties has been among the best non-noble metal HER electrocatalyst reported to date.

Polyacrylonitrile (PAN)-based carbon nanofibers prepared by electrospinning were physically activated using carbon dioxide as the oxidizing agent. The activation procedure was performed at 800 °C for different periods of time ranging from 15 to 60 min. The activated materials have a hierarchical structure with two sets of pore systems in the micropore range centered at ∼0.8 nm and small mesopore range centered at ∼2.8 nm. The activation not only increased the specific surface area and pore volume to 1123 m2 g−1 and 0.64 cm3 g−1, respectively, but also resulted in the evident loss of doped N atoms. The pyridinic and graphitic nitrogen groups are dominant among various N functional groups in the activated samples. CACNF-60, prepared by activating the carbon nanofibers (CNFs) for 60 min, showed excellent electrocatalytic activity for the oxygen reduction reaction (ORR) as well as superior long-term stability and methanol tolerance compared to commercial Pt/C in alkaline media. The excellent electrocatalytic activity of the activated sample is mainly due to its high N content (6.9 at%), unique hierarchical micro-/mesoporosity, and large specific surface area.

•P/S co-doping.•High capacitance of 103.5 F g−1.•Enhanced ORR catalytic performance.Phosphorus (P)/sulfur (S) co-doped porous carbon derived from resorcinol and furaldehyde are synthesized through one-step sol-gel processing with the addition of phosphorus pentasulfide as P and S source followed with freeze-drying and pyrolysis in nitrogen. The P/S co-doping strategy facilitates the pore size widening both in micropore and mesopore regions, together with the positive effect on the degree of graphitization of porous carbon through elimination of amorphous carbon through the formation and evaporation of carbon disulfide. As an electrode for supercapacitor application, P/S co-doped porous carbon demonstrates 43.5% improvement on specific capacitance of the single electrode compared to pristine porous carbon in organic electrolyte at a current of 0.5 mA due to the P-induced pseudocapacitive reactions. As for electrocatalytic use, promoted electrocatalytic activity and high resistance to crossover effects of oxygen reduction reaction (ORR) in alkaline media are observed after the introduction of P and S into porous carbon. After air activation, the specific capacitance of the single electrode of sample PS-pC reaches up to 103.5 F g−1 and an improved oxygen reduction current density.

Dual-doped graphene is synthesized by a facile solvothermal method with the assistance of ionic liquids containing both N and X (X = B, P or S) atoms. All three types of co-doped graphene present excellent catalytic activity, demonstrating preferred four-electron selectivity and low peroxide yields toward oxygen reduction reaction in alkaline solution. Particularly, N, P-graphene exhibits superior catalytic activity to its counterparts in terms of half-wave potential (ΔE1/2 = −70 mV relative to commercial Pt/C), methanol tolerance and long-term stability. This could be attributed to the unique porous nanostructure, change of charge density and high distortion of carbon structures originating from the combination of large electronegativity of N element and big covalent radius of P atoms.

•MnF2 rods and hierarchical CoF2 cuboids were synthesized by the assistance of ionic liquid.•The as-prepared submicro-/nano-sized MnF2 and CoF2 particles exhibit remarkable capacitance.•The cycled electrodes were investigated by different characterization techniques.•The mechanism can be ascribed to the redox reactions between MnF2/CoF2 and MnOOH/CoOOH.Submicro-/nano-sized MnF2 rods and hierarchical CoF2 cuboids are respectively synthesized via a facile precipitation method assisted by ionic liquid under a mild condition. The as-prepared MF2 (M = Mn, Co) submicro/nanoparticles exhibit impressive specific capacitance in 1.0 M KOH aqueous solution, especially at relatively high current densities, e.g. 91.2, 68.7 and 56.4 F g−1 for MnF2, and 81.7, 70.6 and 63.0 F g−1 for CoF2 at 5, 8 and 10 A g−1, respectively. The mechanism of striking capacitance of MF2 is clarified on the basis of analysing the cycled electrodes by different characterization techniques. Such remarkable capacitance is ascribed to the redox reactions between MF2 and MOOH in aqueous alkaline electrolytes, which can not be obtained in aqueous neutral electrolytes. This study for the first time provides direct evidences on the pseudocapacitance mechanism of MF2 in alkaline electrolytes and paves the way of application of transition metal fluorides as electrodes in supercapacitors.Transition metal difluorides (e.g. MnF2 rods) were prepared with the assistance of ionic liquid, exhibiting remarkable pseudocapacitive performance in 1.0 M KOH aqueous electrolyte.

N-doped graphene-wrapped carbon nanoparticles (NGCNPs) are in situ synthesized by a facile bottom-up method. The heat treatment boosts the conversion of N-containing species from the pyrollic N to graphitic N and pyridinic N, thus improving the electrocatalytic activity towards the oxygen reduction reaction (ORR). The physical characterization including X-ray photoelectron spectroscopy, Raman spectra, specific surface area and charge transfer resistance indicates that 600 °C is a pivotal temperature for remarkably improving the electrochemical activity for ORR in terms of onset potential, half-wave potential, electron transfer number and peroxide yields.

Cobalt monoxide (CoO) nanoparticles (NPs) and mesoporous carbon (MC) with large specific surface area were combined as a novel nanocomposite (CoO/MC) using a hydrothermal method to reveal outstanding electrocatalytic activity in the oxygen reduction reaction (ORR). The addition of polyvinylpyrrolidone (PVP) as the surfactant during the hydrothermal process is beneficial for the high dispersion of CoO NPs on the surface of MC. Among the as-acquired products, the CoO/MC nanocomposite prepared with 1.5 g PVP as the surfactant (CoO/MC-1.5) exhibits much better catalytic activity for the ORR with a more positive onset potential, a highly efficient four-electron transfer pathway and a larger current density than the others. Furthermore, the CoO/MC-1.5 nanocomposite demonstrates outstanding durability based on current–time chronoamperometric tests, which significantly prevails over a commercial Pt/C catalyst. The eminent catalytic activities of the CoO/MC-1.5 nanocomposite should be a result of the synergistic effect of the highly dispersed CoO nanoparticles and the ordered mesostructures with large specific surface area, which are advantageous for increasing the exposure of the active sites and promoting fast transfer of the reactants and products.

The lack of efficient electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) has been a fatal issue for the development of metal–air batteries in large-scale commercialization. In this paper, spinel CoFe2O4 (CFO) nanoparticles were successfully in situ grown onto rod-like ordered mesoporous carbon (RC) by a facile, scalable hydrothermal method, followed by annealing at different temperatures. The as-acquired CFO/RC nanohybrid pyrolyzed at 400 °C (CFO/RC-400) has a high specific surface area (150.3 m2 g−1) and two sets of uniform mesopore systems (3.38 and 19.1 nm), all of which are favorable for the improvement of the electrocatalytic activity. The hybridization of CFO nanoparticles and the RC matrix results in increased ORR and OER electrocatalytic activity of the CFO/RC nanohybrids, which is significantly superior to that of unsupported CFO nanoparticles and pure RC. CFO/RC-400 shows better catalytic activity for the ORR with a direct four-electron reaction pathway than those prepared at other temperatures in terms of the onset potential and limiting current density. Furthermore, the CFO/RC-400 nanohybrid exhibits outstanding durability for both the ORR and OER, and can outperform commercial Pt/C. The excellent bifunctional electrocatalytic activities of the CFO/RC nanohybrids are mainly owing to the hierarchical mesoporous structures of the nanohybrids and strong coupling between the CFO nanoparticles and the RC matrix.

A series of novel nitrogen-doped hierarchical carbon monoliths (NCMs) with macroporous scaffolds composed of interconnected mesoporous rods were prepared successfully by a facile nanocasting strategy in combination with pyrolysis in a NH3 atmosphere. After etching off the hard template, the resulting NCMs had large macroporosity (up to 37.4 mL g−1) as well as large specific surface areas (1100–1600 m2 g−1), mesopore volumes (1.4–1.9 mL g−1), and narrow mesopore size distributions (3.8 nm). The nitrogen contents of the NCMs decreased from 4.7 to 1.6 at% with increasing pyrolysis temperature from 650 to 1050 °C. The pyridinic and graphitic nitrogen groups are dominant among various nitrogen-containing groups in the NCMs. Combined with their relatively high nitrogen-doping and unique hierarchical porous textures, NCM-750 exhibited comparable catalytic activity but superior long-term durability and methanol tolerance to commercial Pt/C for oxygen reduction reaction (ORR) with a four-electron transfer pathway in alkaline media. These excellent properties in combination with good recyclability and stability make these NCMs among the most promising electrocatalysts reported so far for efficient ORR in practical applications.

A series of magnetic γ-Fe2O3, Fe3O4, and Fe nanoparticles have been successfully introduced into the mesochannels of ordered mesoporous carbons by the combination of the impregnation of iron salt precursors and then in situ hydrolysis, pyrolysis and reduction processes. The magnetic nanoparticles are uniformly dispersed and confined within the mesopores of mesoporous carbons. Although the as-prepared magnetic mesoporous carbon composites have high contents of magnetic components, they still possess very high specific surface areas and pore volumes. The magnetic hysteresis loops measurements indicate that the magnetic constituents are poorly-crystalline nanoparticles and their saturation magnetization is evidently smaller than bulky magnetic materials. The confinement of magnetic nanoparticles within the mesopores of mesoporous carbons results in the decrease of the complex permittivity and the increase of the complex permeability of the magnetic nanocomposites. The maximum reflection loss (RL) values of −32 dB at 11.3 GHz and a broad absorption band (over 2 GHz) with RL values <−10 dB are obtained for 10-Fe3O4–CMK-3 and 10-γ-Fe2O3–CMK-3 composites in a frequency range of 8.2–12.4 GHz (X-band), showing their great potentials in microwave absorption. This research opens a new method and idea for developing novel magnetic mesoporous carbon composites as high-performance microwave absorbing materials.

It is of great concern to explore new electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In this study, spinel NiFe2O4 nanoparticles cross-linked with the outer walls of multiwalled carbon nanotubes (MWCNTs) were successfully prepared by a simple, scalable hydrothermal method. The as-synthesized NiFe2O4/MWCNT nanohybrid shows not only a better ORR catalytic activity than pure NiFe2O4 and MWCNTs, but also a close four-electron reaction pathway. Meanwhile, the NiFe2O4/MWCNT nanohybrid exhibits a much higher OER catalytic activity when compared to NiFe2O4, MWCNTs and commercial Pt/C in terms of the onset potential and current density. Moreover, the NiFe2O4/MWCNT nanohybrid demonstrates the preeminent long-term durability measured by the current–time chronoamperometric test for both the ORR and OER, which evidently outperforms commercial Pt/C. The excellent bi-functional electrocatalytic activities of the NiFe2O4/MWCNT nanohybrid are attributed to the strong coupling between the NiFe2O4 nanoparticles and the MWCNTs as well as the network structure.

Hierarchical porous activated carbons (ACs) were prepared via a chemical activation procedure with sustainable, renewable biomass fungi as carbon precursor and KOH as activating reagent. The as-produced porous ACs present not only a hierarchical porous structure containing macroporous frameworks and microporous textures, but also a high specific surface area of up to 2264 m2 g−1, a large pore volume of up to 1.02 cm3 g−1, and adjustable heteroatom doping (nitrogen: 2.15–4.75 wt%; oxygen: 8.53–14.48 wt%). The microstructural features can be easily controlled by adjusting the mass ratio of KOH/carbon precursor. The porous ACs possess a specific capacitance of up to 158 F g−1 in organic electrolyte, which significantly outperforms the commercially available ACs. The fungi-based ACs electrode also retains 93% of the specific capacitance as the current density increases from 0.1 to 5 A g−1, and has superior cycling performance (92% retention after 10000 cycles).

The production of efficient and low-cost electrocatalysts for the oxygen reduction reaction (ORR) is one of the key issues for the extensive commercialization of fuel cells. In this paper, we describe a facile one-pot hydrothermal synthesis route to in situ grow spinel NiFe2O4 nanoparticles onto the graphene nanosheets which were produced in advance by a scalable solvothermal reduction of chloromethane and metallic potassium. The resultant NiFe2O4/graphene nanohybrid exhibits superior electrocatalytic activity for the ORR to pure graphene nanosheets and unsupported NiFe2O4 nanoparticles, which mainly favours a desirable direct 4e− reaction pathway during the ORR process. Meanwhile, the NiFe2O4/graphene nanohybrid exhibits the outstanding long-term stability for the ORR, outperforming the commercial 20 wt% Pt/C based on the current–time chronoamperometric test. The excellent catalytic activity and stability of NiFe2O4/graphene nanohybrid are ascribed to the strong coupling and synergistic effect between NiFe2O4 nanoparticles and graphene nanosheets.

A series of microporous carbons (MPCs) were successfully prepared by an efficient one-step condensation and activation strategy using commercially available dialdehyde and diamine as carbon sources. The resulting MPCs have large surface areas (up to 1881 m2 g−1), micropore volumes (up to 0.78 cm3 g−1), and narrow micropore size distributions (0.7–1.1 nm). The CO2 uptakes of the MPCs prepared at high temperatures (700–750 °C) are higher than those prepared under mild conditions (600–650 °C), because the former samples possess optimal micropore sizes (0.7–0.8 nm) that are highly suitable for CO2 capture due to enhanced adsorbate–adsorbent interactions. At 1 bar, MPC-750 prepared at 750 °C demonstrates the best CO2 capture performance and can efficiently adsorb CO2 molecules at 2.86 mmol g−1 and 4.92 mmol g−1 at 25 and 0 °C, respectively. In particular, the MPCs with optimal micropore sizes (0.7–0.8 nm) have extremely high CO2/N2 adsorption ratios (47 and 52 at 25 and 0 °C, respectively) at 1 bar, and initial CO2/N2 adsorption selectivities of up to 81 and 119 at 25 °C and 0 °C, respectively, which are far superior to previously reported values for various porous solids. These excellent results, combined with good adsorption capacities and efficient regeneration/recyclability, make these carbons amongst the most promising sorbents reported so far for selective CO2 adsorption in practical applications.

A set of porous carbons has been prepared by chemical activation of various fungi-based chars with KOH. The resulting carbon materials have high surface areas (1600–2500 m2/g) and pore volumes (0.80–1.56 cm3/g), regardless of the char precursors. The porosities mainly derived from micropores in activated carbons strongly depend on the activation parameters (temperature and KOH amount). All activated carbons have uniform micropores with pore size of 0.8–0.9 nm, but some have a second set of micropores (1.3–1.4 nm pore size), further broadened to 1.9–2.1 nm as a result of increasing either the activation temperature to 750 °C or KOH/char mass ratio to 5/1. These fungi-based porous carbons achieve an excellent H2 uptake of up to 2.4 wt% at 1 bar and −196 °C, being in agreement with results from other porous carbonaceous adsorbents reported in the literature. At high pressure (ca. 35 bar), the saturated H2 uptake reaches 4.2–4.7 wt% at −196 °C for these fungi-based porous carbons. The results imply a great potential of these fungi-based porous carbons as H2 on-board storage media.

A covalent route has been successfully utilized for the surface modification of ordered mesoporous carbon (OMC) CMK-3 by in situ polymerization and grafting of methyl methacrylate (MMA) in the absence of any solvent. The modified CMK-3 carbon particles have a high loading of 19 wt% poly(methyl methacrylate) (PMMA), named PMMA-g-CMK-3, and also maintain their high surface area and mesoporous structure. The in situ polymerization technique endows a significantly enhanced electric conductivity (0.437 S m−1) of the resulting PMMA-g-CMK-3/PMMA composite, about two orders of magnitude higher than 1.34 × 10−3 S m−1 of PMMA/CMK-3 obtained by the solvent mixing method. A minimum reflection loss (RL) value of −27 dB and a broader absorption band (over 3 GHz) with RL values <−10 dB are obtained for the in situ polymerized PMMA-g-CMK-3/PMMA in a frequency range of 8.2–12.4 GHz (X-band), implying its great potential as a microwave absorbing material. The maximum absorbance efficiency for the in situ polymerized sample increases remarkably compared to that (−10 dB) of CMK-3/PMMA prepared by the solvent mixing method. Changing the thickness of the absorber can efficiently adjust the frequency corresponding to the best microwave absorbance ability. The enhanced microwave absorption by the surface modified CMK-3 is ascribed to high dielectric loss. This in situ polymerization for the surface modification of mesoporous carbons opens up a new method and idea for developing light-weight and high-performance microwave absorbing materials.

A series of nitrogen-doped microporous carbons (NCs) was successfully prepared by direct pyrolysis of high-surface-area microporous imine-linked polymer (ILP, 744 m2/g) which was formed using commercial starting materials based on the Schiff base condensation under catalyst-free conditions. These NCs have moderate specific surface areas of up to 366 m2/g, pore volumes of 0.43 cm3/g, narrow micropore size distributions, and a high density of nitrogen functional groups (5.58–8.74%). The resulting NCs are highly suitable for CO2 capture adsorbents because of their microporous textural properties and large amount of Lewis basic sites. At 1 bar, NC-800 prepared by the pyrolysis of ILP at 800 °C showed the highest CO2 uptakes of 1.95 and 2.65 mmol/g at 25 and 0 °C, respectively. The calculated adsorption capacity for CO2 per m2 (μmol of CO2/m2) of NC-800 is 7.41 μmol of CO2/m2 at 1 bar and 25 °C, the highest ever reported for porous carbon adsorbents. The isosteric heats of CO2 adsorption (Qst) for these NCs are as high as 49 kJ/mol at low CO2 surface coverage, and still ∼25 kJ/mol even at high CO2 uptake (2.0 mmol/g), respectively. Furthermore, these NCs also exhibit high stability, excellent adsorption selectivity for CO2 over N2, and easy regeneration and reuse without any evident loss of CO2 adsorption capacity.Keywords: adsorption and separation; CO2 capture; microporous carbon; nitrogen doping;

The high-activity electrocatalysts for the hydrogen evolution reaction (HER) are highly desired to replace precious Pt, but difficult to achieve. Herein, we report the loading of ultrafine tungsten carbide (WC) nanoparticles (NPs) on cobalt-embedded, bamboo-like, nitrogen-doped carbon nanotubes (WC/Co@NCNTs) with high-level N doping via a one-step strategy, leading to a desirable multicomponent nanocomposite with superior activity and stability when used as the HER electrocatalyst. The optimized WC/Co@NCNTs showed a very low onset overpotential (Uonset) of ~18 mV, a small Tafel slope of 52 mV dec−1, a small η10 of only 98 mV to reach a current of 10 mA cm−2, and a large exchange current density (j0) of 0.103 mA cm−2, which also retained its high activity for at least 12.5 h operation in acidic electrolyte. The DFT calculations revealed an important role of the N dopants in the HER as well as a favorable ΔGH* for the adsorption and desorption of hydrogen derived from the synergistic effects between WC NPs and Co@NCNTs.A multicomponent nanocomposite of ultrafine WC nanoparticles anchored on Co-encased, N-doped carbon nanotubes prepared by one-step pyrolysis of low-cost precursors can serve as hydrogen-generating electrocatalyst with excellent activity and superior stability in acidic electrolyte.Download high-res image (191KB)Download full-size image

Nitrogen-doped hollow mesoporous carbon spheres (NHCSs) were successfully prepared via a simple, scalable hydrothermal method, followed by thermal treatment at 650 °C in ammonia atmosphere and subsequent high temperature annealing at 800–1000 °C in nitrogen, respectively. The resulting NHCSs with a particle diameter of ∼150 nm and a shell thickness of ∼20–25 nm have high specific surface areas (738–820 m2 g−1), large pore volume (0.50–0.56 cm3 g−1), bimodal pores system (3.9 and 51.6 nm) and adjustable N-doping levels (3.6–7.8 at.%) depending on the pyrolysis temperature. The unique structure of hollow spheres for NHCSs with uniform mesopores throughout the shells can both promote fast mass transfer and provide inner and outer surfaces with high density of N-related active sites, thus improving the reaction kinetics. The NHCS-1000 (annealed at 1000 °C) exhibited not only comparable ORR activity with a direct four-electron reaction pathway in terms of onset and half-wave potentials, and limiting current densities, but superior long-term durability and methanol-tolerance to commercial Pt/C catalyst, because it has the highest relative content of graphitic-N and pyridinic-N groups, indicating their crucial roles in ORR. The NHCS-1000 with excellent ORR performance is of potential to replace Pt/C catalyst for ORR in practical applications.

The replacement of platinum (Pt) by nonprecious catalysts with superior activity and stability for the oxygen reduction reaction (ORR) remains challenging for fuel cell devices. Herein, we describe a controllable strategy to prepare hollow graphitic carbon spheres with Fe–N-doped mesoporous shells via in situ polymerization and functionalization. The optimized catalyst exhibits very superior ORR activity with a half-wave potential (E1/2) of 0.886 V in 0.1 M KOH, 15 mV more positive than that of commercial Pt/C catalysts. Even in acidic solution, it also shows a competitive 4e− ORR activity compared to Pt/C. Most importantly, it demonstrates much better long-term stability and resistance to methanol crossover than Pt/C in both alkaline and acidic media. The outstanding activity is contributed by the synergy of chemical functions (Fe–Nx-coordinated moieties) and excellent structural properties (hollow large cores (∼91 nm), open mesopores (∼2.1 nm) throughout the shells, and highly graphitic microstructures), ensuring rapid mass-diffusion and electron-transfer kinetics and full accessibility of catalytic sites.

A series of novel nitrogen-doped hierarchical carbon monoliths (NCMs) with macroporous scaffolds composed of interconnected mesoporous rods were prepared successfully by a facile nanocasting strategy in combination with pyrolysis in a NH3 atmosphere. After etching off the hard template, the resulting NCMs had large macroporosity (up to 37.4 mL g−1) as well as large specific surface areas (1100–1600 m2 g−1), mesopore volumes (1.4–1.9 mL g−1), and narrow mesopore size distributions (3.8 nm). The nitrogen contents of the NCMs decreased from 4.7 to 1.6 at% with increasing pyrolysis temperature from 650 to 1050 °C. The pyridinic and graphitic nitrogen groups are dominant among various nitrogen-containing groups in the NCMs. Combined with their relatively high nitrogen-doping and unique hierarchical porous textures, NCM-750 exhibited comparable catalytic activity but superior long-term durability and methanol tolerance to commercial Pt/C for oxygen reduction reaction (ORR) with a four-electron transfer pathway in alkaline media. These excellent properties in combination with good recyclability and stability make these NCMs among the most promising electrocatalysts reported so far for efficient ORR in practical applications.

A series of magnetic γ-Fe2O3, Fe3O4, and Fe nanoparticles have been successfully introduced into the mesochannels of ordered mesoporous carbons by the combination of the impregnation of iron salt precursors and then in situ hydrolysis, pyrolysis and reduction processes. The magnetic nanoparticles are uniformly dispersed and confined within the mesopores of mesoporous carbons. Although the as-prepared magnetic mesoporous carbon composites have high contents of magnetic components, they still possess very high specific surface areas and pore volumes. The magnetic hysteresis loops measurements indicate that the magnetic constituents are poorly-crystalline nanoparticles and their saturation magnetization is evidently smaller than bulky magnetic materials. The confinement of magnetic nanoparticles within the mesopores of mesoporous carbons results in the decrease of the complex permittivity and the increase of the complex permeability of the magnetic nanocomposites. The maximum reflection loss (RL) values of −32 dB at 11.3 GHz and a broad absorption band (over 2 GHz) with RL values <−10 dB are obtained for 10-Fe3O4–CMK-3 and 10-γ-Fe2O3–CMK-3 composites in a frequency range of 8.2–12.4 GHz (X-band), showing their great potentials in microwave absorption. This research opens a new method and idea for developing novel magnetic mesoporous carbon composites as high-performance microwave absorbing materials.

The lack of efficient electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) has been a fatal issue for the development of metal–air batteries in large-scale commercialization. In this paper, spinel CoFe2O4 (CFO) nanoparticles were successfully in situ grown onto rod-like ordered mesoporous carbon (RC) by a facile, scalable hydrothermal method, followed by annealing at different temperatures. The as-acquired CFO/RC nanohybrid pyrolyzed at 400 °C (CFO/RC-400) has a high specific surface area (150.3 m2 g−1) and two sets of uniform mesopore systems (3.38 and 19.1 nm), all of which are favorable for the improvement of the electrocatalytic activity. The hybridization of CFO nanoparticles and the RC matrix results in increased ORR and OER electrocatalytic activity of the CFO/RC nanohybrids, which is significantly superior to that of unsupported CFO nanoparticles and pure RC. CFO/RC-400 shows better catalytic activity for the ORR with a direct four-electron reaction pathway than those prepared at other temperatures in terms of the onset potential and limiting current density. Furthermore, the CFO/RC-400 nanohybrid exhibits outstanding durability for both the ORR and OER, and can outperform commercial Pt/C. The excellent bifunctional electrocatalytic activities of the CFO/RC nanohybrids are mainly owing to the hierarchical mesoporous structures of the nanohybrids and strong coupling between the CFO nanoparticles and the RC matrix.

The development of efficient non-precious-metal electrocatalysts towards the hydrogen evolution reaction (HER), with superior activity and stability, remains a great challenge in the area of renewable energy. In this work, we demonstrated a facile, one-step protocol to synthesize ultrathin graphitic layer (GL)-encapsulated ultrafine ditungsten carbide (W2C) nanoparticles (W2C@GL) with sizes smaller than 10 nm, exhibiting a superior HER activity in acidic solution. An efficient W2C phase, along with an improved electron transfer process by GL wrapping, cooperatively leads to a small Tafel slope of 68 mV dec−1 and a large exchange current density of 0.24 mA cm−2 for W2C@GL, which exceeds the previous W2C materials by far. Over 91% of the current density is maintained after over 8 h of operation, which indicates a good stability of this hybrid catalyst. Thus, W2C@GL with these excellent properties has been among the best non-noble metal HER electrocatalyst reported to date.

Polyacrylonitrile (PAN)-based carbon nanofibers prepared by electrospinning were physically activated using carbon dioxide as the oxidizing agent. The activation procedure was performed at 800 °C for different periods of time ranging from 15 to 60 min. The activated materials have a hierarchical structure with two sets of pore systems in the micropore range centered at ∼0.8 nm and small mesopore range centered at ∼2.8 nm. The activation not only increased the specific surface area and pore volume to 1123 m2 g−1 and 0.64 cm3 g−1, respectively, but also resulted in the evident loss of doped N atoms. The pyridinic and graphitic nitrogen groups are dominant among various N functional groups in the activated samples. CACNF-60, prepared by activating the carbon nanofibers (CNFs) for 60 min, showed excellent electrocatalytic activity for the oxygen reduction reaction (ORR) as well as superior long-term stability and methanol tolerance compared to commercial Pt/C in alkaline media. The excellent electrocatalytic activity of the activated sample is mainly due to its high N content (6.9 at%), unique hierarchical micro-/mesoporosity, and large specific surface area.