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Charge transport processes involving the proton migration and electron transfer for different parts of membrane electrode assemble (MEA) play an essential role for developing the novel electrode and enhancing the electrochemical performance towards proton exchange membrane fuel cells (PEMFCs). However, the coupled charge transport processes make it difficult for evaluating proton conductivity and electronic conductivity of different parts in MEAs under operation conditions of fuel cells. Here in this work, we propose an experiment approach for separating the electronic conductivity and proton conductivity of different components of MEA at the operating conditions of PEMFCs. This approach involves two different measuring devices, which both consist of electron or proton conducting layers, sealing layers and sample layer, followed by tailoring the thickness of sample layers and via electrochemical impedance spectroscopy (EIS) to quantity the electronic conductivity and proton conductivity of different layers. These experiment results show the great potential in the development of different components of MEA. Image 1 • Electronic conducitivity of different parts of MEA are explored. • Proton conductivity of CL and PEM were evaluated. • Interfaces, CL and PEM play a vital role in internal resistance of MEA. [ABSTRACT FROM AUTHOR]

High oxygen transport resistance in the cathode is a main cause of the low performance of high temperature proton exchange membrane fuel cell (HT-PEMFC), and therefore to determine the contribution of different mass transport processes to the oxygen transport resistance is beneficial to the subsequent research work. In this paper, the molecular diffusion resistance (R M) in the cathode was successfully calculated by measuring the limiting currents with using different diluent gases. And the oxygen transport resistance in phosphoric acid (R P A ) was analyzed by changing the humidity and temperature. It was found that the total oxygen transport resistance (R t o t a l ) increased obviously with the increase of the humidify, and the variation of R t o t a l under different conditions was mainly related to the change of R P A . Combined with the phenomenon that the experimental value of R M was less than the calculated value at high humidity, but higher than that at high operation temperature, we speculate that the cause of that R P A increased obviously at high humidity is the occupancy or blockage of gas phase transport channel in catalyst layer (CL) by phosphoric acid due to the water absorption of phosphoric acid in CL and the swelling of membrane. This consequence indicates that it is the change of phosphoric acid distribution that dominate C i s the R t o t a l at high humidity. Image 1 • The separation of molecular diffusion resistance from the total mass transport resistance of HT-PEMFC cathode was realized. • The relationship between the oxygen transport resistance in phosphoric acid and operating conditions was obtained. • The cause of the variation of oxygen transport resistance at different operating conditions was preliminarily analyzing. [ABSTRACT FROM AUTHOR]

Al is one of the principal alloying elements for Mg anodes. In this study, a series of Mg–Al alloys has been evaluated as anode materials for optimizing the Al addition amount in Mg anodes with the intention of improving the discharge performance in aqueous batteries. The effect of Al content on the discharge potential and corrosion resistance of the Mg anode has been investigated through microstructure characterization, electrochemical measurements in a half‐cell, discharge morphology analysis, and Mg–water battery tests. The results show that the Mg–1Al alloy possesses a larger corrosion resistance during discharge, with significant increase of the anode utilization efficiency at 1 and 5 mA/cm2 compared with pure Mg. However, a further increase of Al content does not continuously improve the discharge performance of the Mg anode with the decline of utilization efficiency due to the influence of the precipitated phase. This study contributes to a better understanding about the effect of Al on anodic dissolution and corrosion kinetics of the Mg anode. [ABSTRACT FROM AUTHOR]

The strain effect on oxygen reduction reaction (ORR) activity and stability of FeNC electrocatalysts has been studied using density functional theory in this work. Based on the reaction free energy results, the rate-determining step (RDS) of ORR on FeNC is *OH → H2O, and the reaction proceeds with the pathway O2 → *OOH → *O → *OH → H2O on the Fe site. Tensile stress is favorable to enhance the ORR activity, and the highest ORR activity is obtained on the 6%-FeNC electrocatalyst. On the other hand, when the whole oxygen reduction process needs synergy between Fe and adjacent C atoms and proceeds with the pathway O2 → *OOH → *TS → *O & #OH → *O → *OH → H2O, the applied stress will decrease the ORR activity of the FeNC electrocatalyst. We further constructed a Cu@FeNC core–shell model to simulate strained FeNC. However, the adsorption energy of ORR intermediates on Cu@FeNC (1.9%-FeNC) is much weaker than on the corresponding 2%-FeNC, mainly due to the coordination between the Cu substrate and Fe atom. In addition, the formation energy and binding energy indicate that neither tensile nor compressive stress is conducive to the stability of the FeNC electrocatalyst. In summary, tensile stress could enhance the ORR activity of FeNC electrocatalysts when ORR occurs on the Fe atom only. What's more, we should pay more attention to the influence of interface interaction if utilizing a M@FeNC model to achieve strained FeNC. [ABSTRACT FROM AUTHOR]

Methanol crossover is still a significant barrier to the commercialization of direct methanol fuel cells with wide-used Nafion® membrane. Herein, molecular sieve is introduced into the design of polymer electrolyte membrane to alleviate methanol crossover. The UZM-9 zeolite with an intermediate window size of 0.42 nm can effectively separate hydrated methanol (ca. 1.10 nm) and hydrated proton (ca. 0.23 nm). The methanol diffusion rate through the membrane is effectively suppressed after modified with UZM-9, which is about four times lower than the origin Nafion® membrane. The resulted peak power density reached 80 mW cm−2 with 2 mol L−1 methanol solution feed, which is 2.5-fold higher than that of direct methanol fuel cell with commercial Nafion® membrane. These results open a promising route to alleviate methanol crossover in direct methanol fuel cells. Molecular sieve effect is introduced to alleviate methanol crossover by improving permeation selectivity between the hydrated proton and methanol and one quarter of original methanol diffusion rate produces a 2.5-fold greater peak power density. Image 1 • Molecular sieve effect is used to reduce methanol crossover by improving permeation selectivity. • Membrane is decorated by UZM-9 zeolite with a size window between the hydrated proton and methanol. • One quarter of original methanol diffusion rate produces a 2.5-fold greater peak power density. [ABSTRACT FROM AUTHOR]

• Ultrathin 2D metal-organic frameworks decorated with Pt NPs have been fabricated using an ultrasonication-assisted method. • A "win-win" electron decoration effect has been evidenced on the active sites for both ORR and OER. • Remarkable bifunctional catalytic activity towards ORR and OER with ultralow overpotential gap of 665 mV has been demonstrated. • Excellent performance and durability is achieved in the rechargeable Zinc-air battery assembled with the bifunctional catalyst. To meet the increasing demands for highly active electrocatalysts towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), here in this work, a new strategy of synergistic nano-architecture design based on Platinum nanoparticles (Pt NPs) and ultrathin two-dimensional (2D) metal-organic frameworks (MOFs) is developed for bifunctional electrochemical catalysts. Compared with commercial Pt/C and RuO 2 catalysts, remarkable enhancements in activity and durability of both oxygen reduction and oxygen evolution reactions are achieved on our PtNPs@MOFs composite materials, with one of the lowest over-potential gaps (E gap) of 665 mV that has ever been reported. The tests on the assembled Zn-air batteries have revealed promising electrocatalytic performance and practical advantage of our new materials as air cathode catalyst. Both experimental results and theoretical study have confirmed the synergistic effect between Pt NPs and MOF nanosheets through a "win-win" electron structural modification, demonstrating the effectiveness of our strategy in developing effective bifunctional oxygen electrocatalysts for various types of electrochemical devices. [ABSTRACT FROM AUTHOR]

Construction of advanced electrode architecture, and understanding the electrochemical and mass transport phenomena within its structures are core issues that determine the development of fuel cells and other electrochemical energy technologies. Here in this work, we propose a new scaffold-like electrode with controllable porous volume and size via facile freeze-drying process. Deriving from the delicate surface unevenness and the well-defined macro-pores constructed by the ice template, the electrochemical surfaces and mass transport for methanol and oxygen are greatly enhanced by adapting this electrode structure as anode and cathode for direct methanol fuel cells, respectively. Computational fluid dynamics simulation and mathematic model is adopted to elucidate and predict the intrinsic improvement of mass transport within the newly designed electrode structure. Further practical application of such design is validated in a 10-cell short stack of direct methanol fuel cell systems equipped with this novel electrode. [ABSTRACT FROM AUTHOR]

The microstructure of carbon materials in terms of its specific surface area and pore structure by its activation, are the key issues which determine the electrochemical performance of supercapacitors. In this work, we developed a particular chemical activation process assisted by nitrogen/sulfur co-doping for the preparation of hierarchical porous carbon materials with high specific surface area, aiming at improving the energy density of supercapacitors. The as-obtained hierarchical porous carbon materials exhibited both high Brunauer-Emmett-Teller surface area of up to 3652 m 2 g −1 for more ions adsorption and high porosity (2.61 cm 3 g −1 ) for rapid ion transport. Attributed to the synergistic effects of these two features, the porous carbon displays high gravimetric specific capacitance (324 F g −1 ) in KOH aqueous electrolyte with outstanding rate performance (73.3% capacitance retention at 100 A g −1 ). The symmetrical supercapacitor based on our hierarchical porous carbon displays a maximum specific energy of 9.76 Wh kg −1 and 94.5% retention over 10000 cycles at 15 A g −1 . This synthesis strategy is facile, low-cost and industrialized, which provide a promising route to prepare the hierarchical porous carbon materials for energy storage and renewable delivery devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • Design of the prior PA-resistance electrocatalysts through theoretical calculation. • Discovery of different scaling relationship of the adsorption energy difference of O 2 and H x PO(3-x)- 4 on Pt 3 M(1 1 1) alloy surface. • Pt X Cu as the object for the research of internal mechanism of the potentially high PA resistance property. • Higher PA-resistance performance of Pt 2 Cu compared to the commercial PtC in half-cell and full-cell tests. In high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs), dissociative H 3 PO 4 in cathode will block the active sites of Pt-based electrocatalyst, which thus failure to catalyze the oxygen reduction reaction (ORR). Therefore, the electrocatalysts for the ORR in HT-PEMFCs with high resistance to H 3 PO 4 poisoning are significantly important. Due to the similar bonding structure between H x PO 4 3-x/O 2 and Pt (Pt-O), the design of catalysts which could selectively reduce the adsorption energy of the H 3 PO 4 is urgently needed. In this work, we screen proper H 3 PO 4 resistance electrocatalysts through theoretical calculation based on the adsorption energy difference between H x PO 4 3-x and O 2 as an evaluation criterion. Then, we prepared a series of Pt x Cu catalysts based on the theoretical calculation results and further studied the structure-performance relationship of phosphoric acid-resistant catalysts through combining physical property characterization and electrochemical tests including half-cell and single-cell. The mass activity of Pt 2 Cu/C is 0.51 A/mg Pt , exceeding the DOE's 2020 target of 0.44 A/mg Pt. After add 0.1 M H 3 PO 4 into the HClO 4 electrolyte, the half-wave potential (E 1/2) of Pt 2 Cu/C is only negatively shifted by 47 mV, much lower than 90 mV of TKK Pt/C. Furthermore, the HT-PEMFC with Pt 2 Cu/C in the cathode shows a peak power density of 383.4 mW/cm2, which surpasses that of TKK Pt/C for 231.0 mW/cm2. Our strategy of screening catalysts based on the adsorption energy difference study and further verified by experimental methods provides a promising strategy for the design of practical electrocatalyst in the cathode of HT-PEMFCs. [ABSTRACT FROM AUTHOR]

Heteroatom-doped hierarchically porous carbon materials have attracted great research interests for applications in both energy conversion and storage devices. Rational constructing the architecture, selecting heteroatoms and tuning their bonding structure are keys for the synthesis of high performance carbon based electrode. Here we develop a phase separation approach for the synthesis of a novel porous exfoliated carbon block. Our protocol allows for simultaneous formation of exfoliated porous structure and heteroatom doping through a simple pyrolysis process. The as obtained sample is composed of graphene-like carbon layers, which are enriched with nitrogen dopants in the basal plane and phosphorus functional groups at the carbon edge. The particular structure and surface chemistry of the sample endow the materials with high catalytic properties for oxygen reduction reaction (ORR). On the one hand, the opened-edge thin carbon layers form open channels for efficient mass and ion transportation; On the other hand, the heteroatom dopants and functional groups change the surface chemistry and thus the electronic structure and the surface wettability of the host materials, further enhancing the intrinsic electrochemical performance of the carbon material. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) is becoming increasingly important with the development of fuel cells and metal-air batteries. Manganese oxides have been one of the focuses of recent research for Pt-alternative ORR catalysts. However, the structure-activity relationships of manganese oxides have not been well studied or understood. In the present work, we report a new finding that there is a strong dependence of the ORR activity of Mn 3 O 4 on its morphology. By adopting different solvents in the wet-chemical synthesis, we are able to tailor the morphology of Mn 3 O 4 from nanoparticles (NP-L, 12.5 nm and NP-S, 5.95 nm) to nanorods (NR, exposure of Mn 3 O 4 (101)) and nanoflake (NF, exposure of Mn 3 O 4 (001)). Surprisingly, surface-specific activity of NF toward the ORR was found to be one order of magnitude higher than NP-L. The morphology-activity relationships of Mn 3 O 4 were further studied through a combination of electrochemical experiments and density functional theory (DFT) calculations. It was discovered that the formation of *OOH, concomitant with the first electron transfer, is the potential determining step, which is thermo-dynamically more facile on Mn 3 O 4 (001) than (101) plane. The underlying mechanism could be ascribed to the strong interaction between O 2 and Mn 3 O 4 (001) surface as indicated by the DFT calculations. The study enlarges our understanding of Mn 3 O 4 catalysis and provides clues for rational design of highly efficient transitional metal oxide electrocatalysts for the ORR. [ABSTRACT FROM AUTHOR]

We report a simple route to synthesize iron carbide/carbon yolk–shell composite via a facile two-step process including polymerization of pyrrole using Fe 3 O 4 as a sacrificial template to form a Fe 3 O 4 /polypyrrole composite, followed by annealing at high temperature in N 2 atmosphere. The yolk–shell composite, with iron carbide (Fe 2.5 C) embedded in nitrogen-doped carbon layers, shows impressively high catalytic activity and stability for oxygen reduction reaction in alkaline solution. Both the pyridinic-N and graphic-N in the shell of Fe 3 O 4 –PPy-700, together with the Fe 2.5 C confined in carbon layers are believed to be the active sites for the ORR. [ABSTRACT FROM AUTHOR]

Iron-nitrogen-carbon (Fe-N-C) catalysts for oxygen reduction reaction (ORR) are promising candidates in fuel cell devices but the poor stability remains a grave challenge. The elimination of demetallation is pivotal for extending the life but still incapable due to the ambiguous mechanism. Herein, we show that the structure of FeN 4 site and its structural evolution during ORR has the significant influence. The end-of-test/in-situ Mössbauer spectroscopy and density functional theory study reveal that D1 mainly contributes to the ORR activity but suffers severe demetallation, which is likely due to the instability of FeN 4 C 8. The faster demetallation during ORR, especially at higher potential, can be attributed to the weaker coordination of FeN 4 induced by oxygenated intermediate and electric field according to ab initio molecular dynamics simulations. Finally, the binding energy of Fe-N bond is introduced to describe the influence of structure and structural evolution and give guidance to the improvement of stability. The influence of structure and structural evolution of active site on the demetallation of Fe-N-C is investigated by the end-of-test/in-situ Mössbauer spectroscopy and ab initio molecular dynamics simulation. [Display omitted] • The demetallation related to the degradation of Fe-N-C for ORR is studied. • The stability and activity of FeN 4 varied by structure are identified. • The effect of structural evolution of FeN 4 on demetallation is determined. • The stability and activity mapping of various active sites is exhibited. [ABSTRACT FROM AUTHOR]

Single-crystal (Mn,Co) 3 O 4 octahedra were synthesized through a novel precipitation-aging method. Well-defined single-crystal octahedra can be formed by carefully controlling the precipitation-dissolution equilibrium, oxygen concentration, and solution temperature during synthesis to match the rates of spinel nucleation and octahedra growth. The single-crystal (Mn,Co) 3 O 4 octahedra expose {111} and {011} facets of cubic and tetragonal phases, respectively, depending on the Mn/Co ratio. However, only single-crystal octahedra of Mn 2 CoO 4 and Mn 2.5 Co 0.5 O 4 with exposed {011} facets show the highest selectivity towards 4e − and 2e − oxygen reduction reactions (ORR) in alkaline solution, respectively. Furthermore, the single-crystal Mn 2 CoO 4 octahedra with exposed {011} facets shows ∼30 times higher area specific activity for ORR than that of nanoparticles with random/mixed facets. The high electrocatalytic activity and selectivity towards ORR are correlated with the octahedral shape, the exposed facet, and the ratio of cations on the exposed facets (especially the octahedrally coordinated Mn 4+ cations). This facet dependent catalytic performance provides a new route for obtaining highly selective and active ORR electrocatalysts. [ABSTRACT FROM AUTHOR]

Highlights: [•] The amide-groups are grafted over carbon surface via a simple solvothermal route. [•] Cobalt oxides of 2nm uniformly supporting on the carbon blacks were synthesized. [•] CoO x /XC N shows superior ORR activity than CoO x /XC and CoO x /XC O. [•] The enhanced ORR activity is contributed to the higher content of CoO in composite. [ABSTRACT FROM AUTHOR]

Abstract: Ag-MnOx/C composites were prepared using AgNO3 and KMnO4 as the precursors and Vulcan XC-72 as the support. The physical properties of the Ag-MnOx/C composites were investigated via X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The activity and the stability of the series of Ag-MnOx/C composites toward the oxygen reduction reaction (ORR) in alkaline media were investigated through the electrochemical techniques. The results show that the main species MnO2 and Ag2O in the fresh sample convert into Mn3O4 and Ag(0), respectively, after the heat treatment in N2 at 300°C (Ag-MnOx/C-300). The Ag-MnOx/C-300 sample shows the highest activity toward the ORR, with the half-wave potential of the ORR shifting negatively only 0.035V compared to that on the commercial 40wt. % Pt/C (JM). The electron transfer number during the ORR on the Ag-MnOx/C composite increases with the value close to four after the heat treatment at 300°C, which is mainly attributed to the formation of Ag(0), rather than Mn3O4. The heat treatment brings about a better catalytic stability of the composite, and no obviously negative shift takes place for the half-wave potential of the ORR on the Ag-MnOx/C-300 composite after 1000 cycles accelerated aging test. The maximum power density of the zinc-air battery with the Ag-MnOx/C-300 air electrode reaches up to 130 mW cm−2, higher than those based on the Pd/C and Pt/C cathode catalysts, which shows that the Ag-MnOx/C-300 composite is a promising candidate as the catalyst for the air electrode. [Copyright &y& Elsevier]

Abstract: A series of Ni modified MnO x /C composites were synthesized by introducing NaBH4 to MnO2/C aqueous suspension containing Ni(NO3)2. The physical properties and the activity of the composites toward the oxygen reduction reaction (ORR) were investigated via transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and the electrochemical techniques. The results show that the higher activity of the composites toward the ORR is correlated with the higher content of MnOOH species transformed from Mn(II) on the surface of the composite. The main nickel species in the composites is Ni(OH)2, while Ni(OH)2 shows little activity toward the ORR. However, introducing Ni(OH)2 with proper amount into the MnO x /C improves the distribution of the active material MnO x , which contributes to a surface with more MnOOH. The optimal composite is of the Ni/Mn atomic ratio of 1:2 and the MnO x loading of 28 wt.%. The maximum power density of the zinc–air battery with the optimized Ni modified MnO x /C as the cathode catalyst reaches up to 122 mW cm−2, much higher than the one with the MnO x /C as the air cathode catalyst (89 mW cm−2), and slightly higher than those with the Pd/C and Pt/C as the cathode catalysts. [Copyright &y& Elsevier]

A fiber-reinforced composite membrane has been fabricated using a high-surface-energy substrate via a facile one-step doctor blading technique, which would be a perfect match for roll-to-roll process. The nanofiber mat based on sulfonated polyether-ether-ketone and polyvinylidene fluoride acting as reinforcement frame shows ultra-high surface energy, and enables efficient impregnation of perfluorosulfonated ionomer into porous substrate to form a uniform-layer structure with nanofibers interspersed throughout the composite membrane on the thickness direction. As a result, the fiber-reinforced composite membranes display enhanced mechanical stability and reduced swelling rate. With high packing density and continuous PFSI distribution, the as-prepared composite membranes perform better both on through-plane conductivity and cell performance under a low humidification than those of commercial membranes based on porous poly (tetra fluoroethylene). [Display omitted] • Membranes reinforced with a high-surface-energy substrate (sulfonated polyether-ether-ketone and polyvinylidene fluoride) were prepared as PRS by one-step doctor blading technique. • PRS demonstrates a uniform-layer structure unlike commercially used PTFE-reinforced membranes. • PRS performs better than commercially used PTFE-reinforced membranes in fuel cell under all humidity conditions and is significantly higher without humidification. [ABSTRACT FROM AUTHOR]

Abstract: A highly active porous Pt–PbO x /C composite toward alcohol (methanol, ethanol and ethylene glycol) oxidation in alkaline media is synthesized via a modified polyol method. The crystalline structure, morphology, elemental distribution and the chemical state of metals on surface of the Pt–PbO x /C are evaluated by X-ray diffraction, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The large porous Pt–PbO x /C composite are composed of both Pt and PbO x primary nanoparticles of 1–2 nm which mixed geometrically with unchanged electronic environments of Pt and PbO x . The potentiodynamic and potentiostatic measurements for alcohol electro-oxidation over Pt–PbO x /C in alkaline media show that the activities toward C1–C2 alcohol electro-oxidation were improved remarkably compared to the commercial Pt/C due to both geometric effect, i.e., the addition of PbO x to Pt provides steric hindrance for CO adsorption, and bi-functional effect, i.e., OHad species could be generated over PbO x surface at lower potentials which facilitates the dehydrogenation of the intermediate methoxy. [Copyright &y& Elsevier]

Abstract: Partially graphitized ginkgo-based activated carbon (GGAC) is fabricated from ginkgo shells by pyrolysis, KOH activation and heat treatment using cobalt nitrate as graphitization catalyst. The graphitization temperature is 900°C. The GGAC has a microporous structure and its specific surface area is 1775m2 g−1. XRD patterns show that the carbon becomes more graphitic after heat treatment. The specific capacitance of the GGAC reaches to 178Fg−1 at a potential scan rate of 500mVs−1, which is superior to that of commercial activated carbons and ordered mesoporous carbons. The high electrochemical performance of the GGAC is attributed to its good electronic conductivity and high surface area. Partially graphitized activated carbon is a promising electrode material for electrochemical supercapacitors with high rate performance. [Copyright &y& Elsevier]

Abstract: Methanol electro-oxidation reaction over carbon-supported platinum nanoparticles, including methanol adsorption, apparent reaction order and activation energy, in acidic and alkaline media was investigated comparatively. The results show that the rate constant for methanol adsorption in 1M NaOH is significantly higher than that in 0.5M H2SO4 at the relatively low potential and the COad removal in alkaline media is easier, due to the availability of oxygen-containing species, than in acidic media at the same potential. The apparent activation energy for the MOR in alkaline media is 25.3–14.6kJmol−1, significantly lower than that in acidic media (34.9–28.5kJmol−1). The better MOR activity of Pt/C in alkaline media is attributed to the faster methanol adsorption and the availability of oxygen-containing species. [Copyright &y& Elsevier]

Abstract: Carbon-supported Pt/PdCo and Pt/Au/PdCo catalysts with a low Pt loading were prepared by a combined underpotential deposition and galvanic replacement route. The X-ray diffraction results show that after annealing in H2/Ar atmosphere, the alloy degree of PdCo is enhanced. The average metal particle size of PdCo/C, PdCo/C-H, Pt/PdCo/C and Pt/Au/PdCo/C, characterized by transmission electron microscopy, is about 2.6, 4.1, 5.3 and 5.5nm, respectively. The electrochemical characterizations show that the Pt/PdCo/C electrocatalyst exhibits a high activity toward the oxygen reduction reaction (ORR) but is unstable in electrochemical environment. After the accelerated aging tests (AAT), the electrochemical surface area (ECSA) for the Pt/PdCo/C catalyst decreases by 48% and the half-wave potential of the ORR polarization curve (E 1/2) shifts 35mV negatively. After decorated by Au, both the catalytic activity and stability of the Pt/PdCo/C catalyst are improved significantly. Compared to Pt/PdCo/C, the E 1/2 for Pt/Au/PdCo/C shifts 22mV toward higher potentials. After the AAT, the ECSA decreases only 26%, and the E 1/2 shifts 13mV negatively for Pt/Au/PdCo/C. The enhanced catalytic activity and stability should be due to the high resistance to be oxidized for Pt and the suppressed OH adsorption on the Au-decorated Pt surface. [Copyright &y& Elsevier]

Abstract: Using resorcinol and formaldehyde as carbon precursors, graphitic mesoporous carbons (GMC) with different surface areas were synthesized by adjusting the amount of iron nitrate used as a graphitization catalyst. The BET surface area of the GMC decreases with increasing pore diameter and the material becomes more graphitic with increasing amount of catalyst. Using the GMC as the support, a series of PtRu electrocatalysts (PtRu-GMC) were synthesized. The electrocatalytic activities of the PtRu-GMC toward the methanol oxidation reaction were investigated in both half cells and single cells. The results indicate that the pore size of the GMC is especially important in determining the performance of direct methanol fuel cells. [Copyright &y& Elsevier]

Abstract: The corrosion resistance of several cathode substrates (titanium foam, nickel foam, and silver coated nickel foam) of magnesium–hydrogen peroxide (Mg–H2O2) fuel cells is studied. Titanium foam is found to be the most corrosion-resistant, i.e., the corrosion current density of titanium foam is six orders of magnitude lower than that of nickel or Ag–Ni. Palladium catalyzed titanium foam as a cathode for the Mg–H2O2 fuel cell is prepared by electrodepositing palladium onto the titanium foam substrate. The corrosion resistance of prepared palladium coated titanium is compared with that of titanium foam, nickel foam, and silver coated nickel foam. The structure, morphology and composition of the Pd/Ti are characterized by SEM, EDS, XRD techniques. The influence of the concentration of hydrogen peroxide, sulfuric acid and operation temperature on the performance of Mg–H2O2 fuel cells with the Pd/Ti cathode is studied systematically. The stability of the Mg–H2O2 fuel cell with the Pd/Ti as the cathode is tested and the result shows that Pd/Ti is a promising cathode material for Mg–H2O2 fuel cells. [Copyright &y& Elsevier]

Abstract: Carbon-supported bimetallic PdAg catalysts with Pd/Ag atomic ratios varying from 4/1 to 1/2 were prepared by an impregnation–reduction method. The impregnated black mixture was treated in H2/N2 atmosphere at a temperature varying from 180 to 500°C. The obtained Pd x Ag y /C catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), cyclic voltammetry (CV) and chronoamperometry (CA). XRD results show that the lattice constant of Pd is dilated, suggesting the formation of PdAg alloy. The lattice constant of Pd for the Pd x Ag y /C-500 (reduced at 500°C by H2) increases linearly and the average metal particle size decreases slightly from 6.8 to 5.1nm with increasing Ag fractions from 20% to 67% in the PdAg composition. For Pd x Ag y /C catalysts with a certain specific Pd/Ag atomic ratio, e.g., Pd2Ag1/C, the dilated lattice constant of Pd is independent of the reducing temperature, indicating the alloy degree for the Pd2Ag1/C-t catalysts is comparable. The average metal particle size for the Pd2Ag1/C-t catalysts increases from 3.4 to 5.2nm with H2 reduction temperature increasing from 180 to 500°C. The potentiodynamic measurements on ethanol electrooxidation reaction (EOR) show that the catalytic activities for the Pd x Ag y /C-t catalysts toward the EOR are improved by alloying Pd with Ag. At typical potential of a working fuel cell, e.g., −0.4V vs. Hg/HgO, the EOR current density presents a volcano shape as a function of the Ag fractions in PdAg with the maximum occurs at the Pd/Ag atomic ratios between 2/1 and 3/1. The CA tests show that the Pd x Ag y /C-500 catalysts perform high stability than that of Pd/C-500. The improved EOR activity for the Pd x Ag y /C-t catalysts, compared with whether Pd/C or Ag/C catalyst, may possibly be attributed to the formation of PdAg alloy and the fitted particle size. [Copyright &y& Elsevier]

Abstract: A graphitic mesoporous carbon (denoted as GMC) was synthesized using resorcinol and formaldehyde as carbon precursors and iron nitrate as a graphitization catalyst. The GMC was characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy (TEM), and nitrogen adsorption. The results show that the GMC has a mesoporous structure and a high surface area of 403 m2 g−1, and particularly, a well-defined graphitic framework. Using the GMC as the support, a PtRu/GMC was synthesized to act as an electrocatalyst for the methanol oxidation reaction (MOR). A counterpart with Vulcan® XC-72 (denoted as XC) as the support was prepared for comparison. TEM images show that PtRu nanoparticles are distributed uniformly on the carbon supports for both electrocatalysts. The electrochemical activity of the PtRu/GMC toward the MOR is slightly higher than that of the PtRu/XC in both half cell and single cell measurements. The 1500h stability test of a single cell suggests that the PtRu/GMC is excellent stable. [Copyright &y& Elsevier]

Abstract: Carbon-supported bimetallic Pt m Pb1 (m =1, 2, 3) electrocatalysts with different Pt/Pb atomic ratios were synthesized by a polyol method. The X-ray diffraction results reveal that a PtPb alloy formed in the Pt m Pb1/C electrocatalysts. TEM images show that the PtPb nanoparticles distribute uniformly on the carbon support, and are about 4–5nm in size. The Pt m Pb1/C bimetallic catalysts show superior activities toward methanol electrooxidation reaction (MOR) than the Pt/C in alkaline media. Both CO stripping measurements and density functional theory studies reveal that CO adsorption decreased significantly on the Pt m Pb1/C bimetallic catalysts compared with on pure Pt, which may offer an explanation for the enhanced MOR activity of the Pt m Pb1/C bimetallic catalysts. [Copyright &y& Elsevier]

Abstract: Carbon-supported Ag/Mn y O x composites were prepared by a one step synthesis method, i.e., silver permanganate pyrolysis at different temperatures. The physical and electrochemical properties of the obtained composites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX) and cyclic voltammetry (CV). The electrochemical activity, selectivity and stability for the Ag/Mn y O x /C composites toward oxygen reduction reaction (ORR) in alkaline media were investigated by rotating (ring)-disk electrode (R(R)DE) technique. The XRD results show that the manganese oxides were converted from MnO2 to Mn3O4 and then to MnO gradually with increasing temperature. Among all the Ag/Mn y O x /C composites, Ag/Mn3O4/C obtained at 400°C exhibits the highest activity toward the ORR. Compared with the Ag/C, Mn3O4/C and the physical mixture of Ag/C and Mn3O4/C with the same metal loadings, the ORR activity of the Ag/Mn3O4/C is improved significantly, suggesting a synergic effect between Ag and Mn3O4. At an overpotential of 0.35V, the calculated apparent activation energy for the ORR on the Ag/Mn3O4/C catalyst is 56kJmol−1, which is apparently higher than that on a Pt/C catalyst (36kJmol−1). The results from both Koutecky–Levich plots of the ORR and the RRDE measurements suggest that the ORR proceeds via a 4-electron pathway on the Ag/Mn3O4/C composite. Moreover, the presence of methanol has little influence on the ORR activity toward the Ag/Mn3O4/C catalyst. The accelerated aging tests indicate that the Ag/Mn3O4/C is more stable than the Pt/C in 0.1M NaOH solution. [Copyright &y& Elsevier]

Abstract: In this paper, Fe2O3–SO4 2−/Nafion® composite membranes were prepared by a solution casting method. The physico-chemical properties of composite membranes were characterized by X-ray diffraction (XRD), SEM–EDX and thermogravimetric analysis (TGA). The water uptake ability, proton conductivity, and methanol permeability of the composite membranes were evaluated and compared with the recast Nafion® membrane. The results showed that the proton conductivity and the water uptake of the composite membranes were slightly higher than that of the recast Nafion® membrane. The composite membrane containing 5 wt.% Fe2O3–SO4 2- showed superior ability to suppress methanol crossover, and it further improved the direct methanol fuel cell (DMFC) performances with both 1 M and 5 M methanol feeding, compared with the recast Nafion® membrane. The preliminary 30 h lifetime test of the DMFC with the composite membrane with 5% Fe2O3–SO4 2 − indicated that the composite membrane is stable working at the real DMFC operating conditions at least during the test. These results suggest the applicability of the composite membranes in DMFCs. [Copyright &y& Elsevier]

Abstract: The effect of hydrous RuO2 (RuO2·xH2O) in anode on the performance of direct methanol fuel cells (DMFCs) was examined by voltammetry, methanol stripping analysis, electrochemical impedance spectroscopy, polarization measurement and chronopotentiometry. The results showed that, compared with the DMFC with conventional structures, the dynamic response and quasi-steady state performance of the RuO2·xH2O-introduced DMFCs were significantly improved. The DMFC with RuO2·xH2O layer (ROL) sandwiched between anode catalyst layer and gas diffusion layer exhibited better quasi-steady state performance than those either with ROL sandwiched between anode catalyst layer and electrolyte membrane or with RuO2·xH2O uniformly distributed in anode catalyst layer. The maximum power density of the DMFC with this novel structure was 16% higher than the DMFC with the conventional structure. Moreover, the dynamic response of this RuO2·xH2O-introduced cell was more stable during 250-hour of operation when compared with that of the conventional cell. [ABSTRACT FROM AUTHOR]

Abstract: Na+ is a likely intrinsic impurity in water and is a sort of common cation impurity in the direct methanol fuel cells (DMFCs). In this paper, the effect of Na+ on the DMFC electrochemical response is studied by adding Na+ into the methanol water solution fed in the anode of DMFC. The dynamic variation of cell voltage results shows that the DMFC performance degraded by the presence of Na+ impurity, and the higher concentration of Na+ impurity, the higher poisoning rate is observed. In the meantime, an external reference electrode is used to measure the potential and impedance of the cathode and anode. It is found that the dramatic decrease of the cell voltage is mainly ascribed to the increase of the cathode overpotential which is caused by Na+ exchange with protons in the cathode catalyst layer. The electrochemical impedance measurements suggest that the lack of available protons and low oxygen concentration at the cathode catalytic sites contributed to this degradation. Furthermore, the recovery strategy is introduced and it is found that the poisoned MEA could be partly recovered by immersing in 0.5M H2SO4 solution for 4h. [Copyright &y& Elsevier]

Abstract: Ketjen Black (KB) as an electrocatalyst support was treated at 900°C in the presence of cobalt and nickel nitrates, and characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, transmission electron microscopy and nitrogen adsorption measurement. The treated KB (T-KB) exhibits better graphitization and a larger mesopore volume than the untreated material. A Pt electrocatalyst supported on T-KB was prepared by a modified polyol process. Cyclic voltammetry and single cell tests show that the Pt/T-KB electrocatalyst exhibits better electrochemical activity and stability than a Pt/KB electrocatalyst. [Copyright &y& Elsevier]

Measurement of flow distribution in the fuel cell stack is a challenging task. This study proposes a new method to measure air flow distribution in high-temperature proton exchange membrane fuel cell stacks. The characteristic frequency related to channel impedance is extracted using the distribution of relaxation times analysis. A simple correlation between the air stoichiometry and the characteristic frequency is developed. The influence of various factors on the correlation, including cell operation conditions, fluid physical properties and channel dimensions, are investigated. The experimental results show a good agreement with the correlation. Error estimation indicates that the temperature distribution of the stack, gas humidity and pressure distribution in the inlet manifold have no significant effect on the proposed method under normal conditions. The accuracy and practicability are verified using a three-cell stack with separate mass flow controller (MFC) systems. The results show less than 3.11% of relative error between the reference air stoichiometry given by the MFC and those measured from our proposed method for air stoichiometry below 3.0 at 0.1 A cm−1. The present method provides powerful support for designing high consistency stacks and the real-time monitoring cells state-of-health in stacks. [Display omitted] • Distribution of relaxation times analysis of the channel impedance in fuel cells. • Correlating the characteristic frequency of mass transport and air stoichiometry. • Measuring the air flow distribution in the fuel cell stack through the correlation. • Understanding the impact of the stack parameters' consistency on the measurement. [ABSTRACT FROM AUTHOR]

Abstract: The influence of lithium doping on the crystallization behavior, morphology, and enhancement in photoluminescence intensity of SnO2:Eu was investigated. In order to attain high homogeneous and pure samples, the Pechini type sol–gel method was adopted for the synthesis at low temperature (500°C). The structure and morphology were characterized by using X-ray diffraction (XRD) and transmission electron microscope (TEM). The results indicate that the Li+ doping could accelerate the crystallization of SnO2 and the particle size of the phosphors is below 100nm. In particularly, the incorporation of Li+ ions into SnO2 lattice could induce a remarkable increase of photoluminescence intensity. [Copyright &y& Elsevier]

Abstract: In the present study, a method based on transmission-line mode for a porous electrode was used to measure the ionic resistance of the anode catalyst layer under in situ fuel cell operation condition. The influence of Nafion content and catalyst loading in the anode catalyst layer on the methanol electro-oxidation and direct methanol fuel cell (DMFC) performance based on unsupported Pt–Ru black was investigated by using the AC impedance method. The optimal Nafion content was found to be 15wt% at C. The optimal Pt–Ru loading is related to the operating temperature, for example, about 2.0mg/cm for C, 3.0mg/cm for C. Over these values, the cell performance decreased due to the increases in ohmic and mass transfer resistances. It was found that the peak power density obtained was 217mW/cm with optimal catalyst and Nafion loading at C using oxygen. [Copyright &y& Elsevier]

Abstract: In the present work, direct hydroxylation of benzene to phenol by using in situ generated H2O2 with electricity cogeneration was carried out in a proton exchange membrane fuel cell (PEMFC) reactor. Phenol was produced only when there was current through the external circuit. No other organic products were detected during this electrochemical process. A rotating ring-disc electrode (RRDE) technique was used to quantitatively detect the intermediate H2O2 in an acid electrolyte solution at different potentials and temperatures. The RRDE studies showed that the in situ generated H2O2 may play a crucial role during the formation of phenol. The formation rate of phenol could be controlled by adjusting the current or cell potential. [Copyright &y& Elsevier]

Abstract: Nanocrystalline ZrO2:Eu was synthesized by complexing sol–gel method. The effects of heat treatment on structure, grain size and luminescence properties of ZrO2:Eu were studied with X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence measurements. The dependence between the fluorescence emission and the crystalline structure is discussed. [Copyright &y& Elsevier]

This paper reports the photoluminescence (PL) properties of nanocrystalline YVO4: Tm phosphor synthesized by the polymerizable complex method based on the Pechini-type reaction. The powder was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), absorption spectroscopy and PL. The results of XRD and TEM show that, high-quality nanopowders with controlled morphology and microstructure were prepared at a relatively low temperature about 700°C. Upon ultra violet excitation the vanadate host transferred energy to thulium ions efficiently and strong blue emission (475nm) assigned to 1G4→3H6 transmission is observed. By analyzing excitation and emission spectra of thulium doped yttrium vanadate, we deduced the mechanism of the energy transfer between vanadate host and thulium ions. [Copyright &y& Elsevier]

A series of 40 wt.% Pt/C electrocatalysts were prepared by a modified polyol process and an improved aqueous impregnation method with different impregnation time. The characterization results of TEM and XRD identically reveal that the size and distribution of Pt nanoparticles on carbon are controllable by modifying impregnation time in both routes. High dispersion of Pt nanoparticles on carbon is achieved by both methods with 15 min impregnation, while aggregation of Pt nanoparticles takes place with prolonging the impregnation time to 36 h, especially in the aqueous impregnation procedure. UV–vis spectroscopy measurements verified that the redox reaction between PtCl62- and formaldehyde could take place at a slow rate under ambient conditions via a two-step reaction path, where PtCl42- serves as an intermediate. On the other hand, PtCl62- anion can be directly reduced to Pt0 above 333 K in the modified polyol process through an autocatalytic pathway. The short-time-impregnated 40 wt.% Pt/C as cathode electrocatalysts in direct methanol fuel cell performs better than that of long-time-impregnated electrocatalysts. Experimental evidence provides clues for fundamental understanding of elementary steps of the redox reactions, which helps guiding the design and preparation of highly dispersed Pt catalyst with high metal loadings for fuel cells. [Copyright &y& Elsevier]

Nanocrystalline europium doped yttrium orthovanadate (YVO4:Eu) were synthesized by the polyacrylamide gel method. For a comparative evaluation, bulk YVO4:Eu was prepared by solid-state reaction. On the basis of X-ray powder diffraction, scanning and transmission electron microscopy and luminescence measurements, the polyacrylamide gel method appears to be a more efficient method to prepare the luminescence materials YVO4:Eu with high homogeneity, purity and luminescence intensity. [Copyright &y& Elsevier]

Nafion® membrane is a key component of polymer electrolyte membrane fuel cell. In this paper, transmission and attenuated total reflection (ATR) spectra of Nafion® membrane and the difference of absorption peaks between two modes are presented. The peak shift is attributed to the different chemical environments of surface and bulk. Obvious change was observed after thermal treatment on Nafion® membrane through calculation of the relative absorption intensity ratio of different groups. It was found that side chain may move out of the bulk to the surface for the membrane. And the moving degree increased with the treating temperature. [Copyright &y& Elsevier]

Mg is an important alloying element for Al anode in alkaline batteries. In this work, series of Al–Mg alloys have been investigated as anode materials, focusing on optimizing the Mg addition amount in Al anode with the intention of enhancing its discharge performance. The results show that solid-solute Mg improves the discharge potential of Al anode at low current density and inhibits its self-corrosion. However, excess Mg additions accelerate the self-corrosion of Al anode due to the formation of AlMg intermetallic in Al matrix. To reduce the corrosion rate and improve the discharge activity, Mg content in Al anode is optimized to be 0.5% with cooperation of electrolyte additive Na 2 SnO 3. • Effect of different Mg content on discharge performance of Al anode was investigated. • Mg addition in Al anode was optimized to be 0.5% at operating temperature of 50 °C. • Al-0.5 Mg exhibited coulombic efficiency of 96% at 100 mA cm−2, that of 5N Al was 83%. [ABSTRACT FROM AUTHOR]

Atomically dispersed Fe-N-C catalyst is fabricated by a rational designed dual-MOFs strategy for efficient and low-cost DMFC application. • A dual-MOFs strategy is developed for the fabrication of atomically dispersed Fe-N-C catalyst. • The formation mechanism of the atomically dispersed Fe-N-C catalyst is well investigated. • The as-prepared catalyst demonstrates high ORR activity, excellent methanol tolerance and outstanding stability in acids. • The DMFC assembled with atomically dispersed Fe-N-C catalyst exhibits excellent performance. The rational design of highly efficient, low-cost and methanol-tolerant catalysts toward the oxygen reduction reaction (ORR) is urgently desired for the commercialization of direct methanol fuel cells (DMFCs). Herein, a novel Fe-N-C catalyst (ZIF/MIL-10-900) is derived from a mixture of ZIF-8 and MIL-101(Fe) and atomically dispersed FeN 4 structures are confirmed by Mössbauer spectra and X-ray absorption spectroscopy. Study on the pyrolysis procedure reveals that Fe atoms in FeN 4 are from MIL-101(Fe), while ZIF-8 acts as structural support and nitrogen sources. The as-prepared catalyst demonstrates a comparable ORR activity with the commercial Pt/C possessing a half-wave potential (E 1/2) of 0.78 V in acids, in combination with excellent methanol tolerance and stability. One of the highest peak power density of 83 mW cm−2 in DMFC (3 M CH 3 OH) by adopting ZIF/MIL-10-900 as cathode catalyst is obtained, which is 2.8-fold higher than that of the commercial Pt/C in the same operating condition. [ABSTRACT FROM AUTHOR]

Ultrahigh mass transport resistance and excessive coverage of the active sites introduced by phosphoric acid (PA) are among the major obstacles that limit the performance of high-temperature polymer fuel cells, especially compared to their low-temperature counterparts. Here, an alternative strategy of electrode design with fibrous networks is developed to optimize the redistribution of acid within the electrode. Via structural tailoring with varied electrospinning parameters, uneven migration of PA with dispersed droplets is observed, subverting the immersion model of conventional porous electrode. Combining with experimental and calculation results, the microscaled uneven PA interfaces could not only provide extra diffusion pathways for oxygen but also minimize the thickness of PA layers. This electrode architecture demonstrates enhanced electrochemical performance of oxygen reduction within the PA phase, resulting in a 28% enhancement of the maximum power density for the optimally designed electrode as cathode compared to that of a conventional one.

The chemical stability of the anion exchange membranes (AEMs) is determinative towards the engineering applications of anion exchange membrane fuel cells (AEMFCs) and other AEM-based electrochemical devices, yet remains a challenge due to deficiencies in the structural design of cations. In this work, an effective design strategy for ultra-stable piperidinium cations is presented based on the systematic investigation of the chemical stability of piperidinium in harsh alkaline media. Firstly, benzyl-substituted piperidinium was degraded by about 23% in a 7 M KOH solution at 100 °C after 1436 h, which was much more stable than pyrrolidinium due to its lower ring strain. The introduction of substituent effects at the α-C position was proved to be an effective strategy for enhancing the chemical stability of the piperidinium functional group. As a result, the butyl-substituted piperidinium cation showed no obvious structural changes after being treated in the 7 M KOH solution at 100 °C for 1050 h. Afterwards, GC-MS and NMR analysis indicated that the α-C atoms in the substituents of piperidinium are fragile to the nucleophilic attack of OH - . Based on the above results, the electronic and steric effects of different alkyl substitutions were analyzed. This work provides critical insights into the structural design of chemically stable piperidinium functional groups for the AEM and boosts its application in electrochemical devices, such as fuel cells and alkaline water electrolysis., Competing Interests: The authors declare no competing financial interest., (This journal is © The Royal Society of Chemistry.)

The oxygen reduction reaction (ORR) that occurs on the outermost layer of electrocatalysts is significantly affected by the composition and structure of the electrocatalysts. During the preparation of PtM alloy electrocatalysts, high-temperature annealing in an inert or reducing atmosphere could promote the segregation of M toward the core, forming a highly active Pt-skin structure. However, under fuel cell operating conditions, the adsorption of oxygen-containing groups could stimulate the easily dissolved M to segregate to the surface, reducing the activity and stability of the electrocatalysts. In this work, we conducted segregation energy calculation of PtM (M = Cu, Pd, Au) electrocatalysts under specific adsorption (SA), aqueous solution (AS) and an external electric field (EEF) with a density functional theory method. It was found that different factors have different effects on the segregation energy: ΔΔESA ≫ ΔΔEEEF > ΔΔEAS. The coupling effects have also been considered and compared: ΔΔESA+EEF > ΔΔESA+AS > ΔΔEEEF+AS. When including all three factors, the change of segregation energy could reach 1.63 eV. Therefore, operating conditions have a noteworthy influence on the segregation behavior of PtM ORR electrocatalysts, which should be considered in the further design of PtM ORR electrocatalysts.

Rational electrode design is crucial to promote the performance of the hydrogen evolution reaction (HER) via further enhancing the activity, stability, and utilization of platinum (Pt) in an alkaline electrolyte. Herein, a binder-free low-Pt-content HER electrode, Pt (∼20 μg cm -2 ) decorated on nickel hydroxide grown on nickel foam (Pt-Ni(OH) 2 -2h-NF20), is fabricated at near room temperature in a test tube. To lower the ohmic resistance, for the first time, the Pt nanoparticles were location-selectively anchored on the bottom of height-controlled vertical Ni(OH) 2 nanosheets via utilizing the mass transfer resistance of the dense Ni(OH) 2 film for chloroplatinate. Furthermore, the excellent mass transfer, high specific surface area of Pt, synergistic effect between Pt with Ni(OH) 2 , and stable structure together prompt the resulting electrode with a special structure to exhibit superior HER electrocatalytic activity and stability in 1 M KOH. Typically, this electrode reaches a current density of 35.9 mA cm -2 at an overpotential of 100 mV, which is over 8 times higher than that of commercial Pt/C, and the overpotential only increases by 20 mV at 100 mA cm -2 over 150,000 s of stability test. Benefiting from the simple fabrication process, the electrode with an area of 840 cm 2 was successfully prepared with a steady overpotential of 370 mV at 1000 mA cm -2 and increased potential of 23 mV over 50 h of stability test.

Comprehension of the structure-activity relationship is of great importance for the rational design of electrocatalysts for the oxygen reduction reaction (ORR). Herein, Fe-N-C catalysts obtained from zeolitic imidazolate framework-8 (ZIF-8) with a tunable size ranging from 30 to 400 nm are precisely synthesized. Structural investigation indicates that the catalyst with smaller size possesses a higher proportion of mesopores originating from particle stacking, which leads to enhanced catalyst utilization and accelerated mass transport. The size effect of the catalyst on ORR activity is systematically investigated by rotation disk electrode (RDE) and direct methanol fuel cell (DMFC) tests. The electrochemical performance of the Fe-N-C catalyst is found to be increased with the reduction of its particle size. The correlation among size, mesoporosity and catalyst performance is discussed, giving new inspiration for the development of rational design strategies of non-precious metal catalysts.

A ferrocene-based ionic liquid (Fe-IL) is used as a metal-containing feedstock with a nitrogen-enriched ionic liquid (N-IL) as a compatible nitrogen content modulator to prepare a novel type of non-precious-metal-nitrogen-carbon (M-N-C) catalysts, which feature ordered mesoporous structure consisting of uniform iron oxide nanoparticles embedded into N-enriched carbons. The catalyst Fe(10) @NOMC exhibits comparable catalytic activity but superior long-term stability to 20 wt % Pt/C for ORR with four-electron transfer pathway under alkaline conditions. Such outstanding catalytic performance is ascribed to the populated Fe (Fe3 O4 ) and N (N2) active sites with synergetic chemical coupling as well as the ordered mesoporous structure and high surface area endowed by both the versatile precursors and the synthetic strategy, which also open new avenues for the development of M-N-C catalytic materials., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)