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Abstract The exploration of cheap and stable electrocatalysts with high activity towards oxygen reduction reaction in the acidic and alkaline medium is a vital activity for large-scale applications of fuel cells. In recent years, one-dimensional nanofibrous electrode materials with high surface area and specific porosities have been drawing great attention in energy conversion devices such as fuel cells and metal-air batteries. Nanofibers with a one-dimensional nanostructure can be produced by electrospinning, which has been considered as a particularly low-cost and versatile method. In this review, we summarize the properties of electrospun nanofibers and the recent progress in designing of non-precious nanostructured electrocatalysts for oxygen reduction reaction in fuel cells. More importantly, we also highlight the interesting nanostructures, new synthetic approaches, and the electrocatalytic performance including active sites and stability of electrospun-based electrocatalysts. In addition, we describe the research challenges and future developmental perspectives of electrospun materials in energy technology. Highlights • Non-precious nanostructured electrocatalysts by electrospinning are summarized. • The active sites and reaction mechanism of the electrocatalysts are discussed. • Research challenges and future perspectives are described. [ABSTRACT FROM AUTHOR]

Cyclic voltammetry as a simple electrochemical deposition method was developed in order to prepare a platinum nano-electrocatalyst for oxygen reduction reaction (ORR) in low-temperature fuel cell systems. The morphology of the prepared platinum was evaluated by scanning electron microscopy and energy dispersive x-ray analysis. The effects of platinum concentration in electrodeposition solution and scan numbers of cyclic voltammetry (scan rate: 50 m V s−1, between 1.489 and − 0.311 versus reversible hydrogen electrode) on the performance of prepared electrocatalysts for ORR were studied. The fabricated electrodes were evaluated by cyclic voltammetry, linear sweep voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy. The results revealed that the optimum conditions for the preparation of electrocatalysts were 2E−3 M H2PtCl6 and 30 scan numbers. The optimized electrode showed high stability after 1200 cycles. [ABSTRACT FROM AUTHOR]

Abstract To improve the sluggish oxygen reduction reaction from the cathode of solid oxide fuel cells (SOFCs), a conformal layer of catalytic CoO x grains was deposited onto the internal surface of LSM/YSZ composite cathode of commercial cells, through atomic layer deposition (ALD). Upon the electrochemical operation, the ALD coated cell has dramatic reduction of the polarization resistance, and the power density exhibits continuous increase over the course of 172 h operation at 750 °C and reaches the cell performance enhancement by a factor of 1.6, in comparison with that from the baseline operated for 96 h. Such performance enhancement was attributed to the combination of the newly added triple phase boundaries for promoting the oxygen reduction reaction, as well as the accelerated oxygen transport on the cathode surface. The present work opens the further research direction for ALD coating of non-precious metal catalyst to boost the performance of as-fabricated SOFCs. Highlights • Conformal CoO x layer is deposited on LSM/YSZ backbone of SOFC cathode using ALD. • CoO x ALD layer continuously improves the oxygen reduction reaction upon operation. • CoO x ALD layer interacts with the backbone and formed catalytic Co 0.7 Mn 0.3 O x. • Co 0.7 Mn 0.3 O x exhibits Bi-model distribution on LSM and YSZ surfaces. [ABSTRACT FROM AUTHOR]

Abstract The sluggish oxygen reduction reaction (ORR) in cathode is the bottleneck of polymer electrolyte membrane fuel cell. Discovery of ORR catalysts with high activity and low cost is the key solution for the cell development. In this work, we synthesized a novel polypyrrole modified carbon supported FeS (FeS-PPy-BP) through two-step reaction and used it as cathode catalyst in direct borohydride fuel cell (DBFC). The catalyst had an onset ORR potential of 0.89 V (vs. reversible hydrogen electrode (RHE)), little lower than the onset potential of commercial Pt/C. The ORR on the FeS-PPy-BP was mainly through 4-electron process with a low yield of H 2 O 2 (below 5%). The FeS-PPy-BP exhibited a good catalytic stability. The half-wave potential shift of the FeS-PPy-BP after 5000 cycles was 31 mV while that of the Pt/C was 42 mV. The DBFCs using the FeS-PPy-BP as cathode catalyst achieved a maximum power density of 140.5 and 78.8 mW cm−2 at 60 and 30 °C, respectively. The outstanding electrochemical properties and the cell performances strongly support the FeS-PPy-BP as a promising cathode catalyst for DBFC. Graphical abstract Image 1 Highlights • A new FeS-PPy-BP catalyst was synthesized. • FeS-PPy-BP had high ORR activity and good catalytic stability. • DBFC using FeS-PPy-BP as cathode achieved high power density. • FeS-PPy-BP is promising cathode catalyst for DBFC. [ABSTRACT FROM AUTHOR]

Abstract Presently, the practical application of Fe/N/C catalysts as replacements of Pt for oxygen reduction reaction is still limited by insufficient activity. Herein, we demonstrate a novel design for such catalyst. On one hand, the obtained Fe/N/C SiO 2 ZnCl 2 catalyst owns high densities of well-exposed active-sites derived from three-dimensional well-balanced macro-, meso-, and microporous structures constructed by adopting ZnCl 2 salt and SiO 2 microspheres as combined templates. On the other hand, simulation reveals that a high loading of catalyst in cathode catalyst layer would not benefit cell performance and fast oxygen reduction reaction process occurs only inside a limited thickness of catalyst layer. Particularly, the Fe/N/C SiO 2 ZnCl 2 shows a maximal output power density as high as 480 mW cm−2 at an ultra-low loading of 0.5 mg cm−2. This study firstly exhibits that development of catalysts with high-density active sites and construct of ultra-thin catalyst layer are of great significance for improving the performance of fuel cell. Highlights • Fe/N/C SiO 2 ZnCl 2 was synthesized using ZnCl 2 templating and silica templating. • Fe/N/C SiO 2 ZnCl 2 shows superior ORR activity in both alkaline and acidic medium. • The P max of Fe/N/C SiO 2 ZnCl 2 is as high as 480 mW cm−2 at a 0.5 mg cm−2 loading. [ABSTRACT FROM AUTHOR]

Developing efficient bi-functional electrocatalysts for both oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is crucial for producing hydrogen and utilizing hydrogen effectively to promote electrochemical energy storage in proton membrane exchange fuel cells (PEMFCs). Herein, we report Co@Pd core-shell nanoparticles encapsulated in porous carbon derived from zeolitic imidazolate framework 67 (ZIF-67) for both ORR and HER. The controlled pyrolysis of ZIF-67 can lead to the formation of Co nanoparticles encapsulated in nitrogen-doped porous carbon (Co NC), which subsequently underwent galvanic replacement with Na 2 PdCl 4 to form Co@Pd core-shell nanoparticles embedded in nitrogen-doped porous carbon (Co@Pd NC). The Co@Pd NC exhibited outperformance in ORR and HER than commercial Pd/C, as manifested by more positive onset potential and larger diffusion-limited current density in ORR tests, as well as a small overpotential to drive a current density of 10 mA cm −2 , and much lower Tafel slope in HER tests. It also demonstrated more robust long-term stability than commercial Pd/C for both ORR and HER. Multiple techniques inter-confirmed that the Pd loading in the sample was very low. The findings can pave a path for fabricating a core-shell structured nanocomposite with ultralow noble metal usage as a bifunctional catalyst for electrochemical energy storage and conversion with high-efficiency and remarkable longevity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Different preparation schemes of PBAs are systematically summarized. • Strategy developing high-performance PBAs-based electrocatalyst is proposed. • An insight into the future research direction of PBAs-based electrocatalyst is highlighted. Electrolytic water, metal-air cells and fuel cells are the key fields in the application of new energy. However, these fields are subject to the high overpotential of ORR (oxygen reduction reaction), OER (oxygen evolution reaction) and HER (hydrogen evolution reaction), and these reactions are limited by the efficiency of electrocatalysts. Therefore, developing highly active electrocatalysts becomes a key step to solve the above problems. Prussian blue analogues (PBAs) are ancient synthetic cyanide coordination polymer materials, which are widely used in ORR, OER and HER. The unique three-dimensional open metal frame structure and large specific surface area of PBAs greatly increase the contact area between catalyst and electrolyte, and improve the number of active sites. The easy adjustment of components is beneficial to enhance the inherent activity of each active site in the catalyst. In this paper, the recent progress of PBAs derived materials in electrocatalysis is reviewed. Firstly, different preparation methods of PBAs were summarized, and then the regulatory strategies to improve the electrocatalytic activity of ORR, OER and HER when PBAs derived materials were used as electrocatalysts were discussed in detail, including the chemical composition regulation of doping, as well as the structure and morphology regulation of core–shell structure, open nanoccages structure and composite with other materials. Finally, the major challenges and possible future research orientations in this field were discussed, providing a new vision for further application of PBAs derived materials in electrocatalysis. [ABSTRACT FROM AUTHOR]

Supported ordered intermetallic nanoparticles are of significant interest for catalysis applications owing to their unique surface/near-surface structures and electronic properties. However, the synthesis of small-sized intermetallic catalysts with high mass activity remains a formidable challenge, as high temperatures annealing treatments are generally requisite to achieve ordered intermetallic structures but lead to undesired larger crystallites. Here, we report an industrially relevant impregnation approach for the scalable synthesis of small-sized platinum-based intermetallic nanoparticle catalysts by regulating inter-particle distance on carbon black supports to mitigate metal sintering in high-temperature annealing. We construct a library consisting of 18 binary Pt-based intermetallic nanoparticle catalysts with an average size of < 5 nm. The prepared intermetallic catalyst libraries exhibit outstanding proton-exchange-membrane fuel cells performance, including high mass activities of 1.3–1.8 A mg Pt –1, large peak power densities of 1.2–1.4 W cm–2 in H 2 -air cells, and efficient Pt utilization of ∼0.07 g kW–1 at rated power. [Display omitted] • Intermetallic compounds (IMC) have unique strain/electronic effects in catalysis. • A family of small size Pt-based IMCs was achieved by regulating inter-particle distance. • Small size and ordered IMC structure guarantee outstanding performance in fuel cell. [ABSTRACT FROM AUTHOR]

Developing efficient and durable Pt-based electrocatalysts for oxygen reduction reaction (ORR) is critical for the practical application of fuel cells but still remains challenge at present. Here we successfully synthesized a series of ternary L1 0 -PtCo x Fe 1-x (x=0.33, 0.50 and 0.67) intermetallic nanoparticles (NPs) supported on reduced graphene oxide for ORR catalysis. L1 0 -PtCo 0.50 Fe 0.50 exhibits the highest mass activity (MA) of 0.93 A mg−1 Pt at 0.9 V (1.82 times the corresponding binary L1 0 -PtCo intermetallics) and minimal activity loss (24.73 % loss in MA) after 30,000 potential cycles. By Density Functional Theory calculations, the excellent performance of ternary L1 0 -PtCo 0.50 Fe 0.50 can be ascribed to: (1) more efficient electronic structure regulation caused by dual-element driven electron transfer, which leads to more electron accumulation on Pt and weakens the over-binding of oxygen-containing species, (2) the unique two-center bridge pattern of O 2 adsorption over Pt-Fe site leads to ORR proceeding via. the dissociative mechanism, avoiding the formation of OOH*. [Display omitted] • The L1 0 −PtCo 0.50 Fe 0.50 shows efficient and stable performance for ORR catalysis. • The double-element (Co/Fe) drives more electron transfer to Pt. • The Pt-Fe sites induce ORR proceeding via. the dissociative pathway. • The effect of co-catalytic elements on boosting ORR activity was revealed. [ABSTRACT FROM AUTHOR]

In this work, we synthesized new materials based on Fe(II) phthalocyanine (FePc), urea and carbon black pearls (BP), called Fe-N-C, as electrocatalysts for the oxygen reduction reaction (ORR) in neutral solution. The electrocatalysts were prepared by combining ball-milling and pyrolysis treatments, which affected the electrochemical surface area (ECSA) and electrocatalytic activity toward ORR, and stability was evaluated by cyclic voltammetry and chronoamperometry. Ball-milling allowed us to increase the ECSA, and the ORR activity as compared to the Fe-N-C sample obtained without any ball-milling. The effect of a subsequent pyrolysis treatment after ball-milling further improved the electrocatalytic stability of the materials. The set of results indicated that combining ball-milling time and pyrolysis treatments allowed us to obtain Fe-N-C catalysts with high catalytic activity toward ORR and stability which makes them suitable for microbial fuel cell applications.

Gold nanoclusters (Aun NCs) exhibit a size-specific electronic structure unlike bulk gold and can therefore be used as catalysts in various reactions. Ligand-protected Aun NCs can be synthesized with atomic precision, and the geometric structures of many Aun NCs have been determined by single-crystal X-ray diffraction analysis. In addition, Aun NCs can be doped with various types of elements. Clarification of the effects of changes to the chemical composition, geometric structure, and associated electronic state on catalytic activity would enable a deep understanding of the active sites and mechanisms in catalytic reactions as well as key factors for high activation. Furthermore, it may be possible to synthesize Aun NCs with properties that surpass those of conventional catalysts using the obtained design guidelines. With these expectations, catalyst research using Aun NCs as a model catalyst has been actively conducted in recent years. This review focuses on the application of Aun NCs as an electrocatalyst and outlines recent research progress.

In order to reduce the overall system cost, the development of inexpensive, high-performance and durable oxygen reduction reaction (ORR)N, Fe-codoped carbon-based (Fe/N/C) electrocatalysts to replace currently used Pt-based catalysts has become one of the major topics in research on fuel cells. This review paper lays the emphasis on introducing the progress made over the recent five years with a detailed discussion of recent work in the area of Fe/N/C electrocatalysts for ORR and the possible Fe-based active sites. Fe-based materials prepared by simple pyrolysis of transition metal salt, carbon support, and nitrogen-rich small molecule or polymeric compound are mainly reviewed due to their low cost, high performance, long stability and because they are the most promising for replacing currently used Pt-based catalysts in the progress of fuel cell commercialization. Additionally, Fe-base catalysts with small amount of Fe or new structure of Fe/Fe3C encased in carbon layers are presented to analyze the effect of loading and existence form of Fe on the ORR catalytic activity in Fe-base catalyst. The proposed catalytically Fe-centered active sites and reaction mechanisms from various authors are also discussed in detail, which may be useful for the rational design of high-performance, inexpensive, and practical Fe-base ORR catalysts in future development of fuel cells.

The carbon supported iron selenide catalysts (FeSe2/C) were prepared with various selenium to iron ratios (Se/Fe), namely, Se/Fe = 2.0, 2.5, 3.0, 3.5 and 4.0, through facile microwave route by using ferrous oxalate (FeC2O4·2H2O) and selenium dioxide (SeO2) as precursors. Accordingly, effects of Se/Fe ratio on the crystal structure, crystallite size, microstructure, surface composition and electrocatalytic activity for oxygen reduction reaction (ORR) of FeSe2/C in an alkaline medium were systematically investigated. The results revealed that all the FeSe2/C catalysts obtained with the Se/Fe ratios of 2.0–4.0 exhibited almost pure orthogonal FeSe2 structure with the estimated mean crystallite sizes of 32.9–36.2 nm. The electrocatalytic activities in potassium hydroxide solutions were higher than those in perchloric acid solutions, and two peak potentials or two plateaus responded to ORR were observed from cyclic voltammograms and polarization curves, respectively. The ORR potentials of 0.781–0.814 V with the electron transfer numbers of 3.3–3.9 at 0.3 V could be achieved as the Se/Fe ratios varied from 2.0 to 4.0. The Fe and Se were presented at the surface of FeSe2/C upon further reduction on FeSe2. The Se/Fe ratios slightly influenced the degree of graphitization in carbon support and the amount of active sites for ORR.

Nitrogen-doped ordered mesoporous carbon was synthesized by using polyaniline as the carbon source and SBA-15 as the template. The microstructure, composition and electrochemical behavior were extensively investigated by the nitrogen sorption isotherm, X-ray photoelectron spectroscopy, cyclic voltammetry and rotating ring-disk electrode. It is found that the pyrolysis temperature yielded a considerable effect on the pore structure, elemental composition and chemical configuration. The pyrolysis temperature from 800 to 1100 °C yielded a volcano-shape relationship with both the specific surface area and the content of the nitrogen-activated carbon. Electrochemical tests showed that the electrocatalytic activity followed a similar volcano-shape relationship, and the carbon catalyst synthesized at 1000 °C yielded the best performance. The post-treatment in NH3 was found to further increase the specific surface area and to enhance the nitrogen doping, especially the edge-type nitrogen, which favored the oxygen reduction reaction in both acid and alkaline media. The above findings shed light on electrocatalysis and offer more strategies for the controllable synthesis of the doped carbon catalyst.

Abstract: Atomic layer deposition (ALD) was used to modify two different types of carbon black-based Pt oxygen reduction catalysts with protective TiO2 nanostructures to increase catalyst durability. Rates of ALD growth and the structure of deposited TiO2 were observed to be highly dependent on oxygen content of the catalyst substrate. Electrochemical durability was enhanced with the addition of TiO2 ALD nanostructures, with up to 70% retention in mass activity measured over accelerated durability testing. High-temperature treatment of the top-performing ALD catalyst, which was found to promote structural rearrangement of the TiO2 and Pt phases into hybrid nanoparticles, yielded a twofold increase in activity but was detrimental to durability.Graphical Abstract: [ABSTRACT FROM AUTHOR]

Pt-based bimetallic nanostructures with low content of Pt were considered as one of the attractive nanocatalysts for their high Pt utilization efficiency, remarkable catalytic characters and cost-effectiveness in facilitating the sluggish cathodic reactions in fuel cells. Herein, three-dimensional Pt 47 Ni 53 nanopolyhedrons (NPHs) with abundant active sites were constructed by a facile one-pot solvothermal strategy, in which cytosine and cetyltrimethylammonium chloride (CTAC) worked as the co-structure directing agents. The Pt 47 Ni 53 NPHs were mainly characterized by a series of techniques, showing the high catalytic activity and stability towards oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) in comparison to Pt 13 Ni 87 nanocrystals (NCs), Pt 63 Ni 37 NCs, commercial Pt black and/or Pt/C catalysts. Impressively, the mass activity of Pt 47 Ni 53 NPHs was about 215.80 mA mg Pt −1 for ORR, approximately 4-time increase relative to Pt black (49.60 mA mg Pt −1 ). These results demonstrate the promising applications of the synthesized nanocatalysts in energy storage and transformation. [ABSTRACT FROM AUTHOR]

To improve the power generation of the microbial fuel cell, activated carbon is modified by the Co 3 O 4 /NiCo 2 O 4 double-shelled nanocage, which prepared via a metal-organic framework method. When tested as cathodic material, the mesoporous Co 3 O 4 /NiCo 2 O 4 double-shelled nanocage with a large surface (112.9 m 2  g −1 ) exhibits higher open circuit potential (0.252 V) and higher exchange current density (19.70 × 10 −4  A cm −2 ). Moreover, the maximum power density of the air-cathode microbial fuel cell equipped with the 5% as-prepared catalyst is 1810 mW m −2 , 104% higher than the control. The morphology and crystal structure of Co 3 O 4 /NiCo 2 O 4 are investigated by the Transmission electron microscope and X-ray diffraction. X-ray photoelectron spectroscopy analysis indicates that there exists Co 3+ /Co 2+ and Ni 3+ /Ni 2+ redox couples in the catalyst, and divalence - trivalence - divalence redox cycles contribute to the improved oxygen reduction reaction performance and enhanced power output. Owing to the structural merits and improved electrochemical activity, the synthesized Co 3 O 4 /NiCo 2 O 4 double-shelled nanocage would be considered as a replacement of the new material for Pt in microbial fuel cell. [ABSTRACT FROM AUTHOR]

Colloidal PtCu alloy nanoclusters (NCs) stabilized with acetate ions and ethylene glycol, with small particle size (∼2 nm) and tunable Pt/Cu ratio, are successfully synthesized by a modified alkaline-ethylene glycol method. As tractable building blocks, the prepared PtCu NCs are immobilized on a melem-modified carbon support (MMC) to assemble electrocatalysts (PtCu/MMC) for oxygen reduction reaction (ORR). The influence of Pt/Cu ratio in the alloy NCs of PtCu/MMC on the catalytic activity for ORR is investigated. Pt 75 Cu 25 /MMC exhibits the highest electrochemical mass activity (1.59 A mg −1 Pt ) and specific activity (3.98 mA cm −2 Pt ) at 0.9 V of supported NCs ever reported. After an aging test of 10,000 potential cycles, the loss of mass activity over Pt 75 Cu 25 /MMC is only 9%, which is the best durability compared to previously reported PtCu NCs catalysts measured at the similar conditions. Colloidal PtCu alloy NCs and the immobilization method reported in this work will find wide applications in the development of bimetallic catalysts. [ABSTRACT FROM AUTHOR]

A carbon supported Pt catalyst with tetradecyltrimethylammonium bromide (TTAB) adsorbed to the nanoparticle surface was operated and tested as a cathode in a polymer electrolyte membrane fuel cell. The fuel cell with the TTAB@Pt/C catalyst showed a higher current relative to the amount of Pt used than the fuel cell with a commercial Pt/C catalyst. Besides, CO stripping evidenced that for the TTAB@Pt/C electrode large parts of the Pt surface were covered by TTAB. Hence, the fuel cell with the TTAB@Pt/C cathode showed a larger current related to the electrochemical active surface area as compared to the fuel cell with the commercial Pt/C cathode. This improvement in the ORR kinetics was further investigated by X-ray photoelectron and in-situ X-ray absorption spectroscopy, and was found to have been caused by two effects: (1) the presence of a metal-ligand charge transfer in the TTAB@Pt/C electrode and (2) the prevention of oxygen containing adsorbates which were being formed in large amounts on the Pt/C electrode. Furthermore, the latter effect also explains the higher stability observed for the TTAB@Pt/C compared to the Pt/C electrode. [ABSTRACT FROM AUTHOR]

Abstract: C-MnO2 is an alternative catalyst support in polymer electrolyte membrane fuel cells. In this study, C-MnO2 was prepared by hydrothermal method using KMnO4 as the Mn source. Meanwhile, Pt/C-MnO2 electrocatalyst was prepared by impregnation chemical reduction using ethylene glycol as reducing agent and H2PtCl6 as Pt precursor. The structure and morphology of C-MnO2 and Pt/C-MnO2 were characterized by X-ray diffraction energy-dispersive spectroscopy and transmission electronic microscopy analyses. Electrochemical performance was investigated by cyclic voltammetry analyses. A rotating disk electrode (RDE) was used to examine catalytic oxygen reduction reactions (ORRs) to explore the oxygen reduction of Pt/C-MnO2. The Pt/C-MnO2 exhibited better activity and stability than those of Pt/C. In contrast to Pt/C, MnO2 possessed unique characteristics; the oxide functions as an effective Pt support and hence enhances ORR activity and durability. The RDE results for the ORR indicated that the main reaction of the Pt/C-MnO2 catalyst was the direct reduction of O2-H2O. This reaction is similar to the mechanism of the Pt/C catalyst and both with a four-electron charge transfer. The results of the single cell polarization experiment and the ON-OFF cycling test revealed that MnO2 improves proton exchange membrane fuel cells performance and durability. This paper also investigated the mechanism through which MnO2 promotes oxygen reduction.Graphical Abstract: [ABSTRACT FROM AUTHOR]

Abstract: We evaluated the performance and durability of platinum-iron-copper with an L10 ordered face-centered tetragonal structure (fct-PtFeCu) as cathode catalysts of membrane-electrode assemblies (MEAs) in polymer electrolyte fuel cells. The exchange current density per unit active surface area of Pt in fct-PtFeCu/C, measured in the MEA, was sufficiently higher than that of commercial Pt/C. The durability of the MEAs was evaluated by three accelerated degradation tests: (1) a load cycle durability test, which mainly accelerates the degradation of catalysts; (2) an open-circuit voltage (OCV) hold test, which mainly degrades membranes; and (3) a hybrid of the load cycle test and OCV hold test. Despite the possible negative effects of dissolved transition metals on the durability of MEAs, fct-PtFeCu/C showed higher durability than commercial Pt/C and at least comparable durability with in-house Pt/C in the OCV hold test, and showed high durability in the hybrid test up to 200 h. These results suggest that the presence of Fe and Cu did not negatively affect the durability of the MEA with fct-PtFeCu/C, and rather the other factor, carbon support, affected more in retaining the durability.Graphical Abstract: [ABSTRACT FROM AUTHOR]

Microbial fuel cells (MFCs) as renewable electricity-generation devices are often confronted with the poor long-term durability and high cost of cathodic catalysts. In this study, iron (III) metaphosphate/iron phosphide/partly-graphitized carbon ((Fe(PO 3 ) 3 )/FeP/PGC) catalysts obtained at 750–950 °C are used as air–cathode catalysts for oxygen reduction reaction (ORR) in single-chamber MFCs. As temperature increases, graphitization degree of carbon skeleton in (Fe(PO 3 ) 3 )/FeP/PGCs gradually increases to obtain a higher electrical conductivity. At 900 and 950 °C, monoclinic structured Fe(PO 3 ) 3 is formed in PGC structure to constitute the Fe(PO 3 ) 3 /FeP heterojunctions, which should originate from the partial oxidation of FeP. The maximum power density (1.162 ± 0.022 W m −2 ) of MFCs is obtained by Fe(PO 3 ) 3 /FeP/PGC (900 °C) cathode, which is higher than that of commercial Pt/C (1.052 ± 0.015 W m −2 ) and only has a decline of 4.56% after 1900 h operation (excellent durability). Well-dispersed Fe(PO 3 ) 3 /FeP heterojunctions and abundant oxygen-containing groups (C–O–C, C–O–H and C–OH) play the important roles in achieving the high charge transfer efficiency (8.7 ± 0.2 Ω) and long-term durability in bio-electricity generation. Fe(PO 3 ) 3 /FeP/PGC (900 °C) primarily proceeds the efficient four-electron ORR pathway by exploiting the synergistic effects between the active components (Fe(PO 3 ) 3 /FeP) and porous structure (533.77 m 2  g –1 ). This study provides the promising non-precious-metal ORR electro-catalysts for replacing Pt/C in renewable energy-generation systems. [ABSTRACT FROM AUTHOR]

Cost-effective cobalt oxides were synthesized at mild condition as alternatives to platinum catalyst for oxygen reduction in microbial fuel cells (MFCs). The catalysts were prepared by heating Co(NO 3 ) 2 above its decomposition temperature together with carbon black (CB). At a catalyst loading of 5 mg/cm 2 , cobalt oxide cathodes with a Co(NO 3 ) 2 to CB ratio of 0.732:1 produced a maximum power density of 1220 mW/m 2 , which was slightly lower than that of Pt/C cathodes (1360 mW/m 2 ). Further increase in the loading of cobalt oxides resulted in an increase in performance. The maximum power densities produced by cobalt oxide cathodes increased to 1400 mW/m 2 at a catalyst loading of 20 mg/cm 2 and 1540 mW/m 2 at 30 mg/cm 2 , which outperformed the Pt/C control. The durability of cobalt oxide catalysts was comparable to that of Pt/C in single-chamber MFCs with biological contamination. The costs of cobalt oxide catalysts were much lower than that of Pt/C catalyst, even when the loading of cobalt oxides was several times higher than Pt/C catalyst. These findings show that the facilely synthesized cobalt oxides were cost-effective catalysts for oxygen reduction in air-cathode MFCs. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) is a multi-step catalytic process occurring at the cathode in fuel cells. As an alternative to a conventional Platinum catalyst, PtSn-based alloy catalyst experimentally presents an enhanced ORR activity compared with pure Pt catalysts. However, how the ORR reaction proceeds on PtSn is not yet well understood. On this context, a systematic study of O 2 reduction on the (1 1 1) facets of Pt 3 Sn based on periodic density functional theory (DFT) calculation is presented. With the charge transfer from Sn to Pt, d -band center shifts away from the Fermi level, the electronic structure thoroughly differs from that of pure Pt thus producing ligand (electronic) effect. The ORR intermediates (H, O, OH, O 2 , OOH, H 2 O 2 , and H 2 O) species preferred site, adsorption configuration, binding energies, active barriers, rate constants, equilibrium constant are studied. Additionally, the corresponding transition states in seven elementary reactions are confirmed using the climbing image nudged elastic band (CI-NEB) method, and the thermodynamic and dynamic property in each reaction step are evaluated. Herein, the DFT results imply that on both the Pt 3 Sn(1 1 1) and Pt(1 1 1) surfaces, the ORR share the same mechanism following OOH ad dissociation pathway (O 2ad  → OOH ad  → O ad  → OH ad  → H 2 O ad ). The rate-determining step of the ORR on the (1 1 1) surfaces is found to be the O ad hydrogenation reaction which requires activation barrier of 0.66 eV on the Pt 3 Sn(1 1 1) surface and 0.77 eV on the pure Pt(1 1 1) surface, indicating the introduction of Sn significantly decreases the activation energy barrier. As the same temperature, the reaction rate of ORR on the Pt 3 Sn(1 1 1) surface is faster than that on the pure Pt(1 1 1) surface. Our thermodynamic and kinetic results verify the important role of tin in improving the catalytic activity of ORR. [ABSTRACT FROM AUTHOR]

Ordered mesoporous carbon (OMC) has shown great promising as superior support in the creating highly efficient and stable cathodic catalyst for oxygen reduction reaction (ORR) due to its many merits but there are still many challenges. We demonstrate in this work a facile and large-scale strategy to efficiently embed Pt-based crystals within OMC using supercritical carbon dioxide (scCO 2 ) technique. Typically, PtFe/OMC catalysts with the highly dispersive, ultrafine sizes (1.3–2.3 nm), controllable compositions and loadings have been successfully fabricated. Through control of experimental process and loadings, most of crystals can be deposited into mesochannels of OMC. The integration of highly dispersive and ultrafine PtFe crystals as well as high surface area, mesoporous structure and good electrical conductivity of OMC supports make PtFe/OMC promising as active and stable electrocatalysts toward ORR. By careful comparison, PtFe/OMC catalysts show the overwhelmingly better or comparable electrochemical performance compared with previously reported mesoporous carbon supported Pt-based catalysts. These attractive materials hold great potential in cathodic electrocatalyst for fuel cells and the scCO 2 technique is quite superior for constructing OMC with various embedded nanoparticles (such as PtPd, PtCu etc.) [ABSTRACT FROM AUTHOR]

A cathode of zinc-air fuel cells (ZAFCs) comprises a catalyst layer and a diffusion layer. We propose a new type of cathode, which overcomes the disadvantages of a double-layer cathode used in ZAFCs. To improve the performance of the single-layer cathode, dispersing the particles and reducing their size in the cathode mixture were conducted. The single-layer cathode had the same hydrophobicity as with the diffusion layer of the double-layer cathode and showed better electrochemical properties than the catalyst layer of the double-layer cathode. The single-layer cathode had a dense microstructure and a flat surface. The electrochemical performance and mechanical strength of the single-layer cathode were superior to those of a double-layer cathode. We showed single-layer cathode cell had better electrochemical performance than the double-layer cathode cell through a newly designed flexible-tubular-type ZAFC. [ABSTRACT FROM AUTHOR]

The present work reports novel soft X-ray Fresnel CDI ptychography results, demonstrating the potential of this method for dynamic in situ studies. Specifically, in situ ptychography experiments explored the electrochemical fabrication of Co-doped Mn-oxide/polypyrrole nanocomposites for sustainable and cost-effective fuel-cell air-electrodes. Oxygen-reduction catalysts based on Mn-oxides exhibit relatively high activity, but poor durability: doping with Co has been shown to improve both reduction rate and stability. In this study, we examine the chemical state distribution of the catalytically crucial Co dopant to elucidate details of the Co dopant incorporation into the Mn/polymer matrix. The measurements were performed using a custom-made three-electrode thin-layer microcell, developed at the TwinMic beamline of Elettra Synchrotron during a series of experiments that were continued at the SXRI beamline of the Australian Synchrotron. Our time-resolved ptychography-based investigation was carried out in situ after two representative growth steps, controlled by electrochemical bias. In addition to the observation of morphological changes, we retrieved the spectroscopic information, provided by multiple ptychographic energy scans across Co L3-edge, shedding light on the doping mechanism and demonstrating a general approach for the molecular-level investigation complex multimaterial electrodeposition processes. [ABSTRACT FROM AUTHOR]

We synthesized ordered mesoporous Fe/N/C with highly active Fe-N x /C sites denoted as m-FePhen-C as a non-precious metal catalyst (NPMC) for the oxygen reduction reaction in fuel cells. This was the first study that incorporated a catalyst precursor with Fe-N coordination directly in a simple block co-polymer-assisted soft-template method for the synthesis of mesoporous Fe/N/C. The synthesized catalyst (m-FePhen-C) showed a high catalytic performance comparable to that of Pt/C in half-cell tests, and a membrane electrode assembly (MEA) with an m-FePhen-C cathode exhibited 40% higher power density than did an MEA with a commercial Pt/C cathode in single-cell tests, with comparable electrode thicknesses. This result is highly meaningful in that generation of the Fe-N x /C active sites and formation of ordered mesoporous structure were achieved simultaneously in the simple soft-template-assisted process, and in that the advantages of mesoporous structure with appropriate pore size in metal-containing NPMC were elucidated for high-performance MEAs. [ABSTRACT FROM AUTHOR]

The nitrogen-doped carbon materials express excellent oxygen reduction reaction (ORR) electrocatalytic activity, which can be used as cathode catalyst for fuel cells to replace platinum electrocatalysts. In this paper, polyaniline and glucose as precursors were used to prepare nitrogen-doped carbon materials by hydrothermal reaction combined with high temperature carbonization activation. The results showed that the onset potential of nitrogen-doped porous materials calcined at 900 ℃ (PCPG-900) was −0.171 V, which was close to commercial Pt/C catalyst (−0.03 V) and the limiting current density was 5.4 mA cm −2 , which was 0.9 mA cm −2 higher than that of Pt/C catalyst (4.5 mA cm −2 ). And the (average) number of electrons transfer number per molecule of O 2 was 4.2, indicating that oxygen reduction reaction mainly via four-electron reduction of O 2 to H 2 O. The resulting product may be a promising candidate as alternative catalysts for the cathode side in fuel cells. [ABSTRACT FROM AUTHOR]

Highly-efficient catalysts for the oxygen reduction reaction (ORR) have been extensively investigated for the development of proton exchange membrane fuel cells (PEMFCs). The state-ofthe- art Pt/C catalysts suffer from high price, limited accessibility of Pt, sluggish reaction kinetics, as well as undesirable long-term durability. Engineering ultra-small noble metal clusters with high surface-to-volume ratios and robust stabilities for ORR represents a new avenue. After a simple introduction regarding the significance of ORR and the recent development of noble metal clusters, the general ORR mechanism in both acidic and basic media is firstly discussed. Subsequently, we will summarize the recent efforts employing Pt, Au, Ag, Pd and Ru clusters, as well as the alloyed bi-metallic clusters for acquiring highly efficient catalysts to enhance both the activity and stability of ORR. Molecular noble metal clusters with definitive composition to reveal the relevant ORR mechanism will be particularly highlighted. Finally, the current challenges, the future outlook, as well as the perspectives in this booming field will be proposed, featuring the great opportunities and potentials to engineering noble metal clusters as highly-efficient and durable cathodic catalysts for fuel cell applications. [ABSTRACT FROM AUTHOR]

Graphitic layer encapsulated iron based nanoparticles (G@FeNPs) have recently been disclosed as an interesting type of highly active electrocatalysts for the oxygen reduction reaction (ORR). However, the complex composition of the metal-containing components and their contributions in catalysis remain unclear. As a representative catalyst of the unique encapsulated structure, a series of G@FeNPs catalysts were prepared by a high-pressure pyrolytic process with uniform and essentially identical morphologies but varied compositions. The catalysts exhibited a high onset potential of 0.85 V at 0.1 mA cm −2 in acidic media. By 57 Fe-Mössbauer spectroscopy the iron containing components were identified including α-Fe, γ-Fe, γ-Fe 2 O 3 , and Fe 3 C as well as a minor doublet component due to Fe 3+ in high spin and/or Fe 2+ in low spin state. The ORR activities are evaluated in terms of the mass specific kinetic current density found to be positively correlated with the Fe 3 C content in the range of study, indicating involvement of the encapsulated nanoparticles in the ORR catalysis. The recognition of the Fe compositions and active sites provides new insights to the confined Fe-based ORR electrocatalysts and therefore options for further development of non-precious metal materials. [ABSTRACT FROM AUTHOR]

This work reports the first account of perovskite oxide and carbon composite oxygen reduction reaction (ORR) catalysts integrated into anion exchange membrane fuel cells (AEMFCs). Perovskite oxides with a theoretical stoichiometry of Ca 0.9 La 0.1 Al 0.1 Mn 0.9 O 3-δ are synthesized by an aerogel method and calcined at various temperatures, resulting in a set of materials with varied surface chemistry and surface area. Material composition is evaluated by X-ray diffraction, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The perovskite oxide calcined at 800 °C shows the importance of balance between surface area, purity of the perovskite phase, and surface composition, resulting in the highest ORR mass activity when evaluated in rotating disk electrodes. Integration of this catalyst into AEMFCs reveals that the best AEMFC performance is obtained when using composites with 30:70 perovskite oxide:carbon composition. Doubling the loading leads to an increase in the power density from 30 to 76 mW cm −2 . The AEMFC prepared with a composite based on perovskite oxide and N-carbon achieves a power density of 44 mW cm −2 , demonstrating an ∼50% increase when compared to the highest performing composite with undoped carbon at the same loading. [ABSTRACT FROM AUTHOR]

Network-like metallic alloys of solid nanoparticles have been frequently reported as promising electrocatalysts for fuel cells. The three-dimensional structure of such networks is rich in pores in the form of voids between nanoparticles, which collectively expose a large surface area for catalytic activity. Herein, we present a novel solution to this problem using a precursor comprising a flocculent core-shell PtNi@Ni to produce PtNi network catalysts with nanoparticle intraporosity after carefully controlled electrochemical dealloying. Physical characterization shows a hierarchical level of nanoporosity (intrapores within nanoparticles and pores between them) evolves during the controlled electrochemical dealloying, and that a Pt-rich surface also forms after 22 cycles of Ni leaching. In ORR cycling, the PtNi networks gain 4-fold activity in both j ECSA and j mass over a state of the art Pt/C electrocatalyst, and also significantly exceed previously reported PtNi networks. In ORR degradation tests, the PtNi networks also proved stable, dropping by 30.4% and 62.6% in j ECSA and j mass respectively. The enhanced performance of the catalyst is evident, and we also propose that the presented synthesis procedure can be generally applied to developing other metallic networks. [ABSTRACT FROM AUTHOR]

Improving the performance of oxygen reduction reaction (ORR) electrocatalysts is essential for the commercial efficacy ofmany renewable energy technologies, including lowtemperature polymer electrolyte fuel cells (PEFCs). Herein, we report highly active and stable carbon-supported Ru@Pt core-shell nanoparticles (Ru@Pt/C) prepared by a wet chemical synthesis technique. Through rotating disc electrode testing, the Ru@Pt/C achieves an ORR Pt mass-based activity of 0.50 A mgPt-1 at 0.9 V versus the reversible hydrogen electrode (RHE), which exceeds the activity of the state-of-the-art commercial Pt/C catalyst as well as the Department of Energy 2020 PEFC electrocatalyst activity targets for transportation applications. The impact of various synthetic parameters, including Pt to Ru ratios and catalyst pretreatments (i.e., annealing) are thoroughly explored. Pt-based mass activity of all prepared Ru@Pt/C catalysts was found to exceed 0.4 mgPt-1 across the range of compositions investigated,with themaximumactivity catalyst having a Ru:Pt ratio of 1:1. This optimized composition of Ru@Pt/C catalyst demonstrated remarkable stability after 30,000 accelerated durability cycles (0.6 to 1.0 V vs. RHE at 125mV s-1),maintaining 85%of its initialmass activity. Scanning transmission electron microscopy energy dispersive spectroscopy (STEM-EDS) analysis at various stages of electrochemical testing demonstrated that the Pt shell can provide sufficient protection against the dissolution of the otherwise unstable Ru core. [ABSTRACT FROM AUTHOR]

The preparation of highly efficient and cheap electrocatalysts toward oxygen reduction reaction is significant for many electrochemical cells. Here we facilely synthesized nitrogen doped carbon nanotube by pyrolyzing melamine formaldehyde resin and Fe loading on MgO. There were mainly three morphologies observed, slender bamboo-like CNT, thick bamboo-like CNT, surface smooth, hollow CNT. The content of Fe loading on MgO had little influence on morphologies of CNT, however, when no MgO as support, only carbon ribbon obtained. The MgO as support was also significant for the formation of CNT. The samples with CNT formed represented better catalytic activity than control samples with no-CNT obtained, the morphology of CNT was beneficial for catalytic process. The sample C 1 -CNT with lowest content of Fe on support represented best catalytic activity which was competitive with 20% Pt/C in half-wave potential. The C 1 -CNT also showed outstanding stability and improved selectivity towards ORR, making it a promising alternative to Pt in application of fuel cells and metal-air batteries. [ABSTRACT FROM AUTHOR]

Ag4Bi2O5/MnO2 nano-sized material was synthesized by a co-precipitation method in concentrated KOH solution. The morphology characterization indicates that MnO2 nanoparticles with a size of 20 nm are precipitated on the surface of nano Ag4Bi2O5, forming a structure like corn on the cob. The obtained material with 60% Mn offers slightly higher initial potential (0.098 V vs. Hg/HgO) and limiting current density (-5.67 mA cm-2) at a rotating speed of 1600 rpm compared to commercial Pt/C (-0.047 V and -5.35 mA cm-2, respectively). Furthermore, the obtained material exhibits superior long-term durability and stronger methanol tolerance than commercial Pt/C. The remarkable features suggest that the Ag4Bi2O5/MnO2 nano-material is a very promising oxygen reduction reaction catalyst. [ABSTRACT FROM AUTHOR]

Three-dimensional nitrogen-doped carbon (3D-NCN) has been synthesized via the ionothermal carbonization method using waste soybean dregs (SD) as the precursor. N2 adsorption/ desorption isotherms show that the as-prepared 3D-NCN formed a hierarchically porous structure with a specific BET surface area of 1093.4 m2 g-1 and a total pore volume of 1.77 cm3 g-1. The TEM images clearly show that graphene-like carbon sheets were formed on the edge of the networks. The characterization of the samples collected at different temperature indicated that salt melt plays the key role in the formation of the network structure and rich pores. When 3D-NCN is as electrocatalyst for ORR, it shows an onset potential of 0.945 V with a more positive half-wave potential (0.846 V), which is comparable to that of commercial Pt/C. In addition, the long-term cycle results show that the onset potential and half-wave potential only negatively shifted by 6 mV and 8 mV after 10,000 cycles respectively, which are smaller than those values of commercial Pt/C. Due to its high ORR activity, durability, and low-cost, producing 3D-NCN from SD in molten salt medium provides a promising approach to replace the Pt-based catalysts for use in fuel cells. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) is a characteristic reaction which determines the performance of fuel cells which convert a chemical energy into an electrical energy. Aims of this study are to synthesize Au-based nanostars (AuNSs) and determine their preliminary electro-catalytic activities towards ORR by a rotating-disk electrode method in alkaline electrolyte. The images obtained from a scanning electron microscope (SEM) and a transmission electron microscope (TEM) analyses confirm the formation of the star-shaped nanoparticles. Among the investigated nanostar catalysts, an AuNS5 with smaller size and a few branches showed the higher electrocatalytic activity towards ORR than other catalysts with a bigger size. In addition, the electron numbers transferred for all the catalysts are approximately two. The present study results infer that the size of the Au-based nanostars may influence greatly on their catalytic activity. The present study results show that the further improvement is needed for Au-based nanostar catalysts towards the ORR reaction. [ABSTRACT FROM AUTHOR]

Large-scale production of active and stable porous carbon catalysts for oxygen reduction reaction (ORR) from protein-rich biomass became a hot topic in fuel cell technology. Here, we report a facile strategy for synthesis of nitrogen-doped porous nanocarbons by means of a simple two-step pyrolysis process combined with the activation of zinc chloride and acid-treatment process, in which kidney bean via low-temperature carbonization was preferentially adopted as the only carbon-nitrogen sources. The results show that this carbon material exhibits excellent ORR electrocatalytic activity, and higher durability and methanol-tolerant property compared to the state-of-the-art Pt/C catalyst for the ORR, which can be mainly attributed to high graphitic-nitrogen content, high specific surface area, and porous characteristics. Our results can encourage the synthesis of high-performance carbon-based ORR electrocatalysts derived from widely-existed natural biomass. [ABSTRACT FROM AUTHOR]

Multiwall carbon nanotubes (CNTs) decorated with cobalt oxide (CoO x ) nanoparticles (NPs) are prepared in various synthesis conditions to investigate their capability as oxygen reduction reaction (ORR) catalysts for fuel cells in alkaline media. The synthesis conditions include the use of protecting, reducing or complexing agents and heat treatment. Higher ORR activity is possible for smaller size of Co NPs catalysts due to the enlarged interfaces between Co species and CNTs. The addition of polyvinylpyrrolidone (PVP) as protecting agent and NaBH 4 during the preparation procedure is necessary for obtaining the highest activity since it favors the formation of lower oxidation states for Co species and the incorporation of N groups which improve ORR activity. CNTs loaded with only 1 wt.% of Co NPs prepared by a facile method using PVP, NaBH 4 and subsequent heat treatment at 500 °C under N 2 atmosphere, demonstrates both similar catalytic activity and stability than Pt/Vulcan (20 wt.% Pt on Vulcan). The synergic chemical coupling effects between CNTs and CoO x NPs and the presence of carbon material with pyridinic N and quaternary N groups formed from the protecting agent decomposition, seem to be the main factors responsible for the remarkable electrocatalytic activity. [ABSTRACT FROM AUTHOR]

Tubular type carbon nanofibers (TCNFs) are prepared and used as a catalyst support material for a cathode electrode of low temperature fuel cells through structural modification. The pristine TCNF is treated by graphitization and makes partially torn-tube shape through the surface expansion by rapid thermal treatment of the oxidized graphitized TCNF. Physical properties of the TCNF group are examined, and it is confirmed that the unique ripped texture along fiber axis with graphitic structure is obtained by the surface expansion. Platinum catalysts supported on these TCNF group are prepared and evaluated. Electrochemical properties are examined via cyclic voltammograms and polarization curves for oxygen reduction reaction activity. The platinum catalyst on the surface expanded TCNF has the enhanced activity at initial and the stable performance even after accelerated durability test due to their unique structure. [ABSTRACT FROM AUTHOR]

Electrochemical reduction of oxygen is the heart of the next-generation energy technologies to fuel cells and metal-air batteries, of which the reference catalysts suffer from two critical bottlenecks lying in their insufficient electroactivities and unclear active site structures. Herein, we introduce the effectively hierarchically porous carbons (HPCs) as the active-sites enriched platform for oxygen electroreduction. Three quaternized copolymers (PUB, PAADDA and PICP) with different chemical structures are used to pursue Fe/N/S-tailored ORR electrocatalysts. The most efficient one prepared by PAADDA gives the onset potential of 0.94 V and a half-wave potential of 0.85 V in basic solution, as well as superb electroactivities of low H 2 O 2 % and high electron transfer number in both alkaline and acidic medium. Surprisingly, they all display high discharge power density as applied to Zn-air fuel cells, and the HPCs-PAADDA catalyst thrillingly reaches 516.3 mW cm −2 when catalyst loading is optimized to 5.0 mg cm −2 . The results elucidate that the polymer with long aliphatic chain is propitious to trap metals to create active sites and enwrap silica template to construct uniform pore structure. Only two kinds of nitrogen configuration (pyridinic-N and graphitic-N) are found with distinct structure in these HPCs, which happens to be active sites. [ABSTRACT FROM AUTHOR]

The catalytic activity and stability of electrocatalyst is critical for the commercialization of fuel cells, and recent reports reveal the great potential of the hollow structures with Pt skin coat for developing high-powered electrocatalysts due to their highly efficient utilization of the Pt atoms. Here, we provide a novel strategy to prepare the Pt skin coated hollow Ag-Pt structure (Ag-Pt@Pt) of ∼8 nm size at room temperature. As loaded on the graphene, the Ag-Pt@Pt exhibits a remarkable mass activity of 0.864 A/mg Pt (at 0.9 V, vs. reversible hydrogen electrode (RHE)) towards oxygen reduction reaction (ORR), which is 5.30 times of the commercial Pt/C catalyst, and the Ag-Pt@Pt also shows a better stability during the ORR catalytic process. The mechanism of this significant enhancement can be attributed to the higher Pt utilization and the unique Pt on Ag-Pt surface structure, which is confirmed by the density functional theory (DFT) calculations and other characterization methods. In conclusion, this original work offers a low-cost and environment-friendly method to prepare a high active electrocatalyst with cheaper price, and this work also discloses the correlation between surface structures and ORR catalytic activity for the hollow structures with Pt skin coat, which can be instructive for designing novel advanced electrocatalysts for fuel cells. [ABSTRACT FROM AUTHOR]

Due to the high cost of Pt catalyst, reducing the amount of Pt in electrodes is one of the primary issues in polymer electrolyte membrane fuel cells. In this study, the hybrid cathode catalyst using the electrochemically active carbon composite catalyst and Pt catalyst is developed in order to reduce the amount of Pt and increase the overall catalytic performance. The carbon composite catalyst (CCC) is synthesized by pyrolysis of Fe-Co chelate compound followed by acid leaching. The current density of Pt/CCC is 1.5–6-fold higher than that of Pt/CB when employing ultra-low Pt loading (0.04 mg Pt cm −2 ). It is found that the Pt/CCC with the ultra-low Pt loading at tuned operating conditions exhibits a higher fuel cell performance than the Pt/CB and commercial Pt/C with four times higher Pt loading (0.16 mg Pt cm −2 ). The extensive activity of Pt/CCC is ascribed to the synergistic effect through (1) the combined activity of catalytic sites present in the CCC support and Pt, (2) the well-distributed nanoparticles and (3) the increased metallic Pt 0 concentration which indicated that the pyridinic-N played a role of oxide-cleanser. [ABSTRACT FROM AUTHOR]