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Achieving a highly active cathode surface with extremely efficient electrocatalysts for oxygen reduction kinetics is a fundamental necessity for durable fuel cells. Developing such active materials into desirable nanostructures is crucial in the pursuit of electrocatalysis. A facile preparation of cobalt decorated nitrogen and sulfur co-doped carbon nanostructures (Co–NSC) with the added advantage of Zeolitic imidazolate frameworks (ZIF), ZIF 67@ZIF 8 is reported here. The as-prepared Co, N, S, co-doped carbon (Co–NSC) electrocatalyst comes under platinum group metal-free (PGM-free) catalysts which intends to replace the scarce and highly expensive commercial Pt catalysts. Facile preparation of the Co–NSC catalyst that is scalable, low cost and highly ORR active makes the material advantageous. Co–doping sulfur has dramatically enhanced the intrinsic catalytic activity of the catalyst, and the degree of variation in sulfurization greatly influences the overall catalytic property. Co–NSC 200 with high sulfur doping exhibit a positively shifted onset potential of 0.81 V, and a high yielding current density of 5.5 mA cm−2 at 20 mV s−1. Image 1 • Cobalt on nitrogen and sulfur doped carbon with fine sodalite-like MOF is achieved. • The variation in sulfurization and its influence on catalytic property is studied. • This work confirms the enhancement of the catalytic activity by controlling S doping. • Advantage to develop various advanced carbon based catalysts with heteroatom doping. [ABSTRACT FROM AUTHOR]

A development of electrocatalyst for oxygen reduction reaction (ORR) is one of the crucial reactions for low temperature fuel cell applications. The state-of-the-art catalyst (platinum based) have various limitations such as low abundance, extortionate price and sensitive towards impurities. Therefore, design of high performance non-platinum electrocatalyst is the most challenging issue for low temperature fuel cell. In this work, we discuss the nitrogen doping at defect sites of multiwalled carbon nanotubes (MWCNTs) using melamine foam as a template for efficient CNT assembly with subsequent role of different nitrogen containing agents such as melamine and hexamine. Templated assembly of functionalized CNT through melamine foam provides easy approach towards nitrogen doping that followed effective exposure of active sites (like pyridinic-N and oxidic-N) for electroreduction of oxygen. As-prepared N-CNT catalysts (prepared using both the precursors) show better ORR activity than Pt/C in alkaline medium. A sharp reduction peak in their cyclic voltammogram under O 2 -saturated 0.1 M KOH solution proves their activity towards ORR electrocatalysis. More interestingly, the onset potentials of ~0.92 V and ~1.1 V versus RHE for N-CNT obtained by hexamine and melamine respectively indicate superior onsets than that of Pt/C (~1.04 V vs RHE). Furthermore, the best N-CNT catalyst (obtained by melamine) reveals better stability up to 15,000 cycles than Pt/C with zero response towards methanol, exhibiting an excellent methanol tolerance. A controlled N-doping using melamine foam as a template could furnish remarkable efficiency of oxygen electroreduction. Image 1 • An approach, providing an interesting comparison of N-doping in CNT using different precursors. • Mel-NCNT exhibits superior E onset of 1.1 V and J L 5.7 mA/cm2 at 1600 rpm. • Mel-CNT shows stability up to 15,000 potential cycles. • ORR activity of N-doped CNT depends on the physical properties of precursors. [ABSTRACT FROM AUTHOR]

This work reports non‐noble, cobalt embedded nitrogen doped carbon (CoNC) catalysts for oxygen reduction reaction (ORR) in Nafion‐based acidic proton exchange membrane fuel cells (PEMFCs). CoNC catalysts are synthesized through direct pyrolysis of two different zeolitic imidazolate framework (ZIF) precursors, Zn‐ZIF and Co‐ZIF. Profiting from two different precursor approach, appropriate assimilation of metal, nitrogen and carbon components is achieved which boosts oxygen reduction. Electrochemical results exemplified CoNC 3–1 catalyst derived from Zn‐ZIF:Co‐ZIF precursor in the weight ratio of 3 : 1 as the better ORR catalyst. CoNC 3–1 catalyst exhibited the highest electrochemical surface area (ECSA) (570 cm2), highest limiting current density (‐5.14 mA cm−2) and followed near 4e− reduction of oxygen revealing superior ORR activity. The catalyst also demonstrated remarkable durability with loss of only 6 % of ECSA after 30,000 cycles of accelerated durability test. The enhanced ORR activity and durability is attributed to optimal balance of Co−Nx active sites along with appropriate N contents and graphitic carbon framework. [ABSTRACT FROM AUTHOR]

Atomically dispersed transition metal‐Nx sites have emerged as a frontier for electrocatalysis because of the maximized atom utilization. However, there is still the problem that the reactant is difficult to reach active sites inside the catalytic layer in the practical proton exchange membrane fuel cell (PEMFC) testing, resulting in the ineffective utilization of the deeply hided active sites. In the device manner, the favorite structure of electrocatalysts for good mass transfer is vital for PEMFC. Herein, a facile one‐step approach to synthesize atomically dispersed Fe‐Nx species on hierarchically porous carbon nanostructures as a high‐efficient and stable atomically dispersed catalyst for oxygen reduction in acidic media is reported, which is achieved by a predesigned hierarchical covalent organic polymer (COP) with iron anchored. COP materials with well‐defined building blocks can stabilize the dopants and provide efficient mass transport. The appropriate hierarchical pore structure is proved to facilitate the mass transport of reactants to the active sites, ensuring the utilization of active sites in devices. Particularly, the structurally optimized HSAC/Fe‐3 displays a maximum power density of up to 824 mW cm−2, higher than other samples with fewer mesopores. Accordingly, this work will offer inspirations for designing efficient atomically dispersed electrocatalyst in PEMFC device. [ABSTRACT FROM AUTHOR]

Nitrogen-doped carbon materials were prepared by the pyrolysis of carbon black Vulcan XC-72 impregnated with nitrogen-containing Pd (II) and Ni (II) complexes. The composition of materials was studied at different stages of their synthesis. It is shown that nanoparticles of metals and/or their oxides are not the main electroactive component of materials in the oxygen electroreduction reaction (ORR). It is established that the palladium complex provides a much more efficient doping of carbon with nitrogen compared to the nickel complex of a similar composition. This results in the high ORR electrocatalytic activity of the catalyst obtained, palladium complex being used in an alkaline medium. This material is a promising one to be used as an electrocatalyst in fuel cells with an anion-conducting membrane. [ABSTRACT FROM AUTHOR]

Layered perovskite (La1−xSrx)2CoO4±δ (x = 0.3, 0.4, 0.5) oxides were prepared using sol–gel route and evaluated as the cathode materials for intermediate-temperature solid-oxide fuel cells. (La1−xSrx)2CoO4±δ has a tetragonal structure with space group of I4/mmm in all cases of x levels. The average thermal expansion coefficient of (La1−xSrx)2CoO4±δ is relatively low and slightly increases with x, which can be ascribed to the sway of Sr doping on the spin-state transition of Co ions. X-ray photoelectron spectroscopy and thermogravimetric analysis show that Co ions exist in mixed oxidation states, but the lattice oxygen content considerably varies with x. Regarding transport property, (La1−xSrx)2CoO4±δ behaves like a semiconductor in the temperature range of 200–800 °C, and the electrical conductivity significantly increases with x. As one of the most important results, electrochemical performance of (La1−xSrx)2CoO4±δ cathode is affected by x in a complex manner, and x = 0.4 cathode, i.e., La1.2Sr0.8CoO4±δ, has the most favored area-specific resistance of 0.062 Ω cm2 and the highest power density of 630 mW cm−2 in an electrolyte-supported single cell at 800 °C, showing a rapid kinetics toward oxygen reduction reaction. This study demonstrates that the structural, transport, thermal, and electrochemical properties of (La1−xSrx)2CoO4±δ cathodes significantly depend on the La/Sr ratio at the A-site of lattice. Rietveld refinement profile and temperature-dependent electrochemical performance for La1.2Sr0.8CoO4±δ cathode material [ABSTRACT FROM AUTHOR]

Metal nitrogen-carbon catalysts have become a promising alternative to platinum-based catalysts in fuel cells due to their high stability and platinum-like activity. However, the corrosion and deactivation of active sites in the solution still restrict the inherent reaction kinetic rate. For this reason, it is important to stabilize the catalyst through a controllable doping strategy to obtain high activity catalysts for oxygen reduction reactions (ORR). Herein, the pyrolysis strategy is demonstrated in the synthesis of iron-based catalysts co-doped with nitrogen and biomass-derived phosphorus (denoted as N, P-Fe/C), and the pore size of the catalyst is mostly distributed at 1 nm or 50 nm, respectively. The half-wave potential (0.893 V) and the current density (4.05 mA cm−2) at 0.85 V of the catalyst exceed those of the commercial Pt/C. The remarkable ORR performance can be attributed to its distinct hierarchical pore structure, the modulation effect of nitrogen and phosphorus co-doping on the carbon matrix, and the combined effect of the FeNx active sites, which improves the accessibility of reactants and accelerating the absorption/desorption of the reaction intermediate, thereby increasing reaction rates. And N, P-Fe/C has great potential as a promising substitute for platinum-based catalysts. [ABSTRACT FROM AUTHOR]

A novel and sustainable method was established to prepare a nitrogen doped graphene‐like material from a renewable, secondary raw material with potential application in the catalysis of oxygen reduction reaction (ORR). Alder wood char was used as a precursor material for producing a sustainable graphene‐like carbon catalyst for the ORR. Alder wood char was first activated (AWC) and then doped with nitrogen (N−AWC). The graphene‐like structure was confirmed using transmission electron microscopy (TEM) and Raman spectroscopy. Electrochemical characterization was carried out in 0.1 M KOH, showing that in alkaline media the ORR activity of the N‐doped wood char‐based graphene‐like material is superior compared to non‐sustainable commercial N‐doped graphene. The onset potential of the ORR on N‐AWC was shifted to positive direction by 75 mV in comparison to the commercially available nitrogen‐doped graphene and the half‐wave potential was shifted even by 239 mV. This renewable biomass‐derived graphene‐like carbon catalyst shows a great potential alternative to current synthetic graphite, graphene nanoplatelets and graphene materials in areas such as fuel cells and batteries. [ABSTRACT FROM AUTHOR]

Single‐atom catalysts (SACs) with highly active sites atomically dispersed on substrates exhibit unique advantages regarding maximum atomic efficiency, abundant chemical structures, and extraordinary catalytic performances for multiple important reactions. In particular, M–N–C SACs (M=transition metal atom) demonstrate optimal electrocatalytic activity for the oxygen reduction reaction (ORR) and have attracted extensive attention recently. Despite substantial efforts in fabricating various M–N–C SACs, the principles for regulating the intrinsic electrocatalytic activity of their active sites have not been sufficiently studied. In this Review, we summarize the regulation strategies for promoting the intrinsic electrocatalytic ORR activity of M–N–C SACs by modulation of the center metal atoms, the coordinated atoms, the environmental atoms, and the guest groups. Theoretical calculations and experimental investigations are both included to afford a comprehensive understanding of the structure–performance relationship. Finally, future directions of developing advanced M–N–C SACs for electrocatalytic ORR and other analogous reactions are proposed. [ABSTRACT FROM AUTHOR]

In anion exchange membrane fuel cells, catalytic reactions occur at a well‐defined three‐phase interface, wherein conventional heterogeneous catalyst layer structures exacerbate problems, such as low catalyst utilization and limited mass transfer. We developed a structural engineering strategy to immobilize a molecular catalyst tetrakis(4‐methoxyphenyl)porphyrin cobalt(II) (TMPPCo) on the side chains of an ionomer (polyfluorene, PF) to obtain a composite material (PF‐TMPPCo), thereby achieving a homogeneous catalysis environment inside ion‐flow channels, with greatly improved mass transfer and turnover frequency as a result of 100 % utilization of the catalyst molecules. The unique structure of the homogeneous catalysis system comprising interconnected nanoreactors exhibits advantages of low overpotential and high fuel‐cell power density. This strategy of reshaping of the catalyst layer structure may serve as a new platform for applications of many molecular catalysts in fuel cells. [ABSTRACT FROM AUTHOR]

Great advances have been made in developing Fe/N/C catalyst, which is a potential candidate for replacing the low‐platinum group metal catalysts used in proton‐exchange membrane fuel cells. Herein, a highly efficient porous structure catalyst was synthesised by doping glucose into the zeolitic imidazolate framework, which obtained numerous pores after high‐temperature pyrolysis. The porous carbon structure was conducive to improving mass transport and oxygen reduction reaction (ORR) activities. The Glc‐Fe‐ZIF catalyst exhibited an excellent ORR activity with a half‐wave potential (E1/2) of 0.874 V (RHE) and the maximum power density reached 0.72 W cm−2 in acidic medium. [ABSTRACT FROM AUTHOR]

The ordinary intrinsic activity and disordered distribution of metal sites in zero/one‐dimensional (0D/1D) single‐atom catalysts (SACs) lead to inferior catalytic efficiency and short‐term endurance in the oxygen reduction reaction (ORR), which restricts the large‐scale application of hydrogen−oxygen fuel cells and metal−air batteries. To improve the activity of SACs, a mild synthesis method was chosen to conjugate 1D Fe SACs with 2D graphene film (Fe SAC@G) that realized a composite structure with well‐ordered atomic‐Fe coordination configuration. The product exhibits outstanding ORR electrocatalytic efficiency and stability in 0.1 M KOH aqueous solution. DFT‐D computational results manifest the intrinsic ORR activity of Fe SAC@G originated from the newly‐formed FeN4−O−FeN4 bridge structure with moderate adsorption ability towards ORR intermediates. These findings provide new ways for designing SACs with high activity and long‐term stability. [ABSTRACT FROM AUTHOR]

The design of bifunctional non-precious metal catalyst with good ORR and OER activity is of great significance for the development and commercialization of fuel cells. However, the sluggish and strong irreversible nature of the oxygen electrochemical kinetics makes it difficult to manufacture single bifunctional material. Therefore, we prepared a bifunctional catalyst (Co3O4/N-rGO) with different particle diameters through a one-pot synthesis method, and studied the dependence of the electrocatalytic performance of the catalyst on the particle size of Co3O4. The results showed that Co3O4/N-rGO with 27–31 nm particle size prepared by using N-rGO as the carrier, cobalt acetate concentration of 0.075 M, hydrothermal temperature of 190 °C, and hydrothermal time of 3 h takes a 4e-reaction pathway, which exhibited better ORR and OER activity, excellent current stability and methanol tolerance than JM 20% Pt/C and JM 5% RuO2/C. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) limits the efficiency of oxygen‐associated energy conversion in fuel cells and air‐metal batteries. Today, expensive noble metal catalysts are often utilized to enhance the ORR and the resulting conversion efficiency in those devices. Hence, there is an intensive research to find efficient electrodes, exhibiting a favorable electronic structure, for ORR based on abundant materials that can be manufactured using low cost processes. In that context, metal‐free carbon‐based nanostructures and conducting polymers have been actively investigated. The negatively doped poly(benzimidazobenzophenanthroline) (BBL) as an efficient and stable oxygen cathode material is reported here. Compared to the benchmark p‐doped conducting polymer poly(3,4‐ethylendioxythiophene) (PEDOT), the BBL provides electrocatalysis that fully reduces dioxygen into water, via a (2 + 2)‐electron transfer pathway with hydrogen peroxide (H2O2) as an intermediate; while PEDOT limits the ORR to H2O2. It is demonstrated that n‐doped BBL is a promising air electrode material for low‐cost and ecofriendly model fuel cells, without the need of any co‐catalysts, and its performance is found to be superior to p‐doped PEDOT air electrodes. [ABSTRACT FROM AUTHOR]

Considering the urgent requirement for clean and sustainable energy, fuel cells and metal‐air batteries have emerged as promising energy storage and conversion devices to alleviate the worldwide energy challenges. The key step in accelerating the sluggish oxygen reduction reaction (ORR) kinetics at the cathode is to develop cost‐effective and high‐efficiency non‐precious metal catalysts, which can be used to replace expensive Pt‐based catalysts. Recently, the transition metal and nitrogen co‐doped carbon (M−Nx/C) materials with tailored morphology, tunable composition, and confined structure show great potential in both acidic and alkaline media. Herein, the mechanism of ORR is provided, followed by recent efforts to clarify the actual structures of active sites. Furthermore, the progress of optimizing the catalytic performance of M−Nx/C catalysts by modulating nitrogen‐rich precursors and porous structure engineering is highlighted. The remaining challenges and development prospects of M−Nx/C catalysts are also outlined and evaluated. [ABSTRACT FROM AUTHOR]

The development of low‐cost catalysts containing earth‐abundant elements as alternatives to Pt‐based catalysts for the oxygen reduction reaction (ORR) is crucial for the large‐scale commercial application of proton exchange membrane fuel cells (PEMFCs). Nonprecious metal–nitrogen–carbon (M‐N‐C) materials represent the most promising candidates to replace Pt‐based catalysts for PEMFCs applications. However, the high‐temperature pyrolysis process for the preparation of M‐N‐C catalysts frequently leads to high structural heterogeneity, that is, the coexistence of various metal‐containing sites and N‐doped carbon structures. Unfortunately, this impedes the identification of the predominant catalytic active structure, and thus, the further development of highly efficient M‐N‐C catalysts for the ORR. This Minireview, after a brief introduction to the development of M‐N‐C ORR catalysts, focuses on the commonly accepted views of predominant catalytic active structures in M‐N‐C catalysts, including atomically dispersed metal–Nx sites, metal nanoparticles encapsulated with nitrogen‐doped carbon structures, synergistic action between metal–Nx sites and encapsulated metal nanoparticles, and metal‐free nitrogen‐doped carbon structures. [ABSTRACT FROM AUTHOR]

The sluggish kinetics of oxygen reduction reaction (ORR) seriously restrains the practical implementation of fuel cells and metal-air batteries (MABs). While, Pt-based catalysts are well proven to be effective for the ORR process, they are rather expensive. Therefore, it is critical to developing low-cost and advanced catalysts with a rationally designed structure and abundant reactive sites as alternatives for Pt-based catalysts. Herein, nitrogen-doped hollow carbon polyhedrons (NHCP) have been fabricated by directly pyrolyzing ZIF-8, templated by NaCl. Benefiting from their hollow porous structure, large surface area, high graphitization degree and desired nitrogen bonding type, the as-synthesized NHCP exhibits exceptional ORR electrocatalytic activity with a half-wave potential (E 1/2) of 0.86 V, high selectivity and outstanding long-term stability, exceeding most reported nitrogen-doped metal-free carbon electrocatalysts. Furthermore, the assembled Zn-air battery with NHCP cathode delivers a peak power density of 272 mW cm−2, a specific capacity of 740 mAh g−1 and an operation period of 160 h. This contribution provides a new avenue for designing high-performance electrocatalysts for ORR. Image 1 [ABSTRACT FROM AUTHOR]

• Fe-N-C catalyst was prepared for electrochemical oxygen reduction reactions. • Wetting with water and drying treatments introduced non-negligible activity loss. • Extend of the activity loss was affected by the treatment conditions. • Subtle changes in Fe-N-C surface were observed after the treatments. The membrane electrode assembly (MEA) is a core component of low-temperature fuel cells. The first step of MEA manufacturing is the preparation of a catalyst ink suspension in which the catalyst powder is homogeneously dispersed in a liquid solvent through mechanical or sonic agitation. In this work, we have studied the effects of catalyst dispersion in water or alcohol solutions and subsequent drying processes on the physicochemical properties of Fe-N-C catalysts and their electrocatalytic oxygen reduction activities. We find that dispersing the model Fe-N-C catalyst comprising only FeN x C y moieties in water and subsequent drying treatment change neither its bulk structure nor surface composition, as indicated by various spectroscopic measurements before and after treatment. However, zeta potential measurements, which are very sensitive to the chemistry of functionalities present on the carbon surface, reveal that the Fe-N-C catalyst becomes slightly more acidic, and that the change in their acido-basicity is magnified with a) increasing treatment temperature and b) repetitions of a same wetting/drying treatment. This small change in the surface acido-basicity of the Fe-N-C catalyst results in a measurable and reproducible decrease in its electrocatalytic activity, which shows a positive correlation with the zeta potential changes measured at pH = 1. Observed on the Fe-N-C catalyst but not on Pt/C, it is surmised that the electrocatalytic activities of the oxygen-reducing FeN x C y moieties are influenced by the surface chemistry of the carbonaceous support. Since catalyst wetting and drying processes are essential for MEA fabrication for fuel cells, these results suggest that careful attention should be paid to the conditions employed to prepare and dry catalytic inks for the family of Fe-N-C catalysts in order to obtain their highest possible ORR activity. [ABSTRACT FROM AUTHOR]

The search for a low‐cost metal‐free cathode material with excellent mass transfer structure and catalytic activity in oxygen reduction reaction (ORR) is one of the most challenging issues in fuel cells. In this work, nitrogen‐rich m‐phenylenediamine is introduced into the synthesis of porous carbon spheres to tune the pore structure and nitrogen‐doped active sites. As a result, more pyridinic N and pyrrolic N functional species were observed at the interior and surface of the carbon spheres. The introduction of m‐phenylenediamine also regulated the nucleating of precursors, an urchin‐like mesoporous surface structure ensures point contact and less agglomeration between each particle was obtained. With optimized proportion of micropores/mesopores and improved nitrogen‐contained functional species, the ORR activity can be remarkably improved. The half‐wave potential of this catalyst could achieve to 0.81 V (versus RHE) which is only 42 mV lower than commercial Pt/C catalyst. Furthermore, the optimized cathode catalyst achieved a 69 mW cm−2 maximum power density when operated in direct methanol fuel cells at room temperature. [ABSTRACT FROM AUTHOR]

For improving the performance of platinum electrocatalysts in polymer electrolyte membrane fuel cells (PEMFCs), it is important to enhance the Pt utilization level in the catalyst systems. A high performing electrocatalyst (Pt/3DNG) is developed for PEMFC applications by using nitrogen‐doped 3D graphene (3DNG) as the support material and an in situ grafted active "triple‐phase boundary" to more precisely control the formation of the proton conducting ionomer interface at the active sites. Considering the 3D morphology of the system, during the electrode fabrication for realistic single‐cell evaluation, the concept of in situ generation of the proton conducting‐ionomer based "active triple‐phase boundary" is introduced, which could potentially replace the conventional method of using Nafion ionomer for the electrode preparation. The monomers owing to their small‐size can access the pores and inner regions of the 3DNG support, which on UV‐curing, undergo polymerization and transform into an ionomer with an extended interfacial network into the nanoregimes of 3DNG. Single cell evaluation of the membrane electrode assembly in a high‐temperature PEMFC by using phosphoric acid doped polybenzimidazole membrane demonstrates the utility of the present strategy. [ABSTRACT FROM AUTHOR]

It is highly desired but challenging to develop platinum group metal-free electrocatalysts for oxygen reduction reaction (ORR), which can promote the commercialization of fuel cell technology. To achieve this target, we report a one-step doping method to prepare S-doped Fe–N–C catalysts using zeolite imidazole framework (ZIF-8) and iron (III) thiocyanate (Fe(SCN) 3) as precursor. Different from conventional doping approach, i.e. physical mixing, Fe(SCN) 3 is in-situ added during ZIF-8 formation which would encapsulate Fe(SCN) 3 molecules inside ZIF-8 to avoid structure destruction and create potential replacement of Zn ions by Fe ions to form uniform Fe–N 4 complexes. As a result, the prepared S-doped Fe–N–C catalysts own large specific surface areas with a maximum value of 1326 ​m2 ​g−1 and a dual-scale porous structure that benefits mass transport. Significantly, the composition-optimized catalyst exhibits superior ORR activity in both 0.1 ​M HClO 4 electrolyte and 0.1 ​M KOH electrolyte, in which the half-wave potential reaches 0.81 ​V and 0.92 ​V (vs. RHE), respectively. Remarkable stability is also attained, which loses 2 ​mV only after 10000 potential cycles in O 2 -saturated 0.1 ​M HClO 4 and remains almost constant in O 2 -saturated 0.1 ​M KOH, surpassing commercial Pt/C catalyst in both acidic and alkaline medium. Image 1 • S-doped Fe–N–C electrocatalysts were prepared via one-step doping method. • Prepared catalysts own ultrahigh specific surface area (1062–1326 ​m2 ​g−1). • The catalysts show good activity and durability in both acidic and alkaline medium. [ABSTRACT FROM AUTHOR]

Designing highly active and durable oxygen reduction reaction (ORR) electrocatalysts is essential for developing efficient proton-exchange membrane fuel cells (PEMFCs). In this work, ordered PtCuNi/C nanoparticles (NPs) were synthesized using an impregnation reduction method. This study shows that the incorporation of Ni in ordered PtCu/C can effectively adjust the electronic structure of Pt, thereby optimizing oxygen binding energy for the ORR. The obtained intermetallic ordered PtCuNi/C NPs significantly improved ORR activity and durability compared to ordered PtCu/C. Specifically, PtCu 0 · 5 Ni 0 · 5 /C-700 shows a mass activity of 1.29 ​A ​mg Pt −1 ​at 0.9 ​V vs. reversible hydrogen electrode (RHE), which is about 9.2 times higher than that of commercial Pt/C. PtCu 0.5 Ni 0.5 /C-700 is also shown to be competent cathode catalyst for a single-cell system exhibiting high power density (461 ​mW ​cm−2). This work demonstrates that ordered PtCu 0 · 5 Ni 0 · 5 /C-700 can be used as a highly active and durable ORR catalyst in PEMFCs. The chemically ordered PtCuNi/C nanoparticles (NPs) were synthesized using an impregnation reduction method. Incorporation of Ni in ordered PtCu/C can effectively adjust the electronic structure of Pt, thereby optimizing electrochemical performance for the ORR. Image 1 • The PtCuNi/C ternary intermetallic catalyst was synthesized using an impregnation reduction method. • Incorporation of Ni in ordered PtCu/C can effectively adjust the electronic structure of Pt. • The mass activity of PtCu 0 · 5 Ni 0 · 5 /C-700 is 9.2 times that of commercial Pt/C. • The MEA using PtCu 0 · 5 Ni 0 · 5 /C-700 exhibites high power density of 461 ​mW ​cm−2 in a single-cell system. [ABSTRACT FROM AUTHOR]

The accessibility to highly active oxygen reduction reaction (ORR) catalysts with low cost is a priority for the rapid industrialization of Zn‐Air batteries. Herein, we propose a facile engineering synthesis of high‐activity quasi‐spherical Fe−N−C ORR nanocatalysts by chemical self‐assmbly. The morphological and structural features of the materials have been fully characterized. The synchrotron radiation techniques reveal that the targeted Fe−N−PQS‐900 with highly exposed Fe−Nx active sites well dispersed on the N‐rich micro‐nano carbon framework, endowing them with efficient access to oxygeneous species. The electrochemical measurements show its superior ORR catalytic performance to the commercial Pt/C catalyst, including a more positive half‐wave potential, smaller Tafel slope, better methanol‐tolerance capability, and more sustainable cycloability as well. An assembled Zn‐Air battery using the Fe−N−PQS‐900 as the cathode catalyst shows a specific capacity of 798 mAh g−1 with a power density of 114 mW cm−2 and an energy density of 958 Wh kg−1, enabling this non‐precious metal electrocatalyst very competitive in metal air fuel cell applications. [ABSTRACT FROM AUTHOR]

Atomically dispersed and nitrogen coordinated single metal sites (M‐N‐C, M=Fe, Co, Ni, Mn) are the popular platinum group‐metal (PGM)‐free catalysts for many electrochemical reactions. Traditional wet‐chemistry catalyst synthesis often requires complex procedures with unsatisfied reproducibility and scalability. Here, we report a facile chemical vapor deposition (CVD) strategy to synthesize the promising M‐N‐C catalysts. The deposition of gaseous 2‐methylimidazole onto M‐doped ZnO substrates, followed by an in situ thermal activation, effectively generated single metal sites well dispersed into porous carbon. In particular, an optimal CVD‐derived Fe‐N‐C catalyst exclusively contains atomically dispersed FeN4 sites with increased Fe loading relative to other catalysts from wet‐chemistry synthesis. The catalyst exhibited outstanding oxygen‐reduction activity in acidic electrolytes, which was further studied in proton‐exchange membrane fuel cells with encouraging performance. [ABSTRACT FROM AUTHOR]

Transition metal‐nitrogen‐carbon (M−N−C) materials have received extensive attention as promising catalysts for oxygen reduction reaction (ORR). The surface morphology and the pore structure of the carbon supports have important effects on the ORR activity. Herein, metal‐organic complexes were prepared via a simple NaOH‐mediated method by the organometallic reaction of Fe3+/Co2+ ions and benzimidazole in the presence of polyvinylpyrrolidone. Metal‐organic complexes with either cuboid or cylindrical morphologies were obtained by modulating the initial ratio of Fe3+/Co2+. FeCo containing N‐doped carbon catalysts (FexCoy−N−C) decorated with FexCoy nanoparticles were then fabricated by a direct carbonization of the metal‐organic complexes. FexCoy−N−C catalysts have hierarchical micro‐/mesoporous structure and retain the morphologies of microcuboids and microcylinders of the metal‐organic complexes precursors. The Fe1Co7−N−C exhibits promising catalytic activity with an onset potential of 0.967 V, a half‐wave potential of 0.816 V, and a limiting current density of 4.86 mA cm−2 in 0.1 M KOH. The ORR catalytic activity should be attributed to the FeCo−Nx active sites and the encapsulated FeCo alloy nanoparticles activating the surrounding N‐doped carbon layers. [ABSTRACT FROM AUTHOR]

Exploring low‐cost, highly effective and durable nonprecious electrocatalysts for oxygen reduction reaction (ORR) is the key issue for large‐scale applications of fuel cell technology. However, preparation of Fe−N−C ORR catalysts using biomass without any external sources containing nitrogen and iron elements has rarely been reported. In this paper, hierarchically porous carbon self‐co‐doped with Fe and N promoted by NaCl has been successfully synthesized through a facile one‐step pyrolysis method using pig blood curds (PBCs) without any external Fe and N. Besides, Fe and N are uniformly dispersed within the as‐synthesized electrocatalysts. Electrochemical tests showed that the best performing Fe−N−C electrocatalyst exhibited superior ORR catalytic activity with a positive half‐wave potential of 0.834 V vs. RHE and a high limiting current density of 5.6 mA cm−2. Furthermore, the as‐synthesized electrocatalyst also showed remarkable long‐term stability as well as superior methanol tolerance, outperforming commercial Pt/C. The facile synthesis of high‐performance Fe−N−C electrocatalysts derived from PBCs using NaCl as the pore former provides fundamental insight and offers important guidelines for the future design of biomass‐derived carbons in specific energy applications. [ABSTRACT FROM AUTHOR]

of the high-efficiency multifunctional electrocatalysts is highly demanded for many electrochemical energy devices, such as water electrolyzers, metal-air batteries and fuel cells. Here, Rh–Sn bimetallic nanocrystal catalysts supported on single-walled carbon nanotubes (Rh x Sn y /SWNTs) are reported, and the Rh 1 Sn 2 /SWNTs electrocatalyst show best multifunctional electrocatalytic performance. Strong electron synergy between Rh and Sn is the source of high catalytic activity.Sn transfers electrons from Rh to Sn, forming a unique positive environment around Rh, which effectively optimizes the binding energy of the reaction intermediate and further improves the catalytic activity. An alkaline electrolyzer using Rh 1 Sn 2 /SWNTs catalyst demands an ultra-low cell voltage of 1.56 V at the current density of 10 mA cm−2 for overall water splitting. In addition, Rh 1 Sn 2 /SWNTs demonstrates good oxygen reduction reaction (ORR) performance, making it an excellent catalyst for long-life Zn-air batteries. This work provides a facile strategy for the development of multifunctional electrocatalysts for the highly demanded electrochemical energy technologies. Image 1 • Rh 1 Sn 2 /SWNTs exhibit high active OER, HER and ORR performance. • SWNTs act as the framework to prevent particle agglomeration and improve stability. • Sn induces electron transfer from Rh to Sn to provide a positive environment for Rh. [ABSTRACT FROM AUTHOR]

The sluggish oxygen reduction reaction kinetics hinders the development fuel cells, which needs effective electrocatalyst with low cost and high efficiency to realize 4 e− reduction processes. To alternate commercial Pt/C, herein, hollow carbon nanocubes were successfully prepared and evaluated as oxygen reduction electrocatalyst. Benefit from the effective abundant nitrogen species and unique hollow architecture, the hollow carbon nanocubes exhibit favorable oxygen reduction electrochemical performance with onset potential of 0.94 V, half‐wave potential of 0.82 V, and limited current density of 6.11 mA cm−2, which are comparable to those of Pt/C. Additionally, compared to Pt/C, the HC‐800 shows expressively stability and methanol tolerance. [ABSTRACT FROM AUTHOR]

In the era of the global rise of energy consumption and the accompanying environmental issues, energy production via fuel cells plays a vital role in a clean, secure, and affordable energy future. The development of Pt‐based binary alloy catalysts for the oxygen reduction reaction (ORR) has contributed significantly to the commercial realization of fuel cells, such as polymer electrolyte membrane fuel cells (PEMFCs) and phosphoric acid fuel cells (PAFCs). However, the short lifetime of the Pt‐based binary alloy catalyst remains a significant gap between lab‐scale and real‐device evaluation systems, calling for the development of catalysts that do not have stability issues. Among the various catalyst systems developed as alternatives to Pt‐based binary alloy catalysts, Pt‐based ternary systems with an additional element to the binary systems seem to provide the much‐awaited answer toward enhanced catalyst stability. Here, this progress report focuses on fundamental challenges of industrial fuel cell applications and provides broad and balanced insights on remarkable progress to date. Finally, it presents several perspectives on ideal ternary system design of efficient and robust Pt‐based electrocatalysts and guidance for future development beyond the academic level. [ABSTRACT FROM AUTHOR]

Transition metal- and N-codoped carbon nanotubes (CNTs) have superior catalytic activity because the curling surface enhances the bonding ability of atoms within CNTs to other species. However, it is a great challenge to prepare CNTs with transition metal- and N-doped at high level during the growth of CNTs. Here, (Fe,N-codoped CNT)/(Fe-based nanoparticle) (Fe,N-CNT/FeNP) hybrid nanostructures are for the first time prepared through the carbonization of Fe-doped g-C 3 N 4. The doping of Fe and N is simultaneously realized during the formation of CNTs. Meanwhile, the abundant and homogeneous Fe and N in Fe-doped g-C 3 N 4 ensure high-level and uniform doping of Fe and N in CNTs. The Fe,N-CNT/FeNP hybrid nanostructures have several types of active components, including homogeneously distributed coordinating Fe moieties (FeC x N y or FeN x) and CFe 15.1 nanoparticles embedded in Fe,N-CNTs, towards oxygen reduction reaction (ORR). A superior ORR electrocatalytic performance is therefore obtained on the Fe,N-CNT/FeNP nanohybrids. Our preparation method opens an avenue to preparation of CNTs with transition metal- and N-doping at high-level, and the superior performance of Fe,N-CNT/FeNP nanostructures for ORR will be very helpful to the development of fuel cells and metal-air batteries. [ABSTRACT FROM AUTHOR]

• Nanoporous biomass-derived carbons were successfully applied as ORR ECs. • The electrocatalysts showed good electrocatalytic performances. • Excellent stability/durability and tolerance to methanol crossover were achieved. Electrocatalysts (ECs) for the oxygen reduction reaction (ORR) are crucial in fuel cells and for this reason developing cost-effective metal-free ECs with high electrocatalytic activity and high-volume production remains a huge challenge. Herein, we report the application as ORR electrocatalysts of a series of high grade nanoporous carbons, prepared by chemical activation of acid-chars obtained from the H 2 SO 4 digestion and polycondensation (acid-mediated carbonization) of a biomass residue (Agave sisalana). All the nanoporous carbons presented good ORR electrocatalytic activities in alkaline medium. The AC 1 carbon exhibited the most promising ORR performance with E onset = 0.84 vs. RHE, j L, 0.26 V, 1600 rpm = -3.12 mA cm−2 and n O2 = 3.6 electrons. The Tafel slopes of all carbons varied between 47 mV dec−1 (AC 3) and 250 mV dec−1 (AC 1). Furthermore, the carbons revealed superior tolerance to methanol when compared with commercial Pt/C and a competitive long-term electrochemical stability, with current retentions of 75–85 % after 20,000 s. The results obtained in this work suggest a promising method based on sustainable and economical biomass residues towards the development and engineering of novel value-added biomass-derived carbons as effective metal-free electrocatalysts for alkaline fuel cells. [ABSTRACT FROM AUTHOR]

• Bifunctional OER/ORR electrocatalysts based on Fe-Ni-Co/MWCNT were synthesized. • Both the OER and the ORR activity varied with the Fe:Ni:Co ratio. • Superior bifunctional ORR/OER activity was achieved for trimetallic Fe-Ni-Co oxides. • (Fe-Ni):Co ratio close to 1 led to catalysts with the highest bifunctional ORR/OER activity. • Synergistic interactions improve the stability and selectivity of the electrocatalysts. Fabrication of efficient and cost-effective bifunctional oxygen electrocatalysts for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) remains a challenge for the development of rechargeable metal-air batteries and unitized regenerative fuel cells technologies. Herein, we report high-performance bifunctional ORR/OER electrocatalysts consisting of mixed transition metal (Fe, Co, Ni) oxide nanoparticles supported on oxidized multi-walled carbon nanotubes (MWCNT). Investigation of the ORR and OER activity of samples with different metal compositions showed that trimetallic/MWCNT composites having Fe:Ni:Co = x:x:(1-2x) ratios, with 0.25 ≤ x ≤ 0.4, exhibit highest bifunctional activity in terms of the reversible ORR/OER overvoltage at a given current density. Moreover, the trimetallic catalysts exhibited improved selectivity with respect to the reduction of O 2 to OH− compared to the bimetallic Fe-Ni, Fe-Co and Co-Ni catalysts, thus revealing synergistic interactions among the metal oxide components. Correlation of the electrocatalytic activity with the structure of the composites is discussed for the most representative cases. [ABSTRACT FROM AUTHOR]

Nitrogen (N) doped porous activated carbons (TGC-T) derived from tofu gel are prepared through a facile, economic and eco-friendly method. The as-prepared TGC-900 possesses high specific surface area (651.78 m2 g−1) and homogeneous doping N (Content of N: 5.52 at.%). Reasonably, TGC-900 exhibits excellent oxygen reduction reaction (ORR) activity, stability and methanol resistance in neutral, alkaline and acidic medium. Moreover, TGC-900 also shows outstanding ORR performance in the application of microbial fuel cell (MFC) with the highest output voltage (544 ± 6 mV) and maximum power density (977 ± 32 mW m−2). Inspiringly, four single-chamber air cathode MFCs (AC-MFCs) in series can drive a light-emitting diode (LED) to work is firstly reported which further provides a more intuitively method to evaluate the performance of generating electricity for MFCs. Thus, the high performance and cost-effective ORR catalyst TGC-900 is expected to apply in the field of fuel cells. Tofu gel-derived nitrogen-doped porous activated carbon TGC-900 possesses excellent ORR electrocatalytic activity in neutral, alkaline and acidic medium. Image 1 • The carbonization temperature pays a significant role in TGC-T. • TGC-900 has excellent ORR activities in neutral, alkaline and acidic medium. • TGC-900 exhibits excellent ORR performance in MFCs. [ABSTRACT FROM AUTHOR]

Various catalysts were synthesized by incorporating phosphorus and iron into nitrogen-containing carbon derived from shrimp shell with pyrolysis. These catalysts had high specific surface area, uniform atomic doping and various active sites, which resulted in the high kinetics activity towards oxygen reduction reaction (ORR) under various pH conditions. Based on different doping sources to analyse ORR activity, phosphorus-doped catalyst was suitable for alkaline medium and iron doping for acidic medium, while their synergistic effect induced the highest ORR activity in neutral medium. Besides, the stability measurements investigated their abilities for application. Introducing iron into nitrogen-containing carbon could gradually strengthen the long-term stability for different catalysts in various pH conditions. Especially, phosphorus doping promoted the best ORR performance in alkaline condition with an extremely poor stability, which could be overcome by further adding iron. This work provides a strategy for the doped biomass-based carbon to accommodate different fuel cells. Phosphorus and iron are incorporated in nitrogen-containing carbon derived from shrimp shell to prepare dual-doped and tri-doped catalysts with excellent ORR performance and stability under various pH conditions for different fuel cells. Image 1 • Shrimp shells were oxidized as carbon support to promote efficient active sites. • Various catalysts were designed to meet different pH conditions for ORR. • Introducing phosphorus improved ORR performance and iron enhanced stability. • Phosphorus and iron synergistically facilitated excellent activity and stability in neutral. [ABSTRACT FROM AUTHOR]

Developing high efficiency and durability catalysts for the electrocatalytic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is fundamental to achieve the large‐scale commercial application of fuel cells and metal‐air batteries. Herein, a series of Co−N doped bi‐functional hierarchical porous electrocatalysts were synthesized using polyvinyl pyrrolidone (PVP) as soft template to assist the Zn/Co bimetal Zeolitic Imidazolate Framework (BMZIF) to form micro‐/mesoporous carbon nanospheres via a convenient one‐step solution synthesis method, followed by pyrolysis to form carbon nanospheres catalysts. The as‐prepared Co/N co‐doped carbon exhibits outstanding performances in the ORR and OER due to the formed hierarchical pores architecture and the high surface area. The catalyst displays superior ORR performance with a high half‐wave potential of 0.89 V, and a remarkable long‐term stability in 0.1 M KOH. In addition, the electrocatalyst elicits a low voltage of 1.72 V under the current density of 10 mA cm−2. Moreover, the zinc‐air battery fabricated with P‐CNCo‐3 delivers a power density of 175.1 mW cm−2, a high specific capacity of 791 mAh g−1 and an energy density of 976 Wh kg−1 at 20 mA cm−2. [ABSTRACT FROM AUTHOR]

Oxygen electroreduction is the key reaction among processes and devices of practical importance. Accordingly, the efforts of researchers are directed to the development of catalysts for the oxygen reduction reaction, which provided the effective oxygen reduction and stability at their low cost. Carbon nanotubes modified with oxygen- and nitrogen-containing groups, under the oxygen/nitrogen ratio of 1.3, meet these requirements considerably. In this work, we show that carbon nanotubes modified by oxygen and nitrogen accelerate the oxygen reduction reaction both in acid and alkaline electrolytes. Here, the modifying of carbon nanotubes' surface increased the electrochemical activity in the oxygen reduction reaction significantly which manifests itself in the shift of the half-wave potential in polarization curves in acid electrolyte by ~0.40 V to more positive values in comparison with not modified carbon nanotubes (in acid electrolyte). In alkaline electrolyte, the modified carbon nanotubes approach monoplatinum catalyst in their activity in the oxygen reduction reaction. The stability of modified carbon nanotubes (according to the testing by the potential cycling) is superior to that of the untreated carbon nanotubes. The obtained data show the perspectives of the modified carbon nanotubes' application as supports for cathodic catalysts of low-temperature hydrogen–air fuel cells. In the direct alkaline alcohol–air fuel cells and metal–air power sources of lithium–air type, the modified carbon nanotubes can be used as catalysts per se. The tailor-made synthesis of desired type and amount of nitrogen-containing groups is suggested to be realizable after the preliminary modification of carbon nanotubes with the oxygen-containing groups. [ABSTRACT FROM AUTHOR]

The design and synthesis of metal‐free catalysts with superior electrocatalytic activity, high durability, low cost, and under mild conditions is extremely desirable but remains challenging. To address this problem, a polymer‐assisted electrochemical exfoliation technique of graphite in the presence of an aqueous acidic medium is reported. This simple, cost‐effective, and mass‐scale production approach could open the possibility for the synthesis of high‐quality nitrogen‐doped graphene–polypyrrole (NG‐PPy). The NG‐PPy catalyst displays an improved half wave potential (E1/2=0.77 V) in alkaline medium compared with G‐PPy (E1/2=0.66 V). Most importantly, this catalyst demonstrates excellent stability with high methanol tolerance, and it outperforms the commercial Pt/C catalyst and other previously reported metal‐free catalysts. The content of graphitic nitrogen atoms is the key factor for the enhancement of electrocatalytic activity towards oxygen reduction reactions (ORR). Interestingly, the NG‐PPy catalyst can be used as a cathode material in a zinc–air battery, which demonstrates a higher peak power density (59 mW cm−2) than G‐PPy (36.6 mW cm−2), highlighting the importance of the low‐cost material synthesis approach towards the development of metal‐free efficient ORR catalysts for fuel cell and metal–air battery applications. Remarkably, the polymer‐assisted electrophoretic exfoliation of graphite with a high yield (≈88 wt %) of few‐layer graphene flakes could pave the way towards the mass production of high‐quality graphene for a variety of applications. [ABSTRACT FROM AUTHOR]

• FeNC is a promising cathode catalyst for phosphoric acid fuel cells. • ORR activity of FeNC is projected to be comparable to Pt/C at higher temperatures. • Unlike Pt/C, FeNC is unexpectedly resistant to poisoning by phosphate anions. • A "size-related hindrance effect" is observed during phosphate exposure on FeNC. • Phosphate poisoning of FeNC depends strongly on the nature of carbon support. The greatest challenges facing the large – scale commercialization of the intermediate temperature phosphoric acid fuel cell (PAFC) technology are: (i) the high cost of Pt catalyst that is required to overcome the slow kinetics of oxygen reduction reaction (ORR) on the PAFC cathode, and (ii) deactivation of the Pt catalyst by exposure to the phosphoric acid electrolyte. Inexpensive carbon-based materials, particularly iron-nitrogen-coordinated carbon supported catalysts (FeNC), are promising cathodes for PAFCs. The higher ORR activation energy and phosphate poisoning resistance of FeNC present a clear advantage over the Pt-based commercial catalysts that are easily susceptible to deactivation after exposure to phosphate anions. While the immunity of FeNC catalysts to phosphate anion poisoning has been reported previously, this work explores the counter-intuitive and conditional nature of this poisoning resistance based on the properties of the carbon support used in the preparation of the FeNC catalyst. A combination of electrochemical measurements with characterization experiments performed using X-ray photoelectron spectroscopy, infrared spectroscopy and in-situ X-ray absorption spectroscopy is used to explore the phenomenon of phosphate poisoning on FeNC catalysts synthesized from two different carbon supports. Results from these studies reveal a "size-related hindrance effect" wherein the ORR active Fe centers in FeNC remain inaccessible to larger anions such as phosphate when the Fe sites are present deeper inside the pores of a carbon support with high porosity. However, FeNC catalyst is poisoned by phosphate anions when synthesized using a carbon support with low porosity. This work helps gain insights into the nature of active sites in FeNC catalysts that will be useful in designing precious-metal free ORR catalysts for intermediate temperature fuel cell technologies. [ABSTRACT FROM AUTHOR]

The key to sustainable energy application is the rational utilization of abundant materials on the earth. Fe, Co, and Cu theoretically exhibit high oxygen reduction capability close to Pt. However, their high diffusion behaviors make it difficult to homogeneously incorporate with carbon at elevated fabrication temperature. Here, polyaniline is developed an incorporated frame to realize the homodisperse of Fe, Co, or Cu. Three efficient oxygen reduction catalysts, including Fe-polyaniline/carbon (Fe-N/C), Co-N/C, and Cu-N/C are synthesized by a three-step method combining polymerization, complexation, and pyrolysis. All catalysts with metal doping reveal high catalytic activity, good cyclic stability, and the activity varies with different doping metal. The Fe-doped catalyst exhibits the best oxygen reduction ability with onset and half-wave potentials of − 104 mV and − 199.5 mV. Furthermore, the influence of complexation time and the pyrolysis temperature on the oxygen reduction activity are also studied systematically. These interesting discoveries may contribute to provide important ideas to oxygen reduction catalysts. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) electrocatalysts derived from biomass have become one of the research focuses in hetero-catalysis due to their low cost, high performance, and reproducibility properties. Related researches are of great significance for the development of next-generation fuel cells and metal-air batteries. Herein, the preparation methods of various biomass-derived catalysts and their performance in alkaline, neutral, and acidic media are summarized. This review clarifies the research progress of biomass carbon-based electrocatalysts for ORR in acidic, alkaline and neutral media, and discusses the future development trends. This minireview can give us an important enlightenment to practical application in the future.

The exploration of noble metal-free catalysts with efficient electrochemical performance toward oxygen reduction reaction in the acid electrolyte is very important for the development of fuel cells technology. Novel pyrolyzed heteroatom-doped Fe/N/C catalysts have been regarded as the most efficient electrocatalytic materials for ORR due to their tunable electronic structure, and distinctive chemical and physical properties. Herein, nitrogen- and sulfur-doped (Fe/N/C and Fe/N/C-S) electrocatalysts were synthesized using ferric chloride hexahydrate as the Fe precursor, N-rich polymer as N precursor, and Ketjen Black EC-600 (KJ600) as the carbon supports. Among these electrocatalysts, the as prepared S and N-doped Fe/N/C-S reveals the paramount ORR activity with a positive half-wave potential value (E1/2) 0.82 at 0.80 V vs. RHE in 0.1 mol/L H2SO4 solution, which is comparable to the commercial Pt/C (Pt 20 wt%) electrocatalyst. The mass activity of the Fe/N/C-S catalyst can reach 45% (12.7 A g−1 at 0.8 V) and 70% (5.3 A g−1 at 0.95 V) of the Pt/C electrocatalyst in acidic and alkaline solutions. As result, ORR activity of PGM-free electrocatalysts measured by the rotating-ring disk electrode method increases in the following order: Fe/N/C

It is important to develop cost-efficient electrocatalysts used in the oxygen reduction reaction (ORR) for widespread applications in fuel cells. Palladium (Pd) is a promising catalyst, due to its more abundant reserves and lower price than platinum (Pt), and doping an earth-abundant 3d-transition metal M into Pd to form Pd–M bimetallic alloys may not only further reduce the use of expensive Pd but also promote the electrocatalytic performance of ORR, owing to the synergistic effect between Pd and M. Here we report a cyanogel-derived synthesis of PdFe alloys with porous nanostructure via a simple coinstantaneous reduction reaction by using K2PdIICl4/K4FeII(CN)6 cyanogel as precursor. The synthesized PdFe alloys possess hydrangea-like morphology and porous nanostructure, which are beneficial to the electrochemical performance in ORR. The onset potential of the porous PdFe nanohydrangeas is determined to be 0.988 V, which is much more positive than that of commercial Pt/C catalyst (0.976 V) and Pd black catalyst (0.964 V). Resulting from the unique structural advantages and synergetic effect between bimetals, the synthesized PdFe nanohydrangeas with porous structure have outstanding electrocatalytic activity and stability for ORR, compared with the commercial Pd black and Pt/C.

The goal of this research was to synthesize activated nitrogen-doped nanocarbons with high specific surface area and adjustable pore size distribution using wood charcoal as a raw material. The resulting carbon materials were tested for possible application as oxygen reduction reaction catalysts in alkaline media. Activated carbons were obtained using a thermochemical activation method with NaOH. Nitrogen was introduced into activated carbons using dicyandiamide solution. It was demonstrated that the content of introduced nitrogen depends on oxygen content in the structure of the activated carbon. The oxygen reduction reaction activity of the activated and nitrogen-doped carbon material was comparable with a commercial 20% Pt/C catalyst. Electrocatalytic properties of the synthesized N-doped wood-derived carbon catalysts may be associated with the highly developed surface area, specific ratio of micro- and mesopores, as well as the high percentage of pyridinic nitrogen.

Transition metal-nitrogen-carbon catalysts obtained from pyrolysis of simple sources of metal and nitrogen or metal-organic frameworks are envisioned as promising replacement of Pt-based catalysts for oxygen reduction reaction (ORR) in fuel cells and metal-air batteries. However, the lack of clarity on the active site structure is a fundamental problem in developing efficient catalysts for the complete reduction of oxygen with maximum active site density. In this study, we have synthesized a simple metal-organic complex, Co (bpy) 2 CO 3 NO 3 ⋅ 5 H 2 O , 1 (bpy = 2, 2′-bipyridine) and studied its ORR activity in 0.1 M KOH supporting on Ketjenblack EC-600JD, 1 /C. The crystal structure of 1 was unambiguously determined using single-crystal X-ray diffraction. The onset potential of ORR, Tafel slopes, kinetic current density, the fraction of oxygens reduced to peroxyl ion (χ HO 2 − ) and the electron transfer number (n) were compared with relevant literature and commercial 20 wt % Pt/C. Primarily, 1 /C reduces O 2 through the direct 4-electron pathway. ' n' and χ HO 2 − on 1 /C were found to be 3.87 and 7% at 0.7 V iR-free vs. RHE, respectively. The turn-over frequencies for the 4- and 2-electron process were found to be 0.124 and 0.001 electrons [Co]−1 s−1 at 0.7 V iR-free vs. RHE, respectively. Density-functional theory analysis reveals that the preferential activation of the side-on mode of adsorption on 1 is responsible for high selectivity in the direct 4-electron pathway. Image 1 • The complex, Co (bpy) 2 CO 3 NO 3 ⋅ 5 H 2 O , 1 exhibits high chemical stability in 0.1 N KOH. • Carbon supported 1 , 1 /C, reduces the oxygen mainly through the direct 4-electron pathway. • ' n' and χ HO 2 − at 0.8 V iR-free vs. RHE on 1 /C are 3.9 and 4%, respectively. • The 4-electron oxygen reduction turn-over frequency of 1 /C is more than 2-fold higher compared to that of the 2-electron process. [ABSTRACT FROM AUTHOR]

• α-MnO 2 nanorods have been in-situ supported on 3D-G via a facile hydrothermal method. • α-MnO 2 nanorods are evenly deposited on 3D-G surface which possesses more defects. • The synergistic interaction between α-MnO 2 nanorods and 3D-G improve ORR performance. • α-MnO 2 /3D-G catalyst exhibites excellent activity and durability for ORR in MFCs. Magnesium-air fuel cells are considered as a potential energy conversion device owing to a high theoretical specific capability, economic viability and environmental friendliness. In this work, α-MnO 2 nanorods are supported on three-dimensional graphene (3D-G) which is fabricated with coal tar pitch as the carbon precursor and MgO as the template via hydrothermal reaction. The synergistic interactions between α-MnO 2 nanorods and 3D-G improve the activity and durability performance for oxygen reduction reaction in 0.1 mol L−1 KOH solution. α-MnO 2 /3D-G exhibits a high half-wave potential (0.81 V) and superior to α-MnO 2 /C (0.72 V) and α-MnO 2 /rGO (0.76 V), and close to 20 wt% Pt/C (0.83 V). α-MnO 2 /3D-G also possesses higher durability than commercial Pt/C. Furthermore, the magnesium-air fuel cells based on α-MnO 2 /3D-G, air-cathode display the peak power density (106.2 mW cm−2), and continuously durability (discharge for 16 h at 50 mA cm−2 with the mere decay of cell voltage by 7.6%). These results prove that α-MnO 2 /3D-G catalyst with high activity and durability can be a promising electrocatalyst in magnesium-air fuel cells. [ABSTRACT FROM AUTHOR]

Enhancing the catalytic activity of manganese oxide in oxygen reduction reaction (ORR) is a key issue for its large-scale application in metal-air fuel cells. Ag-doped α -MnO2 nanowires without Ag or Ag2O have been successfully synthesized via a facile hydrothermal method, and the changes in both the structure and electrochemical catalytic performances after Ag doping are investigated. Compared with the pristine α -MnO2, the as-prepared Ag-doped MnO2 exhibits a significantly enhanced catalytic activity in both ORR and Mg-air fuel cell application. With Ag/Mn ratio of 1:25, Ag-doped MnO2 exhibits a typical 4e-reaction pathway and presents a 163 mV higher half-wave potential than that of the pristine α -MnO2. Furthermore, it demonstrates a power density of 75.1 mW cm − 2 at current density of 134.5 mA cm − 2 in the Mg-air fuel cells. The enhanced ORR performances are considered to be contributed from the activation of surface lattice oxygen, the improvement in conductivity and the increase in oxygen vacancies of α -MnO2. These findings provide new understanding for developing high-performance manganese oxide catalysts. A facile hydrothermal route is carried out to synthesize Ag-doped α-MnO2 nanowire, which shows excellent oxygen reduction activity owing to the enhancement in the overall electrical conductivity as well as the increase in the oxygen vacancies. The good performance of Ag-doped nanowire indicates its promising application in Mg-air fuel cell. [ABSTRACT FROM AUTHOR]

The kinetics of oxygen reduction reaction (ORR), being a prime requisite for electrode materials after the higher conductivity. Further, electrodes are observed to dissolute on reaction at triple phase boundary. However, the compositional effect on ORR is least understood. In order to inspect the ORR mechanism with substitution, a series of (1 + x) PrCoO 3 − (1 − x) BaCoO 3 (x = 0.2 to 1.0 with step of 0.2) compositions are prepared using conventional solid-state route method. The Rietveld refinement of X-ray diffractograms and specific heat curves confirms the formation of double phase comprising orthorhombic Pmmm phase corresponding to PrBaCo 2 O 6-δ and Pnma phase corresponding to PrCoO 3 for x = 0.2 to 0.8 with well connected and porous microstructure. The triple phase boundary reactions suggest the formation of Co(OH) 3 along with H 2 gas on reaction of these composite electrodes with H 2 O during electrochemical dissolution. However, chronoamperometric studies prove the suitability of x = 0.6 sample with higher ORR and liberation of H 2 gas at room temperature. • Compositional effect on ORR mechanism of Pr 1+x Ba 1-x Co 2 O 6-δ materials is studied. • XRD and specific heat curves confirm double phase with porous microstructure. • Co(OH) 3 and H 2 are formed in electrochemical dissolution at triple phase boundary. • x = 0.6 showed higher ORR with higher evolution of H 2 gas at 30 °C. [ABSTRACT FROM AUTHOR]

Hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) are two core electrochemical processes involved in hydrogen fuel cell (HFC) technology. ORR is a cathodic reaction occurring in HFC, whereas HER can convert the H2O byproduct from HFCs into H2 gas via water splitting. Platinum (Pt)-based catalysts are the most effective catalysts for both reactions. In this work, we used a fast, facile, and chemical-free method, called solution plasma sputtering (SPS), to synthesize Pt nanoparticles supported on Ketjen Black (KB). The discharge time was varied (5, 10, and 20 min) to alter the Pt loading. Characterization results revealed that the plasma did not affect the morphology of KB, and the Pt loading on KB increased with increasing discharge time (5.5-17.9 wt%). Well-crystallized Pt nanoparticles, ~2-5nmin diameter, were obtained. Electrochemical measurements revealed that Pt/KB exhibited bifunctional catalytic activity toward HER and ORR in 0.5 M H2SO4 solution. Both HER and ORR activities enhanced as the loading of Pt nanoparticles increased with a longer discharge time. Moreover, Pt/KB exhibited better HER and ORR stability than a commercial Pt-based catalyst, which was attributed to the stronger adhesion between Pt nanoparticles and KB support. Thus, SPS can be applied as an alternative synthesis method for preparing Pt/KB catalysts for HER and ORR. [ABSTRACT FROM AUTHOR]

Controllable design and synthesis of catalysts with the target active sites are extremely important for their applications such as for the oxygen reduction reaction (ORR) in fuel cells. However, the controllably synthesizing electrocatalysts with a single type of active site still remains a grand challenge. In this study, we developed a facile and scalable method for fabricating highly efficient ORR electrocatalysts with sole atomic Fe–N4 species as the active site. Herein, the use of cost‐effective highly porous carbon as the support not only could avoid the aggregation of the atomic Fe species but also a feasible approach to reduce the catalyst cost. The obtained atomic Fe–N4 in activated carbon (aFe@AC) shows excellent ORR activity. Its half‐wave potential is 59 mV more negative but 47 mV more positive than that of the commercial Pt/C in acidic and alkaline electrolytes, respectively. The full cell performance test results show that the aFe@AC sample is a promising candidate for direct methanol fuel cells. This study provides a general method to prepare catalysts with a certain type of active site and definite numbers. [ABSTRACT FROM AUTHOR]