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The oxygen reduction reaction (ORR) represents a cornerstone for many clean energy conversion technologies such as fuel cells and metal‐air batteries. Nevertheless, the commercialization of these technologies is largely impeded by the slow kinetics of ORR, for which active, durable and cost‐effective ORR catalysts are needed. In recent years, zeolitic imidazolate framework (ZIF) derived carbon materials emerge as a new class of non‐precious metal catalysts (NPMCs) toward ORR, largely benefiting from their high surface area, abundant porosity, tunable chemical/electronic structure, and superior ORR activity which is comparable or even surpasses those state‐of‐the‐art Pt‐based ORR catalysts. This review offers a comprehensive overview of the recent advances in ZIF‐derived carbons for ORR. The synthesis strategies and the key factors affecting the ORR performance of ZIF‐derived carbon materials are discussed. Future research directions and perspectives on exploring ZIF derived carbons as efficient ORR catalysts are highlighted, with a focus on the principles of rationally engineering the coordination structures of active sites. [ABSTRACT FROM AUTHOR]

The development of precious metal-free (M-N-C) catalysts for the oxygen reduction reaction (ORR) is considered crucial for reducing fuel cell costs. Herein, Co-Zn/NC interconnected frameworks with uniformly dispersed Co nanoparticles and graphitic carbon are designed and successfully synthesized through the in situ growth of zeolitic imidazolate frameworks (ZIF67 and ZIF8) along with biomass nano-microfibrillar cellulose (MFC), followed by pyrolysis. A Co-Zn/NC composite is prepared by combining Co-Zn/NC with a perfluorosulfonic acid polymer. The Co-Zn/NC composite catalyst exhibits excellent ORR catalytic activity (E0 = 0.974 V vs. RHE, E1/2 = 0.858 V vs. RHE) and good long-term durability, with 90% current retention after 10000s, surpassing that of commercial Pt/C in alkaline media. The hierarchical porous structure, coupled with the uniform distribution of Co nanoparticles and nitrogen doping, contributes to superior electrocatalytic performance, while the interconnected frameworks and graphitic carbon ensure good stability. Additionally, the Co-Zn/NC composite demonstrates promising applications in acidic media. This strategy offers significant guidance to develop advanced non-precious metal carbon-based catalysts for highly efficient and stable ORR. [ABSTRACT FROM AUTHOR]

It is essential for the widespread application of proton exchange membrane fuel cells (PEMFCs) to investigate low‐cost, extremely active, and long‐lasting oxygen reduction catalysts. Initial performance of PGM‐free metal‐nitrogen‐carbon (M−N−C) catalysts for oxygen reduction reaction (ORR) has advanced significantly, particularly for Fe−N−C‐based catalysts. However, the insufficient stability of M−N−C catalysts still impedes their use in practical fuel cells. In this review, we focus on the understanding of the structure‐stability relationship of M−N−C ORR catalysts and summarize valuable guidance for the rational design of durable M−N−C catalysts. In the first section of this review, we discuss the inherent degrading mechanisms of M−N−C catalysts, such as carbon corrosion, demetallation, H2O2 attack, etc. As we gain a thorough comprehension of these deterioration mechanisms, we shift our attention to the investigation of strategies that can mitigate catalyst deterioration and increase its stability. These strategies include enhancing the anti‐oxidation of carbon, fortifying M−N bonds, and maximizing the effectiveness of free radical scavengers. This review offers a prospective view on the enhancement of the stability of non‐noble metal catalysts. [ABSTRACT FROM AUTHOR]

In light of the depletion of conventional energy sources, it is imperative to conduct research and development on sustainable alternative energy sources. Currently, electrochemical energy storage and conversion technologies such as fuel cells and metal-air batteries rely heavily on precious metal catalysts like Pt/C and IrO2, which hinders their sustainable commercial development. Therefore, researchers have devoted significant attention to non-precious metal-based catalysts that exhibit high efficiency, low cost, and environmental friendliness. Among them, perovskite oxides possess low-cost and abundant reserves, as well as flexible oxidation valence states and a multi-defect surface. Due to their advantageous structural characteristics and easily adjustable physicochemical properties, extensive research has been conducted on perovskite-based oxides. However, these materials also exhibit drawbacks such as poor intrinsic activity, limited specific surface area, and relatively low apparent catalytic activity compared to precious metal catalysts. To address these limitations, current research is focused on enhancing the physicochemical properties of perovskite-based oxides. The catalytic activity and stability of perovskite-based oxides in Oxygen Reduction Reaction/Oxygen Evolution Reaction (ORR/OER) can be enhanced using crystallographic structure tuning, cationic regulation, anionic regulation, and nano-processing. Furthermore, extensive research has been conducted on the composite processing of perovskite oxides with other materials, which has demonstrated enhanced catalytic performance. Based on these different ORR/OER modification strategies, the future challenges of perovskite-based bifunctional oxygen electrocatalysts are discussed alongside their development prospects. [ABSTRACT FROM AUTHOR]

The anion‐exchange membrane direct ammonia fuel cell, as a carbon‐free fuel cell type, has recently received increasing attention albeit suffering from high cost of using the platinum‐group metal oxygen reduction reaction (ORR) catalysts. To pave the development of this promising power source, the atomically dispersed transition metal‐nitrogen‐carbon (M‐N‐C) materials with low cost and high ORR performance have allured to investigate their ammonia tolerance during the ORR. Herein, it is initially deconvoluted how compositional and structural elements of FeN4 sites modulate catalyst's performance. Furthermore, ORR catalytic activities of the M‐N‐C (M = Fe, Co or Mn) and Pt/C catalysts are investigated in ammonia‐containing electrolytes, showing that M‐N‐C catalysts have better ammonia tolerance than Pt/C. Among others, the Fe‐N‐C exhibits the best ammonia tolerance with only 4 mV negative shifts of half‐wave potential, 2.7% decrease of current, and negligibly irreversible activity loss. The superior ammonia tolerance of MN4 sites to Pt (111) surface is further confirmed by density functional theory calculations. The adsorption capacity of MN4 for O2 is higher than NH3 and the bonding force between MN4 and O2 is stronger than NH3, whereas opposite adsorption capacity and bonding force trends are observed on Pt (111) surface. [ABSTRACT FROM AUTHOR]

With the increasing demand for green and efficient energy storage devices， advanced technologies for clean energy conversion have attracted close attention from researchers. Fuel cells with environmental friendliness and high energy conversion efficiency are promising alternatives to traditional energy sources. However， Pt catalysts with high commercialization degrees in the industrial catalysis field have some problems， such as high cost， poor stability and weak anti-toxicity ability， which limits the further development of fuel cells. The development of non-Pt oxygen reduction reaction （ORR） catalysts with abundant reserves， low cost and excellent performance is an effective way to improve the efficiency of fuel cells. In this paper， based on the research results at home and abroad in recent years， various types of non-Pt system ORR catalysts， including non-precious metal and non-metal catalysts， are systematically introduced. The advantages， disadvantages and modification strategies of various catalysts are summarized， and challenges and prospects for the development of ORR electrocatalysts are put forward. [ABSTRACT FROM AUTHOR]

Fe−N−C represents the most promising non‐precious metal catalysts (NPMCs) for the oxygen reduction reaction (ORR) in fuel cells, but often suffers from poor stability in acid due to the dissolution of metal sites and the poor oxidation resistance of carbon substrates. In this work, silicon‐doped iron‐nitrogen‐carbon (Si/Fe−N−C) catalysts were developed by in situ silicon doping and metal–polymer coordination. It was found that Si doping could not only promote the density of Fe−Nx/C active sites but also elevated the content of graphitic carbon through catalytic graphitization. The best‐performing Si/Fe−N−C exhibited a half‐wave potential of 0.817 V vs. reversible hydrogen electrode in 0.5 m H2SO4, outperforming that of undoped Fe−N−C and most of the reported Fe−N−C catalysts. It also exhibited significantly enhanced stability at elevated temperature (≥60 °C). This work provides a new way to develop non‐precious metal ORR catalysts with improved activity and stability in acidic media. [ABSTRACT FROM AUTHOR]

Exploring efficient non-precious metal cathode catalysts is attracting ever-increasing interest in the development of direct borohydride fuel cell (DBFC). Herein, a cobalt-based nitrogen-doped bamboo-like graphene tube (Co-NGT) is prepared as an efficient cathode catalyst. The Co-NGT consists of bamboo-like graphene tubes (40–130 nm in diameter and ∼10 μm in length), as well as cobalt nanoparticles (50–100 nm in diameter) confined in the graphene tubes. The Co-NGT shows an onset reduction potential of 0.964 V and an almost four-electron pathway towards oxygen reduction reaction, as well as a negative shift of 8 mV in half-wave potential after 10,000 CV cycles. The Tafel slope of the Co-NGT catalyst is 47 mV decade−1, which is by ca. 37.8 mV decade−1 smaller than for Pt/C. A DBFC using the Co-NGT cathode yields the biggest power density of 453 mW cm−2 at 60 °C and a life span of over 120 h. The excellent electrocatalytic properties and superior durability of Co-NGT catalyst arise from the highly graphitized NGT, providing strong interaction with Co nanoparticles and mitigating the agglomeration of Co nanoparticles. Our study guides for composition and structural design of high-efficient cathode catalysts of DBFC. [Display omitted] • The Tafel slope of Co-NGT towards ORR is 47 mV dec−1. • The half-wave potential is only 8 mV negative shift of Co-NGT after 10,000 CV cycles. • Maximum power density of 453 mWcm−2 is achieved by DBFC using Co-NGT cathode. [ABSTRACT FROM AUTHOR]

Summary: In this study, the performance and durability of a Pt/Cu bimetallic catalyst membrane electrode assembly (MEA) for use in polymer electrolyte membrane fuel cells (PEMFCs)—fabricated via plasma‐enhanced atomic layer deposition and sputtering—were investigated. The high production costs of Pt‐based catalysts limit the commercialization of PEMFCs. Therefore, research to dramatically reduce the loadings of noble metal catalysts, such as Pt, has steadily progressed. Atomic layer deposition may considerably reduce the amount of supported catalyst by precisely controlling the composition and thickness of the catalyst via a self‐limiting reaction. According to D‐band theory, the Cu catalyst of the Pt/Cu MEA weakened the bonds between the Pt catalyst and oxygen species and improved the oxygen reduction reaction compared to those of the existing Pt MEA. The performance and electrochemical surface area (ECSA) of the Pt/Cu MEA were determined using I‐V measurements and cyclic voltammetry, and the durability of the Pt/Cu MEA was analyzed using electrochemical impedance spectroscopy and the accelerated stress test. Thus, when the Pt/Cu MEA was used, the performance and ECSA were improved, and the impedance decreased, compared to those of the Pt MEA. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) is of great importance for clean energy storage and conversion techniques such as fuel cells and metal–air batteries (MABs). However, the ORR is kinetically sluggish, and expensive noble metal catalysts are required. The high price and limited preservation of noble metal catalysts has largely hindered the wide application of clean power sources such as fuel cells and MABs. Therefore, it is important to prepare non-expensive metal catalysts (NPMC) to cut the price of the fuel cells and MABs for wide application. Here, we report the preparation of a Co3O4 carried on the N-doped carbon (Co/N-C) as the ORR NPMC with a facile Pharaoh's Snakes reaction. The gas generated during the reaction is able to fabricate the porous structure of the resultant carbon doped with heteroatoms such as Co and N. The catalyst provides a high electrocatalytic activity towards ORR via the 4-e pathway with an onset and half-wave potential of 0.98 and 0.79 V (vs. RHE), respectively, in an electrolyte of 0.1 M KOH. The onset and half-wave potentials are close to those of the commercial Pt/C. This work demonstrates the promising potential of an ancient technology for preparing NPMCs toward the ORR. [ABSTRACT FROM AUTHOR]

The development of electrocatalysts for oxygen reduction reaction (ORR) is important for energy conversion devices, such as fuel cells, and metal‐air batteries. Here, we have developed a confined space strategy to prepare a two‐dimensional (2D) leaf‐like nitrogen (N)‐containing porous carbon as a single‐atom catalyst substrate. ZIF−L materials have been confined in a thin silica layer to regulate the pyrolysis. The obtained Fe single atoms doped N‐containing porous carbons (Fe SAs/N−C) maintain the 2D morphology and have Fe single‐atom active sites. Correspondingly, Fe SAs/N−C exhibits excellent ORR performance (E1/2 of 0.907 V), which is more positive than those of commercially available Pt/C (0.874 V) and most reported non‐noble metal catalysts. The durability test shows that Fe SAs/N−C exhibits good stability during electrocatalytic process. This rational design shows a new strategy to prepare 2D catalyst supports with single‐atom active sites. [ABSTRACT FROM AUTHOR]

The development of high-performance nonprecious metal catalysts for oxygen reduction reactions is critical for the commercialization of fuel cells. In this paper, we report a non-precious catalyst with high-performance, in which Fe and Fe3C is embedded in nitrogen-doped carbon nanofibers (MIL-N-CNFs) by co-electrospinning Fe-MIL and polyacrylonitrile (PAN) and pyrolyzing. The mass ratio of Fe-MIL to PAN in the precursors and the pyrolysis temperature were optimized to be 1.5 and treated at 800 °C, respectively. The optimized catalyst exhibited an onset potential of 0.950 V and a half-wave potential of 0.830 V in alkaline electrolytes, thanks to the improved mass transfer kinetics in a meso-porous structure and enhanced reaction kinetics by confined Fe and Fe3C particles. Additionally, the optimized catalyst showed a better methanol tolerance than the commercial 20 wt.% Pt/C, indicating a potential application in direct methanol fuel cells. Serving as the cathode in CCM, the anion-exchange membrane fuel cell reaches a power density of 192 mW cm−2 at 428 mA cm−2 and 80 °C. [ABSTRACT FROM AUTHOR]

Looking for non‐noble metal catalysts with low cost, high activity, and high stability to replace platinum in oxygen reduction reaction (ORR) has aroused great concern. According to previous studies, Fe‐Nx/C material is one of the most promising non‐noble metal catalysts for ORR. In this study, new Fe‐Nx/C material was synthesized by introducing CeO2 and Fe3O4 nanoparticles into a Fe‐Nx/C material derived from ZIF‐8 as precursors. The new material was called CeO2‐Fe3O4@Fe‐N/C catalyst and the activity of the catalyst was found to be significantly improved in 0.1 mol L−1 KOH. The half‐wave potential of CeO2‐Fe3O4@Fe‐N/C (0.892 V) is higher than that of Pt/C by 67 mV. In the stability test, the half‐wave potential of CeO2‐Fe3O4@Fe‐N/C was only reduced by 4 mV after 5,000 cycles. The high performance is attributed to the introduction of CeO2 and Fe3O4, which gives CeO2‐Fe3O4@Fe‐N/C enhanced electrocatalytic activity and long‐term stability. This approach makes CeO2‐Fe3O4@Fe‐N/C a promising candidate for cathode catalysts in renewable energy conversion devices. [ABSTRACT FROM AUTHOR]

The cathode's oxygen reduction reaction (ORR) plays a crucial role in a variety of fuel cells. Developing affordable and efficient non-precious electrocatalysts for the ORR poses a major hurdle in the realm of electrochemical energy technologies. This work presents a transition metal-based catalyst, Fe-ONC, in which Fe is loaded in an oxygen-enriched nitrogen-doped carbon (NC) material. Oxygen enrichment of the catalyst was achieved by a pre-oxidation strategy. The XPS analysis reveals that Fe-ONC exhibits a higher abundance of oxidized species. The Fe of Fe-ONC exists in the form of Fe 3 O 4 particles and Fe-N x , respectively, which are uniformly distributed in the NC. The even spread of iron sites and the plentiful presence of oxygen-rich species are key factors in the superior ORR efficiency of Fe-ONC. Fe-ONC's half-wave potential (E 1/2) in an alkaline environment (0.1 M KOH) stands at 0.891 V, markedly surpassing the standard commercial Pt/C value (0.840 V). Additionally, Fe-ONC demonstrated enhanced longevity and resistance to ethanol in comparison to commercially available Pt/C. Fe-ONC's outstanding efficacy highlights its potential as an alternative to precious metal catalysts. The document outlines a plan for creating ORR catalytic materials that are sustainable, economical, and efficient. We propose to oxygenate the initial catalyst Fe-NC by pre-oxidation treatment, which increases the content of oxides and iron species with high oxidation valence states in the catalyst Fe-ONC, thus improving the catalyst activity and ORR performance. [Display omitted] • Fe-ONC is oxygenated by pre-oxidation treatment. • Oxygen-enriched Fe-N x sites boost ORR efficiency significantly. • Fe-ONC achieves a notable E 1/2 of 0.891 V in alkaline conditions. [ABSTRACT FROM AUTHOR]

Fe-N-C catalysts have developed into the most promising substitute for Pt-based precious metal catalysts toward cathodic oxygen reduction reaction (ORR) of fuel cells and Zn-air batteries. Hypercrosslinked polypyrrole microspheres coordinated with Fe (HCP-Py-Fe) were first prepared by condensation of pyrrole (Py) and dimethoxymethane (FDA) in the presence of FeCl 3 as both catalyst and Fe source, and then thermally activated with KOH during pyrolysis followed by acid leaching and heat-treatment, thus constructing hierarchically porous Fe-N-C microspheres (denoted as PPy/FDA-Fe y -HT2-x). The morphology and structural properties of the final synthesized PPy/FDA-Fe y -HT2-x could be tailored to a certain extent by controlling the adding quantities of KOH (x) in the initial solid mixture before pyrolysis and FeCl 3 (y) during condensation of Py and FDA. As a result, the PPy/FDA-Fe 0.4 -HT2–0.25 demonstrated the highest half-wave potential of 0.87 V vs. RHE, with a desired 4-electron transfer for ORR in alkaline medium, which is attributed to the hierarchically micro/mesoporous structure, high surface area and extremely low content of magnetic iron species. Remarkable methanol resistance and durability with only a loss of ∼4 mV in half-wave potential after 10000 potential cycles were obtained as well. The aqueous Zn-air battery (ZAB) fabricated with the PPy/FDA-Fe 0.4 -HT2–0.25 as cathode catalyst delivered a comparable discharge performance to that of the Pt/C-based ZAB but far superior cycling stability. This facile route is promising for large-scale production of Fe-N-C materials as cathodic electrocatalyst applied in practical energy conversion devices. [Display omitted] • Fe3+-catalyzed Friedel-Crafts reaction, pyrolysis with in situ activation was adopted. • Texture, Fe/N species percentages could be tuned by Fe3+-catalysis and KOH activation. • The Fe-N-C favored ORR in 4-e- way with a bit higher activity than that of the Pt/C. • The Fe-N-C microspheres showed better methanol resistance and stability than the Pt/C. • The ZAB assembled with Fe-N-C display superior discharge performance and durability. [ABSTRACT FROM AUTHOR]

Opening up electrocatalysts for oxygen reduction reaction (ORR) is essential for practical application in fuel cells and metal-air batteries; however, how to make the catalysts with both good performance and low cost is difficult. Recently, research on the ORR of molybdenum disulfide-based catalysts in alkaline electrolytes has been on the rise. However, the development of MoS2 catalyst for acidic ORR is still in its infancy. Herein, without using reductant and morphology control reagent, we firstly obtained flowerball-like MoS2/Vulcan XC-72R (VC) nanocomposites via hydrothermal method. The designed composite exhibits a nearly 4e− ORR process with 0.78 and 0.92 V onset potentials in 0.1 M KOH and HClO4, respectively. Furthermore, the flowerball-like composite shows utmost electrochemical stability judging by 87 and 80% current retention for about 5.5 h either in alkaline or acid media, long term durability for continuous 10,000 cycles, and stronger resistance to methanol than the commercial Pt/C catalyst. The abundant Mo edges as catalytic active centers of flowerball-like structure, high electron conductivity, and enhanced mass transport in either alkaline or acidic electrolyte are favorable for catalytic performance. The prepared catalyst provides great potential for the substitution of noble metal based catalysts in fuel cells and metal-air batteries. [ABSTRACT FROM AUTHOR]

Nonprecious transition metals [e.g., cobalt (Co), iron (Fe), and zinc (Zn)], and nitrogen doped carbon materials are considered to be the most attractive alternatives to precious metal catalysts. Herein, Cobalt decorated nitrogen-doped carbon nanotubes were synthesized via a facile hydrothermal method and calcination. Benefiting from the N-doping, etching of Co nanoparticles to carbon nanotubes and synergistic effect between the components, the as-prepared Co/nitrogen-doped carbon nanotubes (Co-NCNT) displays a half-wave potential of 0.88 V (vs. RHE), a limiting current density of 5.6 mA cm−2, and electron transfer number of 3.9 in 0.1 M KOH. When applied in metal-air batteries, it delivered maximum power densities of 130.0 mW cm−2, 117.3 mW cm−2 and 58.6 mW cm−2 in alkaline Zn-air, Al-air batteries and neutral Mg-air batteries respectively, outperforming the commercial Pt/C. These demonstrate that the synthesized Co-NCNT is a promising candidate for ORR in metal-air batteries with both alkaline and neutral electrolytes. [Display omitted] • Facile synthesis of cost-effective catalyst in Mass preparation. • The Co-NCNT shows Pt/C comparable activities for ORR. • Synergistic effect leading to enhancement in activity. • The Al/Mg/Zn-Air fuel cells displays superior discharge performances. [ABSTRACT FROM AUTHOR]

Fe N C catalyst containing abundant atomic Fe-N x sites is synthesized using a MgCl 2 -assisted synthesis approach. The catalyst delivered an excellent oxygen reduction activity in alkaline and acidic electrolytes with outstanding stability. [Display omitted] • Highly active Fe N C catalyst is synthesized by a simplified salt-assisted approach. • Only a single heat-treatment step is employed to produce a highly active catalyst. • The synthesized Fe N C catalyst consists of atomic Fe-N x sites exclusively. • Optimized catalyst delivers excellent ORR activity in acidic and alkaline media. Nitrogen-doped porous carbons containing atomically dispersed iron are prime candidates for substituting platinum-based catalysts for oxygen reduction reaction (ORR) in fuel cells. These carbon catalysts are classically synthesized via complicated routes involving multiple heat-treatment steps to form the desired Fe-N x sites. We herein developed a highly active Fe N C catalyst comprising of exclusive Fe-N x sites by a simplified solid-state synthesis protocol involving only a single heat-treatment. Imidazole is pyrolyzed in the presence of an inorganic salt-melt resulting in highly porous carbon sheets decorated with abundant Fe-N x centers, which yielded a high density of electrochemically accessible active sites (1.36 × 1019 sites g−1) as determined by the in situ nitrite stripping technique. The optimized catalyst delivered a remarkable ORR activity with a half-wave potential (E 1/2) of 0.905 V RHE in alkaline electrolyte surpassing the benchmark Pt catalyst by 55 mV. In acidic electrolyte, an E 1/2 of 0.760 V RHE is achieved at a low loading level (0.29 mg cm−2). In PEMFC tests, a current density of 2.3 mA cm−2 is achieved at 0.90 V iR-free under H 2 –O 2 conditions, reflecting high kinetic activity of the optimized catalyst. [ABSTRACT FROM AUTHOR]

Summary: The exploitation of high efficiency non‐precious electrocatalysts for oxygen reduction reaction (ORR) is of great significance for large‐scale commercialization of next‐generation fuel cells. Herein, we report the synthesis of conjugated polymers (CP) based on poly(o‐phenylenediamine) as a nitrogen‐containing precursor for preparation of Co‐ and FeCl3‐doped N‐rich carbon for ORR (abbreviated as Co‐OPD and FeCl3‐OPD). Based on their high specific surface, excellent porosity and large pyridine nitrogen content, the as‐synthesized FeCl3‐OPD, which is prepared at a pyrolysis temperature of 800°C (FeCl3‐OPD‐800), exhibits highest catalytic activity among the resulting electrocatalysts, that is, it possesses a largest half‐wave potential of 0.854 V (≈20 mV more positive than Pt/C), a high diffusion limiting current density of 3.95 mA cm−2 and a biased 4e− reaction pathway. In addition, this catalyst also discloses an excellent methanol tolerance and better durability than the commercial Pt/C. Taking advantage of their high ORR activity as well as simple fabrication which makes it possible using inexpensive FeCl3 as both catalysts for CP precursors and metal dopant for FeCl3‐OPD only by a one‐step pyrolysis, thus such FeCl3‐OPD may hold great potentials as promising alternative of precious metal catalysts for next generation fuel cells. [ABSTRACT FROM AUTHOR]

An Fe/N/C catalyst derived from the pyrolysis of metal–organic frameworks, for example, a zeolitic‐imidazolate‐framework‐8 (ZIF‐8), has been regarded as one of the most promising non‐precious metal catalysts toward oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). However, its ORR mass activity is still much inferior to that of Pt, partly because of the lack of general and efficient synthetic strategies. Herein, a general carboxylate‐assisted strategy that dramatically enhances the ORR mass activity of ZIF‐derived Fe/N/C catalysts is reported. The carboxylate is found to promote the formation of Fe/N/C catalysts with denser accessible active sites and entangled carbon nanotubes, as well as a higher mesoporosity. These structural advantages make the carboxylate‐assisted Fe/N/C catalysts show a 2–10 fold higher ORR mass activity than the common carboxylate‐free one in various cases. When applied in H2–O2 PEMFCs, the active acetate‐assisted Fe/N/C catalyst generates a peak power density of 1.33 W cm−2, a new record of peak power density for a H2–O2 PEMFC with non‐Pt ORR catalysts. [ABSTRACT FROM AUTHOR]

The metal-nitrogen-carbon (M-N-C) type oxygen reduction reaction (ORR) catalysts are promising for hydroxide exchange membrane fuel cells, but catalysts with further improved performance are challenging. Here, we report the efficient improvement of the ORR activity of M-N-C catalysts by employing highly polarizable metal cation Ag+. Ag, Fe single atomic sites embedded in concave nitrogen doped carbon (Ag 1 Fe 1 /CNC) is successfully synthesized and shows high performance towards ORR, indicating by both the ultra-high half-wave potential of 0.917 V and membrane electrolyte assembly performance of peak power density up to 1.26 W cm−2. The binding energy of the ORR intermediates on the highly polarizable Ag site in Ag 1 Fe 1 /CNC was significantly tuned by the adjacent Fe site by more than 0.2 eV, and thus leading to a low theoretical ORR overpotential of only 0.398 V. The employment of the highly polarizable metal cation brings a novel and efficient approach to construct highly active catalysts. [Display omitted] • High performance oxygen reduction reaction catalyst Ag 1 Fe 1 /CNC is synthesized. • The highly polarizable Ag site shows ultra-high catalytic activity. • The Ag sites are significantly affect by the adjacent metals. • High membrane electrolyte assembly performance is achieved by using Ag 1 Fe 1 /CNC. [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]

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 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]

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]

While high cost and lack of long‐term stability of Pt‐based catalysts have been impeding their practical application in oxygen reduction reaction (ORR) in fuel cell technologies, iron and nitrogen codoped carbons (Fe–N–C) are appearing to be stable but unfortunately less‐active catalysts in acidic electrolyte. Herein, an in situ surfactant‐free Pt deposition approach to fabricate Pt nanoparticles (NPs) onto well‐designed Fe–N–C nanostructures for producing highly performing Pt/Fe–N–C catalyst for ORR in acidic electrolyte is reported. Physical and electrochemical characterizations uncovered that electron transfer from Fe–N–C to their supported Pt NPs would weaken the adsorption of O2 on the Pt surface, therefore improving the intrinsic activity of Pt for ORR. On optimizing the Pt loading, the intrinsic and mass‐specific activity data of Pt in Pt/Fe–N–C are maximized at ≈0.93 mA cm−2 and 0.46 A mg−1‐Pt, respectively, much higher than those for commercial Pt/C (0.21 mA cm−2, 0.19 A mg−1‐Pt). The Pt/Fe–N–C catalyst also shows an intriguing long‐term stability during the accelerated durability test. A new avenue for taking the advantages of Pt and non‐noble metal ORR catalysts is pointed for achieving much better ones to accomplish ORR in acidic electrolyte. [ABSTRACT FROM AUTHOR]

Ordered mesoporous carbon (OMC) supported Pt catalysts were prepared by different loading techniques, in order to be used in the catalysis of oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells. OMC was synthesized by an organic-inorganic self assembly route using Pluronic F127 as surface directing agent, resorcinol-formaldehyde as carbon source and tetraethyl ortosilicate (TEOS) as silica source. Pt loading was achieved by three different approaches; one pot in situ synthesis, wet impregnation and surface-modified wet impregnation. Nitrogen adsorption studies showed slight reductions in surface areas, which can be attributed to partial losses of micropore volumes. The XRD and TEM analysis revealed a better metal distribution and smaller particle size in the surface-modified sample with a mean Pt particle size of 3.83 nm. The modified sample also gave the most promising performance among the catalysts with a maximum power density of 73 mW cm−2, which was very close to the commercial Pt/C catalyst. [ABSTRACT FROM AUTHOR]

Carbon‐supported precious metal single‐atom catalysts (PM SACs) have shown promising application in proton exchange membrane fuel cells (PEMFCs). However, the coordination principle of the active site, consisting of one PM atom and several coordinating anions, is still unclear for PM SACs. Here, a sequential coordination method is developed to dope a large amount of PM atoms (Ir, Rh, Pt and Pd) into a zeolite imidazolate framework (ZIF), which are further pyrolyzed into nitrogen‐coordinated PM SACs. The PM loadings are as high as 1.2–4.5 wt%, achieving the highest PM loadings in ZIF‐derived SACs to date. In the acidic half‐cell, Ir1‐N/C and Rh1‐N/C exhibit much higher oxygen reduction reaction (ORR) activities than nanoparticle catalysts Ir/C and Rh/C. In the contrast, the activities of Pd1‐N/C and Pt1‐N/C are considerably lower than Pd/C and Pt/C. Density function theory (DFT) calculations reveal that the ORR activity of PM SAC depends on the match between the OH* adsorption on PM and the electronegativity of coordinating anions, and the stronger OH* adsorption is, the higher electronegativity is needed for the coordinating anions. PEMFC tests confirm the active‐site coordination principle and show the extremely high atomic efficiency of Ir1‐N/C. The revealed principle provides guidance for designing future PM SACs for PEMFCs. [ABSTRACT FROM AUTHOR]

Fuel cells are highly attractive for direct chemical‐to‐electrical energy conversion and represent the ultimate mobile power supply solution. However, presently, fuel cells are limited by the sluggish kinetics of the cathodic oxygen reduction reaction (ORR), which requires the use of Pt as a catalyst, thus significantly increasing the overall cost of the cells. Recently, nonprecious metal single‐atom catalysts (SACs) with high ORR activity under both acidic and alkaline conditions have been recognized as promising cost‐effective alternatives to replace Pt in fuel cells. Considerable efforts have been devoted to further improving the ORR activity of SACs, including tailoring the coordination structure of the metal centers, enriching the concentration of the metal centers, and engineering the electronic structure and porosity of the substrate. Herein, a brief introduction to fuel cells and fundamentals of the ORR parameters of SACs and the origin of their high activity is provided, followed by a detailed review of the recently developed strategies used to optimize the ORR activity of SACs in both rotating disk electrode and membrane electrode assembly tests. Remarks and perspectives on the remaining challenges and future directions of SACs for the development of commercial fuel cells are also presented. [ABSTRACT FROM AUTHOR]

As an alternative for platinum‐based electrocatalysts, the development of non‐precious metal catalysts for oxygen reduction reaction (ORR) is highly desirable for fuel cell applications. In this paper, we propose a facile preparation method for a B, N‐codoped Cu–N/B–C nanomaterial as an efficient electrocatalyst for ORR in alkaline electrolytes. One‐step heat treatment of cyanamide/melamine, boric acid, and cupric chloride loaded on carbon black produces a Cu–N/B–C composite with a high specific surface area. The Cu–N/B–C‐800 composite pyrolyzed at 800 °C has the best ORR performance among all tested composites. Cu–N/B–C‐800 saw an ORR onset potential at 0.95 V and a half‐wave potential (E1/2) at 0.84 V vs. reversible hydrogen electrode (RHE) in 0.1 M KOH solution, which is comparable to the commercial 20 wt% Pt/C catalyst. Moreover, Cu–N/B–C‐800 has a small negatively shifted E1/2 value (−8.0 mV) under the accelerated‐durability test condition, demonstrating superior stability and higher tolerance to the methanol‐crossover effect compared with the Pt/C catalyst. Furthermore, the anion exchange membrane fuel cell (AEMFC) loaded with Cu–N/B–C‐800 as the cathode catalyst has an open cell voltage of 0.85 V and a peak power density of 80 mW/cm2 at 60 °C without backpressure, which is in the list of optimal non‐precious metal catalysts for ORR in AEMFC. [ABSTRACT FROM AUTHOR]

Exploring efficient and durable non-precious metal catalysts for oxygen reduction reaction (ORR) has long been pursued in the field of metal-air batteries, fuel cells, and solar cells. Rational design and controllable synthesis of desirable catalysts are still a great challenge. In this work, a novel approach is developed to tune the morphologies and structures of Fe–N–C catalysts in combination with the dual nitrogen-containing carbon precursors and the gas-foaming agent. The tailored Fe–N 1 /N 2 –C-A catalyst presents gauze-like porous nanosheets with uniformly dispersed tiny nanoparticles. Such architectures exhibit abundant Fe-N x active sites and high-exposure surfaces. The Fe–N 1 /N 2 –C-A catalyst shows extremely high half-wave potential (E 1/2 , 0.916 V vs. RHE) and large limiting current density (6.3 mA cm−2), far beyond 20 wt% Pt/C catalyst for ORR. This work provides a facile morphological and structural regulation to increase the number and exposure of Fe-N x active sites. The tailored Fe–N–C catalyst presents plentiful Fe-N x active sites and highly exposed active surfaces, resulting in an ultra-high ORR activity far beyond the 20 wt% Pt/C catalyst. Image 1 • A novel approach is explored to tune morphology and structure of Fe–N–C catalyst. • The tailored catalyst presents abundant active sites and high exposure surfaces. • The catalyst shows ultrahigh ORR activity, far beyond the commercial Pt/C. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) is a core reaction of fuel cell and metal-air cell. In recent years, it has been a hot topic to study non-precious metal catalysts for ORR. Herein, we have used waste wine mash-derived carbon, melamine and ferric chloride to prepare a Fe- and N- co-doped carbon catalyst. The specific surface area of the catalyst is up to 1066.6 m2 g−1. And its wave potential is 15 mV higher than that of commercial Pt/C catalyst. The ORR on our catalyst followed a four-electron pathway; and it has high stability and high impressive immunity to methanol. After continuous oxygen reduction of 30,000s, the retention rate is 90%. • A N- and Fe-co-doped carbon material is prepared by waste wine mash. • ORR half wave potential of WA-Fe-N is 15 mV higher than that of the commercial 40% Pt/C. • N- and Fe-co-doped and activation treatments improve the electrocatalyst properties. • WA-Fe-N is a new type of low cost ORR catalyst for fuel cell and metal-air cell. [ABSTRACT FROM AUTHOR]

Designing an efficient and stable non-precious metal cathode catalyst is essential to reduce fuel cell cost and promote fuel cell commercialization. Herein, ZIF-67 and carbon powder are rapidly heated using a transient Joule heat device to pyrolyze ZIF-67 to form a CoO/N/C nanocatalysts. The prepared CoO/N/C-90 is comprised of 3–4 nm CoO nanoparticles loaded on a carbon substrate. In alkaline medium the Tafel slope of CoO/N/C-90 is 50 mV dec−1, and a half-wave potential (E 1/2) of 0.82 V towards oxygen reduction reaction (ORR). The E 1/2 only experiences a negative shift of 4 mV after 40,000 cyclic voltammetry (CV) cycles, demonstrating excellent catalytic reaction kinetics and durability. The CoO/N/C-90 is assembled into direct borohydride fuel cells (DBFC) as a cathode, achieving a maximum power density (P max) of 526 mW cm−2 at 60 °C. This work indicates that the CoO/N/C-90 is an efficient and stable non-precious metal catalyst for DBFCs. [Display omitted] • CoO/N/C nanoparticle with a size of 3–4 nm is prepared by CTS method. • CoO/N/C exhibits superior stability and highly electrochemically active area. • A DBFC with maximum power density of 526 mW cm−2 is achieved at 60 °C. [ABSTRACT FROM AUTHOR]

[Display omitted] • Si,N-MWCNT catalyst was prepared by varying ratios of SiPcCl 2 and MWCNT and synthesis temperatures. • The half-wave potential of the best catalyst was 860 mV (vs RHE). • XPS and TEM confirmed the successful doping of Si and N into the carbon matrix. The development of highly efficient and cost effective non-precious metal (NPM) catalysts for fuel cells and metal-air batteries is challenging but of great significance. Although the research and development of non-noble metal and non-metal carbon catalysts for the oxygen reduction reaction (ORR) has gained a lot of attention recently, the electrocatalytic activity of tetravalent metalloids is a less investigated topic. Herein, an effective ORR catalyst based on silica and nitrogen co-doped multi-walled carbon nanotubes (Si,N-MWCNTs) was synthesized via a simple one-pot pyrolysis. The Si,N-MWCNTs catalyst demonstrated exceptional electrocatalytic activity towards the ORR in 0.1 M KOH, with a half-wave potential (E 1/2) of 860 mV (vs. RHE). Furthermore, Si,N-MWCNTs displayed apparent stability and excellent tolerance to methanol compared to the commercially available platinum catalyst. Physical characterization was carried out by employing X-ray photoelectron spectroscopy and transmission electron microscopy, which confirmed the integration of both silicon and nitrogen into the carbon structure. These results clearly shed light on the significance of further study on tetravalent metalloids as cost effective and easily available dopants for the preparation of electrocatalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • A comprehensive overview of atomically dispersed M−N−C catalysts for ORR. • Focus on active site engineering to improve activity and stability in fuel cells and Zn-air batteries. • Future directions of developing advanced M−N−C catalysts for ORR are outlined. Atomically dispersed metal-nitrogen-carbon (M−N−C) oxygen reduction reaction (ORR) catalysts have been proven as one of the most promising non-precious metal catalysts. In this review, we summarize recent advances in the active site engineering toward M−N−C catalysts for ORR, which focuses on modulating coordination environment of active sites to enhance intrinsic activity, such as coordination structures, heteroatomic doping M−N−C, dual-atom sites, coupled catalytic sites, and defective M−N−C. Moreover, the strategies for increasing the density and utilization of active sites are discussed, including chelation, stepwise atom doping, spatial confinement, surface exposed M−N x sites, and porous structure optimization. Thereafter, the performance decline mechanisms are introduced and the strategies for improving stability are systematically analyzed by regulating the structure of the active center and carbon support. Finally, we also proposed the future perspectives of M−N−C catalysts. This review aims to provide some guidelines towards synthesis of M−N−C catalysts for fuel cells and Zn-air batteries. [ABSTRACT FROM AUTHOR]

[Display omitted] • Unitized fuel cells and their operation mechanisms are introduced. • Oxygen reduction and oxygen evolution pathways in alkaline media are explained. • Transition metal oxides for catalysis of oxygen electrode reactions are reviewed. • Systematic comparison of bifunctional ORR/OER performance of TMOs is given. Among many alternatives to fossil fuel-based energy systems, one of the most promising is based on hydrogen energy and its production and use in unitized regenerative fuel cells as the primary energy conversion devices. However, there are some setbacks and challenges when designing suitable and efficient electrocatalysts for these devices. The most effective and durable catalysts are based on platinum–group metals, with low abundance and unbearably high prices. Many attempts were undertaken to overcome this setback by designing catalysts suitable for massive commercial use. This review paper focuses on recent advances in developing bifunctional catalysts for oxygen reduction and oxygen evolution catalysis in alkaline media, based on abundant transition metal oxides (TMOs): MnO 2 , NiO, and TiO 2. The problem of unifying parameters to compare the effectiveness of different electrocatalysts is emphasized. This review discusses the most promising alternative bifunctional electrocatalysts by comparing the performance of TMOs with some precious metal catalysts used as benchmarks. [ABSTRACT FROM AUTHOR]

Non-precious metal electrocatalysts (NPMCs) are a promising alternative to platinum-based catalysts towards the large-scale commercial application of hydrogen fuel cells and metal-air batteries. However, hazardous chemicals or high-temperature pyrolysis are generally involved in the synthesis of these highly-active NPMCs, leading to environmental and safety issues, particularly in scaling up. Exploration of low-cost and straightforward strategies to fabricate high-performance catalysts for ORR are urgently needed. Herein, we report a simple approach to fabricate a new class of the NPMCs by immobilizing iron phthalocyanine (FePc) into a surface of nitrogen-doped electrochemical exfoliated graphene (N-GP950). We highlight that at optimum content of 33 wt% FePc in the composite (FePc-33/N-GP950), the ORR performance significantly improves, exhibiting high current density at 0.8 V (5.0 mA cm−2), which is comparable to 4.0 mA cm−2 of commercial Pt/C in an alkaline media. The optimized sample also displays excellent long-term durability. The present study offers a low cost and straightforward strategy to fabricate inexpensive and durable ORR catalysts for practical hydrogen fuel cells applications and metal-air batteries. A simple and direct approach to fabricate highly active and stable FePc/graphene as a non-precious catalyst for oxygen reduction. Image 1 • A non-paralyzed approach to fabricate Fe–N–C catalyst for oxygen reduction. • FePc on N-doped graphene serves as non-precious metal catalyst. • The FePc/N-doped graphene exhibits excellent ORR activity and long-term durability. • FePc and N-doped graphene display strong π-π electronic interactions. [ABSTRACT FROM AUTHOR]

• A new precursor of Fe-dual pyridine coordination complexes was designed to synthesize Fe-N-C catalyst with hybrid structure of Fe-Nx moieties and exposed Fe carbides/nitrides nanodots. • This characteristic of hybrid active sites contributes the catalyst's excellent electrochemical performance and durability for ORR. • The new dual-pyridine based polymer could be extended to coordinate with various divalent metal ions for exploring non-precious metal ORR catalysts. Iron-nitrogen-carbon (Fe-N-C) materials as the most promising non-precious metal catalysts for oxygen reduction reaction (ORR) to replace Pt-based catalysts are in high demand for large scale application of fuel cells. However, their activity and durability are still critical issues. Development of Fe/N/C-containing precursors is a straightforward strategy for obtaining advanced Fe-N-C ORR catalysts to address these issues. Herein, we report an advanced Fe-N-C catalyst with a hybrid structure of single Fe atom sites (Fe-N x moieties) and exposed Fe carbides/nitrides nanodots with diameters <2 nm embedded onto highly graphitic N-doped carbon matrix. The catalyst is synthesized by pyrolysis of a new kind of Fe-dual pyridine coordinated complex as the precursor. This facile chemical route results in a non-conventional Fe-N-C catalyst with encapsulated Fe-metallic phase nanoparticles or Fe-Nx moieties. The catalyst exhibits excellent ORR activity and remarkable durability in both acidic and alkaline media. Its onset and half-wave potentials are 1.08 V and 0.88 V vs. (RHE) in 0.1 M KOH, respectively, and 0.95 V and 0.81 V vs. RHE, respectively, in 0.5 M H 2 SO 4. Furthermore, a single proton exchange membrane (PEM) fuel cell fabricated by our catalyst generates the output power of 0.65 W cm−2, which indicates great potential of our hybrid structured Fe-N-C catalyst for the practical application in fuel cells. [ABSTRACT FROM AUTHOR]

Abstract: Among various replacement candidates for precious‐metal catalysts towards the cathodic oxygen reduction reaction (ORR) of fuel cells, FeNC material has been perceived as the most promising one. Herein, we report an FeNC catalyst featured with highly uniform texture and high BET specific surface area. This catalyst was synthesized by a facile one‐step pyrolysis process accompanied by the sulfur‐induced in situ delamination effect, using glucose, trithiocyanuric acid and ferrous gluconate as precursors. The structural characteristics led to increased exposed active sites, which may be responsible for the dramatically improved activity of the final S‐doped FeNC catalyst with elevated half‐wave potentials in both acid (0.76 V vs. 0.68 V) and alkaline (0.87 V vs. 0.84 V) media compared to the sulfur‐free control sample. [ABSTRACT FROM AUTHOR]

Developing low-cost and high-performance non-precious metal catalysts (NPMCs) for oxygen reduction reaction (ORR) is of critical importance for commercialization of fuel cells. Herein, we report a NPMC consisting of Fe 3 C nanoparticles encapsulated in mesoporous N-doped carbon (N-C), which is synthesized by a simple two-step strategy comprising pyrolysis of a mixture of MIL-100(Fe) and dicyandiamide under inert atmosphere, followed by treatment of the product with acidic solution to leach removable Fe 3 C species from the material. Fe 3 C@NC-800 (the material prepared at 800 °C) exhibits superior electrocatalytic activity, high durability and excellent methanol tolerance for ORR, with catalytic performance comparable to that of commercial Pt/C in both alkaline and acidic media. Fe 3 C@NC-800's excellent catalytic activity and stability in ORR are due to its large BET surface area, its large total pore volume, its nitrogen dopants and the cooperative effects between the reactive functionalities in it as well as its excellent conductivity. [ABSTRACT FROM AUTHOR]

Abstract: Replacement of rare‐ and noble‐metal catalysts with earth‐abundant, low‐cost, stable, and efficient metal‐free catalyst substitutes is highly desirable, but full of challenges for the oxygen reduction reaction (ORR). Herein, N, P co‐doped hollow carbon spheres (N,P‐HCS) are prepared through a simple pyrolysis method, using hollow carbon spheres (HCS), melamine, and phytic acid (PA) as the C, N, and P sources, respectively. Compared to the N‐doped HCS (N‐HCS) and P‐doped HCS (P‐HCS), the N, P co‐doped sample exhibited much higher ORR catalytic activity. Moreover, in comparison with commercial Pt/C, the as‐prepared N,P‐HCS showed comparable ORR activity, but stronger endurance to methanol and higher durability in alkaline solution. The high performance of N,P‐HCS can be primarily ascribed to the large surface area, high conductivity, porous carbon structure, and high content of heteroatoms (N and P). Considering the excellent catalytic activity and durability, after further structural optimization, N,P‐HCS could be a promising metal‐free catalyst candidate for the ORR in fuel cells. [ABSTRACT FROM AUTHOR]

The development of highly active and durable nonprecious metal catalysts that can replace expensive Pt-based catalysts for the oxygen reduction reaction (ORR) is of pivotal importance in polymer electrolyte membrane fuel cells. In this line of research, metal and nitrogen codoped carbon (M-N/C) catalysts have emerged as the most promising alternatives to Pt-based catalysts. This review provides an overview of recently developed synthetic strategies for the preparation of M-N/C catalysts to enhance the catalytic activity of the ORR. We present five major strategies, namely the use of metal-organic frameworks as hosts or precursors, the use of sacrificial templates, the addition of heteroelements, the preferential generation of active sites, and a biomimetic approach. For each strategy, the advantages capable of boosting catalytic activity in the ORR are summarized, and notable examples and their catalytic performances are presented. The ORR activities and measurement conditions of high-performing M-N/C catalysts are also tabulated. Finally, we summarize this review with some suggestions for future studies. [ABSTRACT FROM AUTHOR]

A non-noble metal Fe/N/C catalyst is prepared by pyrolyzing the ball-milled mixture of graphitized carbon ribbon, iron precursor, and nitrogen precursor in ammonia. The Fe/N/C catalyst shows high ORR activity in alkaline solution, together with much improved stability compared with Pt/C catalyst. In the catalyst, FeN particles are covered by graphitic carbon layers. The activity is proposed to originate from the FeN and Fe/N/C sites. The stability is explained by the protecting effect of the carbon layers surrounding the FeN particles. The ORR mechanism on the Fe/N/C catalyst is proposed to be similar with Pt/C catalyst based on the Tafel plots. The Fe/N/C catalyst shows great potential in ORR in alkaline solution, while the performance in acid still needs improvement. [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]

Controlled synthesis of efficient core-shell non-precious metal catalysts for oxygen reduction reaction (ORR) is undoubtedly crucial but challenging for the extensive application of fuel cells and metal-air batteries. Herein, we prepared a core-shell structured Fe/FeC x nanoparticles and porous carbon composited catalyst (Fe/FeC x @NC) via a facile two-step heat treatment strategy. The Fe/FeC x @NC-800 −0.5 prepared with secondary anneal at 800 °C for 0.5 h exhibits superior ORR performance to the commercial Pt/C in terms of comparable onset potential, higher half-wave potential, and outstanding long-term durability in alkaline media. Through combining the physical and electrochemical characterizations of Fe/FeC x @NC- T − t with different anneal temperature and precursors, the outstanding ORR performance of Fe/FeC x @NC-800 − 0.5 is caused by the synergistic effect between Fe/FeC x core and enriched pyridinic N- and graphitic N-doped carbon shell as well as porous carbon with large specific surface area. The structure-activity relationship of core-shell structured Fe–N–C catalysts for ORR provides directions for the development of advanced nonprecious metals catalysts. [ABSTRACT FROM AUTHOR]

Developments in fuel cell technology have led to the design of new efficient electrocatalysts for the oxygen reduction reaction (ORR). In particular, metal-nitrogen-carbon (M-N-C) catalysts are promising alternatives to conventional noble metal ORR catalysts. Since the M-N-C catalyst has lower intrinsic activity than the noble metal catalyst, M-N-C catalysts should feature large surface areas, accessibility of active sites, short mass/charge transfer lengths, and surface permeability; these properties can lead to excellent catalytic activities. In addition, carbon-based materials, such as carbon nanotubes (CNTs), can be used to effectively improve the conductivity and stability of M-N-C catalysts. However, synthesizing carbon-based metal electrocatalysts with homogeneously distributed active sites and well-controlled structures remains challenging. In this study, we designed a carbon nanotube-encapsulated hollow Co-Fe-NC electrocatalyst by combining ultrasonic spray pyrolysis and a pseudomorphic transformation to a metal-organic framework, followed by carbonization. Spray pyrolysis formed hollow spheres without additional templates, requiring no further acidic leaching steps. Pseudomorphic transformation strategies can preserve the original morphology even after transforming the material to a metal-organic framework. The prepared CoFe-NC-CNT electrocatalyst exhibited high catalytic activity (half-wave potential of 0.924 V) and excellent 4-electron ORR selectivity. [Display omitted] • CoFe-NC-CNT was prepared by combining spray pyrolysis, MOF conversion, carbonization. • Hollow structure of CoFe-NC-CNT provides high electrochemical surface area. • CNTs in CoFe-NC-CNTs increase active site density by improving metal dispersion. • CoFe-NC-CNT exhibits excellent oxygen reduction activity and durability. [ABSTRACT FROM AUTHOR]

It is still a great challenge in preparing non-precious metal catalysts with high activity and long-term stability to substitute for precious metal catalysts for oxygen reduction reaction (ORR) in fuel cells. Herein, we report a novel and facile catalyst-N, S co-doped carbon spheres with highly dispersed CoO (CoO@NS-CSs), where biomass glucose spheres act as carbon precursor and H 2 S, NH 3 derived from the decomposition of thiourea not only provide N, S sources but also can etch carbon spheres to produce nanoporous structure. CoO@NS-CSs catalyst exhibits excellent ORR activity with a high onset potential of 0.946 V vs. RHE (reversible hydrogen electrode) and a half-wave potential of 0.821 V vs. RHE through a four-electron pathway in alkaline solution, which is comparable to commercial Pt/C catalyst (onset potential: 0.926 V vs. RHE, half-wave potential: 0.827 V vs. RHE). Furthermore, both the long-term stability and methanol-tolerance of CoO@NS-CSs catalyst are superior to those of commercial Pt/C catalyst. The excellent ORR performance of CoO@NS-CSs catalyst can be attributed to its micro-mesopore structure, high specific surface area (667 m 2 g −1 ), and highly dispersed CoO. This work manifests that the obtained CoO@NS-CSs catalyst is promising to be applied to fuel cells. [ABSTRACT FROM AUTHOR]

Carbon-supported binary and ternary nanocatalysts based on Pt, Me (Me = Ni, Co, Cu) and Au were synthesized by a “water in oil” microemulsion method and characterized by atomic absorption spectrometry or energy dispersive spectroscopy, X-ray photoelectron spectroscopy, thermogravimetry, transmission electron microscopy, X-ray diffraction, and electrochemical methods. A comparative study of the oxygen reduction reaction on binary and ternary nanocatalysts has been performed. The catalytic activity and the selectivity of the nanocatalysts towards the ORR have been determined in O 2 -saturated 0.1 M HClO 4 electrolyte. For binary systems, it was shown that the addition of Ni and Co to Pt led to an improvement of the catalytic activity, whereas the addition of Cu was detrimental for the ORR. The higher activities were achieved for atomic ratios close to that of Pt 3 Me defined compounds with Pt 7 Ni 3 /C displaying the highest activity. The modification of binary catalysts with gold led to increase the activity in the case of systems containing Co and Cu, and led to maintain the activity in the case of Ni-containing catalysts. The order of initial activity is: Pt 6 Ni 2 Au 2 /C > Pt 6 Co 2 Au 2 /C > Pt 6 Cu 2 Au 2 /C. Aging tests have been carried out on ternary catalysts, showing that a part of activity loss was due to gold segregation from the bulk to the surface of nanoparticles. After aging study for 1000 potential cycles between 0.6 and 1.05 V vs. RHE in O 2 -saturated electrolyte, the order of activity was: Pt 6 Cu 2 Au 2 /C > Pt 6 Co 2 Au 2 /C > Pt 6 Ni 2 Au 2 /C. [ABSTRACT FROM AUTHOR]