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Proton exchange membrane (PEM) fuel cells using Pt-based materials as electrocatalysts have achieved a decent performance, represented by the launched Toyota Mirai vehicle. The ideal PEM fuel cells consume stored pure hydrogen and air. However, SO2, as a primary air contaminant, may be fed along with air at the cathode, leading to Pt site deactivation. Therefore, it is important to improve the SO2 tolerance of catalysts for the stability of the oxygen reduction reaction (ORR). In this work, we develop the Pt/C-TiO2 catalyst against SO2 poisoning during ORR. Impressively, the hybrid Pt/C-TiO2 catalyst with 20 mass % TiO2 shows the best ORR and anti-toxic performance: the kinetic current density of ORR is 20.5% higher and the degradation rate after poisoning is 50% lower than Pt/C. The interaction between Pt and TiO2 as well as the abundant hydroxyl groups on the surface of TiO2 are both revealed to account for the accelerated removal of poisonous SO2 on Pt surfaces. [ABSTRACT FROM AUTHOR]

Transition metal (TM) single atomic catalysts (MSAC-N-C) derived from doped zeolite imidazolate frameworks (ZIF-8) are considered attractive oxygen reduction reaction (ORR) catalysts for fuel cells and metal-air batteries due to their advantages of high specific surface area, more active catalytic sites, adjustable pore size, and coordination topology features. This review provides an updated overview of the latest advances of MSAC-N-C catalysts derived from ZIF-8 precursors in ORR electrocatalysis. Particularly, some key challenges, including coordination environments regulation of catalysis center in MSAC-N-C, the active sites loading optimization and synergistic effects between TM nanoclusters/nanoparticles and the single atoms on MSAC-N-C catalysis activity, as well as their adaptability in various devices, are summarized for improving future development and application of MSAC-N-C catalysts. In addition, this review puts forward future research directions, making it play a better role in ORR catalysis for fuel cells and metal air batteries. [ABSTRACT FROM AUTHOR]

With the increasing consumption of the global energy demand, the electrochemical conversion and storage of new energy sources have drawn increasing attention in scientific research. As a promising energy conversion technology, fuel cells have attracted extensive attention in academia and industry due to their high energy conversion efficiency, environmental friendliness, high power density and wide range of fuels. Especially, oxygen reduction reaction (ORR) at the cathode is considered as an important electrode reaction in fuel cells. However, several factors, including slow kinetic process, extreme dependence on noble metal platinum, and rapid degradation of catalytic performance and durability after long-term operation, have severely restricted the large-scale promotion and application of these fuel cells commercialization. Therefore, the development of low-cost, highly active and stable catalysts is of great significance to promote the commercialization. Recently, Titanium nitride (TiN), as a highly durable support, has attracted extensive attention because of its superior properties of high conductivity, high melting point, high hardness, abrasion resistance and super anti-corrosion to acid and alkaline. When the advanced TiN material with favorable morphology and porous structure, high surface area and nanostructure is used as catalyst support, the electrocatalytic performance of Pt-based catalysts will be enhanced significantly due to the improved utilization of Pt, enhanced metal-support interactions, promoted mass/charge transfer as well as corrosion resistance. Interesting, TiN has also electronic properties similar to noble metal, and exhibits superior catalytic performance and durability toward ORR, thus obtaining widely attention in non-precious metal catalysts. Based on the above analysis, this review has summarized the current preparation method and synthesis mechanism of TiN materials, and elaborated the latest research progress including TiN, transition metal-doped TiN and its carbon-based composite materials as support or catalyst toward ORR. Based on the presented progress, we finally prospect the future application of TiN materials and directions for designing and developing practical fuel cell cathode catalysts. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) plays a key role in the field of fuel cells. Efficient electrocatalysts for the ORR are important for fuel cells commercialization. Pt and its alloys are main active materials for ORR. However, their high cost and susceptibility to time-dependent drift hinders their applicability. Satisfactory catalytic activity of nanostructured transition metal phthalocyanine complexes (MPc) in ORR through the occurrence of molecular catalysis on the surface of MPc indicates their potential as a replacement material for precious-metal catalysts. Problems of MPc are analyzed on the basis of chemical structure and microstructure characteristics used in oxygen reduction catalysis, and the strategy for controlling the structure of MPc is proposed to improve the catalytic performance of ORR in this review. [ABSTRACT FROM AUTHOR]

The development of new synthetic methods for methanol-tolerant catalysts with improved performance is of fundamental importance for the commercialization of fuel cells. Herein, we reported a facile displacement reaction-assisted synthesis of graphene-supported sub-nanometer Pt/Bi catalysts (Pt/Bi/rGO). Bismuth (0) nanoparticles produced by NH3BH3 reduction can be further dissolved into the ethylene glycol, implying Bi(0) has a strong interaction with the hydroxyl group. That is the key interaction between Bi(0) and the functional group on the rGO to form the ultra-small Bi/rGO catalyst. Furthermore, Pt clusters are obtained by the displacement between Bi(0) and HPtCl4 and are directly anchored to the rGO surface. The as-synthesized Pt/Bi/rGO catalyst exhibits high oxygen reduction mass activity and high tolerance to methanol poisoning. In the presence of 0.5 mol/L CH3OH, the initial potential and activity of ORR were almost unchanged, which demonstrated great potential in the application of direct methanol fuel cells. [ABSTRACT FROM AUTHOR]

Porous carbon materials are promising electrocatalysts for the oxygen reduction reaction (ORR). Their active sites, involving porosity and surface chemistry, are different from those of metal-doped carbons. The latter have been widely studied and are adapted to today's popular electrochemical devices, the rotating disk electrode being the most useful preliminary tool to evaluate their activity in ORR. However, porous carbon materials have been less explored, and experimental parameters need to be adjusted to achieve the best ORR performance. Therefore, in this study, the optimization of different key factors was investigated to evaluate their effect on the ORR performance of porous carbon electrocatalysts in alkaline medium. The parameters considered were: (i) the relevance of using RRDE or Koutecky-Levich equations for estimating the number of electrons transferred; (ii) the amount of ionomer (Nafion®); (iii) the carbon loading on the electrode; (iv) the carbon grinding method; and (v) the selection of the upper potential of ORR experiments. We conclude that an optimization of the experimental conditions should be done for each material studied, and we give important benchmarks for the appropriate evaluation of the catalytic activity in ORR of carbon-based catalysts. [Display omitted] [ABSTRACT FROM AUTHOR]

In the development of platinum group metal-free (PGM-free) catalysts like carbon-based catalysts for oxygen reduction reaction (ORR), one of the key factors is increasing active site density to achieve highly catalytic activity. This work proposes a facile method to effectively increase the ORR active site density by controlling the interfacial energy between the carbon support and heteroatomic precursor (FePc)-containing solution during solvothermal treatment. Decreasing the interfacial energy by purposefully choosing solvents with proper surface tension promotes the delivery of FePc into intrinsic pores of the carbon support and enhances Fe and N doping, resulting in an increase of ORR active site density by triple to 6.84 × 1018 sites g−1. The high density of active site helps to achieve higher onset potential (0.937 V vs. RHE) and half-wave potential (0.895 V) than the benchmark Pt/C in a same catalyst loading in 0.1 M KOH, as well as a higher power output (16.1 ± 0.3 mW cm−2) when used for air cathode catalyst in a membraneless direct formate fuel cell. These findings provide insights into synthesis of highly active carbon-based catalysts with high active site density and broaden the development for fuel cell application. [Display omitted] [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) is one of the fundamental reactions that occur on the cathode of fuel cells. The sluggish kinetics of ORR and the high cost of the conventionally used ORR electrocatalyst mandate extensive research towards the development of inexpensive, high‐performance and stable electrocatalysts. Various supported nanostructures of pristine noble metals and its alloys, transition metals/metal oxides (MOs), chalcogens/pnictogens doped metals/MOs, etc. have attracted great attention towards ORR in both acidic and alkaline electrolytes. This review primarily documents the recent advancements and challenges of supported nanomaterials with fascinating properties towards ORR. This study focuses on the use of carbon‐based materials as support. The significant factors like size, morphology, hetero‐atom doping, defects and interfaces (metal/metal, metal/oxide and metal/hydroxide) that can tailor ORR activity are portrayed elaborately. The electrochemical techniques and parameters that are adopted mainly during data collection and evaluation of ORR are also discussed. [ABSTRACT FROM AUTHOR]

Zeolitic Imidazolate Frameworks (ZIFs) derived nitrogen‐doped porous carbon (NPC) materials have been proposed as promising metal‐free electrocatalysts for oxygen reduction reactions (ORR). Herein, we report a strategy to control the morphology of ZIF‐8 and ZIF material‐derived NPC materials by the amount of L‐cysteine. The prepared NPC electrocatalysts exhibit different morphologies and ORR properties. The best of these catalysts exhibited a nanosheet‐like morphology with an onset potential of 0.95 V and a half‐wave potential of 0.87 V in alkaline media, which are comparable to those of commercial Pt/C (20 wt%) catalysts. In addition, this catalyst exhibited high stability and methanol resistance. This work not only reveals the effect of L‐cysteine amount on the growth process of ZIF, but also provides a strategy for designing various excellent catalysts in the fuel cell field. [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]

Exploring low‐cost and efficient oxygen reduction reaction (ORR) electrocatalysts is essential for clean energy conversion devices, such as fuel cells. Herein, a series of N, S co‐doped carbon‐based materials were synthesized by the one‐step pyrolysis route, using ZnCl2‐Zn(OH)2 as templates and solidago biomass as carbon and heteroatom sources. The double‐templated ZnCl2‐Zn(OH)2 system was employed to prepare the appealing carbon materials with hierarchical macro‐meso‐micro structure and high specific area. The invasive species of solidagos, as the precursors, have advantages of low cost and improved ecological diversification to some extent. The optimized catalyst (NSC‐Z2‐L) contains abundant hierarchical macro‐meso‐micro pores, high specific surface area (∼1581 m2 g−1) and N, S content (∼2.25 at.%). The special structure endows the catalyst with excellent ORR half‐wave potential (E1/2) of 0.85 V, 0.77 V and 0.76 V in the alkaline, acidic and neutral media, respectively, which are compatible with those of commercial Pt/C. The remarkable ORR performances are attributed to the hierarchically porous structure, high specific surface area and the synergistic effect of pyridinic‐N, graphitic‐N and C−S−C species. This work provides a valuable reference for achieving high‐performance ORR catalysts derived from low‐cost biomass materials. [ABSTRACT FROM AUTHOR]

Developing efficient and stable Pt‐based oxygen reduction reaction (ORR) catalysts is a way to promote the large‐scale application of fuel cells. Pt‐based alloy nanowires are promising ORR catalysts, but their application is hampered by activity loss caused by structural destruction during long‐term cycling. Herein, the preparation of ordered PtFeIr intermetallic nanowire catalysts with an average diameter of 2.6 nm and face‐centered tetragonal structure (fct‐PtFeIr/C) is reported. A silica‐protected strategy prevents the deformation of PtFeIr nanowires during the phase transition at high temperature. The as‐prepared fct‐PtFeIr/C exhibited superior mass activity for ORR (2.03 A mgPt−1) than disordered PtFeIr nanowires with face‐centered cubic structure (1.11 A mgPt−1) and commercial Pt/C (0.21 A mgPt−1). Importantly, the structure and electrochemical performance of fct‐PtFeIr/C were maintained after stability tests, showing the advantages of the ordered structure. [ABSTRACT FROM AUTHOR]

Developing efficient and stable Pt‐based oxygen reduction reaction (ORR) catalysts is a way to promote the large‐scale application of fuel cells. Pt‐based alloy nanowires are promising ORR catalysts, but their application is hampered by activity loss caused by structural destruction during long‐term cycling. Herein, the preparation of ordered PtFeIr intermetallic nanowire catalysts with an average diameter of 2.6 nm and face‐centered tetragonal structure (fct‐PtFeIr/C) is reported. A silica‐protected strategy prevents the deformation of PtFeIr nanowires during the phase transition at high temperature. The as‐prepared fct‐PtFeIr/C exhibited superior mass activity for ORR (2.03 A mgPt−1) than disordered PtFeIr nanowires with face‐centered cubic structure (1.11 A mgPt−1) and commercial Pt/C (0.21 A mgPt−1). Importantly, the structure and electrochemical performance of fct‐PtFeIr/C were maintained after stability tests, showing the advantages of the ordered structure. [ABSTRACT FROM AUTHOR]

At present, fuel cell is considered to be one of the most ideal application technologies of hydrogen energy. In order to develop fuel cells on a large scale and in a sustainable way, low platinum or non-platinum oxygen reduction catalyst has become a research hotspot. In this work, a kind of doped carbon-based catalyst MPFe 1 Cu 1 -850 is prepared by high temperature synthesis. The catalyst has an ultra-thin lamellar porous structure. In an acidic medium, the MPFe 1 Cu 1 -850 displays good oxygen reduction reaction (ORR) activity (ΔE 1/2 = 0.725 V). In addition, it shows better stability (91%) and higher methanol tolerance than that of commercial Pt/C catalyst. In our catalyst MPFe 1 Cu 1 -850, the contents of nitrogen, iron and copper are 10.31 at.%, 0.51 at.%, and 0.50 at.%, respectively. This work shows that high N content, and the proper ratio of iron to copper (Fe:Cu = 1:1), are conducive to the enhancement of ORR activity. • Design a Fe and Cu bimetallic load on N- and F co-doped carbon material. • The N content of the doped carbon catalyst, MPFe 1 Cu 1 , is up 10.31 at.%. • When the ratio of Fe: Cu = 1, the ORR activity of the catalyst is enhanced. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) is a vital electrochemical reaction for energy conversion that has fascinated the interest of materials researchers to promote active and cost-effective electrocatalysts with improved reaction kinetics. Numerous, researches have been undertaken to achieve the desired characteristic cathode materials to revolutionize energy conversion devices including fuel cells and metal-air batteries (where ORR occurs). More importantly, the evaluation of electrocatalyst efficiency for ORR using typical electrochemical experiments, data collection, and analysis must be performed systematically and uniformly. This review provides a systematic guide to assess the electrochemical efficiency because it includes standard and widely recognized experimental protocols for each electrochemical technique, as well as easy-to-follow lab procedures and a detailed analysis of essential kinetic ORR parameters with a theoretical framework. The major function of each electrode in cyclic voltammetry, hydrodynamic linear scan voltammetry with rotating disc electrodes, and electrochemical impedance spectroscopy for ORR were demonstrated, as well as the construction of a three-electrode electrochemical cell. By following standard protocols and experimental procedures, an aspiring electrochemist would be capable to enforce fundamental and advanced electrochemical techniques much efficiently in their understanding of ORR kinetics evaluation. [Display omitted] • This review provides crucial insights and information on electrochemistry of ORR. • Overview on electrochemical techniques, measurements and calculation procedures. • The desired experimental approach for evaluating ORR electrocatalyst efficiency. • A beginner's guide to perform cathodic ORR for fuel cell applications. [ABSTRACT FROM AUTHOR]

Herein, molybdenum disulfide nanoflakes decorated copper phthalocyanine microrods (CuPc-MoS 2) are synthesized via two step simple hydrothermal method. The as synthesized hybrid along with pure molybdenum disulfide (MoS 2) nanoflower and pure copper phthalocyanine (CuPc) microrods are well characterized by various techniques that confirm phase, morphology, elemental compositions etc. Next, electrocatalytic oxygen reduction reaction towards fuel cell is investigated in alkaline medium and obtained results proclaim that our CuPc-MoS 2 heterostructure outperforms the other two constituent materials. Efficient oxygen reduction is achieved following four electron pathway by CuPc-MoS 2 whereas partial reduction is done through two electron process by CuPc and MoS 2 separately. Long-time durability test reveals almost 97.6% retention after 8000s that eventually dictate us that CuPc-MoS 2 heterostructure can be the efficient cathode electrocatalyst for future generation fuel cell. [Display omitted] • Hierarchical growth of MoS 2 on CuPc rod is formed using low temperature facile route. • Enhanced electrocatalytic ORR of CuPc-MoS 2 is observed than bare counterparts. • Long-time durability test reveals almost 97.6% retention after 8000s for CuPc-MoS 2. • Structure activity relationship and active edge sites play role for enhanced ORR. [ABSTRACT FROM AUTHOR]

[Display omitted] • Oxygen reduction reaction (ORR) has been extensively used in fuel cells and rechargeable metal-air batteries. • This review details the latest developments in ORR electrocatalyst development. • These electrocatalysts specifically include platinum group metals (PGM), transition metals and carbon-based catalysts. • The preparation and ORR performance of various electrocatalysts are discussed in detail. • Speculation and discussion on the development prospects and challenges of ORR electrocatalysts. Oxygen reduction reaction (ORR) has gradually been in the limelight in recent years because of its great application potential for fuel cells and rechargeable metal-air batteries. Therefore, significant issues are increasingly focused on developing effective and economical ORR electrocatalysts. This review begins with the reaction mechanisms and theoretical calculations of ORR in acidic and alkaline media. The latest reports and challenges in ORR electrocatalysis are traced. Most importantly, the latest advances in the development of ORR electrocatalysts are presented in detail, including platinum group metal (PGM), transition metal, and carbon-based electrocatalysts with various nanostructures. Furthermore, the development prospects and challenges of ORR electrocatalysts are speculated and discussed. These insights would help to formulate the design guidelines for highly-active ORR electrocatalysts and affect future research to obtain new knowledge for ORR mechanisms. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) is a critical process for several electrocatalytic and photocatalytic devices. Poly(3,4‐ethylenedioxythiophene), PEDOT, is an efficient ORR catalyst, with hydrogen peroxide (H2O2) being the primary reaction product. Although H2O2 is a green fuel for batteries and fuel cells and used as an industrial oxidant, it is toxic for living systems. As such, its production should be limited when PEDOT films are used in bioelectronic devices. In this work, the ORR behavior of a series of electropolymerized PEDOT films is investigated. By varying the counterion (monomeric vs polymeric), including a hydroxyl‐terminated EDOT monomer in the polymer architecture, or adding a conductivity enhancer in the reaction mixture, the authors aim to understand the parameters governing the ORR properties. It is that the polymer's pristine doping level—influenced by counterion type and the presence of the conductivity enhancer—controls the ORR pathway in PEDOT films. High levels of intrinsic doping led to films with H2O2 as the major ORR product. This work suggests strategies for the design of conducting polymers with optimized performance for electrocatalytic applications and minimized production of harmful chemicals for bioelectronic devices. [ABSTRACT FROM AUTHOR]

In this work copper oxide nanoparticles (CuONPs) are prepared from precursor CuSO4.5H2O using plant leaves extract (PEE) of Eranthemum pulchellum(E. pulchellum).The synthesized CuONPs are characterized by ultraviolet visible (UV‐vis) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X‐ray diffraction (XRD) and transmission electron microscopy (TEM). CuONPs are distorted spherical in shape, with the sizes ranging from 5 to 17 nm. PEE and CuONPs are coated on glassy carbon (GC) electrode and abbreviated as GC/PEE and GC/CuONPs, respectively. The modified electrodes GC/PEE and GC/CuONPs are characterized with cyclic voltammetry (CV) techniques. The modified electrode GC/CuONPs exhibits good electrocatalytic activity for oxygen reduction reaction (ORR). GC/CuONPs also shows excellent operational stability up to 1000 CV cycles. [ABSTRACT FROM AUTHOR]

The structurally ordered PtM with surface coating layers strategy has drawn increasing attention. In this work, we synthesize a structurally ordered PtFe@NC-X-PDA catalyst modified with nitrogen-doped carbon coating layers by confined space annealing strategy. Compared with the current commercial Pt/C catalyst, the structurally ordered PtFe@NC-X-PDA catalyst shows better catalytic activity and stability. Especially, the mass activity and specific activity of the synthesized PtFe@NC-0.06-PDA sample with the optimized poly-dopamine feeding mass content (0.06 g) exhibit 9.95 and 11.53 times higher than that of commercial Pt/C catalyst. In addition, after 20,000 CV cycles, the PtFe@NC-0.06-PDA sample achieves the minimum activity loss (7%). The PtFe alloy catalyst with the different thickness NC shell (PtFe@NC-X-PDA) possesses the enhanced ORR activity and stability owing to the protection of nitrogen carbon shell (NC) and the strong electronic interaction of the ordered PtFe NPs. The improved ORR activity and stability of the structurally ordered PtFe@NC-X-PDA catalyst provide a promising direction for the development of fuel cells. Herein, we have successfully achieved precise modulation of the nitrogen doped carbon coating layers thickness in situ and simultaneously regulation the interfacial or chemical ordering energy at the atomic level that possess enhanced catalytic ORR activity and stability. [Display omitted] • A confined space annealing strategy of poly-dopamine was proposed to improve the performance of PtFe nanoparticles. • The level of alloy degree is turned by the poly-dopamine feeding mass content. • The protection from NC shell and ordered structure collectively guarantee the stability of the catalyst. • The PtFe@NC-0.06-PDA catalyst with suitable NC shell thickness possesses enhanced oxygen reduction performance. [ABSTRACT FROM AUTHOR]

We encapsulate large Pt shell/Ni core (PtNi) particles with thick and porous nitrogen-doped carbon (N–C) layers, and demonstrate that the thick N–C layers can protect the PtNi particles from dissolution and migration for an extremely long service life through both steric hindrance and chemical bond; in addition, the well mass transfer performance of the porous N–C, the thin Pt shell, and the promotion effects of N–C and Ni on Pt lead to excellent activity of the composite catalyst (N–C/PtNi). As a result, the N–C/PtNi keeps the high oxygen reduction reaction activity value of 962–1080 mA mg Pt −1 for 60,000 cyclic voltammetry (CV) cycles and still has a high activity of 265 mA mg Pt −1 even after 120,000 CV cycles. Moreover, the N–C/PtNi shows a max power density of 1.24 W cm−2 at cathodic loading of 0.1 mg Pt cm−2 in H 2 –O 2 fuel cell under 200 kPa absolute pressure of O 2 without performance decrease within 60,000 cycles. Other large noble metal-based particles are believed to gain ultrahigh stabilities and higher activities through performing the similar encapsulation. [Display omitted] 1. Porous N–C encapsulates large PtNi particle by steric hindrance and chemical bond. 2. Thick N–C layer encapsulation gives PtNi particles extreme catalytic stability. 3. Porous structure of thick N–C layer improves mass transfer and Pt activity. 4. Thin Pt shell and promotion effects of N–C and Ni on Pt lead to improved activity. 5. The max power density for H 2 –O 2 fuel cell keeps unchanged within 60k cycles. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) is a key step in the operation of fuel cells and metal air cells, which needs some economic and efficient catalysts to improve its reaction kinetics process. In this work, nitrogen-doped carbon (N-C) catalyst material was prepared by one-step high-temperature pyrolysis with biomass waste cotton stalk as carbon/nitrogen precursor material and urea as auxiliary nitrogen source. The effect of temperature on the structure and performance of the prepared N-C catalyst was investigated. The experimental results show that a small temperature change of 25°C will cause a significant change in the structure of N-C material. N-C-900 samples prepared at 900°C had a larger specific surface area of 620 m2 g−1, significantly improved graphitization degree and nitrogen content (7.30 at%) and showed significantly better ORR performance than other samples in alkaline medium. The ORR activity of N-C-900 sample is the best, indicated by the highest Eonset (0.92 V) and E1/2 (0.85 V) of ORR, which are positively shifted by 20 and 30 mV compared with commercial Pt/C. Its ORR initial potential and half-wave potential are similar to those of commercial Pt/C, and it shows better ORR stability and methanol resistance than Pt/C. [ABSTRACT FROM AUTHOR]

The exploration of non-Pt catalysts with high electrocatalytic activity and durability is especially important for cathodic oxygen reduction reaction (ORR) in fuel cell. Here, cobalt and nitrogen doped hollow carbon sphere-bamboo like carbon nanotube (Co/NHCS-BCNT) is prepared by using SiO 2 sphere as sacrificial template. Co nanoparticles are confined in the cavity and top end of the in-situ formed BCNT, which can not only avoid the agglomeration of Co nanoparticles but also inhibit corrosion in caustic electrolyte. The synergistic effect between NHCS and well-dispersed Co particles makes Co/NHCS-BCNT have superior catalytic activity toward ORR. The electrochemical surface area (ECSA) of Co/NHCS-BCNT is 222 cm2, which is higher than those of NHCS (164 cm2) and HCS (135 cm2). The onset potential and half-wave potential of Co/NHCS-BCNT are 0.941 V and 0.814 V, respectively, which are close to commercial Pt/C (0.949 V, 0.807 V). The Tafel slope of Co/NHCS-BCNT (63.8 mV dec-1) is lower than that of Pt/C (71.7 mV dec-1). In addition, Co/NHCS-BCNT shows excellent durability and fuel selectivity. [Display omitted] [ABSTRACT FROM AUTHOR]

Platinum-based catalysts remain the top choice for oxygen reduction reaction (ORR) in fuel cells. However, their activity and durability in the acidic medium are still under improvement. In this work, the Pt nanoclusters anchored the nitrogen-doped carbon nanotubes (Pt-NCNTs) have been synthesized by using a series process of pyrrole coating on the CNTs and subsequent pyrolysis to the chemical immersion reduction of Pt ions. The inner CNTs of Pt-NCNTs function as the nanowires offering a high-speed pathway for electron transport, and the Pt nanoclusters increases the active sites. The theoretical calculation demonstrates that the local structural defects and the uneven charge distribution induced by nitrogen-containing functional groups and porous structure are favorable to capture Pt ions for the nucleation of Pt nanoclusters. Compared with the commercial 40 wt% Pt/C (0.94 and 0.80 V), the Pt-NCNTs-1000 with Pt loading amount of 33.0 wt% owns the more positive onset potential and half-wave potential of 0.97 and 0.81 V in the sulfuric acid medium. Meanwhile, the strong attachment of Pt nanoclusters on the nitrogen-doped porous carbon layer results in a stable interface to effectively prevent the metallic species from migration and agglomeration during the electrode reactions. Therefore, the ORR current of Pt-NCNTs-1000 retained 84.3% of the initial value after 50000 s operation superior to the commercial Pt/C (64.6%). [Display omitted] • N-doped porous carbon layer coated CNT was used as support to enhance Pt deposition. • Micropores and nitrogen groups strongly anchor Pt nanoclusters deposited on NCNTs. • CNTs act as nanowires to promote charges transport of electrode reactions. • Pt-NCNTs has a good ORR activity and durability compared with commercial 40 wt% Pt/C. [ABSTRACT FROM AUTHOR]

[Display omitted] • HME was applied as an oxygen electrode of the AEM-URFCs. • Introducing 3 D CNT framework provided high ECSA of catalysts, electron transport, mass transport. • The HME_URFC exhibited superior round-trip efficiency of 55% at 20 mA cm−2 with enhanced durability and cyclability. Developing three-dimensional porous oxygen electrodes (OE) is crucial for enhancing round-trip efficiency (RTE) of anion-exchange membrane-based unitized regenerative fuel cells (AEM_URFCs). Herein, a novel OE design of AEM_URFCs is presented based on a hierarchical mesh electrode (HME) with a porous carbon nanotube (CNT) framework. The HME, featuring square-shaped macropores achieved by dispersing catalyst nanoparticles on the CNT framework enhances surface area, mass transport, and electron transport. Half-cell test demonstrated superior oxygen reduction reaction and oxygen evolution reaction activity compared to conventional electrodes. Moreover, the HME maintained stable ORR and OER activity during the stability test. In single-cell tests, the AEM_URFCs with the HME exhibited higher RTE (55% at 20 mA cm−2), surpassing the conventional electrode (52%). Furthermore, RTE was maintained at a remarkable 41% under ultrahigh current density (250 mA cm−2), which is unprecedented in the literature. The AEM_URFCs featuring the HME displayed superior cyclability over 5 cycles and durable performances under both fuel cell and water electrolysis modes. [ABSTRACT FROM AUTHOR]

• Resonance structure as substrate molecules are introduced to form highly ordered PtCo alloys. • Synthesis of PtM (Co, Fe, Ni) ordered alloys use the same low temperature heat treatment conditions. • The ordered PtCo shows efficient electrocatalytic performance. Platinum-based ordered alloys have excellent catalytic performance for the cathodic oxygen reduction reaction (ORR) in fuel cells. However, these alloys exhibit a lower degree of ordering and larger crystal grains after heat treatment. Herein, a series of cyanamide group molecules (cyanamide, dicyandiamide, melamine) was employed as substrates to modify Pt-based alloys by promoting the binding between metal ions, leading to the preparation of ∼ 4 nm PtM (M = Co, Fe, Ni) ordered alloys after heat treatment. Among them, the PtCo ordered alloy prepared using hydrolyzed cyanamide with a unique resonance structure exhibits a high degree of order (93.1 %), and its mass activity of 0.915 A mg Pt -1 at 0.9 V is superior to that of Pt/C. The theoretically calculated adsorption energies of these alloys demonstrate that the resonance structure of the cyanamide substrate is beneficial for alloy formation, thereby facilitating ordered alloy synthesis. [ABSTRACT FROM AUTHOR]

High-efficiency catalysts are required for the oxygen reduction reaction (ORR) in fuel cell applications. Herein, we present a novel hybrid material that is based on uniformly deposited nanoscale molybdenum phosphide (Mo x P y) nanoparticles on the structure of graphene nanolayers doped with phosphorus atoms (PG). With a positive onset potential of only −0.046 V and a half-wave potential value of roughly −0.17 V (vs. Ag/AgCl), the obtained hybrid showed good catalytic activity for ORR in 0.1 M KOH electrolyte. It also demonstrated remarkable durability for oxygen reduction reaction in 0.1 M KOH electrolyte when compared to state-of-the-art Pt/C material. The excellent ORR performance can be correlated to the development of a highly conducting microporous structure with highly active sites, which in turn encourages optimal adsorption of intermediates during the ORR process and thus enhances the catalytic process. This work can open a new path for the growth of promising highly efficient catalysts for affordable fuel cell applications. [Display omitted] • Uniform Mo x P y nanoparticles dispersed P-doped G was prepared by a facile route. • The hybrid offered high catalytic performance for ORR, close to Pt/C. • The synergistic effect from Mo x P y and P-doped Gr produced enhanced ORR performance. • The hybrid showed much better durability and methanol tolerance than Pt/C. [ABSTRACT FROM AUTHOR]

This study presents the preparation of tridoped Fe, N, S carbon-based catalysts using ZIF-8 as the main carbon source and iron(II)acetate, 1,10-phenanthroline, ammonia gas and thiourea as precursors for Fe, N and S elements. Thiourea was mixed via planetary ball-milling with a Fe–N–C catalyst prepared by inert gas pyrolysis, and different pyrolysis conditions were applied thereafter. The main goal of the work is to synthesise active non-precious metal electrocatalysts for oxygen reduction reaction (ORR). High electrocatalytic ORR activity in alkaline media was observed for the two materials obtained after thiourea addition and subsequent pyrolysis. Physico-chemical characterisation revealed successful S- and N-doping for all three catalysts with enhanced porosity for the two materials that were subjected to additional pyrolysis after the thiourea addition. The sulphur doping was highest for the FeNSC3 material that was subjected to a second pyrolysis in N 2 and a third pyrolysis in NH 3 , compared to the FeNSC2 material that was subjected to a single pyrolysis in NH 3 flow after thiourea addition. The ORR activity of FeNSC2 with half-wave potential of 0.88 V was slightly higher than that of FeNSC3, and the former was selected for evaluation as a cathode catalyst in an anion-exchange membrane fuel cell. [Display omitted] [ABSTRACT FROM AUTHOR]

The slow reaction rates observed in the Oxygen Reduction Reaction (ORR) pose a significant obstacle in advancing fuel cell technology. Consequently, ORR plays a pivotal role in determining the operational efficiency of fuel cell and energy storage systems. Accordingly, the synthesis of a cathodic electrocatalyst with high efficiency has become an attractive topic for researchers. In this empirical study, three trimetallic electrocatalysts are synthesized and electrochemically appraised. By introducing three lanthanides, namely Gadolinium (Gd), Samarium (Sm), and Europium (Eu), into CuFeZIF-8, new composites successfully are synthesized as Cu@FeLn (Eu, Sm, and Gd)-N-C. These functional materials find application in the context of the ORR and supercapacitor technologies. In order to enhance stability, control surface area, and prevent agglomeration during high-temperature pyrolysis, the silicon cover protection technique is employed. The primary objective in this investigation is to assess the influence of mSiO 2 coating on the electrochemical parameters of these electrocatalysts. To characterize the fabricated samples, seven characterization tests are utilized. Electrochemical measurements are conducted employing a three-electrode cell configuration within an alkaline environment. The results illustrated that the Cu@FeGd-N-C sample, with an onset potential of −0.043 V vs. Ag/AgCl, exhibited the best ORR performance. Also, the electron transfer number of Cu@FeSm-N-C was computed as 3.56. The half-wave potentials of Cu@FeSm-N-C, Cu@FeEu-N-C, and Cu@FeGd-N-C were found to be −0.34, −0.23, and −0.18 V vs. Ag/AgCl, respectively. A less negative half-wave potential typically suggests superior performance, signifying a lower overpotential requirement for the ORR process. The specific capacitance for Cu@FeGd-N-C electrode at 1 A/g was determined as 144.4 F g−1. The inclusion of lanthanides, Fe, and Cu into ZIF-8 is observed to notably improve both catalytic activity and electron transfer. Also, the outcomes showed that mesoporous silica-protected pyrolysis could be a useful strategy for improving the efficiency of energy conversion and energy storage equipment. [Display omitted] • By introducing three lanthanides into CuFeZIF-8, new composites are synthesized and evaluated. • To prevent irreversible fusion, the strategy of applying an mSiO2 coating is implemented. • The synthesized catalysts were used for two applications: energy conversion and storage. • The best ORR performance is associated with the Cu@FeGd-N-C sample, with an onset potential of −0.043 V vs. Ag/AgCl. • The Cu@FeGd-N-C electrode exhibited a specific capacitance of 144.4 F g−1 at a current density of 1 A/g. [ABSTRACT FROM AUTHOR]

Iron,nitrogen-codoped carbon (FeNC) has emerged as promising alternatives to precious metals for oxygen reduction reaction (ORR). Herein, we demonstrate that the ORR activity of FeNC can be markedly enhanced by the incorporation of adjacent Fe few-atom clusters (Fe AC), where the octahedral field of Fe AC boosts the splitting of the parallelogram field of FeN 4 , and facilitates the transition from high-spin (t 2g 3e g 2) Fe(III)N 4 to medium-spin (t 2g 5e g 1) Fe(II)N 4 and hence the interaction with the π* antibonding orbitals of oxygen. This leads to a remarkable ORR performance due to optimized desorption of the OH* intermediate on FeN 4 , with a half-wave potential of +0.80 in 0.1 M HClO 4 , in comparison to that with only FeN 4 single-atom moieties. In H 2 -O 2 fuel cell tests, a high peak power density of 0.80 W cm−2 is obtained. Results from this work highlight the significance of spin engineering in the manipulation and optimization of the ORR activity of single-atom catalysts. [Display omitted] • Pyrolytic treatment of Fe-doped ZIF-8 and C 3 N 4 at controlled feed ratios. • Formation of Fe few-atom clusters (Fe AC) adjacent to Fe single atom centers (Fe SA). • Transition from high-spin Fe(III)N 4 to medium-spin Fe(II)N 4 by Fe AC. • Enhanced ORR/PEMFC performance by optimized desorption of OH* on FeN 4. [ABSTRACT FROM AUTHOR]

• A catalyst consisting of Pt 2 Ni 4 clusters adjacent to Pd nanoparticles on Ni-hydroxide is developed. • It surpasses the commercial J.M.-Pt/C catalyst by ∼75 times in alkaline ORR. • It shows progressively increasing mass activity up to 15 K stability test cycles. The oxygen reduction reaction (ORR) is a key "showstopper" for the commercial viability of alkaline fuel cells (AFCs). In this study, we developed a ternary nanocatalyst (NC) coloaded with Pt 2 Ni 4 atomic clusters and palladium (Pd) nanoparticles (NPs) on oxygen vacancies (OVs) enriched nickel hydroxide-support (henceforth denoted as NiPP). This material outperforms the commercial J.M.-Pt/C (20 wt%) catalyst by ∼75 and ∼38 times with exceptionally high mass activities (MA)s of 5050.3 mAmg Pt -1 and 952.3 mAmg Pt -1 at 0.85 V and 0.90 V vs RHE, respectively, in alkaline ORR (0.1 M KOH). The high structural reliability of the Pt 2 Ni 4 endows the NiPP NC with outstanding durability, where it achieves an optimum MA of 5755.9 mAmg Pt -1 after 10 K cycles in an accelerated durability test (ADT) and retains the original performance up to 15 K cycles. Moreover, NiPP delivers an outstanding power density (339.1.4 mW cm−2) and short circuit current density (910.8 mA cm−2), which exceeds the commercial J.M.-Pt/C (174.9 mW cm−2 and 720.4 mA cm−2) when serving as the cathodic catalyst in an AFC. The results of physical characterizations, electrochemical analysis and in-situ XAS analysis suggest that the exceptional performance is originated from the potential synergism between the neighbouring reaction sites of Pt 2 Ni 4 (OV in Ni(OH) x and Pd NPs). During ORR, the Pt 2 Ni 4 atomic clusters and OVs boost the O 2 splitting, while the adjacent Pd NPs promote the subsequent relocation of OH– ions. The obtained results provide the potential design strategies for the atomic-scale surface engineering of advanced ORR NCs in alkaline fuel cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • Interfacial electronic structure of metal-support is regulated by heteratom doping. • N/S doping promotes the oxidation of Pt-Lewis acid center to a higher valence state. • S atom re-doping causes the d-band center of Pt to shift upward towards Fermi level. • High content of Ptx+ sites enhance the binding of Pt-Lewis acid to *OOH intermediate. • PtNi@N,S-HMCS with more Pt-Lewis acid shows high ORR activity and 4e- selectivity. Elucidating the mechanism of metal-support interface domain regulation is crucial for designing efficient fuel cell electrocatalysts. Herein, we propose an emerging strategy to enhance oxygen reduction reaction (ORR) activity and selectivity by regulating the Lewis alkalinity of carbon support to adjust the Lewis acidity of metal sites. The experimental results and density functional theory (DFT) simulations show that the introduction of N/S atoms into the carbon support structure will break the charge balance of the carbon skeleton and effectively regulate the charge distribution in the Pt-carbon interface domain, thus promoting the oxidation of the Lewis acid Pt atoms to a higher valence state Ptx+, so as to optimize the adsorption energy of oxygen-containing intermediates. Moreover, Bader charge analysis also verifies that N,S-HMCS, as a Lewis base, can receive more electrons from the Pt sites of Lewis acid, and the electron loss at Pt sites caused by N,S-HMCS strengthens interfacial electron effect. Meanwhile the strong electron adsorption ability of N/S atoms causes the d-band center of Pt atom orbital to shift upward to the Fermi level, which strengthens the binding of metal Lewis acid Pt sites with *OOH intermediates, and improves the 4-electron transfer mechanism. This research reveals the direct role of Lewis acid sites in ORR of fuel cell cathode, and provides a feasible way to guide the design of electrocatalysts with Lewis acid/base double centers. [ABSTRACT FROM AUTHOR]

In this work, we report the high-temperature confinement synthesis of N-doped graphitic carbon shells encapsulated PtCo nanoparticles embedded into porous Ketjenblack (KB) carbon architectures (PtCo@NGCS/KB) for fuel cells by a facile ligand carbonization strategy. [Display omitted] • The confinement synthesis of PtCo@NGCS/KB-800 is achieved by ligand carbonization. • Carbon shell reconstruction effectively improves the accessibility of surface sites. • PtCo@NGCS/KB-800 exhibits more outstanding ORR performance than commercial Pt/C. • PtCo and NGCS synergically account for the enhanced ORR performance. High-temperature reduction technology significantly improves the alloying process but inevitably causes the sintering of metal. Herein, we report the high-temperature confinement synthesis of PtCo nanoparticles encapsulated with N-doped graphitic carbon shells (NGCS) in porous Ketjenblack (KB) carbon architectures (PtCo@NGCS/KB) for fuel cells via ligand carbonization strategy. The optimal PtCo@NGCS/KB-800 exhibits outstanding mass and specific activities (840.2 mA/mg Pt and 0.94 mA/cm2, respectively) for oxygen reduction reaction (ORR), and possesses excellent stability with a smaller peak power density loss rate of 7.1 % than commercial benchmark Pt/C (23.7 %) after the accelerated durability test (ADT) in practical H 2 /air fuel cells. Experimental and theoretical investigations reveal that carbon shell reconstruction improves the accessibility of surface sites, and PtCo and NGCS synergically promote the enhancement of ORR performance. The NGCS encapsulation significantly reduces the energy level of the d-band center of Pt, promotes the desorption of intermediates, and lowers the reaction barrier for efficient ORR. [ABSTRACT FROM AUTHOR]

• The catalytic activity of a series of Fe-BC 3 NT has been theoretically explored in the ORR. • O 2 molecule can be directly dissociated on the Fe-BC 3 NT with 4e pathway. • It is reacting more favorable for the ER mechanism of OH* to convert into H 2 O. • The ORR reaction was found to be thermodynamically favorable in the Fe-BC 3 NT. A critical issue in enhancing the performance of polymer electrolyte membrane fuel cells (FCs) is the slow kinetics of the cathodic oxygen reduction reaction (ORR). The development of electrocatalysts with selectivity toward the four-electron (4e) pathway and high electrochemical activity to ORR reaction is important for fuel cell applications. Within the present study, it was found that boron carbide nanotube (BC 3 NT) is an encouraging ORR-EC based on density functional theory computations. In the pristine BC 3 NT, the neighboring B atoms with positive charges on the surface of the material surface were incapable of providing active sites for the dissociation of O. However, the ORR catalytic activity of BC 3 NT improved under the ligand effect due to the replacement of Fe atom, where there was a slight over-potential that was similar or lower than that of platinum (1 1 1), which demonstrated its superior ORR activity. The results suggest that BC-based materials are considered promising for ORR catalysis and for designing highly efficient ORR-ECs as alternatives to platinum-based catalysts. [ABSTRACT FROM AUTHOR]

Designing efficient and stable single-atom catalysts (SACs) for the oxygen reduction reaction (ORR) is essential to promote fuel cell commercialization. In this study, the Bayesian Regularization Neural Network (BRNN) has been used to determine the carbothermal shock (CTS) conditions for preparing high-loading Pt-Fe/C SACs. The BRNN model effectively identified a low reaction temperature of 283 °C for achieving high-loading (15 wt %) Pt-Fe/C SACs. Based on this model, we successfully synthesized Pt-Fe/C SACs with a metal mass content of 11.31 wt % using the CTS method. These ultrahigh content metal Pt-Fe/C SACs consisted of dispersed single atoms and foam-like atomic constructions, namely Pt-Fe/C atom foam catalysts (AFCs), rendered them promising candidates for electrocatalysis applications. The Pt-Fe/C AFCs exhibited good catalytic activity and durability toward ORR in alkaline conditions. The Pt-Fe/C AFCs were employed in a direct borohydride fuel cell (DBFC) as cathode catalyst, which resulted in a maximum power density of 214 mW cm−2 at 60 °C and demonstrated stable discharge for 40 h at room temperature. The electrocatalytic performance of the Pt-Fe/C AFCs surpassed that of low-loading Pt-Fe/C SACs and commercial Pt/C catalysts. The rapid ramp-up rate and the rapid cooling rate of the CTS process enabled the incorporation of high-loading Pt and Fe metal atoms into the graphitized carbon layer, resulting in an increased number of active sites of the Pt-Fe/C AFCs. This work provides an effective strategy for manufacturing efficient and stable SACs for practical applications in fuel cells. [Display omitted] • The Bayesian Regularization Neural Network is used to determine the CTS conditions. • Pt-Fe/C AFCs with metal content of 11.31 wt % is successfully synthesize by the CTS method. • The Pt-Fe/C AFCs exhibit good catalytic activity and durability towards ORR. • The DBFC using Pt-Fe/C AFCs cathode achieves a maximum power density of 214 mW cm−2. [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]

[Display omitted] • Comprehensive understanding on the effect of C-F bonding on ORR kinetics and mechanism is described. • Special focus on the superiority of F-C vs. N-C carbons towards stability of carbon support is detailed. • Excellent and highly stable catalysts have been noticed with F and F, N co-doped catalysts. • Possible directions of future research & developments on the F-doped catalysts are suggested. Doped carbon materials, particularly N-doped carbon catalysts, have drawn considerable attention in recent years as metal-free catalysts for oxygen reduction reactions (ORR) and as a carbon corrosive resistance support for Pt and non-Pt nanoparticles. While nitrogen-doped carbons (N-doped carbons) were once the standard, F-doped carbons (F-doped carbons) have recently overtaken their popularity. This is because F doping gives carbon materials unique properties that not only differ from the N-doped carbons but also significantly improves the ORR activity and especially the durability. Being the highest electronegative element of the periodic table, F-doping can efficiently modify the electronic band structure of the carbon materials favoring for ORR. The edge F doping to the carbon is found to improve carbon corrosion resistance more than any other heteroatom doped catalyst discovered previously, including N doped carbons, both in highly acidic, alkaline pH conditions and high oxidative potentials that exists in the fuel cell including start-up and shut-down conditions. In this review, the fundamental understanding of effect of F-doping/F co-doping on the electrocatalytic reduction of O 2 into H 2 O and OH− in acidic and alkaline pH conditions, effect of F doping on stability and durability of fuel cell catalysts, careful considerations/guidelines one needs to know before working with F doped carbons (F doping advantages vs. poisoning effect on Pt or M/F-C (M = transition metal) catalysts, are being reviewed systematically. Finally, several strategies for future research directions on F-doped carbons were proposed to bridge the gap between laboratory-scale assessment to commercial aspects. [ABSTRACT FROM AUTHOR]

[Display omitted] • MOF-PPy composites were synthesized in a one-pot reaction. • The CoFe-NC-PPy with single-atom of Fe and Co was successfully synthesized. • PPy served as secondary nitrogen sources for enhanced ORR activity. • The CoFe-NC-PPy showed excellent ORR activity and durability in alkaline media. • The AEMFC performance with CoFe-NC-PPy exhibited remarkable efficiency. Metal-nitrogen-doped carbon (M−N−C) catalysts have emerged as highly active noble-metal-free catalysts for oxygen reduction reactions (ORR) in anion-exchange membrane fuel cells (AEMFCs). However, the performance of existing M−N−C catalysts is limited by the inaccessibility of internal M−N x active sites and loss of nitrogen doping after the carbonization process. Here, a single-atom Co, Fe and N-doped porous carbon catalyst (CoFe-NC-PPy) were constructed using a complex of metal–organic frameworks (MOFs) and polypyrrole (PPy). As a new approach, we synthesized MOF and PPy composites by combining in situ MOF synthesis and pyrrole polymerization in a one-pot reaction. Through pyrolysis, the PPy and MOF composites demonstrated an enhanced specific surface area, a high active-site density, and a high concentration of nitrogen species in the M−N−C catalyst. These contributed to a superior ORR performance (E 1/2 of 0.915 V) and high durability in alkaline media. Additionally, the CoFe-NC-PPy material studied in an AEMFC enabled high performance with a current density of 550 mA cm−2 at 0.6 V and a peak power density of 352 mW cm−2. This study suggests potential in combining polymers and MOFs in the synthesis of ORR catalysts for fuel cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new "NH 3 -free" synthesis of thin carbon-shelled CrN nanoparticle is designed. • 1,2,4-1H-triazole is used as a metal-chelating agent and nitrogen/carbon source. • The hybrid structure is applicable to Cobalt-doped CrN. • The d band of CrN can be manipulated by metal doping. • The Co-CrN@C delivers a greater power density and cyclability than Pt/C in AEMFC. Hydrogen fuel cells are expected to be widely used in transportation and portable power generation. Unfortunately, sluggish cathodic oxygen reduction reaction (ORR) kinetics hamper the commercial application of the fuel cells. The quest for cost effective and highly efficient ORR catalysts is of great importance. Transition metal nitride (TMN) has received widespread attention mainly for its Pt-like characteristics. Here, we propose a new one-step "NH 3 -free" synthesis of thin-carbon-shell-encapsulated binary cobalt chromium nitrides (Co-CrN@C) using 1,2,4-1H-triazole as the nitrogen/carbon source. The Co-CrN@C exhibits almost ideal four-electron reduction of oxygen and achieves remarkable long-term durability and better methanol tolerance due to high-degree graphitization of the carbon shell. The X-ray photoelectron spectra and the density functional theory calculations unveil the origin of the intrinsic activity of the catalyst and the reaction mechanism. Furthermore, Co-CrN@C exhibits an impressive peak power density (PPD) of 488 mW cm−2, surpassing the 423 mW cm−2 for the Pt/C-driven anion exchange membrane fuel cells. These findings offer an indispensable strategy for rational design of high-efficient and durable non-noble catalysts. [ABSTRACT FROM AUTHOR]

• O-Pt 3 Co/CT catalysts are synthesized via repetitive absorption/chemical reaction method. • O-Pt 3 Co/C700 displays an ordered structure with enriched Pt shell. • O-Pt 3 Co/C700 shows a mass and specific activity of 0.53 A mg Pt −1 and 0.91 mA cm−2. Thermal annealing at high temperatures is usually employed to alloy Pt with transitional metals to produce structurally ordered intermetallic electrocatalysts for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells. The most important issue to address in this approach is the particle aggregation during thermal annealing. Herein, the repetitive absorption/chemical reaction method is used to prepare zeolitic-imidazolate-framework-coated carbon and alloy particles by simply soaking an ordered Pt 3 Co (O-Pt 3 Co) sequentially in Co(NO 3) 2 and 2-methylimidazole solutions at room temperature. The as-prepared catalysts display impressive ORR activity and stability relative to their commercial Pt/C counterpart. The optimized catalyst demonstrates a mass and specific activities of 0.53 A mg Pt −1 and 0.91 mA cm−2, respectively. In addition, no obvious decay is observed after 30 000 voltammetric cycles from 0.6 V to 0.9 V. The mechanism study shows that Co and doped N play a key role in promoting ORR activity and stability. [Display omitted] [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) is one of the key reactions in electrochemical energy conversion systems such as fuel cells, and it is significant to develop stable, efficient, and low-cost ORR electrocatalysts for future large-scale application of fuel cells. Metal-organic frameworks (MOFs) are a kind of porous materials that combine organic and inorganic components through coordination bonds. Compared with the conventional MOFs, the MOFs-derived materials can not only retain the unique high specific surface area and high porosity of the precursors, but also improve the electrical conductivity and charge transfer, which are more suitable to be used as efficient ORR catalysts. The research on MOFs-derived electrocatalyst has been long-standing and chaotic, especially with its widespread application in the field of ORR for the past few years. Therefore, this article reviews the latest research progress in MOFs-derived ORR electrocatalysts in recent years, introduces the relevant mechanisms of ORR, and looks forward to the development prospects of MOFs-derived electrocatalysts for ORR. [Display omitted] • The basic principles of ORR and the modification methods of MOFs-derived electrocatalysts were introduced. • MOFs-derived electrocatalysts in the field of ORR in recent years were classified and updated. • The prospect of MOFs-derived electrocatalysts for ORR were presented. [ABSTRACT FROM AUTHOR]

• The polyhedron Cu nanoparticles were synthesized by using PVP as template. • Ultra-thin Cu/Ag bimetallic nanosheets were obtained by adding silver source at room temperature. • The reaction mechanism of Cu/Ag bimetallic was explained. • The Cu/Ag bimetallic nanosheets had high thermal stability and the specific surface area. • This work provided a new idea to fabricate ultra-thin bimetallic nanosheet with high ORR performance. Bimetallic nanomaterials have rich electronic structures due to unique interfacial effects and synergistic effects. In this study, the polyhedron Cu nanoparticles were synthesized by the solvothermal method using polyvinylpyrrolidone (PVP) as a template. Then Ag precursor was added to obtain ultra-thin Cu/Ag bimetallic nanosheets at room temperature. SEM and TEM results showed that the as-prepared Cu/Ag samples changed from polyhedron to nanosheet structure with increased Ag content. When Cu: Ag = 1:1, the specific surface area of the sample reached 17.318 m 2/ g. 8.76 times the specific surface area of pure Cu. At the same time, electrochemical testing showed that the prepared bimetallic nanosheets had high onset voltage and half-peak voltage in alkaline media. Therefore, this work provides a new method for preparing ultra-thin bimetallic nanosheets, expanding their applications in fields such as electrocatalysis, sensors, optical detection, biomedicine, and fuel cells. [ABSTRACT FROM AUTHOR]

Dual sulfur-nitrogen (SN) doped graphene surfaces have been revealed as a powerful active material in fuel cell applications. The experimental results presented in this work show a clear preference of the material doped with SN towards a 4-electron mechanism, almost completely inhibiting the formation of H 2 O 2. However, materials doped only with nitrogen (N) or sulfur (S) favor the 2-electron mechanism, and therefore, the production of H 2 O 2. A reasonable theoretical explanation is proposed to justify the inhibition of the H 2 O 2 reaction with the use of SN doped graphenes in accordance with the experimental results. The interactions and charge transfer between N and S are the origin of an alternative dissociative step that inhibits the generation of H 2 O 2 , which is energetically favored, according to Density Functional Theory (DFT) calculations. These two dopant atoms generate a frustrated Lewis pair (FLP), resulting in an enhancement of the catalytic activity of the graphene. Atomic Dipole Corrected Hirshfeld charges (ADCH model) and Non-Covalent Interactions (NCI) are employed to identify the most active sites and support the explanation of the dissociative pathway which inhibits H 2 O 2 formation. [Display omitted] • Significant improved performance of SN-doped graphene for ORR in acidic media. • Almost completely inhibition of H 2 O 2 , favoring the 4-electron mechanism. • New dissociative step of O 2 chemisorption inhibits H 2 O 2 production. [ABSTRACT FROM AUTHOR]

[Display omitted] Committed to improving the utilization efficiency of Pt atoms and accurately controlling the morphology and composition of nanocatalysts to boost the Pt-based catalyst performance has become the focus of research. Herein, the PtRhNi truncated triangular nanoflakes (TA-NFs) catalyst with a unique PtRh-rich surface structure was successfully prepared by an effective one-pot synthetic method based on the galvanic replace reaction. The freestanding 2D nanostructure of PtRhNi TA-NFs, intrinsically possessing much high specific surface area and surface atomic, and the PtRh-rich characteristics of the surface is undoubtedly the most feasible model to simultaneously achieve high atom utilization. Benefiting from this novel structure, the as-obtained PtRhNi TA-NFs nanocatalyst exhibits excellent performance for ORR and MOR, delivering a mass activity of 0.92 A mg pt -1 for ORR, which is 2.03, 1.64, and 6.9-fold higher than that of PtRhNi nanoparticls (NPs), PtNi truncated triangle nanoflakes (TA-NFs) and commercial Pt/C, respectively. In addition, after 20 k cycles ADT test, PtRhNi TA-NFs show only 10 mV negative shift of half-wave potential and retain 70% of initial value of mass activity. Furthermore, a mass activity is 1.28 A mg pt −1 is achieved after applying this unique nanocatalyst for MOR, which is 1.28,1.5, and 2.6 times higher than that of PtRhNi NPs, PtNi TA-NFs and Pt/C, respectively. Impressively, the PtRhNi TA-NFs nanocatalyst shows an ultrahigh stability even after 2 k cycles ADT measurement in acid solution, and the mass activity is only drop 2% of initial value. This work provides a new strategy to synthesis high-performance of bifunction Pt-based electrocatalyst for ORR and MOR fuel cells. [ABSTRACT FROM AUTHOR]

The highly efficient energy conversion of the polymer‐electrolyte‐membrane fuel cell (PEMFC) is extremely limited by the sluggish oxygen reduction reaction (ORR) kinetics and poor electrochemical stability of catalysts. Hitherto, to replace costly Pt‐based catalysts, non‐noble‐metal ORR catalysts are developed, among which transition metal–heteroatoms–carbon (TM–H–C) materials present great potential for industrial applications due to their outstanding catalytic activity and low expense. However, their poor stability during testing in a two‐electrode system and their high complexity have become a big barrier for commercial applications. Thus, herein, to simplify the research, the typical Fe–N–C material with the relatively simple constitution and structure, is selected as a model catalyst for TM–H–C to explore and improve the stability of such a kind of catalysts. Then, different types of active sites (centers) and coordination in Fe–N–C are systematically summarized and discussed, and the possible attenuation mechanism and strategies are analyzed. Finally, some challenges faced by such catalysts and their prospects are proposed to shed some light on the future development trend of TM–H–C materials for advanced ORR catalysis. [ABSTRACT FROM AUTHOR]

The high cost and deficiency of long‐term durability of carbon supported Pt catalysts have been regarded as obstacle that impeding their practical proton exchange membrane fuel cells (PEMFCs) technologies. Furtherly, iron and nitrogen co‐doped carbons (Fe/NC) are emerging as a steady electrocatalyst. Unfortunately, there are less‐active sites in acidic electrolyte. Herein, combining the advantages of Fe/NC and Pt catalysts, we propose an in‐situ surfactant‐free self‐templating solution reduction strategy to construct Pt nanoparticles (NPs) onto well‐devised Fe/NC porous nanostructures in order to manufacture highly performing Pt−Fe/NC catalyst for oxygen reduction reaction (ORR). The obtained Pt−Fe/NC catalyst displays excellent ORR performance, realizing an account of 2.53 improvement in specific activity and an account of 1.20 strengthening in mass activity toward ORR compared to the commercial Pt/C catalysts. Stability tests confirm that the as‐synthesized Pt−Fe/NC catalyst is more electrochemically steady than the commercial Pt/C catalysts on account of the electronic interaction between Pt and N which result from the difference in electronegativity. Our work provides a promising strategy for exploring the accomplishment of better ORR in acid electrolytes. [ABSTRACT FROM AUTHOR]

The dual heteroatom doped mesoporous carbon (MC) is an excellent substitute for platinum‐based catalyst in cathodic oxygen reduction reaction (ORR) of fuel cells. In this work, nitrogen (N) as the primary heteroatom doping, phosphorus (P), boron (B), and sulfur (S) as the secondary heteroatom doping are introduced in the MC framework. Santa barbara amorphous (SBA‐15) employed as the supporting material to investigate the secondary heteroatom doping effect on MC towards ORR performance. Compared with B and S doping, the P doping modifies the charge delocalization in the MC structure. In addition, it enhances the surface area (971 m2/g), defect sites (1.18), high pyridinic (28.72 %) and high graphitic content (44.42 %) thereby facilitated the remarkable ORR activity. Moreover, electrochemical studies proved that N and P dual doped mesoporous carbon (NPMC) has a better carrier concentration (5.58×1015 cm−3) and higher flat band potential (0.548 V vs RHE) which is confirmed by the Mott‐Schottky analysis. Further, ORR studies demonstrated that NPMC material exhibited more positive onset potential (0.86 V), two‐electron pathway, lower Tafel slope (63 mV/dec) as well as Rct (11 Ω/cm2). In addition, the resultant material is found to be highly active towards ORR with excellent methanol tolerance and stability. [ABSTRACT FROM AUTHOR]

Developing cost‐effective non‐precious metal electrocatalysts (NPMCs) for the sluggish oxygen reduction reaction (ORR) is critical for the large‐scale application of metal‐air battery and fuel cell technologies. Herein, we present an effective Mn/Zn bimetal organic frameworks (MOFs)‐based strategy to synthesize an efficient manganese (Mn) and nitrogen (N) co‐doped porous carbon electrocatalyst with atomically dispersed N‐coordinated single Mn moieties (Mn‐Nx) for ORR catalysis. This strategy involves the adsorption of Mn ions into the Mn/Zn bimetal MOFs followed by the subsequent pyrolysis in Ar and then activation in NH3. Owing to the atomically dispersed Mn‐Nx sites, the large specific surface area and the high content of graphitic‐N, the resulting electrocatalyst shows a superior ORR activity with a half‐wave potential of 0.885 V and an outstanding electrochemical durability in alkaline electrolyte outperforming commercial Pt/C, and it also exhibits a superior performance for an assembled primary Zn–air battery. This work offers a new prospect for the synthesis of MOFs‐derived highly efficient NPMCs for ORR. [ABSTRACT FROM AUTHOR]

Integrating ultralow-Pt alloy into nanocarbons: Ternary PtCoNi alloy with ultralow Pt loading integrated in nitrogen-doped nanocarbon architecture endows an excellent half-cell activity and single-cell performance. [Display omitted] Developing efficient platinum (Pt)-based electrocatalysts is enormously significant for fuel cells. Herein, we report an integrated electrocatalyst of ultralow-Pt alloy encapsulated into nitrogen-doped nanocarbon architecture for efficient oxygen reduction reaction. This hybrid Pt-based catalyst achieves a mass activity of 3.46 A mg pt −1 at the potential of 0.9 V vs. RHE with a negligible stability decay after 10,000 cycles. More importantly, this half-cell activity can be expressed at full cell level with a high Pt utilization of 10.22 W mg Pt −1 cathode and remarkable durability after 30,000 cycles in single-cell. Experimental and theoretical investigations reveal that a highly strained Pt structure with an optimal Pt-O binding energy is induced by the incorporation of Co/Ni into Pt lattice, which would account for the improved reaction kinetics. The synergistic catalysis due to nitrogen-doped nanocarbon architecture and active Pt component is responsible for the enhanced catalytic activity. Meanwhile, the strong metal-support interaction and optimized hydrophilic properties of nanocarbon matrix facilitate efficient mass transport and water management. This work may provide significant insights in designing the low-Pt integrated electrocatalysts for fuel cells and beyond. [ABSTRACT FROM AUTHOR]

[Display omitted] Designing efficient electrocatalysts for the oxygen reduction reaction (ORR) is crucial to enhance the energy efficiencies of metal-air batteries and fuel cells. Palladium (Pd) catalysts show great potential due to their high intrinsic activity towards ORR but suffer from inferior durability. Here, we aim to employ tin oxide (SnO 2) supports to tailor the lattice strain and electron density of Pd catalysts to enhance their ORR performance. By using electrospinning and solvothermal techniques, a hierarchical Pd/SnO 2 hybrid catalyst was facilely synthesized with Pd nanoparticles anchored onto both the inside and outside walls of nanotube-like SnO 2 supports. Owing to the SnO 2 supports and the endowing metal-support interactions, tensile-strain and electron-rich features were both verified for the Pd nanoparticles in the Pd/SnO 2 catalyst. In comparison, no such features were found for the Pd nanoparticles in the Pd/C catalyst. As a consequence, the Pd/SnO 2 hybrid catalyst exhibits 2.5-times higher mass activity than the Pd/C catalyst and greatly improved durability with a current decay of 4% loss over 50 h compared with that (18%) of the Pd/C catalyst. [ABSTRACT FROM AUTHOR]