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Search for a Platinum metal-free catalyst for Proton Exchange Membrane Fuel Cells (PEMFCs) is a concern to scientists as the Pt-catalyzed electrode comprises about 45% of the entire fuel cell stack cost. Due to layered structure, Two-dimensional (2D) MoS2 nanostructured materials have recently drawn attention as effective catalysts for oxygen reduction reaction (ORR). The 1T-phase of MoS2 (1T-MoS2) has higher electronic conductivity than the 2H-phase (2H-MoS2); high surface area 1T-MoS2 can have high electrocatalytic activity towards PEFFCs. Here, we report hydrothermally synthesized 2H-MoS2 and solvothermally synthesized mixed 1T/2H-MoS2 phases as a catalyst for ORR in PEM Fuel Cells. Owing to the high BET-specific surface area, hybrid 1T/2H-MoS2 showed better ORR activity than 2H-MoS2. The limiting current density of the 1T/2H-MoS2 hybrid structure is ‒7.1 mA cm−2 compared to Pt/C (‒8.2 mA cm−2) at 1600 rpm. The Tafel slope values of 2H-MoS2, 1T/2H-MoS2, and Pt/C are 92.7 mV dec−1, 57.5 mV dec−1, and 39.3 mV dec−1, respectively. The electron transferred during ORR are 3.8 and 1.8, respectively, for 1T/2H-MoS2 and 2H-MoS2 (in 0.1 M KOH) ; suggesting less formation of undesirable peroxide formation than 2H-MoS2. The 1T/2H-MoS2 displays better electrochemical durability compared to 2H-MoS2 (after 2000 CV cycles). [ABSTRACT FROM AUTHOR]

The microstructures of the ionomer–catalyst interfaces in the catalyst layers are important for the fuel cell performance because they determine the distribution of the active triple-phase boundaries. Here, we investigate the ionomer–catalyst interactions in hydroxide exchange membrane fuel cells (HEMFCs) using poly(aryl piperidinium) and compare them with proton exchange membrane fuel cells (PEMFCs). It is found that different catalyst layer microstructures are between the two types of fuel cell. The ionomer/carbon (I/C) ratio does not have a remarkable impact on the HEMFC performance, while it has a strong impact on the PEMFC performance, indicating the weaker interaction between the HEMFC ionomer and catalyst. Molecular dynamics simulations demonstrate that the HEMFC ionomer tends to distribute on the carbon support, unlike the PEMFC ionomer, which heavily covers the Pt nanoparticles. These results suggest that the poisoning effect of the ionomer on the catalyst is much weaker in HEMFCs, and the improved ionomer/catalyst interaction is beneficial for the HEMFC performances. [ABSTRACT FROM AUTHOR]

Fe─N─C materials with Fe─N4 sites are considered as most promising non‐precious metal‐based electrocatalysts for low‐cost proton‐exchange‐membrane fuel cells (PEMFCs). Breaking the trade‐off between activity and stability has been a long‐standing challenge in the field of acidic oxygen reduction reaction (ORR). Herein, a "top‐down" thermally‐driven strategy is developed to achieve highly active pyrrolic N‐coordinated Fe sites in a high spin state with Fe atomic cluster (Fen@Fe─Npyrr─C) and discover that the neighboring Fen cluster can synergistically stabilize such vulnerable Fe─N4 sites by inhibiting their protonation. Consequently, the Fen@Fe─Npyrr─C catalysts exhibit much enhanced ORR activity and stability, endowing PEMFCs with a high power density of 804.6 mW cm−2 (testing conditions: 80 °C, 100% RH, 2.0 bar) and over 100 h durability (at 0.5 V). These findings open up opportunities for the exploration of durable Fe─N─C ORR electrocatalysts for non‐precious metal‐based PEMFCs and other applications. [ABSTRACT FROM AUTHOR]

The lifetime of hydroxyl radicals (⋅OH) in the fuel cell catalyst layer remains uncertain, which hampers the comprehension of radical‐induced degradation mechanisms and the development of longevity strategies for proton‐exchange membrane fuel cells (PEMFCs). In this study, we have precisely determined that the lifetime of ⋅OH radicals can extend up to several seconds in realistic fuel cell catalyst layers. This finding reveals that ⋅OH radicals are capable of carrying out long‐range attacks spanning at least a few centimeters during PEMFCs operation. Such insights hold great potential for enhancing our understanding of radical‐mediated fuel cell degradation processes and promoting the development of durable fuel cell devices. [ABSTRACT FROM AUTHOR]

The efficiency and performance of proton exchange membrane fuel cells (PEMFCs) are primarily influenced by ORR electrocatalysts. In recent years, atomically dispersed metal–nitrogen–carbon (M-N-C) catalysts have gained significant attention due to their high active center density, high atomic utilization, and high activity. These catalysts are now considered the preferred alternative to traditional noble metal electrocatalysts. The unique properties of M-N-C catalysts are anticipated to enhance the energy conversion efficiency and lower the manufacturing cost of the entire system, thereby facilitating the commercialization and widespread application of fuel cell technology. This article initially delves into the origin of performance and degradation mechanisms of Fe-N-C catalysts from both experimental and theoretical perspectives. Building on this foundation, the focus shifts to strategies aimed at enhancing the activity and durability of atomically dispersed Fe-N-C catalysts. These strategies encompass the use of bimetallic atoms, atomic clusters, heteroatoms (B, S, and P), and morphology regulation to optimize catalytic active sites. This article concludes by detailing the current challenges and future prospects of atomically dispersed Fe-N-C catalysts. [ABSTRACT FROM AUTHOR]

Platinum-group-metal free catalysts have been widely studied in the last decade as an alternative to Pt, employed in fuel cells. Several carbon precursors have been investigated as carbon matrix for iron-nitrogen-carbon (Fe–N–C) catalysts, characterized by a large amount of micropores, fundamental to create Fe-N x -C active sites. Nonetheless, it is also acknowledged that wider pores are needed to facilitate mass transfer of oxygen/water (reagent/product of fuel cells) towards/from the active sites. Organic xerogels are known as easily tunable materials, that allow doping with a variety of heteroatoms. The present manuscript presents an investigation on the use of organic xerogels combined with iron and nitrogen in a single-step to obtain Fe–N-CXG electro-catalysts for the oxygen reduction reaction (ORR) of proton exchange membrane fuel cells. Several features of both organic xerogels and catalysts on the ORR activity are assessed: the textural properties of the organic xerogel, the iron loading of the Fe–N–C catalysts and the effect of acid-leaching of the catalysts. The present study proves the feasibility of using organic xerogels as carbon precursor to obtain PGM-free catalysts in an easy manner and scalable single-step synthesis. Catalysts obtained from organic xerogels synthesized at mildly acid pHs (5.8 and 6), with a nominal iron loading of 2 wt%, and subjected to two sets of acid leaching/thermal treatments, present enhanced catalytic activity towards the ORR. • Organic carbon xerogels are investigated as carbon matrix for Fe–N–C catalysts. • One-step and template-free synthesis of Fe–N–C catalysts is proposed. • Balanced iron doping creates enough active sites without impacting porosity. • Acid/thermal treatments enhance catalysts improving chemical properties. • High mesopore volume organic xerogels (pH 5.8) yield highly active ORR catalysts. [ABSTRACT FROM AUTHOR]

The transition-metals carbon catalysts belong to intensively studied alternatives to the Pt-based catalysts promoting the oxygen reduction reaction (ORR) in electrochemical fuel cells (FCs). Commonly studied Fe,Co–N–C composites are usually obtained through pyrolysis and used as such or after a chemical post-treatment with an oxidizing agent. This treatment is applied to remove inactive metal species, thus, promoting the electrochemical activity. The impact of an oxidizing agent is poorly addressed in the literature, while its nature may negatively affect the catalyst's performance. Herein we report the first comparative study on the effect of post-treatment with the most common oxidizing agents such as HCl, HNO 3 , H 2 SO 4 and H 2 O 2 , on the structural and electrochemical properties of the Fe,Co–N–C catalyst. The catalyst is made by pyrolysis of the Co,Zn-ZIF metal-organic framework enriched with iron and nitrogen. Its structure was observed withstanding the action of mineral acids but suffers from hydrogen peroxide. The treatment with either nitric or chloric acid may improve the electrochemical performance up to 4%, while other agents decrease that by 6% and slow down the ORR rate. These findings are useful for the careful design of post-treatment procedures for carbon catalysts. • The Fe,Co–N–C carbon-based catalyst was obtained from Fe,Co-ZIF-8 MOF via pyrolysis at 700 °C in an inert atmosphere. • The Fe,Co–N–C catalyst was treated with four oxidizing agents - chloric, nitric and sulfuric acids, and hydrogen peroxide. • Structural and compositional changes were assessed with multi-technique characterization of the catalysts. • The catalysts treated with nitric and chloric acids demonstrated improved performance for ORR in an acidic medium. [ABSTRACT FROM AUTHOR]

Fe−N−C catalysts are an interesting option for polymer electrolyte fuel cells due to their low cost and high activity towards the oxygen reduction reaction (ORR). Since Fe−N−C active sites are preferentially formed in the micropores of the carbon matrix, increasing the microporosity is highly appealing. In this work, carbon xerogels (CXG) were activated by physical and chemical methods to favor the formation of micropores, used as carbon matrices for Fe−N−C catalysts, and investigated for the ORR. The catalysts were characterized by solid‐state techniques to determine chemical composition and pore structure. Physical activation increased microporosity up to 2‐fold leading to catalysts with a larger density of active sites (more than twice iron and nitrogen uptake, pyridinic N and Nx−Fe). This entailed a higher ORR intrinsic activity determined in a 3‐electrode cell (80 mV better half‐wave potential). At the cathode of a fuel cell, the catalysts based on activated carbon materials showed 26 % lower power density ascribed to a more hydrophilic surface, causing a larger extent of flooding of the electrode that counterbalances the higher intrinsic activity. Interestingly, a more stable behavior was observed for the activated catalysts, with up to 2‐fold better relative power density retention after 20‐hour operation. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) is the key reaction in metal air and fuel cells. Among the catalysts that promote ORR, carbon‐based metal‐free catalysts are getting more attention because of their maximum atom utilization, effective active sites and satisfactory catalytic activity and stability. However, the pyrolysis synthesis of these carbons resulted in disordered porosities and uncontrolled catalytic sites, which hindered us in realizing the catalysts' design, the optimization of catalyst performance and the elucidation of structure–property relationship at the molecular level. Covalent organic frameworks (COFs) constructed with designable building blocks have been employed as metal‐free electrocatalysts for the ORR due to their controlled skeletons, tailored pores size and environments, as well as well‐defined location and kinds of catalytic sites. In this Concept article, the development of metal‐free COFs for the ORR is summarized, and different strategies including skeletons regulation, linkages engineering and edge‐sites modulation to improve the catalytic selectivity and activity are discussed. Furthermore, this Concept provides prospectives for designing and constructing powerful electrocatalysts based on the catalytic COFs. [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]

Atomically dispersed Fe-N-C catalysts for the oxygen reduction reaction (ORR) have been synthesized with a template-free method using carbon xerogels (CXG) as a porous matrix. The porosity of the CXGs is easily tunable through slight variations in the synthesis procedure. In this work, CXGs are prepared by formaldehyde and resorcinol polymerization, modifying the pH during the process. Materials with a broad range of porous structures are obtained: from non-porous to micro-/meso-/macroporous materials. The porous properties of CXG have a direct effect on Fe-N-CXG activity against ORR in an acidic medium (0.5 M H2SO4). Macropores and wide mesopores are vital to favor the mass transport of reagents to the active sites available in the micropores, while narrower mesopores can generate additional tortuosity. The role of microporosity is investigated by comparing two Fe-N-C catalysts using the same CXG as the matrix but following a different Fe and N doping procedure. In one case, the carbonization of CXG occurs rapidly and simultaneously with Fe and N doping, whereas in the other case it proceeds slowly, under controlled conditions and before the doping process, resulting in the formation of more micropores and active sites and achieving higher activity in a three-electrode cell and a better durability during fuel cell measurements. This work proves the feasibility of the template-free method using CXG as a carbon matrix for Fe-N-C catalysts, with the novelty of the controlled porous properties of the carbon material and its effect on the catalytic activity of the Fe-N-C catalyst. Moreover, the results obtained highlight the importance of the carbon matrix's porous structure in influencing the activity of Fe-N-C catalysts against ORR. [ABSTRACT FROM AUTHOR]

An oxygen reduction reaction (ORR) is the key half reaction of proton exchange membrane fuel cells (PEMFCs), and is highly dependent on Pt-based nanocrystals as core electrocatalysts. Despite the exceptional ORR activity from adjusting the electronic structures of surface or near-surface atoms, several serious issues, including the corrosion of carbon supports, the preferential leaching of active metal elements, the instability of surface low-coordinated atoms and the sintering/agglomeration of nanocrystals, still exist, challenging the ORR durability of developed Pt-based ORR catalysts. From the point of view of the catalyst structure design, in this review, we summarized the state-of-the-art structural regulation strategies for improving the ORR durability of Pt-based catalysts. The current limitation of Pt-based binary catalysts for ORR electrocatalysis is firstly discussed, and the detailed strategies are further classified into the optimization of supports, metal-doped alloys, core/shell structures, intermetallics and high-entropy alloys, etc. The structure–performance relationship is detailedly explained, especially emphasizing the elimination of the above restrictions. Finally, the existing challenges and future research direction are further presented, aiming at practicing the PEMFC devices of the ultradurable Pt-based catalysts. [ABSTRACT FROM AUTHOR]

ABSTRACTThe increasing demand for universal metrics in material development, particularly in the context of material informatics (MI), emphasises the need for catalytic activity metrics in fuel-cell research, specifically for the oxygen reduction reaction (ORR). In this study, we comprehensively analyse 10 Pt/C catalysts using a constant-current density protocol and correlate the ORR activity with the constant kinetic current density, thereby demonstrating the effectiveness of this alternative metric. Our results reveal that the constant-current density protocol offers a reliable and consistent assessment of catalyst performance, providing a promising alternative to existing evaluation methods. By evaluating various protocols for extracting activity metrics from the datasets of fuel-cell catalysts, we establish an optimised protocol that accounts for experimental and analytical errors in obtaining universal activity metrics. Conventional methods relying on data obtained at a fixed potential are inadequate due to variable contributions of mass transport among the different materials. Instead, we propose a protocol using a constant kinetic current density obtained by the anodic scans of voltammetry (in the range of below 8 μA cm−2, normalized by absolute electrochemically active surface area, or 6 × 10−21 A per active site) to minimise influence of un-compensated resistance and non-ORR current, enabling robust analysis of catalyst activity trends. Depending on the purpose of the MI prediction, multiple metrics obtained at different conditions such as cathodic scans are preferable, and thus a range of metrics should be deposited in a database with their metadata. This unbiased comparison of catalysts emphasises the importance of revisiting assessment protocols. The resulting database of universal activity metrics is expected to be valuable for accelerating catalyst development through the application of materials informatics.

Hydrogen fuel cell vehicles have attracted extensive attention for conversion equipment and new energy storage technologies. As an important component of hydrogen fuel cell vehicles, highly stable and active platinum-based (Pt-based) catalysts with 4-electron oxygen reduction reaction (ORR) selectivity are extremely important for promoting the application of this field. In this mini review, based on the ORR mechanism, the feasible strategies to enhance the catalytic stability and 4-electron selectivity of Pt-based catalysts were summarized. Furthermore, the effect mechanisms of each strategy in enhancing catalytic activity and 4-electron selectivity were emphatically discussed and their superiorities and limitations were evaluated. Finally, the research direction and current challenges of Pt-based catalysts were prospected from the perspective of their practical application in hydrogen fuel cell vehicles. • Research progress of Pt-based catalysts for 4-electron ORR is explored. • The strategies of enhancing 4-electron transfer in Pt-based catalysts are summarized. • The superiorities and limitations of each strategy are summarized. • The future researches of Pt-based catalysts applied in fuel cells is put forward. [ABSTRACT FROM AUTHOR]

Fe–N–C catalysts with excellent performance regarding the oxygen reduction reaction (ORR) have aroused enormous interest in direct-formate fuel cells (DFFCs). However, their limited mass transfer ability, insufficient ORR active sites, and complex fabrication processes remain significant obstacles to the widespread application of Fe–N–C catalysts. Herein, we propose a simple hydrothermal-annealing method with agarose powders to synthesize a uniform spherical Fe–N–C catalyst (∼3 μm) with well-developed mesopores (Fe/rG@C/H-Agar-900). The resultant Fe/rG@C/H-Agar-900 catalyst possesses rich oxygen-containing functional groups and enhanced interconnected pores, which can significantly boost the content of catalytic sites and facilitate mass transport, resulting in a high content of active sites. In the meantime, the mesopore content of Fe/rG@C/H-Agar-900, which can facilitate the formation of the three-phase gas/electrolyte/catalyst interfaces, was optimized by varying the annealing temperature. As a result, the Fe/rG@C/H-Agar-900 demonstrates a half-wave potential of 0.91 V vs. RHE, nearly four-electron pathway selectivity, excellent durability, and excellent formate tolerance for ORR. Furthermore, when used as the air cathode in membrane-less DFFCs, the Fe/rG@C/H-Agar-900-based device exhibits a remarkable peak power density of 24.5 mW cm−2, significantly outperforming the 20 wt% commercial Pt/C. This research facilitates the synthesis of an advanced Fe–N–C catalyst and promotes the practical development of membrane-less DFFCs. [Display omitted] • Spherical mesoporous carbon precursors were prepared by a hydrothermal-annealing method. • Fe–N–C catalyst prepared from agarose powder were used as the air-cathode catalyst for membrane-less DFFCs. • Annealing treatment expands the mesoporous structures of hydrocarbons. • Fe/rG@C/H-Agar-900 exhibits a highly positive E 1/2 (0.91 V vs. RHE) for ORR in alkaline solution. • A P max of 24.5 mW cm−2 is achieved by Fe/rG@C/H-Agar-900, which is 31% higher than that of Pt/C. [ABSTRACT FROM AUTHOR]

This paper proposes an environmentally friendly one-pot synthesis approach for the PtCu and PtNi nanoparticles with the gradient structure on the carbon support. This method offers exceptional advantages over other approaches. Among them there is a surfactant-free synthesis, being low-temperature, simple, fast, and one-pot. The bimetallic electrocatalysts with a reduced platinum content for proton-exchange membrane fuel cells have been obtained. The proposed method is promising in terms of scaling and transition to commercial production. In this study, we first attempted to apply the gradient synthesis strategy to the PtNi/C catalysts in order to make this method versatile. We obtained the high-performance PtNi/C and PtCu/C catalysts, exhibiting the specific ORR activity higher than that of the commercial Pt/C catalyst by 3 and 4.6 times, respectively. [Display omitted] • New Pt-based nanostructured ORR electrocatalysts were obtained by a simple, versatile, and scalable method. • The PtCu and PtNi nanoparticles with Pt overlayers supported on carbon were synthesized by a gradient strategy. • PtNi/C and PtCu/C showed enhanced activity in the ORR compared with the commercial Pt/C. • The surfactant-free one-pot synthesis was used to obtain the PtNi and PtCu nanoparticles. • The environmentally friendly method was used to prepare Pt-based electrocatalysts. [ABSTRACT FROM AUTHOR]

Oxygen reduction reactions (ORRs) are unanimously a key factor of system performances in bioelectrochemical systems (BESs), low-temperature fuel cells, and generally in several electrochemical platforms. Platinum (Pt)-based catalyst is the finest electrocatalyst for ORR in BESs; however, it is constrained by its low abundance, high price, and poor catalytic durability in an electrochemical setup for cathodic reaction kinetics. In recent years, significant efforts in trimming the metal-based catalyst up to nanoscale to cater high performance of ORR have been explored. Still, there are many opportunities to improve catalyst performance at cathode through proper selection of an efficient low-cost metal-based ORR catalyst. Molybdenum (Mo) with its multi-dimensional form as 2D and 3D layers and synergistic combination with other non-metals offers prospects of extraordinary performance as low-cost metal-based ORR catalyst over the Pt in delivering enhanced ORR potential. The present review throws light on current requirements of a sturdier catalyst material and thus provides a comprehensive review on the continuing efforts in exploring the possibility of Mo as a low-cost metal-based ORR catalyst. This literature analysis would enlighten the significance of ORR in BESs, followed by the electrochemistry of Mo-based cathodic catalyst, its underlying mechanism and performance limiting factors in the operation of ORR. Moreover, the extensive and systematic acumen in the context of Mo-based catalytic formulations for increased ORR potentials including nano-composite Mo-cathode catalyst; development of Mo-catalyst with varied configurations; carbon-supported Mo-catalyst; morphological changes; surface area modifications; and Mo-coupling with other transition metal and its derivatives were discussed in great detail to provide prospective application of Mo-based catalyst. Lastly, numerous opportunities and projections for future research in fabrication, juxtaposition, and implementation of Mo-based cathodic catalysts and consequent recommendations were discussed as conclusive remarks for bringing out the state-of-the-art review on this subject. [ABSTRACT FROM AUTHOR]

As a key role in hindering the large-scale application of fuel cells, oxygen reduction reaction has always been a hot issue and nodus. Aiming to explore state-of-art electrocatalysts, this paper reviews the latest development of nonmetallic catalysts in oxygen reduction reactions, including single atoms doped with carbon materials such as N, B, P or S and multi-doped carbon materials. Afterward, the remaining challenges and research directions of carbon-based nonmetallic catalysts are prospected. [ABSTRACT FROM AUTHOR]

Platinum (Pt) based catalysts have multiphase structure, such as two-dimensional (2D) nanosheets structure, with a large specific surface area and high atomic utilization ratio, and a large contact area with carbon support, which promotes the combination of catalyst and support, and improves the activity of catalyst. However, there are still many difficulties in the synthesis of 2D polymetallic alloy nanosheet catalysts. Herein, we synthesized palladium nanosheets (Pd NSs) catalyst with smooth surface structure via solvothermal method, smooth surface structure palladium platinum nanosheets (PdPt NSs) and palladium platinum nickel island particle nanosheets (PdPtNi IPNSs) catalyst. Compared with commercial TKK-Pt/C, the prepared PdPtNi IPNSs catalyst has better catalytic performance for oxygen reduction reaction (ORR), ethanol oxidation reaction (EOR) and methanol oxidation reaction (MOR). This work provides a simple and feasible strategy for the synthesis of stable and efficient polymetallic 2D alloy nanostructured catalysts. • To achieve the smooth surface of Pd nanosheets (Pd NSs) via controllable preparation of catalysts. • The deposition method was used to get palladium platinum nickel island particle nanosheets (PdPtNi IPNSs) catalyst. • In oxygen reduction reaction, PdPtNi IPNSs achieved mass activity 7.59 times the Pt/C. • In ethanol oxidation reaction, the highest current density of PdPtNi IPNSs was 2.06 times that of Pt/C. • In methanol oxidation reaction, the highest current density of PdPtNi IPNSs was 3.47 times that of Pt/C. [ABSTRACT FROM AUTHOR]

Platinum group metal (PGM)-free oxygen reduction reaction (ORR) catalysts are of utmost importance for the rapid development of anion-exchange membrane fuel cell (AEMFC) technology. In this work, we demonstrate the improved ORR performance and stability of Co and Fe oxide-decorated/N-doped reduced graphene oxide (CoOx-Fe3O4/N-rGO) prepared via a hydrothermal method at the low temperature of 150 °C. The catalysts were characterized thoroughly using transmission electron microscopy, high-angle annular dark field-scanning electron microscopy, X-ray diffraction, N2 physisorption, Raman spectroscopy, and X-ray photoelectron spectroscopy to obtain information about morphology, elemental distribution, phases, porosity, defects, and surface elemental compositions. Significant ORR activity improvement (130 mV@-1.5 mA cm−2) was achieved with this catalyst compared to the pristine graphene oxide, and the ORR limiting current was even 12%@0.5 V higher than the commercial Pt/C. The enhanced ORR activity of CoOx-Fe3O4/N-rGO was attributed to the uniform dispersion of Co, Fe, and N on reduced graphene oxide (rGO) sheets. Furthermore, ORR accelerated stress tests revealed excellent durability, suggesting that this material could be a promising and durable catalyst. With a cathode layer of the CoOx-Fe3O4/N-rGO catalyst, we achieved a peak power density of 676 mW cm−2 in an operando H2-O2 AEMFC. To the best of our knowledge, this is the highest reported power density per cathode catalyst mass in a reported PGM-free cathode catalyst. Finally, we quantified the various cell polarization losses as a function of cathode catalyst loadings to obtain insights for future work with AEMFCs based on this catalyst. The improvement in the AEMFC performance using CoOx-Fe3O4/N-rGO as a cathode catalyst can be attributed to the synergistic effects of (i) the high turnover frequency of the transition metals (Co and Fe) for ORR and (ii) the enhancement provided by N doping to the metal distribution and stability. [ABSTRACT FROM AUTHOR]

Finding a platinum‐free cathode catalyst that effectively models the oxygen reduction reaction (ORR) of a proton‐exchange membrane (PEM) fuel cell cathode better than the current commercial Pt/C catalyst has been a major shortcoming in fuel cell technology. Overall, a promising platinum‐free cathode catalyst must offer great ORR activity, ORR selectivity, and acid stability. Due to their enticing ORR activity and selectivity to the preferred four‐electron ORR pathway, the possible dissolution reactions and oxygen‐intermediate reactions of iron phthalocyanine monolayer supported on a pristine graphene (GFePc) and boron‐doped graphene substrate (BGFePc) have been studied to determine the stability as a function of potential and pH through spin‐polarized density functional theory (DFT) calculations at both infinitesimally low (10−9 m) and 1 m Fe2+/Fe3+ ionic concentrations. BGFePc offers higher stability in both concentrations than GFePc. In both cases, the oxygen‐intermediates are more stable than the bare catalytic surface due to the metal d‐band center shifting further away from the Fermi level in the valence band state (higher energy of antibonding). Moreover, at an Fe2+ ionic concentration, both catalysts would be stable in the potential and pH regions at the operating conditions of rotating disk electrode (RDE) experiments and PEM fuel cells. [ABSTRACT FROM AUTHOR]

Advancements in inexpensive, efficient, and durable oxygen reduction catalysts is important for maintaining the sustainable development of fuel cells. Although doping carbon materials with transition metals or heteroatomic doping is inexpensive and enhances the electrocatalytic performance of the catalyst, because the charge distribution on its surface is adjusted, the development of a simple method for the synthesis of doped carbon materials remains challenging. Here, a non-precious-metal tris (Fe/N/F)-doped particulate porous carbon material (21P2-Fe1-850) was synthesized by employing a one-step process, using 2-methylimidazole, polytetrafluoroethylene, and FeCl3 as raw materials. The synthesized catalyst exhibited a good oxygen reduction reaction performance with a half-wave potential of 0.85 V in an alkaline medium (compared with 0.84 V of commercial Pt/C). Moreover, it had better stability and methanol resistance than Pt/C. This was mainly attributed to the effect of the tris (Fe/N/F)-doped carbon material on the morphology and chemical composition of the catalyst, thereby enhancing the catalyst's oxygen reduction reaction properties. This work provides a versatile method for the gentle and rapid synthesis of highly electronegative heteroatoms and transition metal co-doped carbon materials. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) corresponds to the limiting process in fuel cells to convert gaseous hydrogen and oxygen from the air into electricity. Most commonly, electronic structure calculations in the density functional theory (DFT) approximation are applied to comprehend the elementary reaction steps on the atomic scale, including the identification of limiting reaction steps and approximation of electrocatalytic activity. A major challenge in the modeling of the ORR refers to the complexity of the mechanistic pathways given that a plethora of different descriptions, ranging from the mononuclear to OOH dissociation mechanisms, dissociative and oxide pathways, have been reported in the literature. In the present work, the adsorption free energy of the *OH intermediate, ΔG1, is introduced as an effective descriptor for rapid screening of ORR mechanisms. By applying a rigorous thermodynamic analysis in conjunction with a descriptor‐based approach, it is demonstrated how the calculation of a single binding energy in terms of ΔG1 can be used to identify the energetically favored mechanistic description for any ORR catalyst by analyzing the location of the material in the volcano plot. The introduced procedure may support future DFT‐based studies in that the preferred pathway is not missed when modeling the four‐electron ORR by a binding‐energy approach. [ABSTRACT FROM AUTHOR]

To achieve practical application of fuel cell, it is vital to develop highly efficient and durable Pt‐free catalysts. Herein, we prepare atomically dispersed ZnNC catalysts with Zn‐Pyrrolic‐N4 moieties and abundant mesoporous structure. The ZnNC‐based anion‐exchange membrane fuel cell (AEMFC) presents an ultrahigh peak power density of 1.63 and 0.83 W cm−2 in H2‐O2 and H2‐air (CO2‐free), and also exhibits long‐term stability with more than 120 and 100 h for H2‐air (CO2‐free) and H2‐O2, respectively. Density functional calculations further unveil that the Zn‐Pyrrolic‐N4 structure is the origin of high activity of as‐synthesized ZnNC catalyst, while the Zn‐Pyridinic‐N4 moiety is inactive for oxygen reduction reaction (ORR), which successfully explain the puzzle why most Zn‐metal‐organic framework ‐derived ZnNC catalysts in previous reports did not present good ORR activity because of their Zn‐Pyridinic‐N4 moieties. This work offers a new route for speeding up development of AEMFCs. [ABSTRACT FROM AUTHOR]

Developing cost-effective and high-efficiency oxygen reduction reaction (ORR) catalysts is imperative for promoting the substantial progress of fuel cells and metal-air batteries. The coordination and geometric engineering of single-atom catalysts (SACs) occurred the promising approach to overcome the thermodynamics and kinetics problems in high-efficiency electrocatalysis. Herein, we rationally constructed atomically dispersed Co atoms on porous N-enriched graphene material C2N (CoSA-C2N) for efficient oxygen reduction reaction (ORR). Systematic characterizations demonstrated the active sites for CoSA-C2N is as identified as coordinatively unsaturated Co-N2 moiety, which exhibits ORR intrinsic activity. Structurally, the porous N-enriched graphene framework in C2N could effectively increase the accessibility to the active sites and promote mass transfer rate, contributing to improved ORR kinetics. Consequently, CoSA-C2N exhibited superior ORR performance in both acidic and alkaline conditions as well as impressive long-term durability. The coordination and geometric engineering of SACs will provide a novel approach to advanced catalysts for energy related applications. [ABSTRACT FROM AUTHOR]

Finding high‐performance, low‐cost, efficient catalysts for oxygen reduction reactions (ORR) is essential for sustainable energy conversion systems. Herein, highly efficient and durable iron (Fe) and cobalt (Co)‐supported nitrogen (N) and sulfur (S) co‐doped three‐dimensional carbon nanofibers (FeCo−N, S@CNFs) were synthesized via electrospinning followed by carbonization. The as‐prepared FeCo−N,S@CNFs served as efficient ORR catalysts in alkaline 0.1 m KOH solutions that were N2 and O2‐saturated. The experimental results revealed that FeCo−N,S@CNFs were highly active ORR catalysts with defect‐rich active pyridinic N and pyrrolic N and metal bonds to N and S atom sites, which enhanced the ORR activity. FeCo−N,S@CNFs exhibited a high onset potential (Eonset=0.89 V) and half‐wave potential (E1/2=0.85 V), similar to the electrocatalytic activity of commercial Pt/C. Additionally, the durability of the as‐prepared FeCo−N,S@CNFs catalysts was maintained for 14 h with long‐term stability and high tolerance to methanol stability, accounting for their excellent catalytic ability. Furthermore, Co−N@CNFs, Fe−N@CNFs, and varying Fe and Co ratios were compared with those of FeCo−N,S@CNFs. Synergistic interactions between metals and heteroatoms were believed to play a significant role in enhancing the ORR activity. Owing to their excellent catalytic reduction ability, the as‐prepared FeCo−N,S@CNFs can be widely used in battery‐based systems and replace commercial Pt/C in fuel cell applications. [ABSTRACT FROM AUTHOR]

FeN 4 single-atom catalysts are among the most promising electrocatalysts for oxygen reduction reaction (ORR), which has important roles in energy conversion systems, such as fuel cells and metal-air batteries. It has been investigated that the activity of FeN 4 single-atom catalysts is highly dependent on the density and distance of the FeN 4 active centers. However, controllable synthesis of FeN 4 single-atom catalysts with designed active center distance and density is still a remaining difficulty. In this work, a series of pyridyl conjugated microporous polymers with varying types of nitrogen are used as precursors to synthesize carbonaceous single-atom ORR catalysts with different amounts of FeN 4 active centers. The influence of the nature of the nitrogen groups in the precursors on the number of FeN 4 active sites and the ORR activity trend of the obtained FeN 4 –C catalysts was investigated. The catalyst with the highest density of FeN 4 sites showed a high efficiency for ORR, making its application in Zn-air batteries promising. FeN 4 –C catalysts with different active site densities are synthesized by a series of pyridyl conjugated microporous polymers with different amount and position of N as precursors. The FeN 4 –C single-atom catalysts carbonized from polymeric precursors show increasing ORR activity with the increasing of active site density. The optimized FeN 4 –C-4 catalysts with the highest density of FeN 4 active sites show superior ORR performance than Pt/C and having potential for applications in Zn-air battery. [Display omitted] [ABSTRACT FROM AUTHOR]

Highlights: A comprehensive discussion of monitoring the structure evolutions of catalysts during ORR via multiple in-situ techniques to identify the active sites is presented. The extensive applications of in-situ techniques in elucidating the oxygen reduction reaction (ORR) mechanisms/pathways are reviewed. The challenges and recommendations of current in-situ techniques for monitoring the various dynamic evolutions in ORR are pointed out. Electrocatalytic oxygen reduction reaction (ORR) is one of the most important reactions in electrochemical energy technologies such as fuel cells and metal–O2/air batteries, etc. However, the essential catalysts to overcome its slow reaction kinetic always undergo a complex dynamic evolution in the actual catalytic process, and the concomitant intermediates and catalytic products also occur continuous conversion and reconstruction. This makes them difficult to be accurately captured, making the identification of ORR active sites and the elucidation of ORR mechanisms difficult. Thus, it is necessary to use extensive in-situ characterization techniques to proceed the real-time monitoring of the catalyst structure and the evolution state of intermediates and products during ORR. This work reviews the major advances in the use of various in-situ techniques to characterize the catalytic processes of various catalysts. Specifically, the catalyst structure evolutions revealed directly by in-situ techniques are systematically summarized, such as phase, valence, electronic transfer, coordination, and spin states varies. In-situ revelation of intermediate adsorption/desorption behavior, and the real-time monitoring of the product nucleation, growth, and reconstruction evolution are equally emphasized in the discussion. Other interference factors, as well as in-situ signal assignment with the aid of theoretical calculations, are also covered. Finally, some major challenges and prospects of in-situ techniques for future catalysts research in the ORR process are proposed. [ABSTRACT FROM AUTHOR]

The development of non−Pt or carbon−based catalysts for anion exchange membrane fuel cells (AEMFCs) requires identification of the active sites of the catalyst. Since not only metals but also carbon materials exhibit oxygen reduction reaction (ORR) activity in alkaline conditions, the contribution of carbon-based materials to ORR performance should also be thoroughly analyzed. However, the conventional CN− poisoning experiments, which are mainly used to explain the main active site of M−N−C catalysts, are limited to only qualitative discussions, having the potential to make fundamental errors. Here, we report a modified electrochemical analysis to quantitatively investigate the contribution of the metal and carbon active sites to ORR currents at a fixed potential by sequentially performing chronoamperometry with two reaction inhibitors, CN− and benzyl trimethylammonium (BTMA+). As a result, we discover how to quantify the individual contributions of two active sites (Pt nanoparticles and carbon support) of carbon−supported Pt (Pt/C) nanoparticles as a model catalyst. This study is expected to provide important clues for the active site analysis of carbon-supported non−Pt catalysts, such as M−N−C catalysts composed of heterogeneous elements. [ABSTRACT FROM AUTHOR]

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Iron and nickel phthalocyanines along with different carbon supports, i. e., multi‐walled carbon nanotubes (MWCNT), graphene, carbide‐derived carbon, Vulcan carbon, and mesoporous carbon (MC, from Pajarito Powder, LLC), are used to prepare six bimetallic (Fe, Ni) N‐doped carbon‐based catalysts. The aim of this work is to investigate the electrocatalytic activity of bimetal phthalocyanine‐modified nanocarbon catalysts, e. g., the effect of carbon supports on the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), including the anion‐exchange membrane fuel cell (AEMFC) and rechargeable zinc‐air battery (RZAB) configuration. The catalysts exhibit excellent electrocatalytic activity as exemplified by their half‐wave potential (E1/2) for ORR and the potential at which the OER current density reaches 10 mA cm−2 (Ej=10), but the best performing catalysts are FeNiN−MC (E1/2=0.88 V, Ej=10=1.58 V) and FeNiN−MWCNT (E1/2=0.87 V, Ej=10=1.59 V). In AEMFC analyses, FeNiN−MWCNT cathode provides peak power density (Pmax) of 406 mW cm−2, slightly higher than that of FeNiN−MC (Pmax=386 mW cm−2). Both catalysts exhibit a good RZAB performance (Pmax of 85 mW cm−2 for FeNiN−MWCNT). The assembled RZABs run stably for 48 h without any significant loss of performance. [ABSTRACT FROM AUTHOR]

Due to its exorbitant expense and scarcity on Earth, there is a need to anticipate a cost-effective and widely accessible catalyst that can effectively replace platinum, which is known for its efficiency in fuel cells. In this context, catalysts such as OH, H, and COOH group-functionalized cobalt-doped Graphyne-like boron nitride (referred to as BNyen) are being examined to enhance the mechanism of oxygen reduction reaction (ORR) via direct 4e− reduction. According to findings derived from DFT, it has been observed that reactions predominantly take place above Co metal center rather than edge site of BNyen. Additionally, the thermochemical characteristics point to the fact that these reactions release a significant amount of heat, suggesting their feasibility. By examining reversible potential of products and intermediates on phthalocyanines as well as adsorption energy (E ads), it has been determined that Co-BNyen(OH) serves as a superior catalyst for ORR process. In conclusion, this research affirms that BNyen materials hold significant promise as catalysts for ORR, a crucial process in fuel cell applications. [Display omitted] [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]

This work proposes a cost-effective strategy to massively synthesize high-efficiency ORR electrocatalyst. [Display omitted] • A novel type of composite Co/N C was prepared. • A potential strategy was proposed to massively synthesize ORR catalysts. • High ORR activity of Co/N C triggered by Co-N heteroatomic interface. • The high stability of Co/N C in 0.1 M KOH. The development of high-efficiency and low-cost oxygen reduction electrocatalysts have become an urgent need to push fuel cells into practical application. Herein, an effective electrocatalyst Co/N C was successfully constructed, which was derived from abundant peanut shells, obtained by doping with cobalt ions and pyrolyzing in NH 3 atmosphere. Due to the abundant Co-N active sites triggered by Co-N heteroatomic interface, the prepared electrocatalysts present excellent oxygen reduction reaction (ORR) performance with more positive half-wave potential (E 1/2 = 0.83 V), incremental limiting current density (J L = 5.45 mA cm−2), higher durability and stronger resistance to methanol, which is superior to that of Pt/C (E 1/2 = 0.81 V and J L = 5.19 mA cm−2). This work proposes a potential strategy to synthesize efficient ORR electrocatalysts to instead of Pt-based catalysts. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR), one of the key reactions for fuel cells and zinc-air batteries, should be improved for higher performance. Herein, we fabricated hollow Fe, Co, and nitrogen co-doped carbon (H-FeCo-NC) catalyst, which was prepared by carbonization of core-shell particles made of polypyrrole (PPy)-coated polystyrene (PS) spheres as cores and (Zn, Co) bimetallic-zeolitic imidazolate frameworks (ZnCoBZIFs) as shells. PPy was used as a nitrogen and a carbon source. The H-FeCo-NC catalyst had a high surface area of 324.08 m2 g−1 with uniformly distributed Fe and Co species, and excellent ORR performance with the half-wave potential of 0.888 V vs. reversible hydrogen electrode in alkaline media. Furthermore, the H-FeCo-NC catalyst demonstrated exceptional stability, durability, and tolerance to methanol crossover. • Hollow Fe, Co, and N-doped carbon was prepared using polypyrrole and MOFs. • Polypyrrole served as the source of carbon and nitrogen. • Hollow FeCo-NC catalyst showed high surface area with high metal dispersion. • The ORR activity, stability, and durability of the H-FeCo-NC catalyst were excellent. [ABSTRACT FROM AUTHOR]

A new isolation protocol was recently reported for highly purified metallic Fullertubes D5h‐C90, D3d‐C96, and D5d‐C100, which exhibit unique electronic features. Here, we report the oxygen reduction electrocatalytic behavior of C60, C70 (spheroidal fullerenes), and C90, C96, and C100 (tubular fullerenes) using a combination of experimental and theoretical approaches. C96 (a metal‐free catalyst) displayed remarkable oxygen reduction reaction (ORR) activity, with an onset potential of 0.85 V and a halfway potential of 0.75 V, which are close to the state‐of‐the‐art Pt/C benchmark catalyst values. We achieved an excellent power density of 0.75 W cm−2 using C96 as a modified cathode in a proton‐exchange membrane fuel cell, comparable to other recently reported efficient metal‐free catalysts. Combined band structure (experimentally calculated) and free‐energy (DFT) investigations show that both favorable energy‐level alignment active catalytic sites on the carbon cage are responsible for the superior activity of C96. [ABSTRACT FROM AUTHOR]

A non-precious metal electrocatalyst was obtained through the in-situ growth of iron phosphide (Fe 2 P) encapsulated by carbon nanotubes (CNTs) decorated with zeolitic imidazolate framework-8 (ZIF-8). Upon pyrolysis at a specific temperature, the ZIF-8/Fe 2 P@CNT catalyst exhibits high oxygen reduction reaction (ORR) ability and is close to the ideal electron transfer, which number is 3.99. The structure, high number of nitrogen-containing functional groups, and suitable surface properties of ZIF-8/Fe 2 P@CNT are critical for enhancing the ORR activity. ZIF-8/Fe 2 P@CNT exhibits a decay in electrocatalytic activity of 26 mV in the half-wave potential after 30 000 cycles, which is considerably superior to the decay of 123 mV for Pt/C after the same number of cycles. Therefore, ZIF-8/Fe 2 P@CNT exhibits excellent ORR activity and long-term stability and can be used as a fuel cell catalyst. [Display omitted] • ZIF-8 is grown in-situ on synthesized CNTs to form a ZIF-8/Fe 2 P@CNT catalyst. • Specific structure and unoccupied graphitic π∗ could catalyze the ORR activity. • ZIF-8/Fe 2 P@CNT exhibits excellent activity and long-term stability for fuel cell. [ABSTRACT FROM AUTHOR]

Polyazomethine (PAM) prepared from the polycondensation between p-phenylene diamine (PDA) and p-terephthalaldehyde (PTAl) via Schiff reaction can physically crosslink (complex) with Co ions. Co-complexed PAM (Co-PAM) in the form of gel is calcined to become a Co, N-co-doped carbonaceous matrix (Co-N-C), acting as cathode catalyst of an anion exchange membrane fuel cell (AEMFC). The obtained Co-N-C catalyst demonstrates a single-atom structure with active Co centers seen under the high-resolution transmission electron microscopy (HRTEM). The Co-N-C catalysts are also characterized by XRD, SEM, TEM, XPS, BET, and Raman spectroscopy. The Co-N-C catalysts demonstrate oxygen reduction reaction (ORR) activity in the KOH(aq) by expressing an onset potential of 1.19–1.37 V vs. RHE, a half wave potential of 0.70–0.92 V, a Tafel slope of 61–89 mV/dec., and number of exchange electrons of 2.48–3.79. Significant ORR peaks appear in the current–voltage (CV) polarization curves for the Co-N-C catalysts that experience two-stage calcination higher than 900 °C, followed by double acid leaching (CoNC-1000A-900A). The reduction current of CoNC-1000A-900A is comparable to that of commercial Pt-implanted carbon (Pt/C), and the max power density of the single cell using CoNC-1000A-900A as cathode catalyst reaches 275 mW cm−2. [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]

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]

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]

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]

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]

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]

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]

The replacement of Pt/C catalysts with iron−nitrogen−carbon (Fe−N−C) nanomaterials in the oxygen reduction reaction (ORR) is appealing for the large‐scale application of fuel cells. Herein, an extended Stöber method was used to in situ synthesize Fe−N co‐doped porous carbon spheres (Fe−N−Cs) with large surface areas and impressive ORR performance. Fe−N−Cs were synthesized using 3‐aminophenol as N precursor, ferrocenealdehyde (Fc−CHO) as Fe source and crosslinker, and Pluronic F127 as soft template. Among all prepared catalysts, Fe−N−Cs‐1.0 exhibits much enhanced ORR activities. The initial potential and half‐wave potential are 0.992 V, 0.873 V (vs. RHE) and 0.981 V, 0.871 V in alkaline and acidic media, respectively, which are higher than that of commercial Pt/C catalyst (0.986 V, 0.868 V and 0.979 V, 0.843 V). Meanwhile, the methanol tolerance and durability of Fe−N−Cs‐1.0 were far better than Pt/C. This work manifests the Fe−N−Cs electrocatalysts are expected to replace the commercial Pt/C catalyst in the area of ORR. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) can take place either through a two‐electron pathway to form H2O2 or through a four‐electron pathway to form H2O. Both the reactions are important in the respective fields, viz. H2O2 production as well as fuel cell technology, and rational design of catalysts is mandatory to acquire high energy efficiency in both cases. Here, we report the structure‐electrochemical property correlation of a series of perovskite related brownmillerite compounds, Ba2In0.75M0.25O5 (M=Mn/Fe/Co/Ni/Cu), synthesized by solid‐state method. On transition metal doping, octahedral distortions were observed, and the highly disordered material tends to follow the 4e transfer mechanism. More symmetrical structures followed the 2e pathway to form H2O2 as the product with high peroxide selectivity. The distortion in the octahedral arrangement can be a descriptor to finetune the selectivity of the catalysts towards the 2e and 4e pathways of ORR. [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]