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Oxygen reduction reaction (ORR) is the heart of many new energy conversions and storage devices, such as metal‐air batteries and fuel cells. However, ORR is currently facing the dilemma of sluggish intrinsic kinetics and the noble electrocatalysts of high price and low reserves. In this work, isolated Co atoms anchored on defective nitrogen‐doped carbon graphene single‐atom catalyst (Co‐SAC/NC) are synthesized via the proposed movable type printing method. The prepared Co‐SAC/NC catalyst demonstrates admirable ORR performance, with a high half‐wave potential of 0.884 V in alkaline electrolytes and outstanding durability. In addition, an assembled zinc–air battery with prepared Co‐SAC/NC as air‐cathode catalyst displays a high‐peak power density of 179 mW cm−2 and a high‐specific capacity (757 mAh g−1). Density functional theory calculations confirm that the true active sites of the prepared catalyst are Co‐N4 moieties, and further reveal a significantly electronic structure evolution of Co sites in the ORR process, in which the project density of states and local magnetic moment of Co atom varies during its whole reaction process. This work not only paves a new avenue for synthesizing SACs as robust electrocatalysts, but also provides an electronic‐level insight into the evolution of the electronic structure of single‐atom catalysts. [ABSTRACT FROM AUTHOR]

This study demonstrates the intercalation of single‐atom Ni (NiSA) substantially reduces the reaction activity of Ni oxide supported Pd nanoparticle (NiO2/Pd) in the oxygen reduction reaction (ORR). The results indicate the transition states kinetically consolidate the adsorption energy for the chemisorbed O and OH species on the ORR activity. Notably, the NiO2/Ni1/Pd performs the optimum ORR behavior with the lowest barrier of 0.49 eV and moderate second‐step barrier of 0.30 eV consequently confirming its utmost ORR performance. Through the stepwise cross‐level demonstrations, a structure–Eads–ΔE correspondence for the proposed NiO2/Nin/Pd systems is established. Most importantly, such a correspondence reveals that the electronic structure of heterogeneous catalysts can be significantly differed by the segregation of atomic clusters in different dimensions and locations. Besides, the doping‐depth effect exploration of the NiSA in the NiO2/Pd structure intrinsically elucidates that the Ni atom doping in the subsurface induces the most fruitful NiSA/PdML synergy combining the electronic and strain effects to optimize the ORR, whereas this desired synergy diminishes at high Pd coverages. Overall, the results not only rationalize the variation in the redox properties but most importantly provides a precision evaluation of the process window for optimizing the configuration and composition of bimetallic catalysts in practical experiments. [ABSTRACT FROM AUTHOR]

Future renewable energy supply and a cleaner Earth greatly depend on various crucial catalytic reactions for the society. Atomically dispersed metal site electrocatalysts (ADMSEs) have attracted tremendous research interest and are considered as the next‐generation promising oxygen reduction reaction (ORR) electrocatalysts due to the maximum atom utilization efficiency, tailorable catalytic sites, and tunable electronic structures. Despite great efforts have been devoted to the development of ADMSEs, the systematic summary for design principles of high‐efficiency ADMSEs is not sufficiently highlighted for ORR. In this review, the authors first summarize the fundamental ORR mechanisms for ADMSEs, and further discuss the intrinsic catalytic mechanism from the perspective of theoretical calculation. Then, the advanced characterization techniques to identify the active sites and effective synthesis methods to prepare catalysts for ADMSEs are also showcased. Subsequently, a special emphasis is placed on effective strategies for the rational design of the advanced ADMSEs. Finally, the present challenges to be addressed in practical application and future research directions are also proposed to overcome the relevant obstacles for developing high‐efficiency ORR electrocatalysts. This review aims to provide a deeper understanding for catalytic mechanisms and valuable design principles to obtain the advanced ADMSEs for sustainable energy conversion and storage techniques. [ABSTRACT FROM AUTHOR]

Platinum group metal‐free catalysts have been considered the most promising alternative for platinum‐based catalysts for the oxygen reduction reaction in fuel cells. Despite the significant advancement made in activity, their viability as fuel cell catalysts is still questionable due to their low durability. So far, deciphering the degradation mechanisms of this class of catalysts has been hampered by their undefined structure. Herein, we used a molecular model catalyst, iron‐phthalocyanine, featuring Fe−N4 active sites with resemblance to those in the more active Fe−N−C catalysts, and studied their degradation mechanisms. Based on X‐ray photoelectron spectroscopy and the electrochemical measurements, three main demetallation processes were identified: at potentials higher than 0.65 V vs. RHE, where the metal center is Fe3+, an electrochemical oxidation of the ligand ring is occurring, between 0.6 and 0.2 V vs. RHE, Fenton reagents are produced and attack the catalyst and support, and at lower voltages, where peroxide is produced by the catalyst and the carbon support. The combination of the different iron oxidation states together with the oxygen species directs to different degradation mechanisms. The decay rates obtained in the stability measurements establish what is mainly causing the loss of activity. Thereby, this model molecule can aid in understanding the degradation mechanisms of other platinum group metal‐free oxygen reduction reaction catalysts. [ABSTRACT FROM AUTHOR]

High‐performance platinum group metal‐free (PGM‐free) electrocatalysts were prepared from porous organic polymers (POPs) precursors with highly‐porous structures and adjustable surface area. A resin phenol‐melamine‐based POP and an iron salt were used to synthesize Fe−N−C catalysts with different iron contents (0.2–1.3 wt.%). Electrochemical and spectroscopical characterization allowed us to elucidate the effect of Fe content on the material's structure, surface chemistry, and electrocatalytic activity toward the oxygen reduction reaction (ORR). The increase of iron content led to a specific surface area decrease, preserving the morphological structure, with the formation of highly‐active catalytic sites, as indicated by X‐ray photoelectron spectroscopy (XPS) analysis. The rotating ring disk electrode experiments, performed at pH=13, confirmed the high ORR activity of both 0.5 Fe (E1/2=0.84 V) and 1.3 Fe (E1/2=0.83 V) catalysts, which were assembled at the cathode of a H2‐fed anion exchange membrane fuel cells (AEMFC) equipped with a FAA‐3‐50 membrane, evidencing promising performance (0.5 Fe, maximum power density, Max PD=69 mA cm−2 and 1.3 Fe, Max PD=87 mA cm−2) with further advancement prospects. [ABSTRACT FROM AUTHOR]

Four mesoporous carbons (MCs) with tunable pore size were synthesized by soft template synthesis, employing a resorcinol‐formaldehyde resin as a carbon precursor and a polyethylene oxide‐block‐polystyrene block copolymer as a sacrificial template in which the length of the polystyrene block (165, 300, 500, and 1150 units) allowed the modulation of the surface area of MCs (567, 582, 718 and 840 m2 g−1, respectively). The complete set of MCs was also doped with nitrogen by ball milling in the presence of cyanamide and stabilized in a second thermal treatment at 750°C, leading to nitrogen content of ∼2.65% in all samples. The two sets of MCs were used for evaluating both the effect of textural properties and nitrogen doping in the electrochemical reduction of oxygen in acid electrolytes. Each catalyst was characterized by means of elemental analysis and N2 physisorption analysis, whereas the selected series of samples were also characterized by transmission electron microscopy, scanning electron microscopy, X‐ray photoemission spectroscopy, inductively coupled plasma mass spectroscopy (ICP‐MS), and Raman analysis. Voltammetric rotating ring‐disk measurements in 0.5 M H2SO4 demonstrated that the catalytic activity for the O2 reduction scales with the surface area in the non‐doped series, and also the selectivity for the two‐electron process leading to H2O2 increases in the samples having wider pores and higher surface area, even if the leading mechanism is the tetraelectronic process leading to H2O. The doping with nitrogen leads to a general increase of the catalytic activity with a shift of the O2 peak potential to more positive values of 75–150 mV. In the doped series, nitrogen doping prevails on the textural properties for guiding the selectivity toward the two‐ or four‐electron process, since a similar H2O2 yield was observed for all N‐MC samples. The possible presence of FeNx sites derived from the ball milling fixation of nitrogen was evaluated by using the NO‐stripping technique. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) are a promising alternative toward catalysis, due to the unique framework structure and the excellent chemical stability. However, the scarcity of unsaturated metal sites and the low conductivity have constrained the advancement of these materials for catalysis of electrochemical reactions. Exploring next‐generation conductive metal–covalent organic frameworks (M‐COFs) with extra metal active sites is crucial for improving their catalytic activity. Herein, a novel fully‐conjugated M‐COFs (Co‐PorBpy‐Co) with two types of metal sites is proposed and achieved by solvothermal method in the presence of carbon nanotube (CNT). The electrocatalyst constructed by the Co‐PorBpy‐Co exhibits excellent oxygen reduction reaction (ORR) activity (E1/2 = 0.84 V vs RHE, n = 3.86), superior to most COFs‐based catalysts. Theoretical result shows the CoN2 sites are extremely active for ORR, and Co‐PorBpy‐Co exhibits excellent conductivity for electron transfer. The Zn–air battery constructed by Co‐PorBpy‐Co/CNT manifests excellent power density (159.4 mW cm−2) and great cycling stability, surpassing that of 20 wt% Pt/C catalyst. This work not only proposes a novel design concept for electrocatalysts, but establishes a mechanism platform for single‐metal atom electrocatalysis and synergistic effect. [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]

Carbon‐based nanomaterials are renowned for their exceptional properties, making them propitious candidates for oxygen reduction reaction (ORR) electrocatalysis. However, their intrinsic activity is often challenging to investigate unambiguously with conventional methodologies due to the inherent complexities of such systems and the material itself. Zooming into the material and gaining electrochemical information with high resolution is a way to get rid of many experimental factors that influence the catalytic activity in macro‐scale measurements. Herein, we employ nano‐scale scanning electrochemical cell microscopy (SECCM) to investigate individual catalyst agglomerates with and without Nafion content. The intrinsic ORR activity of the catalyst was unravelled by using a unique approach of normalizing the data of all measured points by their distinctive electrochemical surface area (ECSA). When coupling with scanning electron microscopy (SEM), the structure and morphology of the catalytically active agglomerates were visualized. [ABSTRACT FROM AUTHOR]

Fe single‐atom catalysts (Fe‐SACs) have been extensively studied as a highly efficient electrocatalyst toward the oxygen reduction reaction (ORR). Nonetheless, they suffer from stability issue induced by dissolution of Fe metal center and the OH− blocking. Herein, a surface molecular engineering strategy is developed by using β‐cyclodextrins (CDs) as a localized molecular encapsulation. The CD‐modified Fe‐SAC (Fe‐SNC‐β‐CD) shows obviously improved activity toward the ORR with 0.90 V, 4.10 and 4.09 mA cm−2 for E1/2, J0 and Jk0.9, respectively. Meanwhile, the Fe‐SNC‐β‐CD shows the excellent long‐term stability against aggressive stress and the poisoning. It is confirmed through electrochemical investigation that modification of β‐CD can, on one hand, regulate the atomic Fe coordination chemistry through the interaction between the CD and FeNx moiety, while on the other mitigate the strong adsorption of OH− and function as protective barrier against the poisoning molecules leading to enhanced ORR activity and stability for the Fe‐SACs. The molecular encapsulation strategy demonstrates the uniqueness of post‐pyrolysis surface molecular engineering for the design of single‐atom catalyst. [ABSTRACT FROM AUTHOR]

Vacancy engineering is deemed as one of the powerful protocols to tune the catalytic activity of electrocatalysts. Herein, Se‐vacancy with charge polarization is created in the NiSe2 structure (NiSe2‐VSe) via a sequential phase conversion strategy. By a combined analysis of the Rietveld method, transient photovoltage spectra (TPV), in situ Raman and density functional theory (DFT) calculation, it is unequivocally discovered that the presence of charge‐polarized Se‐vacancy is beneficial for stabilizing the structure, decreasing the electron transfer kinetics, as well as optimizing the free adsorption energy of reaction intermediate during two‐electron oxygen reduction reaction (2e− ORR). Benefiting from these merits, the as‐prepared NiSe2‐VSe delivered the highest selectivity of 96% toward H2O2 in alkaline media, together with a selectivity higher than 90% over the wide potential range from 0.25 to 0.55 V, ranking it in the top level among the previously reported transition metal‐based electrocatalysts. Most notably, it also displayed admirable stability with only a slight selectivity decay after 5000 cycles of accelerated degradation test (ADT). [ABSTRACT FROM AUTHOR]

Biphasic interfacial electron transfer (IET) reactions at polarisable liquid|liquid (L|L) interfaces underpin new approaches to electrosynthesis, redox electrocatalysis, bioelectrochemistry and artificial photosynthesis. Herein, using cyclic and alternating current voltammetry, we demonstrate that under certain experimental conditions, the biphasic 2‐electron O2 reduction reaction can proceed by single‐step IET between a reductant in the organic phase, decamethylferrocene, and interfacial protons in the presence of O2. Using this biphasic system, we demonstrate that the applied interfacial Galvani potential difference Δowφ ${{\Delta }_{{\rm o}}^{{\rm w}}\phi{} }$ provides no direct driving force to realise a thermodynamically uphill biphasic IET reaction in the mixed solvent region. We show that the onset potential for a biphasic single‐step IET reaction does not correlate with the thermodynamically predicted standard Galvani IET potential and is instead closely correlated with the potential of zero charge at a polarised L|L interface. We outline that the applied Δowφ ${{\Delta }_{{\rm o}}^{{\rm w}}\phi{} }$ required to modulate the interfacial ion distributions, and thus kinetics of IET, must be optimised to ensure that the aqueous and organic redox species are present in substantial concentrations at the L|L interface simultaneously in order to react. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) is Achilles' heel of zinc‐air battery. The ideal electrocatalyst for ORR should combine both high activity and high stability. In order to achieve this goal, a new N, S co‐doped carbon coated Fe3N nanoparticles electrocatalyst with redistributed charge was designed and synthesized. The doping of S elements destroyed the ordered structure of carbon matrix, which cooperated with Fe3N nanoparticles to cause charge redistribution of carbon atoms. Furthermore, the carbon shell protected Fe3N from corrosion during the electrocatalytic process. Fe3N/NSC electrocatalyst showed excellent ORR property with E1/2=0.86 V, and the zinc‐air battery assembled based on it could run stably for more than 650 hours. This work provides a strategy to regulate the redistributed charge of carbon atoms to boost its electrocatalytic activity and stability together. [ABSTRACT FROM AUTHOR]

Electrocatalytic oxygen reduction reaction (ORR) to generate hydrogen peroxide (H2O2) via a 2e− pathway offers a green alternative to the energy‐extensive anthraquinone process; however, the challenge lies in the development of low cost and effective 2e− ORR catalysts. In this work, a highly selective and stable Mo clusters supported by nitrogen‐doped carbon polyhedrons catalyst for direct H2O2 electrosynthesis are first designed, which shows a high H2O2 selectivity (>77%) in the applied potential range varying from 0.2 to 0.65 V vs RHE, and an excellent mass activity of 29.0 A gcat.−1 (at 0.65 V) with negligible activity decay over 10 000 cycles in an alkaline medium. Moreover, the catalyst displays a yield rate of 136.2 ± 1.5 ppm cm−2 h−1 at −20 mA cm−2 in a continuous flow cell with neutral electrolyte. Taken together, the obtained performance metrics are comparable to the best‐reported ORR results. Density‐functional theory analyses reveal that Mo clusters can donor electrons to activate O2 molecules and strengthen the *OOH binding on Mo sites as well, thus inducing a high H2O2 selectivity. The present work provides a unique insight into the atomic introduction of metal clusters‐based materials for 2e− ORR to H2O2 powered by renewable energy. [ABSTRACT FROM AUTHOR]

Exploring low‐cost and high‐efficient electrocatalyst is an exigent task in developing novel sustainable energy conversion systems, such as fuel cells and electrocatalytic fuel generations. 2D materials, specifically 2D superlattice materials focused here, featured highly accessible active areas, high density of active sites, and high compatibility with property‐complementary materials to form heterostructures with desired synergetic effects, have demonstrated to be promising electrocatalysts for boosting the performance of sustainable energy conversion and storage devices. Nevertheless, the reaction kinetics, and in particular, the functional mechanisms of the 2D superlattice‐based catalysts yet remain ambiguous. In this review, based on the recent progress of 2D superlattice materials in electrocatalysis applications, the rational design and fabrication of 2D superlattices are first summarized and the application of 2D superlattices in electrocatalysis is then specifically discussed. Finally, perspectives on the current challenges and the strategies for the future design of 2D superlattice materials are outlined. This review attempts to establish an intrinsic correlation between the 2D superlattice heterostructures and the catalytic properties, so as to provide some insights into developing high‐performance electrocatalysts for next‐generation sustainable energy conversion and storage. [ABSTRACT FROM AUTHOR]

Homogeneous, aqueous solutions of the natural compound riboflavin were investigated for their electrocatalytic oxygen to hydrogen peroxide (H2O2) reduction performance using cyclic voltammetry and electrolysis. In addition to pH dependencies, interestingly the choice of carbon‐based electrode material had a strong impact on the electrocatalytic performance. Therefore, the three electrode materials, glassy carbon, carbon paper (CP), and carbon felt were electrochemically compared and afterwards investigated with scanning electron microscopy. Attributed to the deprotonation of riboflavin, pH = 13 was identified as the best performing condition. Using CP at pH = 13, the addition of riboflavin enhanced the H2O2 production by a factor of 14 up to 355 μmol after 6 h at an average faradaic efficiency of around 80%. [ABSTRACT FROM AUTHOR]

As the most promising alternative to platinum‐based catalysts for cathodic oxygen reduction reaction (ORR) in proton exchange membrane fuel cells, further performance enhancement of Fe–N–C catalysts is highly expected to promote their wide application. In Fe–N–C catalysts, the single Fe atom forms a square‐planar configuration with four adjacent N atoms (D4h symmetry). Breaking the D4h symmetry of the FeN4 active center provides a new route to boost the activity of Fe–N–C catalysts. Herein, for the first time, the deformation of the square‐planar coordination of FeN4 moiety achieved by introducing chalcogen oxygen groups (XO2, X = S, Se, Te) as polar functional groups in the Fe–N–C catalyst is reported. The theoretical and experimental results demonstrate that breaking the D4h symmetry of FeN4 results in the rearrangement of Fe 3d electrons and increases spin moment of Fe centers. The efficient spin state manipulation optimizes the adsorption energetics of ORR intermediates, thereby significantly promoting the intrinsic ORR activity of Fe–N–C catalysts, among which the SeO2 modified catalyst lies around the peak of the ORR volcano plot. This work provides a new strategy to tune the local coordination and thus the electronic structure of single‐atom catalysts. [ABSTRACT FROM AUTHOR]

Combining isolated atomic active sites with those in nanoparticles for synergizing complex multistep catalysis is being actively pursued in the design of new electrocatalyst systems. However, these novel systems have been rarely studied due to the challenges with synthesis and analysis. Herein, a synergistically catalytic performance is demonstrated with a 0.89 V (vs reversible hydrogen electrode) onset potential in the four‐step oxygen reduction reaction (ORR) by localizing tungsten single atoms around tungsten nitride nanoparticles confined into nitrogen‐doped carbon (W SAs/WNNC). Through density functional theory calculations, it is shown that each of the active centers in the synergistic entity feature a specific potential‐determining step in their respective reaction pathway that can be merged to optimize the intermediate steps involving scaling relations on individual active centers. Impressively, the W SAs/WNNC as the air cathode in all‐solid‐state Zn‐air and Al‐air batteries demonstrate competitive durability and reversibility, despite the acknowledged low activity of W‐based catalyst toward the ORR. [ABSTRACT FROM AUTHOR]

Exploring efficient and cost‐saving electrocatalysts is essential to the renewable energy storage and utilization, which is still in its embryonic period. MOFs have drawn tremendous attention due to their adjustability, abundant active sites, and plentiful pores. Notably, satisfactory electrocatalytic performance has been achieved by MOFs‐based electrocatalysts comparable to traditional electrocatalysts. State‐of‐the‐art works about the MOFs‐based electrocatalysts for hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and ORR were summarized in this review. This review comprises a series of modifying strategies of MOFs and their derivatives, from aspects of structure, composition, and morphology. Furthermore, the active sites and functional mechanisms' recognition are involved in this review expecting to provide reference for rationally designing efficient electrocatalysts. At last, the current status, challenges, and perspectives of MOFs‐based electrocatalysts are also discussed. [ABSTRACT FROM AUTHOR]

Electrochemical 2‐electron oxygen reduction reaction (ORR) is a promising route for renewable and on‐site H2O2 production. Oxygen‐rich carbon nanotubes have been demonstrated their high selectivity (≈80%), yet tailoring the composition and structure of carbon nanotubes to further enhance the selectivity and widen working voltage range remains a challenge. Herein, combining formamide condensation coating and mild temperature calcination, a nitrogen and oxygen comodified carbon nanotubes (N,O‐CNTs) electrocatalyst is synthesized, which shows excellent selective (>95%) H2O2 selectivity in a wide voltage range (from 0 to 0.65 V versus reversible hydrogen electrode). It is significantly superior to the corresponding selectivity values of CNTs (≈50% in 0–0.65 V vs RHE) and O‐CNTs (≈80% in 0.3–0.65 V vs RHE). Density functional theory calculations revealed that the C neighbouring to N is the active site. Introducing O‐related species can strengthen the adsorption of intermediates *OOH, while N‐doping can weaken the adsorption of in situ generated *O and optimize the *OOH adsorption energy, thus improving the 2‐electron pathway. With optimized N,O‐CNTs catalysts, a Janus electrode is designed by adjusting the asymmetric wettability to achieve H2O2 productivity of 264.8 mol kgcat–1 h–1. [ABSTRACT FROM AUTHOR]

Electrochemical 2‐electron oxygen reduction reaction (ORR) is a promising route for renewable and on‐site H2O2 production. Oxygen‐rich carbon nanotubes have been demonstrated their high selectivity (≈80%), yet tailoring the composition and structure of carbon nanotubes to further enhance the selectivity and widen working voltage range remains a challenge. Herein, combining formamide condensation coating and mild temperature calcination, a nitrogen and oxygen comodified carbon nanotubes (N,O‐CNTs) electrocatalyst is synthesized, which shows excellent selective (>95%) H2O2 selectivity in a wide voltage range (from 0 to 0.65 V versus reversible hydrogen electrode). It is significantly superior to the corresponding selectivity values of CNTs (≈50% in 0–0.65 V vs RHE) and O‐CNTs (≈80% in 0.3–0.65 V vs RHE). Density functional theory calculations revealed that the C neighbouring to N is the active site. Introducing O‐related species can strengthen the adsorption of intermediates *OOH, while N‐doping can weaken the adsorption of in situ generated *O and optimize the *OOH adsorption energy, thus improving the 2‐electron pathway. With optimized N,O‐CNTs catalysts, a Janus electrode is designed by adjusting the asymmetric wettability to achieve H2O2 productivity of 264.8 mol kgcat–1 h–1. [ABSTRACT FROM AUTHOR]

The development of efficient catalytic electrode toward oxygen reduction reaction (ORR) is still a great challenge for the wide use of zinc–air batteries. Herein, Co2N nanoparticles (NPs) anchored on N‐doped carbon from cattail were verified with excellent catalytic performances for ORR. The onset and half‐wave potentials over the optimal catalyst reach to 0.96 V and 0.84 V, respectively. Current retention rates of 96.8% after 22‐h test and 98.8% after running 1600 s were obtained in 1 M methanol solution. Density functional theory simulation proposes an apparently increased electronic states of Co2N in N‐doped carbon layer close to the Fermi level. Higher charge density, favorable adsorption, and charge transfer of intermediates originate from the coexistence of Co2N NPs and N atoms in carbon skeleton. The superior catalytic activity of composites also was confirmed in zinc–air batteries. This novel catalytic property and controllable preparation approach of Co2N‐carbon composites provide a promising avenue to fabricate metal‐containing catalytically active carbon from biomass. [ABSTRACT FROM AUTHOR]

Complex solid solutions ("high entropy alloys" with a single solid‐solution phase) hold great promise in electrocatalysis because of their nearly unlimited number of different active sites exposed at the surface. It has been shown by theoretical studies that multiple arrangements of different elements directly neighboring a binding site create millions of differently active catalytic sites. We report a zooming‐in approach using scanning electrochemical cell microscopy (SECCM) to distinguish between the averaged electrochemical response of multiple active sites and active site‐specific electrochemical response. Using a thin film complex solid solution electrocatalyst and a range of SECCM single barrel capillaries with diameters from 1.2 µm to 50 nm, we observed an averaged electrochemical response for the oxygen reduction reaction with minor statistical variations for the larger capillary diameters. In contrast, significant statistical heterogeneity among the measured spots is observed for small capillary diameters. This statistical heterogeneity is attributed to the ability of the smaller probe size to address a comparatively smaller number of active sites with high or low activity dominating the measured electrocatalytic currents. [ABSTRACT FROM AUTHOR]

The manganese dioxide/graphene oxide (MnO2/GO) nanocomposites were prepared from hydrothermally synthesized MnO2 nanorods and graphene oxide. Electrocatalytic performance for the oxygen reduction reactions (ORR) of the fabricated MnO2/GO nanocomposites was evaluated using the rotating disk electrode (RDE) method. It is found that MnO2/GO nanocomposites deliver significantly enhanced performance compared to standalone MnO2 and GO with current density and onset potential values of 5.1 mA/cm2 and 0.93 V versus RHE, respectively. The alkaline membrane fuel cell (AMFC) characteristics were also studied. In particular, the single‐cell alkaline fuel cell stack with MnO2/GO nanocomposite as cathode loading produced a peak power density value of 82 mW/cm2. Our findings revealed great potential for MnO2/GO nanocomposites for their electrocatalytic performance and utilization in AMFC as the cathode. Namely, MnO2/GO achieved fuel cell functionalities that were comparable to the widely used commercial Pt/C. The enhanced electrochemical performance of MnO2/GO is attributed to the synergistic interaction between highly conductive GO sheets and active sites of MnO2 nanorods. The commendable performance of MnO2/GO suggests that it can be used as electrocatalysts in alkaline fuel cell applications. [ABSTRACT FROM AUTHOR]

The felicitous electrolyte with advance electrodes (cathode and anode) results in the development of an improved and efficacious battery/fuel cell. Perovskite based zinc‐air batteries with biological gel electrolyte prove to outperform the aqueous batteries. In this research, a zinc‐air battery was developed using a novel biocompatible electrolyte, Guar‐gum employing LaMnO3 (LMO) perovskite as a bi‐functional electro‐catalyst. The performance of the developed perovskite catalyst in guar‐gum electrolyte was obtained and compared with the performance of the material in both polymer gel (polyvinyl alcohol‐KOH) and aqueous medium. The bi‐functional catalyst shows enhanced catalytic activity, endurance and durability in alkaline medium with an open circuit voltage of 1.40 V, power density of 9.77 mW cm−2 at the current density of 11.12 mA cm−2 and a specific capacity of 2624 mAh g−1 comparatively competent with respect to the PVA‐based battery with the specific capacitance of 753 mAh g−1. Also, the rechargeable LMO zinc‐air battery exhibited excellent cycling stability at a current density of 10 mA cm−2. Thus, the results obtained proved the competent performance of the guar‐gum electrolyte compared to the previous developed polymer electrolyte. This is how the combination of LMO in the guar‐gum electrolyte is seen to be successful for commercial use in metal‐air batteries and fuel cells. [ABSTRACT FROM AUTHOR]

Structure-controlled Pt-based nanocrystals have the great potential to provide a flexible strategy for improving the catalysis of the oxygen reduction reaction (ORR). Here, a new synthetic approach is developed to tune the 3D structure of Pt-based alloys, and switch a synthetic reaction which produces solid PtCu octahedral stars (OSs) to produce PtCu nested skeleton cubes (NSCs) by simple addition of Ni(acac)2. In particular, Ni2+-guided anisotropic growth is observed to generate the nested skeleton structure in PtCu NSCs. Ni2+, though absent from the nanoalloys, not only endows faster Cu reduction kinetics but also acts as a structure-directing agent. Moreover, it is shown that acetic acid treatment of PtCu NSCs/C exposes Pt-rich surface with a fine-tuned Pt d-band center energy and the reduced Cu leaching, resulting in strikingly high activity and stability. Acid-treated PtCu NSCs/C shows a remarkable ORR mass activity of 5.13 A mgPt -1, about 26 times higher than commercial Pt/C catalyst. This catalyst also exhibits excellent stability with a lower activity decay of 11.5% and the negligible variation in structure after 10 000 cycles. [ABSTRACT FROM AUTHOR]

Platinum (Pt) nanoparticles on various supports, such as commercial carbon powder, titanium dioxide (TiO2), and reduced graphene oxide (rGO), were synthesized using a continuous flow microfluidic system. First, the support materials were separately synthesized using the sonochemical technique followed by the loading of Pt. The Pt nanoparticles on different supports were characterized using Brunauer–Emmett–Teller (BET) for surface area and porosity analysis; X‐ray diffraction (XRD) for structural confirmation; Fourier transform infrared (FTIR) spectroscopy and X‐ray photoelectron spectroscopy (XPS) for surface composition; and transmission electron microscopy (TEM) for morphological investigation. Further, polymer electrolyte membrane (PEM) fuel cells were fabricated using the Pt nanoparticles on different supports, and cyclic voltammetry (CV), linear sweep voltammetry (LSV), and power density were performed. Among the three electrocatalysts, Pt/rGO showed the highest electrochemical performance. Pt/rGO showed higher specific activity (119 mA/cm2), mass activity (238 mA/mg), current density (1274 mA/cm2), and power density (497 mW/cm2). We also determined the mass activity and specific activity of the electrocatalysts based on the electrochemical data. This work shows the potential of the microfluidic system to continuously synthesize the technologically important nanomaterials and their application for energy conversion devices. [ABSTRACT FROM AUTHOR]

High dosage of expensive Pt to catalyze the sluggish oxygen reduction reaction (ORR) on the cathode severely impedes the commercialization of proton exchange membrane fuel cells. Therefore, it is urgent to cut down the Pt catalyst by efficiently improving the ORR activity while maintaining high durability. Herein, magic concave Pt–Zn nanocubes with high‐index faceted Pt skin (Pt78Zn22) are proposed for high‐efficiency catalysis toward proton exchange membrane fuel cells. These unique structural features endow the Pt‐skin Pt78Zn22/KB with a mass activity of 1.18 mA μgPt–1 and a specific activity of 3.64 mA cm–2 for the ORR at 0.9 V (vs RHE). Meanwhile, the H2–O2 fuel cell assembled by this catalyst delivers an ultrahigh peak power density of ≈1449 mW cm–2. Both experiments and theoretical calculations show that the electronic structure of the surface is adjusted, thereby shortening the length of the Pt–Pt bond and reducing the adsorption energy of OH*/O* on the Pt surface. This work demonstrates the synergistic effect of the oxidation‐resistant metal Zn and the construction of Pt‐rich surface engineering. Also, it guides the future development of catalysts for their practical applications in energy conversion technologies and beyond. [ABSTRACT FROM AUTHOR]

Developing highly effective and stable non‐precious bifunctional oxygen electrocatalysts is crucial and challenging. Herein, we report nano‐mediated straight bamboo‐shaped nitrogen‐doped carbon nanotubes modified with encapsulated NiCo2S4‐based nanoparticles (E‐NiCo2S4/SBS‐NCNTs) by electrodeposition and procedural calcination strategy, in which nitrogen‐doped carbon nanotubes with straight bamboo shape (SBS‐NCNTs) show more average diameter and encapsulated NiCo2S4‐based nanoparticles (E‐NiCo2S4) are coated by carbon, and what makes us even more excited is that they are evenly dispersed on SBS‐NCNTs surface, not just at the tip or inside. When applied for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), E‐NiCo2S4/SBS‐NCNTs show excellent catalytic activity, and onset potential (Eonset) in OER and ORR is only 1.52 V and 0.95 V (vs. RHE) in 0.1 M KOH, respectively. More importantly, the hybrids exhibit good methanol tolerance, with almost unchanged for ORR performance after adding 0.5 M methanol, and it has highly stability, the current density dropped by 22% after 7 h of reaction. The interaction of NiCo2S4 with the external carbon layer can greatly enhance the electrocatalytic activity toward the OER and it has a complete 4e– reaction process toward the ORR. The excellent electrocatalytic activity is mainly due to synergistic enhancement effect, in which SBS‐NCNTs with highly catalytic activity provide good conductivity, expose more active sites and promotes fast mass transfer; Carbon‐coated NiCo2S4‐based nanoparticles can improve the local work function of SBS‐NCNT through synergistic electronic interaction, promoting O2 adsorption, ensure rapid electron transport, and enable SBS‐NCNT to improve its electrocatalytic activity. Because of the weakness of Ostwald effect and synergistic enhancement, the stability and catalytic activity of NiCo2S4‐based nanoparticles can be greatly improved. All these advantages can synergistically improve the electrocatalytic efficiency and make it become one of the most promising bifunctional oxygen electrocatalysts. [ABSTRACT FROM AUTHOR]

The exploration of cheap, efficient, and durable bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is highly desired to push forward the commercialization of rechargeable metal–air batteries. Here, bifunctional ORR/OER electrocatalysts based on CoxP (0 < x < 2, i.e., Co2P, Co2P/CoP mixture, and CoP) nanoparticles (NPs) anchored on N,P‐doped carbon framework (CoxP@NPC) are developed via one‐step carbonization of the mixture of as‐synthesized ZIF‐67 and melamine–phytic acid supermolecular aggregate (MPSA). The stoichiometric ratio of resultant CoxP NPs can be rationally designed by adjusting the introduced ratio of ZIF‐67 to MPSA, enabling their fabrication in a controlled manner. It is found that the as‐synthesized Co2P@NPC exhibits the best bifunctional ORR/OER activity among the CoxP@NPC analogues, with a reversible oxygen electrode index (ΔE = Ej10 − E1/2) down to ~0.75 V. The constructed Zn–air battery based on Co2P@NPC delivers a peak power density of 157 mW cm−2 and an excellent charge‐discharge stability with negligible voltage decay for 140 h at 10 mA cm−2, superior to those based on Pt/C+RuO2 and most CoxP‐based electrodes ever reported. [ABSTRACT FROM AUTHOR]

Reduced graphene supported Co‐Sn‐Pd nanoparticle catalysts(Co0.2SnxPdy/rGO, x + y = 0.4) were successfully synthesized by reducing the trace amounts of ions (Pd2+, Sn2+, and Co2+) in the presence of reduced graphene via an ultrasonic irradiation method. Characterization of the Co0.2SnxPdy/rGO catalysts by X‐ray diffraction (XRD) and transmission electron microscopy (TEM) indicates that the Co0.2Sn0.2Pd0.2/rGO catalyst with a mean diameter of ~3.8 nm is close to a single‐phase solid solution. X‐ray photoelectron spectroscopy (XPS) shows the binding energy of metallic Pd shifts to a higher angle in the Co0.2SnxPdy/rGO (x + y = 0.4) catalysts, indicating a shift of Pd electronic centre upon alloying with Co and Sn. Conventionally, ternary Co‐Sn‐Pd/rGO catalysts show greater oxygen reduction reaction (ORR) activities and durability than binary Pd‐Co/rGO catalyst and 20 wt% Pt/C catalyst even at a very low Pd content. Among of the synthetic catalysts, the Co0.2Sn0.2Pd0.2/rGO catalyst exhibits the best ORR activity (E1/2 = 0.91 V, k = −57 mV · dec−1) and dominates a 4‐electron pathway in the ORR process (n = 3.95 ± 0.09, H2O2<4%). Also, the Co0.2SnxPdy/rGO (x + y = 0.4) catalysts display a remarkable advantage of high methanol tolerance compared to that of the commercial 20 wt% Pt/C catalyst, which make them potential candidates for direct methanol fuel cells. [ABSTRACT FROM AUTHOR]

The goal of global carbon peak and neutrality gives an impetus to the utilization of clean energy (e.g., fuel cell) and carbon dioxide (CO2) at a large scale, where the oxygen reduction reaction (ORR) and CO2 reduction reaction (CO2RR) are the key reactions via the sustainable system, respectively. As a main precursor for fabricating affordable carbon‐based electrocatalysts with uniformly dispersed active centers and tailorable performances for ORR and CO2RR, metal organic frameworks (MOFs) have captured a surge of interest in recent years. Despite the facilitated development of MOF‐derived carbon‐based electrocatalysts by many investigations, it is still plagued by high overpotential and unsatisfied life span, which are greatly determined by the efficient and alterable confinement effect on synthesis and performance. In this review, firstly, the confined synthetic strategies (doping engineering, defect engineering, geometric engineering, etc.) of MOF‐derived carbon‐based electrocatalysts with multi‐sized active centers (atom, atomic clusters and nanoparticles (NPs)) are systematically summarized; secondly, the confinement effect on the interaction of ORR and CO2RR intermediates, as well as the catalytic durability and activity, was discussed from chemical and physical aspects. In the end, the review discusses the remaining challenges and emerging research topics in the future, including support upgradation and catalyst innovation, high selectivity and effective confinement synthesis, in situ and operando characterization techniques, theoretical investigation, and artificial intelligence (AI) assistant. The new understanding and insights into these aspects will guide the rational confinement concept of MOF‐derived carbon‐based electrocatalysts for ORR and CO2RR with optimized performances in terms of confinement engineering and are believed to be helpful for filling the existing gaps between scientific communities and practical use. [ABSTRACT FROM AUTHOR]

Rational design of metal oxide supported non‐precious metals is essential for the development of stable and high‐efficiency oxygen reduction reaction (ORR) electrocatalysts. Here, an efficient ORR catalyst consisting of binary Fe/Co nanoclusters supported by defective tungsten oxide and embedded N‐doped carbon layer (NC) with a 3D ordered macroporous architecture (3DOM Fe/Co@NC‐WO2−x) is developed. The oxygen deficient 3DOM WO2−x not only serves as a porous and stable support, but also enhances the conductivity and ensures good dispersion of the binary Fe/Co nanocluster, benefiting its ORR catalytic activity. Theoretical calculation shows that there exists a synergistic effect of electron transfer from Fe to Co in the supported binary Fe/Co cluster, promoting the ORR reaction energetics. Accordingly, the 3DOM Fe/Co@NC‐WO2−x catalyst exhibits excellent ORR activity in alkaline medium with a half wave potential (E1/2) of 0.87 V higher than that of Pt/C (0.85 V). The zinc–air batteries assembled by 3DOM Fe/Co@NC‐WO2−x cathode deliver a higher power density and specific capacity than that of Pt/C. A new strategy of combining synergistic binary‐metal nanoclusters and conductive metal oxide support design is provided here to develop efficient and durable ORR electrocatalyst. [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]

Functionalization of the carbon support is a promising strategy for lowering platinum loadings at the cathode of proton exchange membrane fuel cells. Here, nitrogen-containingmoieties are introduced directly onto carbon black by a simple and easily tunable graftingmethod initiated by the thermal decomposition of azo compounds in water. X-ray photoelectron spectroscopy (XPS) and elemental analysis confirm the successful functionalization. After deposition of Pt nanoparticles onto the carbon supports, the electrocatalysts are characterized in thin film rotating disk electrode (RDE) configuration towards the acidic oxygen reduction reaction (ORR). The grafting does not influence the Pt intrinsic ORR activity when the thin film does not include ionomer. However, the functionalization modifies the ionomer/carbon material interaction, leading to higher apparent ORR activity when the ionomer is included in the thin film. Moreover, accelerated stress testing shows durability enhancement as the result of grafting. [ABSTRACT FROM AUTHOR]

Powdery hierarchical porous carbons serve as cost‐effective, functional materials in various fields, namely energy storage, heterogeneous catalysis, electrochemistry, and water/wastewater treatment. Such powdered activated carbons (PAC) limit new module designs and require further preparation steps, for example, adding polymeric binders, to be shaped into a standalone geometry. Polymeric binders, however, can block PACs' catalytic and active sites and, more importantly, pose the risk of secondary pollution for environmental purposes, especially in the context of clean water supply. This study introduces a novel synthesis method for fabricating freestanding nitrogen‐doped carbons with hierarchical porosity using chitosan and sucrose as green precursors. Chitosan supplies nitrogen and acts as a backbone, giving a freestanding geometry to the final product, and sucrose is a carbon‐rich precursor. The proposed method employs ice‐ and hard‐templating for macropores and mesopores and combines carbonization and activation steps with no required activating agent. Final freestanding carbons function as adsorbents for removing persistent pollutants, as binder‐free electrodes with high specific surface area and capacitive current, and as tubular gas diffusion electrodes for oxygen reduction reactions. These freestanding carbons enable new module designs and can be scaled‐up by numbering‐up, serving as bio‐based functional materials for a wide range of applications involving porous heteroatom‐doped carbons. [ABSTRACT FROM AUTHOR]

Atomically dispersed Pt species are advocated as a promising electrocatalyst for the oxygen reduction reaction (ORR) to boost noble metal utilization efficiency. However, when assembled on various substrates, isolated Pt single atoms are often demonstrated to proceed through the two‐electron ORR pathway due to the unfavorable O─O bond cleavage thermodynamics in the absence of catalytic ensemble sites. In addition, although their distinct local coordination environments at the exact single active sites are intensively explored, the interactions and synergy between closely neighboring single atom sites remain elusive. Herein, atomically dispersed Pt monomers strongly interacting on a Mo2C support is demonstrated as a model catalyst in the four‐electron ORR, and the beneficial interactions between two closely neighboring and yet non‐contiguous Pt single atom sites (named as quasi‐paired Pt single atoms) are shown. Compared to isolated Pt single atom sites, the quasi‐paired Pt single atoms deliver a superior mass activity of 0.224 A mg−1Pt and near‐100% selectivity toward four‐electron ORR due to the synergistic interaction from the two quasi‐paired Pt atom sites in modulating the binding mode of reaction intermediates. Our first‐principles calculations reveal a unique mechanism of such quasi‐paired configuration for promoting four‐electron ORR. [ABSTRACT FROM AUTHOR]

The unique chemical and physical properties of graphene and its derivatives (graphene oxide, heteroatom‐doped graphene, and functionalized graphene) have stimulated tremendous efforts and made significant progress in fuel cell applications. This review focuses on the latest advances in the use of graphene‐based materials in electrodes, electrolytes, and bipolar plates for fuel cells. The understanding of structure‐activity relationships of metal‐free heteroatom‐doped graphene and graphene‐supported catalysts was highlighted. The performances and advantages of graphene‐based materials in membranes and bipolar plates were summarized. We also outlined the challenges and perspectives in using graphene‐based materials for fuel cell applications. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) catalysts play a critical role in energy storage and conversion devices and have been attracted enormous interests, and however, it remains challenging to develop highly active cheap catalysts in a simple and green route. Inspired by the heme‐copper oxidases (HOCs), in which the ORR active center is originated from the incorporation of Fe‐N4 with copper atom, we here developed a fine manganese oxide nanosheets (MnOx NSs) integrated with iron phthalocyanine (FePc) anchored on highly conductive graphene (MnOx/FePc‐G) through a green route only involve ethanol as the reagent. The bio‐inspired catalyst MnOx/FePc‐G demonstrated high ORR activity with a half‐wave potential (E1/2) of 0.887 V, about 57 mV more positive than that of Pt/C. And the current density (j) at 0.9 V is about 1.9 mA cm−2, which is three times of Pt/C and FePc‐G. More importantly, the bio‐inspired systems show superior stability in comparison to commercial Pt/C, showing a potential of 0.863 V to deliver a j of 3 mA cm−2 after 18 000 s polarization, about 80 mV higher than that of 0.783 V for Pt/C. The high activity is contributed by the integration of the FePc and MnOx NSs that plays the role to assist the cleavage of the O2 bond. Our approach provides a new evidence to develop highly efficient ORR catalysts through imitate the naturally involved systems through a simple route. [ABSTRACT FROM AUTHOR]

The mechanisms for oxygen reduction reaction (ORR) on the naturally exposed (110) and (111) surfaces of Co3O4 have been investigated with density functional theory (DFT) calculations. Depending on the vertical cutting place, there are type A and B surfaces for each of the (110) and (111) surfaces of Co3O4. Our DFT calculations reveal that the Co3O4 (110) type B and (111) type B surfaces have ORR catalytic activities. In addition, the ORR activity on the (110) type B surface is better than the (111) type B surface. The rate‐determining step on both surfaces is thermodynamically depending on the *OH desorption process. If the solvation effects are taken into accounts, the chemically adsorbed water molecules enhance the ORR activity. According to the barrier heights calculations, O2 → *O2 → *OOH → *O + H2O → *OH → H2O route is the most favorable ORR pathway. [ABSTRACT FROM AUTHOR]

Ligand and strain effects can tune the adsorption energy of key reaction intermediates on a catalyst surface to speed up rate‐limiting steps of the reaction. As novel fields like high‐entropy alloys emerge, understanding these effects on the atomic structure level is paramount: What atoms near the binding site determine the reactivity of the alloy surface? By statistical analysis of 2000 density functional theory calculations and subsequent host/guest calculations, it is shown that three atomic positions in the third layer of an fcc(111) metallic structure fourth‐nearest to the adsorption site display significantly increased influence on reactivity over any second or third nearest atomic positions. Subsequently observed in multiple facets and host metals, the effect cannot be explained simply through the d‐band model or a valence configuration model but rather by favorable directions of interaction determined by lattice geometry and the valence difference between host and guest elements. These results advance the general understanding of how the electronic interaction of different elements affect adsorbate–surface interactions and will contribute to design principles for rational catalyst discovery of better, more stable and energy efficient catalysts to be employed in energy conversion, fuel cell technologies, and industrial processes. [ABSTRACT FROM AUTHOR]

To develop the state‐of‐the‐art polymer membrane fuel cells. Both maximization of oxygen reduction reaction (ORR) activity on Pt cathode and minimization of Pt content in the cathode are required. For this challenge, the defect interface on oxide support was modified by proton beam irradiation method. Pt‐CeOx nanowire/C (Pt/C = 0.02) was fabricated using the proton beam irradiation method. Since the radical density generated by proton beam irradiation is two orders of magnitude greater than that of electron beam irradiation, the CeOx nanowire surface was fully converted to a thin layer of Pt‐O‐Ce bonds under proton beam irradiation. The ORR activity observed for fabricated sample with above active surface layer was higher than that of conventional Pt/C (Pt/C = 0.2) and comparable to that of Pt‐CeOx nanowire/C (Pt/C = 0.2) fabricated by conventional methods. From the combination of microanalysis characterization and surface atomistic simulation, we concluded that the Pt‐O‐Ce bond was formed on defect‐rich regions of the CeOx nanowire and this leads to a maximized ORR activity on the fabricated sample. Based on all experimental data, it is concluded that the surface modification of CeOx nanowire support using proton beam irradiation is useful for a lowering the Pt content of the cathode with high ORR activity. [ABSTRACT FROM AUTHOR]

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

For development and application of proton exchange membrane fuel cell (PEMFC) energy transformation technology, the cost performance must be elevated for the catalyst. At present, compared with noble metal‐based catalysts, such as Pt‐based catalysts, atomically dispersed metal–nitrogen–carbon (M–N–C) catalysts are popularity and show great potential in maximizing active site density, high atom utilization and high activity, making them the first choice to replace Pt‐based catalysts. In the preparation of atomically dispersed metal–nitrogen–carbon catalyst, it is difficult to ensure that all active sites are uniformly dispersed, and the structure system of the active sites is not optimal. Based on this, we focus on various approaches for preparing M–N–C catalysts that are conducive to atomic dispersion, and the influence of the chemical environmental regulation of atoms on the catalytic sites in different catalysts. Therefore, we discuss the chemical environmental regulation of the catalytic sites by bimetals, atom clusters, and heteroatoms (B, S, and P). The active sites of M–N–C catalysts are explored in depth from the synthesis and characterization, reaction mechanisms, and density functional theory (DFT) calculations. Finally, the existing problems and development prospects of the current atomic dispersion M–N–C catalyst are proposed in detail. [ABSTRACT FROM AUTHOR]

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

The rational design of electrode structure with catalysts adequately utilized is of vital importance for future fuel cells. Herein, a novel 3D oriented wholly integrated electrode comprising core–shell Fe3O4@N‐doped‐C (Fe3O4@NC) nanoparticles embedded into N‐doped ordered interconnected hierarchical porous carbon (denoted as Fe3O4@NC/NHPC) is developed for the oxygen reduction reaction (ORR). The as‐prepared catalyst possesses novel structure and efficient active sites. In rotating disk electrode measurements, the Fe3O4@NC/NHPC exhibits almost identical ORR electrocatalytic activity, superior durability, and much better methanol tolerance compared with the commercial Pt/C in acidic media. To the authors' knowledge, this is among the best non‐precious‐metal ORR catalysts reported so far. Importantly, the Fe3O4@NC/NHPC is successfully in situ assembled onto carbon paper by the electrophoresis method to obtain a well‐designed 3D‐ordered electrode. With improved mass transfer and maximized active sites for ORR, the 3D‐oriented wholly integrated electrode shows superior performance to the one fabricated by the traditional method. [ABSTRACT FROM AUTHOR]

With a rising energy demand and anabatic environmental crisis arising from the fast growth in human population and society economics, numerous efforts have been devoted to explore and design plentiful multifunctional materials for meeting high‐efficiency energy transfer processes, which happen in various developed energy conversion and storage systems. As a special kind of multi‐metal oxides, perovskite with attractive physical and chemical properties, is becoming a rapidly rising star on the horizon of high‐performance catalytic materials with substantial research behaviors worldwide. The porous nanostructure in targeted catalysts is favorable to the catalytic activity and thus improves the overall efficiency of these energy‐related installations. In this review paper, recent advances made in the porous perovskite nanostructures for catalyzing several anodic or cathodic reactions in fuel cells and metal–air batteries are comprehensively summarized. Plenty of general preparation methods employed to attain porous perovskite‐type oxides are provided, followed by a further discussion about the influence of various strategies on structures and catalytic properties of the porous perovskites. Furthermore, deep insights gathered in the future development of porous perovskite‐based materials for energy conversion and storage technologies are also provided. [ABSTRACT FROM AUTHOR]

Graphene aerogel‐supported manganese ferrite (MnxFe3−xO4/GAs) and reduced‐graphene oxide/manganese ferrite composite (MnFe2O4/rGO) were synthesized and studied as cathode catalysts for oxygen reduction reactions in urea/O2 fuel cells. MnFe2O4/GAs exhibited a 3D framework with a continuous macroporous structure. Among the investigated Fe/Mn ratios, the more positive oxygen reduction onset potential was observed with Fe/Mn=2/1. The half‐wave potential of MnFe2O4/GAs was considerably more positive than that of MnFe2O4/rGO and comparable with that of Pt/C, while the stability of MnFe2O4/GAs significantly higher than that of Pt/C. The best urea/O2 fuel cell performance was also observed with the MnFe2O4/GAs. The MnFe2O4/GAs exhibited an OCV of 0.713 V and a maximum power density of 1.7 mW cm−2 at 60 °C. Thus, this work shows that 3D structured graphene aerogel‐supported MnFe2O4 catalysts can be used as an efficient cathode material for alkaline fuel cells. [ABSTRACT FROM AUTHOR]

Nanoclusters (NCs) have been demonstrated of outstanding performance in electrochemical energy storage and conversion technologies due to their strong quantum confinement effects and strong interaction with supports. Here, we developed a class of ultrafine metal‐oxide (MOx, M = Fe, Co and Ni) NCs incorporated with iron phthalocyanine (FePc), MOx/FePc‐G, supported on graphene as high‐performance catalysts for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and carbon dioxide reduction (CO2RR). The high activities for ORR and OER are attributed to the electron donation and accepting ability of the highly redox active of FePc‐G that could tune the properties of MOx. The FeOx/FePc‐G exhibits an extremely positive half‐wave potential (E1/2) of 0.888 and 0.610 V for ORR in alkaline and neutral conditions, respectively, which is around 60 mV more positive than that of Pt/C. And NiOx/FePc‐G shows similar OER activity with the state‐of‐the‐art catalysts, Ir/C, and better performance than NiFeO NCs supported on graphene. Remarkably, the CoOx/FePc‐G and NiOx/FePc‐G show high activity and selectivity to reduce CO2 into CO with a low onset potential of −0.22 V (overpotential is 0.11 V). The ultrafine metal‐oxide nanoclusters can be tuned by the closely adjacent iron phthalocyanine (FePc), and the high electron flexibility of the FePc could assist the electrons transfer process for oxygen reduction, oxygen evolution, and carbon dioxide reduction. [ABSTRACT FROM AUTHOR]

1 1 1 08/03/23 20230801 NES 230801 B The Front Cover b shows a schematic representation of the oxygen reduction reaction on our gas diffusion electrode. EN CeO2 electrocatalysts oxygen reduction reaction PEM fuel cell. The composite catalyst is based on Pt/C and non-stoichiometric CeO SB 2. sb The high hygroscopicity of the latter plays a crucial role in optimizing the water drainage and the cathode/Nafion interface, resulting in a considerable improvement in proton conductivity and Fuel Cell performances. [Extracted from the article]