Search

Iron‐nitrogen‐carbon (Fe‐N‐C) single‐atom catalysts are promising sustainable alternatives to the costly and scarce platinum (Pt) to catalyze the oxygen reduction reactions (ORR) at the cathode of proton exchange membrane fuel cells (PEMFCs). However, Fe‐N‐C cathodes for PEMFC are made thicker than Pt/C ones, in order to compensate for the lower intrinsic ORR activity and site density of Fe‐N‐C materials. The thick electrodes are bound with mass transport issues that limit their performance at high current densities, especially in H2/air PEMFCs. Practical Fe‐N‐C electrodes must combine high intrinsic ORR activity, high site density, and fast mass transport. Herein, it has achieved an improved combination of these properties with a Fe‐N‐C catalyst prepared via a two‐step synthesis approach, constructing first a porous zinc‐nitrogen‐carbon (Zn‐N‐C) substrate, followed by transmetallating Zn by Fe via chemical vapor deposition. A cathode comprising this Fe‐N‐C catalyst has exhibited a maximum power density of 0.53 W cm−2 in H2/air PEMFC at 80 °C. The improved power density is associated with the hierarchical porosity of the Zn‐N‐C substrate of this work, which is achieved by epitaxial growth of ZIF‐8 onto g‐C3N4, leading to a micro‐mesoporous substrate. [ABSTRACT FROM AUTHOR]

Doping–dedoping chemistry lays the cornerstone for converting heteroatom dopants into intrinsic defects as the emerging active sites of carbon catalysts, but the defect content is yet hindered by inadequate doping efficiencies. Comprehending crucial factors behind the doping of pristine carbon and their correlation to the catalytic properties of dedoped carbon is thus of high significance. Here, the overlooked impact of native defects in pristine carbon on dopant‐mediated defect engineering of carbon catalysts is explicitly unveiled. Intact fullerene (C60), C60‐derived carbon, and carbon black in distinct pentagon/edge defect states are employed as respective precursors to undergo a nitrogen doping–dedoping treatment. Theoretical and experimental evidence consistently indicates that native pentagons change the preferred N doping site from the edge to the basal plane, leading to a substantially higher doping level. Importantly, in addition to pentagons from the removal of zigzag‐edged pyridinic N, N dopants in in‐plane pentagons are more easily dedoped than those in hexagons, generating even more pentagons in a new pentagon–heptagon–pentagon structure as oxygen reduction active sites. The optimized defect‐rich carbon gives an outstanding half‐wave potential of 0.834 V (0.846 V for Pt/C) via the four‐electron pathway, excellent long‐term durability, and prospective applicability in zinc–air batteries. [ABSTRACT FROM AUTHOR]

Designing effective electrocatalysts tailored for targeted reactions requires fundamental insights into the structure dependence of the reaction microenvironment. Herein, inspired by finite element simulations, N,O co‐doped carbon nanosheets featuring a hierarchical micro/mesoporous structure to form an oxygen‐rich and local alkaline‐like microenvironment for the two‐electron oxygen reduction reaction (2e− ORR) in a neutral medium are designed. The in situ and ex situ test results confirmed that the micro/mesoporous carbon architecture can elevate the local pH and accelerate the generation of intermediates (*O2, *OOH), leading to high‐efficiency H2O2 production. Utilizing this favorable microenvironment, N,O‐CNS0.5 demonstrated exceptional H2O2 electrosynthesis performance in neutral media, achieving a superior H2O2 yield rate (6705 mmol gcatalyst−1 h−1 in a flow cell). Additionally, comparative experiments and density‐functional theory calculations provided confirmation of the bi‐doping of N and O as the active origin responsible for the electrochemical 2e− ORR. This study synergistically manipulates the reaction microenvironment and active sites, providing an opportunity for efficient H2O2 electro‐production in a neutral medium. [ABSTRACT FROM AUTHOR]

Significant advancements in the activity of nitrogen‐coordinated iron single‐atom catalysts (Fe–N–C) have attracted attention as potential alternatives to Pt‐based cathodes in proton exchange membrane fuel cells. However, their limited stability in acidic environments hinders their practical application. Moreover, achieving a synchronous enhancement of both the activity and stability of the Fe sites while preventing demetallation or carbon corrosion remains a formidable challenge. Herein, a synthesis method for Fe–N–C is introduced that exhibits remarkable durability, featuring a protective carbon encapsulation formed by applying an additional heterocyclic organic compound coating. It is demonstrated that stability can be enhanced by converting edge‐rich Fe sites into highly stable FeN4 moieties through precise control of the robustness and packing density of the carbon encapsulation. Furthermore, electrochemical redox behavior along with in situ spectroscopies and online differential electrochemical mass spectrometry provide insights into the structural characteristics of each Fe site and their stabilities. The accelerated stress testing and a long‐term test (>100 h) exhibit that the robust carbon encapsulation can successfully prevent corrosion of carbon support and ensure durable Fe sites during operation. [ABSTRACT FROM AUTHOR]

Minimizing the use of platinum (Pt) in proton exchange membrane fuel cells (PEMFCs) is crucial for expanding the PEMFC market. The most straightforward approach would be to reduce the size of Pt particles. However, small Pt clusters, particularly those <2 nm in size, typically exhibit reduced activity for the oxygen reduction reaction (ORR) due to the overly strong adsorption of oxygen intermediates. Additionally, these small Pt clusters tend to degrade more quickly, resulting in lower durability. In this study, carbon‐embedded Pt alloy cluster catalysts (PtFe, PtCo, PtNi) that demonstrate high activity and durability in the PEMFC cathode are presented. Density functional theory calculations indicate that carbon atoms stably adsorb onto the Fe sites of PtFe clusters, making the neighboring Pt sites active for ORR with an optimal adsorption strength for oxygen intermediates. This research can pave the way for developing durable and efficient ORR catalysts while significantly reducing Pt usage in PEMFCs. [ABSTRACT FROM AUTHOR]

The electrochemical desalination technique is recognized as a promising solution to alleviate freshwater shortages, challenges yet persists in achieving optimal energy efficiency and cost‐effectiveness. Herein, a hybrid acid/alkali zinc air desalination battery (hAA‐ZADB) capable of concurrent desalination and high‐power density is reported. To improve cathodic efficiency and cost‐effectiveness, an electrocatalyst with dual atomic Fe–Mn sites on porous dodecahedral carbon (Mn‐Fe/p‐DC) is fabricated through a simple direct pyrolysis strategy for oxygen reduction reaction (ORR). The Mn–Fe/p‐DC‐900 electrocatalyst demonstrates exceptional electrocatalytic activity (E1/2 = 0.8 V in 0.5 m H2SO4) for ORR. This innovative hybrid acid/alkali cell design, coupled with advanced electrocatalysts, empowers the hAA‐ZADB system to achieve outstanding performance benchmarks with a high open circuit voltage of 2.22 V, an impressive power density of 375 mW cm−2, and notably elevated energy output of 106.9 kJ mol−1 even at a current density of 100 mA cm−2 during desalination. Distinguishing this work is its additional functionality, evident in a rapid salt removal rate of 3.64 mg cm−2 min−1 during desalination, achieving an impressive 88.67% removal of 0.6 M NaCl. This study highlights the promising potential of employing metallic air batteries for a self‐powered desalination technique applicable to specific scenarios. [ABSTRACT FROM AUTHOR]

Designing an electrocatalyst with low Pt content is an immediate need for essential reactions in low temperature fuel cell systems. In the present work, La0.9925Ba0.0075Al0.995Pt0.005O3 is aimed at using with low (only 0.5%) Pt doping as an electrocatalyst for oxygen reduction reaction (ORR). The low doping level renders exsolution of 1–2 nm nanoparticles with uniform dispersion upon reduction in H2/N2 at low temperatures. Pt exsolved perovskite oxides deliver significantly enhanced catalytic activity for ORR and improved stability in alkaline media. This study demonstrates that LaAlO3 with low noble metal content holds immense potential as an electrocatalyst in real fuel cell systems. [ABSTRACT FROM AUTHOR]

Incorporating atom‐nanocluster interactions into Fe─N─C single‐atom catalysts (Fe‐SACs) represents a viable strategy for enhancing their oxygen reduction reaction (ORR) activity, however, further investigation is necessary to elucidate the underlying mechanism. Herein, Cu nanoclusters are incorporated into Fe‐SACs to realize markedly enhanced pH‐universal ORR performance and investigate the underlying mechanism. The rate‐determining step (RDS) investigation reveals that the existence of Cu nanoclusters does not alter the RDS of Fe─N─C despite their differences in acidic, neutral, or alkaline media but instead optimizes the electronic configuration of Fe─N─C and significantly promotes the RDS. The synergistic effect between the Fe single atoms and Cu nanoclusters significantly enhances the half‐wave potential by 45, 90, and 18 mV in the HClO4, PBS, and KOH electrolytes, respectively. The catalysts further demonstrate remarkable maximum power densities of 971.4, 94.9, and 234.7 mW cm−2 in H2/O2 fuel cells, neutral Zn‐air batteries, and alkaline Zn‐air batteries, respectively. [ABSTRACT FROM AUTHOR]

Developing seawater‐based high‐performance oxygen reduction reaction (ORR) electrocatalysts is meaningful to renewable energy storage and conversion, and the Fe‐based derivatives encapsulated by nitrogen (N) doped carbon are the typical representative. Nevertheless, unrevealing the mechanism of N configuration to ORR activity and chlorine resistance is still a great challenge. In this work, a feasible strategy is developed to prepare controllable pyridinic/pyrrolic‐N doped carbon‐coated Fe‐based electrocatalysts (FexN‐NC). Drawing support from the H3PO4 blocking based in situ Fourier transform infrared spectroscopy (FTIR) test and density‐functional theory (DFT) calculation, the tandem effect of pyridinic‐N and pyrrolic‐N on ORR is proved. Additionally, the low hydrogen peroxide (H2O2) yield and 4e− pathway of FexN‐NC demonstrate that N doping effectively reduces the adsorption of Cl−, which is consistent with the low Cl− adsorption energy of DFT. The half‐wave potential (E1/2) of FexN‐NC for ORR reaches 0.874 V in alkaline seawater, and ZABs assembled with FexN‐NC as the air cathode deliver a remarkable power density (162 mW cm−2), along with excellent long‐term durability (>400 h). [ABSTRACT FROM AUTHOR]

Atomically dispersed transition metal–nitrogen–carbon (M–N–C) catalysts guide by the d‐band center theory have been extensively studied for oxygen reduction reaction (ORR) in various energy conversion and storage processes. However, asymmetric p‐block metal single‐atom catalysts (SACs) toward ORR have rarely been reported, and the origin of their catalytic activity is still unclear. Here, an asymmetric N, O coordinated Sn SAC is developed as an efficient ORR electrocatalyst. Remarkably, the optimized Sn SAC (e.g., Sn–N/O–C) exhibit outstanding ORR performance with a half‐wave potential of 0.910 V in alkaline media, outperforming most state‐of‐the‐art ORR catalysts. More importantly, the Sn–N/O–C possesses a long‐term durability in both alkaline and acidic electrolytes. Besides, Zn–air batteries based on the Sn–N/O–C cathode also show a higher energy density (254 mW cm‐2) than that of their reported M–N–C counterparts. Theoretical calculations suggest that the asymmetric N, O coordinated atomic Sn sites have a stronger binding interaction with O2 and better charge transfer ability compared with the symmetric SnN4 sites, thereby facilitating the ORR process. This work provides a nitrogen‐, oxygen‐coordinated engineering strategy for the rational design of highly active and durable carbon‐based catalysts with atomic p‐block metal sites for ORR and beyond. [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]

Discovering new materials that efficiently catalyze the oxygen reduction and evolution reactions is critical for facilitating the widespread adoption of solid oxide fuel cell and electrolyzer (SOFC/SOEC) technologies. Here, machine learning (ML) models are developed to predict perovskite catalytic properties critical for SOFC/SOEC applications, including oxygen surface exchange, oxygen diffusivity, and area specific resistance (ASR). The models are based on trivial‐to‐calculate elemental features and are more accurate and dramatically faster than the best models based on ab initio‐derived features, potentially eliminating the need for ab initio calculations in descriptor‐based screening. The model of ASR enables temperature‐dependent predictions, has well calibrated uncertainty estimates and online accessibility. Use of temporal cross‐validation reveals the model to be effective at discovering new promising materials prior to their initial discovery, demonstrating the model can make meaningful predictions. Using the SHapley Additive ExPlanations (SHAP) approach, detailed discussion of different approaches of model featurization is provided for ML property prediction. Finally, the model is used to screen more than 19 million perovskites to develop a list of promising cheap, earth‐abundant, stable, and high performing materials, and find some top materials contain mixtures of less‐explored elements (e.g., K, Bi, Y, Ni, Cu) worth exploring in more detail. [ABSTRACT FROM AUTHOR]

High‐entropy alloys (HEAs) have offered wide opportunities for materials discovery, property optimization, and application exploration. In spite of some encouraging progress, manipulating HEAs with functional morphology/mesostructure and controlled chemical orderliness remains a big challenge. In this manuscript, a powerful and general strategy to synthesizing libraries of mesoporous high‐entropy intermetallics (MHEIs) with controlled orderliness in both mesoscopic and atomic levels is reported for the first time. Final products feature an ordered polyhedral morphology and double‐gyroid mesostructure as well as long‐range L10 intermetallic phase and HEA composition, delivering multiple advantages for enhancing electrochemical performance in oxygen reduction reaction (ORR) and single rechargeable zinc–air battery. Specifically, MHEI‐PtPdFeCoNi affords remarkable ORR activity (0.63 A mg−1 for mass activity and 1.01 mA cm−2 for specific activity) and superior stability (≈87% activity retained for 50 000 cycles and chronoamperometry tests) compared with the MHEAs with disordered atomic arrangement and commercial Pt/C. The excellent performance comes from the optimized surface HEA multimetallization as well as ordered intermetallic and mesoporous structure that changes the chemisorption of O*/OH* intermediates and lowers the overall energy barrier of oxygen reduction. [ABSTRACT FROM AUTHOR]

Electrocatalytic oxygen reduction to hydrogen peroxide (H2O2) is one of the most promising methods to replace the conventional anthraquinone route for the green and facile synthesis of H2O2. Owing to the outstanding electrochemical active surface area and fast charge transfer capability of carbon nanomaterials or nanostructures with different dimensions, such as 1D, 2D, and 3D, various strategies including nanostructure engineering, defect engineering, and interface engineering have been proposed to promote the catalytic activity of carbon‐based catalysts toward two‐electron (2e−) oxygen reduction reaction (ORR) for H2O2 generation over the past decade. In this review, the latest progress, major achievements, and prospects of the transition metal‐supported carbon with different dimensions for highly efficient electrochemical H2O2 preparation via the 2e− ORR process are summarized. The rational design principles and synthetic strategies of transition metal‐supported carbon are systematically introduced while the representative advances, the identification of active sites, and their possible catalytic mechanisms toward the H2O2 production are discussed. Finally, according to the current development stage and existing shortcomings of 2e– ORR catalysts for H2O2 production, the challenges and prospects of transition metal‐supported carbon with different dimensions are also summarized. [ABSTRACT FROM AUTHOR]

The development of an electrocatalyst for oxygen reduction reaction (ORR) in a seawater electrolyte is the key to realizing the utilization of marine resources and application of Zn–air batteries (ZABs). Exploring the adsorption and desorption behavior of oxygen can guide the design of catalysts fundamentally and improve the catalytic performance. On this basis, WC and Co on nitrogen‐doped carbon (WC‐Co@NC) with an interfacial built‐in electric field (BEF) is designed as an ORR catalyst. The theoretical calculation certifies that the BEF of W─C─Co connections promote charge separation and directional migration, thus realizing the oxygen adsorption equilibrium and speeding up the process of ORR. These give WC‐Co@NC a high half‐wave potential of 0.872 V, and the alkaline seawater‐based ZAB with WC‐Co@NC as the air cathode has a peak power density of 188.8 mW cm−2 and excellent stability. This work can provide a basis for the rational design of the cathode of alkaline seawater‐based ZAB, and can also give a new direction for the utilization of seawater resources. [ABSTRACT FROM AUTHOR]

Precisely designing asymmetric diatomic configurations and studying their electronic regulation effect for improving the oxygen reduction reaction (ORR) performance are important for anion exchange membrane fuel cells (AEMFCs). Here, a Fe, Cu co‐doped 2D crystalline IISERP‐MOF27 nanosheet derived FeN3O‐CuN4 diatomic site nanocatalyst (named as FeCu‐NC) is synthesized for the cathodes of AEMFCs. Thanks to the optimal electronic structure of FeN3O‐CuN4 in the FeCu‐NC catalyst, it shows enhanced half‐wave potential (0.910 V), turnover frequency (0.165e s−1 site−1), and decreased activation energy (19.96 kJ mol−1) in KOH. The FeCu‐NC‐based AEMFC achieves extremely high kinetic current (0.138 A cm−2 at 0.9 V) and rated power density (1.09 W cm−2), surpassing the best‐reported transition metal‐based cathodes. Density functional theory calculations further demonstrate that the Cu‐N4 can break the localization of Fe‐3d orbitals, accelerate the electron transport, and optimize the OH adsorption, thus facilitating the ORR process. [ABSTRACT FROM AUTHOR]

Rational design of heterogeneous catalysts with unique structural and electronic properties is one of the major challenges to improve the activity toward the reversible oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), the bottleneck in the construction of air cathodes for the next‐generation flexible zinc–air batteries (ZABs). Herein, density functional theory calculations are combined with experimental attempts to exploit the roles of the electronic effects at the interface between Co4N nanoparticles and nitrogen‐doped carbon nanowalls/diamond (d‐NCNWs/D) toward the ORR and OER activities. The vacancy defect‐induced Co‐pyridinic N─C bond optimizes the electronic structure of Co 3d orbitals and balances the adsorption energies of intermediates along the reaction pathways. Consequently, as‐synthesized Co4N@d‐NCNWs/D composites exhibit superior bifunctional oxygen catalytic activity. The overpotential of the OER is as low as 340 mV at 10 mA cm−2 and the high half‐wave potential reaches 0.83 V for the ORR. As a binder‐free and flexible ZABs cathode, this composite exhibits an open circuit voltage of 1.41 V and excellent bendable stability, proving its promising potential for the assembly of wearable devices. This work offers theoretical evidence and a controllable strategy to design high‐performance ZAB cathodes for their application in smart electronic devices. [ABSTRACT FROM AUTHOR]

Hydrogen peroxide is an essential chemical that is attracting strong attention for energy and environmental applications. However, the struggle between the growing market demand and the unsustainability of the conventional anthraquinone method motivates the exploration of alternative H2O2 production processes. Although several new production processes have been proposed, the environmental‐friendly solar‐driven H2O2 production attracts most attention because of the only inputs of water, oxygen, and light energy. The rational design of functional photo‐responsive catalysts promotes H2O2 production in the photocatalytic and photoelectrocatalytic approaches. These are, in general, achieved by facilitating the preferential adsorption of key intermediates of OOH*/OH*/O*, enhancing the light absorption, promoting the charge separation, and accelerating the surface charge transfer with selective number of involved charges. This review systematically summarizes strategies for photo(electro)catalysts toward H2O2 production via both the water oxidation and oxygen reduction pathways. Though the oxygen reduction route is perceived as more popular in the community, selective water oxidation is emerging as a convincing alternative. Furthermore, prevailing hypotheses, state‐of‐the‐art catalysts, critical challenges, and perspectives are discussed in depth. This review aims to enhance the comprehension of this research field and promote interest in sustainable H2O2 production. [ABSTRACT FROM AUTHOR]

Disrupting the symmetrical electron distribution of single‐atomic Fe sites is proposed as an effective strategy for improving the intrinsic activity in the oxygen reduction reaction (ORR). Herein asymmetric N, P‐coordinated single‐atomic Fe sites with Fe2P nanoclusters/nanoparticles on porous carbon nanosheets (FePNC) are constructed by a soft‐template self‐sacrificing pyrolysis. The synchrotron X‐ray absorption spectroscopy confirms the coexistence of FeN3P1 moieties by the coordination of Fe atom with three nitrogen atoms and one phosphorus atom, and a small amount of Fe2P nanoclusters/nanoparticles. Benefiting from the unique asymmetric electronic and geometric configurations, the resultant FePNC catalyst exhibits excellent ORR activity with half‐wave potential of 0.76 V (0.5 m H2SO4) and 0.90 V (0.1 m KOH), and good Zn–air battery performance. Theoretical analysis reveals that the synergistic effect of P coordination and Fe2P nanoclusters induces asymmetrical electron redistribution of single‐atomic Fe sites and thus optimize the absorption strength toward the ORR intermediates, which contribute to the improved ORR activity. [ABSTRACT FROM AUTHOR]

The development of highly active and durable platinum‐free oxygen reduction reaction (ORR) catalysts is of vital importance for the practical application of anion‐exchange membrane fuel cells (AEMFCs). Herein, a metal‐free carbon catalyst (marked as NDPC‐1000) with a graphitic N‐regulating defect structure is specifically designed and developed for AEMFCs by integrating theoretical calculations and experiments. Density functional theory calculations first reveal that the graphitic N can tailor the charge density of pentagon and armchair defects to reach the top of the adsorption energy‐activity volcano plot, while the enhanced durability is attributed to the high dissociation energy of the CN covalent bond. Under this guidance, the synthesized NDPC‐1000 demonstrates its high ORR activity and durability in alkaline media. With H2/O2 reacting gases, the AEMFC with this catalyst as the cathode delivers a peak power density of 913 mW cm−2. Unprecedented fuel cell durability is verified via continuous operation over 100 h at 0.25 A cm−2 with only a voltage decay of ≈25%, which is the greatest among all reported metal‐free‐based AEMFCs. Here a theory‐guided experiment strategy is provided for the development of high‐performance and durable ORR catalysts for AEMFCs. [ABSTRACT FROM AUTHOR]

Developing efficient and stable Pt‐based oxygen reduction reaction (ORR) electrocatalysts via both economical and controllable routes is critical for the practical application of electrochemical energy devices. Herein, a scalable, controllable, and general ambient‐O2‐involved aqueous‐solution cultivating strategy to prepare PtxMy (M = Ni, Fe, Co) bunched‐nanocages aerogels (BNCs AG) is demonstrated, based on a newly established high‐M‐to‐Pt‐precursor‐ratio‐and‐B‐incorporation‐facilitated M‐rich core and Pt‐rich shell hydrogel formation process. The Pt83Ni17 BNCs AG shows prominent ORR performance with a mass activity (MA) of 1.95 A mgPt−1 and specific activity of 3.55 mA cm−2, which are 8.9‐times and 9.6‐times that of Pt supported on carbon (Pt/C), respectively. Particularly, the Pt83Ni17 BNCs AG displays greatly enhanced durability (MA 82.6% retention) compared to Pt/C (MA 31.8% retention) after a 20 000‐cycles accelerated durability test. Systematic studies including density functional theory calculations uncover that the excellent activity is closely related to the optimized ligand and strain effects with the optimized Ni content in this aerogel; the outstanding durability is endowed by the lowered‐down Ni leaching with the optimized Pt/Ni ratio and the inhibited sintering due to its appropriate porosity. This work provides new perspectives on the development of electrocatalysts with both high performance and low cost. [ABSTRACT FROM AUTHOR]

Metal‐free carbon‐based materials are considered to be one of the most promising alternatives to precious metal Pt‐based electrocatalysts. However, the electrocatalytic activity of heteroatom‐modulated carbon rarely reaches the level of metal‐based electrocatalysts. Here, electron‐rich carbon and abundant pyridinic‐N adjacent to C vacancies decorated with carbon nanosheets (E‐NC‐V) are synthesized and used as the host for boosting efficient oxygen reduction reaction. Rich pyridinic‐N structures adjacent to C vacancies work in synergy with electron‐rich carbon, which promotes the sharp decrease of |ΔGO*|, resulting in the balanced adsorption and dissociation of oxygen intermediates, and thus activating OO. This can be attributed to the abundant vacancies and d–p orbital hybridization between Zn and N/C. The E‐NC‐V catalyst drives the oxygen reduction reaction (ORR) via a 4e− transfer‐dominated pathway with a half‐wave potential of 0.87 V versus RHE in the alkaline solution, even superior to Pt/C. The assembled Al–air battery exhibits a high peak power density of 113 mW cm−2. This promising strategy sheds light on the design and fabrication of robust, rich‐density, and high‐performance active sites for the ORR. The work is expected to inspire future work on the role of electronic structure modulation and defect engineering for enhanced reaction kinetics. [ABSTRACT FROM AUTHOR]

Single atom catalysts (SACs) comprised of nitrogen‐coordinated transition metal (TM–N–C) moieties show encouraging performance towards the oxygen reduction reaction (ORR). Nevertheless, for the reactions involving multiple intermediates, single‐atom sites fail to satisfactorily optimize the adsorption of all intermediates. Here, a facile strategy is reported to construct Fe, P dual‐atom sites in multimodal porous carbon (Fe,P‐DAS@MPC), and its superiority in synergistically boosting ORR is demonstrated. Fe,P‐DAS@MPC exhibits excellent ORR performance with substantially positive onset potential (Eonset = 1.02 V) and half‐wave potential (E1/2 = 0.92 V). Theoretical analysis unveils the cooperative effect of dual‐atom sites composed of adjacent P and Fe atoms, and the aiding of hydrogen bonding interaction can promote the adsorption/desorption of intermediates. Additionally, a Zn–air battery based on the Fe,P‐DAS@MPC shows a high peak power density and exceptional cycling stability. These findings provide a novel avenue towards the design of electrocatalysts with dual‐atom sites for practical energy conversion applications. [ABSTRACT FROM AUTHOR]

The search for better and cheaper electrocatalysts is vital in the global transition to renewable energy resources. High‐entropy alloys (HEAs) provide a near‐infinite number of different alloys with approximately continuous properties such as catalytic activity. In this work, the catalytic activity for the electrochemical oxygen reduction reaction as a function of molar composition of Ag‐Ir‐Pd‐Pt‐Ru HEA is treated as a landscape wherein it is shown that the maxima are connected through ridges. By following the ridges, it is possible to navigate between the maxima using a modified nudged elastic band (NEB) model integrated in a machine learning NEB algorithm. These results provide a new understanding of the composition space being similar to an evolutionary landscape. This provides a possible new search and design strategy for new catalysts in which the composition of known catalysts can be optimized by following ridges rather than exploring the whole alloy composition space. [ABSTRACT FROM AUTHOR]

A major challenge to overcome in demonstrating solid oxide fuel cells (SOFCs) to be suitable as efficient and environmentally friendly energy conversion devices capable of addressing pressing clean energy and environmental needs is to surmount chemical and thermo‐mechanical instabilities in their operational phase. To date, perovskite‐based mixed conducting cathodes, which include inherent Co and Sr elements for enhanced reactivity and conductivity, have been intensively studied. These Co/Sr‐based oxides, however, exhibit severe thermochemical expansion and suffer from Sr surface segregation, ultimately degrading the electrode performance. Here, high‐performance and durable SOFCs are demonstrated by employing a Co/Sr‐free fluorite‐based mixed conducting (Pr,Ce)O2‐δ (PCO) cathode eminently compatible with fluorite‐based solid electrolytes. The nanocolumnar PCO electrode developed in this study provides not only a remarkable low level of electrode resistance (e.g., ≈0.05 Ω cm2 at 600 °C) but also exceptional long‐term stability (e.g., a degradation rate 15 times slower compared to the state‐of‐the‐art La0.6Sr0.4CoO3‐δ perovskite). The competitive peak power densities of an anode‐supported single cell with the PCO cathode are also successively achieved, recording a value of 0.92 W cm−2 at 600 °C. These findings herald the development of new Co/Sr‐free electrodes for SOFCs at intermediate temperatures. [ABSTRACT FROM AUTHOR]

Traditional calcination usually causes sintering of Pt, which diminishes Pt exposure in proton exchange membrane fuel cell (PEMFC) electrodes. In the present work, a facile self‐confined method for synthesizing highly dispersed PtCo‐alloy on Co, N co‐doped mesoporous carbon (PCN‐MC) is developed via a dual‐template strategy. Owing to the co‐confined effect of Zn in the bimetallic zeolite‐based imidazolate framework (ZIF) and Mg(OH)2 template, ultra‐fine 2.7 nm PtCo‐alloy with 2–3 atomic‐layer Pt‐skin nanoparticles are obtained. By adjusting the Co/Zn feeding‐ratio in the bimetallic ZIF at 8/7, the alloying degree and nanoparticle size are optimized to achieve an outstanding oxygen reduction reaction activity with a high mass activity (MA) of 0.956 A mgPt−1 in 0.1 m HClO4, about 7.5‐fold of that of commercial Pt/C. Furthermore, notable durability is also achieved with 81% retention of the initial MA after 30k cycles conducted between 0.6–1.0 V (versus reversible hydrogen electrode). These features are also verified by a H2–Air fuel cell test with an excellent combination of mass activity, power density, and durability. This strategy provides a feasible route for the large‐scale synthesis of highly‐dispersed PtCo‐alloy catalysts. [ABSTRACT FROM AUTHOR]

One‐dimensional (1D) ultrafine nanowires of different materials, especially noble metals, present an enticing prospect for catalyst applications due to their numerous active sites exposed. However, the controllable synthesis and stability issues hinder their practical applications. Herein, single‐walled carbon nanotubes (SWCNTs) are adopted as the template to synthesize and stabilize ultrafine nanowires of metals. Furthermore, the oxygen reduction reaction (ORR) is employed as an application demonstration. Impressively, the as prepared PdMo nanowires exhibit a half‐wave potential of 0.923 V and the mass activity is 35 times and 130 times higher than those of commercial Pt/C and Pd/C catalysts, respectively. Because of the protection, a superior ORR durability with 50 000 cycles can be achieved. Density functional theory (DFT) calculations reveal that the SWCNTs surface can be activated by the encapsulated PdMo NWs to achieve the exclusive adsorption of O2 and the following reduction reaction. In addition, PdMo NWs@SWCNTs demonstrate excellent catalytic performance as the cathode of lithium‐oxygen batteries. The cell can reach a high discharge capacity of over 10 000 mAh g−1, better than most of the former reported catalytic electrodes. The tailored design PdMo NWs@SWCNTs show widespread applications in various energy storage & conversion fields. [ABSTRACT FROM AUTHOR]

Protonic ceramic fuel cells (PCFCs) are one of the most efficient energy conversion devices. However, the performance of current PCFCs is greatly limited by the sluggish oxygen reduction reaction (ORR) kinetics and the fast degradation of the cathode due to contaminants poisoning (such as Cr species and steam). Here, a surface regulation of a double perovskite PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF) cathode by a Pr0.9Fe0.7Co0.3O3 (PFC) catalyst coating to enhance the ORR activity and stability is reported. When tested in direct contact with Cr in the air with 3% H2O at 650 °C, the polarization resistance (Rp) of the PFC coated PBSCF (PFC‐PBSCF) electrode increases from ≈0.39 to 0.45 Ω cm2 after 100 h operation; in contrast, the Rp of a PBSCF electrode increases from 0.63 to 0.82 Ω cm2. Further, a PCFC with the PFC‐PBSCF cathode demonstrates an excellent peak power density (≈1.08 W cm–2 at 650 °C) and significantly enhanced durability (degradation rate of 0.03% h−1), much better than those of the cells with a PBSCF cathode (≈0.75 W cm–2 and degradation rate of 0.12% h−1). Raman spectroscopy and density functional theory calculations indicate that the PFC catalyst coating diminishes the formation of Cr species, such as (Ba1‐xSrx)CrO4, on the cathode surface. [ABSTRACT FROM AUTHOR]

Discovering and engineering new materials with fast oxygen surface exchange kinetics and robust long‐term stability is essential for the large‐scale, economically viable commercialization of solid oxide fuel cell (SOFC) technology. The perovskite catalyst material BaFe0.125Co0.125Zr0.75O3 (BFCZ75), predicted to be promising from recent density functional theory (DFT) calculations and unconventional due to its extremely high Zr content and low electronic conductivity, exhibits oxygen reduction reaction surface exchange rates on par with Ba0.5Sr0.5Co0.8Fe0.2O3 (BSCF) and excellent stability at typical operating temperatures. New composite electrodes are engineered by integrating BFCZ75 with commercial electrode materials La1–xSrxMnO3 (LSM) and La1–xSrxCoyFe1–yO3 (LSCF) and achieve high performance as measured by low area specific resistance (ASR) values, with the LSCF/BFCZ75 ASR values comparable to top performing noncomposite electrode materials such as SrCo0.8Sc0.2O3–δ, BaNb0.05Fe0.95O3–δ and BaCo0.7Fe0.22Y0.08O3–δ. The use of BFCZ75 as a composite with LSCF achieving low ASR values shows that BFCZ75 is highly active and can easily integrate into existing SOFC material supply chains, lowering the barrier for potential commercial application of new electrode materials. Finally, these findings point to a broader unexplored class of perovskite materials with high fractions of redox inactive species (e.g., Zr, Nb, and Ta) that may unlock new pathways to realizing improved commercial SOFCs. [ABSTRACT FROM AUTHOR]

Rechargeable Zn–air batteries (ZABs) as high‐energy density and cost‐effective power sources for next generation energy storage have attracted considerable attention. However, the sluggish oxygen electrochemistry leads to high polarization of the air electrode during charge/discharge and consequently a low round‐trip energy efficiency of the cell. Here it is shown that the two‐electron oxygen redox chemistry enabled by a redox mediator, anthraquinone‐2,7‐disulfonic acid disodium salt (AQDS), can effectively boost the performance of ZABs. The kinetics and underlying mechanism of the AQDS‐mediated oxygen reduction reaction at different pH are scrutinized both computationally and experimentally to delineate the reaction pathways and rate‐limiting step. An ultrafast catalytic rate constant of 2.53 × 106 s–1 is achieved at a pH of 13.13 and based on a flow cell configuration, the AQDS‐mediated Zn–air flow battery demonstrates considerably enhanced energy efficiency of 85% at 10 mA cm−2. [ABSTRACT FROM AUTHOR]

The development of Fe single‐atom catalysts (Fe SACs) with abundant, accessible Fe sites is a key step toward enhancing the efficiency of the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). In this study, Zn4O(1,4‐benzenedicarboxylate)3 (MOF‐5), which has a 3D microporous cubic structure, is used as the precursor to prepare highly‐porous carbon (denoted as C‐MOF‐5) with an ultrahigh specific surface area (2751 m2 g–1) and high external surface area (1651 m2 g–1). C‐MOF‐5 is demonstrated as an effective carbon support to yield Fe SAC‐MOF‐5 with a large amount of accessible FeNx sites (2.35 wt%). Fe SAC‐MOF‐5 delivers a half‐wave potential of 0.83 V (vs RHE) in a 0.5 m H2SO4 electrolyte, and achieves a peak power density of 0.84 W cm–2 in a 0.2 MPa H2‐O2 PEMFC. This excellent performance originates from the ultrahigh specific surface area of C‐MOF‐5 for the formation of a high density of single Fe atoms, and high external surface area for the increased exposure of active sites. This work may inspire the rational design of metal single‐atom catalysts derived from a wider range of MOF precursors with ultrahigh specific area to improve the performance of the oxygen reduction reaction in PEMFCs. [ABSTRACT FROM AUTHOR]

Proton exchange membrane fuel cells (PEMFCs) have penetrated many commercial markets, especially in the automotive market as Toyota has launched the first commercially mass‐produced fuel cell vehicle, the Mirai in 2014. Electrocatalysts play an irreplaceable role in determining the PEMFCs, performance and account for half of the total cost. Despite substantial progress in exploiting highly active platinum group metal (PGM) and PGM‐free electrocatalysts, current electrocatalysts are faced with significant durability challenges, i.e., high‐performance electrocatalysts usually suffer from rapid degradation during PEMFC operation. The lifetime of the reported electrocatalysts is far from the requirement of performing steadily over the 8000 h of operation in commercialized PEMFCs. To this end, addressing the durability issues of oxygen reduction reaction (ORR) electrocatalysts is imperative for their practical employment in PEMFCs. Herein, the state‐of‐the‐art advances in understanding the durability issues of PGM and PGM‐free catalysts for ORR under fuel cell conditions and the materials engineering strategies to tackle these issues are summarized. The insights into the durability issues, involving the degradation mechanisms and the impact of operation conditions are reviewed. Establishing strategies to mitigate catalyst degradation through rational design of stable PGM and PGM‐free catalysts is highlighted. [ABSTRACT FROM AUTHOR]

Developing a highly efficient and durable proton exchange membrane fuel cell (PEMFC) using a low amount of platinum is essential for minimizing the total cost. Herein, the development of high‐performance PEMFC catalysts is demonstrated using ultra‐low Pt loaded (1 wt%) porous carbon with controlled channel diameters (Dch = 13–63 nm), produced from block copolymer particles. The single cell based on the catalyst with the largest Dch of 63 nm yields an initial maximum power density of 1230 mW cm−2 and high durability showing 1120 mW cm−2 after 30 000 cycles under H2/O2 flow, which outperforms those of commercial Pt/C catalysts despite 1/20 Pt usage. Furthermore, the catalyst shows outstanding performance with 51 kW per gram of Pt (kW gPt−1) after 30 000 cycles in H2/air flow, which is the highest performance reported to date. The channel structure and large Dch of the porous particles are the keys to enhancing the power density by improving the proton and mass transport. [ABSTRACT FROM AUTHOR]

Suppressing the Pt dissolution still remains a big challenge in improving the long‐term stability of Pt‐based catalysts in electrochemical energy conversion. In this work, the degradation of Pt nanoparticles is successfully suppressed via weakening the Pt–O dipole effect by adjusting the electronic structure of surface Pt atoms. The specially designed graphitic‐N‐doped carbon nanosheets with balanced N content and graphitization degree as well as fewer defects are prepared for anchoring Pt nanoparticles to enhance the electronic metal–support interaction. This can accelerate the electron transfer from Pt to substrate, decrease the surface electron density of Pt, and attenuate the Pt–O interaction. As a result, the rate of Pt dissolution decreases by 95% compared to that of commercial Pt/C toward the oxygen reduction reaction and thus the catalytic stability is significantly improved in the electrochemical accelerated durability test. The theoretical simulation shows that the inhibition of surface Pt dissolution is attributed to the enhanced energy barrier in the initial relaxation process. [ABSTRACT FROM AUTHOR]

Proton exchange membrane fuel cells (PEMFCs) are a highly efficient hydrogen energy conversion technology, which shows great potential in mitigating carbon emissions and the energy crisis. Currently, to accelerate the kinetics of the oxygen reduction reaction (ORR) required for PEMFCs, extensive utilization of expensive and rare platinum‐based catalysts are required at the cathodic side, impeding their large‐scale commercialization. In response to this issue, atomically dispersed metal–nitrogen–carbon (M–N–C) catalysts with cost‐effectiveness, encouraging activity, and unique advantages (e.g., homogeneous activity sites, high atom efficiency, and intrinsic activity) have been widely investigated. Considerable progress in this domain has been witnessed in the past decade. Herein, a comprehensive summary of recent development in atomically dispersed M–N–C catalysts for the ORR under acidic conditions and of their application in the membrane electrode assembly (MEA) of PEM fuel cells, are presented. The ORR mechanisms, composition, and operating principles of PEMFCs are introduced. Thereafter, atomically dispersed M–N–C catalysts towards improved acidic ORR and MEA performance is summarized in detail, and improvement strategies for MEA performance and stability are systematically analyzed. Finally, remaining challenges and significant research directions for design and development of high‐performance atomically dispersed M–N–C catalysts and MEA are discussed. [ABSTRACT FROM AUTHOR]

The electrochemical oxygen reduction reaction (ORR) is the key energy conversion reaction involved in fuel cells, metal‐air batteries, and hydrogen peroxide production. Proliferation and improvement of the ORR requires wider use of new and existing high performance catalysts; unfortunately, most of these are still based on precious metals and become uneconomical in mass‐use applications. Recent progress suggests that low cost and durable carbon materials can potentially be developed as efficient ORR catalysts. Significant efforts have been made in discovering fundamental catalytic mechanisms and engineering techniques to guide and enable viable regulation of both the ORR activity and selectivity of these carbon catalysts. Starting from the fundamental understanding, this report reviews recent progress in engineering carbon materials from exotic chemical doping to intrinsic geometric defects for improved ORR. On the basis of both theoretical and experimental investigations reported so far in this area, future improvements in carbon catalysts are also discussed, providing useful pathways for more efficient and reliable energy conversion technologies. [ABSTRACT FROM AUTHOR]

Dual‐sites single atom catalysts hold promise for efficiently regulating multiple reaction processes and explicitly explaining the underlying mechanisms. However, delicate atomic engineering for dual‐site single atom catalysts remains a huge challenge. Herein, atomically dispersed Fe‐Ni single atoms embedded in a nitrogen‐doped carbon matrix (FeNi SAs/NC) are successfully developed with extraordinary activity for electrocatalytic oxygen reduction and evolution reactions (ORR/OER). The atomic FeNi SAs/NC catalyst displays high onset potential (0.98 V) and half‐wave potential (0.84 V) for the ORR, as well as, low overpotential of (270 mV) at 10 mA cm−2 for the OER. The density functional theory calculations indicate that the Fe site as the active center can facilitate the four‐electron reaction process, while Ni sites regulate the electronic structure of Fe sites and further reduce the energy barrier of the rate‐determining step. In addition, the nitrogen‐doped carbon matrix prevents the metal atoms from aggregation and corrosion, leading to the improvement of catalyst durability. As a proof of concept, flexible quasi‐solid‐state zinc– and aluminum–air batteries assembled with the FeNi SAs/NC catalyst exhibit superior peak power densities and discharging specific capacities outperforming the commercial Pt/C. This work provides rational guidance for the synthesis of bifunctional electrocatalysts in next‐generation energy devices for flexible consumer electronics. [ABSTRACT FROM AUTHOR]

Secondary Zn‐air batteries (ZABs) are recognized as one of the most promising power sources for the future with lucrative features of low cost, high energy density, eco‐friendliness, and high safety. However, the widespread implementation of ZABs is still hampered by the sluggish oxygen redox reactions. Thus the deployment of cost‐effective and highly efficient air electrodes to substitute precious metals (Pt/Ir), is highly challenging, however, highly desired. Zeolitic imidazolate frameworks (ZIFs) are emerging functional materials, which demonstrate several outstanding characteristics, such as high specific surface area, high conductivity, self‐doped N, open pore structure, versatile compositions and favourable chemical stability. Through varying the metal/organic moiety or by employing different synthesis protocols, ZIFs with different properties could be obtained. Being adaptable, desired functionalities may be further incorporated into ZIFs through pre‐treatment, in situ treatment, and post treatment. Thus, ZIFs are the ideal precursors for the preparation of variety of bi‐functional air electrodes for ZABs by materials tuning, morphological control, or by materials hybridization. Here, the recent advances of ZIFs‐based materials are critically surveyed from the perspective of synthesis, morphology, structure and properties, and correlated with performance indicators of ZABs. Finally, the major challenges and future prospects of ZIFs associated with ZABs are discussed. [ABSTRACT FROM AUTHOR]

Iron single atom catalysts (FeN4) hosted in the micropores of N-doped carbons offer excellent performance for the oxygen reduction reaction (ORR). Achieving a high density of FeN4 sites accessible for ORR has proved challenging to date. Herein, a simple surface NaCl-assisted method towards microporous N-doped carbon electrocatalysts with an abundance of catalytically accessible FeN4 sites is reported. Powder mixtures of microporous zeolitic imidazolate framework-8 and NaCl are first heated to 1000 °C in N2, with the melting of NaCl above 800 °C creating a highly porous N-doped carbon product (NC-NaCl). Ferric (Fe3+) ions are then adsorbed onto NC-NaCl, with a second pyrolysis stage at 900 °C in N2 yielding a porous Fe/NC-NaCl electrocatalyst (Brunauer--Emmett--Teller surface area, 1911 m² g-1) with an excellent dispersion and high density of accessible surface FeN4 sites (26.3 x 1019 sites g-1). The Fe/NC-NaCl electrocatalyst exhibits outstanding ORR performance with a high half-wave potential of 0.832 V (vs reversible hydrogen electrode) in 0.1 M HClO4. When used as the ORR cathode catalyst in a 1.0 bar H2-O2 fuel cell, Fe/NC-NaCl offers a high peak power density of 0.89 W cm-2, ranking it as one of the most active M-N-C materials reported to date. [ABSTRACT FROM AUTHOR]

Compositional and structural engineering of metal‐metalloid materials can boost their electrocatalytic performance. Herein, a highly efficient and stable electrocatalytic system for the oxygen reduction reaction is obtained by creating heterointerfaces between N‐doped carbon and cobalt boride nanosheets. Furthermore, a detailed investigation on the effect of annealing temperature as well as the amount of carbon and nitrogen sources is conducted to tune their performance. The best electrocatalyst among the prepared materials is found to have an onset potential of 1.05 V and half‐wave potential of 0.94 V, which are 40 and 72 mV positive in comparison to commercial Pt/C, respectively. Finally, a zinc–air battery is also assembled using the catalyst. [ABSTRACT FROM AUTHOR]

Hydrogen peroxide (H2O2) is an environmentally friendly oxidant, finding widespread use across the chemical industry, in sanitation and environmental remediation. Currently, H2O2 is manufactured via the anthraquinone process which has a number of disadvantages including nondistributed production, high‐energy consumption, substantial organic by‐product waste, and the need to transport the obtained H2O2 to the point‐of‐use. Accordingly, the electrochemical synthesis of H2O2 is now attracting a lot of interest as an alternative, cost‐effective, small‐scale, and distributed technology for H2O2 manufacture. This review summarizes recent advancements in the development of Homogeneous and Heterogeneous catalysts for electrocatalytic O2 reduction reaction (ORR) to H2O2. The basic principles of the ORR, and methodologies for investigating the ORR to H2O2 are first introduced. Next, H2O2 production over Homogeneous catalysts is discussed, with a focus on the reaction mechanisms and the factors that influence activity, selectivity, and reaction kinetics. Subsequently, recent breakthroughs in H2O2 synthesis over Heterogeneous catalysts, including nonnoble metal‐based nanomaterials, carbon materials, and single‐atom catalysts are described. The latter are given special attention, since they serve as a bridge between Homogeneous catalysis and Heterogeneous catalysis, while also offering excellent performance. Finally, the challenges and opportunities for electrochemical ORR to H2O2 are critically discussed. [ABSTRACT FROM AUTHOR]

The development of inexpensive and highly efficient nonprecious metal catalysts to substitute Pt in the alkaline oxygen reduction reaction is an appealing idea in the energy field. Herein, a Mn oxygen reduction electrocatalyst with a half‐wave potential (E1/2) as high as 0.910 V under an alkaline oxygen reduction reaction process is developed, and the dynamic atomic structure change of the highly efficient Mn single‐atomic site is investigated using operando X‐ray absorption spectroscopy. These results demonstrate that the low‐valence MnL+N4 is the active site during the oxygen reduction process. Density functional theory reveals that facile electron transfer from MnL+N4 to adsorbed *OH species plays a key role in the excellent electrocatalytic performance. Moreover, when assembled as the cathode in a zinc–air battery, this MnN4 material shows high power density and excellent durability, demonstrating its promising potential to substitute the Pt catalyst in practical devices. [ABSTRACT FROM AUTHOR]

In the face of high costs and the insufficient energy density of current lithium‐ion batteries, aqueous rechargeable zinc (Zn)–air batteries with the advantages of low cost, environmental benignity, safety, and high energy density have been growing in importance in recent years. The practical application of Zn–air batteries, however, is severely restricted by the high overpotential, which is associated with the inherent sluggish kinetics of the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR) of air electrocatalysts. Recently, engineering heterostructured/hybrid electrocatalysts with modulated interface chemistry have been demonstrated as an effective strategy to improve the catalytic performance. Significant electronic effects, geometric effects, coordination effects, synergistic effects, and confinement effects occur at the heterostructure interface, which intensely affect electrocatalysts' performance in terms of intrinsic activity, active site density, and durability. In this review, the recent progress in the development of heterostructured air electrocatalysts by interface engineering is summarized. Particularly, the potential relationship between interface chemistry and oxygen electrocatalysis kinetics is bridged and outlined. This review provides a comprehensive and in‐depth outline of the crucial role of the well‐defined interfaces towards fast oxygen electrocatalysis, and offers a solid scientific basis for the rational design of efficient heterostructured air electrocatalysts and beyond. [ABSTRACT FROM AUTHOR]

Future renewable energy supplies and a sustainable environment rely on many important catalytic processes. Single‐atom catalysts (SACs) are attractive because of their maximum atom utilization efficiency, tunable electronic structures, and outstanding catalytic performance. Of particular note, transition‐metal SACs exhibit excellent catalytic activity and selectivity for the oxygen reduction reaction (ORR)—an important half reaction in fuel cells and metal–air batteries as well as for portable hydrogen peroxide (H2O2) production. Although considerable efforts have been made on the synthesis of SACs for ORR, the regulation of the coordination environments of SACs and thus the electronic structures still pose a big challenge. In this review, strategies for manipulating the coordination environments of SACs are classified into three categories, including regulation of the center metal atoms, manipulation of the surrounding environment connecting to the center metal atom, and modification of the geometric configuration of the support. Finally, some issues regarding the future development of SACs for ORR are raised and possible solutions are proposed. [ABSTRACT FROM AUTHOR]

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

Engineering transition metal‐nitrogen‐carbon (TM‐N‐C) catalysts with high‐density accessible active sites and optimized electronic structure holds great promise in the context of the electrochemical oxygen reduction reaction (ORR). Herein, a novel modification of a lysozyme‐modified zeolitic imidazolate framework with isolated Co atoms anchored on dominated pyridinic‐N doped carbon (Co‐pyridinic N‐C) is reported. The atomically dispersed Co allows the maximum active site exposure while the introduction of pyridinic N can greatly reduce the electron localization around the Co centers and improve the interaction with oxygenated species, and thus lowering the energy barriers of the intermediates and facilitating the favorable four‐electron ORR pathway. Owing to the synergistic effects of single‐atom Co and coordinated pyridinic N, the Co‐pyridinic N‐C catalyst exhibits an exceptional ORR activity and remarkable stability in both alkaline and more challenging acidic media, representing one of the most active Co‐N‐C catalysts reported. This work may open an avenue for the rational design of TM‐N‐C catalysts to boost their catalytic performance for application in the ORR. [ABSTRACT FROM AUTHOR]

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

The oxygen reduction reaction (ORR) is one of the most important reactions in renewable energy conversion and storage devices. The full deployment of these devices depends on the development of highly active, stable, and low‐cost catalysts. Herein, a new hybrid material consisting of Na2Ta8O21−x/Ta2O5/Ta3N5 nanocrystals grown on N‐doped reduced graphene oxide is reported. This catalyst shows a significantly enhanced ORR activity by ≈4 orders of magnitude in acidic media and by ≈2 orders of magnitude in alkaline media compared to individual Na2Ta8O21−x on graphene. Moreover, it has excellent stability in both acid and alkaline media. It also has much better methanol tolerance than the commercial Pt/C, which is relevant to methanol fuel cells. The high ORR activity arises not only from the synergistic effect among the three Ta phases, but also from the concomitant nitrogen doping of the reduced graphene oxide nanosheets. A correlation between ORR activity and nitrogen content is demonstrated. Deep insights into the mechanism of the synergistic effect among these three Ta‐based phases, which boosts the ORR's kinetics, are acquired by combining specific experiments and density functional theory calculations. [ABSTRACT FROM AUTHOR]

The electrochemical reduction of O2 via a two‐electron reaction pathway to H2O2 provides a possibility for replacing the current anthraquinone process, enabling sustainable and decentralized H2O2 production. Here, a nitrogen‐rich few‐layered graphene (N‐FLG) with a tunable nitrogen configuration is developed for electrochemical H2O2 generation. A positive correlation between the content of pyrrolic‐N and the H2O2 selectivity is experimentally observed. The critical role of pyrrolic‐N is elucidated by the variable intermediate adsorption profiles as well as the dependent negative shifts of the pyrrolic‐N peak on X‐ray adsorption near edge structure spectra. By virtue of the optimized N doping configuration and the unique porous structure, the as‐fabricated N‐FLG electrocatalyst exhibits high selectivity toward electrochemical H2O2 synthesis as well as superior long‐term stability. To achieve high‐value products on both the anode and cathode with optimized energy efficiency, a practical device coupling electrochemical H2O2 generation and furfural oxidation is assembled, simultaneously enabling a high yield rate of H2O2 at the cathode (9.66 mol h−1 gcat−1) and 2‐furoic acid at the anode (2.076 mol m−2 h−1) under a small cell voltage of 1.8 V. [ABSTRACT FROM AUTHOR]