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Cobalt‐rich materials have generally been recognized as the prevailing candidates of cathodes for low‐temperature solid oxide fuel cells (LT‐SOFCs, 400–600 °C). Regrettably, their instability and high cost are the major concerns for future commercialization. In response to these drawbacks, here, an A‐site‐deficient low‐cobalt‐containing perovskite‐type oxide, Ba0.95Fe0.7Co0.2Sc0.1O3‐δ (BFCS0.95), as an efficient bifunctional electrode with triple‐conducting (H+|O2−|e−) nature for oxygen‐ion conducting SOFCs (O‐SOFCs) and proton conducting SOFCs (H‐SOFCs) is proposed. BFCS0.95 electrode exhibits impressive versatility in catalyzing oxygen reduction reaction, i.e., ultralow area‐specific resistances (0.072 Ω cm2 for O‐SOFCs and 0.4 Ω cm2 for H‐SOFCs at 550 °C, respectively), extraordinarily high power outputs (1092 mW cm−2 for O‐SOFCs and 419 mW cm−2 for H‐SOFCs at 550 °C, respectively), excellent long‐term durability (>100 h for O‐SOFCs and H‐SOFCs at 600 °C), remarkable reversibility between pure air and CO2‐containing air, and superior resistance against temperature fluctuations. The combined experimental and computational studies elucidate the roles of A‐site deficient state and triple‐conducting behavior, both of which are essential to overall electrochemical performance. Low‐cobalt‐containing feature also makes BFCS0.95 cathode economically competitive among all cobalt‐containing analogues. Overall, the finding paves a highly efficient route to develop bifunctional electrodes for LT‐SOFCs toward a sustainable energy future. [ABSTRACT FROM AUTHOR]

Immobilizing ultrafine high‐entropy Pt alloy nanocrystals (HENs) in porous carbon (PC) with strong interface interaction, which is crucial to efficient and durable oxygen reduction reaction (ORR), remains a challenge. In this study, an anchoring‐carbonization strategy for strongly bonding sub‐3 nm HENs in ordered mesoporous carbon is reported. When heating the orderly assembled composites containing hydrophobic organometallic precursors, structure directing agent F127, and hydrophilic resol, F127 is first removed at moderate temperature region, leading to reduced metallic species directly anchored on partially carbonized resol framework. Then along further temperature increase, in situ carbonization of resol around the HENs, enables more effective plane bonding rather than a single point contact of HENs with carbon. It not only enhances the anchor strength, but also inhibits migration and size growth of HENs along the subsequent high‐temperature carbonization. As a result, senary, septenary, octonary, and denary Pt‐based HENs with average nanocrystal sizes of 2.2, 2.6, 2.9, and 2.8 nm, respectively, are successfully imbedded into porous carbon. In electrocatalytic ORR, porous carbon‐supported senary Pt‐based HENs (6‐HENs/PC) exhibit superior activity and durability, representing a promising electrocatalyst. This strategy allows for the preparation of a range of ultrafine HENs strongly loaded on porous carbon for wide applications. [ABSTRACT FROM AUTHOR]

The surface structure and lattice strain necessary to optimize oxygen reduction reaction (ORR) in a cost‐effective electrocatalyst still requires systematic exploration. Here, by means of oxidative etching of surface confinement stacking faults, a comparative study of the influence of defects on the growth and lattice strain of PtAgPb core‐shell nanoplates for ORR is conducted. Stacking faults are key to forming the core–shell structure and induce tensile and compressive strains to improve catalytic performance of nanoplates. In particular, the compressive strain arising from the optimal composition of nanoplates enhances the ORR activity. The findings show how compressive strain in core–shell nanoplates shift the electronic band structure of platinum (Pt) and weakens chemisorption of oxygenated species. As a result, the obtained PtAgPb‐IV/C nanoplates display superior specific and mass activities (5.06 mA cm−2 and 2.24 A mgPt−1) for ORR that are ≈18 and ≈13 times higher than that of commercial Pt/C, placing it among the best reported Pt based ORR electrocatalysts. Furthermore, the PtAgPb‐IV/C catalyst exhibits substantially improved durability relative to commercial Pt/C catalysts. This work represents a major step toward the deterministic synthesis of Pt‐based multimetallic nanocrystals with specific structure and surface strain for efficient ORR performance. [ABSTRACT FROM AUTHOR]

Photocatalytic hydrogen peroxide (H2O2) production from dioxygen and water is regarded as a promising technology since it can achieve sustainable and green solar‐to‐chemical energy conversion. Herein, oxygen and potassium dual‐heteroatom incorporated polymeric carbon nitride (O/KCN) is rationally designed for H2O2 generation with an ultrahigh rate of 309.44 µM h−1 mg−1, which surpasses that of other C3N4‐based photocatalysts. The enhanced performance can be ascribed to the effective light absorption, fast charge transfer/separation, strong oxygen adsorption, and highly selective two‐electron oxygen reduction reaction (ORR). Density functional theory calculations further confirm that the obtained O/KCN is more favorable than others for electrons migrating from β spin‐orbital to π* orbitals of O2 molecule, thus optimizing O2 molecule activation to promote the formation of intermediate species *OOH and decrease the energy barrier of H2O2 production. This work not only provides in‐depth insights for the photocatalytic H2O2 generation mechanism, but also lays the foundation for further development of highly active photocatalysts for environmental remediation and energy conversion. [ABSTRACT FROM AUTHOR]

Exploiting efficient and stable electrocatalysts with trifunctional catalytic activity toward hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) act has a crucial role with sustainable energy development. Therefore, this study fabricates Co3O4‐RuO2 hollow spheres using a facile and eco‐friendly solvothermal and low temperature oxidation procedure followed by ice water treatment (IW‐Co3O4‐RuO2‐HS). The specific hollow nanostructure could provide sufficient active sites and channels in the electrocatalytic procedure. Then, the IW‐Co3O4‐RuO2‐HS presents small overpotentials toward HER (40 mV@ 10 mA cm−2) and OER (250 mV@ 10 mA cm−2), and high half‐wave potential for ORR (E1/2@ 0.79 V). Remarkably, the IW‐Co3O4‐RuO2‐HS also presents superior catalytic performances toward water‐splitting and flexible rechargeable Zn–air batteries. Furthermore, the water electrolysis can be driven by sustainable energy, including solar, wind, thermal energy, and the assembled flexible rechargeable Zn–air battery. This study provides a valid path to synthesize multifunctional electrocatalysts on energy‐related devices. [ABSTRACT FROM AUTHOR]

Direct electrosynthesis of hydrogen peroxide (H2O2) via two‐electron pathway oxygen reduction reaction (2e− ORR) is crucially essential for a sustainable green economy. However, catalysts inevitably undergo four‐electron pathway oxygen reduction reaction (4e− ORR), resulting in low selectivity and economic benefits. The current challenge is to provide a feasible design strategy for obtaining satisfactory 2e− ORR catalysts with high selectivity. In this work, carbon dots (CDs) act as a cocatalyst to regulate the electron transport kinetics of In2O3/CDs, and the influence of CDs on the ORR pathways of In2O3/CDs is also studied. The electron transfer kinetics on In2O3/CDs composites are studied and analyzed using the transient photo‐induced voltage (TPV) technology. Combining the TPV results and kinetics analysis, it is shown that the electron transport on the In2O3 interface is obviously weakened after the addition of CDs, resulting in a high H2O2 selectivity. It is also demonstrated that CDs can effectively enhance the selectivity of H2O2, and the H2O2 selectivity of In2O3/CDs–10 is in close proximity to 100%, which is much higher than that of pure In2O3 (72%). This work will provide a new understanding and insight into addressing the challenge of low H2O2 selectivity for 2e− ORR catalysts. [ABSTRACT FROM AUTHOR]

Dual–single‐atom catalysts with synergistic effect of adjacent atomic metal sites show a great potential for oxygen reduction reaction (ORR). Herein, a dynamical synthetic strategy is demonstrated for the rational design of dual‐atom catalyst ((Zn, Cu)−NC) with non‐covalent Cu and Zn sites as nitrogen‐doped carbon as support. Owing to the non‐covalent interaction of Zn and Cu atomic pair sites, (Zn, Cu)−NC exhibits significant performances for ORR, surpassing the catalysts with individual Zn or Cu site. The theoretical calculations reveal that (Zn, Cu)−NC can highly activate the linear O2 molecule via the non‐covalent interaction between Zn and Cu pairs, providing the more effective overlap between the metal 3d orbitals and O 2p orbital. Therefore, the ORR activity is optimized with the improvement of the adsorption configuration and adsorption energy of O2. Further, both liquid and quasi‐solid zinc−air batteries with (Zn, Cu)−NC as air cathodes achieve remarkable energy density and stability. This research proposes a facile synthetic strategy to construct single‐atom catalysts and presents an insightful understanding of the non‐covalent interplay between heteronuclear metal atoms in dual‐atom catalysts. [ABSTRACT FROM AUTHOR]

Nitrogen‐doped carbons are among the fastest‐growing class of materials used for oxygen electrocatalysis, namely, the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), thanks to their low cost, environmental friendliness, excellent electrical conductivity, and scalable synthesis. The perspective of replacing precious metal‐based electrocatalysts with nitrogen‐doped carbon is highly desirable for reducing costs in energy conversion and storage systems. In this review, the role of nitrogen and N‐induced structural defects on the enhanced performance of N‐doped carbon electrocatalysts toward the OER and the ORR as well as their applications for energy conversion and storage technologies is summarized. The synthesis of N‐doped carbon electrocatalysts and the characterization of their nitrogen functional groups and active sites for the conversion of oxygen are also reviewed. The electrocatalytic performance of the main types of N‐doped carbon materials for OER/ORR electrocatalysis are then discussed. Finally, major challenges and future opportunities of N‐doped carbons as advanced oxygen electrocatalysts are highlighted. [ABSTRACT FROM AUTHOR]

Surging interests exist in double‐atom catalysts (DACs), which not only inherit the advantages of single‐atom catalysts (SACs) (e.g., ultimate atomic utilization, high activity, and selectivity) but also overcome the drawbacks of SACs (e.g., low loading and isolated active site). The design of DACs, however, remains cost‐prohibitive for both experimental and computational studies, due to their huge design space. Herein, by means of density functional theory (DFT) and topological information‐based machine‐learning (ML) algorithms, we present a data‐driven high‐throughput design principle to evaluate the stability and activity of 16 767 DACs for oxygen evolution (OER) and oxygen reduction (ORR) reactions. The rational design reveals 511 types of DACs with OER activity superior to IrO2 (110), 855 types of DACs with ORR activity superior to Pt (111), and 248 bifunctional DACs with high catalytic performance for both OER and ORR. An intrinsic descriptor is revealed to correlate the catalytic activity of a DAC with the electronic structures of the DAC and its bonding carbon surface structure. This data‐driven high‐throughput approach not only yields remarkable prediction precision (>0.926 R‐squared) but also enables a notable 144 000‐fold reduction of screening time compared with pure DFT calculations, holding promise to drastically accelerate the design of high‐performance DACs. [ABSTRACT FROM AUTHOR]

In sodium–air batteries (SABs), achieving the regulation of the electron transfer number during oxygen reduction reactions (ORRs) in the same electrolyte system remains a significant challenge. In this work, a promising strategy is proposed to dynamically modulate 2e−/4e− transfer in ORRs by regulating the electrolyte structures to realize the different performances of SABs. The 4e− ORR can be realized by decreasing the electrolyte concentration. The solvation sheath of Na+ at dilute concentrations consists mainly of water molecules that hinder the access of Na+ to the cathode surface due to the high solvation energies indicated by theoretical calculations, thereby impeding the 2e− reaction. In contrast, excess free water can easily access the cathode surface and trigger the 4e− ORR. The solvation energies of Na+ can be remarkably reduced by increasing the electrolyte concentration, forming a water‐in‐salt unit, in which the Na+ mainly coordinates with the bis(fluorosulfonyl)imide anion and can be easily released from the solvation sheath. Hence, the 2e− ORR is significantly promoted and becomes the dominant reaction. The SAB based on the 2e− reaction exhibits excellent energy density (15980 Wh kg−1) and good cycle performance (300 times), and the 4e− reaction exhibits excellent power density (12.09 mW cm−2). [ABSTRACT FROM AUTHOR]

Developing efficient Pt‐based alloy as oxygen reduction reaction (ORR) electrocatalysts is critical for practical applications of fuel cells. High‐temperature reduction technology can improve the alloy atoms ordering but inevitably accelerate metal sintering. Here, Pt–Ni nanoparticles (<5 nm) embedded into ordered mesoporous carbon (OMC) matrix are developed, and its confinement effect suppresses nanoparticles sintering up to 900 °C. After an elaborative dealloying process, the surface structure of Pt–Ni nanoparticles changes from a Ni‐rich to Pt‐rich layer (the thickness is about 0.15 nm). The optimized sample (PtNi3@OMC‐A) displays outstanding mass and specific activities of 2.11 A mgPt–1 and 3.23 mA cmPt–2, more than one order of magnitude higher than commercial Pt/C (20 wt%). PtNi3@OMC‐A also exhibits long‐term stability with a negligible activity loss after 10 000 potential cycles. Both experimental results and density functional theory calculations reveal that alloying effect as well as strain effect weaken Pt–O binding strength, thus resulting in an outstanding ORR activity. Furthermore, the high long‐term stability can be attributed to the confinement of OMC, inhibiting the detachment or agglomeration of the embedded alloy nanoparticles. [ABSTRACT FROM AUTHOR]

Single‐atom catalysts (SACs) have shown great potential in the electrochemical oxygen reduction reaction (ORR) toward hydrogen peroxide (H2O2) production. However, current studies are mainly focused on 3d transition‐metal SACs, and very little attention has been paid to 5d SACs. Here, a new kind of W SAC anchored on a porous O, N‐doped carbon nanosheet (W1/NO‐C) is designed and prepared via a simple coordination polymer‐pyrolysis method. A unique local structure of W SAC, terdentate W1N1O2 with the coordination of two O atoms and one N atom, is identified by the combination of aberration‐corrected scanning transmission electron microscopy, X‐ray photoelectron spectroscopy and X‐ray absorption fine structure spectroscopy. Remarkably, the as‐prepared W1/NO‐C catalyzes the ORR via a 2e– pathway with high onset potential, high H2O2 selectivity in the wide potential range, and excellent operation durability in 0.1 m KOH solution, superior to most of state‐of‐the‐art H2O2 electrocatalysts ever reported. Theoretical calculations reveal that the C atoms adjacent to O in the W1N1O2‐C moiety are the most active sites for the 2e– ORR to H2O2 with the optimal binding energy of the HOO* intermediate. This work opens up a new opportunity for the development of high‐performance W‐based catalysts for electrochemical H2O2 production. [ABSTRACT FROM AUTHOR]

In high‐temperature proton exchange membrane fuel cells (HT‐PEMFCs), the poisoning of Pt by phosphoric species severely affects the kinetics of the oxygen reduction reaction, which restricts their commercialized application. Herein, for the first time, the phosphate tolerance of PtFe ordered intermetallic alloys is enhanced by a doping‐modulated strain strategy via employing a low amount of Cu as a dopant to boost HT‐PEMFCs. This Cu doping facilitates the formation of compressive strain in PtFe crystals, consequently altering the electronic structure of electrocatalysts and then benefiting for weakening the adsorption energy between phosphoric acid and Pt surfaces. In addition, the high temperature phosphate adsorption tests also reveal that the dopant of Cu in Pt based electrocatalysts can improve the tolerance of phosphoric acid. The HT‐PEMFCs assembled by those cathodic electrocatalysts with the low‐Pt loading of 0.5 mgPt cm−2 achieve a preeminent peak power of 793.5 and 432.6 mW cm−2 under the condition of H2–O2 and H2–air atmosphere, respectively, or nearly 1.53 and 1.34 times higher as compared with commercial Pt/C electrocatalysts. Moreover, those electrocatalysts also exhibit robust stability under harsh condition in H2–O2 atmosphere with negligible activity loss for at least 100 h, exceeding most of other reported ORR electrocatalysts. [ABSTRACT FROM AUTHOR]

Both the monodispersed Pd/C (2–5 nm) and Fe‐NC single atoms (SAs) are promising non‐Pt catalysts for oxygen reduction reaction (ORR), which belongs to precious metal and nonprecious metal camps, respectively. However, the poles apart of sub‐5 nm Pd/C and Fe‐NC SAs in synthesis and thermostability leave the challenge to integrate them together in one system. Herein, a 1‐naphthylamine protected pyrolysis mechanism is devised to couple the atomically dispersed Fe sites with sub‐5 nm Pd nanocrystals embedded in N‐doped carbon nanobelts (FeN3‐Pd@NC NBs). The FeN3 SAs represent the minimal surface blockage to tune the electronic structure of Pd, while the carbon frameworks are born with ultrathin, porous, and N‐doped feature's. As inspired, the FeN3‐Pd@NC NBs exhibit outstanding activity (E1/2 = 0.926 V) and durability (2 mV decay in E1/2 after 2000 cycles) for ORR, as well as achieving a maximum power density of 831.2 mW cm−2 in a microbial fuel cell operated for over 100 d. Density functional theory calculation reveals that the FeN3 SAs can shift the density of states of Pd toward the Fermi level, and their coupling can decrease the limiting reaction barrier with a value of −0.62 eV, thus greatly accelerating the ORR kinetics. [ABSTRACT FROM AUTHOR]

Atomic transition‐metal‐nitrogen‐carbon catalysts (M‐N‐Cs) hold great promise as Pt‐group‐metal‐free candidates for electrochemical reactions, yet their rational design and controllable synthesis remain fundamental challenges. Here, the molten‐salts mediated pyrolysis is demonstrated to be an effective and facile strategy for simultaneous morphology and electronic structure modulation of prototypical Fe‐N‐C materials, which functions as efficient oxygen reduction electrocatalysts. Taking advantage of the strong polarity and salt templating effects, the as‐obtained Fe‐N/C‐single atom catalyst (SAC) possesses hierarchical porous nanosheet morphology with an impressive specific surface area of 2237 m2 g−1 and unique FeN4Cl moieties as isolated active centers. The Fe‐N/C‐SAC delivers remarkable alkaline oxygen reduction reaction (ORR) activity with a half‐wave potential of 0.91 V and record kinetic current density up to 55 mA cm−2, outperforming the benchmark Pt/C. By virtue of dechlorination treatment, it is experimentally identified that the enhanced ORR activities are essentially governed by the axially bound Cl. Theoretical calculations rationalize this finding and demonstrate that the well‐defined fivefold‐coordinated configuration accelerates 4e− pathway kinetics through near‐optimal adsorption of the *OH intermediates and tunes the potential determining step from *OH reduction to *OOH formation. This study provides fundamental insights into the coordination‐engineered strategy in single‐atom catalysis. [ABSTRACT FROM AUTHOR]

The demands for green production of hydrogen peroxide have triggered extensive studies in the photocatalytic synthesis, but most photocatalysts suffer from rapid charge recombination and poor 2e− oxygen reduction reaction (ORR) selectivity. Here, a novel composite photocatalyst of cyano‐rich graphitic carbon nitride g‐C3N4 is fabricated in a facile manner by sodium chloride‐assisted calcination on dicyandiamide. The obtained photocatalysts exhibit superior activity (7.01 mm h−1 under λ ≥ 420 nm, 16.05 mm h−1 under simulated sun conditions) for H2O2 production and 93% selectivity for 2e− ORR, much higher than that of the state‐of‐the‐art photocatalyst. The porous g‐C3N4 with Na dopants and cyano groups simultaneously optimize two limiting steps of the photocatalytic 2e− ORR: photoactivity, and selectivity. The cyano groups can adjust the band structure of g‐C3N4 to achieve high activity. They also serve as oxygen adsorption sites, in which local charge polarization facilitates O2 adsorption and protonation. With the aid of Na+, the O2 is reduced to produce more superoxide radicals as the intermediate products for H2O2 synthesis. This work provides a facile approach to simultaneously tune photocatalytic activity and 2e− ORR selectivity for boosting H2O2 production, and then paves the way for the practical application of g‐C3N4 in environmental remediation and energy supply. [ABSTRACT FROM AUTHOR]

Atomically dispersed transition metal‐nitrogen‐carbon catalysts are emerging as low‐cost electrocatalysts for the oxygen reduction reaction in fuel cells. However, a cost‐effective and scalable synthesis strategy for these catalysts is still required, as well as a greater understanding of their mechanisms. Herein, iron, nitrogen co‐doped carbon spheres (Fe@NCS) have been prepared via hydrothermal carbonization and high‐temperature post carbonization. It is determined that FeN4 is the main form of iron existing in the obtained Fe@NCS. Two different precursors containing Fe2+ and Fe3+ are compared. Both chemical and structural differences have been observed in catalysts starting from Fe2+ and Fe3+ precursors. Fe2+@NCS‐A (starting with Fe2+ precursor) shows better catalytic activity for the oxygen reduction reaction. This catalyst is studied in an anion exchange membrane fuel cell. The high open‐circuit voltage demonstrates the potential approach for developing high‐performance, low‐cost fuel cell catalysts. [ABSTRACT FROM AUTHOR]

The development of earth‐abundant oxygen reduction reaction (ORR) catalysts with high catalytic activity and good stability for practical metal‐air batteries remains an enormous challenge. Herein, a highly efficient and durable ORR catalyst is reported, which consists of atomically dispersed Co single atoms (Co‐SAs) in the form of Co‐N4 moieties and small Co nanoparticles (Co‐SNPs) co‐anchored on nitrogen‐doped porous carbon nanocage (Co‐SAs/SNPs@NC). Benefiting from the synergistic effect of Co‐SAs and Co‐SNPs as well as the enhanced anticorrosion capability of the carbon matrix brought by its improved graphitization degree, the resultant Co‐SAs/SNPs@NC catalyst exhibits outstanding ORR activity and remarkable stability in alkaline media, outperforming Co‐SAs‐based catalyst (Co‐SAs@NC), and benchmark Pt/C catalyst. Density functional theory calculations reveal that the strong interaction between Co‐SNPs and Co‐N4 sites can increase the valence state of the active Co atoms in Co‐SAs/SNPs@NC and moderate the adsorption free energy of ORR intermediates, thus facilitating the reduction of O2. Moreover, the practical zinc‐air battery assembled with Co‐SAs/SNPs@NC catalyst demonstrates a maximum power density of 223.5 mW cm–2, a high specific capacity of 742 W h kg–1 at 50 mA cm–2 and a superior cycling stability. [ABSTRACT FROM AUTHOR]

Nitrogen doping represents an effective way to induce charge/spin polarization in nanocarbons for promoting oxygen reduction reaction (ORR) activity. However, it remains elusive to define the dominant active sites with respect to two critical N-configurations of pyridinic-N and graphitic-N. Herein, a tandem catalytic graphitization and nitrogen modification strategy for the synthesis of metal-free nitrogen-doped carbon nanoflakes (NCF) featuring the edge-suffused and graphite-analogous structure is presented. NCF exhibits superb Pt-like ORR activity (0.85 V for half-wave potential and 5.9 mA cm-2 for diffusion-limited current density) but much stronger robustness in the alkaline medium. The experimental and theoretical studies suggest the key role of graphitic-N in ORR. Furthermore, it unveils that the high activity of NCF should be traced to a synergistic polarization of the edge-type pyridinic-N/graphitic-N dipole spaced by one edge peak carbon atom on the armchair edges. This study sheds light on the understanding of ORR active sites in the nitrogen-doped nanocarbons for ORR. [ABSTRACT FROM AUTHOR]

Although the carbon‐supported single‐atom (SA) electrocatalysts (SAECs) have emerged as a new form of highly efficient oxygen reduction reaction (ORR) electrocatalysts, the preferable sites of carbon support for anchoring SAs are somewhat elusive. Here, a KOH activation approach is reported to create abundant defects/vacancies on the porous graphitic carbon nanosphere (CNS) with selective adsorption capability toward transition‐metal (TM) ions and innovatively utilize the created defects/vacancies to controllably anchor TM–SAs on the activated CNS via TMNx coordination bonds. The synthesized TM‐based SAECs (TM‐SAs@N‐CNS, TM: Cu, Fe, Co, and Ni) possess superior ORR electrocatalytic activities. The Cu‐SAs@N‐CNS demonstrates excellent ORR and oxygen evolution reaction (OER) bifunctional electrocatalytic activities and is successfully applied as a highly efficient air cathode material for the Zn–air battery. Importantly, it is proposed and validated that the N‐terminated vacancies on graphitic carbons are the preferable sites to anchor Cu‐SAs via a Cu(NC2)3(NC) coordination configuration with an excellent promotional effect toward ORR. This synthetic approach exemplifies the expediency of suitable defects/vacancies creation for the fabrication of high‐performance TM‐based SAECs, which can be implemented for the synthesis of other carbon‐supported SAECs. [ABSTRACT FROM AUTHOR]

The decomposition, electron transfer, and protonation of oxygen molecules are typically assumed to be the rate‐limiting steps of the oxygen reduction reactions (ORR), and the activation energy barriers of these reactions can be surmounted using catalysts. In this study, the physical rate‐limiting step of the ORR consists of the adsorption of gaseous oxygen molecules at the liquid–solid phase boundary, indicating that the formation of a gas–liquid–solid triple‐phase boundary (TPB) is important for accelerating the ORR kinetics. This is experimentally confirmed by analyzing the ORR in aluminum–air batteries. Moreover, the formation of a TPB using the hierarchical pores of sparked reduced graphene oxide is demonstrated, which serve as the cathode, and the remarkable electrochemical performance of the fabricated battery is presented. These findings can be used to accelerate the ORR kinetics by maximizing the TPB, particularly in aluminum–air batteries. [ABSTRACT FROM AUTHOR]

One of the main bottlenecks that limit the performance of reversible protonic ceramic electrochemical cells (R‐PCECs) is the sluggish kinetics of the oxygen reduction and evolution reactions (ORR and OER). Here, the significantly enhanced ORR and OER kinetics and stability of a conventional La0.6Sr0.4Co0.2Fe0.8O3–δ (LSCF) air electrode by an efficient catalyst coating of barium cobaltite (BCO) is reported. The polarization resistance of a BCO‐coated LSCF air electrode at 600 °C is 0.16 Ω cm2, about 30% of that of the bare LSCF air electrode under the same conditions. Further, an R‐PCEC with the BCO‐coated LSCF air electrode shows exceptional performance in both fuel cell (peak power density of 1.16 W cm−2 at 600 °C) and electrolysis (current density of 1.80 A cm−2 at 600 °C at 1.3 V) modes. The performance enhancement is attributed mainly to the facilitated rate of oxygen surface exchange. [ABSTRACT FROM AUTHOR]

Transition metal single‐atom catalysts (SACs) are currently a hot area of research in the field of electrocatalytic oxygen reduction reaction (ORR). In this review, the recent advances in transition metal single‐atom supported by 2D materials as catalysts for ORR with high performance are reported. Due to their large surface area, uniformly exposed lattice plane, and adjustable electronic state, 2D materials are ideal supporting materials for exploring ORR active sites and surface reactions. The rational design principles and synthetic strategies of transition metal SACs supported by 2D materials are systematically introduced while the identification of active sites, their possible catalytic mechanisms as well as the perspectives on the future of transition metal SACs supported by 2D materials for ORR applications are discussed. Finally, according to the current development trend of ORR catalysts, the future opportunities and challenges of transition metal SACs supported by 2D materials are summarized. [ABSTRACT FROM AUTHOR]

The development of iron and nitrogen co‐doped carbon (FeNC) electrocatalysts for the oxygen reduction reaction (ORR) in proton‐exchange membrane fuel cells (PEMFCs) is a grand challenge due to the low density of accessible FeN4 sites. Here, an in situ trapping strategy using nitrogen‐rich molecules (e.g., melamine, MA) is demonstrated to enhance the amount of accessible FeN4 sites in FeNC electrocatalysts. The melamine molecules can participate in the coordination of Fe ions in zeolitic imidazolate frameworks to form FeN6 sites within precursors. These FeN6 sites are then converted into atomically dispersed FeN4 sites during a pyrolytic process. Remarkably, the FeNC/MA exhibits a high single‐atom Fe content (3.5 wt.%), a large surface area (1160 m2 g−1), and a high density of accessible FeN4 sites (45.7 × 1019 sites g−1). As a result, FeNC/MA shows a much enhanced ORR activity with a half‐wave potential of 0.83 V (vs the reversible hydrogen electrode) in a 0.5 m H2SO4 electrolyte solution and a good performance in a PEMFC system with an activity of 80 mA cm−2 at 0.8 V under 1.0 bar H2/air. This work offers a promising approach toward high‐performance carbon‐based ORR electrocatalysts. [ABSTRACT FROM AUTHOR]

Lowering the operating temperature (ideally below 400 °C) for solid oxide fuel cell (SOFC) technology deployment has been an important transition that introduces the benefit of reduced operational costs and system durability. However, the key technical issue limiting the transition is the sluggish cathodic performance, namely the oxygen reduction reaction (ORR) rate of the conventional sponge‐like cathode dramatically drops as the temperature reduces. In this paper, 3D engineering of a cathode is conducted on a protonic ceramic fuel cell to obtain an enhanced ORR between 400 and 600 °C. Compared with a cell using a conventional sponge‐like cathode, 3D engineering improves the cathode ORR by 41% at 400 °C with a peak power density of 0.410 W cm−2. A phase field simulation is applied to assist the engineering by understanding the competition between the cathode mass and charge transfer with different cathode porosities. The results show that structural engineering of existing well‐developed cathodes is a simple and effective method to promote cathode ORR for low temperature SOFC by regulating the mass and charge transfer. [ABSTRACT FROM AUTHOR]

Although Pd is a potential substitution of Pt‐based catalysts for the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR), the binding of *H and oxygenated (*O, *OOH, *OH) intermediates on Pd are stronger than on Pt, leading to its inferior activity for HER and ORR. In this work, CuPd/Pd core/shell nanoparticles with an ultrathin Pd shell (0.5 nm) are developed, which demonstrate the Pt‐like bifunctional activity for HER and ORR in acid electrolytes. The overpotential at 350 mA cm−2 for HER and the half‐wave potential for ORR on the optimal CuPd/Pd core/shell NPs are 76 mV and 0.854 V versus reversible hydrogen electrode (RHE), respectively, which are comparable to that of Pt and among the best of the reported Pd‐based catalysts. Density functional theory calculations indicate that the significantly enhanced HER/ORR activity on CuPd/Pd core/shell NPs with 0.5 nm Pd shell stem from the compressive strain induced downshift of d‐band center for Pd (by 2.0%), which weakens the binding strength of *H and oxygenated intermediates and promotes the reaction kinetics. [ABSTRACT FROM AUTHOR]

Fine control over the physicochemical structures of carbon electrocatalysts is important for improving the sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in rechargeable Zn–air batteries. Covalent organic frameworks (COFs) are considered good candidate carbon materials because their structures can be precisely controlled. However, it remains a challenge to impart bifunctional electrocatalytic activities for both the ORR and OER to COFs. Herein, a pyridine‐linked triazine covalent organic framework (PTCOF) with well‐defined active sites and pores is readily prepared under mild conditions, and its electronic structure is modulated by incorporating Co nanoparticles (CoNP‐PTCOF) to induce bifunctional electrocatalytic activities for the ORR and OER. The CoNP‐PTCOF exhibits lower overpotentials for both ORR and OER with outstanding stability. Computational simulations find that the p‐band center of CoNP‐PTCOF down‐shifted by charge transfer, compared to pristine PTCOF, facilitate the adsorption and desorption of oxygen intermediates on the pyridinic carbon active sites during the reactions. The Zn–air battery assembled with bifunctional CoNP‐PTCOF exhibits a small voltage gap of 0.83 V and superior durability for 720 cycles as compared with a battery containing commercial Pt/C and RuO2. This strategy for modulating COF electrocatalytic activities can be extended for designing diverse carbon electrocatalysts. [ABSTRACT FROM AUTHOR]

Although atomically dispersed Fe‐N4 on carbon materials (Fe‐NC) have enormous potential for the oxygen reduction reaction (ORR), precise control over the electronic structure of Fe to enhance the catalytic performance and a full understanding of the catalytic mechanism remain elusive. Herein, a novel approach is designed to boost the kinetic activity of single Fe‐N4 centers by controlling S‐doped content and species (namely, thiophene‐like S and oxidized S). Due to confinement and catalysis effects, the innovative strategy of combining a Mg(OH)2 template with KOH activation preferentially generates oxidized S and simultaneously constructs porous carbon with a high Fe loading (2.93 wt%) and hierarchical pores. Theoretical calculations suggest that neighboring S functionalities can affect the electronic configurations of Fe‐N4 sites and increase the electron density around Fe atoms, thereby optimizing the adsorption energy of intermediates and substantially accelerating reaction kinetics, following the trend: oxidized S doped > thiophene‐like S doped > pristine Fe‐N4. Benefiting from high activity and accessibility of Fe‐N4 sites, the optimal FeNC‐SN‐2 electrode displays impressive ORR activity with large power density while maintaining outstanding durability in Zn‐air batteries and microbial fuel cells. The work paves the way to prepare stable single‐atom metal‐Nx sites with heteroatom‐doping for diverse high‐performance applications. [ABSTRACT FROM AUTHOR]

Self‐powered sensing systems (SPSSs) are critical components in smart portable electronic devices. Zinc‐air batteries (ZABs) as promising energy devices provide a great opportunity to develop novel SPSS for sensing applications owing to the merit of high open‐circuit potential. Herein, hierarchically porous single‐atom iridium embedded nitrogen‐doped carbon (SA‐Ir/NC) is reported as an efficient catalyst for the oxygen reduction reaction (ORR) in the neutral ZABs, enabling the SPSSs towards glucose detection with a high sensitivity and stable output signal. The resultant SA‐Ir/NC shows superior ORR activity and stability to commercial Pt/C in neutral electrolytes. According to the theoretical calculations, IrN5 active sites in SA‐Ir/NC exhibit moderate adsorption free energy to reaction intermediates, giving SA‐Ir/NC excellent four‐electron ORR activity and well‐enhanced H2O2 tolerance. When SA‐Ir/NC is applied as an air cathode, the as‐prepared ZABs display a large open‐circuit voltage of 1.42 V, a remarkable power density of 90.4 mW cm−2, and excellent long‐term stability. After being integrated with glucose oxidase, the SPSSs are successfully established for sensitive detection of glucose based on a competitive model, holding great promise in biosensing applications. [ABSTRACT FROM AUTHOR]

Single atomic dispersed M‐N‐C (M = Fe, Co, Ni, Cu, etc.) composites display excellent performance for catalytic reactions. However, the analysis and understanding of neighboring M‐N‐C centers at the atomic level are still insufficient. Here, FeCo‐N‐doped hollow carbon nanocages (FeCo‐N‐HCN) with neighboring Fe‐N4‐C and Co‐N4‐C dual active centers as efficient catalysts are reported. Spherical aberration‐corrected high angle annular dark‐field scanning transmission electron microscopy, small area (1 nm2) electron energy loss spectroscopy, and X‐ray absorption spectroscopy data analysis and fitting prove the neighboring Fe‐N4‐C and Co‐N4‐C dual active structure in FeCo‐N‐HCN. Experimental tests and density functional theory calculation results reveal that the FeCo‐N‐HCN catalyst displays better catalytic activity than Fe single‐metal catalyst for oxygen reduction reaction (ORR), which is attributed to the synergistic effect of Fe‐N4‐C and Co‐N4‐C dual active centers reducing the reaction energy barriers for ORR. Although the catalytic performance of the FeCo‐N‐HCN catalyst is not comparable to the‐state‐of‐art catalysts reported due to the low metal contents (Fe: 1.96 wt% and Co: 1.31 wt%), these results can refresh the understanding of neighboring M‐N‐C centers at the atomic level and provide guidance for the design of catalysts in the future. [ABSTRACT FROM AUTHOR]

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

Hierarchical bottom‐up structuring in nature provides inspiration for the construction of self‐assembled complex with advanced properties out of simple building blocks. However, the development of self‐standing assemblies of ultrasmall metal nanoparticles using redox ligands is still challenging. Here, a molecule‐confined reduction strategy to prepare robust self‐organized superstructures through metal–ligand interfacial interactions and hydrogen bonding is reported. High‐density and well‐separated Pd nanoparticles and single atoms are embedded within organometallic matrixes (Pd@eFc) via in situ reduction of the Pd precursor by redox‐active ligands. Furthermore, these metal–organic networks can be disassembled into fragments with highly dispersed Pd nanoparticles and single atoms by solvent mediation. Strikingly, Pd@eFc disassembly delivers excellent oxygen reduction performance, while its assembly can act as a selective hydrogenation catalyst. This viable molecule‐confined reduction strategy can also be applied to other organometallic superstructures (e.g., Au@eFc, Ag@eFc). The findings thus encourage on‐going study to explore controlled hierarchically self‐assembled superstructures for a wide range of catalysis. [ABSTRACT FROM AUTHOR]

Ever‐developing energy storage technologies demand the pursuit of advanced materials with multiple functionalities. Recent studies revealed that multiple heteroatom‐doped carbon has been wildly used for bi‐functional or even tri‐functional energy storage and conversion. However, few efforts have been made to uncover the origin of multi‐functionalities. Herein, a nitrogen, phosphorus, and sulfur tri‐doped carbon is designed in this work with large porosity, rich heteroatoms doping and high mass density, exhibiting excellent bifunctionalities on supercapacitors and oxygen reduction reaction. Importantly, the density functional theory calculations demonstrate the relevant co‐doping and tri‐doping generate more active sites on neighboring carbon atoms than single doping, and the same type of active sites may enhance bifunctionalities simultaneously. The present investigations provide a promising guidance on the design of multi‐functional materials for future energy storage and conversion applications. [ABSTRACT FROM AUTHOR]

The rational design and facile synthesis of 1D hollow tubular carbon‐based materials with highly efficient oxygen reduction reaction (ORR) performance remains a challenge. Herein, a simple yet robust route is employed to simultaneously craft single‐atomic Fe sites and graphitic layer‐wrapped Fe3C nanoparticles (Fe3C@GL NPs) encapsulated within 1D N‐doped hollow mesoporous carbon tubes (denoted Fe‐N‐HMCTs). The successional compositional and structural crafting of the hydrothermally self‐templated polyimide tubes (PITs), enabled by Fe species incorporation and acid leaching treatment, respectively, yields Fe‐N‐HMCTs that are subsequently exploited as the ORR electrocatalyst. Remarkably, an alkaline electrolyte capitalizing on Fe‐N‐HMCTs achieves excellent ORR activity (onset potential, 0.992 V; half‐wave potential, 0.872 V), favorable long‐term stability, and strong methanol tolerance, outperforming the state‐of‐the‐art Pt/C catalyst. Such impressive ORR performances of the Fe‐N‐HMCTs originate from the favorable configuration of active sites (i.e., atomically dispersed Fe‐Nx sites and homogeneously incorporated Fe3C@GL NPs) in conjunction with the advantageous 1D hollow tubular architecture containing adequate mesoporous surface. This work offers a new view to fabricate earth‐abundant 1D Fe‐N‐C electrocatalysts with well‐designed architecture and outstanding performance for electrochemical energy conversion and storage. [ABSTRACT FROM AUTHOR]

Expedited conversion of O2 to H2O with minimal amounts of Pt is essential for wide applicability of PEM fuel cells (PEMFCs). Therefore, it is imperative to develop a process for catalyst management to circumvent unnecessary catalyst loss while improving the Pt utilization, catalytic activity, and durability. Here, the fabrication of a self‐standing nanofiber electrode is demonstrated by employing electrospinning. This film‐type catalyst simultaneously contains Pt–Co alloy nanoparticles and Co embedded in an N‐doped graphitized carbon (Co–Nx) support derived from the electrospun zeolitic imidazolate frameworks. Notably, the flexible electrode is directly transferrable for the membrane‐electrode assembly of high temperature PEMFC. In addition, the electrodes exhibit excellent performance, maybe owing to the synergistic interaction between the Pt–Co and Co–Nx as revealed by the computational modeling study. This method simplifies the fabrication and operation of cell device with negligible Pt loss, compared to ink‐based conventional catalyst coating methods. [ABSTRACT FROM AUTHOR]

Zinc‐air battery is of great interest but its wide‐ranging application is impeded by the sluggish cathodic reactions, especially the oxygen reduction reaction. Despite blooming development in the past decades, achieving further breakthroughs in the activity improvement still appears challenging. Herein, the critical role of bimetal sites in boosting oxygen reduction activity is identified with the combination of theoretical calculations and electrochemical experiments. Density functional theory calculations suggest the elongation of OO bond over the dual‐atom system, which is beneficial to its following dissociation and thus enhances the efficiency of the reaction. The proof‐of‐concept electrocatalyst experimentally delivers a half‐wave potential of 0.92 V versus reversible hydrogen electrode and kinetic current density of 51.9 mA cm−2, significantly outperforming the commercial Pt/C. Both aqueous and all‐solid‐state zinc‐air battery assembled with such catalyst demonstrate superior durability with little performance fluctuation, confirming their potential feasibility in the practical applications. [ABSTRACT FROM AUTHOR]

Iron phthalocyanine (FePc) has inspired substantial interest in the context of the oxygen reduction reaction (ORR) owing to its prominent catalytic activity in alkaline media; however, its poor stability significantly hinders its practical applications. Heterostructures with a strong coupling effect between different components have considerable potential to promote the activity and stability simultaneously. Hence, a heterostructured bimetallic phthalocyanine (FePc/CoPc HS) catalyst with heterogeneous distribution of metallic elements is designed. Compared with FePc, FePc/CoPc HS demonstrates higher kinetic current density (increased by >100%) and more robust durability (enhanced by 20.5%) for the ORR. In addition, a Zn–air battery with FePc/CoPc HS as the cathode catalyst achieves high power density (128 mW cm−2) and high open‐circuit voltage (1.67 V). X‐ray absorption fine structure and theoretical calculations reveal that the heterostructure design induced elongates the FeN bond length, and augments electron density around the Fe active sites, and reduced highest‐occupied molecular orbital and lowest‐unoccupied molecular orbital energy gap are responsible for the boosted ORR performance. This work enriches the understanding of electronic structure modulation of heterostructured bimetallic phthalocyanine based ORR electrocatalysts. [ABSTRACT FROM AUTHOR]

Searching for highly efficient, stable, and cost‐effective electrocatalysts for water splitting and oxygen reduction reaction (ORR) is critical for renewable energies, yet it remains a great challenge. Here, by performing an unbiased structural search and first‐principles calculations, the electrocatalytic performance of the emerging 2D transitional‐metal carbides, MC2 (M represents the transition metal of Ti, V, Nb, Ta, and Mo, C is carbon), is systematically investigated. Owing to their super stability and outstanding electronic conductivity, fast charge transfer kinetics is allowed during catalysis. Specifically, NbC2, TaC2, and MoC2 possess excellent hydrogen evolution reaction (HER) performance under the reaction by the Volmer‐Heyrovsky mechanism. Moreover, taking advantage of the dual‐active‐site catalytic mechanism for oxygen evolution reaction (OER) and ORR over traditional single‐active‐site mechanism, TaC2 presents promising bifunctional electrocatalytic activity with a low overpotential of 0.06 and 0.37 V for HER and ORR, respectively. Meanwhile, the low overpotential endows MoC2 remarkable multifunctional electrocatalytic performance in overall water splitting (0.001 V for HER, 0.45 V for OER) and ORR (0.47 V). These intriguing results demonstrate the robust applicability of MC2 monolayers as effective electrocatalysts. [ABSTRACT FROM AUTHOR]

Zinc–air batteries deliver great potential as emerging energy storage systems but suffer from sluggish kinetics of the cathode oxygen redox reactions that render unsatisfactory cycling lifespan. The exploration on bifunctional electrocatalysts for oxygen reduction and evolution constitutes a key solution, where rational design strategies to integrate various active sites into a high‐performance air cathode remain insufficient. Herein, a multiscale construction strategy is proposed to rationally direct the fabrication of bifunctional oxygen electrocatalysts for long‐lifespan rechargeable zinc–air batteries. NiFe layered double hydroxides and cobalt coordinated framework porphyrin are selected as the active sites considering their high intrinsic activity at the molecular level, and the active sites are successively integrated on three‐dimensional conductive scaffolds at mesoscale to strengthen ion transportation. Consequently, the multiscale constructed electrocatalyst exhibits excellent bifunctional performance (ΔE = 0.68 V), which is even better than that of the noble metal based benchmarks. The corresponding air cathodes endow zinc–air batteries with a reduced voltage gap of 0.74 V, a high power density of 185.0 mW cm−2, and an ultralong lifespan of more than 2400 cycles at 5.0 mA cm−2. This work demonstrates a feasible strategy to rationally integrate various active sites to construct multifunctional electrocatalysts for energy‐related processes. [ABSTRACT FROM AUTHOR]

Precise electrochemical synthesis under ambient conditions has provided emerging opportunities for renewable energy utilization. Among many promising systems, the production of hydrogen peroxide (H2O2) from the cathodic oxygen reduction reaction (ORR) has attracted considerable interest in past decades due to the increasing market demands and the vital role of ORR in the electrocatalysis field. This work describes recent advances in cathodic materials for H2O2 synthesis from 2e- ORR. By using Pt as a stereotype, the tuning knobs are overviewed, including the intrinsic binding strength of oxygenated species, the intermediate diffusion path and the isolation of Pt–Pt ensembles that enable 2e- ORR pathway from 4e- total reduction. This knowledge is successfully applied to other transition metal systems and leads to the discovery of more efficient alloy catalysts with balanced improvement on both activity and selectivity. In addition, mesostructure engineering and heteroatoms doping strategies on carbon‐based materials, which significantly boost the H2O2 production efficiency as compared to intact carbon sites, are also reviewed. Finally, future directions and challenges of transferring developed catalysts from lab scale tests to pilot plant operations are briefly outlooked. [ABSTRACT FROM AUTHOR]

The recent advances in electrocatalysis for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), hydrogen oxidation reaction (HOR), carbon dioxide reduction reaction (CO2RR), and nitrogen reduction reaction (NRR) are thoroughly reviewed. This comprehensive review focuses on the single‐atom catalysts (SACs) including Sc, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Sn, W, Bi, Ru, Rh, Pd, Ag, Ir, Pt, and Au with single‐metal sites or dual‐metal sites. The recent development of single‐atom electrocatalysts with novel configurations and compositions is documented. The understanding of the process–structure–property relationships is highlighted. For the SACs, their electrocatalytic performance and stability in fuel cells, zinc–air batteries, electrolyzers, CO2RR, and NRR are summarized. The challenges and perspectives in the emerging field of single‐atom electrocatalysis are discussed. [ABSTRACT FROM AUTHOR]

The electrocatalytic value of nanoparticles has attracted substantial attention in relation to energy conversion devices, including solid oxide fuel cells. Among various forms of analogs, ex‐solved metal nanoparticles originating from their parent oxides display strong particle‐substrate interactions and thus have the benefits of extended durability and of course enhanced catalytic activity. Inspired by recent advances, here, novel air‐electrode materials based on BaCoO3–δ perovskites decorated with socketed Ag nanoparticles are presented. Doping with niobium (Nb5+) and tantalum (Ta5+) can significantly promote the stability of the cubic perovskite phase. The developed oxides exhibit promising performance outcomes in the highly prized low‐to‐intermediate temperature regimes (450–650 °C). Moreover, the exclusion of Ag particles further activates the parent scaffold, thereby conveying record‐level area‐specific resistance (e.g., ≈0.02 Ω cm2 at 650 °C). Coupled with the unique nanoarchitecture, the newly designed cathode showcases in this study hold great promise for future air‐electrodes in fuel cells. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial reactions in energy conversion and storage systems including fuel cells, metal–air batteries, and electrolyzers. Developing low‐cost, high‐efficiency, and durable non‐noble bifunctional oxygen electrocatalysts is the key to the commercialization of these devices. Here, based on an in‐depth understanding of ORR/OER reaction mechanisms, recent advances in the development of non‐noble electrocatalysts for ORR/OER are reviewed. In particular, rational design for enhancing the activity and stability and scalable synthesis toward the large‐scale production of bifunctional electrocatalysts are highlighted. Prospects and future challenges in the field of oxygen electrocatalysis are presented. [ABSTRACT FROM AUTHOR]

Hydrogen peroxide is a highly valuable chemical, and electrocatalytic oxygen reduction towards H2O2 offers an alternative method for safe on‐site applications. Generally, low‐cost hematite (α‐Fe2O3) is not recognized as an efficient electrocatalyst because of its inert nature, but it is herein reported that α‐Fe2O3 can be endowed with high catalytic activity and selectivity via the engineering of facets and oxygen vacancies. Density‐functional theory (DFT)calculations predict that the {001} facet is intrinsically selective for H2O2 production, and that oxygen vacancies can trigger the high activity, providing sites for O2 adsorption and protonation, stabilizing the *OOH intermediate, and preventing cleavage of the OO bond. The synthesized oxygen‐defective α‐Fe2O3 single crystals with exposed {001} facets achieve high selectivities for H2O2 of >90%, >88%, and >95% in weakly acidic, neutral, and alkaline electrolytes, respectively, and the H2O2 production rate reaches 454 mmol g−1cat h−1 at 0.1 V versus RHE under alkaline conditions. In an anion exchange membrane fuel cell, a maximum H2O2 production of 546.8 mmol L−1 with a high Faradaic efficiency of 80.5% is achieved. Thus, this work details a low‐cost catalyst feasible for H2O2 synthesis, and highlights the feasibility of theoretical catalyst design for practical applications. [ABSTRACT FROM AUTHOR]

Au‐incorporation is a promising strategy to retard composition‐loss in Pt‐based catalyst. However, the unclear mechanism limits guided catalyst design and the performance optimization. Here, direct evidence is provided to validate the outward diffusion of Au atoms in Au‐core/Pt‐based‐shell structures. A Co interlayer is built between the Au‐core and PtCo‐based shell to exclude the possibility of atomic diffusion caused by interfacial alloying. In conjunction with the improved catalytic durability of the Au‐core@Pt‐based‐shell structure, it is reasonable to conclude that it is the subsurface segregated Au atoms rather than interfacial interaction that boosts the catalytic durability of Au‐core/Pt‐based‐shell structured catalysts towards oxygen reduction reaction. More importantly, by constructing Au‐core@Co‐interlayer@PtCoAu‐shell multilayer structure, the specific (1.730 mA cm−2) and mass (0.692 A mg−1Pt) activities are enhanced 7‐ and 4‐ fold relative to the commercial Pt/C. After 10 000 cycles of accelerated durability test, the mass activity loss for the multilayered catalyst is as low as 6.14% while the loss exceeds 35% for the commercial Pt/C catalyst. The improved catalytic performance of the Au@Co@PtCoAu multilayer structure can be ascribed to the finely modulated electronic structure and the compensated composition loss owing to the delicate structure and composition profile design. [ABSTRACT FROM AUTHOR]

Direct carbon fuel cells (DCFCs) are an efficient energy‐conversion technology capable of generating electricity with carbon‐dioxide‐capture chemistry with solid carbon as fuels. The efficiency and performance of DCFCs depend on the kinetics of the carbon oxidation reactions (COR) and the oxygen reduction reactions (ORR), each occurring at anode and cathode, respectively. The limited active sites paired with reduced temperatures greatly decrease the efficiency of the electrochemical reactions. Ultraporous dual‐3D ceramic textiles (dual‐3DCT) are integrated into electrolyte‐supported DCFCs to enhance charge and mass transfer at the electrodes. Improved COR at the anode is achieved by the synergy between the 3DCT NiO–Ce0.8Gd0.2O1.95 (GDC) structure and optimal carbon fuel choice. In a comparative study, DCFCs using graphitic carbon (GC) as fuel show the best COR performance when compared to DCFCs utilizing alternative fuels such as carbon black (CB) and activated carbon (AC). The 3DCT Sm0.5Sr0.5CoO3‐δ–GDC (SSC–GDC) composite cathode shows electrochemical performance superior to that of the conventional screen‐printed SSC–GDC. A peak power density of 392 mW cm−2 at 600 °C is obtained in a DCFC using the 3DCT‐anode/electrolyte/3DCT‐cathode configuration, an unprecedented value for any reported DCFC as of yet. This points toward promising applications of dual‐3DCT electrodes for reduced‐temperature DCFCs. [ABSTRACT FROM AUTHOR]

Fundamental understanding of constructing elevated catalysts to realize fast electron transfer and rapid mass transport in oxygen reduction reaction (ORR) chemistry by interface regulation and structure design is important but still ambiguous. Herein, a novel jellyfish‐like Mott–Schottky‐type electrocatalyst is developed to realize fast electron transfer and decipher the structure–mass transport connection during ORR process. Both spectroscopy techniques and density functional theory calculation demonstrate electrons spontaneously transfer from Fe to N‐doped graphited carbon at the heterojunction interface, thus accelerating electron transfer from electrode to reactant. Dynamic analysis indicates unique structure can significantly improve mass transport of oxygen‐species due to two factors: one is electrolyte streaming effect caused by tentacle‐like carbon nanotubes; the other is effective collision probability in the semi‐closed cavity. Therefore, this Mott–Schottky‐type catalyst delievers superior ORR performance with high onset potential, positive half wave potential, and large current density. It also exhibits low overpotential when serving as an air cathode in Zn–air batteries. This work deepens understanding of the two key factors—electron transfer and mass transport—on determining the kinetic reaction of ORR process and offers a new avenue in constructing efficient Mott–Schottky electrocatalysts. [ABSTRACT FROM AUTHOR]

Tuning the intrinsic strain of Pt‐based nanomaterials has shown great promise for improving the oxygen reduction reaction (ORR) performance. Herein, reported is a tunable surface strain in penta‐twinned ternary Pt–Cu–Mn nanoframes (NFs). Pt–Cu–Mn ultrafine NFs (UNFs) exhibit ≈1.5% compressive strain compared to Pt–Cu–Mn pentagonal NFs (PNFs) and show the superior activity toward ORR in an alkaline environment. Specifically, the specific and mass activity of Pt–Cu–Mn UNFs are 3.38 mA cm−2 and 1.45 A mg−1, respectively, which is 1.45 and 1.71 times higher than that of Pt–Cu–Mn PNFs, demonstrating that compressive strain in NFs structure can effectively enhance the catalytic activity of ORR. Impressively, Pt–Cu–Mn UNFs exhibit 8.67 and 9.67 times enhanced specific and mass activity compared with commercial Pt/C. Theoretical calculations reveal that compression on the surface of Pt–Cu–Mn UNFs can weaken the bonding strengths and adsorption of oxygen‐containing intermediates, resulting in an optimal condition for ORR. [ABSTRACT FROM AUTHOR]

Pt‐based alloy nanocrystals have shown great success in oxygen reduction electrocatalysis owing to their unique surface and electronic structures. However, they suffer from severe stability issues due to the dissolution of non‐noble metal elements, leading to the "trade‐off" between activity and stability. In this work, targeting the stability issue of a PtxCuy‐based alloy, Pt2CuW0.25 ternary alloy nanoparticles are synthesized by thermal reduction strategy based on wet‐chemical method using W(CO)6 as a reductant. Apart from the competitive activity, the obtained Pt2CuW0.25/C shows remarkable stability, whereby the area specific activity and mass activity maintain 89.5% and 95.9% of the initial values, respectively, after 30 000 cycles of accelerated polarization between 0.6 and 1.1 V (vs reversible hydrogen electrode). By using vacancy formation energy of surface Pt as the descriptor, it is found that the enhanced stability of Pt2CuW0.25/C originates mainly from the stronger bonding between W and Pt/Cu atoms, acting as an "adhesive" to stabilize the atoms from dissolution, which is further verified by chemical stability experiments. This work demonstrates a rational design strategy for ternary alloy nano‐electrocatalyst that has high thermodynamic stability while maintaining high activity by employing high‐melting‐point metal. [ABSTRACT FROM AUTHOR]

Discovering precious metal‐free electrocatalysts exhibiting high activity and stability toward both the oxygen reduction (ORR) and the oxygen evolution (OER) reactions remains one of the main challenges for the development of reversible oxygen electrodes in rechargeable metal–air batteries and reversible electrolyzer/fuel cell systems. Herein, a highly active OER catalyst, Fe0.3Ni0.7OX supported on oxygen‐functionalized multi‐walled carbon nanotubes, is substantially activated into a bifunctional ORR/OER catalyst by means of additional incorporation of MnOX. The carbon nanotube‐supported trimetallic (Mn‐Ni‐Fe) oxide catalyst achieves remarkably low ORR and OER overpotentials with a low reversible ORR/OER overvoltage of only 0.73 V, as well as selective reduction of O2 predominantly to OH−. It is shown by means of rotating disk electrode and rotating ring disk electrode voltammetry that the combination of earth‐abundant transition metal oxides leads to strong synergistic interactions modulating catalytic activity. The applicability of the prepared catalyst for reversible ORR/OER electrocatalysis is evaluated by means of a four‐electrode configuration cell assembly comprising an integrated two‐layer bifunctional ORR/OER electrode system with the individual layers dedicated for the ORR and the OER to prevent deactivation of the ORR activity as commonly observed in single‐layer bifunctional ORR/OER electrodes after OER polarization. [ABSTRACT FROM AUTHOR]