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Controlling tire local electronic structure of active ingredients to improve the adsorption-desorption characteristics of oxygen-containing intermediates over the electrochemical liquid-solid interfaces is a critical challenge in the field of oxygen reduction reaction (ORR) catalysis. Here, we offer a simple approach for modulating the electronic states of metal nanocrystals by bimetal co-doping into carbon-nitrogen substrate, allowing us to modulate the electronic structure of catalytic ao five centers. To test our strategy, we designed a typical bimetallic nanoparticle catalyst (FeCo NP/NC) to flexibly alter the reaction kinetics of ORR. Our results from synchrotron X- ray absorption spectroscopy and X-ray photoelectron spectroscopy showed that the co-doping of iron and cobalt could optimize the intrinsic charge distribution of Fe-Co NP/NC catalyst, promoting the oxygen reduction kinetics and ultimately achieving remarkable ORR activity. Consequently, the carefully designed Fe-Co NP/NC exhibits an ultra-high kinetic current density at the operating voltage (71.94 mA/cm2 at 0.80 V), and the half-wave potential achieves 0.915 V, which is obviously better than that of the corresponding controls including Fe NP/NC, Co NP/NC. Our findings provide a unique perspective for optimizing the electronic structure of active centers to achieve higher ORR catalytic activity and faster kinetics. [ABSTRACT FROM AUTHOR]

Single-atom catalysts, especially those with metal−N4 moieties, hold great promise for facilitating the oxygen reduction reaction. However, the symmetrical distribution of electrons within the metal−N4 moiety results in unsatisfactory adsorption strength of intermediates, thereby limiting their performance improvements. Herein, we present atomically coordination-regulated Co single-atom catalysts that comprise a symmetry-broken Cl−Co−N4 moiety, which serves to break the symmetrical electron distribution. In situ characterizations reveal the dynamic evolution of the symmetry-broken Cl−Co−N4 moiety into a coordination-reduced Cl−Co−N2 structure, effectively optimizing the 3d electron filling of Co sites toward a reduced d-band electron occupancy (d5.8 → d5.28) under reaction conditions for a fast four-electron oxygen reduction reaction process. As a result, the coordination-regulated Co single-atom catalysts deliver a large half-potential of 0.93 V and a mass activity of 5480 A gmetal−1. Importantly, a Zn-air battery using the coordination-regulated Co single-atom catalysts as the cathode also exhibits a large power density and excellent stability. The electrochemical oxygen reduction reaction plays an important role in new energy technologies such as fuel cells and metal-air batteries. Here the authors present a cobalt catalyst with a symmetry-broken Cl−Co−N4 moiety capable of dynamically modulating electron occupancy at active sites during practical reaction conditions to optimize oxygen reduction performance. [ABSTRACT FROM AUTHOR]

Developing cost‐effective and sustainable acidic water oxidation catalysts requires significant advances in material design and in‐depth mechanism understanding for proton exchange membrane water electrolysis. Herein, we developed a single atom regulatory strategy to construct Co−Co dinuclear active sites (DASs) catalysts that atomically dispersed zirconium doped Co9S8/Co3O4 heterostructure. The X‐ray absorption fine structure elucidated the incorporation of Zr greatly facilitated the generation of Co−Co DASs layer with stretching of cobalt oxygen bond and S−Co−O heterogeneous grain boundaries interfaces, engineering attractive activity of significantly reduced overpotential of 75 mV at 10 mA cm−2, a breakthrough of 500 mA cm−2 high current density, and water splitting stability of 500 hours in acid, making it one of the best‐performing acid‐stable OER non‐noble metal materials. The optimized catalyst with interatomic Co−Co distance (ca. 2.80 Å) followed oxo‐oxo coupling mechanism that involved obvious oxygen bridges on dinuclear Co sites (1,090 cm−1), confirmed by in situ SR‐FTIR, XAFS and theoretical simulations. Furthermore, a major breakthrough of 120,000 mA g−1 high mass current density using the first reported noble metal‐free cobalt anode catalyst of Co−Co DASs/ZCC in PEM‐WE at 2.14 V was recorded. [ABSTRACT FROM AUTHOR]

Photocatalytic two-electron oxygen reduction to produce high-value hydrogen peroxide (H2O2) is gaining popularity as a promising avenue of research. However, structural evolution mechanisms of catalytically active sites in the entire photosynthetic H2O2 system remains unclear and seriously hinders the development of highly-active and stable H2O2 photocatalysts. Herein, we report a high-loading Ni single-atom photocatalyst for efficient H2O2 synthesis in pure water, achieving an apparent quantum yield of 10.9% at 420 nm and a solar-to-chemical conversion efficiency of 0.82%. Importantly, using in situ synchrotron X-ray absorption spectroscopy and Raman spectroscopy we directly observe that initial Ni-N3 sites dynamically transform into high-valent O1-Ni-N2 sites after O2 adsorption and further evolve to form a key *OOH intermediate before finally forming HOO-Ni-N2. Theoretical calculations and experiments further reveal that the evolution of the active sites structure reduces the formation energy barrier of *OOH and suppresses the O=O bond dissociation, leading to improved H2O2 production activity and selectivity. Here, the authors explore how Ni single-atom sites on carbon nitride evolve under photocatalytic conditions. They show that this evolution plays a pivotal role in enhancing photocatalytic H2O2 production. [ABSTRACT FROM AUTHOR]

The ability to create highly active and CO‐tolerant platinum‐free catalysts toward alkaline hydrogen oxidation reaction (HOR) represents a significant endeavor to enable commercialization of alkaline fuel cells. This, however, remains a grand challenge. Herein, a robust defective‐carbon‐supported Ru catalyst (denoted as Ru@C) is crafted to achieve efficient and CO‐tolerant HOR in alkaline media via delicately tailoring interfacial chemistry of catalyst. Notably, the degree of defects in the carbon support is the key to tune the interface chemistry. An integrated experimental and density functional theory calculations study demonstrates that the favorable interfacial chemical interaction between Ru and carbon support controlled by the covalently bonded Ru─O─C redistributes the d electrons of Ru and downshiftsits d‐band center, which in turn weakens the hydrogen adsorption and suppresses the Ru 4d→CO 2π* back donation. Consequently, the optimized Ru@C catalyst renders a 6.6‐fold enhancement in mass activity (@25 mV) for alkaline HOR over the conventional Ru/C counterpart, which also outperforms the state‐of‐the‐art catalysts. Intriguingly, the catalyst can tolerate 20 000 ppm CO, far exceeding that of commercial Pt/C and PtRu/C catalysts. This work elucidates the correlation between precisely tailored interfacial chemistry and HOR performance, and is expected to further enlighten the design of advanced catalysts. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are the core reactions of a series of advanced modern energy and conversion technologies, such as fuel cells and metal–air cells. Among all kinds of oxygen electrocatalysts that have been reported, single‐atom catalysts (SACs) offer great development potential because of their nearly 100% atomic utilization, unsaturated coordination environment, and tunable electronic structure. In recent years, numerous SACs with enriched active centers and asymmetric coordination have been successfully constructed by regulating their coordination environment and electronic structure, which has brought the development of atomic catalysts to a new level. This paper reviews the improvement of SACs brought by atom‐level interface engineering. It starts with the introduction of advanced techniques for the characterizations of SACs. Subsequently, different design strategies that are applied to adjust the metal active center and first coordination sphere of SACs and then enhance their oxygen electrocatalysis performance are systematically illustrated. Finally, the future development of SACs toward ORR and OER is discussed and prospected. [ABSTRACT FROM AUTHOR]

The electrochemical oxygen reduction reaction (ORR) is at the heart of modern sustainable energy technologies. However, the linear scaling relationship of this multistep reaction now becomes the bottleneck for accelerating kinetics. Herein, we propose a strategy of using intermetallic-distance-regulated atomic-scale bimetal assembly (ABA) that can catalyse direct O‒O radical breakage without the formation of redundant *OOH intermediates, which could regulate the inherent linear scaling relationship and cause the ORR on ABA to follow a fast-kinetic dual-sites mechanism. Using in situ synchrotron spectroscopy, we directly observe that a self-adjustable N-bridged Pt = N2 = Fe assembly promotes the generation of a key intermediate state (Pt‒O‒O‒Fe) during the ORR process, resulting in high reaction kinetics and selectivity. The well-designed Pt = N2 = Fe ABA catalyst achieves a nearly two orders of magnitude enhanced kinetic current density at the half-wave potential of 0.95 V relative to commercial Pt/C and an almost 99% efficiency of 4-electron pathway selectivity, making it one of the potential ORR catalysts for application to the energy device of zinc‒air cells. This study provides a helpful design principle for developing and optimizing other efficient ORR electrocatalysts. Improving kinetics for electrochemical oxygen reduction reaction is relevant to important sustainable energy technologies. The authors propose an atomic-scale bimetal assembly consisting Pt and Fe dual sites to regulate the inherent scaling relationship between intermediates for fast kinetics. [ABSTRACT FROM AUTHOR]

Accurately regulating the selectivity of the oxygen reduction reaction (ORR) is crucial to renewable energy storage and utilization, but challenging. A flexible alteration of ORR pathways on atomically dispersed Zn sites towards high selectivity ORR can be achieved by tailoring the coordination environment of the catalytic centers. The atomically dispersed Zn catalysts with unique O‐ and C‐coordination structure (ZnO3C) or N‐coordination structure (ZnN4) can be prepared by varying the functional groups of corresponding MOF precursors. The coordination environment of as‐prepared atomically dispersed Zn catalysts was confirmed by X‐ray absorption fine structure (XAFs). Notably, the ZnN4 catalyst processes a 4 e− ORR pathway to generate H2O. However, controllably tailoring the coordination environment of atomically dispersed Zn sites, ZnO3C catalyst processes a 2 e− ORR pathway to generate H2O2 with a near zero overpotential and high selectivity in 0.1 M KOH. Calculations reveal that decreased electron density around Zn in ZnO3C lowers the d‐band center of Zn, thus changing the intermediate adsorption and contributing to the high selectivity towards 2 e− ORR. [ABSTRACT FROM AUTHOR]

Atomic‐level design and construction of synergistic active centers are central to develop advanced oxygen electrocatalysts toward efficient energy conversion. Herein, an in situ construction strategy to introduce flexible redox sites of VNi centers onto Ni‐based metal–organic framework (MOF) nanosheet arrays (NiV‐MOF NAs) as a promising oxygen electrocatalyst is developed. The abundant redox VNi centers with flexible metal valence states of V+3/+4/+5 and Ni+3/+2 enable NiV‐MOF NAs excellent oxygen evolution reaction (OER) activity and a long‐term stability under high current densities, achieving current densities of 10 and 100 mA cm−2 at recorded overpotentials of 189 and 290 mV, respectively, and showing ignorable decay of initial activity at 100 mA cm−2 after 100 h OER operation. Operando synchrotron radiation Fourier transform infrared combined with quasi in situ X‐ray absorption fine structure spectroscopies reveal at atomic level that the flexible V sites can continuously accept electrons from adjacent active Ni sites to accelerate OER kinetics for NiV‐MOF NAs during the reaction process, accompanied by a self‐optimized structural distortion of VO6 octahedron for promoting the electrochemical stability. [ABSTRACT FROM AUTHOR]

Atomic interface regulation is thought to be an efficient method to adjust the performance of single atom catalysts. Herein, a practical strategy was reported to rationally design single copper atoms coordinated with both sulfur and nitrogen atoms in metal-organic framework derived hierarchically porous carbon (S-Cu-ISA/SNC). The atomic interface configuration of the copper site in S-Cu-ISA/SNC is detected to be an unsymmetrically arranged Cu-S1N3 moiety. The catalyst exhibits excellent oxygen reduction reaction activity with a half-wave potential of 0.918 V vs. RHE. Additionally, through in situ X-ray absorption fine structure tests, we discover that the low-valent Cuprous-S1N3 moiety acts as an active center during the oxygen reduction process. Our discovery provides a universal scheme for the controllable synthesis and performance regulation of single metal atom catalysts toward energy applications. Engineering the coordination environment of single atom catalysts offers to opportunity to optimize electrocatalytic activity. In this work, the authors prepare an unsymmetrical Cu-S1N3 single atom site on porous carbon with high performance in the oxygen reduction reaction. [ABSTRACT FROM AUTHOR]

We report a semiconducting metal–organic graphene analog, Ni3(HITP)2, with an adjustable crystalline structure for mediating efficient selectivity toward hydrogen peroxide. The as-prepared 5-Ni3(HITP)2 catalyst with low crystallinity can electrocatalyze O2 to H2O2 with a high selectivity of 80% over a wide potential range of 0.2–0.6 V vs. RHE and with a large mass activity of 292 A gNi−1 at 0.25 V in 0.1 M KOH. [ABSTRACT FROM AUTHOR]

Bunches of amorphous α-FeOOH nanoislands are anchored atop Ni-based conductive MOFs to form a phase-tunable hydroxyl-rich inorganic–organic interface toward a favorable two-electron pathway during ORR. [Display omitted] • A regulated FeOOH/Ni-cMOFs interface is designed as efficient H 2 O 2 electrocatalyst. • FeOOH@Ni-cMOFs has almost 100 % H 2 O 2 selectivity and a yield of 900 mmol·g cat −1·h−1. • In situ synchrotron spectroscopy is adopted to determine the synergistic mechanism. • A fast phase transformation during ORR process is deeply revealed for FeOOH@Ni-cMOFs. Delicate interfacial engineering in nanoscale over inorganic–organic heterogeneous interfaces could potentially promote intriguing catalytic activity and selectivity during electrochemical processes. Herein, massive amorphous iron oxyhydroxide nanoislands (∼2 nm) are fully and homogenously distributed onto the surface of a conductive Ni-based metal–organic framework (denoted as FeOOH@Ni-cMOFs), boosting almost 100% two-electron selectivity for superior on-site hydrogen peroxide (H 2 O 2) generation with a yield rate of ∼900 mmol·g cat −1·h−1 during the electrochemical oxygen reduction reaction (ORR). The self-hydroxylation of iron oxyhydroxide nanoislands, revealed by the combination of in situ X-ray absorption spectroscopy and Fourier transform infrared spectroscopy, is found to trigger a fast phase transformation of α-FeOOH into hydroxyl-rich ε-FeOOH during the ORR, which could benefit the dissociation of adsorbed H 2 O molecules over iron oxyhydroxide nanoislands surface and then timely promote the proton coupling of H-*OOH over adjacent Ni sites in FeOOH@Ni-cMOFs. This regulated iron oxyhydroxide/Ni-cMOFs interface with rich hydroxyl synergistically balance the kinetics of key *OOH intermediate formation and H 2 O dissociation toward a preferred two-electron pathway for efficient H 2 O 2 electrosynthesis. [ABSTRACT FROM AUTHOR]

The metal-ligand (M-L) covalent coupling is of very significance for tailoring the activity and selectivity of metal-organic-framework (MOF) functional nanomaterials, yet it still remains elusive. Herein, based on the π-conjugated coordination chemistry, we have developed several conductive MOFs as active oxygen reduction (ORR) electrocatalysts with tunable H 2 O 2 selectivity. Through tailoring the central metal and the first coordination sphere, weakly-electrophilic Cu sites coupled with strongly-oxidized aromatic 2, 3, 6, 7, 10, 11-hexahydroxytriphenylene (HHTP) linkers are of high favor in a two-electron ORR pathway, resulting in an impressive H 2 O 2 selectivity of 95 % and a superior H 2 O 2 yield rate of 792.7 mmol·g cat −1·h−1 during ORR for conductive Cu-HHTP MOF catalysts. By correlative in situ synchrotron radiation XAFS and FTIR spectroscopies, the potential-dependent dynamic-coupling hydroxyl over Cu sites is found to effectively trigger the self-polarization of π-conjugated metal-ligand Cu-O-C centers of Cu-HHTP MOF via shrinking the first Cu-O coordination sphere, realizing fast 2e- ORR kinetics. [Display omitted] • π-conjugated MOFs are designed as active H 2 O 2 catalysts with tunable selectivity. • The optimal Cu-HHTP catalyst performs superior H 2 O 2 selectivity up to 95 %. • In situ synchronous spectroscopy is adopted on electrocatalytic mechanism study. • The metal-ligand covalent coupling is deeply revealed for Cu-HHTP catalysts. [ABSTRACT FROM AUTHOR]