Rechargeable zinc-air batteries (ZABs) are currently receiving extensive attention because of their extremely high theoretical specific energy density, low manufacturing costs, and environmental friendliness. Exploring bifunctional catalysts with high activity and stability to overcome sluggish kinetics of oxygen reduction reaction and oxygen evolution reaction is critical for the development of rechargeable ZABs. Atomically dispersed metal-nitrogen-carbon (M-N-C) catalysts possessing prominent advantages of high metal atom utilization and electrocatalytic activity are promising candidates to promote oxygen electrocatalysis. In this work, general principles for designing atomically dispersed M-N-C are reviewed. Then, strategies aiming at enhancing the bifunctional catalytic activity and stability are presented. Finally, the challenges and perspectives of M-N-C bifunctional oxygen catalysts for ZABs are outlined. It is expected that this review will provide insights into the targeted optimization of atomically dispersed M-N-C catalysts in rechargeable ZABs.

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Highlights Three-dimensional (3D) core‐shell heterostructured NixSy@MnOxHy nanorods grown on nickel foam (NixSy@MnOxHy/NF) were successfully fabricated via a simple hydrothermal reaction and a subsequent electrodeposition process. The fabricated NixSy@MnOxHy/NF shows outstanding bifunctional activity and stability for hydrogen evolution reaction and oxygen evolution reaction, as well as overall‐water‐splitting performance. The main origins are the interface engineering of NixSy@MnOxHy, the shell‐protection characteristic of MnOxHy, and the 3D open nanorod structure, which remarkably endow the electrocatalyst with high activity and stability. Abstract Exploring highly active and stable transition metal-based bifunctional electrocatalysts has recently attracted extensive research interests for achieving high inherent activity, abundant exposed active sites, rapid mass transfer, and strong structure stability for overall water splitting. Herein, an interface engineering coupled with shell-protection strategy was applied to construct three-dimensional (3D) core‐shell NixSy@MnOxHy heterostructure nanorods grown on nickel foam (NixSy@MnOxHy/NF) as a bifunctional electrocatalyst. NixSy@MnOxHy/NF was synthesized via a facile hydrothermal reaction followed by an electrodeposition process. The X-ray absorption fine structure spectra reveal that abundant Mn‐S bonds connect the heterostructure interfaces of NixSy@MnOxHy, leading to a strong electronic interaction, which improves the intrinsic activities of hydrogen evolution reaction and oxygen evolution reaction (OER). Besides, as an efficient protective shell, the MnOxHy dramatically inhibits the electrochemical corrosion of the electrocatalyst at high current densities, which remarkably enhances the stability at high potentials. Furthermore, the 3D nanorod structure not only exposes enriched active sites, but also accelerates the electrolyte diffusion and bubble desorption. Therefore, NixSy@MnOxHy/NF exhibits exceptional bifunctional activity and stability for overall water splitting, with low overpotentials of 326 and 356 mV for OER at 100 and 500 mA cm–2, respectively, along with high stability of 150 h at 100 mA cm–2. Furthermore, for overall water splitting, it presents a low cell voltage of 1.529 V at 10 mA cm–2, accompanied by excellent stability at 100 mA cm–2 for 100 h. This work sheds a light on exploring highly active and stable bifunctional electrocatalysts by the interface engineering coupled with shell-protection strategy.

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Hydrogen (H 2 ) has been proposed as a future energy carrier in the transition from the current hydrocarbon economy. [2] In particular, the production of molecular H 2 from electrocatalytic water splitting is an attractive solution. [3] However, because of the sluggish reaction kinetics caused by high energy barriers, H 2 production from water splitting is not economical, which hinders its large-scale application. Water splitting consists of two half-reactions, including the anodic oxygen evolution reaction (OER) and cathodic hydrogen evolution reaction (HER). Their sluggish kinetics, especially for OER, lead to large overpotentials that require higher energy consumption to drive an electrolytic cell. High-performance electrocatalysts for water splitting can reduce overpotentials efficiently, which can increase the efficiency of the electrochemical process. [4] As yet, precious-metal-based materials, such as Pt, Ru, and Ir, are still the most potential electrocatalysts for water splitting, but the scarcity and high cost of these materials prohibit their wide-scale industrial application for electrolysis. [4,5] Meanwhile, producing different catalysts for OER and HER requires different equipment and processes, which could increase the manufacturing cost. [6] As a result, these above disadvantages have motivated extensive research interest to synthesize various earth-abundant bifunctional electrocatalysts with high activities and stabilities for water splitting in the past few years.Until now, tremendous efforts have been made to develop various transition metals and their derivatives to prepare lowcost and high-performance water-splitting electrocatalysts, such as transition-metal oxides, [7] chalcogenides, [8] phosphides, [9] and nitrides, [10] in which transition-metal phosphides, especially Ni 2 P, [11] have recently attracted increasing research interest owing to their moderate interaction with hydrogen, relatively high mechanical strength, electrical conductivity, and chemical stability. In addition, it has been reported by a large number of articles that Fe can efficiently enhance the OER activities of electrocatalysts. [12] Accordingly, through integrating the above advantages, it may be a promising route to develop nickel-ironbased phosphides as bifunctional electrocatalysts for overall water splitting. In addition, for commercial applications, Exploring highly active and stable bifunctional water-splitting electrocatalysts at ultra-high current densities is remarkably desirable. Herein, 3D nickel-iron phosphides nanosheets modified by MnO x nanoparticles are grown on nickel foam (MnO x /NiFeP/NF). Resulting from the electronic coupling effect enabled by interface modifications, the intrinsic activities of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are improved. Meanwhile, 3D nanosheets provide abundant active sites for HER and OER, leading to accelerating the reaction kinetics. Besides, the shell-protection characteristic of MnO x improves the durability of MnO x /NiFeP/...

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The electroreduction reaction of CO2 (ECO2RR) requires high-performance catalysts to convert CO2 into useful chemicals. Transition metal-based atomically dispersed catalysts are promising for the high selectivity and activity in ECO2RR. This work presents a series of atomically dispersed Co, Fe bimetallic catalysts by carbonizing the Fe-introduced Co-zeolitic-imidazolate-framework (C–Fe–Co–ZIF) for the syngas generation from ECO2RR. The synergistic effect of the bimetallic catalyst promotes CO production. Compared to the pure C–Co–ZIF, C–Fe–Co–ZIF facilitates CO production with a CO Faradaic efficiency (FE) boost of 10%, with optimal FECO of 51.9%, FEH2 of 42.4% at − 0.55 V, and CO current density of 8.0 mA cm−2 at − 0.7 V versus reversible hydrogen electrode (RHE). The H2/CO ratio is tunable from 0.8 to 4.2 in a wide potential window of − 0.35 to − 0.8 V versus RHE. The total FECO+H2 maintains as high as 93% over 10 h. The proper adding amount of Fe could increase the number of active sites and create mild distortions for the nanoscopic environments of Co and Fe, which is essential for the enhancement of the CO production in ECO2RR. The positive impacts of Cu–Co and Ni–Co bimetallic catalysts demonstrate the versatility and potential application of the bimetallic strategy for ECO2RR.

Carbon dioxide (CO2) is one of the end products of fuel combustion and the major component of the greenhouse gases. The reduction of atmospheric CO2 not only decreases environmental pollution but also produces value‐added chemicals, solving energy and environment issues simultaneously. One significant challenge is the low conversion efficiency of CO2 reduction due to the inertness of the CO2 molecule. The design of the catalyst nanomaterials with the high selectivity, stability, and the activation capabilities for the conversion of CO2 is needed. Atomic layer deposition (ALD), capable of constructing catalysts with atomic‐level precision in a highly controllable manner, is a promising technique to address the key problems in CO2 reduction. This review explores the application of ALD in CO2 reduction, emphasizing the designs of the efficient catalyst nanomaterials fabricated by the ALD technique and their applications in CO2 reduction and capture. The significance of the ALD catalysts with the fine structures is highlighted to obtain a better understanding of the catalytic performance–aimed benefits as well as an outlook on the ALD‐designed catalysts for the reduction of CO2.