The design of diatomic catalysts with uniformly dispersed metal atoms is expected to improve catalytic performance, which is conducive to the intensive comprehending of the synergistic mechanism between dual-metal sites for the oxygen evolution reaction (OER) at the atomic level. Herein, we design a strategy to immobilize bimetallic Fe-Co atoms onto nitrogen-doped graphene to obtain a diatomic catalyst (DA-FC-NG) with FeN₃-CoN₃ configuration. The DA-FC-NG shows excellent OER activity with a low overpotential (η₁₀ = 268 mV), which is superior to commercial iridium dioxide catalysts. Theoretical calculations uncover that the excellent activity of DA-FC-NG is due to the interaction between Fe and Co diatoms, which causes charge rearrangement and induces the adsorption of intermediates on the Fe–O–Co bridge structure, thus improving the catalytic OER performance. This work is of great significance for the design of highly active diatomic catalysts to replace noble metal catalysts for energy-related applications.

To realize large-scale hydrogen production by electrolysis of water, it is essential to develop non-precious metal catalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Here, we fabricate Sn-, Fe-, and Co-based sulfide/oxyhydroxide heterostructural catalyst on nickel foam (FeSnCo_0.2S_xO_y/NF) by solvothermal method. The FeSnCo_0.2S_xO_y/NF requires low overpotentials of 48 and 186 mV at 10 mA·cm^–2, respectively, for HER and OER. When it is assembled into an electrolytic cell as a bifunctional electrocatalyst, it only needs 1.54 V to reach 10 mA·cm^–2, far better than IrO₂||Pt/C electrolyzer. The formation of sulfide/hydroxide heterostructural interfaces improves the electron transfer and reduces the reaction energy barrier, thus promoting the electrocatalytic processes.

As a four-electron transfer reaction, oxygen evolution reaction (OER) is limited by large overpotential and slow kinetics. Here, we in-situ synthesized two-dimensional (2D) Ni-Fe metal-organic framework nanosheets on nickel foam (Ni_xFe-TPA/NF, TPA = terephthalic acid) for oxygen evolution in alkaline and alkaline seawater electrolytes. In 1 M KOH, Ni₃Fe-TPA/NF shows a low overpotential (η₁₀) of 189 mV at 10 mA·cm⁻² and an ultra-low overpotential of only 260 mV at 500 mA·cm⁻². In alkaline seawater, Ni₃Fe-TPA/NF still provides impressive OER performance, with an η₁₀ of 265 mV. In-situ Raman characterization results show that the phase transition occurs during the OER, and Ni₃FeOOH with more oxygen vacancies is in-situ formed, reducing the OER energy barrier. Density functional theory (DFT) reveals that the synergy between Ni and Fe reduces the energy barrier and accelerates the rate-determining step. In addition, the ultra-thin 2D sheet structure and the close combination of Ni₃FeOOH and highly conductive NF support ensure the high catalytic OER activity. Therefore, the surface reconstruction and structural modification strategy can be used to design and prepare high-performance OER electrocatalysts for energy-related applications.

Developing transition metal-nitrogen-carbon materials (M-N-C) as electrocatalysts for the oxygen evolution reaction (OER) is significant for low-cost energy conversion systems. Further d-orbital adjustment of M center in M-N-C is beneficial to the improvement of OER performance. Herein, we synthesize a single-Mn-atom catalyst based on carbon skeleton (Mn₁-N₂S₂C_x) with isolated Mn-N₂S₂ sites, which exhibits high alkaline OER activity (η₁₀ = 280 mV), low Tafel slope (44 mV·dec⁻¹), and excellent stability. Theoretical calculations reveal the pivotal function of isolated Mn-N₂S₂ sites in promoting OER, including the adsorption kinetics of intermediates and activation mechanism of active sites. The doping of S causes the increase in both charge density and work function of active Mn center, and ortho-Mn₁-N₂S₂C_x expresses the fastest OER kinetics due to the asymmetric plane.

Owing to stable spatial framework and large electrochemical interface, self-supported transition metal chalcogenides have been actively explored in renewable energy fields, especially in oxygen evolution reaction (OER). Here, we review the research progress of self-supported transition metal chalcogenides (including sulfides, selenides, and tellurides) for the OER in recent years. The basic principle and evaluation parameters of OER are first introduced, and then the preparation methods of transition metal chalcogenides on various self-supporting substrates (including Ni foam (NF), carbon cloth (CC), carbon fiber paper (CFP), metal mesh/plate, etc.) are systematically summarized. Subsequently, advanced optimization strategies (including interface and defect engineering, heteroatom doping, edge engineering, surface morphology engineering, and construction of heterostructure) are introduced in detail to improve the inherent catalytic activity of self-supported electrocatalysts. Finally, the challenges and prospects of developing more promising self-supported chalcogenide electrocatalysts are proposed.

Dual-metal catalysts with synergistic effect exhibit enormous potential for sustainable electrocatalytic applications and mechanism research. Compared with mono-metal-site catalysts, dual-metal-site catalysts exhibit higher efficiency for the oxygen evolution reaction (OER) due to reduced energy barrier of the process involving proton-coupled multi-electron transfer. Herein, we construct dual-metal Fe-Co sites coordinated with nitrogen in graphene (FeCo-NG), which exhibits high OER performance with onset overpotential of only 126 mV and Tafel slope of 120 mV·dec⁻¹, showing that the rate-determining step is controlled by the single-electron transfer step. Theoretical calculations reveal that the FeN₄ site exhibits lower OER overpotential than the CoN₄ site due to appropriate adsorption energy of OOH* on the former, while the O* adsorbed on the adjacent Co site could stabilize the OOH* on the FeN₄ site through hydrogen bond interaction.

Oxygen evolution reaction (OER) is the core electrode reaction in energy-related technologies, such as electrolytic water, electrocatalytic carbon dioxide reduction, rechargeable metal-air batteries, and renewable fuel cells. Development of well-stocked, cost-effective, and high-performance OER electrocatalysts is the key to the improvement of energy efficiency and the large-scale commercial implementation of these technologies. Multicomponent transition metal oxides and (oxy)hydroxides are the most promising OER catalysts due to their low cost, adjustable structure, high electrocatalytic activity, and outstanding durability. In this review, a brief overview about the mechanisms of OER is first offered, accompanied with the theory and calculation criteria. Then, the latest advances in the rational design of the related OER electrocatalysts and the modulation of the electronic structure of active sites are comprehensively summarized. Specifically, various strategies (including element doping, defect engineering, and fabrication of binderless catalysts) used to improve the OER performance are detailedly discussed, emphasizing the structure–function relationships. Finally, the challenges and perspectives on this promising field are proposed.

Oxygen evolution reaction (OER) plays an important role in many energy conversions and storage technologies, such as water splitting, rechargeable metal air batteries, renewable fuel cells, and electrocatalytic carbon dioxide reduction and nitrogen reduction, but its slow kinetics and high overpotential seriously affect the energy efficiency. Fabrication of high-performance and well-stocked OER catalysts is the key to the large-scale implementation of these energy-related technologies. Two-dimensional (2D) materials get a lot of attention as OER catalysts due to their large specific surface area, abundant active sites, and adjustable structures and compositions. Here, an overview is presented for the latest achievements in design and synthesis of 2D materials (including layered double hydroxides, metal-organic frameworks and their derivatives, covalent-organic frameworks, graphene, and black phosphorus) for the OER, emphasizing novel strategies (including metal/nonmetal doping, defect engineering, interface engineering, lattice strain, and fabrication of heterojunction) for achieving high electrocatalytic activity. Peculiarly, the structure–function relationship is analyzed in detail to gain deeper insight into the reaction mechanism, which is crucial to rational design of more high-performance 2D materials for the OER. Finally, the remaining challenges to improve the OER performance of 2D electrocatalysts are put forward to indicate possible future development of 2D materials.

Lack of high-efficiency, cost-efficient, and well-stocked oxygen evolution reaction (OER) electrocatalysts is a main challenge in large-scale implementation of electrolytic water. By regulating the electronic structure of isolated single-atom metal sites, high-performance transition-metal-based catalysts can be fabricated to greatly improve the OER performance. Herein, we demonstrate single-atom manganese coordinated to nitrogen and sulfur species in two-dimensional graphene nanosheets Mn-NSG (NSG means N- and S- codoped graphene) as an active and durable OER catalyst with a low overpotential of 296 mV in alkaline media, compared to that of the benchmark IrO₂ catalyst. Theoretical calculations and experimental measurements reveal that the Mn-N₃S sites in the graphene matrix are the most active sites for the OER due to modified electronic structure of the Mn site by three nitrogen and one sulfur atoms coordination, which show lower theoretical overpotential than the Mn-N₄ sites and over which the O–O formation step is the rate-determining step.

The key challenge for scalable production of hydrogen from water lies in the rational design and preparation of high-performance and earth-abundant electrocatalysts to replace precious metal Pt and IrO₂ for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Although atomic M-N-C materials have been extensively studied in heterogeneous catalysis field, the insufficient antioxidant capacity of carbonous substrates hinders their practical application in OER. Developing highly active and stable OER electrocatalysts is the key for electrochemical water splitting. This review presents feasible design strategies for fabricating carbon-free single-site catalysts and their applications in HER/OER and overall water splitting. The constitutive relationships between structure, composition, and catalytic performance for HER and OER are detailly discussed, providing ponderable insights into rationally constructing high-performance HER and OER electrocatalysts. The perspectives on the challenges and future research orientations in single-site catalysts for electrochemical water splitting are suggested.