Regulation strategy of spinel OER electrocatalyst

<p indent="0mm">The electrocatalytic water decomposition process enables the environmentally friendly separation of water into oxygen and high-energy-density hydrogen, offering significant advantages in terms of environmental preservation, mild operating conditions, and sustainability. Furthermore, this approach holds great potential for effectively mitigating or even eliminating carbon dioxide emissions at their source, thereby facilitating the achievement of “carbon peak” and “carbon neutrality” objectives. The reaction of water separation involves two crucial half-reactions: The cathodic hydrogen evolution reaction and the anodic oxygen evolution reaction. However, the anodic half-reaction includes a multi-step electron-coupled proton transfer process, which significantly raises the activation energy barrier for reaction kinetics. Consequently, additional overpotential is required to drive water electrolysis. Although efficient noble metal-based electrocatalysts (such as RuO₂ and IrO₂) can reduce the overpotential for oxygen evolution, their scarcity and poor durability render them unsuitable for large-scale practical applications. Therefore, it is of great research significance to design low-cost and highly catalytically active materials for oxygen evolution in order to promote sustainable development of hydrogen energy. Spinel oxides with multi-valence states, low-cost and earth-abundance are promising electrocatalysts for the OER. The structure of spinel oxide is AB₂O₄, where A represents elements such as Li, Zn, Mn, Co, Cu, Ni, Mg, Fe, Ca, and B represents elements like Al, Mn, Fe, Co, and Ni. The A site occupies 1/8 of the tetrahedral space resulting in 8 tetrahedral coordination configurations. Similarly, the B-site occupies 1/2 of the octahedral space leading to 16 octahedral coordination configurations. By altering reaction temperature, metal ratio and introducing heteroatom doping, the composition, structure, morphology, and defect characteristics can be modified. These flexible structured multi-valent transition metal oxides with excellent conductivity have emerged as potential candidates for next-generation OER electrocatalysts. The widespread utilization of spinel materials in electrocatalysis could substantially reduce costs associated with water electrolysis devices while offering alternatives to noble metal-based catalysts. In order to maximize the catalytic activity of spinel, many strategies including controlling its morphology, composition, structure, and defects have devoted to optimize its electronic structure for enhancing its binding energy with oxygen-containing groups. However, due to the unique structural characteristics of spinel materials, the research has become particularly complex. Firstly, spinel materials contain tetrahedral and octahedral geometrical structures, providing multiple sites for doping and substitution of transition metal cations. Secondly, some spinel oxides exhibit a structural inversion phenomenon which is an important factor affecting the electrocatalytic activity. Therefore, it is crucial to determine the optimal geometric configuration and active sites of spinel materials while improving their catalytic performance and elucidating the influence of different positions of metal ion doping on catalyst’s electronic structure and performance. Accordingly, modifying and controlling the activity and stability of spinel OER catalysts still remain a big challenge. This article summarizes recent advances in research on spinel-type electrocatalysts. Firstly, it introduces OER mechanisms including conventional adsorbate evolution mechanism and lattice oxygen evolution mechanism; then focuses on discussing various effective modification strategies that have been proven to optimize electrochemical performance of spinel catalysts such as tetrahedral site control, octahedral site control, oxygen vacancy control, strain control, surface reconstruction, etc. Finally, this paper discusses the current challenges in both fundamental research and industrial applications of electrocatalysts, while also highlighting potential solutions to address these issues. These challenges encompass: (1) Reasonable performance comparison; (2) device performance optimization; (3) developing cost-effective methods for industrial-scale synthesis; (4) precise mechanism exploration; (5) advanced characterization techniques.