Unveiling mechanistic regulation strategies in transition metal oxide catalysts for enhanced oxygen evolution reaction.

The oxygen evolution reaction (OER) is an anode reaction for hydrogen production by electrolysis of water. Its slow kinetics and high potential severely limit the overall efficiency. OER usually proceeds via three main mechanisms: adsorbate evolution mechanism (AEM), lattice oxygen oxidation mechanism (LOM), and oxide path mechanism (OPM). AEM is limited by the linear scaling relationship of the intermediate adsorption energy, with the theoretical overpotential having a lower limit of 370 mV. LOM is formed by the direct participation of lattice oxygen in the reaction bypassing OOH*, but the accumulation of oxygen vacancies can lead to structural collapse. OPM synergistically achieves O - O radical coupling through neighboring active sites, which combines high activity and stability, but requires precise regulation of atomic spacing (2.5-3.0 Å). To elucidate the OER pathway, this review summarizes the various assays and in-situ characterization techniques used to identify the different mechanisms. The structural modulation strategies of transition metal oxides (TMOs) are then examined in more detail, including the effects of heterogeneous structure, doping, surface reconstruction, and defect engineering strategies on mechanism regulation. Finally, future research directions are proposed to develop TMO-based electrocatalysts for practical applications.