Advances in oxygen evolution reaction electrocatalysts via direct oxygen–oxygen coupling pathway: Recent progress, challenges, and perspectives

Deep insights into electrocatalytic mechanisms are vital for the rational design of catalysts for oxygen evolution reaction (OER). Mechanistically, the OER driven by adsorbate evolution mechanism (AEM) is limited by the linear scaling relationship, thereby exhibiting large overpotentials. In the lattice oxygen mechanism (LOM), the OER can be enhanced by enabling direct O2 formation. However, this enhancement is accompanied by the generation of oxygen vacancies, which presents a significant challenge to the long-term stability of LOM-OER, particularly when operating at high current densities. Recently, the *O-*O coupling mechanism (OCM) has emerged as a promising alternative; it not only breaks the linear scaling relationship but also ensures catalytic stability. This review encapsulates the cutting-edge advancements in electrocatalysts that are grounded in the OCM, offering a detailed interpretation on the foundational principles guiding the design of OCM-OER catalysts. It also highlights recent theoretical investigations combining machine learning (ML) with Density Functional Theory (DFT) calculations to reveal OER mechanisms. At the end of this review, the challenges and opportunities associated with OCM-OER electrocatalysts are discussed.