Oxygen evolution reaction mechanism and identification procedure

Abstract

Amidst escalating global energy demands and the environmental constraints of conventional fossil fuels, hydrogen energy has emerged as a pivotal zero-emission energy carrier. The four-electron oxygen evolution reaction (OER) exhibits slower kinetics compared to the two-electron hydrogen evolution reaction (HER), constitutes the limiting process in electrolytic hydrogen production, with two principal mechanisms currently understood to govern its kinetics: the adsorbate evolution mechanism (AEM), which typically exhibits high stability but relatively low activity in its conventional framework, and the lattice oxygen oxidation mechanism (LOM), which generally shows high activity but insufficient stability in pristine systems. Notably, recent advances in catalyst engineering have enabled the development of modified AEM/LOM-based catalysts that balance stability and activity. Recent mechanistic developments have broadened this paradigm with proposed oxide pathway mechanisms (OPM) and coupled oxygen evolution mechanisms (COM), which incorporate innovative concepts such as dynamic surface reconstruction and concerted proton–electron transfer processes. This review firstly reviews the OER mechanisms, including AEM, LOM, OPM, and COM, followed by a systematic enumeration of identification strategies based on the core features of each mechanism, including kinetic features, experimental features, and theoretical calculations. Finally, we further highlight emerging opportunities in mechanism-directed material innovation, offering actionable insights for next-generation sustainable energy technologies.

1. Introduction

As an environmentally friendly energy carrier, hydrogen has emerged as a promising candidate due to its carbon-neutral utilization cycle [1–4]. Electrocatalytic water splitting, a technologically feasible method for hydrogen production, has attracted significant research attention owing to its operational simplicity and scalability. This process comprises two half-reactions: the cathodic hydrogen evolution reaction (HER) and the anodic oxygen evolution reaction (OER) [5–8]. Unlike the two-electron HER, the OER involves a kinetically sluggish four-proton-coupled electron transfer process, constituting the rate-limiting step in water electrolysis [9–10]. The development of efficient electrocatalysts to mitigate the high overpotential associated with OER kinetics remains a fundamental challenge. Mechanistic investigations of OER pathways not only facilitate the rational design of advanced catalysts but also provide critical insights for overcoming existing efficiency bottlenecks in water electrolysis systems, thereby enabling sustainable large-scale hydrogen production [11–13].

The oxygen evolution reaction (OER) mechanism is primarily governed by two established paradigms: the adsorbate evolution mechanism (AEM) and the lattice oxygen oxidation mechanism (LOM) [14–15]. As the conventional framework for electrocatalytic water oxidation, AEM involves sequential electron transfers through metal-centered redox states, where adsorbed intermediates (OH*, O*, OOH*) evolve on catalytic sites near the Fermi level [16]. In contrast, LOM features direct participation of lattice oxygen atoms in the O–O bond formation process involving OH− → O2 transitions [17]. Recent the oxide pathway mechanism (OPM), first systematically demonstrated by Cai et al. [18], introduces a dual-site oxygen coupling process where adjacent catalytic centers directly combine adsorbed oxygen atoms into O2 molecules. This configuration circumvents the conventional *OOH intermediate formation step, while preventing lattice oxygen consumption—a critical advancement for catalyst durability. Parallel breakthroughs include the coupled oxygen evolution mechanism (COM) proposed by Wang et al. [19], which elucidates photon-assisted metal–oxygen synergistic catalysis through time-resolved spectroscopic studies. Specifically, light triggers a reversible change in the coordination structure of Ni in the material. This structural change enables the alternation of electronic states near the Fermi level, which exactly circumvents the key rate-limiting steps of the traditional AEM and LOM. These mechanistic revelations not only refine fundamental understanding of multielectron transfer processes but also establish design principles for next-generation electrocatalysts, particularly in addressing the stability–efficiency trade-off that has long cons