Bridging Mechanisms and Strategies: MXene-Based Electrocatalysts for the Oxygen Evolution Reaction

The oxygen evolution reaction (OER) is a key kinetic bottleneck in water electrolysis because it involves multistep proton-coupled electron transfer, the evolution of oxygen-containing intermediates and O–O bond formation. MXenes, as two-dimensional transition-metal carbides, nitrides and carbonitrides, possess high electrical conductivity, hydrophilic surfaces, tunable surface terminations and adjustable layered structures, making them promising platforms for OER catalyst design. However, their limited intrinsic active sites, sheet restacking and oxidative instability under anodic conditions restrict their direct application. This review firstly discusses the fundamental OER pathways based on the adsorbate evolution mechanism (AEM), lattice oxygen mechanism (LOM) and oxide path mechanism (OPM), providing a mechanistic basis for understanding intermediate adsorption, oxygen activation and working-state evolution. Then, a system framework from low-dimensional and micro-level control to high-dimensional and macro-level integration is constructed. The framework covers four levels: atom and local structure, interface, morphology and composite electrode. Drawing on specific examples, this review analyzes the characteristics and mechanisms of modification strategies from four different perspectives, starting with the basic principles of modification. These strategies include micro-scale, low-dimensional approaches such as “Vacancy and other atomic-Level Regulation”, macro-scale, high-dimensional methods like “Composite Engineering”, as well as intermediate approaches involving “Interface engineering” and “morphology engineering”. Special emphasis is placed on distinguishing between beneficial surface reconstruction of catalytically active hydroxyl oxide species and destructive oxidation. Finally, the review identified the unresolved key challenges, including the fuzziness of active sites, the diversity of initial material states and the lack of stability under industrial conditions, and looked forward to the future direction of reasonable design, operational characterization and device-level evaluation. Through this cross-scale analysis, this review aims to clarify the relationship between structure–activity–stability, and provide practical guidance for designing efficient, durable and experimentally verifiable MXene-based OER electrodes.