Recent Advances in Metal Oxide-Supported Low-Iridium Catalysts for Acidic Water Oxidation

Proton exchange membrane water electrolysis (PEMWE) is a promising route to sustainable hydrogen production, but large-scale deployment is limited by sluggish anodic oxygen evolution reaction (OER) kinetics and scarce iridium (Ir). Metal oxide supports can lower Ir demand by improving its dispersion and utilization and by regulating the coordination and electronic structure of active sites. This review classifies representative supports into two nonexclusive families: redox-responsive, electronically adaptive oxides and structurally robust, electronically tunable oxides. Their functions are compared through lattice anchoring and confinement, interfacial charge transfer and redox buffering, vacancy-mediated oxygen migration and spillover, and regulation of adsorbate evolution mechanism (AEM), lattice oxygen mechanism (LOM), oxide pathway mechanism (OPM), and related pathways. Particular emphasis is placed on strong metal oxide–support interactions and the coupled effects of Ir─O─M bonding, charge redistribution, coordination distortion, and spatial confinement. Benefits are assessed alongside trade-offs in conductivity, site accessibility, vacancy dynamics, and support degradation. Catalyst Ir content, half-cell loading, and MEA anode loading are distinguished, with half-cell and device-level performance evaluated separately. This framework links fundamental interfacial chemistry with catalyst-level metrics and realistic device requirements for practical PEMWE implementation. Finally, priorities are identified for operando characterization, dissolution analysis, standardized benchmarking, descriptor-guided support design, and durable low-Ir MEAs.