Polyoxometalates for Oxygen Evolution Electrocatalysis: From Molecular Active Motifs to Interfacial Regulators and Practical Electrolyzers

The oxygen evolution reaction (OER) remains the principal kinetic bottleneck in water electrolysis because its multistep proton-electron transfer is coupled with dynamic structural evolution under anodic bias. Beyond the intrinsic four-electron barrier, practical operation is constrained by metal dissolution, phase reconstruction, interfacial instability, and catalyst-layer degradation at high current densities. Polyoxometalates (POMs), featuring structurally programmable metal-oxygen clusters, reversible multielectron redox chemistry, oxygen-rich surfaces, and versatile coordination sites, offer a distinctive platform for addressing these challenges. This review analyzes the evolution of POMs from discrete molecular catalysts to confined guests, interfacial electronic regulators, reconstruction-directing units, and stabilization modules in OER electrocatalysts. Particular emphasis is placed on how POM structure and interfacial bonding modify metal valence, orbital hybridization, charge transfer, d-band characteristics, and intermediate adsorption energetics, and how these effects govern activity and durability. The discussion further extends to high-current-density electrolysis, saline media, membrane-electrode assemblies, and device-level validation. Key unresolved issues include identification of the true active phase, definition of pH-potential-time stability windows, conductivity and loading limitations, and POM leaching. A six-pathway framework is finally proposed to connect representative POM states with the elementary OER steps and guide mechanism-informed catalyst design. This framework highlights priorities for scalable, durable, and predictable electrolyzer implementation.