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.

In recent years, the depletion risk of fossil fuels has driven increasing interest in renewable energy. Among various technologies, proton exchange membrane fuel cells (PEMFCs) stand out due to their fast startup and high power density. However, the commonly used Nafion membranes suffer from reduced proton conductivity under low humidity and high temperatures, limiting their practical application. Polyoxometalates (POMs), with their excellent proton conductivity and thermal stability, have emerged as promising alternatives. Yet, their high water solubility raises safety concerns, and their water-dependent conduction mechanisms and structure–function relationships remain insufficiently understood. These issues hinder the practical development of POM-based proton conductors. This paper presents a comprehensive review of the key properties and proton conduction mechanisms of POMs, with a particular focus on POM crystals and their composites exhibiting high proton conductivity. Representative studies are analyzed to elucidate design strategies, structure–function relationships, and recent research progress over the past five years. Finally, perspectives and recommendations are proposed to inform future research directions and promote practical applications in the field of proton-conducting materials.