Cross‐Scale Design of Low‐Loading Ru‐Based Catalysts for the Oxygen Evolution Reaction in Proton Exchange Membrane Water Electrolysis

Proton exchange membrane water electrolysis (PEMWE) is a promising route for green hydrogen production, but the acidic oxygen evolution reaction (OER) is constrained by catalyst instability and high noble‐metal demand. Although Ir‐based oxides remain the benchmark catalysts, their scarcity and cost motivate the exploration of Ru‐based catalysts, which exhibit higher intrinsic activity at lower cost. However, Ru suffers from rapid deactivation under high anodic potentials due to overoxidation, lattice reconstruction, and oxidative dissolution, leading to irreversible active‐site loss. This review proposes a cross‐scale design framework for developing low‐loading, acid‐stable Ru‐based OER catalysts. We first analyze Ru dissolution pathways and the intrinsic activity–stability trade‐off, then summarize stabilization strategies across different structural scales. For single atoms, coordination engineering and strong metal–support interactions stabilize isolated sites; for clusters, interfacial confinement and heterostructure design mitigate structural degradation; for nanoparticles, doping and solid‐solution strategies suppress lattice oxygen loss and inhibit RuO ₂ dissolution. Beyond nanoscale catalyst design, practical PEMWE systems require optimization at the membrane electrode scale, where intrinsic activity must be integrated with mass transport and diffusion within the three‐phase interface. Finally, future directions are highlighted, including high‐current‐density kinetics, multiscale catalyst/electrode integration, and artificial intelligence‐assisted catalyst screening for durable low‐Ru PEMWE anodes.