Sub‐Nano Ir‐Based Alloy Clusters by Hierarchical Confinement Effect for Water Splitting

Abstract The synthesis of sub‐nanoscale noble metal catalysts is pivotal for enhancing electrocatalytic performance, yet achieving precise control over particle size at this scale remains a critical challenge. In this work, we propose a hierarchical confinement strategy which combines spatial confinement at nanoscale and anchoring confinement at atomic scale, to overcome the size limitations imposed by high‐temperature sintering. Using this strategy, a series of uniformly sized (∼1 nm) Ir‐based alloy clusters, including IrMn, IrFe, IrCo and IrNi, are successfully fabricated. The synthesized sub‐nanoscale IrCo alloy clusters (denoted as sub‐IrCo cluster) demonstrate exceptional oxygen evolution reaction (OER) catalytic performance, with an ultralow overpotential of 210 mV at 10 mA cm ‐ 2 and a remarkable mass activity 87.5 times greater than that of commercial IrO 2 . Density functional theory (DFT) and molecular dynamics (MD) simulations reveal that the incorporation of N enhances the interaction between Ir atoms and the support. This work provides an effective strategy for preventing particle sintering via a hierarchical confinement effect and achieves precise size control at sub‐nanoscale, opening a new avenue for the development of efficient noble metal catalysts with high atomic utilization.