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

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/cm² and a remarkable mass activity 87.5 times greater than that of commercial IrO2. Density functional theory (DFT) and molecular dynamics (MD) simulations reveal that the incorporation of N enhances the interaction between Ir atoms and the support, which inhibits particle agglomeration. 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.