Regulating Local Coordination Sphere of Ir Single Atoms at the Atomic Interface for Efficient Oxygen Evolution Reaction

Single-atom catalysts dispersed on an oxide support are essential for overcoming the sluggishness of the oxygen evolution reaction (OER). However, the durability of most metal single-atoms is compromised under harsh OER conditions due to their low coordination (weak metal-support interactions) and excessive disruption of metal-O_lattice bonds to enable lattice oxygen participation, leading to metal dissolution and hindering their practical applicability. Herein, we systematically regulate the local coordination of Ir_single-atoms at the atomic level to enhance the performance of the OER by precisely modulating their steric localization on the NiO surface. Compared to conventional Ir_single-atoms adsorbed on NiO surface, the atomic Ir atoms partially embedded within the NiO surface (Ir_emb-NiO) exhibit a 2-fold increase in Ir-Ni second-shell interaction revealed by X-ray absorption spectroscopy (XAS), suggesting stronger metal-support interactions. Remarkably, Ir_emb-NiO with tailored coordination sphere exhibits excellent alkaline OER mass activity and long-term durability (degradation rate: ∼1 mV/h), outperforming commercial IrO₂ (∼26 mV/h) and conventional Ir_single-atoms on NiO (∼7 mV/h). Comprehensive <i>operando</i> X-ray absorption and Raman spectroscopies, along with pH-dependence activity tests, identified high-valence atomic Ir sites embedded on the NiOOH surface during the OER followed the lattice oxygen mechanism, thereby circumventing the traditional linear scaling relationships. Moreover, the enhanced Ir-Ni second-shell interaction in Ir_emb-NiO plays a crucial role in imparting structural rigidity to Ir single-atoms, thereby mitigating Ir-dissolution and ensuring superior OER kinetics alongside sustained durability.