Coordination Engineering of Ir─Mo Atomic Pair Sites to Break Scaling Limitations for Acidic Oxygen Evolution

Coordination engineering of single-atom catalysts (SACs) is a powerful strategy to address durability and activity challenges in the acidic oxygen evolution reaction (OER). Here, we obtain two distinct Ir single-atom configurations on MoO₃ support by regulating the second-shell coordination environment. Compared with the weakly interacting Ir─O─Mo structure, atomic pair sites formed through direct Ir─Mo coordination exhibit strong electronic coupling with the support, thereby enhancing atomic dispersion and structural stability. In situ experimental and theoretical studies reveal that the Ir─Mo pair sites trigger a new oxide-mediated pathway, in which dynamic hydroxyl spillover from Mo to Ir site effectively facilitates *OOH formation. This process breaks the linear scaling relationship between *OH and *OOH adsorption, lowering the energy barrier of the rate-limiting step and enabling superior OER kinetics. As a result, the Ir_O+Mo/MoO₃ catalyst achieves outstanding stability for over 1500 h at 10 mA cm^-2 in acidic electrolyte and sustains continuous operation for 300 h at 1.0 A cm^-2 in the proton exchange membrane water electrolyzer. This work provides novel insights into the coordination engineering of SACs and opens a promising avenue for overcoming scaling limitations in acidic OER catalysis.