Transient Potential-Driven Ir-Site Response Regulates Lattice-Oxygen Participation

Understanding how active sites dynamically respond to electrochemical polarization and control catalytic pathway selection remains a key challenge in multistep electrocatalysis. Here we show that electron-withdrawing Mn doping endows Ca₂IrO₄ with an enhanced transient response of Ir sites under acidic oxygen-evolution conditions. Using time-resolved energy-dispersive x-ray absorption spectroscopy, we directly capture Ir-site evolution during a single voltammetric sweep, revealing a rapid potential-induced increase in Ir oxidation state accompanied by strengthened Ir-O covalency under anodic polarization. Operando characterizations and theoretical calculations demonstrate that this enhanced transient Ir-site response facilitates lattice-oxygen activation, thereby increasing the contribution of the lattice oxygen mechanism under working conditions. Consequently, Mn-doped Ca₂IrO₄ delivers 1 A cm^-2 at 1.675 V in a proton-exchange-membrane water electrolyzer and maintains stable operation for over 500 h. These findings identify the transient Ir-site response as an important factor regulating lattice-oxygen participation in Ca₂IrO₄-based catalysts, providing a basis for designing Ir-based oxides with tunable lattice-oxygen chemistry.