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 Ca 2 IrO 4 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 Ca 2 IrO 4 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 Ca 2 IrO 4 ‐based catalysts, providing a basis for designing Ir‐based oxides with tunable lattice‐oxygen chemistry.