Strong Modulation of Electronic States in IrO₂ by Interstitial Carbon for Highly Active Acidic Water Oxidation

IrO₂ as the most stable electrocatalyst for acidic oxygen evolution reaction (OER) suffers from its low activity and the limited abundance in earth crust. Doping is one of promising strategies to enhance the OER activity and stability of IrO₂. Herein, an interstitial carbon-doped IrO₂ (C_in-IrO₂) catalyst is prepared for acidic OER. The C_in-IrO₂ shows an OER overpotential of 227 mV at 10 mA cm^-2, a mass activity of 565.1 A g_Ir ^-1 at 1.53 V, and a 2000-h stability with a degradation rate of 0.04 mV h^-1. The enhanced OER activity and stability originate from the formation of C─Ir bonds in the C_in-IrO₂, which results in a prominent down-shift of Ir d-band center and the up-shift of O p-band center. Such variations of electronic states not only optimize the adsorption of OER intermediates but also increases the covalence of Ir─O bond. The C_in-IrO₂ also enables an intra-surface hydrogen abstraction from *OOH to produce *OO, which also enhances the OER activity. The C_in-IrO₂-based proton exchange membrane (PEM) water electrolyzer delivers a ultrasmall cell voltages of 1.51 V at 1 A cm^-2 and 1.96 V at 3 A cm^-2. Our findings demonstrate a new method for enhancing the acidic OER performance of IrO₂.