Strong Modulation of Electronic States in IrO ₂ by Interstitial Carbon for Highly Active Acidic Water Oxidation

IrO 2 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 IrO 2 . Herein, an interstitial carbon‐doped IrO 2 (C in ‐IrO 2 ) catalyst is prepared for acidic OER. The C in ‐IrO 2 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 ‐IrO 2 , 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 ‐IrO 2 also enables an intra‐surface hydrogen abstraction from *OOH to produce *OO, which also enhances the OER activity. The C in ‐IrO 2 ‐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 IrO 2 .