Protective Cerium Oxide Coating Promoted Ce‐Doping and Reconstruction of High‐Valence NiFe Sulfide toward Robust Overall Water Splitting

Abstract Active and stable electrocatalysts toward oxygen evolution reaction (OER) are essential for alkaline water splitting. Herein, an efficient and durable high‐valence NiFe‐based OER electrocatalyst is developed, featuring a protective CeO 2− x coating to prevent the corrosion of carbon substrates during oxidative OER operation, ensuring excellent catalyst stability. The incorporation of a CeO 2− x coating also leads to the formation of a Ce‐doped NiFe sulfide catalyst. The Ce modulator enables the dynamic transformation of NiFe sulfide into highly active (oxy)hydroxide species with high‐valence Ni sites and enhanced Ni─O covalency, thereby improving its OER catalytic activity. Accordingly, the prepared NiFeS 2 /CeO 2− x /CC catalyst achieves enhanced OER activity with an overpotential of 260 mV at 100 mA cm −2 in 1.0 m KOH. Moreover, the catalyst achieves 100 mA cm −2 current density at an overpotential of 187 mV for the hydrogen evolution reaction. The anion exchange membrane water electrolyzer reached 500 mA cm −2 at 1.73 V cell voltage with excellent stability for 500 h continuous operation. This study demonstrates a promising approach for the fabrication of robust water‐splitting electrocatalysts.