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

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.