In-situ generation of FeOOH/NiOOH interface in FeS2/NiS2 nanosheets through deep reconstruction for efficient oxygen evolution reaction.

Transition metal sulfides (TMSs) for electrochemical water splitting undergo significant self-reconstruction to form actual active species favorable for high oxygen evolution reaction (OER) performance. However, the complete self-reconstruction of most of the reported TMSs in alkaline media is unfrequent and the active species cannot be efficiently used. Herein, self-supported FeS2/NiS2 nanosheet arrays (FeNiS) are deliberately fabricated as pre-catalysts and then proved to accomplish deep phase transformation into low-crystalline and ultrathin FeOOH/NiOOH (FeNiS-R) nanosheets favorable to alkaline OER. Interestingly, the FeNiS-R with abundant interface is generated via complete reconstruction during electrolysis and the high-valence Fe and Ni in the FeNiS-R interface are the real active sites for high OER activity, as uncovered by various ex situ characterization studies. The reconstructed FeNiS-R exhibits a small overpotential of 290 mV at 100 mA cm-2 and favorable durability (≥80 h), much superior to commercial benchmark IrO2. This work provides a promising avenue to achieve the deep reconstruction of TMSs and the targeted design of OER catalysts in energy devices.&#xD.