FeCo2S4 Nanosheet Arrays Supported on Ni Foam: An Efficient and Durable Bifunctional Electrocatalyst for Overall Water-Splitting

Abstract Efficient and stable bifunctional electrocatalysts composed of Earth-abundant elements are crucial to the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). Herein, FeCo2S4 nanosheet arrays loaded on Ni foam (NF) are synthesized and first employed as a bifunctional electrocatalyst for full water-splitting. Remarkably, the self-assembled, binder-free, and cost-effective FeCo2S4/NF electrode shows high OER catalytic activity, which only requires an overpotential of 270 and 290 mV to achieve current densities of 50 and 100 mA cm–2, respectively. Moreover, the FeCo2S4/NF electrode exhibits considerable OER stability over 20 h at a static current density of 50 mA cm–2, with negligible potential change in alkaline electrolyte. Meanwhile, when serving as a catalyst for the HER under alkaline conditions, an overpotential of just 132 mV is required to deliver the current density of 10 mA cm–2. The structural investigation demonstrates the formation of a Co­(Fe)-(oxy)­hydroxides layer on the catalyst surface during the OER test, which could be the real active species. Furthermore, because of the high catalytic activity and stability of this bifunctional electrocatalyst, we prepared a high-performance overall water electrolyzer that could achieve a current density of 10 mA cm–2 at a cell voltage of 1.56 V.