In Situ Generation of Bifunctional, Efficient Fe-Based Catalysts from Mackinawite Iron Sulfide for Water Splitting

Water splitting requires nonprecious materials that can catalyze efficiently both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Here, we report the synthesis of mackinawite FeS nanosheets grown on iron foam, which can serve as an efficient pre-electrocatalyst for both HER and OER in alkaline media. During electrochemical HER testing, core@shell iron@iron oxysulfide nanoparticles as the catalytically active phase are generated in situ on FeS nanosheets. During electrochemical OER testing, FeS nanosheets totally transform into porous amorphous FeOx film that can mediate the OER efficiently. When assembled as the cathode and the anode in a single electrolyzer, the resulting Fe-based catalysts can give a good overall water splitting output that outperforms the one obtained from a noble-metal-based Pt/C-lrO(2)-coupled electrolyzer. These results provide new insights on the active sites of Fe-based catalysts as well as an impetus for further research on low-cost, iron-containing water-splitting electrocatalysts.