Hydrophilic medium and precursors were used to synthesize a hydrophilic electro-catalyst for overall water splitting. The cobalt sulfide (Co3S4) catalyst exhibits a layered nanosheet structure with a hydrophilic surface, which can facilitate the diffusion of aqueous substrates into the electrode pores and towards the active sites. The Co3S4 catalyst shows excellent bifunctional catalytic activity for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline solution. The assembled water electrolyzer based on Co3S4 exhibits better performance and stability than that of Pt/C-Ruo(2) catalyst. Thereforce the hydrophilic Co3S4 is a highly promising bifunctional catalyst for the overall water splitting reaction. (C) 2017 Elsevier Inc. All rights reserved.