Crystalline nickel sulfide integrated with amorphous cobalt sulfide as an efficient bifunctional electrocatalyst for water splitting

The development of highly efficient and low-cost electrocatalysts is critical to the mass production of hydrogen from water splitting. Herein, a facile yet effective method was developed to synthesize bimetallic sulfides Ni3S2/CoSx, which were aimed for use as the electrocatalysts in both HER and OER. Encouragingly, the Ni3S2/CoSx demonstrated a low overpotential of 110 mV for HER at a current density of 10 mA·cm−2. It was discovered that the surface of Ni3S2/CoSx during OER process would undergo an in-situ oxidation to form MOOH (M = Co, Ni), that is, MOOH/Ni3S2/CoSx were the real functioning species in catalysis, which had an excellent OER activity and a low overpotential of 226 mV. Additionally, the assembled electrolyzer required only a low cell voltage of 1.53 V to achieve a current density of 10 mA·cm−2 in a 1 M KOH solution, and its performance was stable. Overall, this work provided a promising strategy for the facile fabrication of low-cost amorphous electrocatalysts, which is expected to promote the progress of overall water splitting.