Fe-doped Ni3S2 nanoneedles directly grown on Ni foam as highly efficient bifunctional electrocatalysts for alkaline overall water splitting

•Fe-doped Ni3S2 nanoneedles supported on nickel foam are successfully synthesized.•This catalyst provides a current density of 10 mA cm−2 at a cell voltage of 1.58 V.•This catalyst displays excellent long-term stability even after 50 h. Fe-doped Ni3S2 nanoneedles supported on nickel foam (NF) are reported as coupled oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) electrocatalysts for effective overall water splitting. The optimized Fe doping density, vertically grown nanoneedle structure without any binder on the conductive substrate, and abundant surface-active sites make the Fe-doped Ni3S2 an efficient catalyst for both electrochemical reactions. The as-synthesized Fe-doped Ni3S2 nanoneedles on NF show an outstanding electrocatalytic performance, only requiring an overpotential of 269 and 314 mV to provide 100 and −100 mA cm−2 for OER and HER, respectively. A water electrolyzer, assembled with the Fe-doped Ni3S2 as both the anode and cathode, displays an exceptionally low onset potential of 1.39 V and achieves a current density of 10 mA cm−2 at a very low cell voltage of 1.58 V with excellent long-term stability for 50 h. [Display omitted]