Controllable synthesis of core-branch Ni₃S₂/Co₉S₈ directly on nickel foam as an efficient bifunctional electrocatalyst for overall water splitting

Developing efficient and low-cost electrocatalysts for the oxygen evolution reaction and hydrogen evolution reaction is urgently needed for overall water splitting. Herein, three dimensional core-branch Ni₃S₂/Co₉S₈ arrays are directly grown on Ni foam by controllably sulfidizing NiCo-precursor with different concentrations of sulfur source. The unique core-branch Ni₃S₂/Co₉S₈ arrays provide large surface active areas for electrochemical reactions, open channels for effective gas release and intimate contact with Ni foam for fast electron transport. Serving as a free-standing electrocatalytic electrode, the as-synthesized Ni₃S₂/Co₉S₈ arrays show outstanding catalytic activity with an overpotential of 340 mV and 269 mV for oxygen evolution reaction and hydrogen evolution reaction at a current density of 100 mA cm⁻² in 1 M KOH, respectively. Moreover, Ni₃S₂/Co₉S₈ works as a bifunctional electrocatalyst for overall water splitting, where the low cell voltage of 1.55 V at 10 mA cm⁻² and good cycling performance can be successfully achieved. This work provides a facile strategy to construct core-branch nanostructures for an efficient bifunctional electrocatalyst for overall water splitting.