Co/Cu-modified NiO film grown on nickel foam as a highly active and stable electrocatalyst for overall water splitting.

The development and utilization of low-cost and efficient electrocatalysts for overall water splitting is of great significance for future energy supplies. Herein, a Co-doped NiCu mixed oxide film on Ni foam as a bifunctional electrocatalyst for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is synthesized by a facile solvothermal method using methanol as a reactant followed by annealing in air and it exhibits remarkably enhanced HER and OER activities. The well-constructed surface and porous skeleton structure with a large volume provide a large number of catalytically active sites during the electrochemical reaction. Notably, CuO plays an important role in improving the catalytic activity of the electrode; meanwhile, Co doping is beneficial for increasing the conductivity and activating the Ni sites at lower overpotentials via the charge transfer effect. Accordingly, the optimized CuO-NiO/Ni foam electrode exhibits a comparatively low overpotential of 38 mV and 172 mV at 10 mA cm for the HER and OER in 1.0 M KOH, respectively. Moreover, the electrode shows excellent long-term stability for 1000 cyclic voltammetric cycles in both the HER and OER. A self-assembled overall water splitting device using this electrode as both the anode and cathode achieves a current density of 10 mA cm at a low cell voltage of 1.51 V. This study is promising and provides a simple method for depositing a multimetal mixed oxide on a metal substrate resulting in an efficient bifunctional electrocatalyst, holding great significance for future energy applications.