Highly conductive and metallic cobalt-nickel selenide nanorods supported on Ni foam as an efficient electrocatalyst for alkaline water splitting.

Water splitting has long been considered as a promising chemical reaction that can produce clean hydrogen fuel to relieve the energy crisis and environmental pollution. Herein, we report that Co0.75Ni0.25Se/NF formed by two-step growth of metallic cobalt-nickel selenide nanorods on porous nickel foam was used as a bifunctional electrocatalyst. Ni foam serves as a slow-releasing nickel source together with a Co source to form a special proportional cobalt-nickel selenide. Due to its unique rough nanostructure, bimetallic cooperative effects and intrinsic metallic character, the obtained Co0.75Ni0.25Se/NF electrode exhibits a low overpotential of 269 mV (50 mA cm-2) for the oxygen evolution reaction and an overpotential of 106 mV (10 mA cm-2) for the hydrogen evolution reaction. Furthermore, this bifunctional electrocatalyst requires a cell voltage of 1.60 V to achieve a current density of 10 mA cm-2. Besides, based on theoretical calculation, it is further shown that the synergy between Co and Ni elements is beneficial for improving the internal structure of the catalyst, resulting in a high electrical conductivity, and low HER Gibbs free-energy and water adsorption energy. The present results indicate that Co0.75Ni0.25Se/NF exhibits advanced electrocatalytic activity for overall water splitting. This work offers an appropriate methodology and theoretical guidance to synthesize a bimetal-selenide electrocatalyst for water splitting.