Potentiostatically deposited bimetallic cobalt–nickel selenide nanostructures on nickel foam for highly efficient overall water splitting

The fabrication of efficient electrocatalysts for water splitting is vital for production of clean fuels. Herein, cobalt–nickel selenide (CoNi2Se4) nanostructures were fabricated on a Ni foam substrate using a facile potentiostatic method at different deposition solution pH levels. Nanoparticle-, fluffy-, and flake-like CoNi2Se4 nanostructures were deposited by changing the aqueous solution pH to 2.0, 2.5, and 3.0, respectively. The desired flake-like CoNi2Se4 electrode fabricated at pH 3.0 presented the best electrocatalytic performance of all CoNi2Se4 nanostructures in this study and required overpotentials as low as 244 and 184 mV to deliver a current density of 10 mA cm−2 for the OER and HER in 1.0 M KOH, respectively. Furthermore, the electrodes presented long-term stability over 20 h at current densities of 10 and −10 mA cm−2. Besides, this bifunctional flake-like CoNi2Se4 electrocatalyst delivered outstanding overall water splitting performance and required an external potential of 1.63 V to deliver a current density of 10 mA cm−2.