A facile electrochemical fabrication of hierarchically structured nickel–copper composite electrodes on nickel foam for hydrogen evolution reaction

•We prepare 3D NiCu precursor by galvanic replacement reaction between Ni foam and copper ion.•CuCl2 is the best dipping solution because the formation and hydrolysis of CuCln1−n.•An activation process was done to remove the oxide.•CV treatment was done to fabricate a hierarchical architectural structure.•The hierarchical architectural NiCu electrode has the best HER activity of all the electrodes.

A NiCu composite electrode with hierarchical structure has been successfully fabricated by an electrochemical method, which consisted of galvanic replacement reaction (GRR), activation process and cyclic voltammetry (CV) treatment. The three-dimensional (3D) Ni–Cu precursors were prepared firstly by dipping Ni foam into three kinds of different copper ion solutions and identified that CuCl2 is a favorite electrolyte. This may be attributed to the adsorption of chloride ion on copper surface to form the CuCln1−n complex and the hydrolysis of CuCln1−n. After an activation process to reduce the hydrolytic product Cu2O into Cu, a CV treatment was performed to form a hierarchical structure to improve the surface area and to heighten the hydrogen evolution reaction (HER) activity. The optimal number of CV cycles is 3.