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.