α-Ni(OH)2·0.75H2O nanofilms on Ni foam from simple NiCl2 solution: Fast electrodeposition, formation mechanism and application as an efficient bifunctional electrocatalyst for overall water splitting in alkaline solution

A facile electrochemical route was designed for successful deposition of α-Ni(OH)2·0.75H2O nanofilms on Ni foam (NF) here, employing NiCl2 solution as the electrolyte, which differed from the traditional route of the Ni(NO3)2 electrolyte. Experiments uncovered that under the deposition current density of 10 mA cm−2, the initial concentration of NiCl2 electrolyte strongly affected the phase of the final product. Metallic nickel was deposited at the low concentration and α-Ni(OH)2·0.75H2O was obtained at the high concentration. It was found that the amount of Cl− anions and the deposition current density were two important factors affecting the formation of α-Ni(OH)2·0.75H2O. Interestingly, the as-obtained α-Ni(OH)2·0.75H2O/NF exhibited highly efficient electrocatalytic activity in both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 1.0 M KOH. In a two-electrode water-splitting device, the α-Ni(OH)2·0.75H2O/NF deposited at the current density of 10 mA cm−2 for 60 min was selected as the anode and the cathode simultaneously. The electrochemical measurements showed that the as-obtained α-Ni(OH)2·0.75H2O/NF electrode presented excellent electrocatalytic activity and stability matched with Pt/C/NF – RuO2/NF electrodes. Obviously, the present work provides a new path for fast preparation of highly efficient α-Ni(OH)2·0.75H2O electrocatalyst for overall water splitting.