Bimetallic Cobalt–Nickel Electrode Made by a Sputtering Technique for Electrocatalytic Hydrogen Evolution Reaction: Effect of Nickel Ratios

Electrocatalytic hydrogen evolution reaction (HER), a half-reaction of water splitting, is highly important to be developed for green and sustainable hydrogen production. In this work, a bimetallic cobalt–nickel (CoNi_x) alloy is deposited on nickel foam with a home-made target by using a radio frequency (RF) magnetron sputtering technique at a low deposition temperature. The as-sputtered CoNi_x was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy to evaluate its physical and chemical properties. The electrochemical measurement exhibited that the bimetallic CoNi_x alloy had a promising performance for HER in alkaline solutions. CoNi₄, as the optimum ratio, possessed low overpotentials of 53 and 175 mV to achieve current densities of 10 and 100 mA/cm², respectively. Moreover, among the as-sputtered CoNi_x, CoNi₄ had the largest electrochemical surface-active area (485 cm²) and the lowest electron-transfer resistance (1.14 Ω). CoNi₄ was also quite stable under the continuous operation of constant current densities of 10 and 50 mA/cm² for 20 h. This work is based on the RF magnetron sputtering technique for developing bimetallic CoNi_x alloy as an efficient HER catalyst for electrochemical energy.