Sputtered NiCu Thin Films on Nickel Foam for Overall Electrochemical Water Splitting in Alkaline Media

Abstract

Development of high-performance and low-cost electrocatalysts is essential for commercialization of alkaline water electrolysis. The fabrication of nickel-copper (NiCu) thin films is reported with a Ni:Cu atomic ratio of 3:1, directly deposited onto nickel foam using sputtering. The as-prepared films are used as dual-activity self-supported electrodes for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media. The 270 nm thick film (NiCu4) was the nominally best-performing HER electrode, although the differences between film thicknesses were within experimental variability. Initially, the electrode requires an overpotential of 215 mV to deliver a current density of −50 mA cm⁻². Remarkably, after 72 h of stability testing, the overpotential significantly decreased to 136 mV. Operando electrochemical impedance spectroscopy and Raman spectroscopy were used to investigate the HER mechanism and dynamic surface state changes on the NiCu4 electrode. This improvement originates from surface structural changes of the NiCu alloy under HER conditions. For OER, NiCu4 and Ni on Ni foam exhibit equal OER performance in alkaline media, demonstrating a low onset potential of ≈335 mV and an overpotential of 370 mV at 10 mA cm⁻². These results showcase sputtering as a robust, reproducible, waste-free method for the development of electrocatalysts.