Electrodeposition of Ni-Co thin films from ammonia-chloride electrolyte

This study presents the research results on the co-deposition of nickel and cobalt from an alkaline electrolyte containing glycine. For this purpose, cyclic and linear polarization curves of co-deposition were obtained at various cobalt concentrations, different poten-tial sweep rates, and electrolyte temperatures. It was established that the co-deposition process occurs anomalously, with the cobalt content in the deposited films exceeding that of nickel. The deposits obtained under optimal conditions contained 37.25 % Ni and 51.43 % Co. The study of the effect of the potential sweep rate on the co-deposition process of nickel and cobalt revealed a linear relationship between the current peak value and the square root of the potential sweep rate. This indicates that the initial stage of Ni-Co co-deposition is controlled by the diffusion of the metal ions to the cathode surface. When recording polarization curves on a rotating disk electrode at different rotation speeds, the relationship between the current peak value and the square root of the electrode rotation speed was also linear at relatively low rotation speeds. However, at higher rotation speeds, the process was controlled by electrochemical polarization. The co-deposition of Ni with Co was confirmed through X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy analyses. The investigation of the catalytic activity of Ni-Co deposits in a neutral medium (0.5 M Na₂SO₄) demonstrated that the amorphous thin films, not subjected to annealing, exhibited the best electrocatalytic properties for the hydrogen evolution reaction. The Tafel slope was determined to be 118 mV dec-1.