The Effect of Bath Parameters on the Electrocrystallisation of Cox–Cu100−x Alloys on Stainless Steel Cathode

Abstract

The electrocrystallisation of the alloys of Cox–Cu100−x onto stainless steel cathode was investigated by performing cyclic voltammetry (CV) to understand the mechanism of deposition. The deposit morphology and crystal structure of deposit were analysed using scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The kinetic parameters were obtained from the cathodic polarisation of the CV to predict the electron transfer mechanism in the process. The transfer coefficient value (α) of the kinetic parameter revealed that both cathodic and anodic processes were unsymmetrical. It was demonstrated that the current efficiency of the deposit increased from 96.8% at pH 4.0 to 99.2% at pH 7, and then it dropped to 89.7% at pH 8. Before the deposition of the Co–Cu alloy, the initial copper deposition occurred at − 0.24 V and peaked at − 0.66 V. This was followed by the deposition of the Co–Cu alloy at − 1.04 V, which occurred after the deposition potential of Cu2+ (− 0.24 V) and Co2+ (− 0.89 V). The current then increasesd with a small increment in applied potential due to subsequent diffusion-controlled copper reduction along with the co-deposition of Co. The variation in the kinetic parameters was also reflected in the current efficiencies, the deposit morphologies, the crystallographic orientations and the nucleation overpotential values. The percentage of cobalt content in the alloy was observed to decrease in at.% from 54.35% at pH 4 to 49.86% at pH 6 and further to 20.62% at pH 8. The structure of the deposited alloy confirmed the formation of a single solid solution phase having different planes such as (222), (311), (220), (200) and a sharp peak due to face-centred cubic structure with (111) plane. This strong peak along with other similar peaks were observed in all the XRD of the deposit obtained at pH 4, 6 and 8. The morphology of the deposit characterised by the SEM showed that the deposit changed from a bitter gourd to a regular cauliflower-like structure as the pH value changed from 4 to 8.