Influence of pH on the electrolytic deposition of Ni–Co films

Ni–Co alloys obtained by electrolytic deposition on a paraffin impregnated graphite electrode have been characterised by cyclic voltammetry, scanning electron microscopy with energy dispersive X-ray microanalysis, and time of flight secondary ion mass spectrometry (ToF–SIMS), with the objective of qualitatively assessing and comparing their composition and the distribution of chemical species. The effect of pH on the composition and morphology of the deposit and on the proportion of the hydrogenated forms of Ni and Co has been investigated. It has been determined that the predominant species, which give rise to the ToF–SIMS positive ion spectra of the deposits, are the pure metals, their hydrides, hydroxides and oxides as a hydrogen. In negative secondary ion spectra, the most favourable species were found to be: O, OH, as well as hydrides, hydroxides and hydrated ions of the two metals. The proportion of individual species changed depending on the electrolyte pH. The content of Co in the deposit corresponds to the content of Co in the electrolyte and increased moderately with increasing pH value, corresponding to the regular deposition behaviour of Ni–Co film rather than an anomalous deposition.