pH dependence of the composition of electrodeposited Co films in aqueous sulfate solutions

The electrodeposition of cobalt onto gold is studied as a function of the pH of the electrolyte. Electrochemical quartz crystal microgravimetry is used to identify the material deposited. Using a Co sulfate solution without additives, it is found that for pH <-3.2, Co metal deposits. For pH > 3.2 and at sufficiently negative applied potential, first Co hydroxide deposits and then Co metal. The addition of boric acid, H₃BO₃ to cobalt sulfate solutions leads to different results: measurements done up to pH 5.5 indicate that only Co metal deposits, showing that boric acid prevents the formation of cobalt hydroxide. Published in Russian in Elektrokhimiya, 2007, Vol. 43, No. 7, pp. 899–902. The text was submitted by the authors in English.