Electrodeposition and dissolution of Co-W alloy films

Cyclic voltammetric studies were carried out on platinum in alkaline solution containing cobalt sulphate, sodium tungstate, dimethyl sulphoxide and triammonium citrate. Spectral u.v. absorption studies of cobalt citrate complex indicate the species to be [Co L (H2O)(3)](2+), where L is triammonium citrate. The deposition of cobalt involves a stepwise electron transfer mechanism. The observed cyclic voltammetric data show that the alloy deposition is possibly from cobalt-tungstate complex. The citrate ions and dimethyl sulphoxide hinder the alloy deposition. Dimethyl sulphoxide, which specifically adsorbs on the electrode surface, favours the hydrogen evolution reaction (HER), whereas tungstate hinders the HER. Stripping voltammograms show the existence of cobalt rich alloy phases. X-ray diffraction studies further confirm the phases to be Co3W and Co7W.