Electrodeposition and dissolution of Co-W alloy films

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