Electrochemical reduction of the corrosion products formed on copper surface in alkaline-sulphide solutions

Electroreduction of the preformed reaction products on copper in highly oxygenated NaOH solutions, on one hand, and NaOH solutions in presence of S2−, on the other hand, is followed galvanostatically. In sulphide free solutions, two cathodic steps corresponding to the reduction of Cu2O and Cu(OH)2, receptively, before H2 evolution commences were reported. The quantity of electricity consumed during the reduction of both species is found to depend on both the concentration of NaOH and the immersion time. The presence of S2− ions, at any concentration causes the complete elimination of the second step corresponding to the reduction of Cu(OH)2 and the partial disappearance of the step corresponding to the reduction of Cu2O. The reduction of the preformed Cu2S film occurs in a single reduction step. The quantity of electricity consumed along this step depends on the thickness of the sulphide film.