Co2S3 thin layer: unusual electrochemical behaviour during direct Ni electroplating

Abstract

The electrochemical behaviour of Co2S3 layers deposited on glassy carbon and ABS plastic from colloidal Co(III) compound solution was investigated by cyclic voltammetry and X-ray photoelectron spectroscopy, Auger electron spectroscopy, XRD techniques in Watts Ni electroplating and Ni2+ free background electrolytes. On the basis of experimental data, it was assumed that Co2S3 converts into NiS when it is cathodically polarised at E≈−0·2 V (SHE) in the Watts electrolyte. During this process, the sheet resistance of the layer decreases from ∼3 × 109 to ∼3 × 103 Ω □−1. This change goes on with the direct participation of Ni2+ ions in the electrolyte and this is probably of crucial importance for the following electrodeposition of metallic Ni initiated at more negative potentials. Contrary to Cu2–xS and Bi2S3, the layer of Co2S3 cannot be electroreduced to metallic Co in the Ni2+ free background electrolyte.