Characteristics of nickel sulphide reduction in Ni2+ free background and Watts nickel plating electrolytes

The electrochemical behaviour and composition of nickel sulphide coatings deposited on glassy carbon (GC) electrode by the successive ionic layer adsorption and reaction ( SILAR) method using a nickel(II) ammonia complex and Na2S solutions have been studied in Ni2+ free background, Watts nickel plating and 0.05 M H2SO4 electrolytes by the cyclic voltammetry and X-ray photoelectron spectroscopy (XPS) methods. Analysis of XPS data suggests that the coating is a mixture of two sulphides where NiS dominates. In the Ni2+ free background solution at first the electrochemical reduction of the sulphur rich nickel sulphide to NiS occurs. After that the NiS to metallic Ni is reduced in the potential range of H-2 evolution. During the cathodic reduction of the coating in Watts nickel plating electrolyte the sulphur is reduced in the potential range from 0.0 to -0.4 V, while at the potential values <-0.5 V the sulphur rich nickel sulphide and NiS reduction in the H-2 evolution range and Ni plating occur.