Comparison of chloride and sulphate electrolytes in nickel electrodeposition on a paraffin impregnated graphite electrode

Electrodeposition of nickel on a paraffin impregnated graphite electrode (PIGE) has been studied by cyclic voltammetry (CV) and chronoamperometry from chloride and sulphate electrolytes. The differences in mechanisms of nickel deposition from these solutions have been observed. Experimental results obtained from cyclic voltammetry were evaluated by elimination voltammetry with linear scan (EVLS). The elimination procedure, using the linear combination of the total currents measured at different scan rates, makes it possible to reveal processes not detectable by conventional electrochemical methods. The influence of Ni2+ concentration and pH was also investigated. The results indicated two basic differences between the nickel deposition process in both electrolytes: (i) in chloride electrolyte the initial stage is Ni2+ reduction, while in sulphate electrolyte it is the proton reduction; (ii) in chloride electrolyte the charge carrying species is NiCl+, while in sulphate solutions it is NiOH+. The measurements were complemented by recording scanning electron micrographs (SEM), emphasizing the differences between the quality of Ni deposits obtained from the respective electrolytes.