One-step immersion plating method to deposit anticorrosion nickel-sulfur coatings on copper

Although nickel has a lower standard electrode potential than copper, nickel-sulfur coatings were successfully deposited on copper through one-step immersion plating method, which was carried out in the aqueous solution consisting of NiSO4·6H2O and Na2S2O3·5H2O at room temperature. The open circuit potential tests demonstrated that copper had a more negative potential than nickel in Na2S2O3·5H2O solutions, which made the deposition of nickel on copper through immersion plating feasible. Because of the decomposition of sodium thiosulfate, sulfur could be codeposited with nickel and the nickel-sulfur coatings were finally obtained. The surface morphology and composition of the coatings were characterized with SEM, EDS, XPS and XRD analyses, and the results indicated the coatings were mainly composed of metallic nickel and Ni3S2. The deposition process of the nickel-sulfur coatings was investigated by analyzing the morphology evolution of copper substrates. The as-prepared nickel-sulfur coatings possessed good anticorrosion ability for its compact structure and could lower the corrosion current density of copper in 3.5 wt% NaCl solution to its 1/20.