Replacement Deposition of Ni-S Films on Cu and Their Catalytic Activity for Electroless Nickel Plating

Abstract

A Ni-S film was prepared on Cu substrate via the replacement reaction due to the quite negative electrode potential of Cu in high concentrated thiourea solution. A lower pH environment was facilitated to form more uniform Ni-S film. The sulfur content in the Ni-S film increased with the increase of deposition time and the rise of pH in solution. Relative to pure Ni, the existence of sulfur in the Ni-S film was found to result in different electrochemical properties. More importantly, constant current discharge curve and anodic polarization curve measurements indicated that the Ni-S film with higher sulfur content was more prone to be passivated, with negative influences on its catalytic activity. Polarization curve, electrochemical impedance spectroscopy and open circuit potential measurements were employed to investigate the catalytic activity of the Ni-S film for hypophosphite oxidation and electroless nickel (EN) plating. With the optimization of sulfur content by plating conditions, we could significantly improve the catalytic activity of the Ni-S film for hypophosphite oxidation and consequently for EN plating. Compared with the traditional Pd film, the Ni-S film exhibited a comparable catalytic activity, with a uniform electroless Ni-P layer obtained during the EN plating.