Characterization of Pulse Plated Ni and NiZn Alloys

Abstract

Nickel, zinc and nickel-rich NiZn alloys were formed on platinum by galvanostatic pulse plating from aqueous sulfate baths. The alloys were formed in three steps, first in anomalous deposition by a current pulse, secondly by dissolution and oxidation during the open circuit potential in each cycle and finally by anodic stripping of the fully plated sample. The treatment leaves a stable phase with an alloy composition of Ni0.8Zn0.2. The potential-time curves during the plating procedure were used to qualitatively describe the nucleation and growth processes. For Zn a fully covered surface was obtained after one pulse while for Ni and NiZn three-dimensional clusters were obtained in the first pulse. Further growth of these layers involves nucleation on the substrate and deposited clusters. The films were characterized with optical microscopy, SEM/EDX, AFM, XPS, TEM and by electrochemical methods. XPS revealed that the surfaces become gently oxidized by the stripping in the plating solution. For Ni a bi-layer of NiO/Ni(OH)2 was found on the surface while for NiZn mainly the hydroxide was detected. The electrocatalytic properties of the layers toward oxygen reduction in alkaline solution were explored and the NiZn alloy was proven to be an excellent catalyst for hydrogen peroxide production.