EFFECTS OF OXYGEN REDUCTION ON NICKEL DEPOSITION FROM UNBUFFERED AQUEOUS-SOLUTIONS .1. DEPOSITION PROCESS AND DEPOSIT STRUCTURE

In nickel deposition in the presence of dissolved oxygen, oxygen reduction occurred prior to nickel deposition, resulting in the formation of poorly conductive Ni(OH)2 at the electrode surface. The presence of Ni(OH)2 suppressed the adsorption of intermediate Ni(OH)ads, and the nucleation and crystal growth of nickel was inhibited as a result. The effects of oxygen reduction on deposition, however, decreased with increasing NiCl2 concentration in the depositing solutions. This is attributed to the increased competitiveness of Ni(OH)ads adsorption relative to Ni(OH)2 formation at high NiCl2 concentration. Nickel deposits of better uniformity and smaller grain size were produced in the presence of oxygen. However, a porous nickel structure was not obtained under the experimental conditions. This disparity from the reactive deposition of porous cobalt is explained in terms of a charge-transfer controlled electrode kinetics for nickel deposition and the stability of Ni(OH)2 at the electrode surface.