Galvanostatic deposition of nickel hydroxide and cobalt hydroxide films

A fundamental study of the Ni(OH){dollar}sb2{dollar} deposition and Co(OH){dollar}sb2{dollar} codeposition chemistries is presented. Three differential equation models are presented to describe: (1) the inefficiencies in the galvanostatic deposition of Ni(OH){dollar}sb2{dollar} films; (2) the effect of nitrate complexes on the chemistry of Ni(OH){dollar}sb2{dollar} deposition; and (3) the codeposition behavior and the interaction of the nickel and cobalt deposition chemistries. All of these models use a newly hypothesized two-step deposition mechanism. The model predictions agree with experimentally measured deposition rates of Ni(OH){dollar}sb2{dollar} and Co(OH){dollar}sb2{dollar} obtained using an Electrochemical Quartz Crystal Microbalance (EQCM). The anomalous deposition behavior reported previously in which the utilization of the electrochemically generated OH{dollar}sp-{dollar} species decreased drastically as the concentration of Ni(NO{dollar}sb3)sb2{dollar} increased beyond 0.1 M is explained by the Ni(OH){dollar}sb2{dollar} film model. This dissertation verifies that the inefficient use of electrochemically generated OH{dollar}sp-{dollar} species is due to the presence of Ni{dollar}sb4{dollar}(OH){dollar}sb4sp{lcub}4+{rcub}{dollar} as an intermediate in the deposition process. A high concentration of the intermediate yields a large diffusion flux of this species away from the electrode, and thus a decrease in the deposition rate.; The model that includes the effect of nitrate complexes on the galvanostatic deposition of Ni(OH){dollar}sb2{dollar} shows that these complexes decrease the ionic strength of the electrolyte and the concentration of Ni{dollar}sp{lcub}2+{rcub}{dollar} that can form the Ni{dollar}sb4{dollar}(OH){dollar}sb4sp{lcub}4+{rcub}{dollar} species. Ionic strength correlations are derived and used to predict equilibrium quotients of the nickel hydrolysis and Ni(OH){dollar}sb2{dollar} precipitation reactions. A statistical comparison of the deposition data and the model confirm the independently measured values of the Ni{dollar}sb4{dollar}(OH){dollar}sb4sp{lcub}4+{rcub}{dollar} equilibrium quotients.; Inefficiencies in cobalt deposition are explained with a Co{dollar}sb4{dollar}(OH){dollar}sb4sp{lcub}4+{rcub}{dollar} intermediate similar to the nickel system. It is shown that the ionic strength of the moderately concentrated Ni(NO{dollar}sb3)sb2{dollar} solution causes the Co{dollar}sb4{dollar}(OH){dollar}sb4sp{lcub}4+{rcub}{dollar} species to exist at concentrations much higher than that predicted by the Co(NO{dollar}sb3)sb2{dollar} concentration. The results of the codeposition model indicate that the ratio of cobalt to nickel in a galvanostatically deposited film depends on the ratio of Co(NO{dollar}sb3)sb2{dollar} to Ni(NO{dollar}sb3)sb2{dollar} in the electrolyte and the current density. The model predictions agree with experimentally measured nickel and cobalt contents incorporated in the films at various operating conditions. These results are useful for electrochemically impregnated plaques used for nickel electrodes.