THE EFFECT OF TEMPERATURE AND ETHANOL ON THE DEPOSITION OF NICKEL-HYDROXIDE FILMS

The objective of this work was to determine the effect of the temperat ure and the ethanol content of the Ni(NO3)(2) solution on: (i) the eff iciency of electrochemical deposition of nickel hydroxide; and (ii) th e molecular weight of the deposited film. An electrochemical quartz cr ystal nanobalance (EQCN) was used to measure the mass of films electro chemically deposited from Ni(NO3)(2) solutions and constant current di scharges were used to determine the electrochemical capacity of the fi lms. The data indicates that increasing the temperature increases both the efficiency of the deposition reaction and the molecular weight of the deposited film. The increased efficiency at higher temperatures i s attributed to a decrease in the concentration of a nickel complex at the surface of the electrode. The lower complex concentration decreas es the diffusion rate of this species away from the electrode surface and hence increases the rate at which the complex precipitates from th e solution. The increase in the molecular weight at higher temperature is attributed to a combination of increased rate of deposition and an increase in the lattice spacing of the active material. The data also indicate that increasing the ethanol content of the solution had no n oticeable effect on the efficiency of deposition, when water was prese nt. In pure ethanol, however, the chemistry of deposition seemed to ch ange considerably. However, increasing the ethanol content of the solu tion resulted in an increase of the molecular weight of the film. Incr ease in the molecular weight with an increase in the ethanol content o f the solution is due to an increase in the relative percentage of eth anol incorporated in the active material. The data also indicate that the number of electrons in the discharge reaction is approximately 1.4 electrons per nickel atom.