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 temperature and the ethanol content of the Ni(NO3)(2) solution on: (i) the efficiency of electrochemical deposition of nickel hydroxide; and (ii) the molecular weight of the deposited film. An electrochemical quartz crystal nanobalance (EQCN) was used to measure the mass of films electrochemically deposited from Ni(NO3)(2) solutions and constant current discharges were used to determine the electrochemical capacity of the films. 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 is attributed to a decrease in the concentration of a nickel complex at the surface of the electrode. The lower complex concentration decreases the diffusion rate of this species away from the electrode surface and hence increases the rate at which the complex precipitates from the 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 noticeable effect on the efficiency of deposition, when water was present. In pure ethanol, however, the chemistry of deposition seemed to change considerably. However, increasing the ethanol content of the solution resulted in an increase of the molecular weight of the film. Increase in the molecular weight with an increase in the ethanol content of the solution is due to an increase in the relative percentage of ethanol 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.