Kinetics of the cathodic decomposition of silver iodide in molten alkaline nitrates

The cathodic decomposition of AgI was studied using a single pulse galvanostatic technique. The working electrode was an AgI-rotating disc immersed in the molten KNO₃-NaNO₃ eutectic. Linear overpotential-log (current density) plots were obtained for varying concentrations of I⁻. Evidence was found for the existence of two different control steps, depending on the iodide concentration. At lower I⁻ concentrations a chemical reaction forming an adsorbed AgI⁻₂ complex ion is postulated as the rate-determining step. At higher I⁻ concentrations the rds is related to the electrochemical reaction AgI + e = Ag° + I⁻. An alternative charge transfer process is suggested corresponding to the transfer of an I⁻ ion between the two ionic media.