Kinetics and mechanism of anodic oxidation of nitrite ion in nitrate melts on platinum electrodes

Abstract

The electrochemical oxidation of nitrite ion in KNO₃-NaNO₃ eutectic melt on a platinum rotating disk electrode has been studied in the temperature range 247 to 312°C. The current/voltage curves comprise at least two regions. At high overvoltages the process is under a net convective diffusion control whereas at low ones the kinetics of the electrode process involves both convective diffusion and activation-polarization terms. From the current/voltage curves the kinetic parameters of each contribution are evaluated as well as the diffusion coefficient of nitrite ion in the melt. The electrode process is discussed in terms of the over-all reaction NO₂− → NO₂ + e and of the reaction mechanisms previously postulated, where the initial electron-transfer step becomes rate-determining as the nitrite ion concentration diminishes. The results are compared to those obtained with the pure nitrite melt.