Voltage fluctuations at sodium β″-alumina/mercury electrodes

Abstract

Voltage fluctuations at mercury/sodium β″-alumina ceramic electrode interfaces have been investigated over frequencies ranging from 10 −3 to 3 × 10 4Hz. Noise voltages in the absence of current can be explained by Nyquist and interfacial chemical reaction noise. The activation energy of the reaction noise rate constant is determined to be 0.29 eV, which suggests that diffusion of the sodium ions in the electrolyte dominates the reaction. In the presence of a decomposition current, the low frequency noise varies as f ∼1.5. After current flow, the noise voltage decays and can be observed for some tens of hours. Both current and post current noise signals suggest conductivity fluctuations arising from diffusion of the mobile sodium ions. Fitting experimental data to the diffusion and decay equations yields a diffusion constant of 1.8 × 10 −6 cm 2/s and a characteristic lenght equal to the bulk sample lenght.