The Use of Flicker-Noise Spectroscopy for Studying the Mechanism of the Overlimiting Current in a System with Cation-Exchange Membrane
A. V. Kolyubin, A. V. Maksimychev, S. F. Timashev
Российский электрохимический журнал
Spectral analysis of low-frequency fluctuations of the membrane potential, which occur when electrical current passes through a polyamide cation-exchange membrane placed in a NaCl solution, is employedfor studying the mechanism of ionic transport at overlimiting current densities. Spectra of noise density of themembrane potential, SV , as a function of the concentration and viscosity of electrolyte as well as their dependence on the current density are investigated in the frequency region 0.002–500 Hz. Fluctuations of the membrane potential are shown to become discernible when the current density j is approaching the limiting valuejlim. When j is approximately equal to jlim, the fluctuation spectra include reproducible, discrete lines at frequencies 20–250 Hz. At j jlim the SV function becomes smooth and corresponds to the flicker noise. Parametersof the SV spectra depend on the electrolyte viscosity. The spectral regularities observed are interpreted in termsof the model that suggests the appearance of hydrodynamic instabilities in the N-Nernst layer, at the membraneboundary, at j jlim. The mechanism leading to turbulent pulsations and the role played by turbulence in theprocess of ionic transport at overlimiting currents are discussed.