Thermoelectrochemical transfer function under thermal laminar free convection at a vertical electrode

An analysis is presented for the frequency response of the limiting diffusion current to a thermal perturbation under conditions of simultaneous heat and mass transfer at a heated vertical electrode. At the limiting diffusion current plateau, this response is the sum of three terms: the first one corresponds to the diffusion coefficient and is real, the second one is purely imaginary, and die third one corresponds to the flux of electroactive species at the electrode surface. The dimensionless local flux due to the thermal modulation of the electrode temperature is expressed as a series expansion of the dimensionless local characteristic frequency xi in the low-frequency range. and is proportional to xi(-3/2) in the high-frequency range. With 80 terms in the series, the two solutions are shown to overlap fairly well for 1.6 less than or equal to xi less than or equal to 11. The overall transfer function is then obtained for two electrode geometries. rectangular and circular. For a circular electrode. the experimental results obtained for different steady temperature differences. T-e - T-0, between the electrode and the solution and different bulk concentrations, co, are successfully tested with these theoretical predictions. The characteristic parameters are determined with a fitting procedure. (C) 2000 The Electrochemical Society. S0013-465100)03-050-0. All rights reserved.