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

An analysis is presented for the frequency response of the limiting diffusi on 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 co rresponds to the diffusion coefficient and is real, the second one is purel y imaginary, and die third one corresponds to the flux of electroactive spe cies at the electrode surface. The dimensionless local flux due to the ther mal modulation of the electrode temperature is expressed as a series expans ion of the dimensionless local characteristic frequency xi in the low-frequ ency range. and is proportional to xi(-3/2) in the high-frequency range. Wi th 80 terms in the series, the two solutions are shown to overlap fairly we ll for 1.6 less than or equal to xi less than or equal to 11. The overall t ransfer 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 electr ode and the solution and different bulk concentrations, co, are successfull y tested with these theoretical predictions. The characteristic parameters are determined with a fitting procedure. (C) 2000 The Electrochemical Socie ty. S0013-465100)03-050-0. All rights reserved.