Thermal activation of electrochemical processes in a Rf-heated channel flow cell: experiment and finite element simulation

A novel approach to thermoelectrochemistry is presented which involves the direct heating of the working electrode in a channel flow cell system by eddy currents caused by 8 MHz radio frequency (Rf) radiation. For the model redox systems Fe(CN)(6)(3-/4-) and Ru(NH3)(6)(3+/2+) it is shown that it is possible to perform electrochemical experiments with simultaneous thermal activation at temperatures close to the boiling point of the electrolyte solution. Quantitative analysis of data obtained from thermoelectrochemical studies in the Rf-heated channel flow system is possible with the help of a computer model. Numerical simulation results obtained with a finite element program (FIDAP(TM)) for the complex heat and mass flow during voltammetric experiments at the heated electrode are shown to be in quantitative agreement with experimental data. Both the increase in the rate of diffusion as well as the change in the flow pattern in the heated low viscosity region of the channel are shown to contribute significantly to the enhanced mass transport. After confirming the quantitative agreement of the numerical model with the data obtained for the oxidation of Fe(CN)(6)(4-) and the reduction of Fe(CN)(6)(3-) in 0.1 M KCl, the activation energy for the Ru(NH3)(6)(3+/2+) redox system diffusion in 0.1 M KCl is determined. (C) 2000 Elsevier Science B.V. All rights reserved.