Computational Modeling of Electrochemical Systems: Activation-Control vs. Mass-Transport-Control Analysis

The computational modeling of two generic heterogeneous reactions within an electrochemical cell formed by two planar electrodes in contact with an aqueous electrolyte was carried out with the FlexPDE 6 software. Both Red-Ox reactions were initially given identical kinetic and mass transport parameters to corroborate the functionality of the model. The derived steady-state current/overpotential curves, under mass transport control, were compared to the analytical model for Nernstian reactions (1). A very good match was found. The diffusion coefficients and standard reaction-rate-constants were afterwards varied. Inspecting the current/overpotential curve shape helped to rapidly identify the reaction-rate control-mechanism: either mass transport or activation. However, if the current density at each given potential is recorded before a steady-state value is attained, the correct identification of the reaction-rate control-mechanism may be hindered.