First direct experimental evidence of migration contributions through monitoring of concentration profiles at low supporting electrolyte concentration

Abstract

In this work, we address the possibility of monitoring concentration profiles established under conditions involving low concentration of supporting electrolyte employing an ultramicroelectrode as an amperometric probe. The local concentrations of the electroactive species participating to the electrochemical reaction were recorded experimentally within the steady state diffusion layer generated at the surface of a planar electrode. In addition, the specific distribution of the supporting electrolyte ions at the interface was investigated by labelling one of its two ions by an electroactive group. The concentration profiles established under these conditions allow the distribution of all species to be fully characterized in the diffusion layer, showing the dual influence of migration and convection in one-dimensional mass transport. A very good agreement was observed between the experimental concentrations profiles and predictions based on a model accounting for the influence of spontaneous convection in a macroscopically immobile solution.