ELECTROCHEMICAL MASS-TRANSPORT STUDIED BY PROBE BEAM DEFLECTION - POTENTIAL STEP EXPERIMENTS

The deflection of a probing laser beam aligned parallel to a planar electrode was monitored during potential step experiments. The electrochemical systems investigated were Ag deposition and dissolution on Pt, the Fe(CN)63-/4- redox reaction on Pt and the electrochromic charge storage reaction in anodic iridium oxide (AIROF) films. The experimental probe beam deflection (PBD) transients can be simulated using simple models for the concentration profiles developed for mass transport controlled reactions. The results show that different approaches have to be used for mass transport controlled reactions and for reactions limited by a depletion of the reactant or reacting sites. The PBD transients measured for different beam distances allow the determination of the diffusion coefficients of the moving ions. In order to measure the diffusion coefficient of a single ion a supporting electrolyte has to be used. On the basis of the presented examples the relation between cyclic deflectograms and voltammograms is also briefly discussed.