Quantitative discrimination of mass fluxes at electrochemical interfaces by optical beam deflection

The use of the mirage effect, also termed optical beam deflection, as a quantitative and not just a qualitative analytical technique of mass exchange characterization at the electrochemical interface is demonstrated. In situ coupling of the mirage effect technique with cyclic voltammetry gives way, in a first step, to the determination of the nature of the ionic species exchanged between an electroactive surface and a solution. In a second step, mathematical treatment of the signals by temporal convolution is used to rectify the influence of the propagation delay due to the diffusion of species between the electrode surface and the laser beam. In a third step, probing the diffusion layer by measuring several mirage deviations at different distances from the electrode surface, leads to the determination of the specific diffusion coefficients of ions exchanged at the electrode I solution interface in the case of a binary electrolyte. Finally, the application of the mirage technique to the analysis of the redox behavior of unknown materials, but in a known binary electrolyte, allows the discrimination of anionic and cationic fluxes during the electrochemical process. Measurement of transference numbers by this approach shows that they vary with time and potential and therefore that they are dynamic quantities contrary to what it is generally believed. (C) 1999 Elsevier science S.A. All rights reserved.