A new transfer function in electrochemistry: Dynamic coupling between Raman spectroscopy and electrochemical impedance spectroscopy

A new type of transfer function is described in this work as a tool to give support to modeling in electrochemical kinetics. It is based on the response analysis with frequency to a sine wave potential modulation applied to an electrode, of a Raman band, the intensity of which is proportional to the response of surface concentration of an adsorbed species.A set-up, consisting of a Raman spectrometer with a CCD detector from which the Raman intensity was defined and extracted to be converted into a tension sent to the input of a multichannel FRA, was implemented. The procedure for extracting the Raman band intensity is explained and was validated by using, as a substitute to the Raman band, a LED light.The method was applied to the study of the polyaniline doping process in a pH range around 3. Five input channels of the FRA were devoted to Raman bands characterizing leucoemeraldine, emeraldine base and/or salt. For pH lower than 3, the concentrations of all moieties are in phase with the charge, while above 3, emeraldine base shows a significant phase lag. This behavior is consistent with a model in progress involving two electrochemical steps and a chemical one.