Scanning electrochemical microscopy: potentiometric probing of ion fluxes

Abstract

The scanning electrochemical microscope has been used to probe the diffusion layer by measuring the potential difference between a large reference electrode located in the bulk of the solution and a microindicator electrode positioned a few µm away from a substrate electrode. Ag microdiscs (10 and 50 µm diameter) have been used as potentiometric sensors to probe the concentration profile due to the diffusion of Ag⁺ to and from a planar Ag electrode. A similar experiment was carried out with an Ag microcylinder (50 µm diameter) as substrate electrode. In a separate set of experiments, Ag/AgCl microdiscs (10 and 50 µm diameter) were used to monitor the flux of Cl^– consumed and generated by a film of polyaniline electrodeposited on Pt. The tip potential was recorded while cycling the potential of the PANI film past the first oxidation peak. Direct measurement of the ingress and egress of Cl^– ions supports previously reported mechanisms for the oxidation of PANI films.