Ring–disc electrodes. Part 24.—Studies of counterion fluxes at a thionine-coated electrode

Abstract

The ring electrode of a ring–disc electrode can be used as a potentiometric detector for halide ions, X^–, by coating the ring electrode with Ag/AgX. The flux of halide ion at the disc surface can then be measured. The theory for this technique is developed and shown to be in good agreement with experiment when known fluxes of Cl^–, Br^– or I^– are generated at the disc. The technique has been applied to the measurement of the flux of Cl^– entering or leaving a polythionine coated disc electrode as the coat is reduced or oxidised. In either direction the Cl^– transient has the same shape as the current transient. This shows that electron transport, as opposed to counterion diffusion, is the rate-limiting process in the reduction and oxidation of the coat.