Three-phase interlines electrochemically driven into insulator compounds: A penetration model and its verification by electroreduction of solid AgCl

A dynamic three-phase interline model has been developed for the reduction of a solid insulating metal compound to the metal in a suitable electrolyte, focusing on the electrochemically driven penetration of the process (or the three-phase interlines) into the insulator. Consideration is given to the effects of electrochemical, concentration and ohmic polarizations in the reduction-generated porous metal layer on top of the solid compound. Under potentiostatic conditions, reduction in the depth direction (penetration) becomes progressively slower as a result of the rising ohmic and concentration polarizations, whilst the electrochemical polarization exerts a declining effect. The quantitative equations established here also provide simple methods for the determination of some kinetic parameters of the reduction process, including p (total resistivity) and D-R (diffusion coefficient). The model has been experimentally verified by electrochemical reduction of solid AgCl with two novel metal vertical bar AgCl cylinder electrodes in aqueous solutions.