A simple currentless method of determination of ion fluxes to and within electroactive ion-exchange membranes

A simple protocol applicable for the determination of ion fluxes from a solution to an ion-exchange membrane and within it was proposed. Advantages of this method include the application of a simple typical potentiometric set-up, as the method uses open circuit potential measurements; thus, the membrane state is not biased by external polarization. The proposed approach is based on the analysis of potential vs. time dependences in the course of building up or disappearance of a diffusion layer in a solution, controlled by solution stirring. Using equations describing diffusion processes, both ion fluxes from a solution to a membrane and within the membrane can be calculated. Experimental studies were carried out on examples of electrodes coated by two different kinds of membranes: (i) poly(vinyl chloride)-based silver-selective membrane and (ii) polypyrrole film doped by poly(4-styrenesulfonate) ions, in solutions of silver ions. The results obtained for non-saturated silver-selective membranes highlight the role of membrane thickness and conditioning time as well as confirm the role of diffusion in the membrane as a rate-determining step. For polypyrrole layers, the ion flux results from silver deposition in the surface part of a conducting polymer film, and the flux value was found consistent with silver deposition rate determined earlier.