Electrochemical Investigation and Modeling of Ion- and Water Transport Through Polymer Membranes

Abstract

The determination of diffusion coefficients in solid materials as a measure of particle mobility is of great scientific interest. This applies for intentional diffusion as for example in fuel cell- and dialysis membranes, as well as to unwanted diffusion in insulating materials. In any case, diffusion is a measure of performance. Especially when considering solvated ion, the permeability of the solvent must also be taken into account. This work presents a measurement method for the simultaneous determination of coupled ion diffusion and water permeability in polymer membranes. For this purpose, measurement methods for the determination of concentration-, volume- and membrane-potential changes are integrated into a miniaturized concentration cell. For the general description of the coupled transport processes, a system of ordinary differential equations is developed. Furthermore, a FEM model is developed in COMSOL Multiphysics®, which specifically simulates the ion distribution within the membrane and the resulting electrical fields. A freestanding ion exchange membrane with largely known properties is then used to evaluate the new combined measurement setup.