Method for the determination of self-diffusion coefficients of trace metal ions in ion-exchange membrane

Nafion-117 is one of the most studied ionomer membrane and is extensively used in different industries. The self-diffusion coefficient (SDC) of individual cations in the membrane is useful for understanding their transport properties within the membrane. Non-stationary radiotracer method is well established for the determination of SDCs of metal ions and is advantageous over other literature reported methods like radiotracer permeation, conductivity/impedance measurements. This method is essentially based on the analysis of kinetics of isotopic exchange in the membrane using an analytical solution of Fick's second law. In this method, it is assumed that, (i) diffusion is membrane controlled, (ii) SDC of any species within the membrane is constant and (iii) diffusion is one dimensional. However, this method assumes a constant and saturated membrane surface thereby needing infinite solution concentration or continuous renewal of solution. Therefore, the method cannot be used for determining SDC of ions present in trace quantities. With this in view, in the present work, a method based on ion-exchange kinetics has been explored to obtain the SDC of ions present in trace amounts