Electrochemical Studies On Zirconium Phosphotungstate Based Heterogeneous Membranes

Electrode potential measurements have been applied to study electrical characteristics like transport numbers, permselectivity & fixed charge density of ion-exchange membranes. Membrane potential measurements were made across zirconium phosphotungstate cation-exchange membrane maintained at 27◦C, using halide salts of alkali & alkaline earth metals as electrolytes. The effect of concentration of the electrolytes on the transport numbers in the exchanger phase and permselectivity of the membrane has been studied. For the alkali metal salts, transport numbers decrease with increase in concentration. Donnan exclusion of the co-ion becomes less efficient resulting in the decrease in transport number of the counter ion. This phenomenon supports the hypothesis that ion-exchange membranes behave selectively and the permselectivity is established. With an increase in mean electrolyte concentration, permselectivity (Ps) for a cation also decreases, which further supports the hypothesis of Donnan exclusion.