Polystyrene-based vanadium phosphate membranes prepared by a sol-gel route process from aqueous solutions were studied. The uni-univalent electrolytes (KCl, NaCl, and LiCl) were diffused from the feed solution as a carrier through the prepared membranes with saturated calomel electrodes. The Teorell, Meyer, and Sievers equation was used to estimate the membrane potential, surface charge density, distribution coefficient, transport numbers, and other electrochemical parameters to characterize the prepared membranes. The membrane potentials offered by the uni-univalent electrolytes through prepared membranes were cation selective and found to be in the order LiCl > NaCl > KCl. The membranes prepared at lower pressures had wider pores and an essentially low surface charge density, whereas membranes prepared at higher pressures carried a high surface charge density and narrow surface openings. The order of charge effectiveness of the electrolytes in the membranes depended on the hydration of the solute-solute interaction and ionic radii of the counterions. The experimental results for membrane potential were consistent with the theoretical prediction. The morphology of the membrane surface was studied by scanning electron microscopy. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 3023-3030, 2008