An electrochemical and theoretical comparison of ionic transport through a polystyrene-based cobalt arsenate membrane

An organic–inorganic composite material, i.e. polystyrene cobalt arsenate was chemically synthesized by a sol–gel process. The physico-chemical of the membrane was determined using SEM, TGA and XRD studies. The membrane was found to be crystalline in nature with uniform arrangement of particles and no sign of visible cracks. Ionic potentials were measured across polystyrene cobalt arsenate membranes with 1:1 electrolytes at different concentrations. Observed membrane potentials were positive. The membrane potential offered by the electrolytes was in the order of KCl > NaCl > LiCl. The successful application of TMS and Kobatake theory were used for the estimation of the charge density of membranes. The order of charge density for 1:1 electrolytes solution was found to be KCl > NaCl > LiCl. Kobatake's equation was used under two limiting conditions, namely in the high concentration range and in the dilute concentration range. The two limiting forms of Kobatake's equation gave identical values of charge density for the membrane taken in this investigation. The TMS method was used to investigate the transport number of ions, mobility ratio, distribution coefficient, charge effectiveness, perm selectivity and concentration of fixed charge of the membranes.

Plots of membrane potentials versus −log C2 for the polystyrene-based cobalt arsenate membrane. Smooth curves are the theoretical concentration potentials (D¯=1) using electrolytes at different mobility ratios (u¯/v¯=2.1,   2.2,   2.3,   2.4   and   2.5). The broken line depicts the experimental membrane potentials for different concentrations of KCl solution.Figure optionsDownload as PowerPoint slideHighlights
► Membranes were characterized by SEM, XRD and TGA analysis.
► Observed membrane potentials are positive.
► Membrane is cation-selectivity.
► Membrane potential of electrolytes follow order KCl > NaCl > LiCl.
► The successful application of TMS and Kobatake theory to obtain charge density.