Impedance characteristics of a rotating disc electrode coated with a sulfonated polysulfone cation-exchange membrane

The transport of sodium ions through a sulfonated polysulfone (SPSF) cation-exchange membrane coated on a rotating disc electrode is investigated by means of cyclic voltammetry (CV) and a.c. impedance spectroscopy. Impedance plots are analyzed by a non-linear least-squares fitting method. The transport (diffusion coefficient), interfacial parameters (double layer capacitance), and total resistance of the SPSF membrane coated electrodes are investigated as the function of sulfonic acid group concentration in the SPSF membrane, membrane thickness, electrolyte concentration, and reduction potential. The diffusion coefficients are found to vary between 1.082×10−12 and 1.136×10−11 cm2 s−1 as the sulfonic acid group concentration is increased from 0.672 to 1.18 mmol/g membrane at open circuit voltage. The double-layer capacitance depends on electrolyte concentration and reduction potential, and sulfonic acid group concentration, but not on the membrane thickness. The total resistance depends on sulfonic acid group concentration, electrolyte concentration, membrane thickness, and reduction potential.