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 m eans of cyclic voltammetry (CV) and a.c. impedance spectroscopy. Impedance plots are analyzed by a non-linear least-squares fitting method. The transp ort (diffusion coefficient), interfacial parameters (double layer capacitan ce), and total resistance of the SPSF membrane coated electrodes are invest igated as the function of sulfonic acid group concentration in the SPSF mem brane, membrane thickness, electrolyte concentration, and reduction potenti al. The diffusion coefficients are found to vary between 1.082 x 10(-12) an d 1.136 x 10(-11) cm(2) s(-1) as the sulfonic acid group concentration is i ncreased from 0.672 to 1.18 mmol/g membrane at open circuit voltage. The do uble-layer capacitance depends on electrolyte concentration and reduction p otential, and sulfonic acid group concentration, but not on the membrane th ickness. The total resistance depends on sulfonic acid group concentration, electrolyte concentration, membrane thickness, and reduction potential. (C ) 1999 Elsevier Science S.A. All rights reserved.