Electrochemical parameters of sulfonated poly(ether ether sulfone) membranes in HCl solutions determined by impedance spectroscopy and membrane potential measurements

Electrical and electrochemical properties of different samples of sulfonate d poly(ether ether sulfone) (SPEES) membranes with different sulfonation de grees (0%, 5% and 10%) were determined measuring the electrical resistance and concentration potential with the membranes in contact with HCl solution s at different concentrations. Impedance spectroscopy (IS) was used to dete rmine the membrane resistance (R-m) using equivalent circuits as models, an d the results show how the sulfonation clearly affects the membrane electri cal characteristics, strongly reducing the R-m and also changing the type o f circuit associated with the different membranes. The determination of bot h the proton transport number and the membrane permselectivity to H+ ions i n sulfonated samples was performed by measuring concentration potentials (D elta phi). Proton diffusion in the sulfonated membranes were determined fro m R-m and Delta phi values and a strong reduction in the membrane electrica l resistance and an increase in the H+ diffusion coefficient was observed w ith the increase of the sulfonation degree. A chemical characterization of the surface of nonsulfonated and sulfonated samples was also carried out by X-ray photoelectron spectroscopy (XPS). (C) 2001 Elsevier Science B.V. All rights reserved.