Investigation of Proton Conductivity of Cation-Exchanged, Sulfonated Poly(b-Styrene-b-Isobutylene-b-Styrene) Membranes

Abstract : In this study, membranes made with highly sulfonated (81%-97%) poly(styrene-b-isobutylene-b-styrene) polymer were exchanged with a variety of cations: Cu, Ba, Zn, Cs, Ag, Ca, and Mg. Absorption levels of the cation-exchanged materials was determined for water, methanol, and an equimolar water/methanol mixture, measured using a gravimetric technique. Proton conductivity of the membranes was measured in a dry state, as well as swollen in water, methanol, and the equimolar water /methanol mixture. Water-swollen membranes showed proton conductivity in the range of 2 x 10(sup-3) to 1.2 x 10(sup2) S/cm, depending on the cation used for exchange. Conductivity increased proportionally to amount to the water molecules present in the membranes. Different cations promoted different levels of water absorption, with Cs and Ag having the highest amounts of water and conductivity, presumably because these two elements had only one valence electron compared to others used in this study.