ATR-FTIR Analysis of the State of Water in a Sulfonated Block Poly(arylene ether sulfone ketone) Membrane and Proton Conductivity Measurement during the Hydration/Dehydration Cycle

Abstract

We have conducted combined time-resolved ATR-FTIR and proton conductivity measurements of a sulfonated block poly(arylene ether sulfone ketone) membrane, to be called a SPE-bl-1 membrane hereafter, during the hydration/dehydration cycle at room temperature. The result was discussed in comparison with the Nafion NRE211 membrane. Dissociation of the sulfonic acid groups and conductivity change were interpreted in terms of different states of water in the membrane characterized by δ(HOH) bands at 1705 and 1637 cm–1, respectively. The former is assigned to hydrated protons produced by the dissociation followed by hydration. Proton conductivity increases significantly, over 0.1–0.2 S cm–1, after the dissociation is completed at the initial stage of hydration, which is common to both membranes. The 1637 cm–1 band contains contributions from the water in the proton conduction channels as well as some water which is hydrogen bonded to the polar groups in the SPE-bl-1 membrane such as ether (COC), sulfonyl (O═S═O), and carbonyl (C═O). The presence of the latter water lowers the effectiveness of the water in promoting proton conduction in the membrane. It is concluded that incomplete dissociation of the sulfonic acid groups coupled by the lower effectiveness is contributing to the lower proton conductivity of SPE-bl-1 than Nafion NRE211 at low hydration levels.