Effect of polymer sulfonation on the proton conductivity and fuel cell performance of polyvinylalcohol-mordenite direct methanol fuel cell membranes

Abstract

Sulfonated polyvinylalcohol-mordenite (SPVA-MOR) membranes for direct methanol fuel cell use were synthesized and characterized. It had earlier been found out that polyvinylalcohol-mordenite (PVA-MOR) membranes, while having excellent methanol permeability and modest proton conductivity values, had inferior direct methanol fuel cell performances than Nafion™. Sulfonating the polyvinylalcohol matrix had been suggested to improve the proton conductivity. In this work, polyvinylalcohol powder was sulfonated by using propane sultone as the sulfonating agent prior to the membrane synthesis. Morphological analyses revealed that the zeolite particles mixed homogeneously within the polymer matrix. Sulfonating the polymer slightly decreased both water and methanol uptakes. Both in PVA-MOR and SPVA-MOR membranes, water uptake turned out to be higher than the methanol uptake. SPVA-MOR membranes were found to have an average proton conductivity of 0.052 S·cm−1 when compared with the 0.036 S·cm−1 of PVA-MOR membranes, while Nafion™ has a proton conductivity of approximately 0.1 S·cm−1. The increase in the proton conductivity upon sulfonation despite the decrease in water uptake was explained by the dominance of the Grotthuss mechanism over the vehicular mechanism for proton conductivity. Fuel cell test results showed that while SPVA-MOR membranes cannot outperform Nafion™, they give higher power output than PVA-MOR membranes, especially at low temperatures and high methanol concentrations. © 2017 Curtin University of Technology and John Wiley & Sons, Ltd. © 2017 Elsevier B.V., All rights reserved.