Super-Strong Nafion/PVA/Uhmwpe Membranes for Proton and Hydroxide Ion-Exchange Fuel Cells

Abstract

Perfluorosulfonic acid (PFSA) ionomers have been used extensively in proton exchange membranes due to their high proton conductivity and strong electrochemical stability. However, proton and anion conductivity through the PFSA membranes are contingent upon water uptake, but high water content in the membrane causes loss of long-term durability of the fuel cell system because of the water swelling-induced reduction in membrane’s mechanical strengths. Large body of literatures are available to address these issues, for example, hydroscopic nanoparticulate fillers have been used for self-hydration of the membrane, and aligned polytetrafluoroethylene (PTFE) has been employed to reinforce the tensile strengths of the PFSA ionomer. Unfortunately, there is yet no report to date that can resolve pareto fronts issues, i.e., simultaneously having high proton conductivity and high tensile property. Besides, the cost of PFSA membranes, e.g., Nafion, is still prohibitively high. Here, we report a new and low-cost hierarchical membrane with high proton/anion conductivity, low moisture/methanol uptake and super-high tensile strengths. The new membrane is a hybridized composite structure consisting of biaxially oriented nanoporous ultrahigh molecular weight polyethylene (UHMWPE) film coated with Nafion and polyvinyl alcohol (PVA) blend. The tensile strength of the composite membrane is at least 10 times higher than that of the pure Nafion membrane when fully humidified, and the proton and alkaline conductivity is comparable to that of the Nafion/PVA blend. The nanoporous UHMWPE simultaneously acted to provide the high tensile strengths, ion-conductivity selectivity and nanoconfinement to limit the water and methanol uptake. Thus the new hierarchical Nafion/PVA/UHMWPE membrane is potentially an ideal ion-exchange membrane for low temperature hydrogen and direct methanol fuel cells. The work is financially supported by the theme-based research project of the university grants committee of Hong Kong, Grant No. T23-601/17-R