Evaluation of transport mechanism and nanostructure of nonperfluorinated PVA/sPTA proton exchange membrane for fuel cell application

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Abstract
Polyvinyl alcohol (PVA) with sulfophthalic acid (sPTA) as a proton exchange membrane (PEM) for fuel cell applications was prepared by the solvent casting method. The fabricated membranes were obtained by varying the concentration of sPTA from 5 to 30 wt.% of PVA and thermally crosslinked at a temperature of 100°C for 1 h. Crosslinked PVA/sPTA membranes were characterized by FTIR spectroscopy, scanning electron microscopy (SEM), and wide‐angle X‐ray diffraction (XRD). The transport properties were investigated by determining ion exchange capacity (IEC), water uptake, methanol permeability, and proton conductivity. Free volume hole size and its distribution of crosslinked PVA membrane were measured by positron annihilation lifetime spectroscopy (PALS). With an increase in sPTA concentration in the PVA membrane, both IEC and proton conductivity increased, but water uptake and methanol permeability decreased. At room temperature, IEC values were increased from 0.3 to 1.6 meq/g, and proton conductivity varied from 0.2 to 3.5 S/cm. According to PALS data, increasing the sPTA content causes the free volume content of crosslinked PVA membranes to decrease. The results were analyzed and presented in the context of free volume theory, in which the concentrations of nanostructure free volume defects are related to the membrane's transport capabilities.

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