Characterisation of crosslinked poly(vinyl alcohol)-based membranes with different hydrolysis degrees for their use as electrolytes in direct methanol fuel cells

The effect of the degree of hydrolysis of poly(vinyl alcohol) (PVA) substrates on the preparation and properties of crosslinked membranes prepared via esterification with sulfosuccinic acid (SSA) has been studied using attenuated total reflectance—Fourier transform spectroscopy (ATR–FTIR) and thermogravimetric analysis (TGA). Three PVA substrates with degrees of hydrolysis of 89, 96, and 99% were crosslinked using SSA at high temperatures. FTIR spectroscopy revealed that esterification occurred in all the membranes and to some extent, prior to heat treatment. The final morphology of the membranes was dependent on both the SSA concentration and the composition of the PVA substrate. Thermogravimetric analysis showed an increase in the thermal stability of the PVA-SSA membranes with respect to their PVA substrates arising from the formation of a crosslinked structure. In addition, TGA revealed the presence of free and tightly bound water in the PVA-SSA membranes. Thermal treatment had a more pronounced effect on the properties of the PVA substrates having higher degrees of hydrolysis. The results from the swelling tests, the ionic exchange capacities (IEC) and the tests in DMFC monocells demonstrated that a balance between water and methanol selectivity and ionic conduction determines the potential of these materials to act as electrolytes in fuel cells.