Highly stable hydroxyl anion conducting membranes poly(vinyl alcohol)/poly(acrylamide-co-diallyldimethylammonium chloride) (PVA/PAADDA) for alkaline fuel cells: Effect of cross-linking

Highly stable hydroxyl anion conducting membranes have been developed using poly(vinyl alcohol) (PVA) as matrix by incorporation of poly(acrylamide-co- diallyldimethylammonium chloride) (PAADDA) as anion charge carriers. In order to clarifying the cross-linking effect on membrane performances, two series of PVA/PAADDA membranes were prepared by direct and indirect chemical cross-linking ways, and have been characterized in detail at structural and hydroxyl ion (OH^-) conducting property by FTIR spectroscopy, thermal gravity analysis (TG), scanning electron microscopy (SEM), water sorption, ion exchange capacity and alkaline resistance stability. The OH^- conductivity of the membranes increased with increasing the content of PAADDA in polymer and temperature, and reached 0.74-12 mS cm^-1 with direct cross-linking way and 0.66-7.1 mS cm^-1 with indirect cross-linking way in the temperature range 30-90°C. The membranes are found to have the same IEC values but the membranes with direct cross-linking way showed higher water uptake than that with indirect cross-link one. Both membranes showed the thermal stability above 200°C, and can integrity in 100°C hot water and methanol solution, where the swelling are better suppressed as high dense chemical cross-linkages in PVA network. Very low methanol permeability (from 1.82 × 10^-7 to 3.03 × 10^-7 cm² s^-1) in 50% methanol solution was obtained at 30°C. Besides, the chemical stability in 80°C, 6 M hot alkali conditions and long-term stability of 350 h in 60°C hot water revealed that the PVA/PAADDA membranes are promising for potential application in alkaline fuel cells.