Cross-linked poly(vinyl alcohol)/poly (diallyldimethylammonium chloride) as anion-exchange membrane for fuel cell applications

The novel, low-cost anion-exchange membranes (abbreviated as PVA/PDDA-OH^-), made from poly(vinyl alcohol) and poly(diallyldimethylammonium chloride) blends, are successfully synthesized by a combined thermal and chemical cross-linking technique. The hydroxide (OH ^-) conductivity, water uptake, ion exchange capacity (IEC), thermal stability, oxidative stability and alkaline stability of PVA/PDDA-OH^- membranes are measured to evaluate their applicability in alkaline fuel cells. The effects of cross-linking procedure, cross-linking time and membrane composition on OH^- conductivity are studied using AC impedance technique. It is found that by cross-linking modifications, the membranes exhibit excellent thermal stability with onset degradation temperature high above 170 C, a relatively high oxidative stability at 60 C, and a strong alkaline stability in 8 M KOH at 80 C. High OH^- conductivity of 0.025 S cm^-1 is achieved at 25 C and reaches up to 0.037 S cm^-1 at 80 C. For exploring the conducting mechanisms, the concentration and mobility of charge carries of the membranes are also measured. The H ₂/O₂ fuel cell tests with PVA/PDDA-OH^- membranes yield the peak power density of 11.5 mW cm^-2 and greatly increase to 35.1 mW cm^-2 depending on PVA/PDDA mass ratio, on a low metal loading on both the anode and the cathode of 0.5 mg (Pt) cm^-2 at ambient temperature.