Anion exchange membranes for AMFC devices

Alkaline membrane fuel cells (AMFCs) are considered as an alternative to polymer electrolyte fuel cells (PEFCs) regarding to some limitations such as high CO poisoning, higher fuel crossover, a difficult oxygen reduction reaction (ORR) and the use of precious metal catalysts. On the contrary, the problems related to the performance and durability of anion exchange membranes due to degradation mechanisms in alkaline media, are the critical issues to be solved. Moreover, the nature of quaternary agents and the solvent used for membrane preparation have a significant effect on the mechanical properties of the membrane, their swelling and conductivity. In this work, it is reported a series of synthesized quaternary ammonium-functionalized polysulfones. Different functionalization degrees ranging from 60 to 150% were evaluated and triethylamine (TEA) and trimethylamine (TMA) quaternary agents were investigated, in order to identify the optimal functionalization degree for better performance in fuel cell. A degree of functionalization of 100% was found as the best compromise between chemical-physical properties and mechanical stability. A power density of 293 mW/cm2 for TEA based-sample at 60°C in H2/O2 fuel cell was found. Regarding commercial polymers, recast membranes based on a commercial FAA3 ionomer was carried out investigating solvents and temperature (50 and 80°C) of the casting. Ion exchange capacity, water retention, thermal stability, anion conductivity and fuel cell performance were studied. It was found that the solvent effect is more evident when 50°C is used as a casting temperature producing membranes with higher conductivity but lower thermal stability. On the contrary, when 80°C was used as a casting temperature, membranes with a lower water uptake, a higher thermal stability and a slightly lower conductivity were obtained.