Novel cross-linkers for asymmetric poly-AMPS-based proton exchange membranes for fuel cells

Abstract

Polymer electrolyte fuel cells (PEFCs) are an ideal solution leading to clean energy by directly converting the fuel’s chemical energy to electricity in order to achieve high degree of efficiency. One of the main components of PEFCs is the proton exchange membrane which should conduct protons but no electrons and should also separate the electrodes and limit fuel crossover. In addition to Nafion®, polymers of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) have been used as a proton-conducting ionomer since sulfonic groups are known for their good proton conductivity. Since poly-AMPS excessively swells or even dissolve in water, we investigated several commercial cross-linkers and new multifunctional monomers to decrease swelling by cross-linking. Formulations with different concentrations of these cross-linkers have been tested constrained in porous polypropylene membranes. Although formulations with commercial cross-linkers (polyethylene glycol diacrylates) already exceeded the conductivity of Nafion®, with some of the synthesized cross-linkers we achieved more than 2.5 times the conductivity of Nafion®. Moreover, the novel amide-based cross-linkers show good hydrolytical stability in contrast to the commercial ones. Finally, we used one of the new cross-linkers to prepare asymmetric membranes and could achieve about 8 times the conductivity of Nafion.