Synthesis and Characterization of Novel Cross-Linked Proton Exchange Membranes for Fuel Cell Applications

Novel cross-linked proton exchange membrane (PEM) materials are promising candidates for the replacement of the benchmark PEM material, Nafion®. Many chemical properties of the cross-linked membrane are desirable for fuel cell applications. The liquid precursor materials are solvent free, and can be directly cured to desired dimensions. A high acidic group content is achieved without rendering the membrane material water-soluble; styrene sulfonic acid perfluoropolyether composite membranes have an average IEC of 0.88 meq/g. Composite membranes were synthesized by UV-inititiated cross-linking of acrylic acid with styrenated-perfluoropolyether and styrene sulfonic acid with styrenated-perfluoropolyether; the liquid monomers were imbibed within Textratex®, a porous expanded PTFE matrix prior to UV curing.

Composite membranes are of particular interest for fuel cell applications since they have competitive conductivities, but require less PEM material, making them a cost effective option. DMTA and TGA analyses indicate that the cross-linked membrane materials possess improved thermal and mechanical properties. Linear sweep voltammetry was used to determine the diffusion coefficient of dihydrogen through membrane materials; linear sweep voltammetry was also used to determine the kinetics of the oxygen reduction reaction at the membrane Pt electrode interface. The development of cross-linked composite membrane materials facilitates the manufacturing of MEAs without the use of Nafion® or volatile organic solvents, while simultaneously decreasing the cost of PEM production.