In U.S. Patent 7,645,856 National Research Council of Canada (NCRC) (Ottawa, Ontario, CA) fuel cell scientists reveal nanostructured ether nitrile co-polymers containing sulfonic acid groups for proton exchange membrane fuel cell applications. The low cost nanostructured membranes perform as well as current state-of-the-art membranes now on the market.
During the past several years, proton conducting polymers have attracted much attention due to their considerable promise for applications in some electrochemical devices, such as displays or sensors, and which is most important, as proton exchange membranes (PEM) in PEM fuel cells (PEMFC) and direct methanol fuel cells (DMFC).
In PEMFCs and DMFCs, PEMs serve as separators for the reactants, catalysts support and provide the required ionic pathway between the anode and the cathode. Therefore, their properties such as proton conductivity, water maintenance, permeability for fuel and chemical stability are crucial for the fuel cells performance.
Although perfluorosulfonic acid ionomers such as Nafion™, developed by DuPont, are considered state-of-the art, their high cost, difficulty in preparation, high methanol crossover and dramatic decrease in proton conductivity at temperatures over 80.degree. C. due to the dehydration of membranes limit their further applications. As a response to the commercial need for less expensive and more versatile polymer electrolytes, the synthesis and characterization of new membrane materials has become an active research area with literally hundreds of on-going research projects around the world, many involving nanotechnology techniques or nanomaterials.
CNRC researchers Yan Gao, Michael D. Guiver, and Gilles P. Robertson fabricated nanostructured ether nitrile co-polymers containing sulfonic acid groups, including wholly aromatic poly(aryl ether ether nitrile)s containing sulfonic acid groups (SPAEEN)s, and poly(phthalazinone ether ketone nitrile) co-polymers containing sulfonic acid groups (SPPEKN)s, intended for fuel cells applications as proton conducting membrane materials.
P-SPAEENH and m-SPAEENH films show proton conductivities close to or higher than those of Nafion 117 at similar water uptake and swelling values. The combination of inexpensive monomers, high thermal stability, low dimensional swelling, and high proton conductivity makes m-SPAEENH-50, m-SPAEENH-60, P-SPAEENH-50 and P-SPAEEN-60 attractive as PEM materials for fuel cells applications up to 100.degree. C. or 80.degree. C. respectively.
In addition, polar nitriles in the hydrophilic domains of nano phased separated film may also interact with the water molecules confined in the pore, which would assist in enhancing the water confinement. As a result, hot water-soaked rn-SPAEENH-50 and m-SPAEENH-60 show higher proton conductivities even after having been cooled down to room temperature. At higher temperatures, water uptake and proton channels tend to be the same no matter how the membranes were treated initially; their proton conductivities tend to be the same.
