Molecular Optimization of Multiply-Functionalized Mesoporous Films with Ion Conduction Properties

The performance and stability of hydrogen fuel cells could be improved by operation at elevated temperatures (>100 °), which would provide faster kinetics of the anode and cathode reactions, higher permissible CO levels in the hydrogen feed stream, more effective water management, and efficient heat recovery. However, current industrial proton exchange membranes based on perfluorinated sulfonic acids (PFSAs, e.g., Nafion^TM) limit hydrogen fuel cell operation to relatively low temperatures (<100 °) and high humidities, which lead otherwise to reduced proton conductivities as the hydrophilic ion-conducting channels dehydrate and become disconnected. We have developed a novel proton-exchange-membrane material based on PFSA-functionalized nanostructured aluminosilica for the operation of hydrogen fuel cells at elevated temperatures (>100 °) and in dry environments. These organic-inorganic hybrid membranes are designed to maintain their proton-conducting channels by exploiting their robust aluminosilica frameworks with interconnected pores that remain open, independent of the extent of hydration, thus sustaining proton-conduction properties at elevated temperatures and low humidities. The mesoporous membranes are synthesized by using block copolymers to direct the formation of cubic mesostructured silica films, which are subsequently functionalized with aluminosilica and PFSA species. Molecular, mesoscopic, and macroscopic properties of the multiply-functionalized films have been characterized and correlated at each stage of the syntheses by NMR, small-angle X-ray and neutron scattering, transmission electron microscopy, elemental analysis, adsorption, and conductivity measurements. The resulting materials have a novel combination of stable mesopores, high hydrophilicities, and maintain high proton conductivities at elevated temperatures and under low humidity conditions.