(512d) Acid-Functionalized Mesostructured Aluminosilica Films for Proton-Exchange Membrane Applications

Among current technological challenges to the use of Proton Exchange Membrane Fuel Cells (PEMFCs) in automotive or stationary energy applications are their limited operating temperatures. The high ion conduction properties achievable using conventional polymeric PEMFC membranes depend on adequate hydration, which is difficult to maintain at temperatures above 80 ^oC. However, below 100 ^oC, carbon monoxide poisoning of the anode platinum catalyst and diminished oxygen reduction kinetics at the cathode separately limit the performance of PEMFC assemblies.

Acid-functionalized mesostructured aluminosilica materials present a possible solution to the problem of PEMFC operation at elevated temperatures (100-150 ^oC). The membranes are prepared by using amphiphilic block-copolymer species to direct the structures of network-forming silica, which is cast, calcined, and grafted with alumina and acidic species to yield hydrophilic mesostructured channels with interconnected acid-functionalized surfaces. Membrane compositions, structures, and conductivity properties have been characterized by thermogravimetric and elemental analyses, mass spectroscopy, solid-state NMR, electron microscopy, N2 adsorption, small-angle X-ray scattering, and AC impedance spectroscopy. The analyses establish that hydration capacity and water retention of the functionalized membranes exceed those of commercially available Nafion® 117 membranes. Temperature- and humidity-dependent proton conductivities of the membranes will be discussed and compared, along with prospects for integrating the functionalized aluminosilica PEMs into membrane electrode assemblies.