Function and Characterization of Metal Oxide−Nafion Composite Membranes for Elevated-Temperature H₂/O₂ PEM Fuel Cells

Metal-oxide-recast Nafion composite membranes were studied for operation in hydrogen/oxygen proton-exchange membrane fuel cells (PEMFC) from 80 to 130 °C and at relative humidities ranging from 75 to 100%. Membranes of nominal 125 μm thickness were prepared by suspending a variety of metal oxide particles (SiO 2, TiO 2, Al 2 O 3, and ZrO 2 ) in solubilized Nafion. The composite membranes were characterized using electrochemical, X-ray scattering, spectroscopic, mechanical, and thermal analysis techniques. Membrane characteristics were compared to fuel cell performance. These studies indicated a specific chemical interaction between polymer sulfonate groups and the metal oxide surface for systems that provide a good elevated-temperature (i.e., fuel-cell operation above 120 °C) performance. Composite systems that incorporate either a TiO 2 or a SiO 2 phase produced superior elevated-temperature, low-humidity behavior compared to that of a simple Nafion-based fuel cell. Improved temperature tolerance permits the introduction of at least 500 ppm CO contaminant in the H 2 fuel stream without cell failure, in contrast to standard Nafion-based cells, which fail below 50 ppm of carbon monoxide.