No abstract

This paper discusses methodologies to evaluate durability of catalyst and carbon-support materials used in Polymer Electrolyte Membrane (PEM) fuel cells under relevant automotive accelerated test conditions. Durability of carbon-supported Pt and Pt-alloy catalyst is evaluated under an accelerated voltage- cycling protocol, developed by analyzing idle-to-peak power load-transients of various automotive drive-cycles. Results indicate that Pt catalysts on conventional carbon supports (Pt/C) are unlikely to meet automotive durability target; however, given no loss in specific-activity over time, Pt- alloys are likely to be successful. Shutdown/startup of fuel cell stack and local fuel starvation are recognized as an accelerating mechanism for carbon-support corrosion. Conventional and corrosion-resistant supports are evaluated under an accelerated protocol (1.2V vs. RHE). Corrosion of these currently used supports induces unacceptable mass- transport related performance loss at high current densities. Implementation of corrosion-resistant supports in high- performance electrodes, combined with controlled system strategies, will most likely lead to automotive carbon support durability targets being met.

The use of 12-tungstophosphoric acid ͑HPW͒ as the ionomer in high temperature, Ͼ100 °C, proton exchange membrane fuel cells ͑PEMFCs͒ was investigated. Since HPW is a crystalline solid, the material is more conveniently studied in membranes fabricated from composites of polymers and HPW. A commercially available high-temperature epoxy was chosen as the polymer for our initial studies. The ionomer was added, either by mixing the HPW with the uncured epoxy or by soaking a cured epoxy membrane in an aqueous solution of HPW. Sulfonated and unsulfonated epoxy membranes, with and without HPW, were fabricated. The structure of the composite membranes was characterized using attenuated total reflectance infrared spectroscopy, small angle X-ray scattering, scanning electron microscopy, and thermal gravimetric analysis. Fuel cell polarization curves were obtained for the membranes under varying conditions of temperature and humidification. A trend of increasing current density was noted with increasing temperature for the HPW-doped sulfonated epoxy membrane. All of the membranes exhibited sufficient mechanical strength to 165 °C. Where the sulfonated epoxy, without HPW, failed at temperatures above 165 °C, the sulfonated membranes with HPW functioned in the fuel cell to р200 °C.