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.
Conventional carbon MEAs and graphitized carbon MEAs were evaluated for the resistance to carbon corrosion and startup/shutdown durability in this paper. Graphitized carbon MEAs show higher resistance to carbon corrosion than conventional carbon MEAs by a factor of 35 at a point where 5% weight loss had occurred. A graphitized carbon MEA yielded lower degradation rate than that of a conventional carbon MEA by a factor of 5 after 1,000 startup/shutdown cycles. The kinetics of carbon corrosion over both conventional carbon MEAs and graphitized carbon MEAs were measured, and carbon corrosion during startup/shutdown was explained and modeled. The model results correlate to what we have measured from our startup/shutdown durability test. Overall, MEAs with corrosion resistant carbon supports are one of major materials approaches to mitigate cell voltage degradation due to fuel cell startup/shutdown. We believe that a combination of corrosion resistant materials and system operating mitigation strategies is the path to attain the strict automotive durability targets.
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