Two relevant mechanisms that impact Membrane Electrode Assembly (MEA) durability in automotive fuel cells, carbon support degradation and Pt dissolution, are discussed in this paper. In the first section, the topic of carbon support stability is discussed. Carbon support corrosion is a concern, especially during cell start-up/shutdown and if fuel starvation occurs in a stack. An accelerated test was developed by subjecting the cathode to high potentials (1.4 V) for a given interval of time and measuring the amount of CO2 in the cathode exhaust. Various carbons were evaluated using this accelerated test protocol. New graphitic supports were selected that demonstrated significantly lower CO2 generation with similar performance to current electrode technology under relevant automotive operating conditions. Utilizing graphitic supports also resulted in lower Pt surface area loss since the carbon supports are more stable under these conditions. The second part of the paper discusses the mechanism of Pt dissolution. A typical automotive drive cycle results in rapid voltage changes in a cell depending on the power demands from the stack. If the cathode potential at any given time is between 0.9 and 1.0 V, Pt dissolution is likely. A voltage cycling test was developed by cycling a single cell from 0.7 V to the Open Circuit Potential (OCP) rapidly for thousands of cycles. The Pt surface area of the cathode and the polarization performance were also measured at various intervals of time. Both Pt and Pt alloys were evaluated using this test, which clearly demonstrated that alloys show much lower Pt loss under these conditions. Both of these mechanisms suggest the use of Pt alloys and graphitic supports as cathode catalysts for MEAs operating in automotive stacks.
Investigation of degradation mechanisms relevant to automotive fuel cells
Untersuchung der für den Brennstoffzellenantrieb von Kraftfahrzeugen relevanten Degradationsmechanismen
2005
10 Seiten, 10 Bilder, 9 Quellen
Aufsatz (Konferenz)
Englisch
British Library Conference Proceedings | 2002
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