3500

Figure 3: Durability of 4-cell sub-stack operating on simulated reformate/air under stationary power plant conditions - MEA loading 0.80 mgPtcm"2.

The initial performance on reformate fuel is lower than with pure hydrogen but is close to the 30 mV expected for operation on hjdrogen fuel diluted to 70% with inert components. The poisoning effects of carbon monoxide and carbon dioxide have been eliminated by the combined use of the more poison tolerant Pt/Ru anode catalyst, and a low level 2% air bleed passed directly into the anode chamber. After 3,000 hours of continuous operation on reformate fuel there was little degradation in the performance of the cells, with an acceptable decay rate of 4pVhr"'measured for both reformate and pure hydrogen operation.

Cell Reproducibility

In addition to the high performance and durability the low catalyst loading ME As also exhibit excellent cell to cell reproducibility. This has been retained on scale up from sub-stacks to full stack builds. Figure 4 shows the consistent cell voltages produced by the individual cells in an 80 cell stack built for the air independant propulsion (AIP) application. The MEAs comprise cathodes with 0.6 mgPtcm"2, anodes with 0.25 mgPt cm'5 and NationĀ® 117 membrane. The minimal variation in cell performance over a range of current densities on hydrogen/air operation is clearly evident. This highlights the high degree of consistency achieved in the MEA produced from the high volume manufacturing process and the efficient control of operating conditions throughout the stack.

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