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Current Density / mAcm"2

Figure 1: Ballard Mark V single cell performance of high catalyst loading (8.0 mgPtcm"2) and low catalyst loading (0.62 mgPtcm'2) MEAs.

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Figure 1: Ballard Mark V single cell performance of high catalyst loading (8.0 mgPtcm"2) and low catalyst loading (0.62 mgPtcm'2) MEAs.

These extremely encouraging results represent a successful demonstration of low catalyst loading MEA performance in large scale, practical PEMFC hardware functioning at practical operating conditions.

Durability in Advanced Slack Hardware

The durability of the low cost MEA technology has been evaluated in the range of latest generation Ballard stack technologies, currently under development for application in utility, submarine, bus and automotive applications. Excellent durability has been demonstrated on hydrogen fuel in sub-stack units of 4 to 8 cells and full sized stacks. For example, Figure 2 shows the performance of MEAs with the Dow membrane and anode and cathode catalyst loadings of 0.25 and 0.50 mgPtcm'2 respectively, in a 4-cell stack representative of the second generation bus stacks. After operation for 1,000 hours at 0.65 Acm"2, with approximately 5 hour excursions to 1.1 Acm"\ the degradation rate of less than 4 pVhr"1 successfully meets the durability performance goal.

For stationary power plant and light duty vehicle applications it is likely that the anode fuel will be impure hydrogen (reformate) rather than pure hydrogen, produced via the reforming of hydrocarbon fuels such as natural gas or methanol. Demonstration of satisfactory performance and durability in this environment is much more demanding due principally to anode poisoning by trace levels of carbon monoxide, although carbon dioxide poisoning and dilution effects will also reduce performance levels. Figure 3 shows the long term performance of each cell in a 4-cell sub-stack, operating under stationary power plant testing conditions. The cells contain Du Pont NafionĀ® 117 membrane and are operating with air as oxidant and simulated reformate as fuel (70% hydrogen, 25% carbon dioxide and smaller quantities of contaminants including 10 ppm carbon monoxide). The MEAs comprise low catalyst loading electrodes with a total cell loading of 0.8 mgPtcm"*. The stack was run for 3,000 hours at 0.54 Acm'1 on reformate fuel with intermittent control checks on pure hydrogen fuel to provide comparative decay rate data.

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