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Current density / A cm-2 Figure 3 - Average cell potential vs. current density plots for the single cells and 6-cells stack.

The following observations can be made from the results of this work: (i) for Nation 117, the scale-up of the electrodes from 5 to 20 cm2 introduced a small increase in the slope of the linear region of the polarization curves which is an indication of an increase of electrolyte resistance probably associated with the water balance; (ii) for Nation 115, the effect of the electrode scale-up is related to a parallel shift of the curves, probably associated with some gas cross-over and/or a diminution of platinum effective area; (iii) the increase in the number of cells in the stack leads to a increase in the slope of the linear region indicating problems regarding the water management; (iv) the performance of the several stacks assembled in this laboratory with low catalyst loading electrodes showed that the power generation is of the order of 0.35 kW/gPt at 0.5 A/cm2. In the same region of current densities, the values reported for high platinum loading electrodes are in the range of 0.05 to 0.1 kW/gPt (7-13) thus showing that utilization of low catalyst loading electrodes provides a better situation with respect to platinum utilization.

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