Results And Discussion

Figure 2 shows the cell potential vs. current density characteristics obtained at several cell and humidification temperatures for the single cells with S and 20 cm2 electrodes assembled with Nafion 117 membrane. The results obtained at a cell temperature of 80 °C with the humidifiers at Tm = 95 °C and T02 = 85 °C show that the increase in the electrode area fïom 5 to 20 cm2 resulted in a small diminution in the performance of the system. Fig. 2 also shows that for T = 80 °C a pronounced decrease in the performance is observed when the humidification of the reactant gases is carried out at the same temperature of the cell. However, the situation is less critical for lower temperatures, although a leveling of the performance occurs for temperatures below 70 °C.

The average cell potential vs. current density characteristics at 80 °C of the single cells with 5 and 20 cm2 electrodes and of the 6 cell stack with 20 cm2 electrodes assembled with Nafion 115 membrane are presented in Figure 3. It is observed that in the case Nafion 115, there is also a diminution of the single cell performance when the electrode area is increased fïom 5 to 20 cm2, although the performance of the 20 cm2 cell presents better characteristics with Nafion 115 than with Nafion 117. On the other hand it is seen that, for current densities up to 0.5 A/cm2, the increase in the number of cells from 1 to 6 introduces only a small decrease in the cell performance.

Figure 4 presents the effect of temperature on the performance of the 21 cell stack assembled using Nafion 115 membrane and electrodes with 20 cm2. It is observed that the average performance of the individual cells is smaller than those of the single cell or those of the 6-cells stack. It is also seen that the increase of temperature presented a positive effect only up to 50 °C, after which a leveling occurs in the system performance.

Figure 2 - Cell potential vs. current density plots for the single cells with 30 wt.% Pt/C, 0.8 mg Nafion/cm2 electrodes.

Current density / A cm-2

Figure 2 - Cell potential vs. current density plots for the single cells with 30 wt.% Pt/C, 0.8 mg Nafion/cm2 electrodes.

0 0

Post a comment