Figure 2 Polarization curves obtained at various operating conditions

In order to evaluate the durability of IMRA MEMBRANE, the cell was run continuously for about 250 hours. As shown in Figure 3, the cell voltage was stable during this period at the constant current operation. The difference in ion exchange capacity between before and after the run was within experimental error. Thus we concluded that no appreciable decomposition of the membrane occurred in this time range. We are now attempting another life time test for a longer period. It has been reported that sulfonated styrene grafted FEP is subjected to decomposition, when it is used as an electrolyte for a fuel cell, showing the increase in electric resistivity just after the start of cell operation (1). This decomposition has been ascribed to the scission of the grafted polystyrene side chains (1). We also confirmed the similar phenomenon with FEP matrix films. However, the membrane made from ETFE showed different characteristics: higher mechanical strength and chemical stability. If the styrene side chains were subjected to decomposition, the membrane made from ETFE would behave the same way. Thus we postulate another mechanism for the decomposition as follows:

Figure 2 shows polarization curves obtained with IMRA MEMBRANE and electrodes at various running conditions. In the case of hydrogen/oxygen feed gases, the cell could be run at broad temperature range for the cell and humidification bubbler. On the other hand, the cell with air feed gas tended to dry up unless the running condition was carefully chosen. The cell temperature was lowered or the amount of water vapor supplied with gases was increased compared with the case of hydrogen/oxygen feed gases so that the cell could keep constant performance.

> O H2/02 1.5 atm/1.5 atm, gas utilization 50% / 50% ~ 0.4" " A

0> A H2/021.1 atm/1.1 atm, gas utilization 50% /50%

A H2/Airl.5 atm/1.5 atm, gas utilization 50%/20%

0.2" - ^ H2/Air 1.1 atm/1.1 atm, gas utilization 50% /20%

0 0

Post a comment