PBI-based polymer electrolyte membranes fuel cells -: Temperature effects on cell performance and catalyst stability

In this work, it has been shown that the temperature (ranging from 100 to 175 degrees C) greatly influences the performance of H3PO4-doped polybenzimidazole-based high-temperature polymer electrolyte membrane fuel cells by several and complex processes. The temperature, by itself, increases H3PO4-doped PBI conductivity and enhances the electrodic reactions as it rises. Nevertheless, high temperatures reduce the level of hydration of the membrane, above 130-140 degrees C accelerate the self-dehydration of H3PO4, and they may boost the process of catalyst particle agglomeration that takes place in strongly acidic H3PO4 medium (as checked by multi-cycling sweep voltammetry), reducing the overall electrochemical active surface. The first process seems to have a rapid response to changes in the temperature and controls the cell performance immediately after them. The second process seems to develop slower, and influences the cell performance in the "long-term". The predominant processes, at each moment and temperature, determine the effect of the temperature on the cell performance, as potentiostatic curves display. "Long-term" polarization curves grow up to 150 degrees C and decrease at 175 degrees C. "Short-term" ones continuously increase as the temperature does after "conditioning" the cell at 125 degrees C. On the contrary, when compared the polarization curves at 175 degrees C a continuous decrease is observed with the "conditioning" temperature. A discussion of the observed trends is proposed in this work. (c) 2006 Elsevier Ltd. All rights reserved.