A surprising relation between operating temperature and stability of anion exchange membrane fuel cells

Abstract

Anion-exchange membrane fuel cells (AEMFCs) show substantially enhanced (initial) performance and efficiency with the increase of operational temperature (where typical values are below 80 °C). This is directly due to the increase in reaction and mass transfer rates with temperature. Common sense suggests however that the increase of ionomeric material chemical degradation kinetics with temperature is likely to offset the above mentioned gain in performance and efficiency. In this computational study we investigate the combined effect of a high operating temperature, up to 120 °C, on the performance and stability of AEMFCs. Our modeling results demonstrate the expected positive impact of operating temperature on AEMFC performance. More interestingly, under certain conditions, AEMFC performance stability is surprisingly enhanced as temperature increases. While increasing cell temperature enhances degradation kinetics, it simultaneously improves water diffusivity through the membrane, resulting in higher hydration levels at the cathode. This, in turn, encourages a decrease in ionomer chemical degradation which depends on the hydration as well as on temperature, leading to a significant increase in AEMFC performance stability and, therefore, in its lifetime. These findings predict the possible advantage (and importance), in terms of performance and durability, of developing high-temperature AEMFCs for automotive and other applications.