Quantifying the critical effect of water diffusivity in anion exchange membranes for fuel cell applications

Abstract

During the past decade, one of the main goals of research and development of anion exchange membrane fuel cells (AEMFCs), was to increase the hydroxide conductivity of the anion exchange membranes (AEMs); this goal is based on the obvious and known impact of AEM conductivity on AEMFC performance (including efficiency). We propose a paradigm shift according to which a main AEMFC research goal should be to increase membrane water diffusivity. This is a result of detailed and quantitative computational analyses of AEMFC performance and its stability, presented in this manuscript. Our modeling results clearly show that, while improved AEM hydroxide conductivity is truly important for the achievement of high cell performance, enhanced water diffusivity through the membrane is extremely critical to ensure long-term AEMFC performance stability, as required by practical automotive and other applications. Superior water diffusivity, which is imperative for increasing water transport from the anode towards the cathode, provides improved levels of hydration. This has a favorable impact on performance but, more importantly, it promotes a reduction in ionomer chemical degradation and as a result leads to a significant improvement in AEMFC performance-stability and (therefore) in its lifetime.