Properties and Parameters of Importance for Enhanced Performance and Performance Stability of Anion Exchange Membrane Fuel Cells – a Modeling Study

Abstract

Research and development of anion exchange membrane fuel cells (AEMFCs) has placed a large focus on cell performance. For example, one of the main goals of anion exchange membrane (AEM) materials development has been the increase of their hydroxide conductivity, which directly enhances AEMFC performance. Although crucially important, achieving high performance is not enough since robust AEMFCs must exhibit both high performance AND high performance stability (i.e. longevity). In this contribution we present results from one-and-three dimensional modeling studies aimed at elucidating the impact of a number of key AEM material properties, as well as AEMFC design and operating parameters, both on performance and on performance stability. Using a one-dimensional model of AEMFC operation [1], which includes AEM chemical degradation analysis capabilities [2], we discuss the relative importance of membrane conductivity, membrane thickness and membrane water diffusivity. In particular, we demonstrate that although conductivity is an important AEM property where cell performance is concerned, its impact on longevity is minimal. Thus developing an AEM which promotes enhanced cell performance and cell performance stability requires a focus both on conductivity and on other properties and/or parameters which do impact stability. Our results show that one of these is AEM water diffusivity which strongly influences AEMFC performance stability and should therefore (in addition to conductivity) be on the list of important properties and parameters to be tailored in the next generation of AEMs. In addition to our one-dimensional analysis, we employ a full three-dimensional model of an AEMFC to explore additional properties and parameters of importance. In particular, we discuss the impact of system geometry (flow field patterns) as well as gas flow rates (gas stoichiometry) on performance, and propose possible related routes to process improvement.