Elucidating the role of anion-exchange ionomer conductivity within the cathode catalytic layer of anion-exchange membrane fuel cells

Abstract

The anion-exchange ionomer (AEI) is a crucial component of anion-exchange membrane fuel cells (AEMFCs). In this study, computational analysis is employed to study the unexplored and critical effect of AEI hydroxide conductivity, within the cathode electrode, on AEMFC performance and its stability. The cathode is of particular importance due to its tendency to dry-out in a manner that may impact ionomer conductivity during AEMFC operation. Our modeling results clearly show that enhanced AEI hydroxide conductivity, within the cathode, significantly increases AEMFC performance. Less intuitive is its positive impact on cell stability. Superior conductivity is associated with high catalyst utilization and a reduced potential drop across the cathode. This enhances hydration levels in the cathode resulting in slower degradation kinetics. While the cathode reaction kinetics is considered as a major factor restricting cell performance, the transport of water and hydroxide through the cathode catalyst layer is extremely critical to ensure long-term AEMFC performance stability. In addition, a two-step degradation mechanism is observed where initially the voltage loss is controlled by the cathode AEI degradation, and only later membrane degradation becomes dominant. These insights are critical for understanding cell operation and for the achievement of further progress in AEMFC performance stability.