Mechanistic Study of Water Transport in Anion-Exchange Membranes and its Influence on Ionic Conductivity and Fuel Cell Operation.

Abstract

Understanding water transport in anion-exchange membranes (AEMs) is critical to improving their ionic conductivity and operational stability in fuel cell environments. This study investigates the mechanisms governing water uptake and hydroxide ion conduction in two commercial AEMs-FAA-3-50 and A17-featuring distinct polymer backbones and ionic functional groups. After conversion to the hydroxide (OH^-) form, membranes are characterized using gravimetric water vapor sorption, infrared spectroscopy, thickness variation measurements, and conductivity testing under controlled humidity. Results reveal that the chemical nature and spatial accessibility of the ionic group play a central role in modulating hydration, OH^- mobility, and membrane performance. The FAA-3-50 membrane, with a rigid diazabicycle (DABCO)-based group, exhibits limited water uptake and pronounced conductivity hysteresis. In contrast, the A17 membrane, incorporating a more flexible piperidinium group, demonstrates enhanced hydration, lower hysteresis, and better retention of ionic conductivity under varying humidity. The findings underscore the impact of water-ionomer interactions on membrane dimensional stability and conduction mechanisms. Ultimately, the study provides insights into designing advanced AEMs through tailored ionic functionalities and controlled water management, essential for high-performance and durable AEM fuel cells, particularly under low-humidity or dynamically fluctuating conditions.