Water Uptake Study of Anion Exchange Membranes

Anion exchange membrane fuel cells (AEMFCs) have attracted extensive attention in the recent years, primarily due to the distinct advantage potentials they have over the mainstream proton exchange membrane fuel cells. The anion exchange membrane (AEM) is the key component of AEMFC systems. Because of the unique characteristics of water management in AEMFCs, understanding the water mobility through AEMs is key for this technology, as it significantly affects (and limits) overall cell performances. This work presents a study of the equilibrium state and kinetics of water uptake (WU) for AEMs exposed to vapor source H2O. We investigate different AEMs that exhibit diverse water uptake behaviors. AEMs containing different backbones (fluorinated and hydrocarbon-based backbones) and different functional groups (various cations as part of the backbone or as pendant groups) were studied. Equilibrium WU isotherms are measured and fitted by the Park model. The influence of relative humidity and temperature is also studied for both equilibrium and dynamic WU. A characteristic time constant is used to describe WU kinetics during the H2O sorption process. To the best of our knowledge, this is the first time that WU kinetics has been thoroughly investigated on AEMs containing different functional groups. The method and analysis described in this work provide critical insights to assist with the WU level at equilibrium backbones and cationic design of the next-generation anion conducting polymer electrolytes and membranes for use in advanced high-performance AEMFCs.