Anion Exchange Membranes for Fuel Cells: Equilibrium Water Content and Conductivity Characterization

Abstract The ionic conductivity of anion exchange membranes (AEMs) directly determines the performance of anion exchange membrane fuel cells (AEMFCs), which highly depends on the hydration level of the membrane. A better understanding of the relationship between hydration level and membrane ionic conductivity is essential for membrane development and for water and thermal management analyses of AEMFCs. In this study, the effects of water activity and temperature on water uptake, equilibrium water content, and ionic conductivity of three high‐performance AEMs (Alkymer, Orion, and Pention) are quantitatively characterized via the designed experiments. The results show that Orion exhibits the lowest water uptake and highest ionic conductivity among the three membranes at high water activity and Alkymer exhibits good water‐retention capability and the highest ionic conductivity at low water activity. Empirical equations combining water activity and equilibrium water content are proposed based on fitted experimental data to define the hydration level. Empirical equations combining ionic conductivity, equilibrium water content, and temperature are fitted to illustrate the relationship between ionic conductivity and hydration level. The findings of this study can provide solid guidelines and support for the future experimental characterization and water and thermal management analyses of AEMFCs.