Mixed matrix anion exchange membrane containing covalent organic frameworks: Ultra-low IEC but medium conductivity

As an important component in alkaline electrolyte membrane fuel cells (AEMFCs), anion exchange membranes (AEMs) often suffer from the contradiction between ionic conductivity and dimensional stability. In recent years, covalent organic framework (COFs) materials have received increasing attention based on their good pore structure and rigid skeleton. Here, a quaternized COF (or QCOF) was synthesized by a mechanochemical method, and incorporated into a hydroxyl functionalized polysulfone matrix to make a mixed matrix AEM (or MMAEM). The resultant MMAEM contains abundant hydrogen bond networks and micropores, which synergistically enhance hydroxide conduction; at a QCOF content of 20%, it showed an ultra-low IEC of 0.38 mmol/g but a good conductivity of 14.3 mS/cm at 30 degrees C; the low IEC also gave rise to a low swelling ratio of 2.5% at 30 degrees C, which is superior to most of the conventional AEMs. The MMAEM is also advantageous over conventional AEMs in terms of mechanical stability when exposed to prolonged alkali attack because the non-quaternized polymer matrix is more alkali resistant. Our work provides a new and effective strategy to fabricate robust AEM with good conductivity at a low IEC.