Protocol for Evaluating Anion Exchange Membranes for\nNonaqueous Redox Flow Batteries

Nonaqueous redox flow batteries often suffer from reduced battery\nlifetime and decreased coulombic efficiency due to crossover of the\nredox-active species through the membrane. One method to mitigate\nthis undesired crossover is to judiciously choose a membrane based\non several criteria: swelling and structural integrity, size and charge\nof redox active species, and ionic conductivity. Most research to\ndate has focused on reducing crossover by synthesizing modified redox-active\nmolecules and/or new membranes. However, no standard protocol exists\nto compare membranes and a comprehensive study comparing membranes\nhas yet to be done. To address both these limitations, we evaluate\nherein 26 commercial anion exchange membranes (AEMs) to assess their\ncompatibility with common nonaqueous solvents and their resistance\nto crossover by using neutral and cationic redox-active molecules.\nUltimately, we found that all the evaluated AEMs perform poorly in\norganic solvents due to uncontrolled swelling, low ionic conductivity,\nand/or high crossover rates. We believe that this method, and the\ngenerated data, will be useful to evaluate and compare the performance\nof all AEMscommercial and newly synthesizedand should\nbe implemented as a standard protocol for future research.