Screening Process for Assessing the Stability of Advanced Redox-Flow-Battery Membranes

Membranes are a key component in redox flow battery (RFB) cells since they have a critical impact on the performance of these cells, including both the voltaic efficiency and coulombic efficiency. Currently, most RFB cells use materials that are “borrowed” from other electrochemical cells, such as perfluorinated-sulfonic-acid membranes. Therefore, the development of bespoke RFB membranes is a promising pathway to enabling RFB cells with improved performance, cost, and sustainability. Since most RFB systems are intended for long-lifetime applications (e.g., > 10–20 years), it is important to select materials that are not prone to degradation. We herein recommend a series of tests to screen candidate RFB membranes for a variety of possible degradation mechanisms. To date, durability screening of RFB membranes has been typically limited to chemical stability in the oxidizing environment of the positive electrolyte. While this is an important issue, there are other membrane-degradation mechanisms that should also be considered, some of which are less well known. To expedite this screening process, we propose a set of tests that are either accelerated or use highly sensitive techniques to detect evidence of degradation that is likely to continue over much longer time periods.