Mild pH-decoupling aqueous flow battery with practical pH recovery

Xi, Dawei; Alfaraidi, Abdulrahman M.; Gao, Jinxu; Cochard, Thomas; Faria, Luana C. I.; Yang, Zheng; George, Thomas Y.; Wang, Taobo; Gordon, Roy G.; Liu, Richard Y.; Aziz, Michael J.

doi:10.1038/s41560-024-01474-1

DOE OSTI · 2345159

Mild pH-decoupling aqueous flow battery with practical pH recovery

Xi, Dawei·Alfaraidi, Abdulrahman M.·Gao, Jinxu·Cochard, Thomas·Faria, Luana C. I.·Yang, Zheng·George, Thomas Y.·Wang, Taobo·Gordon, Roy G.·Liu, Richard Y.·Aziz, Michael J.

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Abstract

Establishing a pH difference between the two electrolytes (pH decoupling) of an aqueous redox flow battery (ARFB) enables cell voltages exceeding the 1.23 V thermodynamic water-splitting window, but acid–base crossover penalizes efficiency and lifetime. Here we employ mildly acidic and mildly alkaline electrolytes to mitigate crossover, achieving high round-trip energy efficiency with open circuit voltage >1.7 V. We implemented an acid–base regeneration system to periodically restore electrolytes to their initial pH values. The combined system exhibited capacity fade rate <0.07% per day, round-trip energy efficiency >85% and approximately 99% Coulombic efficiency during stable operation for over a week. Cost analysis shows that the tolerance of acid–base crossover could be increased if the pH-decoupling ARFB achieved a higher voltage output and lower resistance. Finally, this work demonstrates principles for improving lifespan, rate capability and energy efficiency in high-voltage pH-decoupling ARFBs and pH recovery concepts applicable for pH-decoupling systems.

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Xi, Dawei, Alfaraidi, Abdulrahman M., Gao, Jinxu, Cochard, Thomas, Faria, Luana C. I., Yang, Zheng, George, Thomas Y., Wang, Taobo, Gordon, Roy G., Liu, Richard Y., Aziz, Michael J.. 2024-02-19. Mild pH-decoupling aqueous flow battery with practical pH recovery. https://doi.org/10.1038/s41560-024-01474-1

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