Mild pH-decoupling aqueous flow battery with practical pH recovery

Dawei Xi, Abdulrahman M. Alfaraidi, Jinxu Gao, Thomas Cochard, Luana C. I. Faria, Zheng Yang, Thomas Y. George, Taobo Wang, Roy G. Gordon (), Richard Y. Liu () and Michael J. Aziz ()
Additional contact information
Dawei Xi: Harvard University
Abdulrahman M. Alfaraidi: Harvard University
Jinxu Gao: Harvard University
Thomas Cochard: Harvard University
Luana C. I. Faria: Harvard University
Zheng Yang: Harvard University
Thomas Y. George: Harvard University
Taobo Wang: Harvard University
Roy G. Gordon: Harvard University
Richard Y. Liu: Harvard University
Michael J. Aziz: Harvard University

Nature Energy, 2024, vol. 9, issue 4, 479-490

Abstract: 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 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. 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.

Date: 2024
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DOI: 10.1038/s41560-024-01474-1

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