Insights into Molecular Oxidation Mechanism to Achieve Highly Stable Aqueous Organic Flow Batteries

Abstract Aqueous organic redox flow batteries (AOFBs) have emerged as promising candidates for large‐scale energy storage systems. However, due to the high sensitivity of organic molecules to O 2 , most AOFBs have to be operated in glove boxes, which limits their practical applications. In this study, the reversible and irreversible oxidation behaviors of 7,8‐dihydroxyphenazine‐2‐sulfonic acid (DHPS) are investigated through in situ UV–vis and ex situ transient absorption spectra. It turned out that the high alkaline concentrations can effectively reduce the reversible auto‐oxidation rate, however, it would also accelerate the irreversible oxidation reaction triggered by the photoexcited singlet oxygen ( 1 O 2 ) when under irradiation. As a result, combining the reducing agents and employing light‐proof storage tanks can improve the cycle life of AOFBs effectively. Batteries encapsulated and operated outside the glove box can achieve a stable operation with a Coulombic efficiency of over 99% and a capacity decay rate of 0.0054%/cycle for 2500 cycles. The work proves that stable AOFBs under ambient conditions are possible, further enabling their application in large‐scale energy storage systems.