Azobenzene‐Based Low‐Potential Anolyte for Nonaqueous Organic Redox Flow Batteries

Abstract Redox flow batteries (RFBs) using organic materials in organic solvents are particularly promising because of the diversity of organic materials and the wide redox‐innocent window of organic solvents, yet the further development of this type of RFB has been hindered by the lack of suitable anolyte materials with high potentials, solubility, and stability. Herein, we examine the physical and electrochemical properties of azobenzene ( AzoPh ) compounds and investigate their degradation mechanism in nonaqueous organic RFB. The azobenzene displayed two‐electron activity at −1.69 and −2.20 V vs. Ag/Ag + . Paired with a well‐established PEGylated phenothiazine ( PEG3‐PTZ ) catholyte, the battery presents a high theoretical cell voltage of 2.08 V. The azobenzene‐based RFB displays a capacity retention of 93.3 % over 50 cycles with an average fade rate of 0.13 % per cycle. The capacity decay mechanism was probed by proton nuclear magnetic resonance spectroscopy, cyclic voltammetry, and high‐resolution mass spectrometry, and revealed proton‐assisted degradation mechanisms.