Proton‐Resistant N ‐Heterocycle‐Linked TEMPO Catholytes for Long‐Lasting Neutral Aqueous Organic Redox Flow Batteries

Abstract TEMPO is a widely studied catholyte for aqueous organic redox flow batteries (AORFBs) but suffers from proton‐induced ring‐opening degradation when its solubility is enhanced via hydrophilic substitution at the 4‐position, leading to structural failure and rapid capacity fade. To address this issue, five TEMPO derivatives were synthesized through N ‐acetylamino bridging and nitrogen‐containing heterocycle grafting strategy. Combined analyses using atomic dipole moment‐corrected Hirshfeld (ADCH) charges, Fukui functions, and linear ion trap mass spectrometry (LTQ‐XL) reveal that aromatic heterocycle functionalization enables favorable charge redistribution during redox cycling, enhancing both redox kinetics and molecular stability. In particular, dimethylaminopyridine‐functionalized TEMPO (DMA‐TEMPO) exhibits enhanced π‐conjugation and basicity, which suppresses proton‐driven ring‐opening and significantly improves structural resilience. 1 M DMA‐TEMPO catholyte delivers exceptional cycling performance, retaining 99.98% of its capacity after 560 cycles, while 2 M system maintains 97% capacity over 100 cycles. Compared to its structural analog 1 M PA‐TEMPO, the cycle life is improved 18‐fold. This study offers a robust molecular design strategy for developing proton‐resistant catholytes, advancing the practical deployment of long‐lasting AORFBs for grid‐scale energy storage.