Proton Competition Induced Stabilization in TEMPO‐Based Redox‐Targeting Flow Batteries

ABSTRACT 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) derivatives are widely studied as positive electrolytes in aqueous organic redox flow batteries (AORFBs) due to their high redox potential. However, TEMPO‐based AORFBs suffer from stability issues with molecule degradation. In this work, a unique stabilization strategy beyond molecular engineering is developed by designing a TEMPO‐based redox‐targeting (RT) flow battery via a proton‐competition mechanism. A RT flow battery is constructed with 4‐acetamido‐TEMPO as redox mediator and polyaniline (PANI) as the solid material, achieving 4.37‐fold enhancement in capacity (35.72 Ah L −1 ), high coulombic efficiency (99.99%) and excellent capacity retention (99.94% per cycle over 500 cycles within 840.82 h). The outstanding stability of the TEMPO‐based flow battery is attributed to the synergistic interaction between proton buffering and RT reactions. This study elucidates a key pathway for suppressing TEMPO radical hydrogenation through a proton competition mechanism, which relies on the reversible doping/de‐doping cycles of the PANI. Operando spectroscopic studies and density functional theory calculations elucidate the mechanism, revealing an intermediate transition state and confirming that proton competition by PANI is pivotal for radical stabilization. This work delves into the mechanism of TEMPO‐based RT flow battery, providing design principles for advancing stable AORFB systems toward long‐duration energy storage applications.