Tetramethylpiperidine-1-oxyl (TEMPO) functional polymers are a type of organic electroactive material featuring a two-electron redox process. However, the electrochemical reduction of TEMPO (TEMPO •/− ) is rarely adopted for energy storage due to its slow reaction kinetics. Here, we report using anthraquinone (AQ) as an organic redox mediator to promote TEMPO reduction kinetics. The catalytic effect of AQ is verified by electrochemical in situ FTIR spectroscopy in a model three-electrode system and further evidenced by cyclic voltammetry and chronoamperometry, providing a turnover frequency of 69 h −1 . To exemplify the AQ catalytic effect in energy storage performance, we incorporate AQ groups into a typical TEMPO polymer (i.e., poly(TEMPO-methacrylate), PTMA). The AQ-catalyzed TEMPO reduction and AQ/carbon π−π interaction synergistically reduce the heterogeneous charge transfer resistance and accelerate the kinetics of the TEMPO •/− process in the PTMA electrode. The half-cell tests of the AQ functional PTMA show two prominent discharge plateaus with an initial capacity of 174 mAh g −1 and a 0.18% capacity loss per cycle. Moreover, the discharge capacity based on the TEMPO •/− couple is about 85 mAh g −1 , 30% higher than that of the pristine PTMA. This new strategy could be widely applied to various organic redox systems to enhance their electrochemical kinetics and particularly improve the energy storage performance of organic polymer redox materials.

No abstract

Nitroxide radicals, such as 2,2,6,6-tetramethylpiperidyl-1-oxy (TEMPO), are typical organic electrode materials featuring high redox potentials and fast electrochemical kinetics and have been widely used as cathode materials in multivalent metal-ion batteries. However, TEMPO and its derivatives have not been used in emerging rechargeable aluminum-ion batteries (AIBs) due to the known disproportionation and possible degradation of nitroxide radicals in acidic conditions. In this study, the (electro)­chemical behavior of TEMPO is examined in organic and aqueous Lewis acid electrolytes. Through in situ (electro)­chemical characterizations and theoretical computation, we reveal for the first time an irreversible disproportionation of TEMPO in organic Al­(OTf)3 electrolytes that can be steered to a reversible process when switching to an aqueous media. In the latter case, a fast hydrolysis and ligand exchange between [Al­(OTf)3TEMPO]− anion and water enable the overall reversible electrochemical redox reaction of TEMPO. These findings lead to the first design of radical polymer aqueous AIBs that are fire-retardant and air-stable, delivering a stable voltage output of 1.25 V and a capacity of 110 mAh g–1 over 800 cycles with 0.028% loss per cycle. This work demonstrates the promise of using nonconjugated organic electroactive materials for cost-effective and safe AIBs that currently rely on conjugated organic molecules.