Anthraquinone-Catalyzed TEMPO Reduction to Realize Two-Electron Energy Storage of Poly(TEMPO-methacrylate)

Abstract

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.

Lewis Acid-Induced Reversible Disproportionation of TEMPO Enables Aqueous Aluminum Radical Batteries

“…With the encouraging electrochemical properties of TEMPO in Al­(OTf) 3 aqueous solution, we next fabricated the first TEMPO radical polymer AAIB using poly­(TEMPO methacrylate) (PTMA), a benchmark polymer cathode. ,,− PTMA with a molecular weight of 157 kDa and dispersity ( Đ ) of 1.46 was synthesized and characterized as described previously . The Swagelok-type cell was assembled using a polymer cathode composed of PTMA/MWCNT/PVDF at a ratio of 3/6/1 (w/w/w) with 1.0 M Al­(OTf) 3 aqueous solution as the electrolyte and aluminum foil as an anode.…”

“…31,32,49−51 PTMA with a molecular weight of 157 kDa and dispersity (Đ) of 1.46 was synthesized and characterized as described previously. 52 The Swagelok-type cell was assembled using a polymer cathode composed of PTMA/MWCNT/ PVDF at a ratio of 3/6/1 (w/w/w) with 1.0 M Al(OTf) 3 aqueous solution as the electrolyte and aluminum foil as an anode. We expect a similar disproportionation reaction and electrochemical reaction to occur in the polymer electrode.…”

Redox-Active Nitroxide Radicals Grafted onto MXene: Boosting Energy Storage via Improved Charge Transfer and Surface Capacitance

“…The development of energy storage devices has raised great demands for electrode materials. Pseudosupercapacitors with high specific capacitance, long cycle life, and high energy density are widely recognized as promising energy storage devices, which could store charges via Faradaic redox reactions. , Organic radicals with unpaired electrons have attracted remarkable interest in the development of catalysis, electrochemically active materials, organic magnetic materials and biological imaging agents. − Among different atom-centered radicals, nitroxide radicals with unpaired electrons delocalized on the N–O bonds are typical organic electroactive materials with high thermodynamic stability and long lifetimes. − The unique chemical structure enables persistent nitroxide radicals to undergo rapid and reversible redox reactions, where they could be oxidized to oxoammonium cations and reduced to aminoxyl anions. − Importantly, the electron transfer rate constant of nitroxide radicals is as high as 10 –1 cm s –1 , which is 6 orders higher than those of other organic redox compounds . These advantages make nitroxide radicals promising electrode materials for supercapacitors and batteries. ,,− However, the low electrical conductivity and poor stability during the charge and discharge process of nitroxide radicals restrict their applications. , Incorporating nitroxide radicals with carbon-based conductive agents is a feasible solution for these problems.…”

Redox: Organic Robust Radicals and Their Polymers for Energy Conversion/Storage Devices

“…76,77,83,123,147 The ambipolar redox property of TEMPO can double the charge/discharge capacity as the active material in rechargeable batteries. 76,77,123,134,148 n-Type reactions are more sensitive to the electrochemical conditions. Reversible redox was detected for the p-type response at around 0.3 V vs Ag/AgNO 3 in the ionic liquids 1ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-1-methylpyrrolidinium triflate, and 1-ethyl-3-methylimidazolium dicyanamide (Figure 7).…”

“…83 However, careful design of the electrode and electrolyte systems has allowed several hundreds of charge/discharge cycles (e.g., use of nanocarbon and redox mediators), and thus, there are still opportunities for the practical use of n-type reactions. 76,77,123,134,148 The redox bistability of TEMPO is crucial for extending the cycle life with battery and catalyst applications. 111,149−152 Neutral TEMPO has a long lifetime unless heated at high temperatures.…”