Redox-Active Tetramino-Benzoquinone π–π Stacking and H-Bonding onto Multiwalled Carbon Nanotubes toward a High-Performance Asymmetric Supercapacitor

Abstract

The energy density of supercapacitors with carbon-based electrode materials is generally restricted by their limited electric double-layer capacitance (EDLC). The introduction of electroactive molecules to acquire abundant pseudocapacitance represents an efficient way to achieve a high-performance capacitor system. Herein, this work anchors redox-active tetramino-benzoquinone (TABQ) with multiwalled carbon nanotubes (MWCNTs) to form a composite (denoted as TABQ-MWCNTs). Due to the strong π–π stacking and H-bonding interaction between TABQ molecules and the MWCNT host, the TABQ-MWCNTs acquire enhanced structural stability and shortened pathway for electrons/charges, which facilitate their energy storage capability. Specifically, by adjusting the mass ratio of TABQ to MWCNTs, the composite can attain a high specific capacitance of 463 F g–1 at 1 A g–1 compared to that of bare MWCNTs (17 F g–1). Theoretical calculations show that TABQ-MWCNTs own a lower adsorption energy toward H+, suggesting its better EDLC capability through charge accumulation. Moreover, in situ Fourier transform infrared spectroscopy (FTIR) and Raman tests reveal that the TABQ molecules hosted on MWCNTs undergo a reversible evolution of the quinone-to-phenol structure during the discharging/charging process, further verifying its promising pseudocapacitance through faradic reactions. In addition to the high capacitance, the TABQ-MWCNT composite also exhibits good cyclability in a three-electrode system, i.e., 76.8% of the initial capacitance is obtained after cycling for 6000 times at 10 A g–1. An asymmetric supercapacitor (ASC) of TABQ-MWCNTs//activated carbon achieves a high energy density of 15.6 Wh kg–1 at a power density of 700 W kg–1. Moreover, it also shows a long-term cyclability of 91.5% after 10,000 cycles at 5 A g–1.

Redox‐Active Organic Electrode Materials for Supercapacitors

“…In addition, the initial specific capacitance of 91.5 % was maintained after 10000 cycles at 5 A g À 1 . [39]…”

“…Note that there are also organic molecules containing amino groups that were used as electrodes in supercapacitors but their pseudocapacitive characteristics were not mentioned. [39,89] This observation is suspected mainly due to the following factors: First, the voltage window adopted for the electrode molecules is not sufficient to activate the amino groups to undergo a reversible redox reaction; Second, the electrode molecules are not electrically conductive to stimulate the pseudocapacitive characteristics of the amino groups. Indeed, amino groups can undergo redox reactions to provide pseudocapacitance if they are conjugated well in the molecular structures, as evidenced in conducting polymers such as polyaniline.…”

“…The assembled asymmetric supercapacitor (ASC) with TABQ‐MWCNTs//activated carbon has an energy density of 15.6 Wh kg −1 at a power density of 700 W kg −1 . In addition, the initial specific capacitance of 91.5 % was maintained after 10000 cycles at 5 A g −1 [39] …”

“…e) In situ FTIR spectral evolutions of TABQ-MWCNTs during charging and discharging. Adapted from Ref [39]. Copyright (2022) American Chemical Society.…”

Redox-Active Phenanthrenequinone Molecules and Nitrogen-Doped Reduced Graphene Oxide as Active Material Composites for Supercapacitor Applications

“…42 To overcome conductivity limitations and mitigate dissolution into the electrolyte, organic molecules can be anchored on the surface of conductive carbon scaffolds. 43,44 Covalent and noncovalent modifications are two approaches undertaken to bind organic molecules to carbon substrates, including reduced graphene oxide. 45 Covalent modification can be done via chemical reactions, which might affect the carbon atom hybridizations in the substrate and transform sp 2 -bonded carbon into sp 3 -bonded carbon, detrimentally impacting the electrical conductivity.…”