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

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.