Encapsulation of Redox p-Benzoquinone into Microporous Carbon Frameworks by a Diamine Covalent-Grafted Strategy for Aqueous Hybrid Supercapacitors

Aqueous hybrid supercapacitors (AHSs) with a wide operating voltage and intrinsic safety are emerging as promising energy storage devices, while their energy densities are still greatly restricted by carbon-based negative electrodes. Developing a high-performance redox system for carbon electrodes is one of the potential strategies to realize the practical utilization of AHSs. Herein, we present a covalent-grafted strategy to encapsulate redox p-benzoquinone (PBQ) into microporous carbon frameworks by using p-phenylenediamine (PPD) as a bridging agent. Both experimental and theoretical analysis reveal that the diamine groups from PPD play a vital role in chemically bonding PBQ with the microporous surfaces of carbon materials, which deliver a great deal of electronic delocalization throughout the redox-active sites and conductive carbon regions. As such, the obtained carbon electrodes grafted by the redox PBQ and PPD species facilitate charge transfer and consequently exhibit excellent charge storage performances. These are highlighted by an extremely high specific capacitance of 377 F g–1 at a current density of 0.5 A g–1 and 276 F g–1 at 100 A g–1 with a superior rate capability of 73%. Impressively, the assembled AHSs based on covalently grafted carbon electrodes (AC-PPD-PBQ) and NiCoAl-layered double hydroxides/carbon nanotubes (NiCoAl-LDH@CNT) demonstrate a maximum energy density of 70.9 W h kg–1 with a wide voltage window of 1.8 V and good cycling stability with 84.4% of initial capacitance after 5000 cycles. This work provides insights into the fabrication of high-performance carbon electrodes by encapsulating redox species into microporous frameworks.