Unveiling the charge storage mechanism of a supercapacitor constructed from an ortho-quinone-derived covalent organic framework on electrophoretically exfoliated graphene

Abstract

Covalent organic frameworks (COFs) exhibit crystalline structures, high chemical and thermal stability, and pseudocapacitive behavior, making them promising candidates for electrochemical energy storage (EES) devices. However, their low electrical conductivity limits their performance in supercapacitors. This study introduces a novel approach of using in situ exfoliated graphene as a conductive substrate for an o-quinone-embedded COF (INIT-1), resulting in a nanohybrid material (INIT-1 EGR). The synthesis of the INIT-1 COF involved a solvothermal reaction between 5′-(4-formyl phenyl)-[1,1′:3,1′′-terphenyl]-4,4′′-dicarbaldehyde and 2,7-diaminophenanthrene-9,10-dione. The subsequent formation of INIT-1-EGR occurred through chronoamperometric exfoliation at 3.5 V. This process led to a regular dispersion of COF sheets on graphene, facilitated by intermolecular π–π interactions and subsequent stacking of graphene sheets. As a result, the nanohybrid INIT-1-EGR exhibited a significantly improved capacitance compared to the bare COF. Specifically, INIT-1-EGR demonstrates a specific capacitance of 15.42 mF cm⁻² at a scan rate of 1 mV s⁻¹ and 14.77 mF cm⁻² at a current density of 1 mA cm⁻² compared to the negligible specific capacitance value obtained for the pristine COF. Further, INIT-1-EGR showed cycling stability of 5500 cycles with a capacity retention of 112%. This enhancement was attributed to the π–π interactions between the framework and exfoliated graphene sheets, resulting in the synergistic effect of abundant redox-active centers within the COF skeleton and graphene layers, creating an efficient charge transport pathway. DFT studies revealed the charge transfer from graphene sheets to the COF leading to its enhanced capacitance by the graphene exfoliation.