High-quality graphene devoid of oxygen functionalities as conductive ink for flexible electronics and bendable all-solid-state supercapacitors

Abstract

High-yielding and scalable naphthalene-assisted ball-mill exfoliation of graphite is reported here aiming at the production of high-quality graphene cost-effectively. The Raman spectral analysis indicates less-defective graphene, whereas the few-layered nature is evident from the XRD pattern and AFM images. Monolayered graphene can also be produced upon ultrasonication, which is evident from the HRTEM images and Raman spectral analysis. XPS indicated the absence of in-plane oxygen functionalities that usually disrupt the aromatic π-conjugation. Graphene is effectively utilized here to formulate a conducting ink for polyimide tape-based wires for lighting LEDs. The supercapacitor performance of the graphene as an electrode material was also assessed, where, in the three-electrode system, graphene exhibited an excellent areal capacitance of 197.22 mF/cm2 at a current density of 2 mA/cm2 and the graphene-modified carbon paste electrode retained 100 % of initial capacitance even after 7500 charge-discharge cycles. A bendable supercapacitor was also fabricated here with graphene-coated carbon cloth electrodes that exhibited a high capacitance of 524.28 mF at 0.05 mA/cm2 with the highest energy and power densities of 14.87 μWh/cm2 and 349.76 μW/cm2 respectively. The bendable device retained 99.9 % of its initial capacitance after 3000 continuous cyclic voltammetric runs. The supercapacitor delivered the same performance as the straight device during bending, twisting and even after bending at different angles.