Large Area Graphene–MXene Quantum Dot Based High Performance Photochargeable Supercapacitor

Abstract

Photochargeable supercapacitors enable the storage of light induced electrochemical energy. A few layers of graphene and MXene (Ti 3 C 2 T x ) quantum dots (QDs) are composited in this work for large photochargeable supercapacitor electrodes. Planar graphene allows overcoming limitations of charge carrier scattering, and MXene QDs on the surface facilitate an efficient light interaction due to the wide band gap. The generated electron–hole pairs in QDs under ultraviolet (UV) illumination are trapped at the interface of graphene and stored in the supercapacitor. An enhancement of 126% in the areal capacitance was observed under UV illumination at a scan rate of 50 mV s –1 . The effect of light interaction on charge storage was further verified by phototransient response and electrochemical impedance spectroscopy under UV illumination. Excellent stability up to 5000 cycles was achieved with a negligible change in capacitance (capacitance retention of ∼105%). A high Coulombic efficiency of ∼95.2% was measured by the galvanic charge–discharge method at a current density of 1 μA cm –2 . The photochargeable supercapacitor provides broad future prospects by exploiting the interface of QDs with graphene to obtain enhanced charge storage capacity.