Large\nArea Graphene–MXene\nQuantum Dot Based\nHigh Performance Photochargeable Supercapacitor

Abstract

Photochargeable supercapacitors enable\nthe storage of\nlight induced\nelectrochemical energy. A few layers of graphene and MXene (Ti₃C₂T_<i>x</i>) quantum dots\n(QDs) are composited in this work for large photochargeable supercapacitor\nelectrodes. Planar graphene allows overcoming limitations of charge\ncarrier scattering, and MXene QDs on the surface facilitate an efficient\nlight interaction due to the wide band gap. The generated electron–hole\npairs in QDs under ultraviolet (UV) illumination are trapped at the\ninterface of graphene and stored in the supercapacitor. An enhancement\nof 126% in the areal capacitance was observed under UV illumination\nat a scan rate of 50 mV s^–1 . The effect of light\ninteraction on charge storage was further verified by phototransient\nresponse and electrochemical impedance spectroscopy under UV illumination.\nExcellent stability up to 5000 cycles was achieved with a negligible\nchange in capacitance (capacitance retention of ∼105%). A high\nCoulombic efficiency of ∼95.2% was measured by the galvanic\ncharge–discharge method at a current density of 1 μA\ncm^–2. The photochargeable supercapacitor provides\nbroad future prospects by exploiting the interface of QDs with graphene\nto obtain enhanced charge storage capacity.