Luminescent MoS₂ Quantum Dots with Tunable Operating Potential for Energy-Enhanced Aqueous Supercapacitors

Wide band gap luminescent MoS₂ quantum dots (QDs) and MoS₂ nanocrystals (NCs) have been synthesized by using laser-assisted chemical vapour deposition and used as an electrode material in supercapacitors. Size-dependent properties of the MoS₂ QDs and NCs were examined by UV-vis absorption, photoluminescence, and Raman spectroscopy. The morphological evolution of the NCs and QDs were characterized by using field emission scanning electron microscopy, high-resolution transmission electron microscopy, and atomic force microscopy. The as-synthesized uniform QDs with a size of ∼2 nm exhibited an extended electrochemical potential window of 0.9 V with a specific capacitance value of 255 F/g, while the NCs values were 205 F/g and 0.8 V and the pristine MoS₂ with values of 105 F/g and 0.6 V at a scan rate of 1 mV s^-1. A shorter conductive pathway and 3D quantum confinement of MoS₂ QDs that exhibited a higher number of active sites ensure that the efficient charge storage kinetics along with the intercalation processes at the available edge sites enable significant widening of operating potential window and enhance the capacitance. The symmetric device constructed with the QDs showed a remarkable device capacitance of 50 F/g at a scan rate of 1 mV s^-1 with an energy density of ∼5.7 W h kg^-1 and achieved an excellent cycle stability of 10,000 consecutive cycles with ∼95% capacitance retention.