SnO2 Nanosphere/Carbon Dot-Embedded Ti3C2Tx MXene Nanocomposites for High-Performance Binder-Free Asymmetric Supercapacitor Electrodes

Abstract

Herein, a 3D-0D-2D-ternary heterostructure nanocomposite comprising pseudocapacitive SnO2 nanospheres (3D) and carbon dot (0D)-embedded Ti3C2Tx (MXene) nanosheets (2D) on Ni-foam was synthesized via a simple hydrothermal strategy for the use of positive electrodes in asymmetric supercapacitor devices. Yellow-emissive carbon dots were synthesized using the nontoxic polyphenolic precursor 2,4,6-tridihydroxybenzoic acid through a simple thermal heating method by dehydrating sulfuric acid medium through dehydration-induced carbonization. SnO2 played a crucial role by providing reactive centers on the surface of the carbon-dot-embedded MXene, thereby significantly enhancing the capacitive performances. Encapsulation of MXene by the 3D SnO2 nanospheres restricted the restacking tendency of the MXene nanosheets, enhancing their ability to store surface charge. Owing to its excellent morphological features, SnO2/carbon dots@MXene afforded superior electrochemical activities, having a specific capacitance of 1074 F/g in a three-electrode study. Moreover, the asymmetric supercapacitor device composed of the synthesized SnO2/carbon dots@MXene nanocomposite exhibited the maximum specific capacitance of 92 F/g at 2 A/g, with an enhanced energy density of 51.11 W h/kg. The supercapacitor device exhibited approximately 103% retention of the specific capacitance after 10,000 cycles and was able to illuminate light-emitting diode bulbs of different colors, demonstrating its practical applicability. Because of its superior electrochemical performance, the SnO2/carbon dots@MXene ternary nanocomposite may be a promising candidate for next-generation binder-free supercapacitor electrodes.