Boosting energy storage performance of Ti3C2Tx composite supercapacitors via decorated chalcogen (S, Se, Te) and new phase-formed binding sites

Abstract

Surface nanoscale modification of two-dimensional (2D) nanomaterials is a decisive method to tune their properties. Among different types of 2D nanomaterials, MXenes have extraordinary properties due to their extensive carrier concentration, superb conductivity, great specific surface area, high volumetric capacitance, and superior hydrophilicity. Thus, it is still demanded to synthesize MXenes with particular functional elements to provide essential characteristics. In this research work, the effect and mechanism of pre-selected group VI chalcogen elements (S, Se, and Te) on Ti3C2Tx MXene for electrochemical capacitance performance were investigated. Along with pristine Ti3C2Tx MXene, three different S/Ti3C2Tx, Se/Ti3C2Tx, and Te/Ti3C2Tx hybrid nanostructures were synthesized via a facile solid-state annealing technique. The electrochemical capacitances of the synthesized nanostructures were then assessed based on the coating of those nanostructures on flexible carbon cloths and assembled symmetric supercapacitor with a neutral electrolyte (1 M Na2SO4). Among the four fabricated devices, the Te/Ti3C2Tx supercapacitor exhibited a high specific capacitance of 150.6 F/g, which is greater than the pristine Ti3C2Tx (64.2 F/g) and Se/Ti3C2Tx (119.2 F/g), and almost close to S/Ti3C2Tx (150.0 F/g). These nearby specific capacitances of the Te/Ti3C2Tx and S/Ti3C2Tx samples may be attributed to the higher SSA value of the S/Ti3C2Tx sample in comparison to the Te/Ti3C2Tx. Besides, a high areal capacitance (760 mF/cm2), very good energy (67.8 Wh/Kg) and power (151 W/kg) densities, as well as cycling stability (>90% capacitance retention over 3000 cycles) were obtained for the Te/Ti3C2Tx supercapacitor. Those recent electrochemical capacitance characteristics of the Te/Ti3C2Tx are close to the S/Ti3C2Tx supercapacitor, however, they are weaker in pristine Ti3C2Tx and Se/Ti3C2Tx supercapacitors. These improvements could be ascribed to the wide specific surface area, the reduction of fluorine content after annealing with the chalcogen elements, the formation of a volume TiO2, and the large polarizability of the Te element compared with the other S and Se elements. The close supercapacitor characteristics of the S/Ti3C2Tx supercapacitor to the Te/Ti3C2Tx may be attributed to the formation of the TiS2 defect semiconductor phase with a high polarizability value.