The surface functional modification of Ti3C2Tx MXene by phosphorus doping and its application in quasi-solid state flexible supercapacitor

Abstract

The surface modification of MXene by heterogeneous atoms shows great potential in improving the charge storage capacity of MXene. Herein, a strategy of rapid in-situ phosphorus doping at low temperature is demonstrated for preparing functionalized Ti₃C₂T_x MXene (Ti₃C₂T_x-P) using sodium hypophosphate as phosphorus source. The phosphorus doping can increase the layer spacing of Ti₃C₂T_x and yield PO and PC bonds in Ti₃C₂T_x, resulting in more rapid paths for the migration of electrolyte ions into electrode and more active sites for pseudocapacitance effects. As flexible electrode of supercapacitor, the specific capacitance of Ti₃C₂T_x-P reaches as high as 476.9F g⁻¹ (745.4F cm⁻³), which is far larger than that of the raw Ti₃C₂T_x (344.4F g⁻¹, 438.5F cm⁻³). In addition, a flexible quasi-solid supercapacitor device assembled by Ti₃C₂T_x-P film shows high specific capacitance of 103F g⁻¹ at 5 mV s⁻¹. When the power density is 250 W kg⁻¹ and 10000 W kg⁻¹, the corresponding energy density reaches 15.8 Wh kg⁻¹ and 6.1 Wh kg⁻¹, respectively. Therefore, our work not only reveals the role of P atom doping in improving the structure, composition and electrochemical performance of Ti₃C₂T_x, but provides a method for surface modification and functionalization of MXene materials.