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

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 Ti3C2Tx MXene (Ti3C2Tx-P) using sodium hypophosphate as phosphorus source. The phosphorus doping can increase the layer spacing of Ti3C2Tx and yield PO and PC bonds in Ti3C2Tx, 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 Ti3C2Tx-P reaches as high as 476.9F g−1 (745.4F cm−3), which is far larger than that of the raw Ti3C2Tx (344.4F g−1, 438.5F cm−3). In addition, a flexible quasi-solid supercapacitor device assembled by Ti3C2Tx-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 Ti3C2Tx, but provides a method for surface modification and functionalization of MXene materials.