Nitrogen-doped Ti3C2Tx MXene prepared by thermal decomposition of ammonium salts and its application in flexible quasi-solid-state supercapacitor

Two-dimensional (2D) Ti 3 C 2 T x MXenes show great potential for application in flexible supercapacitors, due to their good hydrophilicity, metallic conductivity and excellent flexibility. Surface modification of the MXenes by heteroatom doping is a good strategy for adjusting the layer spacing and alleviateing various shortcomings. Herein, the ammonium salt decomposition method is shown to allow rapid nitrogen doping into Ti 3 C 2 T x nanosheets at a low temperature of 350 °C. Compared to the raw Ti 3 C 2 T x , the nitrogen-doped Ti 3 C 2 T x (designated N-Ti 3 C 2 T x ) shows an increased layer spacing of 1.451 nm, nitrogen doping levels of 1.42 at% and a low number of residual fluorine functional groups. For the application as an electrode of supercapacitors, the N-Ti 3 C 2 T x electrode shows an outstanding pseudocapacitance performance and mechanical flexibility, with a high specific capacitance of up to 449 F g −1 at 2 mV s −1 , which is 1.4 times that of the raw Ti 3 C 2 T x MXene (i.e., 321 F g −1 ). Furthermore, a quasi-solid-state symmetric supercapacitor assembled with a H 2 SO 4 -PVA gel electrolyte is shown to deliver an energy density of 9.57 Wh kg −1 at 250 W kg −1 . The outstanding pseudocapacitance of the N-Ti 3 C 2 T x is attributed to the positive effect of nitrogen doping on MXene, such as larger layer spacing and the increased number of surface active sites. The strategy presented herein also opens up a convenient and versatile approach for preparing high performance MXene Materials for energy conversion and storage.