Microwave-assisted rapid synthesis of titanium phosphate free phosphorus doped Ti3C2 MXene with boosted pseudocapacitance

Abstract

Phosphorus (P) doping is well-known for a variety of energy materials with improved energy storage performances; however, it remains rarely explored for Ti3C2 MXene. The primary bottleneck of developing P doped Ti3C2 (P-Ti3C2) is the formation of undesired electrochemically inferior titanium phosphate phases during doping. Herein, for the first time, we presented a solution to this problem by producing titanium phosphate free P-Ti3C2 through a rapid microwave (MW)-assisted doping method (P-Ti3C2-MW). Various prevailing experimental features like the effects of different doping methods (conventional heating vs. MW assisted heating), use of different varieties of doping sources, tunable mixing ratios of functionalized Ti3C2 (Ti3C2Tx) with doping sources (1 : 0 to 1 : 15), MW power (500-1000 W) and time (30 s to 5 min) have been optimized for obtaining titanium phosphate free P-Ti3C2-MW with superior energy storage properties. Detailed mechanistic studies unveil that homogeneous mixing of Ti3C2Tx and doping sources like phytic acid (PA) through electrostatic attraction and the extraordinary MW absorption ability of multilayered Ti3C2Tx, PA and H2O direct the formation of titanium phosphate free P-Ti3C2-MW, whereas the conventional heating fails to do so and mainly produces phosphates (P-Ti3C2-An). The best titanium phosphate free P-Ti3C2-MW electrode exhibits a high volumetric capacitance of 1702 F cm(-3) at 1 A g(-1), a capacitance retention of 82% on moving from 1 A g(-1) to 2.5 A g(-1) and a capacitance retention of 91% after 10 k cycles at 5 A g(-1) by enabling improved pseudocapacitance through an enlarged interlayer spacing of 1.18 nm, which facilitates the intercalation of ions, abundance of P-containing redox active sites, optimized electronic conductivity, and an improved surface area. Furthermore, a parallel-type flexible symmetric supercapacitor made of the titanium phosphate free P-Ti3C2-MW electrode has been able to produce a maximum volumetric capacitance of 1357 F cm(-3) with excellent energy and power densities of 41.7 W h L-1 and 712.5 W L-1, respectively. This work has enormous potential to generate further interest towards the development of titanium phosphate free P-Ti3C2 based various composites suitable for energy generation, catalysis, and energy storage.