Optimizing electronic structure of Mo2TiC2Tx MXene through Nb doping for enhanced electrochemical performance

MXene is a promising electrode material for both high volumetric capacitance and high-rate performance in supercapacitors. However, the current study has mainly focused on the monometallic element Ti3C2Tx MXene until now, while the bimetallic and multimetallic MXene have received comparatively less attention. In this work, we demonstrate that the electronic structure of the Mo2TiC2Tx MXene could be regulated by fine-tuning the content of doped Nb atoms. The enhanced electron cloud density of surface–O termination and the electron spin of the Mo atoms in the Mo2TiC2Tx MXene, leads to the boost of electric double-layer capacitor (EDLC) and improvement of pseudocapacitance. As a consequence, the electrochemical performance of Nb-doped Mo2TiC2Tx MXene (Nb-0.3-MXene) demonstrates a capacitance of 398 F·cm−3, roughly doubling that of the pristine Mo2TiC2Tx MXene electrode at 197 F·cm−3 in the 3 M H2SO4 electrolyte. At the same time, the Nb-0.3-MXene could even maintain a capacitance of 82.75% at 200 mV·s−1, with high cyclic stability for 19,000 cycles at 10 A·g−1. Additionally, Nb-0.3-MXene-based hybrid supercapacitors deliver a remarkable volumetric energy density of 48.1 W·h·L−1 at 230.7 W·L−1, and 34.4 W·h·L−1 at a high power density of 82.6 kW·L−1. There exists a balance between the volumetric capacitance and rate performance with different ratios of Nb atoms in the Nb-doped MXene due to the strong interaction between the Nb-doped MXene and the intercalated protons. Therefore, optimizing the electronic structure of MXene through heteroatom doping is of great potential for enhanced supercapacitor performance.