A new Ti2V0.9Cr0.1C2Tx MXene with ultrahigh gravimetric capacitance

MXenes are a recently discovered family of two-dimensional (2D) early-transition metal carbides and carbonitrides that have already shown many attractive properties and great promise in energy storage and other applications. Although many MXenes have been synthesized, most MXenes contain only one or two transition metals. The preparation of medium-entropy or high-entropy MXenes is an important and challenging task due to the excellent properties resulting from increased configurational entropy. Herein, new three-transition-metal MAX phases, Ti2V1−yCryAlC2, and the corresponding MXenes were synthesized successfully for the first time. By combining aberration-corrected scanning transmission electron microscopy (AC-STEM), density functional theory (DFT) and synchrotron X-ray pair distribution functions (PDF) analyses, we determined the structure of Ti2V0.9Cr0.1C2Tx, which exhibits a Ti-V-Cr solid solution in the three atomic layers. Furthermore, when applying these MXenes as the electrode of a supercapacitor, the single-layer Ti2V0.9Cr0.1C2Tx shows a remarkable gravimetric capacitance (553.27 F g−1 at 2 mV s−1). This work not only expands the family of MXenes, but also provides a strategy to prepare medium-entropy and high-entropy MXenes.