Tailored synthesis approach of (MoY)AlC i-MAX and its two-dimensional derivative MoCT MXene: enhancing the yield, quality, and performance in supercapacitor applications.

A vacancy-ordered MXene, MoCT, obtained from the selective etching of Al and Sc from the parent i-MAX phase (MoSc)AlC has previously shown excellent properties for supercapacitor applications. Attempts to synthesize the same MXene from another precursor, (MoY)AlC, have not been able to match its forerunner. Herein, we show that the use of an AlY alloy instead of elemental Al and Y for the synthesis of (MoY)AlC i-MAX, results in a close to 70% increase in sample purity due to the suppression of the main secondary phase, MoAlC. Furthermore, through a modified etching procedure, we obtain a MoCT MXene of high structural quality and improve the yield by a factor of 6 compared to our previous efforts. Free-standing films show high volumetric (1308 F cm) and gravimetric (436 F g) capacitances and a high stability (98% retention) at the level of, or even beyond, those reported for the MoCT MXene produced from the Sc-based i-MAX. These results are of importance for the realization of high quality MXenes through use of more abundant elements (Y vs. Sc), while also reducing waste (impurity) material and facilitating the synthesis of a high-performance material for applications.