Ordered Double Transition Metal MXenes for High Energy Density Asymmetric Supercapacitors

The very few reports published on the electrochemical properties of Double Transition Metal MXenes (DTMs) suggests that they perform much better than their mono metal counterparts. This is true for both ordered and solid solution DTMs[1-3]. Despite the theoretical predictions on the stability of a number of double transition metal MAX phases, only a few have been synthesized and etched into their corresponding MXenes. In an attempt to scale up the synthesis and processing of DTMs, we present the synthesis and structural studies of ordered Cr₂TiAlC₂, Cr₂Ti₂AlC₃ and solid solution Ti₂NbAlC₂ MAX phases and their etching into corresponding MXenes. In-situ high temperature XRD data collected on the admix of activated metal powders was used to optimize and model the MAX phase synthesis in high temperature tube furnace. Electrochemical studies such as CV, EIS and CCD of the synthesized DTMs compared with Ti₃C₂T_xwill be presented and discussed.<br/><br/><br/>[1] David Pinto et al., “Synthesis and Electrochemical Properties of 2D Molybdenum Vanadium Carbides – Solid Solution MXenes,” <i>J. Mater. Chem. A</i> 8, no. 18 (2020): 8957–68, https://doi.org/10.1039/D0TA01798A.<br/><br/>[2] Likui Wang et al., “Adjustable Electrochemical Properties of Solid-Solution MXenes,” <i>Nano Energy</i> 88 (2021): 106308, https://doi.org/https://doi.org/10.1016/j.nanoen.2021.106308.<br/><br/>[3] Babak Anasori et al., “Two-Dimensional, Ordered, Double Transition Metals Carbides (MXenes),” <i>ACS Nano</i> 9, no. 10 (October 27, 2015): 9507–16, https://doi.org/10.1021/acsnano.5b03591.