Ti₄C_(3-y)N_yT_x: New 2D Carbonitride MXenes Derived from New 413 Carbonitride MAX Phases

Being a single member of carbonitride family, Ti₃CNT<i>_x</i> exhibited unique properties and behavior compared to its carbide counterpart in applications including energy storage, electromagnetic shielding, optics, sensing, etc. It had been the only carbonitride MXene for more than 10 years until we reported on Ti₂C_0.5N_0.5T<i>_x</i>in 2021 which exhibited the highest specific capacity among all reported multilayer MXene electrodes. Previously, we have also shown that Ti₃CNT<i>_x</i>is an excellent electrocatalyst for hydrogen evolution reaction with an onset potential of 56 mV which is significantly lower than that of Ti₃C₂T<i>_x</i>. All of the reports of carbonitride MXenes support the hypothesis that replacing carbon partially with nitrogen in X cites can increase the number of electrons as well as active sites in MXenes. Hence, we focused on enriching the carbonitride MXene family with new members to gain a further understanding of the synthesis and property of carbonitrides. It is noteworthy to mention that synthesis of carbonitride MXene is challenging due to the lower stability of nitride MXenes compared to carbides and also the lower number of Carbonitride MAX Phases to start with. Herein, for the first time, we report on the synthesis of new four titanium carbonitride MXenes Ti₄C_(3-y)N_yT<i>_x</i> (y = 2.2, 2.4, 2.6, and 2.8) derived from four new 413 MAX phases. By tuning the synthesis conditions using potassium fluoride and hydrochloric acid and changing various etching parameters we realized Ti₄C_(3-y)N_yT<i>_x</i> MXenes from Ti₄AlC_(3-y)N_yT<i>_x</i> (y = 2.2, 2.4, 2.6, and 2.8). MXene thin films were also achieved by delaminating the multilayers. The synthesis of Ti₄C_(3-y)N_yT<i>_x</i> (y = 2.2, 2.4, 2.6, and 2.8) MXenes is unique because this is the first study of carbonitride MXenes' where carbon to nitrogen ratio has been modified systematically in X cites. Finally, we will present our new findings on their performances in electrochemical energy storage.