Transition metal carbides, nitrides, and carbonitrides known as MXenes are a growing family (20+ members) of two dimensional (2D) materials that have garnered much attention for the unique physical, electrical, and optical properties of this new class of materials[1]. Titanium Carbide (Ti₃C₂T_x) MXene based electrodes have shown great potential for energy storage applications due to their attractive properties such as their high specific capacitances due to redox active transition metals at their surfaces[2, 3] and the high conductivities of MXenes (5000 S/cm) when they are fabricated into free-standing, flexible films[4]. To date, relatively few MXenes have been used as electrode materials for electrochemical capacitors, all of which have been carbides.

Here we examine for the first time the electrochemical performance of a carbonitride MXene, Ti₃CNT_x, as a supercapacitor electrode material. The structure of Ti₃CNT_x is similar to Ti₃C₂T_x, with nitrogen and carbon layers sandwiched between three layers of titanium instead of only two layers of carbon. The Ti₃CNT_x investigated shows high specific capacitances in acidic electrolytes and good rate performance, similar to previous reports on Ti₃C₂T_x-MXenes, but the charge-discharge response of Ti₃CNT_x-MXene during cyclic voltammetry is completely different from carbide based MXenes. These results show how manipulation of the composition of MXenes can influence their energy storage properties.

1. Naguib, M. and Y. Gogotsi, Synthesis of two-dimensional materials by selective extraction. Acc Chem Res, 2015. 48(1): p. 128-35.

2. Lukatskaya, M.R., et al., Cation intercalation and high volumetric capacitance of two-dimensional titanium carbide. Science, 2013. 341(6153): p. 1502-5.

3. Ghidiu, M., et al., Conductive two-dimensional titanium carbide 'clay' with high volumetric capacitance. Nature, 2014. 516(7529): p. 78-81.

4. Shahzad, F., et al., Electromagnetic interference shielding with 2D transition metal carbides (MXenes). Science, 2016. 353(6304): p. 1137-1140.