Theoretical study of quantum capacitance, mechanical and electronic properties of transition metal nitrides VN, TiN, and NbN for supercapacitor applications

We present the mechanical and electronic properties of the transition metal nitrides (TMNs) VN, TiN, and NbN using density functional theory calculations. These nitrides are thermodynamically stable in the cubic phase with Fm3<overline>m\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$Fm\overline{3 }m$$\end{document} space group symmetry. The elastic constants calculated by applying various volume-conserving strains reveal that NbN and VN are ductile, whereas TiN is brittle and exhibits good mechanical stability. The electronic band structures, density of states, and partial density of states are calculated to investigate the electronic behaviour of these TMNs. The electronic band structures indicate the metallic behaviour of these TMNs. The partial density of states reveals hybridization between d-orbitals of transition metal and p-orbitals of nitrogen. Further, the quantum capacitance (CQ) values are calculated from the total density of states at various operating voltages. We find that VN exhibits the maximum CQ = 2588 F/g at the Fermi level and reaches 5135 F/g at + 0.6 V operating voltage.