Investigation of Structural, Elastic, Electronic, and Thermodynamic Properties of CaXH3 (X = Ti, V) for Hydrogen Storage Applications

In this manuscript, we have studied the structural, elastic, electronic and thermodynamic properties of CaXH3 (X = Ti, V) for hydrogen storage applications using DFT calculations. The generalized gradient approximation in the Perdew-Burke-Ernzerhof (PBE) form is used in this work to investigate the properties of the above compounds. The calculated optimized lattice constants are 3.8185 and 3.7163 & Aring; for CaTiH3 and CaVH3, respectively. The thermodynamic stability for the studied compounds is confirmed by the negative formation energy calculations. The elastic properties results show good mechanical stability. The phonon spectra calculation confirms the dynamical stability of the compound CaVH3. The determined band structure and density of states (DOS) profiles indicate the metallic nature for these compounds. Additionally, CaTiH3 and CaVH3 exhibit brittle behavior, as evidenced by both calculated Pugh's and Poisson's ratios. The specific heat capacities \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{C}_{V}}$$\end{document}, thermal expansion coefficients \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha $$\end{document} and Debye temperature \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\theta $$\end{document} were also investigated and discussed in detail. The obtained values of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\theta $$\end{document} were found to be 590.174 K for CaTiH3 and 644.342 K for CaVH3. The hydrogen storage capacity is found 3.217 and 3.115% for CaTiH3 and CaVH3, respectively. Furthermore, the hydrogen desorption temperatures obtained are 393.85 K for CaTiH3 and 358.28 K for CaVH3, both of which fall within the recommended decomposition temperature range of 298-473 K.