Structure, electronic characteristic and thermodynamic properties of K2ZnH4 hydride crystal: A first-principles study

Density functional theory calculations have been used to investigate the structural stability, electronic characteristics and thermodynamic properties of K2ZnH4 hydride. We find that the orthorhombic structure of K2ZnH4 is more stable than the tetragonal structure base on the total energy and phonon density of states. The calculated lattice parameters of the orthorhombic structure of K2ZnH4 are in good agreement with the experimental data. Analysis of the electronic characteristic suggests that K2ZnH4 crystal is an insulating material with a band gap of 4.010 eV. The calculated average H site energy is 4.540 eV/H, demonstrating that strong covalent bond exist between Zn and H atom. The formation enthalpy of K2ZnH4 is found to be −1.318 eV/f.u at 298 K. Hydrogen desorption from K2ZnH4 takes place via a two-step process, firstly forming KH, Zn and H2, and then K and H2. The first decomposition reaction is predicted at 524 K, and the second decomposition reaction is at 505 K. The reaction enthalpy is estimated to be 49.164 kJ/mol at 524 K for the first decomposition reaction, and 62.523 kJ/mol at 505 K for the second decomposition reaction.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Structural stability and thermodynamic properties of K2ZnH4 hydride are analyzed. ► Decomposition temperature of two-step reactions is predicted based on free energy. ► Orthorhombic structure of K2ZnH4 hydride is much more stable.