Structural evolution, mechanical, electronic and vibrational properties of high capacity hydrogen storage TiH4

Abstract

Titanium tetra hydride is considered for hydrogen storage purposes. Firstly, formation energy, hydrogen desorption temperature and gravimetric hydrogen density of TiH4 is computed. Secondly, an ab initio constant pressure molecular dynamic simulation under pressure is performed to reveal behaviour of TiH4 for the first time. The result exhibits two phase transitions successively. C2/m phase of TiH4 transforms into C2/c phase at 40 GPa simulation pressure. Then, elastic constants of phases are determined to examine mechanical stability of phases. Based on the evolution of elastic constants, it is found that C2/m phase fulfils Born stability criteria for a monoclinic structure, indicating that C2/m phase is mechanically stable whereas C2/c phase is not mechanically stable. Additionally, several critical parameters which are important for hydrogen storage such as brittleness and ductility, Young and Shear modulus are obtained and analysed. In addition, electronic structures of phases are calculated and evaluated. Finally, dynamic stability from phonon dispersion curves is examined. C2/m phase is also found to be dynamically stable. © 2020 Hydrogen Energy Publications LLC