Novel A2CrH6 (A = Ca, Sr, Ba) hydrides explored by first-principles calculations for hydrogen storage applications

Abstract: A theoretical study of a number of properties of A2CrH6 (where A = Ba, Sr, and Ca) hydride perovskites with the Cambridge Serial Total Energy Package (CASTEP). These include structural, hydrogen storage, mechanical, phonon, thermodynamic, electronic, and optical properties. The lattice constants of the compounds studied are in the range from 7.220 {\AA} to 8.082 {\AA}, and they exhibit stable cubic crystal structures. Negative formation energies, elastic constants, phonon dispersion and AIMD simulations testify to their thermodynamic, mechanical, dynamic and thermal stability, respectively. For the perovskite hydrides Ba2CrH6, Sr2CrH6 and Ca2CrH6, the corresponding specific hydrogen storage capacities are 1.82 wt.%, 2.69 wt.%, and 4.37 wt.%, respectively. Among these compounds, Sr2CrH6 exhibits the lowest applicable hydrogen desorption temperature, at 463.7 K. The electronic bands show remarkable spin activity, demonstrating that the change of A2+ cation (where A = Ca, Sr, and Ba) immediately influences the spin polarization and electronic behavior of hydride perovskites. On the basis of the elastic moduli studied, the mechanical behavior determines that Ca2CrH6 is the strongest material. The present results highlight the potential of A2CrH6 (A = Ca, Sr, and Ba) perovskite hydrides, in particular Ca2CrH6, for applications in advanced energy systems and hydrogen storage, as well as for electrical and optoelectronic devices.