First principles study on the structure, hydrogen storage, and physical properties of X2VH6 (X = Mg, Ca, Sr, Ba) perovskite hydrides for hydrogen storage applications

This work presents a comprehensive investigation of the structural, hydrogen storage, mechanical, photoelectric and dynamics properties of X 2 VH 6 (X = Mg, Ca, Sr, Ba) compounds based on density functional theory (DFT) for the first time. The calculated elastic constants, and formation energies determine that cubic Mg 2 VH 6 , Ca 2 VH 6 , Sr 2 VH 6 , and Ba 2 VH 6 crystals possess mechanical, thermodynamic stability. Except for Mg 2 VH 6 , X 2 VH 6 (X = Ca, Sr, Ba) hydrides are dynamically stable due to the absence of imaginary frequencies for their phonon spectra. In addition, according to the Poisson's ratio and G/B ratio values, all X 2 VH 6 compounds are identified as ionically bonded materials, yet only Mg 2 VH 6 is ductile while Ca 2 VH 6 , Sr 2 VH 6 , and Ba 2 VH 6 are brittle materials instead. All these compounds are further found to have metallic properties through the band structure. They have good reflectivity in the visible region and high absorption coefficients in the ultraviolet region. Additionally, the hydrogen storage capacities of Mg 2 VH 6 , Ca 2 VH 6 , Sr 2 VH 6 , and Ba 2 VH 6 are 5.72, 4.41, 2.60, and 1.82 wt%, respectively, with corresponding desorption temperatures of 260, 309, 315, and 241 K, respectively. Overall, these materials exhibit good stability and high hydrogen storage capacity, which make them have great potential for hydrogen storage applications. This study is expected to provide valuable insights for further research on X 2 VH 6 compounds. • These materials are studied using density functional theory for the first time. • The desorption temperature of all materials are within the ideal range (233–333K). • All materials have high refractive index and good reflectivity in the visible region. • These materials have high absorption coefficients in the ultraviolet region. • All materials are thermodynamically and mechanically stable.