First-principles analysis of physical properties of the novel calcium-based hydrides for hydrogen storage application

The current work aims to investigate the physical properties of the new calcium-based perovskite hydride CaXH3 (X= Cu, and Zn) for hydrogen storage applications using DFT studies. Both materials were found to be thermodynamically and mechanically stable owing to their negative formation enthalpies, cohesive energy, and elastic constants. The absence of negative frequencies in the phonon dispersion curve reveals the dynamic stability of the structure. The optimized structure lattice constants were found 3.62Å, and 3.78Å with a bulk modulus of 117.40, and 82.39GPa, respectively. The Poisson and Pugh ratios were confirmed to have ionic bonding, while the Cauchy difference and Pugh ratio (B/G) results exhibited the brittle behavior of both materials. In addition, both materials have anisotropic characteristics, and CaCuH3 is stiffer than CaZnH3. The electronic properties confirmed that both compounds have a metallic nature owing to the zero band gap and high contribution of the Ca and X (Cu, Zn) d states near the Fermi level. These compounds were found non-magnetic by the investigation of magnetic properties. The optical results indicate that CaZnH3 plays a significant role in optoelectronics, solar cells, and photonics applications because of its higher conductivity, refractive index, dielectric function, and reflectivity, as well as its higher adsorption than CaCuH3.The hydrogen storage capacities of CaCuH3 and CaZnH3 hydrides were calculated to be 2.88 wt. % and 2.75 wt.%, respectively, and it was predicted that both compounds have the potential to store hydrogen, as evidenced by storage application.