First-principles to explore the hydrogen storage properties of XPtH3 (X=Li, Na, K, Rb) perovskite type hydrides

Based on the first-principles, the hydrogen storage, mechanical, electronic, optical, thermodynamic and kinetic properties of XPtH3 (X = Li, Na, K, Rb) perovskites are investigated for the first time in this work. The lattice constants of the optimized LiPtH3, NaPtH3, KPtH3, and RbPtH3 are 3.54, 3.63, 3.80, and 3.90 angstrom, respectively. The Cauchy's pressure and the ratio of the bulk modulus to shear modulus (B/G) consistently prove that the XPtH3 hydrides all exhibit ductility. The investigation of electronic properties reveals that XPtH3 compounds exhibit metallic nature. According to Poisson's ratio and charge density distribution, the bonding type of XPtH3 hydrides is mainly ionic. The Bader partial net charges are also calculated to analyze the charge transfer in XPtH3 perovskites. The results of the optical properties of XPtH3 compounds reveal that they are high dielectric constant and high refractive index materials. It is found that the XPtH3 perovskites exhibit thermodynamic, mechanical, and dynamic stability. The gravimetric hydrogen storage capacities are 1.45, 1.35, 1.26, and 1.06 wt% for LiPtH3, NaPtH3, KPtH3, and RbPtH3, respectively. The hydrogen desorption temperatures of LiPtH3, NaPtH3, KPtH3 and RbPtH3 are 237.77, 225.39, 162.43, and 80.11 K, respectively. Our results suggest that LiPtH3 hydride is the most suitable material for hydrogen storage applications among the four compounds.