Theoretical insights into novel RbMH3 (M = Zn, Nb, and Ru) cubic perovskites for hydrogen storage applications: A first-principles DFT Study

Non-toxic, inorganic metal hydride cubic perovskites are promising candidates for commercializing hydrogen storage materials. Due to their enormous potentiality, a comprehensive analysis of the physical properties of RbMH3 (M = Zn, Nb, and Ru) perovskites is analyzed utilizing ab initio Density Functional Theory. The simulated negative formation energies, elastic constants, phonon dispersion, and tolerance factors confirmed the thermodynamic, mechanical, dynamic, and cubic phase stability. These compounds exhibited metallic character when utilized with GGA-PBE functional, but RbRuH3 exhibited a semiconducting nature with the HSE06 functional. The optical study reveals substantial responses to electromagnetic radiation. Moreover, their inherent stiffness, hardness, toughness, and anisotropic behavior are vital for long-term durability in engineering applications. Thermodynamic assessments validated the thermal stability of these perovskites at wide temperature ranges. RbZnH3, RbNbH3, and RbRuH3 exhibited notable gravimetric hydrogen storage capacities of 1.98, 1.67, and 1.59 wt%, respectively, along with volumetric capacities of 80.88, 73.73, and 88.27 g H2/L. The hydrogen desorption temperatures for RbZnH3, RbNbH3, and RbRuH3 are 317 K, 501 K, and 489 K, respectively. These characteristics are particularly valuable for advancing solid hydrogen storage materials.