Study of alkaline metals hydrides RbXH3 (X = Mg/Ca/Sr/Ba) for green energy and hydrogen storage applications

The potential of hydrogen as an energy source has positioned hydrogen storage as a prominent research domain in the current era. Innovative perovskite compounds have emerged as a focal point for investigating hydrogen storage applications. In this study, we have investigated the RbXH₃ (X = Mg/Ca/Sr/Ba) perovskite hydrides by density functional theory (DFT). Our exploration encompasses the analysis of electronic structures, mechanical stability, elastic properties, and optical and thermoelectric response. The cubic crystal structures of RbXH₃ are revealed, with lattice constants of 4.13, 4.54, 4.82, and 5.17 Å for X = Mg, Ca, Sr, and Ba, respectively. Electronic structure calculations indicate ionic bonding with a wide bandgap reduced with increasing size of X. Mechanical stability, essential for meeting the Born stability criterion, is scrutinized, whereas Pugh criteria suggest a ductile and hard nature for these materials. Thermoelectric characteristics regarding electrical and thermal conductivity, Seebeck coefficient, and power factors are elaborated. The figure of merit emphasizes their suitability for thermoelectric devices. The Gravimetric ratios indicate the hydrogen storage capability, potentially contributing to various transportation and power applications.