First-Principles Investigation of Rubidium and Cesium Tin Hydride Perovskites for Sustainable Hydrogen Storage and Thermoelectric Energy Conversion

Hydride perovskites have emerged as promising multifunctional materials for sustainable energy technologies owing to their potential for hydrogen storage and thermoelectric energy conversion. However, despite recent theoretical studies on tin-based hydride perovskites, a comprehensive understanding of the relationship between their structural, electronic, mechanical, thermoelectric, and hydrogen-storage properties remains limited. In this work, a systematic first-principles investigation of cubic XSnH3 (X = Rb, Cs) hydride perovskites was performed using density functional theory within the full-potential linearized augmented plane wave (FP-LAPW) method, combined with Boltzmann transport calculations. The optimized structural parameters are in excellent agreement with previously reported theoretical data, confirming the reliability of the adopted computational approach. Both compounds satisfy the mechanical stability criteria and exhibit metallic electronic behavior dominated by Sn-p states around the Fermi level. The calculated thermoelectric properties reveal that the electrical conductivity decreases with increasing temperature, whereas the electronic thermal conductivity, power factor, and thermoelectric figure of merit increase continuously over the investigated temperature range. Among the studied compounds, RbSnH3 exhibits superior thermoelectric performance together with a higher gravimetric hydrogen content (1.45 wt%) than CsSnH3 (1.18 wt%). These findings demonstrate that alkali-metal substitution provides an effective strategy for tailoring the multifunctional properties of hydride perovskites and identify RbSnH3 as a promising candidate for future hydrogen-storage and thermoelectric energy-conversion applications.