First-principles comparative analysis of structural stability, hydrogen storage, mechanical, and electronic properties of hexahydride perovskites A2(Pd/Pt)H6 (A = alkali metal)

• Theoretical study of A 2 (Pd/Pt)H 6 (A = Li to Cs) hexahydrides for hydrogen storage. • These cubic hexahydrides show good structural stability. • Li 2 PdH 6 exhibits high hydrogen storage capacity (4.79 wt%). • The electronic properties of these hexahydrides are completely disclosed. Efficient hydrogen storage materials are vital for accelerating the development of clean energy solutions. Herein, first-principles calculations are conducted to explore the stability, hydrogen storage, mechanical properties, and electronic characteristics of A 2 (Pd/Pt)H 6 (A = alkali metal) hexahydrides. The thermodynamic, dynamic, and mechanical stability of all hexahydrides are rigorously verified by computing their formation energies, phonon spectra and elastic constants. Our computational analysis of Pugh’s and Poisson’s ratios reveals that while A 2 PdH 6 and A 2 PtH 6 (A = Li, Na) exhibit brittle characteristics, their counterparts A 2 (Pd/Pt)H 6 (A = K, Rb, Cs) demonstrate ductile behavior. The electronic properties of these hexahydrides are elucidated using the HSE06 functional. Furthermore, Pd-based hexahydrides exhibit higher hydrogen storage capacities (1.60 to 4.79 wt%) and lower desorption temperatures (133 to 174 K) in comparison to the Pt-based analogues (1.30 to 2.81 wt% and 259 to 298 K). With its good stability and high storage capacity (4.79 wt%), Li 2 PdH 6 is the most promising candidate for hydrogen storage applications. Our findings not only advance the interpretation of the physical properties of these hexahydrides but also offer crucial theoretical foundations and novel perspectives for the exploration of high-performance hydrogen storage materials.