Abstract
The urgent need for clean renewable energy has stimulated extensive researches into hydrogen storage materials. Double perovskite hydrides have emerged as promising candidates due to their tunable structures and excellent storage capabilities. This study employs first-principles to systematically investigate the structural, hydrogen storage, mechanical, electronic, and optical properties of M₂CaZnH₆ (M = K, Rb, Cs) perovskites. The results reveal that the hydrogen storage capacities of M₂CaZnH₆ (M = K, Rb, Cs) are 3.19, 2.14, and 1.60 wt.%, and the desorption temperatures are 835, 589, and 247 K respectively.Mechanical stability was verified by the elastic constants. K₂CaZnH₆ is ductile, while Rb₂CaZnH₆ and Cs₂CaZnH₆ exhibit brittle behavior. Electronic structure reveals their semiconductor characteristics, and optical properties demonstrate high absorption in the ultraviolet (UV) region, indicating potential applications in UV photodetectors. These findings highlight the potential of M₂CaZnH₆ as versatile materials for hydrogen storage.

Key words
hydrogen storage, double perovskite hydrides, DFT calculations, physical properties

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