Computational analysis of X2CaZnH6 (X = K, Rb and Cs) hydrides for hydrogen storage

Using first-principles calculations, we investigate the structural, thermodynamic, mechanical, electronic, optical, and hydrogen storage properties of the double perovskite hydrides K2CaZnH6, Rb2CaZnH6, Cs2CaZnH6. All three compounds are predicted to form thermodynamically stable cubic phases and satisfy mechanical stability criteria. Hydrogen storage analysis reveals moderate gravimetric capacities together with competitive volumetric densities and favorable desorption temperatures, indicating potential suitability for stationary hydrogen storage applications. The materials exhibit indirect semiconducting behavior and strong optical absorption over a broad photon energy range. Bonding analysis suggests predominantly ionic interactions that are favorable for hydrogen retention. Overall, these results identify K2CaZnH6, Rb2CaZnH6 and Cs2CaZnH6 as promising candidates for hydrogen-related energy applications.