First-principles investigation of hydrogen storage capacity and the effect of physical characteristics on storage capacity of X2BeCuH6 (X = Li, Na)

초록

Hydrogen storage materials play a central role in the shift toward sustainable energy systems as they provide high-capacity, lightweight, and safe solutions to the next generation of fuel cells. In the current report, we present the first-principles investigation of structural, electronic, hydrogen storage, and optical characteristics of X2BeCuH6 (X = Li, Na) double perovskite hydrides utilizing density functional theory. Structural relaxation confirms that both compounds adopt the cubic Fm-3m symmetry, with a lattice constant of 6.78 and 7.05 angstrom for Li2BeCuH6 and Na2BeCuH6, respectively. Their structural stability is reported by the tolerance factor, while thermodynamic stability is confirmed by the negative formation enthalpies and AIMD simulations. The gravimetric H-2 storage capacities 6.54 wt% and 4.85 wt%, with desorption temperatures 193K and 215K, are calculated for Li2BeCuH6 and Na2BeCuH6, respectively. The examination of electronic band structure and density of states shows that metallic conductivity is dominated by Cu-3d and H-1s orbital hybridization. Charge density mapping also defines the co-existence of strong Cu-H covalency and Li/Na-H ionicity, and this forms the basis of stability and transport behavior. Notably, optical analyses display strong dielectric response as well as a high absorption with coefficients of similar to 11.27 x 10(5) cm(-1) (Li2BeCuH6) and 7.25 x 10(5) cm(-1) (Na2BeCuH6) in the visible-UV range. Such a high optical activity is indicative of a promising light-assisted hydrogen release and photocatalytic functionality. So, Li2BeCuH6 is one of the promising dual-purpose materials with high hydrogen storage capacity and optoelectronic-assisted energy applications.

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