A comprehensive DFT study of the structural, mechanical, and optoelectronic properties of novel hydrogen-based A2MgZnH6 (A = Na, K) double perovskites for hydrogen storage applications

The current study investigates two novel, non-toxic, hydrogen-based perovskites, A 2 MgZnH 6 (A = Na, K) using density functional theory in conjunction with the WIEN2k software package. Key properties such as chemical and dynamic stability, as well as mechanical durability, are calculated through the cohesive energy, elastic constants, and phonon dispersion relations. The materials exhibit semiconductor behavior with indirect band gaps of 3.24 eV for Na 2 MgZnH 6 and 2.81 eV for K 2 MgZnH 6 . In addition, they show low effective masses for electrons and holes, along with a high valence band maximum relative to standard O 2 . The optical properties of both materials reveal a high static dielectric constant and significant absorption and conductivity in the ultraviolet range of the spectrum. Furthermore, the calculated gravimetric hydrogen storage capacities are found to be 4.27% for Na 2 MgZnH 6 and 3.48% for K 2 MgZnH 6 . The volumetric hydrogen storage capacity surpasses the DOE target of 40 g H 2 L −1 . Finally, the mechanical properties demonstrate that these materials are brittle, possessing high bulk and shear moduli. Thus, the multifunctional stability, favorable optoelectronic properties, and mechanical characteristics of A 2 MgZnH 6 (A = Na, K) suggest that these materials could play a pivotal role in the future hydrogen economy.