Exploring X2BH6 (X = Li, Na, and K) Double Perovskite Hydrides for Solid‐State Hydrogen Storage Applications
Abstract
Solid‐state hydrogen storage in lightweight hydrides represents a promising pathway toward a sustainable hydrogen economy. In this work, we employ density functional theory to systematically investigate the structural, electronic, mechanical, dynamical, and hydrogen storage properties of X2BH6 (X = Li, Na, and K) hydrides. All hydrides exhibit negative formation energies, confirming their thermodynamic stability. The gravimetric hydrogen storage capacities are remarkably high: 19.71, 9.64, and 6.37 wt% for Li2BH6, Na2BH6, and K2BH6, respectively, all surpassing the 2025 U.S. Department of Energy target of 5.5 wt%. Electronic band structure analysis reveals metallic character for all hydrides. Evaluation of Born mechanical stability criteria reveals that Li2BH6 and K2BH6 are mechanically stable, whereas Na2BH6 is mechanically unstable. Phonon dispersion calculations demonstrate that only K2BH6 is dynamically stable, while Li2BH6 and Na2BH6 exhibit imaginary phonon modes. Combining all stability criteria, K2BH6 emerges as the most promising candidate, possessing simultaneous thermodynamic, mechanical, and dynamical stability alongside a gravimetric capacity of 6.37 wt% and a hydrogen desorption temperature of 308.00 K that falls within the DOE operating target. These findings suggest K2BH6 as a potential candidate for solid‐state hydrogen storage and provide theoretical guidance for future experimental synthesis.