Unveiling hydrogen storage potential: In-depth DFT and AIMD study of strain engineering and diffusion mechanisms in Li2MgH4

In the pursuit of efficient hydrogen storage materials, a novel study has been conducted to explore the thermodynamic stability and diffusion properties of the lithium-based hydride Li₂MgH_4, a material that offers a high gravimetric hydrogen storage capacity of 10.52 wt% and a volumetric capacity of 55.07 g H₂/L, faces challenges due to its high stability, characterized by a ΔH of −81.01 kJ/mol.H₂ and a desorption temperature of 591.96 K. To address these challenges, first-principles calculations based on density functional theory DFT and ab initio molecular dynamics AIMD simulations were employed. This comprehensive research aims to enhance the material's hydrogen storage properties while ensuring compliance with Department of Energy DoE norms for solid-state hydrogen storage (ΔH = −40 kJ/mol.H₂ and T_des = 289 K–393 K). By applying a mechanical strain of −3.5 %, the study demonstrates that Li₂MgH₄ becomes more viable for hydrogen storage, with a 47.89 % improvement in its stability and enhanced storage properties (−42.21 kJ/mol.H₂ and 322.98 K). An in-depth analysis of hydrogen diffusion revealed that the (4 h) → (4 g) pathway is the most favorable, primarily due to lower energy barriers and a crystal structure optimized for migration along this direction. The application of strain significantly enhances this process, reducing the activation energy from 0.63 eV to 0.59 eV. This decrease in activation energy highlights the beneficial effects of strain, which lowers diffusion barriers. Notably, the strain effect is more pronounced for the (4 h) → (4 g) pathway, where the activation energy drops by 6.36 %, compared to a more modest 1.53 % reduction for the (4 h) → (4 h) pathway, emphasizing the greater sensitivity of the (4 h) → (4 g) site to strain.