DFT and AIMD insights into the stability and hydrogen storage performance of Na2XH6 (X = Cr, Mn, and Fe) perovskite hydrides

Abstract

Perovskite-derived materials have appeared as viable alternatives for hydrogen (H2) storage due to their high efficiency, structural stability and environmental compatibility. In this work, a comprehensive density functional theory (DFT) investigation was performed to evaluate the hydrogen storage potential of Na2XH6 (X = Cr, Mn, and Fe) cubic perovskite hydrides by focusing on the key parameters that govern hydrogen adsorption and desorption behavior. Structural optimization confirmed the stable cubic Fm3̄m phase, with favorable tolerance factors and negative formation energies, indicating the thermodynamic feasibility of these materials for hydrogen storage applications. Thermal stability was further validated using ab initio molecular dynamics (AIMD) simulations at 300 K, which revealed negligible structural distortion throughout the simulation. The investigated hydrides exhibited promising H2 storage performance, delivering gravimetric capacities of 5.81 wt% (Na2CrH6), 5.65 wt% (Na2MnH6), and 5.61 wt% (Na2FeH6), with corresponding hydrogen desorption temperatures of 572.83, 488.19 and 395.60 K, respectively, demonstrating a favorable balance between storage capacity and hydrogen release characteristics. Mechanical analysis confirmed that all compounds fulfilled the Born stability criteria, while their Poisson's ratios (0.24, 0.23 and 0.22) and Pugh's ratios (1.47, 1.40 and 1.38) indicated brittle behavior. Electronic structure analysis revealed metallic behavior in Na2CrH6 and Na2FeH6 and semiconducting behaviour in Na2MnH6, whereas optical analysis demonstrated distinct composition-dependent optical responses. These outcomes establish the Na2XH6 (X = Cr, Mn, and Fe) perovskite hydrides as efficient and stable multifunctional materials for future H2 storage and energy conversion technologies.