DFT study of alkaline earth metals NaXH3 (X = Be, Mg, Ca, Sr) for hydrogen storage capacity

Abstract

The potential application of materials referred to as perovskite hydrides in hydrogen storage – a crucial element of renewable energy systems – has sparked a great deal of interest. We use density functional theory (DFT) to investigate the structural, formation energy, hydrogen storage, electronics, thermoelectric and elastic properties of NaXH₃ (X = Be, Mg, Ca, and Sr) hydrides. The band gap is calculated using WC-GGA and WC-GGA+mBJ potentials. WC-GGA+mBJ potentials show improvement in band gap values. The thermoelectric properties of these compound are studied using post-DFT Boltzmann's techniques. The elastic constants and mechanical properties of the hydrides, such as their Shear modulus, Young’s modulus, Pugh ratio, Poisson ratios, anisotropic index and micro-hardness, are also calculated. Our findings show that all materials are mechanically stable and satisfy the Born criteria. The higher gravimetric ratios of all materials are good enough for storing hydrogen and can be used for advanced future applications. Furthermore, NaSrH₃ is the perfect candidate for thermoelectric applications due to its higher power factor and figures of merit ZT (≈ 1).