Enhancement of hydrogen storage characteristics of Na2CaH4 hydrides by introducing the Mg and Be dopant: A first-principles study

This work utilizes the DFT calculations to investigate the physical properties and hydrogen storage capabilities of pristine and Mg/Be (Na2Ca0.5(Mg/Be)(0.5)H-4) doped Na2CaH4 hydrides. First, we modeled the Na2CaH4 hydride and then investigated the effect of Mg and Be dopants on the physical and hydrogen storage properties. Negative formation enthalpies indicate the structural stability of understudy compounds. The computations of elastic constants reveal that the under-investigation compounds are mechanically stable as they fulfill the Born stability criteria. The assessment of electronic properties manifests the reduction of the bandgap from 2.57 to 2.22 eV due to the inclusion of dopants. This tunability has the potential to influence the adsorption properties of the material, which may lead to an increase in the binding energies of hydrogen molecules to pre-adsorbed atoms. As a result, materials having a narrower band gap could be better suited for hydrogen storage and other processes related to it. Furthermore, several optical parameters have been computed and compared to examine the impact of the Mg/Be dopant on the optical response of the host compound. It is worth mentioning that gravimetric and volumetric storage capacities of the Na2CaH4 compound have been enhanced by Mg/Be doping from 4.44 to 5.36 wt% and 59.52 to 71.98 gH(2)l(-1), respectively, satisfying the target of US-DOE. Furthermore, the desorption temperature has also been improved from 498 to 426 K.