Exploring the structural, electronic, optical, mechanical properties and hydrogen storage capabilities of alkali metal molybdenum hydrides XMoH3 (X=Li, Na, K): A DFT study

Abstract

Hydrogen has attracted considerable attention in recent years because of its potential as an energy source, leading to a strong interest in hydrogen storage. The investigations primarily concentrate on analyzing the hydrogen storage properties of recently introduced compounds for potential uses. An analysis of the XMoH₃ (X = Li, Na, K) compounds has been conducted using density functional theory (DFT) calculations. This study aims to uncover their unique characteristics and hydrogen storage capacities, making it the first of its type. The compounds being examined are refined in the cubic phase, leading to refined lattice constants of 3.70 Å, 3.69 Å, and 3.89 Å for LiMoH₃, NaMoH3, and KMoH3, respectively. These hydrides have thermodynamic stability, as indicated by their negative formation enthalpies. The XMoH₃ (X = Li, Na, K), demonstrate significant gravimetric H₂ storing capacities. The LiMoH₃, NaMoH₃, and KMoH₃ have gravimetric H₂ storage densities of 2.86 wt%, 2.49 wt%, and 2.19 wt%, respectively. These characteristics render them potentially appropriate for hydrogen storage applications. Moreover, the electrical properties provide as evidence of the metallic makeup of these compounds. In addition, the mechanical properties of these compounds have been analyzed by evaluating elastic constants such as Young modulus and Pugh's ratio. According to the analysis, these compounds satisfy the stability requirement specified by Born. Furthermore, the examination of Pugh's ratio and Cauchy pressure reveals that these hydrides exhibit a fragile characteristic. Furthermore, the study has examined thermodynamic properties, specifically the Debye temperature.