First-principles quantum computations to investigate prospects of Mg2FeH6 for optoelectronics and hydrogen-storage applications

Abstract

To overcome the growing energy crisis and hazardous effect of conventional energy sources on environment and inhabitants, hydrogen has been proposed as an excellent alternative clean energy source. In particular, the storage of hydrogen in solid-state materials and its on-demand release for potential energy applications is the novel energy-efficient technology. In this regard, metal hydrides have shown promising hydrogen-storage capacity. However, high gravimetric and volumetric density, low thermodynamic stability, and high kinetics of metal hydrides is vital to enhance the hydrogen storage and releasing efficiency at routine temperature and pressure. In this regard, Mg2FeH6 has shown promise on hydrogen-storage applications on account of its high hydrogen volume density 150 kg m−3 (more than double that of liquid hydrogen), and a gravimetric hydrogen density of 5.66 wt%. In this work, we first time employed first-principles density functional (DFT) approach within GGA + U methodology to investigate the structural, electronic, magnetic, and optical properties of Mg2FeH6. Our computed results revealed wide band gap semiconductor nature of Mg2FeH6 having a direct band gap of 3.194 eV at point X. As revealed by the DFT analysis, Mg2FeH6 was magnetic in ground state with magnetic moment 6.40 μB. The calculated optical properties include dielectric constants, absorption coefficient, reflectivity, energy loss function, and refractive index. The structural properties agree with experimental/theoretical results while electronic and optical properties differ considerably from the available theoretical data computed with different methods.