Effect of electronic alteration on hydrogen storage and optical response in NaMgF3 using DFT approach

Abstract

Due to the depletion of non-renewable fossil fuels, energy production and storage is a matter of concern for scientific community. Hydrogen being environmental friendly was presented by the scientists a fruitful replacement of fossil fuel, but the storage of hydrogen is still a matter of concern. Safety concerns are associated with hydrogen as an alternative fuel because it is difficult to store and transport. Perovskite materials have attracted researchers as new materials for solid hydrogen storage. In this present work, Density Functional Theory (DFT) calculations have been performed for perovskite NaMg F3−xHx with the GGA-PBE formalism as implemented in the CASTEP code. The aim of the work is to investigate the structural, electronic and optical properties of NaMg F3−xHx perovskite hydride material for hydrogen storage applications with varying substituent concentrations (x = 0, 0.3, 0.6, 0.9, 1.2). The formation enthalpy of the studied material for each concentration reveals that these compounds are stable and synthesizable experimentally. The hydrogen inclusion in pristine material affects the electronic states significantly which is elaborated using band structure and density of states plots. After Hydrogen inclusion, change in density of states has been observed and the band gap is decreased from 5.74eV to 3.311eV. The alteration of electronic band gap directly influences the optical behavior of the material, thus optical response such as dielectric function, absorption and refractive index was also calculated. For hydrogen storage application, gravimetric storage capacity (Cwt%) was calculated for all concentrations of hydrogen inclusion. The value varied from 0.30% to 1.87%, indicating that the presented material is an efficient material not only for opto-electronic applications but also for the hydrogen storage applications.