Fluorine, nitrogen doping, and triaxial strain effects on the structural stability and hydrogen storage properties of lithium hydride LiH: DFT investigation

Abstract

This research comprehensively addressed various aspects of hydrogen storage, with a focus on metallic hydride materials, lithium hydride LiH, one of the lightest reversible metal hydrides, boasts a remarkable gravimetric density of up to 12.67 wt% and an impressive volumetric capacity of 4.95 Kg/100 L. Despite these strengths, challenges accompany lithium hydride, such as its elevated formation energy and a high desorption temperature around 600 K–700 K. In this work, ab initio calculations based on Density Functional Theory (DFT) were used to study the thermodynamic and electronic properties of this material with the aim of reducing the high temperature of decomposition while preserving a significant gravimetric capacity and satisfactory stability in line with the U.S. Department of Energy (DOE) standards for solid-state hydrogen storage (ΔHf = - 40 kJ/mol.H2 and Td = 289 K–393 K). The results obtained show the influence of the doping effect firstly (Li1-xFxH, Li1-xNxH) on the improvement of the hydrogen storage properties, with a percentage gain of 50.64% for 4% doping with F and 49.08% for 8% doping with N. Secondly, a 38.63% gain in thermodynamic stability was observed by applying triaxial compressive stresses to the LiH compound.