Computational evaluation of KMgO3-xHx as an efficient hydrogen storage material

Abstract

In this present work, Density Functional Theory (DFT) calculations have been performed for perovskite KMgO3−xHxwith the GGA-PBE formalism as implemented in the CASTEP code. It is the first time that with the aim to investigate the structural, electronic, optical, and mechanical properties of KMgO3−xHx perovskite hydride material for hydrogen storage applications is carried out with varying substituent concentrations (x = 0, 0.3, 0.6, 0.9, 1.2, 1.5, 1.8, 2.1, 2.4, 2.7, and 3.0). It is clear from elastic constants and negative formation enthalpies that these compounds are stable and synthesizable. The elastic moduli, anisotropy, and brittleness decline with increasing H-inclusion. Increasing dopant concentration leads to a narrowing wide bandgap and causes a shift from an indirect to a direct-nature semiconductor. These findings indicate that the electronic properties of the compounds can be tailored by introducing dopants, making them suitable for various optoelectronic applications. The structural transformation occurred from cubic to distorted or pseudo-cubic upon hydrogen inclusion. This distortion resulted in a nearly equal value of lattice parameters, with a ≈ b ≈ c. In addition, the optical parameters (dielectric functions, refractive indices, extinction coefficient, optical reflectivity, absorption coefficients, and loss functions) were thoroughly explained within the energy range of 0-10 eV for photons. Optical characteristics enhanced upon H inclusion, making them suitable for optoelectronic applications. The incorporation of hydrogen has also enhanced hydrogen storage characteristics to 4.35 %, despite the challenges associated with high desorption temperatures and improved hydrogen uptake mechanisms, allowing a variety of transportation and practical uses in industry.