Strain-modulated photocatalytic hydrogen production and storage capacity analysis of Li2S monolayer: A DFT approach

Abstract

The theoretical prospect of Li₂S monolayer for hydrogen production and storage is reported. The density functional theory is used to examine its structural, electronic, photocatalytic, optical properties, and hydrogen storage capabilities under biaxial strain. The phonon dispersion graphs alongside AIMD simulations at 300 K & 500 K confirmed the structure as stable. The investigated material revealed itself as a direct band gap semi-conductor and good optical absorption in the visible region under all applied strains. The suitable band edge positions and spontaneous water splitting for hydrogen evaluation reaction under 4% biaxial strain make it a leading candidate for hydrogen production. Furthermore, the hydrogen storage analysis revealed that the highest adsorption energy for H₂ adsorption appears when monolayer is under -4% strains. For full storage analysis, studied monolayer adsorbed 21 H₂ with an average adsorption energy ($\overline{E_{ad}}$) of -0.276 eV and desorption temperature of 352.9 K at -4% strain. Its gravimetric capacity is evaluated as 9.3% which swiftly surpasses the landmark of 5.5% from US department of energy and many renowned materials like C₃N (6.78%), and C₃N₄ (7.29%). Therefore, Li₂S monolayer under biaxial strain can be estimated as an ideal candidate for hydrogen’s production and storage.