Empowering hydrogen storage properties of haeckelite monolayers via metal atom functionalization

Abstract

<p>Using hydrogen as an energy carrier requires new technological solutions for its onboard storage. The exploration of two-dimensional (2D) materials for hydrogen storage technologies has been motivated by their open structures, which facilitates fast hydrogen kinetics. Herein, the hydrogen storage properties of lightweight metal functionalized <i>r</i>₅₇ haeckelite sheets are studied using density functional theory (DFT) calculations. H₂ molecules are adsorbed on pristine <i>r</i>₅₇ via physisorption. The hydrogen storage capacity of <i>r</i>₅₇ is improved by decorating it with alkali and alkaline-earth metals. In addition, the in-plane substitution of <i>r</i>₅₇ carbons with boron atoms (B@r₅₇) both prevents the clustering of metals on the surface of 2D material and increases the hydrogen storage capacity by improving the adsorption thermodynamics of hydrogen molecules. Among the studied compounds, B@<i>r</i>₅₇-Li₄, with its 10.0 wt% H₂ content and 0.16 eV/H₂ hydrogen binding energy, is a promising candidate for hydrogen storage applications. A further investigation, as based on the calculated electron localization functions, atomic charges, and electronic density of states, confirm the electrostatic nature of interactions between the H₂ molecules and the protruding metal atoms on 2D haeckelite sheets. All in all, this work contributes to a better understanding of pure carbon and B-doped haeckelites for hydrogen storage.</p>