Defects induced metallized boron hydride monolayers as high-performance hydrogen storage architecture

Abstract

Experimental synthesis of two-dimensional boron hydride monolayer (BH-ML) (J. Am. Chem. Soc. 2017, 139, 13,761) has motivated us to explore its application in clean energy storage. We have performed first-principles calculations based on spin-polarized density functional theory (DFT) to investigate the ground-state geometries, electronic structures, metal doping mechanism and hydrogen (H₂) storage propensities of BH-ML. Pristine BH-ML barely binds H₂, however the introduction of selected light metal dopants, such as Na, Ca, and Sc, improved the H₂ adsorption mechanism tremendously. Binding energies of dopants under maximum doping concentration are found as −1.51, −2.49, and −4.54 eV for Na, Ca, and Sc, respectively, which are strong enough to ensure their uniform distribution over BH-ML without clustering. Each dopant donated bulk of its charge to BH-ML and transforms into cation and anchored multiple H₂ molecules through electrostatic and van der Waals interactions. We have found that a maximum of 24H₂ molecules could be adsorbed on BH-ML decorated with four metal dopants of Na, Ca, and Sc. Average adsorption energies of H₂ are found within desirable range. Our results show that Na, Ca, and Sc decorated BH-ML could reach to exceptionally high H₂ storage capacities of 14.84, 12.28, and 11.70%, respectively, which easily surpass the US Department of Energy (DOE) target of 5.50 wt% by 2025. We have further applied thermodynamic analysis to explain the H₂ storage proficiencies at practical conditions of temperatures and pressures. Our report confirms that BH-ML decorated with light metal dopants are ideal option for high-capacity H₂ storage applications.