Enhanced H2 adsorption on 2D B4N monolayer modified with Na atoms: A density functional theory exploration

Abstract

In this study, H2 adsorption properties on two-dimensional (2D) B4N monolayer modified with Na atoms are comprehensively investigated via density functional theory (DFT). Our results expose the intrinsic 2D B4N monolayer barely adsorb H2 molecules owes to a weak H2 adsorption energy. However, Na atom can be strongly anchored on the surface of 2D B4N monolayer with a large binding energy, which results in that the metal clustering is prevented. Meanwhile, H2 adsorption energy is drastically enhanced by introduced Na atom on B4N monolayer. Moreover, Na/B4N complex can adsorb up to 10 H2 molecules with average adsorption energy of −0.109 eV/H2 while 2Na/B4N complex can adsorb up to 20 H2 molecules with average adsorption energy of −0.116 eV/H2. The obtained H2 adsorption energy falls into an optimal range between −0.1 eV/H2 and −0.8 eV/H2 for mobile hydrogen storage applications. Also, the hydrogen storage gravimetric density reaches 7.27 wt% and exceeds the latest objective of 6.5 wt% from U.S. Department of Energy (DOE). In addition, Mulliken atomic charges analysis, charges density difference and projected density of states systematically reveal H2 adsorption mechanisms mainly from polarization effect and orbital hybridization. Ab initio molecular dynamic (AIMD) simulations using Nose-Hoover (NH) chain thermostat under canonical (NVT) ensemble manifest H2 molecules can be easily released from the 2Na/B4N complex under indoor temperature at 300 K. Our theoretical study guarantee 2D B4N monolayer modified with Na atoms can be recognized as a prospective hydrogen storage material.