Interplay between van der Waals, Kubas, and chemisorption process when hydrogen molecules are adsorbed on pristine and Sc-functionalized BeN4

Abstract

Inspired by the recent successful synthesis of the Dirac material BeN4, the interaction of dihydrogen with pristine and Sc-functionalized BeN4 is investigated using dispersion-corrected density functional theory and ab-initio molecular dynamics simulations. The simulation results show that hydrogen molecules are physisorbed to pristine BeN4 with an adsorption energy of −0.12 eV and have low H2 uptake (∼1.3 wt%) at 100 K. Functionalization of the scandium atom on BeN4 monolayer enhances adsorption energy and desorption temperature of hydrogen molecules beyond room temperature, as calculated from ab-initio molecular dynamics simulations. Using the DFT-D2 and DFT-D3 dispersion corrected DFT, we report that each Sc atom functionalized on BeN4 surface can reversibly adsorb five hydrogen molecules through Kubas interactions with an average adsorption energy of −0.53 and −0.42 eV/H2, respectively. The storage capacity of hydrogen for Sc-decorated BeN4 is 7.86 wt% at room temperature, which drops to 6% at 400 K. At 500 K, three hydrogen molecules get desorbed from the Sc-decorated BeN4, and the remaining two dissociate into isolated H-atoms, leading to irreversible hydrogen storage. The diffusion barrier for the clustering of Sc atoms is found to be 3.41 eV, calculated using the CI-NEB method. This study builds an understanding of the interaction mechanisms responsible for practically suitable hydrogen uptake in metal-functionalized 2D nanomaterials.