Understanding adsorption of hydrogen atoms on graphene

TL;DR

This study uses first-principles calculations to analyze how hydrogen atoms adsorb onto graphene, revealing binding energies, barriers, and magnetic effects that influence adsorption patterns and stability.

Contribution

It provides detailed computational insights into hydrogen adsorption energetics and magnetic structures on graphene, highlighting the influence of site magnetization on binding and barriers.

Findings

Binding energies range from 0.8 eV to 1.9 eV.

Barriers to sticking are between 0.0 and 0.2 eV.

Magnetic structures can form with localized spin density.

Abstract

Adsorption of hydrogen atoms on a single graphite sheet (graphene) has been investigated by first-principles electronic structure means, employing plane-wave based, periodic density functional theory. A reasonably large 5x5 surface unit cell has been employed to study single and multiple adsorption of H atoms. Binding and barrier energies for sequential sticking have been computed for a number of configurations involving adsorption on top of carbon atoms. We find that binding energies per atom range from ~0.8 eV to ~1.9 eV, with barriers to sticking in the range 0.0-0.2 eV. In addition, depending on the number and location of adsorbed hydrogen atoms, we find that magnetic structures may form in which spin density localizes on a $\sqrt{3}{x}\sqrt{3}{R}30^{\circ}$ sublattice, and that binding (barrier) energies for sequential adsorption increase (decrease) linearly with the site-integrated magnetization. These results can be rationalized with the help of the valence-bond resonance theory of planar $\pi$ conjugated systems, and suggest that preferential sticking due to barrierless adsorption is limited to formation of hydrogen pairs.