Why H Atom Prefers the On-Top Site and Alkali Metals Favor the Middle Hollow Site on the Basal Plane of Graphite

Abstract

In this work, the different adsorption properties of H and alkali metal atoms on the basal plane of graphite are studied and compared using a density functional method on the same model chemistry level. The results show that H prefers the "on-top site" while alkali metals favor the "middle hollow site" of graphite basal plane due to the unique electronic structures of H, alkali metals, and graphite. H has a higher electronegativity than carbon, preferring to form a covalent bond with C atoms, whereas alkaline metals have lower electronegativity, tending to adsorb on the highest electrostatic potential sites. During adsorption, there are more charges transferred from alkali metal to graphite than from H to graphite.

Tunable charge donation and spin polarization of metal adsorbates on graphene using an applied electric field

“…1(a). Among three possible candidate sites (on-top, bridge, and hollow sites), the hollow site was found to be preferable for all three metal atoms, which agrees with the previous work [16] on the Cs atom where the nature of binding was attributed to ionic bonding [2,[16][17][18]. The calcaulated adsorption heights exhibit a trend related to the ionic radius of the metal atom [2].…”

Mass transfer in coal seams for CO2 sequestration

“…The three mechanisms coexist, playing different roles. We speculate that the adsorption induced carbon bond extension quantified by the authors29 could be the dominant mechanism for coal permeability variations. Edge‐site plane deformation due to the solvation pressure change8 and the carbon‐metal bond extension30, 31 in adsorption processes may mainly affect mass transfer in micro‐pores with relatively small effects on cleat permeability.…”

“…Through molecular orbital theory calculations using the software package Gaussian 98, Zhu et al,29 have observed carbon‐carbon (CC) bond extensions during hydrogen adsorption processes. In that work, three types of adsorption sites on single layer graphite are investigated: (1) the “on‐top site” directly above a carbon atom (called t site); (2) the “bridging site” above a CC bond (called b site); and (3) the “middle hollow site” above a hexagon (called m site).…”

“…In that work, three types of adsorption sites on single layer graphite are investigated: (1) the “on‐top site” directly above a carbon atom (called t site); (2) the “bridging site” above a CC bond (called b site); and (3) the “middle hollow site” above a hexagon (called m site). These different sites are graphically shown in the original article 29. The following two models were proposed in the previous study: model 1‐A has an odd electron number with an open‐shell electronic state, and model 2‐B has an even electron number with a closed‐shell electronic state.…”

Theory of Doping: Monovalent Adsorbates

“…This is qualitatively consistent with the electrostatic models, as |q|≪e in both cases, but using the Bader charge in the context of Coulomb scattering would lead to an underestimation of the scattering strength. A hydrogen charge |q|≪e has also been obtained within Mulliken population analysis by Zhu et al (2005). Experimentally, the contribution of H adatoms on graphene to Coulomb scattering has not yet been determined.…”