Oxygen migration on the graphene surface. 2. Thermochemistry of basal-plane diffusion (hopping)

• Published in: Carbon (New York) Vol. 49; no. 13; pp. 4226 - 4238
• Main Authors: Radovic, Ljubisa R., Suarez, Alejandro, Vallejos-Burgos, Fernando, Sofo, Jorge O.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.11.2011; Elsevier
• Subjects: Barriers; Carbon; Charge distribution; Chemistry; Colloidal state and disperse state; Correlation; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Fullerenes and related materials; diamonds, graphite; General and physical chemistry; Graphene; Materials science; Migration; Physics; Porous materials; Specific materials; Spectators; Surface chemistry; Surface physical chemistry; Micropore; Porous materials; Migration; Mobility; Forces; Thermodynamics; Substitution; Diffusion coefficient; Electron density; Epoxides; Activation energy; Reaction intermediates; Oxygen; Scattering; Carbon; Geometry; Microporosity; Density functional; Adsorption; Correlations; Distribution; Density functional method; Affinity; Gas phase; Electrons
• ISSN: 0008-6223; 1873-3891
• DOI: 10.1016/j.carbon.2011.05.037

Thermodynamic affinities, activation energies and diffusion coefficients for oxygen mobility on the graphene surface are calculated using density functional theory (DFT). We report and discuss the effects of geometry, charge distribution and heteroatom substitution on the migration of epoxy oxygen on the basal plane: both the driving force and the ease of surface hopping are very sensitive to their variations. A significant decrease in the hopping energy barrier is observed when graphene contains free edge sites and oxygen functionalities, as well as upon an increase in electron density; conversely, the barrier increases as a consequence of electron removal, and the propensity for graphene ‘unzipping’ also increases. There is a correlation between the hopping barrier and the C–O bond strength of the leaving epoxide group. Under the most favorable conditions investigated, oxygen mobility is quite high, of the same order as that of gas-phase O 2 in micropores (ca. 10 −9 m 2/s). This is consistent with the increasingly acknowledged role of basal-plane oxygen as a protagonist (e.g., reaction intermediate), instead of a spectator, in the wide variety of adsorption and reaction processes involving sp 2-hybridized carbon materials.