Thermodynamic affinities, activation energies and diffusion coefficients for oxygen mobility on the graphene surface were calculated using density functional theory. The effects of geometry, charge distribution and hetero-atom substitution upon the migration of epoxy oxygen on the basal plane were reported (table 14). Both the driving force and the ease of surface hopping were very sensitive to their variation. A significant decrease in the hopping energy barrier was observed when graphene contained free edge sites and oxygen functionalities, as well as an increase in electron density. On the other hand, the barrier increased as a consequence of electron removal, and the propensity for so-called graphene unzipping also increased. There was 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 was quite high, of the same order as that of gas-phase O2 in micropores (about 10-9m2/s). This was 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 sp2-hybridized carbon materials.

Oxygen Migration on the Graphene Surface. 2. Thermochemistry of Basal-Plane Diffusion (Hopping). Radovic, L.R., Suarez, A., Vallejos-Burgos, F., Sofo, J.O.: Carbon, 2011, 49[13], 4226-38

Table 14

Surface diffusivity of O on graphene