Oxygen adsorption and CO desorption behavior of B- and N-doped vacancy defected nuclear graphite by DFT study

Abstract

Oxygen adsorption and desorption of gasification products are two factors that influence graphite oxidation behavior. Whether the catalytic or inhibiting effect occurs after B and N doping still remains controversial. In this paper, the activation energies for the adsorption of oxygen and desorption of CO on a modified nuclear graphite surface, combining vacancy and dopants, are studied by density functional theory (DFT). Vacancy defected graphite is more sensitive to O₂ adsorption because of the unpaired electron on the dangling carbon atom. However, substitution with B or N makes the adsorption more difficult, since substituting C by a B or N atom eliminates the effect of the unpaired electron, which means that these dopants can be applied to improve oxidation resistance of nuclear graphite or other carbon materials. Desorption calculation of adsorbed radical (C–O) indicates that substitutional B or N atoms in graphite facilitate CO desorption, in this respect B or N dopants play a role of catalyst for graphite oxidation. Introduction of dopants such as B, N results in weaker O₂ adsorption capability on vacancy defected graphite while they help desorption of oxidation products such as CO. Both the inhibiting and catalytic effects of these dopants are an example of the compensation effect.