Berlin 2008 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 93: Surface Chemical Reactions

O 93.1: Vortrag

Freitag, 29. Februar 2008, 10:15–10:30, MA 043

A two-step mechanism for the oxidation of vacancies in graphene — •Johan M. Carlsson, Felix Hanke, and Matthias Scheffler — Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin

Complete oxidation of graphitic carbon materials leads to combustion and the formation of CO₂, but it has been suggested that partial oxidation of vacancies on the basal plane can yield catalytically interesting materials. The characterization of such oxidized graphite in temperature-programmed desorption (TPD) experiments detected a surprising amount of CO and significantly less CO₂ [1]. This work aims to clarify the oxidation mechanisms and surface structures under different experimental conditions. We use density functional calculations with PBE exchange-correlation to obtain the structural and energetic properties of oxidized graphene vacancies. To understand the TPD spectra, reaction barriers and rates for CO and CO₂ desorption are calculated from transition state theory and the nudged elastic band method. An ab-initio thermodynamics analysis shows a significant partial pressure-dependence of the oxygen content in vacancies. This indicates a two step mechanism for the initial oxidation, by which strongly bound CO-releasing C-O-C and C=O groups saturate the vacancies under the ultra-high vacuum conditions of TPD experiments. Atmospheric partial pressures lead to additional oxygen adsorption into extended groups such as C-O-C=O and O=C-O-C=O, which in return can desorb as CO₂. [1] B. Marchon et al., Carbon 26, 507 (1988).