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O: Fachverband Oberflächenphysik

O 68: Surface dynamics: Reactions, elementary processes and phase transitions I

O 68.3: Vortrag

Mittwoch, 14. März 2018, 15:30–15:45, MA 043

Free energy landscape of graphene surface reactions from ab initio simulations — •Mateusz Wlazlo and Jacek Majewski — Faculty of Physics, University of Warsaw, Poland

We study methane (CH₄) and carbon dioxide (CO₂) decomposition and adsorption processes on monolayer graphene. These classes of reactions are important in chemical vapor deposition (CVD) growth of graphene or in CH₄-CO₂ exchange reactions, for example. The occurrence of this exchange is advantageous in the removal and storage of atmospheric CO₂.

The studies are based on ab initio molecular dynamics methods implemented in the framework of planewave density functional theory. Free energy profiles featuring energy barriers for different steps of the reaction are computed using the so-called Blue Moon ensemble method. The barriers are much lower than experimental bond dissociation energies for gaseous species, strongly indicating that graphene surface acts as a catalyst of decomposition reactions. However, the barriers are still much higher than on nickel surface. This suggests that monolayer formation should be favored over multilayer graphene, which reinforces the position of nickel as a suitable substrate for large-scale, high-quality CVD graphene growth.

Calculations show different preferred mechanisms of CH₄ and CO₂ adsorption, depending on surface morphology. On ideal graphene, dissociative adsorption is preferred whereas on defect sites, such as the Stone-Wales defect, direct chemisorption of CO₂ occurs with higher likelihood.