It has become an imminent necessity to deal with the ever increasing production of CO2 as the result of employing fossil resources. Carbon dioxide has become the most important factor in the climate change. 32.1 billion tons were emitted in 2015. In order to keep global warming below 2 degree Celsius, the greenhouse gas emission has to be reduced to zero until 2060. Therefore, the emitted CO2 needs to be removed from the atmosphere and captured or reused. The transformation of carbon dioxide into useful chemicals and fuels has therefore become one of the major societal challenges of the future.
2D materials like graphene and 2D metals (like Pt) show very attractive catalytic properties. They can therefore be used in the catalytic conversion of hazardous CO2 molecules to more environmentally friendly hydrocarbons. The present work will take place in a highly intradisciplinary environment. Within this environment, there is a focus on the formation of intercalated 2D metals (i.e., within a SiC/graphene interface). For these types of 2D material, their reactivity towards CO2 will be of a special interest to study. The present project will therefore be focused on the effect of various intercalated SiC//graphene surfaces on the reduction of CO2 species to various more environmentally friendly hydrocarbons (e.g. CH3OH). We intend to study the correlations between CO adsorption energy and the other possible CxHyOz intermediates adsorption energy, the limiting-potential elementary step, and selectivity to CH3OH, CH4, HCOOH, and H2. Examples of intercalated metals are Ge, Ag and Au. There will also be an intercalation with H.
First-principle density functional theory (DFT) calculations have become a useful tool for many inorganic materials of practical importance. The chemical bonding within these materials is a mixture between covalent, ionic and metallic bonding and therefore properties like thermodynamics (e.g., adsorption energies, barrier of migrations) cannot be determined reliably using empirical approaches. An atomic-level understanding of the surface behaviour can, hence, be reached by performing DFT calculations in synergy with corresponding experimental activities. The calculations within the present project will be performed using the vienna ab initio simulation package (VASP) with the generalized gradient approximation (GGA) level as proposed by Perdew−Burke−Ernzerhof (PBE). In order to account for the van der Waals interaction between various layers in the model, the Grimme’s method (DFT-D2) will be employed along with the PBE functional. Transition states will be searched using the climbing-image nudged elastic band method (CI-NEB). The free energy profile will be obtained using ΔG = ΔE – TΔS + ΔZPE, where ΔE is the total energy change as obtained from DFT calculations, ΔS denotes the entropy change, and ΔZPE is the change in the zero point energies. Moreover, the TΔS values of free molecules will be obtained from the NIST database, while the TΔS of the adsorbates and ZPE of the free molecules and adsorbates will be determined by calculating vibrational frequencies through density functional perturbation theory.