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Interaction between Oxygen and Molten Carbonate: A DFT Study

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The interaction between oxygen and selected molten carbonates has been examined in this project using density functional theory DFT modeling. In particular, B3LYP6-31Gd has been used for all geometry optimization, charge calculation, and orbital analysis. Three oxygen species including molecular oxygen O2, superoxide O2 -, peroxide O2 2- and atomic oxygen ion O2- are considered. The combination of oxygen with single carbonate CO3 2- forms molecular complexes, CO5 2- and CO4 2-, respectively. For CO4 2-, the planar trigonal structure is 260.0 kJmol lower in energy than the tetrahedral one. The calculated enthalpy change of 2CO3 2- O2 to CO4 2- is -19.4 kJmol, implying CO4 2- as a likely intermediate. In CO5 2-, the O-O distance is stretched to 1.321 0.106 longer than in the gas phase dioxygen. The total charge of O2 is -0.672 e, indicating partial reduction of oxygen upon binding to carbonate. The binding energy of O2 to CO3 2- is 105.3 kJmol. Structures of K2CO34, Li2CO34 and LiKCO34 were also studied as simplest cluster models for molten carbonates with different compositions. Optimized average K-O and Li-O distances are 2.6602 and 1.9047 , which agrees well with the x-ray diffraction values of 2.7833 and 1.9947 , respectively. When one extra electron is attached to the clusters, DFT charge analysis shows that the electron density is shared by the alkali metals and these electrons will then be used to reduce the oxygen. In future, oxygen will be introduced to the carbonate clusters and its reduction will be studied in more detail. Therefore, we have found that the binding of oxygen to carbonate can promote the ORR in SOFCs and that K2CO34, Li2CO34 and LiKCO34 will be the simplest cluster models to study the ORR process in SOFCs.

Subject Categories:

  • Inorganic Chemistry
  • Physical Chemistry
  • Quantum Theory and Relativity

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