Interaction between Oxygen and Molten Carbonate: A DFT Study
Abstract
The interaction between oxygen and selected molten carbonates has been examined in this project using density functional theory (DFT) modeling. In particular, B3LYP/6-31G(d) 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 kJ/mol lower in energy than the tetrahedral one. The calculated enthalpy change of 2CO3 2- + O2 to CO4 2- is -19.4 kJ/mol, 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 kJ/mol. Structures of (K2CO3)4, ( Li2CO3)4 and (LiKCO3)4 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 (K2CO3)4, (Li2CO3)4 and (LiKCO3)4 will be the simplest cluster models to study the ORR process in SOFCs.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 01, 2011
- Accession Number
- ADA581579
Entities
People
- Arianna M. Gladney
Organizations
- Benedict College