(67f) Morphology of Sodium Carbonate and Its CO2 Adsorption Performance: A First-Principles Investigation

Sodium carbonate (Na₂CO₃) is a promising candidate for CO₂ capture from flue gas. The morphology of sodium carbonate and co-adsorption of CO₂ and H₂O on several low-index surfaces and step edges are investigated by density functional theory (DFT) methods. We have identified six different bulk structures that are a few meV per formula unit lower in energy than the optimized experimental structure of Na₂CO₃. These structures mainly differ from one another in the orientation of the carbonate groups. This means that there are many nearly degenerate structures available to Na₂CO₃ because of rotation of the carbonate groups. The ascending order of surface energy is (101) < (001) < (010) < (111) < (011) < (100) < (110) and the crystal shape of sodium carbonate is predicted by performing a Wulff construction. We find only Na-termination surface is likely to have significant presence by taking a Boltzmann distribution of the energies of surfaces having different terminations. We also find that CO₂ and H₂O adsorb competitively on the surface O sites. The calculated adsorption energies depend significantly on the surface structure, which indicates that the CO₂ adsorption performance of Na₂CO₃ can be tuned by exposing different surface facets. Reaction barriers for bicarbonate formation on terrace, step edge, and defect sites will be discussed.