|AVS 54th International Symposium|
|Surface Science||Wednesday Sessions|
|Session:||Oxide Surface Structure I|
|Presenter:||C. Stampfl, The University of Sydney, Australia|
|Authors:||M. Fronzi, The University of Sydney, Australia
A. Soon, The University of Sydney, Australia
B. Delley, Paul Scherrer Institut, Switzerland
E. Traversa, University of Rome "Tor Vergata", Italy
C. Stampfl, The University of Sydney, Australia
|Correspondent:||Click to Email|
Because of its peculiar and desirable properties, cerium oxide, has been the object of intense interest in relation to solid oxide fuel cells (SOFC) as well as to heterogeneous catalysis, e.g., it can effectively reduce NOx emissions as well as convert harmful carbon monoxide to carbon dioxide. Since it behaves as a good ionic transporter, and at the same time as a good catalyst, cerium oxide finds application both as an electrolyte and as an anode support in SOFCs. In anode reactions, it plays an active part in the catalysis of the fuel cell, and thus it is important to investigate the properties of the oxide surfaces exposed to an anodic fuel cell gas environment (e.g. methane, CH4). Furthermore, for a particular subclass of fuel cells (single chamber) the anodic side is exposed to oxygen as well as the fuel. For this reasons it is of high importance to understand the behavior of cerium oxide in varying oxygen environments. Using density-functional theory as implemented in the DMol3 code,1 we investigate the structure and stability of CeO2 surfaces under realistic conditions using the approach of ab initio atomistic thermodynamics.2 From calculation of the surface free energy, we obtain the pressure-temperature surface phase diagram. This allows us to identify and predict stable, and potentially catalytically important, structures and stoichiometries under varying pressure and temperature conditions. We investigate many different geometries for the low index (100), (110), and (111) surfaces, including structures containing defects. For a wide range of the oxygen chemical potential we find that the thermodynamically most stable surface is CeO2(111). For increasingly more reducing conditions, surfaces with oxygen vacancies become more stable, followed by a structure which through significant atomic relaxation, exhibits an interesting morphological transformation into a structure with a Ce2O3(0001)-like surface.
1B. Delley, J. Chem. Phys. 92, 508 (1990); ibid. 113, 7756 (2000).
2K. Reuter, C. Stampfl and M. Scheffler, in Handbook of Materials Modeling, Volume 1, Fundamental Models and Methods, Sidney Yip (Ed) (2005).