Theoretical Studies of Doped Solid Oxides for Fuel Cell Applications

摘要

Zirconia (ZrO_2) is of great importance as a support for systems where high ionic conductivity and mechanical stability are required. Doping/defects have a significant effect on the physical properties of this oxide by stabilizing the most symmetric phases, increasing the ionic conductivity and possible facilitating three phase interconnections in solid oxide fuel cells (SOFCs). Although Zirconia in its pure form exhibits different structures at high temperatures when it is alloyed with other oxides the high temperature cubic polymorph can be stabilized to temperatures low enough for fuel cell applications. Although there has been tremendous technological investment to obtain better materials, we are still far from an optimum solution. We start in this work with theoretical calculations as a support/participation in the search for more appropriate materials that will make this important technology viable in a wide range of applications in the near future. The calculations were performed in the framework of Density Functional (DFT) pseudopotential theory using the Projector Augmented Wave (PAW) with various approximations to the ex change-correlation functional. We investigate structural, electronic/band structure, density of states and charge densities for pure zirconia taking into consideration as well different dopants, their concentrations as well as vacancies for the various polymorphs with interest in fuel cell electrolyte applications.