CeO2 has received considerable interest as an electrolyte for intermediate temperature solid oxide fuel cells. [1] Unfortunately, within this temperature range (~500-1000K), CeO2 displays poor ionic conductivity, while high temperatures and low oxygen partial pressures can reduce Ce(IV), due to facile oxygen vacancy formation, [2] and cause electronic conductivity. To improve the ionic conductivity, aliovalent doping is commonly employed, with trivalent species (e.g. Y) a particular focus due to their creation of charge compensating vacancies, forming an O2- diffusion pathway without Ce(III). Experimental evidence [3] has corroborated the increased ionic conductivity from trivalent dopants, however a detailed understanding on the effect of the dopant on the electronic structure of CeO2 and a full exploration of the range of trivalent dopants has been lacking. This study considers two aspects of trivalent doping using density functional theory simulations: (i) the formation of charge compensating vacancies and their role in O2- conductivity, and (ii) their effect on the reducibility of CeO2. These aspects are explored for a range of p-, d- and f-block ions. The first part of the study focusses on the position of the dopant ions to the vacancies, as dopant-vacancy association can limit ionic diffusion. The results indicate a clear relationship between the dopant species ionic radius and its position relative to the vacancy. In addition, some rare earth dopants (e.g. Dy, Nd) are found to have low dopant-vacancy association energies, suggestive of better ionic conductivity. The second aspect of the study, which is largely ignored in the literature, shows that the reduction energy correlates with the defect structure, therefore being only indirectly influenced by the ionic radius. [1] Brett et al., Chem. Soc. Rev., 37 , 1568 (2008).[2] Scanlon et al., J. Phys. Chem. C, 113 , 11095 (2009).[3] Fu et al., Int. J. Hydrogen Energy, 35, 745 (2010).

Doping CeO<sub>2</sub> with trivalent cations: Defect structures and reducibility

246th National Meeting (2013)

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Doping CeO2 with trivalent cations: Defect structures and reducibility

Doping CeO₂ with trivalent cations: Defect structures and reducibility