P. R. L. Keating, D. O. Scanlon and G. W. WatsonCeO2 has been shown to be a promising candidate for the electrolye in intermediate temperature solid oxide fuel cells. Stoichiometric CeO2 is a poor ionic conductor, displaying a conductivity of around 3.13x10-3 Scm-1. Furthermore, at low oxygen pressures CeO2 displays unwanted electronic conductivity which can short circuit the fuel cell. However, the ionic conductivity of CeO2 can be greatly increased through the introduction of dopants. The most common candidates for doping CeO2 are trivalent cations such yttrium, lanthanum, gadolinium and bismuth. These dopants form charge compensating oxygen vacancies which can act as potential pathways for ionic diffusion. The advantage of oxygen vacancies formed in this way is that they do no introduce the unwanted electronic conductivity associated with reduced CeO2. We are currently investigating CeO2 doped with a series of trivalent cations using DFT U techniques. Our goal is to determine suitable dopants that will increase the ionic conductivity while hindering further reduction of CeO2. Ultimately we hope to predict suitable materials for the next generation of solid oxide fuel cells.