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Published online by Cambridge University Press: 31 January 2011
In solid oxide fuel cells, the mechanism of hydrogen oxidation is complex. During this process, protonated forms of monoclinic zirconia may be formed, motivating their study within the framework of density-functional theory (DFT). Using the HCTH/120 exchange-correlation functional, the monoclinic phase of zirconia is, correctly, predicted to be more stable than cubic or tetragonal polymorphs at 0 K, in agreement with previous theoretical results. Several local minima are identified of a proton in monoclinic zirconia, modeled using (up to) a 3×3×3 arrangement of unit cells, in which the proton is bonded to one of the two available oxygen atom types, O1 or O2. The lowest energy structure of the proton bonded to O1 is favored by 0.39 eV compared to that of the proton bonded to O2. Based upon a vibrational analysis as well as finite-temperature Born-Oppenheimer molecular dynamic simulations, this preference of the proton for O1 is suggested to persist at fuel cell operating temperatures.