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In-situ TEM Study of Oxygen Surface Exchange on Ceria, Gd-doped Ceria and Pr-doped Ceria

Oxygen exchange reactions play an important role in many energy conversion applications. For example, in solid oxide fuel cells (SOFC), at the cathode interface, molecular oxygen is first reduced to oxygen ions and then diffuses through a solid electrolyte to interact on the anode side for fuel oxidation [1]. Oxygen exchange reactions are complex and consist of multiple steps including O2 absorption/desorption, molecular dissociation/association, electron transfer, and incorporation/removal oxygen into or from surface oxygen vacancies. Nonstoichiometric oxides, such as CeO2 and ceria-based doped materials, are ideal candidates for oxygen exchange applications, because of the ability of reversibly exchange lattice oxygen with the ambient environment while maintaining a stable structure [2]. Doping ceria with aliovalent cations, such as Gd and Pr, can significantly increase the oxygen vacancy concentration resulting in higher ionic conductivity [3]. Due to the complexity of the multi-step oxygen exchange reaction, the surface exchange properties and local electronic structure with different dopants are not well understood. To develop a deeper understanding of the materials, it is desirable to determine the oxygen surface exchange mechanisms that limit the exchange rate.