Facile Conversion of Layered Ruddlesden-Popper-Related Structure Y 2 O 3 -Doped Sr 2 CeO 4 into Fast Oxide Ion-Conducting Fluorite-Type Y 2 O 3 -Doped CeO 2 Ryan Georg Gerlach, Surinderjit Singh Bhella, and Venkataraman Thangadurai* UniVersity of Calgary, Department of Chemistry, 2500 UniVersity DriVe NW, Calgary, Alberta, T2N 1N4, Canada Received September 8, 2008 The present work shows a new solid- and gas-phase reaction technique for the preparation of a fast oxide-ion- conducting Y 2 O 3 -doped Ce 1-x Y x O 2-δ (x ) 0.1, 0.2) (YCO), which involves the reaction of layered (Ruddlesden-Popper K 2 NiF 4 -type) structure Y 2 O 3 -doped Sr 2 CeO 4 (YSCO) with CO 2 at an elevated temperature and subsequent acid- washing. A powder X-ray diffraction study revealed the formation of a single-phase cubic fluorite-type YCO for the CO 2 -reacted and subsequent acid-washed product. Energy dispersive X-ray analysis showed the absence of Sr in the CO 2 -treated and subsequent acid-washed product, confirming the transformation of layered YSCO into YCO. The cubic lattice constant was found to decrease with increasing Y content in YCO, which is consistent with the other YCO samples reported in the literature. The scanning electron microscopy study showed smaller-sized particles for the product obtained after CO 2 - and acid-washed YCO samples, while the high-temperature sintered YCO and the precursor YSCO exhibit larger-sized particles. The bulk ionic conductivity of the present CO 2 -capture-method- prepared YCO exhibits about one and half orders of magnitude higher electrical conductivity than that of the undoped CeO 2 and was found to be comparable to those of ceramic- and wet-chemical-method synthesized rare- earth-doped CeO 2 . Introduction Oxide ion electrolytes are ionic conductors in which the current is carried by the migration of oxide ions through the oxide ion vacancies. 1 They find applications in several solid- state ionic devices such as solid oxide fuel cells (SOFCs), electrolysis, gas sensors (e.g., O 2 ,H 2 , CH 4 , etc.), and oxygen pumps. 2-8 Presently, SOFC technology has generated im- mense interests due to its high efficiency and clean conver- sion of energy and potential to be powered by a wide variety of fuels (e.g., H 2 , NH 3 , hydrocarbons, CO). The current SOFC commercialization is mainly based on the conventional fluorite-type Y 2 O 3 -doped ZrO 2 (YSZ) oxide ion electrolyte, which can be operated in a temperature range of about 800-1000 °C. 2,4,5 The YSZ-based SOFC exhibits several disadvantages that are attributed to the high temperature of operation. They are detrimental as mechanical stress is induced because of different thermal expansion coefficients of the electrolyte and electrodes, interfacial diffusion of Sr and La from the cathode to the electrolyte, a lack of appropriate sealing materials, and a high cost of bipolar separators. 2,3 Therefore, there is a great deal of interest in developing new materials with desired physical, chemical, and mechanical properties for the development of advanced intermediate temperature (IT) SOFCs (500-750 °C). 9-11 A number of inorganic crystal structures that include perovskites, fluorites, pyrochlores, perovskite-related brown- millerites, layered perovskite (K 2 NiF 4 -related), and Aurivilius * Author to whom correspondence should be addressed. Phone: 001 403 210 8649. E-mail: vthangad@ucalgary.ca. (1) Goodenough, J. B. Annu. ReV. Mater. Res. 2003, 33, 91–128. (2) Minh, N. Q. J. Am. Ceram. Soc. 1993, 76, 563–588. (3) Carrette, L.; Friedrich, K. A.; Stimming, U. Fuel Cells 2001, 1, 5–39. (4) Singhal, S. C. Solid State Ionics 2002, 152-153, 405–410. (5) Ormerod, R. M. Chem. Soc. ReV. 2003, 32, 17–28. (6) Weber, A.; Ivers-Tiffee, E. J. Power Sources 2004, 127, 273–283. (7) Yano, M.; Tomita, A.; Sano, M.; Hibino, T. Solid State Ionics 2007, 177, 3351–3359. (8) Ni, M.; Leung, M. K. H.; Leung, D. Y. C. Int. J. Hydrogen Energy 2008, 33, 2337–2354. (9) Kendrick, E.; Kendrick, J.; Knight, K. S.; Islam, M. S.; Slater, P. R. Nat. Mater. 2007, 6, 871–875. (10) Kuang, X.; Green, M. A.; Niu, H.; Zajdel, P.; Dickinson, C.; Claride, J. B.; Jantsky, L.; Rosseinsky, M. J. Nat. Mater. 2008, 7, 498–504. (11) Brett, D. J. L.; Atkinson, A.; Brandon, N. P.; Skinner, S. J. Chem. Soc. ReV. 2008, 37, 1568–1578. Inorg. Chem. 2009, 48, 257-266 10.1021/ic801729x CCC: $40.75  2009 American Chemical Society Inorganic Chemistry, Vol. 48, No. 1, 2009 257 Published on Web 12/05/2008