(499b) Sintering Behaviour of in-Situ Doped Nanoparticles by Flame Spray Pyrolysis for Fuel Cell Applications
AIChE Annual Meeting
Thursday, November 16, 2006 - 9:05am to 9:33am
Ceramic oxygen ion conductors play a key role in solid oxide fuel cells (SOFC) with high power output. Ceria-based electrolytes are considered to be very promising due to their high ionic conductivity in comparison to the commonly used electrolyte material yttria-stabilized zirconia (YSZ). Small amounts of transition metal oxides have shown to be very effective sintering aids for Ce0.8Gd0.2O1.9 (CGO20) and Ce0.9Gd0.1O1.95 (CGO10) [1-4]. Adding as few as 1 mol% of cobalt oxide resulted in much lower sintering temperatures (900°C), higher shrinkage rates, and grain sizes in the final sintered product in the sub-micron range (~120 nm). Several investigations indicated that the necessary and sufficient dopant concentration lies below the reported 2 mol%. It was argued that improved homogeneity of the dopant phase by using a more suitable doping process would reduce the necessary concentration while maintaining the same sintering effect. In order to test this hypothesis, we used an alternative one-step preparation route to Cobalt oxide doped CGO. Flame spray pyrolysis (FSP) has been established as a reliable production process for mixed oxide nanoparticles of high phase homogeneity [5,6]. The continuous high temperature gas process uses suitable organic derivatives of the desired metals as homogeneous mixtures. The precursors are directly sprayed into a flame where they are rapidly converted into the corresponding mixed oxides. Here, we report on the successful pilot-scale preparation of CGO10 and in-situ cobalt oxide doped CGO10 powders by flame spray pyrolysis. We show that cobalt oxide as a dopant is already effective at concentrations as low as 0.1 mol%. At a dopant concentration of 1 mol%, the maximum sintering temperature is lowered by 250°C if compared to undoped CGO10 . The results are further discussed in terms of materials preparation and application.
References:  C. Kleinlogel and L.J. Gauckler, Solid State Ionics, 135 567 (2000),  C. Kleinlogel and L.J. Gauckler, Adv. Mater., 13 1081 (2001),  G.S. Lewis, A. Atkinson, B.C.H. Steele, vol. 2, pp. 773 in Fourth European Solid Oxide Fuel Cell Forum. Edited by U. Bossel, 2000,  G.S. Lewis, A. Atkinson, B.C.H. Steele, J. Drennan, Solid State Ionics, 152 567 (2002),  L. Maedler, W.J. Stark, S.E. Pratsinis, J. Mat. Res., 17 1356 (2002),  W.J. Stark, M. Maciejewski, L. Mädler, S.E. Pratsinis, and A. Baiker, J. Catal. 220 (1) 35-43 (2003); W.J. Stark, L. Maedler, S.E. Pratsinis, Flame Made Metal Oxides WO 2004/005184 (2002),  E. Jud, S.C. Halim, W.J. Stark, L.J. Gauckler, J. Am. Ceram. Soc., accepted 2006.