Doped ceria intermediate temperatures

Due to its high oxygen ion conductivity, doped ceria has been considered as the electrolyte for SOFCs operated at low and intermediate temperatures since the 1990s. 

Bao 5Sr0 5Co08Fe0 2O3 (BSCF) shows extremely high electrochemical activity for the 02 reduction reaction at intermediate temperatures. Shao and Flaile [105] applied BSCF as cathode to a doped ceria electrolyte cell and achieved the power densities of... 

The intermediate- and low-temperature materials exhibit both significant oxygen ion and electron conductivity. This means that the oxygen reduction can take place everywhere in the cathode and is not restricted to the TPBs as in the LSM-type cathodes. An option for compensating the relatively low oxygen ion conductivity of LSC and LSCF at operating temperatures around 600 °C is by mixing the material with (doped) ceria [79, 80],... 

Wang, B.H., Wang, J.D., Liu, R., Yie, Y.H., and Li, Z.J. 2007. Synthesis of ammonia from natural gas at atmospheric pressure with doped ceria -Ca/PO lj-KjPO composite electrolyte and its proton conductivity at intermediate temperature. Journal of Solid State Electrochemistry 11, 27-31. 

The present work was focused on the synthesis of nanocrystalline components for electrochemical cells via the cellulose-precursor technique. This method was used to prepare nanostructured intermediate-temperature (IT) SOFC anodes made of a series of cermets comprising gadolinia-doped ceria (CGO), yttria-stabilized zirconia (YSZ), Gdi.86Cao.i4Ti207.5 (GCTO) pyrochlore, metallic nickel and copper. Perovskite-type SrFcojAlo.sOs.s (SFA) powder, also obtained via the cellulose precursor, was applied onto membranes of the same composition to enhance specific surface area and electrocatalytic activity in the reactors for methane conversion [3]. 

Therefore, it is not suitable to use ceria based solid electrolytes in the cell type shown in Figure 9-23. However, in the case for the other types shown Figures 9-29(a) and (b) [37], both the cathode and the anode are in the same atmosphere where air and fuel gas exist at the same time. Therefore, the volume change of the cell becomes negligible and it is greatly expected to apply the Sm-doped ceria which shows higher oxide ion conductivity than that of YSZ at intermediate temperature. 

The anodes consisting of a nickel catalyst and of cermet mixed with yttria-doped zirconia electrolyte that are used in conventional solid oxide fuel cells also lose their ability to work at lower temperatures because of a loss of conductivity by the ceramic. This suggests that, for the ceramic in the anode, a material having a higher conductivity at intermediate temperatures should be used. It was in fact shown that an anode made with a nickel/samaria-doped ceria cermet has a much lower polarization than the conventional variant. 

Xia C, Li Y, Tian Y, Liu Q, Wang Z, Jia L, Zhao Y and Li Y (2010), Intermediate temperature fuel cell with a doped ceria-carbonate composite electrolyte , / Power Sources, 195,3149-3154. 

Wang F, Chen S, Cheng S (2004b) Gd and Sm + co-doped ceria based electrolytes for intermediate temperature solid oxide fuel cells. Electrochem Commun 6 743-746... 

Morales M, Pinol S, Segarra M (2009) Intermediate temperature single-chamber methane fed SOFC based on Gd doped ceria electrolyte and La(0.5)Sr (0.5)CoO(3-delta) as cathode. J Power Sources 194 961-966. doi 10.1016/j.jpowsour.2009.05.027... 

Other Oxide Electrolyte Systems Ceria-Based Electrolytes Ceria-based solid electrolytes have received an increasing attention for so-called IT-SOFC (solid oxide fuel cells for intermediate temperature) because of their high conductivity. But its electrolytic domain is relatively small so that the working temperature must not be higher than 700 °C without a remarkable loss in efficiency due to the electronic conductivity. By doping with aliovalent stable oxides, a remarkable increase of conductivity... 

Ceria doped with heterovalent cations, such as alkaline earth and rare earth ions, has been considered one of the most promising electrolyte materials for intermediate-temperature solid oxide fuel cells. It was found that doped ceria materials exhibit relatively high ionic conductivity under nonreducing conditions and relatively lower temperatures in comparison to that of YSZ electrolyte. Among the various dopants studied, Gd " and singly doped Sm ceria have been reported to have a high conductivity [8] and to be relatively stable in a reducing environment [49]. 

Kawano, M., Toshiaki, T., Matsui, T., Kikuchi, R., Yoshida, H., Inagaki,T. Eguchi, K. Steam reforming on Ni-samaria-doped ceria cermet anode for practical size solid oxide fuel-cell at intermediate temperature. J. Power Sources 182 (2008), pp. 496-502. 

LSCs are attractive cathode materials for intermediate temperature SOFCs in terms of its high catalytic activity and surface exchange coefficient. However, the material also has a large coefficient of thermal expansion, which is about 23 x 10 almost twice that of typical electrolytes, such as YSZ and doped ceria electrolytes (11-12 x 10 K ). The TEC mismatch between the electrolyte and cathode will result in a thermal stress, which is responsible for delamination at the... 

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