Sm-doped ceria

Solid Oxide Fuel Cells Materials Properties and Performance 

FIGURE 1.26 Composition dependence of the activation energy and conductivity at 600°C for SmICe1.x02.x/2 [114], 

FIGURE1.27 Composition dependence of the apparent lattice conductivity, ag, grain- boundary conductivity, a and the total conductivity, at, for SmICe1 I02 l/2 measured at 300, 400, and 500°C [115].. 

FIGURE 1.29 Composition dependence of the trapping energy, A//, and the critical temperature, Tc, for SmxCe1.x02 I,2 [114]. 

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SEM observations of the surface and the cross-section of the Gd doped ceria coated with YSZ (YSZ GDC) show that the thin YSZ film is porous and the YSZ particles are fairly uniform in size. The thickness of YSZ film was about 20 pm. The conductivity of this composite membrane was 4.39X10 S cm at 500 C under air atmosphere, which was almost same order as that of Sm doped ceria coated with YSZ (YSZISDC) (1.51X10 4 Sxm ). However, either value was lower than that of GDC alone (4.03 X lO Sxm ) or SDC alone (4.66 X lO Sxm ). This may be due to the low conductivity of YSZ film. 

Propene oxidation was carried out by using an electrochemical reactor constructed from a Sm doped ceria electrolyte coated with YSZ (YSZ 1 SDC) as a membrane. In a blank test where nitrogen gas alone was passed over the Au anode instead of the reaction gas at 450 C, it was confirmed that the oxygen pumping was well controlled by the applied current, i.e., the amount of oxygen gas evolved at the anode coincided well the value calculated from the electric current by using Faraday s law. 

In order to clarify the reaction site of the partial oxidation of propene using the ceria-based solid electrolyte coated with YSZ as a membrane, we have studied the dependence of the selectivities to oxygenates on the thickness of YSZ. When the Sm doped ceria coated with YSZ (YSZ SDC), each selectivity of the oxidation products did not dependent on the thickness of YSZ, as shown in Figure 4. 

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. 

Figure 3-8. The images of Sm-doped ceria film on Pt the cross section of the film sintered at 800°C (a) and AFM images of the film surface sintered at 800°C (b) and 1,000°C (c)...

Figure 3-9. The electrical conductivity of Sm-doped ceria film on Pt sintered at different...

Figure 3-11. SEM image of the fracture of Sm-doped ceria skeleton used for soaking (a) and net shape prepared ceramics sintered at 1,000°C (b)...

Liu Y, He T, Wang J, Shu W (2005) The effect of Pr co-dopant on the performance of sohd oxide fuel cells with Sm-doped ceria electrolyte. J AUoy Compd 389 317-322... 

Zhao, S. and Gorte, R.J. (2004) A comparison of ceria and Sm-doped ceria for hydrocarbon oxidation reactions. Appl. Catal. A, 277, 129-136. 

Sanna, S., Esposito, V., Tebano, A., Licoccia, S., Traversa, E., and Balestrino, G. (2010) Enhancement of ionic conductivity in Sm-doped ceria/yttria-stabilized zirconia heteroepitaxial structures. Small, 6, 1863-1867. 

The electrolytic domain ti> 0.99) of doped ceria is limited at low PO2 due to the onset of electronic conductivity on reduction of Ce. The low p02 limit of the electrolytic domain depends on dopant type and doping level, and shifts to higher pOg with increasing temperature. The width of the electrolytic domain is maximized for 10-20 mol% Gd- or Sm-doped ceria, °° due to the optimized total ionic conductivity achieved in these compounds. The low pOg limit of these compounds shifts from ca. 10 atm at 400 °G and ca. 10" atm at 600 °C to ca. 10 atm at 800 For comparison, the... 

S. Sanna, V. Esposito, A. Tebano, S. Licoccia, E. Traversa, G. Balestrino, Enhancement of ionic conductivity in Sm-Doped Ceria/Yttria-stabilized Zirconia Heteroepitaxial Stmctures. Small 6, 1863-1867 (2010)... 

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