Rare earth doped ceria

Finally, another possibility often discussed in the literature is that cation dopants from the electrode may enhance the electronic conductivity of the gas-exposed surface of the electrolyte in the vicinity of the TPB, thereby extending the reduction zone along the electrolyte surface via mixed conduction. The surface exchange rate of oxygen on both YSZ- and rare-earth-doped ceria (as measured by isotope methods) is only about 1 order of magnitude lower than on LSM at 700 Thus, if there were sufficient... 

Figure 52. Effect of binary gas-phase diffusion on the impedance characteristics of porous mixed-conducting electrodes at low Por (a) zero-bias impedance of LSC on rare-earth-doped ceria at 1 atm and 750 °C as a function of Pq using concentrations and balance gases as indicated. (Reprinted with permission from ref 350. Copyright 2000 Elsevier B.V.) (b) Zero-bias impedance of SSC x= 0.5) on SDC at 800 °C and P02 — 9-91 a function of total...

As an example. Figure 54a shows the zero-bias impedance of LSC electrodes on rare-earth-doped ceria in air at 750 °C measured using a symmetric cell incorporating a traditional reference electrode. Although the two screen-printed electrodes (1 and 2) were processed identically and aligned to an accuracy of 0.1 mm, the cell response is highly asymmetric... 

Figure 54. Measured (a) and simulated (b) effect of electrode misalignment, (a) Total-cell and balf-cell impedances of a symmetric LSC/rare-earth-doped ceria/LSC cell with nominally identical porous LSC x= 0.4) electrodes, measured at 750 °C in air based on tbe cell geometry shown. (b) Finite-element calculation of tbe total-cell and half-cell impedances of a symmetric cell with identical R—C electrodes, assuming a misalignment of the two working electrodes (d) equal to the thickness of the electrolyte (L). ...

Figure 2.16. Left oxygen diffusion data of various ceria-coniaining materials 1 CeOj. single crystal 2 CeOj poly crystalline sample 3 CeogYojOiv 4 CCo Yo Oig 5 CeO,g 6 Ceo9Cao,0,/ 7 (0.3%)Od doped CcOj 8 Ce02. shaded area corresponds to oxygen diffusion values calculated from ionic conductivity of rare-earth doped ceria CC. M 02.o,. with x 0.2 and 0.3 using Eq. 2.29. Right details of oxygen diffusion coefficients of rare-earth doped ceria with x=0,3 from top to the bottom (M=Eu,Nd.Ho,Gd.Er.Sm,Y.La.Yb,Dy).

The range of the oxygen partial pressure where the rare earth doped ceria exhibits oxide anion conduction is limited over 10" Pa in P02 at 800°C (The oxide anion transference number decreased to 0.5 at this condition.), whereas the well-known stabilized zirconia shows the stable ion conduction between 10" and 10 Pa. This low stability against reducing atmosphere observed in the rare earth doped ceria is a fatal problem for applications. 

Sakai N, Kishimoto H, Yamaji K, Horita T, Brito ME, Yokokawa H (2007) Intraface stability of Perovskite cathodes and rare-earth doped ceria interlayer in SOECs. J Electrochem Soc 154(12) B1331-B1337... 

Prado-Gonjal, J., Schmidt, R., Espindola-Canuto, J., Ramos-Alvarez, P., and Moran, E. (2012) Increased ionic conductivity in microwave hydrothermally synthesized rare-earth doped ceria Cei RE 02-( /2). 

Among the mixed conductors with fluorite structure, rare earth doped ceria exhibits the highest ionic and electronic conductivity however, its electronic conductivity is still not high enough to match SOFC anode requirements. Up to 70 mol% Nb205... 

Lobera, M. R, Balaguer, M., Garcia-Fayos, J., and Serra, J. M. Rare earth-doped ceria catalysts for ODHE reaction in a catalytic modified MIEC membrane reactor. ChemCatChem 4,2102-2111 (2012). 

H. Mitsuyasu, Y. Nonaka, K. Eguchi, Analysis on Solid State Reaction at the Interface of Yttria-Doped Ceria/Yttria-Stabilized Zirconia, Solid State Ionics 113-115,279-284 (1998) N. Sakai, H. Kishimoto, K. Yamaji, T. Horita, M.E. Brito, H. Yokokawa, Degradation Behavior at Interface of LSCF Cathodes and Rare Earth Doped Ceria, SOFC X, ECS Transactions, 7(1) 389-398 (2007)... 

Guo M, Lu J, Wu Y, Wang Y, Luo M UV and visible Raman studies of oxygen vacancies in rare-earth-doped ceria, Langmuir 27 (7) 3S72-i871, 2011. 

An alternative approach to reduce the operating temperature is to use new electrolyte materials such as scandium doped zirconia (SeSZ), and rare earth doped ceria (RDC) which have the fluorite type stmeture, or lanthanum gallate based oxides such as (La,Sr)(Ga,Mg)03 (LSGM) with perovskite stmeture, all of which have higher ionic conductivities than YSZ. An 1 kW class SOFC stack with (La,Sr)(Ga,Mg,Co)03 electrolyte was demonstrated by the collaboration of Mitsubishi Materials Corp. and The Kansai Electric Power Co., Inc. in 2001,... 

On the other hand, there are few reports about SOFC stacks, which employ rare earth doped ceria electrolytes, although a high power density has been reported for single cell test (Steele, 2000 Bance et al., 2004). The rare earth doped ceria exhibits isothermal expansion in a reducing atmosphere due to the reduction of cerium ion from tetiavalent (Ce +) to trivalent state (Ce " ") accompaitying the formation of oxygen vacancies, which results in the warping or de-straction of the electrolyte plate. The formation of trivalent cerium ion also causes a decrease of oxide ion transport number, which reduces the efficiency of the cell. 

For lanthanum cobaltites, the formation of La2Zr207 can not suppressed except by lowering the temperature. Hence, rare earth doped ceria is often introduced as the interlayer be-... 

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