Yttria-Doped Ceria YDC

Yttria-doped ceria (Yj.Cei J.O2 J./2) shows a peak ioiuc conductivity for an yttria concentration in the range of x = 10%-15%. The peak conductivity data vary from 0.0025 to 0.0044 at 500°C. 

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FIGURE 1.2 Composition dependence of conductivity for yttria-stabilized zirconia (YSZ) measured at 1000°C [7], yttria-doped bismuth oxide (YDB) at 600°C [6], and yttria-doped ceria (YDC) at 700°C [8],... 

Figure 46. Performance characteristics of a cathode-supported thin film Ni—YSZ/YSZ/LSM fuel cell at 600 °C in humidified H2 and air with and without a dense protective yttria-doped ceria (YDC) protection layer introduced between the porous LSM cathode and the thin-film electrolyte. (Reprinted with permission from ref 296. Copyright 1997 Elsevier.)...

Barnett, Perry, and Kaufmann (75) found that fuel cells using 8 im thick yttria-stabiUzed zirconia (YSZ) electrolytes provide low ohmic loss. Furthermore, adding thin porous yttria-doped ceria (YDC) layers on either side of the YSZ yielded much-reduced interfacial resistance at both LSM cathodes and Ni-YSZ anodes. The cells provided higher power densities than previously reported below 700 °C, e g., 300 and 480 mW/cm at 600 and 650 °C, respectively (measured in 97 percent H2 and 3 percent H2O and air), and also provided high power densities at higher temperatures, e g., 760 mW/cm at 750 °C. Other data (Figure 7-25) from the University of Utah (73) show power densities of 1.75 W/cm with H2/air and 2.9 W/cm with H2/O2 at 800 °C for an anode-supported cell. However, no data is presented with regard to electrodes or electrolyte thickness or composition. 

The experiments were performed on an anode supported planar Solid Oxide Fuel Cell which consists of a 525—610 pm thick anode with two layers (both made of MO/8YSZ cermet functional layer 5—10 pm thick support layer 520—600 p thick) a 4—6 pm thick dense electrolyte Yo,i6Zro.g402 (8YSZ) a 2—4 pm thick barrier layer made of yttria doped ceria (YDC) the cathode consists of a 20—30 pm thick layer made of porous lanthanum strontium cobalt ferrite oxide... 

Doped and undoped ceria exhibit ionic and electronic conduction at low oxygen partial pressures. Ce" " gets reduced to Ce ", which is the main cause for mechanical failure due to lattice expansion (for low oxygen partial pressure). The electrolyte/electrode interface may be delaminated due to the formation of cracks. When 40-50% of Ce" " ions are substituted with Gd " ions (Ceo.6Gdo.40i.8-CGO), then a balance between lattice parameters and conductivity with the YSZ electrolyte and an anchoring YSZ layer provides the ability to resist the thermal expansion mismatch. Uchida and co-workers obtained the electrocatalytic activities for the SDC and Yttria doped Ce02 (YDC) for the electrodes sintered at 1150 and 1250°C. The current density of 0.2-0.25 PJcvc is observed for SDC and YDC anodes,... 

The most common electrolyte material is YSZ. Another central one is yttria-(YDC) or gadolinia-doped ceria (GDC). Despite its higher ionic conductivity than 8 YSZ, its drawback are non-negligible electronic conduction at low oxygen partial pressure and isothermal expansion. It can also serve as a compatibility layer, to prevent undesirable reactions between the YSZ electrolyte and an LSCF cathode. The CTEs of both materials exhibit temperature dependence. SRU typically have to withstand spatial temperature differences of 100 K, e.g. 973-1073 K. The corresponding variation of the CTE between RT and 1073 K in one data set is of approximately 9.8—11.0 x 10 for 8YSZ and 12.1 —12.9 x 10 K for GDC, which can lead to imprecision in the calculation of the stress field. 

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