Zirconia doping

S. Seimanides, P. Tsiakaras, X.E. Verykios, and C.G. Vayenas, Oxidative Coupling of Methane over Yttria-doped Zirconia Solid Electrolyte, Appl. Catal. 68, 41-53 (1991). 

Sulfate-doped zirconia was found to have both Lewis and Brdnsted add sites on the surface, where the sulfate groups were the carrier of the protonic site. The ratio of Lewis to Br0nsted sites was found to vary depending on heat treatment, but the percentage of sulfate groups associated with a proton was found to be constant at 12-17%. 

Doped zirconia, yttria and thoria Other oxides (magnesia, alumina, etc.) Electrolytic conductor Nonconductors... 

The anode is generally made of nickel/yttria-stabi-lized zirconia Cermet. The cathode is an LSM layer chemically expressed as Lai- fSi fMn03. The electrolyte is an Y203-doped zirconia called YSZ. 

Oxygen reduction on yttria-doped zirconia (YSZ) was first accomplished over 100 years ago (for the purpose of generating light) using a porous platinum electrode. Since then, oxygen reduction on Pt has been one of the most well-studied electrode reaction... 

SOFCs employ a ceramic oxide (ceria- or yttria-doped zirconia, electrolyte... 

Oxygen gas is reduced to at the right-hand electrode (C). The oxide ions are able to pass through the doped zirconia and are oxidised to oxygen gas at the left-hand electrode (A). The equation for the cell reaction is ... 

Since doped zirconia allows one to extend the oxide electrochemistry up to very high temperatures and since it can serve as a fuel cell electrolyte and even as a heating element in high temperature furnaces, we will briefly formalize the structure element transport in zirconia, which is the basis for all of this. Let us introduce the SE fluxes in their usual form. We know that only oxygen ions and electronic defects contribute to the electrical transport (/ = 02, e, h )... 

For a given composition and a given charge cation, the conductivity increases as the radius of the dopant cation approaches that of zirconium. Thus, scandia-doped zirconia shows the best conductivity (rSc3+ = 0.81 A and zZr4+ = 0.8 A) in this family. 

Polycrystalline yttria-stabilized zirconia (YSZ-8) disks were prepared using 8 mol % Y203-doped zirconia powder (TOSOH zirconia, TZ-8Y, TOSOH Corp.). The powder was pressed uniaxially into disks which were cold isostatically pressed at 40,000 psi and then sintered at 1450°C for 4 h. Pt paste (Engelhard 6926) was painted on both faces of the YSZ-8 disks. Pt wires (0.0025 cm diam) were connected to the YSZ by using Pt meshes (150 X 150 mesh, 0.005 cm wire diam, Unique Wire Weaving Co., Inc.). 

Figure 15. Impedance spectrum of 10 mol% Y2C>3-doped zirconia according to Ref.96 The rhs semicircle represents the grain boundary impedance. Reprinted from S.P.S. Badwal, Solid State Ionics 76 (1995), 67-80. Copyright 1995 with permission from Elsevier.

Li, et al. (2003), Phase Transformation in the Surface Region of Zirconia and Doped Zirconia Detected by UV Raman Spectroscopy , Phys. Chem. Chem. Phys., 5, 5326-5332. 

Oxygen anions travel from the source side through the solid electrolyte to the sink side (anode) under the combination of the influence of an applied dc electric field and an oxygen chemical potential gradient. At the sink side (the anode of the SOFC), the oxygen anions react electrochemically with both zirconium and yttrium reactants from the sink vapor phase to form the desired product, yttria doped zirconia, and release electrons to the metallic anode. Electrons travel through the external electrical circuit back to the source side for further cathodic reaction. 

Eigure 31 shows a schematic diagram of a lab-made PEVD reactor for depositing yttria-doped zirconia. The sample tube was placed at the center of a large fully dense alumina reactor tube in an electric furnace. Thus, the sample tube separated the reactor tube into two chambers the air chamber inside the sample tube and the chloride chamber between the sample and reactor tubes. Both chambers were evacuated separately. 

Based on the preceding microstructural analysis results, it is clear that PEVD is capable of depositing a tbin layer of yttria-doped zirconia to form a composite anode. This phase is not only in intimate contact with both the solid electrolyte and metallic electrode, but also covers... 

---