Solid oxide fuel cells Zirconia-based materials

YSZ is the usual material for use in solid oxide fuel cells. Another interesting application of stabilized zirconia is in the detection of oxygen, where it is used in both oxygen meters and ojg gen sensors, which are based on a specialized electrochemical cell (Section 5.4.4). 

The prevalent material for substrates and anodes in anode-supported solid oxide fuel cells (SOFCs) are porous composites of oxygen-ion conducting ceramics such as yttria-stabilised zirconia (YSZ) and Nickel. Cells based on such substrates and anodes have been found to show very good performance. ... 

Ceria affords a number of important applications, such as catalysts in redox reactions (Kaspar et al., 1999, 2000 Trovarelli, 2002), electrode and electrolyte materials in fuel cells, optical films, polishing materials, and gas sensors. In order to improve the performance and/or stability of ceria materials, the doped materials, solid solutions and composites based on ceria are fabricated. For example, the ceria-zirconia solid solution is used in the three way catalyst, rare earth (such as Sm, Gd, or Y) doped ceria is used in solid state fuel cells, and ceria-noble metal or ceria-metal oxide composite catalysts are used for water-gas-shift (WGS) reaction and selective CO oxidation. 

Related systems It should be noted that specific properties for applications could be enhanced by using solid solutions, doped materials, and composites, instead of pure ceria. For example, ceria-zirconia solid solution is a well known ceria based material for enhanced OSC and high ionic conductivity for solid state fuel cell components. It is also used in the three way catalysts for automobile waste gas cleaning, because of the improved thermal stability, surface area, and reducibility. The synthesis, structure, and properties of ceria-zirconia have been actively studied for a long time. Di Monte and Kaspar et al. presented feature articles on the nanostructured ceria—zirconia-mixed oxides. The studies on phase, structures, as well as the microstructures are discussed and reviewed (Di Monte et al., 2004). 

A key factor in the possible applications of oxide ion conductors is that, for use as an electrolyte, their electronic transport number should be as low as possible. While the stabilised zirconias have an oxide ion transport number of unity in a wide range of atmospheres and oxygen partial pressures, the BijOj-based materials are easily reduced at low oxygen partial pressures. This leads to the generation of electrons, from the reaction 20 Oj + 4e, and hence to a significant electronic transport number. Thus, although BijOj-based materials are the best oxide ion conductors, they cannot be used as the solid electrolyte in, for example, fuel cell or sensor applications. Similar, but less marked, effects occur with ceria-based materials, due to the tendency of Ce ions to become reduced to Ce +. 

The SOFC is a complete solid-state device that uses an oxide ion-conducting ceramic material as the electrolyte. The electrolyte is a nonporous solid, such as Y2O3 stabilized Zr02 with conductivity-based oxygen ions [122, 128, 142-144]. Yttria-stabilized zirconia (YSZ) is the most commonly used material for the electrolyte. It was first used as a fuel cell electrolyte by Baur and Preis in 1937 [145]. The anode is usually made of a C0-Z1O2 or Ni-Zr02 cement [13, 95, 146, 147], while the cathode is made of Sr-doped LaMnOs (LSM) [13,148-150],... 

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