Electrolytes solid oxides

A key factor in the possible application of oxygen ion conducting ceramics is that, for use as solid electrolyte in fuel cells, batteries, oxygen pumps or sensors, their electronic transport number should be as low as possible. Given that the mobilities of electronic defects typically are a factor of 1000 larger than those of ionic defects, a band gap of at least 3 eV is required to minimize electronic contributions arising from the intrinsic generation of electrons and holes. 

As is clear solid oxide electrolytes are not useful for applications as oxygen separation membrane, unless operated with external circuitry (oxygen pump) or as a constituent phase of a dual-phase membrane. Both modes of operation, classified in this paper as electrochemical oxygen separation, are briefly discussed in Section 10.4.3. But we first start with a discussion of the models that have been developed to describe the oxygen semi-permeability of solid oxide 

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Electrochemistry plays an important role in the large domain of. sensors, especially for gas analysis, that turn the chemical concentration of a gas component into an electrical signal. The longest-established sensors of this kind depend on superionic conductors, notably stabilised zirconia. The most important is probably the oxygen sensor used for analysing automobile exhaust gases (Figure 11.10). The space on one side of a solid-oxide electrolyte is filled with the gas to be analysed, the other side... 

T.I. Politova, G.G. Gal vita, V.D. Belyaev, and V.A. Sobyanin, Non-Faradaic catalysis the case of CO oxidation over Ag-Pd electrode in a solid oxide electrolyte cell, Catal. Lett. 44, 75-81 (1997). 

V.A. Sobyanin, V.I. Sobolev, V.D. Belyaev, O.A. Mar ina, A.K. Demin, and A.S. Lipilin, On the origin of the Non-Faradaic electrochemical modification of catalytic activity (NEMCA) phenomena. Oxygen isotope exchange on Pt electrode in cell with solid oxide electrolyte, Catal. Lett. 18, 153-164 (1993). 

Solid-oxide electrolytes are natural choices for oxygen transport since they transfer oxide ions directly ... 

With these solid-oxide electrolytes, designed to operate in relatively 02-rich feed (e.g. air), gas-diffusion electrodes with their enhanced contact area, are not necessary, and electrode materials can be applied directly onto the electrolyte surfaces in thin films. 

Four solid oxide electrolyte systems have been studied in detail and used as oxygen sensors. These are based on the oxides zirconia, thoria, ceria and bismuth oxide. In all of these oxides a high oxide ion conductivity could be obtained by the dissolution of aliovalent cations, accompanied by the introduction of oxide ion vacancies. The addition of CaO or Y2O3 to zirconia not only increases the electrical conductivity, but also stabilizes the fluorite structure, which is unstable with respect to the tetragonal structure at temperatures below 1660 K. The tetragonal structure transforms to the low temperature monoclinic structure below about 1400 K and it is because of this transformation that the pure oxide is mechanically unstable, and usually shatters on cooling. The addition of CaO stabilizes the fluorite structure at all temperatures, and because this removes the mechanical instability the material is described as stabilized zirconia (Figure 7.2). 

The solid oxide electrolyte must be free of porosity that permits gas to permeate from one side of the electrolyte layer to the other, and it should be thin to minimize ohmic loss. In addition, the electrolyte must have a transport number for O as close to unity as possible, and a transport and a transport number for electronic conduction as close to zero as possible. Zirconia-based electrolytes are suitable for SOFCs because they exhibit pure anionic conductivity over a wide... 

DC. Fee, S.A. Zwick, J.P. Ackerman, in Proceedings of the Conference on High Temperature Solid Oxide Electrolytes, held at Brookhaven National Laboratory,... 

Solid oxide fuel cell (SOFC) working between 700 and 1000 °C with a solid oxide electrolyte, such as yttria-stabilized zirconia (Zr02-8% Y2O3), conducting by the... 

Fig. 2.5 A solid oxide electrolyte (SOE) electrolyzer configuration (planar geometry).

Kharton VV, Marques FMB, Atkinson A (2004) Transport properties of solid oxide electrolyte ceramics a brief review. Solid State Ionics 174 135-149... 

It is vital that the solid oxide electrolyte can withstand the extreme conditions of hydrogen at the anode at 800°C or above. Under these conditions, many oxides would be reduced, liberating electrons and thus leading to unwanted electronic conductivity. 

Schematically speaking an elementary SOFC is composed of a solid oxide electrolyte, an oxygen electrode (cathode) and a fuel electrode (anode), as shown in Fig. 1. To form a battery, several elementary cells must be connected using an appropriate material. A SOFC may be considered as an oxygen concentration cell [6] of the following type...

Fig. 26. Diagram of oxygen reduction in solid oxide electrolyte cell with (a) a pure electronic conductor, (b) a mixed (electronic and ionic) conductor. From ref. [76].

A.O. Isenberg, in Proceedings of the High Temperature Solid Oxide Electrolytes Conference. BNL51728, Brookhaven National Laboratory, Associated Universities, Inc., pp. 5-15 (1983). 

Badwal S.P.S., Foger K. (1996) Solid oxide electrolyte fuel cell review. CeramicsInt. 22(3), 257-265. 

High-Temperature Fuel Cell. There is a cell developed to work with molten carbonates at about 650 °C and a corresponding cell involving a solid oxide electrolyte (yttria-zirconia) having high O-mobility and conductance, and operative at 1000 °C. 

As early as 1899, Nemst observed an effect of ionic conductivity in a Zr02 + 9% Y203 system. In this regard, in 1937, the first solid oxide-electrolyte fuel cell using this material was constructed [68],... 

Solid oxide fuel cell Solid oxide electrolyte (yttria, zirconia) o2 1000°C H2, CO, CH4, other hydocarbons (tolerates co2) >50% 2 kW MW range... 

BIMEVOX — Figure. Oxygen ionic conductivity of solid oxide electrolytes at atmospheric oxygen pressure. See Ref. [ii] for details... 

Bismlitil oxide — Figure. Comparison of the - electrolytic domain boundaries for solid oxide electrolyte materials. See ref. [iv] for details... 

Table 2. Component and system costs for 10-MW hybrid CPV project for solid-oxide electrolytic production of hydrogen.

Wachsman, E.D., Ball, G.R., Jiang, N., and Stevenson, D.A., Structural and defect studies in solid oxide electrolytes. Solid State Ionics, 1992, 52, 213-218. 

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