Ceria based electrolytes

Sensitivity of interfacial resistance to various factors. For perovskite mixed conductors on some ceria-based electrolytes, workers have reported virtually zero interfacial resistance such that the electrode overpotential is dominated entirely by dissociation of O2 and transport of intermediates to the electrode/ electrolyte interface. As we will see in section 6, this conclusion is not universally true of all materials additional impedance arcs have been observed for perovskites on YSZ and with ceria at lower temperatures or with certain electrolyte dopants. 

K. Eguchi, T. Hatagishi, and H. Arai, Power generation and steam electrolysis characteristics of an electrochemical cell with a zirconia- or ceria-based electrolyte, Solid State Ionics, 86-8 1245-1249 (1996). 

Kirk, T.J. and Winnick, J., A hydrogen sulfide solid-oxide fuel cell using ceria-based electrolytes, J. Electrochem. Soc., 140, 3494-3496 (1993). 

Lanthanum gallate is doped with divalent metal ions, for instance, strontium and magnesium Lai jSrjMgyGai j,03 usually, x and y have values between 1 and 0. Unlike the ceria-based electrolytes, this electrolyte can also be used at low oxygen partial pressures without the menace of developing an electronic conductivity. When in contact with cathodes of the LSM- or LSC type, some diffusion of manganese and cobalt from the cathode into the electrolyte is possible, but this has little effect on the fuel cell s performance. A certain defect of this electrolyte material is its complicated preparation procedure. 

The maximum value of conductivity for ceria-based electrolytes is attained at a certain concentration of the dopant oxides, in a matmer similar to the zirconia electrolytes. As shown in fig. 7 (Takahashi and Iwahara 1966), the conductivity of Ce02 doped with... 

The electrolytic domain for a ceria-based electrolyte, at any given temperature, is narrower than that of a zirconia-based electrolyte, such that electronic conductivity is acquired in reducing atmospheres. As shown in fig. 8 (Steele et al. 1994), the electrolytic domain of Ce02-0d0i.5 (10 mol%) at 1000 K is such that the electrolyte is not suitable for use at oxygen pressures below 10 atm. The high ionic conductivity, however, makes the electrolyte of considerable interest at low temperatures and/or in environments of moderate oxygen potential. 

Mogensen, M., Sammes, N. M., and Tompsett, G. A. (2000). Physical, chemical and electrochemical properties of pure and doped ceria. Solid State Ionics 129 63-94. Godickemeier, M., and Gauckler, L. J. (1998). Engineering of solid oxide fuel cells with ceria-based electrolytes. J Electrochem. Soc. 145 414—421. 

Wang F, Chen S, Cheng S (2004b) Gd and Sm + co-doped ceria based electrolytes for intermediate temperature solid oxide fuel cells. Electrochem Commun 6 743-746... 

Other Oxide Electrolyte Systems Ceria-Based Electrolytes Ceria-based solid electrolytes have received an increasing attention for so-called IT-SOFC (solid oxide fuel cells for intermediate temperature) because of their high conductivity. But its electrolytic domain is relatively small so that the working temperature must not be higher than 700 °C without a remarkable loss in efficiency due to the electronic conductivity. By doping with aliovalent stable oxides, a remarkable increase of conductivity... 

An overview on ceria-based electrolytes is given in [12], By adding of Tb407 or PreOn (rare earth ions occur in different valence states), mixed conductors with an enhanced electronic conductivity are obtained, which may be used as electrode materials for IT-SOFC. 

As already discussed, the electrolyte is the most important component of a SOFC, the properties of which determine critical parameters such as cell performance and temperature of operation. Because of this, much time has been devoted to developing and understanding the materials and their properties and Raman spectroscopy has been a key tool. This section summarises the key results of studies that have used Raman spectroscopy to investigate electrolytes for SOFCs and is split into three parts. The first focuses on Zirconia based materials the conventional electrolyte of choice. The second will summarise the results of investigations on Ceria based electrolytes the frontrunner electrolyte for intermediate temperature SOFCs. Other novel electrolytes which have some potential for reduced temperature operation will be summarised in the final section. 

Shobit Omar S, Wachsman ED, Nino JC (2008) Higher conductivity Sm " and Nd " codoped ceria-based electrolyte materials. Solid State Ionics 178 1890-1897... 

Goedickemeier M, Gauckler LJ (1998) Engineering of solid oxide fuel cells with ceria-based electrolytes. J Electrochem Soc 145 414-421... 

Chemical stability and relatively low interactions with electrolyte. With YSZ electrodes, many La-based compounds form the insulating La2Zr20 . With ceria-based electrolytes, this issue is not a concern and other cathode materials are considered (e.g. (La,Sr)(Co,Fe)03 or LSCF). 

SOFC anodes are fabricated from composite powdered mixtures of electrol5de materials (YSZ, GDC, or SDC) and nickel oxide. The nickel oxide is subsequently reduced to nickel metal prior to operation. The NiO/YSZ anode material is suited for applications with YSZ material, whereas NiO/SDC and NiO/GDC anode materials are best used with ceria-based electrolyte materials. Typical anode materials have nickel content of approximately 40 volume percent after reduction of the nickel oxide to nickel. Depending upon the application, powders have surface areas of 15 to 20 m /g for screen-printing and 5 to 10 m /g for tape casting. 

For the particular cases of zirconia- and ceria-based electrolytes, the ionic conductivity is mostly related to dopant nature, composition, microstructure, local structure, impurity and processing, and so on [19,20]. In many cases, the... 

Strong effects of the ionic conductivity on the lattice parameter caused by the dopant type and content upon processing parameters (particle size, sintering temperature, and microstructure) and operating temperature (defect formation and transport) were also reported for nanopowder ceria-based electrolytes. 

Zn as sintering aid for ceria-based electrolytes. Solid State Ionics, 262, 522-525. 

Omar, S., Wachsman, EJ5., and Nino, J.C. (2008) Higher conductivity Sm and Nd co-doped ceria-based electrolyte vaaXerisis. Solid State Ionics, 178 (37-38), 1890 1897. 

Composite electrolytes that use ceria as a backbone structure and typically carbonates as the second phase have recently been developed. In this review only single-phase ceria-based electrolytes will be considered even though the topic of composite electrolytes is very interesting as very high-power densities have been demonstrated. " ... 

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