Cathodes Materials for SOFC

Koep E, Jin C, Haluska M, Das R, Narayan R, Sandhage K et al. Microstructure and electrochemical properties of cathode materials for SOFCs prepared via pulsed laser deposition. J. Power Sources 2006 161 250-255. 

Hence, by the combination of structural and transport properties, LSiF-LSNF nanoeomposite appears to be promising as cathode material for SOFC with apatite-type eleetrolyte provided the sintering temperature is below 1200 °C. The most promising approach consists in application of this composite as thin functional interlayer between the eleetrolyte and thin porous perovskite layer comprised of the same LSNF or other complex perovskite. This will help to mateh the thermal expansion coefficient of cathode and eleetrolyte as well as prevent too strong interaction between perovskite and electrolyte if sintering temperature will be high. 

A cathode material for SOFC should meet various requirements in catalytic activity, thermodynamic stability, and compatibility. The following are the requirements for the cathode materials and the proposed approach to find and design a suitable material for high stability and a high-performance cathode. 

Perovskite-type oxides based on Mn, Co, Fe, or K2NiF4-type oxide with Ni are studied as cathode materials for SOFCs. For high-temperature SOFCs, LaMnOs-based materials are mainly used because of the high compatibility... 

Cathode materials for SOFCs based on any of the electrolytes described in Section 2.1.1 are of the perovskite structure type, generally La-based with transition metals located on the B site. Several authors " have summarised the range of perovskites investigated to date, concentrating on the conductivity, ion transport and compatibility of these materials. As such it is superfluous to continue the discussion in detail here. Instead we will refer to the main cathode types only, leaving the reader to consult the relevant literature for further details. 

Furthermore, the analysis of the above oxygen partial pressure dependences (Figs. 13 and 14) points that Lao.4Sro.6Coo,2Feo.803 perovskite should be cata-lytically active already at 650 °C, because at this temperature the dependence of transport properties on p02 is observed. A conclusion may be drawn that this oxide will be useful as cathode material for SOFC working at intermediate temperatures. 

To develop an alternative MIEC cathode not only the ex situ properties, e.g., cr, TEC, /), and k, but also the electrocatalytic activity, structural and chemical stability, and Cr-tolerance must be considered. Beyond testing in small SOFC button cells, the viability of new cathode materials must ultimately be proven in large-scale stack cells under practical current and temperature gradients. The issues involved in the development of cathode materials for large-scale stacks are significantly more complex than those in the small button cells briefly reviewed in this chapter. However, this does provide serious challenges as well as opportunities for materials scientists and engineers in the development of commercially viable ITSOFCs. 

Hagiwara A, Hobara N, Takizawa K, Sato K, Abe H, and Naito M. Preparation and evaluation of mechanochemically fabricated LSM/ScSZ composite materials for SOFC cathodes. Solid State Ionics 2006 177 2967-2977. 

Li Q, Zhao H, Huo L, Sun L, Cheng X, and Grenier JC. Electrode properties of Sr doped La2Cu04 as new cathode material for intermediate-temperature SOFCs. Electrochem. Commun. 2007 9 1508-1512. 

Chiba, R., Yoshimura, F., Sakurai, Y., Tabata, Y., and Arakawa, M. A Study of Cathode Materials for Intermediate Temperature SOFCs Prepared by the Sol-gel Method, Solid State Ionics, 175,23 (2004). 

Since ionic radii and valences of iron and chromium ions are similar to gallium ion, substitution of these cations with gallium ion may result in powders with similar crystal structure and properties to LSGM. Moreover, LaFe03- and LaCr03-based oxides are candidate cathode and anode materials for SOFC, respectively. 

The development of high-performance electrode and electrolyte materials for SOFC is an important step towards reducing the fuel cell operation temperature to the low and intermediate range (500 - 700 °C). As the operating temperature is reduced, many cell ports, such as the auxiliary components can be easily and cost-efficiently produced. To meet long operational lifetime, material compatibility and thermomechanical resistance would be less critical as the range of possibilities for lower temperature increases. To that end, recent research at UFRN, Natal, Brazil has successfully focused on novel synthesis processes based on microwave-assisted combustion and modified polymeric precursor methods in order to synthesize high performance cobaltite-based composite cathodes for low-intermediary-temp>erature SOFCs. 

E. Maguire, B. Gharbage, F. Marquesb, and J. Labrinchab. Cathode materials for intermediate temperature SOFCs. Solid State Ionics 127, (2000) 329-335. 

Despite the number of reports on the structural and transport properties of many apatite electrolytes, their potential use in SOFC devices has not been widely studied (Brisse et al., 2006 Yoshioka et al., 2008 Bonhomme et al., 2009). In this sense,Tsipis et al. (2007) and Yaremchenko et al. (2009) reported the electrochemical behaviour of different cathode materials in contact with silicate apatite electrolytes and they found that silicon migration towards the surface layer blocks the electrochemical reaction zones increasing the electrode polarisation. In addition, high area-specific resistances were found (Brisse et al, 2006) with Ni0-La9SrSi< 026.5 cermets. However, a complete single fuel cell with apatite-type electrolyte, using different electrode materials, has not been reported before. Hence, further studies are still needed for a better characterisation of these potential electrolyte materials for SOFCs on several issues, such as the chemical reactivity and electrochemical performance between apatite electrolytes and different... 

LSCF is another promising cathode material for intermediate-temperature SOFCs [81, 82]. Owing to its much higher oxygen ionic conductivity than LSM,... 

Ralph JM, RossignolC, Kumar R (2003) Cathode materials for reduced-temperature SOFCs. J Electrochem Soc 150(11) A1518—A1522... 

Factors associated with (i)-(v) can be mitigated by searching for low-temperature electrolyte and cathode materials for low-temperature SOFCs since the rates of those steps involved in these factors are usually low at low temperatures. 

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