LSM/YSZ cathodes

Fig. 14.19 Fracture surface of an anode-supported cell. From left to right, the porous Ni-YSZ anode, the dense 8YSZ electrolyte, and the porous LSM-YSZ cathode.

In the second case, YSZ film of thickness 5-20 microns is deposited on a Ni-cermet disc of thickness around 1000 microns and covered by LSM+YSZ cathode. The anode has a multilayer structure active layer and current collector. IPPE developed original technology for deposition of YSZ films in electrostatic field. At 800°C, power density of 300 mW/cm was achieved (Fig.6). 

A SEM micrograph of the cathode/electrolyte interface and preliminary results on the electrochemical activity of YSZ electrolyte-supported SOFCs containing Ni-YSZ anode and a LSCF-SDC composite cathode are shown in Fig. 14. As it can be seen in Fig. 14(a), the composite film not only has good adhesion to the electrolyte, but also possesses a porous microstructure which is required for the oxidant electrochemical reduction. It indicates that such a composite film can have a good performance as SOFC cathode. By the LSV technique, qualitative information about electrochemical activity of this SOFC was acquired. The power density curves (Fig. 14b) revealed that maximum power densities were 19, 26, 36 and 46 mW/cm2 at 800, 850, 900 and 950 °C. It is possible to compare these first results with literature data and safely state that the LSCF-SDC cathode composite is qualitatively better than other plain standard materials or cathode composites already reported. It should also be mentioned that the result obtained at 800 °C is similar to that reported by Mucdllo et al (Mucdllo et al., 2006) for a SOFC single cell with LSM-YSZ cathode, Ni-YSZ anode and 70 pm... 

Tsai, T. Barnett, S. A. (1997). Effect of LSM-YSZ cathode on thin-electrolyte solid oxide fuel cell performance. Solid State Ionics, Vol. 93, No. 3-4, 0anuary 1997), pp. (207-217), ISSN 0167-2738... 

LSM/YSZ cathodes has been produced by Jiang [11] in which a comprehensive data set of electrochemical parameters is presented and to which the reader is directed for further detail. 

Liu, Y.L., Hagen, A., Barford, R., Chen, M., Wang, H.J., Poulsen, F.W. Hendriksen, P.V Microstructural studies on degradation of interface between LSM-YSZ cathode and YSZ electrolyte in SOFCs. Solid... 

One of the problems with anode-supported cells is that any difference in thermal expansion between anode and electrolyte becomes more significant than in conventional high-temperature SOFCs. For this reason many developers use porous nickel cermet anodes with interfacial regions made of NiA SZ doped with ceria. Operating at temperatures below about 700°C means that metallic bipolar plates can be used, and the lower the temperature, the less exotic the steel needs to be. Ferritic stainless steels can be used below about 600°C, and these have the advantage that they have a low thermal expansion coefficient. Conventional doped LSM-YSZ cathodes can be used but there is much development in progress to improve cathode materials as the cathode overpotentials become more significant as the cell temperatures are lowered. A recent review of cathode materials has been published by Ralph (2001). 

Most of the discussion in this chapter is centered on cells made with traditional materials such as YSZ electrolyte, Ni + YSZ anode, and LSM + YSZ cathode although its extension to other materials is essentially straightforward. The relative contributions of various polarisations vary widely among the different cell designs anode-supported, cathode-supported, and electrolyte-supported. Ohmic contribution is the smallest in electrode-supported cells due to the thin... 

Fig. 1 Examples of mechanical failures and microstructural alterations observed in SOFC stacks, a Delamination of cathode current collection layer [21], reproduced here with kind permission from ASME 2008. b cracking of the sealant [10], reproduced here with kind permission from Elsevier 2006, and loss of gas-tighntess [72], reproduced here with kind permission from John Wiley and Sons 2009. c MIC coating delamination [18], reproduced here with kind permission from Elsevier 2008. d anode support reoxidation cycling [25], reproduced here with kind permission from Elsevier 2009 e formation of zirconates in LSM-YSZ cathode [68], reproduced here with kind permission from Elsevier 2009. f chromium deposit in LSM-YSZ cathode [78], reproduced here with kind permission from The Electrochemical Society 2007...

Fig. 12 Le/i Effect of the flow configuration and methane conversion fraction (PR) on the stress. Case of an anode-supported cell with LSM-YSZ cathode and compressive gaskets, a Temperature profile and b First principal stress in the anode. The MIC is displayed in transparency, c First principal stress in the cathode (insert alxtve the symmetry line), d Contact pressure on the cathode GDL and compressive gasket and e vertical displacement along the z-axis, with an amplification factor of 2,000. Right column effect of creep in a cell based on a LSCF cathode and a temperature distribution, on b the evolution of the first principal stress in the anode support in operation and c during thermal cycling to RT and d evolution of the first principal stress in the GDC compatibility layer after thermal cycling. The profiles above and below the symmetry axis refer to different operation time [88, 89]. Reproduced here with kind permission from Elsevier 2012...

---