Ceria-Based Anodes

The doped ceria anode was developed because ceria has been an excellent electro-catalyst for methane oxidations. The methane oxidation at TPB can be expressed as  

Doped and undoped ceria exhibit ionic and electronic conduction at low oxygen partial pressures. Ce gets reduced to Ce , which is the main cause for mechanical failure due to lattice expansion (for low oxygen partial pressure). The electrolyte/electrode interface may be delaminated due to the formation of cracks. When 40-50% of Ce ions are substituted with Gd ions (Ceo.6Gdo.40i.8-CGO), then a balance between lattice parameters and conductivity with the YSZ electrolyte and an anchoring YSZ layer provides the ability to resist the thermal expansion mismatch. Uchida and co-workers obtained the electrocatalytic activities for the SDC and Yttria doped Ce02 (YDC) for the electrodes sintered at 1150 and 1250°C. The current density of 0.2-0.25 PJcvc is observed for SDC and YDC anodes, 

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Murray EP, Tsai T, Barnett SA (1999) A direct-methane fuel cell with a ceria-based anode. Nature 400 649-651... 

Putna ES, Stubenrauch J, Vohs JM, and Gorte RJ. Ceria-based anodes for the direct oxidation of methane in solid oxide fuel cells. Langmuir 1995 11 4832-4837. 

Ceria, particularly when doped with Gd203 or SmzOs," has received some attention for direct hydrocarbon conversion in SOFC. Dating back to Steele and co-workers,interesting properties have been demonstrated for ceria-based anodes in direct utilization of methane. Later work suggested that the performance of ceria-based anodes in hydrocarbons could be improved by the addition of precious-metal catalysts, at dopant levels,but the performance of these cells was still too low for practical considerations. The problem with doped ceria is likely that its electronic conductivity is not sufficient. In general, the electrode material should have a conductivity greater than 1 S/cm in order to be practical since a conductivity of 1 S/cm would lead to a cell resistance of 0.1 Q cm for an electrode thickness of 1 mm, even... 

E. Perry Murray, T. Tsai, and S.A. Barnett. A Direct-Methane Fuel Cell with a Ceria-Based Anode. Nature, 400 651-659,1999. 

The solid oxide fue( cell (SOFC) have been under development during several decades since it was discovered by Baur and Preis in 1937, In order to commercialise this high temperature (600 - 1000°C) fuel cell it is necessary to reduce the costs of fabrication and operation. Here ceria-based materials are of potential interest because doped ceria may help to decrease the internal electrical resistance of the SOFC by reducing the polarisation resistance in both the fuel and the air electrode. Further, the possibility of using less pre-treatment and lower water (steam) partial pressure in the natural gas feed due to lower susceptibility to coke formation on ceria containing fuel electrodes (anodes) may simplify the balance of plant of the fuel cell system, and fmally it is anticipated that ceria based anodes will be less sensitive to poising from fuel impurities such as sulphur. 

IL ACTIVATION OF MIXED-CONDUCTING CERIA-BASED ANODE... 

It appears that instead of a simple electrode a complicated one emerged, and a suitable (cheap and redox stable) current collector material has not yet been demonstrated. Nevertheless, ceria based anodes have important advantages over conventional Ni-based anodes, namely the ability to endure repetitive oxidation and reduction (redoxing) and the ability to avoid (or tolerate) carbon deposition from... 

Murray, E.P., Tsai, T., and Barnett, S.A. (1999) Direct methane solid oxide fuel cell with ceria-based anode. Nature, 400, 649-651. 

Watanabe M, Uchida H, Yoshida M (1997) Effect of ionic conductivity of zirconia electrolytes on the polarization behavior of ceria-based anodes in solid oxide fuel cells. J Electrochem Soc 144(5) 1739-11743... 

Lohsoontorn P, Brett DJL, Brandon NP (2008) Thermodynamic predictions of the impact of fuel composition on the propensity of sulphur to interact with Ni and ceria-based anodes for solid oxide fuel cells. J Power Sources 175 60-67... 

Suzuki, S., Uohida, H. Watanabe, M. Microstmctural analyses of ceria-based anode with highly dispersed Ni eleotrocatalysts for medium-temperature sohd oxide fuel-cells. Electrochem. 73 (2005), pp. 128-134. 

Uchida, H., Suzuki, S. and Watanabe, M. (2003) A high performance electrode for medium-temperature SOFC mixed conducting ceria based anode with highly dispersed Ni electrocatalysts. Proceedings of the eight International Symposium on Solid Oxide Fuel Cells (SOFC VIII), The Electrochemical Society, PV 2003-07, pp. 728-736. 

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