Ceria-based electrodes

2 Ceria-based electrodes 12.7.2.1 Electrodes for hydrogen-based fuels 

Mobius and Rohland showed back in 1964 that ceria could work as an anode in an SOFC fuelled with Hj and CO. Shortiy after, Takahashi et al described Ceo.6Yo.4Oi 8 and Ceo.6Lao.4O13 as being excellent anode materials for SOFCs. Since then, a number of studies have been carried Gd-doped ceria was investigated as 

Despite these recent results, the low electronic conductivity of ceria-based oxides makes it difficult to use them as a single-material fuel electrode at lower temperatures. The surface reaction kinetics and lateral electron transport or rate of removal of electrons from the ceria surface have been reported to be the most likely rate-limiting processes. At temperatures below 1000 °C ceria-based oxides only show promising performance as a component of cermets with Ni or other ceramic electrode materials, or as will be illustrated later, when infiltrated as a nano-sized phase in porous electronic conducting backbones. 

Ceria has been used as the ceramic part (or as an addition) in nickel- or ruthenium-cermet anodes for hydrogen oxidation. Beneficial effects have been reported and interpreted as most likely being due to the broadening of the three-phase boundary zone. However, one of the major drawbacks of using ceria in cells with YSZ-based electrolytes is its chemical reactivity with the YSZ electrolyte at high temperatures. Sintering of a doped ceria anode on a YSZ electrolyte at high temperatures ( 1200°C) results in the formation of a reaction (diffusion) zone with limited oxide ion conductivity.  

However, reactions (12.47) to (12.49) above still represent a very simplified reaction scheme because the cracking process is usually highly complex. In any case, the anode material in SOFGs must be able to oxidize the cracking products, and especially the formed carbon at sufficient rates. The formed carbon (coke) can also be removed by steam or carbon dioxide  

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Oxidation of Hydrocarbons on Ceria Based Electrodes 15.5. References ... 

M. Mogensen, Ceria-Based Electrodes, in A. TrovareUi (ed.). Catalysis by Ceria and Related Materials, Imperial CoUege Press, Ixmdon, p.453,2002. 

Combining Cu with Co in ceria-based electrodes has shown further improvement towards coking, especially with the direct utilization of methane. " ... 

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