Oxidation of Hydrocarbons on Ceria Based Electrodes

Work with the purpose of using ceria based materials as an anode for direct oxidation (i.e. without steam reforming) of methane and other hydrocarbons have been performed by several authors. 

In methane good performances were reported at 1000°C when Pt or Ni metals were present. Originally, it was believed that reduced ceria was a good electrocatalyst for direct methane oxidation.This was based on the observation that in blind tests with the Pt current collector directly on the YSZ electrolyte, a very high polarisation resistance was obtained, and thus it was concluded that Pt was almost inert for the reactions in question as also reported by Steele et al. The 

In spite of this, we believe that there is a real potential in ceria as an anode for conversion of hydrocarbon fuels, because ceria can tolerate carbon precipitation and is able to oxidise the carbon. In this context it should be remembered that one of the oldest applications of ceria has been as a carbon oxidation catalyst, and still today it is used as a catalyst in self-cleaning ovens and for the oxidation of diesel soot in automobiles.  

Recently, sensational papers about direct oxidation of methane and hydrocarbon in solid oxide fuel eells (SOFC) at relative low temperatures about 700°C were published. Even though the conversion of almost dry CH4 on ceramic anodes were demonstrated more than 10 years ago at 1000°C, the reports about high current densities for methane oxidation at such low temperatures are indeed surprising. 

A power density of 0.37 W/cm at 650°C for an SOFC using a 2 pm Ni-YSZ cermet anode on top of a 0.5 pm functional layer of (Y203)o, 5(Ce02)og5 (YDC) on a 8 pm YSZ electrolyte.It was also shown that the polarisation resistance of the YSZ cermet without the YDC-layer was about 6 times higher. The result was interpreted as a direct electrochemical oxidation of CH4 facilitated by the YDC. This interpretation is in strong contrast to the findings that doped ceria in itself is about inert to direct oxidation of and that Ni-YSZ anodes will be quickly 

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

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