Methane fuel oxidation within SOFC

This presentation reports some studies on the materials and catalysis for solid oxide fuel cell (SOFC) in the author s laboratory and tries to offer some thoughts on related problems. The basic materials of SOFC are cathode, electrolyte, and anode materials, which are composed to form the membrane-electrode assembly, which then forms the unit cell for test. The cathode material is most important in the sense that most polarization is within the cathode layer. The electrolyte membrane should be as thin as possible and also posses as high an oxygen-ion conductivity as possible. The anode material should be able to deal with the carbon deposition problem especially when methane is used as the fuel. 

The SOFC module is set (sized) to operate at 0.69 volts per cell. The spent fuel and air effluents of the SOFC are combusted within the module to supply heat for oxidant preheating. Unlike the natural gas case, the fuel does not require a pre-reformer with only 0.3% methane along with 36% hydrogen and 43% carbon monoxide. The carbon monoxide will be either water gas shifted to hydrogen or utilized directly within the fuel cell. A gas recirculation loop for the... 

In any case, one of the most important issues to be prevented in SOFC systems is carbon deposition (coke formation) from the fuels. Figure 6.21 shows the equilibrium products for (a) methane- and (b) methanol-based fuels with the steam-to-carbon (S/C) ratio of 1.5 at elevated temperatures [251]. Assuming thermochemical equilibrium, carbon deposition is not expected to occur within a wide temperature range. The calculated results for various other fuels mentioned above have been shown elsewhere [251]. The minimum amounts of H2O (water vapor) necessary to prevent carbon deposition are shown in Fig. 6.22 for hydrocarbon fuels. While S/C of 1.5 is enough for CH4, higher S/C is needed with increasing carbon number of hydrocarbons, especially at lower temperatures. Such dependencies have also been revealed for O2 (partial oxidation) and CO2 (CO2 reforming) [251] to prevent carbon deposition. 

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