| Summary: | 博士 === 國立清華大學 === 化學工程學系 === 96 === In this study, we devoted to research the carbon deposition (coking) and de-coking on the anode of solid oxide fuel cell (SOFC), which fed with the methane flow. This work is considered as the most potential technology to solve the energy problems in this century. In recent years, there are some fuel cell researches using the methane as the fuel, but the fuel efficiency is quite low due to the carbon deposit on anode easily. Herein, we investigated the electrochemical reaction of the SOFC anode with different operating parameters, such as tuning the voltage, temperature or changing the SOFC material. Moreover, in order to improve fuel efficiency, the catalyst layer was added into anode side to deal with the fuel and product.
In the study of direct methane solid oxide fuel cell (DM-SOFC) , "Electrochemical promotion of lattice oxygen extraction" was observed in the process of electrochemical reaction. This phenomenon was oxygen extracted from lattices on anode side of SOFC reacted with the carbon on the surface of the anode. It can retard the carbon deposition. Furthermore, this phenomenon also brought a kind of current called "the fuel-free current". It’s be resulted the oxygen from the cathode-side three phase boundary (TPB) refilled the vacancies of the bulk lattice-oxygen on the anode side, especially in the absence of fuel.
As the experimental results, the charge δ of oxygen species (Oδ-) decreased with the operating voltage increased. Thereby, the electrochemical effect was more significant. It also found that the oxygen species for transmission in the lattice decreased with the operating temperature increased. Moreover, the activation energy of lattice oxygen extracted under close-circuit was 124 kJ/mol, smaller than the activation energy under open-circuit (262 kJ/mol).
When the catalyst layer was introduced to the anode side, the catalyst layer can promote the methane reforming reaction, reduced the coking on the surface of the anode in DM-SOFC. As the results, the carbon monoxide selectivity was about 0.702~0.547, and no water be detected. It showed that the further reaction of the products can be proceeded in presence of the catalyst layer.
In this study, the addition of the catalyst layer in the DM-SOFC operation effectively improved the fuel efficiency and maintained the SOFC activity in a long-term operation.
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