Aspects of the internal reforming of methane in solid oxide fuel cells

Abstract

Abstract. The tubular concept of the Siemens Westinghouse SOFC is reviewed. The efforts to reduce costs by on-cell reformation of methane on high power density cells are outlined.The problems concerning the internal reformation of methane are discussed from a thermodynamic point of view.Investigations of the steam reformation of methane on Ni-YSZ anodes are reported to clarify the kinetics. The suitability of this material as a catalyst for this reaction is confirmed. On stripes of anodes a steady state utilisation of methane was reached only after many hours, significantly complicating the experiments. This delay was not seen with anodes in cell configurations, suggesting a different process. In neither arrangement the shift reaction was in thermodynamic equilibrium. This reaction seems to be correlated with the reformation. Experiments on stripes with pure mixtures of methane and steam revealed the dissolving of Ni into the gas phase at the leading edge of the sample. This effect can be suppressed by adding a small amount of hydrogen.With gas compositions typical for SOFC operation no degradation of the electrodes was detected during 1000 hours.Assuming an isothermal sample and equilibrium of the shift reaction, the reaction rate was best described being first order in the partial pressures of methane and water for varying lengths of the stripes. But this function failed to describe the variation of the methane utilisation with composition of the input gas, showing that the complexity of the reformation is not fully understood.The reaction rate was found to be too high for on-cell reformation in SOFC stacks. Simulations of a planar design yielded such large temperature gradients that they are likely to result in a disintegration of the cell structure. The same is expected for the tubular design. Tailored catalysts and new cell designs are required to overcome the heat management problem.

A Study of Methane Oxidation over Transition Metal (TM)/CeO2(TM=Ni, Co, Cu, Fe)

“…촉매를 사용하는 메탄 산화 반응은 천연가스로부 터 청정에너지원을 만들어 내는 중요한 요소들 가운 데 하나이다 1,2) . 고체 산화물 연료전지(solid oxide fuel cell: SOFC)는 이러한 에너지원을 연료로 이용 하여 필요한 전기에너지로 변환시키는 장치로써 메 탄 또는 천연가스로부터 추출한 수소를 연료로 사용 하고 있다 [3][4][5][6][7] . 최근…”