蒸氣重組產氫觸媒於SOFC應用研究

本論文的研究是包含是以不同操作條件探討甲烷蒸氣重組反應於Ni-YSZ觸媒介面(三相介面、three phase boundary、TPB)反應行為，同時也利用同位素水追蹤反應走向，根據結果，提出相關結論與問題的解決方法與原理。在固態氧化物燃料電池(SOFC)中，最常見的電極就是Ni-YSZ，其本身具有甲烷重組反應的觸媒特性，而此觸媒特性是影響SOFC性能的重要關鍵。研究中以質譜儀(mass spectrometry、MS)、氣象層析(gas chromatography、GC)、傅立葉轉換紅外線光譜儀(Fourier transform infrared spectrometry、FTIR)觀察甲烷蒸氣重組反應。MS主要是以即時量測方式觀察，追蹤所有物質即時變化，探討反應過程中物質反應途徑與隨著溫度變化的趨勢。GC是較為靈敏量測儀器，若經由校正後，可做定量分析，但其缺點為無法即時監測。FTIR主要是觀察觸媒表面反應物質吸附狀態的變化，藉由吸附狀態可以推測反應路徑與反應中所有物質的生成與消失，用於反應機制與反應活性的討論。本研究中探討觸媒對於甲烷蒸氣重組產氫反應，在不同操作條件下包含反應溫度、不同溫度模式、反應氣體流速與H2O含量等影響參數。為了觀察H2O參與反應的變化，本研究使用D2O來追蹤與觀察。反應物質通過加熱反應器後反應生成之氣體，使用MS分析擷取分壓之訊號，藉以分析反應氣體(CH4) 之轉化率與主要生成氣體(H2)之生成率，另外載流氣體(Ar)、其他生成氣體(CO、CO2)與H2O也同時量測並藉此探討影響因素。GC在本研究中作為微量反應變化分析是有用的，但對於偵測氣體與選用管柱填充物受響應度影響須加以配合，使偵測訊號較明顯，然而本研究偵測氣體有數種，使用的管柱對部分氣體響應度較低，導致訊號較不明顯。FTRI在本研究用使用紅外線擴散反射光譜(Diffuse Reflectance Infrared Fourier Transform Spectroscopy、DRIFTs)模組觀察觸媒表面反應情形，但此模組的可控制溫度只達180oC，與反應溫度有差距，因此僅用來低溫時吸脫附狀態的探討。反應後的觸媒其表面型態與元素分析則使用FE-SEM 和 EDX。本研究結果中發現到與CH4反應後的觸媒，會有龜裂現象，經由FESEM觀察與EDX分析，其龜裂中有大量碳管存在。在H2O的方面，若S/C過低(水蒸氣(steam)與供給的燃料含碳(carbon)莫耳數比稱作S/C)，將促使CH4走向裂解反應方向，使觸媒表面積碳反應更多，觸媒活性降低。以本研究結果，若要降低碳管的形成，應促使CO生成，使表面積碳減少，因此要提供足夠的O原子相關物質與其反應，其來源就是H2O或是是材料中的氧化物部分。D2O的實驗結果觀察到，由D2O與H2O的分壓不斷的減少，在TPB中大部分的是生成D2或H2，而O原子相關部分則是生成CO或CO2。如何降低積碳生成是甲烷重組反應中重要的課題，本研究結果提出促使CO的生成是最直接的方式，在重組器中適當的H2O 供給外，燃料電池自陰極端提供O2-除了產生H2O也可與積碳產生CO，都是甲烷重組反應中減少積碳的方式，也致使觸媒能保持較佳活性與耐用度。

關鍵字

固態氧化物型燃料電池；甲烷蒸氣重組；鎳-釔穩定氧化鋯；三相介面；同位素

並列摘要

Solid oxide fuel cell (SOFC) is a solid device that transforms the chemical energy of fuel such as hydrogen or natural gas to electrical energy and has some unique advantages over traditional power generation methods including lower greenhouse emissions, fuel flexibility, and high efficiency. The basic SOFC consists of anode, the electrolyte, the cathode, and the interconnect layer, which are all essentially made of ceramic materials and fabricated by conventional ceramic processes. The most straightforward fuel in the fuel cell is hydrogen at present, mainly produced from the reforming reaction of hydrocarbons. In SOFC, an internal steam reforming can be applied for hydrogen production, because the Ni in the anode material act as a steam reforming catalyst and the operating temperature is suitable for methane conversion. Nickel based catalysts have been most popularly employed in MSR (methane steam reforming) due to its high activity for the methane decomposition and methane reforming reactions. Currently, they are applied as the anode catalyst of SOFC. Although, the supported nickel catalyst has a high thermodynamic potential in the coke formation during MSR. In this study, methane steam reforming reaction over Ni/YSZ was investigated. The catalyst characterization study was established in terms of reaction conditions, methane conversion, and coke formation. Reactants and products and were analyzed using the mass spectrometer (SRSRGA300). The morphology and elements analysis of the catalysts were examined by ﬁeld emission scanning electron microscope (FE-SEM) and EDX. SEM images show the coke formation on the catalyst. In addition, it is found that water plays an important role in MSR. In addition, the extent coke formation was correlated with the increase of water percentage in air. Furthmore, deuterium oxide (D2O) was used as a probe to label the originated hydrogen species. Finally, the formation of graphitic carbon can be minimized by the following schemes as follows (1) Providing enough O-reactant to react with carbon and produce CO. (2) Deacrasing the production of CO2 or adding CO2 in reactants. (3) Increasing the production of CO.

並列關鍵字

Solid Oxide Fuel Cells ； Methane Steam Reforming ； Ni/YSZ ； Mass Spectrometer ； Deuterium Oxide

參考文獻

1. A. B. Stambouli and E. Traversa, "Solid oxide fuel cells (SOFCs): a review of an environmentally clean and efficient source of energy," Renewable and Sustainable Energy Reviews, vol. 6, 2002, pp. 433-455.

3. N. Q. Minh, "Ceramic Fuel Cells," Journal of the American Ceramic Society, vol. 76, 1993, pp. 563-588.

4. T. Hibino, A. Hashimoto, T. Inoue, J. I. Tokuno, S. I. Yoshida, and M. Sano, "A low-operating-temperature solid oxide fuel cell in hydrocarbon-air mixtures," Science, vol. 288, 2000, pp. 2031-2033.

5. X. Zhai, Y. Cheng, Z. Zhang, Y. Jin, and Y. Cheng, "Steam reforming of methane over Ni catalyst in micro-channel reactor," International Journal of Hydrogen Energy, vol. 36, 2011, pp. 7105-7113.

6. R. M. Ormerod, "Solid oxide fuel cells," Chemical Society Reviews, vol. 32, 2003, pp. 17-28.

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蒸氣重組產氫觸媒於SOFC應用研究

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