以乙醇為中溫型固態氧化物燃料電池之Ni/SmxCe1-xO2-δ (x= 0, 0.1, 0.2) 陽極觸媒製備及其性質研究

Synthesis and Property of Ni/SmxCe1-xO2-δ Catalysts in Anode for IT-Solid Oxide Fuel Cell Using Ethanol as Fue

許又文(You-Wen Hsu)

指導教授 ： 洪逸明

元智大學/工程學院/化學工程與材料科學學系/碩士(2013年)

https://doi.org/10.6838/YZU.2013.00134

摘要

本論文採用中溫型固態氧化物燃料電池之陽極材料Ni/SmxCe1-xO2-δ (x=0, 0.1, 0.2) 作為觸媒載體，使用Ni為主要觸媒材料，以Ni/ SmxCe1-xO2-δ (x=0, 0.1, 0.2) 為陽極觸媒。利用Citric-EDTA 複合法合成不同氧空缺濃度之載體，進行陽極觸媒活性測試，探討不同氧空缺濃度之載體對觸媒產氫與抗碳沉積能力之影響。進而擇一產氫效率高之陽極觸媒量測，進行耐久性測試觀察其產氫與碳沉積現象。
本論文利用直接合成法與間接合成法製備陽極觸媒，其差異為Ni2+與載體前驅物是預先混好 (直接合成法, E系列) 或將Ni2+與製備好之SmxCe1-xO2-δ 載體混合熱處裡 (間接合成法, C系列) ，製備出晶粒尺寸均一之陽極觸媒。將製備好之陽極觸媒，進行材料基本分析、活性反應、老化測試與其碳沉積分析。
於材料分析中，利用XRD 圖譜鑑定活性測試前後，均為Sm0.2Ce0.8O2-δ 與Ni 純相，無其他異相生成，經H2-TPR 之還原溫度變化中，其結果與TEM 之Ni 分布有關，與比表面積較無相關。直接合成之還原溫度高於間接合成，其結果由SEM觀察出直接合成法之燒結現象嚴重，而間接合成法之SEM 表面形貌觀察出其晶粒大小均一且無明顯燒結現象，由H2-TPR 中觀察出隨著氧空缺濃度增加，能抑制Ce4+於高溫下變價。
於活性測試中，利用固定之水醇莫耳比濃度 (1：3)，於固定之操作條件下，利用氣相層析儀偵測 400～800 oC 之產氫效率。直接合成法之產氫效率差，且其產氫效率與穩定性不佳。間接合成法於500 oC 之乙醇轉化率已達100 % ，且其氫氣產率最高為96.62 % ，其氫氣產率穩定，且產物單純。
由碳沉積數據得知，間接合成法之碳沉積含量，與氧空缺含量成反比關係，進而改善觸媒材料之碳沉積現象。SEM與TEM反應後觸媒表面皆生成碳沉積與拉曼及TPO之氧化曲線結果相符，分析結果與推斷之碳沉積機制相符合。
將間接合成法所製備之Ni/Sm0.2Ce0.8O2-δ 進行長時間是24小時之耐久性測試 (老化實驗)，雖其氫氣產率衰退13.6%，但其氫氣產率平均為83 %且穩定。利用SEM、Raman 與TGA分析其碳沉積，觸媒表面確實生成碳管但不影響其產氫之效率。從XRD分析反應後之相結構，結果顯示載體並不隨著長時間高溫操作下產生相變。
總和以上分析，間接合成法所製備之Ni/Sm0.2Ce0.8O2-δ 陽極觸媒為最佳之選擇。從產物之觀點，其氫氣純度高、副產物少及乙醇之轉化效率佳，故可做為新式陽極材料。

關鍵字

SmxCe1-xO2-δ ； 氧缺陷 ； 乙醇 ； 蒸氣重組 ； 鎳

並列摘要

The purpose of this study is to prepare the Ni/SmxCe1-xO2-δ (Ni/SDC, x= 0, 0.1, 0.2) catalysts for the Intermediate-Temperature Solid Oxide Fuel Cell (IT-SOFC) anodic electrode and investigate the material characteristic and electrochemical performance of these catalyst materials. The SDC supporter mixed with nickel as the catalysts to form the Ni/SDC catalyst electrode. The Citric-EDTA complex method was used to synthesize SDC supporter with different oxygen vacancies concentration. The catalytic capabilities of production hydrogen and carbon deposition of catalyst materials after ethanol steam reforming were investigated. The best catalyst was chose to measure the hydrogen production and carbon deposition after long term test.
This study used two processes to synthesize Ni/SDC catalysts. The different processes were used to mix Ni2+ with SDC support precursor: one is mixed the Ni, Sm, Ce precursors during the process (E system) and SDC supporter was first prepared and then Ni2+ precursor coat on SDC supporter (C system). The processes could prepare the same size of Ni/SDC anodic catalysts. Material characteristics, activity test, long term test and carbon deposition of the prepared catalysts were investigated in detail.
The structure of Ni/SDC catalyst was distinguished by XRD. There were no second phases observed in the prepared samples. The catalytic reduce temperature was depend on the amount of Ni, but not depend on the specific surface area of samples. The SEM micrographs show that catalysts E system samples exhibited serious sintering phenomenon, but catalysts of C system samples didn’t. For the activity test of the catalysts, water/ethanol mixture (molar = 3:1) was used as source of ethanol steam reforming. The conditions were measured from 400 to 800 oC. The catalysts of C system had the best catalytic performance. The catalytic of C system not only had high hydrogen production about of 96.62 % but also had good stability, however, the catalysts of E system samples were poor. From the result of carbon deposition analysis, it was found that the catalysts of C system samples had inverse relationship between oxygen vacancies concentrations and amount of carbon deposition. The carbon deposition analysis result consists with the result of SEM, TEM, Raman and TPO. The carbon mechanism was also consists with carbon deposition results.
The new anodic catalyst material of Ni/Sm0.2Ce0.8O2-δ–C was test in long term at 700 oC for 24 hrs. Even though the hydrogen production decreased about 13.6 % but it still stabile maintained at 83 %. The phenomenon of carbon deposition was observed and measured by SEM, TGA and Raman. There is carbon tube grow on the surface of catalyst, but the hydrogen production yield didn’t change a lot with amount of carbon deposition increased. There is no second phase observed after long-term test at high temperature.
In conclusion, the Ni/Sm0.2Ce0.8O2-δ–C (C system) catalyst had the best catalytic performance. This catalyst had high hydrogen production, low byproduct and good ethanol conversion in ethanol steam reforming. The Ni/Sm0.2Ce0.8O2-δ –C (C system) catalyst may be can be used as the new anodic catalyst electrode in IT-SOFC.

並列關鍵字

SmxCe1-xO2-δ ； Oxygen vcancanies ； Ethanol ； Steam reforming ； Ni

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