水電解質子交換膜製氫特性研究

Characteristic of Production of Hydrogen by Proton Exchange Membrane Water Electrolysis

林建智(Chien-Chih Lin)

指導教授 ： 江右君

元智大學/工程學院/機械工程學系/碩士(2007年)

摘要

質子交換膜水電解(PEMWE)泛用之H2電極材料為鉑金屬(Pt)，而O2電極則為鉑與氧化銥之混合材料(Pt/IrO2) 。但是，雖然IrO2之存在可減少Pt之使用量而降低材料成本，但其本身卻非商業可購得之材料，因而會增加整個系統之價格成本；本研究於是自行製備質子交換膜水電解製氫系統的Pt與Pt-Ru觸媒以降低成本。
本研究利用含浸法(Impregnation method)來合成觸媒，並改變不同合成環境、提升pH值來合成觸媒，接著，以乙醇清洗、離心機離心和高溫處理來改質觸媒。最後選出表面特性分析較好的觸媒製作成MEA膜並進行水電解的效能測試。
而自行合成的Pt與Pt-Ru觸媒的純度幾乎都在90 %以上，平均顆粒大小為5-20 nm，提升pH值可以較明顯的看出有提升Pt與Ru的純度。但是，有經過高溫處理的觸媒卻明顯的降低了Ru的純度。自行合成Pt與Pt-Ru觸媒的X光繞射分析圖譜，有明顯晶格為f.c.c.的Pt繞射峰，分別位於 2θ為39、46和67 o的Pt (1 1 1)、 Pt (2 0 0)和Pt (2 2 0)結構。當Pt-Ru合金中的Ru重量百分比低於52 wt. %時只會顯示出f.c.c.的Pt觸媒的繞射峰而已。提升pH值可提高觸媒的比表面積、總孔體積和平均孔徑大小。經過高溫處理後的觸媒的所有表面特性全部明顯降低，這是由於經過高溫處理會使觸媒產生聚集所產生的影響。在水電解效能方面，觸媒：Nafion=3：1時有最好的效能。當氫氣電極觸媒Pt black為2 mg/cm2；氧氣電極觸媒Pt-Ru為4 mg/cm2時有著最佳的水電解效能。對於自行合成的Pt觸媒對水電解效能的影響，以Pt (A10X)為氫極觸媒、Pt-Ru為氧極觸媒的水電解效能最好，而觀察自行合成的Pt-Ru觸媒對水電解效能的影響，則以Pt black為氫極觸媒、Pt-Ru (A10X)為氧極觸媒的水電解效能最佳。

關鍵字

質子交換膜水電解 ； 觸媒 ； 含浸法 ； 表面特性

並列摘要

Pt is usually used as H2 electrode catalyst of proton exchange membrane water electrolysis (PEMWE), and Pt-IrO2 is for O2 electrode. Although the use of IrO2 may reduce the amount of Pt, IrO2 is not a commercial product so that its use will increase the cost of the system. Therefore, this study is intended to synthesize the Pt and Pt-Ru catalysts served as H2 and O2 electrode catalysts of PEMWE and evaluate the performance of production of hydrogen in order to reduce the cost.
The impregnation method was employed to synthesize the catalysts. The modifications of catalysts were conducted by changing different environments and pH values, as well as heat treatments. After characterizing the properties of catalysts, three kinds of individual catalysts were chosen and applied to an electrode membrane assembly (MEA) to determine the performance of PEMWE. In addition, the commercial Pt-black and Pt-Ru catalysts were used for comparison.
The purities of as-prepared Pt and Pt-Ru catalysts are almost higher than 90 %, with an average powder size of 5-20 nm. Increase in pH value can improve the purities of Pt and Ru; however, heat treatment seems to significantly reduce the purity of Ru. The results of X-ray diffraction (XRD) analysis indicate that there are f.c.c. Pt peaks located at 2θ are 39, 46, and 67 o, which can be indexed to Pt (1 1 1), Pt (2 0 0), and Pt (2 2 0), respectively. The reason that there is lack of Ru peak in XRD patterns could be the content of Ru in Pt-Ru powders is less than 52 wt. %. It can be seen from the data that specific surface area, total pore volume and average pore size of catalysts increase with increasing pH value. Heat treatments appear to deteriorate the material properties of catalysts, which could be attributed to the agglomeration of catalyst powders. The ratio of catalyst to Nafion solution of 3, and the loadings of Pt-black of 2 mg/cm2 and Pt-Ru of 4 mg/cm2 show the highest performance of PEMWE. Water is the optimal electrolyte but the temperature impact of electrolyte is different from the results in literature. Moreover, no matter Pt or Pt-Ru, the catalysts prepared in air without pH adjustment and heat treatment can produce the best performance of PEMWE.

並列關鍵字

Proton exchange membrane water electrolysis ； Catalyst ； Impregnation method ； Surface properties

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