商用鉑碳催化劑特性鑑定分析

Characterization of commercial carbon-supported platinum catalyst

張浩恩(Hao-En Chang)

指導教授 ： 沈家傑

元智大學/工程學院/先進能源碩士學位學程/碩士(2011年)

https://doi.org/10.6838/YZU.2011.00301

摘要

鉑碳催化劑為質子交換膜燃料電池常用的觸媒，本論文分為兩部分，第一部分主要以氫氣化學吸附實驗，探討商購觸媒(E-Tek)之分散度，並以TEM及XRD鑑定粒徑，探討不同鉑負載量、前處理條件及吸附溫度對於觸媒之分散度、粒徑與吸附熱影響。實驗結果顯示，隨著鉑附載量增加、觸媒的分散度降低。由不同前處理條件發現，高負載量的觸媒催化劑極易發生燒結現象，使化學吸附分析困難度提高許多，利用程溫還原法順利修正氫氣吸附量計算誤差。
第二部分則以商購Johnson Matthey鉑碳催化劑(10-60 wt.%)藉由不同升溫速率(b = 1、4、7、10 ℃/min)以低溫程溫還原法探討還原活化能，並利用XRD及TEM鑑定觸媒粒徑，以XPS鑑定鉑觸媒氧化態，探討不同鉑附載量之觸媒，其還原溫度、觸媒粒徑、活化能與氧化態比例之間的關係。研究結果發現，升溫速率越快，還原溫度會向高溫偏移。對不同附載量的鉑觸媒而言，越高的鉑附載量其粒徑越容易因聚集而變大。還原峰面積與氧化態比例呈線性關係，並成功以固定氧化態比例與程溫還原峰進行峰值擬合。

關鍵字

鉑碳催化劑 ； 活化能 ； 分散度 ； 程溫還原

並列摘要

Pt/C catalysts are widely used in PEM fuel cell. In this study, the first part was focused on the dispersion characterization for the commercial E-Tek Pt/C catalyst by H2 chemisorption, X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). Experimental parameters such as Pt loading (20 and 40 wt%), H2-tritration, H2-desorption at T = 100, 200 and 300 oC prior to H2 chemisorption were included. The results showed that the dispersion of the catalysts decreased with the Pt loading. Surprisingly, carbon-supported Pt particles were easily to be sintered during H2-tritration and H2-desorption treatments, making H2 chemisorption measurement difficult. Based on the amount of H2 consumption for the reduction behavior of PtOx of the catalyst measured by cryogenic temperature programmed reduction (TPR), the dispersion obtained by H2 chemisorption was calibrated successfully, which is in agreement with that obtained by XRD and TEM.
The second part was the reduction characterization of Pt oxide for commercial Johnson Matthey Pt/C catalysts (Pt loading = 10, 20, 40, 50, 60 wt%) by X-ray photoelectron spectroscopy (XPS) and cryogenic TPR. XPS results indicate that PtsO and PtsO2 species occur on the surface of the specimens. However, the ratio between PtsO and PtsO2 was not regularly changed with the Pt loadings. The variation of the ratio measured by XPS is very close to that characterized by cryogenic TPR based on the reaction of PtsOx + xH2 → Pts + xH2O . For all of the specimens, both PtsO and PtsO2 were reduced below 0 ℃.

並列關鍵字

Pt/C catalyst ； Activation energy ； Dispersion ； TPR

參考文獻

[4] Y. Ji, V. Koot, Ad M. J. van der Eerden, B. M. Weckhuysen, D. C. Koningsberger and D. E. Ramaker, J. Catal., 245 (2005) 415-427.

[11]S. Y. Huang, C. D. Huang, B.T. Chang and C. T. Yeh, J. Phys. Chem. B., 110 (2006) 21783-21787.

[12]J. Freel, J. Catal., 25 (1972) 149-160.

[15]C. P. Hwang and C. T. Yeh, J. Catal., 182 (1999) 48-55.

[18]S. C. Chou, S. H. Lin and C. T. Yeh, J. Chem. Soc. Faraday Trans., 91 (1995) 949-951.