Fabrication of Metallic Catalyst/Carbon Nanotube Composite Electrodes for Direct Methanol Fuel Cells
| Autor: | Jin-Long Wei, 魏金龍 |
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| Rok vydání: | 2009 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 97 This research was divided into two parts to explore. In the part 1, we used three different reduction methods to prepare the same ratios of Pt–Co/CNT catalysts. In the part 2, we used the method of microwave reduction to prepare three kinds of proportion of Pt–Co/MCMB catalysts. Part 1: The electrochemical activities of three types of Pt–Co/CNT catalysts, prepared from different Co depositions, in methanol oxidation have been investigated. X-ray diffraction reveals that these Pt–Co/CNT catalysts possess not only different crystalline sizes but also different levels of atomic distribution. The use of strong reducing agent (NaBH4) enables the formation of a cobalt layer over the Pt surface, inducing bimetallic Pt–Co particles, whereas direct thermal reduction enables the formation of Pt–Co nanoalloy with a high degree of alloying. It has been shown that the normalized active surface coverage increases the alloying degree of Pt–Co catalysts, indicating the importance of atomic distribution. Cyclic voltammetric measurement also reveals that the Pt–Co/CNT catalyst with a good alloying degree exhibits a better electrochemical activity, high CO tolerance, and long-term durability (> 100 cycles). This activity improvement in methanol oxidation can be attributed to the bifunctional mechanism of binary catalysts: since the Pt–Co/CNT catalyst offers a large amount of Pt–Co pairs, the Co site serves as a promoting center for the generation of Co–OH species, and thus more Pt sites are available for methanol oxidation. Accordingly, the synthesis condition is one of the key factors affecting the distribution of surface atoms, significantly related to their catalytic ability in methanol oxidation. Part 2: The method of microwave reduction was used to prepare Pt–Co/MCMB catalysts with different Pt/Co atomic ratios. It revealed that three kinds of catalysts, Pt25Co75/MCMB, Pt50Co50/MCMB and Pt75Co25/MCMB, exhibit different crystal sizes showing different electrochemical activities in methanol oxidation. From CV curve, the electrochemical surface area is the decrease function of scan number. The Pt50Co50/MCMB catalyst displays the best electrochemical properties among the Pt-Co/MCMB catalysts, revealing importance of different proportion. In the methanol oxidization, IF/IB value of Pt25Co75/MCMB, Pt50Co50/MCMB and Pt75Co25/MCMB are 1.08, 1.12 and 1.13 after 100 cycles, respectively. We inference the particle size of the method of microwave reduction to affect the electrochemical activity is one of importance factors, and the method of microwave reduction can substantial decrease reduction time. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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