| Summary: | 碩士 === 國立交通大學 === 材料科學與工程學系 === 100 === Platinum has a superior electrocatalytic activity toward methanol oxidation reaction (MOR) and, therefore, Pt is the most preferred catalyst used in direct methanol fuel cells (DMFCs). In the present time, the most widely studied subject in DMFC research is to reduce the size and to optimize the distribution of Pt nanoparticles for minimizing the use of the precious Pt catalyst and concurrent increasing the electroactivity surface area (ESA) for methanol oxidation. In addition, metal oxides can be used as the Pt support to enhance the electrocatalytic efficiency of the Pt catalyst. In this works, we used plasma-enhanced atomic layer chemical vapor deposition (PEALD) to deposit Pt nanoparticles on the TiO2 substrate, and study the electrocatalytic activity of the Pt nanoparticles toward MOR as a function of the particle size.
A TiO2 thin film was prepared on the Si substrate by electron beam evaporation, and Pt nanoparticles were deposited on the TiO2 thin film by PEALD at 200oC using MeCpPtMe3 as the Pt precursor and O2 as the oxidant of the precursor. The size of Pt nanoparticles can be well controlled by varying the number of the ALD reaction cycle. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that well-dispersed Pt nanoparticles were deposited on the TiO2 surface and the particle size of Pt nanoparticles was in the range between 3 nm and 13 nm depending on the ALD cycle number.
Cyclic voltammetry (CV) and CO stripping analysis were performed to study the electrocatalytic activity of the Pt/TiO2 electrode toward MOR under acidic media. The electrocatalytic activity and the CO tolerance of the electrode are a function of the Pt ALD cycle number. We found that the electrode with a Pt ALD cycle number of 35 had the best electrochemical performance. When the ALD cycle number was larger than 50, Pt nanoparticles coalesced, and the electrode exhibited a electrochemical performance for MOR similar to a Pt thin film. The excellent electrocatalytic activity is ascribed to the synergistic effect of the nanometer sized of Pt nanoparticles and the electronic interaction between the TiO2 support and the Pt nanoparticles. Charge transfer between Pt nanoparticles and the TiO2 support may modify CO chemisorption properties on the Pt nanoparticles, thereby facilitating CO oxidation via the bi-functional mechanism and thus improving the electrocatalytic activity of the Pt catalyst toward methanol oxidation.
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