碩士 / 國立清華大學 / 化學工程學系 / 98 / The key point in water splitting as a heterogeneous reaction is the surface reaction between the catalyst and reactant. In order to enhance the reaction at the interface, there have been many efforts made on increasing the surface area of the catalysts. We first used TiO2 aerogels prepared with a sol-gel process and subsequent supercritical fluid drying, as the photocatalyst in water splitting. The high surface area and 3-D connected pore structure of large porosity are the advantages of aerogels for serving as the photocatalysts. We compared the hydrogen production efficiencies of aerogels, commercial P25, and TiO2 nanoparticles prepared with a hydrothermal process. The properties of these catalysts were characterized with XRD, BET, TEM, and DLS.
The photocatalytic water splitting reaction was carried out in a methanol solution under a 400 W Hg light source for 8 hours. The methanol served as the sacrificial agent. The hydrogen evolution rate of the TiO2 aerogels was 6.4 μmol/g h, which was six times and twice of those achieved by P25 (0.9 μmol/g h) and TiO2 nanoparticle (1.9 μmol/g h), respectively. The results of EIS (Electrochemical Impedance Spectroscopy) Nyquist plot indicated that a more effective separation of photogenerated electron-hole pairs, and faster interfacial charge transfer to the reactant occurred in the TiO2 aerogel system. The activation energy of the reaction in the aerogel system was determined with the Arrhenius equation to be 50.9 kJ/mole, assuming a zeroth order kinetics for the photocatalytic reaction. We raised the hydrogen production rate from 6.4 μmol/g h to 287 μmol/g h by incorporating Pt nanoparticles as an assistant catalyst, by a polyol process based on 0.5 wt% Pt. The activation energy determined for the Pt loaded TiO2 arogel was 13.2 kJ/mole, much reduced from the plain TiO2 arogel case. The result showed that the assistant catalyst indeed provides another reaction path to lower the activation energy.
Another part of this research focused on the ways of loading Pt – polyol process and immersion-calcination-reduction process. We found that the immersion-calcination-reduction process achieved the same level of hydrogen evolution rate by using a much lower concentration of starting Pt, 0.05 wt. % Pt in this case. The result may be due to better dispersion and smaller particle size of the Pt nanoparticle realized in the immersion-calcination-reduction process.
| Identifer | oai:union.ndltd.org:TW/098NTHU5063076 |
| Date | January 2010 |
| Creators | Lin, Chia-Chieh, 林佳潔 |
| Contributors | Lu, Shih-Yuan, 呂世源 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 82 |
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