Photocatalytic Hydrogen Production from Gas-phase Methanol and Water with Nanocrystalline TiO 2 Thin Films in High Vacuu
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Photocatalytic Hydrogen Production from Gas-phase Methanol and Water with Nanocrystalline TiO2 Thin Films in High Vacuum Kei Noda1, Masashi Hattori1, Kouichi Amari1, Kei Kobayashi2, Toshihisa Horiuchi3, and Kazumi Matsushige1 1 Electronic Science & Engineering, Kyoto University, Katsura, Nishikyo, Kyoto, 615-8510, Japan 2 Innovative Collaboration Center(ICC), Kyoto University, Katsura, Nishikyo, Kyoto, 615-8520, Japan 3 Advanced Software Technology and Mechanics Research Institute (ASTEM), Shimogyo, Kyoto, 600-8813, Japan ABSTRACT Photocatalytic hydrogen production with gas-phase reactions in high vacuum was examined for nanocrystalline anatase-type titanium dioxide (TiO2) thin films. The hydrogen generation process on platinized TiO2 specimens was investigated using a quadrupole mass spectrometer at a real-time scale under various partial pressures of gaseous methanol and water. As a result, hydrogen generation was successfully detected under ultraviolet (UV) ray illumination even in high vacuum (~10-7 Torr). And the amount of produced H2 largely depends on the temperature of TiO2 samples, probably due to different surface states of TiO2. This study suggests the possibility of new high-speed H2 production system with gas-phase photocatalytic reactions. INTRODUCTION Nanocrystalline TiO2 thin films have been well studied in various research and industrial fields, which include photocatalysts for water splitting and decomposition of organic molecules, dye-sensitized solar cells and purification methods for air and water [1-4]. In particular, solar hydrogen production from water and alcohols via photocatalytic reaction has been greatly expected as a promising new clean energy resource for solid fuel cells [2, 5]. Generally speaking, larger specific surface area of photocatalysts leads to better photocatalytic activities [4]. That is one reason why nanocrystalline anatase-type TiO2 thin films with larger specific surface area have been widely studied and employed for industrial application. However, for realizing more efficient photocatalytic H2 production, basic mechanisms of photocatalytic reactions and related issues such as surface states, stoichiometry and reaction species should be uncovered. In previous works, gas-phase water photolysis showed stoichiometric reaction in low vacuum, although water splitting is normally performed as liquid-phase reaction [6]. This means using gaseous molecules is quite significant in order to investigate many processes of complicated photocatalytic reactions. Moreover, hydrogen production was normally examined in liquids, where the formation and diffusion of hydrogen bubbles inside solutions limit the speed for taking hydrogen gases out of liquid. This would be a shortcoming for driving vehicles and machines with fuel cells at a higher velocity. Therefore a challenge for developing a new system for high-speed hydrogen production should be done. In this background, we focused here on photocatalytic hydrogen production from gaseous methanol and water using nanocrystalli
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