Role of Pt Nanoparticles in Photoreactions on TiO 2 Photoelectrodes
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Role of Pt Nanoparticles in Photoreactions on TiO2 Photoelectrodes
Woo-Jin An1, Wei-Ning Wang1, Balavinayagam Ramalingam2, Somik Mukherjee2, Dariusz M. Niedzwiedzki3, Shubhra Gangopadhyay2, and Pratim Biswas1 1 Aerosol and Air Quality Research Laboratory, Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, One Brookings Drive, Campus Box 1180, St. Louis, MO 63130, U.S.A. 2 Center for Micro/Nano Systems & Nanotechnology, University of Missouri, Columbia, MO 65211, U.S.A. 3 Photosynthetic Antenna Research Center (PARC), Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130, U.S.A. ABSTRACT Highly efficient Pt-TiO2 composite photoelectrodes were synthesized by combining two novel deposition methods: ACVD and a room temperature RF (radio frequency) magnetron sputtering method. A room temperature RF magnetron sputtering method allowed uniform deposition of Pt nanoparticles (NPs) onto the as-synthesized nanostructured columnar TiO2 films by ACVD. Pt NP sizes from 0.5 to 3 nm demonstrating a high particle density (>1012 cm 2) could be achieved by varying deposition time with constant pressure and power intensity. Assynthesized Pt-TiO2 films were used as photoanodes for water photolysis. Pt nanoparticles deposited onto the TiO2 film for 20s produced the highest photocurrent (7.92 mA/cm2 to 9.49 mA/cm2) and maximized the energy conversion efficiency (16.2 % to 21.2 %) under UV illumination. However, as the size of Pt particles increased, more trapping sites for photogenerated electron-hole pairs decreased photoreaction. INTRODUCTION Ever since Fujishima and Honda developed an innovative method to produce hydrogen (H2) by water photolysis [1], much effort has been made to increase the energy conversion efficiency. Titanium dioxide (TiO2) has been widely used as a photocatalytic material for solar energy applications. Along with the wide bandgap of TiO2, its short electron-hole pair lifetime [2] is a limiting factor for decomposing water into oxygen (O2) and hydrogen (H2). One dimensional single crystal TiO2 films provide favorable electron transport pathways, resulting in enhanced photoreaction [3]. In addition to the film morphology, surface modification by noble metal contacts lead to efficient electron-hole separation, improving photoelectrochemical properties of metal oxide films [4]. Although the size of noble metal particles and the distance between noble metal particles play a significant role in determining the efficiency of solar energy applications [5], existing methods can not precisely control these two factors. In this study, the room temperature RF magnetron sputtering method was employed to deposit monodispersed nano-sized platinum (Pt) metal on the columnar TiO2 films in a controlled manner.
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EXPERIMENT
Figure 1. Sub-nanometer Pt particle deposition on the columnar TiO2 film synthesized by ACVD [6]. Pt-TiO2 photoelectrode synthesis was carried out in two steps. First, using aerosol chemical vapor deposition (ACVD), columnar TiO2 films
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