Hydrothermally grown TiO 2 nanotubes on multi-layered Ti mesh electrodes for enhanced photoelectrochemical reaction
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Hydrothermally grown TiO2 nanotubes on multi-layered Ti mesh electrodes for enhanced photoelectrochemical reaction Hyunsu Kim, Jirapon Khamwannah, Chulmin Choi, Yang Shi, and Sungho Jin*, Materials Science and Engineering, University of California at San Diego, La Jolla, California 92093 *Address all correspondence to Sungho Jin at [email protected] (Received 21 June 2013; accepted 5 September 2013)
Abstract We report here a successful fabrication of three-dimensional (3D) photoelectrodes fully coated with hydrothermally formed TiO2 nanotubes on multi-layered Ti mesh with significantly increased surface area. A near-vertical array of ~8 nm diameter nanotubes of TiO2 was also produced on the metallic surface of folded Ti mesh electrode. The multi-layered mesh was used as a 3D highly conductive electrode, as this architecture intuitively allows for light passage, reflections, and smooth water flow for possible continuous operation of water splitting reaction. By virtue of substantially increased surface area and more efficient light usage, significantly increased photocurrent densities were obtained.
Introduction Energy harvesting directly from sunlight has attracted tremendous attention and has been extensively studied because of its great potential for low-cost, clean hydrogen production.[1,2] For efficient solar energy conversion, a suitable photocatalyst is characterized by strong catalytic behavior, large reacting surface area, good electrical transport, low charge–carrier recombination losses, and intimate contacts between the photocatalytic material and the electrolyte.[3] In particular, the surface area of the employed photocatalytic material is one of the very important factors that influence the photocatalytic efficiency, although the surface area would not necessarily improve the fundamental properties of photocatalyts.[4,5] For this reason, nanostructured electrodes such as nanotubes, nanowires, and nanosheets are commonly utilized architectures for the photocatalyst structure.[6–8] While there have been many previous studies on the structure and reactivity of photocatalysts, there are somewhat limited number of reports on improving the catalyst performance by geometrical engineering of the conducting electrode substrate. Since an optimized structure of the underlying substrate directly influences the catalytic behavior and is therefore important for maximal utilization of photocatalytic material, a photocatalytic electrode should be developed with an emphasis on both the photocatalyst material itself and the supporting substrate. In view of this, one of the approaches to increase surface area is to combine three-dimensionality of substrate architectures with nanostructured photocatalysts.[9] In order to enable eventual high-throughput operation of photoelectrochemical reactions with continuously supplied, flowing water, we have combined a highly apertured electrode design in threedimensional (3D), electrically connected architectures,
combined with nanostructured photocatalysts on a largesurface-area
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