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Fabrication of Au nanoparticles-decorated TiO2 nanotube array for stable photoelectrochemical water splitting by two-step anodization

  • 최진영 (대학원 신소재공학과 신소재공학전공)

초록/요약

Recently, research on clean energy sources has been actively conducted. Among them, a photo-catalyst which directly separates water into hydrogen and oxygen by using sunlight gains huge attentions and hydrogen will be used as an energy source. Among the various materials that can be used as a photocatalyst, there is a method of using TiO2 as a photoelectrode. Among many materials, TiO2 is harmless to the human body and chemically very stable, it becomes spotlighted photo-catalyst material. TiO2 was used as a nanotube array form by anodizing, which is a method of oxidizing both ends of Ti foil by applied voltage. However, TiO2 has a disadvantage that it is difficult to react in the visible region due to a relatively wide band gap of 3.2 eV, and there is another disadvantage that electron and hole pair recombine easily. We deposited gold to overcome these limitations of TiO2. Gold nano-particles can trap electrons so as to inhibit the recombination and it also induced the reaction at the visible range using surface plasmon resonance (SPR) phenomenon, which is higher than the photocurrent density of TiO2. In order to improve stability and quality of TiO2 nanotube, two step annodization method was used. First step fabrication was carried out to grow TiO2 nanotube then grown TiO2 nanotube layer is removed. During second step fabrication, it was possible to produce TiO2 nanotubes aligned on a smooth titanium foil and well organized. As a result, the efficiency and stability TiO2 nanotubes were drastically improved. The XRD was used to analyse that crystalline quality of TiO2 nanotube layers, heat-treated under various temperatures. The optimum heat treatment condition for obtaining single phase, high crystalline quality anatase phase, which is the ideal form of TiO2 nanotube, was set. Crack formation was also minimized under optimized heat treatment condition. Based on the results, the photoelectrode efficiency of TiO2 nanotube was measured. The tendency of anatase phase peak with respect to the pore size and tube length was also analyzed. By deposition of Au nanoparticles on of optimized TiO2 nanotube layer, 1.02 mA / cm2 of photocurrent density was obtained, while bare TiO2 nanotube layer generate only 0.8 mA / cm2 of photocurrent density.

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Contents


Abstract………………………………………………………………………………i
Contents…………………………………………………………………………….iii
List of Figures and Tables………………………………………………………...…v


I. Introduction…………………………………………………………….1

II. Theoretical background
II.-1 Process of Photocatalytic Water Splitting and Photocatalyst material requirements………………………………………………….4
II.-2 Synthesis principle of TiO2 nanotube arrays..................................7

III. Experimental procedure
III.-1 Process for Fabrication Au nanoparticles decorated TiO2 nanotube arrays………………………………………………………………….11
III.-2 Measurement of fabricated Au nanoparticle nanoparticles decorated TiO2 nanotube arrays………………………………………………………………….15

IV. Results and discussions
IV.-1 Increased efficiency and stability of TiO2 nanotube arrays fabricated with 2-step anodization……………………………...17
IV.-2 Correlation of efficiency according to surface area of TiO2 nanotube arrays…………………………………………………22
IV.-2-1 Correlation between TiO2 nanotube and voltage
IV.-2-2 Correlation between TiO2 nanotube and anodization time
IV.-3 Enhancement of efficiency of TiO2 nanotube arrays due to the decoration of Au nanoparticles………………………………...28

V. Conclusion……………………………………………………………33

References………………………………………………………………………….34

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