Plasmon-Induced Water-Splitting Enhanced by Metallic Nanostructures
Date Issued
2015
Date
2015
Author(s)
Huang, Yi-Teng
Abstract
Nowadays, energy issues have become more and more important. Scientists keep searching for clear and reusable energy sources. Undoubtedly, “hydrogen energy” is the most attractive one among them. Hydrogen is a gas with high energy density. It will generate a great energy after Reduction-Oxidation and efficiently transforms the chemical energy into electric energy or energies with different forms. Besides, the only product of hydrogen after redox is water. No waste gas and no pollutant. Until now, the most common technologies acquiring hydrogen are biological hydrogen production, thermal chemical production, water electrolysis and so on. Electron-hole pairs are generated after these semiconductors absorb the sun-light. Theses free carriers will diffuse onto the surface, and electrons may react with hydrogen ions in the water and reduce them into hydrogen gas. However, most semiconductors in these cells have large band gaps. Only UV light can excite electrons from valence band to conduction band. However, UV light only take up about 7% in sun light, which is relatively small compared with visible light and infrared. In recent years, photocatalyst synthesis makes great strides. photocelectrochemical Cells therefore attracts more attraction. These cells are made of semiconductors. The principle for hydrogen production behind them is very simple. Our object is to extend the working wavelength of these semiconductors from UV light to visible light and infrared by the “surface plasmon resonance” effect, which comes from the collective oscillation of electrons induced by the electromagnetic waves. TiO2 is the most common semiconductors used for photocatalyst. In our research, we try to fabricate metallic nanostructures by simple physical deposition methods---evaporation and sputtering on the surface of TiO2. Then we measure the photocurrents of sample under illumination. If the surface plasmon resonance happens on certain wavelength, there will be a great amount of “hot electrons” injected into the semiconductor. A great enhancement of photocurrents will be expected at this situation. Another point in our research is to fabricate regular nanostructures, which can only have single resonance wavelength. We want to know if these regular structures can generate more photocurrents than random structures make. Although random structures may have a broad-band absorption, regular structures usually have a relatively high absorption peaks at resonance wavelength and may have better effects on current generation. We use “nanoimprint lithography” to fabricate regular structures with a large area. Furthermore, we can predict the resonance wavelength of these structures by simulation, which is almost impossible for random structures. We believe that we demonstrate a possible way to increase the efficiency of photocatalysis.
Subjects
surface plasmon resonance
photocatalysis
nanoparticles
nanostructures
hot elctrons
SDGs
Type
thesis
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