This review shows our recent studies of water dissociation depending upon oxygen vacancy structures on a TiO2(110) surface. We tried to control the arrangement structure of surface hydroxyl groups on the TiO2(110) surface, and succeeded to form chain structures of surface hydroxyl groups on the surface that had line oxygen vacancies by exposing water at RT. Noncontact atomic force microscopy (NC-AFM) revealed line oxygen vacancies formed by removal of oxygen atoms on a bridge oxygen row of the TiO2(110) surface. In-situ NC-AFM measurements of the surface with the line oxygen vacancies under exposure to water at RT revealed formation of hydroxyl chain structures, which were composed of hydroxyl groups linearly arranged in a form of two rows on the line oxygen vacancies and on the each one side of bridge oxygen row adjacent to the line oxygen vacancy. We concluded that line oxygen vacancies are an active sites for water dissociation.
We review first-principles theoretical studies on the atomic geometries, electronic properties and chemical reactivity on TiO2(110) surfaces. We first determine the accuracy of the first-principles theory to reproduce the atomic geometry of the surfaces. Then we see if the mutually complementary works between theory and experiment can identify the surface defects. Finally, we review the recent theoretical work on formic acid decomposition on the TiO2(110) surfaces.
TiO2 rutile single-crystal surfaces have served as useful prototypical, well-defined specimens for fundamental investigations of oxide surface science for many years. As a result of both experimental and theoretical efforts, we have gained considerable insight into the structural, electronic, thermochemical and photochemical properties of pristine as well as defective surfaces. In this brief review, I summarize some of the recent advances that have been made in the laboratories of participants of the International Workshop on Oxide Surfaces (IWOX) series, principally on TiO2(110).
TiO2 is one of the most important oxides in surface science and its surface/interface properties have been intensively studied in view of photochemistry and catalysis. Furthermore, TiO2 has attracted a growing attention from the viewpoint of electronics applications today. The state of the art of oxide epitaxy now enables us to design the nano-scale TiO2-based heterostructures. Development of atomically flat TiO2 (rutile) single crystal substrates is a key to a good reproducible growth of rutile thin films by the layer-by-layer method. The resultant high-quality of the films can meet very well with the requirements for the studies of well-defined surface/interface properties of TiO2. In the present review, we would like to report new physics and chemistry in TiO2-based epitaxial heterostructures whose composition and structure are atomically well controlled.
As well known, gold is the noblest of all the metals. That was clarified unambiguously by the ab initio first principles calculations for the dissociative adsorption of H2 on bulk Au. However, it was found that gold becomes pronouncedly active for oxidation of CO, water-gas-shift reaction and so on, if the size decreases to a nano-meter range. Ever since, the growth processes and the electronic properties of gold nano-particles have attracted much attention in the context of the mechanism to enhance the catalytic activities. In this paper, we show our recent findings on the growth processes and electronic properties of Au nano-particles on metal-oxide supports, which were analyzed by high-resolution medium energy ion scattering combined with photoelectron spectroscopy. The catalytic activity in terms of size and electronic property of Au nano-particles are discussed in detail.
We report the photochemical reaction of volatile organic compounds (VOC's), such as acetaldehyde and toluene, over nitrogen doped TiO2(TiO-N) under visible light irradiation, using liquid chromatography (LC), gas chromatography (GC) and gas chromatograph mass spectrometer (GC-MS) for gases analysis, and diffuse reflectance fourier transform infrared spectroscopy (DRIFTS) and ion chromatography (IC) for adsorbed organics. We evaluated the photo degradation rates and intermediates for the above gases. As a result, the degradation rates of acetaldehyde gas on TiO-N were 1.2-3 times greater than those on TiO2, and those of toluene gas on TiO-N were 4-49 times greater than those on TiO2. Low concentrations of acetone and acetic acid were produced during the photo degradation of acetaldehyde by the TiO-N. From toluene, very low concentrations of formaldehyde, acetaldehyde, acetone and benzaldehyde gases were produced. We also revealed the decomposition processes of toluene. Results obtained indicate that toluene, weakly adsorbed on the photocatalyst surface, is initially photooxidized to benzaldehyde which adsorbs onto the TiO-N surface more strongly, leading to the formation of ring-opening products such as carboxylic acids and aldehydes. These intermediate products were gradually photodegraded to CO2 and H2O under visible light irradiation.
Theoretical studies on the local tunneling barrier height on an Al(100) surface are presented. First, the effect of localized states on the local tunneling barrier height (LBH) is discussed. The bias polarity dependence of LBH on the Al(100) surface, containing a vacancy cluster in the layer next to the surface, is studied. It is found that the bias polarity dependence of the LBH can be attributed to the reduction in the effective potential and the change in the surface electron states by the applied bias voltage. Second, the effect of tip atomic species on the LBH is discussed. It is found that, for the tip-sample distance dependence of the LBH, the difference between measurements with the two atomic species is larger in the LBH than in the maximum barrier height evaluated from the calculated potential profile. Furthermore, it is found that the bias polarity dependence of the LBH measured with the Na tip shows behavior opposite to that measured with the Al tip. Finally, the difference in LBH by the approach and modulation methods is discussed. It is found that the change in modulation amplitude, which is caused by the force acting on the tip atom due to the applied bias voltage, can account for the observation that the modulation method provides smaller LBH values than approach method.
The fuel cell is known as environment friendly power generation plant. Among various types of fuel cells, phosphoric acid fuel cell (PAFC) is the only one commercial. In this paper, our process for the development of the fuel cell stack that is the most important part of PAFC is shown. Regarding the reliability, we observed the rapid break of several cells in the fuel cell stack, which is consisted of the new type cells. We found new phenomenon of phosphoric acid movement in the cell. As for durability, we improved air electrode catalyst. We also improved the catalyst layer consisting of catalyst and PTFE with consideration of the zeta potential of the catalyst and PTFE. This is to mix the catalyst and PTFE well. As the result, PAFC has enough durability and reliability for practical use, and we are expanding PAFC business.
A 27 MHz piezoelectric crystal was connected with a network analyzer. Both a frequency shift (ΔF) and energy dissipation change (ΔD) were observed when biomolecules were immobilized on a piezoelectric plate. Linear biomolecules such as DNA strands showed a large energy dissipation due to their flexible structures and the amount of hydrated water. On the contrary, globular proteins showed a small energy dissipation, which means proteins are relatively rigid. The combination of a piezoelectric crystal and a network analyzer will provide a powerful tool to analyze the hydration and viscoelasticity of biomolecules.