Motoi Takahashi

Microstructural and Metal-Support Interactions of the Pt-CeO2/C Catalysts for Direct Methanol Fuel Cell Application

To understand the ceria promotion effect of Pt-CeO(2)/C catalysts on methanol oxidation, microstructural and metal-oxide interactions of Pt-CeO(2)/C catalysts with an atomic ratio of Pt/Ce between 0.14 and 1.4 were systematically examined using high-resolution transmission electron microscopy and electron energy loss spectroscopy (EELS). With an increasing Pt content in the catalysts, Pt particles gradually invaded into the ceria supports and decoration on Pt particles was observed. Simultaneously, the morphology of the supports was dramatically modified with nanocrystalline and amorphous ceria formed between and/or around the Pt particles. It reveals that the Pt-ceria interaction could take place in the catalysts and the influence of the interaction was enhanced with an increasing Pt/Ce ratio. The EELS study demonstrated that the strong Pt-ceria interaction was related to the redox reaction between Pt and ceria. Experimental results also suggested that the strong interaction between Pt and ceria could contribute to the promotion effect of ceria on the oxidation of methanol.

Ionic Conductivities and Microstructures of Ytterbium-Doped Ceria

The ionic conductivities and microstructures of Ce1-xYbxO2-x/2 ( x = 0.10, 0.15, 0.20, and 0.25 ) with average grain sizes in a range of 0.2 - 3.7 mu m were studied systematically. Nanosized domains were confirmed through detailed studies of transmission electron microscopy. The relationships of the domains, doping concentration, and grain size were determined, and their effects on the ionic conductivities were examined. It was concluded that the domains were formed via the segregation of Yb cations so that they could trap the oxygen vacancies and lower the conductivity. Furthermore, the development of the domains, which depends on the doping concentration and grain size, can affect the doping concentration and grain-size dependencies of the conductivity. (c) 2006 The Electrochemical Society.

Development of high quality Pt-CeO2 electrodes supported on carbon black for direct methanol fuel cell applications

Abstract A Platinum (Pt) on pure ceria (CeO2) particles supported by carbon black (CB) was synthesised. The electrochemical activity of methanol oxidation reaction on synthesised Pt–CeO2/CB anodes was investigated. To develop this anode, the influence of surface area of CeO2 particles in Pt–CeO2/CB on anode properties was examined. The anode properties (i.e. onset potential and peak current density) were improved using fine CeO2 particles with high surface area. This indicates that higher activity on surface of CeO2 improves the anode properties. The anode properties on Pt high surface area CeO2/CB was better than that on Pt–Tin oxide(SnO2)/CB or Pt–Ru/carbon. The authors suggest that the rate determining steps of methanol oxidation reaction on Pt–CeO2/CB and other anodes such as Pt–SnO2/CB and Pt–Ru/carbon are different which accounts for the difference in performance. Therefore, it is concluded that a design of active surface of CeO2 is a key for development of Pt–CeO2/CB anode in polymer membrane fuel cells.

Development of high quality Pt-CeO2 composite anode for direct methanol fuel cell applications

A new type composite anode was fabricated to develop direct methanol fuel cell or polymer electrolyte membrane fuel cells. A Pt on nano-sized CeO2 particles which in turn are supported on carbon black (CB) was synthesized in a step wise process. The pure CeO2 was synthesized using an ammonium carbonate precipitation method, and the Pt particles dispersed on the CeO2 in such a way that a uniform dispersion with the CB was obtained (Pt-CeO2/CB). The anode properties (i.e. peak current density and onset potential for methanol oxidation) on our composite anode were better than that on commercially available alloy anode Pt-Ru/Carbon. The peak current density for methanol oxidation on Pt-CeO2 composite anode was 1.9 times higher than that on commercially available Pt-Ru alloy anode. The onset potential of methanol oxidation on Pt-CeO2 composite anode shifted to a lower potential and the activation energy of the Pt-CeO2 composite anode for methanol oxidation reaction was lower than that of the Pt-Ru alloy anode. The high performance and low cost anode material could be obtained using nano size CeO2 particles instead of Ru as rare metal. Importantly, the rare metal, Ru is not required in the present anode material and the amount of Pt required is also significantly reduced. As a consequence, we report a promising candidate Pt-CeO2/CB composite anode for application in the development of direct methanol fuel cells or polymer electrolyte membrane fuel cells.

Improvement of oxidative decomposition activity on hollandite type photocatalyst against pentachlorophenol

Abstract Endocrine-disrupting chemicals such as pentachlorophenol (C6Cl5OH) are hazardous for the generative function of living creatures. Photocatalysts give us an effective route for removing these pollutants. Most of the reports are related to a photocatalyst of titanium dioxide (TiO2) fine particles loaded with metal particles such as Pt or Ag. However, a diversity of photocatalysts is required to deal with the increasing number of identified harmful chemicals which occur under a range of different conditions. Hollandites have one-dimensional tunnel-like framework structure. K2Ga2Sn6O16 (KGSO) is one of hollandite type compounds. In this study, hollandite type KGSO fine powders were fabricated using sol–gel method. The hydrolysis route was carefully observed for preparation of KGSO fine powders with high photocatalytic activity. To prepare the fine powder, the influence of hydrolysis temperature on preparation of fine powder was examined. It was found that the control of aforementioned temperature was very important for preparation of nano-sized KGSO powders with high activity. In addition, the authors controlled particle morphology of KGSO using different preparation conditions. The oxidative decomposition activity against C6Cl5OH on round shape KGSO nano-particles (78%) was much higher than that on the elongated shape KGSO particles (46.2%). It is concluded that the control of morphology and size of KGSO particles maximized the photocatalytic activity on KGSO for oxidative decomposition of C6Cl5OH. In addition, KGSO did not produce organic chlorides as by-products in the photocatalysis. Accordingly, it is expected that KGSO will be one of promising photocatalysts for decomposition of harmful aromatic compound C6Cl5OH under weak UV illumination.

Fabrication and Microanalysis of Nano-Structured CuOX-CeO2 Catalysts for CO Oxidation Reaction

Carbon monoxide (CO) is a significant air pollutant produced in incomplete oxidation of carbon in combustion. From the viewpoint of environmental protection, it is important that the concentration of CO gas is lowered in air. Catalysis is proving to be an effective route for removing this pollutant. Therefore, a design of nano-structured catalysts with high efficiency is required. In the present work, we focus on a development of nano-size CuOx-CeO2 catalysts for CO oxidation reaction. To prepare nano-structured Cu loaded CeO2 catalysts, a combined method of the conventional impregnation and ammonium carbonate co-precipitation was examined. Morphology, crystal phase and surface structure of prepared catalysts were characterized using High-Resolution Transmission Electron Microscopy (HRTEM), Scanning Electron Microscopy (SEM) and Powder X-ray Diffraction (XRD). Catalytic properties of CuOx-CeO2 for CO oxidation were investigated in gas flow reactor system under atmospheric pressure and compared with copper oxide loaded zinc oxide. We expected that nano-structured CuOx-CeO2 catalysts could be used for removing CO produced in a wet reforming reaction of fuel cell applications.

Development of high quality Pt-CeO 2 based anode materials for direct methanol fuel cell applications

Pt-pure Ceria (CeO2) supported by carbon black (CB) anode was synthesized for development of eco-electrode material for fuel cell application. The onset potential for methanol oxidation reaction on Pt-round shaped CeO2 shifted to a lower potential as compared with that on Pt-mixed shape (i.e. round shape + rod like shape) CeO2/CB. This onset potential on Pt-mixed shape CeO2 /CB anode at 60degC was equal to that on commercially available Pt-Ru/CB anode, although the on-set potential on Pt-mixed shape CeO2/CB was lower than that on Pt-Ru/CB at room temperature. This suggests that the anode performance of Pt-CeO2/CB anode is improved at operation temperature (80degC) of fuel cell by enhancement of diffusion and formation of oxygen species from nano-sized CeO2 particles. It is expected that the nano-size Pt-pure CeO 2/CB anode in the present study will be one of promising eco-anode materials for development of direct methanol fuel cells (DMFCs)