Polygonal Barrel-sputtering Method Research Articles

Application of TiO2 nanotubes as bulky supports of highly active CO2 methanation catalysts prepared via the polygonal barrel-sputtering method

Herein, TiO2 nanotubes (TiO2-NTs) were used as bulky supports for the preparation of highly active CO2 methanation catalysts to maintain the stability of the reaction at high gas flow rates. The nanotube shapes of the prepared TiO2-NTs remained unchanged at a calcination temperature of 300 °C. The CO2 methanation reaction on Ru-sputtered catalysts indicated that at high gas flow rates of 10% CO2/Ar and H2, some crack-like gaps were formed in the catalyst bed using raw anatase TiO2 particle supports, whereas no gaps appeared in the case where TiO2-NTs were used as the support, leading to a stable reaction. This result is attributed to the formation of a sparse catalyst bed owing to the bulky TiO2-NT supports.

Practical Application Study of Highly Active CO2 Methanation Catalysts Prepared Using the Polygonal Barrel-Sputtering Method: Immobilization of Catalyst Particles

This study investigated immobilization (without binders and high-temperature heating) of highly active CO2 methanation catalyst particles, prepared by the polygonal barrel-sputtering method, onto porous Al2O3 plates. The catalyst particles were fixed uniformly and firmly on the plates and retained their high CO2 methanation performance.

Electrochemical Long Period Fiber Grating Sensing for Electroactive Species.

We present an electrochemical long period fiber grating (LPFG) sensor for electroactive species with an optically transparent electrode. The sensor was fabricated by coating indium tin oxide onto the surface of LPFG using a polygonal barrel-sputtering method. LPFG was produced by an electric arc-induced technique. The sensing is based on change in the detection of electron density on the electrode surface during potential application and its reduction by electrochemical redox of analytes. Four typical electroactive species of methylene blue, hexaammineruthenium(III), ferrocyanide, and ferrocenedimethanol were used to investigate the sensor performance. The concentrations of analytes were determined by the modulation of the potential as the change in transmittance around the resonance band of LPFG. The sensitivity of the sensor, particularly to methylene blue, was high, and the sensor responded to a wide concentration range of 0.001 mM to 1 mM.

Structure-Sensitivity Factors Based on Highly Active CO2 Methanation Catalysts Prepared via the Polygonal Barrel-Sputtering Method

This study elucidates the factors reducing the CO2 methanation reaction temperature of TiO2-supported Ru catalysts prepared via the polygonal barrel-sputtering method (Ru/TiO2(BS)) to investigate the structure-sensitivity mechanism. The smaller nanoparticles deposited in Ru/TiO2(BS) (<4 nm) were amorphous RuO2 because of air exposure after the preparation, and their surfaces were changed to island-shaped structures consisting of amorphous RuO2 and amorphous Ru metal by H2 exposure. In this case, dissociative hydrogen was also adsorbed in abundance on the amorphous Ru metals. Such hydrogen atoms were not observed in conventional Ru/TiO2 catalysts. Under the supplied CO2 + H2 at a stoichiometric ratio of 1:4, these hydrogen atoms not only contributed to the generation of a unique CO intermediate (Ru–CO–Ru–H) from room temperature, but also reduced this CO adsorbate to methane even in low-temperature ranges (≤120 °C). These reaction steps were completely different from the reported mechanisms. Accordingly, the formation of amorphous Ru metals and the adsorption of hydrogen atoms on them are essential for reducing the CO2 methanation temperature. These are key factors of structure-sensitivity, which would also be useful for improving activities of various catalysts.

Photocatalytic water splitting over Pt-loaded TiO2 (Pt/TiO2) catalysts prepared by the polygonal barrel-sputtering method

Pt-loaded TiO2 (Pt/TiO2) catalysts for photocatalytic water splitting were prepared by the polygonal barrel-sputtering method. The results showed that the evolution rates of H2 and O2 gases for our Pt/TiO2 catalysts were ca. 5–10 times of those prepared by a conventional photodeposition method. The molar ratios of H2 versus O2 were close to be 2, revealing that the stoichiometric water decomposition occurred. The characterizations of the prepared samples implied that the smaller Pt nanoparticles were highly dispersed on the TiO2 particles by the polygonal barrel-sputtering method. The deposition of the smaller Pt particles increased the Pt surface areas, which can improve the water splitting activities. In addition, the particles deposited by the sputtering method were electron-deficient Pt metals that can enhance the water splitting reaction, whereas those by the photodeposition method were electron-rich Pt metals that reduce the effectiveness of the photocatalytic reaction. These different electron states would play an important role in the remarkable differences in the water splitting activities between the Pt/TiO2 catalysts. Consequently, the polygonal barrel-sputtering method is useful for preparing photocatalysts with the high water splitting activities.

Ternary Pt[sbnd]Ru[sbnd]C co-sputtered electrocatalysts having reaction selectivity for anodes and cathodes in direct methanol fuel cells

In the present study, the reaction selectivity of methanol oxidation and O2 reduction at PtRuC co-sputtering samples has been described. The samples were prepared using the polygonal barrel-sputtering method and tested by linear sweep voltammetry in 0.5 mol/L H2SO4 containing methanol and O2. When sputtering was performed at a constant Ar gas pressure of 3 Pa, methanol oxidation became highly selective for the samples prepared at AC powers of 30 and 50 W. This characteristic was likely induced by the existence of O2 reduction intermediates, which can enhance the oxidation of CO, a methanol oxidation intermediate. The samples displaying O2 reduction selectivity were obtained at Ar gas pressure ranging between 0.4 and 3 Pa (AC power: 100 W). The O2 reduction selectivity may be attributed to the deposition of the electron-rich metallic Ru, which exhibits poor methanol oxidation performance. Based on these results, PtRuC samples that show reaction selectivity in methanol oxidation and O2 reduction are independently prepared by the polygonal barrel-sputtering method.

CO2 Methanation on Co-sputtered Ru–Metal Oxides Catalysts Prepared Using the Polygonal Barrel-Sputtering Method

CO2 methanation catalysts were prepared by co-sputtering with Ru and metal oxides such as TiO2 and ZrO2 using the polygonal barrel-sputtering method. The co-sputtering technique not only resulted in the decrease in the reaction temperature but also maintained the deposition of smaller Ru particles during the reaction at higher temperature.

Simultaneous Multiselective Spectroelectrochemical Fiber-Optic Sensor: Sensing with an Optically Transparent Electrode.

We present a spectroelectrochemical fiber-optic sensor with an optically transparent electrode. The sensor was fabricated by coating indium tin oxide (ITO) onto the surface of fiber-optic core chips using a polygonal barrel-sputtering method. The ITO-coated fiber-optic probe can be simply and cheaply mass-produced and used as a disposable probe. The sensing is based on changes in an attenuated total reflection signal accompanying the electrochemical oxidation-reduction of an analyte at the electrode. The properties of an ITO-coated fiber-optic probe as an optically transparent electrode were investigated for varying thicknesses of ITO. The sensor responses were successfully enhanced with an additional level of selectivity via an electrostatically adsorbed, self-assembled monolayer, which comprised a polyanion and polycation.

Addition of electrical conductivity to metal oxide particles using the polygonal barrel-sputtering method

The surface modification of Al2O3 particles with Au was investigated using the polygonal barrel-sputtering method. When the Au was sputtered, a hexagonal barrel loaded with Al2O3 particles was oscillated. As a result, the appearance of the sample changed from white to dark brown. The characterization of the prepared sample showed that the surfaces of the Al2O3 particles were uniformly modified with Au having a face-centered cubic structure. The electrical conductivity of the prepared sample was very high (σ = 1.19 × 103–2.45 × 103 S m−1) and its electrochemical property was similar to that of the bulk Au metal. Thus, the polygonal barrel-sputtering method is concluded to be useful for providing an electrical conductivity to insulators such as metal oxide particles.

Surface Modification of NaCl Particles with Metal Films Using the Polygonal Barrel-Sputtering Method

In this study, the surfaces of NaCl particles were modified with metal films using the polygonal barrel-sputtering method. When Pt was sputtered on NaCl particles, the individual particles changed from white to metallic. Characterization of the treated samples indicated that thin Pt metal films were uniformly deposited on the NaCl particles. Immersion of the treated NaCl particles in water revealed that they floated to the surface of the water with the increase in the immersion time, although their original cubic shapes remained unchanged. The floating phenomenon of the Pt-coated NaCl particles, as mentioned above, suggests that NaCl was dissolved by the permeation of water through invisible defects such as grain boundaries in the Pt films, leading to the formation of hollow particle-like materials. It should be noted that uniform film deposition on the NaCl particles could also be achieved by sputtering with Au or Cu. Based on the obtained results, our sputtering method allows uniform surface modification of water-soluble and water-reactive powders that cannot be treated by conventional wet process using water.

Methanol Oxidation Performance of Electrocatalysts Prepared by the Polygonal Barrel-Sputtering Method

not Available.

Optimum Pt and Ru atomic composition of carbon-supported Pt–Ru alloy electrocatalyst for methanol oxidation studied by the polygonal barrel-sputtering method

The optimum Pt and Ru atomic composition of a carbon-supported Pt–Ru alloy (Pt–Ru/C) used in a practical direct methanol fuel cell (DMFC) anode was investigated. The samples were prepared by the polygonal barrel-sputtering method. Based on the physical properties of the prepared Pt–Ru/C samples, the Pt–Ru alloy was found to be deposited on a carbon support. The microscopic characterization showed that the deposited alloy forms nanoparticles, of which the atomic ratios of Pt and Ru (Pt:Ru ratios) are uniform and are in accordance with the overall Pt:Ru ratios of the samples. The formation of the Pt–Ru alloy is also supported by the electrochemical characterization. Based on these results, methanol oxidation on the Pt–Ru/C samples was measured by cyclic voltammetry and chronoamperometry. The results indicated that the methanol oxidation activities of the prepared samples depended on the Pt:Ru ratios, of which the optimum Pt:Ru ratio is 58:42 at.% at 25 °C and 50:50 at.% at 40 and 60 °C. This temperature dependence of the optimum Pt:Ru ratio is well explained by the relationship between the methanol oxidation reaction process and the temperature, which is reflected in the rate-determining steps considered from the activation energies. It should be noted that at 25–60 °C, the Pt–Ru/C with Pt:Ru = 50:50 at.% prepared by our sputtering method has the higher methanol oxidation activity than that of a commercially available sample with the identical overall Pt:Ru ratio. Consequently, the polygonal barrel-sputtering method is useful to prepare the practical DMFC anode catalysts with the high methanol oxidation activity.

多角バレルスパッタリング法を用いた新しい表面修飾技術

多角バレルスパッタリング法を用いた新しい表面修飾技術

Suppression of Potential Oscillations in PEFCs by Using Anode Catalyst Prepared by Polygonal Barrel‐Sputtering Method

AbstractIn this study, we investigated the suppression of potential oscillations that occur while feeding H2 gas including a large amount of CO to polymer electrolyte fuel cells. A carbon‐supported Pt–Ru alloy (Pt–Ru/C) sample was prepared by the polygonal barrel‐sputtering method. Electrochemical measurement was conducted in 1 N H2SO4 electrolyte solution saturated with H2 gas including CO of 1,000 ppm. From the measurement, it was found that the prepared Pt–Ru/C sample showed higher CO tolerance than a commercially available sample, and therefore, potential oscillations in the case of the prepared sample occurred for slightly longer intervals. Additional samples were prepared by sputtering different amounts of Ru on the prepared Pt–Ru/C sample, and it was observed that the average interval of potential oscillations increased with the amount of Ru. This result suggests that in the case of the polygonal barrel‐sputtering method, Ru plays an important role in suppressing potential oscillations and influences the CO tolerance of Pt–Ru/C.

Methanol oxidation on carbon-supported Pt–Ru and TiO 2 (Pt–Ru/TiO 2/C) electrocatalyst prepared using polygonal barrel-sputtering method

Methanol oxidation performance of a carbon-supported Pt–Ru alloy catalyst used at the direct methanol fuel cell (DMFC) anode is improved by adding TiO 2. However, the methanol oxidation performance of the electrocatalyst described above must be enhanced further to realize practical application in DMFCs. In this study, we used our original surface-modifying technique termed the “polygonal barrel-sputtering method” to prepare a carbon-supported Pt–Ru and TiO 2 (Pt–Ru/TiO 2/C) electrocatalyst offering higher methanol oxidation performance. The obtained results show that the methanol oxidation performance of the prepared Pt–Ru/TiO 2/C is superior to that using wet process as the TiO 2 deposition method. Furthermore, for our sputtering method, the peak current of methanol oxidation on the Pt–Ru/TiO 2/C is enhanced by increasing the TiO 2 deposited amount up to 2.8 wt.%. These results suggest that a Pt–Ru/TiO 2 interface area is increased using the polygonal barrel-sputtering method, providing the high methanol oxidation performance of Pt–Ru/TiO 2/C.

CO oxidation on non-alloyed Pt and Ru electrocatalysts prepared by the polygonal barrel-sputtering method

The CO oxidation on non-alloyed Pt and Ru electrocatalysts prepared by the polygonal barrel-sputtering method was investigated. Samples were prepared by sputtering Pt and Ru separately at room temperature. From the X-ray diffraction (XRD) measurement of the sample prepared on a SiO 2 glass plate, it was found that the sputtered metals are non-alloyed. Subsequently, the non-alloyed Pt and Ru electrocatalysts were prepared by the polygonal barrel-sputtering method using carbon powder as a support. The XRD patterns of these samples showed a single and very broad peak supporting the hypothesis of the non-alloyed Pt and Ru. No separate Ru reflections were visible, which could be attributed to Ru particle sizes smaller than 4 nm, as obtained by transmission electron microscopy (TEM). CO oxidation on the non-alloyed Pt and Ru electrocatalysts were evaluated by CO stripping voltammetry. This measurement revealed that the lower peak potential of CO oxidation varies, depending on the Pt content and the sputtering order. In addition, it was assumed that the CO oxidation reaction site for non-alloyed Pt and Ru electrocatalyst has a limited area including direct contact sites between the Pt and Ru particles.

CO2 methanation property of Ru nanoparticle-loaded TiO2 prepared by a polygonal barrel-sputtering method

Highly dispersed Ru nanoparticles loaded on a TiO2 support (Ru/TiO2(B)), which affects the hydrogenation of CO2 to CH4 (methanation), were prepared by employing a “dry” modification method using a barrel-sputtering instrument. The loaded Ru nanoparticles exhibited a narrow particle-size distribution with a mean diameter of ca. 2.5 nm. Methanation of CO2 on the Ru/TiO2(B) catalyst produced a 100% yield at ca. 160 °C, which is more than 200 °C below that required for Ru/TiO2 prepared by a conventional “wet” impregnation method. In addition, the methanation reaction over Ru/TiO2(B) proceeded at temperatures as low as room temperature with a reaction rate of 0.04 µmol min−1 g−1.

Preparation and Physical and Electrochemical Properties of Carbon-Supported Pt−Ru (Pt−Ru/C) Samples Using the Polygonal Barrel-Sputtering Method

Carbon-supported Pt−Ru alloy (Pt−Ru/C) catalysts were prepared using the “polygonal barrel-sputtering method”. From the preparation of a Pt−Ru alloy with Pt/Ru = ca. 50:50 atom % on a glass plate as support, the optimum sputtering conditions were an Ar gas pressure of 0.9−0.7 Pa and room temperature. The amount of the sputtered Pt−Ru alloy was controlled by changing the ac power and the sputtering time. Subsequently, the Pt−Ru/C samples were prepared under the given optimum conditions. The Pt−Ru alloy was dispersed extensively in the form of nanoparticles on a carbon support. For the ac power levels of 130, 100, and 50 W, the size distributions were narrower when the ac power was lowered. The respective average particle sizes were 4.1 nm (130 W), 3.3 nm (100 W), and 2.2 nm (50 W). In the case of 30 W, however, the size distribution and the average particle size were almost identical to those for 50 W. In addition, when the Pt−Ru/C samples were prepared by changing the sputtering time, only the dispersion density of the alloy nanoparticles increased in the Pt and the Ru deposited without changing the particle size. The atomic ratios of Pt and Ru in individual Pt−Ru alloy nanoparticles for the prepared samples were similar to the sputtering ratio and homogeneous compared with those for the commercially available samples. With regard to the electrochemical properties for the prepared samples, the hydrodynamic voltammograms for H2 oxidation were identical to that of the commercially available sample. However, for CO oxidation, the peak shapes and the peak potentials for the prepared samples were sharper and ca. 20 mV lower than those for the commercially available samples, due to the uniform Pt and Ru atomic ratios of the individual alloy particles for the prepared samples. The coulomb charges of the CO oxidation reaction per amount of Pt and Ru for the prepared samples increased linearly in the reversed average particle sizes, while on the other hand, the charges for the commercially available samples were not proportional to the reversed sizes. This shows that the Pt−Ru alloy for the prepared samples was more efficiently utilized for electrochemical reactions rather than were the commercial ones. In addition, the cell performances for the alloy loading of 0.08 or 0.02 mg/cm2 using the prepared Pt−Ru/C samples were similar to those for 0.50 mg/cm2 using the commercially available sample.