Wataru Sugimoto

Effect of Structure of Carbon‐Supported PtRu Electrocatalysts on the Electrochemical Oxidation of Methanol

Carbon‐supported binary PtRu electrocatalysts were prepared by coimpregnation using ethanolic solutions of as the Pt source, various Ru sources [, , and ], and carbon black by thermal decomposition under reducing conditions, and their structure, morphology, and electrocatalytic properties were investigated. X‐ray diffraction analysis and high resolution scanning electron microscopy indicated that the use of Cl‐free Ru sources, i.e., or afforded highly dispersed and uniform PtRu nanoparticles. Surface area measurements conducted by electro‐oxidation of preadsorbed carbon monoxide indicated that the use of as the Ru source yielded high surface area catalysts. In terms of the surface‐area specific current density (current density normalized by the specific surface area of PtRu metal obtained from preadsorbed CO electro‐oxidation measurements), the electrocatalytic activity of and were equal. PtRu/C electrocatalysts prepared from ethanolic solutions of resulted in high mass‐specific activity toward methanol oxidation, with mass‐specific current density as high as at 500 mV. The efficiency of PtRu/C electrodes is discussed based on the significance of the use of Cl‐free Ru sources.

Effects of the surface area of carbon support on the characteristics of highly-dispersed PtRu particles as catalysts for methanol oxidation

Considerable effects have been observed for the specific surface area of carbon black support on the fundamental properties of PtRu/C catalysts, such as metal particle size, extent of alloying and catalytic activity for the oxidation of methanol. Equimolar ethanolic solutions of Pt(NH3)2(NO2)2 and RuNO(NO3)x and seven different carbon black supports with specific surface areas ranging from 29 to 802 m2 g−1 were used for the preparation of the catalysts by the co-impregnation method. COad stripping voltammetry was adopted for the investigation of the effects of the specific surface area of the carbon black on the catalytic activity of the PtRu/C catalysts as well as for the determination of the actual exposed surface area of the bimetallic particles. A size effect of the PtRu particles on the catalytic activity for the oxidation of methanol was also observed.

Electrophoretic deposition of negatively charged tetratitanate nanosheets and transformation into preferentially oriented TiO2(B) film

A tetrabutylammonium–H2Ti4O9·xH2O intercalation compound was obtained by a guest exchange reaction between tetrabutylammonium hydroxide and an ethylammonium–H2Ti4O9·xH2O intercalation compound, and its dispersion state in aqueous and non-aqueous solutions were studied. Spontaneous exfoliation of H2Ti4O9·xH2O into colloidal nanosheets occurred when the tetrabutylammonium–H2Ti4O9·xH2O intercalation compound was dispersed in water, methyl alcohol, isopropyl alcohol, acetonitrile, N,N-dimethylformamide, dimethyl sulfoxide, and propylene carbonate, while exfoliation did not occur in tetrahydrofuran. A tetrabutylammonium–H2Ti4O9·xH2O film was obtained by a reassembly process by casting the colloidal suspension containing exfoliated nanosheets, while a H2Ti4O9·xH2O film was directly obtained by electrophoretic deposition. Thermal treatment of the electrophoretically deposited film led to an oriented TiO2(B) film with the (0k0) planes lying perpendicular to the substrate.

Fabrication of Thin-Film, Flexible, and Transparent Electrodes Composed of Ruthenic Acid Nanosheets by Electrophoretic Deposition and Application to Electrochemical Capacitors

Ruthenic acid nanosheet colloids were prepared by dispersing a tetrabutylammonium-ruthenic acid intercalation compound in acetonitrile or N,N-dimethylformamide. Nanosheet electrodes were fabricated on gold, indium-tin oxide (ITO)-coated glass, and ITO-coated poly(ethylene terephthalate) (PET) electrodes by electrophoretic deposition using these colloids. Transparent or flexible electrodes could be fabricated by using ITO electrodes as the substrate. The deposited amount of material could easily be controlled by the extent of deposition, which was confirmed from the linear increase in specific capacitance as a function of deposition time. The ruthenic acid nanosheet electrodes using Au substrates exhibited gravimetric capacitance of 620 F (g -RuO 2 ) - 1 . Specific capacitance of 0.82 F cm - 2 ( g e o m e t r i c ) was achieved at a scan rate of 2 mV s - 1 with a film deposited at 5 V cm - 1 for 1 h.

Synthesis of Nanosheet Crystallites of Ruthenate with an α-NaFeO2-Related Structure and Its Electrochemical Supercapacitor Property

Unilamellar crystallites of conductive ruthenium oxide having a thickness of about 1 nm were obtained via elemental exfoliation of a protonic layered ruthenate, H(0.2)RuO(2).0.5H(2)O, with an alpha-NaFeO(2)-related crystal structure. The obtained RuO(2) nanosheets possessed a well-defined crystalline structure with a hexagonal symmetry, reflecting the crystal structure of the parent material. The restacked RuO(2) nanosheets exhibited a high pseudocapacitance of approximately 700 F g(-1) in an acidic electrolyte, which is almost double the value of the nonexfoliated layered protonated ruthenate.

Electrochemical Capacitor Behavior of Layered Ruthenic Acid Hydrate

A hydrous ruthenic acid (H 0.2 RuO 2.1 .nH 2 O) possessing a layered structure with a crystalline framework was prepared by proton exchange of a layered potassium ruthenate. Its electrochemical capacitor behavior was studied by cyclic voltammetry in various electrolytes. Specific capacitance up to 390 F g -1 (RuO 2) at a scan rate of 50 mV s- 1, which is a ten-fold increase compared to conventional anhydrous RuO 2 , was obtained using layered ruthenic acid hydrate in 0.5 M H 2 SO 4 electrolyte. Slightly lower values were obtained for 1 M HClO 4 and 1 M KOH electrolytes. The difference in the specific capacitance of anhydrous ruthenium oxide, hydrous ruthenium oxide, hydrous ruthenic acid, and restacked ruthenic acid nanosheets in the various electrolytes is discussed.

Charge Storage Capabilities of Rutile-Type RuO2 ­ VO 2 Solid Solution for Electrochemical Supercapacitors

Ultrafine ruthenium-vanadate particles possessing a rutile-type structure, Ru 1 - x V x O 2 , were prepared by a polymerizable-complex method and their electrochemical supercapacitor behavior was studied by cyclic voltammetry in an acidic solution. The solid solution exhibited enhanced supercapacitive properties compared to pure RuO 2 . The present electrode material possessed excellent cyclability and specific capacitance. Specific capacitance exceeding 1200 F g - 1 of RuO 2 was obtained for Ru 0 . 3 5 V 0 . 6 5 O 2 .

All-Nanosheet Ultrathin Capacitors Assembled Layer-by-Layer via Solution-Based Processes

All-nanosheet ultrathin capacitors of Ru0.95O20.2-/Ca2Nb3O10-/Ru0.95O20.2- were successfully assembled through facile room-temperature solution-based processes. As a bottom electrode, conductive Ru0.95O20.2- nanosheets were first assembled on a quartz glass substrate through a sequential adsorption process with polycations. On top of the Ru0.95O20.2- nanosheet film, Ca2Nb3O10- nanosheets were deposited by the Langmuir-Blodgett technique to serve as a dielectric layer. Deposition parameters were optimized for each process to construct a densely packed multilayer structure. The multilayer buildup process was monitored by various characterizations such as atomic force microscopy (AFM), ultraviolet-visible absorption spectra, and X-ray diffraction data, which provided compelling evidence for regular growth of Ru0.95O20.2- and Ca2Nb3O10- nanosheet films with the designed multilayer structures. Finally, an array of circular films (50 μm ϕ) of Ru0.95O20.2- nanosheets was fabricated as top electrodes on the as-deposited nanosheet films by combining the standard photolithography and sequential adsorption processes. Microscopic observations by AFM and cross-sectional transmission electron microscopy, as well as nanoscopic elemental analysis, visualized the sandwich metal-insulator-metal structure of Ru0.95O20.2-/Ca2Nb3O10-/Ru0.95O20.2- with a total thickness less than 30 nm. Electrical measurements indicate that the system really works as an ultrathin capacitor, achieving a capacitance density of ∼27.5 μF cm(-2), which is far superior to currently available commercial capacitor devices. This work demonstrates the great potential of functional oxide nanosheets as components for nanoelectronics, thus contributing to the development of next-generation high-performance electronic devices.

Activity and Durability of Ternary PtRuIr ∕ C for Methanol Electro-oxidation

Carbon supported Pt 1 Ru 1 Ir x (0 ≤ x ≤ 2) nanoparticles were prepared by a coimpregnation reductive pyrolysis method and their electrocatalytic activity toward methanol electro-oxidation at 25, 40, and 60°C was investigated. The mass activity (current normalized by the mass of Pt) for methanol electro-oxidation increased as a function of Ir content and cell temperature. Despite the increase in methanol electro-oxidation activity, the addition of Ir does not affect the CO tolerance of the ternary electrocatalyst. The addition of Ir also enhances the durability of the catalyst. The enhancement in activity and durability is discussed based on CO stripping measurements and X-ray photoelectron spectroscopy analysis of the catalysts.

Conductivity of ruthenate nanosheets prepared via electrostatic self-assembly: characterization of isolated single nanosheet crystallite to mono- and multilayer electrodes.

Ultrathin films composed of ruthenate nanosheets (RuO(2)ns) were fabricated via electrostatic self-assembly of unilamellar RuO(2)ns crystallites derived by total exfoliation of an ion-exchangeable layered ruthenate. Ultrathin films with submonolayer to monolayer RuO(2)ns coverage and multilayered RuO(2)ns thin films were prepared by controlled electrostatic self-assembly and layer-by-layer deposition using a cationic copolymer as the counterion. Electrical properties of a single RuO(2)ns crystallite were successfully measured by means of scanning probe microscopy. The sheet resistance of an isolated single RuO(2)ns crystallite was 12 kΩ sq(-1). Self-assembled submonolayer films behaved as a continuous conducting film for coverage above 70%, which was discussed based on a two-dimensional percolation model. Low sheet resistance was attained for multilayered films with values less than 1 kΩ sq(-1). Interestingly, the grain boundary resistance between nanosheets seems to contribute only slightly to the sheet resistance of self-assembled films.