Amorphous RuO Research Articles

Promotion of the Electrochemical Activity of a Bimetallic Platinum−Ruthenium Catalyst by Oxidation-Induced Segregation

An alloy catalyst of 15 wt % Pt(50)Ru(50)/C was prepared by the method of incipient wetness impregnation and activated by hydrogen reduction at 620 K. Physical characterization of the freshly reduced catalyst indicated that bimetallic crystallites, Pt rich in the shell and Ru rich in the core, were finely dispersed in a diameter of dPtRu approximately 2 nm on carbon support. The reduced catalyst was subsequently modified by oxidization in air. On increasing the temperature of oxidation (T(o)), atoms of Ru in the core were found segregated to the surface of bimetallic crystallites and oxidized to amorphous RuO(2). Crystalline RuO(2) (RucO(2)) was formed on extensive segregation at To > 520 K. Catalytic activity of the alloy catalyst for electro-oxidation of methanol was examined by cyclic voltammetry. Electrochemical activity of the Pt-Ru/C catalyst was found to be significantly enhanced by oxidation treatments. The enhancement was, therefore, attributed to the segregation of Ru and the formation of RucO(2). Extensive oxidation treatment at elevated temperatures of To > 600 K, however, caused the deactivation of the electroactivity. The deactivation should be the result of excessive oxidation of the carbon support.

Characterization of Ruthenium Oxide Nanocluster as a Cocatalyst with (Ga1-xZnx)(N1-xOx) for Photocatalytic Overall Water Splitting

The formation and structural characteristics of Ru species applied as a cocatalyst on (Ga(1)(-)(x)()Zn(x)())(N(1)(-)(x)()O(x)()) are examined by scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. RuO(2) is an effective cocatalyst that enhances the activity of (Ga(1)(-)(x)()Zn(x)())(N(1)(-)(x)()O(x)()) for overall water splitting under visible-light irradiation. The highest photocatalytic activity is obtained for a sample loaded with 5.0 wt % RuO(2) from an Ru(3)(CO)(12) precursor followed by calcination at 623 K. Calcination is shown to cause the decomposition of initial Ru(3)(CO)(12) on the (Ga(1)(-)(x)()Zn(x)())(N(1)(-)(x)()O(x)()) surface (373 K) to form Ru(IV) species (423 K). Amorphous RuO(2) nanoclusters are then formed by an agglomeration of finer particles (523 K), and the nanoclusters finally crystallize (623 K) to provide the highest catalytic activity. The enhancement of catalytic activity by Ru loading from Ru(3)(CO)(12) is thus shown to be dependent on the formation of crystalline RuO(2) nanoparticles with optimal size and coverage.

Liquid-phase oxidation of alcohols by oxygen and nitrous oxide catalysed by Ru–Co oxide

Chemoselective catalysts in bulk or supported on γ-Al 2O 3 binary oxides Ru IV–Co III (Ru/Co = 1:1–1:2), prepared by co-precipitation, were used for liquid-phase oxidation of saturated and unsaturated primary and secondary alcohols to aldehydes and ketones with O 2 or N 2O. The catalysts can be separated by filtration and reused. No leaching of Ru or Co in solution was observed. The oxidation is enhanced by the presence of hydration water in the Ru–Co catalyst, which indicates the participation of active Ru IV hydroxo species in the reaction. From XRD and TGA, the Ru–Co oxide can be approximated as a hydrous binary oxide comprising the amorphous RuO 2 and heterogenite-3R cobaltic acid CoO(OH). The alcohol oxidation appears to occur by a nonradical mechanism, which may be viewed as an oxidative dehydrogenation of alcohols to form an aldehyde or ketone. H 2-TPR shows that Co III practically does not affect the oxidising ability of RuO 2. This suggests that the cobalt is likely to enhance catalyst reoxidation by O 2 rather than to play a significant role in the alcohol dehydrogenation. The alcohol oxidation by N 2O exhibits a close similarity to the oxidation by O 2 but is much less efficient. Much more active catalysts are required to make the oxidation with N 2O synthetically useful.

Preparation and characterization of composite electrodes of coconut-shell-based activated carbon and hydrous ruthenium oxide for supercapacitors

The relationship between the structure-specific capacitance (F g −1) of a composite electrode consisting of activated coconut-shell carbon and hydrous ruthenium oxide (RuO x (OH) y ) has been evaluated by impregnating various amounts of RuO x (OH) y into activated carbon that is specially prepared with optimum pore-size distribution. The composite electrode shows an enhanced specific capacitance of 250 F g −1 in 1 M H 2SO 4 with 9 wt.% ruthenium incorporated. Chemical and structural characterization of the composites reveals a homogeneous distribution of amorphous RuO x (OH) y throughout the porous network of the activated carbon. Electrochemical characterization indicates an almost linear dependence of capacitance on the amount of ruthenium owing to its pseudocapacitive nature.

Synthesis and characterization of nanocrystalline RuO 2 powders

The synthesis of nanocrystalline RuO 2 powders by combining “wet” chemical precipitation, autoclaving and thermal treatment of amorphous precursors has been investigated. Amorphous RuO 2 precursors were precipitated from RuNO(NO 3) 3 or RuCl 3 solutions by adding NH 4OH solution up to ∼pH 5. The samples were characterized by DTA, XRD, FT-IR spectroscopy and TEM. The control of particle size was achieved by heating of amorphous precursor due to regular particle (crystallite) growth. Nanosized RuO 2 particles were formed up to 450 °C. However, at 600 °C, the size of RuO 2 particles was significantly increased.

Characterization of RuO 2· xH 2O with various water contents

Hydrous ruthenium oxides (RuO 2· xH 2O) with different contents of water ( x) were prepared by annealing commercial RuO 2·2.6H 2O powders at different temperatures. The morphologies and crystalline structures of RuO 2· xH 2O were investigated using transmission electron microscope (TEM) and selected area electron diffraction (SAED) techniques. From the TEM images, it was observed that the particle size of RuO 2· xH 2O increased with increasing annealing temperature. From the SAED patterns, it was observed that RuO 2· xH 2O powders became an amorphous phase at annealing temperatures <116 °C and became a crystalline phase at annealing temperatures above 116 °C. Amorphous RuO 2· xH 2O prepared at 116 °C reached its maximum specific capacitance as a result of proton insertion into the bulk of RuO 2 but with smaller Ru–Ru distance in the local structure. The more disordered structure induced by proton insertion was obtained by SAED pattern from a sample annealed at 116 °C. The possible connection between the microstructure and specific capacitance of RuO 2· xH 2O is discussed.

Characteristics of Ruthenium Films Prepared by Chemical Vapor Deposition Using Bis(ethylcyclopentadienyl)ruthenium Precursor

We prepared ruthenium thin films by chemical vapor deposition using a liquid bis(ethylcyclopentadienyl)ruthenium [Ru(EtCp) 2 ] precursor in an oxidizing atmosphere, and then investigated the electrical resistivity, thermalstability, and conformality of these films. As a result of amorphous RuO x partly forming in the ruthenium film, the electrical resistivity increased with increasing growth temperature and O 2 /(Ar + O 2 ) ratio, However, the partial oxides did not affect the intrinsic transport mechanism of electrical conduction. In addition, no change in the morphology of the ruthenium film was observed after heat-treatment at 700°C, even when the partial oxides remained in the as-deposited ruthenium films. Precise control of the growth conditions enabled fabrication of conformal ruthenium electrodes. For example, using a low O 2 /(Ar + O 2 ) ratio of 1.3% and a low growth temperature of 230°C or less resulted in excellent step coverage of almost 100%.

Amorphous Tungsten Oxide/Ruthenium Oxide Composites for Electrochemical Capacitors.

AbstractFor Abstract see ChemInform Abstract in Full Text.

High energy and high power density electrochemical capacitors

High energy density electrochemical capacitors were built with a newly discovered electrode material (amorphous RuO 2· xH 2O). Energy densities as high as 96 J/g (26 Wh/kg) were obtained based on the RuO 2· xH 2O electrode material alone. However, the power density of the capacitor is low. By mixing RuO 2· xH 2O powders with about 20% weight of carbon black, power densities greater than 10 kW/kg could be achieved at a delivered energy density of about 72 J/g (20 Wh/kg). Capacitance as a function of cycle life was studied for up to 60 000 cycles. The temperature dependence of capacitance and resistance of the capacitor are also reported in this paper.

Heterogeneous equilibria in the Ru-H 2O, Ru-Cl-H 2O and Ru-S-H 2O systems

Logarithmic activity-activity diagrams, including Eh-pH, log{M}-pH and log{ligand}-pH diagrams have been generated with the aid of the DIAGRAM computer program for the systems Ru-H 2O, Ru-Cl-H 2O and Ru-S-H 2O at 25 °C. Analysis of these diagrams indicates that elemental ruthenium exhibits a large stability field in aqueous solution, dissolving to Ru(III) and Ru(IV) species in acidic solutions only at relatively high oxidation potentials. Anhydrous RuO 2 spans most of the pH range in aqueous solution so it is relatively stable in both acidic and alkaline solutions. Hydrated amorphous RuO 2 is less stable than the anhydrous dioxide. A series of chloro or mixed hydroxo-chloro complexes form in the presence of chloride ions and their stability domains depend on both the Cl − ion concentration and the oxidation potential. The sulfide RuS 2 is also stable in aqueous solution. The implications of these diagrams for dissolution and precipitation processes are discussed.

Electrical properties of sputtered RuO 2 films

RuO 2 films about 40–700 nm thick were prepared from a RuO 2 powder target by RF sputtering in an atmosphere of argon, and their crystal structure and their electrical properties were investigated. The crystallinity of the sputtered RuO 2 films was found to depend on the sputtering power density and the film thickness. At the power density of 3.1 W cm -2, the films with thickness greater than 110 nm showed X-ray diffraction peaks corresponding to RuO 2 (110) and (211) planes. The crystallinity of the sputtered films increased with an increase in the power density. The electrical resistivity of the RuO 2 films was higher than the bulk value by about one order of magnitude. The RuO 2 films with higher crystallinity tend to have lower resistivities. Temperature dependences of the resistivities were also measured. It was found that the RuO 2 films prepared at high power density showed positive TCR, while the specimens prepared at low power density showed negative TCR, and the specimen prepared at 2.3 W cm -2 showed a TCR of zero. These results can be explained by a model in which the sputtered RuO 2 film consists of microcrystalline RuO 2 grains dispersed in amorphous RuO 2 matrix. The amorphous RuO 2 is considered to have a negative TCR.