Hydrous RuO2 Research Articles

Hydrous RuO2–carbon nanofiber electrodes with high mass and electrode-specific capacitance for efficient energy storage

We demonstrate a new strategy for the fabrication of supercapacitor electrodes possessing high mass and area-specific capacitance for efficient charge storage, which can be extremely useful for the development of light, compact and high performance supercapacitors for a variety of high power demanding applications. High mass and electrode area specific capacitances were attained by using Hydrous Ruthenium Oxide (HRO)-Carbon Nanofiber (CNF) hybrid electrodes prepared by the deposition of HRO (~31% Ru content) on both the outer and inner surfaces of a cylindrical hollow CNF having open tips. Electrochemical studies of the uniformly deposited HRO nanoparticles on the CNF surface showed a mass specific capacitance of 645 F g(-1) and an electrode specific capacitance of 1.29 F cm(-2) with a HRO-CNF material loading of 2 mg cm(-2) in the supercapacitor electrodes. The mass specific capacitance of pure HRO is 301 F g(-1), whereas the mass specific capacitance of HRO in the HRO-CNF electrode is ~1300 F g(-1), which is very close to the theoretical capacitance of HRO. This enhanced charge storage ability, high rate capability, better cyclic stability and low ESR of the HRO-CNF will be useful for the development of high performance supercapacitors.

High performance of a solid-state flexible asymmetric supercapacitor based on graphene films

Solid-state flexible energy storage devices hold the key to realizing portable and flexible electronic devices. Achieving fully flexible energy storage devices requires that all of the essential components (i.e., electrodes, separator, and electrolyte) with specific electrochemical and interfacial properties are integrated into a single solid-state and mechanically flexible unit. In this study, we describe the fabrication of solid-state flexible asymmetric supercapacitors based on an ionic liquid functionalized-chemically modified graphene (IL-CMG) film (as the negative electrode) and a hydrous RuO(2)-IL-CMG composite film (as the positive electrode), separated with polyvinyl alcohol-H(2)SO(4) electrolyte. The highly ordered macroscopic layer structures of these films arising through direct flow self-assembly make them simultaneously excellent electrical conductors and mechanical supports, allowing them to serve as flexible electrodes and current collectors in supercapacitor devices. Our asymmetric supercapacitors have been optimized with a maximum cell voltage up to 1.8 V and deliver a high energy density (19.7 W h kg(-1)) and power density (6.8 kW g(-1)), higher than those of symmetric supercapacitors based on IL-CMG films. They can operate even under an extremely high rate of 10 A g(-1) with 79.4% retention of specific capacitance. Their superior flexibility and cycling stability are evident in their good performance stability over 2000 cycles under harsh mechanical conditions including twisted and bent states. These solid-state flexible asymmetric supercapacitors with their simple cell configuration could offer new design and fabrication opportunities for flexible energy storage devices that can combine high energy and power densities, high rate capability, and long-term cycling stability.

Preparation and characterization of RuO2/polyaniline/polymer binder composite electrodes for supercapacitor application

The composite electrodes consisting of amorphous and hydrous RuO 2 , polyaniline and polymeric binder, Nafion ® or poly(vinilydene fluoride) were prepared. The electro­chem­ical and pseudocapacitive properties of the prepared electrodes were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The results show that the responses of composite electrodes are very sensitive to the presence of individual components and their respective ratio in the mixture. The difference in the electro­chemical behavior was explained by the different physico-chemical properties of the polymeric binders.

A Symmetric RuO2∕RuO2 Supercapacitor Operating at 1.6 V by Using a Neutral Aqueous Electrolyte

A novel symmetric RuO2/RuO2 supercapacitor with a high operating voltage of 1.6 V is built using the nanocrystalline hydrous RuO2. The symmetric supercapacitor exhibits an energy density of 18.77 Wh kg −1 at a power density of 500 W kg −1 based on the total mass of active electrode material and excellent cycling stability and power capability. These results demonstrate the potentialities of using RuO2 for symmetric supercapacitor or using RuO2 as negative electrode for asymmetric supercapacitor with high energy density.

Versatile double hydrophilic block copolymer: dual role as synthetic nanoreactor and ionic and electronic conduction layer for ruthenium oxide nanoparticle supercapacitors

The facile synthetic approach to ruthenium oxide nanoparticles using double hydrophilic block copolymers (DHBCs) and their application toward the supercapacitor are presented. Nanostructured hydrous ruthenium oxide (RuO2) nanoparticles are synthesized using a double hydrophilic block copolymer of poly(ethylene oxide)-block-poly(acrylic acid) (PEO-b-PAA) as a template, forming a micelle upon addition of the ruthenium precursor, which then transformed into RuO2 nanoparticles of controlled dimension with reducing agents. The synthesized hydrous RuO2·xH2O nanoparticles are very stable for several months without any noticeable aggregates. Furthermore, we have demonstrated their utility in application as supercapacitors. Through annealing at 400 °C, we found that the crystallinity of RuO2 nanoparticles increases considerably with a simultaneous transformation of the surrounding double hydrophilic block copolymer into ionic and electronic conducting buffer layers atop RuO2 nanoparticles, which contribute to the significant enhancement of the overall specific capacitance from 106 to 962 F g−1 at 10 mV s−1. The RuO2 nanoparticles annealed at 400 °C also exhibit a superior retention of capacitance over 1000 cycles at very high charge–discharge rates at 20 A g−1. We envision that the double hydrophilic block copolymer will provide a facile and general tool in creating functional nanostructures with controlled dimensions that are useful for various applications.

Ab Initio Study of the Charge-Storage Mechanisms in RuO2-Based Electrochemical Ultracapacitors

The charge-storage mechanisms in ruthenium dioxide are investigated with first-principles density-functional theory (DFT) calculations. Both proton-intercalated bulk and proton-adsorbed RuO2(110) surfaces have been studied to obtain insight into the energetics of discharging processes in RuO2-based aqueous supercapacitors. We predict the existence of a stable ruthenium oxyhydroxide (RuOOH) and demonstrate that the RuO2(110) surface as well as a significant fraction of the available subsurface sites remain completely protonated during cyclic voltammetry measurements in aqueous electrolytes. DFT calculations also show that the bulk proton insertion not only is kinetically inhibited by a high energy barrier of proton diffusion in bulk RuO2 (1.62 eV), but also is thermodynamically inactive under the experimental operating conditions due to a low intercalation voltage (0.08 V in the dilute limit). These results exclude simple bulk or surface protonation as the reason for excellent electrochemical performance of hydrous nanocrystalline RuO2 supercapacitors and point to the importance of subsurface and grain boundary effects.

Supercapacitive properties of polyaniline/hydrous RuO2 composite electrode

A composite electrode based on polyaniline (PANI) and hydrous RuO2 is prepared by electrochemical deposition of PANI onto hydrous RuO2 (PANI/RuO2) and its supercapacitive properties are investigated using cyclic voltammetry. The specific capacitances of PANI/RuO2 and hydrous RuO2 electrodes are determined to be 708 and 517 F g−1 at 5 mV s−1, respectively. Simple electrodeposition of PANI on the hydrous RuO2 can achieve comparatively greater capacitance values.

RuO2•xH2O-TiO2 as Catalyst Support for PEM Fuel Cells

Electrocatalytic activities of Pt supported on RuO2•xH2O-TiO2 and anhydrous RuO2-TiO2 were examined. The electrochemically active surface area (ECSA) of Pt/RuO2•xH2O-TiO2 was found to be less than that of Pt/RuO2-TiO2 (3.2m2/g vs. 16.9m2/g), which suggested that RuO2•xH2O interfered with Pt electrocatalytic activity/accessibility. Pt catalytic activity was recovered when Pt/hydrous RuO2-TiO2 was calcined at 450°C, which led to the conversion of hydrous RuO2-TiO2 to anhydrous RuO2-TiO2 as observed from XRD patterns. The BET surface areas of hydrous RuO2-TiO2 and anhydrous RuO2-TiO2 did not change. Converging evidence from CV, XRD and BET analyses confirmed that hydrous RuO2 exhibited lower Pt catalytic activity/accessibility.

Catalysis and characterization of carbon-supported ruthenium for cellulose hydrolysis

Ru catalyst supported on mesoporous carbon CMK-3 shows high activity and durability for the hydrolysis of cellulose to glucose in hot compressed water at 503 K. The Ru/CMK-3 catalyst also hydrolyzes cellobiose to glucose in water at 393 K. Several physicochemical methods such as XRD, TEM, XPS, H 2-TPR, O 2-titration, and XAFS were used to characterize active Ru species on CMK-3 and to clarify the formation pathway of the active species. From these studies, we conclude that hydrous Ru oxide RuO 2·2H 2O is formed on CMK-3 after H 2-reduction of RuCl 3/CMK-3 at 673 K and subsequent passivation at room temperature, and that the Ru oxide nanoparticles with a mean diameter of 1.1 nm are highly dispersed on CMK-3.

Electrochemical capacitance of nanoporous hydrous RuO2 templated by anionic surfactant

The nanoporous RuO2·3.38H2O was synthesized with a surfactant template using sodium dodecyl sulfate. The surface area of the material amounted to 220m2g−1 while the maximum specific capacitance obtained was 870Fg−1 at a scan rate of 10mVs−1. The specific capacitance of nanoporous RuO2·3.38H2O electrode exhibits enhancement, compared with other porous RuO2 materials synthesized by different methods. The nanoporous RuO2·3.38H2O is a very promising material for high performance capacitance.

Methanol Adsorption and Oxidation Behavior of Various Nanostructured Ruthenium-Oxides in Acidic Electrolyte

The electrochemical behavior of anhydrous rutile-type RuO2, hydrous rutile-type RuO2 (RuO2·0.6H2O), and ruthenate nanosheets derived from layered ruthenium oxide (H0.2RuO2.1) in CH3OH containing 0.5 M H2SO4 was studied. The pseudo-capacitance of rutile-type RuO2 nanoparticles decreased under the presence of methanol when cycled between 0.05–1.2 V vs. RHE (60°C), which is attributed to the adsorption of methanol onto the oxide surface. In contrast, the pseudo-capacitance for ruthenate nanosheets was not influenced by the presence of methanol. The results suggest that methanol adsorbs on the surface of RuO2 nanoparticles while no adsorption occurred on ruthenate nanosheets in potential regions of interest for the anodic reaction in direct methanol fuel cells. Thus, ruthenate nanosheets should act as a more efficient co-catalyst for methanol electro-oxidation.

Tailoring of RuO 2 nanoparticles by microwave assisted “Instant method” for energy storage applications

RuO 2 nanoparticles are synthesized by Instant method using Li 2CO 3 as stabilizing agent, under microwave irradiation at 60 °C and investigated for the anodic oxygen evolution reaction (OER) and for their supercapacitance properties in 0.5 M H 2SO 4 medium. Structural and morphological characterizations of RuO 2 are investigated by in situ X-ray diffraction (XRD), thermogravimetric analysis (TG-DTA), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDS) and Raman spectroscopy. The TEM images of as prepared material show the uniform distribution of RuO 2 nanoparticles with mean diameter of ca. 1.5 nm. Analysis on as prepared material indicates the structural formula as [RuO 2·2.6H 2O] 0.7H 2O with low crystallinity. The influence of annealing temperature on RuO 2 is studied in light of electrocatalytic activity for oxygen evolution reaction (OER) and capacitance. Electrochemical performances of RuO 2 electrodes are followed by current–potential curves, galvanostatic charge–discharge cycles and evolved oxygen measurements. The amount of oxygen gas evolved during the OER by the crystalline RuO 2 is found to be consistent with the electrical energy supplied to the catalyst. The cyclic voltammogram of RuO 2 exhibits the typical capacitance behavior with highly reversible nature. The specific capacitance of hydrous RuO 2 is found to be 737 F g −1 at the scan rate of 2 mV s −1, by the balanced transport of proton through the structural water and electron transport along dioxo bridges, which makes a suitable material for energy storage. The specific capacitance decreases with increase in the crystallinity of RuO 2. The present study shows the potential method to synthesize rapid and uniform nano particles of RuO 2 for water electrolysis and supercapacitors.

Hybrid Electrochemical Capacitor of IrO<SUB>2</SUB> Nanocrystal and Hydrous RuO<SUB>2</SUB>

Hybrid Electrochemical Capacitor of IrO<SUB>2</SUB> Nanocrystal and Hydrous RuO<SUB>2</SUB>

Mass changes accompanying the pseudocapacitance of hydrous RuO 2 under different experimental conditions

Pseudocapacitance reaction of hydrous ruthenium oxide was investigated by cyclic voltammetry combined with electrochemical quartz-crystal nanobalance (EQCN) in sulfuric acid as well as in neutral solutions of Na 2SO 4 and K 2SO 4. The ruthenium oxide electrode was prepared by attaching the ruthenium oxide particles on gold covered quartz electrode. The results show that there are different types of charge taking place simultaneously during the redox reaction of ruthenium oxide electrode. Their contribution to the overall charge depends on the experimental conditions. Depending on the potential and electrolyte used the redox reaction of ruthenium oxide is accompanied either by mass loss or by mass gain. The average molar masses of the species exchanged between the solid phase and the electrolyte solution depend on the potential and scan rate. The effect of Nafion™ top layer was also investigated. It has been found that it does not affect significantly the overall specific capacitance of ruthenium oxide electrode but the apparent molar masses of exchanged species decrease in comparison with the uncovered electrodes.

Chemically synthesized hydrous RuO 2 thin films for supercapacitor application

The hydrous RuO 2 thin films have been successfully synthesized at low temperature on glass and stainless steel substrates using lucrative chemical bath deposition (CBD) method. Their structural, morphological, optical, electrical and wettability properties were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), UV–vis–NIR spectrophotometer, two point probe method and water contact angle measurement techniques. The results showed that, the CBD method allows to formation of amorphous, porous, superhydrophilic, semiconducting, hydrous RuO 2 thin films with optical band gap of 2.7 eV. The supercapacitive behavior of hydrous RuO 2 in 0.5 M H 2SO 4 electrolyte examined by cyclic voltammetric (CV) measurements showed maximum specific capacitance of 73 F g −1.

Anchoring Hydrous RuO2 on Graphene Sheets for High‐Performance Electrochemical Capacitors

AbstractHydrous ruthenium oxide (RuO2)/graphene sheet composites (ROGSCs) with different loadings of Ru are prepared by combining sol–gel and low‐temperature annealing processes. The graphene sheets (GSs) are well‐separated by fine RuO2 particles (5–20 nm) and, simultaneously, the RuO2 particles are anchored by the richly oxygen‐containing functional groups of reduced, chemically exfoliated GSs onto their surface. Benefits from the combined advantages of GSs and RuO2 in such a unique structure are that the ROGSC‐based supercapacitors exhibit high specific capacitance (∼570 F g−1 for 38.3 wt% Ru loading), enhanced rate capability, excellent electrochemical stability (∼97.9% retention after 1000 cycles), and high energy density (20.1 Wh kg−1) at low operation rate (100 mA g−1) or high power density (10000 W kg−1) at a reasonable energy density (4.3 Wh kg−1). Interestingly, the total specific capacitance of ROGSCs is higher than the sum of specific capacitances of pure GSs and pure RuO2 in their relative ratios, which is indicative of a positive synergistic effect of GSs and RuO2 on the improvement of electrochemical performance. These findings demonstrate the importance and great potential of graphene‐based composites in the development of high‐performance energy‐storage systems.

Effect of RuO 2· xH 2O in anode on the performance of direct methanol fuel cells

The effect of hydrous RuO 2 (RuO 2· xH 2O) in anode on the performance of direct methanol fuel cells (DMFCs) was examined by voltammetry, methanol stripping analysis, electrochemical impedance spectroscopy, polarization measurement and chronopotentiometry. The results showed that, compared with the DMFC with conventional structures, the dynamic response and quasi-steady state performance of the RuO 2· xH 2O-introduced DMFCs were significantly improved. The DMFC with RuO 2· xH 2O layer (ROL) sandwiched between anode catalyst layer and gas diffusion layer exhibited better quasi-steady state performance than those either with ROL sandwiched between anode catalyst layer and electrolyte membrane or with RuO 2· xH 2O uniformly distributed in anode catalyst layer. The maximum power density of the DMFC with this novel structure was 16% higher than the DMFC with the conventional structure. Moreover, the dynamic response of this RuO 2· xH 2O-introduced cell was more stable during 250-hour of operation when compared with that of the conventional cell.

Microwave-Assited Synthesis of RuO2⋅xH2O/Graphene Nanocomposites for Electrochemical Capacitor Applications

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Planar ultracapacitors of miniature interdigital electrode loaded with hydrous RuO 2 and RuO 2 nanorods

Planar ultracapacitors of miniature interdigital electrode are prepared, using the standard technologies of photolithography and reactive sputtering. The ultracapacitor is denoted by its deposition sequence, for example, hRuO 2NRGT indicates pseudocapacitive hydrous RuO 2 (hRuO 2) and RuO 2 nanorods (NR) are grown on an interdigital stack layer of gold (G) and titania (T). The connection between structure and performance is studied through contrasting the hRuO 2NRGT capacitor with other capacitors built on a less conducting stack layer or without hydrous RuO 2 filling the gaps between the nanorods. The stack layer can be a major source of cell resistance. For instance, a buffer layer of titania could be utilized between the capacitive RuO 2 and the Au current collector to overcome the delamination problem. But the less conductive titania also makes its cyclic voltammograms (CV) elliptical and tilted, and causes a pronounced IR drop during the cell discharging. In contrast, CV of the hRuO 2NRGT capacitor on a conductive stack layer takes the shape of horizontal rectangle, and its discharge curve shows no sign of IR drop. Filling hydrous RuO 2 into the gap reduces the cell resistance between nanorods, improves the discharge performance as well. The power output of hRuO 2NRGT, with the two resistances minimized, is 30.6 μW at 75 μA and 1.23 μW at 5 μA.

Microwave-polyol synthesis of nanocrystalline ruthenium oxide nanoparticles on carbon nanotubes for electrochemical capacitors

The ruthenium oxide nanoparticles dispersed on multi-wall carbon nanotubes (CNTs) were successfully synthesized via microwave-polyol process combined with forced hydrolysis without additional thermal oxidation or electrochemical oxidation treatment. The HRTEM, Raman spectra and TGA curve indicate that CNTs were uniformly coated with crystalline and partially hydrous RuO 2·0.64H 2O nanoparticles of 2 nm diameter and the loading amount of ruthenium oxide in the composite could be controlled up to 70 wt.%. The specific capacitance was 450 Fg −1 of ruthenium oxide/CNT composite electrode with 70 wt.% ruthenium oxide at the potential scan rate of 10 mV s −1 and it decreased to 362 Fg −1 by 18% at 500 mV s −1. The specific capacitance of ruthenium oxide in the composite was 620 Fg −1 of ruthenium oxide at 10 mV s −1. The ruthenium oxide nanoparticles in ruthenium oxide/CNT nanocomposite electrode had a high ratio of outer charge to total charge of 0.81, which confirmed its high-rate capability of the composite through the preparation of the nano-sized ruthenium oxide particles on the external surface of CNTs.