Hydrous Ruthenium Oxide Research Articles

Conductive two-dimensional titanium carbide 'clay' with high volumetric capacitance.

Safe and powerful energy storage devices are becoming increasingly important. Charging times of seconds to minutes, with power densities exceeding those of batteries, can in principle be provided by electrochemical capacitors--in particular, pseudocapacitors. Recent research has focused mainly on improving the gravimetric performance of the electrodes of such systems, but for portable electronics and vehicles volume is at a premium. The best volumetric capacitances of carbon-based electrodes are around 300 farads per cubic centimetre; hydrated ruthenium oxide can reach capacitances of 1,000 to 1,500 farads per cubic centimetre with great cyclability, but only in thin films. Recently, electrodes made of two-dimensional titanium carbide (Ti3C2, a member of the 'MXene' family), produced by etching aluminium from titanium aluminium carbide (Ti3AlC2, a 'MAX' phase) in concentrated hydrofluoric acid, have been shown to have volumetric capacitances of over 300 farads per cubic centimetre. Here we report a method of producing this material using a solution of lithium fluoride and hydrochloric acid. The resulting hydrophilic material swells in volume when hydrated, and can be shaped like clay and dried into a highly conductive solid or rolled into films tens of micrometres thick. Additive-free films of this titanium carbide 'clay' have volumetric capacitances of up to 900 farads per cubic centimetre, with excellent cyclability and rate performances. This capacitance is almost twice that of our previous report, and our synthetic method also offers a much faster route to film production as well as the avoidance of handling hazardous concentrated hydrofluoric acid.

Visible-Light-Driven Aerobic Oxidation of Amines to Nitriles over Hydrous Ruthenium Oxide Supported on TiO2

Aerobic oxidation of amines to nitriles under visible light irradiation was catalyzed by supported hydrous ruthenium oxide catalyst. Both LED (blue, green, or red) and the Sun were effective light sources for the transformation of benzylic and aliphatic amines to the corresponding nitriles under atmospheric pressure of O2. Water can be used as a solvent instead of toluene without the loss of activity and selectivity.

Transmission line model of mixed ionic and electronic conductor: the case of hydrous ruthenium oxide

Composite membranes made of RuO2·xH2O dispersed in an insulating polymer matrix were prepared and used as separators in a conductivity cell filled with H2SO4 electrolyte solution. The volume fraction of RuO2·xH2O was varied between 7 and 18 % and x between 0 and 2.4. The total capacitance of the composite membranes was determined either from galvanostatic charging using a four-electrode configuration or potential cycling using a three-electrode configuration. In the first case, protons are the only charge carriers at the boundaries of the composite membranes. In the four-electrode configuration, a transmission line that accounts for the pseudocapacitive nature of RuO2·xH2O was used to describe successfully the voltage–time profiles of composite membranes with active material contents above 10 V f%. The total capacitance determined with both setups increases for 0 ≤ x ≤ 0.6, and the values are identical in this interval of x. However, the trends diverge afterwards, and the capacitance values measured in the four-electrode configuration are higher by a factor of 2 for x = 2.4. Unlike in the three-electrode configuration, charge storage in the four-electrode configuration is not limited to the sites accessible to both electrons and protons.

SYNTHESIS OF HYDROUS RUTHENIUM OXIDE NANOPARTICLES IN SUB- AND SUPERCRITICAL WATER AND THEIR CAPACITIVE PROPERTIES

Hydrous ruthenium oxide (RuO2 · nH2O) nanoparticles with various particle sizes and water contents were synthesized in sub- and supercritical water in a very short reaction time of 15 min. The particle size, surface area, morphology, crystalline structure, and electrochemical properties were analyzed and compared with those of commercial RuO2 particles. Ultrafine spherical RuO2 · 0.6H2O nanoparticles with an average size of 4.2 nm were produced in subcritical water (250°C, 300 bar), while larger and more highly crystalline rod-shaped RuO2 · (0.3–0.5)H2O particles were produced in supercritical water (400°C, 300 bar). The use of NaOH under the supercritical water conditions resulted in a decrease in particle size. The hydrous RuO2 nanoparticles synthesized in subcritical water exhibited a much higher specific capacitance (255 F g−1) at a scan rate of 10 mV s−1 than those synthesized in supercritical water (77 F g−1) and commercial RuO2 (8 F g−1).

Hydrous ruthenium oxide prepared by steam-assisted thermolysis: Capacitance and stability

Hydrous ruthenium oxides (RuO2·xH2O) with ultra-stable cycling ability were directly prepared on tantalum substrate by thermolysis of RuCl3 in heated steam environment. Characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and wettability test, the RuO2·xH2O showed lower crystallite and better hydrophilic than that are prepared by thermolysis in air. Their specific capacitance is twice as great as the latter. Moreover, this capacitance maintains nearly 100% after 100,000cycles and its coulombic efficiency is 100% due to its good balance of electron/proton conductivity.

Nitride Supercapacitors: Contribution of Surface Oxide to Charge Storage

With the growing interest in alternative energy sources and the cognitive recognition of the benefits of green energy, there is clearly a pressing need for the development of sustainable and clean energy storage systems (1-3). The scope of electrochemical charge storage devices extends beyond mobile devices into large scale grid level charge storage(4). Load leveling and power quality management applications would be perfectly served by storage of excess charge generated from renewable energy sources in supercapacitors. Supercapacitors are unique electrochemical energy storage devices with high power density and long cyclability. State of the art materials such as high surface area carbons, hydrated ruthenium oxide (5-7) and MnO2 (3, 8-10) suffer from either poor capacity or rate capability. We have previously demonstrated excellent charge storage behavior of nanoparticulate vanadium nitride on account of the surface reactions occurring on the surface of the oxide exo-shell. However, there is limited understanding into the exact nature of the charge storage behavior and its dependence on the synthesis and processing route. In the present work, we explore the effect of materials processing and electrode properties on the capacitive charge storage in VN based supercapacitors. Dependence of capacitance on particle and electrode properties are evaluated and reported here-in. Tailoring the particle size, crystallinity and porosity are of paramount importance to achieve high capacitances at high scan rates. To gain a fundamental understanding into the charge storage mechanism of nitride materials shown in Figure 1, slurries of the nitride were cast on nickel current collectors and characterized used various materials and electrochemical characterization techniques including X-ray photo-electron spectroscopy (XPS), cyclic voltammetry and electrochemical impedance spectroscopy. Results of these studies will be presented and discussed.

Hydrous Ruthenium Oxide Nanoparticles Anchored to Graphene and Carbon Nanotube Hybrid Foam for Supercapacitors

In real life applications, supercapacitors (SCs) often can only be used as part of a hybrid system together with other high energy storage devices due to their relatively lower energy density in comparison to other types of energy storage devices such as batteries and fuel cells. Increasing the energy density of SCs will have a huge impact on the development of future energy storage devices by broadening the area of application for SCs. Here, we report a simple and scalable way of preparing a three-dimensional (3D) sub-5 nm hydrous ruthenium oxide (RuO2) anchored graphene and CNT hybrid foam (RGM) architecture for high-performance supercapacitor electrodes. This RGM architecture demonstrates a novel graphene foam conformally covered with hybrid networks of RuO2 nanoparticles and anchored CNTs. SCs based on RGM show superior gravimetric and per-area capacitive performance (specific capacitance: 502.78 F g−1, areal capacitance: 1.11 F cm−2) which leads to an exceptionally high energy density of 39.28 Wh kg−1 and power density of 128.01 kW kg−1. The electrochemical stability, excellent capacitive performance, and the ease of preparation suggest this RGM system is promising for future energy storage applications.

Fabrication of a symmetric micro supercapacitor based on tubular ruthenium oxide on silicon 3D microstructures

A micro-supercapacitor with a three-dimensional configuration has been fabricated using an ICP etching technique. Hydrous ruthenium oxide with a tubular morphology is successfully synthesized using a cathodic deposition technique with a Si micro prominence as a template. The desired tubular RuO2·xH2O architecture facilitates electrolyte penetration and proton exchange/diffusion. A single MEMS electrode is studied using cyclic voltammetry, and a specific capacitance of 99.3 mF cm−2 and 70 F g−1 is presented at 5 mV s−1 in neutral Na2SO4 solution. The accelerated cycle life is tested at 80 mV s−1, and satisfactory cyclability is observed. When placed on a chip, the symmetric cell exhibits good supercapacitor properties, and a specific capacitance as high as 23 mF cm−2 is achieved at 10 mA cm−2. Therefore, 3D MEMS microelectrode arrays with electrochemically deposited ruthenium oxide films are promising candidates for on-chip electrochemical micro-capacitor applications.

Supercapacitive performance of hydrous ruthenium oxide (RuO2 · nH2O) thin films synthesized by chemical route at low temperature

In the present investigation, we report the synthesis of ruthenium oxide (RuO2 · nH2O) thin films by simple chemical bath deposition (CBD) method at low temperature on the stainless steel substrate. The prepared thin films are characterized for their structural and morphological properties by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT–IR) and scanning electron microscopy (SEM). The structural study revealed that the ruthenium oxide thin films are amorphous. Scanning electron microscopy study shows compact morphology with small overgrown particles on the surface of the substrate. FT–IR study confirms the formation of RuO2 · nH2O material. The supercapacitor behaviour of RuO2 · nH2O thin film was studied using cyclic voltammetry (CV) technique in 0 · 5 M H2SO4electrolyte. RuO2 · nH2O film showed maximum specific capacitance of 192 F · g− 1at a scan rate of 20 mV · s− 1. The charge–discharge studies of RuO2 · nH2O carried out at 300 μA · cm− 2current density revealed the specific power of 1 · 5 kW.kg− 1and specific energy of 41 · 6 Wh.kg− 1with 95% coulombic efficiency.

Supercapacitive properties of electrodeposited RuO2 electrode in acrylic gel polymer electrolytes

Hydrous ruthenium oxide (RuO2) is prepared by electrodeposition on a platinum substrate and its supercapacitive properties are characterized adopting acrylic gel polymer electrolytes, such as poly(acrylic acid) (PAA), potassium polyacrylate (PAAK), and poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS). The electrodeposited hydrous RuO2 exhibits an amorphous compact stratified morphology with a higher loading (0.15 mg cm−2) than that of a previous report, and shows broad redox peaks on both cathodic and anodic scans in the cyclic voltammetry. In particular, the RuO2 electrode for supercapacitor adopting the PAMPS electrolyte shows the highest specific capacitance of 642 F g−1 at 20 mV s−1. This is due to the efficient utilization of active RuO2 species and greater proton accommodation toward the negative oxygen sites of PAMPS's side chain. In addition, it is possible to improve sustainability against high-rate current with the RuO2 electrode with the PAMPS electrolyte, due to the crosslinks of the gel electrolyte, which support the mechanical strength.

Fabrication and Properties of a New Type Micro Super-Capacitor

A new type of micro super-capacitor with high working voltage, high over loading, small bulk, and low impedance was fabricated by a new process. The hydrous ruthenium oxide powder was prepared in a solution of RuCl3·xH2O and NaHCO3. Different composites loaded with certain amount of carbon black were synthesized with this technique. Super-capacitor performance was assessed via cyclic voltammetry (CV), charge-discharge studies (DC), and impedance analysis (AC). The results show that the capacitance and resistivity of ruthenium oxide materials were dependent on the sample annealing temperature. The materials heated at 300°C exhibit the highest rate capacitance of 1080 F·g-1. Four to six cells of this capacitor was stacked up in series by conductive films in order to achieve higher working voltage. After packaged in resin, charge/discharge studies and impedance analysis were tested via the electrochemical test system. In the research, super-capacitors with a four-layer structure exhibited fine electrochemical characteristics with high working voltage over 5.5 V and low impedance under 1.5 ohm. Also, it had the ability of high-rate discharge performance and considerable large capacitance.

Unveiling the Origin of Unusual Pseudocapacitance of RuO2·nH2O from Its Hierarchical Nanostructure by Small-Angle X-ray Scattering

Hydrous ruthenium oxide (RuO2·nH2O) has inherent proton–electron mixed-conductive nature and offers huge pseudocapacitance (>700 F g–1), having attracted the attention of many capacitor engineers. However, the origin of the anomalous pseudocapacitance, exhibiting a strong maximum at a specific narrow optimum annealing temperature of ca. 150 °C, has yet to be understood. Here we show a long-awaited explanation for this mystery based on its hierarchical nanostructure unveiled by small-angle X-ray scattering (SAXS). The striking contrast in X-ray atomic scattering factors enables SAXS to exclusively probe heavy RuO2 in subnano- to nanoscale, dispersed in confined water. We demonstrate that the surface area of the first aggregate of subnano primary RuO2 particles dominates the accessible number of proton and hence pseudocapacitance, providing critical insights into the nanoarchitectural design of high-performance electrodes for electrochemical capacitors.

High Rate Performance of Flexible Pseudocapacitors fabricated using Ionic-Liquid-Based Proton Conducting Polymer Electrolyte with Poly(3, 4-ethylenedioxythiophene):Poly(styrene sulfonate) and Its Hydrous Ruthenium Oxide Composite Electrodes

We report the studies on all-solid-state flexible pseudocapacitors based on poly (3,4-ethylenedioxythiophene)-poly (styrene sulfonate) (PEDOT-PSS) and PEDOT-PSS/hydrous ruthenium oxide composite electrodes separated by nonaqueous proton conducting polymer electrolyte. Structural, thermal and electrochemical properties including high ionic conductivity (6.2 × 10(-2) S cm(-1) at 20 °C) of the polymer electrolyte, comprising ionic liquid 1-ethyl 3-methyl imidazolium hydrogen sulfate (EMIHSO4) immobilized in the blend of poly (vinyl alcohol) (PVA) and poly (vinyl pyrrolidone) (PVP), demonstrate its excellent suitability in supercapacitor fabrication. A substantial improvement in the specific capacitance (hence the specific energy) has been obtained when the PEDOT-PSS electrodes in the symmetrical pseudocapacitor are replaced by the composite electrodes PEDOT-PSS/RuO2·xH2O. High rate capability of the capacitor cell (with PEDOT-PSS electrodes) has been observed, as evidenced from the high knee frequency (∼966 Hz), low response time (∼70 ms) and high pulse power (∼10.2 kW kg(-1)), observed by impedance analysis. Almost rectangular (capacitive) cyclic voltammetric patterns for high scan rates (up to 15 V s(-1)) confirm the high rate performance of the pseudocapacitor. The PEDOT-PSS/RuO2·xH2O composite electrodes show the lower rate capability (knee frequency ∼312 Hz, response time ∼1 s, pulse power ∼3.2 kW kg(-1) and capacitive CV response up to 500 mV s(-1)) because of slow exchange of charges at the interfaces via RuO2·xH2O. However, the pseudocapacitor with composite electrodes shows higher rate performance relative to many reported RuO2·xH2O systems. About 15% improvement is noticed in the capacitance value when the capacitor with composite electrodes is initially charged and discharged up to ∼200 cycles. Thereafter, the cell shows almost constant value of specific capacitance (∼70 F g(-1)) for 1000 cycles.

Ruthenium-Based Electrocatalysts Supported on Reduced Graphene Oxide for Lithium-Air Batteries

Ruthenium-based nanomaterials supported on reduced graphene oxide (rGO) have been investigated as air cathodes in non-aqueous electrolyte Li-air cells using a TEGDME-LiCF3SO3 electrolyte. Homogeneously distributed metallic ruthenium and hydrated ruthenium oxide (RuO2·0.64H2O), deposited exclusively on rGO, have been synthesized with average size below 2.5 nm. The synthesized hybrid materials of Ru-based nanoparticles supported on rGO efficiently functioned as electrocatalysts for Li2O2 oxidation reactions, maintaining cycling stability for 30 cycles without sign of TEGDME-LiCF3SO3 electrolyte decomposition. Specifically, RuO2·0.64H2O-rGO hybrids were superior to Ru-rGO hybrids in catalyzing the OER reaction, significantly reducing the average charge potential to ∼3.7 V at the high current density of 500 mA g(-1) and high specific capacity of 5000 mAh g(-1).

Evaporation‐Induced Coating of Hydrous Ruthenium Oxide on Mesoporous Silica Nanoparticles to Develop High‐Performance Supercapacitors

Evaporation‐Induced Coating of Hydrous Ruthenium Oxide on Mesoporous Silica Nanoparticles to Develop High‐Performance Supercapacitors

Integration of solid-state dye-sensitized solar cell with metal oxide charge storage material into photoelectrochemical capacitor

A solid-state photo-rechargeable capacitor (photocapacitor) is obtained here by coupling a dye-sensitized solar cell and a ruthenium oxide based electrochemical capacitor. This integrated system permits direct storage of energy generated by sunlight within a single optoelectronic microelectrochemical device. It utilizes three planar electrodes arranged sequentially to include a polymer hole conductor (poly-(3-hexylthiophene-2,5-diyl)), between the titanium oxide photoanode modified with dye (E)-3-(5-(4-(Bis(20,40-dibutoxybiphenyl-4-yl)amino)phenyl)thiophen-2-yl)-2-cyanoacrylic acid (D35) and the intermediate silver electrode as well as two hydrous ruthenium oxide layers (separated by protonically conducting Nafion™ membrane) between the intermediate (silver) and the external (counter) electrode. Upon integration of the capacitor and dye-sensitized solar cell into a single photocapacitor hybrid device, the following parameters were obtained under simulated 100 mW cm−2 solar illumination: specific capacitance, 407 F g−1 (3.26 F cm−2); energy and power densities, 0.17 mWh cm−2 and 0.34 mW cm−2 and coulombic efficiency, 88%. These data together with results of experiments performed at different light intensities (10–100 mW cm−2) are consistent with very good performance of the optoelectronic device under various light conditions.

High-Speed Annealing of Hydrous Ruthenium Oxide Nanoparticles by Intensely Pulsed White Light for Supercapacitors

We propose and demonstrate an extremely efficient annealing for the RuO2·xH2O nanoparticles incorporated in a supercapacitor employing intensely pulsed white light (IPWL). The IPWL process ensures the significant advantage of a room-temperature and millisecond-scaled process under ambient conditions. Resultant nanomorphology and crystallinity of RuO2·xH2O electrodes are analyzed for process optimization. Electrochemical characteristics of the IPWL-treated electrodes were investigated by cycle voltammetry, resulting in a specific capacitance of 439 F/g at 10 mV/s with the irradiated IPWL energy of 2.04 J/cm2 in 23 msec.

Facile preparation of three-dimensional porous hydrous ruthenium oxide electrode for supercapacitors

A porous hydrous ruthenium oxide for supercapacitors is fabricated by electro-deposition accompanied with hydrogen-evolution reaction. This high-surface-area electrode (207.5 m2 g−1) is developed by electrochemical de-alloying process of copper from as-deposited Ru–(Cu) foam (23.5 m2 g−1). The three-dimensional structures with open pores and numerous dendritic morphologies produce good electrochemical performances by providing the pathway for facile penetration of electrolytes into active electrode surface. The three-dimensional porous hydrous ruthenium oxide exhibits good capacitance performance of 809 F g−1 at 1.5 A g−1, high energy density (112 Wh kg−1), and excellent stability retention (∼98%) even after 3000 cycles.

Electrochemical supercapacitors of electrodeposited PANI/H-RuO2 hybrid nanostructure

Electrodeposited mixed nanostructures composed of conducting polyaniline (PANI) and hydrous ruthenium oxide (H-RuO2) referred as a hybrid nanostructure was synthesized. The surface morphology was investigated from the field-emission scanning electron microscopy digital photoimages. Fibrous network of PANI and spheres of H-RuO2 were obtained. PANI embedded H-RuO2 was confirmed from the Raman spectroscopy analysis. Cyclic-voltammetry, used to characterize the electrochemical capacitive properties of hybrid PANI/H-RuO2 (RP 30) nanostructure, showed a specific capacitance as high as 322 F/g in 0.5 M H2SO4 electrolyte. The electrochemical impedance spectroscopy measurement revealed the low equivalent series resistance.

Effect of the degree of alloying of PtRu/C (1:1) catalysts on ethanol oxidation

The effect of alloying degree on the ethanol oxidation activity of a PtRu/C catalyst with a Pt/Ru atomic ratio of 1:1 was investigated by measurements in a half-cell and in a single direct ethanol fuel cell. The increase of the amount of Ru alloyed from one third to two thirds of the total Ru content in the catalyst clearly resulted in a decrease of the ethanol oxidation activity. As the amount of the highly active hydrous ruthenium oxide was near the same, the lower activity of the PtRu/C catalyst with higher alloying degree was mainly ascribed to the presence of an excessive number of Ru atoms around Pt active sites, hindering ethanol adsorption on Pt sites. The reduced ethanol adsorption could be also related to the decreased Pt–Pt bond distance and to the electronic effects by alloying.