Hydrous Ruthenium Oxide Research Articles

Hydrous ruthenium oxide quantum dots anchored on carbon nanocages for Zn-ion hybrid capacitors

Zn-ion hybrid capacitors (ZICs) are a novel and promising electrochemical energy storage system, while exploring high-performance cathode materials is essential for the development of ZICs. Herein, we propose hydrous ruthenium oxide quantum dots (RuO2 QDs) anchored on porous carbon nanocages (PCNCs) as a new cathode material for ZICs. For the RuO2 QDs@PCNCs material, hydrous RuO2 QDs with a small size of 2–3 nm uniformly disperse on the PCNC support, providing large electrode–electrolyte interface for electrochemical reactions and abundant active sites for ion storage. Consequently, the RuO2 QDs@PCNCs cathode material displays desirable electrochemical performance in ZICs, including a large capacity of 224 mAh g−1 at 0.4–1.8 V, superior rate capability (showing 156 mAh g−1 capacity even at a large current of 20 A g−1) and good stability during a long-term cycling test over 20,000 cycles, significantly superior to currently-reported cathode materials for ZICs. An ultrahigh energy density of 180 Wh/kg is achieved for the RuO2 QDs@PCNCs cathode-based ZICs. Mechanism investigations point out the capacitive behavior-dominated and Zn2+/H+ co-participated charge storage process with fast electrochemical kinetics for the RuO2 QDs@PCNCs cathode in ZICs. This work not only provides a new choice for high-performance cathodes but also enriches the electrochemical theory of ZICs.

Unveiling the role of strontium in 1D SrxRu1−xO2−x compound oxide nanofibers for high-performance supercapacitor

Hydrous ruthenium oxide (RuO2) has been considered a potential electrode for supercapacitors. However, RuO2 is not easy to be hydrous, which impedes advancement in RuO2-based supercapacitors. Here, strontium cation (Sr2+) – with a lower oxidation state than Ru4+ – doping effects on improving the capability of RuO2 to be hydrous are reported. The Sr2+ doping in the RuO2 was simply possible using electrospinning and subsequent calcination, affecting hydrous properties and promoting miniaturization of nanograins in one-dimensional (1D) nanofibers. The compositions of hydrous Sr2+-doped RuO2 (H-SrxRu1-xO2-x) nanofibers were optimized considering correlations between synthesis temperature and degree of hydration. It was found that the H-Sr0.2Ru0.8O1.8 nanofibers synthesized at 400 oC were hydrous compared with the pristine RuO2 and H-Sr0.1Ru0.9O1.9 nanofibers. The H-Sr0.2Ru0.8O1.8 nanofibers (400) could possess the smallest nanocrystallites, increasing electrochemically active surface area and satisfying specific capacitance of 612.6 A/g at a scan rate of 50 mV s–1. Data will be made available on request.

The in-situ formation of supported hydrous ruthenium oxide in aqueous phase during HDO of lignin-derived fractions

The in-situ formation of supported hydrous ruthenium oxide (HRO) from RuO2 over micro-mesoporous materials is reported for the selective hydrogenation of bio-oil under mild reaction conditions (200 °C, 20 bar H2) in an aqueous medium. For the first time, the phase composition of HRO was determined using a variety of characterization techniques. Using synchrotron radiation and in-situ X-ray absorption spectroscopy (XAS), we demonstrated that HRO was generated during the hydrodeoxygenation process. The hydrodeoxygenation (HDO) of real bio-oil was successfully performed at 200 °C, 20 bar H2 on RuO2-containing catalysts. The approximate composition of HRO after 3 h of catalytic hydrogenation, consisted of in approximately equal ratios metallic Ru, RuO2, and RuOOH phases.

Reductive catalytic cracking of industrial phenolics mixture to selective cyclohexanols

Cyclohexanol and its alkyl derivatives are among the most demanding and valuable chemicals. Currently, cyclohexanols are commercially obtained by oxidation of cyclohexanes, derived from fossil-derived benzene and its derivatives. Herein, cyclohexanols are produced from industrial phenolics (IPs) by hydrodeoxygenation (HDO). HDO of IPs was performed over a series of hydrous ruthenium oxide impregnated HY zeolite (HROY) catalysts with varying Ru content. Highest acidity of 10 HROY promoted deoxygenation reactions and strongly interacted small HRO particles with support led to high hydrogenation ability. The effect of solvent mixture (isopropyl alcohol (IPA): water) demonstrated the positive role of water in improving the conversion and selectivity. IPA facilitated the dissolution of IPs while water promoted the adsorption of solubilized molecules on the HRO active sites to lead the proton transfer activity. Maximum conversion (≥99%) was achieved with 87.4% cyclohexanols selectivity (2-methyl cyclohexanol:80.4%, 4-methyl cyclohexanol:5.6% and Cyclohexanol: 1.4%) under optimum reaction conditions.

A Flexible, Redox‐Active, Aqueous Electrolyte‐Based Asymmetric Supercapacitor with High Energy Density Based on Keratin‐Derived Renewable Carbon

AbstractThis work exploits the advantage of asymmetric configuration over symmetric supercapacitor in designing high energy density flexible devices from two active electrode materials–keratin‐based renewable‐resource hierarchically porous carbon and hydrous ruthenium oxide (RuO2). The asymmetric device exhibits significantly high capacitance. Conventional estimation of energy storage parameters, however, cannot be applied for devices with a Faradaic energy storage contribution via redox charge transfer mechanism. Therefore, this work applies a precise measurement of pseudocapacitance contribution at various scan rates to correct the device data that reveals effective capacitance of 120 F g−1 with the energy density of 37 W h kg−1 at 776 W kg−1. It also retains excellent rate capability, >74% at high current density 25 A g−1. The charge storage activity and device stability can be further enhanced by introducing redox‐active electrolytes that improve specific capacitance, but the rate capabilities deteriorate at high current densities. Further, the principle of asymmetric electrode design is applied to fabricate a bending‐tolerant, flexible device by depositing active electrode material on wire‐shaped current collector followed by coupling those separated with polyvinyl alcohol gel containing redox electrolyte; it yields 36.8 mF cm−1 specific capacitance at a 0.2 mA cm−1 current density.

Upgradation of sugarcane bagasse lignin: Fractionation to cyclic alcohols production

Reductive catalytic fractionation (RCF) is a new class of process that produces mono phenolics close-to-theoretical maximum yield by preserving the biomass polysaccharides as solid residues under hydrogen atmosphere or hydrogen transfer conditions. Herein, hydrous ruthenium oxide deposited on carbon (HRO@C) and HY-zeolite (HRO@HYZ) catalysts are prepared and characterized by different analytical techniques (TGA, TPD, TPR, XRD, TEM, XPS, physisorption and chemisorption). Both catalysts have been used for the RCF of sugarcane bagasse (SCB). Effects of catalyst acidity, reaction time, pressure, temperature, and solvent on the RCF of SCB have been investigated. Solid residues after RCF are characterized by FT-IR, TGA, XRD, and fibertec to identify the effects of reaction conditions on lignin-first delignification efficiency (LFDE). High acidity of HRO@HYZ favors a high degree of LFDE (81.2 %) than HRO@C (55.8 %). However, alkyl-substituted phenolic monomers (ASPMs) selectivity is 69 % for HRO@C and 55.7 % for HRO@HYZ, respectively, under the same reaction conditions. NMR and GC-FID/GC-MS analysis indicate the presence of ASPMs in the resulted lignin bio-oil. Moreover, fractionated lignin bio-oil is used for upgradation and the upgraded product analysis confirms > 95 % conversion of lignin bio-oil, in which over 90 % selectivity is towards alkylated cyclic alcohols.

Preparation of cyclohexanol from lignin-based phenolic concoction using controlled hydrogen delivery tool over in-situ Ru catalyst

This work investigated hydrodeoxygenation-hydrogenation of lignin-based methoxyphenols (obtained through hydrothermal liquefaction (HTL) of lignin) to cyclohexanol in high yields over in situ generated Ru(0)@Mg(OH)2 catalyst in aqueous medium. The active catalyst Ru(0)@Mg(OH)2 is generated in situ from hydrous ruthenium oxide (HRO)/Mg(OH)2 under reaction conditions, as confirmed by various physiochemical techniques. Continuous and controlled addition of H2 at constant temperature facilitated in improving the selectivity of cyclohexanol compared to the conventional batch mode (pre-set pressure) process. Complete conversion of methoxyphenols with 93–99% selectivity for cyclohexanol was achieved at 10 mL/min H2 flow under comparatively milder reaction conditions. The adopted procedure and the in situ catalyst reported in this work is also effective for lignin-derived phenolic concoction.

Asymmetric micro-supercapacitors based on electrodeposited Ruo2 and sputtered VN films

Research on micro-supercapacitors remains one of the most important activities in the area of electrochemical energy storage for powering smart and miniaturized electronic devices. Here we design an asymmetric micro-supercapacitor (A-MSC) combining sputtered vanadium nitride film (VN) and electrodeposited hydrous ruthenium oxide (hRuO2) film. Taking advantage of their complementary electrochemical potential windows in 1 M KOH electrolyte, the A-MSC achieves a cell voltage up to 1.15 V, associated to high specific capacitance values for the device (≈ 100 mF cm−2). The energy density of this asymmetric VN / hRuO2 micro-supercapacitor reaches 20 µWh cm−2 at a power density of 3 mW cm−2. Taking benefit from the asymmetric configuration, a 5-fold enhancement factor in energy density is demonstrated for the VN / hRuO2 asymmetric micro-supercapacitor as compared to symmetric VN / VN and hRuO2 / hRuO2 microdevices.

Hydrodeoxygenation of lignin derived phenolics over a hydrous ruthenium oxide based catalyst(s): role of surface water molecules and acidity of the support

HRO@Y has been designed for selective HDO of lignin-derived phenols in aqueous phase and it has showed robust activity and selectivity towards cyclohexanols. This offers new possibility for the production of industrially important building blocks sustainably.

In situ Generated Ru(0)-HRO@Na-β From Hydrous Ruthenium Oxide (HRO)/Na-β: An Energy-Efficient Catalyst for Selective Hydrogenation of Sugars.

A green process for the hydrogenation of sugars to sugar alcohols was designed in aqueous medium using hydrous ruthenium oxide (HRO) as a pre-catalyst supported on Na-β zeolite. Under optimized reaction conditions, sugars such as xylose, glucose, and mannose converted completely to the corresponding sugar alcohols xylitol, sorbitol, and mannitol with 100% selectivity. The pre-catalyst (HRO) is converted in situ to active Ru(0) species during the reaction under H2, which is responsible for the hydrogenation. The catalyst was recyclable up to five cycles with no loss in activity. The reduction of HRO to the active Ru(0) species is dependent on the reaction temperature and H2 pressure. Ru(0) formation increased and consequently an increased hydrogenation of sugars was observed with an increase in reaction temperature and hydrogen pressure. Further, in situ generation of Ru(0) from HRO was assessed in different solvents such as water, methanol, and tetrahydrofuran; aqueous medium was found to be the most efficient in reducing HRO. This work further demonstrates the use of supported HRO as an efficient pre-catalyst for biomass-based hydrogenation reactions.

Study of the pore size effect on the charge storage of hydrous RuO2 nanoparticles supported within the pores of activated carbon

Hydrous ruthenium oxide (RuO2) nanoparticles are hybridized inside the pores of activated carbon (AC) for preparing electrochemical capacitor electrodes. The hybridization consists of the adsorption of an organoruthenium complex and subsequent heat treatment to reduce the complex into Ru nanoparticles within the AC pores, followed by the electrochemical oxidation of the resulting Ru nanoparticles into hydrous RuO2 nanoparticles. Two kinds of AC with only micropores and both micropores and mesopores of ~4 nm are examined to study the effects of pore sizes on the charge/discharge characteristics of the AC/RuO2 hybrids. Since the introduction of hydrous RuO2 nanoparticles is not accompanied by the volumetric expansion of the AC particles, the volumetric capacity is enhanced in comparison with the pristine AC. However, the capacitance retention at high charge/discharge rates is decreased by micropores or an excessive amount of the hydrous RuO2 nanoparticles. This method is free from the use of any organic solvent, concomitant solvent removal and drying process, or reducing and oxidizing reagents, and therefore, can be used to synthesize porous carbon/metal oxide nanoparticle hybrids for versatile applications.

Green Synthesis and Modification of RuO2 Materials for the Oxygen Evolution Reaction

A dynamic ion-exchange method is proposed as a green synthesis route to prepare hydrous ruthenium oxide nanoparticles (H-RuO2 NPs). Physicochemical characterizations indicate that RuO2 crystalline rutile nanoparticles (NPs) are obtained either by direct calcination of the H-RuO2 material at 350 °C (C-RuO2) or by treatment under microwave irradiation of an aqueous suspension of H-RuO2 NPs with 20 vol. % ammonium hydroxide and calcination of the treated H-RuO2 material at 350 °C (A-C-RuO2). The electrocatalytic performances of the H-RuO2, C-RuO2 and A-C-RuO2 catalysts towards the oxygen evolution reaction (OER) are evaluated and compared in a 0.50 mol L-1 H2SO4 electrolyte. The H-RuO2 material displays the low onset potential of ca. +1.40 V vs RHE but is not stable for potentials higher than +1.500 V vs RHE. Improved performances towards the OER, in terms of activity and stability, are obtained with the C-RuO2 catalyst, but the higher catalytic activity is achieved by the ammonia treated A-C-RuO2 catalyst. The characterization of materials by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy shows that the microstructure is affected by the ammonium hydroxide treatment under microwave irradiation: the A-C-RuO2 material displays lower crystallinity level and hydrous rutile content, and smaller mean crystallite size than those determined for the C-RuO2 one. Structure-property correlation has been established to give insights on the higher electrocatalytic activity of the A-C-RuO2 catalyst than that of the C-RuO2 one.

High-performance supercapacitors of ruthenium-based nanohybrid compounds

Abstract Hybrid capacitor materials exhibit good electrochemical performance because they possess the advantages of both electrical double-layer capacitors (EDLCs) and pseudocapacitors (PCs). Here, ruthenium nanohybrid compounds (Ru-com) are synthesized with hydrous ruthenium oxide (RuO2·H2O), EDLCs, and ruthenium nanoparticles capped by cysteine (Ru-cys), which are PCs. The morphologies and structures of Ru-com, RuO2·H2O, and Ru-cys are confirmed by several characterization methods. The electrochemical performances are investigated by cyclic voltammetry, galvanostatic charging-discharging, and electrochemical impedance spectroscopy. The Ru-com exhibits a specific capacitance of 797.7 A g−1 in 0.5 M H2SO4 electrolyte at a scan rate of 10 mV s−1, which is much larger than the specific capacitance of its precursors, due to the synergistic effect of the reversible faradaic redox process and facilitated proton and electron transfer processes. In addition, the Ru-com not only shows a better rate capability than Ru-cys but also exhibits a better electrochemical stability than RuO2·H2O owing to the mutual modification of its components.

Electrochemical performance enhancement of high mass loading H-RuO2NPs electrode and aqueous symmetrical supercapacitor in the neutral electrolyte

Abstract In this work, high water content hydrous ruthenium oxide nanoparticles (H-RuO2NPs) were synthesized using gallic acid monohydrate as a reducing agent. X-ray diffraction and transmission electron microscopy results confirmed the formation of irregular shape H-RuO2NPs with an average size of 5 nm. The thermogravimetric study showed that the synthesized H-RuO2NPs content more than 70 % of water which makes it specifically suitable for the electrochemical application. Moreover, it was observed that increasing the mass loading of synthesized H-RuO2NPs from 0.5 mg cm−2 to 8 mg cm−2, the specific capacitance decreased from 676 to 217 Fg −1 at a scan rate of 5 mVs−1 in 1 M Na2SO4 electrolyte. Furthermore, the aqueous symmetrical supercapacitor with a total mass loading of 16 mg cm−2 exhibited a specific capacitance of 62 Fg −1 at a scan rate of 1 mVs−1 and the specific capacitance retention rate of 91.4 % was observed after 5000 cycles at a current density of 5 Ag−1.

Enhancement of electrochemical properties of hydrous ruthenium oxide nanoparticles coated on chemically activated carbon cloth for solid-state symmetrical supercapacitor application

Electrochemical performance of bare carbon cloth (BCC) and chemically activated carbon cloth (CACC) as current collectors were studied for supercapacitor applications. The prepared hydrous ruthenium oxide nanoparticles (H–RuO2NPs) using gallic acid monohydrate coated on both BCC and CACC and employed as pseudocapacitive electrodes in aqueous neutral (1 M Na2SO4) electrolyte. The specific capacitance obtained for H–RuO2NPs coated on CACC (H–RuO2NPs@CACC) using constant current charge-discharge measurements was 837 F g−1 at a current density of 2 A g−1 which was 3.87 times higher than the H–RuO2NPs coated on BCC (H–RuO2NPs@BCC). Moreover, the capacitance retention rate for H–RuO2NPs@CACC and H–RuO2NPs@BCC was 97.54% and 95.8% after 5000 cycles at 20 Ag-1 respectively. Furthermore, the symmetrical supercapacitor (SS) fabricated using H–RuO2NPs@CACC electrodes delivers the capacitance up to 796 Fg- 1 at 2 mVs−1 with capacitance retention of 91.8% after 5000 cycles at 10 Ag-1 for total mass loading of 10 mg cm−2 in hydrogel polymer electrolyte (PVA- Na2SO4). The energy density of SS was 156 Wh kg−1 at a current density of 5 A g−1. The obtained results of SS suggest that the H–RuO2NPs@CACC electrode can be utilized for a high-performance energy storage device.

Effect of ruthenium on superior performance of cellulose nanofibers/poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate)/ruthenium oxide/ionic liquid actuators

This study proposes novel actuators based on cellulose nanofibre/poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate)/hydrous ruthenium oxide/ionic liquid (CNF/PEDOT:PSS/RuO2/IL) electrodes and the poly(vinylidene fluoride-co-hexafluoropropylene)/IL (PVdF(HFP)/IL) electrolyte, and investigates the effect of hydrous ruthenium oxide on the electrochemical and electromechanical properties of the proposed actuators. The proposed system contains an electrochemical capacitor electrode, which acts as both a faradaic capacitor (FC) and a small electrostatic double layer capacitor (EDLC). This hybrid capacitor is based on the FC (RuO2) mechanism, and a base polymer (PEDOT:PSS) and CNF skeleton replace carbon nanotubes (CNTs). Therefore, this device functions differently from traditional CNT/PVdF(HFP))/IL electrode actuators, which are only used as EDLC units, and CNF/PEDOT:PSS/IL (without RuO2) actuators, where PEDOT:PSS plays the role of both FC and base polymer. Devices built using the proposed actuators exhibit higher strains and greater maximum generated stresses than those exhibited by devices based on CNF/PEDOT:PSS/IL (i.e. without RuO2). Surprisingly, the synergism obtained by combining RuO2 and PEDOT:PSS is considerably greater than the enhancement achieved using PEDOT:PSS. The frequency dependences of the displacement responses of the CNF/PEDOT:PSS/RuO2/IL electrode actuators were then measured and successfully simulated using a double layered charging kinetic model. The developed films are novel, robust, and flexible, and they exhibit potential for use as actuator materials.

Structure and spectroscopy of the supercapacitor material hydrous ruthenium oxide, RuO2·xH2o, by neutron scattering*

Hydrous ruthenium dioxide, RuO2·xH2O, is a material of active investigation as an electrode material for supercapacitors. A combination of elastic and inelastic neutron scattering together with thermal gravimetric studies and DFT calculations have provided new insight into the nature of the surface species present on RuO2·xH2O. Our results confirm that hydrous ruthenium oxide is a nanocrystalline material consisting of a core of RuO2. We show that the surface consists largely of Ru–OH with small amounts of water hydrogen-bonded to the surface. The hydroxyls are stable up to ∼200°C, i.e. over the composition range x = 0.2–2. The optimal supercapacitor material has x = 0.5–0.7, and in this range, the surface is fully hydroxylated. This provides a route for the proton transport: a proton can attach to a surface hydroxyl to generate coordinated water, proton transport then occurs along the hydrogen-bonded chain by a Grotthuss mechanism.

A pH‐Tailored Anodic Deposition of Hydrous RuO2 for Supercapacitors

AbstractA pH‐tailored anodic deposition strategy is reported in this work, by which the hydrous ruthenium oxide (RuO2) can be directly deposited on titanium (Ti) substrates. The prepared RuO2 electrode exhibits a well kinetic performance (the remarkably low equivalent series resistance of Res∼2 mΩ and charge transfer resistance of Rct∼0.11Ω) and a high specific capacitance of 756 F g‐1 at 0.6 A g‐1. More importantly, a symmetric supercapacitor based on the RuO2 electrode delivers a high specific energy of 24 Wh kg‐1 at 150 W kg‐1. Even at a large specific power of 26.25 kW kg‐1, specific energy is still as high as 8.6 Wh kg‐1, meanwhile achieving a long lifespan of 98% retention over 100,000 cycles. All of these distinguishing properties not only enable the prepared RuO2 to be an excellent electrode material for high‐power output and long life supercapacitors, but also indicates that the pH‐tailored anodic deposition strategy reported in this work is effective to prepare high‐performance RuO2 electrode.

Enhanced capacitance of hydrous ruthenium oxide based all-solid-state interdigital in-planar micro-supercapacitors

Pattern design is a critical strategy to improve the performance of interdigital in-planar micro-supercapacitors (μ-SCs) in a fixed footprint area. Pattern optimization can synchronously achieve sufficient improvement without changing the materials used or the fabrication technologies. A simple adjustment of the interdigitated-electrode width-to-length ratio without changing the widths of gaps or the interdigitated electrodes themselves is reported for pattern design in this study. The results show that the geometric configuration plays a key role in improving the electrochemical performance of the interdigital in-planar μ-SCs. Nanocomposites exhibit properties different from those of their individual constituents, leading to new properties. The utilization of hydrous ruthenium oxide/reduced graphene oxide (hRuO2/rGO) composites integrating the merits of both pseudocapacitors and electrical double-layer capacitors is another important strategy for fabricating high-performance μ-SCs. In this report, we investigated the influence of the geometric configuration of interdigitated electrodes and the utilization of a hRuO2/rGO composite for interdigital in-planar μ-SCs. Through the combination of the advantages of both strategies (i.e., pattern design and hRuO2/rGO composite), all-solid-state interdigital in-planar μ-SCs assembled using the hRuO2/rGO composite and a gel electrolyte and constructed with the optimal pattern process exhibited a low electrical resistance, good frequency response and relaxation constant, high areal capacitance, good rate capability, and excellent capacitance retention.

Hydrous RuO2‐Decorated MXene Coordinating with Silver Nanowire Inks Enabling Fully Printed Micro‐Supercapacitors with Extraordinary Volumetric Performance

AbstractThe fabrication of fully printable, flexible micro‐supercapacitors (MSCs) with high energy and power density remains a significant technological hurdle. To overcome this grand challenge, the 2D material MXene has garnered significant attention for its application, among others, as a printable electrode material for high performing electrochemical energy storage devices. Herein, a facile and in situ process is proposed to homogeneously anchor hydrous ruthenium oxide (RuO2) nanoparticles on Ti3C2Tx MXene nanosheets. The resulting RuO2@MXene nanosheets can associate with silver nanowires (AgNWs) to serve as a printable electrode with micrometer‐scale resolution for high performing, fully printed MSCs. In this printed nanocomposite electrode, the RuO2 nanoparticles contribute high pseudocapacitance while preventing the MXene nanosheets from restacking, ensuring an effective ion highway for electrolyte ions. The AgNWs coordinate with the RuO2@MXene to guarantee the rheological property of the electrode ink, and provide a highly conductive network architecture for rapid charge transport. As a result, MSCs printed from the nanocomposite inks demonstrate volumetric capacitances of 864.2 F cm−3 at 1 mV s−1, long‐term cycling performance (90% retention after 10 000 cycles), good rate capability (304.0 F cm−3 at 2000 mV s−1), outstanding flexibility, remarkable energy (13.5 mWh cm−3) and power density (48.5 W cm−3).