Hydrous RuO2 Research Articles

Hydrous ruthenium oxide triggers template-free and spontaneous growth of metal nanostructures.

Intrinsically conductive ruthenium oxide is an excellent material for energy storage and conversion. Herein, we present hydrous RuO2 (H-RuO2) as a potent reducing agent to achieve spontaneous growth of multiple noble metals at room temperature. Self-assembled gold and platinum, comprising small-sized nanoparticles, are generated on the surface of H-RuO2 without the need for additional templates. Structural analysis reveals that the disordered structure and the presence of oxygen vacancies trigger interfacial redox reactions between H-RuO2 and oxidative metal salts. The resulting integrated nanostructures, consisting of a metal oxide and different metals (H-RuO2@metal), are subsequently used to treat inflammatory bowel diseases. In addition to biomedical applications, our developed synthetic strategy, using reactive oxides to spontaneously generate multicomponent nanostructures, also holds great significance for other catalysis-based applications.

Hydrous RuO2 film synthesized in an alkali-assisted steam thermal reactor: Low temperature synthesis and pseudocapacitance

The method of preparing RuO2 thin film by decomposing RuCl3 precursor in steam has shown a potential of having lower temperature and higher capacitance in our previous research work. We have further improved the method of thermal decomposition in steam in our previous work and proposed the alkali-assisted steam thermal reactor (AASTR) method, which has achieved the synthesis of RuO2 thin film with a capacitance of 514 F·g−1 at a low temperature of 150 °C. In the AASTR method, a concentrated sodium hydroxide solution is chosen and placed at the bottom of the reactor. The Ti foil substrates are placed in the vapor phase and do not contact the sodium hydroxide solution. The sodium hydroxide solution is employed to absorb hydrogen chloride generated in the hydrolysis process of RuCl3 and thus promotes the hydrolysis process. As a result, thermal decomposition at a lower temperature (around 150 °C, the critical crystallization temperature) becomes possible due to the modified hydrolysis process. The film exhibits an almost ideal surface controlled pseudocapacitive performance due to its low charge transfer resistance in the charge/discharge process. Therefore, the AASTR method has promising applications in low-temperature synthesis of other hydrous metallic oxides.

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.

Pd/PdO and hydrous RuO2 difunction-modified SiO2@TaON@Ta3N5 nano-photocatalyst for efficient solar overall water splitting

A novel Pd/PdO and hydrous RuO2 difunction-modified SiO2@TaON@Ta3N5 core-shell structured nano-photocatalyst was synthesized successfully, which displayed excellent photocatalytic activity for overall water splitting into H2 (473.52 μmol−1·g−1·h−1), about 2.86 times higher than unmodified SiO2@TaON@Ta3N5 (165.74 μmol−1·g−1·h−1), under the visible-light irradiation with the wavelength ≥420 nm, without any sacrificial agent, as well as excellent stability against photocorrosion. The apparent quantum yield (AQY) reaches to 0.253% under irradiation intensity of 12 mW cm−2 at 420 nm. The spatially separated Pd, PdO and RuO2 clusters were decorated on the Ta3N5 surface to construct local multi-heterojunctions, which were confirmed to enhance the light absorption capability, drive efficient separation of charge carriers and directional transfer, and promote surface redox reaction kinetics of HER and OER. The trace modification of metallic Pd clusters and TaN could mainly contribute to the significant decrease in the HER overpotential, while PdO exhibited a stronger contribution than RuO2 for OER catalytic activity. The synergetic mechanism of enhanced photocatalytic overall water splitting for hydrogen production was discussed in detail. Thus the combination of core-shell heterojunction construction and surface difunction modification provides a promising strategy for develop efficient all-in-one photocatalysts for solar overall water splitting.

A flexible and high energy density -hydrous RuO2 and keratin-derived renewable carbon composite-based asymmetric supercapacitor in redox-mediated electrolytes

The present study exploits a chemical-free, low-cost, simple, scalable, and facile synthesis technique using an in-situ methodology to prepare composite electrodes. The as-synthesized composite is utilized as a hybrid electrode for supercapacitor application. The hydrous RuO2 and keratin fiber-derived carbon (ROKF-2) show excellent specific capacitance of 3542 F g−1 at 2 A g−1. However, true analysis reveals that the actual capacitance is 2556 F g−1. It focuses on delivering the actual performance of the hybrid device by eliminating the use of conventional equations. In symmetric assembly, the excellent device capacitance of 121 F g−1 at 1 A g-1 is achieved while maintaining its coulombic efficiency above 90% throughout the applied current. The double hybridization assembly shows the broadening of working potential with an outstanding energy density of 226 Wh kg−1 at 1000 W Kg−1. Upon introducing redox additives, the performance increases, suggesting their effective contribution to the charge storage process. In the presence of K3Fe(CN)6, the device delivers a remarkable rate capability of 50% till 5 A g−1, whereas, in the KI environment, the device efficiency gets enhanced ∼45%. The wire-shaped flexible device shows a specific capacitance of 142 mF cm−1 at a scan rate of 10 mV s−1 with an energy density of 0.03 mWh cm−1 at 33 W cm−1. The process approaches a chemical-free process for the composite synthesis, which can be utilized in various hybridization modes. The study eliminates the traditional equations to minimize the overestimated electrochemical performance. The prepared composites pave a new path in hybrid energy storage systems.

Synthesis of hydrous RuO2 anchored on seaweed-derived porous carbon for high-performance electrochemical capacitors

Supercapacitors (SCs) have attracted widespread attention due to the fast development of electronics and electrical vehicles. As a potential pseudocapacitive electrode material for SCs, RuO2 is promising for fast energy storage, but its performance is severely restricted by the spontaneous agglomeration and high cost. Here, we prepared seaweed-derived porous carbon (SDC) as a conductive substrate of hydrous RuO2 nanoparticles for electrochemical SCs, and the as-prepared hybrid exhibits high specific capacitance of 807 F g−1 at 2 mV s−1, excellent high-rate (988.1 F g−1 at 0.1 A g−1 and 635.9 F g−1 at 5 A g−1) and cycling performances (93.8% retention after 1000 cycles at 1 A g−1) in 1 M H2SO4. The outstanding performance of the hybrid can be attributed to the interconnected three-dimensional mesoporous structure of the SDC and the uniform dispersion of hydrous RuO2 nanoparticles. This work demonstrates that the hierarchical porous SDC can be used as an excellent conductive substrate to further enhance the electrochemical performance of other easily agglomerated nanoparticles.

Hydrous RuO2 and CoxNy difunction-modified Ta3N5@Ta2N multi-heterojunction nanoplates for efficient visible-light-driven photocatalytic hydrogen production

To overcome the intrinsic drawbacks of Ta3N5 such as charge carrier recombination and serious self-oxidation, constructing difunctional multi-heterojunction is very promising and challenging for local selective modifications. Hydrous RuO2 and CoxNy difuntionally modified Ta3N5@Ta2N multi-heterojunction nanoplates were fabricated by high-temperature nitridation reduction of Co3+-modified Ta2O5@Ta3N5, followed by photooxidation deposition of Ru3+. The structural and compositional features were modulated by optimizing the nitridation time and Ru-modifying amount. Interestingly, synergetic effects of CoxNy/Ta2N/Ta3N5 and RuO2/Ta2N/Ta3N5 on charge carrier separation and transfer, and on decrease in the HER and OER overpotentials about 73 mV and 238 mV, respectively, were observed. Improved visible light absorption was attributed to a localized surface plasmon resonance (LSPR) effect by subnitride Co5.47N, sub-bandgap behavior of Ta2N, and anion defect N-vacancies. Increased charge transfer resistance by CoxNy/Ta2N interface was significantly reduced by further constructing hydrous RuO2/Ta2N heterojunction, where new Ru–O–Ta linkages facilitated fast separation and transfer of charge carriers, and increased surface hydroxyl groups was beneficial to the adsorption of water molecules. Micropores also provided more photoactive sites. All above factors cooperatively enhanced the visible-light photocatalytic H2-evolution activity, which was 1395.35 μmol·g−1·h−1, about 6.53 times higher than that of Ta2O5@Ta3N5. Its apparent quantum efficiency reaches to 5.76% under irradiance intensity of 15 mW cm−2 at 420 nm. Constructing difunctional multi-heterojunction provides a promising avenue to design efficient and stable Ta3N5-based photocatalysts for solar water splitting.

Formation of RuO2 thin film using dopamine as a reducing, chelating, and adhesive agent simultaneously

We demonstrate a facile and seedless wet chemical process to deposit RuO2 thin film on a glass slide. The process entails the use of dopamine and its oxidized form, polydopamine (PDA), as the reducing and chelating agent, as well as the adhesive agent bonding the RuO2 and glass slide. The formula starts with the oxidation of K2RuCl5 to prepare RuO4 solution, followed by its reduction by dopamine to form chelated RuO2 colloids for the deposition of amorphous RuO2 thin film containing 26.5 at% hydrous RuO2 and 73.5 at% RuO2. After a mild Ar annealing, the RuO2 thin film exhibits a rutile phase with (110) preferred orientation. Elemental analysis indicates incomplete pyrolysis of PDA. Results from X-ray absorption spectroscopy confirm the presence of RuO4 and its transformation to RuO2. Electrochemical analysis of the adsorbed dopamine molecules on an ITO substrate validates the oxidative behavior of dopamine. The bonding strength of RuO2 thin film is determined by a tape-peeling test in which both the as-deposited and annealed RuO2 thin films show robust adhesion to the glass substrate.

Salt Adsorption Capacity of Hydrous and Anhydrous Ruthenium Oxides for Capacitive Deionization

Capacitive deionization (CDI) is a promising technology for desalination of seawater and recovery of mineral resources. By applying a voltage to a pair of electrodes within the potential of water electrolysis, ions such as Li+ and Na+ can be recovered by electrosorption. In order to increase the salt adsorption capacity (SAC) of the electrodes, various metal oxides have been proposed.1 For example, manganese oxide, titanium oxide and ruthenium oxide show higher SAC than activated carbon, owing to the contribution from both electric double-layer capacitance and pseudocapacitance. In particular, the SAC of ruthenium oxide electrodeposited on activated carbon was ~4 times higher than that of pristine activated carbon due to the additional pseudocapacitance.2 Since hydrous RuO2 shows higher pseudocapacitance compared with anhydrous RuO2,3 it is anticipated that hydrous RuO2 would show higher SAC compared to anhydrous RuO2. Here we evaluate and discuss the pseudocapacitance and SAC capability of hydrous and anhydrous RuO2-based electrode materials. RuO2·0.5H2O or RuO2 were prepared by heating of RuO2·xH2O at 200°C or 450°C, respectively.3 The slurry, prepared by mixing RuO2·0.5H2O or RuO2, polyvinylidene fluoride and N, N-dimethylformamide, was pasted on a Ti plate and dried at 120oC to prepare electrodes (10-11 mg cm-2) for batch-mode CDI experiments. Activated carbon (MSP-20) electrode was prepared as a control sample. The CDI experiment was carried out with a voltage of 1.2 or 0 V, by circulating 100 mL NaCl feed solution (initial concentration: 5 mM NaCl) at a flow rate of 9.8 mL min-1 per electrode. The SAC was determined by measuring the change in the conductivity on the negative electrode side, using a calibration curve of conductivity and concentration of NaCl solution.The specific capacitance of RuO2·0.5H2O and RuO2 were 172 F g-1 and 13 F g-1, while the SAC was 7.4 mg g-1 and 4.0 mg g-1, respectively. This means that RuO2·0.5H2O shows 13.2 times higher capacitance and twice higher SAC. The results suggest that the increase in the specific capacitance by applying RuO2·0.5H2O might be attributed to the increase in the SAC value. On the other hand, the specific capacitance of RuO2·0.5H2O was higher than that of activated carbon, while the SAC of RuO2·0.5H2O was lower than that of activated carbon. There seems to be a difference in the effect of pseudocapacitance and electric double layer capacitance on the SAC value.This work was supported in part by the Japan Society for the Promotion of Science (JSPS) Grant-in-Aid for Challenging Research (Exploratory) Grant Number 17K19174. References K. Singh, S. Porada, H. D. de Gier, P. M. Biesheuvel and L. C. P. M. de Smet, Desalination, 455, 115 (2019).X. Ma, Y. Chen, K. Zhou, P. Wu and C. Hou, Electrochim. Acta, 295, 769 (2019).W. Sugimoto, H. Iwata, K. Yokoshima, Y. Murakami and Y. Takasu, J. Phys. Chem. B, 109, 7330 (2005). Figure 1

Creating electronic and ionic conductivity gradients for improving energy storage performance of ruthenium oxide electrodes

Robust Ru-based thin films are successfully fabricated by single- (SA) and multiple-annealing (MA) thermal decomposition methods and are utilized as high-performance electrodes for the supercapacitors. Two critical parameters, the annealing temperature and treatment duration, are engineered for synthesizing stable thin-film electrodes. It is found that the SA thermal decomposition technique at 250 °C for 6 h results in stable RuO2 electrodes with remarkable electrochemical performance. The MA approach consists of 2- and 3-stage thermal treatment steps. The maximal capacitance of MA-treated capacitor reaches as high as 308.8 F g−1. The MA-treated electrodes deliver exceptional rate capability as well as superior cycling stability (93% capacitance retention upon 2000 cycles). The enhanced performance is attributed to the multistep thermal stages along with the layer-by-layer deposition, enabling enhanced heat transfer to individual thin layers. An optimal thermal treatment procedure is assessed empowering enhanced capacitive performance due to high hydrous RuO2·xH2O ratio, reduced crystalline structure, facile electrolyte wetting, and stable adhesion between the deposits and the Ti substrate. The robust design of MA-treated thin film deposits paves the way for synthesizing high-performance electrodes for the supercapacitors.

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.

High-performance binder-free RuO2/electrospun carbon fiber for supercapacitor electrodes

Binder-free RuO2/carbon fiber composite electrodes were prepared by depositing RuO2 on electrospun carbon fibers using the incipient wetness impregnation method. The amount of RuO2 in the composites monotonically increased with the number of impregnation cycles. When the composite was thermally treated at 300 °C, RuO2 particles coalesced to form a wrinkle-like structure. Additionally, hydrous RuO2 partly converted to crystalline RuO2. We demonstrated that the relative contents of crystalline and hydrous RuO2 were closely related to the amount of RuO2 in the composite: the crystalline RuO2 content increased, whereas the hydrous RuO2 content decreased with an increase in the amount of RuO2 in the composite. When the composites were used as supercapacitor electrodes, the specific capacitance increased and then decreased with the amount of RuO2 in the composite. The maximum capacitance of 544 F/g in 2 M of H2SO4 at a scan rate of 2 mV/s was achieved with an RuO2 content of 12.23%; this was attributed to the favorable RuO2 content in the composite and the suitable amounts of hydrous/crystalline RuO2. When the amount of RuO2 in the composite was high, RuO2 caused fiber fracture during electrochemical reactions, resulting in poor electrode stability.

Hydrous ruthenium oxide-tantalum pentoxide thin film electrodes prepared by thermal decomposition for electrochemical capacitors

In this work, we have fabricated high-performance thin-film electrodes for electrochemical capacitors (ECs) via thermal decomposition syntheses of RuO2–Ta2O5 coating layers on Ti substrates. The influences of decomposition temperature as well as the Ru/Ta molar ratio on material and electrochemical properties of the EC electrodes are systematically investigated. The thermal decomposition of 300 °C preserves a large fraction of hydrous RuO2·xH2O within the hybrid oxide and consequently improves the electrode capacitance. The amorphous Ta2O5 incorporation can manipulate the RuO2 crystallinity and thus its specific capacitance. An optimal Ru/Ta molar ratio of 7:3 is determined for the RuO2–Ta2O5 electrode, which can deliver an energy density of 4.8 Wh kg−1 at a power density of 8720 W kg−1 (or 8.3 Wh L−1 at 15,000 W L−1). In addition, an excellent durability of 97.6% capacitance retention after 3000 charge-discharge cycles is found for this electrode. The proposed RuO2–Ta2O5 thin-film electrode has paved the way for next-generation ECs with superior capacitances, energy/power densities, and cyclability.

Electrochemical stability of RuO2(110)/Ru(0001) model electrodes in the oxygen and chlorine evolution reactions

RuO2 is commercially employed as an anodic catalyst in the chlor-alkali process. It is also one of the most active electrocatalysts for the oxidation of water, relevant to electrochemical water splitting. However, the use of RuO2 is limited by its low anodic stability under acidic conditions, especially at high overpotentials. In the present work, the electrochemical stability of model RuO2(110)/Ru(0001) anodes was investigated in order to gain a deeper understanding of the relation between structure and performance in Cl2 and O2 evolution reactions (CER and OER, respectively). Online electrochemical mass spectrometry was used to determine the onset potential of CER and OER in HCl and H2SO4 electrolytes, respectively. The onset potential of OER was higher in HCl than in H2SO4 due to competition with the kinetically more favorable CER. A detailed stability evaluation revealed pitting corrosion of the electrode surface with exposure of Ru(0001) metal substrate concomitant with the formation of a hydrous RuO2 in some areas regardless of the applied electrochemical treatment. However, despite local pitting, the RuO2(110) layer preserves its thickness in most areas. Degradation of the electrode was found to be less severe in 0.5 M HCl due to a decrease in the faradaic efficiency of RuO2 oxidation caused by competition with the kinetically more favorable CER.

Visualizing Potential‐Induced Pitting Corrosion of Ultrathin Single‐Crystalline IrO2(110) Films on RuO2(110)/Ru(0001) under Electrochemical Water Splitting Conditions

AbstractSophisticated IrO2(110)‐RuO2(110)/Ru(0001) model electrodes are employed in the oxygen evolution reaction (OER) under acidic conditions. The potential‐induced pitting corrosion of such electrodes is confirmed by a variety of experimental techniques, including scanning electron microscopy (SEM), time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS), and operando scanning flow cell‐inductively coupled plasma mass spectrometry (SFC‐ICP‐MS). The structure of the pits is reminiscent of a cylinder (evidenced by focused ion beam scanning electron microscopy: FIB‐SEM), where the inner surface of the pits is covered by hydrous RuO2 (cyclic voltammetry, ToF‐SIMS) that is formed by electrochemical oxidation of the metallic Ru(0001) substrate. The time evolution of the corrosion process at a fixed electrode potential (1.48 V vs. SHE) is followed via cyclic voltammetry and SEM. The passivating IrO2(110) layer results in an “induction period” for the pit growth that is followed by rapid corrosion of the RuO2(110)/Ru(0001) substrate. The observed narrow and time‐independent size distribution relative to the mean size of the pits is attributed to a sluggish removal of the corrosion products by diffusion across the cracks of the pits covering IrO2 layer, leading to steady state corrosion during a total polarization time of 20 to 60 minutes.

A ternary composite RuO2@SWCNT/graphene for high performance electrochemical capacitors

A hybrid nanostructure of hydrous RuO2 nanoparticles deposited on the surface of SWCNT/graphene (S/G) composite has been prepared through a sol-gel process and low-temperature annealing. Benefiting from the combined advantages of graphene, SWCNTs and hydrous RuO2, the hybrid electrode material (RuO2@S/G-60 of 58.53% RuO2 loading) has a high specific capacitance of 988 F/g at a current density of 1 A/g and excellent rate performance. The results show that S/G is very suitable as a carbon skeleton of hydrous RuO2.

Combustion-driven synthesis route for tunable TiO2/RuO2 hybrid composites as high-performance electrode materials for supercapacitors

Hybrids of micro/nanostructured metals/metal oxides have great potential to provide high performance in electrochemical applications such as supercapacitors. However, their synthesis routes involve complex procedures that limit scalable fabrication. Herein, we report a combustion-driven synthesis route for tunable TiO2/RuO2 hybrid composites as high-performance electrode materials for supercapacitors. Self-propagating combustion waves passing through precursors consisting of TiO2 nanoparticles and combustible nitrocellulose directly fabricated carbon templates as sacrificial layers for the outermost functional metal oxides, while the initial mass loading of nitrocellulose manipulated the residual hybrids. Through substituting the pre-formed carbon templates with RuO2, tunable TiO2/RuO2 hybrid composites of core–shell TiO2@RuO2 nanostructures or RuO2 clusters with embedded TiO2 nanoparticles were selectively obtained. The developed hybrids exhibited outstanding specific capacitances (~1200 F/g at 0.5 A/g) and capacitance retentions (~95.2% after 10,000 cycles) as supercapacitor electrodes, whereas the commercial RuO2-based electrode showed a lower specific capacitance (~600 F/g) and faster degradation of stability (~72%). An optimal thickness of hydrous RuO2 could facilitate inter-diffusion and proton transport for the high specific capacitances, while the amorphous nature of the outermost RuO2 and the inner TiO2 stability could provide robustness against the harsh stresses during charge–discharge cycles. This work can provide new strategies for the scalable fabrication of hybridized metal oxides such as core–shell nanostructures and nanoclusters, which would be useful for electrochemical devices, catalysts, and electromagnetic shielding.

Aqueous asymmetric supercapacitor based on RuO2-WO3 electrodes

Designing high-energy asymmetric supercapacitors(SC) with appropriate positive and negative electrodes is urgently required to expand their practical applicability. The redox-active materials are beneficial for high-energy SC applications because of their multiple oxidation states and higher energy storage capacity than the traditional carbon-based materials. In this work, for the first time, we have designed and developed high-energy aqueous asymmetric SC by combining hexagonal WO3 and hydrous RuO2 in a single cell. Initially, the hexagonal (h) WO3 and hydrous RuO2 is directly prepared on three-dimensional conducting carbon cloth. Because of their higher electrical conductivity, nanoporous surface morphology, and redox activity, the prepared hydrous RuO2 and WO3 exhibit excellent electrochemical features in the positive and negative potential window, respectively, with aqueous H2SO4 electrolyte. The assembled RuO2//h-WO3 asymmetric SC device exhibits outstanding electrochemical performance in an operating voltage window of 1.6 V, excellent cycling stability of ∼171.75% (after 6500 cycles), and energy density of 1.25 Wh/cm3 (16.92 W h/kg) at a power density of 40 W/cm3 (540 W/kg). These results show that redox-active materials can prominently enhance the energy storage capacity of SC than the traditional carbon-based asymmetric SCs.

Sol-Gel Synthesis of Ruthenium Oxide Nanowires To Enhance Methanol Oxidation in Supported Platinum Nanoparticle Catalysts.

A template-directed, sol–gel synthesis is utilized to produce crystalline RuO2 nanowires. Crystalline nanowires with a diameter of 128 ± 15 nm were synthesized after treating the nanowires at 600 °C in air. Analysis of these nanowires by X-ray powder diffraction revealed the major crystalline phase to be tetragonal RuO2 with a small quantity of metallic ruthenium present. Further analysis of the nanowire structures by high-resolution transmission electron microscopy reveals that they are polycrystalline and are composed of interconnected, highly crystalline, nanoparticles having an average size of ∼25 nm. Uniform 3 nm Pt nanoparticles were dispersed on the surface of RuO2 nanowires using an ambient, solution-based technique yielding a hybrid catalyst for methanol oxidation. Linear sweep voltammograms (LSVs) and chronoamperometry performed in the presence of methanol in an acidic electrolyte revealed a significant enhancement in the onset potential, mass activity, and long-term stability compared with analogous Pt nanoparticles supported on commercially available Vulcan XC-72R carbon nanoparticles. Formic acid oxidation LSVs and CO stripping voltammetry revealed that the RuO2-supported Pt nanoparticles exhibit significantly higher CO tolerance, which leads to higher catalytic stability over a period of several hours. X-ray photoelectron spectroscopy results suggest that crystalline RuO2 leads to less-significant oxidation of the Pt surface relative to more widely studied hydrous RuO2 supports, thereby increasing catalytic performance.

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.