Ruthenium Oxide Films Research Articles

An All-Solid-State Ti/RuOx pH Electrode Prepared Based on the Thermal Oxidation Method.

The development of all-solid-state precise pH electrodes holds significant importance in various fields, particularly in marine scientific research. To achieve this goal, we proposed a novel fabrication technique for an all-solid-state ruthenium oxide (Ti/RuOx) pH electrode. We thin-coated the RuCl3 precursor solution on a titanium wire substrate using a heat gun repeatedly and then calcined it in a mixture of Li2CO3 and Na2O2 at 400 °C to obtain a ruthenium oxide (RuOx) film. This RuOx film was subjected to acid treatment with dilute nitric acid, and a polytetrafluoroethylene heat shrink tube was wrapped around the non-RuOx film area. Finally, the RuOx film was fully immersed in a pH 4.00 buffer solution, finalizing the electrode preparation. The RuOx film exhibits a dense and regular conical morphology. The Ti/RuOx electrode demonstrates a good near-Nernstian response slope (e.g., -59.04 mV/pH at 25 °C), high linearity (e.g., R2 = 0.9999), rapid response (<1 s), low hysteresis (<3 mV), excellent reversibility, and good repeatability in the pH range of 2.00-10.00. After full hydration, the Ti/RuOx electrode shows a potential drift of 8.5 mV and a drift rate of approximately 0.27 mV/day over a period of 25 days, indicating good long-term stability. Furthermore, the Ti/RuOx electrode exhibits robust resistance against interference from various ions and low-concentration redox substances, ensuring a long storage life (at least 280 days), and high measurement accuracy (e.g., ± 0.02 pH units) for diverse water samples, including seawater, freshwater, and tap water. This study has evaluated the potential of the Ti/RuOx electrode as a reliable and accurate tool for pH measurements in marine scientific applications.

Effect of Precursors on the Electrochemical Properties of Mixed RuOx/MnOx Electrodes Prepared by Thermal Decomposition.

Growing thin layers of mixed-metal oxides on titanium supports allows for the preparation of versatile electrodes that can be used in many applications. In this work, electrodes coated with thin films of ruthenium (RuOx) and manganese oxide (MnOx) were fabricated via thermal decomposition of a precursor solution deposited on a titanium substrate by spin coating. In particular, we combined different Ru and Mn precursors, either organic or inorganic, and investigated their influence on the morphology and electrochemical properties of the materials. The tested salts were: Ruthenium(III) acetylacetonate (Ru(acac)3), Ruthenium(III) chloride (RuCl3·xH2O), Manganese(II) nitrate (Mn(NO3)2·4H2O), and Manganese(III) acetylacetonate (Mn(acac)3). After fabrication, the films were subjected to different characterization techniques, including scanning electron microscopy (SEM), polarization analysis, open-circuit potential (OCP) measurements, electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), cyclic voltammetry (CV), and galvanostatic charge-discharge (GCD) experiments. The results indicate that compared to the others, the combination of RuCl3 and Mn(acac) produces fewer compact films, which are more susceptible to corrosion, but have outstanding capacitive properties. In particular, this sample exhibits a capacitance of 8.3 mF cm-2 and a coulombic efficiency of higher than 90% in the entire range of investigated current densities.

Charge injection characteristics of sputtered ruthenium oxide electrodes for neural stimulation and recording.

We have studied the charge-injection characteristics and electrochemical impedance of sputtered ruthenium oxide (RuOx ) films as electrode coatings for neural stimulation and recording electrodes. RuOx films were deposited by reactive DC magnetron sputtering, using a combination of water vapor and oxygen gas as reactive plasma constituents. The cathodal charge storage capacity of planar RuOx electrodes was found to be 54.6 ± 9.5mC/cm2 (mean ± SD, n=12), and the charge-injection capacity in a 0.2-ms cathodal current pulse was found to be 7.1 ± 0.3mC/cm2 (mean ± SD, n=15) at 0.6V positive bias versus Ag|AgCl, in phosphate buffer saline at room temperature for ~250 nm thick films. In general, the RuOx films exhibited high charge-injection capacities, with or without a positive interpulse bias, comparable to sputtered iridium oxide (SIROF) coatings. The charge-injection capacity increased monotonically with film thickness from 120 to 630 nm, and reached 11.30 ± 0.34 mC/cm2 (mean ± SD, n=5) at 0.6V bias versus Ag|AgCl at 630 nm film thickness. In addition, RuOx films showed minimal changes in electrochemical characteristics over 1.5 billion cycles of constant current pulsing at a charge density of 408 μC/cm2 (8nC/phase, 200 μs pulse width). The findings of low-impedance, high charge-injection capacity, and long-term pulsing stability suggest the suitability of RuOx as a comparatively inexpensive and favorable choice of electrode material for neural stimulation and recording.

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.

Structural transformations and desirable electronic properties of low-temperature grown ruthenium oxide films under nitrogen atmosphere

Sr2RuO4 has recently attracted intense attentions for its intriguing physical properties. However, the ultra-high growth temperature (≥1000 °C) poses a major challenge for fabricating high-quality Sr2RuO4 films. In sharp contrast to effort previously attempted in traditional oxygen atmosphere, herein, a nitrogen gas is employed to grow ruthenium oxide films during pulsed laser depositions (PLD). It is shown that the present method facilitates a successive SrRuO3–Sr2RuO4 structural transformation via increasing growth temperatures from 700 °C to 900 °C. The high-quality Sr2RuO4 film grown at a relative low deposition temperature exhibits a comparable electrical resistivity, in comparison with counterparts deposited at oxygen atmosphere. Combined X-ray photoelectron and X-ray absorption measurements suggest that the nonreactive nitrogen atmosphere involved during the deposition yields a relative lower kinetic energy of laser ablated plume reaching to substrates, and effectively regulates structural and electronic properties of ruthenium oxide films. These findings may offer a new route for synthesizing other oxide functional films with high deposition-temperature.

Iridium and Ruthenium oxide miniature pH sensors: Long-term performance

The characteristics of electrodeposited Iridium oxide films (EIROF), and Ruthenium oxide films (RUOF) under normal and annealed conditions have been investigated. RUOFs were sputter deposited onto a substrate whilst EIROF sensors were made by electrodeposition. The adhesion of the RUOF sensors was investigated on Platinum and Titanium surfaces. The electrical impedance of the two metal oxides was measured in PBS demonstrating that both films have up to a 100 fold higher electrical double layer capacitance than bright Platinum electrodes. The EIROF films show super-Nernstian response, but the formal potential shows a continuous drift with time of approximately 2 mV day−1, measured over 40 days. Both RUOF sensors show approximately Nernstian behaviour. Short term pH precision of the annealed RUOF falls within a confidence interval of ± 0.1 pH, and stability is maintained within a confidence of ± 0.24 pH for up to 147 days. The un-annealed RUOF maintains the same precision but only for 20 days. Compared to EIROF sensors, no drift correction is required for the annealed RUOF making this metal oxide suitable for long term measurements where re-calibration is not possible.

A multi-parameter integrated chip system for water quality detection

Water pollution has always been an important issue threatening human health. Water quality monitoring is an important step to ensure water quality safety. Water quality parameters such as pH, temperature and conductivity are important indicators in water quality monitoring. In this paper, a multi-parameter water quality detection integrated chip system is studied, and multiple sensors are integrated on the same chip to realize the monitoring of conventional parameters such as pH, temperature and conductivity in drinking water. The chip system was processed by MEMS technology. A ruthenium oxide (RuO2) film is used for pH detection, and the sensor exhibits a super-Nernst response (62.88 mV/pH) in the range of pH 1.92–11.74. The patterned micro Pt film is used as the temperature sensor, and the three-wire orthogonal structure is used for temperature detection. The sensitivity of this temperature sensor is 5.517 [Formula: see text]/[Formula: see text]C in the range of 6 to 80[Formula: see text]C. Conductivity was measured by a four-electrode system, and the electrode constant was 1.667 cm[Formula: see text] measured between 0.994 and 21.167 mS/cm. The test results show that the multi-parameter integrated chip system can realize the simultaneous detection of pH, temperature and conductivity in water, and has the characteristics of miniaturization and low cost, and provides an effective way for simultaneous detection of water quality.

Electrophoretic displays driven by all‐oxide thin‐film transistor backplanes fabricated using a solution process

Precursor solutions and a solution process were developed for the fabrication of amorphous oxide thin‐film transistors (TFTs). All the layers of the TFTs comprised oxide films prepared from precursor solutions. The gate lines, gate insulator, and channel layer comprised ruthenium oxide, lanthanum zirconium oxide, and zirconium indium zinc oxide films. The polysilazane‐based silicon dioxide film was used for the channel stopper layer. The source‐line and drain electrode had a double‐layer structure comprising indium tin oxide and ruthenium oxide films. The silsesquioxane‐based silicon dioxide and ruthenium oxide films were used for the passivation layer and pixel electrodes, respectively. The TFTs exhibited a field effect mobility of 2.68 cm2 V−1 s−1, a sub‐threshold swing of 1.09 V/decade, a threshold voltage of 3.06 V, and an on/off ratio of 105. Active‐matrix electrophoretic displays (EPDs) with a resolution of 101.6 ppi were successfully fabricated using the all‐solution‐processed TFTs. Bi‐stable black/white images were confirmed in these TFT‐EPDs for the first time.

Solution processing of highly conductive ruthenium and ruthenium oxide thin films from ruthenium–amine complexes

Designing of ruthenium–amine complexes leads to preparation of highly conductive thin films of ruthenium (20–40 nm thick) and ruthenium oxide (50–90 nm thick) by a simple solution process.

An Investigation into the Oxygen Evolution Reaction at Manganese/ Manganese Ruthenium and Ruthenium Oxide Films in Base

Alkaline water electrolysis has been proposed as an environmentally inoffensive route to the production of the large volumes of hydrogen gas required by a possible hydrogen economy [1-5]. In practice, the efficiency of water electrolysis is limited by the large anodic over-potential of the oxygen evolution reaction (OER) [5]. Over the past thirty years, considerable research effort has been devoted to the design, synthesis and characterization of OER anode materials, with the aim of achieving useful rates of active oxygen evolution at the lowest possible over-potential, in order to optimize the overall electrolysis process. Currently, the optimal OER anode materials are Ruthenium and Iridium oxides, since these oxides exhibit the lowest overpotentials for the OER at practical current densities [6]. However, the high cost of these materials compared to other metals and their poor long term stability in alkaline solution renders their widespread commercial utilisation uneconomical [7]. For these reasons, the oxides of the first row transition metals (e.g. manganese, iron, cobalt and nickel) offer a compromise solution. Even though they are not as electrocatalytically active, their relatively low cost and long term corrosion resistance in alkaline solution makes them attractive OER anode materials [7-11].In the present work, we focus on the redox properties and electrocatalytic behaviour with respect to anodic oxygen evolution of manganese and ruthenium oxide electrodes prepared at different molar ratios in aqueous alkaline solution. These films can be prepared simply via thermal decomposition of a metal salt [12]. The structure and morphology of the thermally decomposed oxide materials are examined using thin film XRD, high resolution SEM and FTIR. The redox behavior of the resulting oxide films is investigated as a function of molar ratio and annealing temperature using cyclic voltammetry. The kinetics of the OER at these films has been studied using a range of electrochemical techniques including steady-state polarization and open circuit potential decay curves. In particular, Tafel slopes and reaction orders with respect to hydroxide ion activity are determined. Interestingly, the electrochemical performance for the films is strongly dependent on the molar ratio used, as evident from figure attached. Based on the available kinetic data, a reaction mechanism utilizing the active surfaquo group concept, is proposed. Turnover Frequency numbers are also obtained. Acknowledgements This publication has emanated in part from research conducted with the financial support of Science Foundation Ireland (SFI) under Grant Number SFI/10/IN.1/I2969.

The effects of sensing electrode thickness on ruthenium oxide thin-film pH sensor

A miniaturised pH sensor structure employing an R.F. sputtered ruthenium oxide sensing thin-film electrode in conjunction with an electroplated Ag/AgCl reference electrode is developed and the effect of the thickness of the sensing electrode on the measurement accuracy is investigated. Experimental results show that the pH sensor exhibits Nernstian slopes of 66.52mV/pH, 68.63mV/pH, 67.73mV/pH, and 54.83mV/pH for ruthenium oxide film thicknesses of 425, 300, 175 and 50nm, respectively. All the pH measurements were carried out at a temperature of 22°C. The performance and characterisation of the pH sensors in terms of sensitivity, response time, pH resolution, stability and reversibility are discussed.

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.

Low-Temperature All-Solution-Derived Amorphous Oxide Thin-Film Transistors

We prepared thin-film transistors (TFTs) in which all the layers were fabricated using simple chemical solution-processed, vacuum-free routes, followed by thermal annealing at 400°C. A ruthenium oxide film prepared via low-temperature processing was used for both gate and source/drain electrodes. Amorphous lanthanum-zirconium oxide and zirconium-indium-zinc oxide films were used as the gate insulator and channel layer, respectively, which enabled the fabrication of a TFT with the desired performance at a sufficiently low temperature. The ultraviolet-ozone treatment was adopted to channel layer to facilitate precursor decomposition and condensation processes. As a result, the obtained ON/OFF ratio, subthreshold swing voltage, and channel mobility were ~ 6×105, 250 mV/decade, and 5.80 cm2V1 s-1, respectively. This result contributes to the development of sustainable completely printed inorganic electronics.

Flexible ruthenium oxide-activated carbon cloth composites prepared by simple electrodeposition methods

This work focuses on the preparation of flexible ruthenium oxide containing activated carbon cloth by electrodeposition. Different electrodeposition methods have been used, including chronoamperometry, chronopotentiometry and cyclic voltammetry. The electrochemical properties of the obtained materials have been measured. The results show that the potentiostatic method allows preparing composites with higher specific capacitance than the pristine activated carbon cloth. The capacitance values measured by cyclic voltammetry at 10 mV s−1 and 1 V of potential window were up to 160 and 180 F g−1. This means an improvement of 82% and 100% with respect to the capacitance of the pristine activated carbon cloth. This excellent capacitance enhancement is attributed to the small particle size (4–5 nm) and the three-dimensional nanoporous network of the ruthenium oxide film which allows reaching very high degree of oxide utilization without blocking the pore structure of the activated carbon cloth. In addition, the electrodes maintain the mechanical properties of the carbon cloth and can be useful for flexible devices.

Reduction of RuO2 Film to Metallic Ru Film Using Atomic Layer Deposition under Different Oxygen Partial Pressure

Thin ruthenium oxide film deposition on 100 nm SiO2 substrate by thermal atomic layer deposition (ALD) prior to ruthenium deposition. RuO2 was totally reduced to metallic Ru film when Ru deposition process with low oxygen partial pressure. Using this technique, we can improve overall deposition speed by reducing incubation time which is major problem of deposition Ru film. In addition, we compare properties of Ru film deposited by thermal ALD directly deposited on SiO2 substrate and Ru film obtained from reduction of RuO2 film. The Ru film from RuO2 has smoother surface RMS roughness than Ru film directly deposited on SiO2 substrate.

Low Temperature CO Oxidation on Ruthenium Oxide Thin Films at Near-Atmospheric Pressures

Ruthenium model catalysts in the form of thin ruthenium oxide films grown on Ru(0001) were studied in the CO oxidation reaction at near-atmospheric pressures. The surfaces were prepared under vacuum conditions prior to the reactivity measurements carried out in a circulating flow reactor using gas chromatography. The films possessing oxygen in amounts equivalent to 1–4 monolayers (MLE) on Ru(0001) as determined by electron spectroscopy, exposed both the oxidic (RuO2(110)-like) and O/Ru(0001) surfaces. In addition, one-dimensional oxide structures were observed by scanning tunneling microscopy, which are tentatively assigned to the intermediate state for a crystalline ruthenium oxide thin film that covered the entire surface at higher oxygen coverages. At low temperatures studied (400–470 K), the reaction sets in only in the presence of oxidic structures, i.e. when the oxygen coverage, on average, exceeds 1 MLE. The reaction rate slightly increases with increasing the nominal film thickness up to 7 MLE, reflecting primarily the lateral growth of oxide phases. The disordered oxide films showed even higher reactivity. The results suggest that surface ordering and oxide film thickness are not critical for the superior catalytic activity of ruthenium oxides in this reaction.

Supercapacitive performance of hydrous ruthenium oxide (RuO2·nH2O) thin films deposited by SILAR method

The amorphous hydrous ruthenium oxide (RuO2·nH2O) thin films were deposited by a simple and inexpensive successive ionic layer adsorption and reaction (SILAR) method. These films were characterized for their structural, surface morphological, and compositional study by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDAX) techniques. The wettability test was carried out by measuring the water contact angle. The scanning electron microscopy study showed small RuO2 particles are grouped together to form porous agglomerates. The FT-IR study confirmed the formation of hydrous ruthenium oxide films. The hydrophilic nature of ruthenium oxide (RuO2·nH2O) thin films was observed from water contact angle measurement. The presence of Ru and O in the film was confirmed by EDAX analysis. The supercapacitor behavior of these films studied in 0.5 M H2SO4 electrolyte showed maximum specific capacitance of 162 F g−1 at 10 mV s−1 scan rate. These films exhibit 80% cycling performance after 2,000 cycles. The charge–discharge studies carried at 1 mA cm−2 current density revealed the specific power of 3.5 KW kg−1 and specific energy of 29.7 W Kg−1 with 93% coulombic efficiency.

In situ ultraviolet photoemission spectroscopy measurement of the pentacene-RuO2/Ti contact energy structure

In situ ultraviolet photoemission spectroscopy was used during the pentacene layer growth on ruthenium and ruthenium oxide films to measure the energy barrier in the metal-semiconductor contact. The measurement showed that ruthenium oxide film formed lower hole-injection barrier with pentacene than ruthenium or gold metal film due to its high work function of 4.92 eV and low resistivity of ∼350 μΩ cm. Pentacene thin film transistor with ruthenium oxide electrode showed higher mobility of 0.435 cm2/V s and on-off ratio of 106 than ruthenium (μ: 0.205 cm2/V s, on/off ratio: 106) or gold electrode (μ: 0.338 cm2/V s, on/off ratio: 106) of the same structure.

Multiwalled Carbon Nanotubes Encased in Ruthenium Oxide Film as a Hybrid Material for Neurotransmitters Sensor

AbstractA hybrid film (MWCNTs‐RuOx⋅nH2O) which contains multiwalled carbon nanotubes (MWCNTs) along with the incorporation of ruthenium oxide (RuOx⋅nH2O) has been synthesized on glassy carbon electrode (GCE), gold (Au), indium tin oxide (ITO) and screen printed carbon electrode (SPCE) by potentiostatic methods. The presence of MWCNTs in the hybrid film enhances surface coverage concentration (Γ) of RuOx⋅nH2O to ≈2100%. The surface morphology of the hybrid film deposited on ITO has been studied using scanning electron microscopy and atomic force microscopy. These two techniques reveal that the RuOx⋅nH2O incorporated on MWCNTs. Electrochemical quartz crystal microbalance study too reveals the incorporation of MWCNTs and RuOx⋅nH2O. The MWCNTs‐RuOx⋅nH2O hybrid film exhibits promising enhanced electrocatalytic activity towards the biochemical compounds such as epinephrine and norepinephrine. The electrocatalytic responses of these analytes at RuOx⋅nH2O, MWCNTs and MWCNTs‐RuOx⋅nH2O hybrid films have been measured using cyclic voltammetry. The obtained sensitivity values from electrocatalysis studies of analytes for MWCNTs‐RuOx⋅nH2O hybrid film are higher than the RuOx⋅nH2O and MWCNTs films. Finally, the flow injection analysis has been used for the amperometric studies of analytes at MWCNTs‐RuOx⋅nH2O hybrid film modified SPCEs.

The growth mechanism and supercapacitor study of anodically deposited amorphous ruthenium oxide films

In the present study, ruthenium oxide (RuO 2) thin films were deposited on the stainless steel (s.s.) substrates by anodic deposition. The nucleation and growth mechanism of electrodeposited RuO 2 film has been studied by cyclic voltammetry (CV) and chronoamperometry (CA). The deposited films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive analysis by X-rays (EDAX) for structural, morphological, and compositional studies. The electrochemical supercapacitor study of ruthenium oxide thin films have been carried out for different film thicknesses in 0.5 M H 2SO 4 electrolyte. The highest specific capacitance was found to be 1190 F/g for 0.376 mg/cm 2 film thickness.