Ruthenium Dioxide Electrodes Research Articles

Protic Ionic Liquid Electrolytes to Increase Areal Energy Density of RuO2 Micro-Supercapacitors

The rising growth of smart and autonomous microelectronic devices in the IoT (Internet of Things) era urges the development of advanced microscale energy sources with tailor-made features and customized energy/power requirements [1]. Micro-supercapacitors (MSCs) emerged as potential energy storage devices complementing micro-batteries to power ubiquitous sensor networks needed to foster the development of IoT. However, the low cell voltage and low energy density remain major bottleneck that prevents their application at a large scale in real devices. To mitigate this issue, several studies have been devoted to the engineering of MSC electrode materials and structural architecting of current collectors to enhance the surface area and areal energy density by considering the limited available footprint area [2]. This approach however has associated challenges such as complex synthesis route, the deleterious interfacial and mechanical stability of the electrode, and compatibility issues with the electrolyte and the current collector underneath [3]. Another important challenge to solve for reaching high energy density values in MSCs is the limited electrochemical stability window (ESW) of the electrolytes used as energy stored is directly related to the square of the cell voltage [4]. The electrolytes play a major role in deciding the ESW and liquid-state electrolytes currently employed are troublesome for the microfabrication process due to leakage, evaporation, and safety issues. Therefore, it’s imperative to develop alternative electrolytes including solid-state electrolytes reconcilable to the target application of MSCs. To address the low energy density challenge of current MSCs, we have developed interdigitated MSCs using hydrous ruthenium dioxide (RuO2) electrodes in combination with novel protic ionic liquid (PIL)-based electrolytes able to provide pseudocapacitance while affording a higher ESWs as compared to conventional aqueous electrolytes. As a state-of-the-art pseudocapacitive electrode material, RuO2 owns the key merits of excellent conductivity, high electrochemical reversibility, and cycling stability [5], whereas PILs could help alleviate issues facing currently used electrolytes such as evaporation and encapsulation problems pertaining to aqueous-based and flammability of common organic electrolytes [6], [7], [8]. In the next step, the slow proton transport kinetics of PILs were addressed by the doping of silicotungstic acid (SiWa, H4SiW12O40) with the PIL, which further boosted the pseudocapacitive current response with enlarged cell voltage. The real MSC device was realized by the use of RuO2 deposited on interdigitated porous Au current collectors having a high area enlargement factor (AEF) in combination with triethylammonium bis(trifluoromethanesulfonyl)imide (TEAH-TFSI)-based PIL. The resultant 3D MSC rendered a cell voltage exceeding 2V with areal capacitance as high as 86 mF cm-2 at 5 mV s-1 on par with the performance of 3D MSC tested using 0.5 M H2SO4 (cell voltage of 0.9 V and areal capacitance of 85 mF cm-2 at 5 mV s-1) but higher energy density performance (more than 4 times) using similar number of RuO2 deposition cycles. To demonstrate the potential integration in real on-chip device application, ionogel-based all-solid-state MSC is developed that showed performance comparable to liquid-state electrolyte with superior long-term cycling stability. This study gives a new perspective to develop all-solid-state micro-supercapacitors using pseudocapacitive active materials that can operate in ionic-liquid-based non-aqueous electrolytes compatible with on-chip IoT-based device applications seeking high areal energy/ power performance.

Record-high solar-to-hydrogen conversion efficiency based on a monolithic all-silicon triple-junction IBC solar cell

We present a record-high solar-to-hydrogen conversion efficiency (STH) for monolithic all-silicon multi-junction solar devices. The device is based on an interdigitated back-contact silicon solar cell, in which the p- and n-regions are connected in a combination of series and parallel contacts, in order to triple the photovoltage compared to a single-junction cell. Our best device provides an open-circuit voltage of 1.99 V, larger than the water redox potential of 1.23 V plus overpotentials at the electrodes, as well as a short-circuit current density of 12.6 mA/cm2. Coupled to a sulphuric acid electrolysis system, with platinum and ruthenium dioxide electrodes, our device shows an STH of 14.5% at 1.63 V.

Electrochemical Oxidation of the Paracetamol in its Commercial Formulation on Platinum and Ruthenium Dioxide Electrodes

Electrochemical Oxidation of the Paracetamol in its Commercial Formulation on Platinum and Ruthenium Dioxide Electrodes

Electrochemical Oxidation of Amoxicillin in Its Commercial Formulation on Thermally Prepared RuO2/Ti

In this work, a ruthenium dioxide electrode has been prepared by thermal decomposition at 400 C then used for the oxidation of commercial amoxicillin. The physical characterization showed that RuO2 electrode presents a mud cracked structure. Its electrochemical characterization has revealed an increase of the voltammetric charge in acid electrolyte compared to neutral electrolyte indicating the importance of protons in its surface redox processes. The voltammetric study of the oxidation of amoxicillin has been investigated. It has been obtained that the oxidation of amoxicillin is controlled by both adsorption and diffusion processes. Moreover, the oxidation of amoxicillin occurs via direct and indirect processes in free or electrolyte containing chlorides. Through preparative electrolysis, enhancement of amoxicillin oxidation was observed in the presence of chloride where the amoxicillin degradation yield reached more than 50 % compared to less than 5 % in the absence of chlorides. Spectrophotometric investigations have revealed the degradation of intermediates absorbing at 350 nm.

Fabrication of Potentiometric Enzymatic Glucose Biosensor Based on Graphene and Magnetic Beads

In this paper, ruthenium dioxide (RuO2) electrodes were fabricated by radio frequency sputtering and screen-printed technique, and RuO2 sensing films could be as pH sensor to measure different pH solutions. The average sensitivity and linearity of pH sensor were 51.847 mV/pH and 0.987, respectively. A glucose biosensor could be prepared through casting glucose oxidase (GOx) on RuO2 electrode, so the flexible arrayed glucose biosensors modified by magnetic beads (MBs) and graphene (GR) were developed in this paper. In preparation processes, GR solution was first cast on the RuO2, then we introduced carbodiimide hydrochloride (EDC) to connect glucose oxidase (GOx) and MB by covalent bond. Finally, MBs-GOx-nafion composite was dropped on RuO2 to complete preparation of the RuO2/GR/MB-GOx-Nafion glucose biosensor. The electrochemical impedance spectra (EIS) was used to investigate the capability of electron transfer of the different electrodes, and it was found that the additions of MBs and GR which had excellent electric conductivity could decrease the electron transfer resistance ( $R_{\rm ct}$ ) from the experiment results. Besides, EIS could also be used to demonstrate whether the glucose biosensors had already been completely modified by MBs and GR through the different resistances of the biosensors. Furthermore, the glucose biosensor modified by MBs and GR had the superior performance, the average sensitivity and linearity of RuO2/GR/MB-GOx-Nafion glucose biosensor were 10.628 mV/mM and 0.998, respectively. After 28 days, RuO2/GR/MB-GOx-Nafion glucose biosensor still had relative sensitivity of 82.2%.

Electrochemistry of ruthenium dioxide composite electrodes in diethylmethylammonium-triflate protic ionic liquid and its mixtures with acetonitrile

Ruthenium dioxide electrodes store charge via faradaic reactions involving proton exchange with the electrolyte, thereby achieving very high specific capacitance values that make it a very interesting material for electrochemical capacitors. We demonstrated earlier that these faradaic reactions occur for RuO2 in non-aqueous electrolytes based on protic ionic liquids, but the specific capacitance were limited due to the high degree of crystallinity of the material prepared in thin films by thermal decomposition. In order to increase the specific capacitance and to evaluate the impact of proton transport and transfer in high load electrodes, RuO2 was prepared by a conventional sol-gel route and used as the active material in a composite electrode to evaluate its electrochemical response in the protic ionic liquid diethymethylammonium-trifluoromethanesulfonate (DEMA-TfO). Cyclic voltammetry was carried out in the pure DEMA-TfO as well as in mixtures of the ionic liquid with acetonitrile. The results showed a significant impact of the electrolyte viscosity and conductivity at high potential scan rates and a limitation of the proton transfer rate at low scan rates. The specific capacitance can be improved at low scan rates by increasing temperature, reaching a value of 338 F/g at 120°C with a 2 mV/s scan rate. This value is by far the highest reported for RuO2 in a non-aqeuous electrolyte.

Study on Mechanism of Removing the Organic Matter in Heavy Oil Sewage by the Electric Flocculation Method

Oily sewage is one of the wastes produced in the oil industry production process and its quantity has been increasing year by year, which influences the environment and human health severely. Electric flocculation method is one of the wide application electrochemical treatment technologies for the oily wastewater treatment at home and abroad, which has higher efficiency than other technologies at the aspect of the organic pollutants degradation. A simulative experiment device dealing with heavy oil sewage by the electric flocculation method has been designed in this paper. The mechanism of the electric flocculation method in removing organic matter of the heavy oil sewage by analyzing the change of the composition and content of the organic matter in water samples before and after the process of the electric flocculation has been studied. Research results show: the carbon/tin dioxide electrode is better than the carbon/ ruthenium dioxide electrode in removing organic matter; most alkanes matters in the oily wastewater have been removed in the dispersing oil form by the electric flocculation; as the current density increases, the types and quantity of the response organic matter can be improved while types of the new synthetic organics increase. At the same time, this paper provides a theory support in specific optimization of the electricity flocculation flotation in oily wastewater treatment technology and process.

Analysis of a Model for an Electrochemical Capacitor

An isothermal model for an electrochemical capacitor is presented, analyzed and discussed. In essence, the model accounts for the transient conservation of species and charge in the solid and the electrolyte phase; two main length scales are considered: one corresponding to the entire cell (macroscale) and the other for the active material in the porous electrodes (microscale). Based on an electrochemical capacitor with Ruthenium dioxide electrodes, a scaling analysis is carried out after calibration and validation with experiments, for which good agreement is found. The analysis allows us to not only secure the relevant scales and nondimensional numbers characterizing an electrochemical capacitor, but also to identify limits at which the model can be reduced to a one-dimensional counterpart on the macroscale. Furthermore, a quasi-steady state can be achieved under certain conditions at the microscale, which leads to the elimination of the radial coordinate from the system of governing equations. These findings, in turn, lead to reduced model formulations that are computationally efficient and promising for inclusion in detailed stack models. The latter is explored by emulating stacks of ten and hundred cells. Finally, the inclusion of the equation of change for energy and heat generation is discussed.

RF magnetron-sputtering deposition of pyroelectric lithium tantalate thin films on ruthenium dioxide

Lithium tantalate (LiTaO 3) thin films were deposited on ruthenium dioxide (RuO 2) electrode by reactive radio frequency (RF) magnetron sputtering with a lithium dioxide–tantalum pentoxide (Li 2O 2/Ta 2O 5) (50–50% mole ratio) target. This article presents morphological, structural, dielectric and pyroelectric studies of LiTaO 3 thin films as function of growth conditions (RF power, gas pressure and temperature). The final aim is to improve the pyroelectric coefficient for thermal detectors applications. The best pyroelectric coefficient of LiTaO 3 thin films (400 nm) equal to 60 μC/m 2 K was obtained for a growth temperature of 400 °C, and a pressure of 10 mTorr.

Development of ruthenium dioxide electrodes for pyroelectric devices based on lithium tantalate thin films

The aim of this paper is the study of ruthenium dioxide (RuO 2) films, grown on low-stress silicon nitride on silicon (SiN x /Si), in order to develop thermal micro-sensors based on pyroelectric effect. The active part of these micro-sensors is constituted by a new arrangement : lithium tantalate (LiTaO 3)/RuO 2/SiN x/Si. Radio-frequency (RF) sputtering is employed to deposit RuO 2 on SiN x /Si substrate. Morphology, crystallinity and resistivity of RuO 2 are studied as function of growth parameters. Next, RF magnetron sputtering was used to deposit LiTaO 3 on this electrode. Morphology studies, pyroelectric effect and dielectric parameters obtained, indicate that RuO 2 material is a suitable candidate as back electrode for LiTaO 3 thin films.

Pseudocapacitive behaviour of RuO 2 in a proton exchange ionic liquid

We studied the electrochemical behaviour of a thermally-prepared RuO 2 electrode in a protic ionic liquid made from 2-methylpyridine and trifluoroacetic acid to determine if the current obtained on such electrode originates from double-layer charging or from pseudocapacitance. A thorough comparison of the electrochemical behavior in the ionic liquid and in aqueous electrolyte confirmed that pseudocapacitance is observed. The shape of the cyclic voltammograms obtained for the RuO 2 electrode in the protic ionic liquid is similar to that obtained in H 2SO 4 and shows distinct redox peaks attributed to Faradaic reactions across the electrolyte∣electrode interface, which give rise to pseudocapacitance. The specific capacitance of the electrode in the protic ionic liquid (83 F g −1) is in the same order of magnitude to that obtained in water-based electrolyte but is ten times higher than that in an aprotic ionic liquid composed of 1-ethyl-3-methylimidazolium tetrafluoroborate. Our observations lead to the conclusion that pseudocapacitance can occur on a ruthenium dioxide electrode in an ionic liquid. Our results could be of interest to develop new metal oxide electrochemical capacitors based on non-aqueous electrolytes.

In situ Ru K-edge X-ray absorption spectroscopy of a high-area ruthenium dioxide electrode in a Nafion-based supercapacitor environment

Changes in the state of charge of a high-area RuOx electrode in an operating RuOx|Nafion|IrOx supercapacitor were monitored in situ by time-resolved, transmission Ru K-edge X-ray absorption spectroscopy (XAS). Linear and reversible variations in the intensity of the transmitted X-ray beam as a function of time were found by fixing the energy of the incident X-ray beam, Ei, at judiciously selected values within the Ru K-edge X-ray near edge structure (XANES), while the supercapacitor was charged and discharged at constant current. The sign of the slope of these temporal signals was found to vary, depending on the value of Ei. This behavior could be rationalized based on the spectral differences between the Ru K-edge XANES of RuOx in the fully oxidized and fully reduced states, recorded in situ from films of the material electrodeposited on a gold substrate in the fluorescence mode.

Platinum, Ruthenium and Ruthenium Dioxide Electrodes Deposited by Metal Organic Chemical Vapor Deposition for Oxide Applications

Platinum (Pt), ruthenium (Ru), and ruthenium dioxide (RuO 2 ) have been considered as possible candidates as electrodes for high permittivity and ferroelectric oxides. The films were grown by metal organic chemical vapor deposition (MOCVD). High purity Pt films with near bulk resistivities (11 w z cm) were deposited. The Pt, Ru and RuO 2 films were found to be continuous and smooth and exhibited excellent adhesion properties on the underlying substrates. The temperature dependent electrical conductivity of the Ru and RuO 2 films was metallic type. Room temperature resistivities as low as 18 and 30 w z cm were determined for Ru and RuO 2 , respectively.

Effect of RuO2 electrode on polarization fatigue resistance of PbZr0.52Ti0.48O3 thin films

Sol-gel derived lead zirconate titanate (PbZr0.52Ti0.48O3, PZT) films of thickness 300 nm were deposited on RuO2/SiO2/Si and Pt/Ti/SiO2/Si substrates. Either a ruthenium dioxide (RuO2) or platinum (Pt) top electrode was deposited on each film. The ferroelectric properties and the fatigue and current characteristics of the films were investigated. The film has a higher fatigue resistance but also a higher leakage current when one or both of the electrodes are made of RuO2. The RuO2/PZT/RuO2 film exhibits negligible polarization fatigue, while the polarization of the RuO2/PZT/Pt and Pt/PZT/RuO2 films decreases by about 40% after 109 switchings. This suggests that the polarization fatigue in the PZT films is controlled not only by the top RuO2/PZT interface but also by the bottom PZT/RuO2 interface.

Studies of electrochemical behaviour of RuO 2 -PVC film electrodes: dependence on oxide preparation temperature

Ruthenium dioxide electrodes, prepared on a Pt substrate using coatings of PVC-RuO2 mixed in THF (designated as RuO2-PVC film electrode) have been studied for their redox behaviour in 1 M NaOH using variable scan cyclic voltammetry. The various redox transitions in the oxidation state of the central metal ion are characterized using electrochemical parameters such as peak potential, peak current, and surface charge. The effect of oxide preparation temperature, in the range 300–700 °C, on the redox characteristics has also been studied and correlated with the electrochemically active surface area (as measured using small amplitude cyclic voltammetry) and the true surface area (by the BET method).

Amperometric determination of ascorbic acid on screen-printing ruthenium dioxide electrode

Ruthenium oxide (RuO 2) is commonly used in resistive pastes for screen printing. The electrochemical properties of a screen-printing planar RuO 2 electrode have hardly been studied. In this communication, planar electrochemical sensors with a RuO 2 working electrode, an Ag|AgCl reference electrode and a RuO 2 counter electrode are fabricated by screen printing. The electro-oxidation of ascorbic acid, uric acid, and hydrogen peroxide on these RuO 2 electrodes is investigated by means of cyclic voltammetry. Compared to uric acid and hydrogen peroxide, ascorbic acid can be easily oxidized at the low operating potential (<150 mV versus Ag|AgCl). The amperometric measurement of ascorbic acid at 100 mV on a RuO 2 electrode shows fast response and good linearity in the 0–4 mM range. Meanwhile, the electrochemical interference from uric acid and hydrogen peroxide at this potential is very small.

Screen-printed ruthenium dioxide electrodes for pH measurements

Plastic, fully screen-printed, disposable pH sensors based on ruthenium dioxide are described. Application of thick-film technology results in highly reproducible fabrication of the sensors. The electrodes enable fast measurements, with good sensitivity (51 mV/pH), in acidic and neutral solutions (linear range of response up to pH = 8). No interferences from alkaline cations, commonly accompanying anions and complexing ligands were observed. The pH measurements were strongly affected by reducing substances. Some potential analytical applications of the sensors are pointed.

Anomalous low-temperature kinetic effects for oxygen evolution on ruthenium dioxide and platinum electrodes

presumably does not vary with temperature unless a change in mechanism occurs. The possibility to investigate electro- chemical reactions in a wide temperature range using the FREECE technique was demonstrated in a series of papers.&1° This implies performing measurements in an electrolyte of stoichiometric composition, e.g. HC10~5.5H20, in its liquid and frozen state. It is the aim of this work to investigate oxygen evolution kinetics on RuO2 and Pt electrodes as a function of temperature in HClOq5.5H20.

The oxidation of chloride ions and bromide ions on ruthenium dioxide electrodes

The oxidation of solutions containing chloride ions at ruthenium dioxide/titanium dioxide electrodes has been investigated using steady state current-potential and impedance-potential measurements as a function of the chloride ion concentration. At the higher chloride ion concentrations, greater than 0.1 M, a 40 mV Tafel slope is observed at low potentials which increases at the higher potentials. As has now been observed by other workers, the 40 mV Tafel slope is associated with a first order dependence on chloride ion concentration. At lower concentrations of chloride ion, 0.1 M for example, where the oxygen evolution reaction becomes significant, the Tafel slope for the chlorine evolution reaction seems to increase to 70 mV, when the oxygen reaction, measured in the absence of the chloride ions, is taken into account. It is suggested that interaction between the chlorine evolution and the oxygen evolution reactions occurs via a surface intermediate. If this is the case chlorine and oxygen evolution will always occur together, and the proportion of each in the product will depend on the rate constants for the appropriate electron transfer reaction. In this work the double layer capacity-potential curves are used to identify the potential region where the chlorine evolution reaction is behaving simply. A contribution to the capacity in addition to the background is observed which can be understood qualitatively in terms of the theory for a metal electrode. Similar measurements have been made for the oxidation of bromide ions on ruthenium dioxide electrodes, and there seem to be similarities in the mechanisms of the chloride and bromide oxidation reactions.

The direct electrochemistry of redox proteins at metal oxide electrodes

The dc cyclic voltammetry of several redox proteins at thin film ruthenium dioxide electrodes is described. Quasi-reversible voltammetric responses were obtained for cytochrome c, azurin, ferredoxin, rubredoxin and plastocyanin at this electrode with solution conditions, pH 8.0 (5 m M Tricine) and 100 m M NaCl as supporting electrolyte. The values of E 1/2 are in good agreement with those in the literature. On varying the pH and solution ionic strength striking differences in response emerge. For the negatively charged proteins, ferredoxin, rubredoxin and plastocyanin, no measurable faradaic response is observed at lower ionic strength (pH 8.0, 1 m M N2Cl). The electrochemistry can, however, be promoted by multivalent cations (Cr(NH 3) 3+ 6 or Mg 2+) giving rise to a well-defined quasi-reversible response. For cytochrome c, variation of the dc cyclic voltammetric response with pH correlates with the (acid-base) protonation properties of the electrode surface. The electrochemistry of azurin does not vary appreciably with changes of pH or ionic strength. The results found highlight the importance of electrostatics at the electrode/solution interface. Preliminary results using IrO 2, Na 0.7WO 3 and single-crystal RuO 2 electrodes are reported. Subtle differences in behaviour are found at the single-crystal and thin-film RuO 2 electrodes.