Mixed Oxide Electrodes Research Articles

Electrochemical characterization of Li xNi yCo 1− yO 2 electrodes in a 1 M LiPF 6 solution of the ethylene carbonate–diethyl carbonate

The electrochemical characteristics of Li x Ni y Co 1− y O 2 (0.5< y<0.9) prepared by a co-precipitation method were reported. Slow scan cyclic voltammetry (SSCV) and electrochemical impedance spectroscopy (EIS) were used to investigate the kinetic behavior of the composite electrodes. Kinetic data such as the Tafel slope and the charge-transfer resistance were determined based on the experimental results. An equivalent circuit model was proposed to simulate the impedance spectra and gave a good data fit. The present study also demonstrated that the kinetic data were composition-sensitive to varying lithium content and nickel content in the mixed oxide electrodes.

Peculiarity of NO Decomposition by Electrochemical Cell with a Mixed Oxide Working Electrode

The decomposition activity was measured on nonsymmetric electrochemical cell oxide (cathode) yttria-stabilized zirconia (YSZ) (anode) by applying dc voltage lower then 3.5 V in the temperature range from 550 to 700°C. It was found that covering the Pt cathode by a mixture of oxygen ionic conductor (YSZ) and electronic conductor (NiO) increased the NO decomposition even in the presence of excess oxygen. The microstructure of YSZ-NiO mixed oxide electrodes was investigated depending on the mixed oxide electrode sintering temperature. A strong correlation between the microstructure of the mixed oxide electrode and the conversion rate of NO decomposition was observed and investigated. A mechanism for the NO decomposition is proposed and discussed. © 2001 The Electrochemical Society. All rights reserved.

Electrochemical cell with two layers cathode for NO decomposition

An electrochemical cell composed of an yttria-stabilized zirconia disk and two layers cathode was used for nitrogen monoxide decomposition. It was found that covering the Pt cathode by a mixture of oxygen ionic conductor (YSZ) and electronic conductor (NiO) leads to enhancement of the performance of the electrochemical cell for NOx decomposition in the presence of excess oxygen. The decomposition activity was measured for the one-compartment cell oxide|(cathode)|YSZ|(anode) by applying a DC voltage lower than 3.7 V in the temperature range 550–700 °C. The microstructure of the YSZ-NiO mixed oxide electrodes was investigated in dependence of the cell operating condition and the working electrode sintering temperature. The correlation between the microstructure of the mixed oxide electrode and conversion rate of NO was studied. The phenomenon of self-optimization of the microstructure of the NiO-YSZ working electrode during the cell operation was observed and investigated.

Study on the electro-activity and non-stochiometry of a Ru-based mixed oxide electrode

Catalytic oxide electrodes of Ru/Ti, RuSn/Ti, and RuSnTi/Ti effective in destroying refractory organics in aqueous waste were studied in terms of material and electrochemical properties. The portion of non-stochiometry, RuO x (0< x<2) and chloride-bonded Ru within the Ru-based oxide were evaluated by deconvolution of XPS of the oxide with a change of sintering temperature. RuO x mostly existed around 450°C, and disappeared at 600°C. The component of chloride-bonded Ru decreased nearly linearly from 350 to 600°C. The non-stochiometry resulted from the incomplete decomposition of metal chloride in the precursor solution. The existence of non-stochiometry was confirmed to have a close relation to the electrochemical activity of the oxide electrode. The segregation phenomena of Sn and the existence of chloride in RuSnTi/Ti oxide after sintering were confirmed by AES, XPS, and EPMA.

Surface chemistry of RuO(2)/IrO(2)/TiO(2) mixed-oxide electrodes: secondary ion mass spectrometric study of the changes induced by electrochemical treatment.

The IrO(2)/RuO(2)/TiO(2) ternary system is well known for its electrocatalytic activity towards oxygen- and chlorine-evolution reactions. Electrochemical processing induces noticeable chemical and morphological modifications on these electrodes, depending on the noble metal oxide content. In this work, cathodic/anodic polarization and the oxygen-evolution reaction were studied in order to evaluate the electrocatalytic activity at various noble metal oxide percentages. The best performing electrode (30 mol% noble metal oxides) was analyzed before and after electrochemical tests by means of secondary ion mass spectrometry (SIMS) in order to determine the chemical composition modification which occurred on the surface and in deeper regions of the mixed-oxide film.

Influence of the Additives and the Process Parameters on the Electrocatalytic Activity of Ruthenium Based Mixed Oxide Electrodes

SUMMARYTi-supported electrodes of nominal composition (Ru-αM)O2/Ti (α = 0,0,3,0,5,0,7; M is Sn, Al, V, Ce. Nb. Y) have been investigated for the optimisation of chlorine evolution. The results showed that the composition of the catalytic coating, the ratio between its contents of conducting and inert oxides, and the preparation parameters strongly influenced the electrocatalytic activity of the electrodes. SnO2, Al2O3 or VO2, respectively, combined with RuO2, provided a good electrocatalytic activity when these electrodes were heat-treated in appropriate environments. In particular, when the electrodes (Ru-0.7V)O2/Ti were thermally decomposed in argon, the catalytic activity was increased by 30% compared with decomposition in oxygen, and 100% compared with in air.

The study of the electrooxidation of chloride at RuO 2/TiO 2 electrode using CV and radiotracer techniques and evaluating by electrochemical kinetic simulation methods

The mechanism of the chloride electrooxidation was investigated by CV and radiotracer techniques, as well as PC simulation methods on RuO 2/TiO 2 mixed oxide electrodes. The voltammetric behavior of an adsorbed intermediate was studied. Both the experimental and simulation results show that the electrooxidation of chloride is going through the steps of the Volmer–Heyrovsky mechanism on this working electrode.

Structural, morphological and surface properties as a function of composition of Ru+Ti+Pt mixed-oxide electrodes

Abstract A systematic investigation of the structural, morphological and surface properties of thermally prepared Ru0.3Ti(0.7−x)PtxO2 (0⩽x⩽0.7) electrodes was conducted by ex situ (SEM, EDX, XPS) and in situ (voltammetry and open circuit potential) techniques. Significant changes were observed on substituting TiO2 for PtOx. The electrochemical surface area increased dramatically (∽10 times) reaching a maximum at 40% PtOx (nominal). Ru surface enrichment was observed while Pt+Ru segregates as rectangular crystals from the coatings. At the higher Pt-contents, surface electrochemistry is mainly dominated by Pt solid-state transitions, especially after continuous potential cycling (0.4–1.4 V vs r.h.e.). Pt-containing coatings were revealed to be unstable (erosion) when the cathodic switching potential, Eλ,c, was fixed at 0.4 V. Limiting Eλ,c to 0.9 V vs r.h.e. eliminates coating instability. Preferential Ru dissolution, promoted by cathodic Pt dissolution, was revealed by ICPES. With the exception of the 0–20% PtOx containing coatings, where evidence for the presence of RuVI was found, Ti and Ru are present in the +4 oxidation while the +2 oxidation state predominates for Pt.

Activation of Ruthenium Oxide, Iridium Oxide, and Mixed RuxIr1 − x Oxide Electrodes during Cathodic Polarization and Hydrogen Evolution

Ruthenium, iridium, and mixed ruthenium/iridium oxide layers on titanium substrates have been obtained by thermal decomposition of chloride solutions. The decomposition temperature of and was varied from 300 to 500°C and from 400 to 500°C, respectively. That on the mixed layer was kept constant at 400°C. For the mixed oxide electrode, the Ru content was varied over the whole compositional range. Current‐potential curves and cyclic voltammetry measurements were performed in 1 M . It is shown that such oxide layers can be activated through cathodic polarization, leading to an increase of the electrocatalytic activity for hydrogen evolution. The ratio between the current density at a given electrode potential before and after completion of the activation process or the ratio between the exchange current density before and after the completion of the activation process was used to quantify this activation phenomenon. Values as high as 100 have been observed in some cases, but typical values are around ten. Through a series of specific measurements and comparison with data taken from the literature, it is shown that this activation phenomenon is not related to an increase of the electrochemically active surface area as determined through cyclic voltammetry measurements. An explanation is proposed whereby H‐chemisorption within the oxide layer is ultimately responsible for the increase of the electrocatalytic activity of the oxide layer.

Electrocatalytic properties of Ru + Ti + Ce mixed oxide electrodes for the Cl 2 evolution reaction

A series of ternary oxides of nominal composition Ru 0.3Ti (0.7 − x) Ce x O 2 was prepared by thermal decomposition on Ti supports and used as electrodes to study the effect of substituting Ce for Ti on the kinetics and electrocatalysis of the Cl 2 evolution reaction. The surface properties were evaluated by cyclic voltammetry. Integration of the voltammetric curves provided the voltammetric charge, q ∗ , which is proportional to the active surface area. Kinetic data showed that Cl 2 evolution occurs with a single mechanism over the whole explored potential range and at all electrode compositions. Fractional reaction orders with respect to both Cl − and H + revealed double-layer effects attributed to the occurrence of Cl − specific adsorption. The apparent activity increased with CeO 2 content, whereas the true electrocatalytic properties, estimated by normalizing the current to unit surface charge, decreased in the presence of CeO 2 with a minimum of 10% CeO 2. The presence of CeO 2 also makes the oxide layers more prone to mechanical erosion by the evolving gas bubbles.

Analytical Applications of Modified Lead Dioxide Electrodes.

Electrochemical activity and stability of pure lead dioxide(PbO 2 ) and lead dioxide incorporated with metal ions (As 5+ , Bi 3+ , Cr 3+ , Fe 3+ and Nι 2+ were studied. Heterogeneous rate constants for oxidation of numerous inorganic and organic compounds at PbO 2 were compared with those at mixed lead dioxide electrodes. Among the tested metal ions, it turns out that arsenic is one of the promising elements. The electrochemical stability of the mixed oxide electrode prepared in an optimum condition, i.e., As 5+ /Pb 2+ in the deposition solution, was increased compared to that of PbO 2 . For the application of the electrode material to electroanalysis, detection of thiourca, for example, at PbO 2 , and As incorporated lead dioxide electrodes(As/PbO 2 ) as working electrodes in a thin layer electrochemical cell for flow injection analysis(FIA) was investigated by a constant-potential amperometry. Sensitive detection of thiourea with a detection limit of 1.4 x 10 -7 M was achieved with PbO 2 and As/PbO 2 electrodes.

Electrocatalytic properties of ternary oxide mixtures of composition Ru0.3Ti(0.7−x)CexO2: oxygen evolution from acidic solution

Mixed oxide electrodes of general composition Ru0.3Ti(0.7−x)Ce x O2 were prepared by thermal decomposition of the respective chlorides using Ti as a support. x was varied between 0 and 70 mol %. Oxygen evolution was used as a model reaction to investigate the dependence of the electrocatalytic properties on oxide composition. Kinetics was studied by quasistationary current-potential curves and reaction order determination. A minimum Tafel slope of about 30 mV has been found in the 10–30% CeO2 composition range. On the basis of a zero reaction order at constant overpotential, a reaction mechanism has been proposed accounting for the composition dependence of the Tafel slope. It has been concluded that the replacement of TiO2 with CeO2 brings about an increase in the electrocatalytic activity for oxygen evolution, while the layer becomes more prone to mechanical erosion.

Identification of the adsorbed intermediate of the electrooxidation of chloride by the cv technique

The adsorbed intermediate of the chloride electrochemical oxidation process on a RuO 2 TiO 2 mixed oxide electrode was studied by cv technique in a large range of sweep rate. The existence of a reverse adsorption peak was directly proved by the preliminary results summarised here. The electrocatalytic activity of different electrodes used as working electrode for chloride oxidation can be qualified by the cv method.

Secondary ion mass spectrometry studies on the formation of the valve metal oxide in ruthenium- and iridium-based mixed oxide electrodes

The process of TiO 2 evolution from titanium diisopropoxide bis-2,4-pentanedionate precursor on nickel and titanium supports was followed by secondary ion mass spectrometry. Concentration depth profiles of rutile (TiO 2) at higher temperatures showed completely different patterns for the two supports, indicating the influence of the base metal on the formation and properties of the oxide coating. The formation and surface accumulation of elemental carbon during combustion of the organic matter were followed as a function of temperature. The results obtained are in agreement with those of previous measurements by simultaneous thermogravimetry-differential thermal analysis, thermogravimetry combined with mass spectrometry and emission FTIR spectrometry.

Photoelectrochemical study of potentiodynamically anodized H 2-reduced PbTiO 3 + PbO mixed-oxide electrode in 0.1 M NaOH + 0.1 M Na 2SO 4

The mechanism of lead oxide formation and the enhanced photoresponse produced by potentiodynamic anodization of the H 2-reduced surface of a PbTiO 3 + PbO sintered pellet were investigated in the potential region from −1.25 to +2.35 V/SCE in 0.1 M Na 2SO 4 + 0.1 M NaOH at 80°C. The anodized electrode was characterized by X-ray diffraction, UV-visible reflectance spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy with energy dispersive X-ray analysis and various photoelectrochemical techniques. An 11-fold increase in solar to electrical power conversion efficiency and an enhanced quantum yield of 9% in 0.1 M Fe(CN) 3− 4− 6 redox electrolyte (pH 9.2) was observed with the H 2-reduced PbTiO 3 + PbO electrode anodized for 30 min compared with the unanodized H 2-reduced PbTiO 3 + PbO electrode.

Preparation and characterization of a PbTiO3 + PbO mixed-oxide photoelectrode

Abstract A new PbTiO 3 + PbO photoelectrode system for a photoelectrochemical cell has been prepared from a mixture of β-PbO 2 and TiO 2 by solid state sintering. The crystal structure and surface morphology of the mixture were determined by X-ray diffraction and scanning electron microscopy respectively, and energy dispersive X-ray analysis measurements were used to establish the phases present. These studies reveal the photoelectrode as a PbO-rich PbTiO 3 mixed-phase oxide with high tetragonality and a crystalline nature. Mott-Schottky plots and photoelectrochemical measurements, such as the action spectrum, I – V characteristics etc., of this mixed oxide were evaluated in 0.1 M Fe(CN) 3−/4− 6 (pH 9.2 buffer) redox electrolyte. These investigations suggest that the mixed-oxide electrode exhibits n-type conductivity, a decreased band-gap energy and an enhanced absorption range in the visible region.

CO 2 recycling for hydrogen storage and transportation —Electrochemical CO 2 removal and fixation

Experimental results of a combined absorption and electrodialysis process for the CO 2 recovery from the atmosphere are presented as the first step in an environmentally neutral fuel production. Furthermore, preliminary results on the electrochemical reduction of CO 2 on porous electrodes in aqueous solutions, on mixed oxide electrodes in a high pressure electrochemical cell in liquid CO 2 and some aspects of the electrochemical adsorption and reduction of CO 2 on Pd-Fe alloys are discussed.

Fabrication of mixed oxide electrodes by PM techniques: C.O. Augustin et al (Central Electrochemical Research Inst., Tamil Nadu, India)

Fabrication of mixed oxide electrodes by PM techniques: C.O. Augustin et al (Central Electrochemical Research Inst., Tamil Nadu, India)

The effect of RuO 2/TiO 2 ratio on the rate of an outer-sphere electron transfer reaction on mixed oxide electrodes

The apparent heterogeneous rate constants can be determined by a special cv technique in solutions containing both the oxidized and the reduced forms of a redox couple. The electrode materials are characterized by the difference between the k 0 ox and k 0 red. The effect of RuO 2/TiO 2 ratio on the electrochemical effective surface area and the apparent rate constants of a redox system are investigated. The optimal composition of the RuO 2/TiO 2 electrode seems to be in the 0.6–0.9 RuO 2 mole fraction range.

Electrocatalysis of H 2 evolution on RuO 2 + IrO 2 mixed oxide electrodes

H 2 evolution from acid solutions has been studied on IrO 2 + RuO 2 electrodes over the whole oxide composition range. Kinetics has been investigated by means of cyclic voltammetry, quasi-stationary current—potential curves and reaction order determination. Results have shown that the Tafel slope for as-prepared electrodes is close to 40 mV and independent of oxide composition. The Tafel slope changes on electrodes aged by H 2 evolution: it varies from about 60 mV for pure RuO 2 to about 20 mV for pure IrO 2. The anomalously low Tafel slope for IrO 2-rich electrodes, and the apparent reaction order varying from 1 to ca. 2.5 have been interpreted on the basis of a single mechanism with different rate determining steps in which the back-reaction may have an appreciable effect due to oversaturation of the solution adlayer in the presence of quasi-equilibrium of the H 2 reaction in the pores of the oxide layer.