Physicochemical properties of electrodepositedβ-lead dioxide: Effect of deposition current density

The influence of current density on the coulometric efficiency of -PbO₂ deposition in 0.5 M cM lead nitrate, the nonstoichiometry, impurity of -PbO₂ and voltammetric double layer capacitance have been studied. While the coulometric efficiency is about 95% at current densities less than 30 mA cm^–2, it decreases at higher current densities. The oxygen deficiency, , in -PbO_2- has been found to be invariant with the current density. X-ray diffraction studies provide a linear decrease in the weight percent of -PbO₂ as an impurity in the -PbO₂ with increase in current density, and the -PbO₂ is found to be absent at 100mA cm^–2 or higher. The estimated double layer capacitance from the cyclic voltammograms recorded in the potential range 0.70–1.10V, increases with deposition current density, indicating enhanced surface area.     

Hydrous ruthenium dioxide/multi-walled carbon-nanotube/titanium electrodes for supercapacitors

Composite electrodes prepared by vertically aligned multi-walled carbon nanotubes (MWCNTs) coated with hydrous ruthenium dioxide (RuO₂·nH₂O) have previously been used in various supercapacitors. The specific capacitance when using RuO₂·nH₂O/MWCNT/Ti as electrodes in 1.0 M H₂SO₄ aqueous solution can reach up to 1652 F/g at a scan rate of 10 mV/s, which is larger than that of RuO₂·nH₂O/Ti or MWCNT/Ti. In this study, a RuO₂·nH₂O/MWCNT/Ti composite electrode was examined by X-ray photoelectron spectroscopy, which revealed the existence of hydrous ruthenium dioxide in the Ti current collector. The capacitive behavior of the electrode was analyzed by cyclic voltammetry and the galvanostatic charge–discharge method, and the morphology of the composite electrode was examined by scanning electron microscopy.     

Electrosynthesis of 4,4′-dinitroazobenzene on PbO2 electrodes

Parameters which affect the electrosynthesis of 4,4-dinitroazobenzene from p-nitroaniline on platinum and PbO₂ electrodes were investigated and optimum conditions were determined. Maximum conversion efficiency for electrosynthesis was 95% with a pure -PbO₂ electrode. It was found that the electrocatalytic activity of a PbO₂ electrode depends upon its / ratio and its degree of crystallinity. The effects of the added base and water on the conversion efficiency were also elucidated.     

Hydrated structures in the anodic layer formed on lead electrodes in H2SO4 solution

SEM and TEM observations of the corrosion layer obtained during the potentiostatic oxidation of lead electrodes in H₂SO₄ solution have shown that, at potentials above 1.00 V vs Hg/Hg₂SO₄, a lead dioxide layer is formed with crystal and gel-like (hydrated) structures. The crystal zones of the corrosion layer contain - and -PbO₂ crystals. Applying controlled thermal degradation it has been established that hydrated zones (denoted as PbO(OH)₂) comprise about 10% of the corrosion layer. For comparison, the lead dioxide active mass of the lead-acid battery is hydrated over 30%. On prolonged polarization of the lead dioxide electrode at 1.50 V, the basic electrochemical reaction that takes place is oxygen evolution. It has been suggested that this reaction occurs mainly at the interface crystal/gel-like zones. On opening the circuit, the electrode potential reaches the equilibrium potential for the PbO₂/PbSO₄ system within a rather long period. This potential decay is related to the diffusion of oxygen through the bulk of the corrosion layer (probably through its hydrated zones) to the solution and to the metal. A suggestion is made that hydrated zones are also involved in the oxygen reaction.     

Comportement électrochimique des variétés alpha et beta PbO2 et influence de l'antimoine sur leur reactivité électrochimique en milieu H2SO4, 8N

Résumé L'expérience a montré qu'il est possible d'obtenir par l'oxydation anodique des variétés- et-PbO₂ parfaitement pures au point de vue cristallographique, et que la réduction de-PbO₂ se déroule à un potentiel plus élevé et plus constant que celui observé sur-PbO₂. La réactivité électrochimique de-PbO₂ est plus importante que celle de-PbO₂. L'introduction de Sb dans les réseaux cristallins de ces variétés diminue fortement leur cristallinité et dans le cas de-PbO₂ on obtient toujours simultanément- et-PbO₂. Du point de vue réactivité électrochimique, l'accroissement dû à la présence de Sb est de l'ordre de 33%.

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The results demonstrate the possibility of preparing through anodic oxidation rigorously pure, from the crystallographic point view,- and-PbO₂ phases, and that the reduction of-PbO₂ takes place at a potential which is more positive and more constant than the one obtained with-PbO₂. In a battery, the electrochemical reactivity of-PbO₂ is more important. The introduction of Sb into the lattice of these forms of PbO₂ decreases their crystallinity, and for the case of-PbO₂ we obtained simultaneously- and-PbO₂. Their electrochemical reactivity can increase by about 33%.

     

On the behaviour of carbon black in positive lead-acid battery electrodes

The addition of carbon black to the positive paste led to an alteration in structure of the PbO₂/PbSO₄ electrode due to an increase in porosity, in active mass coarsening and in the /-PbO₂ ratio. These structural effects are explained as being caused by the ability of carbon black to increase the water-accumulating capacity of the paste, to influence the local formation conditions and to participate in the charge transport within the unformed mass. Oxidative removal of carbon black from the active mass was studied.     

Characterization of DSA®-type oxygen evolving electrodes: Choice of a coating

In the search for a DSA^®-type electrode for oxygen evolution in acidic solutions, nine binary coatings with IrO₂, RuO₂, Pt as conducting component, and TiO₂, ZrO₂, Ta₂O₅ as inert oxides, have been deposited on titanium, examined for their microstructural properties and tested for their electrocatalytic activity and anodic stability. Electrochemical true surfaces of the coatings were found to be dependent on structure and morphology: the mixtures that form a solid solution (RuO₂–TiO₂), or allow limited miscibility (IrO₂–TiO₂), show the lowest dispersion of active material. Differences in service lives, were attributed to differences in wear mechanism of the electrodes. It was found that Ti/IrO₂ (70 mol%)-Ta₂O₅ (30 mol%) is by far the best electrode.     

Multichemical defense of plant bugHotea gambiae (westwood) (Heteroptera: Scutelleridae)

Chemical defense in larvae of the plant bugHotea gambiae has been investigated. Results of analyses (GC, GC-MS) on the secretions from the three dorsally situated larval abdominal defense (scent) glands are reported. The secretion from the first abdominal gland consists of a mixture of C₁₀ and C₁₅ isoprenoids: (C₁₀) -pinene, -pinene, limonene, -phellandrene; (C₁₅) -caryophyllene, caryophyllene oxide, -humulene, and (the major component) humulene epoxide II. The secretions from the second and third abdominal glands are similar mixtures consisting of (E)-2-decenal, (E)-4-oxohex-2-enal, andn-tridecane together with lesser amounts of (E)-2-hexenal,n-dodecane, and other materials. Isoprenoid defense is now known from four species of plant bugs (Heteroptera) associated with Malvaceae.     

On the RuO2TiO2 interlayer of PbO2 electrodeposited Ti anode

The degradation mechanism of electrodeposited β-PbO₂ on the RuO₂TiO₂ loaded Ti substrate was studied. The electric resistance of the PbO₂ anode was increased the Ti/Ru ratio of the interlayer and the current density of electrodeposition, probably due to oxidation of the interlayer at the initial stage of electrodeposition, so that the electric contact between PbO₂ and the interlayer might fail. The β-PbO₂ deposited anodes prepared carefully to avoid destructive oxidation of the interlayer were examined as the oxygen evolution electrode in 1 M H₂SO₄. The Ti substrate became passive, caused by permeation of oxygen through PbO₂ and the interlayer, when electrolysis was conducted for many hours. The service life time depended on the Ti/Ru ratio of the interlayer and the operating current density.     

A novel PbO2 electrode preparation and its application in organic degradation

PTFE (polytetrafluoroethylene)-doped β-PbO₂ (PTFE-β-PbO₂) electrode on Ti base (Ti/PTFE-β-PbO₂) or on ceramic base (ceramic/PTFE-β-PbO₂) was prepared by electrodeposition. Its accelerated lifetime was tested in 9.0 mol/L H₂SO₄ solution under a current density of 100.0 A dm⁻². The experimental results showed that PTFE-β-PbO₂ electrode had a longer lifetime than common β-PbO₂. PTFE inlayed in β-PbO₂ could weaken the inner stress of the coating and help to get a smoother coating. Ceramic/PTFE-β-PbO₂ electrode had a longer accelerated lifetime (about 1338 h) than Ti/PTFE-β-PbO₂ electrode (about 827 h). The characteristics of ceramic/PTFE-β-PbO₂ anode in treating 4-chlorophenol-contaminated water indicated that it exhibited both good electro-catalytic activity and high electrochemical stability. This electrode has, then, a strong potential for future applications.     

Proton diffusion in crystalline ruthenium dioxide

Porous powder electrodes of ruthenium dioxide (RuO₂) with varying chlorine contents were prepared. A potential-step technique was used to measure the chemical diffusion coefficient for protons in these RuO₂ powders and the results were correlated with published data on proton diffusion in thin films of RuO₂.     

Electrochemical treatment of aqueous solutions containing urea

Investigations on the anodic decomposition of urea using Ti/Pt and Ti/(RuO₂–TiO₂)_40:60 electrodes were carried out. The kinetics of the process were examined in a periodic electrolyser. The effect of anodic current density, initial urea concentration, and sodium chloride concentration on the effectiveness of the basic process (average rate of urea decomposition, current efficiency, and unit power consumption) is discussed. When a Ti/Pt electrode is applied for urea removal from aqueous solution urea is not decomposed directly at the surface of the electrode, but rather in the bulk of the solution by hypochlorite formed during the process. When the Ti/(RuO₂–TiO₂)_40:60 electrode is used for the removal of urea from aqueous solutions, the reaction of urea with chlorine adsorbed at the electrode predominates. In both cases non-toxic products of urea decomposition (N₂, CO₂,) are formed. Comparison of the effectiveness of anodic decomposition of urea for the Ti/Pt and Ti/(RuO₂–TiO₂)_40:60 electrodes in the periodic electrolyser at optimum process parameters has revealed that the former electrode is more favorable.     

Performance characteristics of a new type of lead dioxide-coated titanium anode

A new type of PbO₂-coated metal anode, useful for electrochemical processing requiring the use of high-overpotential anodes, was prepared by applying to a titanium substrate an undercoating of Ti-Ta oxides, then covering the undercoating with an intermediate coating of stress-free -PbO₂ deposit, and finally covering the intermediate coating with a Ta₂O₅ particle-admixed -PbO₂ deposit. The anode thus produced was found to be superior to the anodized Pb or platinized Ti anode in respect of oxygen overvoltage, and corrosion resistance, even in solutions containing organic solvents. The possibility for use in chromium plating is also indicated.     

Ruthenium(IV) dioxide-catalyzed reductive gasification of intractable biomass including cellulose, heterocyclic compounds, and sludge in supercritical water

Catalytic reduction gasification in the presence of ruthenium(IV) dioxide (RuO₂) in supercritical water was used to decompose intractable biomass. The gasification of model biomass samples (glucose, cellulose, and heterocyclic compounds), and low-purity biomass samples obtained from a paper-recycling facility (paper sludge) and from a sewage treatment plant (sewage sludge) were studied. In clear contrast to another catalysts, the RuO₂ catalyst completely gasified cellulose to produce mainly hydrogen, methane, and carbon dioxide under various conditions (e.g., 673 K at 30 MPa and 773 K at 50 MPa). As for heterocyclic compounds, nitrogen compounds did not deactivate the RuO₂ catalyst; the gasification of carbazole proceeded completely. Furthermore, paper sludge was almost completely decomposed in supercritical water with RuO₂ at 723 K.     

Electrocatalytic oxidation of nitrophenols in aqueous solution using modified PbO2 electrodes

Various kinds of modified lead dioxide (PbO₂) electrodes, doped with bismuth oxides and cobalt oxides, were prepared by electrodeposition in acid solution, and were characterized in terms of their morphological (SEM) and structural (XRD) features. Mineralization experiments on o-nitrophenol (ONP) in an electrocatalytic oxidation system showed that the electrocatalytic activity of Ti/Bi–PbO₂ was superior to the traditional dimensionally stable anodes (DSAs) Ti/β-PbO₂ and other modified PbO₂ electrodes. The mineralization, reaction kinetics and nitro-group transformation of nitrophenols (ONP, p-nitrophenol (PNP) and m-nitrophenol (MNP)) on Ti/Bi–PbO₂ electrodes were studied and compared. NPs were degraded completely under the present experimental conditions by applying a 30 mA cm⁻² current density at pH 4.3 in 0.1 M Na₂SO₄ and 0.01 M NaCl. The degradation of NPs lay in the order: ONP > MNP > PNP. A simple degradation mechanism model is proposed.     

NiO-based composite electrode with RuO2 for electrochemical capacitors

NiO/RuO₂ composite materials were prepared for use in electrochemical capacitors (ECs) by co-precipitation method followed by heat treatment. X-ray diffraction (XRD) spectra indicated that no new structural materials were formed and ruthenium oxide particles were coated by NiO particles. RuO₂ partly introduced into NiO-based electrode had improved its electrochemical performance and capacitive properties by using electrochemical measurements. A maximum specific capacitance of 210 F/g was obtained for NiO-based composite electrode with 10 wt.% RuO₂ in the voltage range from −0.4 to 0.5 V in 1 mol/l KOH solution. By comparison of effect of modified modes on the specific capacitance, chemically modified composite electrodes had more stable cycling properties than those of physically modified electrodes. After 200 cycles, specific capacitance of NiO-based chemical composite electrode with 5 wt.% RuO₂ kept 95% above, while that of physical electrode was only 79% of initial specific capacitance.     

Initial rate of alternating copolymerization of anethole with maleic anhydride in methyl ethyl ketone analysis by a complex model

Summary Dilatometrically determined initial rate of alternating copolymerization of anethole (M₁) and maleic anhydride (M₂) in methyl ethyl ketone (MEK) is reported for the total monomer concentrations of 1M, 2M and 3M polymerized at 50°C with AIBN. The rate is larger than the first order with respect to the monomer concentration. The simplified complex model adopted by Shirota et al is found to be consistent with the data. The equilibrium constant of donor-acceptor complexation (C) of the comonomers is measured to be K=0.057 M^–1 in MEK at 26°C. The ratios of the propagation rate constants are calculated to be k_1c/k₁₂=_D=2 and k_2c/k₂₁=_A=6.     

Electrodeposited MnO2 as electrocatalyst for carbohydrate oxidation

The electrochemical oxidation of dextrose, fructose and sorbitol under galvanostatic conditions was carried out using both anodically and cathodically deposited MnO₂ layers on platinum and carbon. The coated electrodes showed better electrocatalytic activity for the oxidation of carbohydrates than the bare substrates. Catalytic participation of some higher valent states of manganese in electron transfer relay is speculated, which finds support in the chronopotentiogram and the observed pH-dependence of the electrochemical parameters. The current potential plots showed Tafel behaviour for the MnO₂/Pt electrode. The Tafel slopes were found to be relatively high, indicating kinetic complications. The observed unusual negative values of electrochemical reaction order on MnO₂/Pt electrode were accounted for by considering slow desorption of oxidation products from the electrode surface. The adsorption isotherms of dextrose and fructose on MnO₂ were determined. The current efficiencies of oxidation of carbonyl and hydroxyl groups were found to be and % respectively. SEM pictures showed the cathodically deposited MnO₂ on carbon to be more fine-grained and smoother than the corresponding anodic deposits.     

Stable Ti/RuO2-Sb2O5-SnO2 electrodes for O2 evolution

RuO₂-based electrodes are generally known to be unstable for O₂ evolution. In this paper, a stable type of RuO₂-based electrode, Ti/RuO₂-Sb₂O₅-SnO₂, is demonstrated for O₂ evolution. In the ternary oxide coating, RuO₂ serves as the catalyst, SnO₂ as the dispersing agent, and Sb₂O₅ as the dopant. The accelerated life test showed that the Ti/RuO₂-Sb₂O₅-SnO₂ electrode containing 12.2 molar percent of RuO₂ nominally in the coating had a service life of 307 h in 3 M H₂SO₄ solution under a current density of 0.5 A cm⁻² at 25 °C, which is more than 15 times longer than other types of RuO₂-based electrodes. Instrumental analysis indicated that RuO₂-Sb₂O₅-SnO₂ was a solid solution with a compact structure, which contributed to the stable nature of the electrode.     

Preparation and electrochemical performance of uniform RuO2/Ti and RuO2‐IrO2/Ti electrode for electrolysis of NaCl solution

The electrochemical preparation of NaClO has been widely used for the production of industrial disinfectant. To reduce the cost of electrode preparation using the brushing method, this paper introduces a method for the electrodeposition for RuO₂/Ti and RuO₂‐IrO₂/Ti preparation and NaCl solution electrolysis. The deposition of Ir improves the uniformity and stability of the RuO₂/Ti electrode. The optimum preparation conditions and additive concentrations were investigated in detail through the orthogonal experiment. By adjusting the electroplating time, temperature and voltage, the electrode with a high content of available chlorine was synthesized successfully. The physicochemical properties of the as‐prepared RuO₂/Ti and RuO₂‐IrO₂/Ti were determined by XRD, SEM‐EDS, and XPS, and the electrochemical performance and lifetime of the RuO₂/Ti and RuO₂‐IrO₂/Ti was verified via an electrochemical workstation. Uniform and stable RuO₂/TiO₂ and RuO₂‐IrO₂/TiO₂ were synthesized successfully for the electrolysis of the NaCl solution.