Insoluble anode of porous lead dioxide for electrosynthesis: preparation and characterization

Preparation of a novel type of titanium-substrate lead dioxide anode with enhanced electrocatalytic activity for electrosynthesis is described. It has been demonstrated that in the presence of a suitable surfactant in the coating solution, an adherent and mainly tetragonal form of lead dioxide is deposited on a platinized titanium surface such that the solution side of the coating is porous while the substrate side is compact. By an analysis of anodic charging curves and steady-state Tafel plots with such porous electrodes in contact with sodium sulphate solution, it has been proved that the electrochemically active area of these anodes is higher by more than an order of magnitude when compared to the area of conventional titanium-substrate lead dioxide anodes. The electrocatalytic activity is also thereby enhanced to a significant degree.     

Lectrochemical oxidation of oxalate in alkaline solutions

Experimental results show that the electrochemical oxidation of oxalate in alkaline solutions at lead dioxide anodes can be achieved at conditions of much higher alkalinity than previously reported in the literature using other types of electrodes. The oxalate in solutions containing 0.05 mol/L ∽0.1 mol/L sodium oxalate was anodically oxidized to carbonate with high efficiency in the presence of up to ∽0.1 mol/L NaOH at 70°C by using lead dioxide anodes doped with silver and tin. The addition of small amounts of silver and tin (e.g., 0.06% by weight) to lead dioxide films significantly increases the oxalate oxidation currents and current efficiencies. These metals can be incorporated into the lead dioxide films by in situ oxidation of lead-silver-tin alloys. Although oxalate could not be electrochemically oxidized using lead dioxide electrodes at extremely high pH's (greater than ∽ 14), reduction of the oxalate concentration to less than about 0.04 mol/L could be achieved at greater than 50% current efficiency at pH's up to about 13.     

Leadlead dioxide bielectrodes

Anodic polarization of lead an lead alloys at high cds in chloride solution results in the formation of a thick, voluminous, porous deposit of lead chloride. When a platinum microelectrode is introduced into lead, lead dioxide is formed on the surface of lead in chloride medium during anodic polarization at high cds.As a replacement for costly platinum, lead dioxide pieces which fell during the electrodeposition of lead dioxide were shaped into small cylindrical microelectrodes, inserted into the lead or lead alloys and anodically polarized in chloride solution. In this case lead dioxide is also formed on the surface of the lead or lead alloy. It has been found that the formation of lead dioxide on the leadlead dioxide bielectrode is good in 3% NaCl solution at an anode cd of 3 A/dm² and at room temperature. The effect of withdrawal and insertion of lead dioxide microelectrode, and of the relative area of lead dioxide microelectrode, to lead on the formation of lead dioxide is also studied. Studies on the weight change during anodic polarization of lead and lead alloys embedded with lead dioxide microelectrode, in chloride solution and in synthetic sea water show that leadsilver (1%) alloy is by far the best anode from the point of view of the formation of a compact and crackfree deposit of lead dioxide on the surface.     

The fabrication of lead dioxide layers on a titanium substrate

It is shown that stable and active lead dioxide on titanium anodes (including mesh electrodes) may be fabricated by appropriate pretreatment of the substrate and a strategy involving the anodic deposition of two PbO₂ layers—a thick underlayer with the lead dioxide doped with fluoride and iron and a top layer with the lead dioxide doped with bismuth. Periods on open circuit, especially in solutions containing an oxidisable organic or inorganic species must, however, be avoided since all forms of PbO₂ are reducible unless protected by an anodic current; the rates of the reduction does depend on the medium, the dopants in the PbO₂ and the morphology of the layer. It is also shown that, as at gold substrates, the morphology of the PbO₂ layer on titanium (consequently, their properties including adhesion and electrocatalytic activity) depend strongly on the deposition conditions including the bath composition (including Pb(II) concentration, acid concentration, concentration and choice of dopant ion), temperature, current density and deposition charge.     

Material problems encountered in anodic MnO2 deposition

The characteristic material problems in electrolytic manganese dioxide (EMD) deposition concern the electrolysis cell components and, especially, the anodes. Temperature, sulphuric acid concentration, and current density are the most critical parameters which determine the corrosion and life times of the lead, graphite or titanium anodes. The corrosion of lead, even under the cover of electrodeposited manganese dioxide, pollutes the technical product. Graphite anodes are slowly oxidized, a process which limits their life time. The behaviour of titatanium as anode material is determined by the conductivities of the TiO _x interlayer as well as of the manganese dioxide deposits in the layered system Ti–TiO _x MnO₂. Passivation and depassivation reactions in conventional EMD electrolysis are described and the improved behaviour of titanium anodes in the suspension bath process is explained.Paper presented at the meeting on Materials Problems and Material Sciences in Electrochemical Engineering Practice organised by the Working Party on Electrochemical Engineering of the European Federation of Chemical Engineers held at Maastricht. The Netherlands, September 17th and 18th 1987.     

Microstructure of new composite electrocatalyst and its anodic behavior for chlorine and oxygen evolution

The first layer of active coating made from a rutile-structured solid solution of ruthenium and titanium dioxides having an average crystal grain size of 30 nm was thermally deposited on an adequately prepared titanium metal substrate. Then, at a temperature of 500 °C, the second layer was formed on the first layer from a mixture of amorphous particles of metallic platinum and rutile-structured iridium dioxide nanocrystals having an average crystal grain size of 26 nm.Rutile phase nanocrystals are characterized by a high density of chaotically distributed dislocations and high internal microstrain values. The coatings exhibit a compact granular morphology without cracks on the surface. Their catalytic activity is similar to that of conventional DSAs for the anodic oxidation of chloride ions from both concentrated and dilute sodium chloride solutions. The anodic current efficiency both during chlorate formation and active chlorine production was several percentage points higher in electrolyzers containing these anodes than in those containing DSAs. The catalytic activity of anodes having these coatings is about 50 mV lower than that of DSAs and about 350 mV higher than that of lead/antimony alloy electrodes, for oxygen evolution from acid sulfate solutions (0.5 mol dm^?3 H₂SO₄) characteristic of processes for the production of some metals. An accelerated corrosion test showed that the stability of the double-layer anodes is about twelve-fold higher than that of conventional DSAs.     

A preliminary investigation of some anodes for use in fluidized-bed electrodeposition of metals

The development of fluidized-bed electrowinning for copper and other metals appears to be impeded by the high electrical energy consumption associated with the anodes used in such electrowinning. This paper describes preliminary work aimed at seeking anodes which consume less energy and are suitable for scale-up. Using laboratory-scale cells in which copper was electrowon from strong (25 g dm^–3 Cu), acidified (100 g dm^–3 H₂SO₄) sulphate solutions on to fluidized cathodes, the following anodes were tested: fluidized-bed anodes of catalyst-coated titanium particles, packed-bed anodes of lead shot and graphite, single and double layers of catalyst-coated titanium mesh, and cloth-covered anodes placed directly in the fluidized cathode. In addition, the possibility of using alternative anode reactions, namely oxidation of sulphur dioxide, ferrous ions or cuprous ions, as well as fluidized-bed electrowinning from a cuprous-ion catholyte, were examined. Except for the fluidized anode and the lead packed-bed anode, all the above systems yielded energy savings. The investigation was not sufficiently detailed to define which of the above was best, although, at 2.0 kW h kg^–1 Cu, electrowinning from cuprous solutions with cuprous oxidation on a graphite packed-bed anode offered an energy consumption better than that of the conventional electrowinning plants.     

The correlation between the interference colour and growth procedure of anodic titanium dioxide nanotube arrays

Titanium dioxide nanotube arrays were anodised from titanium foils in an aqueous electrolyte solution of hydrofluoric acid. The formed oxide showed visually different colours owing to light interference in the titanium dioxide layer. The behaviour of interference colour in anodic titanium dioxide film was investigated by varying anodisation parameters such as the applied voltage and the anodisation time. The morphologies and the crystalline phases of anodised samples were studied on a field emission scanning electron microscope and X‐ray diffractometer. The correlation between the interference colour and growth procedure of anodic titanium dioxide nanotube arrays was studied. The anodic films prepared under different conditions consisted of a compact oxide film with a nanoporous/tubular structure upon/beneath it. The crystalline phase of the anodic oxide layer was amorphous. The optical properties of the oxide film were investigated on a spectrophotometer. Optical interference could be detected in compact oxide layers when the thickness of the titanium dioxide was as small as 70 nm. In general, the interferences of the nanoporous/tubular structures were lower than those for compact structures. The empirical colour properties were estimated by the L*a*b* system. The relationships between the interference colour of anodic titanium dioxide film and its thickness and morphology are discussed.     

The rôle of antimony in the lead-acid battery: Part 1. The effect of antimony on the anodic behaviour of lead

Linear sweep voltammetric (LSV) and impedance studies of lead/antimony binary alloys (0–12% Sb) are described. The formation of a solid antimony-containing species in close contact with a passivating layer of lead sulphate at sufficiently positive potentials (before lead dioxide formation) is indicated. In the presence of antimony, changes in the characteristics of the passivating layer occur, in accordance with a reduction in thickness and an increase in porosity.     

Modified titanium electrodes: Application to Ti/TiO2/PbO2 dimensionally stable anodes

Titanium is a valve metal able to withstand corrosion, due to the presence of a passivating layer of titanium oxide on its surface. But, due to that more or less insulating layer, titanium cannot be used directly as an anodic material. However, modification of the surface of a Ti/TiO₂ substrate may lead to the formation of new structures: Ti/TiO₂/M or Ti/TiO₂/OX, in which M is a metal such as platinum and OX a conducting oxide exhibiting electrocatalytic properties. These structures have interesting electrochemical properties and may be used as efficient electrode materials.In this paper, after a review of the electrochemical behaviour of these structures, we give new results concerning the selective electrodeposition of lead dioxide on Ti/TiO₂ substrates and we propose an interpretation of the results taking into account the dielectric properties of the underlying TiO₂. It is shown that there is a dramatic decrease of the resistance of the electrode when a PbO₂ layer is electrodeposited onto a Ti/TiO₂ structure. That effect allows the preparation of electrodes (low-cost DSAs) that may be used as anodes in spite of the presence of the underlying TiO₂ layer, that layer being useful to avoid corrosion of the titanium substrate. At last, the effect of stabilization of the underlying TiO₂ layer is discussed.     

Nb doped TiO2 nanotubes for enhanced photoelectrochemical water-splitting

Nanostructured titanium dioxide is one of the classic materials for photoelectrochemical water splitting. In the present work we dope TiO(2) nanotube anodes. For this, various low concentration bulk-Nb-doped TiO(2) nanotube layers were grown by self-organizing anodization of Ti-Nb alloys. At Nb-contents around 0.1 at%, and after an adequate heat-treatment, a strongly increased and stable photoelectrochemical water-splitting rate is obtained.     

Influence of anode material on the electrochemical oxidation of 2-naphthol: Part 2. Bulk electrolysis experiments

The electrochemical oxidation of 2-naphthol has been studied by galvanostatic electrolysis, using a range of electrode materials such as lead dioxide, boron-doped diamond (BDD) and Ti-Ru-Sn ternary oxide anodes. The influence of some operating parameters, such as current density, flow-rate and chloride concentration on naphthol oxidation has been investigated in order to find the optimum experimental conditions. Measurements of chemical oxygen demand, HPLC and total organic carbon have been used to follow the oxidation. The experimental data indicate that on PbO₂ and BDD, naphthol oxidation takes place by reaction with electrogenerated hydroxyl radicals and is favoured by low current density and high flow-rate. On the contrary, on a Ti-Ru-Sn ternary oxide the mineralisation of naphthol occurs only in the presence of chloride ions that act as redox mediators and COD removal is affected by chloride concentration and is not significantly influenced by the current density and mass-transfer coefficient. From a comparison of the results of the three electrodes it has been found that boron-doped diamond gives a faster oxidation rate and better current efficiency.     

Technique for Measuring Stresses Which Occur During Sintering of a Fiber-Reinforced Ceramic Composite

A new technique for monitoring stresses during sintering of a ceramic composite has been developed. The stress is measured by means of the heterogeneity stresses that build up in a sandwich compact, which consists of a layer, or plane, ofSiC fibers between two layers of ceramic powder of different thicknesses. Upon sintering, this configuration produces an asymmetric stress field across the thickness of the specimen, which results in the bending of the compact, as characterized by the curvature of the fibers. In situ observations of ihe process provide information about the temperature dependence of stress initiation.     

基于铝合金/铝化合物的锂金属负极的研究进展

介绍了近年来基于铝合金/铝化合物的锂金属负极的研究进展,总结了使用铝合金或铝化合物对锂金属负极进行修饰或作为负极材料的典型工作,展望了基于铝合金/4吕化合物的锂金属负极的研究方向.     

Effects of Gd and Nd on microstructure,corrosion behavior,and electrochemical performance of Mg-Y-based anodes for magnesium air batteries

Journal of Applied Electrochemistry - As-cast Mg-3Y-8Gd (VW83) and Mg-4Y-3(Gd/Nd) (WE43) alloys were used as anodes for Mg–air batteries in this study. The discharge behaviors of the anodes...     

Synthesis, characterization and electrochemical performances of new antimony-containing graphite compounds used as anodes for lithium-ion batteries

Graphite intercalation intercalated with metal alloys able to alloy reversibly lithium constitute a large set of new anodic materials for lithium-ion batteries of significantly improved reversible capacities. Especially, graphite intercalated with cesium-antimony alloys can be used as materials for anodes in lithium-ion batteries. Electrochemical insertion of lithium in such chemically modified precursors shows that lithium both intercalates in the empty van der Waals spaces of graphite and alloys reversibly with antimony. The total electrochemical reversible capacities, measured between 0 and 2 V vs Li⁺/Li, close to 700 mAh g⁻¹ have been currently obtained.     

Electrodeposition of aluminium-copper alloys from alkyl benzene electrolytes

An experimental programme in which aluminium-copper alloys were electroplated from alkyl benzene/ AlBr₃ electrolytes is described. The investigation showed that Al-Cu alloys (0–3.5 wt% Cu) can be plated onto steel and that the resulting coatings are bright, adherent and less porous than equivalent coatings of pure aluminium. The composition of the cathode deposits can be readily controlled by using Al-Cu anodes of specified copper content. About half the copper dissolved from the anodes is transferred to the cathode, the remainder being precipitated from the electrolyte as CuBr. Coating composition varies with current density and this parameter can also be used to control the process. In a parallel investigation, potential differences between aluminium and a number of other metals (Zn, Pb, Cd, Sn, Cu, Ag) were measured. Potential differences in the alkyl benzene electrolytes were found to be 10–30 times less than in aqueous electrolytes which indicates that the alkyl benzenes should be useful for plating other alloys in addition to those of aluminium and copper.     

An electrochemical approach to total organic carbon control in printed circuit board copper sulfate plating baths Part I: Anode performances

An electrochemical approach to decreasing high levels of total organic carbon (TOC) in printed circuit board (PCB) copper sulfate plating baths has been investigated. The organic contaminants build-up over the course of pattern plating of PCBs, and at high concentrations they interfere with the quality of the plated copper. The electrochemical approach involves destroying the organic contaminants using electrochemical oxidation. Various anode materials (glassy carbon, lead, lead dioxide, platinum, iridium dioxide and doped tin dioxide) were screened for this application. Some corrosion data is presented for these anodes and their performance for TOC removal at various current densities has been roughly quantified using an apparent first order rate constant. The three best performing anode materials gave increasing oxidation rates going from platinum to doped tin dioxide to lead dioxide, unfortunately anode stability decreased in the same order.     

Influence of anode material on the electrochemical oxidation of 2-naphthol: Part 1. Cyclic voltammetry and potential step experiments

The anodic oxidation of 2-naphthol has been studied by cyclic voltammetry and chronoamperometry, using a range of electrode materials such as Ti-Ru-Sn ternary oxide, lead dioxide and boron-doped diamond (BDD) anodes. The results show that polymeric films, which cause electrode fouling, are formed during oxidation in the potential region of supporting electrolyte stability. IR spectroscopy verified the formation of this organic film. While the Ti-Ru-Sn ternary oxide surface cannot be reactivated, PbO₂ and BDD can be restored to their initial activity by simple anodic treatment in the potential region of electrolyte decomposition. In fact, during the polarization in this region, complex oxidation reactions leading to the complete incineration of polymeric materials can take place on these electrodes due to electrogenerated hydroxyl radicals. Moreover, it was found that BDD deactivation was less pronounced and its reactivation was faster than that of the other electrodes.     

Electrolytic recovery of iron from pickling solutions by tungsten carbide gas-diffusion anodes

The performance of gas-diffusion electrodes catalysed with tungsten carbide as anodes for the electrolytic recovery of iron from pickling solutions was investigated. The conditions under which the cathodic current efficiency of electrolytic cells utilizing such anodes increases significantly were determined. It was found that the energy consumption is two times lower than for a conventional electrolysis using lead anodes.