Lead Dioxide Anode Research Articles

Fabrication and Electrochemical Treatment Application of A Novel Lead Dioxide Anode with Superhydrophobic Surfaces, High Oxygen Evolution Potential, and Oxidation Capability

A novel PbO(2) electrode with a high oxygen evolution potential (OEP) and excellent electrochemical oxidation performance is prepared to improve the traditional PbO(2) electrode, which is modified by changing the microstructure and wetting ability. A middle layer of TiO(2) nanotubes (NTs) with a large surface area is introduced on Ti substrate, and a small amount of Cu is predeposited at the bottom of TiO(2)-NTs. The modification will improve the electrochemical performance by enhancing the loading capacity of PbO(2) and the combination between PbO(2) and Ti substrate. The hydrophilic surface becomes highly hydrophobic by adding fluorine resin. The improved PbO(2) electrode exhibits a similar morphology, surface wetting ability, high OEP, and electrochemical performance with boron-doped diamond film (BDD) electrode. However, the physical resistance of the PbO(2) electrode is much lower than that of BDD, exhibiting higher conductivity. The hydroxyl radical utilization is significantly enhanced, resulting in a higher oxidation rate and higher removal for 2,4-dichlorophenoxyacetic acid.

Applicability of electrochemical methods to carwash wastewaters for reuse. Part 1: Anodic oxidation with diamond and lead dioxide anodes

Abstract The anodic oxidation of a real carwash wastewater has been comparatively studied using lead dioxide (PbO2) and boron-doped diamond (BDD) anodes in an electrolytic flow cell. The influence of several operating parameters such as current (from 1A to 3A), liquid flow rate (from 100 to 300 dm3 h−1) and temperature (25 °C and 40 °C) on the performance of both systems with a stainless steel cathode has been studied and the energy consumption has been also evaluated. Surfactants concentration and COD have been monitored during the treatment. Galvanostatic electrolyses always lead to complete COD removal due to the high amounts of effective hydroxyl radicals generated from water oxidation at each anode and the COD removal rate increases with rising applied current and liquid flow rate, while it as almost unaffected by temperature. The performance of the BDD anode is always better than that of PbO2, requiring shorter electrolysis time to reach overall mineralization, thus leading to remarkably higher current efficiency and lower specific energy consumption, that was 375 kWh m−3 and 770 kWh m−3 for BDD and PbO2, respectively.

Comparative study of the electrocatalytic oxidation and mechanism of nitrophenols at Bi-doped lead dioxide anodes

The electrocatalytic oxidation of o-nitrophenol (o-NP), m-nitrophenol (m-NP) and p-nitrophenol (p-NP) has been studied at Bi-doped lead dioxide anodes on acid medium by cyclic voltammetry and bulk electrolysis. The results of voltammetric studies indicated that these nitrophenol isomers were indirectly oxidized by OH radical in the solutions. Within the present experimental conditions used (50mg of nitrophenol L−1, pH 4.3, 30mAcm−2, 303K), the complete decomposition of nitrophenols (NPs) was achieved. The electrocatalytic oxidation of NPs lay in the order: p-NP>m-NP>o-NP. Molecular configuration including the electron character and hydrogen bonds of NPs significantly influenced the electrocatalytic oxidation of these isomers. Hydroquinone, catechol, resorcinol, benzoquinone, aminophenols, glutaconic acid and maleic acid and oxalic acid have been detected as soluble products during the electrolysis of NPs. The possible degradation pathways of these isomers were proposed. The first stage is the release of nitro group from the aromatic rings. As a consequence, hydroquinone, catechol, resorcinol and benzoquinone are formed. These organic compounds are oxidized initially to carboxylic acids (glutaconic acid, maleic acid and oxalic acid) and later to carbon dioxide and water. Simultaneously, the reduction of NPs to aminophenols takes place at the cathode.

Examination of in situ Generation of Hydroxyl Radicals and Ozone in a Flow-through Electrochemical Reactor

Generation of hydroxyl radicals and ozone in a low ionic strength influent (0.001 M Na2SO4) treated in a continuous flow electrochemical (EC) reactor equipped with a cobalt-promoted lead dioxide anode was examined using p-chlorobenzoic acid (pCBA) and indigotrisulfonate (ITS) probes. EC generation of hydroxyl radicals via the oxidation of water was determined to precede that of ozone. OH· current yields were affected virtually solely by the current density, with almost negligible effects of variations of pH and carbonate concentrations. Absolute values of the current yields of EC generated OH· radicals were close to 1.0% for current densities > 30 mA/cm2. The EC generation of ozone was suppressed in the presence of organic species, primarily due to the interception of OH· radicals that react with oxygen to form ozone. Apparent kinetic constants of major reactions associated with the EC generation of ozone were determined based on a steady-state model of an EC-controlled continuous flow reactor.

A comparison of electrochemical degradation of phenol on boron doped diamond and lead dioxide anodes

This work compares two electrode materials used to mineralize phenol contained in waste waters. Two disks covered with either boron doped diamond (BDD) or PbO2 were used as anodes in a one compartment flow cell under the same hydrodynamic conditions. Efficiencies of galvanostatic electrolyses are compared on the basis of measurements of Total Organic Carbon (TOC) and Chemical Oxygen Demand (COD). Galvanostatic electrolyses were monitored by analysis of phenol and of its oxidation derivatives to evaluate the operating time needed for complete elimination of toxic aromatics. The experimental current efficiency is close to the theoretical value for the BDD electrode. Other parameters being equal, phenol species disappeared at the same rate using the two electrode materials but the BDD anode showed better efficiency to eliminate TOC and COD. Moreover, during the electrolysis less intermediates are formed with BDD compared to PbO2 whatever the current density. A comparison of energy consumption is given based on the criterion of 99% removal of aromatic compounds.

Electrochemical degradation of Acid Blue and Basic Brown dyes on Pb/PbO 2 electrode in the presence of different conductive electrolyte and effect of various operating factors

Electrocatalytic degradation of Acid Blue and Basic Brown dyes from simulated wastewater on lead dioxide anode was investigated in different conductive electrolytes. It was shown that complete degradation of these dyes is dependent primarily on type and concentration of the conductive electrolyte. The highest electrocatalytic activity was achieved in the presence of NaCl (2 g/l) and could be attributed to indirect oxidation of the investigated dyes by the electrogenerated hypochlorite ions formed from the chloride oxidation. In addition, contribution from direct oxidation could also be possible via reaction of these organic compounds with the electrogenerated hydroxyl radicals adsorbed on the lead dioxide surface. In the presence of NaOH, the electrocatalytic activity of the employed anode was not comparable to that in NaCl due primarily to the absence of chloride. This indicates that dyes degradation in NaOH occurs exclusively via direct electrochemical process. However, in H 2SO 4, the electrode performance was poor due partially to the absence of chloride from the conductive solution. The possibility of electrode poisoning as a result of growth of adherent film on the anode surface or production of stable intermediates not easily further oxidized by direct electrolysis in H 2SO 4 might also be accountable for the poor performance observed in this conductive electrolyte. Optimizing the conditions that ensure effective electrochemical degradation of Acid Blue and Basic Brown dyes on lead dioxide electrode necessitates the control of all the operating factors.

The Influence of Deposition Conditions and Dopant Ions on the Structure, Activity, and Stability of Lead Dioxide Anode Coatings

β-lead dioxide layers have been electroplated onto gold from nitric acid solutions and the influence of lead(II) concentration, dopant ions in the bath, pH, temperature, current density, and deposition time on the characteristics of the deposits and their properties as anode materials for synthesis and effluent treatment have been examined. The most adhesive, abrasion resistant and chemically stable deposits were prepared in /1 M at a temperature of 333 K and using a current density of ; these deposits had a morphology consisting of angular crystallites but they were rather inactive as anode materials. In many other conditions, deposits were made up of overlapping hemispherical centers. Such layers were significantly less stable in open-circuit conditions and were both dissolved slowly in acids and reduced by dimethyl sulfoxide in acidic solutions. On the other hand, they supported the anodic oxidation of organic molecules. Bismuth(III) was a preferred dopant ions; it led to a preference for deposits consisting of hemispherical centers even in conditions where angular crystallites were formed in the absence of Bi(III). The Bi(III) doped coatings represent the best compromise between stability and the ability to support anodic oxidations.

Long Life Modified Lead Dioxide Anode for Organic Wastewater Treatment: Electrochemical Characteristics and Degradation Mechanism

Recent studies have shown that the lack of ideal anodes with both good activity and stability is still one of the critical problems in electrochemical oxidation for organic wastewater treatment. The electrochemical properties, the activity and stability for anodic oxidation of various phenolic compounds, and the degradation mechanism on a novel beta-PbO2 electrode modified with fluorine resin were investigated. The anode life after modification was greatly improved to be more than 10 yr in common electrochemical current conditions. Such an anode was effective for partial degradation of phenolic compounds, but selective because reactive activities were varied with different substituents. Characterized by SEM and XRD, the crystal form of the anode was verified to be mainly beta-PbO2, and it hardly changed when used for p-nitrophenol degradation for around 320 h although there existed slow electrode corrosion. The active species generated during anodic oxidation were determined to be mainly hydroxyl radical and little ozone. The reactions between hydroxyl radical and phenolic compounds were proved to be electrophilic reactions, based on which a general electrochemical degradation mechanism for aromatic compounds was proposed. In general, such a novel anode has a good performance for organics degradation with perfect electrode life, showing potential for environmental application.

Electrochemical degradation of phenol in aqueous solution on bismuth doped lead dioxide : a comparison of the activities of various electrode formulations

This paper describes the development of electrochemical processes for the oxidative degradation of toxic organic chemicals in waste waters. Doped bismuth lead dioxide anodes have been tested by the kinetic study of phenol anodic oxidation in aqueous solution. The main products during oxidative degradation of phenol are 1,4- benzoquinone, maleic acid and carbon dioxide. Several deposits of Bi2O5–PbO2 on Ti/(IrO2–Ta2O5) substrates have been prepared by anodic oxidation of Pb2+ and Bi3+ in aqueous solutions containing perchloric acid to increase the solubility of bismuth. To study the effect of perchlorate ions, the efficiency of the PbO2 deposit prepared from lead nitrate in an aqueous solution (pure PbO2) was compared with that of a deposit prepared from perchloric acid solution (perchlorate doped PbO2). Although the phenol is oxidized at the same rate on the two deposits, the charge corresponding to the total elimination of 1,4-benzoquinone is three times higher for perchlorate doped PbO2 than for pure PbO2. Phenol degradation is more efficiently carried out on a PbO2 anode doped with perchlorate and with bismuth than on the same electrode doped only with perchlorate. Among the electrodes tested in this work, the pure PbO2 anode is the most efficient for phenol degradation. It is assumed that certain active sites on the anode occupied by perchlorate ions do not participate in the transfer of oxygen atoms and that for the PbO2 electrode doped with bismuth, oxygen evolution is favoured to the detriment of oxygen atom transfer.

Electrochemical degradation of organic substances at PbO 2 anodes: Monitoring by continuous CO 2 measurements

A new method is presented for the continuous detection of the complete degradation of organic compounds during anodic oxidation. The oxidation of different model compounds was studied at lead dioxide anodes in undivided cells employing various current densities. Considerable differences in oxidizability of organic substances were found, e.g. between acetic and oxalic acid. Phenol, 4-hydroxycinnamic acid, glucose and oxalic acid could be mineralized at room temperature. Humic acid could be degraded nearly completely. A conventional DOC analyser was used as a reference standard.

The conversion of isosafrole to piperonal and anethole to anisaldehyde: electrochemical active manganese dioxide

Non-stoichiometric manganese dioxide prepared electrochemically at room temperature and suspended in dilute sulphuric acid is used to oxidise isosafrole to piperonal in 54% isolated yield. The manganese dioxide-manganese(II) sulphate system can be recycled electrochemically at high current density. It has the further advantage that water-soluble materials derived from the chemical oxidation step can be removed by filtration at the manganese dioxide stage. Direct oxidation of isosafrole at a lead dioxide anode leads to further oxidation of the piperonal.

Lectrochemical oxidation of oxalate in alkaline solutions

AbstractExperimental 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.

Electrochemical Incineration of Wastes

Waste biomass oxidation was carried out on platinum and lead dioxide anodes using a electrolyte. Total organic carbon in the electrolyte was reduced by 95%. The use of ultrasound and the addition of the Ce3+/Ce4+ redox couple to the electrolyte enhanced the rates of waste oxidation. Urine‐waste biomass mixtures were electrolyzed indirectly through the anodic generation of OCl−; constituted only 0.1% of the evolved gases. These oxidation treatments offer a means of human waste disposal without producing undesirable chemicals such as , , , , and in the effluent gas.

The Lead Dioxide Anode. II. The Kinetics and Participation of the Lead Dioxide Electrode in Electrochemical Oxidation Reactions in Sulfuric Acid

Lead dioxide is a strong oxidizer in sulfuric acid, consequently electrochemical oxidation of solution species at a lead dioxide anode may occur by a two-step, C-E process (chemical oxidation of solution species by PbO2 followed by electrochemical regeneration of the reduced lead dioxide surface). The maximum rate of each step has been determined in sulfuric acid for specified lead dioxide surfaces and compared with the rates observed for the electrochemical oxidation of cerium(III) and manganese(II) on the same electrode surfaces. While the rate of electrochemical oxidation of a partially reduced PbO2 surface may be sufficient to support the observed rates of CeIII and MnII oxidation at the lead dioxide anode, the rate of chemical reaction between PbO2 and the reducing species is not. Hence it is concluded that the lead dioxide electrode functions as a simple, 'inert' electron-transfer agent during the electrochemical oxidation of CellI and MnII in sulfuric acid. In general, it will most probably be the rate of the chemical step which determines the feasibility or otherwise of the C-E mechanism.

The Lead Dioxide Anode. I. A Kinetic Study of the Electrolytic Oxidation of Cerium(III) and Manganese(II) in Sulfuric Acid at the Lead Dioxide Electrode

The electrolytic oxidation reactions of cerium(III) and manganeseII) in sulfuric acid have been used as probes to investigate the mechanism of the lead dioxide anode. The kinetics observed for such reactions at the lead dioxide surface provide no direct support for the proposal that the lead dioxide anode functions by a sequential 'two-step' mechanism (heterogeneous chemical oxidation of solution species followed by electrochemical oxidation of the reduced lead dioxide surface); rather the kinetics show characteristics similar to those observed previously for the oxidation of cerium(III) and manganese(II) at the platinum electrode, suggesting that the lead dioxide surface functions as a simple, 'inert' electron-transfer agent.

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.

Kinetics and mechanism of anodic oxidation of chlorate ion to perchlorate ion on lead dioxide electrodes

The kinetics and mechanism of anodic oxidation of chlorate ion to perchlorate ion on titanium-substrate lead dioxide electrodes have been investigated experimentally and theoretically. It has been demonstrated that the ionic strength of the solution has a marked effect on the rate of perchlorate formation, whereas the pH of the solution does not influence the reaction rate. Experimental data have also been obtained on the dependence of the reaction rate on the concentration of chlorate ion in the solution at constant ionic strength. With these data, diagnostic kinetic criteria have been deduced and compared with corresponding quantities predicted for various possible mechanisms including double layer effects on electrode kinetics. It has thus been shown that the most probable mechanisms for anodic chlorate oxidation on lead dioxide anodes involve the discharge of a water molecule in a one-electron transfer step to give an adsorbed hydroxyl radical as the rate-determining step for the overall reaction.

Reactive intermediates during oxindation of water lead dioxide and platinum electrodes

Experiments on the interception of reactive intermediates in anodic of water were performed, using p-nitrosodimethylaniline (RNO) as a selective scavenger. At lead dioxide anodes hydroxyl radical OH . and singlet oxygen 1O 2 can be found while at platinum anodes singlet oxygen and peroxo compounds, HOO . or H 2O 2 appear. A mechanism regarding the role of “free” hydroxyl radicals in the formation of ozone at lead dioxide anodes is proposed.

Elektrochemische abscheidung von sauerstoff und ozon an bleidioxid und platin-anoden in wässrigen elektrolyten mit 18O-markiertem wasser

During the electrolysis of water, especially on lead dioxide anodes, a considerable amount of ozone is evolved. It has been proposed by several authors, that a significant contribution to the oxygen atoms of molecular oxygen and ozone originates from the anions of the electrolyte. We have used marked water containing 18O isotopic tracer for solvent, with some of the important oxo-acids and phosphate buffer as electrolytes. On both platinum and lead dioxide anodes we have shown that under the conditions of our experiments at relatively low current densities (200 mA cm 2) all oxygen atoms originate from water only. This applies too for simultaneous reactions as in the case of chlorate oxidation.

Specific orientation of electrochemically deposited PbO 2 crystals

Lead dioxide anodes were prepared by electrodeposition of Pb 2+ on titanium in acidic Pb(NO 3) 2 solutions at 30, 50, 70, 90 and 130°C. The electrodes plated at higher temperatures revealed a progressive increase in the content of β-PbO 2 relative to α-PbO 2. The individual crystals were larger and a higher O 2 O 3 overpotential was observed during the electrolysis of water on such anodes in 0.5 M HClO 4. At higher temperatures the 110 orientation parallel to the geometrical plane of the electrode predominates for the crystallographic planes. An opposite trend can be established for the crystallographic planes 200 and 101.