Lead Dioxide Electrode Research Articles

Fundamentals of lead acid cells: Part IV. The reduction of porous PbO 2 electrodes in sulphuric acid

The reduction behaviour of porous lead dioxide electrodes is shown to be independent of rotation speed in a large excess of 5 M H 2SO 4. The reduction peak is broadened by the porosity. This porosity broadening is interpreted in terms of the reaction being driven more deeply into the pore structure as the front of the electrode becomes progressively more ressstive. The effect of different potential sweep rates on the current response and the effects of progressive redox cycles can be fully explained on this model.

An investigation of the surface structure of some lead dioxide and related electrodes

S.E.M. observations have been carried out on PbO2 and related electrodes after electrochemical reaction in 5 M H2SO4. The morphology of the surfaces examined is strongly effected by their history, particularly their charge/discharge cycles. PbSO4 formed by the self-corrosion process is much more porous than that formed by the electrochemical reduction of PbO2.

ChemInform Abstract: PREPARATION AND APPLICATIONS OF GRAPHITE SUBSTRATE LEAD DIOXIDE (GSLD) ANODE

AbstractÜbersicht.

Electrically generated lead(IV) acetate and manganese(III) acetate as reagents for coulometric redox titrations in acetic acid

The conditions were investigated for electrochemical generation of lead(IV) acetate in acetic acid by oxidation of lead(II) acetate on a lead dioxide electrode and on a platinum electrode. Bivalent manganese ions are quantitatively oxidized on a platinum electrode to the tervalent state in the same solvent. Coulometric titration methods for the determination of small amounts of hydroquinone in acetic acid were developed on the basis of the electrically generated oxidizing agents. Better results were obtained in titration with electrogenerated manganese(III) acetate. The titration end-point was detected by the biamperometric method. Suitable redox indicators were found.

The anodic oxidation of benzene, toluene and anisole

The oxidation of benzene, toluene and anisole was studied on lead dioxide electrodes and platinum and graphite anodes. Product analysis showed that partial oxidation of benzene to benzoquinone occurred on lead dioxide electrodes with up to 100% current efficiency in the lower potential region studied. At higher anodic potentials, with concurrent oxygen evolution, fragmentation occurred yielding maleic acid and CO 2. Work with a RDE showed that for benzene and toluene the oxidations were reaction-controlled in the lower potential regions and it was here that the effect of pH and reactant concentrations were studied. The reaction was second order with regard to the organic species and zero order in pH. In the case of anisole the reaction appeared to be mass transport controlled over the RDE rotation rate studied. The kinetic data and comparisons with reactions found on Pt and C tend to support the mechanism based on electrochemical formation of PbO 2 followed by a chemical reaction of this with the substrate, rather than the other, purely electrochemical mechanisms which have been recently proposed.

The formation of lead dioxide electrodes by the planté process

The effects of forming agents (aggressive ions) on the electro-oxidation of massive lead (the Planté electrode process) in sulphuric acid solution are reported. Linear sweep voltammetric measurements corresponding to the most effective forming agents, ClO − 4, NO − 3, BF − 4 and CH 3COO −, are presented. The current peaks characteristic of the lead → lead sulphate reaction are not affected by the aggressive ions. The attacking effect of the ions lies in promoting the direct conversion of lead to lead(II) species in the presence of a coherent (usually passivating) film of lead sulphate. The order of effectiveness of the aggressive ions is ClO − 4 > NO − 3 > = CH 3COO −. Other methods of Planté electrode production involving “a.c./d.c.” and “immediate post-deposition oxidation” are described. Although these are slightly more effective than the reaction in the absence of a forming agent, they are nothing like so effective as the aggressive ion promoted reaction.

Zum verlauf der entladereaktion positiver aktivmassen des bleiakkumulators

With the progressive discharge of porous lead dioxide electrodes the PbO 2 content decreases and that of PbSO 4 increases correspondingly. If

Cyclic behaviour of lead dioxide electrodes in tetrafluorborate solutions*

Lead dioxide electrodes of the first kind (thin layers on Pt) have been investigated in tetrafluorborate solutions with the aid of slow (40 mV min−1) cyclic voltammetry. Reaction orders for protons of 0.7 to 1 are found for cathodic dissolution and of 0 to −1 for anodic deposition in the range of 0.1 to 4.5 M HBF4. Large overvoltages in both directions are greatly reduced at elevated temperatures (up to 85°C). A cathodic reaction-limited current is found to increase sharply with proton concentration and temperature. The activation energy is 40.6 kJ mol−1 (9.7 kcal mol−1). Some new aspects of the mechanism of reactions at lead dioxide electrodes are derived. A continuous sequence of electrochemical and chemical steps (protonation, hydration) occurs at the interface of a polarized electrode. Normally, the electrochemical formation of the Pb(III) intermediate is rate determining, but in special cases chemical steps with Pb(II) species predominate. Arguments for formation of a gel film, at least at cathodic polarization, are given.

Cyclic behaviour of lead dioxide electrodes in tetrafluorborate solutions

Lead dioxide electrodes of the first kind (thin layers on Pt) have been investigated in tetrafluorborate solutions with the aid of slow (40 mV min −1) cyclic voltammetry. Reaction orders for protons of 0.7 to 1 are found for cathodic dissolution and of 0 to −1 for anodic deposition in the range of 0.1 to 4.5 M HBF 4. Large overvoltages in both directions are greatly reduced at elevated temperatures (up to 85°C). A cathodic reaction-limited current is found to increase sharply with proton concentration and temperature. The activation energy is 40.6 kJ mol −1 (9.7 kcal mol −1). Some new aspects of the mechanism of reactions at lead dioxide electrodes are derived. A continuous sequence of electrochemical and chemical steps (protonation, hydration) occurs at the interface of a polarized electrode. Normally, the electrochemical formation of the Pb(III) intermediate is rate determining, but in special cases chemical steps with Pb(II) species predominate. Arguments for formation of a gel film, at least at cathodic polarization, are given.

Thermal Decomposition Mechanism of Formed and Cycled Lead Dioxide Electrodes and Its Relationship to Capacity Loss and Battery Failure

The structural changes accompanying capacity loss in the electrode were followed using differential thermal analysis. The thermal decomposition mechanism of formed plates was found to differ, depending on the method of manufacture. All cycled plates, however, gave the same decomposition mechanism after a few cycles. The major changes in the DTA curves, as the positive electrode was cycled to failure, was the gradual disappearance of the exothermic peak at 200°C and the endothermic peak at 358°C. It is believed that these peaks are associated with an electrochemically active amorphous form of . As the electrochemically active is cycled to failure it is converted to an electrochemically inactive form of . This latter form of gives DTA results similar to those obtained on reagent . The continual conversion of electrochemically active to the electrochemically inactive is one of the major factors that accounts for the loss in battery capacity and ultimate failure.

Determination of sulfur dioxide by anodic oxidation on lead dioxide electrodes.

Determination of sulfur dioxide by anodic oxidation on lead dioxide electrodes.

A mathematical model for the porous lead dioxide electrode. II. The pseudo-steady state approach for low rates of discharge

A theoretical analysis of the discharge behaviour of the porous lead dioxide electrode at low current densities is made on the basis of a previously proposed model. The pseudo-steady state approach proves to be useful for low rates of discharge, while it fails for rapid discharges. The current distribution at low rates of discharge becomes non-uniform during discharge because of concentration changes and decreasing porosity. The maximum of the current distribution moves inwards into the electrode during discharge, as a result of the gradual insulation of the electrode surface by lead sulphate crystals. At the end of a slow discharge the electrode material has been uniformly utilized along the depth of the electrode, provided that the porosity is sufficiently high. If, however, the initial porosity is less than about 50% the inner parts of the electrode may not always be fully utilized because of the extensive plugging of the pores by lead sulphate crystals.

A mathematical model for the porous lead dioxide electrode

A theoretical model for the porous lead dioxide electrode is proposed on the basis of the macrohomogeneous model for porous electrodes. The structural changes during discharge, due to precipitation of lead sulphate, are considered. The two main structural effects, plugging of the pores and gradual insulation of the active electrode surface by the reaction product, lead sulphate, are both considered by relating them to the local degree of discharge. The numerical results show that, at high current densities, the discharge capacity is limited by both structural and transport restrictions. At the end of discharge a layer of lead sulphate crystals blocks the electrode surface in the outer layers of the electrode. The current can then neither be transferred across this insulated surface nor reach remaining active material in the inner parts of the electrode because of acid depletion, which is furthermore accelerated by the decreasing porosity.

Current Distribution in the Porous Lead Dioxide Electrode

A theoretical analysis of initial current distribution in the porous lead dioxide electrode is made by application of the macrohomogeneous model for porous electrodes. The parameters in the model have been determined experimentally for the investigated lead‐dioxide battery plates. The theoretical results are in good agreement with experimental determinations by means of electron microprobe analysis of the ‐distribution within partly discharged positive lead‐acid plates. The experimental studies of current distribution shows that at high current densities the electrode reaction takes place mainly in the outer layers of the electrode. At low discharge currents, the initial current distribution is uniform while after the first quarter of discharge, the outer layers are more utilized than the inner parts. A mechanism for the passivation of the positive plate in the lead‐acid battery is proposed.

Lead dioxide electrode

Lead dioxide electrode

The Crystallography of Formed and Cycled PbO2 Electrodes

The discharge‐recharge cycle process of the lead dioxide electrode was followed by means of optical microscopy. The lead dioxide microstructure obtained from the original formation, using cured electrode materials consisting of a mixture of and basic lead sulfates, was different from that obtained by recharge from an electrode reduced to normal lead sulfate. The lead dioxide electrodes, obtained from various sources and with various microstructures in the original as‐formed condition, all converted to practically the same microstructure after receiving only a few cycles. Although the microstructure underwent further change with increasing cycling, the plates from different manufacturers continued to resemble one another after any given number of cycles.

Morphological Changes in the Lead Dioxide Electrode During Its Reduction and Reoxidation

The discharge and recharge of the electrode was followed by optical microscopy. During discharge the dissolved with simultaneous growth of relatively large crystals. nucleated at preferred sites on the and did not form a passivating film over other parts of the surface. The remaining at the end of discharge, however, had been encapsulated within crystals grown during the discharge. During recharge these particles within the crystals offered a conductive path through the highly resistive , and the formation of began within the encapsulating crystals at the surface of these residual particles. thus formed grew rapidly toward the surface of the crystals and, when reaching the surface, appeared to spread to surround the crystals, encapsulating them in turn and leaving hollow shells as the crystals dissolved.

Voltammetry at the lead dioxide electrode: Anodic EDTA currents

In the presence of 10−5 Mor larger concentrations of EDTA in acetate buffer, a lead dioxide electrode exhibits relatively high anodic currents at positive potentials. The mechanism for this electrode reaction was investigated. The results of experiments including manual current-voltage plots, u.v. absorption, coulometry, chronopotentiometry, and linear sweep voltammetry are presented. A mechanism is suggested which involves oxidation of non-stoichiometric (defect) lead species in the electrode lattice by electroinductive coordination effects of EDTA and a catalytic electrode reaction mechanism.

Voltammetry at the lead dioxide electrode: anodic EDTA currents

In the presence of 10−5 Mor larger concentrations of EDTA in acetate buffer, a lead dioxide electrode exhibits relatively high anodic currents at positive potentials. The mechanism for this electrode reaction was investigated. The results of experiments including manual current-voltage plots, u.v. absorption, coulometry, chronopotentiometry, and linear sweep voltammetry are presented. A mechanism is suggested which involves oxidation of non-stoichiometric (defect) lead species in the electrode lattice by electroinductive coordination effects of EDTA and a catalytic electrode reaction mechanism.

Gegenwärtiger stand der forschungsarbeiten an positiven elektroden in bleiakkumulatoren

Since Planté invented the conventional lead—acid accumulator in 1859, research on its electrochemical basis has continued. Particular interest has been laid upon the reaction of the active positive mass. Particularly because of the discovery of a second lead—dioxide modification, experiments have been reanimated during the past 15 years. The present report outlines the essential facts known about the characteristics of positive lead-dioxide electrodes and gives a survey of the literature on the subject.