The preparation and behaviour of Ti/Au/PbO2 anodes

Ti/Au/PbO₂ electrodes have been prepared and their stability in H₂SO₄ (2–12 mol dm^–3) has been studied. It has been found that incorporation of a gold layer between the Ti substrate and the PbO₂ decreases the resistance of the electrode. The corrosion of an electrode polarized anodically increases with H₂SO₄ concentration especially above 8 mol dm^–3 H₂SO₄.     

Mechanism of the action of Ag and As on the anodic corrosion of lead and oxygen evolution at the Pb/PbO(2−x)/H2O/O2/H2SO4 electrode system

When a Pb electrode, immersed in H₂SO₄ solution, is polarized anodically in the PbO₂ potential range the Pb/PbO(_2−x)/H₂O/O₂/H₂SO₄ electrode system is established. Oxygen is evolved at the oxide—solution interface. The oxygen atoms formed as intermediates diffuse into the anodic layer and oxidize the metal. Through a solid-state reaction, the metal is oxidized first to tet-PbO and then to PbO₂. By studying the changes in the rate—potential relations of the above reactions, as well as the phase and chemical composition of the anodic layer, it was possible to elucidate the effect of Ag and As on these processes. The additives were introduced into the electrode system either by alloying with lead or by dissolving them in the H₂SO₄ solution. When added to the solution, both Ag and As lower the overvoltage of the oxygen evolution reaction. They have practically no effect on the corrosion reaction under galvanostatic polarization conditions. If alloyed in the metal, Ag reduces the oxidation rate of Pb significantly, while As enhances it. Both additives lower the stoichiometric number of the anodic oxide layer, ie they retard the oxidation of PbO to PbO₂. The results of these investigations were used to develop further the model of the mechanism of the reactions proceeding during the anodic oxidation of lead in H₂SO₄ solutions.     

Dependence of the phase composition of the anodic layer on oxygen evolution and anodic corrosion of lead electrode in lead dioxide potential region

At potentials more positive than 1300 than 1300 mV with respect to a Hg/Hg₂SO₄ electrode the partial currents of lead corrosion and oxygen evolution in 7_n H₂SO₄ follow the Tafel's dependence. X-ray investigations and wet analyses of the anodic layer show that it consists of tet-PbO and α PbO₂. Besides, at potentials more negative than 1530 mV, β PbO₂ forms at the oxide/solution interface.It is established that lead anodic corrosion proceeds in two stages. During the first Pb is oxidized to tet-PbO. During the second stage tet-PbP is oxidized to PbO₂. If this process is performed in solid state, α PbO₂ forms. If PbO is dissolved and then oxidized, β PbO₂ crystals are formed. The oxidation of tet-PbO to α PbO₂ proceeds at different rates in the bulk of the oxide and at its surface with the solution. At potentials more positive than 1530 mV the oxidation of tet-PbO to α PbO₂ at the surface of the oxide with the solution leads to the dropping off of part of the oxide layer.The oxidation of Pb and PbO is carried out under the action of O atoms and O^? radicals which evolve at the oxide/solution interface and penetrating the oxide reach the metal/oxide surface.     

Electrochemical deposition of lead dioxide in the presence of polyvinylpyrrolidone: A morphological study

In this work, we investigate the effect of polyvinylpyrrolidone (PVP) on the morphology and the interfacial properties of lead dioxide (PbO₂). The electrodeposition of lead dioxide was achieved in the presence of PVP on Pt and Ti substrates under constant current density from solutions containing Pb(NO₃)₂ and NaF in HClO₄. Scanning electron microscopy (SEM) showed that the morphology and particle size of PbO₂ are strongly affected by the concentrations of Pb(NO₃)₂, PVP and HClO₄. It seemed that PVP can control both the morphology and particle size of lead dioxide and increases the overpotential for oxygen evolution during the electrodeposition of lead dioxide. The resulting lead dioxide was composed of nano-metric globular particles aligned in rice shaped structure with diameter in the range of 30-50 nm. It was suggested that the growth of PbO₂ crystals is affected by the aqueous network of self-assembled surfactant formed on the electrode surface during the electrodeposition process. The electrochemical impedance spectroscopy (EIS) was used to investigate the interfacial behavior of deposited lead dioxide in 0.5 M H₂SO₄ solution. The EIS results revealed a typically porous electrode behavior consisted of a straight line, at high frequency region, turning to a potential dependent semicircle, at low frequency region, the diameter of which being decreased with increasing potential increments. The X-ray diffraction (XRD) patterns show that samples were composed of β-PbO₂.     

Fundamentals of lead-acid cells. XVII. The a.c. impedance of lead dioxide formed in sulphuric acid on some lead alloys

The impedances of PbO₂ formed on lead and some lead alloys have been measured over a wide range of potential. Conditions were chosen so that well-defined electrode states were obtained. Considerable differences were observed in the behaviour of alloys containing antimony and bismuth. The latter alloying ingredient appears to contribute some semiconducting properties to lead sulphate films formed on PbO₂ by polarizing them at potentials negative to the reversible potential in sulphuric acid.Nomenclature C _L double-layer capacitance - C _X series capacitance - D diffusion coefficient - E potential - R _CT charge-transfer resistance - R electrolyte resistance - Z _D impedance as defined by Equation 1 - Z _F impedance as defined by Equation 2 - Z impedance as defined by Equation 3 - Warburg coefficient - angular frequency     

The distribution of antimony in the oxide layer formed by potentiostatic oxidation of Pb-Sb alloy

The distribution of antimony within the oxide films on Pb-Sb alloy prepared by potentiostatic oxidation in H₂SO₄ solutions was examined by SIMS. The study of oxide films prepared by applying different potentials for three hours showed that two types of film were obtained depending on whether the potential was more negative or more positive than 1·5 V. Antimony profiles were obtained for films at several stages in the initial growth. It was found that antimony was retained in the oxide film at 1·5 V during both nucleation and two- or three-dimensional growth of PbO₂ and at 1·6 V during the lateral overlaps of three-dimensional centres of PbO₂. Relationships between the antimony distribution profiles and the oxide film growth are discussed.     

Effect of H3PO4 on the PbSO4/PbO2 electrode in H2SO4 solutions

The influence of H₃Po₄ small additions on the polarization behaviour of the PbSO₄/PbO₂ electrode, in H₂SO₄ solutions of different concentrations, was studied using the microelectrode technique and the coulometric method. The reference electrode was the Hg/Hg₂SO₄/H₂SO₄ electrode. The potentiogram analysis and the coulometric measurements show that the main effect of the H₃PO₄ is the drastic passivation of the electrode processes, within the potential range under study, ie the +800 mV to +1650 mV potential range. The Q_a and Q_c electricity amounts are of about 5–10 times smaller in the H₂SO₄ solution with H₃PO₄ addition, compared with the H₂SO₄ solution free of H₃PO₄ addition. A high increase of the oxygen evolution overvoltage could also be seen. Taking into account the ratio between the H₃PO₄ addition amount, in % (w/o) and the PbO₂ active mass per unit surface area, from the lead acid batteries, we can conclude that the small H₃PO₄ additions do not decrease the capacity of the active mass of the battery, but they hinder the insulator film formation between the active mass and the grid.     

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.     

Electrodeposited PbO2 thin film as positive electrode in PbO2/AC hybrid capacitor

Lead dioxide (PbO₂) thin films were prepared on Ti/SnO₂ substrates by means of electrodeposition method. Galvanostatic technique was applied in PbO₂ film formation process, and the effect of deposition current on morphology and crystalline form of the PbO₂ thin films was studied by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The energy storage capacity of the prepared PbO₂ electrode was investigated by means of cyclic voltammetry (CV) and charge/discharge cycles, and a rough surface structure PbO₂ film was selected as positive electrode in the construction of PbO₂/AC hybrid capacitor in a 1.28 g cm⁻³ H₂SO₄ solution. The electrochemical performance was determined by charge/discharge tests and electrochemical impedance spectroscopy (EIS). The results showed that the PbO₂/AC hybrid capacitor exhibited high capacitance, good cycling stability and long cycle life. In the voltage range of 1.8-0.8 V during discharge process, considering the weight of all components of the hybrid capacitor, including the two electrodes, current collectors, H₂SO₄ electrolyte and separator, the specific energy and power of the device were 11.7 Wh kg⁻¹ and 22 W kg⁻¹ at 0.75 mA cm⁻², and 7.8 Wh kg⁻¹ and 258 W kg⁻¹ at 10 mA cm⁻² discharge currents, respectively. The capacity retains 83% of its initial value after 3000 deep cycles at the 4 C rate of charge/discharge.     

Fundamentals of lead-acid cells. X. The formation of PbO2 on lead and antimonial lead

The electrochemical oxidation of films of lead sulphate formed by the cyclic sweep method has been examined using the potential step technique. Gross differences in behaviour are observed between the lead and antimonial lead alloy, the most important being the appearance of an additional peak in the transient response of the antimony alloy. An interpretation is given in terms of the structure of the grown lead sulphate film. The oxidation behaviour of the lead sulphate deposits depends on the length of time the electrode is held potentiostatically controlled in the lead sulphate region before being stepped to the PbO₂ region. The results can be readily interpreted in terms of the density of nucleation sites and the formation of the PbO₂phase by the two-dimensional growth of instantaneously nucleated layers.     

Investigation on electrochemical properties of cerium doped lead dioxide anode and application for elimination of nitrophenol

The present work focused on the investigation of electrochemical properties of cerium doped lead dioxide anode, i.e. Ti/Ce–PbO₂. SEM, AFM, XRD and XPS were used to characterize the morphology, crystal structure and elemental states of the modified anode. Electrochemical impedance spectroscopy (EIS) was also utilized to study the electrochemical property of Ti/Ce–PbO₂. The electrochemical activity of the Ti/Ce–PbO₂ anode was investigated by means of bulk electrolysis and compared with that of a PbO₂ anode. The accelerated life test and oxidants determination were also conducted. The results indicated that the incorporation of cerium improved the electrocatalytic activity and stability of PbO₂ anode. The service life of Ti/Ce–PbO₂ electrode was much longer than that of traditional lead dioxide electrode. The electrochemical activity obtained from degradation of o-nitrophenol (o-NP) outperformed the traditional lead dioxide electrode as well. The Ti/Ce–PbO₂ electrode is considered a promising anode for the treatment of organic pollutants.     

Three electrolyte high voltage acid–alkaline hybrid rechargeable battery

Performance characteristics of a three electrolyte rechargeable acid–alkaline hybrid battery using a PbO₂ positive plate and a nickel metal hydride (NiMH_x) negative electrode in separate electrolyte of H₂SO₄ and KOH were studied. This hybrid battery has three electrolytes in a single cell. A neutral K₂SO₄ salt solution was placed between the acid and alkaline compartments of the cell, in which a cation exchange membrane and an anion exchange membrane, were employed to separate these three electrolytes. The open circuit voltage of this hybrid cell was found to be 2.64 V in an electrolyte configuration of 1 M H₂SO₄|0.2 M K₂SO₄|2 M KOH electrolyte configuration, compared to 1.92 V in the conventional lead-acid cell in 1 M H₂SO₄ and 1.40 V in a NiMH_x cell in 2 M KOH. This hybrid acid–alkaline PbO₂/NiMH_x battery was shown to operate with a voltage 20% higher than the conventional lead acid battery and 110% higher than nickel–metal hydride battery at 1/3 C discharging rate. The concentrations of the three electrolytes, the dimension of the electrolyte chamber, and other cell/operation parameters with impacts on the hybrid cell performance were investigated.     

Formation d'un film conducteur de PbO2 sur electrodes de niobium et de tantale

The electrochemical behaviour of Nb and Ta electrodes in H₂SO₄ and HClO₄ acids as well as in NaOH alkaline solutions has been studied. The current-voltage curves show that these metals undergo immediate passivation in acid medium. Whereas, in alcaline solutions, the oxydation rate is extremely slow; so, it is possible to reach potentials positive enough to let electrocrystallization of PbO₂ take place, which is in contradiction with the thermodynamic previsions derived from Pourbaix diagrams.These properties lead to the preparation of Nb or Ta electrodes, coated with an electronic conducting oxide, which can be used as positive electrodes in H₂SO₄ solutions.     

The electrochemical production of cobaltic sulphate

The electrochemical preparation of cobaltic sulphate has been studied and we have found that the reaction is best effected in 40 wt% H₂SO₄ in the presence of silver ions as the catalyst, using PbO₂ as the anode, with a low current density and a low conversion.     

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.     

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.     

The behaviour of PbO2 in concentrated sulphuric acid

Linear sweep experiments on Pb in H₂SO₄ at concentrations in excess of 5 mol dm^–3 have been conducted using computer controlled techniques. Measurements have indicated that the maximum charge in the PbO₂ reduction peak occurs at 5 mol dm^–3, the available capacity decreasing with the concentration of H₂SO₄.     

Electrocatalytic oxidation of 2-chlorophenol on a composite PbO2/polypyrrole electrode in aqueous solution

The electrocatalytic oxidation of 2-chlorophenol on a composite PbO₂/polypyrrole (PPy) electrode was carried out in 0.1 m H₂SO₄ solution. The composite PbO₂/PPy electrode was developed by the codeposition of polypyrrole and PbO₂ microparticles on the PbO₂/SnO₂/Ti substrate. The PbO₂ microparticles and polypyrrole in the composite electrode were observed to be hydrophilic active-sites and hydrophobic inactive-sites, respectively. The results indicated that the conversion of 2-chlorophenol and the efficiency of electrooxidation were improved on the hydrophobic-modified PbO₂/PPy electrode. The performance for electrooxidation of 2-chlorophenol on the composite PbO₂/PPy electrode was better than that on Pt or PbO₂/SnO₂/Ti electrodes. The thicker the composite (PbO₂/PPy) layer, the more active-sites in the composite electrode and the more 2-chlorophenol could be oxidized.     

Controllable preparation of Ti/TiO2-NTs/PbO2–CNTs–MnO2 layered composite materials with excellent electrocatalytic activity for the OER in acidic media

High oxygen evolution overpotential and low corrosion resistance are the main challenges for oxygen evolution materials in acidic media. In this study, a novel composite material, Ti/TiO₂-NTs/PbO₂–CNTs–MnO₂, with high oxygen evolution electrocatalytic activity was successfully prepared. First, TiO₂ nanotubes (TiO₂-NTs) were synthesized in situ on a Ti sheet via anodization and used as an intermediate layer. Subsequently, the adhesion and conductivity of the TiO₂-NTs layer were increased through additional anodization, annealing, and electrochemical reduction. Finally, PbO₂ was electrodeposited with a constant current in a lead acetate medium and doped with carbon nanotubes (CNTs) and MnO₂. The surface morphology, phase composition, and electrochemical performance of the composite materials were investigated. Notably, in an acidic electrolyte (150 g/L H₂SO₄), Ti/TiO₂-NTs/PbO₂–CNTs–MnO₂ exhibited good stability (30 h) and a low oxygen evolution overpotential of 410 mV at 50 mA/cm², which is almost equivalent to that of precious metals (RuO₂ and IrO₂) and 499 mV lower than that of the industrial Pb–0.76 wt% Ag alloy. The outstanding performance is mainly attributed to the high aspect ratio of the TiO₂-NT structure, synergistic effects of the active particles, and inherently good electrochemical properties of the active particles. Therefore, this study provides a new synthetic route for oxygen evolution materials in acidic media.     

Lead oxides as cathode for lithium non-aqueous cells

The cathodic behaviors of PbO (red and yellow), Pb₃O₄, Pb₂O₃ and PbO₂ (α and β) in lithium cells were presented. A single plateau at 1.4–1.5 V was observed over the wide range in discharge curves at 0.1 mA. cm^?2 for PbO (red), Pb₃O₄ and Pb₂O₃ cathodes, and two plateaus were observed for PbO (yellow) cathode. The both types of PbO₂ showed the complicated behaviors in discharge curves. For a low current density discharge to 2 V end-voltage, the cell with α-PbO₂ showed 95–100% of utilization based on one electron transfer per molecule.The structural changes of these lead oxides during discharge were examined, and the final reduction product was proved to be lead metal. The cell reaction of these lead oxides were also examined from X-ray and electrochemical data.The performance of 1.5 V lithium cell system with PbO (red), Pb₂O₃ and Pb₃O₄ cathodes, and 3 V lithium cell system with α-PbO₂ cathode were demonstrated and discussed.