PbO2 Electrode Research Articles

Preparation and Electrocatalytic Performance of Three-Dimensional Porous Structure PbO2 Electrodes Using Oxygen Bubble as Dynamic Templates

The three-dimensional porous structure PbO2 electrodes (3D-PbO2) were successfully prepared in the lead nitrate solution by potentiostatically electrodeposition methods using oxygen bubbles as dynamic template. The morphology and structure of 3D-PbO2 electrodes were investigated by scanning electronic microscopy (SEM) and X-ray diffraction (XRD). Compared with the traditional PbO2 electrodes (Flat-PbO2), 3D-PbO2 electrodes possess the three-dimensional porous structure and finer grain size. The electrochemical properties of 3D-PbO2 electrodes were investigated by linear sweep voltammetry (LSV), cyclic voltammetry (CV) and electrochemical impedance spectrum (EIS). The 3D-PbO2 electrodes show larger electrochemical active surface area, lower charge transfer resistance and higher oxygen evolution overpotential than Flat-PbO2 electrodes. In the electrocatalytic degradation process of malachite green, the degradation rate constant of 3D-PbO2 electrodes (0.05189 min−1) was 5.8 times than that of Flat-PbO2 electrodes (0.00889 min−1).

Anodic Oxidation of Chlorinated Pesticides on BDD and PbO2 Electrodes: Kinetics, Influential Factors and Mechanism Determination

In this work, the removal of two pesticides 1, 2- dichlorobenzene and 1, 4- dichlorobenzene by electrolysis using BDD and Pb/PbO2 as anodes is studied. Different operating conditions and factors affecting the treatment process including anode material, applied current density, supporting electrolyte and initial pH value were studied and optimized. Results demonstrate, as expected, that the influence of the anode material used on the degradation of pesticides was very significant in all cases. Infact electrolysis with diamond electrodes can attain the complete depletion of the pesticide and its mineralization faster than with PbO2 anode. Electrolysis experiments strongly improves that the complete degradation of pesticides occurred in the presence of Na2SO4 as conductive electrolyte at current density equals 20 mA cm-2. Acidic pH would accelerate dichlorobenzene degradation, whereas alkaline condition showed negative effects. The disappearance of the pesticides followed a pseudo-first-order kinetics. Reversed-phase chromatography allows detecting Catechol, 2-chlorophenol and Pyrogallol as primary aromatic intermediates of 1,2-DCB and Hydroquinone, Benzoquinone and 4-chlorophenol for 1,4-DCB. Dechlorination of these products gives chloride ions Cl-. Ion-exclusion chromatography reveals the presence of maleic, formic, fumaric, malonic, glyoxylic, acetic and oxalic acid. An oxidation mechanism is proposed in agreement with other works shown in the literature.

Electrochemical Degradation of Methyldopa on a Fe Doped PbO2 Electrode: Electrode Characterization, Reaction Kinetics and Energy Demands

The electrochemical degradation of methyldopa in aqueous solution using a Fe-PbO2 electrode was systematically investigated. In contract with the traditional undoped PbO2 electrode, the constructed Fe-PbO2 electrode displayed a more compact structure with smaller crystal size, accompanying with larger electrochemically active surface area and higher electrochemical activity. The effects of operational parameters were studied, and according to the degradation efficiency and energy efficiency, the relative optimal experimental conditions were identified as electrolyte concentration 0.1 mol/L, current density 30 mA/cm2, initial methyldopa concentration 800 mg/L and initial pH 3. The EE/O values were calculated among all the experiments, providing the economic evaluation for the treatment of organic pollutants using electrochemical oxidation method. Kinetic investigations demonstrated that the degradation of methyldopa followed the pseudo-first-order kinetic model.

Fabrication and Water Treatment Application of High Efficient PbO<sub>2</sub> Electrode

A novel and high efficient PbO2 electrode has been fabricated in the present study for refractory wastewater treatment. The traditional Ti plate is made into honeycomb by electronic corrosion to be used as electrode basement. The novel surface topography improves the specific surface area of the electrode material and enhances the adhesion of surface coating. SnO2-Sb layer is deposited between basement and PbO2 layer which reduces the thermal stress and improve electrode life. Rare earth element La is doping into PbO2 layer to improve the lattice structure and the catalytic performance. Finally, F ion is adding into the catalytic layer to improve the smoothness of the material surface. Characterized by SEM and XRD, results showed that the electrode prepared has novel surface morphology. Pollutants degradation results and electrode life test showed that the PbO2 electrode investigated in the present study has great advantage compared with traditional electrodes and has good application prospect.

Effects of Tungsten Carbide on the Electrocatalytic Activity of PbO2-WC Composite Inert Anodes during Zinc Electrowinning

β-PbO2-WC composite electrodes were prepared via direct electrodeposition in a lead nitrate solution that contains WC microparticles. The effect of WC concentration in the composite anode material was emphasized. The surface microstructure was characterized by scanning electron microscopy (SEM), and the electrocatalysis of oxygen evolution behavior was investigated using anodic polarization curves, cyclic voltammetry curves and electrochemical impedance spectroscopic (EIS) measurements in a synthetic zinc electrowinning electrolyte of 50 g·L−1 Zn2+ and 150 g·L−1 H2SO4 at 40°C. The results show that the addition of WC can clearly decrease the grain size of PbO2 electrodes, and the electrodes become more compact. The addition of WC can increase the exchange current density j0 of a composite electrode during the process of oxygen evolution, reduce the apparent activation energy Ea of the oxygen evolution reaction, increase the values of electric double layer capacitance Cdl during the charging process, increase the electric double layer capacitance Qdl of oxygen evolution reaction process, and reduce the values of charge transfer resistance Rct; and also can improve the electrocatalytic stability. The doping of WC in the Ti/β-PbO2 composite electrode can effectively improve the electrode coating microstructure, increase the electrocatalytic activity of the oxygen evolution reaction in the electrolytic zinc liquid and exert positive effects on the application of the composite electrode.

Hydroxyl multi-walled carbon nanotube-modified nanocrystalline PbO2 anode for removal of pyridine from wastewater

We prepared a hydroxyl multi-wall carbon nanotube-modified nanocrystalline PbO2 anode (MWCNTs-OH-PbO2) featuring high oxygen evolution potential, large effective area, and excellent electrocatalytic performance. The oxygen evolution potential and effective area of the MWCNTs-OH-PbO2 electrode were 1.5 and 3.7-fold higher than the traditional PbO2 electrode. Electrochemical degradation of pyridine in aqueous solution was investigated by using the MWCNTs-OH-PbO2 anode. Based on pyridine decay rate (93.8%), total organic carbon reduction (84.6%), and energy consumption (78.8WhL−1order−1) under the optimal conditions, the MWCNTs-OH-PbO2 electrode modified with MWCNTs-OH concentration of 1.0gL−1 exhibited higher electrochemical oxidation ability than the traditional PbO2 electrode. The intermediate, hydroxypyridine, was found at the first stage of electrolysis. The primary mineralization product, NO3−, was detected in aqueous solution after electrolysis. A possible electrochemical mineralization mechanism including two potential routes, i.e., via formation of small organic molecules by ring cleavage reaction and direct mineralization to CO2 and NO3−, was proposed. The results demonstrated that the MWCNTs-OH-PbO2 electrode exhibited high efficiency for pyridine mineralization in aqueous solution under mild conditions.

Comparison of the electrooxidation performance of three-dimensional RVC/PbO2 and boron-doped diamond electrodes

Although studies reported in the literature have described the electrooxidation of organic compounds using flat PbO2 and boron-doped diamond (BDD) electrodes, the use of three-dimensional anodes for this purpose is very scarce. As far as we know, there have been no comparisons of the electrooxidation performance of 3D anodes and BDD electrodes. In this work, we demonstrated that outstanding oxidation kinetics, current efficiency, and energy consumption were obtained when a flat plate PbO2 electrode was replaced by a three-dimensional RVC/PbO2 anode. The synergic effects of greater surface area and enhanced mass transfer resulted in electrooxidation of glyphosate and phenol comparable to that obtained with a boron-doped diamond electrode, in terms of reaction rate, current efficiency, and energy consumption. These results showed that the 3D anode could be employed as an inexpensive option for the degradation of organic compounds.

Highly efficient and stable Zr-doped nanocrystalline PbO2 electrode for mineralization of perfluorooctanoic acid in a sequential treatment system.

Zr-doped nanocrystalline PbO2 (Zr-PbO2) film electrodes were prepared at different bath temperatures. The Zr-PbO2 electrode doped at 75°C (75-Zr-PbO2) featured high oxygen evolution overpotential, large effective area and good electrocatalytic performance. The oxygen evolution potential and the effective area of 75-Zr-PbO2 achieved 1.91V (vs. SCE) and 9.1cm2, respectively. The removal efficiency and the defluorination ratio of PFOA reached 97.0% and 88.1% after 90min electrolysis. The primary mineralization products (i.e., F- and intermediates) and their change trends were determined. The 75-Zr-PbO2 electrode was introduced to sequentially treat the PFOA wastewater. In an 116h of 75-Zr-PbO2 electrocatalysis sequential process, the PFOA, PFHpA, PFHxA, PFPeA, PFBA, PFPrA, TFA, and TOC concentrations were reduced to below 30, 2.5, 1.3, 1.0, 0.5, 0.2, 0.1, and 9mgL-1, respectively, demonstrating the promising application of the sequential treatment system for the treatment of PFOA wastewater.

Electrochemical oxidation of ofloxacin using a TiO2-based SnO2-Sb/polytetrafluoroethylene resin-PbO2 electrode: Reaction kinetics and mass transfer impact

Electrochemical oxidation has been proposed for the destruction of organic contaminants; however, this process is hampered by low oxidation efficiency and high energy cost. Accordingly, we developed a TiO2-based SnO2-Sb/polytetrafluroethylene resin (FR)-PbO2 electrode that was based on TiO2 nanotubes. We tested the performance of the electrode on an antibiotic, ofloxacin, and identified the major pathway of ofloxacin oxidation. We found growing TiO2 nanotubes on Ti material increased current efficiency, and the electrical efficiency per order (EE/O, kWh/m3) for oxidation was decreased by 16.2%. Our electrode requires a large overpotential before electrons flow, which minimizes oxygen evolution, reduces hydrogen peroxide and ozone generation, and favors hydroxyl radicals (HO) production. We found the electron efficiency (EE) during oxidation was as high as 88.45%. In other words, 88.45% of the electrons that flow out of the electrode cause oxidation. The effects of current density, initial concentration, pH value and electrolyte concentration were investigated. A differential column batch reactor (DCBR) was used to simulate the performance of continuous plug flow reactor and we found that the destruction of ofloxacin followed pseudo-first order model. We also evaluated the impact of mass transfer on electrochemical performance. The effects of fluid velocity and electrode spacing on oxidation rate were evaluated by determining the mass transfer coefficient and the effectiveness factor Ω (between 0 and 1). Our experiments and calculations indicated that the mass transfer reduced oxidation rate by more than 55% (Ω<0.45) for an electrode spacing of 1cm at a fluid velocity of 0.033m/s. Unlike studies carried out using completely mixed batch reactor, the DCBR can simulate the flow conditions in pilot or full scale reactors; consequently, observed pseudo-first order rate constants in the DCBR can be used for preliminary design.

Three-dimensional anodes prepared by electrodeposition of β-PbO2 onto reticulated vitreous carbon with different porosities

Abstract

Fabrication and characterization of PbO2 electrode modified with polyvinylidene fluoride (PVDF)

A novel PbO2 electrode with a high oxygen evolution potential (OEP) and long service life was successfully fabricated by doping polyvinyl fluoride (PVDF) (marked as PbO2-PVDF) through co-deposition method. The morphology (SEM), elemental analysis (EDX), hydrophobic property (contact angle), crystalline structure (XRD), chemical state (XPS), electrochemical performances (Lsv and EIS) and stability (accelerated life test) were characterized. The results showed that PVDF doping could improve the film morphology, increase oxygen evolution potential (OEP) and reduce the electrode film impedance. In addition, the proportion of adsorbed hydroxyl oxygen (Oad) on the electrode also increased. During the electrochemical oxidation process, the PbO2-PVDF(2.0) electrode showed the best performance on degradation of phenol due to the highest removal rate, lowest energy consumption and minimum Pb dissolution, which could be attributed to its hydrophobic surface, high oxygen evolution potential (OEP) and strong capability of HO generation. Furthermore, the stability of the electrodes were greatly improved after PVDF modification. PbO2-PVDF(1.0) electrode showed the longest service life (501h), which was more than 4 times longer than PbO2 electrode (118.5h).

Electrocatalytic Processes on PbO2 Electrodes at High Anodic Potentials

The determination of the electrocatalytic activity and selectivity of electrodes with respect to the target process is considered to be of interest both in the theoretical aspect for the development of electrocatalysis theory and in application for efficient electrocatalysts which can be used in electrochemical systems for wastewater treatment. The purpose of the given work was to identify the relationship between the chemical and phase composition of materials based on lead dioxide, their physicochemical properties, and their electrocatalytic activity. The main research methods were quasi-stationary polarization and impedance spectroscopy, photocolorimetry, fluorescent and spectrophotometry in the UV and visible regions, atomic absorption spectroscopy, and high performance liquid chromatography (analysis of the solutions). It was shown that the modification of lead dioxide by ionic additives results in significant changes in the electrocatalytic activity of the system in respect to the oxygen evolution reaction and electrochemical oxidation reactions of organic compounds. It was found that, at low polarizations, the oxygen evolution reaction is limited by the electrochemical desorption step (the second electron transfer), and its overpotential at PbO2-modified electrodes increases in the order that coincides with the dependence in which the number of oxygen-containing particles strongly bound to the electrode surface increases. It was found that the rate of oxidation of organic substances on the anode materials involved is directly proportional to the amount of oxygen-containing radicals formed on the electrode during the water oxidation.

Electrochemical Oxidation of Environmentally Persistent Perfluorooctane Sulfonate by a Novel Lead Dioxide Anode

Ti/TiO2-NTs/Ag2O/PbO2 anode was prepared by electrodeposition technique and characterized by scanning electron microscope-energy dispersive spectrometer (SEM-EDS), X-ray diffraction (XRD), linear sweep voltammetry (LSV), and accelerated life test. Electrochemical oxidation of persistent organic pollutant wastewater perfluorooctane sulfonate (PFOS) was carried out with the novel PbO2 anode. Ti/TiO2-NTs/Ag2O/PbO2 anode exhibited a pyramid structure, which was the typical PbO2 electrodes prepared using electrochemical deposition method. XRD spectra indicated that diffraction peaks of PbO2 coating conformed to that of JCPDS (Joint Committee on Powder Diffraction Standards) card for β-PbO2. Ti/TiO2-NTs/Ag2O/PbO2 anode showed high oxygen evolution potential, and longer life service, compared with Ti/PbO2 and Ti/TiO2-NTs/PbO2 anodes. The degradation ratio of PFOS (90mL of 0.0929mmolL−1) was 74.87%, with a pseudo first-order kinetic constant of 0.0165min−1 and a half-life of 43.18min−1 at a constant current density of 30mAcm−2 after 180min of electrolysis. PFOS oxidation yielded sulfate, fluoride, and perfluorocarboxyl anions (i.e., C3F7COO−, C4F9COO−, C5F11COO−, C6F13COO−, and C7F15COO−). The electrospray ionization (ESI) mass spectrum confirmed that oxygen in the intermediate products originated from a heavy-oxygen water electrolyte, and the degradation of PFOS was initiated by the dissociation of a sulfonic group. A possible mechanism was revealed; that was, PFOS was desulfated at the anode to form C8F17· and then transformed into C8F17OH, followed by intramolecular rearrangement and hydrolysis reactions to form C7F15COO−. Kolbe decarboxylation occurred in C7F15COO− at the anode to generate C7F15·, which evolved into C6F13COO− in a similar way and the CF2 unit fell off from C7F15COO−. PFOS was gradually degraded into short-chain perfluorocarboxyl anions by repeating the CF2 unzipping cycle.

Electrochemical degradation of Musk ketone in aqueous solutions using a novel porous Ti/SnO2-Sb2O3/PbO2 electrodes

This paper investigates the electrochemical degradation of Musk ketone (MK) in aqueous solution with a novel porous Ti/SnO2-Sb2O3/PbO2 electrode. The influence of electro-deposition preparation parameters on the surface structure and crystal characteristics of porous PbO2 electrode was systematically investigated by SEM and XRD in detail, including electro-deposition time, current density and deposition temperature. Compared with the conventional plate PbO2 electrode, the novel porous PbO2 had a higher stability, safety and removal efficiency for Musk ketone. Besides, the optimal degradation conditions were obtained by studying the effecting of different factors, such as electrolyte concentrations (0–0.12molL−1), current densities (10–50mAcm−2), initial pH (3−11) and initial Musk ketone concentrations (10–90mgL−1). The results showed that the removal rates of Musk ketone reached 99.93% after 120min electrolysis at initial 50mgL−1 Musk ketone at constant current density of 40mAcm−2 with 0.06molL−1 Na2SO4 supporting electrolyte. In addition, cyclic voltammograms tests indicated that the degradation of Musk ketone was mainly achieved via indirect electrochemical oxidation mediated by hydroxyl radical. Moreover, a possible electrochemical degradation pathway for Musk ketone was deduced based on the intermediates identified by GC–MS methods.

Electrodeposition of Ni2+-doped PbO2 and physicochemical properties of the coating

The kinetics of PbO2 electrodeposition from nitrate electrolytes containing nickel ions, and the influence of deposition conditions on the physicochemical properties of obtained materials, have been investigated. This study reveals that the mechanism of Ni2+/PbO2 electrodeposition is not in conflict with that of PbO2 formation in the absence of foreign species that we described earlier. Accordingly, electrochemical formation of PbO2 occurs in four stages, two of which are electron transfer steps while the other two are chemical reactions involving formation and decay of soluble intermediates consisting of 3 and 4-valent lead species. We observed an inhibition of Pb2+ electrooxidation in the presence of Ni2+ that is attributable to partial blocking of the active surface sites by the adsorbed foreign cations. Interestingly though, blocked active sites that inhibit the growth of PbO2 show, at the same time, a high activity for O2 evolution. Changing of the electrolyte composition and conditions of electrodeposition of PbO2 (deposition potential, temperature and pH) significantly influences the physicochemical properties of the PbO2 deposits. In particular, the phase and chemical composition, the crystallographic orientation, the content of structural water and the nature of adsorbed oxygen-containing particles on the electrode surface. Concerning the last point, bearing direct relevance to the electrocatalytic properties, we noted that Ni2+/PbO2 electrodes feature a significant increase in the amount of labile oxygen intermediates on the electrode surface which are responsible of a high electrocatalytic activity in the O2 evolution reaction.

New insights into electrocatalytic ozone generation via splitting of water over PbO2 electrode: A DFT study

The viable mechanisms for O3 generation via the electrocatalytic splitting of H2O over β-PbO2 catalyst were identified through Density Functional Theory calculations. H2O adsorbed onto the surface was oxidized to form OH then O; the latter reacted with a surface bridging O to form O2 which in turn reacted with another surface O to form O3. The final step of the mechanisms occurs via an Eley–Rideal style interaction where surface O2 desorbs and then attacks the surface bridging oxygen, forming O3. A different reaction pathway via an O3H intermediate was found less favoured both thermodynamically and kinetically.

Electrochemical oxidation metronidazole with Co modified PbO2 electrode: Degradation and mechanism

This study presents an electrochemical method for the degradation of metronidazole (MNZ) in aqueous solution with novel PbO2 electrode, which was prepared via electrodeposition in nitrate solution. The influencing factors on electrochemical decomposition of pollutants were evaluated and the removal of MNZ and chemical oxygen demand (COD) reached 78.09% and 21.77% after 120 min treatment under the optimal conditions with the concentration of supporting electrolyte, the initial concentration of MNZ, the pH and the current density were 0.10 mol/L, 100 mg/L, 6.4 and 10 mA/cm2, respectively. Then, the Co doped PbO2 electrodes were prepared and used to degrade MNZ under the optimal conditions. Relatively good performance was achieved when the molar ratio of Pb and Co was 100:1. Compared to pure PbO2 electrode, the steady-state polarization curves and cyclic voltammetry analysis showed that 1.0% Co-PbO2 electrode had a higher oxygen evolution potential and greater current of reduction and oxidation peaks, which increased the electrochemical activity and decreased the energy consumption. Finally, based on the intermediate products identified by IC and GC/MS, the main degradation pathway of MNZ was proposed including ring open, denitrification and radical reactions.

Study on the electrocatalytic degradation of 4-chlorophenol on PbO2–ZrO2 composite electrode and its electrochemical property

PbO2–ZrO2 composite electrodes were prepared by anodic electrodeposition in the lead nitrate solution. The electrochemical property of this electrode was studied by cyclic voltammetry, polarization curves and open-circuit potential–time curves. The results show that PbO2–ZrO2 composite electrodes possess higher oxygen evolution overpotential and better anti-corrosion performance than traditional PbO2 electrodes. Electrocatalytic oxidation of 4-chlorophenol (4-CPs) in aqueous solution was studied to evaluate the applications of this electrode in environmental protection. The influence of experimental parameters on the COD removal efficiency was studied on PbO2–ZrO2 composite electrodes as a function of the current density, initial concentration of the 4-CPs, initial pH, supporting electrolyte concentration and electrolysis time. The results show that the 4-CPs removal efficiency in 0.1 mol L–1 Na2SO4 solution containing 8 mmol L–1 4-CPs could reach 89.2% with the current density at 200 mA cm–2 and pH value at 6.5 after 4 h. Compared with traditional PbO2 anodes, the PbO2–ZrO2 composite electrodes show higher instantaneous current efficiency with degradation of 4-CPs. The experimental results demonstrate that the PbO2–ZrO2 composite electrodes possess the excellent electrocatalytic activity in refractory pollutants degradation.

Electrochemical degradation of dye on lead dioxide electrodeposited on stainless steel: effect of cyclic voltammetry parameters

The effect of cyclic voltammetry (CV) on electrochemical behavior of PbO2 layer electrodeposited by pulsed method on stainless steel (AS30) has been studied. The field emission scanning electrons microscope and X-ray diffraction (XRD) were used to characterize the surface morphology and crystal structure of different electrodes with CV effect, respectively. The content of PbO2 particles has been tuned by altering the cycle number, of CV through which the content of PbSO4 also increased. It is related to reduction phenomena depending on electron transfer through the pores into β-PbO2 layer. Electrochemical behavior of the prepared samples was investigated in 0.5M H2SO4 solution by CV and electrochemical impedance spectroscopy (EIS) techniques. EIS results revealed that the charge-transfer resistance significantly increased because the lead sulfate layer is more compact and the access of electrolyte ions to the internal layer is blocked. Anodic oxidation of solutions containing Amaranth as a dye model was studied to evaluate the use of these electrodes as anodes in environmental issue. After five cycle of CV, PbO2 film becomes more resistive according to value of Rf and this may have a deleterious effect on the electrochemical degradation activity compared to that without CV treatment. Based on the obtained results, after electrolysis time of 5 h at acidic pH medium, the color and the chemical oxygen demand removals on PbO2 electrode treated by 1 CV achieved nearly to 97 and 83%, higher than that without CV treatment (77 and 47%), respectively.

A comparison of electrochemical oxidation performance of PbO2 and SnO2 electrodes

PbO2 and SnO2 are two promising anode materials for electrochemical oxidation. In order to highlight the difference between two kinds of electrodes in an electrochemical oxidation process, their morphology, structural, oxygen evolution overpotential (OEP), electrochemical activity and service life-time were compared in detail in this paper. Surface characterization by scanning electron microscope shows that the film of the PbO2 electrode is even, compact, non-porous, and non-cracked, while many cracks are present on the film of the SnO2 electrode. Electrochemical studies based on linear sweep voltammetry (LSV) and cyclic voltammetry (CV) prove that the OEP for the SnO2 electrode was much higher than that of the PbO2 electrode, and the electron-transfer kinetics and the reversibility of electrode reaction of the SnO2 electrode were superior to those of the PbO2 electrode. In electrochemical decomposition of p-nitrophenol, the degradation ratios at PbO2 and SnO2 anodes achieved 86.9% and 96.5%, respectively, after 120 min electrolysis, which verified the results of LSV and CV. The accelerated lifetime tests show that the service life time of the SnO2 electrode is far shorter than that of the PbO2 electrode, even though it was shown to be superior to the PbO2 in electrocatalytic activity.