Higher Oxygen Evolution Overpotential Research Articles

Fabrication of Ti/Zr-SnO2/PbO2-Nd Electrode for Efficient Electrocatalytic Degradation of Alizarine Yellow R

Introduction: A novel attempt to degrade alizarine yellow R (AYR) by lead dioxide (PbO2)/ neodymium (Nd) coated Ti anode was investigated. Method: Ti/Zr-SnO2/PbO2-Nd electrode showed high oxygen evolution potential, high current density, and neutral conditions, which favored the degradation of AYR. The PbO2-Nd layer on Ti/Zr-SnO2 was further characterized by scanning electron microscopy, and X-ray diffraction analysis, and X-ray photoelectron spectroscopy. The electrochemical properties of Ti/Zr- SnO2/PbO2-Nd electrode were evaluated by cyclic voltammetry, AC impedance spectroscopy, and accelerated life test. Result: The relatively higher oxygen evolution overpotential (~1.80 V) of the developed electrode can effectively suppress the occurrence of surface side reactions and oxygen evolution. A relatively lower charge transfer resistance (Rct, 18.0 Ω) of Ti/Zr-SnO2/PbO2-Nd electrode could be found. The Ti/Zr-SnO2/PbO2-Nd electrode exhibited an accelerated lifetime of 110 min under a very high current density of 10,000 A/m2. The doping of Nd could produce loosely-stacked sheet-like structures, thus, the number of active sites on the electrode surface increases. Conclusion: Moreover, an outstanding conductivity of Ti/Zr-SnO2/PbO2-Nd electrode was obtained, which favored the electron transfer and catalytic activity of the modified electrode. The Ti/Zr-SnO2/PbO2-Nd electrode exhibited improved electrochemical performances and higher oxygen evolution potential, and the highest oxygen evolution potential is 1.80 V. Under the current density of 30 mA/cm2, the electrocatalytic degradation of 92.3% could be achieved in 180 min. The electrochemical oxidation of AYR at the Ti/Zr-SnO2/PbO2-Nd electrode proved to be feasible and effective, indicating that it might be used for the elimination of AYR from wastewater. conclusion: The electrochemical oxidation of AYR at the Ti/Zr-SnO2/PbO2-Nd electrode proved to be feasible and effective, indicating that it might be used for the elimination of AYR from wastewater.

Fabrication of a highly active β-PbO2-Co3O4 electrode for zinc electrowinning by pulse electrodeposition: Characterization and catalytic performance analysis

High oxygen evolution overpotential and low corrosion resistance are regarded as the main drawbacks of anode materials in zinc electrowinning. To improve the electrocatalytic activity of oxygen evolution reactions (OER) and reduce energy consumption in zinc electrowinning, a Co3O4 nanoparticle-modified PbO2 anode was prepared on a Ti substrate with Sn-SbOX as an interlayer through pulse electrodeposition. The surface morphology, phase composition, and electrochemical properties of the as-prepared anode were systematically investigated. The introduction of Co3O4 nanoparticles refined the crystal size of PbO2 and increased the surface roughness of the anode. Electrochemical tests suggested the excellent electrocatalytic activity of the Co3O4 nanoparticle-modified PbO2 anode. Density functional theory (DFT) calculations revealed that Co3O4 nanoparticles reduced the OER free energy (1.58 eV) and that pulse electrodeposition reduced the PbO2 crystal size and increased the active surface area of the anode. In the simulated zinc electrowinning test, an improved current efficiency (90.6 %) was achieved, and the low energy consumption (2,508.29 kW·h) for zinc production per ton was significantly reduced as compared with that for the conventional Pb-0.75 %Ag anode. The lifetime of the modified electrode is increased by approximately 36.8 %. This provides a reference for the design and development of anode materials with high oxygen evolution activity and strong corrosion resistance in zinc electrowinning systems.

Strategies for controlling gas evolution reactions to boost the divergent paired electrochemical upgrading of furfural in acidic environment

Electrochemical methods for catalytic furfural conversion have drawn significant interest in both academic and industrial research communities. Paired electrocatalytic conversion has been identified as a promising strategy for reducing energy consumption and promoting carbon neutrality. To optimize product distribution and conversion efficiency, we have developed a divergent paired electrochemical upgrading approach for furfural in acidic environments, with a focus on prioritizing strong gas evolution reactions and product transformations. The high electrocatalytic activity of CuSn/CuF@Cu prepared by electrodeposition can effectively inhibit the hydrogen evolution. The performance of the electrocatalysts and the pathways of electrocatalytic hydrogenation (ECH) of furfural to 2-methylfuran (MF) were investigated by combination of experiments and the density functional theory (DFT) calculations. A stable Ti/PbO2 electrode with high oxygen evolution overpotential was prepared for anodic electrocatalytic oxidation (ECO) and the product transformation route was described. The conversion of furfural to maleic acid (MA) and MF in acidic environment was successfully achieved. In the paired electrosynthesis system, the electrons generated from anodic ECO of furfural are utilized in valuable and controllable cathodic ECH. It significantly and continuously reduces the power cost associated with renewable energy sources and further promotes the development of biomass electrochemical conversion.

Non-traditional power supply mode: Investigation of electrodeposition towards a better understanding of PbO2 electrode for electrochemical wastewater treatment

The power supply mode is a non-negligible character in electrochemical process. Constant current mode is used in the traditional electrodeposition preparation process of PbO2 electrode, and there are very few studies on its electrodeposition power supply mode. In this paper, two non-traditional power supply modes (linear increase power supply mode and linear decrease power supply mode) were used to fabricate PbO2 electrodes, and the properties of prepared electrodes were compared with those of the traditional constant current power supply mode. On the premise of improving the electrode properties, the non-traditional power supply mode also significantly reduced the energy consumption of the electrodeposition process of PbO2. After material characterization (Scanning electron microscope, X-ray diffraction), electrochemical characterization (Electrochemical impedance spectroscopy, linear sweep voltammetry etc.) and stability test, it can be seen that the electrode surface prepared by the non-traditional power supply mode was spherical particles and its average grain size was smaller than that of the traditional one. The PbO2 electrode prepared by linear increase power supply mode had higher oxygen evolution overpotential (1.962 V), more active sites, smaller membrane impedance (33.15 Ω) and better stability (accelerated life up to 125.1 h). In the electrocatalytic oxidation tests of the three electrodes, the PbO2 electrode prepared by linear increase mode had the best performance in decolorization rate, Chemical oxygen demand removal rate, average current efficiency and energy consumption. Owing to favorable effects obtained, non-traditional power supply mode could be considered a promising alternative for PbO2 electrode preparation and applied electrochemical process for wastewater treatment.

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.

Study on the preparation, characterization, and electrocatalytic performance of Gd‐doped PbO2 electrodes

AbstractIn this work, Gd‐doped PbO2 electrodes were prepared by electrodeposition procedure. In the accelerated life test, the service life of Gd‐doped PbO2 electrodes are more stable and durable. Scanning electron microscope and x‐ray diffraction tests reveal that Gd‐doped PbO2 electrodes have more compact structure and finer grain size. Electrochemical measurements and fluorescence experiments show that Gd‐doped PbO2 electrodes have higher oxygen evolution overpotential, a larger electrochemically active surface area, and stronger ability to generate hydroxyl radicals. The electrocatalytic performance of the Gd‐doped PbO2 electrode for the electrochemical degradation of thiamethoxam was studied. The degradation process accorded with pseudo‐first‐order kinetics, with higher thiamethoxam and total organic carbon removal capabilities, as well as higher mineralization current efficiency and lower energy consumption. In the degradation process, it has favourable reusability. The experimental results demonstrate that Gd‐doped PbO2 electrodes have an excellent treatment effect and a wider application prospect in the field of pollutant degradation.

PbO2 modified with TiO2-NTs composite materials with enhanced OER electrocatalytic activity for Zn electrowinning.

The high oxygen evolution overpotential of the Pb–Ag anode is one of the main reasons for the high energy consumption in Zn electrowinning. PbO2, owing to its high conductivity, good corrosion resistance and low cost, is widely used as an excellent coating material. In present research, a novel composite Ti/TiO2-NTs/PbO2 material was synthesized through a facile anodization, annealing, electrochemical reduction and galvanostatic deposition. The surface morphology, internal structure and the mechanisms of TiO2-NTs enhancing electrochemical performance were discussed. The results show that the self-organized high aspect ratio TiO2-NTs with diameter of ∼120 nm and length of ∼8 μm were obtained on Ti substrate. The Ti/TiO2-NTs/PbO2 composite material exhibits excellent oxygen evolution performance and good stability in Zn electrowinning simulation solution (50 g L−1 Zn2+, 150 g L−1 H2SO4) at 35 °C. Its oxygen evolution overpotential is only 630 mV under current density 50 mA cm−2, which is 332 m lower than that of Pb-0.76 wt% Ag (η = 962 mV) and only increases 22 mV after 5000 cycles of CV scanning. Its outstanding electrochemical performance is mainly ascribed to the introduction of TiO2-NTs in Pb(CH3COO)2 media since it refines the crystal grains, increases the electrochemical surface area, greatly reduces the charge transfer resistance (25.4 Ω cm2 to 2.337 Ω cm2) and enhances corrosion resistance. Therefore, the Ti/TiO2-NTs/PbO2 material prepared in Pb(CH3COO)2 medium may be an ideal anode for Zn electrowinning.

Electrochemical Decolorizaton of Dye in Solution with Modified Ti/α-PbO2/β-PbO2 Mesh Electrode

The synthetic dyes with high stable aromatic structures severely impair watery environments, due to their low biodegradability and deep color-staining. Furthermore, dye pollution would inhibit aquatic plants’ photosynthsis process, decrease the concentration of dissolved oxygen, and contain substances that are toxic to the human body.The electrochemical oxidation is an attractive advanced wastewater oxidation process, which has been applied in toxic or refractory wastewater treatment, owing to its simplicity, easy operation, environmental compatibility, mild condition and high efficiency. Their degradation performance depends strongly on the selected anode materials. Thus, it is necessary to develop excellent anode materials with high stability and electrocatalytic activity.Recently, various anode materials have been fabricated and studied. PbO2 electrodes could be regarded as important metal oxide anodes for pollutant remediation, because of their high chemical stability, easy preparation, high oxygen evolution overpotential, good conductivity, high catalytic activity, cheap and available. However, PbO2 film can peel off easily for its relatively large internal stress. The phenomena cause the leakage of Pb ions and releasing into the solution. Therefore, the improvements of stability and electrocatalytic performance for PbO2 electrodes are significant for the application. Recently, many studies have been investigated for the enhancement of electrode performance, such as the modification of substrate, the introduction of interlayers and the doping of metal ions or particles [1-3].In the previous study, the electrochemical decolorizaton of Methylene blue in solution with Ti/α-PbO2/β-PbO2 Sheet electrode has been investigate. In the present work, Ti/α-PbO2/β-PbO2 Mesh electrode was modifeid by the doping of metal, and have been applied into the electrochemical remediation of Methylene blue in the solution.

Preparation and characterization of hydrophobic stearic acid-Yb-PbO2 anode and its application on the electrochemical degradation of naproxen sodium

A novel hydrophobic stearic acid-Yb-PbO2 (SA-Yb-PbO2) electrode with high oxygen evolution overpotential and long service lifetime was successfully fabricated through electrodeposition approach. The characterization of SA-Yb-PbO2 electrode, including surface morphology, elemental components, hydrophobicity, and crystal lattice structure, were performed. The results indicated that stearic acid's adulteration could enhance oxygen evolution overpotential and increase active specific surface area and the amounts of active sites. Then, the hydrophobic electrodes were used as anodes for electrolysis of naproxen sodium. The SA-Yb-PbO2 electrode showed better performance on naproxen sodium degradation than Yb-PbO2 electrode, exhibiting higher removal efficiency, lower energy consumption and higher mineralization current efficiency. Furthermore, the adulteration of stearic acid could greatly promote the stability and reusability of the electrodes for naproxen sodium degradation. The enhancement of electrode performance and oxidation power was related to high oxygen evolution overpotential and strong generation capability of OH caused by electrode's hydrophobic surface. Moreover, the degradation pathway and corresponding byproducts of naproxen sodium were obtained by HPLC and HPLC/MS assay, which revealed that naproxen sodium could be effectively mineralized by hydrophobic SA-Yb-PbO2 anode. These results presented that the organic pollutant wastewater containing naproxen sodium could be effectively decontaminated by electrochemical approach using hydrophobic SA-Yb-PbO2 electrode as anode.

Electro-Fenton Regeneration of Activated Carbon Fibers for the Removal of Pharmaceutical Residues

Introduction The electro-Fenton process is based on in-situ production of the Fenton’s reagent in order to continuously generate hydroxyl radicals in the bulk solution [1]. It is also possible to promote the generation of additional powerful oxidant species by using anode material with high oxygen evolution overpotential. Therefore, such electrochemical advanced oxidation process (EAOP) is able to degrade a large range of organic pollutants [1]. However, energy efficiency of EAOPs is strongly affected by mass transport limitations during the treatment of low concentrations of pollutants such as pharmaceutical residues. In fact, a large amount of hydroxyl radicals are wasted in parasitic reactions such as hydroxyl radical dimerization. The combination of adsorption and electro-Fenton processes aims at overcoming this drawback. Adsorption on activated carbon fibers (ACFs) is used for pre-concentration of organic pollutants. Then, ACFs can be directly used as cathode during the electro-Fenton process for desorption, degradation and mineralization of organic compounds as well as for regeneration of ACFs for additional adsorption steps [2]. The possibility to easily regenerate ACFs improve the cost-effectiveness of this material, which presents more suitable characterisitcs than grain or powder activated carbon (e.g. low intra-particle diffusion limitation leading to fast adsorption kinetics, narrow pore size distribution leading to selective adsorption of micropollutants). This innovative strategy was applied for the removal of pharmaceutical residues. Scale-up from batch to continuous filtration reactor was investigated. Material and methods A first set of experiments was performed in batch reactor for both adsorption and electro-Fenton processes, by using clofibric acid and ofloxacin as model pharmaceutical residues. Design parameters (e.g. anode material: boron-doped diamond (BDD) or TiOx) and operational parameters (current density, treatment time) were optimized for improving regeneration efficiency and mineralization of pharmaceutical residues. Regeneration efficiency was assessed by comparing the adsorption capacity of regenerated ACFs and pristine ACFs. Mineralization rate of desorbed organic compounds was measured by total organic carbon analysis. Biodegradability and acute toxicity (Microtox®) of the solution was also assessed. ACFs were characterized by scanning electron microscopy, Hg porosimetry, and Raman spectroscopy. Then, the study was focused on the design, implementation and optimization of this combined process in a single continuous filtration reactor and using a real effluent. Results and discussion Batch experiments using clofibric acid as model pollutant were performed in order to better understand the influence of critical design and operational parameters. The efficiency of the process was discussed as regards to (i) desorption of organic compounds and regeneration efficiency, (ii) degradation and mineralization of organic compounds and (iii) stability of ACFs for several successive adsorption/regeneration cycles. By using BDD as anode and a current density of 21 mA cm-2, it was observed that increasing the treatment time from 3 to 6 h strongly improved the regeneration effectiveness from 45 to 75%. Further increasing the treatment time to 9 h did not show significant positive effect because of the lower availability of a portion of adsorbed compounds within the ACF porosity. Besides, dividing the current density by a factor of 2.5 (8 mA cm-2) only reduced the regeneration efficiency from 75 to 64%, indicating that low current density might be more cost-effective. Using TiOx instead of BDD anode also only reduced the regeneration efficiency from 64 to 60%. TiOx is a new promising electrode material that is much less expensive than BDD. Therefore, using TiOx anode was considered as a more cost-effective configuration. A great advantage of this process is also that >80% of organic compounds desorbed from ACF were mineralized, thus avoiding the production of a toxic effluent. Regeneration efficiency was then assessed during 10 cycles of adsorption/regeneration without significant decrease due to the protection of the ACF surface by the cathodic polarization effect. Finally, this treatment strategy was implemented in a continuous filtration reactor where both adsorption and electro-Fenton regeneration could take place sequentially. Process efficiency for treating a real effluent was assessed by comparing breakthrough curves of pristine and regenerated filters. The development of this technology is currently focused on point-of-use filters for domestic applications (about 5 liters per day) as well as on industrial wastewater treatment (pilot-scale unit able to treat 10-20 liters per hour).

Electrochemical removal of metribuzin in aqueous solution by a novel PbO2/WO3 composite anode: Characterization, influencing parameters and degradation pathways

Abstract In this work, we fabricated PbO2/WO3 composite electrode through composite electrodeposition method and employed it in electrocatalytic degradation of metribuzin. The effects of WO3 particles on surface morphology, structure and electrochemical characters of PbO2 electrodes were investigated. Different from PbO2 electrodes, the PbO2/WO3 composite electrodes owned higher oxygen evolution overpotential, longer service life and higher hydroxyl radicals generation performance. The effect of key operating parameters, for instance, current density, initial metribuzin concentration, initial pH values, and supporting electrolyte concentration, upon electrochemical removal process of metribuzin were studied. The current density and initial metribuzin concentration exerted prominent effects on electrochemical degradation of metribuzin. Kinetic analysis indicated that the electrochemical decomposition of metribuzin was a pseudo-first-order reaction. The byproducts during metribuzin degradation process were identified, several aromatic products and inorganic ions were generated along with the reaction time. Finally, the electrochemical pathways of metribuzin degradation at the PbO2/WO3 composite electrode were proposed based on the identified reaction byproducts, which were separated into three parallel sub-pathways according to the different degradation reactions by hydroxyl radicals, and quantities of hydroxylation, oxidation, demethylation, deamination, and addition reactions’ products were generated. All the byproducts were finally decomposed into inorganic H2O, CO2, NO3−, and NH4+.

Electrochemical oxidation of acetamiprid using Yb-doped PbO2 electrodes: Electrode characterization, influencing factors and degradation pathways

The Yb-doped PbO2 electrodes were fabricated by electrodeposition method. SEM and XRD experiments revealed that the adulteration of Yb can decrease the crystal grain size and make the electrodes more compact. Electrochemical measurements, accelerated service lifetime and bulk electrolysis experiments proved that Yb-doped PbO2 electrodes had higher oxygen evolution overpotential, stability and acetamiprid removal ratio than pure PbO2 electrodes. The effect of operating parameters, such as current density, initial acetamiprid concentration, and pH value, on the electrocatalytic degradation of acetamiprid were systematically studied. The electrocatalytic oxidation reaction of acetamiprid on Yb-doped PbO2 electrodes was highly effective, which obeyed the pseudo-first-order kinetics model. Intermediates analysis and electrocatalytic degradation mechanism of acetamiprid by Yb-doped PbO2 electrodes were implemented, and the degradation pathways were divided into three different sub-routes due to three function groups on acetamiprid initially attacked by hydroxyl radicals. Finally, all the byproducts were decontaminated into CO2 and H2O. These results proved that Yb-doped PbO2 electrodes have more promising application potential for the electrocatalytic degradation of refractory organic pollutants.

Preparation and electrochemical treatment application of Ce-PbO2/ZrO2 composite electrode in the degradation of acridine orange by electrochemical advanced oxidation process.

Novel Ce-PbO2/ZrO2 composite electrodes were successfully fabricated in lead nitrate solution containing cerium ions and ZrO2 particles by composite electrodeposition method. SEM images and XRD results indicated that Ce-PbO2/ZrO2 composite electrodes have compact structure and fine grain size. Ce-PbO2/ZrO2 composite electrode has higher oxygen evolution overpotential and stability than Ce-PbO2 electrode. The service life of Ce-PbO2/ZrO2 composite electrode reaches 318 h, which is 4.2 times as that of Ce-PbO2 electrodes (74 h). The novel Ce-PbO2/ZrO2 composite electrode was employed as anode to decontaminate acridine orange (AO) by electrochemical oxidization methods. The effect of initial concentration of AO, current density, and initial pH values on the removal ratio of AO were analyzed. The results showed that AO could be completely removed after 90 min electrolysis under the optimal condition: initial AO concentration was 30 mg L-1, current density was 50 mA cm-2, and the initial pH value was 5.0. Moreover, the possible degradation pathway of AO was elucidated based on the identification of stable byproducts generated during the electrochemical degradation process by HPLC-MS, which revealed that AO and its byproducts could be effectively eliminated and mineralized into CO2, H2O, ammonium and nitrate ions.

Effect of lead dioxide high dispersion on titania nanotubes electrodes on the enhanced electrooxidation of aqueous p-nitrophenol and methyl red: An electrode comparative study

Titanium dioxide nanotubes (TiO2-Nts) array morphology and its high specific surface area provide a suitable substrate for PbO2 electrodeposition. PbO2 was effectively dispersed on the whole nanotubes surface, including both their walls and mouths (electrocatalyst of the type: Ti/TiO2-Nts::PbO2). Scanning electron microscopy and EDS microanalyses showed that PbO2 grows from the bottom to the surface of the nanotubes, firstly covering their walls. A simple growth mechanism previously proposed was confirmed by electrochemical methods. Cyclic voltammetry characterization of Ti/TiO2-Nts::PbO2 electrodes (2cm2 geometric area) allowed to obtain the double layer capacitances that were directly related to PbO2 electroactive area, indicating that it grows inversely with deposition time. Also, electrocatalytic features (high oxygen evolution overpotential, open-edge morphologies and larger network structures to PbO2 crystals formed) depend on the PbO2 dispersion as well as electrodeposition time. Their electrooxidation properties were tested for electrolysis of 15ppm methyl red (MR) and 50ppm p-nitrophenol (PNP) acidic aqueous solutions at a current density of 30mAcm−2. Results clearly showed the effect of PbO2 deposition time on the electrocatalytic area and on the electrooxidation of PNP and MR. That is, Ti/TiO2-Nts::PbO2 with the shortest electrodeposition time has the highest surface and active area, efficiently degrading MR (100% of discoloration and 90% of organic removal) and PNP (90% of concentration removal after 3.5h) in solutions. HPLC analyses of the final samples showed that carboxylic acids are the main remnant of electrooxidation.

Effects of peak current density on the structure and property of PbO2–CeO2 nanocomposite electrodes prepared by pulse electrodeposition

PbO2–CeO2 nanocomposite electrodes were prepared by pulse electrodeposition method in the lead nitrate solution containing CeO2 nanoparticles with different peak current density. The content of CeO2 nanoparticles in the electrodes increase with the increase of peak current density. The effects of peak current density on the morphology and structure of PbO2–CeO2 nanocomposite electrodes were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The SEM and XRD results show that the increase of peak current density can make the morphology finer and more compact, and the crystal size decreases with the increase of peak current density. The oxygen evolution overpotential and stability of PbO2–CeO2 nanocomposite electrodes enhance with the increase of peak current density. The electrocatalytic property of PbO2–CeO2 nanocomposite electrodes was examined for the electrochemical oxidation of rhodamine B (RhB). The results show that the RhB removal efficiency on PbO2–CeO2 nanocomposite electrodes increase with the increase of peak current density, which can be attributed to the higher oxygen evolution overpotential and CeO2 content in the composite electrodes.

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.

Localization of Electrochemical Reactions in Electrocatalytic Processes on Nanocomposite Electrodes

A principle of reaction localization is proposed, which explains the catalytic properties of nanocomposites materials in the reaction under study. By changing the route of electrochemical reactions from the catalyst to the support or vice versa one can influence electrocatalytic properties. The catalytic activity can be judged from the difference in the electrochemical overpotential of separation of the reactant under investigation in a particular medium between the catalyst and the support. The action of this principle was demonstrated on the basis of oxygen reduction and hydrogen oxidation reactions for fuel cells and for the reaction of electrochemical hydrogen accumulation at a hydride electrode. For an oxygen electrode with carbon support in an alkaline medium, materials with high oxygen evolution overpotential are good catalysts. For a hydrogen electrode with carbon support in an alkaline medium, materials with low hydrogen evolution overpotential are good catalysts. In the case of electrochemical hydrogen accumulation at intermetallic compounds with low hydrogen evolution overpotential in an alkaline medium, catalysts with high hydrogen evolution overpotential must be used. Making use of this principle one can carry out goal-directed synthesis or select new organic or inorganic catalytic materials.

Preparation and characterization of carbon nanotube and Bi co-doped PbO2 electrode

A novel carbon nanotube and Bi co-doped PbO2 electrode (CNT-Bi-PbO2) was prepared by thermal deposition and electrodeposition technologies. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were used to characterize the surface morphology and crystal structure of the electrodes. In contrast with PbO2, Bi-PbO2, and CNT-PbO2 electrodes, the CNT-Bi-PbO2 electrode had smaller crystal particles and more compact structure. The linear voltammetry was utilized to determine the oxygen evolution overpotential of electrodes. The electro-catalytic activity of electrodes was investigated by cyclic voltammetry. The yield of ·OH and electro-catalytic oxidation degradation of p-nitrophenol (p-NP) at four kinds of electrodes were tested. Besides, the stability of electrodes was also determined by accelerated service life tests. The results show that the prepared CNT-Bi-PbO2 electrode had higher oxygen evolution overpotential and more excellent electrochemical oxidation performance than other three kinds of electrodes. The reaction rate constant of p-NP on the CNT-Bi-PbO2 electrode was 1.69 times and the mineralization current efficiency at 180min on CNT-Bi-PbO2 electrode was 1.36 times that on PbO2 electrode. Moreover, the service lifetime of CNT-Bi-PbO2 electrode was 4.16 times as much as that of PbO2 electrode.

Electrocatalytic degradation of methylene blue on PbO2-ZrO2 nanocomposite electrodes prepared by pulse electrodeposition

PbO2-ZrO2 nanocomposite electrodes (P) were prepared by pulse electrodeposition and used for the electrocatalytic degradation of methylene blue (MB). The SEM and XRD tests show that PbO2-ZrO2 nanocomposite electrodes (P) possess more compact structure and finer grain size than PbO2-ZrO2 nanocomposite electrodes (D) prepared by direct electrodeposition. The electrochemical measurements show that PbO2-ZrO2 nanocomposite electrodes (P) have higher oxygen evolution overpotential and the oxidation regions of MB and water are significantly separated. The experimental parameters on electrocatalytic degradation of MB by PbO2-ZrO2 nanocomposite electrodes (P) were evaluated, such as initial MB concentration, current density, pH value and supporting electrolyte concentration. The results indicate that MB and COD removal efficiency of PbO2-ZrO2 nanocomposite electrodes (P) reach 100% and 72.7%, respectively, after 120min electrolysis at initial 30mgL−1 MB concentration at current density of 50mAcm−2 in 0.2molL−1 Na2SO4 supporting electrolyte solution, and the degradation of MB follows pseudo-first-order kinetics. Compared with PbO2-ZrO2 nanocomposite electrodes (D), PbO2-ZrO2 nanocomposite electrodes (P) show higher COD removal efficiency and instantaneous current efficiency with MB degradation. The experimental results demonstrate that PbO2-ZrO2 nanocomposite electrodes (P) possesses the excellent electrocatalytic properties and show great potential applications in refractory pollutants.

Preparation of Ti/PbO2–Sn anodes for electrochemical degradation of phenol

The novel Sn-doped Ti/PbO2 (Ti/PbO2–Sn) anodes have been prepared by cathodic deposition and anodization processes. The effect of Sn content on the structure and electrocatalytic performance of Ti/PbO2–Sn anodes has been studied. The surface coating structure and composition of the anodes were characterized by SEM, EDX and XRD. The results reveal that a limited amount of doping Sn can improve the coating structure of the PbO2 layer, and an over-doping of Sn has an adverse effect on the coating structure and crystallinity of β-PbO2. Linear polarization curves analysis shows that the novel Ti/PbO2–Sn anodes have higher oxygen evolution overpotential when compared to pure Ti/PbO2 electrode. The performance of electrodes for the electrochemical degradation of a model pollutant (phenol) was enhanced using the Ti/PbO2–Sn anode. The effects of current density, initial pH and supporting electrolyte on the electrochemical degradation of phenol by Ti/PbO2–Sn electrode were investigated.