Oxygen Evolution Potential Research Articles

Au-coated carbon cathodes for improved oxygen reduction and evolution kinetics in aprotic Li–O2 batteries

Metal-oxygen systems are an attractive option to enhance the specific energy of secondary batteries. However, their power is limited by the oxygen electrode. In this communication we address the issue of the sluggish kinetics of the oxygen cathode in the aprotic Li–O2 batteries. The electrochemical performances of newly designed carbon electrodes coated with 50Å thick Au layer are evaluated and compared with those of unmodified electrodes. Despite the low noble metal content (~2wt.%), the Li–O2 batteries built with the abovementioned Au-coated cathodes show considerably enhanced kinetics as demonstrated by the higher onset potentials for the oxygen reduction reaction (~2.6V at a current rate of 1000mAg−1), together with reduced oxygen evolution potentials.

Electrochemical behavior of rolled Pb–0.8%Ag anodes

In this paper, the oxygen evolution kinetics and oxide layer properties of Pb–0.8%Ag rolled alloy anodes obtained over 15days of galvanostatic electrolysis in acid zinc sulfate electrolyte solution were investigated using anodic polarization curves, quasi-stationary polarization (Tafel), and electrochemical impedance spectroscopy techniques. The microscopic morphology and phase composition of the anodic oxide layers were observed by scanning electron microscopy and X-ray diffraction, respectively. The activity and reaction kinetics of the anodes varied noticeably during electrolysis, indicating the formation and stabilization of the anodic oxide layer. With increasing electrolysis time, the potential and overpotential of oxygen evolution of the anodes mainly presented a declining trend, whereas their electrode surface exchange current density demonstrated a rising trend. This depolarization can be accounted for by the increasing roughness of the anodic surface and the catalytic effect of increasing β-PbO2 content. The anodic oxide layer obtained after 15days of electrolysis presented the most compact and the best regular structure among five experimental samples. The corrosion phases of the anodic oxide layers mainly consisted of PbSO4, PbO, α-PbO2, and β-PbO2. With increasing electrolysis time, the α-PbO2 content presented a declining trend, whereas the β-PbO2 content demonstrated a rising trend. α-PbO2 and β-PbO2 showed preferential growth orientations toward the (111) and (101) planes, respectively.

Bismuth-Doped Tin Oxide-Coated Carbon Nanotube Network: Improved Anode Stability and Efficiency for Flow-Through Organic Electrooxidation

In this study, a binder-free, porous, and conductive 3D carbon-nanotube (CNT) network uniformly coated with bismuth-doped tin oxide (BTO) nanoparticles was prepared via a simple electrosorption-hydrothermal method and utilized for the electrooxidative filtration of organics. The BTO-CNT nanocomposite was characterized by scanning electron microscopy, thermogravimetric analysis, transmission electron microscopy, X-ray photoelectron spectroscopy, linear sweep voltammetry, and Tafel analysis. The submonolayer BTO coating is composed of 3.9±1.5 nm diameter nanoparticles (NPs). The oxygen-evolution potential of the BTO-CNT nanocomposite was determined to be 1.71 V (vs Ag/AgCl), which is 440 mV higher than an uncoated CNT anode. Anodic stability, characterized by CNT oxidative corrosion to form dissolved species, indicated that the BTO-CNT incurred negligible corrosion up to Vanode=2.2 V, whereas the uncoated CNT was compromised at Vanode≥1.4 V. The effect of metal oxide-nanoparticle coating on anodic performance was initially studied by oxalate oxidation followed by total organic carbon (TOC) and chemical oxygen demand (COD) analysis. The BTO-CNT displayed the best performance, with ∼98% oxalate oxidation (1.2 s filter residence time) and current efficiencies in the range of 32 to >99%. The BTO-CNT anode energy consumption was 25.7 kW h kgCOD(-1) at ∼93% TOC removal and 8.6 kW h kgCOD(-1) at ∼50% TOC removal, comparable to state-of-the-art oxalate oxidation processes (22.5-81.7 kW h kgCOD(-1)). The improved reactivity, current efficiency, and energy consumption are attributed to the increased conductivity, oxygen-evolution potential, and stability of the BTO-CNT anode. The effectiveness and efficiency of the BTO-CNT anode as compared to the uncoated CNT was further investigated by the electrooxidative filtration of ethanol, methanol, formaldehyde, and formate, and it was determined to have TOC removals 2 to 8 times greater, mineralization current efficiencies 1.5 to 3.5 times greater, and energy consumption 4 to 5 times less than the uncoated CNT anode. Electrooxidation and anode passivation mechanisms are discussed.

Effect of pH in the Electrochemical Response ofSnO2-Carbon Black Composites and its Use as Anodes

In this work is carried out electrochemical characterization of SnO2-Carbon Black composites in electrolytes systems with different pH by means of lineal sweep voltammetry and chronoamperometry. The electrochemical responses were compared with Pt and DSA (Ti/IrO2/SnO2/Sb2O5) electrodes, considering them as well behavior electrodes for water oxidation reaction. This study allows us to identify that SnO2-nCFE electrode depresses the water oxidation potential, the reaction is catalyzed, and the SnO2-SCFE electrode extends the oxygen evolution potential. Consequently the electrodes were evaluated in 0.1M KHCO3/CO2 with pH 6.8, and 0.1M KHCO3 2% Reactive Blue dye, respectively. The assessment in these specific systems enables to evaluate their possible use as anodes. In a future work, the efficiency and cell potential will be reported in order to confirm the effective performance of these electrodes materials.

Fabrication and enhanced electrocatalytic activity of 3D highly ordered macroporous PbO2 electrode for recalcitrant pollutant incineration

By virtue of the self-assembled colloidal crystal template with face-centered cubic structure, a novel three-dimensional highly ordered macroporous PbO2 (3DOM-PbO2) electrode was fabricated by electrochemical deposition method. In the 3DOM-PbO2 film, every spherical cavity was interconnected to three adjacent spherical cavities on the upper and lower layer, respectively, and the pore size was about 500nm. Compared to the traditional flat microcrystalline PbO2 (Flat-PbO2), the nanocrystalline 3DOM-PbO2 with β-PbO2 crystal phase possessed larger specific surface area (46 m2g−1), higher oxygen evolution potential (1.92V), smaller electron transfer resistance (35.5Ω), and more abundant crystal defect sites, resulting in better electrocatalytic performance. The electrochemical mineralization of refractory metalaxyl with 3DOM-PbO2 anode demonstrated that, the electrocatalytic reaction followed pseudo-first-order kinetics and the value of apparent rate constant (kapp) is 0.017min−1, about 2.4 times that with Flat-PbO2, and total organic carbon (TOC) and chemical oxygen demand (COD) removals are all approximately 95% after 300min. The mineralization current efficiency with the 3DOM-PbO2 was much higher than that with the Flat-PbO2, and corresponding electrical energy consumption was lower. Moreover, the intermediates were identified by high-performance liquid chromatography (HPLC) and Gas chromatography–Mass spectrometer (GC–MS), and possible electrocatalytic oxidation mechanism of metalaxyl on the 3DOM-PbO2 electrode was also discussed in detail.

Electrochemical Behaviors of Pb–0.3%Ag-0.06%Ca Rolled Alloy Anode during and after Zinc Electrowinning - Tafel Investigations

In this paper, the oxygen evolution potential and kinetics of Pb–0.3%Ag-0.06%Ca rolled alloy anode during the 15 days electrolysis in acid zinc sulphate electrolyte solution were investigated with galvanostatic polarization curve and Quasi-stationary polarization (Tafel) techniques. The results revealed that the anodic oxygen evolution potential and reaction kinetics varied a lot during the electrolysis for it is a process indicating the formation and stabilization of anodic oxide layer. With the increasing electrolysis time, the potentials (MSE) and overpotentials of oxygen evolution mainly present a declining trend while the electrode surface exchange current density a rising trend.

Enhanced Electrochemical Performance of [Ni<sub>4</sub>Al(OH)<sub>10</sub>]OH by Mechanically Blending Nanometric Zinc Oxide

Nanometric zinc oxide was prepared by the methods of precipitation and subsequent hydrothermal treatment, and used as an additive of a layered double hydroxide, [Ni4Al (OH)10]OH, to prepare the positive electrode of Nickel/metal hydride battery through mechanical blending. ZnO particles show sphere-like aggregates, and the particle size is around 100 nm in diameter. The influence on the electrochemical performance was investigated in positive electrode with different mass fraction of ZnO. The results indicate that the addition of ZnO can improve charge/discharge performances and electrochemical cyclic reversibility; also, elevate the oxygen evolution potential, decrease the double layer capacitance and the charge transfer resistance.

Structure and Properties of CNT-PbO<sub>2</sub> Anodes on Stainless Steel

An ideal anodes used for the electrochemical oxidation of organic wastewater should have excellent activity, stability and high oxygen evolution potential. In this paper the CNT (Carbon Nanotubes)-PbO2 films electrodeposited on stainless steel were prepared. X-ray diffraction (XRD) patterns and SEM images indicated that CNT particles and PbO2 were able to achieve co-deposit and the composite CNT-PbO2 films were compact. The cyclic voltammograms of the CNT-PbO2 films studied in 0.5M H2SO4 at a scan rate of 100 mV/s showed that the CNT-PbO2 film has high electrochemical stability. The results of wastewater treatment indicated that the CNT-PbO2 anodes have excellent activity in ammonia wastewater treatment.

Effect of surface modification of zinc oxide on the electrochemical performances of [Ni4Al(OH)10]OH electrode

Surface modification of zinc oxide on the [Ni4Al(OH)10]OH has been performed by a chemical surface precipitation method. Inductively coupled plasma measurements show that the amount of ZnO of prepared samples increases with the increase of initial concentration of Zn2+ in the mother solution. Powder X-ray diffraction measurements and scanning electron microscope images show that the modification of ZnO has little effects on the lattice parameters and the particle sizes of the [Ni4Al(OH)10]OH, but does change the morphology. The charge–discharge cycles results show that the deterioration rate of discharge capacity for the electrode with ZnO is only 4.0 % after 255 cycles, which is lower than that of electrode without ZnO (8.5 %); meanwhile, the maximal numbers of exchanged electrons per nickel atom for the electrodes with ZnO are basically over 1.83, which are higher than that of the electrode without ZnO (1.73), indicating that the modification of ZnO can improve the utilization of active material. In addition, the cyclic voltammogram tests results show that the modification of ZnO not only improves electrochemical cyclic reversibility but also elevates the oxygen evolution potential. Electrochemical impedance spectroscopy measurements show that the modification of ZnO can lower the double layer capacitance and the charge transfer resistance.

Electrochemical Oxidation of Carboxylic Acids in Water at Boron-Doped Diamond (BDD) Anodes in the Range of Potential of Oxygen Evolution: Detection Measurements and Studies on the Reaction Mechanism

The electrochemical oxidation in water solutions of selected carboxylic acids (namely oxalic, formic, acetic, maleic, and succinic) at boron-doped diamond (BDD) anodes was investigated by polarization and chronoamperometric measurements. In the presence of low concentrations of carboxylic acids, current densities changed approximately linearly with the acid concentrations. Furthermore, when the current densities were plotted as a function of the chemical oxygen demand, a similar response was observed for all the investigated acids with the exception of oxalic acid. For high carboxylic acid concentrations, the linear variation is often loosen and different behaviors are observed depending on the nature of the acid and on the value of the applied working potential. Smaller increases of current densities were observed in water solutions of NaCl as a result of the chlorides oxidation to active chlorine. The effect of pH, boron doping level, BDD pretreatment, and of the nature of the supporting electrolyte on the amperometric response of carboxylic acids was also studied in detail. Some theoretical considerations were briefly presented in order to rationalize the observed behaviors.

Comparison of electrocatalytic characterization of boron-doped diamond and SnO2 electrodes

Boron-doped diamond (BDD) and SnO2 electrodes were prepared by direct current plasma chemical vapor deposition (DC-PCVD) and sol–gel method, respectively. Electrochemical characterization of the two electrodes were investigated by phenol electrochemical degradation, accelerated service life test, cyclic voltammetry (CV) in phenol solution, polarization curves in H2SO4. The surface morphology and crystal structure of two electrodes were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis. The results showed a considerable difference between the two electrodes in their electrocatalytic activity, electrochemical stability and surface properties. Phenol was readily mineralized to CO2 at BDD electrode, favoring electrochemical combustion, but its degradation was much slower at SnO2 electrode. The service life of BDD electrode was 10 times longer than that of SnO2. Higher electrocatalytic activity and electrochemical stability of BDD electrode arise from its high oxygen evolution potential and the physically absorbed hydroxyl radicals (OH) on electrode surface.

Smoothening of niobium by electropolishing

The effects of various electropolishing (EP) parameters such as duration, applied voltage, working temperature, mechanical prepolishing and acid volume ratio on the EP process, and surface smoothness of high purity niobium (Nb) were systematically investigated using electrochemical technique and optical profilometry. The electropolishing parameters had a significant influence on the smoothness of the Nb by controlling the current density. Prolonged EP duration caused different dissolution rates of grains. Applied voltages above the oxygen evolution potential resulted in severe pitting of the Nb. High working temperature-caused roughening of the Nb surface via different dissolution rates of grains and mechanically ground smooth surfaces were roughened by the formation of valleys on the surfaces. A lower fluoride ion concentration in the acid solution gave rise to a rougher surface of the Nb because the fluoride ions were transport-limited species during the EP process.

Research of Ti/NanotubeTiO<sub>2</sub>/Sb-SnO<sub>2</sub> Electorde and its Electrochemical Performance

In this paper nanotube TiO2 coating as an interlayer was produced on Ti substrate and the performances of the Ti/nanotube TiO2/Sb-SnO2 electrodes were investigated. It is shown that the microstructure of the nanotubes changes with the anodic oxidation voltage and time, and the introduction of the nanotube TiO2 in the electrodes gives rise to both the oxygen evolution potential and the accelerated life of the electrodes.

Structure and Performance of Ti/TiN/PbO<sub>2 </sub>Electrodes with Plasma-Sprayed TiN Interlayer

TiN coating as an interlayer in Ti/TiN/PbO2 electrode and PbO2 catalytic layer were fabricated by reactive plasma spray and electro-deposition, respectively. It is shown that because of good effect of the TiN interlayer, the Ti/TiN/PbO2 electrode exhibits a higher oxygen evolution potential and much improved accelerated life compared with the Ti/PbO2 electrode.

Fabrication of cerium-doped lead dioxide anode with improved electrocatalytic activity and its application for removal of Rhodamine B

The electrochemical properties of a titanium dioxide nanotubes/cerium-doped lead dioxide (TiO2-NTs/Ce-PbO2) anode and its removal of Rhodamine B (RhB) from aqueous solution were investigated. Cerium doping content and electrodeposition time were optimized to get the highest electrocatalytic activity. Scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy were used to characterize the morphology, crystal structure and elemental states of the modified anode. The accelerated life test and linear sweep voltammetry indicated that TiO2-NTs/Ce-PbO2 possessed 2.3 times longer accelerated service life and higher oxygen evolution potential than TiO2-NTs/PbO2. The removal of RhB by TiO2-NTs/Ce-PbO2 anode was investigated under different conditions. It was found that a higher current density, acidic or quasi-neutral solution and the presence of chloride ions promoted the removal efficiency of RhB. The good electrocatalytic performance of TiO2-NTs/Ce-PbO2 makes it a promising anode for treatment of organic pollutants in aqueous solution.

Anodic behavior of cobalt silicides in potassium hydroxide solutions

Anodic behavior of a CoSi2 electrode in 0.1–4 M KOH solutions and a Co2Si electrode in 1 M KOH was studied in a range from the corrosion potential (Ecor) to the oxygen evolution potentials with the use of polarization and impedance measurements. A number of results indicate enrichment of electrode surface layers in cobalt. At potentials from Ecor to Etp transpassivation potential, impedance spectra correspond to the passive state of the silicides. At potentials from Etp to the onset potential of oxygen evolution, impedance spectra can be described taking into account the inclusion of hydroxide ions in the passivating film. Equivalent electric circuits are proposed for different electrode potential ranges.

Preparation and Characterization of Titanium Based PbO2 Electrodes Doped with Some Common Elements

Abstract Four kinds of PbO2 electrodes were prepared by electrochemical deposition and three of them were doped by Fe, Ni and Ag, respectively. The characters of the electrodes were analyzed by SEM, XRD, accelerated life tests, and linear scanning voltammetry. The results show that the electrode surfaces are covered by quadrangular β-PbO2 crystals. The average grain sizes of the undoped PbO2 electrode and Ni-doped PbO2 electrode are similar and smaller than that of the Fe-doped PbO2 and Ag-doped PbO2 electrodes. The Fe-doped PbO2 electrode has the longest accelerated test life due to its dense surface. The LSV tests show that the Ni-doped PbO2 electrode possesses the highest oxygen evolution potential. From the phenol electrolysis, the Ni-doped PbO2 electrode demonstrated the best performance in COD removal efficiency, average current efficiency, and energy consumption.

The Study on the Effect of Er on the Structure and Properties of Ti/SnO<sub>2</sub>-Sb Anode Prepared by Pechini’s Method

The Ti/SnO2-Sb electrode with/without Er were manufactured by Pechini’s method. The electrodes were characterized using SEM, EDS, XRD, FT-IR, the oxygen evolution potential test and their electro-catalytic abilities were evaluated though nitenpyram degradation. XRD and FT-IR results showed that the structure of the electrodes were Sn-base sosoloid without Er and Sb phases. The Er3+iron entering the unit cell of SnO2(Sn4+) could cause the grain refinement, the surface enrichment of Sb and Er, stronger water absorbability, and higher anode potential. These consequently generated more active sites and less oxygen vacancies on the anode surface, leading the improving of the electro-catalytic performance. The grain refinement mechanism for Er doping may be ascribed to the increase of the surface composition supercooling, the acceleration of the SnO2generation rate, and the restrain of its growth rate.

Novel lead–cobalt composite anodes for copper electrowinning

PbO2–CoOx and PbO2–Co3O4 composite-coated anodes, using titanium and nickel substrates, have been successfully prepared and tested under typical copper electrowinning conditions. The aim of depositing a well-adhered composite coating onto the surface of the titanium and nickel substrate materials was pursued using three different coatings. The performance of the produced anodes was examined in terms of oxygen evolution potential and service life. Both of the anodes with PbO2–CoOx or PbO2–Co3O4 deposited on titanium resulted in reduction of the oxygen evolution potential of 300 to 400mV compared with a conventional PbCaSn anode. The anodes prepared by applying the same coatings onto a nickel substrate showed poor stability in the acidic electrolyte media used in this experiment to represent typical copper electrowinning conditions. Of the different coatings tested, a combination of thermal deposition of a SnO2–Sb2O3 interlayer on the surface of a titanium substrate followed by electrodeposition of the top layer of the composite coating resulted in the best electrochemical activity and service life for the anodes. A Tafel slope of 88mV dec−1 was recorded for the anode with a top coating of PbO2–CoOx and 47mV dec−1 for the anode with a top coating of PbO2–Co3O4, which both compare favourably to the 122mV dec−1 which was observed for a conventional PbCaSn anode. Anodisation tests were carried out for a period of 16h both in the presence and in the absence of the organic additive thiourea in the electrolyte. Corrosion rates were estimated from these tests and the results showed that the titanium-based anode with a SnO2–Sb2O3 interlayer and PbO2–CoOx coating has a lower corrosion rate than a conventional PbCaSn anode, whereas the corrosion rate of the titanium-based anode with same interlayer and PbO2–Co3O4 coating might be much greater but this remains to be confirmed. The results also showed that the addition of thiourea appears to increase the corrosion rate of the composite-coated anodes although it reduces the corrosion rate of a PbCaSn anode. Thiourea showed no obvious effect on the anode potential.

Strategic Modification of BiVO4 for Improving Photoelectrochemical Water Oxidation Performance

To improve the photoelectrochemical (PEC) performance of BiVO4, three different modifications (doping, heterojunction, and catalyst deposition) using earth-abundant elements are performed and their effects are compared in a 0.1 M phosphate electrolyte at pH 7 under AM1.5 light (100 mW/cm2). When a hexavalent element (Cr6+, W6+, or Mo6+) is doped at various levels, the Mo6+-doping effect is most significant at 10 atomic % with about two times higher photocurrent generation at the oxygen evolution potential (1.23 VRHE). Such enhancement is attributed to a decrease in charge transfer resistance (Rct) by donor doping, resulting in an approximate 2-fold increase in charge separation efficiency (ηsep) to about 25%. W6+ is less effective than Mo6+, whereas Cr6+ has a detrimental effect. To further improve the charge separation efficiency of Mo6+-doped BiVO4 (Mo-BiVO4), a approximate 600 nm thick WO3 layer is deposited under a similarly thick Mo-BiVO4 layer. This binary heterojunction (WO3/Mo-BiVO4) exhibits ηsep of about 50% along with more than 3 times higher photocurrent generation. On the other hand, an oxygen evolving cobalt-phosphate (Co-Pi) catalyst electrodeposited to Mo-BiVO4 (Mo-BiVO4/Co-Pi) enhances charge injection efficiency (ηinj) from ∼50 to ∼70% at 1.23 VRHE. These two binaries are coupled into a ternary heterojunction (WO3/Mo-BiVO4/Co-Pi) in order to improve the charge transfer efficiencies (ηsep and ηinj). The PEC performance of this ternary is significantly high with photocurrent density of about 2.4 mA/cm2 at 1.23 VRHE (corresponding to the solar-to-hydrogen efficiency of ca. 3%) due to ηsep and ηinj of ∼60 and 90%, respectively.