Application Of Anodic Potential Research Articles

Reaction Kinetic-Induced Changes in the Electrochemically Promoted C2H4 Oxidation on Pt/YSZ

The electrochemical promotion of C2H4 oxidation reaction has been investigated under various feed gas compositions and temperatures over a Pt/Y2O3-stabilized ZrO2 catalyst electrode. It was found that under oxidizing conditions the reaction exhibits electrophobic behavior, i.e. the catalytic rate of CO2 formation increases with anodic potential application, while it shifts to electrophilic behaviour, i.e. the rate increases with cathodic potential application, under near stoichiometric feed conditions. At intermediate C2H4 to O2 ratios and low temperatures volcano type behavior is observed, i.e. the rate is poisoned both with anodic and cathodic potential application. The effect of feed gas composition on the electrochemical promotion behaviour is related to changes in the reaction kinetic order with respect to C2H4 and O2. The results are in excellent agreement with the rules of electrochemical and chemical promotion.

Influence of anodization parameters on the expansion factor of TiO2 nanotubes

Growth of titania nanotubes was carried out in fluoride containing electrolytes using photolithographically defined thin film patterns to determine the amount of expansion when the metal is converted to oxide. This expansion of TiO2 nanotubes is studied for a large set of electrochemical conditions. We show that this parameter strongly depends on the applied anodization potential and the water content in the electrolyte whereas the fluoride content is only of minor influence. Expansion factors were found to vary between 1.3 and 2.8 depending on the anodizing parameters. This variation is explained in terms of efficiency of oxide growth, as well as of chemical composition, density, and porosity of the TiO2 nanotubular array.

Ion velocity and plasma potential measurements of a cylindrical cusped field thruster

Measurements of the most probable time-averaged axial ion velocities and plasma potential within the acceleration channel and in the plume of a straight-channeled cylindrical cusped field thruster operating on xenon are presented. Ion velocities for the thruster are derived from laser-induced fluorescence measurements of the 5d[4]7/2-6p[3]5/2 xenon ion excited state transition centered at λ=834.72nm. Plasma potential measurements are made using a floating emissive probe with a thoriated-tungsten filament. The thruster is operated in a power matched condition with 300 V applied anode potential for comparison to previous krypton plasma potential measurements, and a low power condition with 150 V applied anode potential. Correlations are seen between the plasma potential drop outside of the thruster and kinetic energy contours of the accelerating ions.

One-step unipolar pulse electrodeposition of nickel hexacyanoferrate/chitosan/carbon nanotubes film and its application in hydrogen peroxide sensor

Unipolar pulse waveforms consist of an applied anode potential during the on-period and an open-circuit potential during the off-period. Unipolar pulse electrodeposition (UPED) was used to fabricate nickel hexacyanoferrate/chitosan/carbon nanotubes (NiHCF/CS/CNTs) nanocomposite films with controllable structure on the electrode surface of a hydrogen peroxide (H2O2) sensor. One-step electrodeposition of NiHCF/CS/CNTs film with insoluble-structure NiHCF nanoparticles was performed, and the whole procedure took only several minutes. The morphology and the composition of the NiHCF/CS/CNTs film were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray (EDS). With the introduction of CNTs, the NiHCF/CS/CNTs system formed showed synergy between CNTs and NiHCF with a significant improvement of redox activity of NiHCF due to the excellent electron-transfer ability of CNTs. Electrochemical experiments revealed that the modified electrode allowed low potential (−0.2V) detection of H2O2 and showed high electrocatalytic activity towards the reduction of H2O2. The linear range for the detection of H2O2 was 0.04–5.6mM with a high sensitivity of 654mAM−1cm−2 and a rapid response (less than 2s). The detection limit for H2O2 was as low as 2.8×10−7M (S/N=3).

Synthesis of Highly Ordered Nanotubular Oxide Layers on Ti-6Al-4V Alloys by Anodization Technique

Highly ordered nanotube arrays were fabricated via electrochemical anodization of Ti-6Al-4V (TC4) alloy foils in aqueous fluorine containing electrolytes. The formation of ordered nanotubular films was affected by the applied anodization potential and the anodization time. The optimal applied voltage and anodization time were 20V and 1h, respectively, as-prepared anodic nanotubular films were in highly ordered with the average inner diameter of about 120nm, the wall thickness of 17nm and the tube length about 300nm. The tubular nanostructures were examined by field emission scanning electron microscopy. The possible nanotube formation mechanism was also discussed.

A New Insight into Potential Regulation on Growth and Power Generation of Geobacter sulfurreducens in Microbial Fuel Cells Based on Energy Viewpoint

The anode potential in microbial fuel cells (MFCs) defines the possible metabolic energy gain (PMEG) for the bacteria growth. This study focused on the mechanism behind anode potential controlling microbial growth and power generation in MFCs from an energy perspective. Four sets of MFCs were operated with varied conditions: three with different applied anode potential (-160, 0, and 400 mV vs standard hydrogen electrode (SHE)) and one with an external resistor (500 Omega). A model strain Geobacter sulfurreducens was used here. The evolution of biomass was measured and its quantitative relationship with PMEG was analyzed. Linear voltammetry and cyclic voltammetry were also carried out. Results indicated a notable gain in biomass and power density when anode potential increased from -160 to 0 mV. However, no gain in biomass and power generation was detected when anode potential further increased to 400 mV. At anode potential of 0 mV and below, G. sulfurreducens extracted a significant portion of PMEG for growth, while utilization of PMEG significantly decreased at 400 mV. Furthermore, the anode potential has a minor influence on individual G. sulfurreducens cell activity, and the maximum power density of MFC proportionate to biomass.

Electrosorption/Electrodesorption of Arsenic on a Granular Activated Carbon in the Presence of Other Heavy Metals

The adsorption, electrosorption, and electrodesorption of aqueous, inorganic arsenic on the granular activated carbon (GAC), DARCO((R)) 12x20 GAC was investigated in solutions containing arsenic as the only contaminant, as well as with chromium, nickel and iron. Darco 1220 was selected for these investigations primarily because it is relatively ineffective as a normal (unassisted) arsenic adsorbent in the chosen electrolytes at the low loadings used. It is shown that the application of anodic potentials in the 1.0 - 1.5V range, however, result in enhanced uptake, most probably due to charging of the electrochemical double-layer at the electrode surface. 100% regeneration of electrosorbed arsenic was achieved via electrodesorption at a cathodic potential of 1.50V. The presence of ad-metal ions was observed to have a significant and complex effect on arsenic adsorption, electrosorption, and electrodesorption. In particular, the Cr:As ratio was shown to have complex effects, decreasing adsorption uptake when present as 3:2, but enhancing adsorption when present as 5:1. Nickel was found to have less of an effect than chromium except at the highest anodic potential used of 1.50V, where it exhibited better performance than chromium. The presence of iron significantly enhanced uptake. With a 1.50V anodic potential, the bulk arsenic concentration was reduced to less than detectable limits, well below the USEPA MCL for drinking water. Regeneration efficiency by electrodesorption for the As-Fe system was greater than about 90%.

Anodic Formation of Ordered TiO2 Nanotube Arrays: Effects of Electrolyte Temperature and Anodization Potential

Highly ordered TiO2 nanotube arrays were fabricated via electrochemical anodization of high purity Ti foil and Ti thin film coated indium tin oxide (ITO) glass in fluorine containing electrolytes (both aqueous and nonaqueous). The formation of ordered TiO2 nanotube arrays was affected by the electrolyte temperature and the applied anodization potential. In aqueous electrolyte, the anodization potential exerted significant influence on the formation of TiO2 nanotube arrays, while little effect from the electrolyte temperature was observed. In nonaqueous electrolyte, the electrolyte temperature markedly affected the TiO2 nanotube dimensions, while the anodization potential exhibited slight influence in this regard. As a consequence, TiO2 nanotube arrays with tube diameters ranging from 20 to 90 nm and film thicknesses ranging from several hundred nanometers to several micrometers were obtained. The TiO2 nanostructures were examined by scanning electron microscopy. Thermal annealing on the anodized Ti induce...

Study of passive films formed on mild steel in alkaline media by the application of anodic potentials

In this paper, iron oxide thin layers formed on mild steel substrates in alkaline media by the application of different anodic potentials were studied in order to characterize their morphology, composition and electrochemical behaviour, in particular under conditions of cathodic protection. The surface composition was evaluated by X-Ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES). The morphology of the surface oxides was studied via Atomic Force Microscopy (AFM). The electrochemical behaviour of the surface oxides was studied using Electrochemical Impedance Spectroscopy (EIS). The results showed that the surface film is composed by Fe 2+oxides and Fe 3+ oxides and/or hydroxides. The contribution of Fe 2+ species vanishes when the potential of film formation increases in the passive domain. Two distinct phases were differentiated in the outer layers of the surface film, which proves that film growing is topotactic in nature.

Fast Fourier Transform Analysis of Pore Pattern in Anodized Alumina Formed at Various Conditions

A quantitative investigation of the effect of process parameters such as electrolyte concentration, temperature, anodization duration and anodization potential on the pore pattern (including pore diameter and distribution) in anodic alumina was performed based on aluminum anodization experiments. Using fast Fourier transform (FFT) analysis, we developed a method to quantify the orderedness of pore distribution. We found that at a lower temperature the anodization protocol of a 1 hr first step followed by a 4 hr second step did not cause any change in pore orderedness as opposed to the anodization protocol of a 12 hr first step followed by a 1 hr second step, but at a higher temperature the former improved the pore orderedness. Increasing the electrolyte concentration, improved the pore orderedness. Varying the electrolyte concentration, temperature, and anodization duration did not have any effect on the pore diameter. Increasing the anodization potential, however, not only improved the pore orderedness but also increased the pore diameter. Linear relationships exist between the pore diameter and anodization potential and between the center to center pore spacing and applied anodization potential.

Effects of migrating inhibitors on corrosion of reinforcing steel covered with repair mortar

The present study concerns the investigation of the protective effect of migrating corrosion inhibitors, against rebar corrosion, in specimens of repair fiber reinforcement mortars, in relation to these containing corrosion inhibitors. The strain gauge (SG) measurement technique was used for fast corrosion measurements, under anodic potential application in corrosive environment of 3.5% wt NaCl solution. The corrosion protection effectiveness was also tested by galvanic current measurements between different categories of specimens in order to estimate the galvanic corrosion between repaired and non-repaired areas. According to these investigations the positive effect of the migrating corrosion inhibitors in fiber-reinforced mortars against corrosion of the rebars is evident, providing a prevention of steel rebars' corrosion in the cases of repairing concrete structures. The presence of fiber reinforcement in repair mortar specimens prevents the microcracking effects, resulting in decrease of concrete cracking due to reinforcement corrosion.

Electrode reactions of palladium(II) in chloride solution at carbon paste electrodes modified with derivatives of N-benzoylthiourea

The study of the electrode reactions of palladium(II) at non-modified carbon paste electrodes (CPEs) in chloride solution has revealed the existence of a chloropalladate(II) complex at the electrode surface. The complex is formed during the application of anodic potentials after preceding palladium deposition. In the present paper the electrode reactions of PdII at CPEs modified with some N′,N′-disubstituted derivatives of N-benzoylthiourea [as selective ligands for palladium(II)] are studied in chloride solution by cyclic voltammetry. Two reduction peaks are observed in the cathodic scans recorded after deposition of palladium and anodization of the electrode. From the results it is concluded that [in addition to the chloropalladate(II) complex, observed at the non-modified electrode] a second palladium complex is formed at positive potentials. The formation of the palladium(II) complex of the N-benzoylthiourea derivatives by ligand exchange at the electrode surface is assumed. The ligand exchange itself occurs without charge transfer across the electrode|solution interface; therefore, it cannot be detected electrochemically. After palladium deposition and anodic treatment a pronounced "inverse" peak (i.e., an anodic peak in the cathodic scan) with peak currents up to 100 µA is observed at about +0.8 V. Its peak current increases with the amount of deposited palladium and the number of cycles. The reactions at the electrode surface are discussed. The results of the study reveal the existence of two different surface complexes of palladium(II) at ligand-modified CPEs, but the surface reactions could not be elucidated in detail.

Formation of Palladium Complex at Carbon Paste Surface in Chloride Solution as Studied by Cyclic Voltammetry

The deposition and dissolution of palladium at non-modified carbon paste electrode (CPE) is studied by cyclic voltammetry in chloride solutions (c ≥ 0.5 M KCl and pH 3 to 6). The Pd0 is deposited from tetrachloropalladate solution by potential cycles from E ≥ 0 V (vs Ag/AgCl) or positive potentials up to -0.5 V or by potentiostatic treatment at E ≤ 0 V. Oxidation peaks appear during potential sweep to positive direction after the preceding deposition of Pd. The appearance of two anodic peaks depends mainly on the amount of Pd0 deposited. The peak at about +0.1 V is caused by the dissolution of a palladium mono- or submonolayer, whereas the oxidation peak at more positive potentials is attributed to the dissolution of Pd from a palladium multilayer. After palladium deposition and potential sweep to positive potentials E > +0.8 V (or potentiostatic treatment at E > +0.8 V), a cathodic peak appears at about 0 V and corresponding anodic peak at +0.1 V. It is concluded that these peaks are caused by reduction and oxidation of the chloropalladate surface complex formed during preceding application of anodic potentials. Reaction schemes of PdII/Pd0 and chloropalladate complex are discussed.

Electrolytic partial fluorination of organic compounds. 36 . Regioselective anodic fluorination of phenylthiolated benzofuranone and benzothiazole derivatives

The anodic fluorination of 3-phenylthio-2-benzofuranones and α-phenylthio-2-benzothiazolylacetonitrile was investigated. Both derivatives were selectively fluorinated in good yields at the carbon α to the sulfur atoms in Et 4NF·3HF/DME using a platinum anode and an undivided cell. The fluorination yields of the benzofuranone derivatives were improved by the addition of Ph 2S, which was not effective in the case of the benzothiazole derivative. The fluorination yield of the benzothiazole derivative was strongly affected by the stirring state of the electrolytic solution or the applied anode potential.

Fluorescence emission as a probe to investigate electrochemical polymerization of 9-vinylanthracene

The cationic polymerization of 9-vinylanthracene can be initiated at a transparent SnO/sub 2/ electrode with the application of anodic potentials (E > 1.1 V vs. saturated sodium chloride calomel electrode) in acetonitrile solutions. The excimer emission (emission maximum approx.500 nm) of poly(9-vinyl-anthracene) which is distinguishable from the monomer fluorescence emission (emission maxima 410, 430 nm) has been used to probe the electrochemical polymerization process directly. The in situ spectroelectrochemical technique, which would be useful in obtaining kinetic and mechanistic information of the electropolymerization process, is described.

The Effect of Thermal Treatments on Stress Corrosion Cracking of Alloy-800 in a Caustic Environment

Abstract Stress corrosion cracking (SCC) tests under controlled potentials were conducted on plastically stressed C-rings of Alloy-800 to evaluate the effect of thermal treatments (at 500 to 850 C) on SCC of Alloy-800 steam generator tubing. The tests were conducted in a caustic solution at 300 C; such alkaline environments may sometimes form in crevices in nuclear steam generators. The results are presented in the form of a time-temperature-SCC diagram. Thermal treatments generally inhibited the SCC of Alloy-800, and the improvement was substantial in a few cases. Application of anodic potential and increasing stress generally accelerated SCC.

Polymer-modified electrodes. Electrochemical and photoelectrochemical polymerization of 1-vinylpyrene

Polymerization of 1-vinylpyrene in acetonitrile was achieved electrochemically at a conducting SnO/sub 2/ electrode by application of anodic potentials and photoelectrochemically at a n-GaAs semiconductor electrode under visible light irradiation. Both polymers exhibited characteristic excimer emission ..lambda../sub max approx. 480 nm) in both films and THF solutions similar to poly(vinylpyrene) synthesized by using Ziegler-Natta catalyst. The lifetime of the excimer emission was approx.110 ns. The mechanism of photodegradation of poly(vinylpyrene) was elucidated by using ESR techniques. 22 references, 7 figures, 1 table.

Surface films and stress-corrosion cracking in Ti−Al alloys

The characteristics of film growth on a series of binary Ti−Al alloys and on two commercial titanium alloys have been examined by ellipsometry and correlated with the velocity of stress-corrosion cracking in these alloys as a function of both applied potential and pH of the environment. It has been found that factors which stimulate film growth,i. e. high pH and the application of anodic potentials, reduce the velocity of cracking while factors which restrict film formation, such as increasing the aluminum content of the alloy or the presence of Ti3Al, facilitate cracking. These studies indicate that the occurrence of stress-corrosion cracking in Ti−Al alloys is confined to an environmental regime in which surface films are relatively thin.

Oxide Growth on Copper and Alpha‐Brasses in Aqueous Ammonia

An ellipsometric study of the kinetics of oxide growth for pure copper and a series of alpha‐brasses immersed in tarnishing ammoniacal environments has established that the growth of the oxide, shown to be cuprous oxide, obeys a linear law in each case, and that the rate of growth increases significantly with (a) increasing zinc content of the solid, (b) increasing temperature, and (c) the application of anodic potentials. On the basis of these results it is suggested that the oxide is porous and that oxide growth involves the dissolution of metal ions at the base of the pore (anodic reaction) and their deposition at the oxide surface (cathodic reaction), electrons flowing through the oxide film. The influence of zinc content on the oxide‐growth rate is attributed to its effect on the dissolution kinetics.

Passivity of electrodeposited tin-nickel alloy and other intermetallic tin compounds

Electrodeposited SnNi immersed in aqueous solutions forms a thin protective oxide film which is stable over a wide range of pH and potential. The formation of the film is accompanied by a marked rise in corrosion potential. As an anode SnNi is passive except in HCl and in certain electrolyte solutions from which it may be electrodeposited. A sufficient increase in the applied anode potential leads to the formation of a higher oxide which has good electronic conductivity, and to the evolution of O 2. Anode corrosion during O 2 evolution is negligible except in chlorides. Two compounds with structures similar to SnNi: FeSn 2 and Cu 6Sn 5, also display strong tendencies to form protective films accompanied by a marked rise in potential in the absence of applied potentials. This has an important bearing on the corrosion of tinplate and tinned copper, where these alloys occur as intermediate layers.