Cyclic Polarization Measurements Research Articles

CNx-modified Fe3O4 as Pt nanoparticle support for the oxygen reduction reaction

A novel electrocatalyst support material, nitrogen-doped carbon (CNx)-modified Fe3O4 (Fe3O4-CNx), was synthesized through carbonizing a polypyrrole-Fe3O4 hybridized precursor. Subsequently, Fe3O4-CNx-supported Pt (Pt/Fe3O4-CNx) nanocomposites were prepared by reducing Pt precursor in ethylene glycol solution and evaluated for the oxygen reduction reaction (ORR). The Pt/Fe3O4-CNx catalysts were characterized by X-ray diffraction, Raman spectra, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The electrocatalytic activity and stability of the as-prepared electrocatalysts toward ORR were studied by cyclic voltammetry and steady-state polarization measurements. The results showed that Pt/Fe3O4-CNx catalysts exhibited superior catalytic performance for ORR to the conventional Pt/C and Pt/C-CNx catalysts.

Electrochemical characterization of ZrTi alloys for biomedical applications

The electrochemical behaviour of three ZrTi alloys (Zr5Ti, Zr25Ti and Zr45Ti) in Ringer's solution has been investigated. Their resistance against localized corrosion has been determined from cyclic potentiodynamic polarization (CCP) and electrochemical impedance spectroscopy (EIS) measurements, whereas scanning electrochemical microscopy (SECM) was applied to investigate the local reactivity of the passive films developed on the materials, and scanning electron microscopy (SEM) was employed to characterize the surface morphology of the alloys subjected to anodic polarization. An increased reactivity could be detected with SECM when the metal samples were polarized at +0.50VSHE, though the extent of this feature greatly depended on the nature of the metallic material. In addition, At 37°C, the Zr5Ti alloy was susceptible to localized corrosion. Though Zr25Ti alloy presented rather low pitting potential, the spontaneous corrosion potential of the material was sufficiently negative to require overpotentials around 600mV for breakdown to occur. Finally, the Zr45Ti alloy exhibited a larger passive range in the polarization curve, and it was resistant to localized corrosion.

Influence of zirconia nanoparticles on the surface and electrochemical behaviour of polypyrrole nanocomposite coated 316L SS in simulated body fluid

Current efforts of recent implant technology have been aimed principally at the improvement of corrosion resistance and biocompatibility. The present study demonstrates that the electro polymerisation of pyrrole and incorporation of zirconia (ZrO2) nanoparticles can be successfully combined to produce bioactive polypyrrole nanocomposite coatings for orthopaedic implants. Polypyrrole/ZrO2 nanocomposite coatings were electrochemically synthesised by cyclic votametric technique on 316L stainless steel (SS) in aqueous solution of oxalic acid. The existence of ZrO2 nanoparticles in polypyrrole (PPy) matrix was confirmed by Fourier Transform Infrared (FT-IR) spectroscopy and X ray diffraction (XRD) analysis. The surface morphology of coated 316L SS substrates was observed using Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM). Micro hardness of coated 316L SS was examined using Vickers hardness method. The electrochemical studies were carried out using cyclic polarisation and electrochemical impedance spectroscopy (EIS) measurements. In order to describe the biocompatibility, contact angle measurements and in vitro characterisation were carried out in simulated body fluid (SBF) solution. The results showed that the nanocomposite coatings exhibit superior biocompatibility and enhanced corrosion protection performance over 316L SS due to their hydrophilic, smooth, compact and less porous surface morphology than that of pure polypyrrole coatings.

A study on the electrochemical polymerization, characterization, and corrosion protection of o-toluidine on steel

Poly(o-toluidine) (POT) coatings were electrochemically synthesized on 304 stainless steel using cyclic voltammetric method. These coatings were characterized by Fourier transform infrared spectroscopy, UV–vis absorption spectroscopy, and cyclic voltammetry. The corrosion performance of POT coating in aqueous 3 wt% sodium chloride was assessed by the electrochemical techniques such as open circuit potential measurements, potentiodynamic polarization technique, cyclic potentiodynamic polarization measurements, and electrochemical impedance spectroscopy. The results reveal that POT coating on 304 stainless steel prevents general and localized corrosion, and reduces the exchange current density almost by a factor of 45 than bare 304 stainless steel.

Corrosion protection of commercial steel using stainless steel coatings deposited by Cathodic Arc Plasma Deposition technique

The commercial steel AISI 1010 was coated with AISI 316L steel using Cathodic Arc Plasma Deposition (CAPD) technique. The coatings were deposited in vacuum and in the presence of nitrogen, acetylene and mixture of the two as reactive gases. The coatings were deposited as a function of time while other parameters remained constant. The coatings 0.75 to 1.3 μm thick were adherent and amorphous. The aqueous corrosion properties of the coated samples in 3.5 wt % NaCl solution were studied by Tafel, cyclic and potentiodynamic polarization measurements. The derived corrosion parameters were then compared among the various uncoated and coated samples. The study revealed that the coated samples were more corrosion resistant than the uncoated one. Similarly, the samples coated in the nitrogen + acetylene mixture atmosphere were more corrosion resistant than the samples coated in only nitrogen and acetylene atmospheres. The corrosion parameters were also compared as a function of coating time to ascertain best coating thickness.

Kinetic investigation of zinc electrodeposition from sulfate electrolytes in the presence of impurities and ionic liquid additive [BMIM]HSO4

The effects of some common impurities such as copper, iron, nickel, cobalt, lead and their interaction with an ionic liquid additive 1-butyl-3-methylimidazolium hydrogen sulfate-[BMIM]HSO4 on zinc electrodeposition from acidic sulfate electrolyte were characterized in terms of the polarization behavior and the kinetics of zinc deposition using cyclic voltammetry and potentiodynamic polarization measurements. The results showed that these metallic impurities studied exerted some different changes in cyclic and cathodic polarization voltammograms. The addition of [BMIM]HSO4 was observed to counteract the detrimental effects of these impurities and induced a blocking effect on the zinc electrodeposition process through its cathodic adsorption on the electrode surface. The adsorption of this additive shifted the electroreduction potential of zinc ions towards more negative values, restricted impurities ions from being electroreduced, and inhibited hydrogen evolution. Moreover, the kinetics analysis of cathodic polarization suggested that the presence of these impurities alone and in combination with [BMIM]HSO4 had no effect on the Tafel slope and transfer coefficient but affected the exchange current density for the zinc deposition.

Effect of Oxygenated Additives on the Corrosion Behavior of Al-Si-Cu Alloy in Synthetic Condensed Automotive Solution

t. This work involves studying the effect of adding alcohols on corrosion behavior of Al-Si-Cu alloy in synthetic condensed automotive solution (CSAS) at room temperature. Alcohols used were methanol (MeOH), ethanol (EtOH), porpanol (PropOH), Butanol (ButOH), and mixture of (MeOH-EtOH), (MeOH-PropOH) and (MeOH-ButOH). According to potentiodynamic polarization test, the results of corrosion resistance indicate that additive alcohols increase the resistance of Al-Si-Cu alloy, except addition of ethanol to the CSAS and the resistance follows the sequence: MeOH. > ButOH > MeOHButOH > MeOH-PropOH > PropOH > MeOH-EtOH. Cyclic polarization measurements were carried out to estimate the pitting resistance of Al-Si-Cu alloy in CSAS in the absence and presence of alcohols, this test shows that the hysteresis loop appears only in cases of presence of ethanol and (MeOH-EtOH) mixture in CSAS indicating the disadvantage of adding ethanol and (MeOH-EtOH) mixture to automotive fuel.

Kinetics of hydrogen evolution reaction on stabilized Ni, Pt and Ni–Pt nanoparticles obtained by an organometallic approach

Both (Ni, Pt) and bimetallic (NixPt; x=1, 2, 3) nanoparticles have been synthesized by hydrogenation of Ni(cod)2 ad Pt2(dba)3 in the presence of a weak coordinating ligand, hexadecylamine (CH3(CH2)15NH2, HDA). These nanostructures were characterized by different techniques (Fourier Transform-Infrared Spectroscopy (FT-IR), High-Resolution Transmission Electron Microscopy (HRTEM)), and were evaluated as Hydrogen Evolution Reaction electrocatalysts in 0.5M sulfuric acid. The effects of varying the platinum amount during the synthesis were systematically studied by Cyclic Voltammetry (CV), polarization measurements and electrochemical impedance spectroscopy (EIS) techniques. HRTEM shows that the bimetallic nanostructures display a different morphology compared to that observed for pure Ni and Pt ones. The process of hydrogen adsorption–desorption in the as-prepared electrodes seems to occur in (110) and (100) facets. It was found that the increase in the activity for the HER is due to an increased electrochemical active surface area (ECSA) and/or stabilization in the case of elemental electrode materials; and to the effect of Pt amount in the case of the Ni–Pt nanostructures (synergistic effect leads to lower overpotential). It has been established that the main pathway for the HER is Volmer–Heyrovsky.

Corrosion and nanomechanical properties of vanadium carbide thin film coatings of tool steel

The corrosion and nanomechanical characteristics of tool steel coated with vanadium carbide thin films deposited by DC reactive magnetron sputtering were investigated. Cyclic polarization and electrochemical impedance spectroscopy measurements in a 3.5% sodium chloride solution indicated that corrosion decreases as the C content and the substrate temperature during deposition increase. The maximum hardness is reached for VC coatings with C/V ratios around unity, decreasing for either higher or lower C/V ratios. Complementary physicochemical analyses, made here or elsewhere, are used to clarify the reasons for such behavior. The present results are discussed in terms of the optimization of the deposition parameters aiming at concomitantly good corrosion resistance and high hardness.

Pitting Corrosion of Zinc in Na2S2O3 Solutions. Part I. Polarization Studies and Morphology of Pitting

Abstract As a first step towards studying pitting corrosion of Zn in aerated neutral 1.0 M sodium thiosulphate solution (pH 6.6), we have reported the results of cyclic polarization measurements on the passivity and passivity breakdown of Zn in this solution. The recorded voltammograms involved two oxidation processes labeled as AI and AII, and two reduction processes labeled as CII and CI on the forward (anodic) and reverse (cathodic) scans, respectively. The cathodic peak CII was attributed to the reduction of the pitting corrosion products (process AII). On the other hand, the cathodic process CI was related to the reduction of Zn2+ species formed during the course of the forward scan (process AI and the subsequent formation of the passive region), and the reduction of the adsorbed S2O3 2− anions to S2− and SO3 2−. The reduction products of S2O3 2−, namely S2− and SO3 2− anions, were detected in solution as a function of starting potential and time of holding the electrode at a cathodic potential of −2.0 V (Ag/AgCl). These anions were found to cooperate with the aggressive S2O3 2− anion itself in passivity breakdown and initiation of pitting corrosion. The effect of solution temperature (15–70 ºC) on the cyclic polarization behaviour of Zn was also studied, and metastable and stable pitting events observed at high temperatures were discussed. The morphology of pitting was also studied by ex situ scanning electron microscopy (SEM) as a function of applied anodic potential, bulk concentration of S2O3 2− and solution temperature. Cross-sectional view of pits revealed the formation of irregular deep and shallow pits. The aspect ratios (the ratio of pit width to pit depth) of the growing pits were estimated as a function of potential, electrolyte concentration and solution temperature. The aspect ratio of the growing pits was found to be potential and concentration independent, while it increased with temperature.

Promotional Effects of Ir Addition in Carbon-Supported Pt5Rh Electrocatalysts for the Electrooxidation of Ethanol at Room Temperature

The high CO2 selectivity of Pt–Rh catalysts in the ethanol electrooxidation reaction has been known for some time. However, this high selectivity is often realized at the expense of catalytic activity. This study investigates the use of Ir modification to improve the performance of Pt–Rh catalysts. Specifically a series of Vulcan XC-72 carbon-supported Pt5Rh1Irx catalysts were prepared by the NaBH4 reduction of the metal precursors in ethylene glycol. X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed good dispersion of ∼2.5 nm Pt–Rh–Ir nanoparticles on the carbon support. Evaluations of catalytic activity in 1 M ethanol solution in 0.1 M HClO4 by cyclic voltammetry (CV), polarization measurements, and chronoamperometry (CA) all indicated Pt5Rh1Ir0.6/C as the catalyst composition with the highest current density between 0.4 and 0.7 V. Electrochemical impedance spectroscopy (EIS) detected a decrease in the charge transfer resistance after the Ir modification, which could be attribute...

Effects of 5-(3-aminophenyl)-tetrazole on the inhibition of unalloyed iron corrosion in aerated 3.5% sodium chloride solutions as a corrosion inhibitor

The effects of 5-(3-aminophenyl)-tetrazole (APT) on the inhibition of unalloyed iron corrosion in aerated 3.5% NaCl solutions as a corrosion inhibitor have been studied using open circuit potential (OCP), cyclic potentiodynamic polarization (CPP), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) measurements. The inhibited iron surface was characterized by scanning electron spectroscopy (SEM) and energy dispersive X-ray (EDS) investigations. The OCP showed positive shifts of potential in the presence of APT and the increase of its concentration. CPP and CA measurements indicated that APT molecules decrease the pitting and uniform corrosions through decreasing the pitting and absolute currents, and corrosion rate as well as shifting the corrosion and pitting potentials of iron towards the noble values. EIS plots revealed that APT increases the surface and polarization resistances of iron. SEM/EDS investigations proved that the inhibition of iron corrosion in NaCl containing APT solutions is achieved by the adsorption of APT molecules onto iron to preclude the dissolution process by blocking the active sites on its surface.

Electrochemical oxidation of boron containing compounds on titanium carbide and its implications to direct fuel cells

Electrochemical oxidation of sodium borohydride (NaBH 4) and ammonia borane (NH 3BH 3) (AB) have been studied on titanium carbide electrode. The oxidation is followed by using cyclic voltammetry, chronoamperometry and polarization measurements. A fuel cell with TiC as anode and 40 wt% Pt/C as cathode is constructed and the polarization behaviour is studied with NaBH 4 as anodic fuel and hydrogen peroxide as catholyte. A maximum power density of 65 mW cm −2 at a load current density of 83 mA cm −2 is obtained at 343 K in the case of borhydride-based fuel cell and a value of 85 mW cm −2 at 105 mA cm −2 is obtained in the case of AB-based fuel cell at 353 K.

Corrosion susceptibility investigation of Ti–O film modified cobalt-chromium alloy (L-605) vascular stents by cyclic potentiodynamic polarization measurement

Ti–O film was deposited on cobalt-chromium alloy (L-605) coronary stents by metal vacuum arc source deposition. The corrosion resistance of the Ti–O film modified and bare L-605 stents was investigated by cyclic potentiodynamic polarization tests in phosphate buffered solution (PBS, 37 ± 1 °C). The optical microscopy and scanning electron microscopy (SEM) images of the modified stents indicated that the surface of all stent cells was very smooth and uniform, and the thickness of Ti–O film was about 10 nm. There were not any cracks and delamination on stent surface after dilation by angioplasty. The polarization results showed that the natural corrosion potential of the Ti–O film modified and bare stents was similar. But the corrosion current density of Ti–O film modified stent was lower than that of the bare stent at all scanned potential range. Compared with Ti–O film modified stent, the bare stent was more susceptible to corrosion. After cyclic potentiodynamic polarization test, the slight localized corrosion was found on the surface of bare stents. But no film flakes or localized pitting can be observed on Ti–O film modified stent. All these results showed that Ti–O film modified stent had the better corrosion resistance, compared with the bare L605 stent.

Nitrogen-doped carbon coated palygorskite as an efficient electrocatalyst support for oxygen reduction reaction

An electrocatalyst support, nitrogen-doped graphitic layer (CN x ) coated palygorskite (PLS) (donated as PLS@CN x ), is synthesized by carbonizing the polypyrrole (PPy) coated PLS and is explored for the first time as a cathode electrocatalyst support in proton exchange membrane fuel cell. The structural and chemical properties of the PLS@CN x are investigated by Fourier-Transform infrared spectrometer, thermogravimetric analysis, X-ray diffraction and transmission electron microscopy. The electrocatalytic activity and stability of Pt/PLS@CN x toward oxygen reduction reaction (ORR) are studied by cyclic voltammetry (CV) and steady state polarization measurements. Upon loading Pt (20 wt%), the catalysts exhibit superior catalytic performance during ORR, surpassing the conventional Pt/C (Vulcan XC-72) catalysts. High electrocatalytic activity and good stability can be attributed to the nitrogen atom incorporation and SiO 2 component in PLS.

Effect of scan rates and imposed potentials on the formation and growth of oxide film on Ti6Al4V alloy surface in 3% NaCl

In the present study, the formation and growth of an oxide film on a titanium alloy Ti6Al4V surface immersed in 3% NaCl solution using anodisation at various imposed potentials was investigated by two electrochemical techniques, cyclic polarisation and impedance measurements. In the cyclic polarisation studies at different scan rates, the obtained curves show a large range of passivation, due to the formation of a protective oxide film, generally TiO2 . In addition, the negative hysteresis that appeared during the cyclic polarisation with the shift of the corrosion potential in the more noble direction (approximately +260 mV) may be explained by a reduction of the corrosion products. It was found that the lower the scan rates the lower the passivation current, and the scan rates did not have a significant effect on the potential or current of corrosion. The impedance measurements (Nyquist and Bode plots) at various imposed potentials show that Ti6Al4V has a capacitive behaviour in the passive field, due to the formation and growth of the oxide film.

Corrosion effects of runway de-icing chemicals on aircraft alloys and coatings

Corrosion effects of five runway de-icing chemicals on aluminium alloy 2024, magnesium alloy RZ5 and cadmium-plated and subsequently chromate-treated steel 4340 were investigated by cyclic polarisation measurements, open circuit potential monitoring and cyclic chemical exposure tests. The runway de-icing chemicals included in the study contained urea, which has a long history as a runway de-icing chemical, and four new commercial de-icing chemicals, which were based on betaine and potassium formate. Corrosion effects of urea on aluminium alloy 2024 were more pronounced than those of the new de-icing chemicals. In urea, the breakdown potential, indicating the onset of pitting, was clearly distinguishable in the cyclic polarisation curve and pitting corrosion was detected on the specimen surface after all three types of tests. Weight losses during the chemical exposure tests were also higher for urea than for the other four chemicals, where pitting corrosion was only occasionally detected. The opposite was true in the case of magnesium alloy RZ5: although the alloy experienced general corrosion in each de-icing chemical included in the study, the rate of corrosion was often higher in the new de-icing chemicals than in urea. Corrosion effects of the five de-icing chemicals on cadmium-plated and chromate-treated high-strength steel 4340 were slightly different in all three tests, indicating that differences in coating quality, particularly in the thickness of the coating layers, might have influenced the results. Overall, however, partial loss of the coating layers occurred in all studied de-icing chemicals.

Pit initiation and growth control of Al in KSCN solutions

Abstract The inhibitive action of a newly synthesized glycine derivative, namely 2-(4-(dimethylamino)benzylamino)acetic acid hydrochloride (GlyD) on pitting corrosion of Al in KSCN solutions was studied. Obtained results were compared with glycine (Gly) itself. Cyclic polarization, potentiostatic and galvanostatic measurements were made, complemented with ex situ scanning electron microscope (SEM) examinations. Cyclic polarization measurements indicated that the presence of Gly and GlyD in aggressive SCN - solutions shifted the pitting potentials to more noble values and decreased the anodic currents in the passive region. Transient studies showed that nucleation of pit takes place after an incubation time ( t i ). The rate of pit nucleation ( t i −1 ) and growth was found to decrease to an extent depending on the type inhibitor. The SEM images showed that the severity of the pitting corrosion of Al in KSCN solution decreased to an extent depending on type of inhibitor. GlyD was much better than Gly in controlling pit initiation and growth of Al in these solutions.

Pitting of Al and Al–Si alloys in KSCN solutions and the effect of light

The pitting corrosion susceptibility of pure Al and three Al-Si alloys, namely (Al-6%Si), (Al-12%Si) and (Al-18%Si) has been studied in 0.04M KSCN solution. Measurements were carried out under the effect of various experimental conditions using cyclic polarization, potentiostatic and galvanostatic techniques. In all cases, the potentiodynamic anodic polarization curves do not exhibit active dissolution region due to spontaneous passivation. The passivity is due to the presence of a thin film of Al2O3 on the anode surface. The passive region is followed by pitting corrosion, at a certain critical potential, pitting potential (Epit), as a result of breakdown of the passive film by SCN− anions. Cyclic polarization measurements allowed the determination of the pitting corrosion parameters, namely the pitting potential and the repassivation potential (Erp). Alloyed Si decreased the passive current (jpass) and shifted both Epit and Erp towards more positive values. Thus alloyed Si suppressed pitting attack. The effect of illumination on passivity and the initiation of pitting corrosion on Al in KSCN solutions was also studied. It is observed that illumination of Al leads to an increase in its pitting corrosion resistance-apparent from jpass, Epit, and Erp measurements in aggressive KSCN solutions.

Effect of Ti n+ defects on electrochemical properties of highly-ordered titania nanotube arrays

In this paper, highly-ordered TiO 2 nanotube (TNT) electrodes fabricated by anodization at 20 V in 0.1 M F −-based solution were annealed in O 2, N 2 and CO respectively. The surface properties of the TiO 2 electrodes after annealing treatment by different gases were studied by means of photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical properties of the TNT electrodes were investigated by cyclic voltammetry, steady-state polarization and photocurrent response measurements. The results showed that Ti n+ (n = 0–3) cations and oxygen vacancies existed in the TNT electrode after annealing in CO, leading to a very efficient electron transfer rate of 1.34 × 10 − 3 cm/s. Steady-state polarization measurement and photocurrent response demonstrated that the electrode potential of oxygen evolution reaction (OER) reduced by 20% and the photocurrent response increased by 50% for CO-annealed TNT electrode compared with O 2-annealed TNT electrode.