Small Amplitude Cyclic Voltammetry Research Articles

Cobalt ferrite coated on Ti/Ni/PbOx with enhanced electrocatalytic stability for chloride ions-contained water splitting

The advance of efficient, low-cost, and bifunctional catalysts for seawater splitting to produce hydrogen fuel is a challenge. However, by relying on transition metal-based compounds, a unique and attractive arrangement can be proposed. Here, a four-step process was used for the synthesis of the Ti/Ni/PbOx/CoFe2O4 electrocatalyst. First, thin films of nickel (by cathodic electrodeposition) and lead dioxide (by anodic electrodeposition) were synthesized on the activated titanium substrate. Then, using nitrate solution, CoFe coating with a thickness of ∼ 5 µm was applied. Finally, the coating is oxidized to form cobalt ferrite (CoFe2O4). The structure of the arrangement formed in each step was examined by X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), and energy dispersive X-ray spectroscopy (EDS) and the electrocatalytic performances were evaluated in 1 M KOH and 1 M KOH + 0.5 M NaCl solutions by electrochemical methods such as linear sweep voltammetry(LSV), electrochemical impedance spectroscopy (EIS), small amplitude cyclic voltammetry (SACV), accelerated chronopotentiometry (CP), and multi-step CP. The Ti/Ni/PbOx/CoFe2O4 electrode requires an overpotential less than 400 mV at 50 mA/cm2 with Tafel constant of 47.7 V/dec for OER. The results of the stability test in accelerated conditions and the alkaline solution containing chloride ions showed that the special arrangement of the cobalt ferrite electrocatalyst in this work improves its lifetime by more than 5 times compared to the normal cobalt ferrite. The synthesized Ti/Ni/PbOx/CoFe2O4 as a bifunctional electrode requires only a potential of 1.53 V at a current density of 10 mA/cm2 for overall seawater splitting. The dual-purpose properties of the Ti/Ni/PbOx/CoFe2O4 electrocatalyst can be considered for its wide use in the fields of sustainable and renewable energy.

Corrosion mechanism of sulfate, chloride, and tetrafluoroborate ions interacted with Ni-19 wt% Cr coating: A combined experimental study and molecular dynamics simulation

This study aimed to investigate the corrosion behavior of a relatively resistant nickel‑chromium coating in the presence of SO42−, Cl−, and BF4− ions. The electrochemical measurements including linear polarization, small amplitude cyclic voltammetry (SACV), and electrochemical noise (EN) analysis, were used, along with molecular dynamics simulation (MD) to evaluate the interactions between the coating and the corrosive ions. Results of the EN analysis showed that the charges of events exchanged in the HBF4 and HCl solutions were in the range of 1 μC to 1 mC; i.e., the coating was locally damaged in these media. However, the rates of pit progress in the coating exposed to BF4− and Cl− were not similar because the polarization resistances (Rp) of the coating in these two solutions were 1745.6 Ω·cm2 and 2766.2 Ω·cm2, respectively. The most negative adsorption energy, alongside the highest diffusion force of tetrafluoroborate ions, compared to chloride and sulfate, led to severe pitting corrosion of the coating. In the H2SO4 medium, the passivation mechanism prevailed over the pit growth, so that the Rp increased to 5747.3 Ω·cm2. Among the passive layers constructed on the coating surface, Cr2O3 (001) formed the low-energy chemical bonds with all three destructive species of SO42−, Cl−, and BF4−. Also, NiO (111) provided a compressed structure of Ni and Cr oxides, which could impede the penetration of corrosive ions in the alloyed coating.

Influence of glycine additive on corrosion and wear performance of electroplated trivalent chromium coating

The aim of this study is to evaluate the effect of various molar ratios of glycine to chromium salt (Gly: Cr) and different current densities on the corrosion and wear behaviors of Cr(III) electroplated coatings. The morphology and thickness of the coatings were investigated by scanning electron microscopy. The wear properties of the coatings were studied using pin on disk and hardness tests, while corrosion behavior of the coatings was identified using linear polarization, small amplitude cyclic voltammetry, and electrochemical impedance spectroscopy methods. By increasing the glycine concentration, a structure with low crack density was obtained. In all molar ratios, maximum thickness and current efficiency was observed at a current density of 150 mA-cm−2. All the electrochemical methods had a consistent result, and maximum corrosion resistance of approximately 16000 Ω m2 was obtained in the case of Gly: Cr = 3:1 and current density of 200 mA-cm−2

Effect of TIG Welding and Rare Earth Elements Alloying on Corrosion Resistance of Magnesium Alloys

The corrosion resistance of the welds made of QE22, ZRE1, and WE43 rare-earth-metals-containing magnesium alloys was investigated in 0.5% NaCl solution saturated with Mg(OH)2 using the electrochemical methods: linear sweep voltammetry, small amplitude cyclic voltammetry, and electrochemical impedance spectroscopy. These tests elucidated how welding influences the susceptibility to corrosion of that class of magnesium alloys. For the sake of comparison AZ91 magnesium alloy was investigated too. All welds were obtained by tungsten inert-gas welding method. In the case of all investigated alloys welds showed corrosion resistance comparable to the base material. However, all rare-earth-metals-containing magnesium alloys show corrosion resistance inferior to AZ91 alloy. Significant differences in corrosion resistance evaluated by different electrochemical methods were observed.

Characterization of Metal Hydride Electrodes via Microperturbation and In Situ Intrinsic Resistance Measurement

Microperturbation methods, including galvanostatic intermittent titration using applied microcurrent pulses (GIT), small amplitude cyclic voltammetry, and electrochemical impedance spectroscopy (EIS), together with in situ intrinsic (i.e., physical) resistance measurements, have been applied to investigate charge/discharge kinetics of a metal hydride (MH) electrode as a function of cycling. The results show that electrode capacity loss was caused by reduced ability to absorb hydrogen. High frequency semicircles in the Nyquist plots may be attributed to hydrogen transition between the adsorbed and the absorbed states, and are unrelated to contact resistance between the current collector and the hydride particles, although this showed contact resistance between alloy particles and current collector. This contradicts a generally accepted interpretation of EIS data. It was difficult to obtain hydrogen diffusion resistance from EIS results when the potential change in the electrode charge‐discharge plateau is smaller than the EIS voltage perturbation, because long charge/discharge times in the low frequency range change the state of discharge. Alternating current EIS is more suitable than alternating voltage studies to investigate hydrogen diffusion kinetics in MH alloys with a flat potential plateau. Similarly, it is also difficult to obtain hydrogen diffusion resistance from small amplitude cyclic voltammetry because of the size of the charge/discharge capacitance. However, the total reaction resistance may be obtained from GIT. © 2000 The Electrochemical Society. All rights reserved.

Studies of electrochemical behaviour of RuO 2 -PVC film electrodes: dependence on oxide preparation temperature

Ruthenium dioxide electrodes, prepared on a Pt substrate using coatings of PVC-RuO2 mixed in THF (designated as RuO2-PVC film electrode) have been studied for their redox behaviour in 1 M NaOH using variable scan cyclic voltammetry. The various redox transitions in the oxidation state of the central metal ion are characterized using electrochemical parameters such as peak potential, peak current, and surface charge. The effect of oxide preparation temperature, in the range 300–700 °C, on the redox characteristics has also been studied and correlated with the electrochemically active surface area (as measured using small amplitude cyclic voltammetry) and the true surface area (by the BET method).

The effect of soft tap water chemistry on fatigue crack growth of steel

The electrochemical effects of water chemistry on fatigue crack growth of AISI 1018 steel are investigated. Results obtained show that by changing the langelier index from typical negative values of soft tap waters to positive values by adding appropriate amounts of sodium bicarbonate, the fatigue crack growth rate is reduced, thus resulting in a longer life for a structure subjected to this environment. An attempt is made to explain this phenomenon and to supplement mechanical testing using electrochemical corrosion measurements. Electrochemical corrosion measurements were conducted using cyclic potentiodynamic scans in order to elucidate localized corrosion activity and Small Amplitude Cyclic Voltammetry (SACV) to investigate uniform corrosion activity. Results agree with previous findings, in that as long as the Langelier index is greater than 0.3, both uniform and localized corrosion tendencies are reduced.

On the Effects of Common Pollutants on the Corrosion of Copper‐Nickel Alloys in Sulfide Polluted Seawater

Various pollutants are often introduced in seawater by wet and dry deposition and by improper dumping of municipal wastewater. These pollutants often affect the corrosivity of seawater on copper‐based alloys which might be thought to be resistant in this environment and do not receive sufficient research efforts. In the present investigation the effect was determined of some common pollutants such as urea, sodium sulfite, sodium nitrate, sodium phosphate, copper sulfate, lead acetate, ammonium sulfate, and ammonium chloride at a level of 10 ppm and of chlorine at 1 ppm concentration on the corrosion characteristics of the 90Cu‐10Ni and the 70Cu‐30Ni alloys in seawater, both in the presence and in the absence of 10 ppm sulfide. Both small amplitude cyclic voltammetry (SACV) and the Tafel extrapolation technique were employed as test procedures. All pollutants under investigation have led to an increase in corrosion rate and their effect was more pronounced when sulfide was also present. The effects of pollutants were more intense on 90Cu‐10Ni as compared to 70Cu‐30Ni alloys. In unpolluted seawater, the worst pollutant for 90Cu‐10Ni alloy is sulfide followed by urea and chlorine, while for the 70Cu‐30Ni alloy, the worst pollutant was ammonium chloride followed by sulfide and sodium phosphate. In unpolluted seawater, the introduction of pollutants led to a corrosion reaction which was under cathodic control except for sulfide where the reaction was under anodic control and resulted in a sharp negative shift in the corrosion potential. In sulfide polluted seawater, the worst pollutant for 90Cu‐10Ni alloy was ammonium sulfate followed by urea while for 70Cu‐30Ni alloy, the worst pollutant was urea followed by ammonium chloride, ammonium sulfate, and sulfite ions.

Electrochemical investigation into the environmental degradation of YBa2Cu3O7 superconductors

YBa2Cu3O7(YBC) high-Tc superconductors degrade rapidly when exposed to humidity or water. In an attempt to gain a better understanding of the degradation behavior and to study the effect of porosity on degradation susceptibility, small amplitude cyclic voltammetry (SACV) is performed. Microelectrodes are fabricated from YBC superconducting pellets of porosities approximately 50% and < 1%. SACV is performed in methyl alcohol saturated with sodium chloride and 1 M NaCl in distilled water before and after exposure to water. It is found that the corrosion rate of bulk superconductors increases with exposure time. The dense specimens seem to stabilize after 36 h while the porous specimens continue to deteriorate at first rapidly and after 24 h slowly. The BaCO3 film produced by corrosion is non-protective.

Development of Controlled Hydrodynamic Techniques for Corrosion Testing

Abstract A systematic study was carried out to investigate the effect of hydrodynamic variables, such as flow rate and geometry, on the corrosion of 90/10 Cu-Ni alloy in 1 M sodium chloride solution at 25°C under the air-saturated condition. Three hydrodynamic geometries were investigated: a flow-through pipe system, an annular flow system, and a rotating cylinder system. Flow rates spanned the range from laminar flow to highly turbulent conditions, and all hydrodynamic conditions were characterized in terms of Reynolds and Schmidt numbers. Corrosion rates have been measured using small amplitude cyclic voltammetry (SACV), electrochemical impedance spectroscopy, and the direct weight loss method. Good agreement was obtained between SACV and electrochemical impedance techniques for measuring the polarization resistance, and the calculated weight losses were in reasonable agreement with the directly measured values. The corrosion rate measured in all three hydrodynamic systems was independent of the geometr...

Electrochemical control of metallic copper and chalcopyrite-xanthate flotation

The surface oxidation of copper dipped in xanthate-free and xanthate-containing borate solutions of pH 9.2 was analysed by small amplitude cyclic voltammetry. The influence of the electrochemical potential on the floatability of copper and chalcopyrite particles was investigated. It was demonstrated that the formation of copper-xanthate species derives not only from the direct reaction between copper and xanthate ions but also from the one between xanthate ions and chalcopyrite. Evidence was found that the species responsible for the hydrophobization of copper and chalcopyrite particles are copper-xanthate species and dixanthogen. Flotation tests carried out in a microflotation-electrochemical cell and in an electrochemical Denver cell demonstrated that maximum floatability is obtained when both species are present on the surface. A potential decay measurement was conducted in order to analyse the stability of the species responsible for hydrophobization.

Preliminary investigation on the corrosion behavior of amorphous (Ti90Ru10)87Si13 in saline solutions

Amorphous alloys also known as metallic glasses appear to have unique corrosion resistant properties. The corrosion characteristics of a (Ti90Ru10)87Si13 alloy have been measured in 0.5 M NaCl and in artificial seawater (ASW) by linear polarization resistance, ac impedance and small amplitude cyclic voltammetry (SACV). Results show a low corrosion rate of the alloy in these media, with the rate of corrosion in seawater slightly faster than the rate of corrosion in sodium chloride.

General corrosion of B-strengthened Ni- and Fe-based microcrystalline alloys in de-aerated 1 M HCI solution

The general corrosion characteristics of four boride-strengthened microcrystalline alloys, two Ni-based and two Fe-based, were studied in de-aerated 1 M HCI solution at room temperature in a rotating cylinder system at three rotation speeds (600, 1200 and 1800 rpm), using electrochemical small amplitude cyclic voltammetry and AC impedance techniques. For comparison, two commercial materials, namely Alloy 600 and AISI Type 316 SS, were studied too. Good agreement was obtained between small amplitude cyclic voltammetry and AC impedance measurements of the polarization resistance. Both the corrosion potential and corrosion rate became independent of time after log exposures. In the case of Ni-based materials and in that of 316SS, both the corrosion potential and rate were not affected by changes in the speed of rotation. In the case of Fe-based microcrystalline alloys, the corrosion rate decreased while the corrosion potential increased with Re. This finding was explained by corrosion-induced surface enrichment in Mo, the extent of which increased with increasing speed of rotation. Within the range of rpm tested, the corrosion rates measured for the Fe-based materials were generally higher than those measured for the Ni-based materials and the corrosion rates decreased with increasing Ni contents in the alloy. No extraordinary resistance to general corrosion in 1 M HCl at room temperature was found for the four boride-strengthened microcrystalline alloys tested.

Investigation of xanthate interaction on platinum and chalcopyrite by small amplitude cyclic voltammetry

The surface oxidation of platinum and chalcopyrite in borate solutions of pH 9.2 has been studied by small amplitude cyclic voltammetry. Triangular voltage sweeps of small amplitude and relatively high potential sweep rates were used at different off-set potentials. The apparent polarization resistance, diagonal resistance and Delta I values were calculated from the current-potential hysteresis loop responses. It was found that the formation of dixanthogen which is not revealed by classical high amplitude cyclic voltammetry, was observed by the present technique. The presence of CuEtX resulting from a direct reaction between chalcopyrite and xanthate was substantiated. The present research supports thus the importance of CuEtX on the onset of chalcopyrite flotation.

SACV Measurement of the Polarization Resistance and Capacitance of Copper Alloys in 3.4 Weight Percent NaCl Solution

Using small amplitude cyclic voltammetry (SACV) in a new voltage sweep rate mode, the polarization resistance and interfacial capacitance of several copper alloys in 3.4 weight percent solution were measured at 23°C during formation of the corrosion product layer. The electrochemical system was combined with a microcomputer by using a potentiostat with an interface. The results compare favorably with those obtained by the transient method of galvanostatic charging curve, ac impedance and weight loss measurements, demonstrating the validity of the method. The SACV method has an operational advantage over the ac impedance technique for obtaining the polarization resistance, and the accuracy for obtaining is good. From the results an initial time period of surface layer formation could be defined for each of the copper alloys.

Application of small amplitude cyclic voltammetry for the investigation of Naβ-alumina/metallic electrode interface electric properties

The use of small amplitude cyclic voltammetry for investigation of the β-alumina/metallic electrode interface is proposed. Voltammetric curve analysis is based on the electric circuit consisting of three elements. The plots of the reciprocal of capacity determined from voltammograms versus the reciprocal of voltage sweep period square root are extrapolated to obtain the limiting value of capacity. This limit corresponds to C LF obtained in the ac impedance technique. This method can be mostly useful when the low frequency limit in impedance measurements is insufficient for exact determination of capacitive components of the electric equivalent circuit.

The electrochemical characteristics of the galvanic corrosion of sulphide minerals in short-circuited model galvanic cells

An investigation was made of the galvanic corrosion of minerals in model galvanic cells composed of two different mineral electrodes, short-circuited through an external circuit of zero impedance and immersed in an acidic solution saturated with oxygen. The electrodes were made of four minerals: galena, chalcocite, chalcopyrite and pyrite. A small-amplitude cyclic voltammetry method was employed in experiments. A periodic, symmetrical, triangular-shaped potential difference versus the potential of the short-circuited galvanic couple was imposed between the electrodes and the current response was recorded. The parameters characterizing the action of the galvanic couple, such as Tafel slopes for the reactions taking place at the surfaces of electrodes or the ratio of galvanic current to total corrosion current, were calculated on the basis of experimental results.

Studies in the Corrosion and Inhibition of Mild Steel in Sodium Fluoride Solutions by Small Amplitude Cyclic Voltammetry

AbstractCorrosion of ASTM 212 steel in sodium fluoride solutions has been studied by small amplitude cyclic voltammetry (SACV) and by direct weight loss measurements. The results from these two methods are comparable. Corrosion rates vary between 19·5 and 33·3 mg.dm−2d−1 (mdd) in sodium fluoride concentrations between zero and 2% in systems open to the atmosphere. In nitrogen saturated sodium fluoride solutions the corrosion rates were found to be very low (∼5 mdd). Corrosion inhibition by sodium chromate was also examined. Inhibitive efficiencies derived from 1/RP measurements and from direct weight loss are comparable. About 90% inhibition was achieved with 800 ppm of sodium chromate in 0·5% sodium fluoride.

The Corrosion of Cu-Ni Alloys 706 and 715 in Flowing Sea Water. II – Effect of Dissolved Sulfide

Abstract The corrosion of 90:10 Cu:Ni and 70:30 Cu:Ni alloys in sulfide polluted flowing sea water has been studied as a function of sulfide concentration. The experimental techniques used include small amplitude cyclic voltammetry, AC impedance measurements, large amplitude cyclic voltammetry, and extensive surface examination by scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis, X-ray diffraction, and Auger electron spectrometry (AES). It is shown that the presence of sulfide induces a loss in passivity of the alloy surface due to the formation of cuprous sulfide as the principal corrosion product. Furthermore, accelerated corrosion of these materials in sulfide polluted sea water appears to arise from a shift in the corrosion potential to sufficiently active values that hydrogen evolution becomes a viable cathodic process.

Discussion of “An Impedance Interpretation of Small Amplitude Cyclic Voltammetry I . Theoretical Analysis for a Resistive‐Capacity System” [Digby D. Macdonald (pp. 1443–1449, Vol. 125, No. 9)

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