Study of the electrochemical behaviour of a carbon steel electrode in sodium sulfate aqueous solutions using electrochemical impedance spectroscopy

The study of a plain carbon steel (AISI 1020) in Na₂SO₄ aqueous solutions at different concentrations was carried out by electrochemical impedance spectroscopy (EIS) in order to determine the corrosion mechanism and to obtain representative corrosion rates of the system. EIS was used to measure corrosion current densities at high concentrations in the range 0.1–1 wt% Na₂SO₄, but in the low concentration range, from 0.001 to 0.01 wt%, a scattered Nyquist plot was obtained. Other electrochemical techniques, such as polarization resistance (PR), Tafel plots and electrochemical noise (EN), were also used in this analysis. The charge transfer resistance was determined and compared with the PR and noise resistance. Electronic Publication     

Evaluating the performance of organic coatings under mechanical stress using electrochemical impedance spectroscopy

Stress in coatings originating from a mechanical load imposed during exploitation is a relatively unexplored field of investigation. Paradoxically, a number of constructions and installations seem to operate under such conditions. The purpose of this work was to investigate the impact of a cyclic mechanical load exerted on coating/metal systems. It was the authors aim to verify whether repeated mechanical stress constitutes a significant factor contributing to coating degradation. Epoxy coated St3SAl steel samples were subjected to 21,000 uniaxial strain/release cycles. The maximum force applied assured maintenance within the elastic deformation region of the metal substrate. The state of the protective film was monitored using electrochemical impedance spectroscopy. The coating response to the mechanical load occurred in a three-stage process. The system subjected to the strain/release cycles revealed signs of degradation earlier compared to a non-strained, reference sample.Contribution to the 3rd Baltic Conference on Electrochemistry GDASK-SOBIESZEWO, 23–26 April 2003.Dedicated to the memory of Harry B. Mark, Jr. (February 28, 1934–March 3rd, 2003)     

Microstructure and corrosion behavior of electroless deposited Ni-P/CeO2 coating

Electroless Ni-P/nano-CeO2 composite coating was prepared in acidic condition, and its microstructure and corrosive property were compared with its CeO2-free counterpart. Scanning electronic microscopy （SEM） and X-ray diffraction （XRD） spectrometer were used to examine surface morphology and structure of the as-plated coating. Differential scanning calorimeter （DSC） and transmission electronic microscopy （TEM） were used to study the coating＇s phase change at high temperature. The coating＇s corrosive behavior in 3%NaCl ＋ 5%H2SO4 solution was also investigated. The results showed that Ni-P coating had partial amorphous structure mixed with nano-crystals, while the Ni-P/CeO2 coating had perfect amorphous structure. In high-temperature condition, Ni3P precipitation and Ni crystallization took place in both coatings but at different temperatures, while the Ni-P/CeO2 coating had sintered phase of NiCe2O4 spinels. The anti-corrosion property was better in the CeO2-containing coating, and this was due to its less liability to undergo local-cell corrosion than its CeO2-free counterpart. Ni-P/CeO2 coating＇s pure amorphous structure was the result of Ni＇s hindered crystal-typed deposition and P＇s promoted deposition.     

Aptamer-based biosensor for label-free detection of ethanolamine by electrochemical impedance spectroscopy

A label-free sensing assay for ethanolamine (EA) detection based on G-quadruplex-EA binding interaction is presented by using G-rich aptamer DNA (Ap-DNA) and electrochemical impedance spectroscopy (EIS). The presence of K⁺ induces the Ap-DNA to form a K⁺-stabilized G-quadruplex structure which provides binding sites for EA. The sensing mechanism was further confirmed by circular dichroism (CD) spectroscopy and EIS measurement. As a result, the charge transfer resistance (R_CT) is strongly increased as demonstrated by using the ferro/ferricyanide ([Fe(CN)₆]^3−/4−) as a redox probe. Under the optimized conditions, a linear relationship between ΔR_CT and EA concentration was obtained over the range of 0.16 nM and 16 nM EA, with a detection limit of 0.08 nM. Interference by other selected chemicals with similar structure was negligible. Analytical results of EA spiked into tap water and serum by the sensor suggested the assay could be successfully applied to real sample analysis. With the advantages of high sensitivity, selectivity and simple sensor construction, this method is potentially suitable for the on-site monitoring of EA contamination.     

High-frequency phenomena and electrochemical impedance spectroscopy at nanoelectrodes

Electrochemical impedance spectroscopy (EIS) is a powerful probe of the processes taking place at an electrode. Depending on frequency, it is sensitive to the solid-liquid interface as well as to processes taking place in the solution further from the electrode. In principle, shrinking electrode dimensions allows probing these processes on the nanometer scale. In practice, however, this represents a formidable challenge. Signals resulting from the stray capacitance of the interconnects can dramatically exceed those from the electrode itself. Furthermore, miniaturized electrodes exhibit faster dynamics, and thus necessitate working at higher frequencies in order to achieve comparable performance. Here we discuss recent advances in nanoscale impedance measurements. We begin with a theoretical discussion of the main concepts and inherent tradeoffs, followed by a review of recent experimental efforts. As this field remains in its infancy, we place particular emphasis on the conceptual and technical aspects of the approaches being developed.     

Development of an enrofloxacin immunosensor based on label-free electrochemical impedance spectroscopy

Enrofloxacin is the most widespread antibiotic in the fluoroquinolone family. As such, the development of a rapid and sensitive method for the determination of trace amounts of enrofloxacin is an important issue in the health field. The interaction of the enrofloxacin antigen to a specific antibody (Ab) immobilized on an 11-mercapto-undecanoic acid-coated gold electrode was quantified by electrochemical impedance spectroscopy. Two equivalent circuits were separately used to interpret the obtained impedance spectra. These circuits included one resistor in series with one parallel circuit comprised of a resistor and a capacitor (1R//C), and one resistor in series with two parallel RC circuits (2R//C). The results indicate that the antigen-antibody reaction analyzed using the 1R//C circuit provided a more sensitive resistance increment against the enrofloxacin concentration than that of the 2R//C circuit. However, the 2R//C circuit provided a better fitting for impedance spectra, and therefore supplies more detailed results of the enrofloxacin-antibody interaction, causing the increase of electron transfer resistance selectively to the modified layer, and not the electrical double layer. The antibody-modified electrode allowed for analysis of the dynamic linear range of 1-1000 ng/ml enrofloxacin with a detection limit of 1 ng/ml. The reagentless and label-free impedimetric immunosensors provide a simple and sensitive detection method for the specific determination of enrofloxacin.     

Electrochemical copolymerization of pyrrole and 2,2-bithiophene and semiconducting characterization of the resulting copolymer films by electrochemical impedance spectroscopy and photoelectrochemistry

The electrochemical copolymerization of pyrrole and bithiophene was studied at a polymerization potential of 1.1 V for various monomer ratios. The cyclic voltammograms showed that the electrochemical properties of the resulting copolymer films changed gradually from those of polypyrrole to polybithiophene with an increase in concentration of bithiophene in the initial electrolyte. The evidence for copolymer formation is based on the analytical results of electrospray ionization mass spectroscopy, thermoanalysis, and Raman spectroscopy. The results showed that cooligomers and homooligomers were found in the electrolyte after copolymerization. The difference between the morphology of a copolymer of pyrrole and bithiophene and a polymer mixture of polypyrrole and polythiophene was demonstrated by scanning electron microscopy. Electrochemical impedance and photocurrent measurements were carried out in order to achieve information on the semiconducting properties of the homopolymers and copolymers obtained. A model of a very thin layer of polypyrrole formed immediately on the electrode surface covered by a thicker copolymer film was developed to explain the results.Dedicated to Zbigniew Galus on the occasion of his 70^th birthday.     

Technology of electrochemical impedance spectroscopy for an energy-sustainable society

Electrochemical impedance spectroscopy has been widely used to understand the chemistry and physics of battery systems. This review covers electrochemical impedance spectroscopy used for the interpretation of impedance data of lithium-ion batteries (LIBs) from advanced equivalent circuit models to the mathematical model, which is developed by John Newman. In addition, as a method to realize an energy-sustainable society using diagnostics based on the combination of LIBs and electrochemical impedance spectroscopy, on-board diagnostics of battery packs are achieved based on an input signal generated by a power controller in a battery management system instead of the conventionally used frequency response analyzer. The diagnostic system is applicable to energy management systems which are installed in homes, buildings, and communities, accumulating the impedance data on state of health of LIBs. Finally, a future possibility regarding the diagnostics of battery packs coupled with the machine learning of impedance data is introduced.     

Oligonucleotides-based biosensors with high sensitivity and selectivity for mercury using electrochemical impedance spectroscopy

A novel electrochemical biosensor with high sensitivity and selectivity for mercuric ion detection, based on DNA self-assembly electrode, is designed. Thiol functionalized poly-T oligonucleotides were used as gold electrode modifier through formation of Au–S bond between DNA and gold electrode. In presence of Hg²⁺ ions, the specific coordination between Hg²⁺ and thymine bases can change parallel ss-DNA from linear to hairpin structures, which can cause the release of partial DNA molecules from the surface of the electrode. The density of DNA on the surface of electrode correlated with the concentration of mercury in the solution and can be monitored by electrochemical impedance spectroscopy. The limit of detection of this method is pM level of mercuric ions which is far below the upper limit of Hg²⁺ mandated by United States Environmental Protection Agency (EPA), 2 ppb (10 nM). In addition, this method showed excellent selectivity. A series of divalent metal ions, including Ni²⁺, Co²⁺, Mg²⁺, Zn²⁺, Ba²⁺ and Cd²⁺, have little interference with the detection of Hg²⁺.     

Use of electrochemical impedance spectroscopy to characterise the physical properties of ex situ reconstructed sea surface microlayer

The objective of this work was to develop electrochemical impedance spectroscopy (EIS) to characterise the physical properties of the sea surface microlayer ( ssm ). Samples from Lake Rogoznica in Croatia were extracted by n-hexane and dichloromethane (dcm) respectively and transferred to mercury electrodes. The EIS results were compared with those of a model phospholipid, dioleoyl phosphatidylcholine (DOPC) which forms near defect-free monolayers on a mercury surface. The ssm extracts formed inhomogeneous monolayers on the mercury surface and the dcm ssm extract monolayer showed greater surface roughness than the hexane ssm extract. The hexane ssm extract introduced defects and a greater surface roughness into mixed DOPC- ssm extract monolayers than the dcm ssm extract due to the lower compatibility of the non-polar hexane extract with the DOPC than that of the polar ssm extract. In addition, the dcm ssm component in the mixed DOPC- ssm monolayer showed an association with pyrene added to the solution.     

Voltammetry and electrochemical impedance spectroscopy of gold electrodes modified with CdTe quantum dots and their conjugates with nickel tetraamino phthalocyanine

This work reports on the synthesis of conjugates of cadmium telluride quantum dots (CdTe-QDs) caped with thioglycolic acid and peripherally substituted nickel tetraamino phthalocyanine (NiTAPc) complex. The conjugates are characterized using cyclic (CV) and differential pulse (DPV) voltammetries, electrochemical impedance spectroscopy, X-ray powder diffraction, infrared spectroscopy, Raman spectroscopy, atomic force microscopy and time correlated single photon counting. CV and DPV show that NiTAPc stabilizes the CdTe QDs against oxidation to metallic products.     

A monoclonal antibody-based immunosensor for detection of Sudan I using electrochemical impedance spectroscopy

Sudan I monoclonal antibodies (Mabs) were prepared by hybridoma technique and firstly used to develop a Sudan I immunosensor by immobilizing the Mabs on a gold electrode. o-Mercaptobenzoic acid (MBA) was covalently conjugated on the gold electrode to form a self-assembled monolayer (SAM). The immobilization of Sudan I Mabs to the SAM was carried out through a stable acyl amino ester intermediate generated by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydrosuccinimide (NHS), which could condense antibodies reproducibly and densely on the SAM. The changes of the electrode behavior after each assembly step were investigated by cyclic voltammetric (CV) technique. The Sudan I concentration was measured through the increase of impedance values in the corresponding specific binding of Sudan I and Sudan I antibody. A linear relationship between the increased electron-transfer resistance (Ret) and the logarithmic value of Sudan I concentrations was found in the range of 0.05-50 ng mL⁻¹ with the detection limit of 0.03 ng mL⁻¹. Using hot chili as a model sample, acceptable recovery of 96.5-107.3% was obtained. The results were validated by conventional HPLC method with good correlation. The proposed method was proven to be a feasible quantitative method for Sudan I analysis with the properties of stability, highly sensitivity and selectivity.     

One saccharide sensor based on the complex of the boronic acid and the monosaccharide using electrochemical impedance spectroscopy

A novel saccharide sensor based on the covalent interaction between the boronic acid and saccharides was developed. Poly (aminophenylboronic acid) (PABA) was prepared by electropolymerizing 3-aminophenylboronic acid on gold electrode surface in acidic solution. The boronic acid group of the PABA film can form covalent-bond with different saccharides, which can change the dielectric characteristics of the PABA film, and the change of the dielectric characteristic was saccharides concentration dependent. Four kinds of saccharides could be detected by using electrochemical impedance spectroscopy. Good linear relationship and high sensitivity were obtained by this method.     

Microstructure, surface and electrochemical studies of electroless Cr–P coatings tailored for the methanol oxidative fuel cell

Cr–P is a new material of great importance as a decorative coating with nickel in automobile industries. Electroless plating of Cr–P alloy has been carried out using a suitable plating bath solution and working conditions. The deposit is characterized by X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray diffraction, X-ray photoelectron spectroscopy and polarization techniques. New phases appear on heat treatment of the coating. The composition (Cr/P) of the coating and the oxidation states of alloying elements vary from the surface to the bulk of the material. The coatings acted as a novel electrode material with good electrocatalytic activity (low overvoltage) and good corrosion resistance for anodic oxidation of methanol in H₂SO₄ at normal working temperature. The good corrosion resistance of the Cr–P film is accounted for by the existence of a double oxyhydroxide passive film on the surface. The electrocatalytic activity of Cr–P is very high when compared with chromium alone.     

不同材料表面纳米复合化学镀层镍-磷-硅酸锌的XPS和AES分析

对Q235碳钢片和D310硅钢片表面表面镍－磷－硅酸锌纳米复合化学镀层，用SEM观察外貌，称重法测定厚度；10％NaCl、1％H2S加速腐蚀试验，10％CuSO4溶液点滴试验循环伏安（CV）、抗粘性及抗高温氧化试验等测定其性能。用X－射线电子谱（XPS）及俄歇电子能谱（AES）测定其价态及组成。结果表明其性能优镍－磷镀层和其它微米复合化学镀层，表面的镀层Q235碳钢片优于D310硅钢片表面的镀层，镀层的原子百分组成为：D235碳钢片：Ni79.00,P10.06,Zn2.01,Si1.88,O5.87,C1.18;D310硅钢片：Ni80.50,P10.67,Zn1.70,Si1.52,O4.83,C0.78.     

The effect of component concentrations in electroless nickel plating solution on topography and microrelief of Ni-P coatings

Topography and microrelief of Ni-P coatings deposited by electroless plating from solutions with different composition are examined as a function of concentrations of nickel and acetate ions, solution pH, and stabilizing additives, namely, PbCl₂ and thiourea. The coating growth involves the formation of surface spheroids of which a large percentage are strongly extended in the substrate plane and grow by the layered-growth mechanism. In terms of this mechanism, the changes in the topography and microrelief of coatings and also in the spheroid size as a function of the composition of electroless nickel plating solutions are explained. In solutions studied, the rates of formation of new two-dimensional layers and their propagation in the substrate plane are assessed. As the concentration of hydrated nickel ions in solution decreases, spheroids less extended in the substrate plane are formed and grow probably by the normal growth mechanism. The size distribution of spheroids is obtained and the reasons for the partial formation of spheroids with sizes deviating from those predicted by the normal law are analyzed.     

Analysis of large experimental datasets in electrochemical impedance spectroscopy

An approach for the analysis of large experimental datasets in electrochemical impedance spectroscopy (EIS) has been developed. The approach uses the idea of successive Bayesian estimation and splits the multidimensional EIS datasets into parts with reduced dimensionality. Afterwards, estimation of the parameters of the EIS-models is performed successively, from one part to another, using complex nonlinear least squares (CNLS) method. The results obtained on the previous step are used as a priori values (in the Bayesian form) for the analysis of the next part. To provide high stability of the sequential CNLS minimisation procedure, a new hybrid algorithm has been developed. This algorithm fits the datasets of reduced dimensionality to the selected EIS models, provides high stability of the fitting and allows semi-automatic data analysis on a reasonable timescale. The hybrid algorithm consists of two stages in which different zero-order optimisation strategies are used, reducing both the computational time and the probability to overlook the global optimum. The performance of the developed approach has been evaluated using (i) simulated large EIS dataset which represents a possible output of a scanning electrochemical impedance microscopy experiments, and (ii) experimental dataset, where EIS spectra were acquired as a function of the electrode potential and time. The developed data analysis strategy showed promise and can be further extended to other electroanalytical EIS applications which require multidimensional data analysis.     

Assessment of corrosion resistance of surface-coated galvanized steel by analysis of the AC impedance spectra measured on the salt-spray-tested specimen

In the present work, corrosion resistance of surface-coated galvanized steel was quantitatively determined by an analysis of the alternating current (AC) impedance spectra measured on the salt-spray-tested specimen. To evaluate the corrosion resistance of the surface-coated galvanized steel, AC impedance spectroscopy was performed on the salt-spray-tested specimen previously exposed to salt-sprayed corrosive environment. From the analysis of the impedance spectra, the area fraction transient of white rust θ ₂(t) was theoretically derived from the equivalent circuit equation by using two fitting parameters. The values of the two fitting parameters were determined by fitting the empirical transient equations to the area fraction of the resin coating layer and to the total resistance obtained from the impedance spectra measured, respectively. From the analyses of θ ₂(t) for four kinds of surface-coated galvanized steels with various resin coating layers, it is indicated that as the values of the two fitting parameters decrease in the order of CP, GI, OD and OM (commercial trade names) specimens, the corrosion resistance increases in that order as well. Furthermore, from the quantitative comparison of the two fitting parameters with the polarization resistance of the upper resin coating layer R _p determined from the potentiodynamic polarization curve, it is suggested that the two fitting parameters decrease in value as well with increasing R _p.     

Label-free detection of DNA molecules on the dendron based self-assembled monolayer by electrochemical impedance spectroscopy

We report preparation of a novel platform for effective DNA hybridization and its application to the detection of single mismatched DNA. Cone-shaped dendrimer molecules have been immobilized on the gold surface at equidistance, 3.1 nm, from each other with a probe DNA molecule attached to the top of each dendrimer so that enough space would be secured for effective hybridization. This arrangement allows each probe DNA molecule to form a natural DNA double helix upon hybridization with a target DNA molecule. The single nucleotide polymorphism at either the central or end position of the 25-mer target DNA has been shown to be effectively discriminated against on this platform from each other as well as from a complementary DNA by electrochemical impedance measurements. We also report adverse effects exerted by probe ions, Fe(CN)₆^3−/4−, on DNA hybridization reactions. The significance of the results for the use in DNA analysis is discussed.     

Fluoropolyether coatings: Relationships of electrochemical impedance spectroscopy measurements,barrier properties,and polymer structure

Ten model coatings, selected and obtained from a family of fluorinated resins synthesized by the reaction of perfluoroether oligomeric diols of different molecular weights with polyisocyanurates of hexamethylenediisocyanate (HDI) and isophoronediisocyanate (IPDI), were characterized with differential scanning calorimetry, mechanical testing, and electrochemical impedance spectroscopy measurements. The electrochemical and chemico‐physical measurements show that the glass‐transition temperature of the starting isocyanate trimers greatly influences the properties of the final urethane coatings; the IPDI trimer gives harder coatings with lower water permeabilities than the corresponding HDI‐based materials. Moreover, for each class of materials (from IPDI or HDI), the fluorine content plays a relevant role: the higher the fluorine percentage, the lower the water absorption into the coatings. Furthermore, the chain length of the polyols used for the synthesis of the prepolymers is a variable that exhibits great influence on the coating properties: coatings containing shorter perfluoropolyether segments show better barrier properties. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 52–64, 2002