Analysis Of Electrochemical Impedance Spectroscopy Data Research Articles

Investigations on the effect of 2-[(furan-3ylmethylene)-amino]-benzenethiol on corrosion in carbon steel

A Schiff base namely, 2-[(furan-3ylmethylene)-amino]-benzenethiol (2-FAB) was synthesized and its influence on the inhibition of corrosion in carbon steel immersed in 0.5 M H2SO4 was investigated by weight loss analysis, potentiodynamic polarization studies, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and FT-IR spectroscopy. The weight loss measurements showed that 2-FAB has an excellent inhibiting efficiency of 95.51% at a concentration of 250 ppm. The inhibitor efficiency was found to depend on both the concentration and molecular structure of the inhibitor. Potentiodynamic polarization curves revealed that the studied inhibitors represent a mixed-type, predominantly cathodic control. An equivalent circuit is suggested based on an analysis of EIS data. Surface analysis using scanning electron microscope (SEM) and atomic force microscopy (AFM) show a significant morphological improvement on the mild steel surface with the addition of 2-FAB. The negative value of standard free energy of adsorption in the presence of inhibitor suggests the spontaneous adsorption of inhibitors on the carbon steel surface. The Temkin and Langmuir adsorption isotherms were found to provide a accurate description of the adsorption behavior of the inhibitor. Taken as a whole, this work demonstrates that 2-FAB shows promising results in resisting the deterioration of carbon steel in 0.5 M H2SO4 environment. The inhibitor forms a protective film on the surface of the carbon steel, significantly reducing its corrosion rate.

Ageing processes of coil-coated materials: Temperature-controlled electrochemical impedance analysis

In the present work, an industrial polyester coil-coated steel was characterized by electrochemical impedance spectroscopy (EIS) during immersion in a 0.5 M NaCl solution for different temperatures (30, 40, 50 and 60 °C). The objective was to propose a methodology to follow the ageing of the coil-coated system, from the first stage of water uptake until the blistering appearance. Relevant parameters were extracted from the EIS diagrams to analyse ageing processes of the polymer and of the metal/polymer interface. Water uptake was determined from the high-frequency part of the impedance diagrams using a linear rule of mixtures. By increasing the temperature, both the water uptake kinetics and the water content in the coating increased. The effect of water uptake on the physical structure of the coating (plasticization) was discussed through the analysis of a time constant corresponding to the dielectric manifestation of the polymer glass transition.At 40, 50 and 60 °C, appearance of corrosion was detected on the impedance spectra by a decrease, at low frequency, of the impedance modulus and of the phase angle. For 60 °C, the corroded surface area as a function of time, was assessed from the EIS data analysis with adapted equivalent circuits. The corroded surface areas followed similar trend as blister surface areas determined from images analysis.

Deconvolution of electrochemical impedance spectroscopy data using the deep-neural-network-enhanced distribution of relaxation times

Electrochemical impedance spectroscopy (EIS) is widely used to characterize electrochemical systems. The distribution of relaxation times (DRT) has emerged as a powerful, non-parametric alternative to circumvent the inherent challenges of EIS analysis through equivalent circuits or physical models. Recently, deep neural networks have been developed to estimate the DRT. However, this line of research is still in its infancy, and several issues remain unresolved, including the long training time and unknown accuracy of this method. Furthermore, deep neural networks have not been used for deconvolving DRTs with negative peaks. This work addresses these challenges. A pretraining step is included to decrease the computation time; error analysis allows error estimation and the development of error reduction strategies. Furthermore, the training loss function is modified to handle DRTs with negative peaks. For most cases tested, this new framework outperforms ridge regression. Moreover, these advances are validated with an array of synthetic and real EIS spectra from various applications, including lithium-metal batteries, solid oxide fuel cells, and proton exchange membrane fuel cells. Overall, this research opens new avenues for the development and application of the deep-neural-network-based analysis of EIS data.

Detailed Mechanistic Studies of Electrochemical Reactions on Pt and Au Electrodes in Solid Oxide Cells Via EIS Data Analysis

In order to reduce the environmental impact of fossil fuels, a range of sustainable technologies for power generation and storage are currently being developed. In addition, efficient and low-cost methods for CO2 capture and conversion to form useful products are critically needed. One of the promising technologies towards achieving these goals involves the use of solid oxide cells (SOC), which are unique devices that can be employed in both the fuel cell mode for clean power generation and in the electrolysis mode to achieve CO2 conversion through its electrochemical reduction (‘CO2RR’).One of the burning problems that is impeding SOC implementation is catalyst selection, with many promising materials having been reported over the last 50 years, including metals and mixed ionic and electronic conducting (MIEC) metal oxide materials. However, the reasons for better or worse activity, as well as the mechanism of the CO2RR at these catalysts remains unknown and it is often unclear what factors limit the catalyst activity during cell operation and how this can be improved. This is due, in part, to the limited number of techniques that can be used to evaluate these performance metrics, especially at high operating temperatures. One of the most useful techniques is electrochemical impedance spectroscopy (EIS). However, data interpretation is often quite complex and thus other methods, such as CNLS fitting or the determination of the distribution of relaxation times (DRT), are needed.While CNLS fitting allows the fit parameters to be correlated with specific physical properties, a precise model of the system is required. Since SOC systems are relatively unexplored and good models are not yet available, this could lead to the mis-interpretation of the EIS data. DRT, on the other hand, can be a useful tool since it does not require any pre-existing models of the system. Unlike CNLS fitting, DRT can provide the correct number of time constants present (from the number of peaks obtained), as well as the associated resistance and capacitance values. According to the literature, each peak is typically related to a specific reaction step with a unique capacitance value, identified by changing conditions such as temperature, polarization or gas composition.In the present work, DRT analysis of Pt and Au electrodes on YSZ electrolytes was carried out in order to determine the origin of each resistance and to determine the effect of temperature, electrode polarization and gas composition on both the resistance and capacitance values. Here, both porous and point metal electrodes were investigated as no double phase boundary activity or chemical capacitance effects should be present, making data interpretation less complex. Furthermore, to avoid the challenges of porous electrodes, point electrodes, produced by pressing the metal wire to a flat YSZ surface by applying pressure with a spring, followed by softening at 1100 °C to achieve better contact, were used to achieve a controllable triple phase boundary (TPB) length. This allowed the true activity of the metal/YSZ TPB to be measured as a function of reactive interface length, rather than just per geometric surface area. Porous electrodes were also studied, made by depositing Pt or Au paste onto YSZ, followed by sintering at 600 °C for 20 min. Polymeric YSZ precursors were then infiltrated into the metallic backbone, then sintered at 750 °C for 2 hours. Then, a thin layer of the same metal paste was applied in order to provide better conductivity. The point electrodes were made by attaching 0.3 mm thick Pt and Au wires onto dense and flat YSZ electrolyte by a spring-loaded cell holder, then held at 1050 °C for 1 hour to soften and produce a fixed TPB length. Electrochemical testing of the porous electrodes was conducted at 750 °C in both half- full cell modes in air, CO2 and CO2/CO mixtures, while the wires were tested at 650-750°C in the same gases, but in half-cell mode.8 individual process were seen for both the porous and point electrodes, including both electrodes in each cell. The time constant with the smaller capacitors are likely related to the electrode-electrolyte interface, while the mid-range capacitors are associated with electrode surface processes, such as surface diffusion, molecular species dissociation, and adsorption. The high capacitance steps are likely related to gas-phase processes, such as gas diffusion and the possible presence of a conversion layer. More detailed analysis of polarization and gas atmosphere dependence is ongoing in order to confirm the nature of each process.

The Deep-Prior Distribution of Relaxation Times

Electrochemical impedance spectroscopy (EIS) is the established tool for the study of many electrochemical experiments. While the analysis of EIS data is challenging, this can be assisted by the distribution of relaxation time (DRT) method. However, obtaining the DRT is difficult as the underlying problem is ill-posed. Inspired by recent advances in image analysis, we develop a completely new approach, named the deep prior distribution of relaxation time (DP-DRT), for the deconvolution of the EIS to obtain the DRT. The DP-DRT uses a deep neural network fed with a single random input to deconvolve the DRT and fit the EIS data. The DP-DRT has the peculiarity of having a number of parameters much larger than the number of observations. Further, unlike most supervised deep learning models, large datasets are not needed as the DP-DRT is trained against a single available EIS spectrum. The DP-DRT was successfully tested against both synthetic and real experiments displaying considerable promise and opportunities for extensions.

Studies on Corrosion of Titanium and Air-Oxidized Titanium in Fluorinated Nitric Acid

Titanium (Ti) is a lustrous transition metal which possesses excellent corrosion resistance in several aggressive environments but is attacked by acidic fluoride media. In this work, the addition of fluoride ion to nitric acid on the corrosion behavior of Ti and air-oxidized Ti was studied. Air oxidation of Ti at 800 °C for 5 h resulted in the formation of an intact rutile TiO2 layer with a thickness of about 35 μm. The corrosion resistance was investigated from the polarization resistance (R_{text{P}}) values which were obtained from linear polarization and electrochemical impedance spectroscopy (EIS) measurements. A decrease in the R_{text{P}} value of Ti with the addition of fluoride ion in nitric acid was observed, and this indicated the formation of an unstable layer, which resulted in accelerated dissolution. The several order increase in the R_{text{P}} value of air-oxidized Ti in nitric acid containing fluoride ions pointed the improved resistance to corrosion. The diffusivity of species through the air-oxidized TiO2 layer was estimated from the electrochemical equivalent circuit (EEC) analysis of EIS data. Even though the diffusivity increased by several orders with the addition of fluoride ions, air-oxidized Ti provided better protection against nitric acid containing fluoride ions than Ti. The corrosion rates of Ti and air-oxidized Ti in boiling nitric acid containing fluoride ions were also estimated from weight loss experiments. Even in boiling fluorinated nitric acid, air-oxidized Ti provided better corrosion protection, with corrosion rates of about 1000 times less than that of Ti.

Label-free electrochemical impedance spectroscopy using a micro interdigitated electrode inside a PCR chip for real-time monitoring

Conventional real-time PCR using fluorescence detection requires expensive optical detection systems with fluorescence labeling. To simplify this PCR system, we proposed an electrochemical impedance spectroscopy (EIS) using an interdigitated electrode integrated inside the PCR chip. The electrode makes a direct contact with the PCR sample and does not require any labeling or immobilization pretreatment. The input AC voltage for EIS showed the lowest noise at 100 mV. Electrical impedances in a frequency domain were measured during 30 cycles in the PCR of Escherichia coli genomic DNA region (of length 180 bp, 10 ng/μl). From the analysis of EIS data, the magnitude of imaginary value steadily increased with an increase in the PCR cycles and showed the greatest change rate at 186 Hz. For comparing the quantitative performance with previous researches, the figure of merit (FM) was defined as the ratio of normalized sensitivity (NS) to the normalized root mean square error (NRMSE). The performance of the proposed EIS method is similar to that reported in other studies, and the damage of the sample monitored through electrophoresis by EIS measurement was confirmed to be negligible.

Electrooxidation of cyanide ion on a platinized Ti electrode

Decontamination of highly concentrated cyanide solutions by the method of electrochemical oxidation is presented in this work. By using a Ti electrode covered with 600 nm average thickness layer of Pt, the effective electrooxidation of 0.1 M KCN solution is possible when 25 mA cm−2 current density is applied. Current efficiencies of ~60 % are achieved, and almost full removal of the cyanide ions (from 0.1 to 0.00016 M) are reached when 69 kC L−1 of charge is passed. The kinetics of electrochemical reaction of cyanide oxidation was investigated by voltammetry and fast Fourier transform electrochemical impedance spectroscopy (EIS). The kinetic parameters of cyanide ion electrooxidation reaction are determined and the mechanism of anodic reaction is suggested by considering the analysis of EIS data.

Analysis of Electrochemical Impedance Spectroscopy Data Using the Distribution of Relaxation Times: A Bayesian and Hierarchical Bayesian Approach

Electrochemical impedance spectroscopy (EIS) is one of the most important experimental techniques employed in electrochemistry because it can be used to deconvolve physico-chemical phenomena occurring at disparate timescales. Unfortunately, the analysis of EIS data is frequently challenging since it can require the selection of ad hoc equivalent circuits. The distribution of relaxation times (DRT) method is complementary to the approach of fitting equivalent circuits because the DRT maps the EIS data onto a function containing the timescale characteristics of the system under study. While conceptually simple, the DRT cannot be obtained by simple minimization of the least squares because the corresponding optimization problem is ill posed. Regularization methods, such as ridge/Tikhonov or Lasso regression, add a penalty term to the least squares minimization problem enabling the DRT deconvolution. In this work, we show that such regularization methods may be understood in a Bayesian context. For example, ridge/Tikhonov regression implicitly encapsulates the prior insight that the derivatives of the DRT are regular. We use this Bayesian approach as a starting point to extend the DRT regularization by considering frequency dependent oscillation levels. This approach is shown to be more robust with respect to both discontinuities and over smoothing than typical regularized DRT methods. Furthermore, the Bayesian approach is versatile and may be extended to include more informative priors.

Corrosion Inhibition of N,N- diethylammonium O,O′- di (p-chlorophenyl) dithiophosphate for Carbon Steel in HCL Solution

A new corrosion inhibior N,N-diethylammonium O,O-di (p-chlorophenyl) dithiophosphate (EDPDP) has been synthesized and its inhibition effect towards the corrosion of carbon steel in 1.0 molL-1 HCl solution at 25 °C has been investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods. The obtained results show that EDPDP is a excellent inhibitor and the inhibition efficiencies exceed 90 %. The polarization measurements reveal that EDPDP is a mixed type inhibitor and the equivalent circuit model of the corrosion inhibition process is obtained by the analysis of EIS data.

ChemInform Abstract: The Accurate Use of Impedance Analysis for the Study of Microbial Electrochemical Systems

AbstractReview: 203 refs.

Comparative study of N-[(4-methoxyphenyl) (morpholin-4-yl)methyl]acetamide (MMPA) and N-[morpholin-4-yl(phenyl)methyl]acetamide (MPA) as corrosion inhibitors for mild steel in sulfuric acid solution

Two Mannich bases namely, N-[(4-methoxyphenyl)(morpholin-4-yl)methyl]acetamide (MMPA) and N-[morpholin-4-yl(phenyl)methyl]acetamide (MPA) were synthesized and their influence on the inhibition of corrosion of mild steel in 1.0M H2SO4 was investigated by weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and FT-IR spectroscopy. The weight loss measurements showed that these inhibitors have excellent inhibiting effect at a concentration of 0.01M. The inhibitor efficiency was found to depend on both concentration and molecular structure of the inhibitor. Both the compounds have been found to be relatively good inhibitors. Potentiodynamic polarization curves revealed that the studied inhibitors represent a mixed-type, predominantly cathodic control. An equivalent circuit is suggested based on an analysis of EIS data. The negative value of standard free energy of adsorption in the presence of inhibitor suggests spontaneous adsorption of inhibitors on the mild steel surface. The activation energy of corrosion and other thermodynamic parameters were calculated to elaborate the mechanism of corrosion inhibition. The Temkin isotherm was found to provide an accurate description of the adsorption behavior of the inhibitors. Surface analysis using scanning electron microscope (SEM) shows a significant morphological improvement on the mild steel surface with the addition of inhibitors. FT-IR spectra revealed the interaction between inhibitor molecules and mild steel surface.

AC Impedance Analysis of Electrorheological Fluids - Activated Biomedical Devices

Electrorheological fluids (ERFs) have been described as highly engineered variable-impedance fluids that possess rheological and electrical properties that demonstrate dramatic nonlinear change with an applied electric field. ERF is a two-phase composite colloidal suspension of electrically polarizable particles dispersed in insulating media. This article describes an application of low-voltage electrochemical impedance spectroscopy (EIS) to comparative characterization of four different ERFs and a prediction of their performance in ER-activated medical prosthetic devices. The ERF impedance response is interpreted in the context of a classical Debye relaxation model. EIS data analysis allows the determination of the electrical characteristics of polarizable particles and base fluid, an investigation of the preferred conduction mechanisms in the fluid, an evaluation of the potential for chemical agglomeration, and modification of the electrical properties of the ERF to achieve better fluid performance. The ERF performance improves significantly for highly concentrated suspensions of well-dispersed, small, closely packed particles. The recent introduction of nanoparticles-based ERF has created an opportunity for further development of fluids with transformationally superior performance.

Investigation of the inhibitive effect of p-substituted 4-(N,N,N-dimethyldodecylammonium bromide)benzylidene-benzene-2-yl-amine on corrosion of carbon steel pipelines in acidic medium

The corrosion inhibition efficiency of carbon steel pipelines in 1 M HCl by the synthesized novel surfactants was studied using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and weight loss measurements at 20 °C. Temperature effect on the corrosion behaviour was studied at a temperature range from 20 to 80 °C. The results showed that all synthesized inhibitors were good inhibitors and their inhibition efficiencies were significantly increased with increasing both the concentration and temperature. The inhibition efficiency was also influenced by the type of the functional groups substituted on the benzene ring. Polarization curves revealed that the studied inhibitors represent a mixed-type of inhibitors. An equivalent circuit is suggested based on analysis of EIS data. Adsorption of inhibitors was found to obey Langmuir isotherm and was chemisorption.

Electrochemical impedance spectroscopic study on cathodic polarisation of 5083 Al alloy under stagnant and dynamic flow conditions in 3·5% NaCl solution

This research was conducted to compare the cathodic polarisation behaviour of 5083 Al–Mg alloy under stagnant and dynamic flow conditions in 3·5% NaCl solution. The effect of flow velocity upon corrosion processes under cathodic polarisation was studied by electrochemical impedance spectroscopy (EIS) using rotating cylinder electrode. Cathodic behaviour of the specimens was determined by potentiodynamic tests. Specimens were cathodically polarised to –0·8, –0·9 and –1 VSCE for 20 h, EIS data were obtained at intervals of 0, 2·5, 5, 10, 15 and 20 h after the exposure without interrupting the polarisation. The EIS data analysis shows that the existence of fluid flow increases pit initiation level. It seems that under stagnant condition cathodic polarisation has an adverse effect on corrosion resistance; however, under dynamic flow condition it may have a positive and favourable effect on corrosion resistance. The removal of intermetallic particles may lead to gradual improvement of corrosion resistance and a decrease in pit surface growth rate. The applied cathodic polarisation and the hydrodynamic forces at the walls of specimens are two possible major factors in particles removal processes; furthermore, it seems that these two factors complement each other.

Electroless Deposition of Silver by Galvanic Displacement on Aluminum Alloyed with Copper

In this paper, a procedure is described for the electroless deposition of silver on films containing 99.5% aluminum and 0.5% copper. The deposition proceeds in the absence of external reducing agents via the galvanic displacement mechanism by which silver cations are reduced and copper is oxidized. Although aluminum is a stronger reducing agent than copper, the galvanic displacement of aluminum by silver is not observed with pure (99.997%) aluminum substrates. By alloying aluminum with copper, aluminum films are made amenable to electroless deposition of silver by galvanic displacement. To generate a clean surface for electroless deposition with a controlled and minimal thickness of surface oxide, the aluminum films alloyed with copper are anodized in oxalic acid and etched in a mixture of chromic and phosphoric acids. Thinning of the barrier aluminum oxide during etching and deposition of silver particles are monitored with electrochemical impedance spectroscopy (EIS). Analysis of EIS data indicates that...

Investigation of the inhibitive effect of ortho-substituted anilines on corrosion of iron in 0.5 M H 2SO 4 solutions

The inhibiting action of six o-substituted anilines against the corrosion of iron (99.9999%) in solutions of sulphuric acid has been studied using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). At inhibitor concentration range (10 −3 to 10 −2 M) in 0.5 M acid, the efficiency of the inhibitors increases in the order o-toluidine < 2-chloroaniline < 2-ethylaniline < 2-fluoroaniline < o-aminoanisole < 2-amiophenetole. Comparable results were obtained by the different electrochemical methods used. Adsorption of these compounds on the iron surface was found to obey a Langmuir adsorption isotherm. An equivalent circuit is suggested based on analysis of EIS data.

EIS studies of coated metals in accelerated exposure

One of the most popular uses of electrochemical impedance spectroscopy (EIS) is the characterization of the protective properties of coatings on corrodible metals. From early studies up to the present time, many EIS studies have been devoted to the study of the changes in the impedance of coated metals as they undergo either natural or artificial exposure to conditions that cause corrosive failure of such systems. With the current improvements in instrumentation and software for EIS studies of coated metals, one no longer needs to be an expert electrochemist to utilize EIS in one’s studies of protection by coatings. In this paper, the use of EIS from the point of view of the coatings scientist will be presented, with an emphasis on its application simultaneous with accelerated exposure. EIS is used by coating scientists for several purposes, among them the detection of changes due to exposure, prediction of the lifetime of corrosion protection, identification of the corrosion processes that lead to failure, ranking of coatings systems, measurement of water uptake by coatings, and the development of models for coating/metal system performance. This paper will discuss several specific examples of the use of EIS in the study of coatings in accelerated exposure and the analysis of EIS data from such studies. The importance of cyclic vs. steady state exposure of samples will be shown by EIS results, and some of the problems in the use of standard continuous salt fog exposure as exemplified by ASTM B117 for a coating specification will be discussed. Considering T g effects on EIS data will show the importance of considering thermal effects in the testing of coatings. The extremely important role of water uptake in coatings during exposure will also be discussed using EIS results to analyze changes in both the coating resistance (low frequency | Z| data) and capacitance (higher frequency Z data). During exposure to cyclic changes in temperature and electrolyte solution concentration, a coating over a metal substrate appears to undergo both “physical aging” and chemical degradation. The coating appears to have a memory of past exposure events such that each subsequent exposure to water and temperature creates and enlarges transport pathways within the coating for water and electrolyte. As cyclic exposure continues, damage to the bulk-coating layer above the coating/metal interface accumulates until there begins to be a permanent accumulation of electrolyte at this interface and local small-scale corrosion begins. This is the initiation of corrosion failure of the system, but it only occurs following the decrease of bulk-coating layer barrier properties caused by cyclic temperature and humidity processes characteristic of exterior exposure. This whole process can be accelerated by immersion in a flowing electrolyte, emphasizing the role of transport processes in coating degradation processes. If there is simultaneous UV exposure, as Skerry has so well described, one must also account for photodegradation of the outermost layer of the coating system. The role of the coating scientist is now to assimilate the data that EIS now provides us during the exposure process and develop meaningful models for the molecular level changes that occur in the coating film in order to enable use of the EIS results for true coating performance ranking and lifetime prediction.

Evaluation of localized corrosion phenomena with electrochemical impedance spectroscopy (EIS) and electrochemical noise analysis (ANA)

AbstractThe use of electrochemical impedance spectroscopy (EIS) and electrochemical noise analysis (ENA) for non‐destructive evaluation of corrosion processes is illustrated for three model systems. EIS can be used to detect and monitor localized corrosion of Al alloys and determine pit growth laws which can be used for lifetime prediction purposes. Electrochemical potential and current noise data can be analyzed in the time and the frequency domain. A comparison of noise data obtained for Pt and an Al 2009/SiC metal matrix composite (MMC) exposed to 0.5 N NaCl has shown that the use of potential noise data alone can lead to erroneous conclusions concerning corrosion kinetics and mechanisms. The electrochemical noise data have been evaluated using power spectral density (PSD) plots in an attempt to obtain mechanistic information. The system Fe/NaCl has been used to determine the relationship between the polarization resistance Rp obtained from EIS data and the noise resistance Rn determined by statistical analysis of potential and current noise data. Potential and current noise can be recorded simultaneously allowing construction of noise spectra from which the spectral noise resistance R can be obtained as the limit for zero frequency. Good agreement between RP, Rn and R has been observed for iron exposed to NaCl solutions of different corrosivity. For polymer coated steel exposed to 0.5 N NaCl for five months analysis of EIS data allows to draw conclusions concerning the degree of disbonding of the coating and the decrease of the coating resistivity with exposure time. Rn and R obtained from electrochemical noise data for an alkyd coating on cold rolled steel agree with each other and show the same time dependence as Rp and the pore resistance Rpo determined from EIS data, but are significantly lower than Rp and Rpo. The relationships of derived noise parameters such as Rn and R to coating properties and to the remaining lifetime of a polymer coating are not clear at present.