Use Of Electrochemical Impedance Spectroscopy Research Articles

The use of electrochemical impedance spectroscopy with segmented electrodes to study inhibition at the cut-edge of coil-coated systems

Abstract The use of multiple metal segmented electrodes has been applied to study the inhibition mechanisms for several anti-corrosion pigments that are commonly used in organic coatings. The relatively novel experimental methodology involves, firstly, polarisation of the coupled metal system at the common coupled potential but with the currents on the separated electrodes recorded individually and, secondly, the application of electrochemical impedance spectroscopy at the same coupled potential. For example, at the cut-edge of a coil-coated galvanised steel sheet, electrochemical data may be gathered simultaneously at an anodic potential for the zinc and at a cathodic potential for the steel substrate. Using this methodology the inhibitive efficiency for strontium chromate, calcium ion-exchanged silica and zinc molyphosphate inhibitors were determined under the electrochemical condition expected in service.

Electrochemical study of chalcopyrite dissolution in sulfuric, nitric and hydrochloric acid solutions

Electrochemical and surface analyses were carried out to study the leaching of chalcopyrite in acid media, aiming to increase copper extraction from low-grade chalcopyrite ores. Unpublished results include the use of electrochemical impedance spectroscopy (EIS) to characterize the dissolution resistance of chalcopyrite surfaces in 0.1mol·L−1 of hydrochloric, nitric or sulfuric acids. Potentiodynamic polarization, atomic absorption spectrometry and EIS analysis showed that hydrochloric acid solutions are more efficient leaching agents than nitric and sulfuric acids. The impedance results suggested that the chalcopyrite dissolution is a diffusion-controlled process in hydrochloric and sulfuric acids. The use of Raman spectroscopy and scanning electron microscopy with energy dispersive spectrometers (SEM/EDS) allowed the partial identification of lead and bismuth sulfides as impurities. Two products were identified on the surface of chalcopyrite after anodic polarization, i.e., sulfur in the sulfuric acid only and covellite in all three acids.

Reaction Kinetics of Protons and Oxide Ions in LSM/Lanthanum Tungstate Cathodes with Pt Nanoparticle Activation

Composite electrodes of La0.8Sr0.2MnO3 (LSM)/La28–xW4+xO54+3x/2 (x = 0.85, “LWO56”) on LWO56 electrolytes have been characterized by use of electrochemical impedance spectroscopy vs. pO2 and temperature from 900°C, where LWO56 is mainly oxide ion conducting, to 450°C, where it is proton conducting in wet atmospheres. The impedance data are analyzed in a model which takes into account the simultaneous flow of oxide ions and protons across electrolyte and electrodes, allowing extraction of activation energies and pre-exponential factors for the partial electrode reactions of protons and oxide ions. One composite electrode was infiltrated with Pt nanoparticles with average diameter of 5 nm, lowering the overall electrode polarization resistance (Rp) at 650°C from 260 to 40 Ω cm2. The Pt-infiltrated electrode appears to be rate limited by surface reactions with activation energy of ∼90 kJ mol−1 in the low temperature proton transport regime and ∼150 kJ mol−1 in the high temperature oxide ion transport regime. The charge transfer reaction, which makes a minor contribution to Rp, exhibits activation energies of ∼85 kJ mol−1 for both oxide ion and proton charge transfer.

Feasibility of combining electrochemical impedance spectroscopy and synchrotron X-ray radiography for determining the influence of liquid water on polymer electrolyte membrane fuel cell performance

In this work, we present a feasibility study of the simultaneous use of electrochemical impedance spectroscopy (EIS) and synchrotron X-ray radiography in a polymer electrolyte membrane fuel cell (PEMFC) for studying the relationship between the presence of liquid water and cell performance. X-ray radiography was used to quantify liquid water in the anode and cathode fibrous carbon paper substrate and microporous layer (MPL). EIS was used as a complementary diagnostic tool to quantify the equivalent resistances of the fuel cell. Two fuel cell cases with varying MPL thicknesses were compared under constant current density operation. The fuel cell with a 150 μm-thick MPL resulted in an equivalent mass transport resistance that was 13% lower than the fuel cell with a 100 μm-thick MPL. This notable difference in mass transport resistance was attributed to the smaller quantity of liquid water in the cathode substrate, particularly in the transition region between the MPL and carbon paper.

Use of Electrochemical Impedance Spectroscopy (EIS) to monitoring the corrosion of reinforced concrete

AbstractElectrochemical techniques are among the most commonly techniques used for the evaluation and study of corrosion in reinforced concrete, including electrochemical impedance spectroscopy (EIS). Electrochemical impedance spectroscopy (EIS) is a powerful technique for characterizing a wide variety of electrochemical systems and for determining the contribution of electrode or electrolytic processes in these systems. The analysis of EIS results on samples of concrete is highly complex due to overlapping arcs from simultaneous phenomena and noise measurement, of course, associated with the heterogeneity of the samples and that complicate the analysis considerably. Thus, this paper proposes a new form of analysis based on the characteristic relaxation angular frequency, w, of each phenomenon and associating the typical capacitances and frequencies.

Determination of Battery Stability with Advanced Diagnostics

The increasing demand of lithium ion batteries for vehicle electrification is changing the typical use conditions that batteries may see. Over time, batteries may develop defects that are difficult to detect with traditional measurements. It is also possible that batteries may be left in an unknown state after failure of the monitoring system, loss of communication, or a potentially damaging event (such as an auto accident). It is therefore useful to explore other monitoring and interrogation methods that can better determine the stability of a battery in an unknown state. This work explores the use of electrochemical impedance spectroscopy as a method to determine the stability of batteries by observing changes in the complex impedance measurement as the cell is exposed to abusive conditions. Very dramatic changes to the internal resistance were observed when single cells were exposed to abusive conditions, suggesting that even single frequency impedance measurements could be effective with single cells. However tests on three cell series and parallel strings yielded smaller changes, primarily to the charge transfer resistance, showing that complex impedance measurements are more appropriate as the system increases in complexity. A rapid impedance tool developed at Idaho National Laboratory was tested and compared to traditional potentiostat tools as well. This was shown to yield similar data to the traditional tools, providing a potential method for continuous monitoring of a battery system. It was observed, however, that shifts in the data are difficult to detect in very transient systems.Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Measurement, semi-process and process modeling of proton exchange membrane fuel cells

Despite the extensive use of electrochemical impedance spectroscopy (EIS) in diagnosing proton exchange membrane fuel cells, the differences between EIS-based measurement and process models are still not clear, causing often dubious interpretations. These differences, mainly related to the approach used in obtaining the equivalent circuit, are discussed here. The procedure for obtaining the equivalent circuit from the analytical solution and the importance of such a procedure, which distinguishes the process models from other analytical models, are also outlined. In addition, the paper presents the new semi-process model category, presenting the equivalent circuit in a different way than the process models.

An electrochemical DNA-sensor developed with the use of methylene blue as a redox indicator for the detection of DNA damage induced by endocrine-disrupting compounds

An electrochemical biosensor capable of indirect detection of DNA damage induced by any one of the three endocrine-disrupting compounds (EDCs) – bisphenol A (BPA), 4-nonylphenol (NP) and 4-t-octylphenol (OP), has been researched and developed. The methylene blue (MB) dye was used as the redox indicator. The glassy carbon electrode (GCE) was modified by the assembled dsDNA/graphene oxide-chitosan/gold nano-particles to produce a dsDNA/GO-CS/AuNPs/GCE sensor. It was characterized with the use of electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and scanning electron microscopy (SEM) techniques. The loading/release of the MB dye by the dsDNA/GO-CS/AuNPs film was investigated, and the results showed that the process was reversible. Based on this, the sensor was used to measure the difference between the loading capabilities of intact and damaged dsDNA in the films. The sensor was then successfully applied to detect DNA damage electrochemically. The differential pulse voltammetry (DPV) peak current ratio for MB, observed before and after DNA damage, increased linearly in the presence the BPA, NP or OP compounds; the treatment range was 10–60min, and the respective damage rates were 0.0069, 0.0044 and 0.0031min−1, respectively. These results were confirmed by the binding constants: 2.09×106M−1 (BPA-DNA), 1.28×106M−1 (NP-DNA) and 9.33×105M−1 (OP-DNA), all of which were obtained with the use of differential pulse stripping voltammetry (DPSV).

Limiting ac frequency and dc current of electrochemical double layer capacitors

The general aim of the present paper was to compare and correlate factors describing operation rate limits of electrochemical double layer capacitors (EDLCs), under both ac and dc conditions. Six laboratory-made and six commercial EDLCs were investigated with the use of electrochemical impedance spectroscopy (EIS) and galvanostatic charging/discharging. A typical EIS spectrum, taken under ac conditions, consisted of two straight lines. The intersection of both straight lines indicates the frequency (transition frequency ftr) at which the device loses its capacitive properties. Similarly, during dc charging/discharging the I(dU/dt)−1 value (often called EDLCs capacitance), expressed as a function of the current I, also shows two straight lines. The intersection of the lines indicates a transition current Itr and the corresponding (dU/dt)tr voltage changes rate. A linear correlation was found between transition parameters determined under ac and dc conditions ((Redrftr)−1 and Itr(dU/dt)tr−1), with a high correlation parameter r2 = 0.99. The correlation enables estimation of the limiting operation rate of EDLCs under dc conditions based on the analysis of ac impedance spectroscopy curves.

Improvement of Light Harvesting by Addition of a Long-Wavelength Absorber in Dye-Sensitized Solar Cells Based on ZnO and Indoline Dyes

A pathway to improve the light-harvesting efficiency of dye-sensitized solar cells based on porous electrodeposited ZnO films is presented. Cosensitization with the indoline dyes D149 and D131 and the squaraine dye SQ2 leads to panchromatic light harvesting and photovoltaic activity. When coadsorbates are employed to prevent dye aggregation on the ZnO surface, an increase in the short-circuit photocurrent and overall efficiency compared to reference cells with D149, or D149 and D131 is attained. The overall performance of cosensitized cells containing SQ2, however, is limited by low open-circuit voltages and fill factors. By use of electrochemical impedance spectroscopy, current–voltage characterization in the dark and under illumination, and charge extraction measurements, recombination reactions and the distribution of trap states in the ZnO films are investigated, and the origins of the limited open-circuit voltages and fill factors in cells with SQ2 are revealed.

Fabrication and electrochemical performance of a stable, anode supported thin BaCe0.4Zr0.4Y0.2O3-δ electrolyte Protonic Ceramic Fuel Cell

The present work deals with the fabrication and electrochemical characterisation of a potential protonic ceramic fuel cell based on a Ni–BaZr0.85Y0.15O3-δ anode supported thin film proton conducting BaCe0.4Zr0.4Y0.2O3-δ electrolyte with a Pr2NiO4+δ cathode. Anode and electrolyte materials were prepared by an acetate–H2O2 combustion method. A thin (∼5 μm), dense and crack free BaCe0.4Zr0.4Y0.2O3-δ electrolyte film was successfully obtained on a porous anode support by spin coating and firing at 1450 °C. Maximum power densities of 234, 158, 102 and 63 mW cm−2 at 700, 650, 600 and 550 °C, respectively were achieved for the Ni–BaZr0.85Y0.15O3-δ/BaCe0.4Zr0.4Y0.2O3-δ/Pr2NiO4+δ single cell under fuel cell testing conditions. Electrode polarisation resistance was assessed at open circuit conditions by use of electrochemical impedance spectroscopy (EIS) and is shown to dominate the area specific resistance at low temperatures. Postmortem analysis by scanning electron microscopy (SEM), reveals that no delamination occurs at anode/electrolyte or electrolyte/cathode interfaces upon cell operation.

Experimental investigation of the effect of indium content on the CuIn5S8 electrodes using electrochemical impedance spectroscopy

This paper reports on the use of electrochemical impedance spectroscopy to investigate the electrochemical behavior of spinel CuIn5S8/electrolyte interface. The CuIn5S8 spinel films have been potentiostatically deposited onto indium tin oxide (ITO)-coated glass substrate. CuCl2 and InCl3 mixed solutions with different [Cu]/[In] ratios were used as cation precursor and Na2S2O3 as the anion precursor in acidic solution and at room temperature. The effect of the [Cu]/[In] ratio in the precursor solution on the structural, chemical stoichiometry, and morphological properties of prepared samples, as well as the electrochemical behavior of the CuIn5S8/electrolyte interface was investigated. The electrochemical impedance spectroscopy data have been modeled using an equivalent circuit approach. Several parameters such as, flat-band potential and free carrier concentration were determined by the change in the Mott–Schottky plots.

Use of electrochemical impedance spectroscopy to determine double-layer capacitance in doped nonpolar liquids

Electrochemical impedance spectroscopy in a thin cell (10μm) was used to infer conductivity, permittivity and the differential double-layer capacitance of solutions of dodecane doped with OLOA 11000 [poly(isobutylene) succinimide] for concentrations of dopant between 0.1% and 10% by weight. All spectra (frequencies between 1Hz and 100kHz) were well fit by an equivalent circuit having four elements including a constant-phase element representing the double-layer capacitance. Using Gouy–Chapman theory for small zeta potentials and assuming univalent charge carriers, the double-layer capacitances were converted into charge carrier concentration which was found to be directly proportional to the weight percent of dopant with a 1wt% solution having 87 carriers/μm3 (the concentration of either positive or negative charges). This is only 17ppm of the total monomer concentration calculated from the average molecule weight of the dopant. Dividing the measured conductivities by the charge carrier concentration, we inferred the mobility and hydrodynamic diameters for the charged micelles. The hydrodynamic diameters of carriers were significantly larger than the average diameter of all micelles measured independently by dynamic light scattering. This suggests that only large micelles become charged.

Interaction study of paraquat and silver electrode using electrochemical impedance spectroscopy: Application in milk and tomato samples

Abstract This paper reports on the use of electrochemical impedance spectroscopy (EIS) for analytical determination of paraquat herbicide at a silver electrode. The electrochemical technique was applied to aqueous solution, at pH 7.0, containing different concentrations of paraquat. The impedance measurements were carried out in the frequency range from 100 mHz to 100 KHz at a potential of 0.0 mV versus Ag/AgCl. The Nyquist plots were modeled with a Randle equivalent circuit, by identifying the charge transfer resistance as the relevant concentration dependent parameter. The silver surface adsorbs paraquat and the transfer process is controlled by diffusion. The response of the working electrode was attributed to the electron-exchange mechanism at the electrode–contact interface and the ion exchange at the electrode–solution interface. The proposed methodology offers good repeatability (RSD = 1.03%) with (n = 8) and impedimetric response to paraquat in the range from 1.0 × 10−14 to 8.0 × 10−4 mol L−1. The detection limit (DL, 3σ) and quantification limit (QL, 10σ) were 7.37 × 10−16 mol L−1 and 24.59 × 10−16 mol L−1 respectively. The method was satisfactorily applied to determine paraquat in milk and tomato samples.

Interface Investigations and Bulk Behaviors of an All-Solid-State Lithium Microbattery By Means of Electrochemical Impedance Spectroscopy

Constant miniaturization of electronic devices leads nowadays to the conception of smaller batteries. In this domain, using an all solid state thin film technology has many advantages over conventional lithium cells. These microbatteries are thin, bendable, with a long service lifetime and can also be produced with customizable shapes for better integration in electronic devices. Moreover, without liquid electrolyte, they are safe and comply well with environmental standards. Unfortunately their design and relative small dimensions imply some difficulties to accurately characterize them (from a physico-chemical point of view) without damages.This paper will present the use of Electrochemical Impedance Spectroscopy to understand the behavior of thin film batteries built by stacking several active layers thanks to physical vapor deposition technics (with LiCoO2 as positive electrode, lithium phosphorus oxynitride vitreous glass as electrolyte (LiPON) and lithium metal as negative electrode). The first step of this study was to distinguish the impedance response between each individual active layer and interface by testing different systems. Metal-insulator-metal stack let us access to the ionic transport properties in LiPON [1]. Half-cells composed with electrolyte and LiCoO2 or lithium, give us information about the electrolyte/active material interfacial behavior. At last, the insertion electrode bulk electronic conductivity can be obtained with a Pt/LiCoO2/Pt symmetrical cell. Thanks to all these results it is thus possible to determine an electrical equivalent model for the complete battery. The model is composed of serial contact and collector resistivity (A), bulk electrolyte (B), capacitance and resistance interfaces (C, D), semi-infinite diffusion in LiCoO2 (E) and charges accumulation phenomena (F). The Second step was to explain the reasons for spectrum evolutions in function of state of charge, aging or other external conditions. EIS was systematically performed after battery manufacturing and after aging, from 1 MHz to 50 mHz and between 3V and 4.2V. The most obvious observation is the evolution of the “D” contribution with cell potential. Iriyama et al. already attributed it to the charge transfer process at the LiCoO2/LiPON interface [2]. But after aging a new potential dependent R//C contribution appears and could correspond to bulk phenomena in the insertion electrode created by crystalline evolution during aging.To conclude, thanks to electrochemical impedance spectroscopy, we will propose an electrical equivalent model of the operating microbattery to predict its evolution, failure and aging. [1] X.Yu, J. Bates, G. Jellison anf F. X. Hart, J. Electrochem Soc., 144, 524 (1997) [2] Y. Iriyama, T. Kako, C. Yada, T. Abe and Z. Ogumi, Solid State Ionics, 176, 2371 (2005).

Graphite|LiFePO4 lithium-ion battery working at the heat engine coolant temperature

Electrochemical properties of the graphite anode and the LiFePO4 cathode, working together with the 1 M LiPF6 in TMS (sulpholane) at 90 °C have been studied. The general aim of the investigation was to demonstrate a potential application for a Li-ion cell working in the cooling system of a car heat engine (90 °C). Electrodes were characterized with the use of electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) as well as galvanostatic charging/discharging tests. SEM images of both electrodes after charging/discharging processes were covered with a film (electrochemical SEI formation). The charge transfer resistance at 90 °C, Rct, of the C6Li|Li+ anode and the LiFePO4 cathode was 24 Ω and 110 Ω, respectively. Reversible capacity of the LiC6 anode after 10–20 cycles, at a low current rate was close to the theoretical value of 370 mAh g−1 however an increasing current rate decreased to ca. 200 mAh g−1 (for 1C). The reversibility of the process was close to 95%. The capacity of the LiFePO4 cathode was ca. 150 mAh g−1, almost independent of the current rate and close to the theoretical value of 170 mAh g−1.

An Indirect Impedance Technique to Determine Reinforcing Steel Properties

Studies have shown that the application of an electric field to the surface of an electrolytic medium can indirectly polarize a metal within the solution.1,2,3,4 This technique can be applied to the study of reinforcing steel in concrete, and in this particular paper, to the study of post-tensioning steel in grouted cylinder tendons used in bridge construction. With the use of Electrochemical Impedance Spectroscopy, a finite-element model has been developed to solve for the frequency-dependent potential distribution through a cylindrical grout specimen containing one axially-located steel strand. Impedance simulations were performed at different steel corrosion states while incorporating the kinetics at the current-injecting electrodes.Following the procedure of Huang et al.5, the electrode kinetics are expressed as an oscillating current density as the summation of a charging and faradaic current. The grout is modeled as a uniform conductivity media and Laplace’s equation is used to solve for the potential distribution. The impedance is simulated over a range of frequencies as the potential difference between two reference electrodes divided by the current of the working electrode. The results are compared to experimental measurements throughout the hydration process.The effectiveness of this method relies on the use of accurate representations of the steel surface impedance. Passive film models developed from rotating disk experiments in simulated pore solution are used to describe the steel boundary condition in the finite element model. The simulated results incorporating these models show a similar impedance response as the measured impedance of an aged cylinder put through a wetting and drying cycle.Barring an accurate model, this technique has the potential to effectively determine the interface properties of the embedded steel from the overall response of the system. References J. Zhang, P. J. Monteiro, F.H. Morrison, “Noninvasive surface measurement of corrosion of reinforcing bar in concrete: Part I Experimental results”, ACI Materials Journal, 98 (2001) pg. 116-125.M Keddam, X. R. Novoa, V. Vivier, “The concept of floating electrode for contact-less electrochemical measurements: Application to reinforcing steel-bar corrosion in concrete,” Corrosion Science, 51 (2009) pg. 1795-1801.C. Andrade, I. Martnez, “Metal corrosion rate determination of different solutions and reinforced concrete specimens by means of a noncontacting corrosion method,” Corrosion 66 (2010) pg. 056001-056001.C. Andrade, J. Sanchez, I. Martinez, N. Rebolledo, Analogue circuit of the inductive polarization resistance,” Electrochimica Acta 56 (2011) pg. 1874-1880.V. M. W. Huang, V. Vivier, M. E. Orazem, N. Pbre, B. Tribollet, “The apparent constant-phase-element behavior of a disk electrode with faradaic reactions a global and local impedance analysis,” Journal of the Electrochemical Society 154(2007) C99-C107.

All-Solid-State Lithium Microbattery Characterization By Electrochemical Impedance Spectroscopy

The race for miniaturization of microelectronics components makes the way to the development of much smaller devices in which the integration of a conventional battery is no longer possible. All-solid-state thin film batteries have many advantages over conventional lithium cells, and thus are developed by several laboratories or industrial manufacturers. They are bendable, thin and safe with a long service lifetime and can be produced with a customizable shape for an optimized integration. Moreover, these microbatteries built without a liquid electrolyte comply with safety and environmental standards. The first applications planned for microbatteries are numerous around the emerging Internet of Things market (RFID Tags, autonomous sensors, powered SmartCards, sportswear microsystems…). Finally, one of the major challenges to ensure mass production is to reduce the final testing time and its associated cost. In this context, the use of Electrochemical Impedance Spectroscopy (EIS) is the most promising tool for a fast assessment of the production.In this work thin film batteries composed of a stack of several active layers comprising a platinum current collector, a LiCoO2 positive electrode, a LiPON vitreous solid electrolyte and a lithium negative electrode, were characterized by EIS. These measurements were performed at different states-of-charge between 3.6V and 4.2V (figure 1) and at different temperatures in the frequency range from 1 MHz to 50 mHz. It was found that the Warburg diffusion impedance decreases as the potential is increased, which is related with the growth of the diffusion path into the LiCoO2 during his delithiation. Then, 3 R//C contributions are observed (A, B, C) but only one (C) in the low frequency region depends on potential step. Iriyama and al. [1] showed that it corresponds to the charge transfer step at the LiPON/LiCoO2 interface. The contribution (A) is the most obvious to assign and corresponds to the bulk solid electrolyte. Measurements on Pt/LiPON/Pt blocking electrode cells allowed confirming this assignation and to determine intrinsic electrolyte parameters. The determination of LiPON resistance and capacitance by fitting impedance spectra, the knowledge of layer thickness and active surface allow us to calculated ionic conductivity and dielectric constant of LiPON respectively around 2.10-6 S.cm-1and 20. The activation energy of ionic conductivity in LiPON was found to be close to 0.56 eV. The origin of contribution B is more difficult to clarify. This latter is not important after the first charge of the microbattery (figure 2), but increases consistently after few months of storage at 100% SOC. Actually, the electrochemical deposition of lithium during the charge is likely to lead to a change in the geometry of the Li/LiPON interface and in its chemical composition (pollution through the voids formed at the interface) inducing an increase of interfacial resistance. In previous studies, Bates and al. [2] showed that a little part of transferred lithium no longer participates to the reversible capacity of the microbattery. We show here that a specific cycle can restore the interface quality then restoring a lower internal resistance.AC impedance was used to understand microbattery behavior without disassembling them. This technique allowed to confirm the presence of three R//C contributions and to follow their evolutions with potential or storage conditions. Analysis of Pt/LiPON/Pt cells confirmed that electrolyte is the major contribution to the whole impedance and allowed to extract intrinsic parameter values of LiPON. Futures studies will focus on the interfacial degradations mechanisms and modeling to improve the description of microbatteries behavior. [1] Y. Iriyama, T. Kako, C. Yada, T. Abe and Z. Ogumi, Solid State Ionics, 176, 2371 (2005).[2] B. J. Neudecker, N. J. Dudney and J. B. Bates, J. Electrochem. Soc., 147, 517 (2000).

An electrochemical sensor based on multiwall carbon nanotubes and molecular imprinting strategy for warfarin recognition and determination

A sensitive electrochemical sensor for warfarin was prepared based on molecular imprinting strategy by electropolymerization qof o-phenylenediamine (o-PD) on a glassy carbon electrode via cyclic voltammetry (CV). In order to enhance the electrode sensitivity and electronic transmission, multiwall carbon nanotubes (MWCNT) containing carboxylic functional group (f-MWCNTs) were introduced on glassy carbon electrode (GCE). Thin film of molecularly imprinted polymer (MIP) with specific binding sites for warfarin was cast on the modified electrode using electrochemical deposition. In order to form a double layer with MIP layer as an insulating electrolyte, Au nanoparticles (AuNPs) was introduced at the MIP surface to form final modified electrode (AuNP/MIP/f-MWCNT/GCE). The properties of AuNP/MIP/f-MWCNT/GCE were studied in the presence of K3Fe(CN)6 as a probe for signal transduction and also by the use of electrochemical impedance spectroscopy (EIS). AuNP/MIP/f-MWCNT/GCE exhibits fast binding kinetics and good selectivity to template due to their high ratio of surface imprinted sites, large surface-to-volume ratios and large affinity to template. The modified electrode was used to detect the concentration of warfarin with a linear range and detection limit (S/N=3) of 0.031–0.616ngmL−1 and 0.024ngmL−1, respectively. Finally, the modified electrode was successfully applied to determine warfarin in human serum sample.

The effect of hydrogen sorbed by iron on anodic dissolution of metal in sulfate electrolytes

The mechanism of anodic dissolution of hydrogenated iron in sulfate electrolyte (pH 5.5) is studied with the use of electrochemical impedance spectroscopy in combination with bipolar membrane electrode. Based on comparison of rate constants of elementary stages of the anodic process in acidic (pH 1.3) and weakly acidic (pH 5.5) sulfate electrolytes, the reaction scheme of active dissolution of iron is made more accurate.