Impedance spectroscopy of lithium-tin film electrodes

A method of electrochemical impedance spectroscopy was used to study the reversible lithium intercalation from nonaqueous electrolyte into tin films with the thickness of 0.1–1 μm. The impedance spectra of lithium-tin (Li _x Sn) electrodes have a complicated shape depending on the electrode state and prehistory; they reflect the occurrence of several consecutive and parallel processes, including the lithium migration, diffusion, and accumulation. The formation of a solid-electrolyte layer on the surface at Li intercalation into Sn is observed. Equivalent circuits are proposed that adequately model the experimental data on the Li _x Sn electrodes both freshly prepared and after prolonged cycling. Problems associated with the choice of equivalent circuits and determination of their parameters, the accuracy of the diffusion coefficient determination, the trends in the parameters’ variation with electrode potential (composition) are discussed.     

电化学双石英晶体阻抗分析新方法

电化学石英晶体微天平已被广泛应用于电分析化学与电化学领域[1] .电化学现场的石英晶体阻抗分析法能动态实时地提供电化学扰动下石英晶体谐振的多维信息 ,已用于研究电沉积与溶出[2 ,3] 、高聚物性质[4～ 6 ] 、耗尽层内溶液粘密度效应与金电极腐蚀[7,8] 等 .然而 ,以往的石英晶体阻抗分析均只涉及到一个石英晶体 ,同时对两个晶体 (分别作为工作电极和对电极 )谐振的阻抗分析未见报道 .本文以蔗糖溶液粘密度效应和氨性介质中铜沉积 /溶出过程为例 ,研究电化学双石英晶体阻抗分析新方法 .1　实验部分电化学双石英晶体阻抗分析系统由 HP43 9…     

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.     

Impedance spectroscopy of oxide ceramics with overall composition of Bi<Subscript>4</Subscript>V<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>Me<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>11 − δ</Subscript>

The paper presents a generalization for some studies of conducting properties of ceramics based on solid solutions with the general composition of Bi₄V_{2 − x} Me _x O_{11 − δ} of the BIMEVOX family obtained using the impedance spectroscopy method. The regularities of the impedance spectra and typical complex plane plots are considered and the corresponding equivalent circuits are analyzed.     

Simultaneous Impedance Analysis of Three Parallel Piezoelectric Quartz Crystals for Electrochemical Depletion Layer Effect Study

Simultaneous impedance analysis of three one-face sealed resonating piezoelectric quartz crystals (PQCs) in parallel is proposed through admittance measurements of the three PQCs on one impedance analyzer and then non-linear fitting according to the parallel combination of three Butterworth-Van Dyke circuits. Responses of each PQC obtained from the three-PQC mode agreed well with those measured separately in series sucrose aqueous solutions. This novel method has been used for the study of depletion-layer effect during ferri-/ferrocyanide electrochemical reactions.     

Binary electrolyte small-signal frequency response

The frequency response is considered of a two-electrode linearized system containing a single positively charged species and a single negatively charged species. These species may have arbitrary valences and mobilities and may individually react at the electrodes. The results follow from a detailed solution of the equations of charge motion given earlier. Normalized response is exhibited for this unsupported, intrinsic-conduction situation for a wide range of mobility ratios, valence number ratios, and reaction rate ratios. Results are given in the form of specific formulas, impedance-plane plots, and the dependences on normalized frequency of series and parallel resistive and capacitative components of the normalized total impedance of the system.Impedance-plane plots exhibit from one to three connected arcs, depending on the specific situation. Approximate Warburg frequency response appears for the “interface” impedance over a certain frequency region when normalized reaction rate parameters differ, but it only shows up strongly in the total impedance when the mobility ratio departs appreciably from unity as well. Under such conditions, a plateau region, where the total parallel capacitance remains essentially independent of frequency over a wide frequency range, may appear at frequencies just above the Warburg region. The plateau capacitance is close to but not identical to the conventional double-layer capacitance present when both species of charge are completely blocked. In incomplete blocking cases, however, this double-layer capacitance only makes a significant appearance in the approximate equivalent circuit under slow reaction conditions; it is thus not present when one of the reaction rate constants is infinite.In general, the system can show ω^?m frequency response for the parallel capacitance over a wide frequency range with 0?m?2, and with the experimentally common regions where m≌0, 0.5, 1.5, and 2 especially likely. Particular attention is given to deviations from ideal Warburg behavior which led to a combined charge-transfer and heterogeneous chemical reaction resistance. Results are compared to those from conventional supported treatments and show both important similarities and differences. Finally, several new equivalent circuits are presented which are pertinent in various frequency ranges for the unsupported situation.     

Influence of nanoporous carbon electrode thickness on the electrochemical characteristics of a nanoporous carbon|tetraethylammonium tetrafluoroborate in acetonitrile solution interface

Electrochemical characteristics for the nanoporous carbon|Et₄NBF₄+acetonitrile interface have been studied by cyclic voltammetry and impedance spectroscopy methods. The influence of the electrolyte concentration and thickness of the nanoporous electrode material on the shape of the cyclic voltammetry and impedance curves has been established and the reasons for these phenomena are discussed. A value of zero charge potential, depending slightly on the structure and concentration of the electrolyte, the region of ideal polarizability and other characteristics have been established. The nanoporous nature of the carbon electrodes introduces a distribution of resistive and capacitive elements, giving rise to complicated electrochemical behaviour. Analysis of the complex plane plots shows that the nanoporous carbon|Et₄NBF₄+acetonitrile electrolyte interface can be simulated by an equivalent circuit, in which two parallel conduction paths in the solid and liquid phases are interconnected by the double-layer capacitance in parallel with the complex admittance of the hindered reaction of the charge transfer or of the partial charge transfer (i.e. adsorption stage limited) process. The values of the characteristic frequency depend on the electrolyte concentration and electrode potential, i.e. on the nature of the ions adsorbed at the surface of the nanoporous carbon electrode. The value of the solid state phase resistance established is independent of the thickness of the electrode material.     

A study of the electrical behaviour of isolated tomato cuticular membranes and cutin by impedance spectroscopy measurements

Different isolated tomato fruit cuticular membranes (ripe and green tomato cuticles and the cutin of these membranes) were studied by impedance spectroscopy measurements when the membranes were in contact with NaCl solutions at different concentrations. Remarkable differences in the impedance plots and the equivalent circuits associated to each membrane sample were obtained: the ripe tomato cuticle and the cutin, only present a relaxation process, but for the green tomato cuticle two relaxation processes were obtained. Using the equivalent circuits as models, electrical and electrochemical parameters for each membrane were determined. These results permit us to assign the relaxation processes to the different components of the tomato membrane (polyester matrix, carbohydrates and pigments), obtaining in this way a detailed picture of the different environments of the plant interface. Variation with NaCl concentration for the different electrical parameters was also studied, and the electrical resistance of the biopolymer matrix was obtained.     

熔盐热腐蚀的电化学交流阻抗谱研究

采用电化学阻抗谱技术研究了Ｎｉ３Ａｌ、ＩＮ１００和ＩＮ７３８合金在７００℃熔融（Ｎａ,Ｋ,Ｌｉ）２ＳＯ４中的腐蚀行为．结果表明,Ｎｉ３Ａｌ和ＩＮ１００合金的腐蚀呈典型的扩散控制特征,在合金表面形成疏松的腐蚀层;而ＩＮ７３８合金因在表面形成保护性的Ｃｒ２Ｏ３膜,腐蚀不受扩散控制．提出了等效电路并计算了相应的电化学参数．     

Electrochemical Impedance Spectroscopy of Oxide Layers on the Titanium Surface

The method of electrochemical impedance spectroscopy is used to study oxide layers formed at the titanium surface by a variety of methods. The sample’s polarization permitted the isolation, in an impedance spectrum, of the response caused by the capacitance of the space-charge region, which obeys the Mott-Schottky dependence. It is established that the high-frequency portion of an impedance spectrum is defined by morphological peculiarities of the porous portion of coatings. Assumptions, concerning the nature of a time constant, which reveals itself in the region of low frequencies at polarizing biases, are made. Equivalent circuits, intended for modeling impedance spectra, are proposed. The circuits take into consideration the effect of the space-charge region, as well as the peculiarities of the structure and morphology of the oxide film formed at the titanium surface.__________Translated from Elektrokhimiya, Vol. 41, No. 8, 2005, pp. 963–971.Original Russian Text Copyright © 2005 by Gnedenkov, Sinebryukhov.     

Simultaneous impedance measurements of two one-face sealed resonating piezoelectric quartz crystals for in situ monitoring of electrochemical processes and solution properties

Through admittance measurements of two piezoelectric quartz crystals in parallel on one impedance analyzer and then non-linear fitting according to an equivalent circuit of two parallel Butterworth-Van Dyke circuits, we have simultaneously obtained accurate and precise impedance responses of two one-face sealed crystals to changes in solution density and viscosity, temperature, conductance, and/or electrode mass. A series of sucrose aqueous solutions, ferri-/ferrocyanide redox switching, hot water cooling, a series of NaClO₄ aqueous solutions, bovine serum albumin adsorption and silver electrodeposition/stripping were selected as model systems for such purposes. Galvanostatic charging/discharging reactions at positive and negative poles in a Ni-Zn battery were synchronously monitored, with some quartz crystal microbalance (QCM) insights into the second reduction process of nickel hydroxide film. In all cases, the crystal immersion angle effect was found to be negligible. The present method as a versatile one is highly recommended for informative two-electrode monitoring of two concurrent chemical or biological events, or for check and/or compensation of effects due to solution density, viscosity, temperature and/or conductance during QCM researches.     

A systematic approach to the impedance of surface layers with mixed conductivity forming on electrodes

Electrode impedance can be evaluated on the basis of the electrode reaction kinetics in many systems, even for complicated electrode reactions. However, when a surface layer is present on the electrode surface, the theoretically well-established impedance model of the electrode reaction is often completed with phenomenological equivalent circuit elements in order to achieve the number of time constants as derived from the electrode impedance spectra measured. In these cases, the meaning of the phenomenological equivalent circuit elements are often unclear, though the presence of these elements is helpful to describe the system throughout the frequency domain used for the measurement. In the present work, an attempt will be shown to separate the effect of the electronic and ionic charge transfer in a surface layer and to identify the appropriate equivalent circuits. Examples are shown from the fields of lithium-ion batteries where a solid electrolyte interface as a surface layer is present at the negative electrode and the contribution of various charge carriers may be of importance.     

Relaxation spectra of the electrode impedance

A new analytical form is proposed enabling one to calculate the impedance of systems that contain no inductances. The method is based on breaking the overall impedance into a sum of isolated contours corresponding to a set of intrinsic frequencies of the system. Intrinsic frequencies, which exist in any real system, can be uniquely determined from the frequency characteristics. In this, they advantageously differ from speculative elements of equivalent circuits. For inductionless circuits, sets of intrinsic frequencies are replaced by intrinsic sets of reciprocal relaxation times. This allows one to construct a relaxation spectrum for the system, which describes quantitative contributions made by each relaxation contour to the overall impedance. As a result, one can estimate quantitatively conditions under which the system’s individual parameters may be observed, evaluate the resolving power of the experimental setup, and determine the full information capacity of an experiment (the maximum number of system’s parameters that can be determined).     

EIS study on passive films of AISI 304 stainless steel in oxygenous sulfuric acid solution

Electrochemical impedance spectroscopy (EIS) and Kramers–Kronig (K–K) transforms were made on American Iron and Steel Institute (AISI) 304 stainless steel (SS) in naturally aerated sulfuric acid solution at room temperature. The K–K relations testify that the systems under investigation comply with the linearity, causality, and stability constraints of linear system theory (LST) and thereby validate the EIS data. The polarization resistance decreased with removing of passive film and pitting formed in the passive layer, due to layer thinning or pitting caused by chloride. The impedance data for 304 SS with passive films can be accurately modeled using individual components of the equivalent circuits. The polarization resistances (Rp) of the 304 SS can be confirmed by Nyquist plots and estimated from the anodic polarization curves. The reaction model of the dissolution‐passivation process of 304 SS in acid solution is proposed. Copyright © 2009 John Wiley & Sons, Ltd.     

Distinguishability of equivalent circuits containing CPEs: Part I. Theoretical part

Constant phase elements (CPEs) with impedance Z_CPE=1/(Qs^α_f) are widely used to explain electrochemical impedance spectroscopy (EIS) data. It has long been known that different circuits can explain EIS data in an equivalent manner because they exhibit identical impedance for all frequencies (two-terminal non-distinguishable (TTND) circuit). Equivalent circuits containing two CPEs are considered here. TTND circuits containing two CPEs become distinguishable, at least theoretically, if the CPE exponents are different. The experimental distinguishability of these circuits is discussed. The 12 transformation formulae between the four circuits containing two CPEs and two resistors are given for CPEs with equal exponents.     

Universal equivalent circuit of electrochemical cell

A detailed analysis of the mathematical model of a random-structure RC two-terminal network is performed. It is shown that a circuit of any RC two-terminal network can be reduced to a universal form consisting of a set of parallel branches. Each branch corresponds to a single relaxation process and represents a circuit of serially connected resistance and capacitor. The equivalent circuit under consideration is a compact representation of experimental data obtained using the impedance spectroscopy method. It is recommended to use the universal circuit as an intermediate model of an electrochemical cell.     

A new floating electrode structure for generating homogeneous electrical fields in microfluidic channels

In this article a new parallel electrode structure in a microfluidic channel is described that makes use of a floating electrode to get a homogeneous electrical field. Compared to existing parallel electrode structures, the new structure has an easier production process and there is no need for an electrical connection to both sides of the microfluidic chip. With the new chip design, polystyrene beads suspended in background electrolyte have been detected using electrical impedance measurements. The results of electrical impedance changes caused by beads passing the electrodes are compared with results in a similar planar electrode configuration. It is shown that in the new configuration the coefficient of variation of the impedance changes is lower compared to the planar configuration (0.39 versus 0.56) and less dependent on the position of the beads passage in the channel as a result of the homogeneous electrical field. To our knowledge this is the first time that a floating electrode is used for the realization of a parallel electrode structure. The proposed production method for parallel electrodes in microfluidic channels can easily be applied to other applications.     

Hydrogen Evolution on Catalytically Active Electrodeposited Ni–Re Alloy: Electrochemical Impedance Study

Hydrogen evolution reaction on the catalytically active Ni–Re alloy is studied by the method of electrochemical impedance. The alloy was fabricated by the electrodeposition from the ammonium—citrate solutions. The experiments were performed in the 0.1 M sodium hydroxide solution. Based on the analysis of equivalent circuits, it is found that the absorption of hydrogen atoms on the Ni–Re cathode is controlled by diffusion. The parameters of structural elements of equivalent electric circuits are calculated, and the effect of cathodic overpotential on these parameters is analyzed.     

Electrochemical impedance spectroscopic studies of copper dissolution in glycine–hydrogen peroxide solutions

Anodic dissolution of copper in glycine solution at various hydrogen peroxide concentrations was investigated. The dissolution rate increases, reaches a maximum, and then decreases with hydrogen peroxide concentration. Anodic polarization studies and electrochemical impedance spectroscopy (EIS) studies were carried out to determine the mechanistic pathway of anodic dissolution of copper in glycine system at three different hydrogen peroxide concentrations: one at low hydrogen peroxide concentration in the active dissolution region, another in the maximum dissolution region, and the third at the high hydrogen peroxide concentration in the post-peak-dissolution region. The EIS data in complex plane plots show presence of two capacitance loops and one negative capacitance loop. The impedance plot patterns strongly depend on the hydrogen peroxide concentration in solution. Reaction mechanism analysis technique was employed to model the EIS data. A three-step mechanism with two intermediate adsorbates and a parallel dissolution by catalytic mechanism simulates EIS patterns which match the experimental trends. The intermediates are likely to be cupric and cuprous oxides. The essential features of impedance spectra at various overpotentials at three different hydrogen peroxide concentrations are captured by the proposed mechanism. The results also show that the film present on the copper surface in glycine and hydrogen peroxide solutions does not passivate the surface.     

Impedance of solid electrolyte systems

The main regularities of studying electrode processes in the systems with solid electrolytes are described using the method of electrochemical impedance with the relationships of Ershler-Randles and Frumkin-Melik-Gaykazyan and analysis of results based on equivalent electric circuits.