An integrated approach to electrochemical impedance spectroscopy

A philosophy for electrochemical impedance spectroscopy is presented which integrates experimental observation, model development, and error analysis. This approach is differentiated from the usual sequential model development for given impedance spectra by its emphasis on obtaining supporting observations to guide model selection, use of error analysis to guide regression strategies and experimental design, and use of models to guide selection of new experiments. These concepts are illustrated with two examples taken from the literature. This work illustrates that selection of models, even those based on physical principles, requires both error analysis and additional experimental verification.     

An analysis of drifts and nonlinearities in electrochemical impedance spectra

The response of an electrochemical reacting system to potential perturbations during electrochemical impedance spectrum measurement is investigated using numerical simulation. Electrochemical metal dissolution via an adsorbed intermediate species is analyzed and it is shown that applying the potential perturbation causes the average surface coverage to drift. For high frequency perturbations, the final value of the average surface coverage depends mainly on the kinetic parameters and the amplitude of the applied perturbation. Acquiring the data during the first few cycles of perturbations leads to an incorrect calculation of the impedance, particularly for large amplitude perturbations. Repeating the experiments will not identify this drift, while Kramers–Kronig Transform (KKT) can successfully detect this problem. The correct experimental methodology to overcome this effect and obtain the impedance spectra is also described. Another reaction with two adsorbed intermediates is also investigated and it is shown that in certain cases, the violations of linearity criteria can also be detected by KKT. The results illustrate the importance of validating the impedance data with KKT before further analysis.     

Fourier analysis of complex impedance (amplitude and phase) in nonlinear systems: A case study of diodes

The general framework of Fourier analysis of complex impedance including both the amplitude and phase information is presented. For the single frequency sine/cosine input, Fast Fourier Transform can be used to obtain the amplitude and phase of the harmonics in the output signal. Complex nonlinear least squares fitting can then be applied to correlate the experimental and calculated results as in conventional impedance spectroscopy. General purpose p-n junction diodes were used as model systems to test the method as well as to compare it to other means of analysis.     

Electrochemical impedance spectroscopy for in situ petroleum analysis and water-in-oil emulsion characterization

The measurement of electrochemical impedance spectroscopy used in situ is a suitable technique for the characterization of oil and water-in-oil emulsions. Nyquist diagrams for dehydrated oils are characterized by the formation of one semi-circle. The equivalent circuit proposed for the dehydrated oil is a resistance and capacitor (R_OC_O) in parallel. The resistance and conductivity of the oil calculated by impedance were 2.96 Gohm and 486 nS m^?1, respectively. Nyquist diagrams for the system composed of water emulsions in oil are mainly characterized by two semi-circles with different relaxation for oil and water-in-oil emulsions. The equivalent circuit is formed by R_O and CPE_O in parallel and in series with the arrangement of R_W/O and CPE_W/O in parallel, where R_O and CPE_O represents the oil, and R_W/O and CPE_W/O represents water-in-oil emulsions. The resistance of oil (R_O) and water-in-oil (R_W/O) emulsions increase with the increasing amount of water in the preparation. The increase in resistance shows that the emulsions become more stable with the addition of water. This result is consistent with the formation of rigid films on water–oil interfaces. The impedance measurements were applied to the analysis of the demulsification of the water-in-oil emulsions under an electrostatic field.     

变频器谐波危害分析及解决措施

从谐波的概念入手,结合变频器内部结构的相关知识,分析变频器谐波产生的原因及其危害,在此基础上提出了抑制谐波的常用方法。     

Indirect identification of Hads relaxation on different metals by electrochemical impedance spectroscopy

For the hydrogen evolution reaction, the coverage rate of the electrode surface by adsorbed hydrogen is generally difficult to evidence especially in presence of bubbles. In the present paper, a parallel competing reaction was incorporated to the interface by the addition of ferricyanide to a NaOH solution. This reaction was supposed to take place on the free electrode surface and allowed the relaxation of adsorbed hydrogen to be identified. Models taking into account hydrogen evolution, hydrogen absorption, and ferricyanide reduction were proposed. Three metals were tested: platinum, iron, and palladium, which absorb hydrogen in very different quantities. In these conditions, low frequency loops related to the H_ads surface coverage appeared in the electrochemical impedance diagrams, whose properties depend on the tested metal. Very good agreement was found between the experimental data and model predictions.     

Influence of dc electric current on the electrochemical impedance of ion-exchange membrane systems

The influence of dc electric current on the electrochemical impedance and the linearity of the current–voltage relationship in ion-exchange membrane systems, has been investigated. The system under study is constituted by a membrane with negative fixed-charge and two diffusion boundary layers on both sides of the membrane, ionic transport being described by the Nernst–Planck and Poisson equations. The electrochemical impedance and a decomposition into Fourier components of the potential–time response of the system to a sine electric current superimposed on a dc electric current, have been obtained by using the network simulation method. Some of the results obtained for the electrochemical impedance are compared with the corresponding analytical expressions for ideal membranes. The great influence that the dc component of the electric current exerts on the linearity of the current–voltage relationship of an ion-exchange membrane system, is also shown.     

曲线剥离分峰法的改进与混煤比的准确计算

通过改进峰参数初值确定方法,解决了曲线剥离分峰法应用中遇到的有关问题。补充限制条件后,解决了剥离出的少数单煤峰分布曲线过宽问题。分析了混煤比计算的误差来源与范围。引入镜质组含量校正后,能够准确计算混煤比。     

供电系统的无功补偿与谐波治理

在谐波负载下用电容器进行无功补偿时，谐波电流会严重放大，甚至引起谐振。分析了电容器无功补偿装置中的谐波问题，介绍了能同时实现无功补偿和谐波治理的装置的工作原理。     

Improved system identification method for Hammerstein-Wiener processes

We propose a new system identification method for Hammerstein-Wiener processes, in which an input static nonlinear block, a linear dynamic block, and an output static nonlinear block are connected in a series. The proposed method can estimate the model parameters in a very simple way without solving the full-dimensional nonlinear optimization problem by activating the process with a specially designed test signal, composed of a relay feedback signal, a binary signal and a multi-step signal. The proposed method analytically identifies the output nonlinear static function and the input nonlinear static function from the relay signal and the multi-step signal, respectively. The linear dynamic subsystem is identified from the relay feedback signal and the binary signal with existing well-established linear system identification methods. We demonstrate with a simple example that the proposed method can be successfully applied to identify the Hammerstein-Wiener-type nonlinear process.     

Finite element modeling of resistive surface layers by micro-contact impedance spectroscopy

Micro-contact impedance spectroscopy (MCIS) is potentially a powerful tool for the exploration of resistive surface layers on top of a conductive bulk or substrate material. MCIS employs micro-contacts in contrast to conventional IS where macroscopic electrodes are used. To extract the conductivity of each region accurately using MCIS requires the data to be corrected for geometry. Using finite element modeling on a system where the resistivity of the surface layer is at least a factor of ten greater than the bulk/substrate, we show how current flows through the two layers using two typical micro-contact configurations. This allows us to establish if and what is the most accurate and reliable method for extracting conductivity values for both regions. For a top circular micro-contact and a full bottom counter electrode, the surface layer conductivity (σ_s) can be accurately extracted using a spreading resistance equation if the thickness is ~10 times the micro-contact radius; however, bulk conductivity (σ_b) values can not be accurately determined. If the contact radius is 10 times the thickness of the resistive surface, a geometrical factor using the micro-contact area provides accurate σ_s values. In this case, a spreading resistance equation also provides a good approximation for σ_b. For two top circular micro-contacts on thin resistive surface layers, the MCIS response from the surface layer is independent of the contact separation; however, the bulk response is dependent on the contact separation and at small separations contact interference occurs. As a consequence, there is not a single ideal experimental setup that works; to obtain accurate σ_s and σ_b values the micro-contact radius, surface layer thickness and the contact separation must all be considered together. Here we provide scenarios where accurate σ_s and σ_b values can be obtained that highlight the importance of experimental design and where appropriate equations can be employed for thin and thick resistive surface layers.     

Study of the electrochemical impedance and the linearity of the current-voltage relationship in inhomogeneous ion-exchange membranes

The electrochemical impedance and the linearity of the current-voltage relationship in inhomogeneous ion-exchange membrane systems, have been investigated. The system under study is constituted by a membrane with negative fixed charge varying linearly with position inside the membrane and two diffusion boundary layers on both sides of the membrane, ionic transport being described by the Nernst-Planck and Poisson equations. The electrochemical impedance and a decomposition into Fourier components of the current-time response of the system to a sine electric potential, have been obtained by using the network simulation method. The influence of the degree of inhomogeneity of a membrane on the electrochemical impedance and the linearity of the current-voltage relationship of ion-exchange membrane systems, is analyzed and discussed.     

Weighted Estimation of Harmonic Components in a Musical Sound Signal

The study of musical sound has become a popular research field. Harmonic regression signal plus noise statistical models have been used to analyze sound signals. However, it is common to give estimates of harmonic parameters without indications of their uncertainties. Least squares estimates for harmonic models have been studied and asymptotic variance expression have been developed. In practice, window-based estimates are used. This paper studies the statistical properties of such estimates; in particular, we use asymptotic variance expressions to develop standard errors and construct confidence intervals. We present applications and examples of the statistical techniques to musical sound signal analysis.     

振动台有限元动力学分析

为了得到某成型模振动台在未知频率下的生产应用最佳振幅,利用有限元方法对其进行模态和谐响应分析,得到振动台的前十二阶振型与确定了振动台随正载荷激励下的稳定响应。对计算结果进行分析得到了在一个频率的左右小范围内的到了振动台的最佳振幅,某为类似振动台设计与改进提供了理论依据。     

PEM fuel cells as membrane reactors: kinetic analysis by impedance spectroscopy

Proton exchange membrane fuel cells (PEMFC) are considered as electrochemical reactors, performances of which are regarded in the context of the various effects influencing FC output, such as mass transports, kinetic of electrode reactions and charge transfer in polymer electrolyte membrane (PEM). An experimental approach, involving the employment of impedance spectroscopy (IS), which allows a deep insight into the nature of these effects, is discussed and its applications to the different aspects of PEMFC functioning are reported. As examples of the use of IS in PEMFC studies, the investigations of the membrane conductivity and in situ studies of the anode and the cathode processes during FC operation are presented.     

Identification of inductive behavior for polyaniline via electrochemical impedance spectroscopy

Polyaniline (PANI) film electrodeposited in HCl medium using cyclic voltammetry (CV) with an upper potential limit of 0.90 V, exhibited an inductive behavior. PANI films deposited with different conditions were subjected to various applied potentials and the impedance characteristics were recorded through electrochemical impedance spectroscopy (EIS). The impedance results clearly reveal the existence of inductive behavior to PANI. Inductive behavior was observed for PANI films deposited with conditions which favor benzoquinone/hydroquinone (BQ/HQ) formation and further evidenced by X-ray photoelectron spectroscopy (XPS). A comparative analysis of the EIS and XPS results of PANI films prepared under similar conditions with the upper potential limits of 0.75 and 0.90 V, respectively, clearly documented that the presence of BQ/HQ, the degradation product of PANI, formed during the electrochemical polymerization at the upper potential limits causes inductive behavior to PANI.     

大型化工电解整流装置谐波分析

叙述了整流装置电流波形畸变的原因,介绍了公用电网谐波标准,谐波计算方法,以某大型化工电解装置谐波计算为例,说明大型整流装置在单台整流变压器组成等效12脉波整流时11次、13次谐波电流有效值超标,23次、25次谐波电流有效值没有超标,故提出若要满足国家标准要求谐波电流不超标,理论上需要24脉波整流。     

Instantaneous electrochemical impedance spectroscopy of electrode reactions

Continuous STFT transforms of a sinusoidal perturbation signal and current have been found for the first order electrode reaction. Electrode impedance has been determined in the joint time-frequency domain. Measurements of the Cd(II) reduction reaction have been performed on a dropping mercury electrode as a function of time. A possibility of instantaneous impedance spectra generation has been presented. Time characteristics of charge transfer resistance, Warburg coefficient and double layer capacitance has been described.     

Mechanism and equivalent circuits in electrochemical impedance spectroscopy

The utility and limitations of using equivalent circuits to analyse electrochemical impedance spectroscopy (EIS) data for electrochemical reaction mechanisms are reviewed. The difficulty of assigning physical meaning to elements is discussed. The utility of equivalent circuits as measurement models is emphasized, and ways to use them to find mechanistic information are discussed. The rules about which mechanisms can show inductive behavior are of interest, since this is a visually obvious feature. We review our previous rules for mechanisms that can show inductive behavior, and show that inductive behavior is more common for mechanisms with two adsorbed species. We discuss two variations of a simple cycle mechanism (A → B → C → A) in more detail.The interpretation of the charge-transfer resistance and the polarization resistance has some subtleties. Transfer coefficients extracted from Tafel plots of steady-state current–potential measurments are often used to determine where in the mechanism the rate-determining step is. We show that transfer coefficients from Tafel plots of the charge-transfer resistance do not have the same mechanistic significance. The polarization resistance is simply related to the slope of the polarization curve. We discuss the validity of this relationship and its utility in interpreting spectra.     

Resistometry and impedance spectroscopy for characterization of powders used in SHS reactions

Presented are some examples of successful application of dc resistometry and impedance spectroscopy to characterization of micro and nano powders commonly used in SHS technology.