Electrochemical Impedance Spectroscopy System Research Articles

An electrochemical impedance spectroscopy study on ion-fouling of forward osmosis membranes

Forward osmosis (FO) has been rapidly developed and employed in the industrial and environmental wastewater treatment, whose performance is affected profoundly by membrane fouling. Electrochemical impedance spectroscopy (EIS), as a nondestructive and low-cost evaluation technique, has been increasingly used for the characterization of membrane structures and membrane fouling. However, monitoring ion fouling of FO membranes is difficult with EIS due to the weak signal. In this work, the ion-fouling of various FO membranes was successfully characterized by EIS and the inductance variation was firstly utilized to interpret the degree of FO membrane fouling. Multi-walled carbon nanotubes (MWCNTs) and polydopamine (PDA) were modified onto the thin film nanofibrous composite membrane (#FO-0) as anti-fouling modification (#FO-MWCNTs and #FO-PDA), respectively. The structural measurements of #FO-0, #FO-MWCNTs, and #FO-PDA were achieved by a two-electrode EIS system. Then the ion fouling of FO membranes was monitored by a four-electrode EIS system. Through the equivalent circuit fitting, the correlation between the inductance variation and the membrane fouling was established. The FO experiments further validated the effectiveness of the proposed EIS method. The results indicate that inductance as a detection index is expected to be a convenient tool for studying the ion-fouling phenomenon in the FO process.

An EV-Scale Demonstration of In-Situ Battery Electrochemical Impedance Spectroscopy and BMS-Limited Pack Performance Analysis

State-of-Power (SOP) and State-of-Charge (SOC) estimation inaccuracy manifests throughout the EV battery lifetime due to the non-linear degradation trajectory that is unique to each use-case. The inaccuracy leads to premature termination of charge and discharge operations, which results in the virtual loss of battery performance. In-situ Electrochemical Impedance Spectroscopy (EIS) has been proposed to provide real-time battery impedance measurements, which can theoretically improve the SOP/SOC estimation accuracy. In this work, an EV-scale in-situ EIS system is demonstrated experimentally, from impedance measurement to Equivalent Circuit Model (ECM) extraction. The pack-level discharge energy versus SOP/SOC estimation errors is also simulated, which quantifies the virtual loss of battery performance. The measured-impedance error tolerance of three common ECM extraction techniques is then examined through a randomised set of simulated EIS tests with injected measurement noise. Finally, in-situ impedance measurement is performed on 20 battery sub-modules using an electric pickup truck EIS system. The ECM-predicted voltage output is compared against measured driving data. Experimental results indicate approximately 8-9% improvement in SOP estimation accuracy at 3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> C and 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> C between the in-situ extracted models and a representative baseline.

Analysis of Electrochemical Impedance Data: Use of Deep Neural Networks

Technology advancements in energy storage, photocatalysis, and sensors have generated enormous impedimetric data. Electrochemical impedance spectroscopy (EIS) results play an essential role in analyzing the interfacial properties of materials. Nonetheless, in many situations, the data is misinterpreted due to the complexity of the electrochemical system or the compromise between the experimental result and the theoretical model, resulting in partiality in the interpretation process, especially for the impedimetric results. Typically, the experimenter interprets impedimetric results using a searching approach based on a theoretical model until the best‐fitting model is obtained, which is a time‐consuming process, and errors can occur. To reduce misinterpretation by the experimenter, herein, the machine‐learning strategy is demonstrated for the classification of an EIS circuit model and parameter prediction using a deep neural network (DNN). The DNN model shows a highly accurate classifier for the commonly used EIS circuit with an average area under the receiver operating characteristic curve of more than 0.95. Additionally, the model demonstrates high accuracy in the prediction of EIS parameters on a complex EIS system, with a maximum R2 of 0.999. These reveal that the machine‐learning strategy may open a new room for studying electrochemical systems.

Biosensor for Multimodal Characterization of an Essential ABC Transporter for Next-Generation Antibiotic Research.

As the threat of antibiotic resistance increases, there is a particular focus on developing antimicrobials against pathogenic bacteria whose multidrug resistance is especially entrenched and concerning. One such target for novel antimicrobials is the ATP-binding cassette (ABC) transporter MsbA that is present in the plasma membrane of Gram-negative pathogenic bacteria where it is fundamental to the survival of these bacteria. Supported lipid bilayers (SLBs) are useful in monitoring membrane protein structure and function since they can be integrated with a variety of optical, biochemical, and electrochemical techniques. Here, we form SLBs containing Escherichia coli MsbA and use atomic force microscopy (AFM) and structured illumination microscopy (SIM) as high-resolution microscopy techniques to study the integrity of the SLBs and incorporated MsbA proteins. We then integrate these SLBs on microelectrode arrays (MEA) based on the conducting polymer poly(3,4-ethylenedioxy-thiophene) poly(styrene sulfonate) (PEDOT:PSS) using electrochemical impedance spectroscopy (EIS) to monitor ion flow through MsbA proteins in response to ATP hydrolysis. These EIS measurements can be correlated with the biochemical detection of MsbA-ATPase activity. To show the potential of this SLB approach, we observe not only the activity of wild-type MsbA but also the activity of two previously characterized mutants along with quinoline-based MsbA inhibitor G907 to show that EIS systems can detect changes in ABC transporter activity. Our work combines a multitude of techniques to thoroughly investigate MsbA in lipid bilayers as well as the effects of potential inhibitors of this protein. We envisage that this platform will facilitate the development of next-generation antimicrobials that inhibit MsbA or other essential membrane transporters in microorganisms.

A 380-μW Electrochemical Impedance Measurement System for Protein Sensing

Diagnostic testing plays an important role in modern medicine, helping physicians make informed decisions regarding disease diagnosis and treatment. Proteins’ biomarkers are utilized to detect disease onset, progression, efficacy of medicines, and patient susceptibility to get a specific kind of disease. Electrochemical impedance spectroscopy (EIS) is likely to underpin the progressive drive toward sensitive, miniaturized, and portable biomarker detection practices. The EIS is a highly sensitive detection method adopted to find the electrical response of chemical samples by applying low amplitude ac voltages/currents with tunable frequency. Conventional EIS systems use mixers and lock-in amplifiers to find both the real and imaginary components of the complex impedance. In this article, we present a partially integrated EIS measurement system to find the impedance of a biological sample. It includes a programmable sine-wave synthesizer (SWS) block with a frequency range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$500 \mu $ </tex-math></inline-formula> Hz to 100 kHz. The implementation is based on switched-capacitor filters that adjust the cutoff frequency by changing the clock. The sample impedance is measured through mostly digital magnitude and phase-detection blocks. The proposed EIS system is realized using a 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> technology with a 0.35-mm2 active area and 380- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> power consumption. The proposed magnitude detection archives a differential nonlinearity (DNL) performance of −0.34/+0.3 LSB and an integral nonlinearity (INL) of −0.75/+2 LSB. The system is used to measure the impedance of biological samples containing tumor necrosis factor alpha (TNF- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha$ </tex-math></inline-formula> ) protein at variable concentrations.

Multichannel Electrochemical Impedance Spectroscopy and Equivalentcircuit Synthesis of a Kw-Scale Vanadium Redox Flow Battery

An original multichannel Electrochemical Impedance Spectroscopy (EIS) system operating at high bias current and suitable for kW-class Vanadium Redox Flow Batteries (VRFBs) is presented. Power and signal connections, whose stray parameters affected measurements, required a careful optimization and calibration in the implementation of the measurement chain. In any cases, electromagnetic interferences set an upper limit to the applied stimulus frequency that limited the set of measurement data at each bias point. The work provides early results obtained with this EIS system, which were used to identify an equivalent circuit of the whole stack in which each cell is represented with a dynamic Thévenin equivalent, i.e. the series of a voltage source, a variable resistor and a variable RC loop. The dependence of the equivalent parameters on the operating conditions has been experimentally analyzed, confirming that only the RC-loop resistance is strongly affected by mass transport. In addition, more complex equivalent circuits have been proposed, i.e. a Randles cell modified with CPE, a Randles cell modified with CPE and Warburg element and a two-loop model of ZARC elements. The inclusion of the constant phase element constitutes a substantial improvement in the fit, Fig. 1. Conversely, the addition of the Warburg element, which aims to model the mass transfer in the electrochemical process, does not produce significant effects for the frequencies at which we have experimental data. To our knowledge, this is the first dynamic equivalent circuit of a whole stack that has been validated against EIS measurements taken on a real industrial-scale VRFB. Building on the measurement methodology here presented, advanced online state of health of industrial flow batteries can be developed and implemented.

Analysis of High-Throughput Electrochemical Impedance Spectroscopy via Hierarchical Bayesian Models

Electrochemical impedance spectroscopy (EIS) is a powerful characterization technique that enables in-situ investigation of electrochemical processes over a wide range of timescales, making it particularly effective in analysis of electrochemical energy conversion devices such as fuel cells and batteries. The advent of automated high-throughput EIS systems presents an exciting opportunity for materials discovery, rapidly providing detailed information about candidate materials. However, the utility of EIS as an electrochemical method is paralleled by the complexity of interpreting the resulting data: overlapping features, noise, and measurement artifacts make EIS spectra notoriously difficult to analyze. Equivalent circuit models (ECMs) are widely used to deconvolute EIS data, but there is significant ambiguity in model selection; meanwhile, the distribution of relaxation times (DRT) has become increasingly popular as an alternative/complementary deconvolution method, but faces similar uncertainty in the choice of regularization parameters. The sheer volume of data produced by high-throughput methods amplifies these challenges, necessitating automated, self-consistent analysis procedures.Here, we discuss high-throughput EIS characterization of protonic ceramic electrode thin films and demonstrate the application of hierarchical Bayesian models for robust analysis of the data. The calibrated hierarchical Bayesian DRT resolves much of the ambiguity in regularization parameters by encoding desired properties of the DRT in prior distributions [1]. Meanwhile, the versatility of the DRT enables appropriate deconvolution of thousands of spectra without predetermined model selection. The DRT may be translated to an ECM for further quantitative analysis of individual relaxation timescales and magnitudes by leveraging a flexible semi-empirical model. In addition, advanced Bayesian DRT models can be implemented to address outliers, sample drift, and multi-spectrum deconvolution. These tools enable conversion of raw spectra to a dataset amenable to further interpretation via machine learning and other methods, thereby expanding opportunities to distill meaningful insight from high-throughput electrochemical studies.

A Novel On-Board Electrochemical Impedance Spectroscopy System for Real-Time Battery Impedance Estimation

This article proposes a real-time electrochemical impedance spectroscopy (EIS) technique that can provide high accurate estimation of the impedance of each lithium-ion (Li-ion) cell of a battery (BT) stack, even for less than mΩ. Thus, the suggested EIS technique can be used in high demanding applications, such as nearly zero-energy buildings, microgrids, and electric vehicles. This is attained because a smooth cell excitation current is utilized that is provided by the proper control of the gate-source of each cell's parallel-connected MOSFET and thus, effective harmonic analysis can be accomplished. Since the circuit topology of the EIS is implemented without requiring expensive electronic equipment, it is affordable to be applied in the BT system of any application. The proposed EIS system can cooperate with a BT cell equalization (BCE) system that utilizes the same MOSFET control scheme to provide the excitation current. Thus, a combined EIS-BCE system is developed that can be used to improve the performance of a Li-ion BT management system. The accuracy of the EIS technique and its high performance by operating within a combined EIS-BCE system are experimentally validated.

Multichannel Electrochemical Impedance Spectroscopy and equivalent circuit synthesis of a large-scale vanadium redox flow battery

An original multichannel Electrochemical Impedance Spectroscopy (EIS) system operating at high bias current and suitable for kW-class Vanadium Redox Flow Batteries (VRFBs) is presented. Power and signal connections, whose stray parameters affected measurements, required a careful optimization and calibration in the implementation of the measurement chain. In any cases, electromagnetic interferences set an upper limit to the applied stimulus frequency that limited the set of measurement data at each bias point. The paper provides early results obtained with this EIS system, which were used to identify an equivalent circuit of the whole stack in which each cell is represented with a dynamic Thévenin equivalent, i.e. the series of a voltage source, a variable resistor and a variable RC loop. The dependence of the equivalent parameters on the operating conditions has been experimentally analyzed, confirming that only the RC-loop resistance is strongly affected by mass transport. To our knowledge, this is the first dynamic equivalent circuit of a whole stack that has been validated against EIS measurements taken on a real industrial-scale VRFB. Building on the measurement methodology here presented, advanced online state of health of industrial flow batteries can be developed and implemented.

Electrochemical Impedance Spectroscopy System Based on a Teensy Board

This article describes a portable low-cost device for performing electrochemical impedance spectroscopy (EIS) measurements, which is based on an off-the-shelf TeensyDuino. The instrument does not make use of other components, such as operational amplifiers, so it can be readily set up by anyone having a Teensy device and some resistors. Teensy 3.2, Teensy 3.5, and Teensy 3.6 can be used to realize the EIS system. The instrument can measure the impedance in the frequency range from 0.01 to 50 000 Hz, and by selecting the shunt resistor, it can be adapted to different impedance values. No special instrumentation is required for the system calibration. The proposed system uncertainty is less than 5% for an impedance of up to $50 {~\mathrm {k\Omega }}$ , a value which is lower than the usual intrinsic uncertainty of most corrosion experiments.

Pairing electrochemical impedance spectroscopy with conducting membranes for the in situ characterization of membrane fouling

Protein fouling within a polymeric microfiltration membrane was characterized in situ and in real time with non-Faradaic electrochemical impedance spectroscopy (EIS). The polymeric membrane was prepared with a conductive gold coating, allowing the membrane surface to serve as a working electrode in a three-electrode EIS system. Utilizing the membrane surface as the working electrode allowed for differentiation between internal and external contributions to fouling. Protein fouling was able to be monitored qualitatively by observing changes in the resulting Bode and Nyquist plots and quantitatively by modeling the electrochemical system with equivalent circuit components comprised of resistive and capacitive elements. To our knowledge, this work represents the first attempt to deploy a conductive polymeric membrane as an active electrode in an EIS setup.

Electrochemical Impedance Spectroscopic Detection of E.coli with Machine Learning

Electrochemical impedance spectroscopy (EIS) is a common method in biosensing detection of pathogens for public health and safety. In its most general form, increases of charge transfer resistance or decrease of double layer capacitance at the interface are used for reporting EIS system changes due to pathogens. However, this strategy is not universally adaptable to various EIS sensors and could lead to inaccurate detection. Herein, we demonstrated a machine learning-based EIS biosensor for E.coli detection with improved accuracy. EIS data was obtained from gold electrodes immobilized with E.coli through antibody binding and fitted with the Randles model to extrapolate multiple impedimetric parameters. A machine learning model, using principle component analysis and support vector regression, was trained to automatically establish a quantitative relationship between multiple impedimetric parameters and bacterial concentrations. Results showed an improved accuracy in determining bacterial concentration. The improvement is due to the integration of both capacitance and resistance information. These results thus pave the way for automatic and accurate EIS biosensors in various applications.

Mineral oil moisture measurement with the use of impedance spectroscopy

In this study, an attempt was made to evaluate very small water content (below 0.05% in volume) in the ‘20–30’ mineral oil using both electrochemical impedance spectroscopy (EIS) and dielectric constant calculation based on the measured impedance values. Measurements were performed with the use of laboratory EIS system and were designed to verify experimentally that it is possible to develop an IS-based measuring system that would be able to work in situ, be relatively cheap and fast alternative compared with systems widely used nowadays. Known amounts of water were added to the oil samples, which were not treated by any other factors, e.g. solvents, contrary to other researchers’ findings. Impedance of the samples was measured in the frequency range of 0.01–100 Hz. Equivalent circuit was proposed and used to reveal how electric properties of the oil change due to water addition. Both calibration curves based on the value of an equivalent circuit element and dielectric constant showed linear correlation of their values with the water amount. Thus, experimental results confirm that with some discussed limitations, EIS and dielectric constant calculation can be used to estimate even such small quantities of water in mineral oil.

Development of a Portable Electrochemical Impedance Spectroscopy System for Bio-Detection

A portable electrochemical impedance spectroscopy (EIS) system has been developed based on FPGA for bio-detection. FPGA is a programmable signal processing chip, which cooperates with DAC module to generate the sweep excitation signal, controls ADC module to perform dual channel acquisition of voltage of a peripheral circuit, performs FFT and parameter calculation and transmits the result to PC for data processing. Based on FPGA internal programming, the system greatly reduces the size and achieves a single multi-frequency measurement, which enhances integration and portability of the system. The measurements of the electrical equivalent circuit by using the EIS system is compared with a high-precision commercial ZX70A impedance analyzer in the range of limited frequency of 100 Hz – 500 kHz. The result shows that the maximum relative error of amplitude and the maximum absolute error of phase are 2.42% and 0.936°, respectively. Finally, the EIS system is used to measure electrical impedance change during egg heating. The result shows that the impedance amplitude of egg decreases linearly with the increase of heating time and electrical characteristics of raw eggs and heated eggs are significantly different. These results verified that the developed EIS system achieve portable high-precision measurement of biological tissue.

A simple Arduino-based EIS system for in situ corrosion monitoring of metallic works of art

Metallic artifacts of archaeological and historical interest, exposed to outdoor environmental conditions, can be affected to a great extent by degradation, due to the presence of aggressive compounds in the surrounding environment. The development of suitable preventive conservation strategies for these important signs of our culture, requires their corrosion behaviour to be investigated in order to understand the electrochemical phenomena that occur on the metallic surface. This investigation can easily be performed in a laboratory by means of different chemico-physical techniques, which provide information on the composition, microstructure and morphology of the corrosion products, as well as by means of electrochemical measurements, which allow the corrosion resistance of the metal to be estimated. Unfortunately, these measurements are often invasive and require microsampling. Electrochemical Impedance Spectroscopy (EIS), thanks to the its high degree of sensitivity, and to the small perturbation applied to the corroding system, can be considered a useful non-destructive testing method to obtain valuable information on the conservation state of metallic works of art.This paper describes an innovative, portable, low-cost and user-friendly solution for EIS in situ measurements, based on the widely diffused Arduino board, and on specifically designed measuring probes. The proposed solution cannot provide the detailed knowledge of the corrosion mechanisms that occur on metallic surface, but it can be an extremely useful tool for conservators and art historians for the assessment and long-time monitoring of the stability of the artifacts.

In Situ Study of Buried Metal–Polymer Interfaces Exposed to an Aqueous Solution by an Integrated ATR-FTIR and Electrochemical Impedance Spectroscopy System

This study investigates the interfacial bonding variations of carboxylic polymers on Zn surfaces upon exposure to an aqueous solution by means of an integrated ATR-FTIR and electrochemical impedance spectroscopy (EIS) analysis in Kretschmann geometry. In situ ATR-FTIR probes water molecules reaching Zn surfaces and subsequent interfacial bonding degradation at the hidden polymer–metal interfaces. Furthermore, EIS characterizes the polymer film capacitance and resistance determining the exposed polymer bulk and metal–polymer interfacial changes. Consequently, the integrated ATR-FTIR and EIS system is used to resolve the processes of polymer saturation with water and interfacial bonding degradation complementarily and simultaneously. Additionally, two types of carboxylic polymers, i.e., a polyester and a cured unsaturated polyester, are applied on a set of differently pretreated Zn samples to evaluate the effects of the curing process and surface pretreatments on water transport within the polymer structure and subsequent interfacial bonding degradation. Furthermore, Zn surface hydroxyl fractions are calculated by means of X-ray photoelectron spectroscopy (XPS) and correlated to the interfacial bonding degradation process. The results show that the hydroxyl fraction is a determining factor in accomplishing proper initial and durable interfacial bonding. Additionally, the polymer curing process plays an important role in barrier performance against water.

Characterization of forward osmosis membranes by electrochemical impedance spectroscopy

Forward osmosis (FO) has a potential role in desalination and water reclamation. However, the efficiency of FO processes is significantly limited by internal concentration polarization (ICP), which is difficult to detect by conventional characterization methods. In this work, we aimed to apply electrochemical impedance spectroscopy (EIS) to FO systems, and to develop a methodology for interpreting the interplay between the membrane structure and the polarization phenomena. Three commercial FO membranes with different substrate structures were characterized by an EIS system that was modified to accommodate FO processes, and the impedance spectra were analyzed based on their equivalent circuits. In the static tests (without osmosis), the limit behaviors of the impedance spectra were exploited to resolve the structural information of the FO membranes from the electrolyte background, which was in turn compared with the characterization results via scanning electron microscope (SEM). Associated with the different membrane orientations, the dynamic tests (with osmosis) were implemented to verify the ability of the EIS system to detect the variation of the developed concentration profiles within the membrane structure. The characterization results indicate that EIS is promising to be a handy tool to investigate the polarization phenomena during the FO processes.

Real-time detection of β1 integrin expression on MG-63 cells using electrochemical impedance spectroscopy

Beta 1 integrin is a membrane protein responsible for attachment and migration of osteosarcoma cells. In this study, expression of β1 integrin on MG-63 cells, a human osteogenic sarcoma cell line, was monitored using electrochemical impedance spectroscopy (EIS). ITO-based biochips were developed using a semiconductor technique. Differences in electric resistance (ΔR) were measured continuously when cells binding with anti-β1 integrin antibody coagulated with nano-scale gold particles. The results of the EIS system were compared with traditional immunofluorescence staining. We found that sample chambers with higher cell densities had larger ΔR values. When the cell densities increased from 5×104 cells/ml to 5×105 cells/ml, the ΔR value dose-dependently increased from 14Ω to 37Ω. In addition, a highly linear relationship (correlation coefficient, 0.921) was found between the ΔR values and the corresponding fluorescence intensities (p<0.05). These results suggest that electrochemical impedance spectroscopy can be a useful tool for evaluating β1 integrin expression on cell membranes.

Low-cost electrochemical impedance spectroscopy system for corrosion monitoring of metallic antiquities and works of art

Electrochemical impedance spectroscopy (EIS) is recognized to be a powerful and noninvasive technique to test the integrity of protective coatings on memorials, but commercial EIS systems are rather costly though versatile devices. This paper describes a low cost and portable EIS system that is based on a compact digital signal processor (DSP) board and embeds the potentiostatic function so that it can be used without requiring an external potentiostat. The software that runs on the DSP is designed to analyze the electrochemical impedance only in a reduced frequency range in order to produce a simple corrosion alert result. The device is equipped with a digital interface and can be connected to a personal computer to carry out a complete frequency analysis and perform a more complex data processing.