Low-frequency Impedance Spectroscopy Research Articles

Multiple Diffusion Processes in Lithium-Ion Battery Electrolytes

Numerical simulations are a powerful tool for the development and improvement of Li-ion batteries[1]. Modelling the mass transport of the involved electrolytic solutions requires precise determination of the corresponding electrolyte parameter. However, the determination methods are still controversially discussed.In this work, we attempt to measure the complete set of electrolyte parameter for a system of 0.5 M LiPF6 dissolved in a blend of ethylene carbonate and ethyl methyl carbonate (EC:EMC, 3:7 weight) at 20°C and 50°C. In order to determine the conductivity, the diffusion coefficient, the transference number and the thermodynamic factor we conduct a combination of concentration cell measurements, galvanostatic polarization experiments and electrochemical impedance spectroscopy[2].While the conductivity and concentration cell measurements show comparable results to the literature, we find the potential response in the polarization experiments deviating from theoretical expectations. Applying galvanostatic polarization experiments to symmetrical metal Li | electrolyte + separator | Li metal cells result in slower, impeded diffusion processes. This indicates the presence of additional, undesired porous structures on the Li electrodes, preventing a reliable evaluation of the electrolyte parameters[3]. To spectrally resolve the diffusive processes, we conduct very low frequency impedance spectroscopy in an attempt to identify the impedance for the sole diffusion through the separator[4].1. Max Schammer et al 2021 J. Electrochem. Soc. 168 0265112. Johannes Landesfeind and Hubert A. Gasteiger 2019 J. Electrochem. Soc. 166 A30793. Talian et al. The Journal of Physical Chemistry C 2019 123 (46), 27997-280074. F. Wohde et al 2016 J. Electrochem. Soc. 163 A714Figure 1: VLF-IS measurements with amplitudes of 60µA, 500µA and 10µA together wit the corresponding equivalent circuits, fits and Kramers-Kronig transformations at 20° C and 50°C respectively Figure 1

General Capacitance Upper Limit and Its Manifestation for Aqueous Graphene Interfaces

Double-layer capacitance (Cdl) is essential for chemical and biological sensors and capacitor applications. The correct formula for Cdl is a controversial subject for practically useful graphene interfaces with water, aqueous solutions, and other liquids. We have developed a model of Cdl, considering the capacitance of a charge accumulation layer (Cca) and capacitance (Ce) of a capacitance-limiting edge region with negligible electric susceptibility and conductivity between this layer and the capacitor electrode. These capacitances are connected in series, and Cdl can be obtained from 1/Cdl = 1/Cca + 1/Ce. In the case of aqueous graphene interfaces, this model predicts that Cdl is significantly affected by Ce. We have studied the graphene/water interface capacitance by low-frequency impedance spectroscopy. Comparison of the model predictions with the experimental results implies that the distance from charge carriers in graphene to the nearest molecular charges at the interface can be ~(0.05–0.1)nm and is about a typical length of the carbon-hydrogen bond. Generalization of this model, assuming that such an edge region between a conducting electrode and a charge accumulating region is intrinsic for a broad range of non-faradaic capacitors and cannot be thinner than an atomic size of ~0.05 nm, predicts a general capacitance upper limit of ~18 μF/cm2.

Inductive Type Impedance of Mo/<i>n</i>-Si Barrier Structures Irradiated with Alpha Particles

In silicon microelectronics, flat metal spirals are formed to create an integrated inductance. However, the maximum specific inductance of such spirals at low frequencies is limited to a value of the order of tens of microhenries per square centimeter. Gyrators, devices based on operational amplifiers with approximately the same specific inductance as spirals, are also used. Despite the fact that such solutions have been introduced into the production of integrated circuits, the task of searching for new elements with high values of specific inductance is relevant. An alternative to coils and gyrators can be the effect of negative differential capacitance (i.e., inductive type impedance), which is observed in barrier structures based on silicon.The purpose of the work is to study the low-frequency impedance of Schottky diodes (Mo/n-Si) containing defects induced by α-particles irradiation and determination of the parameters of these defects by methods of low-frequency impedance spectroscopy and DLTS (Deep Level Transient Spectroscopy).Unpackaged Schottky diodes Mo/n-Si (epitaxial layer of 5.5 μm thickness and resistivity of 1 Ohm∙cm) produced by JSC “Integral” are studied. Inductance measurements were carried out on the as manufactured diodes and on the diodes irradiated with alpha particles (the maximum kinetic energy of an αparticle is 5.147 MeV). The impedance of inductive type of the Schottky diodes at the corresponding DC forward current of 10 µA were measured in the AC frequency range from 20 Hz to 2 MHz. DLTS spectra were used to determine the parameters of radiation-induced defects. It is shown that irradiation of diodes with alpha particles produces three types of radiation-induced defects: A-centers with thermal activation energy of E1 ≈ 190 meV, divacancies with activation energies of E2 ≈ 230 meV and E3 ≈ 410 meV, and Ecenters with activation energy of E4 ≈ 440 meV measured relative to the bottom of c-band of silicon.

Fabrication of cornstarch biopolymer-derived nano porous carbon as electrode material for supercapacitor application

Porous carbon is prepared from the cornstarch biopolymer by simple carbonization process initially at 800 °C. This carbon sample has been activated by gasification with the help of oxidizing gas and by reaction with certain chemicals for its pore development. The final product of activated carbon is then characterized by techniques like XRD, RAMAN, BET, TGA, FESEM, and EDX to study all its behavior. The results of these characterizations have been thoroughly studied in the Sect. 3. The carbon is used as an electrode material to decorate the supercapacitor electrode by 1 mg of coating. Polymer electrolyte film of PVDF-HFP doped with 300 wt% of 1-ethyl-3-methylimidazolium tricyanomethanide (TCM) (optimized for better conductivity) ionic liquid is used as a separator. A supercapacitor device is then fabricated at laboratory scale with the prepared porous carbon electrodes sandwiched with the electrolyte film which yield a specific capacitance of 188.4 F/gm at 10 mHz confirmed from the electrochemical low-frequency impedance spectroscopy plot. Cyclic voltammetry results were also measured, yielding a high specific capacitance of 184.8 F/gm at 5 mV/s.

A General Control Strategy to Micropattern Topological Defects in Nematic Liquid Crystals Using Ionically Charged Dielectric Surface

AbstractTailoring self‐organized nano/microstructures in soft materials is crucial for exploiting intrinsic functional properties toward emerging applications. Engineered topological defects in liquid crystals are interesting for electro‐optical devices as well as for soft actuators morphing surface. Despite the promising potential, there are currently few bottom‐up methods for positioning a large number of defects periodically over a large area. It is highly challenging to develop essential techniques for achieving high‐throughput fabrication with simple procedure. Using ultraviolet/ozone treatment, herein we present a general and robust strategy to produce the surface that can be a platform for a self‐organized micropattern of topological defects in nematic liquid crystals, irrespective of the chemical structure of compounds including polymerizable monomers. The micropattern formation is controllable by applying area‐selective surface modification, which dramatically improves the fabrication efficiency. By low frequency impedance spectroscopy, the distinctive frequency dependence of the apparent threshold voltage at the micropattern formation is experimentally assigned to a unique reorientational response which occurs when a dielectric surface is charged by ionic additives. This characterization provides crucial guidance in further engineering self‐organized topological defects in liquid crystals.

Ionic liquid impregnated Allium cepa peel for supercapacitor application

This paper report a new biodegradable epidermis of onion (Allium cepa) doped with low viscosity ionic liquid as novel electrolyte for EDLC application. The porous membrane used in present study was epidermis of onion (onion peel membrane) and low viscosity ionic liquid (IL) i.e. 1-ethyl 3-methyl imidazolium thiocynate. The electrical, structural, optical characterization was carried out in detail. The optical micrographs show addition in amorphosity with adding IL. Fourier transform infrared spectroscopy (FTIR) revealed the interaction between ionic liquid and membrane as well as composite nature of membrane electrolyte. Impedance spectroscopy revealed the twofold enhancement in conductivity value by doping IL. Electrical double layer supercapacitor (EDLC) has been fabricated using carbon nanotube (CNT). Cyclic voltammetry and low frequency impedance spectroscopy data further affirm the reasonable value of specific capacitance (Csp = 9.2F/g).

Yeast Propagation Control: Low Frequency Electrochemical Impedance Spectroscopy as an Alternative for Cell Counting Chambers in Brewery Applications

Electrochemical impedance spectroscopy is a powerful tool in life science for cell and pathogen detection, as well as for cell counting. The measurement principles and techniques using impedance spectroscopy are highly diverse. Differences can be found in used frequency range (β or α regime), analyzed quantities, like charge transfer resistance, dielectric permittivity of double layer capacitance and in off- or online usage. In recent contributions, applications of low-frequency impedance spectroscopy in the α regime were tested for determination of cell counts and metabolic burden in Escherichia coli and Saccharomyces cerevisiae. The established easy to use methods showed reasonable potential in the lab scale, especially for S. cerevisiae. However, until now, measurements for cell counts in food science are generally based on Thoma cell counting chambers. These microscopic cell counting methods decelerate an easy and quick prediction of yeast viability, as they are labor intensive and result in a time delayed response signal. In this contribution we tested our developed method using low frequency impedance spectroscopy locally at an industrial brewery propagation site and compared results to classic cell counting procedures.

Radio-Frequency Electrochemical Sensor Arrays for Biological Imaging

Cells and tissues have subtle and complex electrical properties, but it can be challenging to access these properties at fine spatial and temporal resolution. Custom CMOS microelectronics can offer some solutions, but planar electrodes are always limited by Debye screening, which causes traditional low-frequency impedance spectroscopy at physiological conditions to be sensitive to chemical conditions within only a few nanometers of the working electrode. Radio frequency dielectric spectroscopy can enable measurements of features farther from the surface, but this sensing regime remains under-explored, in part due to the challenge of designing microelectronics with suitably low noise, high bandwidth, high density, and low parasitics. We have fabricated prototype integrated CMOS sensor arrays which can produce electrochemical images at 100 MHz, using dense arrays of thousands of micrometer-scale pixels. These sensor arrays can also be combined with other chemical and optical sensor elements, for rich multi-modal biological imaging.

Electrochemical low-frequency impedance spectroscopy algorithm for diagnostics of PEM fuel cell degradation

Prognostics and health management for fuel cells in real-world applications are important for optimization of lifetime and operation. A parameter that has been shown to indicate the state of ageing is the low-frequency intercept with the real axis of the Nyquist diagram in a fuel cell's impedance spectrum. This article presents a method for direct identification of this parameter, without the need to carry out a full electrochemical impedance spectroscopy, and with an algorithm that can be realized within a typical fuel-cell control system. The proposed method is based on relay excitation feedback, a proven solution from controller tuning.

Characterization of sulfate diffusion into cement paste by low frequency impedance spectroscopy

In this study, EIS was used to investigate sulfate diffusion process into cement paste. Cement paste samples with w/c ratio of 0.35 and 0.45 were immersed in 10wt% sodium sulfate solutions for different durations. An equivalent circuit model of cement paste exposed to sulfate attack was proposed, and some relevant parameters of the equivalent circuit were obtained by EIS analysis. The validations of the effectiveness of EIS on investigating the sulfate diffusion have been provided by SEM and XRD analysis. As the results shown, it is sensitive to use EIS to characterize the diffusion process of sulfate ions into cement paste. The relationship between ingress depth of sulfate obtained from EIS analysis and the square root of exposing time is approximately linear.

The Peculiarities of the Electrical Conductivity of LiNbO<sub>3</sub> Crystals, Reduced in Hydrogen

The low-frequency impedance spectroscopy method has been used to investigate the electrical conductivity peculiarities of lithium niobate (LN) crystals reduced in hydrogen. It has been found that the activation energy value of the dark electrical conductivity of such crystals in a temperature range of 288...370 К is equal to 0.68±0.02 eV. It has been demonstrated that the multiple heating of «black» LN crystals up to a temperature of about 420 K results in surface layers with modified electrical properties to occur in the crystal’s polar faces. The electrical conductivity mechanism of LiNbO3 crystals reduced in the hydrogen-containing atmosphere, and the causes of the instability of these properties are discussed.

A four-electrode low frequency impedance spectroscopy measurement system using the AD5933 measurement chip

This paper presents the design of a four electrode impedance measurement circuit dedicated to bioimpedance embedded applications. It extends the use of the AD5933 measurement chip to allow it to operate in a four electrode configuration in order to limit the effects of the parasitic impedances between the medium under test and the electrodes. The circuit has shown a good measurement accuracy on various test circuits. In association with a four microband electrode system it has been successfully used to characterize small physiological samples (50 μl) with conductivities ranging from 0.14 to 1.2 S m−1. It can be used as an alternative bioimpedance measurement approach for embedded applications operating in the four electrode configuration.

Reduction of electrode polarization capacitance in low-frequency impedance spectroscopy by using mesh electrodes

Dielectric measurements of biological samples are obscured by electrode polarization, which at low frequencies dominates over the actual sample response. Reduction of this artifact is especially necessary in studying interactions of electric field with biological systems in the α-dispersion range. We developed a method to reduce the influence of electrode polarization by employing mesh instead of solid electrodes as sensing probes, thereby reducing the area of the double layer. The design decreases the electrode–electrolyte contact area by almost 40% while keeping the bulk sample capacitance the same. Interrogation electric fields away from the electrode surface and sensitivity are unaffected. Electrodes were microfabricated (600μm×50μm, spacing of 100μm) with and without mesh holes 7.5μm×7.5μm in size. Simulations of electric field performed using Comsol Multiphysics showed non-uniformity of the electric field within less than 1.5μm from the electrode surface, which encompasses the double layer region, but at greater distance the solid and mesh electrodes gave the same results. Mesh electrodes reduced capacitance measurements for water and KCl solutions of different concentrations at low frequencies (<10kHz), while higher frequency capacitance remained the same for both electrode types, confirming our hypothesis that this design leaves the electric field mainly unaffected. Impedance measurements at low frequencies for water and mice heart mitochondrial suspension were lower for mesh than for solid electrodes. Comsol simulations confirmed these results by showing that mesh electrodes have a greater charge density than solid electrodes, which affects conductance. These electrodes are being used for mitochondrial membrane potential studies.

Low frequency impedance spectroscopy of cell monolayers using the four-electrode method

We have developed an impedance spectroscopy system for monitoring changes in extracellular conductivity and cell-to-cell coupling in cells cultured on microelectrode arrays (MEAs). Impedance spectra were measured at low frequencies (0.5-10kHz) using the four-electrode technique and standard electrophysiological instruments. A reduction in extracellular conductivity (using isotonic sucrose solution) was observed as an elevation of impedance at all measured frequencies. A reduction in cell coupling (using heptanol) was observed as an elevation of impedance at low frequencies (<100Hz) and small reductions or no change in impedance at higher frequencies. Monolayer confluency and cell adhesion to electrodes were major factors in the measurements. The effect of disrupting cell adhesion (using trypsin) was most apparent at frequencies below 1kHz. Impedance was dependent upon the spacing between stimulating electrodes. Impedance reduced with increasing spacing. Overall, using commercially available MEAs and the four-electrode method provides a fast and reliable way to measure cell monolayer impedances.

Bacteria Counting with Impedance Spectroscopy in a Micro Probe Station

A method to quantify the density of viable biological cells in suspensions is presented. The method is implemented by low-frequency impedance spectroscopy and based on the finding that immobilized ions are released to move freely in the surrounding suspension when viable Escherichia coli cells are killed by a heat shock. The presented results show that an amount of ions corresponding to approximately 2 x 10(8) unit charges are released per viable bacterium killed. A micro probe station with coplanar Ti electrodes was electrically characterized and used as a measuring unit for the impedance spectroscopy recordings. This unit is compatible with common microfabrication techniques and should enable the presented method to be employed using a flow-cell device for viable bacteria counting in miniaturized on-line monitoring systems.

Electrical characterization of gel collected from shark electrosensors.

To investigate the physical mechanism of the electric sense, we present an initial electrical characterization of the glycoprotein gel that fills the electrosensitive organs of marine elasmobranchs (sharks, skates, and rays). We have collected samples of this gel, postmortem, from three shark species, and removed the majority of dissolved salts in one sample via dialysis. Here we present the results of dc conductivity measurements, low-frequency impedance spectroscopy, and electrophoresis. Electrophoresis shows a range of large protein-based molecules fitting the expectations of glycoproteins, but the gels of different species exhibit little similarity. The electrophoresis signature is unaffected by thermal cycling and measurement currents. The dc data were collected at various temperatures, and at various electric and magnetic fields, showing consistency with the properties of seawater. The impedance data collected from a dialyzed sample, however, show large values of static permittivity and a loss peak corresponding to an unusually long relaxation time, about 1 ms. The exact role of the gel is still unknown, but our results suggest its bulk properties are well matched to the sensing mechanism, as the minimum response time of an entire electric organ is on the order of 5 ms.

On the time scale of the structural change of polyaniline in the reversible electrochemical process

The conducting polymer system is presented for the first time that exhibits the usual quasi-reversibility under the very slow cyclic voltammetry conditions. The hysteresis in the cyclic voltammograms of the secondary trichloroacetate counterion–polyaniline system decreases with a decrease of scan rate. The behavior is not observed for the primary chloride counterion–polyaniline system. The low frequency impedance spectroscopy results are invoked to discuss the observed phenomenon. The time scale of the polymer structural rearrangement due to the reversible electrochemical oxidation process is estimated to be at least of the order of 10 3 s. A specific molecular interactions are postulated to interpret the difference observed between the secondary and primary counterion systems.

Development of Skin Barrier Function in Premature Infants

Histologic analysis suggests that epidermal development is complete in utero at approximately 34 wk gestational age. Infants born more prematurely have elevated rates of both transepidermal water loss and transcutaneous heat loss, and have difficulty maintaining homeostasis. The underdeveloped integument is also a portal of entry for infection and the percutaneous uptake of toxins. Previous measurements of transepidermal water loss have suggested that, regardless of gestational age, competent barrier function is attained within 2-4 wk postnatal age. In this study we have utilized another noninvasive biophysical technique, low frequency impedance spectroscopy, to complement transepidermal water loss measurements. We present longitudinal data from infants ranging from 23 to 32 wk gestational age. The results suggest that, for ultra-low birth weight infants (23-25 wk gestational age), the complete development of a fully functional stratum corneum can require significantly longer than 4 wk. In contrast, the data from the older infants suggest that a postnatal existence period of 2-4 wk may not be necessary to attain functional maturity, because infants born at 30 and 32 wk gestational age were found to have barrier function comparable with that of adults.

Reversible Metal-Insulator Transition in Ordered Metal Nanocrystal Monolayers Observed by Impedance Spectroscopy

Low frequency impedance spectroscopy was applied on a Langmuir monolayer of alkylthiol passivated 35 A diameter silver quantum dots, as a function of interparticle separation distance. As interparticle spacing decreases below 30% of particle diameter, a reduction in interparticle charge tunneling time is observed. On further compression, the complex impedance of the films undergoes a transition from a parallel RC equivalent circuit to an inductive circuit. Optical reflectance changes in the films are consistent with the deduced metal-insulator transition.

Polarization conductivity in dehydrated zeolites NaY and HY

The ionic conductivity of the dehydrated faujasite zeolites NaY and of its protonated form HY is determined experimentally by low-frequency impedance spectroscopy. Experiments were carried out in the frequency range 10 Hz-10 MHz at temperatures from ambient to 634 K. It is clearly shown that the measured conductivity could be considered as a sum of two terms. The dc term obeys the Arrhenius equation while the polarization term could be expressed as Aω 8. The conduction phenomena, including the polarization processes, are ascribed to cation movements localized in supercages. Moreover, it is found that the parent zeolite NaY is more conductive than its protonated form HY.