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A new method and device for the selective measurement of humidity at high temperature is presented. It consists of a TiO2 sensor element and a Fourier-based impedance spectrometry (FobIS) device with a dynamic range from 100 Hz to 100 kHz. For selective humidity detection we use an electrical equivalent circuit model presented earlier [1]. In this model, the humidity can be attributed to a constant phase element describing the ionic conduction of humidity related species. In this work, we can demonstrate that humidity can be quantified at 320 °C in the range from 80 to 450 mbar with an accuracy of 12 mbar with this approach. Furthermore, we can show that the circuit element for ionic conduction is not dependent on reducing gas tested with 1000 ppm ethanol. The response to ethanol, however, contributes to an ohmic resistor describing the electronic conductance within the TiO2. With compensation of reducing gas, humidity can be quantified with an error of 13 mbar.

Reliable battery model and identified model parameter are the preconditions for Power battery state estimation with high precision. Aiming at the disadvantage of existing integer order impedance modeling in characterizing the dynamic characteristics of Lithium-ion ferrous phosphate (LFP) batteries, a simplified fractional order (FO) impedance model including constant phase element and Warburg element is proposed based on the analysis of simplified electrochemical impedance spectroscopy curve. With the Grunwald–Letnikov definition based factional order numerical calculation, the FO Kalman filter (FO-KF) method based on the derived model is designed to identify the FO impedance model parameter and terminal voltage. The proposed FO impedance model can better represent the nonlinear dynamic performances of LFP batteries, and the Grunwald–Letnikov definition based FO-KF algorithm can maintain good accuracy in the numerical calculation of FO parameter identification. The experimental validation results show that the combination of simplified FO impedance model and FO-KF method can improve the modeling precision and parameter identification performance compared with the common integer order impedance model under two different test conditions.

Fe doped ZnO nanocrystals (NCs) were synthesized from low cost sol gel method and the effect of iron content on their structural, transport and dielectric properties was studied. X-ray diffraction (XRD) measurements exhibit good crystalline quality of all the prepared NCs and a reduction of the crystallite size with Fe doping. Raman spectra confirmed the good crystallinity and revealed the formation of ferric phases for highly doped samples. Investigations of the impedance characteristics indicate that the samples are perfectly modulated from equivalent circuits using a constant phase element (CPE). Analysis of complex impedance and electrical modulus revealed a relaxation process dependent on temperature and of non-Debye type. Single activation energy was estimated for the electronic conduction, based on the Arrhenius plots. The conduction mechanism was governed from small polaron hopping in all the ZnO:Fe materials. The frequency dependence of the electric conductivity followed a simple Jonscher power behavior σ a c ( ω ) = σ d c + A ω s (0.5≤ s ≤ 1), where the exponent s increased with temperature. The dielectric measurements, in both medium and high frequency regions, exhibited high dielectric constant values and low dielectric losses for all the samples, which could favor the use of Fe doped ZnO a as promising candidate for energy storage. The electrical modulus provides double relaxation times with low values. All the properties indicate that the ZnO:Fe material is suitable for device applications.

For this study, we synthesized Aurivillius Bi5Ti3FeO15 ceramic using the generic solid-state reaction route and then performed room-temperature X-ray diffraction to confirm that the compound had a single phase with no impurities. The surface morphology of the prepared sample was observed to contain microstructural grains approximately 0.2–2 µm in size. The dielectric properties of the sample were determined as a function of frequency in a range of approximately 100 Hz to 1 MHz at various temperatures (303 K ≤ T ≤ 773 K). Nyquist plots of the impedance data were found to exhibit a semi-circular arc in the high-temperature region, which is explained by the equivalent electrical circuit (R1C1)(R2QC2), where R1 and R2 represent the resistances associated with the grains and grain boundaries, respectively, C1 and C2 are the respective capacitances, and Q is the constant phase element (CPE), which accounts for non-Debye type of behavior. Our results indicate that both the resistance and capacitance of the grain boundaries are more prominent than those of the grains. The alternating current (ac) conductivity data were analyzed based on the Jonscher universal power law, which indicated that the conduction process is dominated by the hopping mechanism. The calculated activation energies of the relaxation and conduction processes were very similar (0.32 to 0.53 eV), from which we conclude that the same type of charge carriers are involved in both processes.

One of the main challenges during the integration of a carbon/polymer-based nanocomposite sensor on textile substrates is the fabrication of a homogeneous surface of the nanocomposite-based thin films, which play a major role in the reproducibility of the sensor. Characterizations are therefore required in every fabrication step to control the quality of the material preparation, deposition, and curing. As a result, microcharacterization methods are more suitable for laboratory investigations, and electrical methods can be easily implemented for in situ characterization within the manufacturing process. In this paper, several textile-based pressure sensors are fabricated at an optimized concentration of 0.3 wt.% of multiwalledcarbon nanotubes (MWCNTs) composite material in PDMS. We propose to use impedance spectroscopy for the characterization of both of the resistive behavior and capacitive behavior of the sensor at several frequencies and under different loads from 50 g to 500 g. The impedance spectra are fitted to a model composed of a resistance in series with a parallel combination of resistance and a constant phase element (CPE). The results show that the printing parameters strongly influence the impedance behavior under different loads. The deviation of the model parameter α of the CPE from the value 1 is strongly dependent on the nonhomogeneity of the sensor. Based on an impedance spectrum measurement followed by parameter extraction, the parameter α can be determined to realize a novel method for homogeneity characterization and in-line quality control of textile-integrated wearable sensors during the manufacturing process.

Ca[Fe]2O4 prepared by nitrate route is a narrow band gap semiconductor crystallizing in the normal spinel structure. The direct optical band gap Eg (1.93 eV), determined from the diffuse reflectance, is due to the lifting of degeneracy of Fe3+: 3d orbital, octahedrally coordinated. The semi-logarithm plot of the oxide shows a chemical stability at pH ~ 7 with an exchange current density of 2×10−7 mA cm−2 and a corrosion potential of −0.664 VSCE. The photoelectrochemical properties of CaFe2O4 are investigated for the first time to assess its photocatalytic activity. A flat band potential (Efb) of 0.33 VSCE was obtained from the capacitance measurement in Na2SO4 (0.1 M) solution. The n-type comportment, rare for spinels, is confirmed by the chrono-amperometry and inferred to the metal insertion in the FeO6 octahedra. The electronic concentration ND (7.1 ×1015 cm−3) agrees with a non-degenerate semi-conductivity and a wide space charge region (W ~ 850 nm). The electrochemical impedance spectroscopy (EIS) shows depressed semicircles with the existence of a constant phase element (CPE) and a bulk resistance of 10.89 kΩ cm2 which decreases down to 2.24 kΩ cm2 under visible irradiation. A Warburg diffusion is observed at low frequencies. The valence band (2.09 VSCE) deriving from Fe3+: eg character is more anodic than the potential of H2O/•OH couple. As an application, the Basic Blue 41 (BB 41), a recalcitrant dye, is successfully oxidized; an abatement of 85% is obtained within 3 h under solar light (980 W m−2) and the BB 41 oxidation follows a first-order kinetics with a photocatalytic half-life of 69 min.

In the paper, a fractional-order RLC circuit is presented. The circuit is realized by using a fractional-order capacitor. This is realized by using carbon black dispersed in a polymeric matrix. Simulation results are compared with the experimental data, confirming the suitability of applying this new device in the circuital implementation of fractional-order systems.

Here we study the electrochemical impedance spectra of glassy carbon electrodes modified with a polypyrrole + sodium polystyrene sulfonate composite, GC/(PPy + PSS). This composite material was electrochemically deposited by using a potentiodynamic method, yielding ~120 nm-thick films. The impedance of the modified electrodes, in contact with two different electrolyte solutions, was studied in the range 10-1 to 105 Hz, at electrode potentials where the film is completely reduced and then at increasing levels of oxidation. The spectra were interpreted by using a modified version of the Randles equivalent circuit, where the Warburg impedance of the original circuit was replaced by a constant phase element. For a reduced or a slightly oxidized film, the impedance characteristics in the low frequency region is not consistent with charge transport within the film being controlled by diffusion but rather by either a mixed diffusion-migration control or anomalous diffusion, due to the internal structure of the material.

The discovery of ferroelectricity in hafnium zirconium oxide (HZO) thin films has attracted wide attention from academia to industry due to the application in ferroelectric non-volatile random access memories (FeRAM) with prominent performance in scalability and CMOS process compatibility. Dielectric behavior of ferroelectric HZO thin films is a key factor affecting the dynamic effect, piezoelectric and electrostrictive effect. Interface between HZO and capping electrodes plays an important role in regulating the dielectric properties. In this paper, the impedance frequency response and dielectric spectrum of ferroelectric HZO thin films were analyzed. Parameters of the interface were extracted to analyze the regulating effect on the dielectric properties based on an impedance model with constant phase element (CPE). Besides, dielectric spectrums at elevated temperatures were identified to verify this analysis.

This paper presents a simple, inexpensive, and highly sensitive electrochemical sensor based on new polymeric membrane incorporating kinetin (6-furfurylaminopurine) as a specific sensitive molecule deposited on the surface of a glassy carbon electrode for the detection of cadmium in water. The electrochemical characterization was examined using electrochemical impedance spectroscopy and cyclic voltammetry. Additive effect and selectivity for cadmium over many common cations, such as copper, lead, and zinc, at pH 4.5 are studied. We showed that the cadmium selectivity is better for membrane based on potassium tetrakis(4-chlorophenyl)borate (KTpClPB) with a significant decrease of the Rct and an increase in constant phase element CPE, the sensor exhibits a LOD of 3.96 × 10–10 M with a linear response towards cadmium ions over a wide concentration range of 10–6 to 10–9 M. Finally, the proposed sensor was applied to the determination of cadmium in water and can be proposed to use successfully in real water samples.

Low-cost, high-performance coatings for hydrogen production via electrolytic water-splitting are of great importance for de-carbonising energy. In this study the Raney2.0 coating was analysed using various electrochemical techniques to assess its absolute performance, and it was confirmed to have an extremely low overpotential for hydrogen evolution of just 28 mV at 10 mA/cm2. It was also confirmed to be an acceptable catalyst for oxygen evolution, making it the highest performing simple bifunctional electrocatalyst known. The coating exhibits an extremely high capacitance of up to 1.7 F/cm2, as well as being able to store 0.61 J/cm2 in the form of temporary hydride deposits. A new technique is presented that performs a best-fit of a transient simulation of an equivalent circuit containing a constant phase element to cyclic voltammetry measurements. From this the roughness factor of the coating was calculated to be approximately 40,000, which is the highest figure ever reported for this type of material. The coating is therefore an extremely useful improved bifunctional coating for the continued roll-out of alkaline electrolysis for large-scale renewable energy capture via hydrogen production.

We investigated the charging current in cyclic voltammetry and the galvanostatic charging/discharging behavior of a controversial constant-phase element (CPE) to describe an electrical double layer used only in electrochemical impedance spectroscopy. The linear potential sweep in the time domain was transformed into the frequency domain using a Fourier transform. The current phasor was estimated by Ohm’s law with the voltage phasor and a frequency-dependent CPE, followed by an inverse Fourier transform to determine the current in the time domain. For galvanostatic charging/discharging, the same procedure, apart from swapping the voltage signal with the current signal, was applied. The obtained cyclic voltammetry (CV) shows (1) a gradual increase in the charging current, (2) a higher charging current at a low scan rate, and (3) a deviation from the linear relationship between the charging current and the scan rate. For galvanostatic charging/discharging, the results demonstrate (1) curved charging/discharging behavior, (2) a higher voltage in the early stage, and (3) a lower voltage during longer charging periods. In contrast to a previous approach based on solving a differential equation with a simple RC circuit, our Fourier transform-based approach enables an analysis of electrochemical data with an arbitrary and complex circuit model such as a Randles equivalent circuit. The CPE model is more consistent with previous experimental results than a simple ideal capacitor, indicating a ubiquitous CPE in electrochemistry and a fair figure of merit for supercapacitors.

The electrical properties of cubic, calcia-stabilised zirconia ceramics, CaxZr1-xO2-x: 0.12 ≤ x ≤ 0.18 have been investigated using impedance spectroscopy to separate bulk, grain boundary and electrode contact impedances. The most appropriate equivalent circuit to characterise the bulk response required inclusion of a dielectric component, represented by a series RC element, in parallel with the oxide ion conductivity represented by a parallel combination of a resistance, capacitance and constant phase element. The dielectric component may be attributed to defect complexes involving immobile oxygen vacancy pairs whereas long range conduction involves single oxygen vacancies.

Nanocrystalline Zn2SnO4/SnO2 powder was obtained by a solid state reaction of ZnO and SnO2 nanopowders mixed in the molar ratio 1:1. The phase composition of the obtained powder was studied by XRD and Raman spectroscopy, morphology and texture were characterized by FESEM, TEM, BET and Hg porosimetry, while XPS and FTIR spectroscopy were used to determine the surface chemistry. The influence of humidity on complex impedance was monitored on bulk samples in the relative humidity (RH) range 30–90% in a climatic chamber in the frequency range 42 Hz- 1 MHz at working temperatures of 25 and 50 °C. Change in RH had a significant influence on impedance reduction, especially noticeable in the lower frequency range, indicating potential application of this nanocomposite as a humidity sensing material. Increase in RH led to an increase in AC conductivity that changed with frequency according to the Jonscher power law. The frequency exponent decreased with increase in RH and sample temperature indicating that the correlated hopping barrier model is the dominant conduction mechanism. Complex impedance was analyzed using an equivalent circuit consisting of a parallel resistance and constant phase element, showing the dominant influence of grain boundaries at both working temperatures (25 and 50 °C). The resistance decreased, while the capacitance and relaxation frequency increased with increase in RH. At high humidity an added Wartburg element enabled modeling of the charge diffusion process.

The accurate modeling of electrical impedance over a wide range of frequency is essential for precise dynamic modeling and control problems of Electroactive Polymer (EAP) actuators. Recently, fractional order modeling has attracted more attention due to the high accuracy. This paper deals with a fractional order electrical impedance model and its identification procedure for a class of EAP actuator named Ionic Polymer Metal Composite (IPMC). To take IPMC’s fractional characteristic into account, constant phase element (CPE) is used to construct a model structure according to Electrochemical Impedance Spectroscopy (EIS). By employing the Levy’s method in combination with genetic optimization algorithm, the unknown parameters of the resulting fractional transfer function are identified. Finally the proposed model is verified, by comparing with experimental EIS data. The results show that the fractional order model has high accuracy for representing the electrical impedance of IPMC actuator. The proposed modeling procedure is general and can also be used for any type of EAPs.

The Au/Pd/Ti–SiO2-(n) GaAs properties have been analyzed via impedance spectroscopy (IS), as well as DLTS and ICTS, to identify the origin of electron processes responsible for existence of constant phase elements (CPE) in an equivalent circuits of that structure. We showed that CPEs connected in series with resistance represents the electron processes associated with deep levels in GaAs and/or interface states at SiO2-(n) GaAs interface, depending on the value of n of CPE parameter. CPE with n close to 1 characterize the electron processes associated with EL2 deep level, and CPE with n = 0.5–0.65 the complex electron processes associated with EL3 deep level and interface states together. We stated that constant phase elements in equivalent circuits of MIS-GaAs structures with large frequency dispersion of electrical characteristics can be the result of more than one electron process.

Coaxial arc plasma deposition (CAPD) was employed to manufacture n-type silicon/boron-doped p-type ultrananocrystalline diamond heterojunctions. Measurement and analysis of their dark current density-voltage curve were carried out at room temperature in order to calculate the requisite junction parameters using the Cheung and Norde approaches. For the calculation based on the Cheung approach, the series resistance (Rs), ideality factor (n) and barrier height (Φb) were 4.58 kΩ, 2.82 and 0.75 eV, respectively. The values of Rs and Φb were in agreement with those calculated using the Norde approach. Their characteristics for alternative current impedance at different frequency values were measured and analyzed as a function of the voltage (V) values ranging from 0 V to 0.5 V. Appearance of the real (Z′) and imaginary (Z″) characteristics for all V values presented single semicircles. The centers of the semicircular curves were below the Z′ axis and the diameter of the semicircles decreased with increments of the V value. The proper equivalent electrical circuit model for the manufactured heterojunction behavior was comprised of Rs combined with the parallel circuit of resistance and constant phase element.

In this work, a complex impedance spectroscopy study of bismuth vanadate (BiVO4) ceramics with different additions of ZnO (25, 50, and 75 wt %) was performed. BiVO4 (BVO) was synthesized by the reaction method in solid-state and calcined at 500 °C and BVO–ZnO composites were moulded in sintered ceramic pellets at 700 °C. X-ray diffraction (XRD) was used to analyse the crystal structure of BVO and the BVO–ZnO composites; none spurious phase was observed during the synthesis. Analysis by complex impedance spectroscopy (CIS) showed that increasing the concentration of ZnO reveals increased activation energy due to thermo-activated charge transfer for the sample with 25 wt % ZnO. At room temperature, the increase in the ZnO concentration in the BVO matrix maintained a high value for the dielectric constant (e), in the order of 104 at a frequency of 1 Hz. Average normalized change (ANC) was used to identify the temperature at which the available density of trapped charge states vanishes in each sample. The temperature coefficient of capacitance was positive for BVO and negative for composites. The adjustment through the equivalent circuit presented excellent electrical response for the composites, and identified an association with three resistors, each in parallel a constant phase element, showing the influence of grain and grain boundary on the process of thermo-active conduction.

This paper presents a state-of-the-art survey in the area of fractional-order element passive emulators adopted in circuits and systems. An overview of the different approximations used to estimate the passive element values by means of rational functions is also discussed. A short comparison table highlights the significance of recent methodologies and their potential for further research. Moreover, the pros and cons in emulation of FOEs are analyzed., his article is based upon work from COST Action CA15225, a network supported by COST (European Coop- eration in Science and Technology). Research described in this paper was financed by the Ministry of Education, Youth and Sports under grant LTC18022 of Inter-Cost program.

The behavioral features of the spectra of impedance components and electric module for copper-doped polycrystalline zinc-sulfide layers are investigated. The dispersion of the frequency dependences of the electrical parameters corresponding to the distribution of the relaxation time is established. An equivalent sample circuit that includes a constant phase element and describes electric transport features in the polycrystalline system under study is used to interpret the experimental data.

In this paper, an impedance-transduced sensor is developed based on a nanostructured graphene (GN) and poly (methyl methacrylate) (PMMA) sensing film for the detection of individual volatile organic compounds (VOCs) in aqueous media. Benefiting from a porous and high surface area, the nanostructured nanofiber is characterized by scanning electron microscopy (SEM) and optimized by the electrochemical impedance spectroscopy (EIS) technique. The recorded EIS data indicate the selective recognition of four VOCs of interest at a constant pH while there is no redox probe. The non-faradaic responses to each analyte at different concentrations are correlated with a three-element equivalent circuit (resistances of the solution and the film, and a pseudo-capacitance). To analyze the ability of the sensing film in distinguishing between VOCs with similar average boiling points, the values of the individual equivalent circuit elements are used as features and clustered in three-dimensional (3D) plots. Among the features, the two representing the maximum differences between the VOCs are represented in a two-dimensional (2D) plot to show the selectivity of the sensor. The feature extraction analysis demonstrates that the constant phase element (CPE) of the equivalent circuit is a more accurate predictor of VOCs than the interfacial capacitance. These results show high selectivity of the sensorial platform due to the synergistic pairing of nanostructured GN and PMMA.

Potential-step chronoamperometry was made at a platinum wire electrode in KCl aqueous solution at the aim of finding the behavior of the power law of the time or the constant phase element for the double-layer (DL) capacitances. The logarithmic current decays linearly with the time shorter than 0.1 ms, and then it obeys the power law in which it has a linear relation with the logarithmic time in the millisecond time domain. The transition from the exponential decay to the power law was expressed theoretically for the model of a series combination of the resistance and the DL capacitance. The expression predicts that the double logarithmic plots of the current–time provide a capacitance value at 1 s from the intercept, independent of the resistance. This prediction was demonstrated experimentally in KCl solutions of which concentrations ranged from 1 mM to 0.5 M. The capacitance can be evaluated simply by chronoamperometry on a 1 s time scale without considering any resistance effect. The capacitance values did not vary with the applied potential.

In this work, we report the synthesis of undoped ZnO and In-doped ZnO nanoparticles by sol–gel method from 0 to 5 wt% of In amount. The effect of indium incorporation on structural and electrical properties of these samples was investigated. X-ray diffraction analysis confirms the formation of undoped ZnO and In-doped ZnO nanopowders with a hexagonal wurtzite crystalline structure and the average crystallite size varies between 31 and 55 nm. The morphological study shows that the shape of the crystallites is hexagonal and it changes into cylindrical prismatic after doping. Further, the study of electrical response was carried out by impedance spectroscopy. The electrical properties of these samples are dependent on temperature and frequency. We find that the conductivity increases with increasing In dopant. It has been found that the highest conductivity corresponds to the concentration 3% of indium content. Concerning the complex impedance analysis, the equivalent circuit of grain consists of resistance and constant phase element in parallel. These results contribute to various technological applications.

In this study, nanostructured tungsten trioxide (WO3) thin films were deposited on Indium tin oxide (ITO)-coated glass substrate using electrochemical deposition (ECD). After deposition, the films were annealed at 450 °C for 2 h in an air atmosphere. X-ray diffraction (XRD) analysis confirmed that the prepared WO3 thin films have crystalline phases. According to the absorption measurements, the optical bandgap of the WO3 film was calculated as Eg 2.80 eV. Based on the scanning electron microscopy (SEM) images, the surface morphology of the thin films was influenced by deposition conditions. Raman spectroscopy analysis was also used to further examine the structure and chemical compositions of the thin films. The nature of the nanostructured WO3 thin films was studied with Electrochemical Impedance Spectroscopy (EIS) and Tafel. Nyquist, open circuit potential and Bode analysis were used to evaluate structural changing and corrosion behavior of the prepared WO3 thin films. With the help of these measurements and analyzes, the parameters such as solution resistance (Rs), polarization resistance (Rpo), a constant phase element (CPE) and a CPE exponent (n) were calculated as 43.43 Ω cm2, 2.67 × 106 Ω cm2, 18.45 × 10−6 Ω−1 s cm−2, 0.958, respectively. Also, the corrosion features of the WO3 thin films were investigated with the help of tafel measurements and the corrosion potential and current values were calculated as −0.583 V and 5.09 × 10−15 A, respectively. It is thought that the prepared thin film might have the potential to be used industrially with these features.

A class of fractal-chain fractance approximation circuit (FCFAC) has been discussed in this paper. The FCFAC type 1 (FCFAC-1) can achieve the rational approximation of negative-half-order fractance...

In the present research, heterojunctions comprised of n-type Si wafer substrates and B-doped p-type ultrananocrystalline diamond/hydrogenated amorphous carbon composite films were produced successfully by using pulsed laser deposition. Their alternating current impedance characteristics, under various frequencies, were measured and studied as a function of temperature in the range 200 to 400 K. Both the real (Z') and imaginary (Z″) parts of the complex impedance were temperature dependent. It was apparent that the Z″-Z' curve for all temperatures exhibited single semicircles. The center of these semicircles was below the Z' axis. With temperature increment, the diameter of the semicircles decreased. The characteristics of the semicircular curve indicated that the parallel resistance (Rp) and constant phase element (CPE) in parallel combination with the series resistance (Rs) should be appropriate for the equivalent electrical circuit model for the produced heterojunctions. Through simulation, the value of Rs at 200 K was found to be 5.04×10³ Ω, and fell to 252.05 Ω at 400 K. Also, the value of Rp was 1.34×107 Ω at 200 K and decreased to 3.37×105 Ω at 400 K. Moreover, the value of CPE at 200 K was 95.91×10-12 F with a deviation from the standard (n) value of 0.90 and rose slightly to 115.60×10-12 F with an n value of 0.98 at 400 K.

Electrochemical sensors based on antibody-antigen recognition events are commonly used for the rapid, label-free, and sensitive detection of various analytes. However, various parameters at the bioelectronic interface, i.e., before and after the probe (such as an antibody) assembly onto the electrode, have a dominant influence on the underlying detection performance of analytes (such as an antigen). In this work, we thoroughly investigate the dependence of the bioelectronic interface characteristics on parameters that have not been investigated in depth: the antibody density on the electrode’s surface and the antigen incubation time. For this important aim, we utilized the sensitive non-faradaic electrochemical impedance spectroscopy method. We showed that as the incubation time of the antigen-containing drop solution increased, a decrease was observed in both the solution resistance and the diffusional resistance with reflecting boundary elements, as well as the capacitive magnitude of a constant phase element, which decreased at a rate of 160 ± 30 kΩ/min, 800 ± 100 mΩ/min, and 520 ± 80 pF × s(α-1)/min, respectively. Using atomic force microscopy, we also showed that high antibody density led to thicker electrode coating than low antibody density, with root-mean-square roughness values of 2.2 ± 0.2 nm versus 1.28 ± 0.04 nm, respectively. Furthermore, we showed that as the antigen accumulated onto the electrode, the solution resistance increased for high antibody density and decreased for low antibody density. Finally, the antigen detection performance test yielded a better limit of detection for low antibody density than for high antibody density (0.26 μM vs 2.2 μM). Overall, we show here the importance of these two factors and how changing one parameter can drastically affect the desired outcome. Graphical abstract Electronic supplementary material The online version of this article (10.1007/s00216-020-02417-x) contains supplementary material, which is available to authorized users.

The impedance of a battery can be modelled with an elegant fractional-capacitor or “constant phase element” (CPE) equivalent circuit and a series resistor. In this manuscript, we present new evidence that suggests that a linear model similar to Randles' comprised solely of this impedance network is able to predict both the charge-voltage relationship epitomised by the familiar hysteresis curve of voltage as a function of charge as a battery charges and discharges through its linear region, and the recovery or “equilibration” transient that results from a step change in load current. The proposed model is unique in that it does not contain a source, either voltage or current, nor any purely reactive elements. There are important potential advantages of a passive battery model.

Corrosion inhibition of carbon steel in hydrochloric acid solution was inspected using newly Benzylidene-aniline derivatives namely: (E)-N(2-Chlorobenzylidene)-2-Fluorobenzenamine (NCF) and (E)-N(2-Chlorobenzylidene)-3-Chloro-2-Methylbenzenamine (NCCM), by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The experimental results showed that both NCF and NCCM are good inhibitors for carbon steel in 1 M HCl. The inhibition efficiency increases with inhibitors concentration rise, reaching a value up to 89.72% at 10−3 M for the inhibitor NCF. Electrochemical impedance data show a frequency distribution of the capacitance, simulated as constant phase element (CPE). Polarization curves study revealed that both inhibitors are mixed type. The adsorption on the carbon steel surface follows Langmuir isotherm model with negative values of ΔGads0. Thermodynamics data for the adsorption process are calculated and discussed. The effect of molecular structure on inhibition efficiency was investigated by quantum chemical calculations using density function theory (DFT). Furthermore, Monte Carlo simulation technique incorporating molecular mechanics and molecular dynamic was applied to search for the best configurationally space for (NCCM or NCF)/100H2O/α-Fe2O3 (1 1 1) systems. The results indicate that the adsorption energy of NCF was greater than NCCM which is in accordance with the experimentally determined inhibition efficiency. Keywords: Corrosion inhibition, HCl, Benzylidene-aniline, Carbon steel, Electrochemical techniques, DFT, Molecular Dynamics Simulation

A conventional solid-state method was used to prepare Pb(Fe1/3Ti1/3W1/3)O3 single perovskite material. The sample sintered at 900?C was studied by XRD and after Rietveld refinement the orthorhombic structure with Pbam space group was confirmed. The FTIR frequency bands corresponding to Pb-O, Ti-O, O-lattice, W- O-W and Fe-O stretching vibrations together with the XRD data also confirmed that Fe2+ and W6+ ions are incorporated in the structure and most probably substituted Ti4+ ions at the B site of the perovskite ABO3 structure. The average grain size of the perovskite ceramics, estimated from SEM micrograph, was 1 to 2 ?m. Variation of dielectric properties and AC conductivity with frequency and temperature revealed that the material had semiconducting nature and negative temperature coefficient of resistance (NTCR). The Nyquist plots were modelled with an equivalent circuit consisted of parallel capacitance, resistance and constant phase element corresponding to the grains (bulk) and grain boundaries. It was observed that grain resistance (Rb) of the sample decreases with the rise of temperature, which supports the NTCR behaviour. The semi-circular arcs of the Nyquist and Cole-Cole plots confirm the semiconducting nature of the sample.

For NiTiCu SMA, the Ni atoms are substituted by Cu atoms, which not only greatly reduce the alloy cost, but also have excellent shape memory effect. Four kinds of shape memory alloy films (Ni49.6Ti50.4, Ni48.2Ti50.4Cu1.4, Ni45.6Ti50.4Cu4, Ni42.7Ti50.4Cu6.9) were prepared using magnetron sputtering. Corrosion behaviors of the four films in phosphate buffered saline (PBS) solutions at 37°C were examined using electrochemical impedance spectroscopy (EIS) method. It was found that the corrosion resistance of the NiTi film is superior to the three NiTiCu films. The EIS data were fitted using a parallel resistance-capacitance (as a constant phase element) circuit associated with the surface oxide film. The thickness of the surface oxide layer of the three NiTiCu films increases with applied potential till 0.8 V, while that of the NiTi film can reach to 1.2 V.

In this study, strontium is used as an alloying element for improving the pitting resistance of Mg-5Al-4Sn based alloys in an alkaline solution. Potentiodynamic polarization measurements suggest that the addition of strontium increases the robustness of the pitting resistance as a result of the higher pitting potential and wider range of passive potential. Electrochemical impedance spectroscopy (EIS) confirms the formation of a solid passive film on the alloy surface due to a significant increase in the passive film and the charge transfer resistance, as well as lower film and double layer constant phase element magnitude values. Additionally, the potentiostatic polarisation results also show a lower passive current density and passive film stability, resulting in an increase in the breakdown time when the amount of strontium added to the alloy increases from 0.0 to 1.0 wt%. Furthermore, the scanning electron microscopy results indicate that insignificant corrosion is observed on alloy specimens containing strontium, whereas there is fierce corrosion on alloy based surfaces. This robust corrosion resistance could be attributed to the α-grain reduction and refined precipitates at the alloy grain boundaries, resulting in promoted formation of the passive film which is formed from a mixture of magnesium, aluminum and tin oxides/hydroxides, as confirmed by the X-ray photoelectron spectroscopy results.

The lithium-ion batteries in the electric vehicles are nonlinear systems with complex electrochemical dynamics, and estimation of battery state-of-charge (SOC) is affected by factors such as environmental temperature and battery current. Considering the above problems, the accurate estimation of battery SOC has always been a difficult and the critical issue of battery management system (BMS). In this paper, the constant phase element (CPE) is introduced to the traditional time domain circuit model by analyzing the electrochemical impedance spectra of lithium-ion batteries. Accordingly, an equivalent circuit model based on electrochemical impedance is constructed by using fractional order theory, which has specific physical significant, leading to the improved estimation accuracy to represent battery voltage. Moreover, the polarization resistance in the model is replaced by Butler-Volmer (BV) equation, which can solve the problem caused by large current and temperature variation during the actual operation of electric vehicles. Next, based on the model, an $\text{H}\infty $ observer is designed for battery SOC estimation, and the proposed SOC observer is tested by real-time experimental data of battery. The efficiency of the proposed model and observer are validated by some simulations and experiment tests.

Fractional calculus is a mathematical framework that has attracted considerable interest from mathematicians, physicists, and engineers. Among its applications, the use of fractional calculus in the automatic control field has led to interesting results, such as more robust controllers, compared to their integer-order counterparts. The proposed work utilizes the physical realization of a solid-state fractional-order capacitor for the implementation of a fractional-order lead compensator. The proposed capacitor is realized using a carbon black-based dielectric. Therefore, a fully analog closed-loop system implementation is realized. A suitable case study is conducted to validate the controller performance, both from simulations and experimentally. The obtained results further confirm the possibility of realizing and applying a fully analog fractional-order controller.

Here, we reported a study on the detection and electrical characterization of both cancer cell line and primary tumor cells. Dielectrophoresis (DEP) and electrical impedance spectroscopy (EIS) were jointly employed to enable the rapid and label-free differentiation of various cancer cells from normal ones. The primary tumor cells that were collected from two colorectal cancer patients, cancer cell lines (SW-403, Jurkat, and THP-1), and healthy peripheral blood mononuclear cells (PBMCs) were trapped first at the level of interdigitated microelectrodes with the help of dielectrophoresis. Correlation of the cells dielectric characteristics that was obtained via electrical impedance spectroscopy (EIS) allowed evident differentiation of the various types of cell. The differentiations were assigned to a “dielectric phenotype” based on their crossover frequencies. Finally, Randles equivalent circuit model was employed for highlighting the differences with regard to a series group of charge transport resistance and constant phase element for cancerous and normal cells.

Background Lead is a nonessential heavy metal, which can inhibit heme synthesis and has significant cytotoxic effects. Nevertheless, its effect on the electrical properties of red blood cells (RBCs) remains unclear. Consequently, this study aimed to investigate the electrical properties and the electrophysiological mechanism of lead exposure in mouse blood using Electrical Impedance Spectroscopy (EIS) in 0.01–100 MHz frequency range. Data characteristic of the impedance spectrum, Bodes plot, Nyquist plot and Nichols plot, and Constant Phase Element (CPE) equivalent circuit model were used to explicitly analyze the differences in amplitude–frequency, phase–frequency, and the frequency characteristics of blood in electrical impedance properties. Results Compared with the healthy blood in control mice, the changes in blood exposed to lead were as follows: (i) the hematocrit decreased; (ii) the amplitude–frequency and phase–frequency characteristics of electrical impedance decreased; (iii) the characteristic frequencies (f0) were significantly increased; (iv) the electrical impedance of plasma, erythrocyte membrane, and hemoglobin decreased, while the conductivity increased. (v) The pseudo-capacitance of cell membrane (CPE_Tm) and the intracellular pseudo-capacitance (CPE-Ti) were decreased. Conclusions Therefore, EIS can be used as an effective method to monitor blood and RBC abnormalities caused by lead exposure. The electrical properties of the cells can be applied as an important observation in the evaluation of the toxic effects of heavy metals.

International audience; The different contributions of the interfacial capacitance are identified in the case of passive materials or thin protective coatings deposited on the electrode surface. The method is based on a graphical analysis of the EIS results to determine both the passive-film capacitance in the high-frequency domain and the double-layer capacitance in the low-frequency domain. The proposed analysis is shown to be independent of the physicochemical origins of the frequency dispersion of the interfacial capacitances which results, from an analysis point of view of the experimental results, in the use of a constant-phase element. However, for a correct evaluation of the thin-film properties such as its thickness, the high-frequency data must be corrected for the double-layer contribution. In particular, it is shown that if the double-layer capacitance gives a frequency-dispersed response, it is necessary to correct the high-frequency part for the double-layer CPE. This is first demonstrated on synthetic data and then used for the determination of the thickness of thin oxide film formed on Al in neutral pH solution.

This contribution presents and experimentally analyzes the idea how to reach the constant magnitude as well as the phase response in the fractional-order (FO) phase when shifting two-ports. The straightforward method employing the automatic gain control circuit (AGC) in a cascade after so-called constant phase block approximating FO integrator or differentiator is studied. The variable gain amplifier utilized in AGC and simple RC-based FO constant phase elements (approximating capacitors with order alpha = 1/4 and alpha = 1/2 as an example) connected in the feedback of operational amplifier-based integrator are established in the experimental setup. The operation indicated in three decades (between 100 Hz and 100 kHz) is evaluated. The known solutions of the standard FO phase shifting circuits are discussed and generally compared with the features obtained in this paper, together with the supposed effects of AGC on their performances.

n-Type Si/p-type B-doped ultrananocrystalline diamond heterojunction photodiodes were built using pulsed laser deposition at a heated substrate temperature of 550 °C. Following the capacitance-voltage-frequency (C-V -f) and conductance-voltage-frequency (G-V -f) plots, the series resistance (Rs) values at zero bias voltage were 154.41 Ω at 2 MHz and 1.72 kΩ at 40 kHz. Rs should be ascribed to Rs occurring in the metallic contact and the bulk resistance in the active layer. At 40 kHz, the interface state density (nss) was 1.78 x 1013 eV-1 cm-2 and dropped exponentially to 1.39 x 1012 eV-1 cm-2 at 2 MHz. An assessed nss occurring at the heterojunction interface was the cause of deterioration in the photo-detection properties. At different V values, the appearance of the real (Z') and imaginary (Z'') characteristic curves revealed single semicircles whose centers lay below the Z' axis. The magnitude of the curve was diminished with the increment of V. The particularities of Z''-Z' plots can be identified as an equivalent circuit model. The appropriate model included Rs, which was combined with the parallel circuit of resistance and constant phase element.

New benzodiazepine derivatives, namely 8-Chloro-1,2,3,4,10,11-hyxahydrospiro[cyclohexane-1,11-dibenzo[1,4]diazipine] and 8-methyl-1,2,3,4,10,11-hyxahydrospiro[cyclohexane-1,11 dibenzo[1,4]diazipine] are heterocyclic and their inhibitive action against the corrosion of carbon steel in 1.0 M HCl solution was studied at 303 K by electrochemical impedance spectroscopy and polarization curves The results marked that the learned benzodiazepine product are good corrosion inhibitors to carbon steel in 1.0 M HCl medium, their inhibition efficiency increased with inhibitor concentration, and BND–Cl is slightly more effective than BND–CH3. Potentiostatic polarization study showed that BND–CH3 and BND–Cl are mixed-type inhibitors in 1.0 M HCl. Impedance experimental data disclose a frequency distribution of the capacitance, simulated as a constant phase element. The results obtained from electrochemical studies were in reasonable accordance. The adsorption of BND–Cl and BND–CH3 on steel surface obeyed Langmuir’s adsorption isotherm. Thermodynamic data clearly proper that the adsorption mechanism of benzodiazepine products on carbon steel surface in 1.0 M HCl solution is physical adsorption which implies electrostatic forces among the electric charge or ionic charges at metal/solution interface and dipoles of the adsorbent verify by the a chemisorption. Quantum chemical calculations employ the Density Functional Theory (DFT) were performed on benzodiazepine products to define the link between molecular structures and their inhibition efficiencies. Furthermore, the structures mentioned are stimulated by the Monte Carlo simulation to comprehend the adsorption mechanism. Finally, the correlation among experimental and theoretical returns was discussed.

Transport of redox species (VO2+/VO2+, V2+/V3+, Ti3+/Ti4+, and Fe2+/Fe3+) across the electrode/electrolyte interface is investigated in a thin-film rotating disk electrode configuration using electrochemical impedance spectroscopy (EIS). The transport features depend on the constituents of the thin-film catalyst layer and on the rate constant of the redox reaction. On Nafion-free porous electrodes, semi-infinite linear and finite transport features are observed under static and hydrodynamic conditions of the electrode, respectively. Depending on the rate constant of the electrochemical reaction, an equivalent circuit consisting of either resistance (R) and constant phase element (Q) or the Warburg short (Ws) element is proposed to explain the finite transport features. Addition of Nafion (binder) in the electrode offers extra resistance to the transport of redox species, which helps resolve EIS features of the transport of redox species through the porous thin-film electrode and that through the bulk of t...

Epoxy/ITO nanocomposites containing various filler ITO concentrations by weight were successfully fabricated. Using Differential Scanning Calorimetry (DSC), a thermo-analytical technique used to study the glass transition temperatures, we expected to find a restriction in the molecular mobility of the polymer chains that might confirm the influence of incorporating ITO contents into the epoxy material. Several complementary techniques were investigated, such as dielectric relaxation spectroscopy (DRS) at the range of frequency (10−1–106) Hz and over the temperature range from − 80°C to 240°C, and time-domain spectroscopy (TDS) with frequency domain (10−5–10−1) Hz. The experimental data were investigated and interpreted in terms of various dielectric formalisms. For TDS results, the neat epoxy is affected by the added ITO nanoparticles. In the low-frequency domain of TDS measurements, the depolarization current curves of the nanocomposites are precisely fitted in a parallel circuit (RiCi) association model. The obtained dielectric data of TDS analysis shows two interfacial relaxation processes. The first wide peak was mainly ascribed to the charge accumulations ITO-polymer interfaces and the additional peak can be related to the charge accumulated at the interface material-electrodes. Impedance evaluated data were analyzed using a consistent electrical circuit formalism. From − 80°C to 60°C, the nanocomposites exhibited an ohmic behaviour within the added ITO nanofiller. Between 60°C and 120°C, the nanocomposites exhibit a capacitive contribution behavior which makes the material suitable for capacitors devices. Above 120°C, the Nyquist design illustrations [(− Z″) versus (Z′)] are well theoretical fitted to an equivalent circuit model achieved by impedance with designed parameters: resistance (Rb) and constant phase element (CPE) combinations.

With electrical impedance spectroscopy (EIS), a method is presented which is possibly suitable for the independent determination of the content of dissolved and crystalline sucrose and the concentration of salts during the crystallization of sucrose from thick juice. Therefore, a sensor using this measurement principle could be an ideal tool for process analytical technology (PAT). We present a first, promising feasibility study on the model system water-sucrose-NaCl. The impedance spectra were recorded with an immersion probe. Spectra of samples of known composition were fitted with an equivalent electrical circuit. Resistance and capacitance of the suspension as well as the constant phase element describing the double-layer at the solution-electrodes interface are related to the sample composition by semi-empirical equations. The temperature dependence is expressed by the viscosity and the relative permittivity of aqueous sucrose solutions. In principle, the found equations allow to calculate the composition from spectra of unknown samples via the fitting to the equivalent circuit, although some improvements of the measurement equipment are required. After a successful validation of the method with technical sucrose suspensions and typical industrial processing regimes, crystallization processes can be monitored with a single sensor, even if incoming and outgoing mass flows should not be known.

The current methods used for estimating the electrical parameters of organic solar cells (OSC) from time-domain measurements are based on integer-order impedance models. Meanwhile, in the frequency-domain, the adopted circuit models usually contain a constant phase element which is known to capture effectively the fractional-order dispersive behavior of these devices. Therefore, inconsistency arises between the two analyses. In this work, we derive the time-domain relaxation response of an OSC, found to follow a Mittag-Leffler function, using the same fractional-order impedance model. The classical integer-order model that results into the exponential decay of the photocurrent can be easily recovered and should be used as a valid approximation only when the dispersion coefficient is close to unity.

The review summarises the results of EIS analysis of sulphide films formed on steel during hydrogen sulphide and microbiologically induced corrosion, as well as inhibition of these processe...

Hydrogen oxidation (HOR) and oxygen reduction (ORR) reactions are important reactions in the polymer electrolyte membrane fuel cell (PEMFC). However, there are other reactions relating to the kinetics of HOR and ORR, i.e. hydrogen adsorption and oxide formation reactions. Development of the PEMFC catalyst (mostly use Pt) requires kinetic understanding of these reactions taking place at electrodes. In present study, the HOR, ORR, hydrogen adsorption, and oxide formation taking place at Pt/H2SO4 interface were kinetically investigated in the whole potential range. Mechanistic study was performed by establishing kinetic equations from the proposed mechanism, derived to the Faradaic current density and impedance in order to fit to the experimental results. Fitting results indicated that the HOR has more kinetic activity on the Pt(110) than Pt(100) sites with the rate constants of 1.60 and 1.20 s−1, respectively. For the Pt oxidation/reduction process, fitting results showed the fast reaction rate of ORR compared with the Pt oxidation. Additionally from the impedance fitting, the electrical parameters (solution resistance, capacitance, Warburg coefficient, constant phase element parameter) of the electrode reactions were determined to complete the interpretation of the reaction mechanisms. This study demonstrated the acquisition of the mathematical model to predict the kinetic information of an electrochemical reaction. The model can be used to predict the electrochemical behavior of any electrochemical reactions, which is benefit for the design of an electrocatalyst.

Battery models are the cornerstone to battery state of charge (SOC) estimation and battery management systems in electric vehicles. This paper proposes a novel fractional-order model for a battery, which considers both Butler–Volmer equation and fractional calculus of constant phase element. The structure characteristics of the proposed model are then analyzed, and a novel identification method, which combines least squares and nonlinear optimization algorithm, is proposed. The method is proven to be efficient and accurate. Based on the proposed model, a fractional-order unscented Kalman filter is developed to estimate SOC, while singular value decomposition is applied to tackle the nonlinearity of Butler–Volmer equation and fractional calculus of constant phase element. The systematic comparison between the proposed model and traditional fractional order model is carried out on two LiNiMnCo lithium-ion batteries at different temperatures, ageing levels, and electric vehicle current profiles. The comparison results show that the proposed model has higher estimation accuracy in battery terminal voltage and SOC than the traditional model over wide range of temperature and ageing level under electric vehicle operation conditions. Furthermore, the hardware-in-the-loop test validates that the proposed SOC estimation method is suitable for SOC estimation in electric vehicles.