Fourier Transform Electrochemical Impedance Spectroscopy Research Articles

Interaction of KLAKLAK-NH2 and Analogs with Biomimetic Membrane Models.

Specifically designed peptide mimetics offer higher selectivity regarding their toxicity to mammalian cells. In addition to the α-helix conformation, the specific activity is related to the peptide's ability to penetrate the cell membrane. The alterations in lipid membrane properties were addressed in the presence of the peptide KLAKLAK-NH2 and analogs containing β-alanine, strengthening the antibacterial activity and/or naphtalimide with proven anticancer properties. The molecular interactions of the peptide mimetics with POPC bilayers were studied using FTIR-ATR spectroscopy. The thermal shape fluctuation analysis of quasispherical unilamellar vesicles was applied to probe the membrane bending elasticity. The impedance characteristics of bilayer lipid membranes were measured using fast Fourier-transform electrochemical impedance spectroscopy. A lateral peptide association with the membrane is reported for β-alanine-containing peptides. The most pronounced membrane softening is found for the NphtG-KLβAKLβAK-NH2 analog containing both active groups that corroborate with the indications for 1,8-naphthalimide penetration in the lipid hydrophobic area obtained from the FTIR-ATR spectra analysis. The β-alanine substitution induces strong membrane-rigidifying properties even at very low concentrations of both β-alanine-containing peptides. The reported results are expected to advance the progress in tailoring the pharmacokinetic properties of antimicrobial peptides with strengthened stability towards enzymatic degradation. The investigation of the nonspecific interactions of peptides with model lipid membranes is featured as a useful tool to assess the antitumor and antimicrobial potential of new peptide mimetics.

Diagnosis of Water Failures in Proton Exchange Membrane Fuel Cells via Physical Parameter Resistances of the Fractional Order Model and Fast Fourier Transform Electrochemical Impedance Spectroscopy

AbstractThe identification of water status is the foundation for fuel cell water management, which is helpful to fuel cell reliability and longevity. In this article, a novel and reliable method for diagnosing the hydration condition of proton exchange membrane fuel cells (PEMFCs) was presented using a fractional-order model (FOM) to represent the PEMFCs impedance. The results show that the mean root-mean-squared error (RMSE) and mean absolute percentage error (MAPE) between the proposed model and experimental data (in normal, drying, or flooding cases) are about 0.034 and 0.473, respectively. The fast Fourier transform–electrochemical impedance spectroscopy technique (FFT-EIS) was used as an alternative technique that is simple and efficient to electrochemical impedance spectroscopy (EIS). The PEMFCs hydration state is monitored by observing the changing effect of the physical resistor values (membrane resistance, polarization, and diffusion resistances) of the proposed model. These resistors, characterized by their high sensitivity to the drying and flooding of PEMFCs, affect the Nyquist impedance spectra and frequency spectrum amplitudes at low and high frequencies. Based on the obtained results, it is concluded that the proposed strategy can be used to develop new domains in which the PEMFCs’ hydration states can be properly predicted.

Feasibility of Applying Fourier Transform Electrochemical Impedance Spectroscopy in Fast Cyclic Square Wave Voltammetry for the In Vivo Measurement of Neurotransmitters.

We previously reported on the use of fast cyclic square wave voltammetry (FCSWV) as a new voltammetric technique. Fourier transform electrochemical impedance spectroscopy (FTEIS) has recently been utilized to provide information that enables a detailed analytical description of an electrified interface. In this study, we report on attempts to combine FTEIS with FCSWV (FTEIS-FCSWV) and demonstrate the feasibility of FTEIS-FCSWV in the in vivo detection of neurotransmitters, thus giving a new type of electrochemical impedance information such as biofouling on the electrode surface. From FTEIS-FCSWV, three new equivalent circuit element voltammograms, consisting of charge-transfer resistance (Rct), solution-resistance (Rs), and double-layer capacitance (Cdl) voltammograms were constructed and investigated in the phasic changes in dopamine (DA) concentrations. As a result, all Rct, Rs, and Cdl voltammograms showed different DA redox patterns and linear trends for the DA concentration (R2 > 0.99). Furthermore, the Rct voltammogram in FTEIS-FCSWV showed lower limit of detection (21.6 ± 15.8 nM) than FSCV (35.8 ± 17.4 nM). FTEIS-FCSWV also showed significantly lower prediction errors than FSCV in selectivity evaluations of unknown mixtures of catecholamines. Finally, Cdl from FTEIS-FCSWV showed a significant relationship with fouling effect on the electrode surface by showing decreased DA sensitivity in both flow injection analysis experiment (r = 0.986) and in vivo experiments. Overall, this study demonstrates the feasibility of FTEIS-FCSWV, which could offer a new type of neurochemical spectroscopic information concerning electrochemical monitoring of neurotransmitters in the brain, and the ability to estimate the degree of sensitivity loss caused by biofouling on the electrode surface.

In Situ Real-Time Monitoring of ITO Film under a Chemical Etching Process Using Fourier Transform Electrochemical Impedance Spectroscopy.

As a novel approach to the in situ real-time investigation of an ITO electrode during the wet etching process, step-excitation Fourier-transform electrochemical impedance spectroscopy (FT-EIS) was implemented. The equivalent circuit parameters (e.g., Rct, Cdl) continuously obtained by the FT-EIS measurements during the entire etching process showed an electrode activation at the initial period as well as the completion of etching. The FT-EIS results were further validated by cyclic voltammograms and impedance measurements of partially etched ITO films using ferri- and ferrocyanide solution in combination with FESEM imaging, EDS, XRD analyses, and COMSOL simulation. We also demonstrated that this technique can be further utilized to obtain intact interdigitated array (IDA) electrodes in a reproducible manner, which is generally considered to be quite tricky due to delicacy of the pattern. Given that the FT-EIS allows for instantaneous snapshots of the electrode at every moment, this work may hold promise for in situ real-time examination of structural, electrokinetic, or mass transfer-related information on electrochemical systems undergoing constantly changing, transient processes including etching, which would be impossible with conventional electroanalytical techniques.

Implementation of Second-Generation Fourier Transform Electrochemical Impedance Spectroscopy with Commercial Potentiostat and Application to Time-Resolved Electrochemical Impedance Spectroscopy.

We report the implementation of second-generation Fourier transform electrochemical impedance spectroscopy (2G FT-EIS) with commercial potentiostat. Although 2G FT-EIS based on chronoamperometry has several advantages of short measurement time and ability of time-resolved EIS, a special home-built electrochemical system is essential, which has been an obstacle to the wide application of 2G FT-EIS. Current commercial potentiostat and software, however, has sufficient power thanks to recent state-of-the art electronics and software industry. 2G FT-EIS requires two signals of time versus voltage and time versus current from chronoamperometry with a high sampling rate. In this work, auxiliary input of a commercial potentiostat was used to record voltage signal concomitant with typical chronoamperometry that consisted of time versus current. This simple approach enables the 2G EIS without expensive frequency response analyzer (FRA) and the complex home-built instrument. EISs with various charge transfer kinetics were investigated by the formation of a self-assembled monolayer (SAM) on Au with different chain lengths. More to the point, in situ time-resolved EISs during the SAM were obtained, demonstrating the ability of a commercial potentiostat for time-resolved EIS.

Formation and properties of phospholipid bilayers on fluorine doped tin oxide electrodes

Commercially available fluorine doped tin oxide (FTO) films on glass were functionalized by the octadecyltrichlorosilane (OTS) self-assembled monolayers (SAM), which upon exposure to a multilamellar phospholipid vesicle solutions trigger vesicle fusion and formation of a tethered phospholipid bilayer membrane (tBLM). The formation of tBLMs was monitored in real-time by the Fast Fourier Transform (FFT) electrochemical impedance spectroscopy (EIS), which attested for the completion of the fusion process within 2000 s. We established that highly insulating complete bilayers can be accomplished only in some specific cases of OTS functionalized FTO films. In particular, only OTS functionalized FTO films exhibiting double semicircular features on the Cole – Cole EIS plots produced tBLMs with the specific capacitance below 1 μF cm−2 comparable to capacitances of the free-standing phospholipid bilayers. The double-semicircular features of EIS spectra can be used as a diagnostic tool for predicting the suitability of silanized FTO substrates for the complete vesicles fusion leading to a formation of the tBLMs. The average value of the capacitance of DOPC bilayers containing 40% (mol) cholesterol was of 0.82 ± 0.10 μF cm−2 consistent with the 3.02 nm thick dielectric film with the relative dielectric constant of 2.8. In contrast to the gold substrates, tBLMs on OTS functionalized FTO films can be regenerated at least 3 times by washing off lipid layer and re-assembling tBLM via the vesicle fusion process. EIS provided direct evidence of the susceptibility of the tBLMs to phospholipase A2, which triggered degradation of the films. However, transmembrane reconstitution of the pore-forming toxin vaginolysin (VLY) proteins was not detected. Surface constructs described in this study may be utilized in peripheral protein studies or in applications in which planar phospholipid layers supported on a semiconductor metal oxide surfaces are required.

Effect of Electrode Mixing Conditions on the Performance of Lithium-Ion Batteries Analyzed by Fast Fourier Transform Electrochemical Impedance Spectroscopy

We have investigated the influence of mixing conditions during the positive electrode fabrication on the discharge performance and internal resistances under high rate discharge of a test lithium-ion battery at 30 °C, employing fast Fourier transform electrochemical impedance spectroscopy in-situ to minimize the change in the state of charge. The internal resistances are assigned to each component in the positive electrode by comparing with cross-sectional scanning electron micrographs. The mixings of the active material and conductive filler with too low rotating speed both before and after the addition of the binder and solvent, pre-mixing and slurry mixing, respectively, give smaller active contact area between agglomerated conductive filler and the active material, leading to larger interfacial resistance. The pre-mixing and slurry mixing under too high rotating speed both result in larger interfacial resistances due to poor contacts of agglomerated active material with the conductive filler and the electrolyte.

Effect of Electrode Mixing Conditions on the Performance of Lithium-Ion Batteries Analyzed by Fast Fourier Transform Electrochemical Impedance Spectroscopy

High power and energy density lithium-ion batteries (LIBs) with high charge/discharge rate are required for electric vehicles. Although it is inevitable to clarify the appropriate electrode manufacturing methods to enhance the performance of LIBs, there have been many uncertain points. In the present study, we investigate the influence of positive electrode mixing conditions on the performance of LIBs at 30 °C. Test cells were assembled with positive electrodes of LiCoO2 mixed with acetylene black as conductive filler and PVDF binder, electrolyte solution of ethylene carbonate (EC)/dimethylcarbonate (DMC) (1:1 vol.) containing 1 M LiPF6, and negative electrodes of graphite mixed with PVDF binder.We employed fast Fourier transform electrochemical impedance spectroscopy (FFT-EIS) to analyze the internal resistances under discharge to take advantage of its short measurement time since measurable decrease in the state of charge (SOC) cannot be avoided during EIS measurements with the conventional frequency response analyzer (FRA). Cross-sectional scanning electron microscope (SEM) observations of the positive electrodes were also carried out.Pre-mixing of LiCoO2 particles and acetylene black under an appropriate mill rotation speed is effective for the performance enhancement. In both cases without the pre-mixing and with pre-mixing under too high mill rotation speed, the discharge capacities decrease.The impedance spectrum by FFT-EIS exhibits two semi-circles at 1000 mA/g. In the case without the pre-mixing, the high frequency arc becomes significantly large, while both high and low frequency arcs become significantly large in the case with pre-mixing by too high mill rotation speed.The appropriate pre-mixing possibly thus decreases the resistance of electron transfer, i.e. contact resistance, between the LiCoO2 particles and acetylene black by good dispersion increasing the contact between them. This view corresponds to the assignment that the high frequency arc is attributed to the surface insulating layer of LiCoO2 particles[1,2] contacting with acetylene black. The SEM observations support this view.On the other hand, the pre-mixing by too high mill rotation speed possibly increases the contact among LiCoO2 particles, decreasing the contact between the LiCoO2 particles and acetylene black. This also decreases the contact between the LiCoO2 particles and the electrolyte. This view agrees with the assignment that the high frequency arc is ascribed to the surface insulating layer of LiCoO2 particles described above while the low frequency arc represents the Li ion charge transfer at the interface between the LiCoO2 particles and the electrolyte[1,2]. The SEM observations support this view also in this case.

Consideration on the Non-linearity of Warburg Impedance for Fourier Transform Electrochemical Impedance Spectroscopy

Department of Chemistry, Pukyong National University, 45 Yongso-ro, Nam-gu, Busan 608-739, Korea(Received March 28, 2014 : Accepted May 12, 2014)Abstract: Here I report on how Fourier Transform Electrochemical Impedance Spectroscopy(FTEIS) overcomes the potential-current linearity problem encountered in the impedance cal-culation process. FTEIS was first invented to solve the time-related drawback of the conven-tional impedance technique. The dramatic time reduction of FTEIS enabled the real-timeimpedance measurement but brought about the linearity problem at the same time. While theconventional method circumvents the problem using the steady-state made by a sufficiently longmeasurement time, FTEIS cannot because of its real-time function. However, according to themathematical development reported in this article, the potential step used in FTEIS is provedto avoid the linearity problem. During the step period, the potential and the current are lin-earized by the electrochemical impedance. Also, Fourier transform of the differentiated potentialand current is proved to give the same result of the original ones. Keywords : Impedance Spectroscopy, Electrochemistry Theory, Warburg Impedance

Electrocatalysis of Hypophosphite on Nickel Investigated Using Time Resolved Fourier Transform Electrochemical Impedance Spectroscopy

Electro-oxidation of hypophosphite plays an important role in the electro-less deposition of Ni used to fabricate surface engineered films, alloys, and coatings for a variety of applications. At the same time, the kinetic details of this oxidation reaction comprise an ideal framework for studying many general mechanistic aspects of electrocatalysis on transition metal substrates. The present work utilizes these specific attributes of hypophosphite oxidation to probe the underlying function of the incipient hydrous oxide of Ni in promoting the catalytic properties of this metal in an alkaline medium. The experiments reported here use time-resolved Fourier-transform electrochemical impedance spectroscopy (FT-EIS), strategically coupled with scan-rate controlled voltammetry. The results suggest that the incipient hydrous oxide Ni(OH)ad formed at the onset of hypophosphite oxidation catalytically promotes the latter's precursor de-hydrogenation step. While voltammetry provides suggestive evidence for these Ni(OH)ad induced effects, the FT-EIS data serve to gather more direct signatures of the catalytic function of Ni(OH)ad.

Electrochemical behavior of PbO2 nanowires array anodes in a zinc electrowinning solution

Free-standing PbO2 nanowires were prepared by an electrodeposition process onto the titanium foil. The morphology of nanowires was investigated by SEM analyses. The contact angle of the nanowires was compared with that of planar film, which indicated higher hydrophilicity and surface energy of nanowires. Cyclic voltammetric and real-time Fourier transform electrochemical impedance spectroscopy (FTEIS) experiments were employed to study the anodic reaction on the surface. The cyclic voltammetric data showed the overpotential of nanowire array electrode decreased by more than 100mV compared to that of the planar film electrode at an anodic current density of 400A/m2. A large body of impedance data acquired from the two electrodes as a function of scanned potential by running combined staircase cyclic voltammetry and FTEIS experiments led to systematic comparative analysis on the electrode/electrolyte interface. The changes in solution resistances, film resistances and capacitances, double layer capacitances, and polarization resistances observed during oxygen evolution process were compared and explained by corresponding electrochemical reactions. The nanowires of PbO2 showed a large active surface area led to higher capacitance than that of the planar electrode.

Development of Galvanostatic Fourier Transform Electrochemical Impedance Spectroscopy

Here, we report development of the galvanostatic Fourier transform electrochemical impedance spectroscopy (FTEIS), which monitors impedance of electrochemical reactions activated by current steps. We first derive relevant relations for potential change upon application of a step current, obtain impedances theoretically from the relations by simulation, and verify them with experimental results. The validity of the galvanostatic FTEIS technique is demonstrated by measuring impedances of a semiconductive silicon wafer using the conventional frequency response analysis (FRA), the potentiostatic FTEIS, and the galvanostatic FTEIS methods, and the results are in excellent agreement with each other. This work is significant in that the galvanostatic FTEIS would allow one to record impedance changes during charge/discharge cycles of secondary batteries and fuel cells as well as electrochemically irreversible systems which may produce noise level chronoamperometric currents by potentiostatic techniques.

Fourier transform electrochemical impedance spectroscopic studies on anodic reaction of lead

Lead oxidation and subsequent oxygen evolution have been studied in a zinc electrowinning solution employing cyclic voltammetric and real-time Fourier transform electrochemical impedance spectroscopy (FTEIS) experiments. A large body of impedance data obtained as a function of scanned potential by running combined staircase cyclic voltammetry and FTEIS experiments led to systematic analysis on the electrode/electrolyte interface. The changes in solution resistances, film resistances as well as film capacitances, double layer capacitances, polarization resistances, and Warburg admittances observed during lead oxidation satisfactorily explain corresponding electrochemical reactions. Various electrode reaction kinetic parameters for oxidation of lead and oxygen evolution were obtained from the impedance data. The reaction mechanism is discussed based on the impedance data.

Zinc Oxidation in Dilute Alkaline Solutions Studied by Real-Time Electrochemical Impedance Spectroscopy

Electrochemical oxidation of zinc has been studied in dilute alkaline solutions, 0.010 and 0.10 M KOH, employing cyclic voltammetric and real-time Fourier transform electrochemical impedance spectroscopy (FTEIS) experiments. Thermodynamic analysis of cyclic voltammetric data indicates that Zn(OH)42– is produced as a major product in both 0.10 and 0.010 M KOH although ZnO/Zn(OH)2 may also be produced as a minor product in 0.010 M. A large body of impedance data was obtained as a function of swept potential by running combined staircase cyclic voltammetry and FTEIS (SCV-FTEIS) experiments at every 10 mV and 200 ms interval, which allowed a systematic and complete analysis to be made on the interface. Analysis of the extensive impedance data demonstrates that electron transfer takes place across the thin oxide/hydroxide film, whose electrical state undergoes drastic changes at the potential where charge transfer occurs. The capacitance of the film covering the surface was shown to undergo a large change during the charge transfer indicating that the electrode/electrolyte interface is strongly electrified during the charge transfer across it. Various electrode reaction kinetic parameters for oxidation of zinc are also reported by treating the impedance data and the reaction mechanism is discussed based on the data.

Characterization of LiFePO4 Cathodes and Zinc Anodes by Novel Fourier Transform Electrochemical Impedance Spectroscopy Experiments

not Available.

Direct Evaluation Method on the Effect of Additives in Copper Electroplating using FTEIS (Fourier Transform Electrochemical Impedance Spectroscopy)

not Available.

Fourier Transform Electrochemical Impedance Spectroscopic Studies on LiFePO4 Nanoparticles of Hollow Sphere Secondary Structures

Real-time impedance behaviors of LiFePO4 nanoparticles of two different structures have been investigated as cathode materials for lithium ion batteries using real time Fourier transform electrochemical impedance spectroscopy (FTEIS) techniques during potentiodynamic charging and discharging cycles. The effects of their nanostructures were examined employing hollow sphere secondary structured LiFePO4 particles prepared by sequential precipitations and commercially available non-hollow structured LiFePO4 particles. The battery constructed with the hollow sphere secondary structured LiFePO4 cathode material exhibited improved performances during charging and discharging processes as judged from various impedance parameters compared to those observed for the cell using its non-hollow counterpart. These results appear to have resulted from the enhancement of intrinsic capabilities for electron and charge transport characteristics of LiFePO4 by modifying its secondary structures. The real time impedance measurements were shown to be powerful in studying behaviors of battery electrodes during charging and discharging processes.

Electrochemical investigation of surface reactions for chemically promoted chemical mechanical polishing of TaN in tartaric acid solutions

In this work we use cyclic voltammetry, linear polarization resistance (LPR) measurements and Fourier transform electrochemical impedance spectroscopy (FT-EIS) to study the chemical mechanisms of chemical mechanical polishing (CMP) of TaN wafers in pH-controlled solutions of Tartaric acid (C 4H 6O 6) and H 2O 2. These solutions can support CMP of TaN diffusion-barriers in the fabrication of interconnect structures, and can be particularly useful for chemically dominant low-pressure CMP in a non- or weakly alkaline environment to avoid OH − induced damages to Si-based low- k dielectrics. Electrochemical results presented here demonstrate how the individual and synergistic chemistries of C 4H 6O 6 and H 2O 2 control the removal of TaN surface layers. LPRs measured in tartaric acid solutions at pH 3–8 exhibit strong correlations with TaN wafer polish rates obtained in these solutions. A.C. impedance measurements help to clarify the underlying chemical mechanisms of material removal. These findings indicate that the Ta sites of TaN are oxidized to Ta 2O 5 by O 2 and H 2O 2 in the solution, followed by structural weakening of the oxide film due to the formation of Ta(OH) 5 and mechanically fragile Ta-tartarate surface complexes.

Physical Methods of Fast Reactions Investigation

This review presents the basic concepts of the methods used for investigation of fast reactions kinetics, such as: flow methods, with particular emphasis on the stopped-flow approach, NMR, ESR, electrochemical methods, with particular emphasis on the time resolved Fourier Transform electrochemical impedance spectroscopy, flash photolysis, and several others. It offers a brief description of fast reactions commonly encountered in chemical systems, providing an insight into the possibilities of performing kinetic investigations of such reaction systems.

Investigation of dissolution inhibitors for electrochemical mechanical planarization of copper using beta-alanine as a complexing agent

Dissolution inhibition capabilities of benzotriazole (BTAH) and ammonium dodecyl sulfate (ADS) are investigated, in combination with β-alanine, as a complexing agent for applications in electrochemical mechanical planarization (ECMP) of copper. Cu electrodissolution is induced by linear sweep voltammetry (LSV), and Fourier transform electrochemical impedance spectroscopy (FT-EIS) is combined with LSV to examine the relative roles of the electrolyte additives in governing the surface reactions of Cu under voltage activated conditions of ECMP. The experiments focus on the electrochemical rather than mechanical component of ECMP, and are designed to probe both the individual and combined effects of BTAH and ADS on Cu electro-dissolution in the absence of abrasion.