Dynamic Electrochemical Impedance Spectroscopy Research Articles

Li-Si alloy pre-lithiated silicon suboxide anode constructing a stable multiphase lithium silicate layer promoting Ion-transfer kinetics

Enhancing the initial Coulombic efficiency (ICE) and cycling stability of silicon suboxide (SiOx) anode is crucial for promoting its commercialization and practical implementation. Herein, we propose an economical and effective method for constructing pre-lithiated core–shell SiOx anodes with high ICE and stable interface during cycling. The lithium silicon alloy (Li13Si4) is used to react with SiOx in advance, allowing for improved ICE of SiOx without compromising its reversible specific capacity. The pre-lithiated surface layer contains uniform multiphase lithium silicates (L2SiO3, Li4SiO4, and Li2Si2O5) in the nanoscale. This multiphase lithium silicate layer exhibits mechanical robustness against variation of micro-stress, which can act as a buffer layer to relieve volume variation. In addition, analysis of dynamic electrochemical impedance spectroscopy (dEIS) and distribution of relaxation time (DRT) confirm that the multiphase lithium silicate layer enhances Li-ion diffusion kinetics and contributed to constructing stable SEI. As a result, the optimal L10-850 anode shows a high ICE of 85.3 %, together with a high specific capacity of 1771.5mAh mg−1. This work gives a perspective strategy to modify SiOx anodes by constructing a pre-lithiated surface layer with practical application potentials.

Reduced artifacts in dynamic electrochemical impedance spectroscopy applied to battery degradation analysis

Lithium-ion batteries (LIBs) degradation can be classified into capacity reduction and increase of the internal resistance. Accurate estimation of degradation is important to determine the economic value and the remaining useful life of the battery. This paper adopts dynamic electrochemical impedance spectroscopy (EIS) to evaluate degradation while charging the battery, without requiring additional time for the analysis. A new method is proposed to remove the artifacts arising from the time-variance of the system during the measurement. The validity of the method is confirmed by comparing it with the results obtained by static EIS measurements at equilibrium. The spectra are fitted to an equivalent circuit containing three resistances (R0, R1, R2). The method is applied to data obtained before and after aging cycles performed at 1.4C charge and 2.0C discharge rates, at 25 °C, 10 °C and −5 °C. The resistance of the films (R1), which is obtained from the semicircle at high frequencies in the EIS spectrum, has proved to be the key indicator of aging, and linearly depends on the SoC. The increase of R1 dominates among all the resistances, particularly at higher temperatures. Dynamic EIS is considered a powerful tool to diagnose LIBs in practical applications.

Why Charge Rate Capability Tests Fail to Characterize Structured Electrodes in Lithium-Ion Batteries and How to Modify Them

Fast charging is one of the most essential criteria for the user acceptance of battery electric vehicles. Especially for high-loaded electrodes used in automotive applications, the rate capability is limited due to the transport limitations of lithium ions in the pores.1 Electrode structuring is a powerful tool to overcome those limitations by creating additional directed diffusion channels for lithium ions.2 Despite the frequently described reduction of the transport limitation of lithium-ion batteries,3 there are hardly any charge rate capability tests in the literature that demonstrate the improvement through structuring. Instead, most studies present discharge rate capability tests showing the desired performance increase due to structuring.4-8 This study will explain why charge rate capability tests fail to characterize electrodes in the transport-limiting C-rate range. For this purpose, graphite anodes underwent “structure calendering”, where electrodes are simultaneously mechanically structured and calendered using an embossing roller. Thus, identical electrode properties, except for the lower tortuosity, can be achieved compared to the non-structured graphite anodes that were only calendered. Despite their different tortuosities, we will show that structured and non-structured graphite anodes exhibit minimal capacity differences in the charge rate capability test. This is attributed to lithium plating, which shifts the anode potential to similar values, regardless of the transport properties of the investigated electrode. We will modify the test to characterize the charge rate capability of electrodes in the transport-limiting regime where lithium plating occurs. For this purpose, in the charge rate capability test, the current is superimposed with a sinusoidal signal and the voltage response is measured. This allows the continuous estimation of the cell impedance during charging. Previous studies have shown that this method allows to track the onset of the lithium plating reaction.9-10 Applying the modified charge rate capability test will demonstrate that this detrimental side reaction occurs significantly later in structured electrodes. Günter, F. J., & Wassiliadis, N. (2022). State of the Art of Lithium-Ion Pouch Cells in Automotive Applications: Cell Teardown and Characterization. Journal of The Electrochemical Society, 169(3), 030515. https://doi.org/10.1149/1945-7111/ac4e11Pfleging, W. (2017). A review of laser electrode processing for development and manufacturing of lithium-ion batteries. Nanophotonics, 7(3), 549–573. https://doi.org/10.1515/nanoph-2017-0044Mai, W., Usseglio-Viretta, F. L. E., Colclasure, A. M., & Smith, K. (2020). Enabling fast charging of lithium-ion batteries through secondary-/dual- pore network: Part II - numerical model. Electrochimica Acta, 341, 136013. https://doi.org/10.1016/j.electacta.2020.136013Keilhofer, J., Schaffranka, L., Wuttke, A., Günter, F., Hille, L., Dorau, F., & Daub, R. (2023). Mechanical Structuring of Lithium‐Ion Battery Electrodes Using an Embossing Roller. Energy Technology. https://doi.org/10.1002/ente.202200869Dubey, R., Zwahlen, M. D., Shynkarenko, Y., Yakunin, S., Fuerst, A., Kovalenko, M. V., & Kravchyk, K. V. (2021). Laser Patterning of High-Mass-Loading Graphite Anodes for High-Performance Li-Ion Batteries. Batteries and Supercaps, 4(3), 464–468. https://doi.org/10.1002/batt.202000253Habedank, J. B., Kriegler, J., & Zaeh, M. F. (2019). Enhanced Fast Charging and Reduced Lithium-Plating by Laser-Structured Anodes for Lithium-Ion Batteries. Journal of The Electrochemical Society, 166(16), A3940–A3949. https://doi.org/10.1149/2.1241915jesHabedank, J. B., Kraft, L., Rheinfeld, A., Krezdorn, C., Jossen, A., & Zaeh, M. F. (2018). Increasing the Discharge Rate Capability of Lithium-Ion Cells with Laser-Structured Graphite Anodes: Modeling and Simulation. Journal of The Electrochemical Society, 165(7), A1563–A1573. https://doi.org/10.1149/2.1181807jesHille, L., Xu, L., Keilhofer, J., Stock, S., Kriegler, J., & Zaeh, M. F. (2021). Laser structuring of graphite anodes and NMC cathodes – Proportionate influence on electrode characteristics and cell performance. Electrochimica Acta, 392, 139002. https://doi.org/10.1016/j.electacta.2021.139002Koseoglou, M., Tsioumas, E., Ferentinou, D., Jabbour, N., Papagiannis, D., & Mademlis, C. (2021). Lithium plating detection using dynamic electrochemical impedance spectroscopy in lithium-ion batteries. Journal of Power Sources, 512(September), 230508. https://doi.org/10.1016/j.jpowsour.2021.230508Straßer, A., Adam, A., & Li, J. (2023). In operando detection of Lithium plating via electrochemical impedance spectroscopy for automotive batteries. Journal of Power Sources, 580(July), 233366. https://doi.org/10.1016/j.jpowsour.2023.233366

Deciphering the structural and kinetic factors in lithium titanate for enhanced performance in Li+/Na+ dual-cation electrolyte

The widespread application of Li4Ti5O12 (LTO) anode in lithium-ion batteries has been hindered by its relatively low energy density. In this study, we investigated the capacity enhancement mechanism of LTO anode through the incorporation of Na+ cations in an Li+-based electrolyte (dual-cation electrolyte). LTO thin film electrodes were prepared as conductive additive-free and binder-free model electrodes. Electrochemical performance assessments revealed that the dual-cation electrolyte boosts the reversible capacity of the LTO thin film electrode, attributable to the additional pseudocapacitance and intercalation of Na+ into the LTO lattice. Operando Raman spectroscopy validated the insertion of Li+/Na+ cations into the LTO thin film electrode, and the cation migration kinetics were confirmed by ab initio molecular dynamic (AIMD) simulation and electrochemical impedance spectroscopy, which revealed that the incorporation of Na+ reduces the activation energy of cation diffusion within the LTO lattice and improves the rate performance of LTO thin film electrodes in the dual-cation electrolyte. Furthermore, the interfacial charge transfer resistance in the dual-cation electrolyte, associated with ion de-solvation processes and traversal of the cations in the solid-electrolyte interphase (SEI) layer, are evaluated using the distribution of relaxation time, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Our approach of performance enhancement using dual-cation electrolytes can be extrapolated to other battery electrodes with sodium/lithium storage capabilities, presenting a novel avenue for the performance enhancement of lithium/sodium-ion batteries.

High entropy alloy nanoparticles decorated carbon-based electrode as interfacial Li-ion localized accelerators for anode-free lithium metal batteries

Lithium metal is deemed as the main representative of the material for next-generation energy storage cells. Nevertheless, the problems of lithium dendrite growth and anode electrode volume expansion have become difficult problems in practical applications. Here, we introduced lithophilic CuInNiSnCd HEA-NPs on the surface of three-dimensional (3D) carbon hosts through a high-temperature redox strategy (HEA/CF). The application of the HEA/CF 3D framework can effectively decrease the non-uniform current density of the anode electrode, thereby slowing down the volume expansion of lithium metal during cycling. The introduction of CuInNiSnCd HEA-NPs improves the lithophilic of the carbon substrate and reduces the nucleation potential of lithium. Meanwhile, their evolution process was monitored in situ by the dynamic electrochemical impedance spectroscopy (DEIS) with relaxation time (DRT) distribution analysis, and the introduction of the HEA was beneficial to improving Li+ migration kinetics. Consequently, the symmetric battery with Li@HEA/CF anode has an excellent cycle life of over 3000 h (10 mA cm−2/10 mAh cm−2). Furthermore, the anode-free HEA/CF assembled full cell has excellent rate performance with a stable CE of more than 99.2 % after 160 cycles at 1C. This research contributes to the use of high-entropy materials in advanced energy storage batteries and provides valuable guidance for enhancing the performance of lithium batteries.

Three modes of electrochemical impedance spectroscopy measurements performed on vanadium redox flow battery

This article presents an innovative approach to monitor working redox flow batteries using dynamic electrochemical impedance spectroscopy, diverging from the commonly sequential impedance methods carried out under potentiostatic or galvanostatic conditions close to the open circle voltage. The authors introduce a fresh variation of dynamic impedance measurement that leverages an amplitude-modulated multi-frequency alternating current perturbation signal. This technique leads to a reduction in measurement time, making it possible to monitor impedance in real-time under typical operational conditions. Consequently, it effectively addresses the limitations stemming from the absence of stationary conditions during impedance measurements. There is no doubt that measurement techniques enabling the study of processes during the operational life of a battery provide the most valuable insights into the properties of these systems. The potential of this proposed approach is exemplified through the examination of a full vanadium redox flow battery as a case study. Classical impedance measurements were also conducted under potentiostatic and galvanostatic conditions with sequential frequency signal change, which requires stopping the battery operation, resulting in electrode potential changes of over 200 mV compared to the working system. Spectra for all modes of measurements were compared. In the case of dynamic measurements, such significant differences in spectra during charging and discharging are not observed, which is characteristic of classical measurements. The authors deliberately and consciously refrain from analyzing the results by fitting equivalent circuits.

Validation of dynamic electrochemical impedance spectrograms using autocorrelation function

Validation of impedance data is essential for checking the reliability of experimental data. Kramers – Kronig transformation is used to verify data obtained from classical Electrochemical Impedance Spectroscopy (EIS) measurements. Data obtained from Dynamic Electrochemical Impedance Spectroscopy (DEIS) could be validated in the same way, but in this case, there is no information about internal consistency between every single spectrum in the whole spectrogram. To address these challenges, the authors proposed an approach using the autocorrelation function ACF to validate DEIS time series. The reasoning conducted showed that ACF function is appropriate tool for validating DEIS spectrograms.

EVOLUTION OF WEAR AND CORROSION RESISTANCE OF Bi ALLOY-LAMINATED Al/TiO2 COMPOSITE STRIPS FABRICATED VIA APB PROCESS

In this study, Bi alloy AA1100/TiO2/AA5083 composites were produced by accumulative press bonding (APB) for the first time. In the first step, two bars of aluminum alloys 1100 and 5083 with 5[Formula: see text]wt.% of uniformly scattered TiO2 particles were stacked together and pressed with a 50% reduction ratio. Then, this process was continued up to six steps. Corrosion properties of composites were studied by potential dynamic polarization and electrochemical impedance spectroscopy measurement in 3.5[Formula: see text]wt.% NaCl solution. So, in this investigation and as its novelty, a considerable improvement was revealed in the main electrochemical parameters as a result of enhancing the influence of APB steps and the inert character of the particles. Moreover, using the wear test, the wear resistance of these bi alloy composites has been studied vs the APB steps. Also, the wear and electrochemical experiments showed that corrosion and wear resistance of samples were improved by the APB steps by 70% and 34%, respectively.

Exploring mechanism of corrosion inhibition of WE43 and AZ31 alloys by aqueous molybdate in Hank’s solution by multisine impedimetric monitoring

The concept of utilizing multisine dynamic electrochemical impedance spectroscopy to monitor effectiveness of a model molybdate inhibitor for AZ31 and WE43 Mg alloys is proposed. The corrosion kinetics and instantaneous values of inhibition efficiency (IE) of molybdate at concentrations up to 150 mM were examined. The inhibitor provides inhibition in Hank’s solution at concentrations starting from ca. 25 mM, with the IE of about 90%. These data together with results of the surface analysis allowed to propose the mechanism of the corrosion inhibition of AZ31 and WE43 Mg alloys by aqueous molybdate in Hank’s solution.

Effect of Cu2+ on deposition mechanism and structure of ZrO2-based conversion coatings on AA6060 aluminium alloys and their susceptibility to filiform corrosion

Zirconium oxide-based conversion coatings (CCs) were prepared from hexafluorozirconic acid, H2ZrF6, with and without CuII as an additive. The CCs were prepared on primary and recycled AA6060. The deposition mechanism, structure, electrochemical properties and effectiveness in protection against filiform corrosion (FFC) have been explored. In presence of CuII additives, a two step deposition mechanism is observed, evidenced by open circuit potential measurements and in situ dynamic electrochemical impedance spectroscopy. Copper deposits predominantly as copper(II) hydroxyfluoride on the top surface, and metallic Cu0 at the metal/CC interface, as evidenced by x-ray photoelectron spectroscopy and glow-discharge optical emission spectroscopy. The presence of a CuII additive induces a different distribution of the ZrO2-based products. After deposition of a weak organic model coating, aluminium pretreated with the CuII-containing system shows a 10%–30% lower maximum filament length compared to the CuII-free system in FFC tests, despite a ca. one order of magnitude higher cathodic activity of the former.

Dynamic Electrochemical Impedance Spectroscopy for Characterization of the State of Health of Graphite Electrodes

Graphitic carbon is the most used material as anode in lithium-ion batteries since the last 30 years. To make batteries cost-effective for mobility or stationary applications the optimization of every aspect is crucial. Advanced techniques can be implied to undercover or demonstrate the main chemical processes at the graphite electrode such as the Electrochemical Impedance Spectroscopy (EIS). EIS is a powerful technique able to reveal and separate resistive and capacitive properties of an interface in a non-destructive way. It has been applied for the characterization of graphite in order to quantify the charge transfer resistance on the intercalation process, to study the mechanism of formation of solid-electrolyte-interface (SEI), and reveal the lithium plating process [1]. There are high requirements for the collection of impedance spectra on a broad range of frequencies (typically from kHz to tens of mHz) at different electrode potentials regarding measurement time and the condition of a system in equilibrium. To overcome these requirements a technique has been developed called Dynamic Electrochemical Impedance Spectroscopy (DEIS). For DEIS a multi-frequency signal, containing all frequencies to probe in a form of summed sine waves, is superimposed to the galvanostatic current. Using this method, it is possible to measure the time-varying impedance while the system is drifting through non-equilibrium states, e.g. during charge/discharge cycling.In this study we propose DEIS measurements performed on a freshly assembled graphite/lithium half-cell cycled at current rates of C/10 and C/5 and 1C (for aging). Figure 1 A shows the working electrode voltage profile of the first 16 cycles. The chosen geometry for the cell is a three-electrode pouch cell with 2x2cm square electrodes and an insulated copper wire with lithium plated at the tip as micro-reference electrode (see Figure 1 B).The novelty of the proposed method is the fully automatized procedure to acquire the dynamic impedance on a wide frequency band (1kHz-10mHz) continuously over an arbitrary number of cycles to investigate the degradation of the electrode. The experimental set-up is shown as a scheme in Figure 1 C [2]. On base of the recorded current and voltage signals, we computed the time-varying impedance using the Dynamic Multi-Frequencies Analysis (DMFA). This method allows to calculate the impedance at the low frequency band by filtering of the sine components in the Fourier domain; the voltage drift is calculate in the same way [3]. An example of the computed time-varying impedance and the respective potential profile for the first cycle is reported in Figure 1 D.

In-Operando Detection Method for Lithium Metal Deposition during Fast Charging of Lithium-Ion Batteries Derived from Impedance Modeling

Lithium-ion batteries play a key role in the electrification of the transport sector. However, to replace combustion engines with battery-powered electric drive trains, the fast charging capability is essential. Therefore, it is necessary to identify the optimum operating window for lithium-ion cells. A strict criterion for optimization is to prevent lithium metal deposition at the anode, as this undesired side reaction can pose serious safety risks. An efficient technique to optimize charging strategies while tracking lithium plating is needed, as existing approaches have limitations such as a lack of in-line capability, low time precision, or complex experimental setups. In this study, a simple lithium metal deposition detection method is derived from a three-electrode setup. This in-operando method is applied during fast charging using dynamic electrochemical impedance spectroscopy. To model the acquired impedance spectra, a novel equivalent circuit is developed. The model is used to elucidate characteristic impedance features of anodes with deposited lithium metal. These observed characteristic features are then applied to a simplified measurement method in full cells using a single-frequency signal. The precision and high temporal resolution of both methods are demonstrated through validation. Furthermore, the simplified method can be applied in in-operando applications, making it suitable for diverse research and industrial contexts.

Deposition Mechanism, Structure and Corrosion Protection of ZrO2-Based Conversion Coatings on AA6060 Primary and Recycled Aluminum Alloys

Chemical conversion coatings (CC) are amongst the most common surface pretreatments for aluminium alloys before further organic coating steps. The presence of a conversion layer can increase the resistance towards underpaint corrosion such as filiform corrosion (FFC). Here we explore the deposition mechanism, structure and protective properties against FFC of a ZrO2-based CC on AA6060 aluminium alloy by means of electrochemical techniques as open circuit potential measurements, potentiodynamic polarization and dynamic electrochemical impedance spectroscopy (dEIS). Surface composition and elemental distribution are characterized by X-ray photoelectron spectroscopy (XPS), Glow Discharge Optical Emission Spectroscopy (GD-OES) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The variation of important parameters such as charge transfer resistance and capacitance during the conversion layer deposition gives insight into the deposition mechanism. GD-OES and XPS shed light into the structure and composition of the formed CC layer constituted of a mixture of Zr (hydr)oxides based products, redistribution of alloy elements and the nature of deposited additives. Finally, FFC tests reveal a comparable performance between primary and recycled alloys.

A Probe into the Corrosion Behavior of a WE43B Magnesium Alloy in a Simulated Body Fluid using Dynamic Electrochemical Impedance Spectroscopy

A Probe into the Corrosion Behavior of a WE43B Magnesium Alloy in a Simulated Body Fluid using Dynamic Electrochemical Impedance Spectroscopy

Determination of Electrode Kinetics Parameters from Dynamic Electrochemical Impedance Spectroscopy Measurements via Potential-Program Invariant Functions.

Dynamic electrochemical impedance spectroscopy, dEIS, comprises repetitive impedance spectrum measurements while slow scan-rate voltammetry is running. Its main virtue is the short measurement time, reducing the danger of contamination of the electrode surface. To further the use of dEIS, we have recently elaborated a set of theories aimed at the related data processing for three groups of fundamental electrode reactions: diffusion-affected charge transfer, charge transfer of surface-bound species, and adsorption-desorption. These theories yielded equations by which the voltammograms can be transformed to potential-program invariant forms, allowing an easy calculation of the rate coefficients; similar equations have been derived for the potential dependence of equivalent circuit parameters obtained from the impedance spectra. In this Perspective, the above derivations are condensed into a single, unified one. The theory is recommended to evaluate electrode kinetic measurements, particularly when the potential dependence of rate coefficients is under study.

Influence of Al contents on the long-term corrosion behaviors of cold-sprayed Zn-xAl coatings

ZnAl coating is considered one of the most economic candidates for marine static immersive corrosion protecting technology, in which the Al/Zn ratio is quite crucial to achieve a certain aggressive ions concentration corrosion. In this study, different Al contents Zn-xAl composite coatings were prepared using low-pressure dynamic cold spraying, potentiodynamic polarization and electrochemical impedance spectroscopy techniques were implied to reveal the long-term corrosion behaviors in 3.5 wt% NaCl solution and experimentally optimize the Al and Zn composition of the composite coating for marine static immersion corrosive resistance. The results showed that the weight loss kinetics curve of Zn-xAl composite coatings conforms well to a linear equation over time after logarithms, an increase in Al content leads to enhanced corrosion resistance of Zn-xAl composite coatings. After 1440 h immersion, the optimum Zn95Al composite coating, with high ECorr (−1.522 V) and low ICorr ((4.881 ± 0.98) × 10−5 A/cm2), presented the best corrosion resistance, due to the compact network passive film composing of Al(OH)3 and Al2(OH)5Cl∙2H2O, which slowed down mass-transfer step of Zn/Al elements.

Dynamic Electrochemical Impedance Spectroscopy for the Evaluation of Localised Corrosion on Aluminium Alloys

AbstractDynamic electrochemical impedance spectroscopy (dEIS), an extension of conventional EIS, was used for rapid measurements of initiation of localised corrosion on 3005 aluminium alloys with different Mn (1.08–1.39 wt. %) and Cu (0.15–0.22 wt. %) content by evaluating the onset and evolution of a Faradaic process observed in 0.5 M Na2SO4+0.1 M NaCl. Differences between samples were detected with highest sensitivity from the charge transfer resistance during chronoamperometry at ca. 120 mV above the corrosion potential. These differences were caused by differences in pitting initiation, and correlated well with filament density from a filiform corrosion (FFC) test of samples coated with a 20 μm epoxy topcoat. The observation can be explained by the role of pitting in FFC initiation and the similarity in FFC propagation with pit growth. The results suggest that dEIS is an efficient method for screening alloys for their FFC susceptibility.

Prediction of fuel cell performance degradation using a combined approach of machine learning and impedance spectroscopy

Accurate prediction of performance degradation in complex systems such as solid oxide fuel cells is crucial for expediting technological advancements. However, significant challenges still persist due to limited comprehension of degradation mechanisms and difficulties in acquiring in-situ features. In this study, we propose an effective approach that integrates long short-term memory (LSTM) neural network and dynamic electrochemical impedance spectroscopy (DEIS). This integrated approach enables precise prediction of future evolutions in both current-voltage and EIS features using historical testing data, without prior knowledge of degradation mechanisms. For short-term predictions spanning hundreds of hours, our approach achieves a prediction accuracy exceeding 0.99, showcasing promising prospects for diagnostic applications. Additionally, for long-term predictions spanning thousands of hours, we quantitatively determine the significance of each degradation mechanism, which is crucial for enhancing cell durability. Moreover, our proposed approach demonstrates satisfactory predictive ability in both time and frequency domains, offering the potential to reduce EIS testing time by more than half.

Multivariate Data Analysis of Multisine Impedimetric Fingerprints in Electroanalysis of Biochemical Compounds

While Electrochemical Impedance Spectroscopy (EIS) is found as one of the most versatile tools of electrochemical characterization, it suffers a major drawback when the process in question is non-stationary. On the other hand, Dynamic Electrochemical Impedance Spectroscopy (DEIS) offers an ultra-fast measurement time. DEIS utilizes an approach where all the elementary components are superimposed as one multi-component perturbation signal, offering impedance spectra collection in seconds. This particular advantage allows for the effective use of DEIS in the monitoring of the adsorption processes in multiple fields, such as (bio)sensing, corrosion science, energy storage, or AFM-coupled impedance mapping.This presentation aims at highlighting the DEIS monitoring utility carried out with changes of an independent variable, such as adsorbate concentration or even under linear polarization sweep. Rapid and accurate determination of adsorption isotherms for green organic corrosion inhibitors or Michaelis-Menten constant for enzyme-based glucose (bio)sensors with DEIS operating in galvanostatic mode and under iDC = 0 were already established. When it comes to impedimetric macromolecular electroanalysis, measuring charge transfer resistance upon analyte adsorption is the most common approach. However, the detection may also base on other factors, such as adsorbed layer capacitance or even disturbance in frequency dispersion of capacitance. Most recently, DEIS under polarization sweep mode allowed us to obtain the unique fingerprint of the electric parameter changes, specific to studied macromolecules (such as DNA strings, viral proteins, RNA polymerase, and enzymes). To effectively use our approach DEIS is combined with multivariate data analysis (principal component analysis with partial least square regression). Multivariate data analysis processes large amounts of generated impedimetric data and defines analyte-sensitive conditions (DC polarization, AC amplitude, frequency range, etc.), which can be done just by using the raw data by the singular-value decomposition method to support the sensing mechanisms. The proposed approach neglects some of the reproducibility issues induced by non-specific adsorption and fouling and reveals the measurement conditions that offer the highest variation of studied parameters upon specific analyte adsorption. The authors acknowledge the financial support of these studies by the National Science Centre (Republic of Poland) under project 2020/37/B/ST7/03262.

Potential program invariant representation of diffusion-adsorption related voltammograms and impedance spectra

A theory is presented by which voltammograms, and dynamic electrochemical impedance spectroscopy (dEIS) measurements of diffusion-hindered adsorption processes can be analyzed. By the proposed procedure, from a set of voltammograms, taken at varied scan-rates, parameters of the kinetics and isotherm of the adsorption can be calculated. These are scan-rate independent functions of potential. The theory also comprises the analysis of the high frequency impedance spectra of the same system, which have been measured during dynamic conditions, i.e., during potential scans. The properties of the analysis are illustrated by transformation of simulated cyclic voltammograms. The presented theory is a synthesis of previous ones on diffusion-controlled charge transfer and on adsorption. The theory supports the determination of rate coefficients as a function of electrode potential from fast dEIS measurements.