Time-resolved Impedance Research Articles

Towards mass-production of ion-selective electrodes by spotting: Optimization of membrane composition and real-time tracking of membrane drying

Solid-contact ion-selective electrodes present tools for rapid assessment of charged species within a vast number of samples. Commercially available point-of-care electrochemical sensing systems are most often produced by screen-printing. However, this method is not applicable to polymeric membrane deposition, due to the mismatch of the membrane physical characteristics to those intended for screen printing. Herein, an industrial automated dispensing machine was used for fast and controlled deposition of small volumes of ion-selective membrane. Compared to the previously published literature, the dry solute membrane content was not altered. Rather, we optimized the solvents for the ISM preparation, thus significantly lowering the required overall number of membrane deposition steps. It was shown that dry membrane uniformity strongly depends on the solvent carrier system, with the best uniformity for the membrane prepared in a solvent mixture consisting of equal volumes of THF and cyclohexanone. The volume of a single membrane deposit (spot) was estimated based on colorimetric absorbance measurements to be 0.20 μL. Already with a single spot of the ion-selective membrane, an adequate potentiometric response to potassium ions was obtained, supporting the efficiency of the production technique. Evaporative membrane drying was investigated for the first time using time-resolved impedance spectroscopy, giving useful information on the influence of the solvent composition to the characteristics of the evaporative time profiles. With this approach, the overall production and drying of the described devices takes less than 30 min.

Investigating the Mechanisms of Li Dendrite Formation in Sulfide Solid Electrolytes for All-Solid-State Batteries

As the primary use of Li-ion batteries shifts from small electronic devices to electric vehicles, there is a need to increase the stability and energy density of Li-ion batteries. In order to achieve high energy density, use of lithium metal as an anode has being considered due to its high theoretical capacity (3860 mAh g-1) and low reduction potential (-3.04 V vs. SHE). However, the liquid electrolyte used in Li-ion batteries is not only dangerous due to the risk of fire in case of leakage, but also has the disadvantage of shortening the lifetime of the battery due to the generation of lithium dendrites during cycling when lithium metal is used as anode. To overcome these disadvantages, all-solid-state batteries using solid electrolytes have emerged, which are expected to improve safety and cycling stability even when using lithium metal anodes. Among the various types of solid electrolytes, sulfide solid electrolytes are widely used due to their high ionic conductivity and ductility, which allows easy formation of good interfaces, resulting in high performance all-solid-state batteries.To date, many attempts have been made to use lithium metal anodes with solid electrolytes, but dendrite growth has not been completely suppressed.1 Dendrite growth is affected by many interface-related factors, such as void ratio, grain size, elastic modulus, reductive decomposition products, and electrical conductivity of the electrolyte, which must be clarified before the use of lithium metal anodes can be realized.2 It is essential to observe and analyse the changes during electrochemical tests in order to reveal the formation of Li dendrites under the conditions in which actual real cells operate. We have attempted to elucidate the dynamic structural changes at the interface using multimodal/multiscale operando X-ray CT under an applied pressure, as well as the reactions taking place at the interface by observing the interface products using X-ray absorption spectroscopy. In this study, X-ray diffraction, X-ray absorption spectroscopy, time-resolved impedance measurements and multi scale operando X-ray CT are used to determine the electrochemical and chemical mechanisms of Li dendrite formation in different sulfide solid electrolytes. By investigating and comparing the particle size, porosity, doping effect of halides and reduction resistance of solid electrolytes used in lithium metal solid-state batteries, the mechanism of Li dendrite growth and how each factor affects dendrite growth are investigated.Here, we discuss Li3PS4, halogen-doped Li3PS4, and argyrodite-based Li6PS5Cl as typical sulfide-based solid electrolytes; Li3PS4 is known to have a low elastic modulus, and a simple cold press could be used to reduce the inter-particle voids. However, Li3PS4 has a very narrow potential difference, which resulted in unwanted oxidation and reduction byproducts during battery cycling. The high electronic conductivity of the reduction products at the interface also led to the formation of electronic pathways, resulting in the concentration of current in several locations and ultimately triggering the formation of Li dendrites. On the other hand, in argyrodite Li6PS5Cl, the formation of an interfacial phase with low electronic conductivity, which is mainly composed of lithium chloride at the interface, suppresses the reduction reaction and thus the formation of Li dendrites. In the presentation, the relationship between the lithium dendrite formation and the operating conditions such as temperature and pressure will also be presented.

Dynamics of Water Absorption in Polymer Skin Adhesives.

Skin adhesives are used to attach medical devices to the body and are required to adhere to the skin also during challenging conditions such as exposure to moisture and sweat. In order to maintain good skin-adhesive contact in these situations, the adhesives should be able to absorb water and remove fluids from the skin-adhesive interface. Consequently, the water absorption properties and distribution of water in the adhesives influence the overall adhesive properties. Understanding how the material composition impacts the absorption and distribution of water in these adhesives is required for rational formulation of skin adhesives. Here, we probe the dynamic water absorption in different skin adhesives using time-resolved impedance measurements and gravimetric analysis. Skin adhesive formulations consisting of soft, hydrophobic polymers providing stickiness, rigid block copolymers enhancing the structure, and hydrogel particles allowing for water uptake were designed. The hydrogel particle content and polymer matrix rigidity were varied, and the adhesives were systematically investigated to link the material composition and water absorption functionality.

CsH2PO4 is not stable at 260 °C unless confined. Comments to article by C.E. Botez, I. Martinez, A. Price, H. Martinez, and J.H. Leal in J. Phys. Chem. Solids 129 (2019) 324-328

Botez, Martinez, Price, Martinez and Leal claim in J. Phys. Chem. Solids 129 (2019) 324–328 that superprotonic CsH2PO4 (CDP) is stable in dry air at 260 °C. We discuss their observations and conclude that CDP is not stable unless sufficiently confined under a high humidity and high-pressure atmosphere, eventually formed from the sample itself. Temperature- and time-resolved impedance spectroscopy data show that a superprotonic CDP pellet measured in a hermetically sealed chamber holds a stable superprotonic conductivity of ~2 × 10−2 S cm−1 over a time span of 50 h at a temperature of 260 °C if the amount of sample is large enough and the container small and tight. Nyquist plots have confirmed the superprotonic nature of the conduction. X-ray diffraction data have revealed that CDP is present after the heating cycle to obtain superprotonic conductivity, but possibly CDP partly was decomposed to Cs2H2P2O7 during the heating and was reformed reacting with water during the cooling.

Superprotonic CsH2PO4 in dry air

The first observation of a stable superprotonic CsH2PO4 (CDP) phase in the absence of high humidity and high pressure is reported. Temperature- and time-resolved impedance spectroscopy data show that the superprotonic conductivity of a CDP pellet measured in dry air (22%rh) in a hermetically sealed chamber holds at σ∼1.5 × 10−2 S cm−1 over a timespan t = 50 h at a temperature T = 260 °C. Nyquist plots confirm the superprotonic nature of the conduction and x-ray diffraction data reveal that no dehydration of the CDP superprotonic phase occurs under the above-mentioned conditions.

On the use of instantaneous impedance for post-electrochemical treatment analysis

For many electrochemical treatments, surface modifications and processes occurring during the relatively short post-treatment time are difficult to monitor using traditional surface analysis techniques. Instantaneous impedance, i.e. time-resolved impedance calculated from an in situ odd random phase multisine electrochemical impedance spectroscopy measurement, may allow for monitoring of these surface modifications. In this work, the AC electrograining process is used as a case study to investigate the possibility of post-electrochemical treatment analysis. It is found that the expected surface changes are indeed found in the instantaneous impedance data. The technique described in this paper can be used to monitor a variety of post-electrochemical treatment surface modifications in situ.

Interfacial reactivity and interphase growth of argyrodite solid electrolytes at lithium metal electrodes

Lithium superionic conductors with the argyrodite structure Li6PS5X (X=Cl, Br, I) are considered as suitable candidates for the fabrication of all-solid-state batteries (SSB) facilitating Li metal anodes. The use of metal anodes is required to achieve SSB with high energy densities, however, the thermodynamic stability of the different argyrodites in contact with Li metal has not been systematically investigated yet. The stability against lithium metal is of practical interest for long-term stability of SSB utilizing argyrodites. Here, data on the stability of Li6PS5X (X=Cl, Br, I) in contact with Li metal are reported, obtained from an in situ X-ray photoemission technique in combination with time-resolved impedance spectroscopy. In contact with Li metal, Li6PS5X decomposes into an interphase composed of Li3P, Li2S and LiX, which serves as an SEI and results in an increasing interfacial resistance. The growth of the SEI and the resulting resistance evolution is further analyzed in terms of its kinetics and is compared to other thiophosphate superionic conductors. Li6PS5I is found to show particularly strong SEI formation with severe resistance growth.

The relation of electrical conductivity profiles and modulus data using the example of STO:Fe single crystals: A path to improve the model of resistance degradation

Resistance degradation in perovskites is characterized by an increase in current over time with applied electric field. This behavior can be simulated and spatially resolved conductivity profiles can be measured, but some inconsistencies remain. A new approach to address these problems is presented that utilizes time-resolved impedance spectroscopy with an applied DC voltage to provide new insight into the resistance degradation phenomenon. In particular, this method allows the in-situ acquisition of spatio-temporal variations in conductivity. In SrTiO3 a single bulk-dominated maximum of the imaginary part of the modulus M″ transitions to two maxima during degradation, reflecting the hole conductivity in the anode region and the electron conductivity in the cathode region. To clarify the influence of conductivity profiles on impedance data, the reversed route is presented by using simulated conductivity profiles to calculate impedance data. It will be emphasized that this methodology is not limited to the perovskite system considered here, but can be adapted to any kind of system characterized by a spatially varying conductivity.

Direct Experimental Observation of the Interfacial Instability of the Fast Ionic Conductor Li10GeP2S12 at the Lithium Metal Anode

High capacity and low potential anode materials like lithium metal are preferred for high energy densities in all solid-state batteries. Due to the highly reducing potential of lithium metal, the electrochemical and thermodynamic stability of a solid ion conductor at the interface plays a crucial role for the performance of all solid-state batteries. When a solid electrolyte is in contact with lithium metal, three different types of interfaces may occur:1 (I) A stable interface may form with electrolytes that are thermodynamically stable against Li contact. (II) A reaction occurs and a mixed ionic-electronic conducting (MCI) new interphase forms,2 which rapidly growths due to the electronic percolation pathways. (III) A reaction occurs and a solid electrolyte interphase (SEI) forms,3 which only conducts ions. While (I) may be preferred and (II) is exclusively detrimental, due to a proceeding reaction front, the impact of (III) on the battery performance depends on the type of forming SEI. Here we will shortly introduce the types of possible interphases/interfaces and discuss the expected effects on the overall resistance and performance of an all-solid-state battery. Using time-resolved impedance spectroscopy and time-resolved cyclic voltammetry we introduce a guideline to characterize solid electrolytes for their stability against metal interfaces. The solid electrolyte Li10GeP2S12 will be shown as an example of an instability,4 as has been theoretically predicted.5,6 SEI formation occurs, affecting the overall cell resistance detrimentally. Using a novel in situ X-ray photoelectron technique we study the resulting interphase formation when Li10GeP2S12 is in contact with Li. Using the observed chemical species, in combination with time-resolved electrochemical measurements, we suggest a reaction mechanism for the interphase formation as well as provide an understanding of the growth kinetics. 1Wenzel S., Leichtweiss T., Krüger D., Sann J., Janek J. Solid State Ion. 2015, 278, 98-105 2Hartmann P., Leichtweiss T., Busche M., Schneider M., Reich M., Sann J., Adelhelm P., Janek J. J. Phys. Chem. C 2013, 117, 21064-21074 3 Wenzel S., Weber D., Leichtweiss T., Busche M., Sann J., Janek J. Solid State Ion. 2016, 286, 24-33 4Wenzel S., Randau S., Leichtweiss T., Weber D., Sann J., Zeier W.G., Janek J. submitted 5Zhu Y., He X., Mo Y. ACS Appl. Mater. Int. 2015, 7, 23685-23693 6Zhu Y., He X., Mo Y. J. Mater. Chem A 2016 DOI: 10.1039/C5TA08574H.

Enhanced motility of alveolar cancer cells induced by CpG-ODN-functionalized nanoparticles

Lysosomal TLR-9 is stimulated in A549 lung epithelial cells through administration of nanoparticles (NPs) either based on γ-Fe2O3 or MnO. Synthetic single-stranded immunostimulatory CpG-oligodeoxynucleotides (CpG-ODN) are covalently attached to fluorescently labelled γ-Fe2O3- and MnO-NPs in order to monitor the impact of TLR-9 activation on motility and cell morphology employing time-resolved impedance spectroscopy. In contrast to cytotoxic MnO-based particles, particles made from Fe2O3 are non-toxic carriers for pathogen-mimicking CpG-ODNs, which efficiently stimulate endogenous TLR-9, resulting in enhanced micromotility and a loss of barrier properties. Compared to neat CpG-ODNs administered in the absence of particles, the nucleotides displayed by NPs are found to be considerably more efficient in stimulating A549 cells attributed to a larger local concentration of ligands on the particles’ surface. The study shows that particle-based CpG-ODNs added to tumour cells increase their motility even further and therefore might also enhance their invasiveness and metastatic potential, foiling the original strategy of immunotherapy.

Dynamics of TGF-β induced epithelial-to-mesenchymal transition monitored by Electric Cell-Substrate Impedance Sensing

The epithelial-to-mesenchymal transition (EMT) is a program of cellular development associated with loss of cell–cell contacts, a decreased cell adhesion and substantial morphological changes. Besides its importance for numerous developmental processes, EMT has also been held responsible for the development and progression of tumors and formation of metastases. The influence of the cytokine transforming growth factor β1 (TGF-β1) induced EMT on structure, migration, cytoskeletal dynamics and long-term correlations of the mammalian epithelial cell lines NMuMG, A549 and MDA-MB231 was investigated with time-resolved impedance analysis. The three cell lines show important differences in concentration dependency, cellular morphology and dynamics upon their response to TGF-β1. A549 cells and the non-tumor mouse epithelial cell line NMuMG show a substantial change in morphology mirrored in stepwise changes of their phenotype upon cytokine treatment. Impedance based measurements of micromotility reveal a complex dynamic response to TGF-β1 exposure which leads to a transient increase in fluctuation amplitude and long-term correlation. These changes in fluctuation amplitude are also detectable for MDA-MB231 cells, whereas the long-term correlation remains unvaried. We were able to distinguish three time domains during EMT. Initially, all cell lines display an increase in micromotion lasting 4 to 9h termed transitional state I. This regime is followed by transitional state II lasting approximately 20h, where cellular dynamics are diminished and, in case of the NMuMG cell line, a loss of cell–cell contacts occurs. Finally, the transformation into the mesenchymal-like phenotype occurs 24–30h after exposure to TGF-β1.

Impedance analysis of adherent cells after in situ electroporation: Non-invasive monitoring during intracellular manipulations

In this study adherent animal cells were grown to confluence on circular gold-film electrodes of 250 μm diameter that had been deposited on the surface of a regular culture dish. The impedance of the cell-covered electrode was measured at designated frequencies to monitor the behavior of the cells with time. This approach is referred to as electric cell-substrate impedance sensing or short ECIS in the literature. The gold-film electrodes were also used to deliver well-defined AC voltage pulses of several volts amplitude and several hundred milliseconds duration to the adherent cells in order to achieve reversible membrane electroporation ( in situ electroporation = ISE). Electroporation-assisted introduction of membrane impermeable molecules into the cytoplasm was studied by using FITC-labeled dextran molecules of different molecular weights. Probes as big as 2 MDa were successfully loaded into the cells residing on the electrode surface. Time-resolved impedance measurements before and immediately after the electroporation pulse revealed the kinetics of membrane resealing as well as subsequent changes in cell morphology. Cells recovered from the electroporation pulse within less than 90 min. When membrane-impermeable, bioactive compounds like N 3 − or bleomycin were introduced into the cells by in situ electroporation, concomitant ECIS readings sensitively reported on the associated response of the cells to these toxins as a function of time (ISE-ECIS).

Electrochemical Impedance Spectroscopy

This review describes recent advances in electrochemical impedance spectroscopy (EIS) with an emphasis on its novel applications to various electrochemistry-related problems. Section 1 discusses the development of new EIS techniques to reduce measurement time. For this purpose, various forms of multisine EIS techniques were first developed via a noise signal synthesized by mixing ac waves of various frequencies, followed by fast Fourier transform of the signal and the resulting current. Subsequently, an entirely new concept was introduced in which true white noise was used as an excitation source, followed by Fourier transform of both excitation and response signals. Section 2 describes novel applications of the newly developed techniques to time-resolved impedance measurements as well as to impedance imaging. Section 3 is devoted to recent applications of EIS techniques, specifically traditional measurements in various fields with a special emphasis on biosensor detections.

Combining Impedance Spectroscopy with Cyclic Voltammetry: Measurement and Analysis of Kinetic Parameters for Faradaic and Nonfaradaic Reactions on Thin-Film Gold

The technique of time-resolved impedance spectroscopy can be combined with dc cyclic voltammetry (CV) to study mechanisms and kinetics of electrochemical reactions at solid-liquid interfaces. Utilization of these techniques in a combined framework, however, is based on a number of specific considerations of measurement procedures and data analysis. The present work discusses certain essential elements of this topic, focusing primarily on the analysis of time-resolved impedance spectra where interdependent dc and ac effects of parallel faradaic and nonfaradaic reactions are present under potentiodynamic conditions. A thin gold film is used as a model experimental system where oxidation and reduction of the sample surface is voltage-controlled both in the presence and in the absence of specifically adsorbing Cl- ions in neutral background electrolytes of NaF. Impedance spectra are recorded under transient conditions of CV, and kinetic parameters based on electrode-equivalent circuit models are obtained as functions of CV scans.

Surface Interactions ofs-Triazine-Type Pesticides. An Electrochemical Impedance Study

Two pesticides, atrazine and terbutylazine, have very similar chemical structures differing only by iso-propyl and tert-butyl substituents on their 6 amino groups. This minor structural difference causes profound effects in decomposition rates in the environment, leading to a ban of atrazine in the European Union. Here we present a study of adsorption at ideally polarized electrochemical interface in the absence of specifically adsorbed halides. The interfacial charge and the temperature determine which type of an adsorbed film is formed. The double layer capacitance measurements yield the critical temperature of the surface film transition, which is markedly different for the two pesticides. The time-resolved impedance spectroscopy indicates slow changes within the film structure that becomes disordered and can be characterized in terms of the fractal geometry.

Role of iodate ions in chemical mechanical and electrochemical mechanical planarization of Ta investigated using time-resolved impedance spectroscopy

Chemical mechanical planarization (CMP) is currently used in the processing of Cu/Ta interconnect structures. Electrochemical mechanical planarization (ECMP) is an emerging extension of CMP that can potentially allow low down-pressure planarization of newer interconnect structures containing easily breakable porous dielectrics. In both CMP and ECMP of Ta, it is necessary to chemically (or electrochemically) form a “soft” surface film that can be easily removed by minimum mechanical abrasion. Alkaline KIO3 solutions appear to serve this purpose in CMP of Ta and, as we show in this work, may also be utilized in ECMP of Ta. Using time-resolved impedance spectroscopy we study here the relevant surface reactions of IO3− that lead to a structurally weak surface film of soluble hextantalate [(Ta6O19)8−] embedded in (native or electro-generated) Ta2O5 on Ta. Catalytic reduction of IO3− on Ta2O5 enhances the local pH at the oxidized surface and promotes the conversion of Ta2O5 to (Ta6O19)8−. The chemical role of iodate ions in material removal through these reactions is similar to that of hydrogen peroxide in CMP of Ta in alkaline media.

Chemical roles of peroxide-based alkaline slurries in chemical–mechanical polishing of Ta: investigation of surface reactions using time-resolved impedance spectroscopy

This work presents an electrochemical investigation of chemical reactions kinetics in chemical–mechanical polishing of Ta in a peroxide-based alkaline medium. Time resolved Fourier transform electrochemical impedance spectroscopy is combined with cyclic voltammetry to probe the chemical roles of H 2O 2 and OH − in chemical–mechanical polishing. Competitive effects of electro-oxidation and oxide dissolution at a Ta disc electrode are studied in four different (nearly neutral, alkaline, peroxide-free and peroxide-containing) electrolytes. In alkaline peroxide solutions with pH≥10, surface catalyzed breakdown of interfacial H 2O 2 promotes certain reactions of oxide-removal from the Ta surface. These reactions are analyzed in detail. The results demonstrate how the detailed chemical aspects of the process, and kinetics of surface reactions in particular, can be probed in real time by using the method mentioned above.

A new impedance spectrometer for the investigation of electrochemical systems

The development of a computer-controlled electrochemical impedance spectrometer, based on a Fourier transform algorithm is described. Together with a fast potentiostat the system can be used in the frequency range 1 mHz to 100 kHz. The perturbation signal is a superposition of sine waves with properly chosen frequencies. The overall measurement time is limited only by the lowest frequency in the spectrum and by the data transfer to the computer, thus, time-resolved impedance spectra measurements can be performed. The principle of operation and technical details are presented and discussed.