Time-resolved Electrochemical Impedance Spectroscopy Research Articles

Time-Resolved Electrochemical Impedance Spectroscopy of Stochastic Nanoparticle Collision: Short Time Fourier Transform versus Continuous Wavelet Transform.

This work demonstrates the utilization of short-time Fourier transform (STFT), and continuous wavelet transform (CWT) electrochemical impedance spectroscopy (EIS) for time-resolved analysis of stochastic collision events of platinum nanoparticles (NPs) onto gold ultramicroelectrode (UME). The enhanced electrocatalytic activity is observed in both chronoamperometry (CA) and EIS. CA provides the impact moment and rough estimation of the size of NPs. The quantitative information such as charge transfer resistance (Rct ) relevant to the exchange current density of a single Pt NP is estimated from EIS. The CWT analysis of the phase angle parameter is better for NP collision detection in terms of time resolution compared to the STFT method.

Operando Characterization and Theoretical Modeling of Metal|Electrolyte Interphase Growth Kinetics in Solid-State Batteries. Part I: Experiments.

To harness all of the benefits of solid-state battery (SSB) architectures in terms of energy density, their negative electrode should be an alkali metal. However, the high chemical potential of alkali metals makes them prone to reduce most solid electrolytes (SE), resulting in a decomposition layer called an interphase at the metal|SE interface. Quantitative information about the interphase chemical composition and rate of formation is challenging to obtain because the reaction occurs at a buried interface. In this study, a thin layer of Na metal (Na0) is plated on the surface of an SE of the NaSICON family (Na3.4Zr2Si2.4P0.6O12 or NZSP) inside a commercial X-ray photoelectron spectroscopy (XPS) system while continuously analyzing the composition of the interphase operando. We identify the existence of a solid electrolyte interphase at the Na0|NZSP interface, and more importantly, we demonstrate for the first time that this protocol can be used to study the kinetics of interphase formation. A second important outcome of this article is that the surface chemistry of NZSP samples can be tuned to improve their stability against Na0. It is demonstrated by XPS and time-resolved electrochemical impedance spectroscopy (EIS) that a native Na x PO y layer present on the surface of as-sintered NZSP samples protects their surface against decomposition.

A new approach to time-resolved electrochemical impedance spectroscopy using the Impedance Camera to track fast hydration processes in cement-based materials

In this paper, usefulness and accuracy of the new Impedance Camera working in the time-resolved electrochemical impedance spectroscopy (TR-EIS) mode was demonstrated. Flash setting monophase hydraulic binder material Ca7ZrAl6O18 (C7A3Z), and traditional both Ordinary Portland Cement (OPC) and calcium aluminate cement (CAC)-based alumina spinel castables (CMAS castables) were selected and evaluated. The TR-EIS measurements were conducted in the frequency range from 100 Hz to 1 MHz with 17 point per decade. TR-EIS results were correlated with the hydration heat release determined by calorimetry, and thermal behavior (DSC-TG-EGA(MS)) and phase composition (XRD) of the C7A3Z cement paste. In this work, a new approach to divide the curve of speed impedance changes into few characteristic periods of hydration, different than presented so far as the periods on the heat flow curve obtained by isothermal calorimetry was implemented.

Synthesis and performance of aluminous cements containing zirconium and strontium as alternatives to the calcium aluminate cements designed for the production of high performance refractories

Composite cements belonging to the CaO–Al2O3–ZrO2 (C-A-Z) and CaO–SrO–Al2O3–ZrO2 (C–Sr-A-Z) systems were evaluated as alternatives to calcium aluminate cements (CACs) for use in the refractory castables technology. The mineralogical phases in the as-synthesized C-A-Z and C–Sr-A-Z clinkers confirmed by XRD and SEM-EDS were CaAl2O4, Ca7ZrAl6O18 and CaZrO3 or (Ca,Sr)Al2O4, (Ca,Sr)Al4O7 and (Ca,Sr)ZrO3, respectively. The present work aimed at developing novel Zr-containing cements with excellent mechanical performance, i.e. modulus of rupture and cold crushing strength. Both hydration behavior of the C-A-Z, C–Sr-A-Z, CAC and their hydration products, were studied with isothermal calorimetry, XRD, SEM-EDS and NMR. Impedance camera instrument was firstly successfully applied for time-resolved electrochemical impedance spectroscopy measurements under nonstationary conditions and record the time-dependent evolution of the Nyquist plots for hydrating cement pastes. A sharp increase in the real part of impedance Z’ versus hydration time were corresponded to the second exothermic peak detected on the calorimetry curves.

Detection and Characterization of Single Particles by Electrochemical Impedance Spectroscopy.

We present an electrochemical impedance spectroscopy (EIS) technique that can detect and characterize single particles as they collide with an electrode in solution. This extension of single-particle electrochemistry offers more information than typical amperometric single-entity measurements, as EIS can isolate concurrent capacitive, resistive, and diffusional processes on the basis of their time scales. Using a simple model system, we show that time-resolved EIS can detect individual polystyrene particles that stochastically collide with an electrode. Discrete changes are observed in various equivalent circuit elements, corresponding to the physical properties of the single particles. The advantages of EIS are leveraged to separate kinetic and diffusional processes, enabling enhanced precision in measurements of the size of the particles. In a broader context, the frequency analysis and single-object resolution afforded by this technique can provide valuable insights into single pseudocapacitive microparticles, electrocatalysts, and other energy-relevant materials.

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.

Improving Cell Resistance and Cycle Life with Solvate/Thiophosphate Hybrid Electrolytes in Lithium Batteries

Solid electrolytes (SEs) have become a practical option for lithium ion and lithium metal batteries due to their improved safety over commercially available ionic liquids. The most promising of the SEs are the thiophosphates whose excellent ionic conductivities at room temperature are comparable to those of the commercially-utilized ionic liquids. Hybrid solid-liquid electrolytes exhibit higher ionic conductivities than their bare solid electrolyte counterparts due to decreased grain boundary resistance, enhanced interfacial contact with electrodes, and decreased degradation at the interface. In this study, we add lithium bis(triflouromethane sulfonyl)imide (LiTFSI) and a highly fluorinated ether (HFE) solvate electrolyte to the surface of Li7P3S11 (LPS) and Li10GeP2S12 (LGPS) pellets and evaluate their overall cell resistance in Li-Li symmetric cells relative to their bare Li/SE/Li counterparts. Time-resolved electrochemical impedance spectroscopy (EIS) shows an order of magnitude lower cell resistance for the LGPS-solvate than for the bare LGPS. Cyclic voltammetry (CV) of the bare and hybrid SE cells shows an order of magnitude higher current density for the LGPS-solvate cell over the bare LGPS. Interestingly, hybrid electrolytes made by combining HFE-modified solvates and SE exhibit all the benefits of the interlayer modified SEs, without the necessity of pellet manufacture. This study suggests that solvates can be used to improve the cell resistance and current density of solid electrolytes by altering the grain boundary structures and the interphase between electrode and electrolyte.

Improving Cell Resistance and Cycle Life with Solvate-Coated Thiophosphate Solid Electrolytes in Lithium Batteries.

Solid electrolytes (SEs) have become a practical option for lithium ion and lithium metal batteries because of their improved safety over commercially available ionic liquids. The most promising of the SEs are the thiophosphates, whose excellent ionic conductivities at room temperature are comparable to those of commercially utilized ionic liquids. Hybrid solid-liquid electrolytes exhibit higher ionic conductivities than their bare SE counterparts because of decreased grain boundary resistance, enhanced interfacial contact with electrodes, and decreased degradation at the interface. In this study, we add lithium bis(trifluoromethane sulfonyl)imide and a highly fluorinated ether solvate electrolyte to the surface of Li7P3S11 (LPS) and Li10GeP2S12 (LGPS) pellets and evaluate their overall cell resistance in Li-Li symmetric cells relative to their bare Li/SE/Li counterparts. Time-resolved electrochemical impedance spectroscopy shows an order of magnitude lower cell resistance for LGPS-solvate than for bare LGPS. In contrast, the LPS-solvate system exhibits a higher cell resistance than bare LPS. Scanning electron microscopy and energy dispersive X-ray spectroscopy show that LGPS allows for the total permeation of the solvate into the bulk SE. Although LPS has smaller grain sizes and higher porosity, it has a higher solubility in 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE), which results in an LPS-TTE interlayer on the surface of the pellet, thereby increasing overall cell resistance. Cyclic voltammetry of the bare and hybrid SE cells shows an order of magnitude higher current density for the LGPS-solvate cell over the bare LGPS. Bare LPS shorts after two cycles, whereas the LPS-solvate cell does not short within the timeframe of the experiment (100 cycles). This study suggests that solvates can be used to improve the cell resistance and current density of SEs by altering the grain boundary structures and the interphase between electrode and electrolyte.

Stability of the superprotonic conduction of (1-x)CsH2PO4/xSiO2 (0 ≤ x ≤ 0.3) composites under dry and humid environments

We have used temperature- and time-resolved electrochemical impedance spectroscopy, x-ray diffraction, and thermal analysis methods to investigate the effect of mixing CsH2PO4 with nano-silica on the superprotonic conduction of this solid acid. We collected data on (1-x)CsH2PO4/xSiO2 (0 ≤ x ≤ 0.3) composites in dry (air) and humid (PH2O ∼ 0.38 atm) environments at temperatures below and above the superprotonic transition of CsH2PO4 (TSP ∼ 234 °C). We first observed that a three-order-of-magnitude proton conductivity jump occurred in the unmixed sample (x = 0) at TSP, even under dry conditions and despite chemical changes (dehydration). We also found that the proton conductivity of the x = 0.1, 0.2 and 0.3 composites measured at T = 260 °C in air is nearly one order of magnitude greater than that of the unmixed phosphate (x = 0). Even more significantly, we found that humid sample environments have no effect on the stability of the proton conductivity of the x = 0.2 composite measured over a 10 h timespan at temperatures above TSP. This is contrary to the behavior of the x = 0 sample, which is known [31] to be stable under humid conditions, but undergoes a three-order-of-magnitude proton conductivity drop in air.

Time resolved impedance spectroscopy analysis of lithium phosphorous oxynitride - LiPON layers under mechanical stress

Abstract In this paper we present investigations on the morphological and electrochemical changes of lithium phosphorous oxynitride (LiPON) under mechanically bent conditions. Therefore, two types of electrochemical cells with LiPON thin films were prepared by physical vapor deposition. First, symmetrical cells with two blocking electrodes (Cu/LiPON/Cu) were fabricated. Second, to simulate a more application-related scenario cells with one blocking and one non-blocking electrode (Cu/LiPON/Li/Cu) were analyzed. In order to investigate mechanical distortion induced transport property changes in LiPON layers the cells were deposited on a flexible polyimide substrate. Morphology of the as-prepared samples and deviations from the initial state after applying external stress by bending the cells over different radii were investigated by Focused Ion Beam- Scanning Electron Microscopy (FIB-SEM) cross-section and surface images. Mechanical stress induced changes in the impedance were evaluated by time-resolved electrochemical impedance spectroscopy (EIS). Due to the formation of a stable, ion-conducting solid electrolyte interphase (SEI), cells with lithium show decreased impedance values. Furthermore, applying mechanical stress to the cells results in a further reduction of the electrolyte resistance. These results are supported by finite element analysis (FEA) simulations.

Label-free toxin detection by means of time-resolved electrochemical impedance spectroscopy.

The real-time detection of trace concentrations of biological toxins requires significant improvement of the detection methods from those reported in the literature. To develop a highly sensitive and selective detection device it is necessary to determine the optimal measuring conditions for the electrochemical sensor in three domains: time, frequency and polarization potential. In this work we utilized a time-resolved electrochemical impedance spectroscopy for the detection of trace concentrations of Staphylococcus enterotoxin B (SEB). An anti-SEB antibody has been attached to the nano-porous aluminum surface using 3-aminopropyltriethoxysilane/glutaraldehyde coupling system. This immobilization method allows fabrication of a highly reproducible and stable sensing device. Using developed immobilization procedure and optimized detection regime, it is possible to determine the presence of SEB at the levels as low as 10 pg/mL in 15 minutes.

Change of electrochemical impedance spectra (EIS) with time during CO-poisoning of the Pt-anode in a membrane fuel cell

Abstract This paper focuses on the electrochemical characterisation, e.g. current-voltage-measurement and time resolved electrochemical impedance spectroscopy (TREIS) of polymer electrolyte fuel cells (PEFCs) during operation of the fuel cell with oxygen and H 2 +100 ppm CO respectively. Due to the poisoning effect of carbon monoxide, the system changes its state during the experiment. The reconstruction of quasi-causal impedance spectra was made by using enhanced numerical procedures. The reconstructed impedance spectra recorded at constant load, in galvanostatic mode of operation of the fuel cell show a strong time dependence and exhibit pseudo-inductive contributions at the low frequency part of the spectra which increase during the experiment. The analysis of the spectra suggests that the pseudo-inductive behaviour can be attributed to a surface relaxation process of the anode. Furthermore, the influence of the carbon monoxide on the electrochemical behaviour of the contaminated fuel cell may be interpreted by means of a Faraday impedance in addition with a potential-dependent hindrance of the charge transfer. Otherwise, the impedance spectra recorded during CO poisoning of the anode at constant cell voltage, in the potentiostatic mode of operation of the fuel cell, show also a strong time dependence, but no pseudo-inductive contribution in the low frequency part of the spectra.

Fast time-resolved electrochemical impedance spectroscopy for investigations under nonstationary conditions

A new experimental technique for fast electrochemical impedance spectroscopy (EIS), compatible with both the frequency domain and the time domain measurement techniques, is described. It can be successfully applied for time-resolved EIS measurements under nonstationary conditions. Impedance spectra obtained in situ during the current relaxation in a potential step experiment, using Pt electrode in Fe 2 + Fe 3 + redox electrolyte, are presented as an application example.