Electrochemical Impedance Response Research Articles

Exploring the hydration feature and microstructure evolution of MK-Q-LS blended cementitious materials with electrochemical techniques

The hydration process of blended cementitious materials is primarily affected by the effect mechanism of supplementary cementitious materials. This study utilizes electrochemical impedance spectroscopy (EIS) method to investigate the hydration kinetics of cementitious materials incorporating metakaolin (MK), quartz (Q) and limestone powder (LS). The experimental results reveal the influence of MK+Q+LS on the hydration kinetics, phase assemblage, and microstructure of the blended systems. Besides, the electrochemical impedance response of blended cement materials exhibits variation based on the MK contents and the curing age. Furthermore, the resistance of the continuously connected micro-pores (Rccp) in the blended cementitious material progressively increases throughout the hydration process. The inclusion of MK reduces the Rccp values at early ages, while contributes to an increase in Rccp values from 7 days onward. Additionally, positive correlations are established between the Rccp value and compressive strength/heat release across different MK contents and curing ages. The combination of Rccp values and other characterization method can effectively reveal the microstructure evolution process. Therefore, as a nondestructive method, EIS can be effectively applied to predict the hydration of cementitious materials and the mechanical properties.

Covalent electrografting of aryl groups on AA2060-T8 surfaces, and their modification with Ce(4OHcin)3 to incorporate additional anticorrosive activity

The aluminum alloys used in aerospace applications are susceptible to corrosion. This has led to the development of methodologies that ensure the durability of the parts and pieces of aircraft. These anticorrosive processes involve the use of coatings containing chromate-based corrosion-inhibitor compounds. Although these coatings provide an excellent solution to this problem, their use in protection protocols is restricted owing to their high toxicity and carcinogenic nature.This study evaluates a different process to protect aluminum alloy surfaces that incorporates the derivatization of organic compounds using potentiostatic techniques. The metallic surface was modified in situ by the potentiostatic reduction of aryl diazonium salts, leaving the surface covered with molecular grafts. The grafting of molecules onto the surface is modulated by the application of a potential that causes the formation of aryl radicals. The organic compound selected in this study was p-toluidine in protic medium. The derivatization process in the AA2060-T8 alloy was carried out at different pHs and potentials, observing from the potential/current responses in 0.1 M NaCl solution that the maximum optimization is obtained at pH 3 and -1 V.Likewise, the E/I and electrochemical impedance (EIS) responses of the electrografted samples modified and functionalized with cerium 4-hydroxycinnamate (Ce(4-OHcinn)3) revealed that the presence of this compound in the arylic structure significantly increased the protective capacity of the organic film electrografted on the aluminum alloy.The morphologies and characteristics of the modified surface were studied by SEM, TEM, and XPS. Furthermore, TEM examinations of ultramicrotomed sections of the electrografted specimens revealed the presence of a film approximately 10 nm thick on the AA2060-T8 surface.

Development and electrochemical investigations of enhanced corrosion-resistant Polyvinylcarbazole-TiO2 hybrid nanocomposite coatings on 316L SS for marine applications

The present study focuses on evaluating the corrosion resistance of 316L stainless steel substrates with Polyvinylcarbazole (PVK)/TiO2 hybrid nanocomposite coatings (HNC). Using the chronoamperometry approach, the HNC were electrochemically synthesized on 316L stainless steel substrates, incorporating various weight (%) 1 %, 2 %, 3 % of TiO2 nanoparticles into the PVK matrix. The findings of the surface morphology investigation verified that the 316L SS had a dense and smooth PVK/TiO2 coating. A low surface roughness and high contact value of the PVK/TiO2 coatings are also responsible for the decrease in corrosion rate of the 316L SS. The corrosion protection efficiency of the PVK/TiO2 HNC were investigated through open circuit potential (OCP) measurement, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) analysis in 3.5 wt% NaCl solution. The corrosion rate obtained from the polarization studies of the HNC coatings as follows PVKT-2 < PVKT-3 < PVKT-1 < PVK < 316L SS. Results revealed that an optimal loading of 2 wt% TiO2 nanoparticles significantly enhanced the corrosion resistance of the coating. The enhanced electrochemical impedance response for PVK/TiO2 coatings was verified by EIS experiments. The study demonstrates that the incorporation of TiO2 nanoparticles into the PVK matrix effectively creates a barrier layer at the coating-metal interface, inhibiting the entry of aggressive ions. Microhardness studies revealed the increase in hardness value of the PVK and PVK/TiO2 coatings indicated the protective nature of the coating and provided high mechanical strength to 316L SS. The tape adhesion tests carried out on the coated specimens also indicated a good adhesion of the PVK/TiO2 on the 316L SS surface.

Electrochemical impedance response of a thick and porous calcium carbonate layer deposited by thermal growth on a carbon steel electrode

Thermal calcareous scaling has been studied on a simulated heat-exchange carbon steel cylinder set-up in a CaCO3 -rich CO2-saturated solution (SIcalcite=2) using in situ electrochemical methods and ex situ surface characterization. Open circuit potentiometry (OCP) and electrochemical impedance spectroscopy (EIS) indicate dramatic increases to the impedance of the electrode over the first two days. The response quickly changes from a single capacitive loop in the early hours to an impedance characterized by a 45° slope at low frequency in Nyquist format, suggesting fast precipitation kinetics towards a protective state. At the end of 14-day tests, SEM and µ-Raman spectroscopy detected a distinctly layered aragonite-calcite scale. The bi-layered precipitate film is proposed to limit the diffusion of cathodic reactants across the porous, permeable scale, resulting in the 45° slope linear tail characteristic of the so-called transmission line response. EIS responses are experimentally re-evaluated away from open circuit, prior to proposing a bespoke equivalent circuit based on De Levie’s porous electrode model to link the electrochemical data to surface observations.

Enhancing Photocatalytic Attributes of Perovskite Nanocrystals in Aqueous Media via Ligand Engineering.

The remarkable catalytic potential of perovskite nanocrystals (NCs) remains underutilized due to their limited stability in polar media, resulting from the vulnerability of their structure to disruption by polar solvents. In this study, we address this challenge by employing the bolaamphiphilic NKE-12 ligand, which features multiple denticities to effectively shield the surface of CsPbBr3 NCs from polar solvent interactions without compromising their light-harvesting properties. Our research, utilizing electrochemical impedance and photocurrent response measurements, highlights efficient charge separation and charge transfer enabled by NKE-12 ligands, which feature multiple ionic groups and peptide bonds, compared to conventional oleylamine/oleic acid ligands on CsPbBr3 NCs. Through the utilization of purely ligand-derived water-dispersed CsPbBr3/NKE-12 NCs, we successfully showcased their photocatalytic activity for acrylamide polymerization. A series of control experiments unveil a radical-based reaction pathway and suggest the synergistic involvement of photogenerated electrons and holes in producing the O2·- and OH· free radicals, respectively. Our findings emphasize the crucial role of ligand engineering in stabilizing perovskites in water and harnessing their exceptional photocatalytic attributes. This study opens new avenues for applying perovskite NCs in various catalytic processes in polar media.

Construction novel highly active photocatalytic H2 evolution over noble-metal-free trifunctional Cu3P/CdS nanosphere decorated g-C3N4 nanosheet

Hydrogen energy possesses immense potential in developing a green renewable energy system. However, a significant problem still exists in improving the photocatalytic H2 production activity of metal-free graphitic carbon nitride (g-C3N4) based photocatalysts. Here is a novel Cu3P/CdS/g-C3N4 ternary nanocomposite for increasing photocatalytic H2 evolution activity. In this study, systematic characterizations have been carried out using techniques like X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM), Raman spectra, UV–Vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), surface area analysis (BET), electrochemical impedance (EIS), and transient photocurrent response measurements. Surprisingly, the improved 3CP/Cd-6.25CN photocatalyst displays a high H2 evolution rate of 125721 μmol h−1 g−1. The value obtained exceeds pristine g-C3N4 and Cu3P/CdS by 339.8 and 7.6 times, respectively. This could be the maximum rate of hydrogen generation for a g–C3N4–based ternary nanocomposite ever seen when exposed to whole solar spectrum and visible light (λ > 420 nm). This research provides fresh perspectives on the rational manufacture of metal-free g-C3N4 based photocatalysts that will increase the conversion of solar energy. By reusing the used 3CP/Cd/g-C3N4 photocatalyst in five consecutive runs, the stability of the catalyst was investigated, and their individual activity in the H2 production activity was assessed. To comprehend the reaction mechanisms and emphasise the value of synergy between the three components, several comparison systems are built.

Simulation of Impedance Changes with Aging in Lithium Titanate-based Cells Using Physics-Based Dimensionless Modeling

Quantifying aging effects in lithium-ion cells with chemistries that have a flat open circuit potential is challenging. We implement a physics-based electrochemical model to track changes in the electrochemical impedance response of lithium titanate-based cells. Frequency domain equations of a pseudo two-dimensional model are made dimensionless, and the corresponding non-dimensional parameters are estimated using a Levenberg-Marquardt routine. The model weighs the relative contributions of changes in diffusion, ionic conduction within the electrolyte phase against solid phase electronic conduction towards cell aging. Solid-phase diffusion, charge transfer resistance and double layer capacitance at the solid-liquid interface are accounted for in the particle impedance. The estimation routine tracks dimensionless parameters using accelerated cycling data from full cells over 1000 cycles. The model can be deployed within a short time for state estimation using physics-based models without requiring prior knowledge of the battery chemistry, format, or capacity.

Analytical transfer function for the simulation of the frequency-domain and time-domain responses of the blocked-diffusion Warburg impedance

In this study, an analytical transfer function has been developed to simulate the frequency impedance spectrum and the time-domain potential response of the blocked-diffusion Warburg (BDW) impedance. Fundamental electrode and diffusion theories are considered for the derivation of the analytical transfer function representing the BDW impedance. The validation of the analytical transfer function is carried out using parameters extracted from the electrochemical impedance response of a Li-ion battery electrode comprised of silicon nanowires. A Simulink model is developed considering the architecture of the Randles electrical circuit and the new analytical transfer function of the BDW impedance to simulate the frequency impedance spectrum and the dynamic voltage of modern batteries. The Simulink model requires parameters extracted from electrochemical impedance measurements for the simulation of the dynamic voltage of a Li-ion battery electrode and a NiMH battery. The Simulink model comprising the analytical transfer function of the BDW impedance could be a valuable tool for the simulation of the voltage of modern batteries for different applications.

Effect of pH on Electrochemical Impedance Response of Tethered Bilayer Lipid Membranes: Implications for Quantitative Biosensing

Tethered bilayer lipid membranes (tBLMs) are increasingly used in biosensor applications where electrochemical impedance spectroscopy (EIS) is the method of choice for amplifying and recording the activity of membrane-damaging agents such as pore-forming toxins or disrupting peptides. While the activity of these biological agents may depend on the pH of the analytes, there is increasing evidence that the sensitivity of tethered bilayer sensors depends on the pH of the solutions. In our study, we addressed the question of what are the fundamental reasons for the variability of the EIS signal of the tBLMs with pH. We designed an experiment to compare the EIS response of tBLMs with natural membrane defects and two different membrane disruptors: vaginolysin and melittin. Our experimental design ensured that the same amount of protein and peptide was present in the tBLMs, while the pH was varied by replacing the buffers with different pH values. Using a recently developed EIS data analysis algorithm from our research group, we were able to demonstrate that, in contrast to previous literature which relates the variability of tBLM, EIS response to the variation in defect density, the main reason for the observed variability in EIS response is the change in the sub-membrane properties of tBLMs with pH. Using surface-enhanced infrared absorption spectroscopy (SEIRAS), we have shown that pH changes from neutral to slightly acidic leads to an expulsion of water, presumably bound to ions, from the sub-membrane reservoir, resulting in a marked decrease in the carrier concentration and specific conductance of the sub-membrane reservoir. Such a decrease is recorded by the EIS as a decrease in the conductance of the tBLM complex and affects the sensitivity of a biosensor. Our data provide important evidence of pH-sensitive effects that should be considered in both the development and operation of biosensors.

Electrochemical impedance response of the nanostructured Ti–6Al–4V surface in the presence of S. aureus and E. coli

Implant infections associated with biofilm are a significant problem in current healthcare. Early detection of the development of bacterial infection would allow the deployment of antibiotic treatment to suppress complications. Biofilm detection can be based on the changes in the electrochemical response of a metal oxide sensor. The nanostructured surface of titanium alloys provides a large active/geometric surface area ratio and may respond to the presence of bacteria by changing its behaviour. In this work, the changes in impedance response of nanostructured Ti–6Al–4V alloy surface in the presence of E. coli and S. aureus were studied. The nanostructures were prepared by anodic oxidation in a fluoride ions-containing environment. The change in impedance spectra and open circuit potential of the prepared surfaces was monitored for 48 h. Furthermore, a series of measurements in model systems were carried out to help identify the processes leading to the change in the electrochemical behaviour of the surface. The measurements showed significant changes in the surface impedance response over a wide range of frequencies and for both bacterial strains. Based on the results, the implantable sensor based on the nanotubular titanium oxide seems to be a possible and simple way how to detect bacterial infection.Graphical

Unbiased and Signal-Weakening Photoelectrochemical Hexavalent Chromium Sensing via a CuO Film Photocathode.

Photoelectrochemical (PEC) sensors show great potential for the detection of heavy metal ions because of their low background noise, high sensitivity, and ease of integration. However, the detection limit is relatively high for hexavalent chromium (Cr(VI)) monitoring in addition to the requirement of an external bias. Herein, a CuO film is readily synthesized as the photoactive material via reactive sputtering and thermal annealing in the construction of a PEC sensing photocathode for Cr(VI) monitoring. A different mechanism (i.e., Signal-Weakening PEC sensing) is confirmed by examining the electrochemical impedance and photocurrent response of different CuO film photoelectrodes prepared with the same conditions in contact with various solutions containing concentration-varying Cr(VI) for different durations. The detection of Cr(VI) is successfully achieved with the Signal-Weakening PEC response; a drop of photocathode signal with an increasing Cr(VI) concentration from the steric hindrance effect of the in situ formed Cr(OH)3 precipitates. The photocurrent of the optimized CuO film photocathode linearly declines as the concentration of Cr(VI) increases from 0.08 to 20 µM, with a detection limit down to 2.8 nM (Signal/Noise = 3) and a fitted sensitivity of 4.22 µA·μM-1. Moreover, this proposed sensing route shows operation simplicity, satisfactory selectivity, and reproducibility.

Effect of expired doxofylline drug on corrosion protection of soft steel in 1 M HCl: Electrochemical, quantum chemical and synergistic effect studies

The corrosion inhibition property of expired Doxofylline (DF) was tested for soft steel in 1 M hydrochloric acid solution by adopting mass change and electrochemical measurement techniques. At 200 ppm concentration of DF, maximum of 72.84% inhibition efficiency was noticed. However with addition of 50 ppm of KI, it enhances the percentage inhibition efficiency up to 88.48%. DF resists both anodic and cathodic reactions and functioned as mixed-inhibition mechanism. At higher temperatures, electrochemical impedance response noticed that, the diameter of the semicircle decreases as solution temperature increases As a result, in both absence and presence of the inhibitor the Rp values were decreased. Quantum chemical studies revealed about structural and electronic effects in relation to the inhibition efficiencies. Surface morphology of both inhibited and corroded soft steel was assessed by means of scanning electron microscopy (SEM)) and atomic force microscope (AFM). The SEM images of soft steel reflect the inhibitive property of the DF at optimized concentration and a significant decrease in the surface roughness was observed (surface roughness was reduced from 606 nm to 294 nm as measured by AFM)). UV-Visible absorption peaks signifies that CC and CO groups from the inhibitor were interacted with iron cations, which is the evidence for the formation protective film over the soft steel surface.

Performance Characteristics of Polymer Electrolyte Membrane CO2 Electrolyzer: Effect of CO2 Dilution, Flow Rate and Pressure

CO2 electrolyzer designed to operate on dilute CO2 feed and low stoichiometric ratio would alleviate the separation costs for CO2 purification and electrolyzer exit gas processing, respectively. The effect of CO2 concentration, CO2 flow rate, and CO2 pressure on current density and faradaic efficiency of a solid polymer electrolyte membrane CO2 electrolyzer was quantified. An approach for estimating voltage breakdown into activation overpotential for CO2 reduction reaction as well as oxygen evolution reaction, ohmic losses, and concentration overpotential is introduced. No enhancement in current density (∼160 mA cm−2) was observed above stoichiometry ratio of 4 whereas reducing the stoichiometric ratio to 2.7 still yielded a current density of ∼100 mA cm−2. Dilution of CO2 in the feed from 100 mol% to 30 mol%, at ∼90kPa of cell pressure, resulted in a monotonically decreasing current density. A square root dependency on CO2 partial pressure was observed under these conditions. Operation with pure CO2 at different total pressure yielded only a minor increase in current density indicating some form of saturation-limited behavior. Long-term potentiostatic operation over 85 h revealed continuous drop in current density and a corresponding increase in electrode resistance, observed in electrochemical impedance response.

Developing an Automated Tool for Quantitative Analysis of the Deconvoluted Electrochemical Impedance Response of a Solid Oxide Fuel Cell

Despite being commercially available, solid oxide fuel cell (SOFC) technology requires further study to understand its physicochemical processes for diagnostics, prognostics, and quality assurance purposes. Electrochemical impedance spectroscopy (EIS), a widely used characterization technique for SOFCs, is often accompanied by the distribution of relaxation times (DRT) as a method for deconvoluting the contribution of each physicochemical process from the aggregated impedance response spectra. While EIS yields valuable information for the operation of SOFCs, the quantitative analysis of the DRT and its shifts remains cumbersome. To address this issue, and to create a replicable benchmark for the assessment of DRT results, a custom tool was developed in MATLAB to numerically analyze the DRT spectra, identify the DRT peaks, and assess their deviation in terms of peak frequency and DRT amplitude from nominal operating conditions. The preliminary validation of the tool was carried out by applying the tool to an extensive experimental campaign on 23 SOFC button-sized samples from three production batches in which EIS measurements were performed in parametric operating conditions. It was concluded that the results of the automated analysis via the developed tool were in accordance with the qualitative analysis of previous studies. It is capable of providing adequate additional quantitative results in terms of DRT shifts for further analysis and provides the basis for better interoperability of DRT analyses between laboratories.

Fabrication and Performance of Micro-Tubular Solid Oxide Cells

Solid Oxide Cells (SOC) are the kind of electrochemical devices that provide reversible, dual mode operation, where electricity is generated in a fuel cell mode and fuel is produced in an electrolysis mode. Our current work encompasses the design, fabrication, and performance analysis of a micro-tubular reversible SOC that is prepared through a single dip-coating technique with multiple dips using conventional materials. Electrochemical impedance and current-voltage responses were monitored from 700 to 800 °C. Maximum power densities of the cell achieved at 800, 750, and 700 °C, was 690, 546, and 418 mW cm−2, respectively. The reversible, dual mode operation of the SOC was evaluated by operating the cell using 50% H2O/H2 and ambient air. Accordingly, when the SOC was operated in the electrolysis mode at 1.3 V (the thermo-neutral voltage for steam electrolysis), current densities of −311, −487 and −684 mA cm−2 at 700, 750 and 800 °C, respectively, were observed. Hydrogen production rate was determined based on the current developed in the cell during the electrolysis operation. The stability of the cell was further evaluated by performing multiple transitions between fuel cell mode and electrolysis mode at 700 °C for a period of 500 h. In the stability test, the cell current decreased from 353 mA cm−2 to 243 mA cm−2 in the fuel cell mode operation at 0.7 V, while the same decreased from −250 mA cm−2 to −115 mA cm−2 in the electrolysis operation at 1.3 V.

A sensitive electrochemical bisphenol A sensor based on molecularly imprinted polydopamine-coated Fe3O4 microspheres.

Bisphenol A (BPA) interferes with the reproduction and endocrine system of humans and wild animals. For the detection of BPA, a sensitive and rapid detection method was established. BPA was imprinted on the surface of Fe3O4 nanoparticles through dopamine self-polymerization. After the removal of BPA, molecularly imprinted microspheres with BPA recognition cavity were formed. The electrochemical impedance response increased with BPA embedded in the molecular imprinting layer. The electrochemical signal was proportional to the concentration of BPA with a linear range from 1 × 10-11 to 1 × 10-3M and a detection limit of 5.78 × 10-12M. The proposed biosensor was used to detect the BPA in vegetable oil indicating a promising application in food-field monitoring.

The low-frequency limiting behavior of ambipolar diffusive models of impedance spectroscopy

The Poisson–Nernst–Planck (PNP) diffusional model is a successful theoretical framework to investigate the electrochemical impedance response of insulators containing ionic impurities to an external ac stimulus. Apparent deviations of the experimental spectra from the predictions of the PNP model in the low frequency region are usually interpreted as an interfacial property. Here, we provide a rigorous mathematical analysis of the low-frequency limiting behavior of the model, analyzing the possible origin of these deviation related to bulk properties. The analysis points toward the necessity to consider a bulk effect connected with the difference in the diffusion coefficients of cations and anions (ambipolar diffusion). The ambipolar model does not continuously reach the behavior of the one mobile ion diffusion model when the difference in the mobility of the species vanishes, for a fixed frequency, in the cases of ohmic and adsorption–desorption boundary conditions. The analysis is devoted to the low frequency region, where the electrodes play a fundamental role in the response of the cell; thus, different boundary conditions, charged to mimic the non-blocking character of the electrodes, are considered. The new version of the boundary conditions in the limit in which one of the mobility is tending to zero is deduced. According to the analysis in the dc limit, the phenomenological parameters related to the electrodes are frequency dependent, indicating that the exchange of electric charge from the bulk to the external circuit, in the ohmic model, is related to a surface impedance, and not simply to an electric resistance.

Time-Fractional Phase Field Model of Electrochemical Impedance

In this paper, electrochemical impedance responses of subdiffusive phase transition materials are calculated and analyzed for one-dimensional cell with reflecting and absorbing boundary conditions. The description is based on the generalization of the diffusive Warburg impedance within the fractional phase field approach utilizing the time-fractional Cahn–Hilliard equation. The driving force in the model is the chemical potential of ions, that is described in terms of the phase field allowing us to avoid additional calculation of the activity coefficient. The derived impedance spectra are applied to describe the response of supercapacitors with polyaniline/carbon nanotube electrodes.

Transient Response of a Continuous Glucose Monitor

Blood glucose is indirectly measured with a subcutaneous continuous glucose monitor (CGM). Glucose within the interstitial space is converted into hydrogen peroxide via an enzymatic reaction with glucose oxidase. Electrochemical oxidation of the hydrogen peroxide produces a faradaic current proportional to the hydrogen peroxide concentration. In vitro CGM experiments during transient operation demonstrate a range of time constants in the current response. A transient model adaptation of the steady model from Gao et al. was prepared. [1] The transient responses to potential and glucose steps were investigated experimentally and numerically.The transient current response of an electrochemical system with coupled homogeneous and heterogeneous reactions yields time constants dependent on the charging of the electrode, rates of homogeneous reactions, and mass transfer of the participating species. For nonlinear homogeneous reactions involving species of varying diffusion coefficients, analytic expression of these time constants is nontrivial and more readily obtained numerically.A transient model was discretized in space and time with finite differences and the Crank-Nicolson method. Numerical solutions of the model were obtained with Newman’s BAND algorithm. [2] The model demonstrates the charging current, faradaic current, and concentration profile responses within the sensor. When the model is perturbed with a potential step, the initial response is characterized by a charging current; whereas, larger time constants are due to both the mass transfer to the electrode through diffusion and homogeneous reactions.Steady, transient, and impedance responses of the CGM were experimentally obtained. Steady-state current was measured as a function of glucose concentration which provided an estimate for the permeability of glucose in the sensor. Current response to a glucose step was obtained, and the short-time behavior was fit with a single time constant. An equivalent circuit, fabricated based on the impedance spectra, demonstrated a potential step response similar to the sensor. The influence of dissolved oxygen concentration on the transient response was also investigated.The model was fit to the experimental current responses by adjusting diffusion and partition coefficients, rate and equilibrium constants, and electrolyte resistance and capacitance. The numerical model shows the short time constant is due to charging of the sensor, and the larger time constants are due to diffusion and enzymatic reactions. The large time constants of the current response are significantly larger than those predicted by a simple Gerischer model.[3,4] The presence of both diffusing and non-diffusing species involved in the homogeneous reactions may give rise to current instabilities and time constants.References Gao, M., Harding, M., Kong, R., & Orazem, M. (2018). Mathematical Model for the Electrochemical Impedance Response of a Continuous Glucose Monitor. Electrochimica Acta, 275. 119-132.Newman, J., & Thomas-Alyea, E. (2004). Electrochemical Systems (3rd ed.). NJ: John Wiley & Sons, Hoboken.Gerischer, H. (1951). Wechselstrompolarisation Von Elektroden Mit Einem Potentialbestimenden Schritt Beim Gleichgewichtspotential. Zeitschrift fur Physikalische Chemie, 198. 286-313.Orazem, M., & Tribollet, B. (2017). Electrochemical Impedance Spectroscopy. Hoboken, NJ: John Wiley & Sons. AcknowledgementThe support of Medtronic Diabetes (Northridge, CA), Mike Miller, program monitor, is gratefully acknowledged.

Experimental corroboration of theory for impedance response of solid electrolytes: Doped cubic garnet LLZO

• Theory is corroborated with experimentally recorded impedance for Al and Ta-doped LLZO. • Theory resolves impedance of solid electrolyte into contribution from grain and grain boundary. • Phenomenological time scales are characterized through impedance of SSE. • Al and Ta-substituted cubic garnet Li 7 La 3 Zr 2 O 12 are synthesized using solid-state method. We corroborate phenomenological theory for the electrochemical impedance response of solid state electrolyte (SSE) with experimental data for the garnet structured oxide LLZO synthesized using conventional solid-state method. Theoretical analysis of experimentally recorded impedance spectrum indicates three characteristic frequency regimes, viz. (i) high frequency regime, ion relaxation dynamics in grain (g) and space charge layer (SCL) in grain boundary (gb) controls the impedance response, (ii) intermediate frequency regime, depicts the ion transfer and reorganization across heterogeneous grain and grain boundary and (iii) low frequency regime, response is attributed to the capacitive behavior due to the formation of double layer at solid electrolyte/partially blocking metal interface. Theory identifies phenomenological time scales associated with different electrochemical processes occurring in grain, grain boundary and their interface. The material characterization of samples is carried out using powder X-ray diffraction, scanning electron microscopy and Raman spectroscopy. The characteristic phenomenological time scales are extracted from the impedance response of Ta-doped and Al-doped LLZO unraveling the influence of doping. Finally, theory provides an alternative approach as it has rigor of phenomenological ab initio methodology as well as captures the simplicity of equivalent circuit models.