Dynamic Electrochemical Impedance Spectroscopy Measurements Research Articles

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.

The influence of external operating conditions on membrane drying faults of proton-exchange membrane fuel cells

A study of the influence of water management failure can help improve water management strategies, relieve flooding or drying faults. To explore the influence of drying faults on proton-exchange membrane fuel cells (PEMFCs) under different operating conditions, this study adopted an experimental measurement method combining a cathode voltage drop, voltage signal and electrochemical impedance spectroscopy (EIS). First, multiple sets of drying experiments were performed under different operating conditions, cathodic pressure drop and voltage data were collected during the experiments, and dynamic EIS measurements were performed. Then, by analyzing the pressure drop and voltage trends, the influence of different operating conditions on drying faults was obtained. In addition, the EIS results were parametrically identified using an RL(RQ-RC) equivalent circuit model to obtain ohmic, charge transfer, and mass transfer impedance values. Finally, the evolution and influence of drying faults were verified by impedance variations. The experimental results showed that the ohmic and charge transfer impedance increased significantly with the degree of drying fault, while the mass transfer impedance showed only a small fluctuation or slight increase. Increasing the cathodic back-pressure relieved drying; a larger cathodic stoichiometric ratio increased the drying rate, and a higher cell temperature was more likely to cause severe drying.

Performance degradation analysis of solid oxide fuel cells using dynamic electrochemical impedance spectroscopy

The commercial application of solid oxide fuel cells (SOFCs) is now facing the challenge caused by limited lifetime and durability. More in-depth understanding and scientific evaluation of the complex and coupled performance degradation mechanisms become a priority. In this study, a quantitative evaluation method is established based on dynamic electrochemical impedance spectroscopy (DEIS) measurements under different DC biases. The contributions of ohmic resistance and different polarization resistances to the overall performance degradation are separately determined through coupled distribution of relaxation time (DRT) analysis, equivalent circuit model (ECM) fitting and integral voltage loss calculation. This method is used to investigate the performance degradation of a single cell which is operated under galvanostatic mode for more than 1000 h. Precise contributions of individual processes to the overall degradation are quantitatively determined. Afterwards, post-test characterization on electrode microstructures is provided to support the impedance-based analysis results. In addition, the results are compared with our previously reported analysis of initial-stage rapid performance degradation. Since the proposed method is based on DEIS measurements, it can be further applied to performance degradation analysis of practical stacks as well as other electrochemical devices.

Investigating the oxygen evolution reaction on Ir(111) electrode in acidic medium using conventional and dynamic electrochemical impedance spectroscopy

In this study, conventional and dynamic electrochemical impedance spectroscopy measurements (EIS and DEIS, respectively) were performed on Ir(111) single crystal electrode and Ir nanoparticles supported onto high-surface area carbon in acidic electrolyte and different potential ranges. We found that the EIS and DEIS results compare fairly well below the onset of oxygen evolution reaction (OER). However, in the OER potential region, some differences were observed between the information derived from these measurements. Cyclic voltammetry and inductively-coupled plasma mass spectrometry experiments revealed that the long time required by EIS cause chemical and structural changes of the Ir(111) surface and oxygen evolution, thus adversely affecting the reliability of the impedance measurement. On the contrary, the short time required for DEIS measurements help mitigating these negative effects, thus highlighting the benefits of such technique to investigate the early stages of surface oxide formation on Ir single crystals.

Corrosion inhibition of carbon steel in diethanolamine–H2O–CO2 system by some organic sulphur compounds

ABSTRACTThis paper presents an electrochemical investigation of the corrosion inhibition of carbon steel in diethanolamine–water–carbon dioxide systems by four sulphur-containing organic compounds: 2-mercaptobenzothiazole, 2-mercaptobenzimidazole, diethyl thiourea and dimethyl sulfoxide which were found to be effective in the same order as introduced. Potentiodynamic polarisation revealed their cathodic mechanism of action. The adsorption–desorption behaviour of the inhibitors was studied using capacitance-potential and the constant phase element exponent-potential profiles obtained from dynamic electrochemical impedance spectroscopy measurements. Furthermore, quantum chemical calculations at the density functional theory level were performed to help in the analysis of the experimental results. The inhibition power of mercaptobenzazoles was found regardless to whether they were dissociated or not. The double layer capacitance values showed a rather consistent increasing trend with some theoretical parameters namely, the fraction of transferred electrons, the highest occupied molecular orbital energy level, and the permanent dipole moments of the inhibitor molecules.

A new approach to measure the non-linear Butler–Volmer behavior of electrochemical systems in the time domain

A new approach to measure the non-linear Butler–Volmer behavior of electrochemical systems in the time domain is presented. The method is based on two superimposed currents, one large pulse as an offset and a small pulse which is transformed into the frequency domain. The advantage of this new method is the decreased measurement time compared to frequency domain measurements. This allows the characterization at lower frequencies with less distortion from change in SOC and temperature. In order to reduce spectral leakage of the fast Fourier transform the derivative of the measured signals is taken. The measurement time can be as small as the theoretical limit T=1/f with a negligible error. For the characterization of large automotive cells high currents are needed which were provided by a reprogrammed BaSyTeC HPS cell test system, also used to conduct dynamic electrochemical impedance spectroscopy measurements to validate the new method. The equality of the two completely different hardware and software systems is shown for a 50Ah cell for automotive applications at −20°C in a current range from 0 to 100A.

Unveiling the Dynamic Processes in Hybrid Lead Bromide Perovskite Nanoparticle Thin Film Devices

Hybrid and all‐inorganic perovskite (PK) materials are a promising next generation of semiconducting materials due to their outstanding light‐harvesting features, as well as their color‐tunablility and efficient luminescent properties that lead to highly efficient photovoltaic and lighting devices. Bulk PK films are both ionic and electronic conductors under the presence of an externally applied electric field. In this work, the internal ion motion behavior is demonstrated within PK nanoparticles in thin‐film devices by means of different long‐time poling scheme assays and both static and dynamic electrochemical impedance spectroscopy measurements. In particular, the existence of a dynamic device behavior is related to the migration and rearrangement of different ionic species upon applying different driving schemes. The latter resembles the well‐known signatures of the ionic motion in light‐emitting electrochemical cells (LECs), that is, (i) the formation of electrical double layers due to the ionic distribution at the electrodes' interfaces, (ii) the growth of the doped regions once the charge injection is effective, and (iii) the subsequent formation of a non‐doped region in the bulk of the device. Hence, this comprehensive study opens up an alternative route toward understanding the dynamics inside hybrid perovskite materials based on the large body of knowledge of LECs.

Instantaneous impedance evaluation of dissolution of AISI 304 stainless steel during intergranular corrosion

PurposeThe purpose of this paper is to focus on diversification between electrical parameters determined on the basis of instantaneous impedance measurements within the activation and reactivation scan of dissolution of sensitized AISI 304 stainless steel during a proceeding intergranular corrosion process.Design/methodology/approachThe investigations were carried out by means of dynamic electrochemical impedance spectroscopy (DEIS). DEIS measurements were conducted “on‐line” while the samples were polarized in agreement with a measurement procedure presented in the ASTM G108‐94 standard, in order to guarantee conditions equivalent with the DL‐EPR tests performed on AISI 304 stainless steel.FindingsPerformed researches revealed the advantages of the DEIS technique over standard double‐loop electrochemical potentiokinetic reactivation (DL‐EPR) tests in the field of intergranular corrosion investigations. Application of the DEIS technique made it possible to trace instantaneous changes in the examined system's impedance versus potential during the intergranular corrosion process. The form of recorded DEIS spectra and obtained distribution of measurement frequencies within the reactivation potential range were equivalent to those obtained for pure iron dissolution in sulfuric acid medium. As a result, instantaneous changes of electrical double layer capacitance and charge transfer resistance as a function of potential have been obtained in the range of activation and reactivation scans.Originality/valueThe paper provides information regarding diversification between the electrical double layer capacitance and the charge transfer resistance determined for sensitized AISI 304 stainless steel with respect to polarization conditions during the standard DL‐EPR test, which were obtained in order to evaluate the susceptibility to intergranular corrosion.

Passivation process of X80 pipeline steel in bicarbonate solutions

The passivation process of X80 pipeline steel in bicarbonate solutions was investigated using potentiodynamic, dynamic electrochemical impedance spectroscopy (DEIS), and Mott-Schottky measurements. The results show that the shape of polarization curves changes with HCO 3 − concentration. The critical ‘passive’ concentration is 0.009 mol/L HCO 3 − for X80 pipeline steel in bicarbonate solutions. No anodic current peak exists in HCO3/− solutions when the concentration is lower than 0.009 mol/L, whereas there are one and two anodic current peaks when the HCO3/− concentration ranges from 0.009 to 0.05 mol/L and is higher than 0.1 mol/L, respectively. DEIS measurements show that there exist active dissolution range, transition range, pre-passive range, passive layer formation range, passive range, and trans-passive range for X80 pipeline steel in the 0.1 mol/L HCO 3 − solutions. The results of DEIS measurements are in complete agreement with the potentiodynamic diagram. An equivalent circuit containing three sub-layers is used to explain the Nyquist plots in the passive range. Analyses are well made for explaining the corresponding fitted capacitance and impedance. The Mott-Schottky plots show that the passive film of X80 pipeline steel is an n-type semiconductor, and capacitance measurements are in good accordance with the results of DEIS experiment.

Investigations of pitting corrosion of magnesium by means of DEIS and acoustic emission

The paper presents methodology and results of electrochemical examination of magnesium in 0.1 M NaCl solution with different pH. The measurements were conducted under potentiodynamic conditions using Dynamic Electrochemical Impedance Spectroscopy (DEIS). Analysis of DEIS results was performed based on electrical equivalent circuit. As the result of analysis changes of separate parameters of the equivalent circuit vs. potential for different pH values of the environment were obtained. Simultaneously with DEIS measurements an investigation using acoustic emission was conducted. The results showed that for pH higher than 12.50 the properties of layers on the surface of magnesium change significantly. One can observe a stable passive state that has properties considerably different from those of the layers that form in solutions with lower alkalinity. In such conditions the beginning of pitting corrosion process can be unequivocally determined by the level of acoustic emission and the values of electrochemical parameters.

ANODIC ELECTROCHEMICAL BEHAVIOR OF X80 PIPELINE STEEL IN NaHCO<SUB>3</SUB> SOLUTION

X80 steel has the potential to be widely used for building the gas transmission pipelines because of its high-intensity and high-toughness. Its corrosion performance is a key problem for the life expectancy, especially in soil environment. The anodic electrochemical behavior of X80 pipeline steel in NaHCO3 solution was studied using potentiodynamic polarization curve, dynamic electrochemical impedance spectroscopy (DEIS) as well as SEM observation. The results show that the shape of the polarization curves changes with HCO 3 concentration. The corrosion rate of X80 pipeline steel first increases and then decreases with the increase of HCO 3 concentration. 0.009 mol/L is the critical concentration of HCO 3 for forming the passive film of the X80 pipeline steel. There is no anodic current peak in the solution when HCO 3 concentration is below 0.009 mol/L, and one anodic current peak below 0.05 mol/L and two anodic current peaks above 0.1 mol/L. The results of the DEIS measurements are in complete agreement with the potentiodynamic polarization curve. The corrosion products change with polarization potential and two equivalent circuits are used to explain the experimental spectra of X80 pipeline steel in the whole corrosion process. Therefore, the combination of dynamic polarization curve and DEIS methods can be well used to investigate the corrosion behavior of X80 pipeline steel in NaHCO3 solution at various potentials. In addition, different corrosion products forming at various potentials and the corrosion mechanisms of X80 pipeline steel are briefly analyzed.

Electrochemical investigations of Al–Mg alloy subjected to tensile test

Tensile process of Al–Mg alloys exposed to electrochemical environment is accompanied by numerous electrochemical phenomena, the reasons of which depend on both mechanical and electrochemical factors. Identification and description of these phenomena is of fundamental importance. This paper presents the results of impedance investigations carried out during a tensile test of Al–Mg alloys till rupture. The impedance measurements were performed using a dynamic electrochemical impedance spectroscopy (DEIS) technique. It was found that a phenomenon of mechanical cracking of a passive layer occurs in the elastic range, what results in significant breakdown of barrier properties of the layer and thus in an initiation of corrosion processes on the samples’ surface. In the plastic range oscillatory changes of electrochemical properties of the samples were identified. The investigations revealed that they were associated with the Portevin–LeChatellier effect. The DEIS measurements were conducted under different electrochemical (various levels of anodic polarization) and mechanical (various strain rates) conditions in order to identify and evaluate the factors influencing a dynamics of changes of electrochemical properties of the alloys.

Impact of sensitization on dissolution process of AISI 304 stainless steel during intergranular corrosion evaluated using DEIS technique

The paper presents the results of instantaneous impedance changes measurements vs. reactivation potential performed by means of dynamic electrochemical impedance spectroscopy (DEIS) technique for AISI 304 stainless steel (SS) dissolution process during intergranular corrosion (IG) in 0.5 M H2SO4 + 0.01 M KSCN solution. With the use of DEIS method, it was possible to estimate dynamic changes of the examined system’s impedance in conditions of proceeding IG process. Furthermore, the paper proposes an alternative way of evaluating AISI 304 stainless steel dissolution rate during intergranular corrosion based on approximation to theory of iron dissolution in sulfuric acid medium. Simultaneously, based on the DEIS measurements, information about the degree of sensitization of the examined material were obtained. Performed research revealed the advantages of the DEIS technique over the classical double-loop electrochemical potentiokinetic reactivation tests when investigating intergranular corrosion process.

DEIS assessment of AISI 304 stainless steel dissolution process in conditions of intergranular corrosion

Results presented in this paper are first that demonstrate instantaneous impedance changes versus reactivation potential detected by means of dynamic electrochemical impedance spectroscopy (DEIS) technique for AISI 304 stainless steel dissolution process proceeding during intergranular corrosion (IG) in 0.5 M SO 4 2− + 0.01 M KSCN solution of different pHs. Application of DEIS method made it possible to evaluate dynamic changes of the examined system's impedance in conditions of IG. As a result, controlling stage of the overall rate of AISI 304 SS dissolution process was determined. Moreover, the paper proposes an alternative way of assessment of AISI 304 SS dissolution rate during intergranular corrosion based on approximation to theory of iron dissolution in sulfuric acid medium. Simultaneously, on the basis of the DEIS measurements it was possible to obtain information about the degree of sensitization (DOS) of the examined material. Accordingly, performed researches revealed the advantage of the DEIS technique over the electrochemical potentiokinetic reactivation (EPR) tests when investigating intergranular corrosion process.

Evaluation of localised corrosion behaviour of super austenitic stainless steels using dynamic electrochemical impedance spectroscopy

AbstractPotentiodynamic polarisation and dynamic electrochemical impedance spectroscopic (DEIS) measurements were carried out in natural sea water on type 316L SS, Alloy 926 and Alloy 31. In order to study the localised corrosion resistance, the dynamic electrochemical impedance spectroscopy measurements were performed in a wide range of potentials covering corrosion potential (OCP or Ecorr), passive region, break down region and dissolution region. In this report we have shown that the impedance measurement in potentiodynamic condition allows simultaneous investigation of the changes in the passive layer structure and the ion transport process that occurs through the passive layer. The Nyquist plots were fitted using nonlinear least square (NLLS) method for different potential regions. Finally, the experimental results of polaraisation data were found in good agreement with that of DEIS measurement.

Chemical Pickling of 304 Stainless Steel in Fluoride- and Sulfate-Containing Acidic Electrolytes

The mechanism and kinetics of pickling of high-temperature oxidized 304 stainless steel in electrolyte were investigated by surface finish, weight loss, corrosion potential, and dynamic electrochemical impedance spectroscopy measurements. A three-stage pickling mechanism was proposed. In the first pickling stage, the low-frequency resistance is low because the chromium-depleted layer exposed is active, and thus a significant weight loss takes place. Corrosion kinetics is related to the duration of the active state and the corresponding corrosion potential. Both are influenced by composition of the electrolyte. The oxide scales become undercut by the removal of the underlying metal. While the exposed alloy becomes enriched in chromium, an active-to-passive transition initiates the second stage. A dense passive layer that develops on the surface during that second stage increases the low-frequency resistance. A local attack at grain boundaries and at honeycombed recesses proceeds during the third stage while the remaining exposed area is cathodically protected.