scholarly journals Further Understanding of Uncertainties in the Impedance Spectrum of the Polymer Electrolyte Fuel Cell due to Inductive Effects and Oxygen Diffusion Time Constant

2020 ◽  
Vol 2 (4) ◽  
Author(s):  
Samuel Cruz-Manzo ◽  
Keyword(s):  
Charge Transfer ◽  
Time Constant ◽  
Oxygen Diffusion ◽  
Electrochemical Impedance ◽  
Impedance Spectrum ◽  
Diffusion Time ◽  
Polymer Electrolyte Fuel Cell ◽  
Low Frequencies ◽  
High Frequencies ◽  
Eis Measurements

In this study, uncertainties during the assessment of the electrochemical impedance spectrum of the polymer electrolyte fuel cell (PEFC) attributed to inductive artefacts at high frequencies and inductive loops at low frequencies as well as oxygen diffusion time constant are discussed. A validated impedance model represented as an equivalent electrical circuit of a PEFC allowed the simulation of the effect of inductive artefacts, inductive loops and oxygen diffusion time constant on electrochemical impedance spectroscopy (EIS) measurements represented in the Nyquist plot. This study considers EIS measurements reported in previous studies and provides an insight into the EIS measurements with positive imaginary components at high frequencies attributed to the intrinsic inductance of the measurement cables during EIS tests and at low frequencies attributed to electrochemical mechanisms (e.g. side reactions with intermediate species) during PEFC operation. In addition, an overview of overlapping mechanisms (charge transfer and oxygen transport resistances during the oxygen reduction reaction) on the PEFC impedance spectrum attributed to oxygen diffusion across the cathode catalyst layer is presented. EIS measurements with positive imaginary components and with overlapping effects could yield to ambiguities when studying or relating electrochemical mechanisms (ion conduction, capacitance, charge transfer and mass transport resistances) of the PEFC through a defined single frequency or a single measured value represented in the Nyquist complex-impedance plot.

Inductive Effect on the Fuel Cell Cathode Impedance Spectrum at High Frequencies

2012 ◽  
Vol 9 (5) ◽  
Author(s):  
Samuel Cruz-Manzo ◽  
Rui Chen ◽  
Pratap Rama
Keyword(s):  
Fuel Cell ◽  
Theoretical Analysis ◽  
Measurement System ◽  
High Frequency ◽  
Inductive Effect ◽  
Electrochemical Impedance ◽  
Impedance Spectrum ◽  
High Frequencies ◽  
Eis Measurements ◽  
Electrical Cables

The high frequency electrochemical impedance measurements with positive imaginary components in the impedance complex plot of a polymer electrolyte fuel cell (PEFC) are attributable to the inductance of the electrical cables of the measurement system. This study demonstrates that the inductive effect of the electrical cables deforms the high frequency region of the cathode impedance spectrum and as such leads to an erroneous interpretation of the electrochemical mechanisms in the cathode catalyst layer (CCL). This study is divided into a theoretical analysis and an experimental analysis. In the theoretical analysis a validated model that accounts for the impedance spectrum of the CCL as reported in the authors’ previous study is applied with experimental impedance data reported in the literature. The results show that the ionic resistance of the CCL electrolyte which skews the oxygen reduction reaction (ORR) current distribution toward the membrane interface is masked in the cathode impedance spectrum by the inductive component. In the experimental analysis cathode experimental impedance spectra were obtained through a three-electrode configuration in the measurement system and with two different electrical cables connected between the electronic load and the PEFC. The results agree with the theoretical analysis and also show that the property of causality in the Kramers-Kronig mathematical relations for electrochemical impedance spectroscopy (EIS) measurements is violated by the external inductance of the measurement cables. Therefore the experimental data presenting inductance at high frequencies do not represent the physics and chemistry of the PEFC. The study demonstrates that a realistic understanding of factors governing EIS measurements can only be gained by applying fundamental modeling which accounts for underlying electrochemical phenomena and experimental observations in a complementary manner.

MONITORED DEFORMATION BY POTENTIAL-INDUCED DEFECTS IN CH3(CH2)n−1SH SELF-ASSEMBLED MONOLAYERS ON GOLD: EIS STUDY OF CHAIN LENGTH EFFECT ON SUBDIFFUSION AND SAMs’ HETEROGENEITY

2019 ◽  
Vol 26 (10) ◽  
pp. 1950067 ◽  
Author(s):  
AHMED MOUGARI ◽  
MOKHTAR ZABAT ◽  
SMAIL BOUDJADAR
Keyword(s):  
Charge Transfer ◽  
Electrochemical Impedance ◽  
Defect Density ◽  
Charge Transfer Resistance ◽  
Electrical Circuit ◽  
Transfer Resistance ◽  
Low Frequencies ◽  
Interface Evolution ◽  
Impedance Measurements ◽  
Self Assembled

From the defects-free self-assembled organic layers (SAMs) of CH3([Formula: see text]SH molecules with short chain lengths ([Formula: see text]) electrodeposited on the (111) surface of monocrystalline gold previously prepared, monitored defects (pinholes) were potential-induced from cyclic partial reduction of SAMs at an appropriate potential. Electrochemical impedance measurements were in-situ conducted and [Fe(CN)6][Formula: see text] ions were used as probes for mass and charge transfer. Interface evolution was modeled with an equivalent electrical circuit containing two distinct constant-phase elements (CPEs). One is a generalized semi-infinite Warburg element in series with a charge transfer resistance attributed to subdiffusion phenomenon through leaky sublayers at low frequencies; the other CPE is used for characterizing the interface heterogeneity at medium and high frequencies. At low frequencies, electrochemical impedance measurements show subdiffusion phenomenon, which depends on the remaining sublayer and its thickness. When the defect density increases, diffusion tends to be ordinary, obeying the Fick’s law.

scholarly journals The effects of time-variance on impedance measurements: examples of a corroding electrode and a battery cell

2020 ◽  
Vol 10 (2) ◽  
pp. 127-140 ◽  
Author(s):  
Nicolas Murer ◽  
Jean-Paul Diard ◽  
Bogdan Petrescu
Keyword(s):  
Polarization Resistance ◽  
Electrochemical Impedance ◽  
Steel Sample ◽  
Impedance Method ◽  
Battery Cell ◽  
Low Frequencies ◽  
Impedance Measurements ◽  
Time Variance ◽  
Eis Measurements ◽  
Resistance Decrease

When performing electrochemical impedance spectroscopy (EIS) measurements on a system, we must make sure it fulfills certain conditions. One of them is that it should be stationary that is to say, steady-state and time-invariant. Commonly studied systems are time-variant, for example a corroding electrode or a battery under operation. A corroding electrode sees its polarization resistance decrease with time. A passivating electrode sees its polarization resistance increase with time. These phenomena cause a deformation of the Nyquist impedance at low frequencies. This result was first simulated and validated by experimental measurements on a corroding steel sample undergoing uniform cor­rosion. The effect of performing impedance measurements on a discharging battery was also shown. Several methods are available to check and correct time-variance. The non-stationary distortion (NSD) indicator is used to separate valid and invalid data samples and the so called “4D impedance” method can easily produce instantaneous impedance data.

scholarly journals Galvanic Corrosion Study between Tensile-Stressed and Non-Stressed Carbon Steels in Simulated Concrete Pore Solution

Metals ◽  
2022 ◽  
Vol 12 (1) ◽  
pp. 98
Author(s):  
Zheng Dong ◽  
Chuanqing Fu ◽  
Amir Poursaee
Keyword(s):  
Charge Transfer ◽  
Tensile Stress ◽  
Electrochemical Impedance ◽  
Pore Solution ◽  
Charge Transfer Resistance ◽  
Open Circuit ◽  
Carbon Steels ◽  
Cyclic Polarization ◽  
Transfer Resistance ◽  
Low Frequencies

The present study investigated the galvanic effect between tensile-stressed and non-stressed carbon steels, in addition to the influence of the tensile stress on the passivation and corrosion behavior of steel in a simulated concrete pore solution. Three different levels of tensile stress, ranging from elastic to plastic stress on the surface, were applied by adjusting the displacement of C-shape carbon steel rings. Different electrochemical measurements including the open circuit potential (OCP), the electrochemical impedance spectroscopy (EIS), the zero-resistance ammetry (ZRA), and the cyclic polarization were performed. Based on the results of EIS, the tensile stress degraded the resistance of the oxide film in moderate frequencies while enhancing the charge transfer resistance in low frequencies during passivation. As corrosion propagated, the stressed steel yielded a similar charge transfer resistance to or an even lower charge transfer resistance than the non-stressed steel, especially in the case of plastic tensile stress. The galvanic effect between the tensile-stressed and non-stressed steels increased the chloride threshold value of the tensile-stressed steel, although the susceptibility to pitting corrosion was exhibited after being corroded.

scholarly journals Combined Spectrophotometric— Electrochemical Impedance Imaging System for Biofilm Research

2005 ◽  
Vol 10 (1) ◽  
pp. 16-23 ◽  
Author(s):  
Chirag Patel ◽  
Stanley Dunn ◽  
Paul Takhistov
Keyword(s):  
Electrochemical Impedance ◽  
Imaging System ◽  
Impedance Analysis ◽  
Low Frequencies ◽  
High Frequencies ◽  
Impedance Imaging ◽  
Noninvasive Analysis ◽  
A Cell ◽  
Computer Controlled ◽  
Automatic Scanning

We propose an automatic scanning microscope that is capable of analyzing the properties of the biofilm-associated cells by using optical and impedance spectroscopy. The operating principle of the instrument is based on measuring the electrical impedance of cell culture grown on a conductive substratum that is used as one of the electrodes. At low frequencies, the impedance analysis is capable of characterizing a biofilm at the macroscale, and at high frequencies it is capable of analyzing the peculiarities of a cell layer at the level of single microorganisms. The combination of these two techniques is sufficient to give a quantitative and structural composition of a biofilm at both levels. The developed instrument can be useful in the broad range of biofilmrelated research studies, providing the data for detailed, real-time, computer-controlled, noninvasive analysis of cell-to-cell and cell-to-surface interactions.

scholarly journals Performance of Photovoltaic Modules After an Accelerated Thermal Cycling Degradation Test

2019 ◽  
Vol 11 (1) ◽  
Author(s):  
Aramis Perez ◽  
Luis Gabriel Marin ◽  
Fernando Fuentes ◽  
Patricio Mendoza ◽  
Guillermo Jimenez ◽  
...  
Keyword(s):  
Thermal Cycling ◽  
Electrochemical Impedance ◽  
Low Frequencies ◽  
High Frequencies ◽  
Photovoltaic Modules ◽  
Pv Module ◽  
Pv Modules ◽  
Degradation Test ◽  
Accelerated Thermal Cycling ◽  
Eis Analysis

Typically, datasheets of photovoltaic (PV) modules state that the guaranteed power production remains constant for a certain period of time and after this point, a linear reduction begins reaching an estimated 80% of the original rated power. Moreover, literature reports that the degradation of PV modules reaches less than 1% per year. In this regard, after 20 years of operation a typical PV module will deliver approximately 20% less energy than a the beginning of its life. In this article, the results of an accelerated thermal cycling degradation test are compared to its brand new conditions. These results demonstrate that although the performance among the PV modules is variable when new, after the cycling test the performance of the degraded PV modules is similar. In this case, the power reduction of the degraded module varies from 1.4% up o 7.6% when compared to the initial condition. Furthermore, an Electrochemical Impedance Spectroscopy (EIS) analysis demonstrates that at high frequencies the results are practically the same regardless if the panel is new or degraded, but at low frequencies the variation of the impedance is notorious.

Characteristic Time Constants Derived From the Low-Frequency Arc of Impedance Spectra of Fuel Cell Stacks

2018 ◽  
Vol 15 (2) ◽  
Author(s):  
Stefan Keller ◽  
Tansu Özel ◽  
Anne-Christine Scherzer ◽  
Dietmar Gerteisen ◽  
Ulf Groos ◽  
...  
Keyword(s):  
Fuel Cell ◽  
Time Constant ◽  
Characteristic Time ◽  
Gas Flow ◽  
Electrochemical Impedance ◽  
Air Flow ◽  
Low Frequency ◽  
Impedance Spectrum ◽  
Gas Diffusion ◽  
Electrical Circuit

Electrochemical impedance spectroscopy is used during operation of different polymer electrolyte membrane fuel cell (PEMFC) stack assemblies at various conditions with special interest given to the characteristic time constant τlow-f derived from the low-frequency arc of the spectra which is typically in the range of approximately 15–0.5 Hz. This was done by fitting an equivalent electrical circuit (EEC) consisting of one resistor and two RC-elements to the data. Parameter variation performed on a 90-cell stack assembly suggests that conditions leading to different air flow velocities in the flow channels affect τlow-f while other parameters like humidity influence the impedance spectrum, but not τlow-f. Comparison of the stoichiometry variation between short stack and locally resolved single cell shows similar results with the stack's time constant matching that of the cell's segments which are located off-center toward the outlet. However, a nonlinear dependency between gas flow velocity and τlow-f especially at low stoichiometric values is obvious. Results from stoichiometry variations at different pressure levels suggest that this could be attributed to the different steady-state oxygen partial pressures during the experiments. Comparison of the stoichiometry variation between different stack platforms result in similar dependencies of τlow-f on air flow rate with respect to a reference oxygen partial pressure regardless of size, flow field, geometry, or cell count of the stack. The time constant caused by oxygen diffusion through the gas diffusion layer (GDL), τGDL, was approximated and compared to τlow-f. While it was found that τlow-f ≫ τGDL at low stoichiometric values, τlow-f decreases toward τGDL at very high gas flow rates, suggesting that τGDL offsets τlow-f and becomes dominating if no oxygen concentration variation along the flow channel was present.

scholarly journals Oxidation Behavior of an Austenitic Steel (Fe, Cr and Ni), the 310 H, in a Deaerated Supercritical Water Static System

Metals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 571
Author(s):  
Aurelia Elena Tudose ◽  
Ioana Demetrescu ◽  
Florentina Golgovici ◽  
Manuela Fulger
Keyword(s):  
Stainless Steel ◽  
Supercritical Water ◽  
Nuclear Reactor ◽  
Electrochemical Impedance ◽  
Electrochemical Methods ◽  
Metallographic Analysis ◽  
Gravimetric Analysis ◽  
Static System ◽  
Eis Measurements ◽  
Supercritical Temperature

The aim of this work was to study the corrosion behavior of a Fe-Cr-Ni alloy (310 H stainless steel) in water at a supercritical temperature of 550 °C and a pressure of 250 atm for up to 2160 h. At supercritical temperature, water is a highly aggressive environment, and the corrosion of structural materials used in a supercritical water-cooled nuclear reactor (SCWR) is a critical problem. Selecting proper candidate materials is one key issue for the development of SCWRs. After exposure to deaerated supercritical water, the oxides formed on the 310 H SS surface were characterized using a gravimetric analysis, a metallographic analysis, and electrochemical methods. Gravimetric analysis showed that, due to oxidation, all the tested samples gained weight, and oxidation of 310H stainless steel at 550 °C follows parabolic rate, indicating that it is driven by a diffusion process. The data obtained by microscopic metallography concord with those obtained by gravimetric analysis and show that the oxides layer has a growing tendency in time. At the same time, the results obtained by electrochemical impedance spectroscopy (EIS) measurements indicate the best corrosion resistance of Cr, and (Fe, Mn) Cr2O4 oxides developed on the samples surface after 2160 h of oxidation. Based on the results obtained, a strong correlation between gravimetric analysis, metallographic analysis, and electrochemical methods was found.

scholarly journals Experimental, DFT and MD Assessments of Bark Extract of Tamarix aphylla as Corrosion Inhibitor for Carbon Steel Used in Desalination Plants

Molecules ◽  
2021 ◽  
Vol 26 (12) ◽  
pp. 3679
Author(s):  
Ismat H. Ali
Keyword(s):  
Corrosion Inhibitor ◽  
Potentiodynamic Polarization ◽  
Inhibition Efficiency ◽  
Electrochemical Impedance ◽  
Effect Of Temperature ◽  
Bark Extract ◽  
Plant Sample ◽  
Gravimetric Analysis ◽  
Sample Collection ◽  
Eis Measurements

This study aimed to examine the extract of barks of Tamarix aphylla as a corrosion inhibitor. The methodology briefly includes plant sample collection, extraction of the corrosion inhibitor, gravimetric analysis, plotting potentiodynamic polarization plots, electrochemical impedance spectroscopic measurements, optimization of conditions, and preparation of the inhibitor products. The results show that the values of inhibition efficiency (IE%) increased as the concentrations of the inhibitor increased, with a maximum achievable inhibition efficiency of 85.0%. Potentiodynamic polarization (PP) tests revealed that the extract acts as a dual-type inhibitor. The results obtained from electrochemical impedance spectroscopy (EIS) measurements indicate an increase in polarisation resistance, confirming the inhibitive capacity of the tested inhibitor. The adsorption of the inhibitor on the steel surface follows the Langmuir adsorption isotherm model and involves competitive physio-sorption and chemisorption mechanisms. The EIS technique was utilized to investigate the effect of temperature on corrosion inhibition within the 298–328 K temperature range. Results confirm that the inhibition efficiency (IE%) of the inhibitor decreased slightly as the temperature increased. Lastly, the thermodynamic parameters for the inhibitor were calculated.

Sign in / Sign up

Export Citation Format

Share Document