Impedance of an Oxygen Reducing Gas-Diffusion Electrode

1984 ◽  
Vol 39 (2) ◽  
pp. 157-162 ◽  
Author(s):  
Dietrich Wabner ◽  
Rudolf Holze ◽  
Peter Schmittinger
Keyword(s):  
Diffusion Processes ◽  
Impedance Analysis ◽  
Electrode Reaction ◽  
Gas Diffusion ◽  
Porous Electrodes ◽  
Least Square ◽  
Impedance Spectra ◽  
Least Square Fit ◽  
Measured Impedance ◽  
Small Charge

The impedance of teflon bonded electrodes was measured in the frequency domain. These electrodes based on activated carbon as electrocatalyst were developed for fuel cell applications. When feeding the electrode with air or oxygen the impedance spectra could be explained by two Nernst diffusion processes and a small charge transfer process.Two methods for separating the measured impedance into partial impedances related to different steps of the electrode reaction are presented. A least square fit procedure is described which has been applied successfully to the impedance analysis of porous electrodes

Least-square refinement of structure parameters from CBED integrated intensities: application to determination of temperature factors in Y BA2CU3O7

1992 ◽  
Vol 50 (2) ◽  
pp. 1456-1457
Author(s):  
Kjersti Gjønnes ◽  
Jon Gjønnes
Keyword(s):  
Least Square ◽  
Measured Intensity ◽  
Structure Information ◽  
Accurate Temperature ◽  
Least Square Fit ◽  
Case Application ◽  
Integrated Intensities ◽  
Temperature Factors ◽  
Narrow Bands

Electron diffraction intensities can be obtained at large scattering angles (sinθ/λ ≥ 2.0), and thus structure information can be collected in regions of reciprocal space that are not accessable with other diffraction methods. LACBED intensities in this range can be utilized for determination of accurate temperature factors or for refinement of coordinates. Such high index reflections can usually be treated kinematically or as a pertubed two-beam case. Application to Y Ba2Cu3O7 shows that a least square refinememt based on integrated intensities can determine temperature factors or coordinates.LACBED patterns taken in the (00l) systematic row show an easily recognisable pattern of narrow bands from reflections in the range 15 < l < 40 (figure 1). Integrated intensities obtained from measured intensity profiles after subtraction of inelastic background (figure 2) were used in the least square fit for determination of temperature factors and refinement of z-coordinates for the Ba- and Cu-atoms.

Impedance Analysis of Layer Structured NBT–CBT Mixed Ceramics

1998 ◽  
Vol 12 (11) ◽  
pp. 433-441 ◽  
Author(s):  
P. S. Rama Sastry ◽  
T. Bhimasankaram ◽  
G. S. Kumar ◽  
G. Prasad
Keyword(s):  
Comparative Study ◽  
Complex Impedance ◽  
Impedance Analysis ◽  
Equivalent Circuits ◽  
Impedance Spectra ◽  
Ceramic System ◽  
Different Temperatures ◽  
Mixed Ceramics ◽  
Mixed Ceramic ◽  
Complex Impedance Spectra

Complex impedance spectra of ferroelectric mixed ceramic system ( Na 0.5 Bi 0.5)1-x Ca x Bi 4 Ti 4 O 15 with x=0, 0.1, 0.3, 0.5, 0.7 and 1 was studied as a function of frequency and temperature in the range 1 KHz to 10 MHz and 30°C to 620°C respectively. Equivalent circuits involving resistive and capacitive elements at different temperatures, activation energies of relaxations and conduction were evaluated using impedance plots. A comparative study of impedance and conductivity facilities an insight in understanding the electrical nature of these electroceramics.

scholarly journals Holistic Approach to Design, Test, and Optimize Stand-Alone SOFC-Reformer Systems

Processes ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 348
Author(s):  
Michael Höber ◽  
Benjamin Königshofer ◽  
Philipp Wachter ◽  
Gjorgji Nusev ◽  
Pavle Boskoski ◽  
...  
Keyword(s):  
Rural Communities ◽  
High Efficiency ◽  
Diffusion Processes ◽  
Holistic Approach ◽  
Maximum Error ◽  
Gas Diffusion ◽  
Electrochemical Analysis ◽  
Internal Reforming ◽  
Operation Conditions ◽  
Wide Range

Reliable electrical and thermal energy supplies are basic requirements for modern societies and their food supply. Stand-alone stationary power generators based on solid oxide fuel cells (SOFC) represent an attractive solution to the problems of providing the energy required in both rural communities and in rurally-based industries such as those of the agricultural industry. The great advantages of SOFC-based systems are high efficiency and high fuel flexibility. A wide range of commercially available fuels can be used with no or low-effort pre-treatment. In this study, a design process for stand-alone system consisting of a reformer unit and an SOFC-based power generator is presented and tested. An adequate agreement between the measured and simulated values for the gas compositions after a reformer unit is observed with a maximum error of 3 vol% (volume percent). Theoretical degradation free operation conditions determined by employing equilibrium calculations are identified to be steam to carbon ratio (H2O/C) higher 0.6 for auto-thermal reformation and H2O/C higher 1 for internal reforming. The produced gas mixtures are used to fuel large planar electrolyte supported cells (ESC). Current densities up to 500 mA/cm2 at 0.75 V are reached under internal reforming conditions without degradation of the cells anode during the more than 500 h long-term test run. More detailed electrochemical analysis of SOFCs fed with different fuel mixtures showed that major losses are caused by gas diffusion processes.

Array design

1968 ◽  
Vol 58 (3) ◽  
pp. 977-991
Author(s):  
Richard A. Haubrich
Keyword(s):  
High Resolution ◽  
Data Processing ◽  
Least Square ◽  
Wave Number ◽  
Array Design ◽  
Least Square Fit ◽  
The Difference ◽  
Set Of Points ◽  
Array Output

abstract Arrays of detectors placed at discrete points are often used in problems requiring high resolution in wave number for a limited number of detectors. The resolution performance of an array depends on the positions of detectors as well as the data processing of the array output. The performance can be expressed in terms of the “spectrum window”. Spectrum windows may be designed by a general least-square fit procedure. An alternate approach is to design the array to obtain the largest uniformly spaced coarray, the set of points which includes all the difference spacings of the array. Some designs obtained from the two methods are given and compared.

Gas Diffusion-Type Oxygen Electrode Using Perovskite-Type Oxides for Metal-Air Batteries

1995 ◽  
Vol 393 ◽  
Author(s):  
Takeo Hyodo ◽  
Norio Miura ◽  
Noboru Yamazoe
Keyword(s):  
Active Sites ◽  
Electrode Reaction ◽  
Oxygen Electrode ◽  
Gas Diffusion ◽  
Air Cathode ◽  
Diffusion Type ◽  
Reduction Behavior ◽  
Term Operation ◽  
Electron Reduction ◽  
Perovskite Type

ABSTRACTIn order to develop an air cathode of metal-air batteries, oxygen reduction behavior of gas diffusion-type carbon electrodes loaded with perovskite-type oxides, Lai-xA'xFe03(A'=Ca, Sr, Ba, 0<x<1.0), was examined in 8 M KOH at 60 °C. Among the oxide catalysts tested, La0.5Sr0.5Fe03(specific surface area : 21.5 m2.g−1) gave the highest electrode performance. On the basis of electrode reaction kinetics, H2O2decomposition rates, and temperature programed desorption of oxygen, it was concluded that such a performance was attributable to the active sites of the oxide for the direct 4-electron reduction of oxygen. Moreover, the electrode using Lao.5Sro.5FeO3was found to be rather stable in a short-term operation for 90 h at 300 mA-cm−2.

Design of New MEA Structure for Mciro Direct Methanol Fuel Cell

2013 ◽  
Vol 694-697 ◽  
pp. 1565-1568
Author(s):  
Wen Bin Zhang ◽  
Da Da Wang
Keyword(s):  
Layer Structure ◽  
Catalyst Layer ◽  
Electrode Reaction ◽  
Gas Diffusion ◽  
Cathode Side ◽  
Catalyst Loading ◽  
The Novel ◽  
Anode Side ◽  
Pore Former ◽  
Direct Methanol

A novel double-catalyst layer MEA using CCM-GDE (Catalyst Coated Membrane,CCM;Gas Diffusion Electrode,GDE) fabrication method is provided. The double-catalyst layer is formed with an inner catalyst layer (in anode side: PtRu black as catalyst, in cathode side: Pt black as catalyst) and an outer catalyst layer (in anode side: PtRu/C as catalyst, in cathode side: Pt/C as catalyst). By study of the catalyst loading in the double-catalyst layer, an optimization of the catalyst layer structure is obtained, that is the cell may perform best when the ratio of the inner catalyst and outer catalyst is 1:1 (both in inner and outer catalyst layer, the catalyst loading is 1.5mg/cm2). As the hydrophilicity and pore structure are important to the MEA performance, they are optimized by adding pore former and Nafion in the GDL and outer catalyst layer, respectively. Thus three gradients from the PEM to the GDL are formed in the novel MEA: catalyst concentration gradient, porosity gradient and hydrophilicity gradient. These gradients may increase the mass transfer and quicken the electrochemistry reaction in MEA. The CCM-GDE technology may enhance the contact properties between the catalyst and PEM, and increase the electrode reaction areas, resulted in increasing the performance of the μDMFC.

scholarly journals Semi-Analytic Evaluation of 1, 2 and 3-Electron Coulomb Integrals with Gaussian Expansion of Distance Operators W= RC1-nRD1-M, RC1-Nr12-M, R12-Nr13-M

2019 ◽  
Author(s):  
Sandor Kristyan
Keyword(s):  
Gaussian Function ◽  
Approximate Solutions ◽  
Equation System ◽  
Least Square ◽  
Position Vector ◽  
Least Square Fit ◽  
Analytic Expressions ◽  
The One ◽  
Analytical Expressions ◽  
Coulomb Integrals

The equations derived help to evaluate semi-analytically (mostly for k=1,2 or 3) the important Coulomb integrals Int rho(r1)…rho(rk) W(r1,…,rk) dr1…drk, where the one-electron density, rho(r1), is a linear combination (LC) of Gaussian functions of position vector variable r1. It is capable to describe the electron clouds in molecules, solids or any media/ensemble of materials, weight W is the distance operator indicated in the title. R stands for nucleus-electron and r for electron-electron distances. The n=m=0 case is trivial, the (n,m)=(1,0) and (0,1) cases, for which analytical expressions are well known, are widely used in the practice of computation chemistry (CC) or physics, and analytical expressions are also known for the cases n,m=0,1,2. The rest of the cases – mainly with any real (integer, non-integer, positive or negative) n and m - needs evaluation. We base this on the Gaussian expansion of |r|^-u, of which only the u=1 is the physical Coulomb potential, but the u≠1 cases are useful for (certain series based) correction for (the different) approximate solutions of Schrödinger equation, for example, in its wave-function corrections or correlation calculations. Solving the related linear equation system (LES), the expansion |r|^-u about equal SUM(k=0toL)SUM(i=1toM) Cik r^2k exp(-Aik r^2) is analyzed for |r| = r12 or RC1 with least square fit (LSF) and modified Taylor expansion. These evaluated analytic expressions for Coulomb integrals (up to Gaussian function integrand and the Gaussian expansion of |r|^-u) are useful for the manipulation with higher moments of inter-electronic distances via W, even for approximating Hamiltonian.

scholarly journals An Impedance Study of the Membrane Polarisation Effect in Simulated Rock Systems

2021 ◽  
Author(s):  
◽  
Michael Charles Harold McKubre
Keyword(s):  
Low Frequency ◽  
Impedance Measurement ◽  
Impedance Analysis ◽  
Laboratory Model ◽  
Pore Geometry ◽  
Impedance Spectra ◽  
Clay Rock ◽  
Polarisation Effect ◽  
Diffusional Limitation ◽  
Electrochemical Model

<p>Work is reported on the development of a high precision, low frequency impedance bridge, and the use of impedance measurement in characterising the induced polarisation effect of unmineralised material. Impedance spectra for a variety of laboratory model clay/rock/electrolyte systems are analysed in terms of an equivalent circuit. By measuring the dependence of the parameters of this circuit, on such variables as electrolyte type and concentration, temperature and pore geometry, an electrochemical model for membrane polarisation has been developed. Polarisation is considered to arise from diffusional limitation of cations at the membrane/electrolyte interface of clay aggregations in rock pores, and this is found to be amenable to a Warburg diffusional impedance analysis.</p>

scholarly journals Metallic Porous Electrodes Enable Efficient Bicarbonate Electrolysis

2020 ◽  
Author(s):  
Zishuai Zhang ◽  
Faezeh Habibzadeh ◽  
Danielle A. Salvatore ◽  
Shaoxuan Ren ◽  
Eric W. Lees ◽  
...  
Keyword(s):  
Carbon Capture ◽  
Performance Metrics ◽  
Flow Cell ◽  
Gas Diffusion ◽  
Porous Electrodes ◽  
Free Standing ◽  
Faradaic Efficiency ◽  
Performance Loss ◽  
Bicarbonate Solutions ◽  
Porous Silver

We demonstrate here that a porous free-standing silver foam cathode in an electrolytic flow cell mediates efficient electrolysis of 3.0 M bicarbonate solutions into CO. These results have direct implications for carbon capture schemes where OH- solutions react with CO2 to form bicarbonate-rich solutions that need to be treated to recycle the sorbent and recover the CO2. Our study shows a viable path for replacing the high-temperature thermal process currently used to recover CO2 from these carbon capture solutions by using electricity to drive the conversion of bicarbonate into CO2 and subsequently into CO. The use of free-standing porous silver electrodes was found to yield electrolysis performance parameters (e.g., a Faradaic efficiency for CO production, FECO, of 78% at 100 mA cm2; <3% performance loss after 80 h operation) that are superior to results obtained in bicarbonate electrolyzers that utilize conventional carbon-based gas diffusion electrodes (GDEs) designed for gaseous CO2 fed electrolyzers. These performance metrics are comparable to any electrolytic flow cell fed directly with a CO2 feedstock, with the added benefit of not requiring an energy-intensive pressurization step that would be necessary for the electrolysis of gaseous CO2. These findings represent a potentially important step in closing the carbon cycle.

Method for extracting kinetic parameters from measured impedance spectra

1989 ◽  
Vol 34 (8) ◽  
pp. 1179-1185 ◽  
Author(s):  
P. Kurzweil ◽  
J. Ober ◽  
D.W. Wabner
Keyword(s):  
Kinetic Parameters ◽  
Impedance Spectra ◽  
Measured Impedance
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