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Electrochemical performance of porous MCFC cathodes
KTH, Superseded Departments, Chemical Engineering and Technology.ORCID iD: 0000-0002-2268-5042
1997 (English)Doctoral thesis, comprehensive summary (Other scientific)
Place, publisher, year, edition, pages
Stockholm: KTH , 1997. , ix, 55 p.
Series
Trita-KET, ISSN 1104-3466
Keyword [en]
molten carbonate fuel cell, MCFC cathode, LiCoO2, NiO, porous electrode, polarisation, performance, reaction mechanisms, conductivity
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-2473ISBN: 99-2384406-4 OAI: oai:DiVA.org:kth-2473DiVA: diva2:8062
Public defence
1997-03-01, 00:00 (English)
Note
QC 20100511Available from: 2000-01-01 Created: 2000-01-01 Last updated: 2010-05-18Bibliographically approved
List of papers
1. MATHEMATICAL-MODELING OF THE MCFC CATHODE
Open this publication in new window or tab >>MATHEMATICAL-MODELING OF THE MCFC CATHODE
1993 (English)In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 38, no 18, 2669-2682 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:kth:diva-12809 (URN)A1993ML00500004 ()
Note
QC 20100511Available from: 2010-05-11 Created: 2010-05-11 Last updated: 2017-12-12Bibliographically approved
2. SYNTHESIS AND PERFORMANCE OF LICOO2 CATHODES FOR THE MOLTEN CARBONATE FUEL CELL
Open this publication in new window or tab >>SYNTHESIS AND PERFORMANCE OF LICOO2 CATHODES FOR THE MOLTEN CARBONATE FUEL CELL
1994 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 141, no 11, 2959-2966 p.Article in journal (Refereed) Published
Abstract [en]

A method for fabricating LiCoO2 electrodes has been developed. LiCoO2 powder was synthesized from Li2CO3 and CoCO3 powder by calcining in air at 650-degrees-C. Electrodes were tape cast in a nonaqueous slurry with and without a graphite poreformer. They were sintered in air at temperatures between 700 and 850-degrees-C. Powders and electrodes were characterized by using x-ray diffraction, thermogravimetric analysis, the Brunauer, Emmett, and Teller method, Hg porosimetry, scanning electron microscopy, and a van der Pauw conductivity measurement setup. The electrodes were electrochemically characterized by polarization measurements at different temperatures. Performance of the electrodes, with and without poreformer, respectively, was also determined by measuring polarization curves at different degrees of electrolyte fill.

Identifiers
urn:nbn:se:kth:diva-12878 (URN)A1994PQ52400011 ()
Note
QC 20100518Available from: 2010-05-18 Created: 2010-05-18 Last updated: 2017-12-12Bibliographically approved
3. INVESTIGATION OF POROUS ELECTRODES BY CURRENT INTERRUPTION APPLICATION TO MOLTEN CARBONATE FUEL CELL CATHODES
Open this publication in new window or tab >>INVESTIGATION OF POROUS ELECTRODES BY CURRENT INTERRUPTION APPLICATION TO MOLTEN CARBONATE FUEL CELL CATHODES
1995 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 142, no 3, 787-797 p.Article in journal (Refereed) Published
Abstract [en]

A transient agglomerate model for simulation and analysis of experimental data, obtained by current interruption on porous molten carbonate fuel cell cathodes, is presented. The initial fast change of the potential after current interruption on a polarized NiO electrode is due to the closed-circuit potential distribution in the electrode. Conventional estimation of the iR corrected overvoltage by current interruption on porous electrodes, with finite electronic conductivity in the solid phase and a finite ionic conductivity of the pore electrolyte, leads to an overcompensation of the external potential drop and an underestimation of the total steady-state overvoltage due to the internal currents passing in the electrode after interruption. The overcompensation of the external potential drop is directly proportional to the geometric current density and to the thickness of the electrode and inversely proportional to the sum df the effective conductivities in the electrode matrix and the pore electrolyte.

Keyword
POLARIZATION, MODEL, ANODE
Identifiers
urn:nbn:se:kth:diva-12879 (URN)A1995QL58500027 ()
Note
QC 20100518Available from: 2010-05-18 Created: 2010-05-18 Last updated: 2017-12-12Bibliographically approved
4. Mathematical modelling of the MCFC cathode: On the linear polarisation of the NiO cathode
Open this publication in new window or tab >>Mathematical modelling of the MCFC cathode: On the linear polarisation of the NiO cathode
1997 (English)In: Journal of Electroanalytical Chemistry, ISSN 0022-0728, E-ISSN 1873-2569, Vol. 432, no 1-2, 121-128 p.Article in journal (Refereed) Published
Abstract [en]

Experimental polarisation curves for the porous lithiated NiO cathode used in molten carbonate fuel cells very often exhibit a linear shape over a wide potential range. It is shown by means of mathematical modelling that this linear behaviour can be explained by the interplay of intrinsic electrode kinetics, diffusion of electroactive species through an electrolyte film and the effective ohmic resistance of the pore electrolyte, providing that the cathodic transfer coefficient has a value of about 1.5. In contrast, with the generally assumed value of 0.5 of this transfer coefficient and with reasonable values of the effective electrolyte conductivity, predicted polarisation curves will always bend downwards over the overvoltage region of interest. The evolution of the polarisation curves with increasing electrolyte fill can be simulated by a model according to which the electroactive surface area becomes gradually blocked with the increasing amount of electrolyte.

Keyword
fuel cell, MCFC, gas diffusion electrodes, mathematical modelling, oxygen reduction, CARBONATE FUEL-CELLS, MOLTEN, REDUCTION, OXYGEN, ELECTRODE, PERFORMANCE, ANODE
Identifiers
urn:nbn:se:kth:diva-12880 (URN)A1997YC70200014 ()
Note
QC 20100518Available from: 2010-05-18 Created: 2010-05-18 Last updated: 2017-12-12Bibliographically approved
5. Influence of gas phase mass transfer limitations on molten carbonate fuel cell cathodes
Open this publication in new window or tab >>Influence of gas phase mass transfer limitations on molten carbonate fuel cell cathodes
1997 (English)In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 27, no 10, 1149-1156 p.Article in journal (Refereed) Published
Abstract [en]

The purpose of this paper is to elucidate to what extent mass transfer limitations in the gas phase affect the performance of porous molten carbonate fuel cell cathodes. Experimental data from porous nickel oxide cathodes and calculated data are presented. One and two-dimensional models for the current collector and electrode region have been used. Shielding effects of the current collector are taken into account. The mass balance in the gas phase is taken into account by using the Stefan-Maxwell equation. For standard gas composition and normal operating current density, the effect of gas-phase diffusion is small. The diffusion in the gaseous phase must be considered at operation at higher current densities. For low oxygen partial pressures, the influence of mass transfer limitations is large, even at low current densities. To eliminate the influence of conversion on polarization curves recorded on laboratory cell units, measurements should always be performed with a five to tenfold stoichiometric excess of oxygen. Two-dimensional calculations show rather large concentration gradients in directions parallel to the current collector. However, the influence on electrode performance is still small, which is explained by the fact that most of the current is produced close to the electrolyte matrix.

Identifiers
urn:nbn:se:kth:diva-12883 (URN)A1997XZ13900004 ()
Note
QC 20100518Available from: 2010-05-18 Created: 2010-05-18 Last updated: 2017-12-12Bibliographically approved
6. The effects of oxidant gas composition on the polarization of porous LiCoO2 electrodes for the molten carbonate fuel cell
Open this publication in new window or tab >>The effects of oxidant gas composition on the polarization of porous LiCoO2 electrodes for the molten carbonate fuel cell
1997 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 144, no 11, 3813-3818 p.Article in journal (Refereed) Published
Abstract [en]

Stationary polarization curves were obtained for porous lithium cobaltite cathodes under varying temperatures and oxidant compositions. The exchange current densities were determined from the slope at low overpotentials by means of numerical calculations, taking into account the current density distribution. Positive influences on the exchange current density were found both for the partial pressure of oxygen and carbon dioxide. The results are similar to earlier data obtained from measurements on NiO electrodes. The values are not consistent with either the peroxide mechanism or the superoxide mechanism, two mechanisms often proposed in the literature.

Identifiers
urn:nbn:se:kth:diva-12882 (URN)A1997YF27200027 ()
Note
QC 20100518Available from: 2010-05-18 Created: 2010-05-18 Last updated: 2017-12-12Bibliographically approved
7. Experimental determination of effective conductivities in porous molten carbonate fuel cell electrodes
Open this publication in new window or tab >>Experimental determination of effective conductivities in porous molten carbonate fuel cell electrodes
1998 (English)In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 44, no 2-3, 503-511 p.Article in journal (Refereed) Published
Abstract [en]

In this work an electrochemical impedance spectroscopy method fbr the determination of the effective conductivities of the pore electrolyte and electrode matrix in porous electrodes has been used. The technique has been employed on porous nickel oxide and lithium cobaltite cathodes partly flooded with lithium-potassium carbonate melt in cathode gas environment. The experimental results show that the effective conductivity of the pore electrolyte of a porous nickel oxide cathode is 0.9-2.2 Omega(-1) m(-1) at the most. If data are approximately corrected for the faradaic reaction the effective conductivity becomes 0.1-0.7 Omega(-1) m(-1). For the lithium cobaltite cathode the measured conductivity of the solid phase is similar to the data measured ex-situ. The effective conductivity of the pore electrolyte is 0.8 Omega(-1) m(-1), i.e. close to the results found for nickel oxide cathodes. The effective conductivity of the pore electrolyte calculated by means of a theoretical model is 0.5-3.5 Omega(-1) m(-1).

Identifiers
urn:nbn:se:kth:diva-12881 (URN)000076093200032 ()
Note
QC 20100518Available from: 2010-05-18 Created: 2010-05-18 Last updated: 2017-12-12Bibliographically approved

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