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Electrode Kinetics of the Ni Porous Electrode for Hydrogen Production in a Molten Carbonate Electrolysis Cell (MCEC)
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.ORCID iD: 0000-0001-9203-9313
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.ORCID iD: 0000-0002-2268-5042
2015 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 162, no 9, F1020-F1028 p.Article in journal (Refereed) Published
Abstract [en]

The purpose of this study was to elucidate the kinetics of a porous nickel electrode for hydrogen production in a molten carbonate electrolysis cell. Stationary polarization data for the Ni electrode were recorded under varying gas compositions and temperatures. The slopes of these iR-corrected polarization curves were analyzed at low overpotential, under the assumption that the porous electrode was under kinetic control with mass-transfer limitations thus neglected. The exchange current densities were calculated numerically by using a simplified porous electrode model. Within the temperature range of 600-650 degrees C, the reaction order of hydrogen is not constant; the value was found to be 0.49-0.44 at lower H-2 concentration, while increasing to 0.79-0.94 when containing 25-50% H-2. The dependence on CO2 partial pressure increased from 0.62 to 0.86 with temperature. The reaction order of water showed two cases as did hydrogen. For lower H2O content (10-30%), the value was in the range of 0.47-0.67 at 600-650 degrees C, while increasing to 0.83-1.07 with 30-50% H2O. The experimentally obtained partial pressure dependencies were high, and therefore not in agreement with any of the mechanisms suggested for hydrogen production in molten carbonate salts in this study.

Place, publisher, year, edition, pages
Electrochemical Society, 2015. Vol. 162, no 9, F1020-F1028 p.
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-173295DOI: 10.1149/2.0491509jesISI: 000359177100077Scopus ID: 2-s2.0-84937054026OAI: oai:DiVA.org:kth-173295DiVA: diva2:852535
Note

QC 20150909

Available from: 2015-09-09 Created: 2015-09-09 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Molten carbonate fuel cells for electrolysis
Open this publication in new window or tab >>Molten carbonate fuel cells for electrolysis
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The molten carbonate fuel cell has evolved to current megawatt-scale commercial power plants. When using the fuel cell for electrolysis, it provides a promising option for producing fuel gases such as hydrogen and syngas. The cell can thereby operate reversibly as a dual energy converter for electricity generation and fuel gas production. The so-called reversible molten carbonate fuel cell will probably increase the usefulness of the system and improve the economic benefits.

This work has investigated the performance and durability of the cell in electrolysis and reversible operations. A lower polarization loss is found for the electrolysis cell than for the fuel cell, mainly due to the NiO electrode performing better in the MCEC. The stability of the cell in long-term tests evidences the feasibility of the MCEC and the RMCFC using a conventional fuel cell set-up, at least in lab-scale.

This study elucidates the electrode kinetics of hydrogen production and oxygen production. The experimentally obtained partial pressure dependencies for hydrogen production are high, and they do not reasonably satisfy the reverse pathways of the hydrogen oxidation mechanisms. The reverse process of an oxygen reduction mechanism in fuel cell operation is found to suitably describe oxygen production in the MCEC.

To evaluate the effect of the reverse water-gas shift reaction and the influence of the gas phase mass transport on the porous Ni electrode in the electrolysis cell, a mathematical model is applied in this study. When the humidified inlet gas compositions enter the current collector the decrease of the shift reaction rate increases the electrode performance. The model well describes the polarization behavior of the Ni electrode when the inlet gases have low contents of reactants. The experimental data and modeling results are consistent in that carbon dioxide has a stronger effect on the gas phase mass transport than other components, i.e. water and hydrogen.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2016. 57 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2016:18
Keyword
Durability, electrode kinetics, gas phase mass transport, molten carbonate electrolysis cell, molten carbonate fuel cell, performance, reversible.
National Category
Chemical Sciences
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-185433 (URN)978-91-7595-928-3 (ISBN)
Public defence
2016-05-20, Kollegiesalen, Brinellvägen 8, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20160419

Available from: 2016-04-20 Created: 2016-04-18 Last updated: 2016-04-20Bibliographically approved

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Lindbergh, GöranLagergren, Carina

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