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Steady-State and EIS Investigations of Hydrogen Electrodes and Membranes in Polymer Electrolyte Fuel Cells: I. Modeling
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.ORCID iD: 0000-0001-9203-9313
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
2006 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 153, no 4, A749-A758 p.Article in journal (Refereed) Published
Abstract [en]

Electrochemical impedance spectroscopy (EIS) and steady-state models have been developed for the porous hydrogen electrode with water concentration dependence and water transport in a polymer electrolyte fuel cell membrane. Because the hydrogen electrode performance is influenced by its water content, the hydrogen electrode model was coupled to the membrane model. The EIS model for the hydrogen electrode gave three to four loops in the complex plane plots. The high-frequency semicircle was attributed to the Volmer reaction and the medium-frequency semicircle to the hydrogen adsorption. The additional low-frequency loops were connected to changes in the hydrogen electrode performance with water concentration, due to changes in kinetics or proton conductivity. Those loops appear in a frequency range depending on the water transport in the membrane, changing with D/L-m(2), where D is the water diffusivity and L-m is the membrane thickness. Modeling of the membrane alone showed that the membrane gives rise to a loop in EIS. The difference between the high- and low-frequency intercepts of the loop is idR/di, where the high-frequency intercept is equal to the membrane resistance. The loop appears in the same frequency range as the hydrogen electrode low-frequency loops and thus overlaps.

Place, publisher, year, edition, pages
2006. Vol. 153, no 4, A749-A758 p.
Keyword [en]
Adsorption, Diffusion, Electric resistance, Electrodes, Fuel cells, Hydrogen, Polyelectrolytes, Porosity
National Category
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-10083DOI: 10.1149/1.2172559ISI: 000235723600017Scopus ID: 2-s2.0-33644804381OAI: oai:DiVA.org:kth-10083DiVA: diva2:207510
Note
QC 20101104Available from: 2009-03-12 Created: 2009-03-11 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Modelling and Experimental Investigation of the Dynamics in Polymer Electrolyte Fuel Cells
Open this publication in new window or tab >>Modelling and Experimental Investigation of the Dynamics in Polymer Electrolyte Fuel Cells
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In polymer electrolyte fuel cells (PEFC) chemical energy, in for example hydrogen, is converted by an electrochemical process into electrical energy. The PEFC has a working temperature generally below 100 °C. Under these conditions water management and transport of oxygen to the cathode are the parameters limiting the performance of the PEFC.

The purpose of this thesis was to better understand the complex processes in different parts of the PEFC. The rate-limiting processes in the cathode were studied using pure oxygen while varying oxygen pressure and humidity. Mass-transport limitations in the gas diffusion layer using oxygen diluted in nitrogen or helium was also studied. A large capacitive loop was seen at 1-10 Hz with 5-20 % oxygen. When nitrogen was changed to helium, which has a higher binary diffusion coefficient, the loop decreased and shifted to a higher frequency.

Steady-state and electrochemical impedance spectroscopy (EIS) models have been developed that accounts for water transport in the membrane and the influence of water on the anode. Due to water drag, the membrane resistance changes with current density. This gives rise to a low frequency loop in the complex plane plot. The loop appeared at a frequency of around 0.1 Hz and varied with D/Lm2, where D is the water diffusion coefficient and Lm is the membrane thickness. The EIS model for the hydrogen electrode gave three to four semicircles in the complex plane plot when taking the influence of water concentration on the anode conductivity and kinetics into account. The high-frequency semicircle is attributed to the Volmer reaction, the medium-frequency semicircle to the pseudocapacitance resulting from the adsorbed hydrogen, and the low-frequency semicircles to variations in electrode performance with water concentration. These low-frequency semicircles appear in a frequency range overlapping with the low-frequency semicircles from the water transport in the membrane. The effects of current density and membrane thickness were studied experimentally. An expected shift in frequency, when varying the membrane thickness was seen. This shift confirms the theory that the low-frequency loop is connected to the water transport in the membrane.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2009. 46 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2009:6
Keyword
polymer electrolyte fuel cell, modelling, electrochemical impedance spectroscopy, water transport, membrane
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:kth:diva-10087 (URN)978-91-7415-241-8 (ISBN)
Presentation
2009-04-03, D2, Lindstedtsvägen 5, KTH, Stockholm, 10:15 (Swedish)
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Supervisors
Note

QC 20121011

Available from: 2009-03-18 Created: 2009-03-11 Last updated: 2012-10-11Bibliographically approved

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Lindbergh, Göran

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