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Transient techniques for investigating mass-transport limitations in gas diffusion electrodes: II. Experimental characterization of the PEFC cathode
KTH, Superseded Departments, Chemical Engineering and Technology. (Tillämpad elektrokemi)
KTH, Superseded Departments, Chemical Engineering and Technology. (Tillämpad elektrokemi)ORCID iD: 0000-0001-9203-9313
KTH, Superseded Departments, Chemical Engineering and Technology. (Tillämpad elektrokemi)
2003 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, Vol. 150, no 12, A1711-A1717 p.Article in journal (Refereed) Published
Abstract [en]

The current-interrupt technique and electrochemical impedance spectroscopy were employed in order to study the behavior of a polymer electrolyte fuel cell (PEFC) cathode containing 30 wt % Nafion and 70 wt % Pt/C. The steady-state polarization curves were also recorded. The experimental results were analyzed with help of the mathematical models developed in Part I of this paper. The effect of a varying oxygen pressure and humidity on the dynamic response of the cathode was investigated. The double-layer capacitance, Tafel slope, oxygen solubility, a group containing the effective O-2 diffusion coefficient and agglomerate size, and finally, the effective proton conductivity in the cathode were obtained. The parameter values were reasonable and attest the robustness of the agglomerate model for describing the PEFC cathode. At low humidity, a second, low-frequency loop was observed that was attributed to the membrane behavior.

Place, publisher, year, edition, pages
2003. Vol. 150, no 12, A1711-A1717 p.
Keyword [en]
Capacitance, Cathodes, Diffusion, Electrolytes, Fuel cells, Mass transfer, Mathematical models, Oxygen, Polarization, Pressure effects, Solubility, Spectroscopic analysis
National Category
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-10085DOI: 10.1149/1.1624295ISI: 000186902400023OAI: oai:DiVA.org:kth-10085DiVA: diva2:207517
Note
QC 20101104Available from: 2009-03-16 Created: 2009-03-11 Last updated: 2010-11-04Bibliographically 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)
Opponent
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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