The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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Studies on Limiting Factors of Polymer Electrolyte Membrane Fuel Cell Cathode Performance

Mikko Mikkola

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Engineering Physics and Mathematics for public examination and debate in Auditorium F1 at Helsinki University of Technology (Espoo, Finland) on the 4th of May, 2007, at 12 o'clock noon.

Overview in PDF format (ISBN 978-951-22-8590-7)   [1458 KB]
Dissertation is also available in print (ISBN 978-951-22-8589-1)

Abstract

Fuel cells are electrochemical devices that convert the chemical energy of fuel into electricity and heat. Polymer electrolyte membrane fuel cells (PEMFCs) are a type of fuel cells which use a proton conducting polymer membrane as the electrolyte. PEMFCs are envisioned to replace conventional power sources in many applications, including transportation, stationary distributed and backup power generation, and portable devices. This work concentrated on the limiting factors of the PEMFC cathode performance, focusing on mass transport and water management. Overpotential of oxygen reduction reaction was outside the scope of this thesis. The main study subject was the porous transport layer (PTL). Physical properties of the PTL have a significant effect on reactant and reaction product transport, as well as electrical and thermal fluxes.

PTL research concentrated on three main areas, characterization of PTL media, correlation of PTL physical properties to fuel cell performance, and the effects of inhomogeneous compression distribution. An improved method for PTL characterization was developed and used to investigate the performance of PTL materials under different operating conditions. It was observed that the flooding on the cathode side begins in the PTL, not the electrode itself. A clear relation between PTL properties and fuel cell performance could not be established.

Inhomogeneous compression of PTLs was found to cause local variations in the mass transport properties, electrical conductivity and contact resistance at various interfaces. A method for determining the bulk conductivity of the PTL and the contact resistance at the PTL-flow field plate interface as a function of compression was developed.

The applicability of titanium sinters as porous transport layers for free-breathing PEMFC was investigated. The mechanical properties of titanium sinters were found acceptable, but due to high hydrophilicity, the sinter was prone to flooding. Furthermore, contact resistance between the sinter and other components was high.

The effect of sodium chloride on PEMFC performance was investigated experimentally and found to cause an irreversible performance loss. Sodium ions were found to replace protons in the electrolyte membrane and thus increase resistance. Chloride ions were not observed to interfere with fuel cell operation under the conditions used in the experiments.

This thesis consists of an overview and of the following 6 publications:

  1. Tuomas Mennola, Mikko Mikkola, Matti Noponen, Tero Hottinen and Peter Lund, Measurement of ohmic voltage losses in individual cells of a PEMFC stack, Journal of Power Sources 112 (1) 2002, pp. 261-272. © 2002 Elsevier Science. By permission.
  2. Matti Noponen, Tuomas Mennola, Mikko Mikkola, Tero Hottinen and Peter Lund, Measurement of current distribution in a free-breathing PEMFC, Journal of Power Sources 106 (1-2) 2002, pp. 304-312. © 2002 Elsevier Science. By permission.
  3. T. Hottinen, M. Mikkola, T. Mennola and P. Lund, Titanium sinter as gas diffusion backing in PEMFC, Journal of Power Sources 118 (1-2) 2003, pp. 183-188. © 2003 Elsevier Science. By permission.
  4. J. Ihonen, M. Mikkola and G. Lindbergh, Flooding of gas diffusion backing in PEFCs: Physical and electrochemical characterization, Journal of The Electrochemical Society 151 (8) 2004, pp. A1152-A1161. © 2004 The Electrochemical Society (ECS). By permission.
  5. Iwao Nitta, Tero Hottinen, Olli Himanen and Mikko Mikkola, Inhomogeneous compression of PEMFC gas diffusion layer – Part I. Experimental, Journal of Power Sources, accepted for publication, Dec 2006. © 2007 Elsevier Science. By permission.
  6. Mikko S. Mikkola, Tommy Rockward, Bryan S. Pivovar and Francisco A. Uribe, The effect of NaCl in cathode air stream on PEMFC performance, Fuel Cells, accepted for publication, May 2006.

Keywords: PEMFC, cathode, porous transport layer, gas diffusion layer, water management, impurities

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© 2007 Helsinki University of Technology

Last update 2011-05-26