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.
Aalto

Characterization of Transport Phenomena in Small Polymer Electrolyte Membrane Fuel Cells

Olli Himanen

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Faculty of Information and Natural Sciences for public examination and debate in Auditorium K216 at Helsinki University of Technology (Espoo, Finland) on the 1st of February, 2008, at 12 noon.

Overview in PDF format (ISBN 978-951-22-9147-2)   [1179 KB]
Dissertation is also available in print (ISBN 978-951-22-9146-5)

Abstract

In small fuel cell systems, energy consumption and size of auxiliary devices should be minimized. One option is to use passive controlling methods that rely on material and structural solutions. Therefore it is important to understand transport phenomena occurring in the cells. In this thesis, charge, mass, and heat transport phenomena related to small PEMFCs were studied experimentally and by modeling.

A new method was developed for the characterization of water transport properties of polymer electrolyte membrane under realistic operating conditions. The method was used to evaluate the diffusion coefficient of water in the membrane.

Due to channel-rib structure, cell components are inhomogeneously compressed. Charge and mass transport parameters were experimentally evaluated as a function of compression. The effect of inhomogeneous compression on cell operation was studied by modeling. Inhomogeneous compression does not significantly affect the polarization behavior of the cell, but it creates uneven current and temperature distributions inside the cell. This affects both cell performance and life-time and should not be ignored in cell design and modeling.

The operation of a free-breathing PEMFC was studied at subzero temperatures. To be able to operate at low temperatures, current density must be high enough to avoid freezing of reactant product water inside the cell. Start-up at cold temperatures requires active heating.

To maximize fuel efficiency, the operation of a free-breathing PEMFC in dead end mode was investigated. Dead ended operation with periodic purging enables high fuel utilization rate and the test cell operated without significant water management problems or performance loss.

This thesis consists of an overview and of the following 7 publications:

  1. Olli Himanen, Tero Hottinen, Mikko Mikkola, Ville Saarinen, Characterization of membrane electrode assembly with hydrogen–hydrogen cell and ac-impedance spectroscopy Part I. Experimental, Electrochimica Acta 52, pp. 206-214, 2006. © 2006 Elsevier Science. By permission.
  2. Olli Himanen, Tero Hottinen, Characterization of membrane–electrode assembly with hydrogen–hydrogen cell and ac-impedance spectroscopy Part II. Modeling, Electrochimica Acta 52, pp. 581-588, 2006. © 2006 Elsevier Science. By permission.
  3. Olli Himanen, Tero Hottinen, Saara Tuurala, Operation of a planar free-breathing PEMFC in a dead-end mode, Electrochemistry Communications 9, pp. 891-894, 2007. © 2007 Elsevier Science. By permission.
  4. Tero Hottinen, Olli Himanen, Peter Lund, Performance of planar free-breathing PEMFC at temperatures below freezing, Journal of Power Sources 154, pp. 86-94, 2006. © 2006 Elsevier Science. By permission.
  5. Iwao Nitta, Tero Hottinen, Olli Himanen, Mikko Mikkola, Inhomogeneous compression of PEMFC gas diffusion layer Part I. Experimental, Journal of Power Sources 171, pp. 26-36, 2007. © 2007 Elsevier Science. By permission.
  6. Tero Hottinen, Olli Himanen, Suvi Karvonen, Iwao Nitta, Inhomogeneous compression of PEMFC gas diffusion layer Part II. Modeling the effect, Journal of Power Sources 171, pp. 113-121, 2007. © 2007 Elsevier Science. By permission.
  7. Tero Hottinen, Olli Himanen, PEMFC temperature distribution caused by inhomogeneous compression of GDL, Electrochemistry Communications 9, pp. 1047-1052, 2007. © 2007 Elsevier Science. By permission.

Keywords: PEMFC, transport phenomena, membrane, water management, free-breathing

This publication is copyrighted. You may download, display and print it for Your own personal use. Commercial use is prohibited.

© 2008 Helsinki University of Technology

Last update 2011-05-26