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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Performance Limitations and Improvements of Small-Scale Free-Breathing Polymer Electrolyte Membrane Fuel Cells

Tero Hottinen

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 1st of October, 2004, at 12 o'clock noon.

Overview in PDF format (ISBN 951-22-7255-5)   [836 KB]
Dissertation is also available in print (ISBN 951-22-7254-7)

Abstract

Fuel cell is an electrochemical device that converts the chemical energy of fuel directly into electricity and heat without combustion with flame. The range of potential applications is from small-scale portable electronics to transportation and large-scale power production. An interesting approach for small-scale applications are free-breathing fuel cells, i.e. cells that take the oxygen needed in the reactions passively from ambient air. This thesis concentrates on performance limitations caused by the use of passive air supply in small-scale polymer electrolyte membrane fuel cells (PEMFCs) and aims to find solutions for these limitations.

A conventional free-breathing PEMFC with vertical cathode channels was studied with a current distribution measurement system at different cell temperatures and ambient conditions. In addition, different overpotential distributions were determined with a flow pulse method, and a mass transport model for the cathode side of the cell was developed. The results showed that with this kind of a cell design, the main limiting factor is the mass transfer in the cathode channels. In order to enhance the air flow and thus to improve mass transfer, there should be a high temperature difference between the cell and ambient air. High cell temperature would also decrease liquid water saturation, which would be beneficial since it causes additional mass transfer limitations.

The mass transfer limitations can also be reduced with wider channels. However, wide channels require a rigid gas diffusion backing in order to offer adequate support for the membrane. A potential mechanically rigid material, titanium sinter, was introduced in the thesis. Another possible solution for reduction of mass transfer limitations is a so-called planar free-breathing cell design in which there is more effective area for cathode side mass transfer than in traditional design. This cell design was introduced and its performance with different cathode structures was studied in the thesis. The results with certain cathode structure showed very high power densities for a free-breathing fuel cell.

According to the results achieved in this thesis, it seems that free-breathing PEMFCs are a very potential power source for small-scale applications such as consumer electronics. As an outcome of this thesis the performance limitations of free-breathing PEMFCs are better known, and possible solutions for them are introduced.

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

  1. Noponen M., Mennola T., Mikkola M., Hottinen T. and Lund P., 2002. Measurement of current distribution in a free-breathing PEMFC. Journal of Power Sources 106, numbers 1-2, pages 304-312. © 2002 Elsevier Science. By permission.
  2. Hottinen T., Noponen M., Mennola T., Himanen O., Mikkola M. and Lund P., 2003. Effect of ambient conditions on performance and current distribution of a polymer electrolyte membrane fuel cell. Journal of Applied Electrochemistry 33, number 3, pages 265-271. © 2003 Kluwer Academic Publishers. By permission.
  3. Noponen M., Hottinen T., Mennola T., Mikkola M. and Lund P., 2002. Determination of mass diffusion overpotential distribution with flow pulse method from current distribution measurements in a PEMFC. Journal of Applied Electrochemistry 32, number 10, pages 1081-1089. © 2002 Kluwer Academic Publishers. By permission.
  4. Mennola T., Noponen M., Aronniemi M., Hottinen T., Mikkola M., Himanen O. and Lund P., 2003. Mass transport in the cathode of a free-breathing polymer electrolyte membrane fuel cell. Journal of Applied Electrochemistry 33, number 11, pages 979-987. © 2003 Kluwer Academic Publishers. By permission.
  5. Hottinen T., Mikkola M., Mennola T. and Lund P., 2003. Titanium sinter as gas diffusion backing in PEMFC. Journal of Power Sources 118, numbers 1-2, pages 183-188. © 2003 Elsevier Science. By permission.
  6. Hottinen T., Mikkola M. and Lund P., 2004. Evaluation of planar free-breathing polymer electrolyte membrane fuel cell design. Journal of Power Sources 129, number 1, pages 68-72. © 2004 Elsevier Science. By permission.
  7. Hottinen T., Himanen O. and Lund P., 2004. Effect of cathode structure on planar free-breathing PEMFC. Journal of Power Sources 138, numbers 1-2, pages 205-210. © 2004 Elsevier Science. By permission.

Errata of publications 4 and 5

Keywords: PEMFC, mass transfer, free convection, flooding, fuel cell, cathode

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© 2004 Helsinki University of Technology

Last update 2011-05-26