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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Mass Transport in Polymer Electrolyte Membrane Fuel Cells Using Natural Convection for Air Supply

Tuomas Mennola

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 2nd of April, 2004, at 12 o'clock noon.

Overview in PDF format (ISBN 951-22-6984-8)   [2163 KB]
Dissertation is also available in print (ISBN 951-22-6983-X)

Abstract

A fuel cell converts chemical energy into electricity and heat through electrochemical reactions. Polymer electrolyte membrane fuel cells (PEMFCs) are approaching commercialization in many applications, including transportation, stationary power, and portable devices. In this thesis, the focus was on small-scale PEMFCs, in which natural convection is used as the air supply method.

A cell design with straight vertical cathode channels was studied using experimental and modeling methods, in order to obtain a quantitative insight into mass transport phenomena and to identify the performance limiting processes. The variation of mass transport conditions over the active area of the cell was studied using a current distribution measurement system, which was based on the use of a segmented current collector. The accuracy of the method was analyzed by experimental work and numerical simulation. In order to quantify the local mole fractions of water and oxygen, and the velocity of buoyancy-driven air flow in the cathode channel, a numerical model was developed to describe mass transport in the cathode channel and the gas diffusion layer. Water transport across the polymer membrane was studied by measuring the fraction of product water exiting through the anode. The results give indication of the variation of net water transport coefficient across the active area. The redistribution of water along with the hydrogen flow was also observed. The effect of ambient temperature and relative humidity on cell performance was investigated in a climate chamber. For stack research, a measurement approach was developed for determining the ohmic voltage losses of individual cells in a stack by the current interruption method.

As an overall conclusion, it was found that the cell design should be improved especially from the point of view of water management. In order to reduce flooding problems, the cross-section and length of the cathode channels were identified as key parameters to be optimized. It was also found that mechanically rigid gas diffusion layer materials are advantageous for designing an optimized geometry. In addition, it was found that the choice of the anode flow geometry can be used to control the distribution of water across the active area.

This thesis consists of an overview and of the following 6 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. 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.
  3. Mennola T., Noponen M., Kallio T., Mikkola M. and Hottinen T., 2004. Water balance in a free-breathing polymer electrolyte membrane fuel cell. Journal of Applied Electrochemistry 34, number 1, pages 31-36. © 2004 Kluwer Academic Publishers. By permission.
  4. 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.
  5. Mennola T., Mikkola M., Noponen M., Hottinen T. and Lund P., 2002. Measurement of ohmic voltage losses in individual cells of a PEMFC stack. Journal of Power Sources 112, number 1, pages 261-272. © 2002 Elsevier Science. By permission.
  6. 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.

Keywords: PEMFC, cathode, natural convection, water management, mass transport, current distribution, modeling, current interruption, stack

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© 2004 Helsinki University of Technology

Last update 2011-05-26