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

Studies on the Direct Methanol Fuel Cell: Characterization of Proton Conducting Polymer Membranes and Investigations of Current Distribution at the Cathode

Ville Saarinen

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Chemical Technology for public examination and debate in Auditorium AS1 at Helsinki University of Technology (Espoo, Finland) on the 16th of November, 2007, at 1 p.m.

Overview in PDF format (ISBN 978-951-22-8981-3)   [1747 KB]
Dissertation is also available in print (ISBN 978-951-22-8980-6)

Abstract

Novel proton conducting membranes for the direct methanol fuel cell (DMFC) are characterized widely by combining methods of physical chemistry, electrochemistry and material science. This work mainly concentrates on the sulphonated poly(ethylene-alt-tetrafluoroethylene) (ETFE-SA) membrane. Other investigated membranes are poly(vinylidene fluoride)-graft-poly(styrene sulphonic acid) (PVDF-g-PSSA), sulphonated poly(phenylene sulphone) (sPSO2) and the commercial Nafion® membrane as a reference material. The swelling properties of the membranes are investigated in different alcohol – water and H2SO4 – water mixtures. Clear trends are observed for the water / alcohol selectivity: preferential water uptake (alcohol rejection) correlates with high ion exchange capacity (IEC) and low solvent uptake (swelling). The total swelling significantly decreases in the presence of H2SO4 indicating that osmosis is a major driving force in the swelling process. The membrane properties are characterized with sophisticated microscopic techniques (AFM, SEM & EDX, SECM) and many benefits of the extensive characterization are demonstrated. The surface hydrophobicity is investigated by water contact angle (CA) measurement. During the measurements, the surface properties of the different membranes are found to differ significantly from each other and the properties of the ETFE-SA membrane to vary also as a function of the manufacturing parameters. Also, the ETFE-SA membrane has exceptionally low water uptake, high water selectivity against methanol and good chemical and mechanical stability. Methanol permeability through the membranes is investigated both with a diffusion cell and under actual DMFC conditions. The membranes are investigated in a laboratory-scale DMFC system and the connections between different operation parameters are clarified in detail. The main observation is that durability of ETFE-SA is sufficient for DMFC applications at low temperatures (T < 80 °C), as over 2 000 h DMFC testing was carried out without any loss of performance. The methanol crossover and other mass transfer phenomena have been investigated in a free-breathing DMFC both experimentally and computationally. The information on local concentrations of the reacting species is obtained by measuring the current distribution profile using a resistor network approach and a segmented cathode. The developed numerical 3D model describes the behaviour of the free-breathing DMFC and gives spatial information on mass transfer phenomena, e.g. predicts the existence of the observed electrolytic domains, i.e. regions of negative current densities.

This thesis consists of an overview and of the following 5 publications:

  1. V. Saarinen, T. Kallio, M. Paronen, P. Tikkanen, E. Rauhala, K. Kontturi, New ETFE-based membrane for direct methanol fuel cell, Electrochimica Acta 50 (2005) 3453-3460.
  2. V. Saarinen, M. Karesoja, T. Kallio, M. Paronen, K. Kontturi, Characterization of the novel ETFE-based membrane, Journal of Membrane Science 280 (2006) 20-28.
  3. V. Saarinen, K. D. Kreuer, M. Schuster, R. Merkle, J. Maier, On the swelling properties of proton conducting membranes for direct methanol fuel cells, Solid State Ionics 178 (2007) 533-537.
  4. V. Saarinen, O. Himanen, T. Kallio, G. Sundholm, K. Kontturi, Current distribution measurements with a free-breathing direct methanol fuel cell using PVDF-g-PSSA and Nafion® 117 membranes, Journal of Power Sources 163 (2007) 768-776.
  5. V. Saarinen, O. Himanen, T. Kallio, G. Sundholm, K. Kontturi, A 3D model for the free-breathing direct methanol fuel cell: Methanol crossover aspects and validations with current distribution measurements, Journal of Power Sources 172 (2007) 805-815.

Keywords: DMFC, membrane, characterization, methanol crossover, current distribution

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

© 2007 Helsinki University of Technology

Last update 2011-05-26