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Förslaget inkom 2003-04-09

Investigation of catalysts based on non-noble metals for polymer electrolyte fuel cells

OBS! ANSÖKNINGSTIDEN FÖR DETTA EXJOBB HAR LÖPT UT.
Polymer electrolyte fuel cells (PEFC) convert directly chemical energy of a fuel into electricity through an electrochemical process. Pure hydrogen, hydrogen reformed from hydrocarbons or methanol are suitable fuels for the half-cell reaction at anode side (oxidation). PEFCs are low temperature fuel cells (up to 100C) and are therefore subject to kinetic limitations, especially at the cathode side (oxygen reduction). Today, the only suitable catalysts for PEFCs are platinum or platinum alloyed with
other precious or transition metals. This constrained choice of catalysts comes from the low reaction rates of the electrochemical reactions at low temperature, stability problems of transition metals in acidic environment (polymer electrolytes are acidic). Therefore, precious metals such as platinum are to be used. Unfortunately, the use of precious metals raises the cost of electrodes (platinum is more expensive than gold) and moreover would imply a high recovery rate in case of a mass production of PEFCs

Stable catalysts for the oxygen reduction reaction (half-cell reaction) based on transition metals (e.g. Fe, Co) can be obtained from a high temperature pyrolysis of metal-organic macrocycles (e.g. porphyrins, phtalocyanines) or from the pyrolysis of metal salts with a suitable carbon support in ambient containing nitrogen. These catalysts are at the present state less active than platinum, but cheaper. Another advantage against platinum is that they are almost insensitive to impurities or poisons. Such
catalysts have been developed and investigated in the past years at a research institute in Canada (Montréal). Following the stay of a PhD student there, we have a collaboration with that laboratory. While their domain of expertise is the synthesis of catalysts and material characterization, we are focused on modelling and experimental investigation of the functioning of porous electrodes for PEFCS.

Purpose of the thesis
The task of the thesis work is to study catalysts based on iron and pyrolysed at 900C in NH3 atmosphere on various carbon supports. The catalysts have been synthetized at INRS, Québec, Canada. The thesis would include the fabrication of porous electrodes, their electrochemical investigation in fuel cells using steady-state and transient techniques in order to determine mass-transport limitations and long-term stability tests (500h and more) for the best catalysts. Depending on the time schedule, optimisation of the porous electrodes can be studied. We have about 7 stations for testing fuel cells at our laboratory and the experimental techniques have already been
used for studying porous electrodes based on Pt. Thus the focus of the thesis is not the development of new experimental techniques but to apply them on new materials.

Fuel cells can be applied to several applications, e.g. electrical vehicles, distributed power generation, mobile telephones or laptop computers. Actually fuel cells could
be an ideal substitute for batteries in most cases where high energy density is important.

Proposed project plan
Literature survey: During a first stage, a literature survey has to be done in order to get an overview of the state of the research
Electrode preparation: Development of a procedure for preparing electrodes, possibly screening a few fabrication parameters and study their effect on electrochemical performance for a given catalyst.
Electrochemical investigation: Prepared electrodes are installed in fuel cells and studied with steady-state and transient techniques
Stability investigation: The most active catalysts are run for 500h or more to study their stability.
Evaluation: Analyses and evaluation of the tested materials.

Contact
Göran Lindbergh Tel: +46 8 790 81 43, E-mail Goeran.Lindbergh@ket.kth.se
Frédéric Jaouen Tel: +46 8 790 8174, E-mail: frederic.jaouen@ket.kth.se (cannot be reached before 14 april)


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