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Förslaget inkom 2005-01-17

Investigating the effect of magnetized fuel cell cathodes for improved oxygen reduction

1 Introduction

The polymer electrolyte fuel cell is an interesting alternative for various future electric power applications. The energy efficiency of the fuel cell is lowered considerably by more than 25 % by the slow and sluggish electrochemical oxygen reduction reaction.

The standard electrode used today for oxygen reduction is a thin layer of platinum nano-particles deposited on small carbon support grains mixed with an ion-conducting polymer. Platinum is, however, a rare and expensive noble metal, and much investigation is directed towards lowering platinum loading and researching alternative catalysts. Alternative catalysts candidates often consist of platinum alloyed with a transition metal.

Recently, there have been results published on improving the oxygen mass transport in the cathode by magnetizing the electrode \cite{Wakayama}, \cite{Okada}. This promotion effect would be due to the paramagnetic properties of the oxygen gas, a result of the parallel spin configuration of the oxygen gas molecule, in combination with the diamagnetic properties of water. (A paramagnetic material experiences a force towards an increase in magnetic field intensity, a diamagnetic material experiences a force in the direction of decreased magnetic field intensity.)

2 Proposal
More investigation in this field would definitely be interesting. The benefits could be deepened knowledge about the oxygen reduction reaction as well as a technological advance in the fuel cell technology. An interesting question is wether the reported enhanced performance of magnetized electrodes is only due to improved masstransport or if there is an improvement in kinetics as well. A diploma work at the department could be following the outline presented below.

2.1 Starting point
Our suggestion is the work to start with a short litterature study in combination with a first experimental RDE study.

2.1.1 Literature study on the magnetic properties of catalyst candidates
The references listed at the end of this document will be thorougly studied, other questions to answer might be: What magnetic materials could be suitable to introduce in the corrosive fuel cell environment? Many catalyst candidates investigated today are probably magnetic, to what extent? How strong permanent magnetic fields is it possible to attain, and how is it done?

2.1.2 Oxygen reduction studies on a magnetized rotating disk electrode
Following the procedure in \cite{Wakayama} a small permanent magnet is placed behind the rotating platinum disk electrode and the effect on the kinetic current and Tafel slope when introducing this magnet is studied. By using different magnets the effect of changed magnet field intensity may be studied.

2.2 Continuation
Depending on the outcome of the above first study, and if there is time for it, the diploma worker might want to continue in either an experimental or a more theoretical ``branch''.

2.2.1 Preparation and electrochemical behaviour of a magnetized fuel cell membrane-electrode-assembly

Recently there have been commercial PtCo-catalysts introduced in the market, depending on the availability of these the natural step could be to use these when preparing a magnetized polymer electrolyte fuel cell cathode. PtCo is known to be ferromagnetic, but since the behaviour changes to superparamegnetic as the grain size decreases \cite{Kumbhar}, the magnetic promotion effect might decrease because of this. There are also Cobalt-based new alternative non-noble catalyst materials available at the departement.

Introducing small amounts of separate magnetic particles in the electrode should be another way to magnetize the electrode to some extent. The fuel cell environment is, however, very corrosive and much care has to be taken when selecting the material, iron dust will, for example, probably not work. Technological developments will have to be made in order to magnetize the electrode. Cell performance could be comparedt


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