| Nov 30, 2011 |
Modelling can help to improve fuel cell function
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(Nanowerk News) In her doctoral dissertation (Modelling Approaches to Mass Transfer and Compression Effects in Polymer Electrolyte Fuel Cells), M. Sc. (Tech.) Suvi Karvonen examines the local and cell level modelling of PEMs, or polymer electrolyte membrane fuel cells. Her dissertation, which will be examined at Aalto University, states that the functioning of PEM fuel cells can be substantially improved through a very simple modelling exercise.
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According to Karvonen, experimental research in many questions relevant to fuel cells is expensive and slow. Instead of manufacturing a number of cells and experimentally testing their functioning, different variations can be produced by modelling, which is much faster and less expensive. On the other hand, there are aspects that cannot be studied, not even by experimental methods.
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For example, owing to the practical limitations of temperature sensors and current measurements, it is simply not possible to measure current density or temperature everywhere inside the cell, says Karvonen.
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Current density fluctuations may affect cell function negatively
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The fuel cell modelling produced information on the distribution of cell compression pressure and its impact on cell function locally. The modelling results indicate that among others, transversal electric currents are generated locally in the cell. This phenomenon may have a negative impact on fuel cell function and life span.
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According to Karvonen, an irregular current density distribution causes uneven ohmic heating in the cell. As a result the Nafion membrane, or the cell electrolyte, at the core of the cell may dry out and become damaged.
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In order for the cell to work, the Nafion membrane must be moist. Heating may dry out the membrane or burn a hole in it. In that case, the cell will leak fuel and oxygen through the hole and perish, or at least start working poorly, explains Karvonen.
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A fuel cell for an electric car?
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Fuel cells are electrochemical devices producing electricity to which the reactant is fed from outside. The cells can be used to replace batteries, and plenty of research has already been conducted on their suitability for such applications as electric cars. The fuel cell could extend the distance an electric car can travel.
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In a battery, all fuel must be contained inside the battery. In order for the car to travel a long distance, the batteries would need to be really large. This would make the car extremely heavy, and the batteries would not necessarily fit in the car. A fuel cell car, on the other hand, could go and fill up every now and then, as it is possible to feed more fuel into it, Karvonen illustrates.
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According to Karvonen, however, the current problem is the availability of fuel. The most common fuel used for the cells is hydrogen, which does not occur freely on earth. Storing hydrogen is also difficult.
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