Improving fuel cell batteries
9/22/09

Raising the temperature

There are many kinds of fuel cell batteries. Those which appear to be most popular with researchers seem to be the solid electrolyte fuel cell batteries, that is to say those where the electrolyte is a thin film of polymer, and which makes it possible to create very thin units and therefore to pile them on top of each other to make compact batteries with a high energy density. In this way it is possible to make two batteries of two kilowatts which occupy a volume of one litre. In a car, a 100-kilowatt battery, sufficient for propulsion would therefore only occupy a volume of some fifty litres. Professor Germain, whose laboratory studies the problem of polymers, explains. «The problem with polymers is that they are unstable at high temperatures. They function up to temperatures of about 80 to 100 degrees. This is an interesting temperature to start with, but at these temperatures, the chemical reactions are slow. It is for this reason that a lot of Platinum is necessary. Our objective is therefore to raise the temperature level. By doing this we can improve performances which will make it possible to reduce the quantity of Platinum necessary.»

Micrograph of carbon xerogels-morphology

The creation of fuel cell batteries at higher temperatures presents another advantage. In order to understand it, we must take another look at how the battery works. Even if the yield of a fuel cell battery is very good, it is never 100%. There is therefore a loss of energy in the form of heat, and it is not easy to cool anything that is at 80°C, especially in a confined space like a car. Professor Albert Germain continues, «One of our objectives is, therefore, to develop systems that work at higher temperatures. We have formed a team with the CERM of Professors Jerome and Detrembleur, the EMIC laboratory of Professor Huynen of UCL and the Certech at Seneffe, a centre of technological development, to finalize membrane electrodes which are stable at higher temperatures. Other channels are also being explored in collaboration with the LASSC of Professor Heyen, IT4IP (a company that manufactures particular polymers) and Nanocyl, a company producing carbon nanotubes, because the polymer can be modified by incorporating nanotubes into them and which have excellent electrical properties. The objective here is to succeed in reaching a technique that works at around 200 degrees centigrade.» This, it must be noted, is easier to cool than at 80°C because it is the temperature difference that counts. From the point where thermal transfer has been improved in this way, another field of application opens up: combined heat and electricity generation. We could envisage a point where a single battery would supply domestic heating and electrical energy. The heating would be free because it would be guaranteed by the losses from the system of electrical energy production! The very notion of electricity yield would thus lose its meaning as anything that is not electricity would become heat. Albert Germain explains «This is evidently a big development. In the system we know, that of contemporary electrical power stations, the losses in yield are converted into useful energy. Even if the electrical yield is not 100%, what is not used for electrical energy is used for thermal energy.» Professor Germain’s team has produced membranes which resist temperatures of up to 200 degrees, but they are very fragile and difficult to manipulate. Their mechanical properties must be improved so that they do not break during procedures of battery assembly. A battery is always an assembly of elements, an element which supplies around 0.7 volts being composed of two electrodes and the electrolyte that separates them. There is, therefore, an operation of pressing, during which the membranes can break.

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