Fuel cells
What is a Fuel Cell?
A Fuel Cell is an electrochemical device in which a fuel and an oxidant react to directly produce electricity. Since this process is not governed by Carnot's law high operating temperatures are not strictly needed to obtain a good efficiency. Apart from being efficient, fuel cells have the advantage of being silent and non-polluting.
Normal use (combustion) of fuel
Normally, fuels are burned in flames or internal combustion engines. Thereby the atoms in the fuel combine directly with oxygen atoms. In this process, fuel atoms donate electrons to the oxygen atoms. The fuel is said to be oxidised, the oxygen is reduced. Because the oxidation and reduction reactions take place in intimate contact, charge transfer is direct.
The priciple of Fuel conversion in a Fuel Cell
In a fuel cell, the oxidation and reduction reactions are separated by an electrolyte. The separation of reactions results in a build-up of negative charge at the anode, and positive charge at the cathode. By applying a current loop, electrical energy can be withdrawn from the reaction. Although there is great similarity with the processes occurring in batteries, it is important to realise that in a fuel cell, the reactants (fuel and oxygen) are supplied from an external source. The fuel cell therefore cannot be "empty", and does not need to be recharged.
Efficient and clean
Although fuel cells can be quite efficient, the conversion of chemical energy into electricity is not without heat production. For some applications this heat can be used, thereby increasing total efficiency. The waste product is the burnt fuel. Normally the fuel is hydrogen and as a consequence, the products are water. Carbon dioxide may be present as well, if a hydrocarbon is used. The operating temperature of all fuel cells is too low to produce NOx.
