PEM Fuel Cells
The PEMFC is easy to handle. It is very light, it is very efficient and as reaction gas it requires only atmospheric oxygen instead of pure oxygen. The hydrogen has to have the typical purity.
PEM (Proton Exchange Membrane or Polymer Electrolyte Membrane) fuel cells are very sensitive to carbon monoxide (CO). This gas might block the anode catalyst and subsequently lead to a reduced performance.
The electrolyte consists of a solid proton exchange membrane (PEM) made from sulphonated polymer.
The power output of a PEM fuel cell can be controled very dynamically. Therefore it is perfectly suitable for mobile applications and decentralised power plants.
Among the development of fuel cells the PEMFC is most paramount at the moment. One reason is the cell`s enormous potential to be mass produced. The target costs for a fuel cell stack are about 100 EUR/kW.
The function of the PEM fuel cell
- Step 1
Inside the two seperate gas supply cicuits the gaseous oxygene and hydrogen flow into the gas area and the catalyzer.
- Step 2
While getting in contact with the catalyzer the hydrogen molecules (H2) are splitted into two H+ protons. At the same time each hydrogen atom sends out one electron.
- Step 3
The protons move through the electrolyte (membrane) to the cathode area.
- Step 4
The electrons move from the anode to the cathode and cause an electric current. This electric current supplies an electric capacitor with electric power.
- Step 5
Respectively four electrons recombine with one hydrogen molecule at the cathode.
- Step 6
The now generated oxygene ions have a negative load. They move to the positiv loaded protons.
- Step 7
The oxygene ions give their electrons to the two protons and oxidize to water.
Applications for PEM fuel cells
The PEM fuel cell can be used for a great variety of applications such as mobile phones, cogeneration of power and heat or drive trains for automobiles.
PEM fuel cell drive systems are now demonstrated in many prototype vehicles. Motorcars, minibuses and city buses will be the first types of vehicles to be fitted and sold with fuel cells.
Later on vans and some other light commercial vehicles will be added. Only heavy trucks are not probable to be offered with PEM fuel cells in the near future because very large hydrogen tanks would be needed to drive long distances and in addition the diesel engines work very efficiently in big trucks.
PEM fuel cells are also suitable for rail vehicles like trams or regional railways. In this case overhead lines are not required.
PEM fuel cells are perfectly suitable for the co-generation of electric power and heat. Small applications e.g. in houses as well as applications for large buildings like hospitals are in the development stage.
It must be reckoned that the commercialisation will take place in the next two years. In these applications the hydrogen is generated from natural gas or liquid gas in reformers.
Portable devices which require electric power are also possible applications of PEM fuel cells. Most prominent is the field of camping equipment. But also accumulator-drills or lawn-mowers could be driven by PEM fuel cells. The first fuel cell systems for mobile phones and laptops have already been developed.