Solid Oxide Fuel Cells – SOFC
The solid oxide fuel cell -SOFC operates with atmospheric oxygen and hydrogen. Its operating temperature is between 800 and 1000°C. The high temperature allows a partial reforming from natural gas to hydrogen within the cell. Thus the necessary effort for the generation of hydrogen is decreasing immensely.
There are two different SOFC designs: planar (shaped like a plane) and tubular (shaped like a tube). With the tubular SOFC cathode, electrolyte and anode are arranged at the inside of a ceramic pipe. The fuel gas is led through the inside of the tube and the atmospheric oxygen is led around the outside. The tubular SOFC is used for the decentralised supply of energy with a power rating of more than 100 kW.
The function of the SOFC:
- 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 electrons move into the anode and cause an electric current. This electric current supplies an electric capacitor with electric power.
- Step 4
Respectively four electrons recombine with one hydrogen molecule at the cathode.
- Step 5
The now generated oxygene ions have a negative load. They move through the electrolyte (ytrium endowed circon dioxide) to the anode area.
- Step 6
The oxygene ions change their electrons with the two protons and oxidize to water.
Applications for SOFC
Solid oxide fuel cells are suitable for stationary and for mobile applications.
Stationary plants for the cogeneration of power and heat are in the development for different sizes of residential buildings and also for large buildings and for industrial or commercial applications.
Heat can be gained at a high temperature range and therefore can be used as process heat.
Apart from that big power stations on the basis of SOFCs are in the development stage. In this case the waste heat is used for the power generation in gas turbines. In future this type of power plant is to reach efficiencies of up to 70%.
With regard to mobile applications SOFCs at the moment are not developed for drive trains but as a substitute for vehicle batteries. The reason for this is on the one hand the constantly increasing number of devices requiring electric power in cars and on the other hand the possibility to have electric power at ones disposal for a long time - even when the engine is not operating. As fuel serves gasoline which has to be converted in a simple reformer and also has to be desulfurised.