High temperature electrolysis appears to have the potential of becoming a viable economic solution to the production of hydrogen and synthesis gas, a mixture of hydrogen and carbon monoxide (CO), which can easily be transformed into synthetic fuels, such as synthetic natural gas or petrol. High temperature cells are very effective compared to other electrolysis methods, i.e. they produce more hydrogen and CO from a certain amount of electricity. This is due to the fact that at higher temperature both water and carbon dioxide will be partially split by the heat. This consumes heat, and thus the electrolyser is able to cool itself: The heat inevitably created from the electric current passing through the cell is actually needed for the electrolysis process. In addition, it is also possible to utilise heat, which is often available as surplus heat from e.g. power plants.
There is a need for alternative fuels for the transport sector
Today 60 % of Denmark’s total oil consumption is used for transport purposes, a percentage rate that is still growing. Therefore, it is necessary to apply renewable energy in the transport sector. One solution could be using wind turbine power for cars by producing synthetic fuel. The wind turbine power is used in the electrolysis cells to split water and carbon dioxide into hydrogen, carbon monoxide and oxygen.
Synthetic fuel is CO2 neutral
The advantage of synthetic fuel is that the existing infrastructure may be used. The exhaust from the car consists of water and CO2. As the amount of CO2 used in the electrolysis is exactly the same as the amount produced by combustion in the engine, the synthetic fuel becomes entirely CO2 neutral.
Must be produced cheaply
A major challenge is to produce synthetic fuel at a sufficiently low price. An important activity at Risø DTU is the development of high temperature electrolysis for the rational production of large quantities of synthesis gas, among other things. High temperature electrolysis takes place in an SOFC (Solid Oxide Fuel Cell) that is operated in ”the reverse way”, i.e. it is supplied with power from a wind turbine for instance, water and carbon dioxide and then produces synthesis gas. The cells are then called SOEC (Solid Oxide Electrolyzer Cell).
Reverse fuel cell challenges
It is not a simple task to operate a fuel cell in the reverse direction. Electrolysis has other requirements for the optimization of the materials it is made of. The production of hydrogen in the SOEC may happen at a temperature of 950 degrees Celsius and a voltage of 1.48 Volt. Under these conditions the Fuel Cells and Solid State Chemistry Department has broken the international record with regard to current density in the cell. It is 3.6 A/cm2, which is far better than what other groups in the world have achieved.
Cheaper than oil - under the right circumstances
Risø DTU has calculated that under certain conditions, hydrogen may be cheaper than the present oil price, when produced using renewable power. The calculations made by Risø DTU have been published in a scientific article: Jensen, S.H., Larsen. P.H., Mogensen, M., Hydrogen and synthetic fuel production from renewable energy sources, Int. J. Hydrogen Energy, 32, p. 3253– 3257 (2007). In the article the authors show a graph where the calculated hydrogen price (converted into equivalent crude oil price) is shown as a function of electricity price.
The figure shows the hydrogen price (converted into equivalent crude oil price) as a function of electricity price.
The potential for Risø DTU’s technology is assessed in the figure. The graph also shows that even with an electricity price of 4 – 5 U.S. cents there is certainly a commercial potential in the technology, if the scientists at Risø DTU will achieve the goals used for this calculation.
A good reason to continue researching
As Research Professor Mogens Mogensen from the Fuel Cells and Solid State Chemistry Department says: ”We think that we have accounted for why it is such a good idea to continue with R&D in this field”.
However, a commercial production of hydrogen in the new SOECs needs further research and development to ensure that the cells endure long term operation. The cells degrade under operation, and it is important to reach a lifetime of approximately 5 years if the cells are going to be of commercial interest.
For more information visit the website of the department |