Heat-Resistant Materials Required
SOFCs with an operating temperature above 700 °C are estimated to be ready for the market within less than four years, for example as auxiliary power units in trucks. The temperature changes involved during startup and shutdown is still difficult to handle. These processes expose the sealant material to particularly extreme conditions.
Jülich scientists have succeeded in developing glass sealants that can cope well with the cooling down of the SOFCs to a stand-by temperature of approximately 350°C. They also found a way to repair seals: scientists focus a laser beam on the defect to melt the broken glass sealant material. When the material cools down and solidifies, the defective spot is completely sealed again.
Jülich researchers recently succeeded in assembling cells with a low operating temperature. At a temperature of 550°C, their performance is the same as that of cells operated at 950°C 15 years ago. The researchers achieved this enormous progress by reducing the electrolyte layer thickness to one to two thousandths of a millimetre.
Hot within Three Minutes: HT-PEFC Fuel Cells
The researchers are also working on an alternative to SOFCs: high-temperature polymer electrolyte fuel cells or HT-PEFCs for short. Their advantage: they only need three minutes to heat up. In contrast, it takes SOFCs 20–30 minutes before they are ready for use. Compared to the requirements of a conventional PEFC, HT-PEFCs do not require hydrogen that is as pure. It is therefore possible to produce the hydrogen in an upstream reformer.
The key factor for the efficiency of such a reformer is that the diesel is mixed well with air and water. To this end, researchers have calculated and simulated the flows of gases and liquids in the mixing chamber of a reformer with the Jülich supercomputer JUGENE. In this way, they were able to optimize the shape of the mixing chamber so that initially, 99.999% of the diesel are utilized – and even after 1,000 operating hours, as much as 99.7%.