World Record at EIFER: 23,000 Hours of Operation of a High Temperature Steam Electrolysis Cell

A test with a ceramic solid oxide cell for steam electrolysis was recently completed at EIFER after a duration of 23,000 hours – which is more than two and a half years. At present, this is by far the longest test for such a cell worldwide. The cell represents the heart of a steam electrolyser producing hydrogen with electrical energy.

The experiment was performed in the frame of the sunfire research project of the German Federal Ministry of Education and Research, BMBF, using an electrolyte supported cell from the German cell producer KERAFOL®. The project milestone of 1,000 hours was finally exceeded by a factor of 23! The cell remained fully operational until the end of the test, without indications for accelerated degradation. Therefore, there is little doubt that operation times of above 40,000 hours, required for industrial applications, are reachable. Most of the testing was done with a current density of 0.9 Acm-2, comparable to the values of low temperature electrolysers, but at lower voltage and therefore higher efficiency (the final cell voltage was 1.3 V at a cell temperature of 850°C). Voltage degradation was only 0.6 % /1,000 hours.

View of the electrolyser cell after dismantling. The cell of 45 cm2 area and 0.2 mm thickness has finally consumed 300 kg water for the production of 370 cubic metres of hydrogen.

Crucial for the high electrical-to-chemical energy conversion efficiency are the fast reaction kinetics at the electrodes, achieved without the use of noble metals. That efficiency further increases when heat from a downstream process becomes available for steam generation, such as from power-to-gas / liquid reactors which convert hydrogen and carbon dioxide to synthetic fuels. Moreover, reversible (fuel cell / electrolyser cell) operation is feasible with solid oxide cells. All this offers a number of applications in the context of the storage and efficient use of fluctuating renewable electrical energy.

The test is further proof of the longevity of the solid oxide cell technology, adding to a record-breaking test of a fuel cell stack recently reported by the Research Centre Jülich in Germany (press release 22nd October 2015). That test ran for 70,000 hours, though with a total production of electrical energy per unit area below the consumption of the electrolyser cell in the EIFER test. The reason for this is a largely increased power density in the electrolyser cell with a more than two times higher current density. Operation with current densities above the ones used in the fuel cell mode is a development goal for electrolysis, in order to benefit from the ‘thermal neutral’ operation mode (i.e. an operation without heat flow to or from the cell).

EIFER has been active in the field of electrolysis research for more than 10 years, with a focus on long-term testing of cells and cell stacks. Details of the work will be presented at the World Hydrogen Conference (WHEC) and at the European Fuel Cell Forum (EFCF) later this year. The first 11,000 hours of the test have already been published. (Schefold, J., Brisse, A., Poepke, H., ‘Long-term Steam Electrolysis with Electrolyte-Supported Solid Oxide Cells,’ Electrochimica Acta, 179 (2015) pp. 161-168).

Contact: Josef Schefold