Reversible Solid Oxide Cells

Permission of Sunfire GmbH

Germany,  France


Splitting water into hydrogen and oxygen using renewable energy is a good way to store renewable energy for long periods of time. This is typically done using an electrolyser. The resulting hydrogen can be converted back to electricity in a fuel cell. Normally electrolysers and fuel cells are different devices, which means that two devices are required in order to have a system that can store renewable energy when a surplus is available and provide electricity when renewable energy production is low. As a result, such systems are currently still too expensive for widespread use.


The innovation of the Reversible Solid Oxide Cell is that a single device can split water to produce hydrogen, as well as convert hydrogen back to electricity. Solid oxide cells typically operate at very high temperatures. This avoids the need for precious metal catalysts. However, the high temperatures mean that the materials in such a solid oxide cell need to have extraordinary properties. Many years of research were needed to find materials that are up to the task.


The company Sunfire has developed its technology, supported by several research grants from the Federal Government of Germany. The PowerCore — a solid oxide cell (SOC) stack — is Sunfire’s key technology integrating a steam electrolyser (solid oxide electrolyser cells, SOECs) and a high-temperature fuel cell (solid oxide fuel cells, SOFCs). The merits of the solution have been demonstrated in several demonstration projects, together with partners from industry and science. Sunfire offers the opportunity to use green electricity as a renewable feedstock for industry and mobility. Linking the energy sectors thus turns the electricity transition into an energy transition which will help achieve climate goals.


This solution could enable the production of hydrogen or other chemical energy carriers in places where cheap renewable energy is available. In addition it could be used in an urban environment, where the excess heat resulting from the process can be used for space heating, thereby greatly increasing the overall efficiency. It could also provide hydrogen, which is still predominantly produced based on fossil fuels, for industrial processes. At the same time the reversible solid oxide cell can provide back-up power.