Solid Oxide Fuel Cells (SOFCs)
Solid oxide fuel cells (SOFCs) based on ceramic cells are one type of high-temperature fuel cell. They are operated at 600–1000 °C, yielding very high electrical efficiencies of approximately 60 %. They can be used for domestic energy supply, industrial combined heat and power generation (CHP systems), for electricity generation in power plants, and for on-board power supply in vehicles. SOFCs can run on hydrogen, as well as methane (i.e. natural gas) or diesel reformate.
Fuel cells based on oxide ceramics
Forschungszentrum Jülich has been developing solid oxide fuel cells since the early 1990s, concentrating on cells with an output of 5–100 kW for stationary, decentralized energy supply – i.e. for domestic energy supply (1–10 kW), and decentralized combined heat and power generation (> 10 kW). The focus is on the anode-supported planar concept. Activities at Jülich comprise the entire process of research and development, from materials synthesis and materials development for cells, to the production of layers, structures, and components, and their characterization by means of single-cell and stack tests, to system operation and modelling as well as the development of periphery units. Five institutes at Forschungszentrum Jülich are involved in SOFC development.
In addition, Jülich and its research and industry partners in Germany, Europe, and beyond are developing SOFCs for on-board power supply in vehicles and ships. Apart from the conventional anode-supported concept, the scientists are also exploring a cell concept based on metallic substrates, on which diffusion barriers, electrodes, and electrolytes are deposited step by step by means of ceramic technology and physical vapour deposition processes.
In addition, scientists are investigating whether conventional SOFCs can also be utilized for high-temperature electrolysis in order to produce hydrogen, either as a fuel or as a basis for further processing steps, for example to produce methane (‘power-to-fuel’ or ‘power-to-liquid’). SOFCs are also being developed as high-temperature metal-air batteries. In this concept, SOFCs serve as an electrolyser cell when excess electricity is available, and as a fuel cell when the demand for energy is greater than the amount available. The ‘electricity’ is saved in the form of oxygen, which is used to reduce a metal – i.e. to charge the battery in electrolysis mode – or to oxidize it – i.e. to discharge the battery in fuel cell mode.
more information on collaborations:
- ENSA (SOFC APU)
- MetAPU (lightweight SOFC stacks)
- Scotas (development of special anodes for SOFCs)
- MeMO (high temperature batteries)
- Sunfire (high temperature electrolysis)
SOFC development all over the world concentrates primarily on two main variants: SOFCs based on pipes or flat membranes. The active electrodes are applied either to a ceramic pipe or a flat ceramic surface. Individual developers are also working on other variants with various other geometries.
At Jülich, SOFC activities focus on the state-of-the-art concept of anode-supported SOFCs with thin electrolytes. Due to the low resistance of the thin layers, a greater performance can be achieved at a lower operating temperature. The anode material (yttria-stabilized zirconia and nickel) serves as a substrate for the cells, hence their classification as ‘anode-supported’ cells. Each single cell has a voltage of about one volt.
At Jülich, the cells are integrated into a steel frame and stacked with intermediate plates made of steel (interconnects) to form a stack. As a result, the overall voltage becomes technically useful and the power output of the stacks increases accordingly. Due to the high temperatures, the researchers use glass-ceramic materials to seal and join the individual components. The materials developed at Jülich are designed in such a way that no excess mechanical loads on the stacks are caused by heating and cooling during the start-up and shut-down phases. A new steel alloy has been developed specifically for this purpose and is being marketed by ThyssenKrupp under the name of CroFer 22 APU.