Ceria-based Cathodes for High Performance Electrolysis Cells
In view of the current energy and climate crisis, a transition of the energy supply from fossil to sustainable energy sources is of utmost urgency. For this, it is necessary to store energy temporarily in order to adapt the intermittent availability of renewable energy sources such as wind and solar (day/night, weather, seasons) to the demand. In addition, the provision of sustainable chemical energy sources such as hydrogen or carbon monoxide is essential for the decarbonization of industry. Electrolysis of water and carbon dioxide represents a very important method to meet both requirements.
High-temperature electrolysis in solid oxide cells is a key technology in this context, since on the one hand it is able to achieve the highest efficiency of the currently available electrolysis systems, and on the other hand, due to its high operating temperatures, it is best suited for splitting the very stable CO2 molecule. However, a well-known problem of current solid oxide electrolysis cells – and especially their cathodes – is their high degradation rates, even if the same cell type is stable under fuel cell conditions (i.e. reverse current as well as reaction direction as in electrolysis cells). The reason for this is, on the one hand, microstructural changes of the cathodes under electrolysis conditions, as well as their susceptibility to carbon deposition (coking) in the presence of carbon-containing, reducing gases such as carbon monoxide.
The aim of this international project is to develop long-term stable cathode materials for high-temperature solid oxide electrolysis cells. CeO2-based ceramics are a very promising choice, as they already exhibit excellent kinetics in fuel cell mode and the material is considered coking-tolerant. In order to tailor the properties of this electrode material through doping, a profound understanding of a multitude of material parameters is necessary – e.g., ionic and electronic conductivity, catalytic activity for CO2 splitting, coking resistance, sintering behaviour, lattice expansion under electrochemical polarization, and fracture behaviour.
The team of international researchers from Germany, Austria and Switzerland has been assembled to meet this highly complex requirement: The investigation of the electrochemical and catalytic properties of novel cathode materials based on doped CeO2 is carried out at TU Wien. Forschungszentrum Jülich is responsible for the processing of the material and the corresponding production of real, 3D-porous cathodes. Electrochemical cell tests as well as the investigation of microstructural changes during electrolysis operation are performed at EPFL. Based on the experimental data obtained, phase field simulations are performed at Karlsruhe University of Applied Sciences, which allow predictions of the long-term behavior as well as the fracture mechanics of the electrolysis cells. The findings obtained in this way can in turn be used to derive necessary changes in the composition of the cathode material, which are then incorporated into the material design. This close cooperation between several disciplines thus allows targeted, knowledge-driven material optimization, which paves the way to long-term stable high-performance cathodes for CO2 reduction in high-temperature electrolysis cells.