The ongoing expansion of renewable power generation capacities, such as wind power or photovoltaic, poses many challenges due to their volatile nature. Hydrogen, which can be produced with high efficiency and the use of surplus renewable electricity through high-temperature electrolysis in solid oxide cells, is considered to be a promising storage medium. In phases of low renewable electricity generation, the energy stored in hydrogen or its derivatives can be harnessed in solid oxide fuel cells or established power generation plants, such as turbines or engines.
In this work, the rare earth nickelate La2Ni0.8Co0.2O4+δ is investigated for its suitability as an air electrode material in solid oxide cells. For this purpose, symmetrical solid oxide cells are characterised by means of electrochemical impedance spectroscopy (EIS). The focus of this work is on the variation of the sintering procedure for the production of the electrode layers, as well as the optimisation of the measurement setup for the characterisation of a total of eight symmetrical solid oxide cells. By investigating the cell state after the EIS (post-test analyses), as well as examining trends in the recorded impedance spectra, conclusions can be drawn about the stability of the electrode and their degradation behaviour, as well as the adhesion of the air electrodes on the electrolyte substrates made of gadolinium-doped ceria. By means of light microscope and scanning electron microscope (SEM) images of the cells, the microstructure and morphology of the La2Ni0.8Co0.2O4+δ electrodes are characterised and related to the manufacturing parameters and electrochemical performance. With an optimised sintering procedure derived from this, an anode-supported solid oxide cell was fabricated, which was characterised by current density/voltage measurements in both electrolysis and fuel cell mode. Furthermore, the influence of setup modifications on the electrochemical characterisation was investigated.
The results of the work show that the electrochemical performance as well as the long-term stability of symmetrical solid oxide cells are strongly influenced by the sintering procedure used in the electrode preparation. For the electrode material La2Ni0.8Co0.2O4+δ, the performance of symmetrical cells in terms of polarisation resistance was improved by more than 50 % by optimising the sintering procedure previously used for rare-earth nickelates. These performance improvements were validated in the current density/voltage characteristics of the solid oxide cell in electrolysis mode, where the optimised temperature procedure was applied. Using SEM imaging, it was also possible to establish relationships between the improvement in cell performance and the optimisation of the microstructure of the electrode layers.