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TY - THES AU - Wolf, Stephanie Elisabeth TI - Electrochemical analysis and development of novel electrode materials for high-temperature electrolysis PB - RWTH Aachen University VL - Dissertation CY - Aachen M1 - RWTH-2025-01207 SP - 1 Online-Ressource : Illustrationen PY - 2025 N1 - Veröffentlicht auf dem Publikationsserver der RWTH Aachen University N1 - Dissertation, RWTH Aachen University, 2025 AB - This work focuses on the analysis of the performance and degradation behavior of Ni-cermet and Ni-free perovskite materials for the fuel gas electrode under steam, CO<sub>2</sub>, and co-electrolysis conditions. Degradation tests of commercial solid oxide cells with a Ni-8YSZ fuel electrode were carried under a constant current density of −1 A · cm<sup>−2</sup> for 1000 h. Subsequent microstructural analysis showed nickel particle migration and agglomeration at the interface between the active and support layer. These significant microstructural changes led to an increased cell potential during the degradation tests under steam electrolysis conditions. As the main degradation process of Ni-cermet electrodes was identified as Ni depletion, Ni-free Sr<sub>2</sub>FeMoO<sub>6−δ</sub> electrode materials were synthesized and tested. Electron microscopy measurements showed that nanoparticles are dissolved from the SFM perovskite matrix in a hydrogen atmosphere, forming a new perovskite-metal heterointerface that increases the reactive surface area. Conductivity studies showed that Sr<sub>2</sub>FeMoO<sub>6−δ</sub>-based materials exhibit higher conductivities in reducing atmospheres than other perovskite materials considered as alternatives to Ni-cermet electrodes. The materials Sr<sub>2</sub>FeMoO<sub>6−δ</sub> (SFM) and Sr<sub>2</sub>FeMoO<sub>6−δ</sub>-GDC (SFM-GDC) were electrochemically investigated and achieved higher current densities at 1.5 V than Ni-8YSZ in steam and co-electrolysis, but lower current densities than Ni-GDC. Long-term testing under steam electrolysis conditions showed significantly higher degradation for SFM compared to SFM-GDC, which was attributed to microstructural changes in the SFM electrode. The effect of doping was investigated by synthesizing the double perovskite Sr<sub>2</sub>FeMo<sub>0.65</sub>M<sub>0.35</sub>O<sub>6−δ</sub> with M = Ti, Co, Cu, Mn, and Ni. B-site doping showed an increased conductivity in oxidizing and reducing atmospheres up to 152 S · cm<sup>−1</sup> for Sr<sub>2</sub>FeMo<sub>0.65</sub>Cu<sub>0.35</sub>O<sub>6−δ</sub>-GDC due to the exsolution of bimetallic Fe-Cu nanoparticles. The highest current density of all materials studied, compared to Ni-GDC and Ni-8YSZ, was found for Sr<sub>2</sub>FeMo<sub>0.65</sub>Ni<sub>0.35</sub>O<sub>6−δ</sub> (SFM-Ni). After 500 h under steam electrolysis conditions, however, the SFM-Ni microstructure showed particle agglomeration and electrode densification. To investigate the effect of the fuel gas, SFM-based electrode materials were tested for CO<sub>2</sub> electrolysis in an atmosphere of 80 LB - PUB:(DE-HGF)11 DO - DOI:10.18154/RWTH-2025-01207 UR - https://publications.rwth-aachen.de/record/1003680 ER -