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@PHDTHESIS{Winterhalder:1038889,
      author       = {Winterhalder, Franziska Elisabeth},
      title        = {{E}ntwicklung alternativer {B}renngaselektroden für die
                      {H}ochtemperatur-{E}lektrolyse},
      volume       = {655},
      school       = {RWTH Aachen University},
      type         = {Dissertation},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2025-01700},
      isbn         = {978-3-95806-805-6},
      series       = {Schriften des Forschungszentrums Jülich Reihe Energie $\&$
                      Umwelt / Energy $\&$ Environment},
      pages        = {vii, 161},
      year         = {2025},
      note         = {Dissertation, RWTH Aachen University, 2024},
      abstract     = {The production of hydrogen is vital for a CO2-neutral,
                      hydrogen-based energy system, essential for achieving
                      national and international climate goals. Solid oxide
                      electrolysis cells (SOECs) powered by renewable energy are
                      key to producing green hydrogen and can achieve electrical
                      efficiencies over $100\%$ when coupled with waste heat.
                      However, there are challenges concerning long-term stability
                      and cost efficiency. Current materials used in these cells
                      degrade significantly under SOEC conditions, leading to
                      reduced performance. In particular, the commonly used Ni-YSZ
                      fuel electrode shows considerable degradation due to Ni
                      agglomeration and migration. A potential solution is using
                      alternative fuel electrodes. This study aimed to develop
                      alternative perovskite-based fuel electrodes for steam
                      electrolysis in SOECs. Five alternative perovskite materials
                      were synthesized and characterized:
                      La0.6Sr0.38Fe0.8Mn0.2O3-δ – LSFM, La0.35Sr0.63TiO3-δ –
                      LST, Sr0.98Ti0.7Fe0.3O3-δ – STF30, Sr0.98Ti0.5Fe0.5O3-δ
                      – STF50 and Sr1.98FeNbO6-δ – SFN. In particular, the
                      stability under reducing conditions and the compatibility of
                      the perovskites with 8YSZ under the production conditions of
                      fuel electrode-supported SOECs were investigated. It was
                      found that SFN exhibits the highest stability in a reducing
                      atmosphere as well as low reactivity with 8YSZ under the
                      tested conditions. Based on the results of the
                      characterizations, SFN and STF50 were selected as fuel
                      electrode materials for all subsequent experiments. First,
                      the stability of the perovskites under realistic SOEC
                      conditions was tested. The results showed that both
                      materials can be considered chemically stable, although a
                      small amount of Fe3O4 secondary phase formation was observed
                      in STF50. Furthermore, the compatibility of SFN/STF50 with
                      8YSZ and GDC under SOEC conditions and the manufacturing
                      conditions for electrolyte-supported cells was investigated.
                      SFN showed no interactions with 8YSZ or GDC, while STF50 was
                      compatible only with GDC under the tested conditions.
                      Overall, a barrier layer between the perovskite electrode
                      and the 8YSZ electrolyte is beneficial for preventing or
                      reducing chemical reactions. Electrochemical measurements of
                      cells with SFN and STF50 fuel electrodes at different
                      temperatures (650–800 °C) and varying H2O content in the
                      fuel gas (3–90 $vol.-\%)$ indicated that the contact layer
                      significantly impacts resistance values. It was also
                      observed that both the ohmic resistance (RΩ) and the
                      polarization resistance (RPol) decrease with increasing
                      temperature but increase with a higher water vapor content.
                      A degradation study of a full cell with an STF50 fuel
                      electrode and an LSCF oxygen electrode over approximately
                      1700 h at 800 °C in 50 $vol.-\%$ H2O + H2 and a current of
                      i = -0.43 A∙cm-2 revealed comparatively high degradation
                      rates of 0.195 V kh-1, 0.162 Ω∙cm2 kh-1, and 0.361
                      Ω∙cm2 kh-1 for voltage, RPol, and RΩ, respectively. A
                      subsequent SEM analysis of the microstructure of the STF50
                      fuel electrode before and after the degradation study showed
                      no significant changes in the electrode microstructure,
                      except for diffused Ni particles. Whether the Ni particles
                      that diffused from the NiO/Ni contact layer into the STF50
                      fuel electrode and the GDC barrier layer have an impact on
                      the cell's performance cannot be confirmed or ruled out at
                      the current stage. In addition to producing
                      electrolyte-supported cells, the integration of STF50 and
                      SFN into the manufacturing route for fuel
                      electrode-supported cells (FESCs) was investigated. Planar
                      half-cells with STF50 fuel electrodes were successfully
                      produced, though they did not meet the required gas
                      tightness. In general, integrating perovskite-based
                      alternative fuel electrodes into the FESC manufacturing
                      process is not feasible without modifications. In summary,
                      this work demonstrates that STF50 and SFN have considerable
                      potential as alternative fuel electrodes in steam SOECs.
                      Although they exhibit a certain degree of stability and, in
                      the case of STF50, sufficient baseline performance, further
                      optimizations and long-term studies are necessary to
                      establish these materials as potential replacements for
                      Ni-YSZ fuel electrodes.},
      cin          = {IMD-2},
      cid          = {I:(DE-Juel1)IMD-2-20101013},
      pnm          = {1231 - Electrochemistry for Hydrogen (POF4-123)},
      pid          = {G:(DE-HGF)POF4-1231},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      doi          = {10.34734/FZJ-2025-01700},
      url          = {https://juser.fz-juelich.de/record/1038889},
}