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@PHDTHESIS{Unachukwu:1050640,
      author       = {Unachukwu, Ifeanyichukwu Daniel},
      title        = {{F}uel electrode degradation study for solid oxide
                      electrolysis},
      school       = {RWTH Aachen},
      type         = {Dissertation},
      publisher    = {RWTH Aachen University},
      reportid     = {FZJ-2026-00392},
      pages        = {123},
      year         = {2025},
      note         = {Dissertation, RWTH Aachen, 2025},
      abstract     = {The conversion of electrical energy into a chemical energy
                      carrier in the form of hydrogen, carbon monoxide and
                      synthesis gas can be achieved with high efficiency by using
                      the solid oxide electrolysis technology. However, long term
                      degradation issues, especially of the fuel electrode remain
                      a challenge that must be resolved. This thesis therefore
                      investigates the electrochemical performance and degradation
                      behaviour of three different fuel electrodes: gadolinium
                      doped ceria (GDC), Nickel-GDC and Nickel with
                      yttria-stabilized zirconia (Ni-YSZ) under three different
                      electrolysis modes: steam, CO2 and co electrolysis. The fuel
                      electrode material was fabricated on an 8YSZ electrolyte
                      support while the air electrode is made of lanthanum
                      strontium cobalt ferrite (LSCF) with a GDC barrier layer
                      sandwich between the electrolyte and the LSCF. Thus, the
                      cell configuration is represented as Fuel
                      electrode//8YSZ//GDC//LSCF. Their performance and
                      electrochemical processes were investigated by direct and
                      alternating current measurements in the different
                      electrolysis modes in the 750-900 °C temperature range.
                      Distribution of relaxation times (DRT) analysis and
                      non-linear least square method were employed to resolve
                      frequency-dependent electrode processes. The analysis
                      reveals that the GDC fuel electrode is dominated by
                      low-frequency surface exchange processes originating from
                      the double phase boundary sites (DPB), while the Ni-GDC
                      electrodes are dominated by sub-surface mid-frequency
                      processes. For the Ni-YSZ, the underlying processes are
                      dominated by mid/high-frequency processes, mostly from the
                      triple-phase boundary sites (TPB). With regard to the
                      performance, the Ni-GDC single cells exhibited the highest
                      current density across the three electrolysis modes while
                      the GDC and Ni-YSZ showed similar current density in the
                      different electrolysis modes. In the degradation analysis,
                      Ni-YSZ exhibited the highest degradation rate in steam
                      electrolysis followed by Ni-GDC while the GDC showed the
                      least degradation. On the other hand, during CO2
                      electrolysis, the GDC electrodes showed the highest
                      degradation rate, while Ni-YSZ exhibited a degradation rate
                      slightly higher than those of Ni-GDC. The post-test analysis
                      reveals that GDC particle coarsening and loss of GDC
                      percolation was the major contributor to the degradation
                      rates in the GDC and Ni-GDC single cells. Furthermore, GDC
                      migration and covering of the Ni particles were also seen to
                      contribute to the degradation rates in the Ni-GDC cells. For
                      the Ni-containing cermet of Ni-YSZ and Ni-GDC, Ni migration
                      and agglomeration remain significant contributors to the
                      degradation rate. The degradation processes were observed to
                      be facilitated by an increase in steam partial content.},
      keywords     = {Hochschulschrift (Other)},
      cin          = {IET-1},
      cid          = {I:(DE-Juel1)IET-1-20110218},
      pnm          = {1231 - Electrochemistry for Hydrogen (POF4-123) / HITEC -
                      Helmholtz Interdisciplinary Doctoral Training in Energy and
                      Climate Research (HITEC) (HITEC-20170406)},
      pid          = {G:(DE-HGF)POF4-1231 / G:(DE-Juel1)HITEC-20170406},
      typ          = {PUB:(DE-HGF)11},
      doi          = {10.18154/RWTH-2025-06190},
      url          = {https://juser.fz-juelich.de/record/1050640},
}