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@PHDTHESIS{RojekWckner:825972,
      author       = {Rojek-Wöckner, Veronika Anna},
      title        = {{E}ntwicklung und {C}harakterisierung von {N}ickel /
                      {G}adolinium-{C}eroxid-basierten {A}noden für die
                      metallgestützte {F}estoxid-{B}rennstoffzelle},
      volume       = {343},
      school       = {Universität Bochum},
      type         = {Dissertation},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2017-00244},
      isbn         = {978-3-95806-182-8},
      series       = {Schriften des Forschungszentrums Jülich Reihe Energie $\&$
                      Umwelt / Energy $\&$ Environment},
      pages        = {XVI, 133 S.},
      year         = {2016},
      note         = {Dissertation, Universität Bochum, 2016},
      abstract     = {The present work aims at the development of an
                      ageing-resistant and sulfur-tolerant high-performance anode
                      for the metal supported solid oxide fuel cell (MSC). As a
                      starting point, the current MSC concept of Plansee with an
                      Ni/YSZ cermet as anode material, which is already
                      established in the fuel cell technology, is used. The
                      work’s main innovation is the replacement of the purely
                      ionic conducting YSZ phase by a mixed ionic/electronic
                      conducting oxide Ce$_{1-x}$Gd$_{x}$O$_{2-\delta}$ (GDC). In
                      the first part of the work, a comparison of the sintering
                      behavior between GDC and the reference material YSZ was
                      made. The results from studies on powder compacts and by
                      means of dilatometry indicate that the sintering atmosphere
                      (air/hydrogen) does not affect the shrinkage of YSZ, whose
                      maximum sintering rate is reached at T$_{max}$ = 1330 °C.
                      In contrast, GDC’s shrinkage is strongly increased in
                      reducing hydrogen atmosphere compared to the shrinkage in
                      air. The maximum sintering rate T$_{max}$ is noted at 1100
                      °C for GDC in hydrogen. In reducing atmospheres and at high
                      temperatures, the enhanced solid state diffusion of GDC is
                      caused, according to literature, by the following factors:
                      (i) an increased quantity of oxygen vacancies, (ii) a change
                      of valence from Ce$^{4+}$ to Ce$^{3+}$ and (iii) a reduced
                      Gd/Ce lattice mismatch induced by the valence change of
                      Cerium. Based on these findings, a series of cermet anode
                      layer samples with different Ni/GDC ratios and sintering
                      conditions was prepared and characterized, from which a set
                      of Best Choice manufacturing parameters (sintering at 1100
                      °C, +3 K/min, 3 h, H$_{2}$) with a cermet ratio 60/40 wt.\%
                      for Ni/GDC was derived. An impedance spectroscopical
                      characterization of symmetrical cells for partial decoupling
                      of particular electrode processes was performed in a
                      single-compartment system. The Ni/GDC anode stands out both
                      by a much lower polarization resistance and a small
                      temperature dependence as compared to the Ni/YSZ anode. For
                      both anode types two electrode processes could be decoupled,
                      which differ in their relaxation times. One of the processes
                      is associated with a limitation due to gas diffusion and the
                      second process is linked to a hydrogen surface reaction. The
                      entire polarization of the Ni/GDC anode is dominated by a
                      gas diffusion limitation, which additionally is superimposed
                      by a further unknown electro-catalytic process. The greatest
                      optimization potential of the Ni/GDC anode, according to
                      conducted experiments, lies therefore within the
                      optimization of the anode microstructure. Single cell
                      measurements served to demonstrate the functionality of the
                      Ni/GDC anode within the real MSC system, with comparing of
                      the cell performance to the Plansee MSC. At 700 °C, the MSC
                      based on a Ni/YSZ anode (with an anode layer thickness of d
                      = 3 $\mu$m) reached a current density of 0,55 A/cm$^{2}$ at
                      the operating point of 0,7 V. A subsequent variation of the
                      Best Choice Ni/GDC-based MSC with an increased anode layer
                      thickness of d = 8 $\mu$m led to an improvement of
                      performance by more than 100 \%, by achieving j0,7V = 1,12
                      A/cm$^{2}$ at 700 °C. Concluding from those results: (i)
                      compared to the Plansee Ni/YSZ anode, the electrochemical
                      reaction zone of Ni/GDC extends an electrode layer thickness
                      of 3 $\mu$m, (ii) the cell voltage of Ni/GDC based MSC is
                      only slightly reduced by an activation overvoltage, what
                      presumably can be attributed to a high catalytic activity
                      and a low temperature dependence of the Ni/GDC system, (iii)
                      the anode performance of Ni/GDC anodes is clearly limited by
                      gas diffusion, what was shown by means of symmetrical cells
                      as well as single cell measurements, which is why a high
                      optimization potential in terms of improved microstructure,
                      with attention to high porosity and enhanced catalytic
                      surface, is on hand.},
      cin          = {IEK-1},
      cid          = {I:(DE-Juel1)IEK-1-20101013},
      pnm          = {135 - Fuel Cells (POF3-135) / SOFC - Solid Oxide Fuel Cell
                      (SOFC-20140602)},
      pid          = {G:(DE-HGF)POF3-135 / G:(DE-Juel1)SOFC-20140602},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/825972},
}