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@PHDTHESIS{Karaca:912054,
      author       = {Karaca, Ali},
      title        = {{E}ignung von nickelhaltigen {K}atalysatorsystemen in
                      sauren {M}edien zur {N}utzung im {B}etrieb von
                      {B}rennstoffzellen},
      volume       = {594},
      school       = {RWTH Aachen University},
      type         = {Dissertation},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2022-05281},
      isbn         = {978-3-95806-663-2},
      series       = {Schriften des Forschungszentrums Jülich Reihe Energie $\&$
                      Umwelt / Energy $\&$ Environment},
      pages        = {iv, 249},
      year         = {2022},
      note         = {Dissertation, RWTH Aachen University, 2022},
      abstract     = {Catalysts for the oxygen reduction reaction in fuel cells
                      are more favorable when platinum is replaced by alternative
                      materials such as non-precious metals and their catalytic
                      activity is increased. This work addresses a reduction of
                      platinum in the cathode of a direct methanol fuel cell by
                      using nickel. Two approaches are investigated:
                      platinum-nickel alloys and core-shell structures. Automated
                      ultrasonic spraycoating was used to produce mechanically
                      stable electrodes with reproducible electrochemical
                      properties. In addition, whole catalyst-coated membranes
                      (CCMs) were integrally fabricated using ultrasonic spray
                      technology. The ionomer to carbon ratio (I/C) in the
                      electrode was shown to have a significant effect on the
                      electrochemically active surface area (44.7 (I/C 0.87) and
                      53.0 m2 g-1 (I/C 0.5)). Core-shell catalysts have lower
                      powerdensities than the alloys. Long-term stability of at
                      least 1000 hours of operation with increase in performance
                      is given for both. Both catalyst types experience
                      significant nickel discharge from the surface of the
                      particles, which explains the performance increases. Both
                      alloy and core-shell catalysts exhibit increased methanol
                      tolerance compared to commercial platinum particles. In
                      addition, fabrication of membraneelectrode assemblies has
                      been demonstrated as an integral process by ultrasonic
                      spraying of the electrode and membrane. Thermal modification
                      could be used toimprove the conductivity of the membranes
                      but is not practical in real processes and results in
                      performance losses under the selected conditions.
                      Modification of the membranes with high-boiling solvents
                      also does not result in any improvements. Trace amounts or
                      degradation products of the solvents (DMAc, DMF) lead to
                      membrane poisoning and higher ionic resistivities (0.18
                      untreated, 0.30 with DMAc and 2.18 Ω cm2 with DMF).
                      Membranes with very good protonic conductivity and low
                      permeations are obtained using graphene oxide as an
                      additive. Thin membranes (20 30 μm) with graphene oxide
                      have up to $20\%$ better protonic conductivity and $50\%$
                      lower hydrogen permeation. However, the methanol permeation
                      does not decrease. In the long term, the results and
                      findings obtained in this work can lead to a significant
                      reduction in theplatinum content in fuel cells, a
                      simplification of the manufacturing process and an
                      improvement in the properties in terms of permeation,
                      performance, and stability of the membrane-electrode
                      assemblies},
      cin          = {IEK-14},
      cid          = {I:(DE-Juel1)IEK-14-20191129},
      pnm          = {1231 - Electrochemistry for Hydrogen (POF4-123)},
      pid          = {G:(DE-HGF)POF4-1231},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      urn          = {urn:nbn:de:0001-2023013169},
      url          = {https://juser.fz-juelich.de/record/912054},
}