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@TECHREPORT{Erning:863796,
      author       = {Erning, J. W.},
      title        = {{U}ntersuchungen zur {S}auerstoffreduktion an {K}athoden
                      für {H}ochtemperatur-{B}rennstoffzellen},
      volume       = {3561},
      number       = {Juel-3561},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich, Zentralbibliothek, Verlag},
      reportid     = {FZJ-2019-03783, Juel-3561},
      series       = {Berichte des Forschungszentrums Jülich},
      pages        = {145 p.},
      year         = {1998},
      abstract     = {Lanthan-Strontium-Manganite perowskites are the most
                      widespread materials in use for Solid Oxide Fuel Cell
                      cathodes. The electrode reaction taking place, i.e. the
                      reduction of oxygen supplied by air, was investigated by
                      electrochemical means to obtain further knowledge about the
                      electrode processes. The high activation energy of this
                      reaction (200 kJ/mol), preventing lower operation
                      temperatures of the SOFC, was the starting point for the
                      investigation. Quasi steady state current voltage
                      measurements and impedance spectroscopy were perfouned in a
                      three electrode configuration. The electrodes were of
                      circular shape with a diameter of 10 mm. The preparation was
                      made by screen printing as well as Wet Powder Spraying onto
                      plates made of Yttria-stabilized Zirconia. Perowskite
                      powders of varying chemical and stoichiometric composition
                      were used. To obtain higher power densities and, more
                      important, lower apparent activation energies, catalytic
                      layers were added at the interface electrode/electrolyte.
                      Additionally, a less complex system, a model
                      electrode/electrolyte setup made from single-crystal YSZ as
                      electrolyte and gold in liquid and solid state as electrode
                      was developed to create a better defined system. This setup
                      was used to investigate the behaviour of the
                      electrode/electrolyte interface. Reliable, reproducible
                      results could be obtained using either setup. The
                      experimental conditions i.e. oxygen partial pressure,
                      temperature and overpotential were varied in order to
                      determine the kinetic properties of the electrodes. Apparent
                      activation energies, pre-exponential factors, apparent
                      charge-transfer coefficients and electrochemical orders of
                      reaction were calculated from the current-voltage data in
                      order to propose possible reaction steps. The catalytic
                      layer made of palladium lowered the apparent activation
                      energy to about 138 kJ/mol, but lowered the apparent
                      pre-exponential factor as well, thus resulting in current
                      densities one order of magnitude higher than without
                      catalyst. By using a mixture of platinum and palladium, the
                      current densities obtained were even higher, caused by a
                      higher pre-exponential factor. Several electrodes showed a
                      charge-transfer reaction determined behaviour for small
                      cathodic overpotentials (<100 mV). For these potentials the
                      behaviour of the electrodes with additional catalytic layers
                      was dominated by the influence of the catalyst. The apparent
                      electrochemical reaction orders for intermediate
                      temperatures were calculated in the region between 0.4 and
                      0.8 giving evidence for dissociative adsorption of oxygen.
                      The analysis of the charge-transfer coefficient a and its
                      temperature dependence showed negative values for the
                      entropic part $\alpha^{s}_{c}$. Impedance data gave further
                      evidence for the proposed reaction steps but it was not
                      possible to correlate the time constants with singular
                      reaction steps. All results indicate a complex reaction
                      mechanism involving several rate-determining steps. The use
                      of the model electrode/electrolyte setup made it possible to
                      isolate several reaction steps which are depending on the
                      geometry of the electrode. The combination of all results
                      gave evidence for the formulation of possible reaction
                      mechanisms which were verified by using a complex simulation
                      program which simultaneously fits current-voltage and
                      impedance measurements using a model based on the kinetic
                      analysis of an assumed reaction mechanism. The activation
                      energies computed by the simulation program for single
                      reaction steps are similar to those calculated from specific
                      potential regions for the current potential measurements.
                      Thus the assumption of potential regimes in which specific,
                      different reactions are rate-determining is affirmed.},
      cin          = {PRE-2000},
      cid          = {I:(DE-Juel1)PRE2000-20140101},
      pnm          = {899 - ohne Topic (POF3-899)},
      pid          = {G:(DE-HGF)POF3-899},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)29},
      url          = {https://juser.fz-juelich.de/record/863796},
}