Microengineered cathode interface studies Page: 4 of 8
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ionic conductivity in the cathode is undoubtably a function of potential in the cathode near the
Extension of the reaction area away from the triple interface by the mixed-conduction
mechanisms discussed above is probably necessary to some extent for good cathode performance.
However, the more important characteristic may in fact be the geometry of the electrode near the
interface. Even if the reaction can occur over a large surface area, performance is still dependent
on transport of the reactants and electrons through the porous electrode. The density and tortuosity
of the sintered cathode particles, as well as the interfacial area with the electrolyte, may be the
factors most in need of optimization to improve cathode performance. Recent research by many
groups has shown that cathode/electrolyte interface characteristics such as the pore structure-and
cathode density at the interface must be carefully controlled to reduce the cathode overpotential
Our approach has been to fabricate and test highly controlled interface structures that are
designed to affect the three possible rate-limiting factors in the cathode reaction discussed above.
The electrochemical performance of these interfaces has been correlated with the observed
Commercially available 300-pm thick zirconia wafers were used as substrates for these
tests, for the sake of reproducibility. The only designed variability in the electrolyte is in the
immediate vicinity of the cathode, as discussed below.
The electronic conductivity of the electrolyte has been altered by using ion implantation
to dope the surface with manganese. Ion implantation adds a controlled amount of dopant
directly into the bulk zirconia in a thin layer near the surface. Manganese is implanted uniformly
over a 1 cm2 sample area using a 50-60 keV machine, which results in a peak concentration of
dopant about 0.1 pm below the electrolyte surface. Saturation typically is reached at about 10 wt
% dopant after a few minutes. Ion-implanted electrolytes are then used as substrates for porous
The role of ionic conductivity in the electrode has been examined primarily through the
study of dense La09SroMnO3 layers. When nonporous electrodes are used, the triple interface
is effectively eliminated, and the cathode reaction must take place at the cathode surface, with
oxygen ion transport taking place through the cathode. There exist significant experimental
difficulties in performing such tests. The presence of any porosity or incomplete coverage of the
electrolyte (including edge effects) adds triple-interface areas that may render the oxygen ion
transport unimportant. We have looked at films formed by a number of methods.
The density and tortuosity of the sintered cathode particles, as well as the interfacial area
with the electrolyte, have been controlled primarily through densification of the cathode in
reducing conditions. Cathodic current conditioning has been shown to create significant
microstructural changes, and this method has been used to demonstrate the importance of the
cathode geometry near the interface.
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Kueper, T.; Doshi, R. & Krumpelt, M. Microengineered cathode interface studies, article, October 1, 1996; Illinois. (https://digital.library.unt.edu/ark:/67531/metadc683824/m1/4/: accessed April 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.