Porous normalLa1−xnormalSrxConormalO3−δ (LSC) electrodes having Sr composition x=0.4 (LSC-64) and x=0.2 (LSC-82) were fabricated on Sm-doped ceria electrolytes, and studied using electrochemical impedance spectroscopy between T=650–750°C and pnormalO2=0.01–1.0atm . The faradaic portion of the impedance was found to exhibit Gerischer or Gerischer-like characteristics, indicating colimitation by kinetics and transport. The characteristic resistance and frequency response was analyzed using a transport and reaction model that considers parallel bulk and surface diffusion of oxygen, as well as three-dimensional transport effects near the electrode electrolyte interface. In the case of LSC-64, measured characteristics appear to be largely consistent with a bulk transport path, based on independent measurements of the thermodynamic, kinetic, and transport properties of LSC-64. In the case of LSC-82, which has a much lower bulk vacancy concentration under the same conditions, results were inconsistent with an entirely bulk transport path. Results for LSC-82 could be rationalized assuming a parallel surface transport path, where surface mobility is governed by some kind of interstitial or adatom diffusion mechanism.

Planar cells incorporating a microelectrode as the working electrode were prepared using materials and techniques commonly employed in fabrication of planar solid oxide fuel cells. Initial results of ac and dc polarization measurements suggest that these cells potentially offer excellent isolation of working electrode frequency response (impedance), and quantification of steady-state current-overpotential relationships. The success of the technique relies heavily on how precisely the geometry of the microelectrode pattern is defined and characterized. Some of the challenges in implementing this technique are discussed.

Porous La 1-x Sr x CoO 3-δ (LSC) electrodes with Sr composition x = 0.2 (LSC-82) and x = 0.4 (LSC-64) were prepared by screenprinting LSC powders onto rare-earth doped ceria electrolytes, followed by sintering at 950 ∼ 1100 • C, and characterization using scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface-area analysis, 3-D morphological imaging based on focused ion beam scanning electron microscopy (FIB-SEM), and energy dispersion X-ray spectroscopy (EDX/EDS). The batch-tobatch variability and degradation (over 1000 ∼ 2000 hours) of the electrochemical performance of these cells were studied using electrochemical impedance spectroscopy (EIS) and measurements of nonlinear electrochemical impedance (NLEIS). These measurements reveal a strong correlation between the characteristic frequency (ω c ) and characteristic resistance (R c ) of the electrodes, which, when analyzed in light of microstructural data, indicates that performance variability and degradation are caused primarily by variations in the surface rate coefficient k(T) for O 2 exchange.

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