Performance Variability and Degradation in Porous La_1-xSr_xCoO_3-δElectrodes

Abstract

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.

Prediction of SOFC Performance with or without Experiments: A Study on Minimum Requirements for Experimental Data

“…However, as shown in Figure 5(b), the limiting current is reduced when we increase the tortuosity due to the reduction of the effective diffusion coefficient in Eq. [9]. This means that the value of tortuosity, hence effective diffusion coefficients, cannot be calibrated when only impedance behavior is used.…”

“…Nonlinear electrochemical impedance spectroscopy (NLEIS) was also developed to distinguish the nonlinear processes in electrochemical reactions by capturing both linear and higher harmonic voltage response due to moderate-amplitude current excitation. With this approach, the role of electrochemical kinetics, surface rate for oxygen exchange, and material properties were quantified (7)(8)(9). Numerical simulations have also been performed to study the details of the processes occurring within solid oxide fuel cells.…”

Study of Electrode Performance for Nanosized La0.4Sr0.6Co0.8Fe0.2O3-Δ IT-SOFC Cathode

“…On the other hand, the nanomaterials are liable to suffer from crystallites coarsening, even at the temperatures typical of IT-SOFC operation. The particle coarsening can be a dominant contribution to long-term degradation for nanostructured cathodes, as this leads to reduced surface area (11)(12). In this work, the cathode performance of La0.4Sr0.6Co0.8Fe0.2O3-δ (LSCF4682)) nanocrystallites was evaluated by RC,P measurements as a function of temperature and time.…”