Application of the Adler-Lane-Steele model to porous La2NiO4+d SOFC cathode : influence of interfaces with gadolinia doped ceria
Résumé
Electrochemical impedance spectroscopy measurements carried out on La2NiO4+δ(LNO)//Ce0.8Gd0.2O2−δ(GDC)//3mol.%Y2O3-ZrO2(TZ3Y) half-cells from 500°C to 800°C revealed that the impedance of the LNO electrode is Gerischer-like. Based on experimental data of the porosity, tortuosity, surface area, molar volume and thermodynamic factor of the LNO electrode sintered at 1200°C, the ionic conductivity σi(LNO) and the surface exchange coefficient ℜ0 of the LNO electrode are calculated using the Adler-Lane-Steele (ALS) model. Surprisingly, the polarization resistance of the half-cell is shown to depend on the sintering temperature of the GDC interlayer, which is varied from 1200°C up to 1450°C. Whatever the sintering conditions of GDC, the calculated ℜ0 values agree with those obtained by recently published pulse isotopic exchange (PIE) experiments. Indeed, the oxygen reduction reaction mostly occurs at the LNO grain surface. However, the calculated ionic conductivity of the electrode vary depending on the GDC sintering temperature. X-ray diffraction studies of the LNO//GDC and GDC//TZ3Y interfaces reveal that cations interdiffusion occurs in both cases. The interfacial GDC layer may act as a bottleneck for the oxide ion transfer from the LNO electrode toward the TZ3Y electrolyte, and vice-versa, resulting in an increase of the series and polarization resistances.
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