Starting from recent and promising results obtained by the authors [1], this study concerned the La0.6Sr0.4Co0.2Fe0.8O3-? (LSCF) - Ba0.5Sr0.5Co0.8Fe0.2O3-? composite system as cathode for intermediate temperature soli oxide fuel cells (IT-SOFCs). Particularly, the effect of LSCF/BSCF volume ratio was investigated, in relation to electrochemical and stability performance. Three volume ratios were considered: BSCF-LSCF 70-30 v/v% (BL70), 50-50 v/v% (BL50) and 30-70 v/v% (BL30). Composite cathodes were deposited on a Ce0.8Sm0.2O2-?-electrolyte system and impedance spectroscopy was applied in different working conditions, by varying temperature (500 to 650 °C) and cathodic overpotential (50 to 300 mV). X-rays diffraction analyses highlighted an important structural degradation during the sintering stage, resulting in the appearance of a rhombohedral La0.4Sr0.6FeO3 phase enriched in Sr (LSF). Peaks compatible with a Co-rich La0.5Ba0.5CoO3-type cubic phase (LBC) were also pointed out, suggesting the simultaneous presence of both structures. Nevertheless, the system showed very good electrochemical activity; excellent values of 0.021 ? cm2 at 650°C and 0.26 ? cm2 at 500°C were found for BL70 composition (Fig. 1 (a)), these resistances being much more lower than the ones found for pure BSCF [3]. Analyses of the impedance results carried out by distribution of relaxation time (DRT) (Fig. 1 (b)) and equivalent circuit models showed two different kinetic regimes governing the electrocatalytic activity: at low temperature (500 °C), a Gerischer-type behaviour was identified, pointing out a co- control by surface oxygen exchange and bulk diffusion [2]; at high temperature (650 °C) this model was any longer suitable, the main resistance being in these conditions identified at the high frequency domain (see Fig. 1 (b)). Polarisation resistances kept an acceptable value even after an ageing test conducted at 700 °C for 200 hours with a current load of 200 mA/cm2, thus offering the possibility of promising future developments for such composite system.
Impedance characterisation of perovskites as cathodes for IT-SOFCs: from typical La0.8Sr0.2MnO3-? to high-performing La0.8Sr0.2Co0.2Fe0.8O3-? and Ba0.5Sr0.5Co0.8Fe0.2O3-delta materials
M P Carpanese;S Presto;M Viviani;A Barbucci
2017
Abstract
Starting from recent and promising results obtained by the authors [1], this study concerned the La0.6Sr0.4Co0.2Fe0.8O3-? (LSCF) - Ba0.5Sr0.5Co0.8Fe0.2O3-? composite system as cathode for intermediate temperature soli oxide fuel cells (IT-SOFCs). Particularly, the effect of LSCF/BSCF volume ratio was investigated, in relation to electrochemical and stability performance. Three volume ratios were considered: BSCF-LSCF 70-30 v/v% (BL70), 50-50 v/v% (BL50) and 30-70 v/v% (BL30). Composite cathodes were deposited on a Ce0.8Sm0.2O2-?-electrolyte system and impedance spectroscopy was applied in different working conditions, by varying temperature (500 to 650 °C) and cathodic overpotential (50 to 300 mV). X-rays diffraction analyses highlighted an important structural degradation during the sintering stage, resulting in the appearance of a rhombohedral La0.4Sr0.6FeO3 phase enriched in Sr (LSF). Peaks compatible with a Co-rich La0.5Ba0.5CoO3-type cubic phase (LBC) were also pointed out, suggesting the simultaneous presence of both structures. Nevertheless, the system showed very good electrochemical activity; excellent values of 0.021 ? cm2 at 650°C and 0.26 ? cm2 at 500°C were found for BL70 composition (Fig. 1 (a)), these resistances being much more lower than the ones found for pure BSCF [3]. Analyses of the impedance results carried out by distribution of relaxation time (DRT) (Fig. 1 (b)) and equivalent circuit models showed two different kinetic regimes governing the electrocatalytic activity: at low temperature (500 °C), a Gerischer-type behaviour was identified, pointing out a co- control by surface oxygen exchange and bulk diffusion [2]; at high temperature (650 °C) this model was any longer suitable, the main resistance being in these conditions identified at the high frequency domain (see Fig. 1 (b)). Polarisation resistances kept an acceptable value even after an ageing test conducted at 700 °C for 200 hours with a current load of 200 mA/cm2, thus offering the possibility of promising future developments for such composite system.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
