Electrocatalytic activity of perovskite-based cathodes for solid oxide fuel cells

A very active cathode material for intermediate temperature - solid oxide fuel cells (IT-SOFCs) is obtained by mixing La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3- ? (LSCF) and Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3- ? (BSCF) powders. Three different volume ratios are considered: BSCF-LSCF 50-50 v/v% (BL50), BSCF-LSCF 70-30 v/v% (BL70) and 30-70 v/v% (BL30). The electrodes are slurry coated on Ce 0.8 Sm 0.2 O 2- ? electrolyte and sintered at 1100 °C. After the sintering step XRD-analyses highlight relevant cation inter-diffusion within the mixed powders. As a result, an enhanced activity of BL30-BL70 electrodes towards oxygen reduction reaction is detected in comparison to LSCF or BSCF pure powders. A polarization resistance of 0.021 ? cm2 at 650 °C for BL70 is obtained, one of the lowest value reported in literature for SOFC cathodes. Furthermore, all the electrodes show lower activation energy than the two reference materials in the considered temperature range (500-650 °C) and two different kinetic regimes are identified at the extremes of this range. Effect of the applied overpotential (0-0.3 V) on the electrode kinetic is also investigated. After a preliminary ageing, performed at 650 °C for 200 h by applying a current density of 200 mA cm-2, the electrodes preserve a remarkable performance as IT-SOFC cathodes, despite an initial degradation. A stable value of 0.048 ? cm2 of polarization resistance for the sample richer in BSCF is recorded.