Characterisation of La0.6Sr0.4Co0.2Fe0.8O3-δ – Ba0.5Sr0.5Co0.8Fe0.2O3-δ composite as cathode for solid oxide fuel cells

A novel composite electrode, obtained by combining two high performing perovskite materials, such as La0.6Sr0.4Co0.2Fe0.8O3-δ and Ba0.5Sr0.5Co0.8Fe0.2O3-δ, was investigated as promising cathode for intermediate temperature solid oxide fuel cells (IT-SOFCs). The two perovskites possess high catalytic activity for the oxygen reduction (ORR), although some problems related to their chemical and structural stability have still to be overcome in view of improving durability of the cell performance. The purpose of this study was a stable and high-performing composite material, by mixing the powders through a very simple procedure. In principle, equilibrium at the LSCF-BSCF interface could be reached due to ions interdiffusion during the sintering treatment (1100 °C), resulting in the chemical stabilization of the material. The composite-cathode/Ce0.8Sm0.2O2-δ-electrolyte system was investigated by Electrochemical Impedance Spectroscopy (EIS) as a function of temperature, overpotential and time, exhibiting rather low activation energy for the oxygen reduction reaction (∼ 96 kJ mol−1). XRD analysis was performed to detect any structural modification during thermal or operation stages and it was found that after the sintering the two starting perovskites were no longer present, while two new phases were identified: a Co-rich La0.5Ba0.5CoO3 cubic and a Sr-rich La0.4Sr0.6FeO3 rhombohedral phase. The polarization resistance at 700 °C (0.07 Ω cm2) appeared higher than for pure BSCF (0.036 Ω cm2), but reasonable considering the improvement in durability achieved under the considered operating conditions (200 mA cm−2, 700 °C): 5% degradation over 200 h for the composite, against 38% for pure BSCF over the same aging time and a 29% for pure LSCF over 72 h. The obtained results motivate further investigations to be performed on different compositions, in order to evaluate whether the LSCF to BSCF ratio has an influence on the structural stability during SOFC operating conditions.