Peculiar Properties of the La 0.25 Ba 0.25 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ Perovskite as Oxygen Reduction Electrocatalyst.

The electrochemical reduction of molecular oxygen is a fundamental process in Solid Oxide Fuel Cells and requires high efficiency cathode materials. Two La 0.25 Ba 0.25 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ -based perovskite compounds were prepared by solution combustion synthesis, and characterized for their structural, microstructural, surface, redox and electrochemical properties as potential cathodes in comparison with Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ and La 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ perovskites. Results highlighted that calcination at 900 °C led to a "bi-perovskite heterostructure", where two different perovskite structures coexist, whereas at higher calcination temperatures a single-phase perovskite was formed. The results showed the effectiveness of the preparation procedures in co-doping the A-site of perovskites with barium and lanthanum as a strategy to optimize the cathode's properties. The formation of nanometric heterostructure co-doped in the A-site evidenced an improvement in oxygen vacancies' availability and in the redox properties, which promoted both processes: oxygen adsorption and oxygen ions drift, through the cathode material, to the electrolyte. A reduction in the total resistance was observed in the case of heterostructured material.