Clarifying the Role of the Reducers-to-Oxidizers Ratio in the Solution Combustion Synthesis of Ba0.5Sr0.5Co0.8Fe0.2O3-delta Oxygen Electrocatalysts

Ba0.5Sr0.5Co0.8Fe0.2O3-delta perovskite-type compounds are well-known mixed ionic-electronic conductors for oxygen electrocatalytic applications, although their performance is strictly dependent on the selected preparation methodology and processing parameters. The reducers-to-oxidizers ratio (phi) is a very important parameter in the solution combustion synthesis of mixed ionic-electronic conductors. Selection of phi is not trivial and it strongly depends on the type of fuel used, the chemical composition and the specific application of the material. This work clarifies the role of phi in the solution combustion synthesis of Ba0.5Sr0.5Co0.8Fe0.2O3-delta for application as oxygen electrocatalysts. Ba0.5Sr0.5Co0.8Fe0.2O3-delta powders were synthesized by solution combustion synthesis using sucrose-polyethylene glycol fuel mixtures with reducers-to-oxidizers ratio values between 1 (stoichiometric) and 3 (over-stoichiometric). Chemical-physical properties were studied by X-ray diffraction, scanning electron microscopy, N-2 adsorption at -196 degrees C, H-2-temperature programmed reduction and thermogravimetric analysis. The results evidenced the direct role of phi on the intensity and redox environment of the combustion process, and its indirect influence on the Ba0.5Sr0.5Co0.8Fe0.2O3-delta electrode materials properties. Taking into account the general picture, the highly over-stoichiometric phi was selected as the optimal one and the electrochemical activity of the corresponding powder was tested by electrochemical impedance spectroscopy on electrolyte-supported half-cells employing a Ce0.8Sm0.2O2-x electrolyte.