Clarifying the role of the reducers-to-oxidizers ratio in the solution combustion synthesis of Ba0.5Sr0.5Co0.8Fe0.2O3-? oxygen electrocatalysts

Ba0.5Sr0.5Co0.8Fe0.2O3-? 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 (?) is a very important parameter in the solution combustion synthesis of mixed ionic-electronic conductors. Selection of ? 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 ? in the solution combustion synthesis of Ba0.5Sr0.5Co0.8Fe0.2O3-? for application as oxygen electrocatalysts. Ba0.5Sr0.5Co0.8Fe0.2O3-? 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, N2 adsorption at -196oC, H2-temperature programmed reduction and thermogravimetric analysis. The results evidenced the direct role of ? on the intensity and redox environment of the combustion process, and its indirect influence on the Ba0.5Sr0.5Co0.8Fe0.2O3-? electrode materials properties. Taking into account the general picture, the highly over-stoichiometric ? 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.