Role of Cerium and Cobalt on the structural, redox and electrochemical properties of doped SrFeO3

Nowadays, optimization of technologies for green energy supply is one of the most important challenges. In this context, solid oxide fuel cells (SOFCs) are valid alternatives for renewable energy production. Doped SrFeO3 have already been studied in the literature as electrodes of fuel cells [1, 2]. In this work, the effect of chemical composition of Cerium and Cobalt doped SrFeO3 was investigated in order to apply them as cathodes for Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFCs). In particular, monophasic Sr1-xCexFe1-yCoyO3-δ perovskite-type oxides were synthesized by solution combustion synthesis [3] and then calcined at 1000°C/5h. These materials were carefully characterized by X-ray Diffraction coupled with Rietveld analysis, temperature programmed oxidation and reduction, oxygen chemisorption pulses, N2 adsorption, overpotential and conductivity measurements. Electrochemical experiments were carried out by using a three-electrode cell supported on a gadolinia-doped ceria (CGO, Ce0.8Gd0.2O2) electrolyte. The addition of the perovskite catalyst promotes the oxygen ion conductivity of about half order of magnitude with respect to the CGO electrolyte and the Co-doping improves the conductivity. Furthermore, Co-doping has a significant effect on the temperature for the perovskite reduction as demonstrated by the shift at lower temperature observed for the peaks at 400 °C and 800 °C, regardless of very similar surface area values . Moreover, it was found that the H2 consumption of the first TPR peak is smaller for the perovskite containing more Co, indicating a higher amount of B-site cations with lower oxidation state. Furthermore, it was observed that Ce doping stabilizes the cubic structure of Co-doped SrFeO3, as previously noticed for Ce-doped SrFeO3 without cobalt [1]. On the other hand, the oxygen chemisorption does not seem to be a determining factor for the electrochemical properties of doped SrFeO3. In conclusion, results show that the electrochemical performances of doped SrFeO3 cannot be optimized without investigating the synthesis-composition-structure-properties relationships in these materials. [1] F. Deganello, L.F. Liotta, A. Longo, M.P. Casaletto, M. Scopelliti “Cerium effect on the phase structure, phase stability and redox properties of Ce-doped strontium ferrates”, Journal of Solid State Chemistry, 179, 11, 2006, 3406 - 3419 . [2] H. Choi, A. Fuller, J. Davis, C. Wielgus, U. S. Ozkan " Ce-doped strontium cobalt ferrite perovskites as cathode catalysts for solid oxide fuel cells: Effect of dopant concentration", Applied Catalysis B: Environmental, 127, 2012, 336– 341. [3] F. Deganello, G. Marcì, G. Deganello “Citrate-nitrate auto-combustion synthesis of perovskite-type nanopowders: A systematic approach”, Journal of the European Ceramic Society, 29, 3, 2009, 439 - 450.