Influence of B-site doping and co-doping on the electrochemical properties of Sr0.85Ce0.15FeO3-delta IT-SOFC cathodes

Introduction SrFeO3 perovskite-type oxides are an interesting class of materials where iron is present at the B-site as Fe4+ and is partially reduced to Fe3+ by doping. Doped SrFeO3 have been already developed for clean energy purposes, especially as cathodes for Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFCs) [1]. In this study, the effect of B-site modifications was evaluated in terms of dopant stoichiometry, Cobalt doping and Cobalt-Copper co-doping. Cobalt and Copper were chosen as dopant and co-dopant elemens thanks to their ability to improve conducibility and interaction with oxygen, a fundamental step in IT-SOFCs cathode reactions [2]. Materials and methods Doped Sr0.85Ce0.15FeO3-? were synthesized by Solution Combustion Synthesis (SCS) [3] in which metal nitrates (oxidizers and metal sources) react with citric acid (combustion fuel and reducing agent). Materials formation and properties were characterized through temperature-time profiles, X-ray diffraction coupled with Rietveld analysis, thermogravimetric Analysis (TGA), nitrogen adsorption, temperature programmed reduction (TPR) and electrochemical impedance spectroscopy (EIS). Results and discussion Investigations about the influence of stoichiometry clearly showed that the B-site defectivity is deleterious for the electrochemical performance, because of the formation of non-active phases. B-site doping is advantageous, as demonstrated by the increment in conductivity and by the improvement of redox properties. The Co-Cu co-doping has a relevant effect on the structural, microstructural and redox properties, and this is also discussed in relation to the electrochemical behavior. Conclusions The influence of B-site stoichiometry and composition in doped Sr0.85Ce0.15FeO3-? on their physical-chemical-electrochemical properties was deepened, in order to select the best doping strategy for the optimization of their electrochemical properties. Acknowledgments Authors are grateful to Dr. Giordano for XRD measurements and to PON-TESEO project for funding. References 1. Choi H., Fuller A., Davis J., Wielgus C., Ozkan U.S., Appl. Catal. B: Environ., 2012, 127, 336- 341. 2. Lakshminarayanan N., Choi H., Kuhn J. N., Ozkan U.S., Appl. Catal. B: Environ., 2011, 103, 318-325. 3. Deganello F., Marcì G., Deganello G., J. Eur. Ceram. Soc., 2009, 29, 439-450.