Multi-Element Substitution for Improving the Electrocatalytic Properties of IT-SOFC Cathodes

摘要

Electrocatalytic properties of A_(0.58)Sr_(0.4)Fe_(0.8)Co_(0.2)O_(3-δ) perovskite system were optimized by systematically combining several rare-earth metals (lanthanides) in the A-position and by partially replacing these lanthanides by barium. Cathode materials were obtained by sol- gel methods using a robotic workstation and tested for electrochemical oxygen activation in the range of 450-650 oC using AC impedance spectroscopy in two-point symmetrical configuration. The coupled oxygen reduction reaction with the solid state diffusion have been stated to be the rate limiting step in the whole polarization resistance of cathode materials, following an Adler-like behavior. Modeling of the multivariate space has been done using different statistical and data mining techniques, enabling the extraction of rules and identification of synergetic or cooperative effects between A-cations. In addition, XPS measurements confirm the presence of multiple oxidation states of the substituted A- elements, involving changes in catalytic properties for oxygen reduction reaction and oxygen diffusion rates. Most promising combination materials were tested as cathode on anode-supported cells in the range of 450-900 oC using DC voltamperometry. High- temperature powder XRD was carried out for different cathode compositions and in different gas environments, allowing following the perovskite symmetry changes and the unit cell expansion as a function of temperature and environment composition.