Strontium and copper doped LaCoO3 : new cathode materials for solid oxide fuel cells ?
Résumé
In the field of solid state electrochemistry, lanthanum cobaltites are very good electronic conductors used as SOFC cathode materials. In this work, Sr and Cu-doped LaCoO3 perovskites (LaCo0.5Cu0.5O3−δ, La0.5Sr0.5Co0.5Cu0.5O3−δ) have been prepared by means of the citrate route procedure and investigated. XRD confirms the formation of the desired phase and no secondary phases are detected. XPS and EDX results suggest that doping affects cations' surface segregation: lanthanum and copper are surface segregated in the LaCo0.5Cu0.5O3−δ whereas this is not observed in the La0.5Sr0.5Co0.5Cu0.5O3−δ. TPD experiments revealed that doping greatly increases the desoprtion of α and β oxygen species. The oxygen permeability was also determined in order to evaluate mixed ionic and electronic conductivity in addition to the surface activity in oxygen reduction reaction: in particular copper doping was observed to enhance permeability even at rather low temperature (500 °C). Finally, electrochemical impedance spectroscopy measurements carried out on a symmetrical half-cell with Ce0.9Gd0.1O2 as electrolyte to characterize the effect of doping on electrochemical properties, revealed that the Cu and Sr doping enhances the performance as SOFC cathode.