Effect of Cobalt-Doped Electrolyte on the Electrochemical Performance of LSCFO/CGO Interfaces

LAURA BAQUÉ; K. PADMASREE; MÓNICA A. CENICEROS REYES; HORACIO TROIANI; MAURICIO ARCE; ADRIANA SERQUIS; ANALÍA SOLDATI

San Diego

Encuentro; 229th Electrochemical Society (ECS) Meeting; 2016

The Electrochemical Society

Solidoxide fuel cells (SOFCs) are efficient and environmental friendly devices whichdirectly convert hydrogen and fosil fuels into electric energy. The operationtemperature of these devices is mainly determined by the nature of itselectrolyte. Conventional SOFCs are composed of yttria based electrolytes requiringoperation temperatures around 1000ºC, whereas ceria based electrolytes haveallowed reducing the temperature down to the 500-700ºC range. Nevertheless,these materials require sinterization temperatures in the 1300-1600ºC range to achievecomplete densification, which produces very large grain sizes and poormechanical properties. In the last years, several research works havedemonstrated that the addition of transition metals oxides is effective inimproving the densification and thus, lowering the sinterization temperaturesof ceria based electrolytes. Such research works, generally focalize on how theaddition of these sintering aids affect the properties (density, sinteringtemperature, conductivity) of the electrolyte. Nonetheless, it is well establishedthat SOFC performance depends not only on the characteristics and performanceof its individual components (i.e. cathode, electrolyte and anode) but also ontheir interfaces. Hence, a comprehensive study on how the addition ofelectrolyte sintering aids affects the cell performance is still missing.In this work, we have studied La0.4Sr0.6Co0.8Fe0.2O3-d/Ce0.8Gd0.2O2-d/La0.4Sr0.6Co0.8Fe0.2O3-dsymmetrical cells containing Ce0.8Gd0.2O2-d electrolytessynthesized by a molten salt route with and without Co oxide doping. La0.4Sr0.6Co0.8Fe0.2O3-dnanostructured cathodes with high electrochemical performance weredeposited by spin coating techniques on both sides of the electrolyte pellets.The assemblies were studied by Electrochemical Impedance Spectroscopy (EIS), X-RayDiffraction and Transmission and Scanning Electron Microscopy. EIS resultsindicate that both electrolyte and cathode impedance response are affected bythe addition of the sintering aid to the electrolyte, despite using cathodeswith similar microstructure according to SEM observations. A possibleexplanation for such behavior was founded during TEM characterization whichreveals the formation of columnar structures at the cathode/electrolyteinterface of the cell with cobalt-doped electrolyte. These columnar structureswould negatively affect the cell performance hindering the diffusion of oxideions from the cathode to the electrolyte.