THE ELECTRODE REACTION FOR La1-xSrxCo1-yFeyO3-d AND Ln2NiO4+d (Ln: La, Nd) BY USING EIS AND FIB-TEM TECHNIQUES

A. CANEIRO; L. BAQUE; A. SOLDATI; L. MOGNI; A. SERQUIS; H. TROIANI; A, FERNÁNDEZ ZUBICH; A. SCHREIBER; F. SOLDERA

Joao Pessoa

Conferencia; ICE 2013; 2013

  The oxygen reduction at the cathode of SOFC and IT-SOFC is the main cause of efficiency loss for these devices.  The search of new cathode materials for IT-SOFC is focused on transition metal oxides with perovskites or related structures exhibiting mixed conductivity, that is electronic and ionic conductivity simultaneously.  The electronic conductivity is associated to the presence of a mixed valence transition metal in the B-site and the ionic conductivity to oxygen defects (oxygen vacancies or interstitials).  The catalytic activity  for the O2 reduction in the gas phase to O2- in the electrolyte depends on many factors such as the electric transport properties (electronic and ionic conductivities of the electrode), the electrode surface properties and mainly on the electrode microstructure (grain size, porosity, effective electrode/electrolyte contact area). The Electrochemical Impedance Spectroscopy (EIS) is a technique widely used to study the electrode reaction. In this talk I will present results obtained in our  group on the electrode reaction for two different types of electrode materials: the oxygen deficient La1-xSrxCo1-yFeyO3-d  (LSCFO) perovskite and the oxygen-excess  Ln2NiO4+d (LnNO; Ln: La, Nd)   Ruddlesden Popper phase,  on CGO, YSZ and LSGM electrolytes. I will show that the use of atmospheres with controlled oxygen partial pressure (pO2) makes EIS a powerful technique which allows the separation of different contributions or steps of the whole electrode reaction for both electrode materials. Results of the effect of the microstructure on the electrode reaction for LSCFO and LnNO will be also presented.  EIS is a very sensitive technique to detect any interfacial phenomena, particularly the presence of  reactivity at the electrode/electrolyte interface.  In the second part of this talk, I will present a TEM-FIB study of the LSFC/CGO and LnNO/YSZ, CGO  interfaces and its correlation with the EIS spectra behavior.