FIB-TEM y FIB-SEM Characterization of the electrode/electrolyte interface in solid oxide fuel cell materials

SOLDATI, ANALIA L.; BAQUÉ, LAURA; TROIANI, HORACIO; COTARO, C.; SCHREIBER, ANJA; WIRTH, RICHARD; CANEIRO, ALBERTO; SERQUIS, ADRIANA C.

Montreal

Simposio; 219th ECS Meeting & Twelfth International Symposium on Solid Oxide Fuel Cell Cells (SOFC-XII); 2011

ECS - The Electrochemical Society

The Focused Ion Beam (FIB) technique allows preparing and extracting very thin samples from bulk materials of mixed structure, composition and hardness. A Ga-ion beam uniformly sputters the surface of a selected area, forming a slab of 10 x 15 mm and 150-100 nm thickness. The slice can be transfered afterwards (with help of a micromanipulator) to a Cu grid to facilitatemanipulation and handling. In addition, a Scanning Electron Microscope (SEM) coupled to the FIB allows selecting specific areas of the sample with high spatial precision and convert this technique in an exceptional tool to prepare samples of interfacial regions between two different materials. Once deposited in the grid, composition and structural analysis can be done byTransmission and Scanning Electron Microscopy (TEM and SEM).The cathode/electrolyte interface plays an important role in the total efficiency of an intermediatetemperatura solid oxid fuel cell (IT-SOFC)2. Therefore, the preparation of interfacial region samples with FIB allows a complete structural characterization, even at atomic levels. However, reported studies using this kind of samples are more oriented to a morphological and compositional study of the interface using SEM as analyzing tool.In this work, we present a high resolution SEM and TEM analysis of the electrode/electrolyte interface in potentially interesting materials for IT-SOFC3, using FIB as sample preparation tool. Particullarly, we will show the results for La0.4Sr0.6Co0.8Fe0.2O3-d (LSCF), a nanostructured mixed conductor cathode, deposited by spin-coating on a Ce0.9Gd0.1O2-d (CGO) electrolyte. The  structural observations were done with a Philips CM 200 UT TEM operated at 200 keV, in normal and high resolution modes. A puntual compositional analysis was performed by using a coupled Energy Disersive Spectrometer (EDS). High resolution images and compositon maps were adquired in the same samples using backscatter electrons and EDS in a FEI Field Emission Gun SEM.Although cathode and electrolyte present very different composition and microstructure, the Ga-ions sputtered both sides homogeneusly. Thickness in both parts is similar and no preferential erosion was observed (Fig. 1). Compositional studies show that CGO ishomogeneouly distributed in the electrolyte, and no elements from the LSCF spreads into it. However, some Ce difussion is observed near the interface, at the LSCFside. TEM imaging (Fig. 2) shows that LSCF/CGO interface occurs in less than 20 nm; diffraction and high resolution imaging could be use to identify growth mechanisms. The relation between these structural parameters and the electrochemical performace is furtherinvestigated.