High resolution FIB-TEM and FIB-SEM characterization of electrode/electrolyte interfaces in solid oxide fuel cells materials

A.L. SOLDATI; L. BAQUE; H. TROIANI; C. COTARO; A. SCHREIBER; A. CANEIRO; A. SERQUIS

INTERNATIONAL JOURNAL OF HYDROGEN ENERGY

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2011 vol. 36 p. 9180 - 9188

0360-3199

A Focused Ion Beam (FIB)/lift-out technique was used to prepare site-specific thin samplesof the cathode/electrolyte interface of Intermediate Temperature Solid Oxide Fuel Cells (ITSOFC)materials. The cathode under study was a nanostructured perovskite of compositionLa0.4Sr0.6Co0.8Fe0.2O3-d (LSCF) deposited by spin coating on a Ce0.9Gd0.1O2-d (CGO) supportingsubstrate. We compared the results for a 15 mm and a 5 mmthickness cathode layers, beforeand after a thermal treatment of 1000 h at 500
C, with the aim of simulating operationconditions. Both, Transmission (TEM) and Scanning (SEM) Electron Microscopy, coupledwith Energy Dispersive Spectroscopy (EDS) systems, were used to characterize thecomposition and nanostructure at both sides of the cathode/electrolyte interface. To ourknowledge, this is the first time that a semi-coherent interface between LSCF and CGO wasobserved by Electron Diffraction as well as by High Resolution TEM in many points at theinterfacial boundary. A large difference in total contact area was observed between thethickest and the thinnest cathode layers, despite they present the same composition andnano sized structure. The real contact area in the 5 mm cathode sample is around 50% lessthan in the 15 mm sample due to the presence of pores at the interface. This observationmay partially explain the difference in resistivity observed for these two half cellsassemblies. On the other side, no differences were found comparing composition andnanostructure at the interface before and after the thermal treatment. Thus, this studybecomes fundamental to understand the role played by the interface for improving theperformance of IT-SOFC under long time operation conditions: a necessary premise for itsreal application.