Degradation of oxygen reduction reaction kinetics in porous La0.6Sr0.4Co0.2Fe0.8O3-d cathodes due to aging-induced changes in surface chemistry

L. BAQUÉ; A. SOLDATI; H. TROIANI; A. SCHREIBER; A. SERQUIS

JOURNAL OF POWER SOURCES

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2017 vol. 337 p. 166 - 172

0378-7753

The modification of surface composition after long-term operation is one of the most reported degradationmechanisms of (La,Sr)(Co,Fe)O3-d (LSCFO) cathodes for Solid Oxide Fuel Cells (SOFCs). Nevertheless,its effect on the oxygen reduction reaction kinetics of porous LSCFO cathodes has not been yetreliably established. In this work, La- and Sr-enrichment at the LSCFO surface of porous cathodes hasbeen induced after 50 h aging at 800 C under air. Such cation redistribution can extend up to ~400 nmdepth under the LSCFO surface as detected by high resolution Scanning Transmission ElectronMicroscopy-Energy Dispersive Spectroscopy maps acquired inside the cathode pores. The observedsurface chemical changes hamper the oxygen surface exchange reaction at the LSCFO/gas interface.Accordingly, a suitable Electrochemical Impedance Spectroscopy analysis revealed that the oxygen ionconductivity remains practically unaltered during the aging treatment while the oxygen surface exchangeresistance increases up to 1.8 times. As a result, the cathode impedance response deteriorateswithin the 10e0.1 Hz frequency range during the aging treatment, resulting in a total cathode area