La/Ba-based cobaltites as IT-SOFC cathodes: a discussion about the effect of crystal structure and microstructure on the O2-reduction reaction

D. GARCES; A. SOLDATI; H. TROIANI; A. MONTENEGRO HERNÁNDEZ; A. CANEIRO; L. MOGNI

ELECTROCHIMICA ACTA

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2016 vol. 215 p. 637 - 646

0013-4686

This work discusses the effect of the crystal structure and microstructure on the electrocatalytic activity of Lanthanum-Barium cobaltite (LBC), evaluatedas IT-SOFC cathode. Two systems with similar microstructures (particle sizes dp 1?5 mm) are used to compare the effect of the crystal structure: the cubic La0.5Ba0.5CoO3-d with La/Ba cations randomly distributed, and a tetragonal LaBaCo2O6-d with La/Ba layered distribution. In addition, the effect of microstructure is studied by using a newsol-gel route which allows obtaining LaBaCo2O6-d with smallest particle size (dp 500 nm). The electrode reactionisstudied by electrochemical impedance spectroscopy (EIS) as a function of temperature (T) and oxygen partial pressure (pO2). The electrode polarization resistance (RC,P) presents two contributions, a low frequency (RLF) and a high frequency Gerischer-resistance (RG). On one side, RLF, associated to the O2-gas diffusion across the gas layer boundary, presents low activation energy (Ea) and is proportional to pO2 -1,presenting the same values regardless the microstructure.On the other side, RG is in agreement with an O2-reduction mechanism co-limited by O-surface exchange and O-bulk diffusion. RG is strongly influenced by structure (trough the diffusion coefficient DV) and microstructure (inversely proportional to dp). Besides, RG decreases by reducing dp and by modifying the La/Ba ordering from layered to randomly distributed.