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

D. GARCÉS; 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 reaction isstudied 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 pO21, presenting the same values regardless the microstructure.On the other side, RG is in agreement with anO2-reduction mechanismco-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.