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

DIANA GARCÉS; ANALIA L. SOLDATI; HORACIO TROIANI; ALEJANDRA MONTENEGRO-HERNÁNDEZ; ALBERTO CANEIRO; LILIANA MOGNI

ELECTROCHIMICA ACTA

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2016

0013-4686

This work discusses the effect of the crystal structure and microstructure on the electrocatalytic activityof Lanthanum-Barium cobaltite (LBC), evaluatedas IT-SOFC cathode. Two systems with similarmicrostructures (particle sizes dp1?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 routewhich allows obtaining LaBaCo2O6-d with smallest particle size (dp500 nm). The electrode reactionisstudied by electrochemical impedance spectroscopy (EIS) as a function of temperature (T) and oxygenpartial pressure (pO2). The electrode polarization resistance (RC,P) presents two contributions, a lowfrequency (RLF) and a high frequency Gerischer-resistance (RG). On one side, RLF, associated to the O2-gasdiffusion 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 withanO2-reduction mechanismco-limited by O-surface exchange and O-bulk diffusion. RG is stronglyinfluenced by structure (trough the diffusion coefficient DV) and microstructure (inversely proportionalto dp). Besides, RG decreases by reducing dp and by modifying the La/Ba ordering from layered torandomly distributed.