An insight into the electrochemical performance of La0.5-xPrxBa0.5CoO3-δ as cathodes for solid oxide fuel cells: study of the O2-reduction reaction.

GARCES, DIANA; WANG, HONGQIAN; BARNETT, SCOTT; LEYVA, ANA GABRIELA; NAPOLITANO, FEDERICO; FUENTES, RODOLFO; TROIANI, HORACIO E; MOGNI, LILIANA VERONICA

Journal of Materials Chemistry A

The Royal Society of Chemistry

Año: 2018

2050-7488

New LT-SOFC cathodes with La0.5xPrxBa0.5CoO3d (0 # x # 0.5) compositions were studied. The La-richcompounds exhibit an inter-growing cubic and tetragonal structure whereas the Pr-rich show a tetragonalstructure. Cathode polarization resistances, estimated from electrochemical impedance (EIS), take valuesaround 0.15 and 0.04 U cm2 in air at 600 and 700 C, respectively. The O2-reduction mechanism and itskinetic coefficients, O-ion diffusion (Dchem) and O-surface exchange (kchem), were studied by applyingthe ALS model for macro homogenous porous electrodes to the EIS data, in combination withmicrostructural parameters obtained from three-dimensional tomography using focused ion beamscanningelectron microscopy (3D FIB-SEM). The diffusion coefficients for samples with mixing of phasestake values of Dchem 106 cm2 s1, at 700 C in air, whereas the pure tetragonal phases present lowervalues Dchem 108 cm2 s1. On the contrary the kchem for all samples takes values ranging between 0.4and 1 104 cm s1 at 700 C in air. In addition, the origin of time evolution of polarization at 700 C inair was evaluated by combining the EIS spectra as a function of time and the ex situ samplecharacterization of fresh and tested samples by 3D FIB-SEM tomography and inductively coupledplasma-optical emission spectrometry (ICP-OES). Little changes of microstructures were detected,whereas an increasing of the amount of a water-soluble Ba surface species in comparison with totalcation surface segregation was observed for all samples after the ageing. This may constitute the mainreason causing the polarization resistance degradation. However, the analysis of time evolution shows,that contrary to the situations reported for SrO segregation in Sr-based perovskites, the Dchem is thecoefficient mainly affected for compositions with inter-grown phases. At the same time, both Dchem andkchem decreases with time when only the tetragonal phase is present.