Study of the Rate Limiting Steps and Degradation of a GDC Impregnated La_0.6Sr_0.4Co_0.8Fe_0.2O_3-δCathode

Abstract

In this work, a Solid Oxide Fuel Cell (SOFC) cathode surface modification by nanoparticle impregnation was carried out. La 0.6 Sr 0.4 Co 0.8 Fe 0.2 O 3-δ (LSCF) ceramic cathodes impregnated with Ce 0.8 Gd 0.2 O 3-δ (GDC) nanoparticles were characterized with scanning (SEM) and transmission (TEM) electron microscopy. The electrochemical response as a function of temperature, oxygen partial pressure (pO 2 ) (10 -4 < pO 2 < 1 atm) and time was evaluated by electrochemical impedance spectroscopy (EIS). We obtained reproducible and homogeneous impregnations, which reduce the total cathode´s polarization resistance more than 20% in the temperature range between 400ºC and 800ºC and during 500 h at 700ºC. The impregnated cathode was found to be electrochemically limited by the same processes as the nonimpregnated cathode, namely gas diffusion, ion bulk diffusion and dissociative adsorption. The impregnation produced a reduction of more than 20% of the oxygen surface resistance; such difference remained stable through 500h of continuous operation at 700ºC.

Oxygen Diffusion and Surface Exchange Coefficients of Porous La0.6Sr0.4Co0.2Fe0.8O3−δ Decorated with Co3O4 Nanoparticles

“…18,22,43 Apart from this, in the last few years much research attention has been devoted to the surface modification of MIEC cathodes. The objective is to increase the reactivity of the surface for the electrode gas reaction and to help avoid segregation of passivating cations, with the aim to improve the ORR efficiency [45][46][47][48][49][50] and the electrode's temporal stability. [51][52][53] One method used to modify the surfaces of the electrodes is the so called "wet infiltration technique" [54][55][56] with which significant reductions of the ORR resistance have been reported, for example decorating transition metal oxides onto MIEC electrodes, such as PrO x into La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3−δ (LSCF), 57 Cobalt Oxide into (Sc 2 O 3 ) 0.1 (Y 2 O 3 ) 0.01 (ZrO 2 ) 0.89 58 and LSM-YSZ composites 59 and other materials combinations.…”