Study of the Rate Limiting Steps and Degradation of a GDC Impregnated La_(0.6)Sr_(0.4)Co_(0.8)Fe_(0.2)O_(3-δ) Cathode

摘要

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 400°C and 800°C and during 500 h at 700°C. The impregnated cathode was found to be electrochemically limited by the same processes as the non-impregnated 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 700°C.