Effects of Current Polarization on Stability and Performance Degradation of La_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.8)O3 Cathodes of Intermediate Temperature Solid Oxide Fuel Cells

摘要

The stability of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) cathodes was investigated at a constant current density of 200mA cm~(-2) and 750 C in air. The mechanisms of performance degradation for impregnated LSCF cathodes were compared with screen-printed LSCF cathodes. The cathode polarization resistance (Rp) of LSCF impregnated YSZ (LSCF+YSZ) cathodes increased from 0.24Ω cm~2 to 0.4Ω cm~2 and the ohmic resistance (RO) from 2.27Ω cm~2 to 2.74Ω cm~2 after current polarization at 200mA cm~(-2) for 24h, respectively; due to the damage of well-connected porous structure. In contrast, Rp of screen-printed LSCF cathodes had no significant change and RO changed from 2.22Ω cm~2 to 3.18Ω cm~2 after current polarization at 200mA cm~(-2) for 24h. This indicates that LSCF+YSZ cathodes, which have high surface activity, are more instable than screen- printed LSCF cathodes. Performance degradation of LSCF+YSZ cathodes is mainly caused by the damage of well-connected porous structure and coalescence of LSCF particles. While less porosity and microstructure coarsening played a dominate role in performance degradation of screen-printed LSCF cathodes.