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Kinetics of oxygen reaction in porous La0.6Sr0.4Co0.2Fe0.8O3–δ (LSCF) and La0.6Sr0.4Co0.2Fe0.8O3–δ-Ce0.8Gd0.2O1.9 (LSCF-GDC) electrodes are systematically studied. Normally, there are two pathways of oxygen reaction in porous LSCF: in reaction region with oxygen exchanging at electrode/air interface, and around electrode/electrolyte interface with oxygen exchanging at electrode/electrolyte/air triple-phase boundary (TPB). GDC in porous LSCF-GDC accelerates oxygen transport and oxygen gas diffusion during oxygen reaction. In addition, because the formation of LSCF/GDC interface increases the length of TPB and affects the geometry of reaction region, oxygen reaction in LSCF-GDC tends to proceed in the TPB pathway. The performance and oxygen reactions of LSCF-GDC are evaluated at 650 °C and 850 °C. Oxygen reaction in LSCF-GDC is suppressed by CO2, but increasing GDC content is able to improve the CO2 tolerance of electrode. Though the performance reduction by H2O is unobvious, H2O can aggravate CO2 degradation at low temperature.

Degradation suffering from ambient water vapor in air is harmful for cathodes of solid oxide fuel cells (SOFCs), it is necessary and important to research its attenuation mechanism and related preventive methods. Here, effects of humidity on SrTi0.05Co0.95O3-δ (STC) cathode have been discussed in detailed. X-ray diffraction analysis reveals that STC is relatively stable in wet air with a little crystal contraction, but without obvious impurities. Because active sites of STC for oxygen reduction reaction (ORR) are covered by water vapor, the electrical conductivity decreases while the polarization resistance (Rp) increases with the increasing of the water vapor concentration in air. Compared with Rp measured in dry air, the enhanced Rp value is 0.0347 Ω cm2 and 0.0493 Ω cm2 in containing 3% and 5% H2O air after a continuous testing for 96 h at 800 °C, respectively. Furthermore, a maxium power densities of 832 mW cm−2 and 814 mW cm−2 can be obtained for STC/LSGM/STC in dry air and containing 5% H2O air after 96 h operating at 800 °C, respecctively. Interestingly, the degradation coming from humidity can be recovered partially by switching the feedgas back to dry air again. The Rp of STC becomes ~0.0402 Ω cm2 again after switching the operating atmosphere from 5% H2O air to dry air for 5 h.

Under actual operating conditions, cathode materials of Solid Oxide Fuel Cell (SOFC) tend to react with CO2 and/or H2O in air, resulting in degraded performances and stabilities. Here, effects of CO2 and H2O on Ba0.95La0.05FeO3-δ (BLF) cathode are systematically discussed by X-ray diffraction patterns (XRD), electrochemical impedance spectra (EIS) and scanning electron microscope (SEM). The results show that BaCO3 can be formed at 400 °C in a simulated air atmosphere. The content of CO2 and H2O has a significant influence on the polarization resistance (RP) of BLF, the RP of BLF is 0.161 Ω·cm2 in fresh air and 0.649 Ω·cm2 in 3% CO2–5% H2O-92% Air at 700 °C, respectively. But such degradation is reversible by switching working gas into fresh air again. In addition, we propose two alternative ways to improve tolerance of BLF cathode against CO2 and H2O: surface coating Ce0.9Gd0.1O2-δ (GDC) nano-particles on BLF cathode via spray-drying method and mechanical mixing GDC with BLF cathode. Compared with mechanical mixing, surface coating method is more advantageous in lowering the Rp of BLF cathode, which keeps 0.160 Ω·cm2 with 3% CO2–5% H2O-92% Air at 700 °C for 24 h.