Stability evaluation and quantitative analysis of filmy cathode in solid oxide fuel cells under operating conditions

Abstract

For interface-modified cathodes via the infiltration method, the quantitative analysis of degradation mechanism in solid oxide fuel cells (SOFCs) is the key to optimizing cell stability. Here, we prepare the anode-supported SOFC with a multifunction layer (MFL) cathode-infiltrated filmy La0.6Sr0.4CoO3-δ (LSC), which provides a peak power density as high as 1.1 W cm−2 at 750 °C, and outstanding durability with slight voltage loss under 0.5 A cm−2 and 750 °C for over 1000 h. According to collected data from electrochemical impedance spectroscopy (EIS) at different operating times, the distribution of relaxation time (DRT) and equivalent circuit model (ECM) methods are applied to quantify the contribution of different electrode processes to the whole voltage degradation during the cell operation. The result shows that oxygen ionic transport and charge transfer at the MFL/electrolyte interface dominate almost all voltage degradation (95.31%), while the oxygen surface exchange and oxygen ionic bulk diffusion in the cathode just contributes 1.82%. Microtopographic characterization provides that the filmy morphology of LSC cathode remains intact, but the Sr element enriches at the MFL/electrolyte interface. Therefore, the exacerbation of oxygen ionic transport and charge transfer at the MFL/electrolyte interface due to Sr enrichment is identified as the predominant degradation mechanism during long-term galvanostatic operation.