Modeling and Analysis of Polarization Losses in Solid Oxide Fuel Cells with Siloxane Contamination

Abstract

The degradation of the solid-oxide fuel cell (SOFC) nickel-yttria stabilized zirconia anode under decamethyltetrasiloxane (L4) contamination was examined with experiments and modeling. A model was developed for the polarization losses based on the charge transfer coefficient, α, and diffusion layer thickness, δ, and fitted to the experimental data to understand how the siloxane degrades the SOFC performance with time. The results of the model indicate that the total polarization losses increase approximately 44% over the course of the 180 min experiment at 350 mA/cm2. Activation losses dominate the polarization losses initially but decrease in their total contribution while concentration losses increase. Scanning electron microscopy with wavelength dispersive X-ray spectroscopy elemental mapping indicates that silicon deposition is highest at the outer edge of the anode and forms a barrier layer to fuel diffusion, increasing concentration losses. When the model was applied to other previous D4 and L4 siloxane experiments conducted over a period of 40 hours, similar trends in polarization losses were observed. Polarization losses increase more rapidly with D4 compared to L4 siloxane contamination, with concentration losses increasing the fastest with both types of siloxane.