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

Abstract

In this study, the degradation of solid-oxide fuel cells (SOFC) nickel-yttria stabilized zirconia anode under siloxane contamination is examined. The experiments were conducted inside a furnace heated to 800°C with an Ni-YSZ-supported (Nickel-yttria-stabilized zirconia) fuel cell. A fuel source with a flow rate of 20 mL/min of hydrogen gas (66.3%), 10 mL/min of nitrogen gas (33.2%) and 0.15 mL/min (0.5%) of L4 siloxane was fed to the anode. Air was supplied to the cathode. Polarization losses are recorded at intervals of 30 minutes over a period of 3 hours. The polarization losses (activation, ohmic, and mass transport) are modeled with the parameters α and δ. The model is fitted to the experimental polarization curve, to understand how the siloxane degrades the SOFC performance with time. Ohmic losses are dominant in the anode due to much higher anode thickness (380 μm) compared to electrolyte thickness (13 μm). Activation losses vary with α, which decreases from 0.31 to 0.25, significantly lower than the accepted value of 0.5 found in existing literature. The current density is limited by mass transport losses at higher current densities (limiting current density j). Mass transport losses vary with both δ and α. The value of δ, which represents the diffusion layer thickness, varies from 45 μm to 66 μm. The results of the model indicate that the total polarization losses increase for each subsequent time interval, with a total increase of approximately 45% from 0 to 180 min. Activation loss dominates the polarization losses initially, but decrease over time while mass transport losses increase. With current density being constant at 500 mA/cm2, the activation losses decrease from 58% to 55%, ohmic losses decrease from 28% to 20% and mass transport losses increase from 14% to 21% of the total polarization loss over a period of 180 mins.