Electrochemical Sulfur Oxidation in Solid Oxide Fuel Cells Studied by Near Infrared Thermal Imaging and Chronocoulometry

Abstract

A newly adapted electrochemical technique, chronocoulometry, was used to characterize sulfur’s effect on the performance of porous Ni-YSZ anodes in electrolyte supported, solid oxide fuel cells (SOFCs) operating with dry H2 at 600 °C, 650 °C, 700 °C and 800 °C. Chronocoulometry data together with near-infrared thermal imaging show that H2S poisoning is more complex than sulfur simply blocking electrochemically active sites. Thermal imaging supports findings that SOFC susceptibility to sulfur poisoning depends strongly on temperature with higher performance and greater sulfur tolerance at higher temperatures. Chronocoulometry data are consistent with this description. Chronocoulometry results, however, are also more nuanced and show that sulfur adsorbed to the triple phase boundary (TPB) can be electrochemically oxidized, thereby limiting performance loss that would result simply from blocked or inaccessible electrochemically active sites. Furthermore, chronocoulometry results imply an increased TPB length at higher operating temperatures and suggest that the spatial extent of a SOFC electrode’s electrochemically active region plays a significant role in electrode surface chemistry. A simple model is developed to interpret the chronocoulometry results and determine the relative amount of sulfur adsorbed to the anode’s active triple phase boundary.