Assessing Sulfur-Induced Degradation Mechanisms in SOFCs with Chronocoulometry and Operando Optical Imaging

Sulfur contamination in SOFC fuels leads to pronounced losses in conversion efficiency and eventual device failure as sulfur adsorbs onto nickel-based anodes, eventually forming nickel sulfide. Strategies intended to improve electrode tolerance to sulfur poisoning are based largely on electrochemical measurements coupled with ex situ assessments of electrode composition and microstructure following device disassembly. Studies presented in this work employ chronocoulometry operando NIR-thermal imaging, to make real-time measurements of anode performance and thermal behavior during exposure to sulfur in devices operating at 650°C. Changes occurring on Ni-YSZ electrodes were monitored as a function of H2S concentrations (10 - 50 ppm). Together with quantitative chronocoulometry and electrochemical impedance measurements, imaging data create a compelling description of sulfur-induced degradation mechanisms in SOFCs where significant utilization of adsorbed S leads to decreased performance when incident S concentrations ≥ 30 ppm.