In Situ Optical Investigations of Contaminants in Operating Solid Oxide Fuel Cells

Abstract

Solid oxide fuel cells (SOFCs) can generate electricity efficiently and with broad fuel flexibility, but practical applications require them to be more durable and resistant to degradation when subjected to impurities. In order to better understand poisoning mechanisms and guide strategies for developing more durable materials and devices, we have used operando optical methods combined with electrochemical measurements to investigate the effects of sulfur (170 ppm H2S) on SOFC Ni/YSZ anodes operating on methane at high temperature (700 °C). There is clear evidence of reduced anode catalytic activity based on near infrared thermal imaging which shows not only that the cooling associated with endothermic methane cracking is reduced but also that an elevated temperature is observed that is temporally correlated with drastic electrochemical changes indicative of substantial anode degradation. Mid infrared emission measurements indicate less fuel consumption and fewer oxidation products in agreement with the trend of suppressed anode activity. The effects are compared to similar studies of chlorine contamination where reversibility and degradation mechanism have been mapped out more extensively to show they depend sensitively on temperature and type of fuel; the effects are more pronounced and seem to be promoted in electrochemically active regions for sulfur.