The presence of fuel impurities, such as sulfur, siloxane and phosphorus, in biogas, diesel and natural gas can cause Solid Oxide Fuel Cell (SOFC) degradation due to surface poisoning of Ni-containing anodes. In this regard, Ni/CGO anodes were shown to display higher sulfur tolerance than Ni/YSZ anodes and a comparable high performance. In order to allow for a more profound understanding of the processes underlying sulfur poisoning, this study presents an extensive experimental investigation of commercial Ni/CGO-based SOFC operating on H₂/H₂O gas and reformate fuel mixtures with trace amounts of hydrogen sulfide (H₂S).

The short-term poisoning behavior of high-performance electrolyte-supported Ni/CGO10-based cells was systematically investigated by means of transient voltage stability experiments and electrochemical impedance measurements for a wide range of operating conditions. The effects of temperature (800 – 950 °C) and current density (OCV – 0.75 A·cm^‒2) on the extent of sulfur poisoning (1 – 20 ppm H₂S) was evaluated. The poisoning behavior was shown to be completely reversible for short exposure times in all cases. By means of equivalent circuit modeling, the chemical capacitance of Ni/CGO10 anodes was demonstrated to be strongly dependent on temperature and gas phase composition reflecting a changing Ce³⁺/Ce⁴⁺ ratio in the CGO phase. Using a model reformate as fuel gas, it was shown that CO can still be electrochemically converted under sulfur exposure.

Furthermore, long-term experiments of 1000 h were conducted at 900 °C and 0.5 A·cm^‒2 with and without sulfur exposure and the degradation progress was monitored by impedance spectroscopy. Moreover, comprehensive post-mortem analysis including FIB/SEM, TEM and XRF was carried out in order to identify the nature and location of the occurring microstructural changes.