Evaluation of the effect of sulfur poisoning on the performance of Ni/CGO based SOFC anodes

Kurzfassung

Although the increased sulfur tolerance of Ni/CGO anodes in comparison to Ni/YSZ is well-known, their full potential is not yet fully explored. So far, most investigations have been carried out in H2/H2O fuel gases and different hypothetic explanations for the superior tolerance in these systems have been suggested. (1–3) However, no consensus has been achieved so far. In the present work, the sulfur poisoning behavior of commercial electrolyte-supported cells with Ni/CGO10 anodes operated with reformate fuels was investigated by means of current-voltage characteristics and electrochemical impedance spectroscopy and compared with the behavior of Ni/YSZ anodes. Different methane and carbon monoxide containing fuels were used to gain insights into the underlying fuel oxidation reaction mechanism. Significant performance drops were observed for both anodes. However, the ability of Ni/CGO anodes to electrochemically convert carbon monoxide even at H2S concentrations up to 20 ppm was demonstrated, while this was not possible for Ni/YSZ. However, methane steam reforming was shown to be fully deactivated on both anodes. It is proposed that during sulfur poisoning the Ni surface is blocked and thus, the water gas shift reaction is fully deactivated as well. However, electrochemical CO oxidation on the CGO surface was shown to be still active, demonstrating the active (electro-)catalytic role of CGO. The presented results clearly show that Ni/CGO displays a superior sulfur tolerance also towards the oxidation of carbon monoxide containing gases.