Sulfur Poisoning of Anode-Supported SOFCs under Reformate Operation

• Published in: Fuel cells (Weinheim an der Bergstrasse, Germany) Vol. 13; no. 4; pp. 487 - 493
• Main Authors: Weber, A., Dierickx, S., Kromp, A., Ivers-Tiffée, E.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.08.2013; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: Cermet Anode; Chemistry; Fuel cells; Impedance Spectroscopy; Poisoning; Reformate; SOFC; Sulfur; Sulfur Poisoning
• ISSN: 1615-6846; 1615-6854
• DOI: 10.1002/fuce.201200180

The impact of sulfur‐poisoning on reforming chemistry and electrochemistry of anode‐supported solid oxide fuel cells is analyzed via electrochemical impedance spectroscopy. Different types of anode supported cells are operated in hydrogen/steam – as well as simulated reformate – (H2 + H2O + CO + CO2 + N2) fuels containing 0.1–15 ppm of H2S. A detailed analysis of impedance spectra by the distribution of relaxation times (DRT) and a subsequent complex nonlinear least squares (CLNS) fit separates the impedance changes taking place at the anode and the cathode. Two main features were detected in the DRT, a decreased reaction rate of the electrochemical hydrogen oxidation and a deactivation of the catalytic conversion of CO via the water‐gas shift reaction. During the first exposure of the cell to a H2S‐containing fuel, an enhanced degradation is observed. The degradation rate increases several hours after H2S was added to the fuel and decreases after the poisoning is completed. The polarization resistance increased by a factor of 2–10, depending on H2S‐content, fuel composition and cell type. Comparing the temporal characteristics of the polarization resistance of two different anode supported cells, it could be shown that the accumulated H2S‐amount divided by the Ni‐surface area inside the anode substrate and anode functional layer determine the onset of the degradation.