Electrochemical impedance study of the poisoning behaviour of Ni-based anodes at low concentrations of H2S in an MCFC

The effect was investigated of low H2S concentrations, simulating biogas impurity, on the poisoning behaviour of a Ni-based, molten carbonate fuel cell anode. A conventional Ni-Cr anode was coated with ceria using dip coating to form a rare earth metal oxide thin layer on the surface of the anode. Electrochemical studies of the Ni-based samples were performed in symmetric cells under anode atmosphere (H2, CO2, H 2O and N2 as balance) with 2, 6, 12, and 24 ppm of H 2S by means of electrochemical impedance spectroscopy. The recorded data showed that the poisoning resistance was enhanced at low coating percentages of ceria; effects depend on H2S concentration and the applied load. These results were confirmed by electrochemical impedance tests where the cerium oxide addition appears through stable polarization behaviour up to 6 ppm of H2S, particularly in the mass transfer region. The protection is explained by the depression of poisoned Ni active sites and formation of a protective layer to the metal surface. The ceria coating layer is a potential solution to reduce H2S poisoning of MCFCs fuelled with biogas. Copyright © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.