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, H2O and N2 as balance) with 2, 6, 12, and 24 ppm of H2S by means of electrochemical impedance spectroscopy. corded 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.