Effect of H2S on SOFC model anodes of nickel and ceria

Solid Oxide Fuel Cells are recently gaining much interest considering their high efficiency, their fuel flexibility and the possibility to be used in combined heat and power systems or coupled with micro gas turbine. Thus, in order to reduce the worldwide dependence on fossil fuel and to increase the efficiency of the existing power plants, many efforts have been made in developing SOFC-based systems fed by biomass derived fuels. Importance of biomass as a sustainable primary energy source is widely acknowledged and gasification offers a technology for converting solid biomass into biosyngas, suitable to be fed to SOFC. Thus, the department of Process&Energy at TU Delft is focused on investigating the effect of biosyngas contaminants on the performances of SOFC. In particular in this research, impedance spectroscopy has been used to study the effect of H2S on nickel and ceria anodes. Commercial SOFC electrodes have a complicated 3D structure and it is hard to isolate the contributions of different processes such as diffusion, charge transfer, adsorption etc. Thus, in order to overcome this problem, in this work we used 2D model anodes, with a well-defined TPB, which allowed us to focus on studying the detailed electrochemistry of oxidation reactions on the anode surface, neglecting the gas diffusion effect. Both nickel and ceria pattern electrodes have been firstly tested under H2-H2O atmosphere in order to identify the rate limiting process, also through a comparison of the results with previous studies. Hence experiments with contaminated hydrogen have been performed: impedance spectra have been recorded before, during and after contamination at both 5 ppm and 20 ppm of H2S. The results show that the contamination leads to an increase in the total polarization for both cell. While Ni cells recover the previous polarization value after H2S removal, ceria cells showed an irreversible poisoning. Since few data are available in literature, we underline the need of further investigation on ceria poisoning mechanism.