Enhancement of Performance and Sulfur Tolerance of Ceria-Based Fuel Electrodes in Low Temperature SOFC

The trend of operating the solid oxide fuel cell at significantly lower operation temperatures enables the application of electrodes with finer microstructure or even nanostructured electrodes with increased active surface and enhanced performance. To maintain the high performance in hydrocarbon fuels commonly impurified with sulfur compounds, a required sulfur tolerance has to be maintained. In this study we compare performance and H₂S-poisoning of four ceria-based electrodes: conventional Ni/Ce_0.9Gd_0.1O_2−δ cermets and sub-μm scaled Ce_0.8Gd_0.2O_2−δ -electrodes with and without infiltrated nickel. Symmetrical cells were operated in a hydrogen/steam/nitrogen gas mixture with and without minor amounts of H₂S at 600 °C. The performance is analyzed by electrochemical impedance spectroscopy. The distribution of relaxation times is applied to deconvolute the electrochemical processes followed by a complex nonlinear least square fit to quantify the loss processes and the impact of sulfur. Whereas two different Ni/Ce_0.9Gd_0.1O_2−δ cermet electrodes exhibit polarization resistances at 600 °C without/with 0.1 ppm H₂S of 2.89/5.56 Ωcm² and 2.15/2.75 Ωcm², the single phase Ce_0.8Gd_0.2O_2−δ electrode reaches 0.98/2.37 Ωcm². With an infiltration of Ni-nitrate forming nickel nanoparticles on the gadolinia-doped ceria-surfaces, the ASR could be drastically reduced to 0.32/0.37 Ωcm².