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

Abstract

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/Ce0.9Gd0.1O2-δ cermets and sub-µm scaled Ce0.8Gd0.2O2-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/Ce0.9Gd0.1O2-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 Ce0.8Gd0.2O2-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.

In-situ electrochemical impedance analysis of a commercial SOFC stack fueled by real wood gas

“…It is important to note, that the primary objective of the work was to perform a coupling with a real gasification system and obtain a more detailed interpretation via EIS to acquire a more comprehensive interpretation using the DRT approach in contrast to a more general investigation utilizing, for example voltage-current curves. While previous studies [ 7 , 9 , 13 , 21 , 24 , 30 , 31 , 33 , 34 , 37 , 39 , [53] , [54] , [55] ] have investigated the impact of real wood gas on SOFC performance using current-voltage curves, post-mortem techniques or EIS, the present work provides a unique contribution by applying the DRT approach to interpretate the EIS spectra. With the application of DRT analysis approach, it is possible to extract the most dominant time constants or frequencies for the processes involved, providing deeper insights into the electrochemical processes within the SOFC stack.…”