Development of improved anodes in solid oxide fuel cells for conversion of synthesis gas from thermo-chemical gasification of biomass

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Oxide ceramic fuel cells (SOFC) offer the possibility of converting synthesis gas from thermochemical biomass gasification into electricity with very high efficiency in small decentralised systems. This has already been proven in several pilot plants with conventional SOFC fuel cells. The main difficulties are the impurities contained in biosyngas, such as components containing sulphur and chlorine or even higher hydrocarbons (tars). In the first project phase SynSOFC I new SOFC anodes have been developed and important findings regarding the effect of different contaminants on standard cells and new cells could be obtained. Contents of few ppm of sulfur-containing molecules already caused a high, partially reversible performance degradation. However, different tar substances had different effects on the cells. While toluene showed little effect on the cells, naphthalene addition resulted in strong, mostly reversible performance declines. In contrast, structural degradation of anode substrate structures without a noticeable decrease in cell performance was observed under the influence of phenol. Since during SynSOFC I the material of the anode substrate has been proven to be partially susceptible to degradation processes, the stability of the anode support is to be investigated and optimized in the context of SynSOFC II together with the anode itself. It is therefore planned to use the already developed Ni/GDC anodes in electrolyte-supported cells. In addition, full-ceramic anodes will be investigated in electrolyte-supported cells as well. The investigations on standard anodes of Ni(O) and 8 YSZ (zirconium oxide doped with 8 mol% yttrium) will be elaborated to clarify the microscopic mechanisms responsible for performance losses and degradation. In order to optimize the gain of knowledge, the chemical tolerance of the new and standard anode materials is to be investigated in addition to electrochemical characterization. The test stand installed during SynSOFC I for the coupling of SOFC stacks with an allothermal fluidized bed gasifier serves to validate the newly developed anode structures on 10x10cm² full cells in a system environment.