We report on the materials interaction of gadolinium doped ceria (GDC) and yttria stabilized zirconia (YSZ) in the context of high temperature sintering during manufacturing of anode supported solid oxide fuel cells (AS-SOFC). While ceria-based anodes are expected to show superior electrochemical performance and enhanced sulfur and coking tolerance in comparison to zirconia-based anodes, we demonstrate that the incorporation of a Ni-GDC anode into an ASC with YSZ electrolyte decreases the performance of the ASC by approximately 50% compared to the standard Ni-YSZ cell. The performance loss is attributed to interdiffusion of ceria and zirconia during cell fabrication, which is investigated using powder mixtures and demonstrated to be more severe in the presence of NiO. We examine the physical properties of a GDC-YSZ mixed phase under reducing conditions in detail regarding ionic and electronic conductivity as well as reducibility, and discuss the expected impact of cation intermixing between anode and electrolyte.
The operation of SOFCs on biomass-derived fuels demands an intrinsic tolerance of the cells towards biogenic contaminants like tars. In order to develop more robust cells, the behaviour of state-of-the-art Ni/YSZ anode supported cells at 700 °C in presence of naphthalene as model tar was extensively studied. As reported in literature naphthalene blocks the active sites of nickel catalysts and therefore hinders the utilisation of methane and carbon monoxide in the fuel gas. This study shows that the loss in performance is greater than only the contribution of this inertisation of CH4 and CO and that the behaviour of the cell voltage is similar to the poisoning with H2S. We also found that the operation temperature is a major parameter when tolerance limits for naphthalene have to be defined. The analysis of electrical impedance data helped to understand the underlying poisoning processes.
In the context of energy transition and climate change, a combination of highly efficient modern solid oxide fuel cells (SOFC) and thermo‐chemical conversion of biogenic residues could complement other intermittent renewable sources such as wind and solar. In order to reduce required gas cleaning efforts and to increase the process efficiency, the influence of hydrocarbons on SOFC performance is experimentally investigated in this study. For the first time, the operation of Ni/YSZ anode‐supported cells in Jülich F10 stacks is performed with pre‐reformed and with bio‐syngas containing full hydrocarbon content at realistic current densities. Sulfur and other impurities were removed in both cases. No degradation could be observed within normal operation on clean gas. With the tar reformer bypassed, the pressure drop over the stack increased due to severe carbon deposition on the anode substrate and the nickel current collector mesh inside the SOFC stack, so that operation had to be terminated after five hours. This behavior is different from single‐cell tests, where electrochemical degradation is the limiting factor. The results show that improvements are not only necessary for cell materials and that future research must also consider other stack components.
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