Experimental Investigation of Naphthalene Induced Degradation of Reversible Solid Oxide Cells Operated on Bio-Syngas

Abstract

To tackle the demand for renewable alternatives to natural gas and for renewable energy, the operation of reversible solid oxide cells (rSOC) with syngas from biomass gasification is a highly efficient option. The fuel gas, produced close to carbon neutrality by the gasifier can be either converted to electrical power via the fuel cell mode or energetically upgraded via the electrolysis mode for e.g. utilization in chemical synthesis processes. Due to the reversible operation, a system based on an rSOC perfectly fits in an energy system with a high share of fluctuating renewable energy. However, impurities in fuel gas result in a fast degradation of the cells performance. This requires a comprehensive syngas cleaning to enable a stable operation of the cell. For the design of such a system, a deeper knowledge about the degradation processes is required. Especially the influence of tars is part of an ongoing research due to their ambivalent role as fuel and poison.In this work, the model tar Naphthalene is used to experimentally investigate the influence of polycyclic aromatic components on the performance of 10 x 10 cm² fuel-electrode supported solid oxide cells operated at artificial bio-syngas under internal reforming conditions. Two different fuel electrodes based on yttrium-stabilized zirconia (YSZ) and gadolinium-doped ceria (GDC) are investigated. A parameter study of the operational temperature and the operation mode is conducted with the YSZ based fuel electrode to quantify the effect on the degradation. The influence of the set-up is investigated by an experiment without the cell. The cell temperature distribution, the pressure drop and the fuel off-gas composition is measured. Electrochemical impedance spectroscopy is used to characterize the cell prior to the experiment and to monitor its performance during the poisoning and regeneration process. The measurements are interpreted via the distribution of relaxation times.The electrolysis mode is observed to be more vulnerable towards poisoning with the tar than the fuel cell mode. The poisoning effects, whether it is a performance degradation or carbon deposition, are not only dependent on the tar but also on the operational conditions. The GDC fuel-electrode did not show the expected high robustness. The investigated cells are prototypes of an ongoing development process; hence a more detailed investigation is required when the development is finished.