Extensive analysis of an SOC stack for mobile application in reversible mode under various operating conditions

The reversible solid oxide cell (rSOC) is a key technology that is capable of generating electricity, heat, and valuable fuels in a highly efficient manner. By integrating an rSOC module and all of the necessary components into a compact unit, it is possible to realize an autonomous reversible system. In order to learn more about the durability and reliability of a ten-cell rSOC stack, originally developed for mobile applications, was operated in both fuel cell and electrolysis modes under realistic operating conditions. The stack was fed with gas mixtures of H-2, H2O, CO2 and CO. The stack examined in the course of these experiments consists of large, planar, anode-supported cells (ASC). Compared to stacks with conventionally produced interconnects, the concept used for this stack was based on stamped metal sheet plates of CroFer22 APU, which means that they are lightweight and easy to assemble. The present study includes a detailed characterization of the stack's performance during reversible operation and evaluates its applicability for real operation. To this end, a comprehensive stack analysis including electrochemical impedance spectroscopy (EIS), chronopotentiometry, a gas analysis, polarization curves, and temperature measurements. In consideration of system integrations, the stack was operated in galvanostatic mode under system-relevant, steady-state conditions: at a fuel utilization of 80% in fuel cell mode, and at a reactant utilization of 70% in electrolysis mode. The feasibility of this SOC stack's long-term operation has thus been proven for an operating time of >2000 h. Finally, degradation analyses of both the stack and the individual cells were performed, whereby the stack was observed to have a degradation rate of 3.7%/kh. (C) 2019 Elsevier Ltd. All rights reserved.