Performance of a ten-layer reversible Solid Oxide Cell stack (rSOC) under transient operation for autonomous application

Abstract

A state-of-the-art ten-layer solid oxide stack was electrochemically characterized and system-oriented experimentally investigated in reversible operation. The stack in question consists of 5YbSZ electrolyte supported planar cells promising high performance. The stack is integrated into a stackbox and is considered to be operated in an autonomous system, thus system-relevant operating conditions in terms of reversibility, inlet mixtures and temperatures were applied. A high fuel utilization, respectively reactant conversion of 80% in either mode was deployed in steady state experiments in a transient operation regime. Polarization curves were dynamically recorded and electrochemical impedance spectroscopy was performed to evaluate the performance of the stack in reversible operation feeding hydrogen and/or carbonaceous gases. Recorded temperature profiles obtained by means of thermocouples placed directly on the air electrodes showed distinct characteristics with a maximum deviation of 24.8 K in the exothermic and 14.9 K in the endothermic operating mode. The stack showed a small dependency on the applied operating temperatures of 780, 800, and 820 °C. A maximum current density of −0.7 A cm−2 was applicable under H2O electrolysis. A comparable performance was observed for co-electrolysis corroborated by current density independent syngas ratios of 9.0 and 4.0 when feeding H2/H2O/CO2-compositions of 20/70/10 and 20/60/20, respectively. Particular attention must be paid to thermal integration in the context of the implementation as a stand-alone system. The resulting operating maps related to maximum current densities, gas production and temperatures can be considered and used for simulation and design of the envisaged stand-alone system including the auxiliary power requirements.