Pressurized operation of a 10 layer solid oxide electrolysis stack

Abstract

Solar and wind energy are becoming the fundament of the power supply system. However, the increasingly significant amount of renewable electrical power associated with natural intermittency due to varying weather conditions requires flexible storage options. One promising path is the solid oxide electrolysis cells (SOECs) technology which can provide hydrogen or derived hydrocarbons as fuel in transport, as chemical in industry or for repowering or heating.

SOECs offer a great potential for a highly efficient energy conversion due to their high operating temperature that may lead to reduced electrochemical losses. Previous studies have shown that the efficiency of solid oxide fuel cells (SOFCs) can be significantly improved by operating at elevated pressure. Similar effects on the electrochemistry can also influence the cell when operated in electrolysis mode and may also cause improved performance. Another reason for pressurization is the use of pressurized hydrogen in downstream processes like storage or especially in the case of co-electrolysis methanation or Fischer-Tropsch synthesis.

Experimental results of water electrolysis in a pressurized SOEC stack are presented. The stack consists of ten electrolyte supported cells. The pressure ranges from 1 to 8 bar. Reactant gas composition (xH2O=0.80…0.98), steam utilization (0.60…0.85) and temperature (750…850 °C) are the experimental parameters that are varied. Pressure influence on open circuit voltage (OCV) and power density is examined. Furthermore current voltage characteristics and impedance spectroscopy are performed to investigate the influence of pressure on the stack performance.