Integration of hydrogen production and greenhouse gas treatment by utilizing nitrogen oxide as sweep gas in a solid oxide electrolysis cell

Abstract

Solid oxide electrolysis cells (SOECs) for hydrogen production are generally operated at a thermoneutral voltage, a voltage at which the cell does not generate or require additional heat. When an SOEC is operated above the thermoneutral voltage, it consumes more electrical energy. However, operating below the thermoneutral voltage cools the cell and results in a temperature gradient within the electrode because of the endothermic reaction. To prevent these phenomena, an SOEC requires additional heat input to maintain a constant temperature. Recently, nitrous oxide has become a global concern because of its high global-warming potential. In this study, we propose the use of nitrogen oxide instead of air or pure oxygen as the sweep gas for SOEC operation, integrating the hydrogen production and greenhouse gas treatment. This study investigated the influence of different types of sweep gas on the heat demand of water electrolysis. To examine this SOEC system, we conducted a simulation study, and the effects of operating conditions and cell geometrical parameters on the system performance were analyzed in detail. With the heat released from the decomposition of nitrogen oxide, operation of the SOEC below the thermoneutral voltage and a higher hydrogen production efficiency are achieved.