The utilization of high saline sodium chloride containing waters in solid oxide electrolysers

Abstract

State-of-the-art electrolyser systems are based on the utilization of highly pure freshwater. This could lead to an increase in freshwater demand and a worsening of freshwater water scarcity. One solution is the direct use of saline waters such as seawater or wastewaters from industry. In this work, the impact of sodium chloride contamination in waters on high temperature solid oxide electrolysis cells is investigated. Thus, the utilization of high saline wastewater from industry and an accelerated stress test for the use of seawater in SOECs is evaluated. The initial performance and stability are compared with results gathered by utilizing high-purity freshwater for steam generation. An increased degradation rate was observed for the sodium chloride solution after 400 h of operation. The increased degradation is mainly caused by an accelerated increase in ohmic and polarisation resistance. More specifically, the charge transfer process in the Ni-YSZ fuel electrode was found to contribute significantly to the increased degradation. Post-test characterization using XPS and SEM-EDX showed sodium particle deposition on the fuel electrode surface contact layer confirming the transport of salt to the cell. The cross-section analysis by SEM showed an accelerated Ni agglomeration in the Ni-YSZ fuel electrode compared to pure water operation.