(Invited) Recent Progress in Redox Flow Deionization

Abstract

Recently, redox flow deionization (RFD) has gained great interest in water desalination as a promising electrochemical ion separation process. The RFD system advances the redox flow battery by adapting intervening channels for the water stream. As a unique cell feature, the system is comprised of multi-channels allowing the independent control of the flow streams (e.g., water stream and redox flows). This leads to several advantages compared to the conventional electrochemical ion separation processes such as capacitive deionization and electrodialysis: (1) sustainable redox reaction enables low operational cell voltage and high diversity in the employment of electrode materials, (2) the mild reaction environments allow less byproduct production and less variation in pH as this system facilitating downstream processes, and (3) the stored energy at redox couples provides energy recovery process with a simultaneous ion separation leading to high energy efficiency in water desalination.In line with the development of RFD, this presentation aims to introduce the basic principle of the RFD system and recent progress, including cell architecture, electrodes, operations, and scale-up strategy. In addition, various applications are addressed such as resource recovery and pollutant control. Finally, we briefly propose the practical challenges and opportunities for future research direction.