Enhanced Rocking Chair Capacitive Deionization for Accelerated Water Desalination

Abstract

Based on a report from the World Economic Forum, the global demand for water is projected to exceed supply by 40 percent, raising concerns about the prospect of achieving clean water supply for all[1]. This challenge emphasizes the need for technologies that enable the supply of clean water with minimal economic cost and footprint on the environment. Capacitive deionization (CDI) has emerged as an effective technology for desalinating brackish water for human consumption by removing ions through the passage of electrons [2]. Although the technology has gained prominence particularly because of its environmental friendliness, it is still limited in desalination performance (e.g., rate and capacity), spurring research into ways of improvement [3]. In a bid to improve the desalination rate of CDI, rocking-chair capacitive deionization (RCDI) eliminates the need for a subsequent cycle of salt concentration following a cycle of salt rejection by enabling simultaneous salt concentration and rejection in a single cycle. The RCDI cell design which typically consists of a pair of capacitive electrodes and respective channels separated by an ion-exchange membrane, enables continuous charging-discharging. This design results in the alternating production of a dilute and concentrate stream within two separate channels in the cell[4].In this work, insights into a new design will be introduced that leverages the blueprint of RCDI to further expedite water desalination rate by incorporating ion-exchange resins into the cell design. By integrating the ion resins into the cell design, in this meeting, faster salt removal and concentration in both compartments of the cell will be demonstrated, when operated under similar conditions with a typical RCDI cell. This new design provides an opportunity for not only improved desalination rate but also energy savings for desalination. In addition, we will also elucidate the competition between faradaic reactions and capacitive storage occurring in the compartments of the desalination cells by examining pH swings during operation. References https://www.weforum.org/our-impact/closing-the-water-gap/ X. Gao, A. Omosebi, Z. Ma, F. Zhu, J. Landon, M. Ghorbanian and K. Liu, Environmental Science: Water Research & Technology, 5(4), 660-671 (2019).Y. Liu, X. Gao, K. Wang, X. Dou, H. Zhu, X. Yuan, L. Pan, Journal of Materials Chemistry A,8(17), 8476-8484 (2020).D. Lu, C. Xu, Y. Wang and W. Cai, Desalination, 510, 115090 (2021).