Rocking-Chair Capacitive Deionization for Continuous Brackish Water Desalination

Abstract

Capacitive deionization (CDI) is considered an alternative desalination technology due to its easy operation, high energy efficiency, and environmentally friendly process. However, a separate regeneration step is required in typical CDI technologies that releases the absorbed ions on the electrodes which results in an inefficient and cost-intensive process. This study proposed a novel CDI system referred to as rocking-chair capacitive deionization (RCDI) that has a continuous brackish water desalination process which consists of a pair of Nafion-coated activated carbon electrodes and an anion-exchange membrane. The coated Nafion contributed to the cation selectivity of the carbon electrode, and it enabled a continuous desalination process during constant-current operation through a rocking-chair ion movement. From the desalination tests that included the analysis of the CDI Ragone plot, the RCDI has a high salt adsorption capacity (maximum of 44.5 mg g–1) with continuous operation. Furthermore, the RCDI desalted brackish water under rapid operation conditions (up to ±30.0 A m–2) which is a constant-current operation condition that is several times higher than that of previously reported desalination technologies using battery materials. Consequently, this study proposes a new strategy for a continuous desalination CDI system that provides a high-performance and energy-efficient desalination process for brackish water.