Rocking-Chair Capacitive Deionization for Continuous Brackish Water Desalination

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.