A review on free-standing electrodes for energy-effective desalination: Recent advances and perspectives in capacitive deionization

Water is one of the most important and precious natural resources for living. Purification and desalination devices for effective seawater and brackish water treatment are among the key strategic areas in sustainable environment research globally. The ability to desalinate and purify water at low energy is critical in sustainable water supplies. Currently, most of the available industrial desalination and purification technologies are energy and cost intensive, which need large investments in expensive infrastructure, large-scale facility and skilled manpower for maintenance. To avoid these obstacles, lower energy demand water treatment technologies are increasingly recognized as desirable approach to meet the needs of providing a sustainable source of clean water. Capacitive deionization (CDI) holds great promise to be used as an energy-effective desalination method for brackish water desalination. Conventionally, CDI electrodes are prepared through a slurry casting procedure, which normally use powder-based materials as raw material. However, in practical application, free-standing electrodes are preferred as they eradicate the limitation of using polymeric binders and facilitate the fabrication of the electrodes. Herein, the most recent progress and techniques of free-standing (mostly binder-free) electrodes are summarized, and their corresponding performances are evaluated. Besides, we present our perspective on the development of future materials and technologies for the advanced free-standing CDI electrodes with an efficient performance and applicable structure.