Advances and challenges in capacitive deionization: Materials, architectures, and selective ion removal

Capacitive deionization is a promising and low-environmental-impact desalination technology that has gained significant momentum in recent years. This review presents a comprehensive analysis of hot topics in CDI, including electrode materials, cell architectures, selective ion removal, energy consumption, and salinity ranges. Improvements in CDI involve optimizing carbon materials through structural optimization, the introduction of surface functional groups, heteroatom doping onto nanocarbon materials, the modification of carbon materials with metal oxides, and the application of protective polymer coatings. Furthermore, a remarkable breakthrough has emerged in the form of Faradaic materials, which has led to a transformative surge in the desalination capacity of CDI. The evolution of the CDI cell architectures from the static electrode to the flow electrode, achieved continuous production. These innovations in electrode materials and cell architectures have not only bolstered energy efficiency and enabled energy recovery but have also broadened the salinity range that CDI can effectively address. Future research should focus on understanding ion-selective mechanisms, enhancing electrode stability, optimizing hydraulic designs, and conducting comprehensive economic and environmental assessments. Addressing these areas will be crucial for advancing CDI technology, enhancing its scalability, and improving its practical application in various settings.