Structure and functionality design of novel carbon and faradaic electrode materials for high-performance capacitive deionization

Capacitive deionization is an energy-saving and environmental friendly water treatment technique with cost advantage especially for salt water with low/medium concentration. Upon sophisticated structure design and functionality regulation, novel derived carbon materials with optimized hierarchical pore structure and well-tailored surface characteristics and Faradaic materials with unique ion intercalation effects have exhibited enhanced salt adsorption capacity, high removal rate, increased ion selectivity and excellent long-term cycling stability, showing great potential in expanding CDI technique to the practical application in treatment of real waters with different salinity and complex compositions. Despite the great progress, there is absent of a review that emphasizes the design strategies of such materials from the point of view of structure/functionality-CDI property relationship and provides insight into the key factors in designing CDI electrode materials with enhanced performance. Herein, the effect and mechanism of pore structure and surface characteristics on the desalination performance of carbon electrode materials is firstly elucidated. Correspondingly, the Faradaic nature of intercalating materials in improving the salt removal performance is introduced. The design principles of carbon and intercalating CDI electrode for better deionization are summarized. Secondly, recent progresses in high-performance carbon electrode materials derived from graphene, metal-organic frameworks and biomass are introduced based on varied synthetic methods, relationship connecting the rational pore structure and functionalization is emphasized. Thirdly, the materials development and cell design of intercalating electrodes for improved desalination performance is highlighted. At last, the opportunities and development directions in CDI electrode materials are overviewed.