Recent advances in covalent organic frameworks for capacitive deionization: A review

Capacitive Deionization (CDI) technology achieves ion immobilization through a reversible electrochemical process, gradually emerging as a substitute for conventional desalination techniques due to its simplicity, efficiency, and energy-saving advantages. Materials design has played a pivotal role in the continuous refinement and development of the CDI theoretical framework, with substantial efforts directed towards the design of high-performance novel electrode materials. Among them, Covalent Organic Frameworks (COFs) have been explored as exceptionally promising candidates. COFs represent a burgeoning class of porous crystalline materials, characterized by pronounced intrinsic features encompassing high tunability, highly ordered pore structures, elevated surface areas, and an abundance of functional sites. Consequently, it becomes more facile to tailor channels with facile ion transport and immobilization, facilitating the seamless integration of ion-selective electrochemical redox-active sites. This ultimately fulfills the design objectives for CDI materials. This comprehensive review aims to systematically and comprehensively explore the underlying design fundamentals, principles and frontiers of COFs materials for CDI. Specifically, discussions encompass the three major research challenges of enhancing intrinsic conductivity, suppressing co-ion effects and Faradaic side reactions, and delving into mechanistic studies. These insights provide valuable guidance for the future design of sustainable, high-performance, and ion-selective capacitive deionization electrode materials.