The recently developed techniques for desalination and wastewater treatment are costly and unsustainable. Therefore, a cost-effective and sustainable approach is essential to achieve desalination through wastewater treatment. Capacitive deionization (CDI), an electrochemical desalination technology, has been developed as a novel water treatment technology with great potential. The electrode material is one of the key factors that promotes the development of CDI technology and broadens the scope of CDI applications. Biochar-based electrode materials have attracted increasing attention from researchers because of their advantages, such as environmentally friendly, economical, and renewable properties. This paper reviews the methods for preparing biochar-based electrode materials and elaborates on the mechanism of CDI ion storage. We then summarize the applications of CDI technology in water treatment, analyze the mechanism of pollutant removal and resource recovery, and discuss the applicability of different CDI configurations, including hybrid CDI systems. In addition, the paper notes that environmentally friendly green activators that facilitate the development of pore structure should be developed more often to avoid the adverse environmental impact. The development of ion-selective electrode materials should be enhanced and it is necessary to comprehensively assess the impact of heteroatoms on selective ion removal and CDI performance. Electrooxidation of organic pollutants should be further promoted to achieve organic degradation by extending to redox reactions.
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