Carbon nanotube-based materials as capacitive deionization electrodes
Capacitive deionization (CDI) is an emerging desalination technology that removes dissolved salts from brackish water via ion electrosorption at electrically charged electrode interfaces. It has gained recognition as a sustainable and cost-effective alternative to conventional methods such as reverse osmosis, electrodialysis, and thermal distillation, which often suffer from high energy consumption and environmental impact. Among electrode materials, carbon nanotubes (CNTs) are particularly attractive due to their high specific surface area, superior electrical conductivity, and excellent electrochemical stability. This review comprehensively analyzes recent advances in performance optimization strategies for CNT-based CDI electrodes, including material engineering and structural design. Key strategies include hybridization with activated carbon, graphene, metal oxides, and metal-organic frameworks (MOFs), as well as surface functionalization and three-dimensional architecture construction. These approaches enhance salt adsorption capacity, charge efficiency, and cycling stability. For instance, dispersing CNTs in activated carbon electrodes improves conductivity and ion transport, while MOF-derived nitrogen-doped carbon/CNT heterostructures exhibit high desalination performance. The review also evaluates the pivotal role of CNT-based electrodes in driving technological progress in CDI and discusses persistent challenges such as electrode fouling, scalability, and cost-effectiveness. Promising research directions, including flow-electrode systems and selective ion removal, are highlighted to overcome current limitations. Overall, CNT-based materials hold significant promise for advancing CDI as a viable water purification technology.