Membrane-Free Hybrid Capacitive Deionization System Based on Redox Reaction for High-Efficiency NaCl Removal

Capacitive deionization (CDI) is a promising technology for desalination due to its advantages of low driven energy and environmental friendliness. However, the ion removal capacity (IRC) of CDI is insufficient for practical application because such a capacity is limited by the available surface area of the carbon electrode for ion absorption. Thus, the development of a novel desalination technology with high IRC and low cost is vital. Here, a membrane-free hybrid capacitive deionization system (HCDI) with hollow carbon@MnO 2 (HC@MnO 2 ) to capture sodium via redox reaction and hollow carbon sphere with net positive surface charges (PHC) for chloride adsorption is introduced. The as-obtained HC@MnO 2 with unique structure and high conductivity can improve the utilization of MnO 2 pseudocapacitive electrodes. Meanwhile, the PHC can selectively adsorb Cl – and prevent the adsorption of Na + due to electrostatic repulsion. As expected, the membrane-free HCDI system demonstrates excellent desalination performance. The system’s IRC and maximum removal rate are 30.7 mg g –1 and 7.8 mg g –1 min –1, respectively. Moreover, the proposed system has a low cost because of the absence of expensive ion exchange membranes (IEM), which is suitable for practical application. The excellent performance of this HCDI makes it a promising desalination technology for future use.