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

Wang, Shiyong, Wang, Gang, Wu, Tingting, Li, Changping, Wang, Yuwei, Pan, Xin, Zhan, Fei, Zhang, Yunqi, Wang, Shuaifeng, Qiu, Jieshan
Environmental science & technology 2019 v.53 no.11 pp. 6292-6301
absorption, adsorption, carbon, carbon electrodes, deionization, desalination, electrostatic interactions, energy, ion-exchange membranes, manganese dioxide, redox reactions, sodium, sodium chloride, surface area
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@MnO₂ (HC@MnO₂) 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@MnO₂ with unique structure and high conductivity can improve the utilization of MnO₂ 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.