▎ 摘　　要

Currently, hybrid capacitive deionization (HCDI) with faradaic material cathode and active carbon (AC) anode has attracted much attention due to its very excellent desalination performance even in highly-concentrated saline water. However, the carbon oxidation reaction occurring at a potential of 0.7-0.9 V in a CDI system still exists at the carbon anode in a HCDI system, which causes the performance degradation during long-term operation. Introducing costly ion exchange membranes has been reported to solve this issue. In this work, we report a more simple and cost-saving approach to improve the desalination performance of membrane-free HCDI cell by using nickel hexacyanoferrate/reduced graphene oxide (NiHCF/rGO) cathode which possesses high theoretic capacity and low Na+ intercalation/extraction potential at a low voltage operation (0.6 V). A high desalination capacity of 22.8 mg g(-1) is achieved for this membrane-free HCDI cell, higher than those for the conventional AC//AC CDI cell. More importantly, the AC//NiHCF/rGO cell shows a stable cycling performance with a capacity retention of 78% at 0.6 V over 100 desalination-regeneration cycles, significantly improved compared with that at 1.2 V. The strategy should provide a helpful guidance for practical CDI operation.