In-situ-derived carbon coated sea urchin-like Na3V2(PO4)3 from V2C MXene for high-performance capacitive deionization

Cathode materials with high capacity and cyclic durability are urgently needed for capacitive deionization. Na3V2(PO4)3 is an emerging pseudocapacitive candidate for this process on account of its high capacity and Na+ reversible insertion, while it suffers from the intrinsic low electrical conductivity and small electrolyte-accessible surface area. Herein, a sea urchin-like Na3V2(PO4)3 @carbon (NVP@C) compound material was synthesized from MXene-V2C via hydrothermal method followed by annealing treatment, and then assembled as capacitive deionization (CDI) electrode material. Benefiting from three-dimensional sea urchin-like structure, where the nanoneedles of NVP@C serve as fast transport channel for Na+, NVP@C performed high specific capacity (437 F g−1 at 5 mV s−1) and fast ionic diffusion kinetics. Moreover, the NVP@C showed attractive desalination performance as cathode material for CDI, achieving a remarkable adsorption capacity of 74.0 mg g−1 in a NaCl salt solution (1000 mg L−1) and long life cycle stability. The present work provides a novel perspective to construct practical redox-active and stable CDI electrode with 3D structure from MXene for highly capacitive and durable desalination application.