Construction of 2D-2D heterojunctions of VN nanosheets within Ti3C2 nanosheets for improved flow-electrode capacitive deionization performance

Abstract

2D layered transition metal carbides (MXenes) have high hydrophilicity, high specific capacitance and excellent electronic conductivity, which have more potential for application in flow-electrode capacitive deionization (FCDI) than conventional carbonaceous electrode materials. However, the lamellar structure of MXenes is prone to stacking due to van der Waals forces between the layers, and it is also prone to oxidation, which affects its desalination capacity and service life. In this work, VN nanosheets with high electronic conductivity and specific capacity are assembled in the interlayer and surface of the Ti₃C₂ MXene. The VN nanosheets effectively alleviate the stacking of the Ti₃C₂ lamellar structure and reduce the oxidation of its surface. Meanwhile, the combination of highly conductive VN and Ti₃C₂ further accelerated the ion transfer rate, and the designed 2D-2D heterostructures had excellent desalination performance. The desalting capacity of the VN/Ti₃C₂ reached 1627.5 mg g⁻¹ in 500 mg L⁻¹ NaCl solution at an external voltage of 1.2 V.