Electrospun sodium Titanate-MXene/Carbon nanofibers as Binder-Free electrode for enhanced hybrid capacitive deionization

Abstract

Sodium titanate (Na₂Ti₃O₇, NTO) is a promising electrode material for sodium storage in capacitive deionization (CDI) applications due to its open, tunnel-like layered structure, which facilitates the rapid transport and storage of Na⁺ ions. However, its poor electronic conductivity and significant volume changes during the Na⁺ insertion/extraction process limit its practical application. Constructing an NTO composite with high electronic conductivity is an effective strategy to address these issues. In this work, flexible and self-supporting NTO-MXene/CNF films were prepared using electrospinning, carbonization, and hydrothermal methods. In these films, MXene is either embedded within the CNFs or overlapped on their surface, forming a conductive network that significantly reduces the resistance of the composite film to less than 3.6 Ω. The NTO, derived from part of the MXene, grows in situ on the surface of the MXene, effectively addressing the issues of NTO agglomeration and poor conductivity while also enhancing the hydrophilicity of the composite film. As a result, the NTO-MXene/CNF films exhibit self-supporting properties and excellent CDI performance. The optimized NTO-MXene/CNF film demonstrates an impressive desalination capacity of 49.3 mg g⁻¹ and a rapid desalination rate of 9.9 mg g⁻¹ min⁻¹ under a constant voltage mode of 1.2 V and an initial conductivity of 500 μS cm⁻¹ in saline solution, along with good cycling stability. The insights gained from this work will provide valuable guidance for the development of novel flexible composite films with high desalination performance for applications in the CDI field.