Ti₃C₂T_x-MXene based 2D/3D Ti₃C₂–TiO₂–CuTiO₃ heterostructure for enhanced pseudocapacitive performance

Ti₃C₂T_x MXene family is a promising electrode material for electrochemical energy storage, but it suffers from insufficient pseudocapacitive charge storage because of self-aggregation and oxidation degradation. To resolve the issue, this paper proposes a two-step process for synthesizing oxidation-controlled MXene-derived 2D/3D heterostructures that beneficially utilize oxidation and simultaneously improve conductivity. The first step generates in-situ 3D floral Ti₃C₂– TiO₂ nanoribbons under partial oxidation of MXene. As the second step, further controlled oxidation with Cu ions transforms the 3D floral Ti₃C₂–TiO₂ nanoribbons into 2D/3D Ti₃C₂–TiO₂–CuTiO₃ heterostructure. Leveraging the synergistic effects of MXene, TiO₂, and CuTiO₃, this 2D/3D heterostructure enhances the interlayered spacing, redox-active site concentration and alleviates low conductivity issue associated with TiO₂ nanoribbons. At 2 mA/cm², the proposed 2D/3D Ti₃C₂–TiO₂–CuTiO₃ heterostructure achieved a significantly higher capacitance of 599.2 mF/cm², compared to MXene with a capacitance of 249.16 mF/cm² and 3D floral Ti₃C₂–TiO₂ nanoribbons with 498.5 mF/cm². For practical evaluation, an asymmetric supercapacitor (ASC) device (Ti₃C₂–TiO₂–CuTiO₃//AC) was fabricated, which exhibited an energy density of 31.1 Wh/kg, power density of 1041.7 W/kg and capacitance retention of 83.7 % after 5000 continuous charging/discharging cycles. It opens new avenues for utilizing controlled oxidation to enhance pseudocapacitive properties.