Cold sintered TiO2–Ti3C2Tx MXene nanocomposites for supercapacitor electrode materials†

MXene-based materials exhibit unique electrochemical properties due to their 2D layered structure with high surface areas, making them ideal candidates for electrode materials in advanced electrochemical energy storage systems. The capacitive properties of Ti₃C₂T_x MXenes (T_x denotes the surface terminator group, such as –F, –OH, and O) can be enhanced by decorating surface layers with transition metal oxides, such as TiO₂. Conventional in situ synthesis methods lack precise control over the TiO₂ content within the MXene structure. In this study, a contemporary cold sintering process (CSP) was employed to fabricate the TiO₂–Ti₃C₂T_x nanocomposite, enabling a controlled amount of TiO₂ particle addition into the MXene matrix. Consequently, it provided a means to correlate the electrochemical performance of the nanocomposites with the TiO₂ content. Through the CSP, the nanocomposites were fabricated at low temperature (150 °C) and pressure (150 MPa) assisted by a transient liquid, achieving high relative density (>85%). The electrochemical performance analysis revealed an increase in specific capacitance with increasing TiO₂ content, reaching up to 117 F g⁻¹ for (40 wt%) TiO₂/MXene at a 10 mV s⁻¹ scan rate surpassing that of the pristine MXene (55.29 F g⁻¹). Additionally, the charge transfer resistance substantially declined from 4.01 Ω cm² for the pristine MXene to as low as 0.51 Ω cm² for (40 wt%) TiO₂/MXene. Surprisingly, the nanocomposite samples demonstrated more than a 200% increase in the specific capacitance after 1000 charging–discharging cycles at 1.5 A g⁻¹, attributed to the ion intercalation and surface terminator group (T_x) alteration in MXenes. Overall, this study highlights the application of the CSP as a valuable tool for precisely tailoring the electrochemical properties of TiO₂–Ti₃C₂T_x MXene nanocomposites.