Green synthesis of MXene@TiO₂ nanocomposites for high-performance flexible supercapacitors: Synergistic enhancement via polypyrrole polymerization and dopant engineering

Titanium dioxide (TiO₂) is a material with high chemical stability and safety characteristics, offering a large energy storage capacity. MXene (Ti₃C₂Tₓ transition metal carbides), on the other hand, is notable for its high electrical conductivity and excellent ion transport properties. These materials serve as ideal electrode materials for high-capacity, fast-charging, and long-cycle-life batteries and supercapacitors. In this study, nanoparticles with dimensions of 13–60 nm were successfully synthesized using the green synthesis method. The interface size that enhances electrode/electrolyte interaction in supercapacitor electrode materials and the presence of materials exhibiting redox behavior increased the supercapacitor performance of polypyrrole (PPy) by 16 times. The charge storage properties of PPy/MXene, PPy/MXene/TiO₂GC, and PPy/MXene@TiO₂GC electrode materials at different concentrations and through different synthesis methods were compared. The electrode material manufactured at PPy(10 mg)/MXene@TiO₂GC(20 mg) weights exhibited a specific capacitance value of 467.7 F g⁻¹, determined at a scan rate of 5 mV s⁻¹ in the 3-electrode system. A symmetrical device was created from the electrodes formed by coating this electrode material on wearable flexible carbon felt. According to the results obtained, the highest energy density achieved was 5.0 Wh/kg at 0.1 mA cm⁻², and the highest power density value achieved was 1000 W/kg at 1.0 mA cm⁻². It was observed that the symmetrical supercapacitor with 10,000 cycles retained 82.03 % of its capacitance.