Electrochemical and Defect Characterization of APTES-Functionalized Ti₃C₂T_x MXene for Supercapacitor Devices

This work comprehensively investigates the structural, surface, and electrochemical properties of MAX phase, MXene, and (3-aminopropyl)triethoxysilane-functionalized MXene (APTES-MXene) electrodes. The study developed a high-performance electrode design by APTES functionalization without incorporating conductive polymers, metal oxides, or carbon additions. The findings in the two-electrode system revealed that the APTES-MXene electrode exhibited a specific capacitance of 207.62 F g^-1, an energy density of 28.83 Wh kg^-1, and a capacity retention of 93.8%. The Dunn approach is utilized to determine the pseudo-capacitive contribution, demonstrating that the surface-controlled charge storage mechanism is dominant, with the capacitive contribution reaching 70.61%. The increase in charge transfer resistance following APTES modification in the EIS data signifies the creation of a more complicated ion transport structure due to the functional surface groups of the material and an extended interlayer distance. The increased capacity and cycle stability obtained can be attributed to the multifaceted influence of APTES on surface chemistry and ion accessibility. This study investigates the application of functionalized MXene in energy storage systems and highlights the significance of two-electrode measurements in assessing material performance under realistic operating conditions.