Synergistic graphene-MXene heterostructures for enhanced energy storage in supercapacitors

The restacking of Ti₃C₂T _x MXene nanosheets prevents ions from being accessible and restricts the practical charge-storage performance of MXene-based supercapacitor electrodes. This study aims to explore the growth of MXene (Ti₃C₂T _x )/graphene composites with controlled graphene contents, synthesized using a simple one-step ultrasonication method. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR) were performed to characterize the as-synthesized MXene/graphene composites and ascertain the successful incorporation of graphene-like honeycomb flakes into the Ti₃C₂T _x sheets. The electrochemical evaluation of fabricated samples was investigated using galvanostatic charge-discharge (GCD), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) techniques. Among all the fabricated electrodes, the MG-II composites with 30% filler concentration within the MXene sandwich structure demonstrated a greater specific capacitance of 366.3 F g^-1 when subjected to a current density of 0.5 A g^-1. This electrode material also exhibited satisfactory cycling stability, with approximately 85.39% retention following 5000 cycles at 1 A g^-1 with a coulombic efficiency value of 91.69%. In comparison to pristine graphene and Ti₃C₂T _x materials, the as-synthesized composites have shown increased specific capacitance, cycle stability, capacitance retention, coulombic efficiency, and the synergistic interfacial effects of both the two-dimensional structures. Additionally, in the assembly of an asymmetric supercapacitor (ASC), MG-II is utilized as the cathode and activated carbon as the anode. The manufactured device achieved an impressive energy density of 41.95 Wh kg^-1, leading to a power density of 1000 W kg^-1, and exhibited 86.6% capacity retention following 10 000 cycles. First-principles density functional theory (DFT) computations revealed enhanced charge mobility through a combination of conduction and valence bands. Analysis of the total density of states (TDOS) and orbital contributions indicated that the Ti₃C₂T _x /graphene composite enhances the density of states at the Fermi level, facilitating significant charge transfer from Ti₃C₂T _x to graphene, suggesting improved electronic properties. These results highlight that MXene/graphene shows promise as a reliable, high-performing electrode material for advanced energy storage applications.