Synergistic graphene–MXene heterostructures for enhanced energy storage in supercapacitors

Abstract

The restacking of Ti3C2Tx 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 (Ti3C2Tx)/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 Ti3C2Tx 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 Ti3C2Tx 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 Ti3C2Tx/graphene composite enhances the density of states at the Fermi level, facilitating significant charge transfer from Ti3C2Tx 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.