Exploring the Electronic and Atomic Structures of Fe2O3 Nanoparticles Grown on Ti3C2Tx MXene for Flexible Supercapacitor 

Ti₃C₂Tₓ (MXene), a two-dimensional material derived from titanium carbide, exhibits excellent electrical conductivity, high surface area, and outstanding energy storage capability. These properties make MXene highly promising for applications in energy storage, electrocatalysis, and composite materials.

In this study, Fe2O3 nanoparticles (NPs) were integrated with MXene at specific volume ratios (Fe₂O₃/MXene-X, where X = 0.5, 1, and 2) to fabricate Fe2O3 NPs@MXene nanocomposites. Their electronic and atomic structures were investigated to evaluate their electrochemical performance for supercapacitor applications.

X-ray diffraction (XRD) patterns confirmed the coexistence of characteristic peaks from both Fe2O3 and MXene in all Fe2O3 NPs@MX composites. Transmission electron microscopy (TEM) images revealed visible lattice fringes, and further analysis indicated that the lattice spacings correspond to the crystal planes of Fe2O3, confirming the successful growth of Fe2O3 nanoparticles on the MXene surface.

Cyclic voltammetry (CV) tests showed that Fe2O3 /MXene-1 exhibited more symmetric curves with mild redox peaks. Its larger CV area indicated higher specific capacitance and enhanced energy storage capability. Galvanostatic charge-discharge (GCD) measurements demonstrated that Fe2O3 /MXene-1 displayed nearly symmetric triangular curves with longer discharge times, reflecting superior capacitance and ideal capacitive behavior.

Electrochemical impedance spectroscopy (EIS) results showed that Fe2O3 /MXene-0.5 and Fe2O3 /MXene-1 possessed lower internal resistance (Rs) and charge transfer resistance (Rct), indicating excellent conductivity and fast ion/electron transport.

The X-ray absorption near-edge structure (XANES) in Fe K-edge indicated that the Fe in these samples is primarily in the 3+. A shift of the absorption edge toward lower energy in Fe2O3 /MXene-2 suggested a slightly lower oxidation state compared to Fe2O3 /MXene-0.5 and Fe2O3 /MXene-1.

The extended X-ray absorption fine structure (EXAFS) results revealed Fe-O and Fe-Fe/Ti bond lengths of ~1.5 Å and ~2.6 Å, respectively. In the first Fe-O shell, Fe2O3/MXene-1 has a stronger peak compared to the other two samples, which means that Fe2O3/MXene-1 has a higher coordination number or lower structural disorder. A trend also observed in the Ti K-edge spectra.

Additionally, Fe, Ti L3,2-edge XANES measurements were used to explore further the electronic structures associated with 3d orbitals in these samples. These detailed structural insights are valuable for optimizing Fe2O3/MXene nanocomposites for enhanced supercapacitor applications.