Elevating electrochemical, electrical, anti-corrosion features and investigation of excitation dependent optoelectronic properties of binder free Fe decorated Ti2NTx MXene heterostructures

Two-dimensional (2D) nitride MXenes are promising candidates for energy storage, corrosion protection, and optoelectronics, but their practical use is limited by layer restacking, structural instability, and insufficient active sites. Herein, we report the synthesis of binder-free Fe-decorated Ti₂NT_x MXene heterostructures via fluoride salt etching followed by in situ chemical reduction. Fe incorporation introduces redox-active centres (Fe²⁺/Fe³⁺, Fe/Fe²⁺), stabilises the MXene surface through Fe–Ti and Fe–N bonding, and alters the defect-state distribution responsible for excitation-dependent photoluminescence (PL). The optical band gap narrowed from 4.78 eV in Ti₂AlN MAX to 3.7 eV in Ti₂NT_x MXene and was further tuned from 3.57 to 5.35 eV in Fe@Ti₂NT_x heterostructures. PL analysis confirmed the presence of shallow defect states (blue emission ∼470 nm) and deep-level defects (green/yellow emission ∼530–580 nm), with Fe decoration suppressing Al-related traps and stabilizing defect distributions across excitation wavelengths. X-ray photoelectron spectroscopy (XPS) deconvolution further confirmed the coexistence of Ti–N, Ti–O, Fe–Ti, Fe–Fe, and Fe–N bonding configurations, highlighting strong electronic interactions between Fe and the Ti₂NT_x host. The optimized 1 mM Fe@Ti₂NT_x electrode delivered a specific capacitance of 124.53 F/g at 1 A g⁻¹ and 57.08 F/g at 0.005 V/s, with 97.25 % retention after 10,000 cycles. Corrosion current was reduced to 0.28 μA with a suppressed corrosion rate of 1.49 × 10⁻⁹ mm y⁻¹ in 1 M H₂SO₄. These results establish Fe@Ti₂NT_x MXene as a multifunctional heterostructure with enhanced charge storage, durability, and defect-engineered optoelectronic response.