Metal–support interaction induced electron localization in rationally designed metal sites anchored MXene enables boosted electromagnetic wave attenuation

As 5G, IoT, and AI technologies boom, electromagnetic (EM) pollution and interference have become critical challenges—demanding high-performance EM wave (EMW) absorbers that can efficiently dissipate unwanted radiation. Traditional absorbers often struggle to balance broad absorption bandwidth, strong attenuation, and thin thickness. Now, a team led by Professors Yang Yang and Wei Lu from Tongji University has published a breakthrough in Nano-Micro Letters, introducing a novel "electron localization" strategy. By anchoring nickel (Ni) nanoclusters on Ti₃C₂T_x MXene, they created Ni-MXene composites that achieve an exceptional minimum reflection loss (RL_min) of −54 dB and an ultra-wide effective absorption bandwidth (EAB) of 6.8 GHz—setting a new benchmark for MXene-based EMW absorbers.

Why This Ni-MXene Composite Stands Out

EMW absorption relies on converting EM energy into heat via dielectric or magnetic loss. MXene (Ti₃C₂T_x) is a promising absorber due to its metallic conductivity and high surface area, but its excessive conductivity causes poor impedance matching (EM waves reflect instead of penetrating), limiting performance. The Tongji team solved this by engineering electron localization—confining electron movement to enhance polarization, the key to efficient EMW dissipation:

• Electron Localization via Metal-Support Interaction (MSI): Ni nanoclusters anchored on MXene create strong MSI. This interaction disrupts MXene’s symmetric electron distribution, confining electrons to local regions. These localized electrons act as "micro-dipoles," strengthening dipole polarization and dielectric loss when exposed to alternating EM fields.
• Balanced Impedance & Attenuation: Pure MXene has too high conductivity (1.37 S m^-1), leading to reflection. Ni doping reduces conductivity to 0.33 S m^-1 (for optimal Ni3-MX), improving impedance matching (|Z_in/Z₀| ≈ 1) while preserving attenuation ability. This balance ensures EM waves penetrate the material and are fully dissipated.
• Dual Loss Mechanisms: Ni nanoclusters add weak magnetic loss (saturation magnetization = 0.459 emu g^-1 at 300 K) to MXene’s dielectric loss, further enhancing EMW absorption. In situ Raman and radar cross section (RCS) simulations confirm the composite nearly eliminates EM reflection—achieving a 17 dB m² RCS reduction at 12.2 GHz.

Core Innovation: How Ni-MXene Is Designed

The team’s synthesis is precise and scalable, tailoring Ni morphology to control electron localization:

1. MXene Preparation: Etch Ti₃AlC₂ (MAX phase) with HCl/LiF to remove Al layers, producing Ti₃C₂T_x MXene with surface vacancies and functional groups (O, OH, F)—ideal for anchoring Ni.
2. Ni Anchoring: Mix MXene with NiCl₂·6H₂O and melamine, then heat-treat at 500 °C under argon. By adjusting Ni precursor concentration, they create three morphologies:
   1. Ni Single Atoms (Ni1-MX/Ni2-MX): Dispersed Ni atoms enhance dipole polarization but lack sufficient localization.
   2. Ni Nanoclusters (Ni3-MX): ~1–2 nm Ni clusters create the strongest MSI, optimizing electron localization and polarization loss.
   3. Ni Nanoparticles (Ni4-MX/Ni5-MX): Larger particles cause excessive electron scattering, reducing conductivity and polarization.
      Advanced characterizations validate the design: spherical aberration-corrected STEM images show uniform Ni nanoclusters on MXene, while XPS confirms Ni-N-C bonds—key to stabilizing MSI and electron localization.

Performance: Ultra-Strong Absorption & Broad Bandwidth

When tested in the 2–18 GHz range (critical for 5G and radar), the Ni-MXene composites show remarkable results:

• Exceptional RL_min: Ni3-MX (Ni nanoclusters) achieves RL_min = −54 dB at 2 mm thickness—meaning 99.999% of EM waves are absorbed. This is 4x stronger than pure MXene (RL_min = −11.9 dB).
• Ultra-Wide EAB: EAB (RL ≤ −10 dB, i.e., ≥90% absorption) reaches 6.8 GHz—covering 89% of the 2–18 GHz range. For comparison, Ni single-atom MXene (Ni2-MX) only has an EAB of 4.04 GHz.
• High Stability: Even at high Ni loading (5 wt%), the composite maintains performance over cycles. Power loss density (PLD) simulations show Ni3-MX converts 15.7 × 10⁶ W m^-3 of EM energy into heat—far more than other Ni-MX samples.
• Thin & Lightweight: The optimal thickness is just 2 mm, and the composite’s low density (from MXene’s 2D structure) makes it suitable for flexible or space-constrained applications (e.g., 5G devices, aircraft stealth).

Future Impact: Beyond EMW Absorption

This work redefines how electron localization can optimize functional materials. The strategy isn’t limited to EMW absorbers—it can be applied to:

• Electromagnetic Interference (EMI) Shielding: The composite’s high conductivity and absorption ability could replace heavy metal shields in electronics.
• Catalysis & Spintronics: Electron localization modulates active sites, improving catalyst selectivity or spintronic device efficiency.
  For EMW absorption specifically, Ni-MXene composites address the long-standing trade-off between bandwidth, attenuation, and thickness. As 5G and autonomous systems demand more efficient EM management, this material could become a key component in next-generation devices.

The Tongji team’s "electron localization" approach proves that tuning electronic structure at the atomic scale is the key to high-performance EMW absorbers. By leveraging MSI to control electron movement, they’ve unlocked MXene’s full potential—paving the way for greener, more efficient solutions to EM pollution.