Engineering electronic structures of Nb₆I superatomic clusters by metal atom incorporation: a first-principles study

Area of Science:

• Materials Science
• Computational Chemistry
• Catalysis

Background:

• Niobium-iodide (Nb6I) octahedron clusters serve as versatile superatomic building blocks for advanced materials and catalysts.
• Precise tuning of cluster properties is achievable through atom-by-atom substitution, impacting magnetic and electronic characteristics.

Purpose of the Study:

• To investigate the feasibility of tuning the valence electron concentration (VEC) in Nb6I clusters by endohedral doping with 3d-block transition metals (M = Sc-Zn).
• To analyze the structural stability, electronic properties, and catalytic potential of these doped clusters for the hydrogen evolution reaction (HER).

Main Methods:

• State-of-the-art density functional theory (DFT) calculations were employed.
• Energetics, cohesive energy per atom, and formation energy (FE) were analyzed for various structural isomers.
• HSE06 hybrid functionals were used to determine the HOMO-LUMO gap; Gibbs free energy of hydrogen adsorption (ΔGH) was correlated with d-band centers.

Main Results:

• Endohedral doping of most 3d transition metals (except Sc, Ti) into Nb6I clusters is energetically feasible, with high iodine concentrations.
• Clusters with 18 and 24 VEC exhibit electronic shell closures and significant HOMO-LUMO gaps (0.72–1.76 eV).
• MNb6I18 clusters demonstrate robust formation stability under M-rich conditions. Promising HER catalytic activity was observed for VNb6I18 to CoNb6I18, comparable to Pt(111).

Conclusions:

• Endohedral doping offers a viable route to tune the atomic structure, stability, and electronic properties of Nb6I clusters.
• These doped clusters present significant potential as catalysts for the hydrogen evolution reaction.
• The findings pave the way for applications in catalysis, molecular electronics, spintronics, and further experimental validation.