CO₂ adsorption via charge-state engineering in transition metal-doped germanium clusters-a DFT study

Understanding and optimizing CO₂ activation at the nanoscale is essential for the rational design of efficient catalysts for carbon capture and conversion. In this work, density functional theory calculations demonstrate that the CO₂ adsorption and activation performance of transition metal-doped Ge₁₂ nanoclusters (TM = Co, Pd, Tc, Zr) is strongly governed by their charge state. Anionic TM@Ge₁₂⁻ clusters exhibit substantially higher binding energies (-2.49 to -2.80 eV) than cationic systems (-1.36 to -1.71 eV), resulting in enhanced stability and stronger electronic coupling. CO₂ adsorption on anionic clusters is highly exergonic (- 0.53 to - 1.80 eV) and is accompanied by pronounced molecular bending, C-O bond elongation, and significant charge transfer into the CO₂ π* orbitals, indicating effective chemisorption and activation. In contrast, cationic TM@Ge₁₂⁺ clusters show weaker, near-physisorptive interactions (- 0.28 to - 0.48 eV). Reactivity analysis reveals reduced chemical hardness and increased softness for anionic systems, consistent with higher polarizability and reactivity. Among the studied clusters, Co@Ge₁₂⁻, Pd@Ge₁₂⁻, and Zr@Ge₁₂⁻ emerge as the most promising candidates for efficient CO₂ activation. These findings highlight charge-state engineering as a viable strategy for tailoring nanoscale catalysts for CO₂ capture and conversion.

All calculations were performed using density functional theory (DFT) as implemented in the Gaussian 16 software package. The B3LYP exchange-correlation functional was employed for all geometry optimizations and electronic structure calculations. All atoms were described using the LANL2DZ effective core potential (ECP) basis set. Frequency calculations were carried out to confirm the nature of the stationary points. Binding energies, adsorption energies, charge transfer analysis, and global reactivity descriptors were computed at the same level of theory.