Akademik Veri Yönetim Sistemi
Computational Materials Science, cilt.267, 2026 (SCI-Expanded, Scopus)
Reversible hydrogen storage on single-site platforms requires interactions strong enough to offset the gas-to-adsorbate entropy penalty, yet weak enough to avoid H2 activation. Here we investigate a scandium metalloporphyrin (Sc-MP) as a model single-site adsorbent for multi-H2 loading (n = 1–20) using dispersion-corrected DFT (ωB97X-D/def2-TZVP) combined with a van't Hoff thermodynamic analysis. Across all coverages, the optimized geometries show strictly molecular adsorption: H-H bond lengths remain near the gas-phase value (0.74–0.76 Å), the proximal Sc···H2 contact is essentially load-invariant (2.33–2.50 Å), and a distal shell with Sc···H2 ≥ 5 Å emerges beyond n = 9, evidencing a compact first shell plus a weakly coupled second shell. The average adsorption energy per H2 decreases from −0.157 eV (n = 1) to −0.012 eV (n = 20), while the adsorption enthalpy |ΔH| weakens from 17.6 to 2.2 kJ mol−1 and ΔG(298 K, 1 bar) remains positive. Entropies extracted from ΔH/ΔG (−95 to −76 J mol−1 K−1) feed a van't Hoff treatment that yields a quantitative T–p map: at 77 K and 1–10 bar, moderate reversible loadings (upper-bound n = 4–6) are thermodynamically favored, whereas at 150 K only n = 1 is stable. Electronic-structure signatures, an essentially constant HOMO–LUMO gap (3.95–3.97 eV), modest charge redistribution on Sc (+1.16 → +0.40 |e|), and PDOS with weak H- s intensity and no σ*(H2) band, corroborate a polarization-dominated, weak-Kubas regime. Sc-MP thus provides a cluster-resistant single-site scaffold that supports reversible cryogenic storage (up to 10.24 wt% H2-only) and suggests concrete design levers: modest field tuning to strengthen early adsorption toward the 15–20 kJ mol−1 window and reticulation into porphyrinic frameworks to increase site density while preserving single-site character.