Hydrogen Adsorption on Transition-Metal-Decorated Graphene: Thermodynamic and AIMD Insights from DFT and Post-Hartree–Fock Methods

High Resolution Image Download MS PowerPoint Slide Hydrogen adsorption on transition-metal-decorated graphene was investigated using a finite graphene nanoflake model combined with revPBE-D4 geometry optimizations and ωB97M-V single-point energies, complemented by PNO–CCSD(T) and DLPNO–CCSD(T) benchmarks for representative systems. Particular attention was paid to the role of spin-state effects and finite-size electronic structure, which are often neglected in periodic models. Electronic-structure analysis reveals size-dependent open-shell character in graphene nanoflakes ─one larger (G) and one smaller (G2)─where G exhibits robust, where G exhibits robust multiconfigurational singlet behavior and G2 a weaker, functional-dependent tendency. CASSCF/NEVPT2 calculations support this picture and corroborate the high-spin assignments of Sc–G and Y–G. Among the metals examined, Y, Nb, and Pd exhibit strong binding to graphene (−0.67 to −1.02 eV), whereas Sc, Zr, and Ni show moderate stabilization. Hydrogen adsorption is strongly system-dependent: the first H 2 adsorption is exergonic for Y, Zr, Nb, Ni, and Pd (−0.56 to −1.63 eV), while Sc becomes favorable only upon adsorption of a second H 2 molecule. In contrast, additional H 2 uptake is generally disfavored for Y, Nb, and Ni, and only moderately favorable for Zr (−0.32 eV) in the second adsorption step. Three representative systems (Pd, Zr, and Sc), spanning distinct bonding regimes─molecular adsorption, dissociative hydride formation, and high-spin configurations─were used to assess the methodology, with ωB97M-V//revPBE-D4 showing close agreement with coupled-cluster interaction energies within these cases. AIMD simulations on Sc–G–2H 2 and Pd–G–H 2 reveal distinct finite-temperature responses: desorption of one H 2 molecule and metal mobility in the Sc system versus persistent H 2 coordination with bond elongation in the Pd case. Overall, the results show that hydrogen adsorption on TM-decorated graphene nanoflakes depends sensitively on the interplay between metal identity, spin state, and finite-size electronic structure.