Rational design of metal-doped graphdiyne for hydrogen storage: A comparative DFT investigation

Hydrogen storage materials require a balance between hydrogen uptake and adsorption strength. Here, density functional theory (DFT) calculations were performed to investigate H 2 adsorption on a finite hydrogen-terminated graphdiyne (GDY) cluster and its Ca-, Zn-, Ga-, La-, and Y-doped derivatives. B3LYP-D3 calculations with basis set superposition error (BSSE) correction were combined with formation energy, frontier molecular orbital (FMO), partial density of states (PDOS), molecular electrostatic potential (MESP), natural bond orbital (NBO), and noncovalent interaction (NCI) analyses. The BSSE-corrected H 2 adsorption energies for pristine GDY, CaGDY, GaGDY, LaGDY, YGDY, and ZnGDY were 3.47, −7.74, −9.20, −11.21, −21.88, and −3.85 kJ/mol, respectively. YGDY showed the strongest interaction, with an H 2 –Y distance of 2.38 Å and a highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gap of 0.48 eV, compared with 2.61 eV for pristine GDY. NBO analysis yielded an E 2 value of 90.30 kcal mol −1 for the C–Y→σ*(H 2 ) interaction, while the Y atomic charge changed by −0.155e, these results indicate enhanced interaction at the Y site. Sequential adsorption showed favorable adsorption of up to seven H 2 molecules, corresponding to hydrogen storage capacity (HSC) of 1.57 wt%. The incremental adsorption energy became positive for the eighth H 2 molecule. For YGDY, the enthalpy change (ΔH), entropy change (ΔS), and Gibbs free energy change (ΔG) at 298.15 K and 1 atm were −23.28 kJ mol −1 , −0.106 kJ mol −1 K −1 , and +8.32 kJ mol −1 , respectively. Overall, Y substitution modifies the electronic structure and H 2 adsorption of the finite GDY, while storage capacity remains theoretical.