Tricycloquinazoline-based monolayer conjugated metal–organic frameworks as promising hydrogen storage media: A theoretical investigation

The pursuit of sustainable energy has driven a significant interest in hydrogen (H₂) as a clean fuel alternative. A critical challenge is the efficient storage of H₂, which this study addresses by examining the potential of tricycloquinazoline-based monolayer metal–organic frameworks (MMOFs with the first “M” representing metal species). Using density functional theory, we optimized the structures of MMOFs and calculated H₂ adsorption energies above the open metal sites, identifying ScMOF, TiMOF, NiMOF, and MgMOF for further validation of their thermodynamic stability via ab-initio molecular dynamics (AIMD) simulations. Force field parameters were fitted via the Morse potential, providing a solid foundation for subsequent grand canonical Monte Carlo simulations. These simulations revealed that the maximum of saturated excess gravimetric H₂ uptake exceeds 14.16 wt% at 77 K, surpassing other reported MOFs, whether they possess open metal sites or not. At 298 K and 100 bar, both the planar and distorted structures derived from our AIMD simulations demonstrated comparable excess gravimetric H₂ uptake within the range of 3.05 wt% to 3.94 wt%, once again outperforming other MOFs. Furthermore, lithium (Li) doping significantly enhanced the excess H₂ uptake, with Li-TiMOF achieving an impressive 6.83 wt% at 298 K and 100 bar, exceeding the ultimate target set by the U.S. Department of Energy. The exceptional H₂ adsorption capacities of these monolayer MOFs highlight their potential in H₂ storage, contributing to the design of more efficient hydrogen storage materials and propelling the sustainable hydrogen economy forward.