  The storage of hydrogen gas (H$_2$) has presented a significant challenge
that has hindered its use as a fuel source for transportation. To meet the
Department of Energy's ambitious goals of achieving $50$ g L$^{-1}$ volumetric
and $6.5$ wt \% gravimetric uptake targets, materials-based approaches are
essential. Designing materials that can efficiently store hydrogen gas requires
careful tuning of the interactions between the gaseous H$_2$ and the surface of
the material. Metal-Organic Frameworks (MOFs) and Covalent-Organic Frameworks
(COFs) have emerged as promising materials due to their exceptionally high
surface areas and tunable structures that can improve gas-framework
interactions. However, weak binding enthalpies have limited the success of many
current candidates, which fail to achieve even $10$ g L$^{-1}$ volumetric
uptake at ambient temperatures. To overcome this challenge, We utilized quantum
mechanical (QM) based force fields (FF) to investigate the uptake and binding
enthalpies of 3 linkers chelated with 7 different transition metals (TM),
including both precious metals (Pd and Pt) and first row TM (Co, Cu, Fe, Ni,
Mn), to design 24 different COFs in-silico. By applying QM-based FF with grand
canonical Monte Carlo (GCMC) from 0-700 bar and 298 K, We demonstrated that
Co-, Ni-, Mn-, Fe-, Pd-, and Pt-based MSUCOFs can already achieve the
Department of Energy's hydrogen storage targets for 2025. Surprisingly, the
COFs that incorporated the more affordable and abundant first-row TM often
outperformed the precious metals. This promising development brings us one step
closer to realizing a hydrogen-based energy economy.
