Multi-Binding Sites United in Covalent-Organic Frameworks (MSUCOF) for H₂ Storage and Delivery at Room Temperature

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, material-based approaches are essential. Designing materials that can efficiently store hydrogen gas requires careful tuning of the interactions between 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 tuneable 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 (FFs) to investigate the uptake and binding enthalpies of three linkers chelated with seven different transition metals (TMs), including both precious metals (Pd and Pt) and first row TM (Co, Cu, Fe, Ni, and Mn), to design 24 different COFs in silico. By applying QM-based FF with grand canonical Monte Carlo from 0 to 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.