Design principles to exceed the DOE 2017 standards for delivery and storage of H_2 at room temperature using nitrogen bases covalent organic frameworks

Physisorption in porous materials is a promising route to meet mol. hydrogen (H_2) storage and delivery requirements for \ntransportation because it is both fast and fully reversible at mild conditions. However, most current candidates have binding \nenthalpies to H_2 that are too small, which lead to volumetric capacity at 298 K of less than 10 g/L compared to the system \ntarget of 40 g/L. Using accurate quantum mech. (QM) methods, we det. the H_2 binding enthalpy of 48 compds. (5 linkers and \n11 different transition metals) used for porous covalent org. frameworks (COF) which we metalated with different transition \nmetals (TM) , including first row TM (Sc though Cu) and precious TM (Pd and Pt) . We showed that first row TM give similar and \nsometimes superior van der Waals interactions with H_2 than precious TMs. Based on these results, we constructed 26 new \nCOFs based on these linkers and we det. the uptake using force fields (FF) based on QM and grand canonical Monte Carlo \nsimulations. We detd. new COFs that reach the DOE 2017 target of 40 g/L. This work highlights the designing principles for \nthe optimal interaction enthalpy in the next generation of H_2 storage materials.