Role of the Quantum Interactions in H2 Adsorption on Late Transition Metal Chelated Linkers of Covalent Organic Frameworks

Transition metal (Tm) chelation is an effective strategy to achieve optimal binding enthalpy (▵H) of H2-adsorption in the linkers of covalent organic frameworks (COFs). The first principle-based DFT method has been implemented to determine the H2 adsorption in nine organic linkers chelated with transition metal atoms from Cr to Zn. The obtained range of binding enthalpy for single H2 adsorbed on the pure and chelated complexes is -7 to -20 kJ/mol, which is required for onboard H2 storage. The Linker-3 chelated with Ni (II) metal exhibits the most favorable binding enthalpy of approximately -18.72 kJ/mol for the single adsorbed H2 molecule, which falls within the physisorption range. Some of the complexes have shown the binding enthalpy range between physisorption and chemisorption, i. e., in that case, H2 binds via Kubas interactions. However, physisorption-based complexes are preferable to others because physisorption is a reversible process with rapid kinetics. This study reveals that the dispersion, polarization, and electrostatic interactions mainly contribute to the binding enthalpy of H2 adsorption. Molecular surface potential analysis verifies the origin of induced dipole moment in the H2 molecule, which enhances the hydrogen adsorption in transition metal chelated COFs.