Modeling the Hydrogen Storage Materials with Exposed M²⁺ Coordination Sites

Abstract

Recent experimental work has shown that exposed coordination sites of metals can enhance the binding of hydrogen in nanoporous inorganic and hybrid inorganic−organic framework materials. First principles calculations have been carried out on molecular analogs of such sites in order to compare the binding of dihydrogen molecules to Ni²⁺ and Mg²⁺. The binding to Mg²⁺ is found to be 1 kJ/mol or less, whereas that to Ni²⁺ varies between 6 and 23 kJ/mol, depending on the geometrical arrangement of the ligands. Analysis of the computational results shows that the preferred binding to Ni²⁺ is consistent with the general binding mode of H₂ to metal centers. The implications of these results for the design of superior materials for hydrogen storage are discussed.