Tunable H2 binding on alkaline and alkaline earth metals decorated graphene substrates from first-principles calculations

Based on first-principles calculations, the H2 adsorptions onto six types of modified graphene substrates decorated with light metals (Li, Na, K, Be, Mg, Ca) are investigated to shed light on the factors affecting the H2 binding energies. It is demonstrated that the introduction of defects and dopants into graphene substrates is essential to prevent the metal clustering and achieve dispersed metal atoms desirable for H2 adsorption. The interaction between H2 and alkali/alkali-earth metal decorated graphene systems is attributed to the electrostatic effect induced by polarized dipole--dipole interaction. Via introducing defects and hetero-atoms to modify the electronegativity of the local structure, the H2 adsorption energy can be tuned by choosing the combination of suitable metals and substrates. The calculated H2 binding strength is positively correlated to the charge transfer from the metal to the substrates and the dipole momentum of metal decorated substrates. Compared the cases with different metals decoration, Mg and Ca are expected to the most promising candidates for multiple H2 adsorptions.