A model study of effect of M = Li +, Na +, Be 2+, Mg 2+, and Al 3+ ion decoration on hydrogen adsorption of metal-organic framework-5

Abstract

The effect of light metal ion decoration of the organic linker in metal-organic framework MOF-5 on its hydrogen adsorption with respect to its hydrogen binding energy (ΔB.E.) and gravimetric storage capacity is examined theoretically by employing models of the form MC 6H 6: nH 2 where M = Li +, Na +, Be 2+, Mg 2+, and Al 3+. A systematic investigation of the suitability of DFT functionals for studying such systems is also carried out. Our results show that the interaction energy (ΔE) of the metal ion M with the benzene ring, ΔB.E., and charge transfer (Q trans) from the metal to benzene ring exhibit the same increasing order: Na + < Li + < Mg 2+ < Be 2+ < Al 3+. Organic linker decoration with the above metal ions strengthened H 2-MOF-5 interactions relative to its pure state. However, amongst these ions only Mg 2+ ion resulted in ΔB.E. magnitudes that were optimal for allowing room temperature hydrogen storage applications of MOF-5. A much higher gravimetric storage capacity (6.15 wt.% H 2) is also predicted for Mg 2+-decorated MOF-5 as compared to both pure MOF-5 and Li +-decorated MOF-5.