Interaction of hydrogen molecules with polycyclic aromatic hydrocarbons modified with Zr atoms: different modifications yield distinct properties

Ability of polycyclic aromatic hydrocarbons (PAH), namely coronene (C 24 H 12 ), circumcoronene (C 54 H 18 ) and circumpyrene (C 42 H 16 ) modified with Zr atoms to bind H 2 molecules is investigated using density functional theory. It is shown that PAHs doped with Zr atoms show different H 2 binding properties than the ones decorated with Zr atoms. The studied Zr-doped PAHs are able to bind up to seven H 2 molecules per one Zr atom via weak chemisorption regardless of their size (number of C atoms). Calculated gravimetric H 2 densities of Zr-doped PAHs increase in the following order: Zr-circumcoronene (1.9 wt%) < Zr-circumpyrene (2.3 wt%) < Zr-coronene (3.7 wt%). In the case of Zr-decorated PAHs, the first H 2 molecule undergoes dissociation upon interaction with Zr atom, with an energy outcome of approximately –160 kJ mol –1 . Additional five H 2 molecules can be bound to Zr-decorated PAH either by Kubas interaction or physisorption. The H 2 binding capacity of these systems can be increased by decoration with Zr atoms from both sides of the PAH backbone. In particular, coronene decorated with two Zr atoms is able to bind up to twelve H 2 molecules, corresponding to gravimetric density of 5.0 wt%.