Uptake of $H_2$ and $CO_2$ by graphene

Abstract

Graphene samples prepared by the exfoliation of graphitic oxide and conversion of nanodiamond exhibit good hydrogen uptake at 1 atm, 77 K, the uptake going up to 1.7 wt %. The hydrogen uptake varies linearly with the surface area, and the extrapolated value of hydrogen uptake by single-layer graphene works out to be just above 3 wt %. The $H_2$ uptake at 100 atm and 298 K is found to be 3 wt % or more, suggesting thereby the single-layer graphene would exhibit much higher uptakes. Equally interestingly, the graphene samples prepared by us show high uptake of CO,,, the value reaching up to 35 wt % at I atm and 195 K. The first- principles calculations show that hydrogen molecules sit alternately in parallel and perpendicular orientation on the
\nsix-membered rings of the graphene. Up to 7.7 wt % of hydrogen can be accommodated on single-layered graphene. $CO_2$ molecules sit alternatively in a parallel fashion on the rings, giving use to a maximum uptake of 37.93 wt % in single-layer graphene. The presence of more than one layer of graphene in our samples causes a decrease in the $H_2$ uptake.