Theoretical investigation of adsorption of gas molecules on Li metal adsorbed at H-site of graphene: A search for graphene based gas sensors

Adsorption of small gas molecules (such as CO, O2, NO and NO2) on pristine graphene (PG) and Li-adsorbed graphene (PG-Li) have been investigated using first principles methods within density functional theory (DFT). The adsorption energy, equilibrium graphene-molecule distance, density of states (DOS) and PDOS of small gas molecules adsorbed on PG and PG-Li have been calculated. We find that electronic properties of PG are sensitive to the adsorption of O2 and NO2 molecules while it remains insensitive to the adsorption of O2 and NO2 molecules. We also notice that PG-Li, with Li atom adsorbed on hollow site(H-site) of graphene, has a higher chemical reactivity towards the gas molecules as compared to PG and these molecules have higher adsorption energy on this surface. Simultaneous adsorption of Li at mixed sites has a higher chemical reactivity towards the NO/CO gas molecules and shows higher adsorption energy as compared to its adsorption at single site. Moreover, the strong interactions between PG-Li and the adsorbed molecules (as compared to PG and gas molecules) induce dramatic changes to the electronic properties of PG adsorbed with Li and make PG-Li a promising candidate as sensing material for CO, O2, NO and NO2 gases.