DFT study of hydrogen adsorption on Eu-decorated single- and double-sided graphene

We carry out density functional theory calculations to study the adsorption of hydrogen molecules on Eu-decorated single- and double-sided graphene sheets. It is found that Eu prefers to adsorb on the hollow site of carbon ring above both the single- and double-sided graphene. The hybridization of Eu on graphene is mainly between the Eu-5d orbital and the C-2p orbital. The charge of Eu is enhanced when the first hydrogen molecule approaches the Eu atom. As more hydrogen molecules are introduced, the charge population of Eu-5d and 6p orbital is increased. Each Eu can stably bind up to six hydrogen molecules with an average adsorption energy of -0.404 and -0.392eV for Eu decorated single- and double-sided graphene, respectively. Eu atoms carry negative charge when 12 hydrogen molecules are attracted by the Eu-decorated double-sided graphene. The main interaction between hydrogen and Eu is similar to Kubas binding, which contains hybridization of H-σ* and Eu-5d orbital and charge transfer between them.