Divacancy-nitrogen-assisted transition metal dispersion and hydrogen adsorption in defective graphene: A first-principles study

We propose a route to dispersing hydrogen-adsorbing transition metals (TMs) on a large scale onto vacancy-engineered defective graphenes by employing natural carbon-nitrogen-TM complexes, i.e., TM-containing porphyrins. Based on first-principles density-functional calculations, the TM-porphyrin core-made of one central TM and four surrounding nitrogen atoms-can be effectively generated by three defect-engineering processes of graphenes: (1) creation of carbon divacancies, (2) nitrogen substitution of unsaturated carbons, and (3) TM incorporation. The atomistically dispersed Sc, Ti, and V are able to adsorb hydrogen molecules as strongly as 0.2-0.4 eV with the Kubas coordination. The Fe-porphyrin-like unit in graphenes can also have the Kubas adsorption of hydrogen, if the exchange splitting is reduced by a compressive in-plane strain.