Hydrogen-induced magnetization and tunable hydrogen storage in graphitic structures

Hydrogen interactions with undefective and defective graphitic structures were investigated by first-principles simulations. Structural vacancies were identified to promote the dissociation of molecular hydrogen with a reduced activation barrier of 0.63 eV, compared to 2.38 eV for a perfect graphene. However, the vacancies bind the hydrogen too strongly for spill-over mechanisms to be effective. An isolated vacancy in a graphene can bind four hydrogen atoms, but a metastable and magnetic structure binds six hydrogen atoms at the vacancy site at room temperature. The thermodynamics, magnetic properties, and hydrogen binding energies vary with graphene layer spacing. A metastable structure becomes energetically favorable for a layer spacing of 3.19 angstrom, while the binding of hydrogen becomes exothermic at a layer spacing of 2.72 angstrom. This phenomenon suggests the possibility of using hydrogen-rich carbon structures for reversible magnetic and hydrogen storage applications.