Transition-metal dispersion on carbon-doped boron nitride nanostructures: Applications for high-capacity hydrogen storage

Abstract

Using density-functional theory calculations, we investigated the adsorption of transition-metal (TM) atoms (TM = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni) on carbon doped hexagonal boron nitride (BN) sheet and the corresponding cage (B${}_{12}$N${}_{12}$). With carbon substitution of nitrogen, Sc, V, Cr, and Mn atoms were energetically favorable to be dispersed on the BN nanostructures without clustering or the formation of TM dimers, due to the strong binding between TM atoms and substrate, which contains the half-filled levels above the valence bands maximum. The carbon doped BN nanostructures with dispersed Sc could store up to five and six H${}_{2}$, respectively, with the average binding energy of 0.3 \ensuremath{\sim} 0.4 eV, indicating the possibility of fabricating hydrogen storage media with high capacity. We also demonstrated that the geometrical effect is important for the hydrogen storage, leading to a modulation of the charge distributions of $d$ levels, which dominates the binding between H${}_{2}$ and TM atoms.