Adsorption and diffusion of hydrogen on C60-supported Pt n clusters Article uri icon

abstract

  • We present extensive pseudopotential density functional theory calculations dedicated to analyze the adsorption properties and migration behavior of hydrogen on C60-supported Ptn (n = 1, 2, 5, 13) clusters. When adsorbing Pt species on C60, we find that the systems gain energy when the platinum atoms aggregate on the fullerene surface, forming clusters of different sizes and symmetries. Notable structural variations around the adsorption sites are obtained, consisting in expansions and contractions of the C-C, Pt-Pt, and Pt-C bond lengths as large as 7%25. The adsorption energies vary in the range of 1.5-3.1 eV, and there is a notable Pt → C charge transfer (∼0.15e) that leads to the formation of robust Pt-C bonds. When the C60Ptn compounds are exposed to molecular hydrogen, the Pt-rich regions of the surface are the ones favorable for the dissociative chemisorption of H2. The density of states around the Fermi level is very sensitive to the presence and location of the hydrogen species in our C60Ptn structures, a result that could have strong effects on the transport properties of our fullerene compounds and can be used as a fingerprint to identify precise structural features in these kind of complexes. Using the nudged-elastic-band method, we obtain that atomic hydrogen diffuses very easily on the surface of both free-standing and C60-supported Ptn clusters. However, H-atom migration on the carbon surface is very unlikely, since barriers of the order of 1.5 eV need to be overcome. Hydrogen transfer events between platinum and carbon regions on our here-considered C60Ptn structures, so-called spillover processes, are highly dependent on the local atomic environment. When going from the single Pt atom to the small cluster regime, the spillover energy barriers vary between 0.7-1.6 eV, a result that is important to consider in order to more clearly understand recent experimental studies addressing hydrogen storage in carbon nanostructures via chemical adsorption. © 2013 American Chemical Society.

publication date

  • 2013-01-01