Hydrogen adsorption on carbon nanotubes decorated with Pd, Rh and Ru: a DFT study

ROMINA LUNA; VALERIA VERDINELLI; ESTEFANÍA GERMÁN; IGNACIO LÓPEZ CORRAL; CAROLINA PISTONESI

Montevideo

Workshop; 5th Workshop on Novel Methods for Electronic Structure Calculations; 2013

Facultad de Química, Universidad de la República

In this work we studied the adsorption of hydrogen onto single-walled carbon nanotubes (SWCNTs) decorated with different transition metals: Pd, Rh and Ru. Spin-polarized density functional theory (DFT) simulations were performed using VASP [1] and SIESTA [2] codes. The exchange-correlation term was calculated with the generalized gradient approximation (GGA). We selected a (8,0) zigzag SWCNT modeled by a supercell containing 64 C atoms. Several decoration sites on the nanotube surface were investigated before atomic or molecular hydrogen adsorption.According to previous reports [3], the most stable location of a single Pd atom on the SWCNT is the regular bridge site above an axial C-C bond, with a binding energy of Eb(Pd) = -1.80 eV. Adsorption of atomic hydrogen on the Pd/SWCNT system is possible, but the classic HPdH hydride is unstable on the nanotube surface. In effect, the preferential carbon-supported PdH2 system is a Kubas-type dihydrogen complex [4], with a binding energy of Eb(H2) = -0.66 eV. Although in this configuration the H-H bond is elongated due to the Kubas bonding, the H2 molecule is not dissociated. The adsorption of a terminal Pd-H-H coordination structure leads to a much lower Eb(H2). We also found that two donor-acceptor interactions are present in the H2/Pd/SWCNT Kubas-type system: (1) Pd 4d to C 2s donation and C 2p to Pd 5s back-donation; and (2) H2 sigma to Pd 5s donation and Pd 4d to H2 sigma* back-donation.Preliminary results involving Ru/SWCNT and Rh/SWCNT systems, which present magnetic effects, show that hydrogen adsorption is stronger than on Pd/SWCNT.