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

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

Workshop; V Workshop on novel methods for electronic structure calculations; 2013

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  to Pd 5s donation and Pd 4d to H2 * 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.