Influence of hydrogen impurities on atomic and electronic structure of palladium nanowires and nanocontacts

We present an ab initio study of the influence of hydrogen impurities (atoms and molecules) on the atomic structure and electronic properties of Pd nanowires and atomic-size nanocontacts. Various atomic positions for hydrogen adsorption within palladium structures are considered. It is found that adsorbed hydrogen can penetrate into the atomic structure of Pd nanocontacts and nanowires and by that increase their stability close to and beyond their breaking points. The interaction between hydrogen and palladium atoms alters the interatomic bonding and hybridization of electronic states of palladium atoms. The interaction of palladium with hydrogen leads to the suppression of magnetic properties of Pd nanowires and nanocontacts. Additionally, the possibility of dissociation of molecular hydrogen at palladium nanocontacts is discussed, which is an important issue for catalytic applications.

Figure 1

Studied adsorption positions of hydrogen atoms (light balls) in an infinite Pd (dark balls) nanowire: (a) “aside,” (b) “middle,” (c) “linear,” (d) “zigzag,” and a “pure” Pd nanowire (e).

Figure 2

Change of the local magnetic moments of Pd atoms as a function of interatomic distance for a pure nanowire (black circles) (Ref. 27) and for atoms Pd1 (red up-triangles), Pd2 (green down-triangles), and Pd3 (blue squares) of a nanowire with an adsorbed hydrogen atom (“middle” configuration) (solid lines).

Figure 3

PDOS of palladium atoms in nanowire in presence of hydrogen impurities for “middle” configuration at interatomic distance $2.7\AA$. Red arrows mark the positions of low-energy levels of the hydrogen atom.

Figure 4

Available adsorption positions of hydrogen atom in Pd nanocontacts: (a) “linear” configuration, (b) “zigzag” configuration, (c) “aside” configuration.

Figure 5

The difference of total energy ($\Delta E$) of “linear” and “zigzag” configurations as a function of the interelectrode distance.

Figure 6

PDOS of Pd atoms in the nanocontact’s chain in “zigzag” configuration: (a) edge atom (Pd1) and (b) central atom (Pd2). Top panels present the PDOS in presence of hydrogen atom while the bottom ones present pure NC’s PDOS for comparison. Vertical arrows mark the positions of low-energy $s$ states of the hydrogen atom.

Figure 7

Dependence of the local magnetic moments of Pd atoms in nanocontact’s chain on interelectrode distances for pure Pd nanocontact (dot lines) and for Pd nanocontact with the hydrogen atom (“zigzag” configuration) (solid lines).

Figure 8

Available adsorption positions of the hydrogen molecule in palladium nanocontacts: (a) “in-chain horizontal,” (b) “in-chain vertical,” (c) “aside horizontal,” and (d) “aside vertical.”

Figure 9

PDOS of Pd atoms nearest to the ${\mathrm{H}}_2$ molecule adsorbed on a Pd NC in different positions: (a) “in-chain horizontal,” (b) “in-chain vertical,” (c) “aside horizontal,” and (d) “aside vertical.” Red arrows mark the position of low-energy (bonding) states of $\mathrm{H}/{\mathrm{H}}_2$.