Size effects on rhodium nanoparticles related to hydrogen-storage capability

Abstract

To unveil the origin of the hydrogen-storage properties of rhodium nanoparticles (Rh NPs), we investigated the electronic and crystal structures of the Rh NPs using various synchrotron based X-ray techniques. Electronic structure studies revealed that the hydrogen-storage capability of Rh NPs could be attributed to their more unoccupied d-DOSs than that of the bulk near the Fermi level. Crystal structure studies indicated that lattice distortion and mean-square displacement increase while coordination number decreases with decreasing particle size and the hydrogen-absorption capability of Rh NPs improves to a greater extent with increased structural disorder in the local structure than with that in the mean structure. The smallest Rh NPs, having the largest structural disorder/increased vacancy spaces and the smallest coordination number, exhibited excellent hydrogen-storage capacity. Finally, from the bond-orientational order analysis, we confirmed that the localized disordering is distributed more over the surface part than the core part and hydrogen can be trapped on the surface part of Rh NPs which increases with a decrease in NP diameter.

Reducing-agent-free facile preparation of Rh-nanoparticles uniformly anchored on onion-like fullerene for catalytic applications

“…[18][19][20] Generally, due to strong resistance to etching of acid/base and heat, the Rh-based catalysts are stable and more versatile in catalytic reaction even under harsh reaction conditions. 21,22 Hence, signicant efforts have been taken for developing simple and efficient wet-chemistry approaches for the preparation of Rh-nanostructures with unique size and shape. [18][19][20][21][22][23] Jiang et al, 24 reported an efficient chemical reduction method for the preparation of mesoporous Rh nanostructures.…”

“…21,22 Hence, signicant efforts have been taken for developing simple and efficient wet-chemistry approaches for the preparation of Rh-nanostructures with unique size and shape. [18][19][20][21][22][23] Jiang et al, 24 reported an efficient chemical reduction method for the preparation of mesoporous Rh nanostructures. Recently, Kang and co-workers 25 obtained three types of Rhbased nanostructures (nanoshells, nanoframes, and porous nanoplates) through an inverse-directional galvanic replacement reaction.…”

The relationship between crystalline disorder and electronic structure of Pd nanoparticles and their hydrogen storage properties

“…49,50 In addition, the width and center position of the d-band are related to the coordination numbers of the metal. 24 The broadening of the VB spectra decreased and the d-band center position increased with decreasing particle diameter, as indicated by the black squares in Fig. 5(b).…”

“…4 The high surface area to volume ratio of metal NPs results in an enhanced catalytic effect. [22][23][24] With decreasing particle size, the amount of hydrogen storage and equilibrium pressure for the formation of Pd-H bonding both decrease. 25,26 In addition, the hydrogen storage properties of metal NPs have been shown to be related to their electronic structure.…”

“…[27][28][29] It is expected that the electronic structure of metal NPs can be tuned by adjusting the particle size and local structure. 24,[30][31][32] Furthermore, in 2008, Yamauchi et al reported that the strength of Pd-H bond formation of smaller Pd NPs is weaker than that of larger Pd NPs and that the unavailable surface part of smaller NPs should be accounted for in determining the hydrogen capacity. 26 These authors assumed that the large surface atoms in Pd NPs affected the hydrogen storage properties.…”