Changes in Surface Oxygen Vacancy Formation Energy at Metal/Oxide Perimeter Sites: A Systematic Study on Metal Nanoparticles Deposited on an In₂O₃(111) Support

Abstract

Metal/oxide support perimeter sites can provide unique properties because the local environment on the support surface is changed by the nearby metal. This study modeled perimeter sites when metal nanorods were adsorbed in lieu of nanoparticles on the (111) surface of an In2O3 support. The metal element M was one of Ag, Au, Cu, Ir, Pd, Pt, and Re. Changes in the surface oxygen vacancy formation energy (E Ovac) with nanorod adsorption were evaluated using systematic first-principles calculations under the same approximations and conditions and were found to be driven by two major factors. First, if the Fermi energy of the metal is deeper than the defect energy level of surface O vacancies, the metal may act as an electron scavenger to accept excess electrons upon O removal from sites close to the metal. The minimum E Ovac for each M correlated very well with the Bader charge transfer to the nanorod upon O removal. The effect of geometrical relaxation of the nanorod after O removal was not found because there was barely any spontaneous rearrangement of nanorod atoms after O removal. As a consequence, the minimum E Ovac in a surface tends to decrease with the increasing work function of M. Second, among different O sites on the same surface, E Ovac is lower in O sites when there are interface states with the adsorbed metal at energy levels higher than the valence band of the support. These insights would help in planning strategies to obtain active O sites.

Revealing hydrogen spillover pathways in reducible metal oxides

“… 49 Hinuma et al showed that manifestation of the electron scavenger effect is determined by the order of the oxide defect level after O removal and the metal work function. 50 Compared to late transition metals typically adsorbed as nanoparticles, fully oxidized group 3, 4, 5 oxides as well as CeO 2 have very large ionization potentials (IPs), or in other words, the valence band maximum is very deep with respect to the vacuum level. However, the IPs become smaller when the cation is reduced.…”

Surface activation by electron scavenger metal nanorod adsorption on TiH2, TiC, TiN, and Ti2O3

“…Removal of an anion leaves behind electrons, and part of the charge would be accommodated by the nanorod if the nanorod is an electron scavenger. Charge flow between metal and oxide through work function engineering has been previously proposed, for example by Pacchioni 31 , and demonstrated on various metal nanorods adsorbed on the In2O3 (111) surface 43 . Fig.…”

“…Activation was typically accompanied by transfer of electrons to the nanorod upon anion removal in TiH2, TiN, and Ti2O3, therefore the activation is a result of the electron scavenger effect that was previously reported in oxides. [42][43]…”

Understanding and controlling the formation of surface anion vacancies for catalytic applications

“…Our study considered the adsorption of metal nanoparticles on an In 2 O 3 slab with a (111) surface, 88 and the metal element, M, was selected from among Cu, Ag, Au, Pd, Pt, Ir, and Re. The M/In 2 O 3 system was modeled as a semiinfinite M nanorod supported on In 2 O 3 (111); similar models have been employed for investigating metal/oxide sites at perimeters and interfaces (Fig.…”

“…The charge transfer in the case of M = Cu, Ag, Au, and the case where O atoms far away from the nanorods were removed has been investigated in our previous reports. 88 Charge transfer from the O-defect sites near the Pd nanorods (blue spheres, highlighted by blue inverted lines) onto the Pd nanorods can be observed. Similar results were obtained for Ag and Au, and the amount of charge transfer from the support to the nanorod qualitatively becomes larger in the order Ag, Au, and Pd, which means that more charge is transferred from the support site to the metal nanorod when the WF of the metal is larger.…”