Factors Controlling the Reactivity of Catalytically Active Monolayers on Metal Substrates

Abstract

The focus of this work is on the Pt/MS structures (MS = Au, Ir, Ru, or Pt substrate), as promising electrocatalysts and a prototype for more general systems: (active element monolayer)/(metal substrate) (AE/MS). We evaluate from first principles the effects of AE monolayer strain and the interlayer AE-MS electronic state hybridization on surface reactivity and reveal rationale for the interlayer hybridization to dominate over the strain effect in determining the AE/MS surface reactivity. We find, however, that, if AE is weakly bound to MS, the surface electronic structure does not suffice to characterize the surface reactivity, because of involvement of other factors related to lattice response to adsorption of a reaction intermediate. Guided by our findings, we trace surface reactivity to a newly introduced hybridization parameter that reflects important features of the electronic structure of the AE/MS surface, which are not taken into account in the original d-band center model.

Au/Ta(110) and Au/Nb(110) as Highly Active, Stable, and Inexpensive Catalysts for Oxygen Reduction Reaction on Hydrogen Fuel Cell Cathodes: Prediction from First Principles

“…One can see that, as expected, Au binds to all ETM under consideration much stronger than to bulk Au, and the formation energy for Au on Nb and Ta is significantly higher than that on Mo and W. One reason for this could be that the Au‐ETM bond‐length mismatch for Mo and W is larger than for Nb and Ta. On the other hand, differences in Au−ETM hybridization can also be very important . It is worth mentioning that higher hybridization may affect the Au electronic density of states (DOS) more effectively and in this way increase the reactivity of Au.…”

“…On the other hand, differences in AuÀ ETM hybridization can also be very important. [19] It is worth mentioning that higher hybridization may affect the Au electronic density of states (DOS) more effectively and in this way increase the reactivity of Au.…”

“…It is known that the strength of the bonds between small molecules and a metal surface depends on the local densities of electronic states (LDOS) of surface atoms around the Fermi-level (E F ): the higher the LDOS around E F , the stronger bonds are expected to be. [19,24] For transition metal surfaces, the strength of the covalent bonding between adsorbates and metal surfaces is usually associated with the d-states of the surface atoms. [28] Therefore, first we analyze the d-LDOS of Au in Au/ ETM.…”

The perturbation energy: A missing key to understand the “nobleness” of bulk gold

“…So far, some works have reported the so-called relaxation energy (E rx ) of an adsorbed surface, which is the energy contribution to the calculated E B (O) obtained by allowing to relax the interatomic forces on substrate atoms of the composite system. 17,30,35,43,44 One way to calculate E rx involves the total energy of (1) the totally relaxed O-metal system (E R total (O/metal)) and (2) the O-metal system in which the substrate atoms are kept in the same positions as in the clean substrate E U total (O/metal): 17,35,44 This energy has been found important for O-adsorption on 100-atom transitionmetal clusters, particularly for Au and Pt ones. 44 In our calculations, inspection of the structural distortions undergone by the metal substrates upon O-adsorption clearly hints that the O-induced disturbance is significantly stronger for Au than for any other metal.…”

“…(e) It has been reported that despite a significant enhancement of the number of unoccupied antibonding states of Pt/Au(111) with respect to Pt(111), the binding energy of OH is negligibly enhanced with respect to that on Pt(111). 30 …”