First-Principles Study of Mo Segregation in MoNi(111): Effects of Chemisorbed Atomic Oxygen

Abstract

Segregation at metal alloy surfaces is an important issue because many electrochemical and catalytic properties are directly correlated to the surface composition. We have performed density functional theory calculations for Mo segregation in MoNi(111) in the presence of chemisorbed atomic oxygen. In particular, the coverage dependence and possible adsorption-induced segregation phenomena are addressed by investigating segregation energies of the Mo atom in MoNi(111). The theoretical calculated results show that the Mo atom prefers to be embedded in the bulk for the clean MoNi(111), while it segregates to the top-most layer when the oxygen coverage is thicker than 1/9 monolayer (ML). Furthermore, we analyze the densities of states for the clean and oxygen-chemisorbed MoNi(111), and see a strong covalent bonding between Mo d-band states and O p-states. The present study provides valuable insight for exploring practical applications of Ni-based alloys as hydrogen evolution electrodes.

First‐principles study of surface segregation in bimetallic Ni3M (M = Mo, Co, Fe) alloys with chemisorbed atomic oxygen

“…The first feature is that, consistent with results of other transition metals, the oxygen binding strength has the order of fcc > hcp > bridge > top, except for the Mo‐segregated and nonsegregated Ni 3 Mo(111) surfaces where the adsorption at the hcp site is stronger than at the fcc site. This phenomenon is in agreement with our previous calculations .…”

“…For instance, Song et al investigated the variations of surface morphology and chemical composition of Ni 65 Nb 35 alloy under an oxygen environment at different temperatures, and found that at the lower temperature range Nb segregates at the surface, while in the higher temperature range Ni segregates at the surface. Our recent theoretical calculations showed that Mo atom prefers to be embedded in the bulk for clean MoNi(111), while it segregates to the top‐most layer when the oxygen coverage is greater than 1/9 ML . Recent experiments have found that Mo atoms segregate to the NiMoCo electrode surfaces and induce an enrichment of the surface Mo composition .…”

“…However, the preparation of nickel‐based electrodes usually takes place in the reactive environment with various adsorbates , and in practical applications the alloy catalysts cannot avoid interacting with reactive adsorbates. A reactive environment may change the chemical composition and structure of an alloy surface and thus the electrocatalytic performance of a catalyst, if one alloy component interacts more strongly with a gas‐phase species than the others, resulting in adsorbate‐induced segregation . For instance, Song et al investigated the variations of surface morphology and chemical composition of Ni 65 Nb 35 alloy under an oxygen environment at different temperatures, and found that at the lower temperature range Nb segregates at the surface, while in the higher temperature range Ni segregates at the surface.…”

Ag surface segregation in nanoporous Au catalysts during CO oxidation

“…Moreover, Ag surface segregation enhances the catalytic activity, indicating a pivotal role of the residual Ag in the activation of molecular oxygen (O 2 ) beneficial to the catalytic CO oxidation 20 . The evidence that catalytic transformations promote the coarsening of NP Au foams 6 , 20 – 25 and that chemically active surface sites also participate in surface diffusion processes mediating coarsening 6 , 20 – 25 , further complicates the conceptual framework.…”

Correction: First-Principles Study of Mo Segregation in MoNi(111): Effects of Chemisorbed Atomic Oxygen. Materials 2016, 9, 5

“…The authors wish to make the following corrections to this manuscript [ 1 ]. The published Figure 1 was incorrect of MoNi(111) alloy systems showing one Mo monomer substituting one Ni atom in the (a) first; (b) second, (c) third; and (d) fourth nickel layer.…”