Surface segregation in the AgAuCuPdPt high entropy alloy: insights from molecular simulations

Abstract

High entropy alloys (HEAs) are emerging as a novel class of superior catalysts for diverse chemical conversions. The activity of a catalyst is intimately related to the composition and atomic...

Effects of Segregation on the Catalytic Properties of AgAuCuPdPt High-Entropy Alloy for CO Reduction Reaction

“…Figure a shows that, among random alloys, the top branch is occupied by those alloys that mainly contain Ag/Au/Cu atoms while the alloys in the bottom branch contain one or both Pd and Pt atoms. In earlier work, we had shown that Ag and Au atoms preferentially segregate to the surface while Pt atoms stay in the bulk of AgAuCuPdPt HEA. As a result, in Figure b, we notice that almost all the alloys that were present in the bottom branch of Figure a have migrated to the top branch for the segregated alloy.…”

“…Segregation on the (111) surfaces of the AgAuCuPdPt FCC HEA was studied using hybrid MC/MM simulations. The atomic interactions were described using the EAM potential of Zhou et al An extensive validation of this potential against experimental surface segregation data on a few binary and ternary alloys formed from components in our HEA was presented in our prior work . All the (111) surfaces were modeled as an (8 × 8) supercell with 6 atomic layers for a total of 384 atoms.…”

“…The atomic interactions were described using the EAM potential of Zhou et al 46 An extensive validation of this potential against experimental surface segregation data on a few binary and ternary alloys formed from components in our HEA was presented in our prior work. 35 All the (111) surfaces were modeled as an (8 × 8) supercell with 6 atomic layers for a total of 384 atoms. The cell lengths in the periodic directions were obtained from the composition weighted average of the lattice parameters of the pure metals present in the outermost layers of the slab.…”

“…The MC/MM evolution of the (111) surfaces was carried out for a total of 10 atomic swaps/atom using an earlier developed protocol. 35 For each HEA composition, MC/MM simulations were carried out beginning from 25 different initial random arrangements of atoms.…”

“…39 As a result, the "near surface" composition of the alloy differs significantly from its bulk composition, which alters both the types of elements as well as their numbers at the surface. 35 Catalysis being a surface phenomenon, such changes are expected to have a direct impact on the activity and selectivity of a catalyst for any target reaction. Indeed, recent results on bimetallic alloys have shown that engineering such a "disorderto-order" transformation can enhance the activity of the parent random alloy.…”