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Single atom alloy (SAA) clusters formed by anchoring single atoms in small supported host clusters are emerging as catalysts with high performance. In this work, density functional theory (DFT) calculations and ab‐initio molecular dynamics (AIMD) simulations are performed to study the stability and the structure evolution of γ‐alumina‐supported platinum/copper SAA clusters of sub‐nanometer size in hydrogen environment. Due to the strong dynamic nature of both Cu cluster and anchored Pt single atom and their evolving interaction with the support, different isomers with different geometric and energetic properties are predicted. Extensive sampling through AIMD simulations reveals strong effect of hydrogen on the location of Pt single atom and strong variation of the cluster shape, evolving from 3D to concave and planar shapes wetting the alumina support. Interfacial site location of Pt single atom is found to be hydrogen coverage dependent. When the hydrogen coverage increases, the Pt single atom located preferentially at the interfacial site is pulled up by hydrogen atoms toward the upper surface Cu layers. The interaction of Pt/Cu cluster with alumina is predicted to decrease with increasing hydrogen coverage. Finally, electronic structure analysis reveals dramatic effect of hydrogen on the metallic nature of the catalysts. [ABSTRACT FROM AUTHOR]

We present a joint experimental and density functional theory (DFT) study on the effect of atomic vacancies on the restructuring of platinum-transition metal alloy nanocatalysts and the associated changes in electrocatalytic activity. Atomic vacancies were introduced into slabs composed of pure Pt monolayers, and the structures were relaxed using the Vienna ab initio simulation package code. Effects of i) the concentration and ii) the spatial distribution of atomic vacancies in the slabs on surface and bulk restructuring were investigated. Highly disordered nanostructures featuring large variations of the in-plane and out-of-plane nearest-neighbour distances around the mean were observed upon relaxation. These findings were confirmed experimentally by using hollow PtNi/C nanoparticles synthesized by a combination of galvanic replacement and the nanoscale Kirkendall effect (a vacancy-mediated interdiffusion mechanism). The experimental results also show that hollow PtNi/C nanoparticles feature a combination of oxophilic and oxophobic catalytic sites on their surface and are thus highly active both for electrochemical oxidation and reduction reactions. [ABSTRACT FROM AUTHOR]

Enhancing the specific activity and the mass activity of catalysts for the oxygen reduction reaction (ORR) in proton-exchange membrane fuel cells is currently achieved by alloying Pt with an early or late transition metal. By using hollow PtNi/C nanoparticles with different physicochemical properties (Ni content, lattice parameter, specific surface area), we show that structural defects such as grain boundaries also contribute to the enhancement of the ORR kinetics. Their concentration was quantified by means of the structure sensitivity of the electrooxidation of a COads monolayer, that is, the presence of an oxidation prepeak in the COads stripping voltammogram. A straightforward relationship is established between the ratio of the charge under the prepeak Qpp,CO to the total COads electrooxidation charge and the specific activity for the ORR. The present study provides a knowledge base for designing more efficient ORR electrocatalysts. [ABSTRACT FROM AUTHOR]