title: PdCu Nanoalloy Electrocatalysts in Oxygen Reduction Reaction: Role of Composition and Phase State in Catalytic Synergy.
abstract: The catalytic synergy of nanoalloy catalysts depends on the nanoscale size, composition, phase state, and surface properties. This report describes findings of an investigation of their roles in the enhancement of electrocatalytic activity of PdCu alloy nanoparticle catalysts for oxygen reduction reaction (ORR). Pd(n)Cu(100-n) nanoalloys with controlled composition and subtle differences in size and phase state were synthesized by two different wet chemical methods. Detailed electrochemical characterization was performed to determine the surface properties and the catalytic activities. The atomic-scale structures of these catalysts were also characterized by high-energy synchrotron X-ray diffraction coupled with atomic pair distribution function analysis. The electrocatalytic activity and stability were shown to depend on the size, composition, and phase structure. With Pd(n)Cu(100-n) catalysts from both methods, a maximum ORR activity was revealed at Pd/Cu ratio close to 50:50. Structurally, Pd50Cu50 nanoalloys feature a mixed phase consisting of chemically ordered (body-centered cubic type) and disordered (face-centered cubic type) domains. The phase-segregated structure is shown to change to a single phase upon electrochemical potential cycling in ORR condition. While the surface Cu dissolution occurred in PdCu catalysts from the two different synthesis methods, the PdCu with a single-phase character is found to exhibit a tendency of a much greater dissolution than that with the phase segregation. Analysis of the results, along theoretical modeling based on density functional theory calculation, has provided new insights for the correlation between the electrocatalytic activity and the catalyst structures.
authors.affiliation: Department of Chemistry and Chemical Engineering, Chongqing University , Chongqing 400030, China.|Department of Chemistry, State University of New York at Binghamton , Binghamton, New York13902, United States.
authors.forename: Jinfang
authors.initials: J
authors.lastname: Wu
authors.affiliation: Department of Chemistry, State University of New York at Binghamton , Binghamton, New York13902, United States.
authors.forename: Shiyao
authors.initials: S
authors.lastname: Shan
authors.affiliation: Department of Chemistry, State University of New York at Binghamton , Binghamton, New York13902, United States.
authors.forename: Jin
authors.initials: J
authors.lastname: Luo
authors.affiliation: Department of Chemistry, State University of New York at Binghamton , Binghamton, New York13902, United States.
authors.forename: Pharrah
authors.initials: P
authors.lastname: Joseph
authors.affiliation: Department of Physics, Central Michigan University , Mt. Pleasant, Michigan 48859, United States.
authors.forename: Valeri
authors.initials: V
authors.lastname: Petkov
authors.affiliation: Department of Chemistry, State University of New York at Binghamton , Binghamton, New York13902, United States.
authors.forename: Chuan-Jian
authors.initials: CJ
authors.lastname: Zhong
keywords: activity−composition synergy; atomic pair distribution function; fuel cells; nanocatalysts; oxygen reduction reaction; palladium−copper alloy; synchrotron X-ray diffraction