title: Carbon monoxide-assisted size confinement of bimetallic alloy nanoparticles.
abstract: Colloid-based chemical synthesis methods of bimetallic alloy nanoparticles (NPs) provide good monodispersity, yet generally show a strong variation of the resulting mean particle size with alloy composition. This severely compromises accurate correlation between composition of alloy particles and their size-dependent properties. To address this issue, a general CO adsorption-assisted capping ligand-free solvothermal synthesis method is reported which provides homogeneous bimetallic NPs with almost perfectly constant particle size over an unusually wide compositional range. Using Pt-Ni alloy NPs as an example, we show that variation of the reaction temperature between 160 and 240 °C allows for precise control of the resulting alloy particle bulk composition between 15 and 70 atomic % Ni, coupled with a constant mean particle size of ∼4 nm. The size-confining and Ni content-controlling role of CO during the nucleation and growth processes are investigated and discussed. Data suggest that size-dependent CO surface chemisorption and reversible Ni-carbonyl formation are key factors for the achievement of a constant particle size and temperature-controlled Ni content. To demonstrate the usefulness of the independent control of size and composition, size-deconvoluted relations between composition and electrocatalytic properties are established. Refining earlier reports, we uncover intrinsic monotonic relations between catalytic activity and initial Ni content, as expected from theoretical considerations.
authors.affiliation: The Electrochemical Energy, Catalysis, and Materials Science Laboratory, Department of Chemistry, Chemical Engineering Division, Technical University Berlin , Berlin 10623, Germany.
authors.forename: Chunhua
authors.initials: C
authors.lastname: Cui
authors.forename: Lin
authors.initials: L
authors.lastname: Gan
authors.forename: Maximilian
authors.initials: M
authors.lastname: Neumann
authors.forename: Marc
authors.initials: M
authors.lastname: Heggen
authors.forename: Beatriz Roldan
authors.initials: BR
authors.lastname: Cuenya
authors.forename: Peter
authors.initials: P
authors.lastname: Strasser