title: Size-Dependent Disorder-Order Transformation in the Synthesis of Monodisperse Intermetallic PdCu Nanocatalysts.
abstract: The high performance of Pd-based intermetallic nanocatalysts has the potential to replace Pt-containing catalysts for fuel-cell reactions. Conventionally, intermetallic particles are obtained through the annealing of nanoparticles of a random alloy distribution. However, this method inevitably leads to sintering of the nanoparticles and generates polydisperse samples. Here, monodisperse PdCu nanoparticles with the ordered B2 phase were synthesized by seed-mediated co-reduction using PdCu nanoparticle seeds with a random alloy distribution (A1 phase). A time-evolution study suggests that the particles must overcome a size-dependent activation barrier for the ordering process to occur. Characterization of the as-prepared PdCu B2 nanoparticles by electron microscopy techniques revealed surface segregation of Pd as a thin shell over the PdCu core. The ordered nanoparticles exhibit superior activity and durability for the oxygen reduction reaction in comparison with PdCu A1 nanoparticles. This seed-mediated co-reduction strategy produced monodisperse nanoparticles ideally suited for structure-activity studies. Moreover, the study of their growth mechanism provides insights into the size dependence of disorder-order transformations of bimetallic alloys at the nanoscale, which should enable the design of synthetic strategies toward other intermetallic systems.
authors.affiliation: Department of Chemistry, Indiana University , 800 East Kirkwood Avenue, Bloomington, Indiana 47405, United States.
authors.forename: Chenyu
authors.initials: C
authors.lastname: Wang
authors.affiliation: Department of Chemistry, Indiana University , 800 East Kirkwood Avenue, Bloomington, Indiana 47405, United States.
authors.forename: Dennis P
authors.initials: DP
authors.lastname: Chen
authors.affiliation: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory , One Bethel Valley Road, Oak Ridge, Tennessee 37831, United States.
authors.forename: Xiahan
authors.initials: X
authors.lastname: Sang
authors.affiliation: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory , One Bethel Valley Road, Oak Ridge, Tennessee 37831, United States.
authors.forename: Raymond R
authors.initials: RR
authors.lastname: Unocic
authors.affiliation: Department of Chemistry, Indiana University , 800 East Kirkwood Avenue, Bloomington, Indiana 47405, United States.
authors.forename: Sara E
authors.initials: SE
authors.lastname: Skrabalak
keywords: disorder−order transformation; electrocatalysis; nanocrystals; seed-mediated co-reduction