title: Activity descriptor identification for oxygen reduction on platinum-based bimetallic nanoparticles: in situ observation of the linear composition-strain-activity relationship.
abstract: Despite recent progress in developing active and durable oxygen reduction catalysts with reduced Pt content, lack of elegant bottom-up synthesis procedures with knowledge over the control of atomic arrangement and morphology of the Pt-alloy catalysts still hinders fuel cell commercialization. To follow a less empirical synthesis path for improved Pt-based catalysts, it is essential to correlate catalytic performance to properties that can be easily controlled and measured experimentally. Herein, using Pt-Co alloy nanoparticles (NPs) with varying atomic composition as an example, we show that the atomic distribution of Pt-based bimetallic NPs under operating conditions is strongly dependent on the initial atomic ratio by employing microscopic and in situ spectroscopic techniques. The PtxCo/C NPs with high Co content possess a Co concentration gradient such that Co is concentrated in the core and gradually depletes in the near-surface region, whereas the PtxCo/C NPs with low Co content possess a relatively uniform distribution of Co with low Co population in the near-surface region. Despite their different atomic structure, the oxygen reduction reaction (ORR) activity of PtxCo/C and Pt/C NPs is linearly related to the bulk average Pt-Pt bond length (RPt-Pt). The RPt-Pt is further shown to contract linearly with the increase in Co/Pt composition. These linear correlations together demonstrate that (i) the improved ORR activity of PtxCo/C NPs over pure Pt NPs originates predominantly from the compressive strain and (ii) the RPt-Pt is a valid strain descriptor that bridges the activity and atomic composition of Pt-based bimetallic NPs.
authors.affiliation: Department of Chemistry and Chemical Biology and ‡Department of Biology, Northeastern University , Boston, Massachusetts 02115, United States.
authors.forename: Qingying
authors.initials: Q
authors.lastname: Jia
authors.forename: Wentao
authors.initials: W
authors.lastname: Liang
authors.forename: Michael K
authors.initials: MK
authors.lastname: Bates
authors.forename: Prasanna
authors.initials: P
authors.lastname: Mani
authors.forename: Wendy
authors.initials: W
authors.lastname: Lee
authors.forename: Sanjeev
authors.initials: S
authors.lastname: Mukerjee
mesh_terms: D002244:Carbon / Q000737:chemistry; D002384:Catalysis; D003035:Cobalt / Q000737:chemistry*; D004563:Electrochemistry; D053768:Metal Nanoparticles; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D010984:Platinum / Q000737:chemistry*; D013314:Stress, Mechanical; D013329:Structure-Activity Relationship
chemical_list: D003035:Cobalt; D010984:Platinum; D002244:Carbon; D010100:Oxygen
keywords: Pt-bimetallic nanoparticles; X-ray absorption spectroscopy; activity descriptor; oxygen reduction reaction; strain effects