Browsing by Subject "gold nanoparticles"

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    Au@Pt Dendrimer Encapsulated Nanoparticles As Model Electrocatalysts for Comparison of Experiment and Theory
    (2012-01) Yancey, David F.; Zhang, Liang; Crooks, Richard M.; Henkelman, Graeme; Yancey, David F.; Zhang, Liang; Crooks, Richard M.; Henkelman, Graeme
    In this paper we report the electrochemical synthesis of core@shell dendrimer-encapsulated nanoparticles (DENs) consisting of cores containing 147 Au atoms (Au-147) and Pt shells having similar to 54 or similar to 102 atoms (Au-147@Pt-n (n = 54 or 102)). The significance of this work arises from the correlation of the experimentally determined structural and electrocatalytic properties of these particles with density functional theory (DFT) calculations. Specifically, we describe an experimental and theoretical study of Pb underpotential deposition (UPD) on Au-147 DENs, the structure of both Au-147@Pb-n and Au-147@Pt-n DENs, and the activity of these DENs for the oxygen reduction reaction (ORR). DFT calculations show that Pb binding is stronger on the (100) facets of Au as compared to (111), and the calculated deposition and stripping potentials are consistent with those measured experimentally. Galvanic exchange is used to replace the surface Pb atoms with Pt, and a surface distortion is found for Au-147@Pt-n particles using molecular dynamics simulations in which the Pt-covered (100) facets shear into (111) diamond structures. DFT calculations of oxygen binding show that the distorted surfaces are the most active for the ORR, and that their activity is similar regardless of the Pt coverage. These calculations are consistent with rotating ring-disk voltammetry measurements.
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    A Theoretical and Experimental Examination of Systematic Ligand-Induced Disorder in Au Dendrimer-Encapsulated Nanoparticles
    (2013-04) Yancey, David F.; Chill, Samuel T.; Zhang, Liang; Frenkel, Anatoly I.; Henkelman, Graeme; Crooks, Richard M.; Yancey, David F.; Chill, Samuel T.; Zhang, Liang; Henkelman, Graeme; Crooks, Richard M.
    In this paper we present a new methodology for the analysis of 1-2 nm nanoparticles using extended X-ray absorption fine structure (EXAFS) spectroscopy. Different numbers of thiols were introduced onto the surfaces of dendrimer-encapsulated Au nanoparticles, consisting of an average of 147 atoms, to systematically tune the nanoparticle disorder. An analogous system was investigated using density functional theory molecular dynamics (DFT-MD) simulations to produce theoretical EXAFS signals that could be directly compared to the experimental results. Validation of the theoretical results by comparing to experiment allows us to infer previously unknown details of structure and dynamics of the nanoparticles. Additionally, the structural information that is learned from theoretical studies can be compared with traditional EXAFS fitting results to identify and rationalize any errors in the experimental fit. This study demonstrates that DFT-MD simulations accurately depict complex experimental systems in which we have control over nanoparticle disorder, and shows the advantages of using a combined experimental/theoretical approach over standard EXAFS fitting methodologies for determining the structural parameters of metallic nanoparticles.