(547a) Alloy-Core@Shell Nanoparticles for Catalysis

Alloy-core@shell nanoparticles are designed to combine the strengths
of the alloy and core@shell particles, and avoid
their flaws. The noble shell protects the particle core during the catalytic processes,
and the alloy-core composition allows for fine tuning of the catalytic
properties.^1,2 The Dendrimer-encapsulated nanopartilces (DENs) as a model catalyst is sufficiently
small and well-characterized that its function can be directly predicted by
theory. Specifically, our work seeks to develop a fundamental and detailed
understanding of the relationship between the structure of nanoscopic
electrocatalysts and their function. Two categories
of stories will be given in the talk:

1) tailoring catalytic function by tuning
compositions: Trends in reaction descriptor (binding energies of key
reactants) were calculated with density functional theory (DFT) to probe the
catalytic activity of two types of alloy nanoparticles structures: random alloy
(X/Y)³ and alloy-core@shell (X/Y@Z)^1,2
with various compositions. Establishing the general principal of correlation
between compositions and activities provides guidelines for designing novel
catalysts.⁴ First-principal theory prediction of PdAu@Pt
DENs for ORR were examined by experiment and leads to a great agreement with
experiment results.²

2) enhanced stability by alloying core: Pd_xAu_{140_x}@Pt
DEN electro catalysts were tested for CO oxidation at wider alloying range.⁵
Both experiments and DFT calculations suggest that this unusual behavior is
caused primarily by structural changes of the DENs at high and low values of x.
The alloy PdAu cores stabilize the core@shell structures by preventing Au and Pd from escaping the core.⁵ These findings
illustrate the importance of controlling both the stability and reactivity of
the catalysts, and they provide guidance as to how core composition can be used
to do that.

Overall, we demonstrate that iteration
between theory and experiment can facilitate an understanding of nanoparticle
catalysts and reduce the time and effort involved in the design of new
catalysts. ^6,7

[1]  L.
Zhang, G. Henkelman, J. Phys. Chem. C 116
20860-20865 (2012).

[2] L. Zhang, R. Iyyamperumal, D. F. Yancey, R. M. Crooks, and G. Henkelman, ACS Nano 7,
9168-9172 (2013).

[3]
W.  Tang, L. Zhang, G. Henkelman J. Phys. Chem. Lett.
2011, 2, 1328-1331.

[4] L. Zhang and G. Henkelman, ACS Catal. 5,
655-660 (2015)

[5] L. Luo, L. Zhang, G. Henkelman, and R. M. Crooks, J. Phys. Chem. Lett. 6, 2562-2568 (2015)

[6] L.
Zhang, R. M. Anderson, R. M. Crooks, and G. Henkelman,
Surf. Sci. 640 65-72 (2015)

[7] R. M. Anderson, D. F. Yancey, L.
Zhang, S. T. Chill, G. Henkelman, and R. M.
Crooks, Acc. Chem. Res. 48 1351-1357 (2015).