(537d) Enhanced Activity for Oxygen Reduction Reaction By Gold at Step/Edge Sites of Ni@Aupt Core-Shell Nanoparticles: A DFT Investigation

Enhanced Activity for Oxygen Reduction Reaction by Gold at Step/Edge Sites
of Ni@AuPt Core-Shell Nanoparticles: A DFT Investigation

Wei An*, Hao Wang

College of Chemistry and Chemical Engineering,
Shanghai University of Engineering Science, Songjiang District, Shanghai
201620, China.

*E-mail: weian@sues.edu.cn

ABSTRACT

Modifying
Ni@Pt nanoparticle (NP) with Au has been proved to be an efficient strategy to enhance not only the activity of
Ni@Pt nanoparticles for oxygen
reduction reaction (ORR) demonstrated by previous theoretical study,¹ but also
the stability of cathode from experimental observations.^2-3 Still, there
is an urgent need for understanding
the ORR behaviors at step/edge
sites of a NP considering the large
portion of surface Pt atoms consumed by step/edge sites for the closure of a NP buildup besides the key roles of step/edge
¡®defect¡¯ sites that play in
promoting a catalytic reaction.

In
view of the remarkable effect of Au, we investigate ORR
at step/edge sites of Ni@AuPt NPs employing periodic spin-polarized density
functional theory (DFT) method. We built high-index
(221) facets as model catalysts and found that the ORR activity can be greatly
enhanced by replacing the surface Pt atoms at edge site with Au atoms. Our results show that ORR activity at edge
site is much higher than that at step site. Inert
Au atoms localized at the surface edge sites of Pt-based NPs can effectively
promote the elementary steps of
ORR. At working potential (U=0.8V), the rate-determining
step of ORR at step/edges sites of Ni@AuPt core-shell NPs is likely to be O₂ protonation to
*OOH, compared with *O protonation to *OH on Pt NPs. Furthermore, the BEP relations are held for O₂ dissociation in the
form of the linear correlation between the transition-state and final-state
energies on potential energy surface, and are held for *O protonation in the
form of the linear correlation between the activation barrier and reaction
energy in which the rate of *O protonation is increased as the reaction becomes
more exothermic. We identified that the surface activity of Pt atoms of
core−shell NPs can be well explained by either d-band model or
coordination-number model, which have the same origin of chemical nature. Our
study provides fundamental understanding of functionality of step/edge sites of
Pt-based core−shell NPs for ORR that can be used for engineering of practical
cathode catalyst with atomic efficiency and precision by maximizing occupancy
of gold atoms at edge sites.  

REFERENCES

1.     An, W.; Liu, P.
Rationalization of Au Concentration and Distribution in AuNi@Pt Core-Shell
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6328-6336.

2.     Zhang, J.; Sasaki,
K.; Sutter, E.; Adzic, R. R. Stabilization of platinum oxygen-reduction
electrocatalysts using gold clusters. Science 2007, 315,
220-222.

3.     Gatalo, M.; Jovanovič, P.; Polymeros,
G.; Grote, J. P.; Pavlišič, A.; Ruiz-Zepeda, F.; Šelih, V. S.; Šala, M.;
Hočevar, S.; Bele, M.; Mayrhofer, K. J. J.; Hodnik, N.; Gaberšček, M. Positive
Effect of Surface Doping with Au on the Stability of Pt-Based Electrocatalysts.
ACS Catal. 2016, 6, 1630-1634.