jp7b03043_si_001.pdf (2.03 MB)
Understanding Composition-Dependent Synergy of PtPd Alloy Nanoparticles in Electrocatalytic Oxygen Reduction Reaction
journal contribution
posted on 2017-06-22, 19:43 authored by Jinfang Wu, Shiyao Shan, Hannah Cronk, Fangfang Chang, Haval Kareem, Yinguang Zhao, Jin Luo, Valeri Petkov, Chuan-Jian ZhongGaining
an insight into the relationship between the bimetallic
composition and catalytic activity is essential for the design of
nanoalloy catalysts for oxygen reduction reaction. This report describes
findings of a study of the composition–activity relationship
for PtPd nanoalloy catalysts in oxygen reduction reaction (ORR). PtnPd100‑n nanoalloys with different bimetallic compositions are synthesized
by wet chemical method. While the size of the Pt50Pd50 nanoparticles is the largest among the nanoparticles with
different compositions, the characterization of the nanoalloys using
synchrotron high-energy X-ray diffraction (HE-XRD) coupled to atomic
pair distribution function (PDF) analysis reveals that the nanoalloy
with an atomic Pt:Pd ratio of 50:50 exhibits an intermediate lattice
parameter. Electrochemical characterization of the nanoalloys shows
a minimum ORR activity at Pt:Pd ratio close to 50:50, whereas a maximum
activity is achieved at Pt:Pd ratio close to 10:90. The composition–activity
correlation is assessed by theoretical modeling based on DFT calculation
of nanoalloy clusters. In addition to showing an electron transfer
from PtPd alloy to oxygen upon its adsorption on the nanoalloy, a
relatively large energy difference between HOMO for nanoalloy and
LUMO for oxygen is revealed for the nanoalloy with an atomic Pt:Pd
ratio of 50:50. By analysis of the adsorption of OH species on PtPd
(111) surfaces of different compositions, the strongest adsorption
energy is observed for Pt96Pd105 (Pt:Pd ≈
50:50) cluster, which is believed to be likely responsible for the
reduced activity. Interestingly, the adsorption energy on Pt24Pd177 (Pt:Pd ≈ 10:90) cluster falls in between
Pt96Pd105 and Pd201 clusters, which
is believed to be linked to the observation of the highest catalytic
activity for the nanoalloy with an atomic Pt:Pd ratio of 10:90. These
findings have implications for the design of composition-tunable nanoalloy
catalysts for ORR.