Angewandte
Chemie
DOI: 10.1002/anie.200905413
Electrooxidation Catalysts
High-Index Faceted Platinum Nanocrystals Supported on Carbon
Black as Highly Efficient Catalysts for Ethanol Electrooxidation**
Zhi-You Zhou, Zhi-Zhong Huang, De-Jun Chen, Qiang Wang, Na Tian, and Shi-Gang Sun*
Platinum nanoparticles supported on carbon black (Pt/C) are
the most important electrocatalysts, especially in polymer
nanospheres. The square-wave potential led to periodic
oxygen adsorption and desorption on the Pt NCsꢀ surfaces
and played a key role in controlling the surface structure of
the Pt NCs and in increasing the quantity of atomic steps. It
has been confirmed that the THH Pt NCs exhibit superior
[1]
electrolyte fuel cells. The catalytic activity of Pt nano-
particles is highly dependent on their surface structures.
Surface defects, that is, step and kink atoms with low
coordination numbers (CN < 8), usually exhibit very high
chemical reactivity and catalytic activity for most structure-
sensitive reactions, for example, oxygen reduction and
[6]
catalytic activity to commercial Pt/C catalysts. Other shapes
of Pt and Pd NCs bounded by high-index facets, such as
trapezohedron with 24 {hkk} facets, concave hexoctahedron
with 48 {hkl} facets, and multiple twinned nanorods with {hk0}
and {hkk} facets have also been synthesized by applying this
[
2]
electrooxidation of small organic fuel molecules. Therefore,
the preparation of Pt nanoparticles with a high density of
atomic steps on their surface is an effective way to further
boost their catalytic activity. However, according to crystal
growth habits, the growth of Pt nanocrystals (NCs) tends to
form thermodynamic equilibrium shapes such as cubes,
tetrahedra, and cuboctahedra, which are bounded by low-
[5,7,8]
square-wave potential method.
Note that previously
synthesized Pt NCs are all relatively large (greater than
20 nm) and deposited on glassy carbon, which obstructs
potential applications such as in fuel cells owing to low
utilization efficiency of noble metals. Usually, practical Pt
electrocatalysts are supported on carbon black.
[
3]
index {111} and {100} facets of low surface energy. In theory,
atoms with low coordination numbers exist on such nano-
particles only at the edges and vertices, and are thus quite
limited. In contrast, high-index planes of Pt single crystals
contain a high density of low-coordinate atomic steps and
Herein, we report our new results in the synthesis of high-
index faceted Pt NCs supported on carbon black (HIF-Pt/C)
with a size (2–10 nm) comparable to that of commercial
catalysts by using a square-wave potential method. The key
for decreasing size is the employment of insoluble Cs PtCl
[
4,5]
kinks and therefore exhibit very high catalytic activity.
As
2
6
a result, the synthesis of Pt nanocrystal catalysts with high-
index facets is a desirable and challenging target in the
catalysis community.
dispersed on carbon black instead of large Pt nanospheres as
the precursor. Aberration-corrected high-resolution trans-
mission electron microscopy (HRTEM) and cyclic voltam-
metric characterizations revealed that the HIF-Pt/C catalysts
contain a much higher density of atomic steps than do
commercial Pt/C catalysts. The HIF-Pt/C catalysts exhibit two
to three times higher electrocatalytic activity than the
commercial Pt/C catalysts for ethanol oxidation thanks to
their high density of atomic steps. More importantly, the HIF-
Pt/C catalysts can promote the cleavage of the CꢀC bond of
Recently, we developed an electrochemically shape-
controlled method and successfully synthesized tetrahexahe-
dral Pt nanocrystals (THH Pt NCs) enclosed by {730} and
[6]
vicinal high-index facets. In this method, Pt nanospheres (ca.
50 nm in diameter) were first deposited on glassy carbon
GC) and then subjected to an electrochemical square-wave
7
(
potential treatment. Through dissolution and recrystalliza-
tion, THH Pt NCs with a defined size that can be varied from
ethanol to generate twice as much CO as commercial Pt/C
2
2
0 to 200 nm were grown on the GC at the expense of Pt
catalysts under the same conditions, as evidenced by in situ
FTIR reflection spectroscopy.
Figure 1 shows TEM images of the HIF-Pt/C catalysts.
Platinum nanoparticles are highly dispersed on the carbon
black support. The average size of the nanoparticles is (5.1 ꢁ
[
*] Dr. Z. Y. Zhou, Z. Z. Huang, D. J. Chen, Q. Wang, Dr. N. Tian,
Prof. S. G. Sun
State Key Laboratory of Physical Chemistry of Solid Surfaces
Department of Chemistry, College of Chemistry and Chemical
Engineering
Xiamen University, Xiamen 361005 (China)
Fax: (+86)592-2180-181
1
.2) nm, as illustrated by the size histogram (Figure 1c). This
size is comparable to that of commercial catalysts (usually 2–
10 nm). Energy-dispersive X-ray (EDX) spectroscopy (Fig-
ure 1d) indicates that there are no other impurities besides
carbon and oxygen, and the typical weight percent of Pt is
about 17%.
E-mail: sgsun@xmu.edu.cn
[
**] This study was supported by NSFC (20873113, 20833005, and
0933004), the MOST (2007DFA40890), Research Fund for New
Teachers of the Doctoral Program of Higher Education of China
200803841035), and Fujian Provincial Department of Science and
2
Aberration-corrected HRTEM was employed to charac-
terize the surface structure of the HIF-Pt/C catalysts. This
technology provides atomic-resolution images of the outmost
layer of nanoparticles, which are important in identifying
(
Technology (2008F3099 and 2008I0025). We thank Zhiying Cheng
and Yueliang Li at the Beijing National Centre for Electron
Microscopy for the aberration-corrected HRTEM tests.
[
9]
catalytic active sites. Three aberration-corrected HRTEM
images of the HIF-Pt/C nanoparticles are shown in Figure 2,
in which the border atoms are clearly resolved. The crystal
Angew. Chem. Int. Ed. 2010, 49, 411 –414
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
411
Zhou, Zhi-You
