Efficient Synthesis of Bimetallic Pt3Zn Alloy Nanocrystals with Different Shapes and their Enhanced Electrocatalytic Activity

Article abstract of DOI:10.1002/cctc.201900649

Highly uniform dispersed bimetallic Pt₃Zn alloy nanocrystals (NCs) with unique geometries are obtained via a facile one-pot synthesis process by regulating different reductants. To investigate the morphology and composition of the prepared catalysts, the transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy are utilized. Electrochemical measurements reveal that the Pt₃Zn NCs significantly exhibited larger electrochemically active surface areas and excellent catalytic activity towards electro-oxidation of methanol and ethanol in comparison to the commercial Pt/C. The optimized Pt₃Zn (AA) NCs exhibit excellent mass activities in both methanol oxidation reaction (1251.4 mA mg_Pt ^?1) and ethanol oxidation reaction (975.7 mA mg_Pt ^?1) in acidic media, which are respectively 4.28 times and 3.02 times higher than those of commercial Pt/C. Moreover, the Pt₃Zn NCs show a higher stability and better resistance to the CO_ads poisoning. The activity enhancements are attributed to electronic effects and a bifunctional mechanism.

Full text of DOI:10.1002/cctc.201900649

Accepted Article
Title: Efficient synthesis of bimetallic Pt3Zn alloy nanocrystals with
different shapes and their enhanced electrocatalytic activity
Authors: Xinran Zhang, Iahaia Gomes Ali Ossufo, Huanyu Ye, Yunxia
Huang, Shuaipeng Ge, Zhongcheng Xiang, Yimin Cui, and
Rongming Wang
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10.1002/cctc.201900649
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Efficient synthesis of bimetallic Pt3Zn alloy nanocrystals with
different shapes and their enhanced electrocatalytic activity
Xinran Zhang,[a],[b] Iahaia Gomes Ali Ossufo,[b] Huanyu Ye,[a] Yunxia Huang,[b] Shuaipeng Ge,[b] Dr.
Zhongcheng Xiang,[b] Prof. Yimin Cui*[b] and Prof. Rongming Wang*[a]
Dedication ((optional))
Abstract: Highly uniform dispersed bimetallic Pt3Zn alloy
nanocrystals (NCs) with unique geometries are obtained via a facile
one-pot synthesis process by regulating different reductants. To
investigate the morphology and composition of the prepared
catalysts, the transmission electron microscopy, X-ray diffraction and
X-ray photoelectron spectroscopy are utilized. Electrochemical
measurements reveal that the Pt3Zn NCs significantly exhibited
larger electrochemically active surface areas and excellent catalytic
activity towards electro-oxidation of methanol and ethanol in
comparison to the commercial Pt/C. The optimized Pt3Zn (AA) NCs
introduce non-precious metals to build bimetallic NCs because
of their possible synergetic effects[5]. Tremendous efforts have
already proved that these works can improve the activity of
catalysts while decreasing the usage of noble-metal, and
enhance the resistance ability to CO poisoning. It is well known
that Pt-based NCs with diverse shapes and structures have
shown their improved catalytic performance towards the
oxidation reaction of organic small molecules，such as PtCu[6],
PtNi[7], PtCo[8], PtFe[9] and so on. Pt-based bimetallic have
attracted considerable attention due to the lattice strain and
downshift of the d-band center in Pt-based alloys[10]. Additionally,
the catalytic activity of Pt-based catalysts is enhanced by
improved CO-poisoning tolerance as well as the advanced
catalytic performance through hindering the CO production,
exhibit excellent mass activities in both methanol oxidation reaction
-1
(1251.4 mA mgPt-1) and ethanol oxidation reaction (975.7 mA mgPt
)
in acidic media, which are respectively 4.28 times and 3.02 times
higher than those of commercial Pt/C. Moreover, the Pt3Zn NCs
show a higher stability and better resistance to the COads poisoning.
The activity enhancements are attributed to electronic effects and a
bifunctional mechanism.
which is also ascribed to modified transition metal atoms[11]
.
Zn, as a candidate material for preparing Pt-based bimetallic
catalysts, has an indelible position in new energy materials, due
to the abundant storage of the earth crust, low cost, and
excellent catalytic activity. In recent years, related articles have
reported the application of Pt-Zn bimetallic in the field of
catalysis. For example, Pt-Zn intermetallic nanoparticles (iNPs)
have been proven as active catalysts toward small organic
molecules electrooxidation. Moreover, Pt-Zn alloy catalysts
exhibit higher selectivity in carbon dioxide (CO2) rather than
carbon monoxide (CO) for DLFCs, such as methanol and formic
acid[12]. Huang et al. reported the synthesis of small and uniform
PtZn iNPs (3.2 ± 0.4 nm) supported on multiwalled carbon
nanotubes, and their electrooxidation activity for methanol
oxidation reaction (MOR) have greatly enhanced. Meanwhile,
DFT calculation results have proved that PtZn iNPs were more
Introduction
Direct liquid fuel cells (DLFCs) are considered to be effective
and renewable energy sources due to their high energy yield
power, friendly environment, low toxicity, conducive to storage
and transportation in mobile applications[1]. The fuel molecules
such as methanol, ethanol and formic acid are being intensively
studied as promising fuel[2]. It is well known that noble-metal
nanocrystals are primary catalysts for electrooxidation of all
these fuels, such as Pt and Pd catalysts[3]. However, their high
cost and low CO poisoning tolerance limits the large-scale
practical application of noble-metal catalysts[4]. One effective
strategy to solve these problems is to fabricate nano-sized
catalysts with appropriate structures, while another strategy is to
favorable for MOR[13]
.
Similarly, an intermetallic PtZn
nanocrystals were successfully synthesized via vapor-solid
reaction between Pt nanocrystals and Zn vapor at 500°C by
Akira et al. and the PtZn nanopaticles had high catalytic activity
toward small molecule oxidation[14]. However, most of them were
synthesized with the assistance of high temperature, template
and post heat-treatment, generally making the synthesis
procedures complicated and time-consuming. Therefore, for
these novel and available catalysts, we should not only optimize
their activity and stability, but also synthesize them by a simple
process so that they could be capable for cost-effective mass
production.
In this work, a simple and feasible strategy was advocated to
achieve uniform dispersed Pt3Zn alloy NCs with various
morphologies and well-defined structure features. The one-step
coreduction approach was reduction of metal precursors with
DMF as solvent in a weak reducing environment, based on the
weak reducibility of ascorbic acid (AA), glucose (Glc) and
[a]
Xinran Zhang, Huanyu Ye, Prof. Rongming Wang
Beijing Advanced Innovation Center of Materials Genome
Engineering, Beijing Key Laboratory for Magneto-Photoelectrical
Composite and Interface Science, School of Mathematics and
Physics, University of Science and Technology Beijing, Beijing
100083, R. P. China.
E-mail: rmwang@ustb.edu.cn
[b]
Xinran Zhang, Gomes Ali Ossufo, Yunxia Huang, Shuaipeng Ge, Dr.
Zhongcheng Xiang, Prof. Yimin Cui
Key Laboratory of Micro-nano Measurement-Manipulation and
Physics Ministry of Education, Department of Physics, Beihang
University, Beijing 100191, P. R. China.
E-mail: cuiym@buaa.edu.cn.
Supporting information for this article is given via a link at the end of
the document.
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10.1002/cctc.201900649
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sodium citrate (SC). Furthermore, AA, Glc and SC colud be
used as protective agent and structure directing agent, which
were demonstrated to play a vital role in altering the reduction
kinetics of metal precursors, thus determining the final
8a,
morphology of the bimetallic Pt3Zn NCs[1b,
15]. In addition,
optimizing the structure of catalyst and morphology of catalyst
was critical to the achievement of the required catalytic
performance. Impressively, the obtained bimetallic Pt3Zn (AA),
Pt3Zn (Glc) and Pt3Zn (SC) catalysts showed superior long-term
stabilities and excellent catalytic performance for the catalytic
oxidation of methanol and ethanol compared with the
commercial Pt/C.
Results and Discussion
The morphology evolution of the as-prepared Pt3Zn (AA), Pt3Zn
(Glc) and Pt3Zn (SC) NCs with using different reductants was
briefly described in scheme 1. For the synthesis of bimetallic
Pt3Zn alloy NCs, the structure characteristics were first
characterized by TEM and HR-TEM, as shown in Figure 1(a-
c).The typical images clearly showed that the obtained Pt3Zn
(AA) NCs were monodispersed and uniform heart-like structure
when using AA as a reductant and structure-directing agent (in
Figure 1a1-a3). The HR-TEM image showed well-fined lattice
fringes in Figure 1a3, where d-spacing of the lattice was
determined to be 0.220 nm ascribed to the (111) and 0.196 nm
to (220) facets plane for Pt3Zn (AA) alloy, indicating that the
sample was well-crystallized. The selected area electron
diffraction (SAED) patterns showed several bright concentric
rings indexed to (111), (200), (220), (311) lattice planes of
polycrystalline, as shown in Figure 1a4. Furthermore, when
using Glc and SC as alternative reductant, the regular cuboid-
like Pt3Zn (Glc) and rod-like Pt3Zn (SC) nanocrystals were
obtained (Figure 1b1-b3 and Figure 1c1-c3). The images clearly
Figure 1. TEM images, HR-TEM images, SAED patterns and particle size
distribution histograms with the fitted Gaussian curves of (a) Pt3Zn (AA), (b)
Pt3Zn (Glc) and (c) Pt3Zn (SC).
The average particle sizes of these products were determined
for each sample by measuring 100 randomly selected
nanoparticles in the TEM images with distribution histograms in
Figure 1a5, Figure 1b5 and Figure 1c5. Meanwhile, the average
particle sizes of the three samples were 9.0, 6.7 and 13.5 nm,
respectively.
The composition information of Pt3Zn (AA), Pt3Zn (Glc) and
Pt3Zn(SC) was detected by TEM energy-dispersive x-ray
spectroscopy (TEM-EDS) and ICP-MS. According to the TEM-
EDS analysis, it was confirmed that the products were
composed of Pt and Zn elements. The atomic percentages of Pt
and Zn in the alloy were 74.4 : 25.6 for Pt3Zn (AA), 73.8 : 26.2
for Pt3Zn (Glc) and 77.1 : 22.9 for Pt3Zn (SC), as shown in
Figure S1(a-c) in the Supporting Information, respectively. The
conclusions were consistent with the ICP-MS (Table S1 in the
Supporting Information). To further investigate the distribution of
Pt and Zn in these samples, HAADF-STEM- EDS elemental
mapping were carried out with the Pt3Zn (AA) as an example (in
Figure 2a-d). Both of the investigations revealed the coexistence
of Pt and Zn elements in the product, which were
homogeneously distributed on the entire NCs showing their alloy
nature. The EDS line scanning analysis of Pt3Zn (AA) alloy also
demonstrated both Pt and Zn signal areas across the entire
nanocrystal, as shown inserted in Figure 2a. In addition,
elemental mapping and line scanning analysis of the Pt3Zn (Glc)
and Pt3Zn (SC) were displayed in Figure S2 and Figure S3,
which suggested their alloy composition as well.
showed that the obtained products displayed
a uniform
dispersed morphology. The HR-TEM images and SAED clearly
indicated the lattice fringes of 0.220 nm in (111) facets of Pt3Zn
(Glc), as shown in Figure 1b3 and Figure 1b4. Besides, the HR-
TEM images and SAED patterns of Pt3Zn (SC) nanocrystal
indicated that it was a well-crystallized structure with well-
defined fringes of 0.219 nm in (111) facets (in Figure 1c3-c4).
The XRD patterns of the Pt3Zn (AA), Pt3Zn (Glc) and Pt3Zn
(SC) NCs catalysts showed that they were highly crystalline with
alloy phase, which were compared with the commercial Pt/C in
Figure 3. For Pt3Zn (AA) NCs, the typical diffraction peaks
appeared at 23.6 °, 32.1°, 40.4°, 46.2°, 68.2°, and 81.4°,
corresponding to the (100), (110), (111), (200), (220) and (311)
Scheme 1. Morphological evolution of Pt3Zn alloy NCs with different
reductants.
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Figure 3. XRD patterns for Pt3Zn (AA), Pt3Zn (Glc) and Pt3Zn (SC) NCs, the
dash lines represent the diffraction peak positions of Pt.
75.1 eV for Pt 4f5/2). It is noteworthy that the binding energy of Pt
peaks had a negative shift, quite probably originated from
electron donation from Zn to Pt because of different
electronegativities[17] and thus confirmed the formation of Pt3Zn
(AA) alloy NCs. The XPS spectrum of Zn 2p of Pt3Zn (AA) was
shown in Figure 4b, as an example. It can be seen that the two
peaks at binding energy 1021.5 eV for Zn 2p3/2 and 1044.60 eV
for Zn 2p1/2 originate from metallic Zn, respectively. Furthermore,
two peaks located at 1022.5 and 1045.5 eV were clearly
observed, indicating the presence of Zn2+, for Zn could be easily
oxidized under ambient conditions. However, the metallic Zn
was the dominant species in the Pt3Zn (AA) alloy and interacted
with Pt on surfaces leading to the electron transfer from Zn to Pt.
In addition, the Zn species of these three samples were
presented in Figure S4, which also suggested that the Pt3Zn
Figure 2. (a) HAADF-STEM image of Pt3Zn (AA) NCs, (b) Pt mapping in
green, (c) Zn mapping in red, and (d) Overlapped mapping of Pt and Zn. The
insets in (a) showed the EDS line scanning analysis of Pt3Zn (AA) NCs.
planes, respectively. All the diffraction peaks of the sample can
be assigned to ordered intermetallic (JCPDS No. 65-3257,
AuCu3 structure)[16]. The XRD pattern, which is consistent with
the HR-TEM image in Figure 1a3, clearly showed the
intermetallic Pt3Zn alloy phase for the Pt3Zn (AA) sample. It is
noted that the peak positions shift to higher angles relative to
pure Pt. This shift was due to the decreased lattice constant
after incorporation of Zn into Pt to form Pt3Zn (AA) alloy.
Furthermore, no impurity peaks of pure Pt and/or pure Zn were
observed, which confirmed that only a single compound Pt3Zn
phase existed in the products. For the Pt3Zn (Glc) and Pt3Zn
(SC) NCs, these peaks position were similar to the peaks
position of Pt3Zn (AA) NCs. The results were agreement with
SAED images in Figure 1(a4, b4 and c4) which indicated that
added Zn was incorporated into the final Pt3Zn NCs.
alloy NCs were formed, in correlation with the previous reports[18]
In general, the addition of a second metal lowered bimetallic d-
band center, which resulted a decrease in its adsorption
energy[19]. With respect to catalytic reactions, lowering the d-
band center reduced the binding energy of poisonous species
.
on surface active sites, thereby enhancing the rate of reaction[20]
.
It is well known that changes to the surface chemical states of
catalysis are believed to play critical roles in modifying the
catalyst properties. To investigate the surface composition and
element valence of intermetallic Pt3Zn alloy NCs, the XPS
experiments were conducted. The transfer of the surface
electrons of Pt and Zn in the Pt3Zn NCs was investigated by
XPS, as shown in Figure 4 and Figure S4. The XPS spectrum of
Pt 4f7/2 and Pt 4f5/2 can be utilized to probe the electronic
structure of Pt, and evaluate its d-band center shifting after
being corrected by C1s peak at 284.8 eV. As shown in Figure.
4a, the binding energy positions of Pt3Zn (AA) were located at
71.52 eV for Pt 4f7/2 and 74.8 eV for Pt 4f5/2. The peak positions
of Pt3Zn (Glc) and Pt3Zn (SC) NCs were similar, which were
evidently lower than that of the Pt/C (71.7 eV for Pt 4f7/2 and
Figure 4. XPS spectra of Pt3Zn NCs catalysts (a) Pt 4f of the four samples and
(b) Zn2p of Pt3Zn (AA). All binding energies were calibrated using C1s (284.8
eV).
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It has been reported in some literatures that the synthesis of
the intermetallic Pt3Zn NCs was a simultaneous co-reduction
process with Pt by the underpotential deposition process of Zn,
and the uniformity of Pt3Zn NCs was synthesized by adjusting
the temperature[13, 16]. In this work, using different reducing agent
was an effective strategy to produce various shapes for Pt3Zn
NCs in DMF solution. Take the reducing agent (AA) as an
examples, the dosage of AA was adjusted excessive to ensure
the complete reduction of precursor salts. Interestingly, when AA
was not added, the solid solution PtZn alloy NCs could be
obtained under similar condition. The structure of PtZn alloy NCs
has been confirmed by TEM and XRD pattern, as shown in
Figure S5(a-b). The TEM image showed that the NCs were a
non-uniform structure and had
a large size than 20 nm.
Nevertheless, the XRD pattern indicated that the intensity of the
(110) peak (the characteristic of the intermetallic Pt3Zn phase)
disappeared. The results may be ascribed to the relatively low
redox potential for Zn2+ species (Zn2+/Zn= - 0.76V vs. standard
hydrogen electrode (SHE)) relative to that for the Pt precursor
(Pt2+/Pt = 0.75 V vs. SHE), the reduction of Zn2+ is more difficult
than that of Pt2+ in DMF solution with the weak reducing ability.
Thus, the Zn atoms cannot deposit on Pt accurate position in a
shorter time reaction. This may lead to form PtZn alloy with solid
solution structure[16a] and the obtained PtZn alloy without any
impurities. When the dosage of the reducing agent (AA) was
turned to 50 mg, 100 mg, 150 mg, 250 mg, 350 mg and 400 mg,
the different morphologies of Pt-Zn alloy NCs were also obtained,
as shown in Figure 5(a-f). Interestingly, increasing the quantity
of the AA to 250 mg, the intermetallic Pt3Zn alloy NCs would be
synthesized. The XRD pattern with a characteristic peak and
TEM-EDS spectral could confirm the above result (in Figure S6
(a-b)). To better understand the formation mechanism of Pt3Zn
alloy NCs, temperature-dependent experiments were carried out.
It has been experimentally proved that Zn2+ is not easily reduced
to Zn at lower temperatures[16a]. When the temperature was
adjusted to the optimum temperature of 180°, we could get the
intermetallic Pt3Zn alloy NCs with different shapes in a short time
(6h) by the impact of reducing agents. In addition, PVP mainly
as dispersing agent was essential for the uniform distribution of
Pt3Zn alloy, which was in favor of the Zn underpotential
deposition without the active surface area loss caused by the
NCs aggregation. The synthesis provided a general approach to
obtain noble-based bimetallic NCs and would enable further
investigation of Pt-based alloy NCs for electro-oxidation and
other catalytic reactions.
Figure 5. TEM characterization of the morphology evolution of the Pt-Zn alloy
NCs. The products were obtained at (a) 50 mg, (b) 100 mg, (c) 150 mg, (d)
250 mg, (e) 350 mg and (f) 400 mg after adding AA.
The electrocatalysis performances of as-obtained catalysts as
probe were studied by low-temperature fuel cells fed with small
organic molecules. Pt-based catalysts are the most active
catalyst in these fuel cells. On this basis, the successful
preparation of Pt3Zn (AA), Pt3Zn (Glc) and Pt3Zn (SC) should
have improved catalysis performance with their unique chemical
composition and surface structure. The electrochemically active
surface areas (ECSAs) are closely associated with the number
of available active sites. The ECSAs of Pt-based electrocatalysts
are based on the hydrogen desorption region after subtraction of
the double-layer charge. In this paper, commercial Pt/C catalyst
was used as the reference for comparison. The ECSAs of Pt3Zn
(AA), Pt3Zn (Glc), Pt3Zn (SC) and Pt/C catalysts were calculated
to be 73.5 m2 g-1, 63.3 m2 g-1, 60.1 m2 g-1 and 46.6 m2 g-1,
respectively, as shown in Figure 6a. The high surface area
catalysts could be well distributed over the entire surface of the
electrode and hence high catalyst utilisation can be achieved.
Moreover, the uniform structure of Pt3Zn alloy NCs provided a
reasonably accessible surface area. Then, the methanol
oxidation reaction (MOR) catalytic activity was measured by
linear sweep voltammetry from -0.25V - 0.9 V in an aqueous
solution of 0.1 M HClO4 and 0.5 M CH3OH. In order to compare
the catalytic activity, the currents were normalized with respect
to both the ECSAs and the loading amounts of Pt. The Pt3Zn
NCs exhibited an enhanced specific activity and mass activity
compared to those of Pt/C, and the curves were demonstrated in
Figure 6(b-c). All the catalysts showed the typically characteristic
MOR peaks in the forward (If) and backward (Ib) peak currents
was related to the tolerance of a catalyst to the catalysis
generated during the electrooxidation of methanol directions. In
the forward scan, the forward peak at high potential (around
0.56 V) was corresponding to MOR, which was first oxidized to
CO2, CO and other carbonaceous intermediates. The backward
peak at around 0.2 V was owing to the removal of incompletely
oxidized absorbed CO or other carbonaceous intermediates[1b, 13,
21]. The specific current density of the Pt3Zn (AA), Pt3Zn (Glc)
and Pt3Zn (SC) showed excellent MOR oxidation specific
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activities of 1.69, 1.40 and 1.47mA cmPt-2, which were about
site was prone to dehydrogenation of water, while the Pt site
was prone to methanol[13, 22]. The dehydrogenation reaction thus
reduced the probability of poisoning of the Pt catalysts[17]. The
If/Ib ratio was an important index of the conversion of CO2
amount to CO amount, oxidized from methanol fuel. Meanwhile,
the If/Ib ratio of Pt3Zn (AA) (1.5), Pt3Zn (Glc) (1.34) and Pt3Zn
(SC) (1.22) was higher than those of Pt/C (1.15). The high If/Ib
ratio of Pt3Zn NCs implied their good tolerance for the adsorption
of the carbonaceous intermediates. To further compare the
catalytic activities of the these samples, loaded Pt mass activity
in forward peak current and specific activity in forward peak
-
2.73, 2.26 and 2.37 times higher than that of Pt/C (0.62 mA cmPt
-1
2). The corresponding mass activities were 1251.4 mA mgPt for
-1
the Pt3Zn (AA), 880.6 mA mgPt for the Pt3Zn (Glc) and 833.6
-1
mA mgPt for the Pt3Zn (SC), 4.28, 3.01 and 2.85 times higher
than that of Pt/C (292.1 mA mgPt-1), respectively, indicating the
enhanced electro-oxidation ability of the Pt3Zn NCs catalysts.
Among them, Pt3Zn (AA) NCs had the highest mass activities,
which may be due to the unique heart-like structure and rough
surface morphology of Pt3Zn (AA) NCs and can expose more
active sites. That is to say, the amount of active sites may have
different catalytic activities for nanocrystals of different structures. current for MOR were summarized in the histogram in Figure 6d.
Moreover, the enhanced catalytic performance for MOR could
be explained by electronic effects with Zn content to modify the
electronic structure of the Pt atoms. Furthermore, the unique
geometry of Pt3Zn NCs was also associated with the synergistic
effect of Zn and Pt in the alloy. Previous works have
demonstrated that in the Pt-Zn alloy catalysts, the Zn component
induced the direct methanol oxidation reaction at the active site
of Pt. It has also been reported by DFT calculations that the Zn
The CO stripping experiments were also conducted to explore
the CO poisoning tolerance. The current density and the onset
potential were important parameters for MOR electrocatalytic
activity[23]. The CO stripping voltammograms of Pt3Zn NCs and
Pt/C were shown in Figure 6e. The CO stripping peak of Pt3Zn
(AA) showed the lowest onset and peak potential at 0.31 V and
0.44 V, meaning that CO oxidation was much easier than Pt/C
with its potentials at 0.42 V and 0.51 V. The onset potential of
CO stripping for Pt3Zn (Glc) was 0.37 V and for Pt3Zn (SC) was
0.39 V, lower than that of Pt/C. Obviously, these results also
implied that the strength of CO on the Pt3Zn NCs were weaker,
and the removal of CO species only required
a lower
overpotential, indicating that the Pt3Zn NCs were more active for
CO oxidation than Pt/C catalysts.
In order to further evaluate the stability of the Pt3Zn (AA),
Pt3Zn (Glc), Pd3Zn (SC) and Pt/C catalysts with different
morphologies, long-term chronoamperometric measurement
technique was carried out. The i-t curves were obtained at 0.01V
vs SCE for 4000s, as shown in Figure 6f. The Pt3Zn (AA), Pt3Zn
(Glc) and Pt3Zn (SC) NCs displayed higher current density with
slow decay than that of Pt/C catalysts during the electrochemical
measurements, indicating Zn element could efficiently reduce
the current decay and enhance stability for MOR.
The electrocatalysts for ethanol oxidation reaction (EOR) of
the Pt3Zn (AA), Pt3Zn (Glc), Pt3Zn (SC) and Pt/C catalysts were
also studied in a mixed electrolyte containing 0.1 M HClO4 and
0.5 M CH3CH2OH, as shown in Figure S7a. The peak current
densities of catalysts were normalized over the Pt loading to get
the mass activity. The peak current density value of Pt3Zn (AA)
also reached 975.7 mA mgPt-1, which was higher than that of
Pt/C (322.4 mA mgPt-1). The mass activity of these catalysts was
compared as follows: Pt3Zn (AA) > Pt3Zn (Glc) > Pt3Zn (SC) >
Pt/C, which was consistent with the change regulation of the
electrochemical oxidation of methanol. Furthermore, the long-
term chronoamperometric measurement was used to manifest
the stability of the catalyst toward ethanol electrooxidation, as
shown in Figure S7b. The electrochemical activity and stability of
Pt3Zn NCs were higher compared to Pt/C catalyst. The decay of
the current density occurred from the initial value due to the
formation of poisoning species during the oxidation reaction.
As we know, the activity, selectivity and stability of the catalyst
are not only strongly dependent on the size, shape, composition
and electronic structure of the metal particles, but also on the
interaction with the second metal, which has a significant impact
on the catalytic performance of catalysts[11, 24]. Based on the
Figure .6 Electrochemical measurements of the Pt3Zn NCs and Pt/C catalysts
in N2 saturated solution. (a) CV curves in 0.1 M HClO4 solution at a scan rate
of 50 mV s-1. (b) ECSA-normalized and (c) Mass-normalized curves in 0.1 M
HClO4 and 0.5 M CH3OH at a scan rate of 50 mV s-1. (d) The histogram
showing the mass activity and specific activity of Pt3Zn NCs and Pt/C,
respectively. (e) CO stripping curves of Pt3Zn NCs and Pt/C catalysts in 0.1 M
HClO4 at a scan rate of 20 mV s-1. (f) CA curves of Pt3Zn NCs and Pt/C
catalysts at 0.01 V in 0.1 M HClO4 and 0.5 M CH3OH at a scan rate of 50 mV
s-1.
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The morphology of the samples was determined by Transmission
electron microscopy (TEM) and high-resolution TEM (HR-TEM) on a
JEM-2100FS transmission electron microscope operated at an
acceleration voltage of 200 kV equipped with selective area electron
diffraction (SAED). The elemental mappings were recorded on high-
angle annular dark-field scanning transmission electron microscopy
coupled with energy-dispersive X-ray spectroscopy (HAADF-STEM-EDS).
The inductively coupled plasma-mass spectrometry (ICP-MS) analysis
was conducted using a Thermo Scientific. The X-ray diffraction (XRD)
experiments were carried out on a Rigaku Dmax-2000 diffractometer
using Cu Ka radiation source. The X-ray photoelectron spectroscopy
(XPS) measurements were performed on an ESCALAB 250 system
(Thermo fisher) with an Al Kα radiation. The binding energy scale was
calibrated by the main C1s peak at 284.8 eV to ensure no significant
variations.
above analysis, it is found that the Pt3Zn NCs alloy effect was
caused by introduction of Zn, leading to the formation of new
structure and morphology and increasing the surface area of
alloy NCs. These results indicated that the Pt3Zn NCs catalysts
significantly promoted the catalytic activity and enhanced CO
poisoning tolerance as well as the long-term stability for MOR
and EOR.
Conclusions
In summary, it is shown that Pt3Zn alloy NCs catalysts can be
facilely synthesized in DMF solution with AA, Glc and SC as the
weaker reductants and structure directing agents. The results
revealed that weaker reductants guided the formation of the
heart-like, cuboid-like and rod-like morphology should be
responsible for the engineering of the size, shape and stucture
of Pt3Zn NCs. On the basis of the above results, the yielded
binary combination exhibited better electrochemical activity, CO
poisoning tolerance ability and long-term cycle ability for MOR
and EOR on the Pt3Zn NCs, compared to Pt/C catalysts. The
better performance was attributed to the optimized synergistic
effect of Zn and Pt. Meanwhile, this work may provide a simple
pathway for preparing diverse morphology electrocatalysts with
evident electrocatalytic performance and present a potential to
reduce the high cost of noble-metal catalysts for practical use in
DLFCs.
Electrochemical Measurements
The electrochemical measurements were performed on a CHI 660E
electrochemical workstation at room temperature at a scan rate of 50 mV
s-1. A three electrode cell was used with a Pt wire as counter electrode
and a saturated calomel electrode (SCE) as reference electrode. The
glassy carbon electrode (GC, 3 mm in diameter) coated with the alloy
catalysts were used as working electrode. Herein, all of the potentials
were against with reversible hydrogen electrode (RHE). To prepare the
working electrode, the prepared catalysts homogeneous ink was dropped
on a freshly polished glassy carbon electrode with the loading amount
about 1.1 μgPt using a micropipette. After drying in air, a Nafion (3 μL, 5
wt%) solution was used to cover the surface of the catalyst electrode. For
comparison, the electrochemical measurement of commercial Pt/C was
also carried out under the same conditions. Electrocatalytic
measurement was carried out in 0.1 M HClO4 solution deaerated by
ultrapure N2 for 15 min before test.
Experimental Section
CO stripping voltammetry was performed by running chronoamperometry
in 0.1 M HClO4 with bubbling CO gas for 30 min at 0.01 V vs SCE.
Following this, N2 was bubbled to remove the CO in the solution. Then,
cyclic voltammetry (CV) was run at 20 mV s-1. The measured currents
were converted to current density by normalization to the real surface
area of the electrode[25]. The specific activities and mass activities were
given as the forward peak currents normalized in reference to the
electrochemical active surface areas (ECSAs) and loading amount of Pt
metal, respectively.
Materials and reagents
Platinum(II) acetylacetonate (Pt(acac)2), zinc(II) acetylacetonate
(Zn(acac)2),
Poly
(vinylpyrrolidone)
(PVP,
MW≈30,000),
dimethylformamide (DMF), ascorbic acid (AA), glucose (Glc) and sodium
citrate (SC) were purchased from Chinese reagent companies.
Commercial Pt/C (20 wt% Pt) was purchased from Alfa Aesar. All
chemicals were used without any prior treatment. The water (18 MΩ/cm)
was used in all experiments.
Synthesis of Pt3Zn (AA), Pt3Zn (Glc) and Pt3Zn (SC) alloy NCs
Acknowledgements
To synthesize Pt3Zn (AA) alloy NCs catalysts, 30 mg of Pt(acac)2 and
18.0 mg of Zn(acac)2 were dissolved in 4 ml of DMF. Subsequently, 4 ml
DMF containing 350 mg of AA and 5 ml DMF containing 50 mg of PVP
were added to the above solution and magnetically stirred for 15 min.
The homogeneous solution was then transferred to a 25 mL Teflon-lined
stainless autoclave. The autoclave was heated to 180°C and maintained
at this temperature for 6 h, and then cooled to room temperature. Finally,
the precipitate was collected by centrifugation (10,000 rpm, 10 min),
completely washed with ethanol several times and then dried at room
temperature in vacuum. The preparation of Pt3Zn (Glc) and Pt3Zn (SC)
NCs catalysts took the similar one-step method except using the similar
ratio of Glc and SC to replace AA as reductants.
This work was supported by the National Natural Science
Foundation of China under 11674023, 51571006 and 111
Project (No. B170003).
Keywords: Pt3Zn nanocrystals • electrocatalytic activity •
methanol oxidation • fuel cells • CO stripping
[1]
a) M. H. Shao, Q. W. Chang, J. P. Dodelet, R. Chenitz, Chem Rev
2016, 116, 3594-3657; b) J. Y. Liu, G. R. Xu, B. C. Liu, J. Zhang,
Chem. Commun. 2017, 53, 7457-7460; c) H. Fan, M. Cheng, L.
Wang, Y. Song, Y. Cui, R. Wang, Nano Energy 2018, 48, 1-9.
a) L. Zhang, Q. Chang, H. Chen, M. Shao, Nano Energy 2016, 29,
198-219; b) L. Chen, J. Zhu, C. Xuan, W. Xiao, K. Xia, W. Xia, C.
Lai, H. L. Xin, D. Wang, J. Mater. Chem. A 2018, 6, 5848-5855.
a) H. Fan, M. Cheng, Z. Wang, R. Wang, Nano Res. 2017, 10,
187-198; b) R. Chen, M. Sun, G. Pang, J. Zhou, L. Hou, F. Gao,
Chemelectrochem 2017, 4, 1081-1087; c) A.-J. Wang, K.-J. Ju, Q.-
[2]
[3]
Characterizations
This article is protected by copyright. All rights reserved.

10.1002/cctc.201900649
ChemCatChem
FULL PAPER
L. Zhang, P. Song, J. Wei, J.-J. Feng, J. Power Sources 2016, 326,
227-234.
L. Luo, F. Zhu, R. Tian, L. Li, S. Shen, X. Yan, J. Zhang, ACS
Catal. 2017, 7, 5420-5430.
[12]
[13]
S. B. Lee, J. Park, P. A. van Aken, Nanoscale Res. Lett. 2016, 11.
Z. Qi, C. Xiao, C. Liu, T. W. Goh, L. Zhou, R. Maligal-Ganesh, Y.
Pei, X. Li, L. A. Curtiss, W. Huang, J. Am. Chem. Soc. 2017, 139,
4762-4768.
[4]
[5]
[6]
L. Dai, S. G. Mo, Q. Qin, X. J. Zhao, N. F. Zheng, Small 2016, 12,
1572-1577.
[14]
[15]
[16]
A. Miura, H. Wang, B. M. Leonard, H. D. Abruna, F. J. DiSalvo,
Chem. Mater. 2009, 21, 2661-2667.
J. J. Mao, Y. J. Chen, J. J. Pei, D. S. Wang, Y. D. Li, Chem.
a) Z. Zhang, Z. Luo, B. Chen, C. Wei, L. Zhao, J. Chen, X. Zhang,
Z. Lai, Z. Fan, C. Tan, M. Zhao, Q. Lu, B. Li, Y. Zong, C. Yan, G.
Wang, Z. J. Xu, H. Zhang, Adv. Mater. 2016, 28, 8712-8717; b) L.
Guo, L.-B. Huang, W.-J. Jiang, Z.-D. Wei, L.-J. Wan, J.-S. Hu, J.
Mater. Chem. A 2017, 5, 9014-9021; c) T. Y. Liu, K. Wang, Q.
Yuan, Z. B. Shen, Y. Wang, Q. H. Zhang, X. Wang, Nanoscale
2017, 9, 2963-2968.
a) Q. Sun, W. Liu, R. M. Wang, Crystengcomm 2012, 14, 5151-
5154; b) W. H. Gong, Z. Jiang, R. F. Wu, Y. Liu, L. Huang, N. Hu,
P. Tsiakaras, P. K. Shen, Appl. Catal. B-Environ. 2019, 246, 277-
283; c) X. L. Xu, X. Zhang, H. Sun, Y. Yang, X. P. Dai, J. S. Gao,
X. Y. Li, P. F. Zhang, H. H. Wang, N. F. Yu, S. G. Sun, Angew.
Chem. Int. Edit. 2014, 53, 12522-12527; d) J. F. Huang, P. K.
Tseng, Chem. Sci. 2018, 9, 6134-6142.
a) Q. Chen, Z. Cao, G. Du, Q. Kuang, J. Huang, Z. Xie, L. Zheng,
Nano Energy 2017, 39, 582-589; b) J. T. Ding, S. Ji, H. Wang, B.
G. Pollet, R. F. Wang, Electrochim. Acta 2017, 255, 55-62; c) H. H.
Huang, X. L. Hu, J. B. Zhang, N. Su, J. X. Cheng, Sci. Rep. 2017,
7, 9; d) L. Zhang, X. F. Zhang, X. L. Chen, A. J. Wang, D. M. Han,
Z. G. Wang, J. J. Feng, J. Colloid Interface Sci. 2019, 536, 556-
562.
a) X. L. Sun, D. G. Li, S. J. Guo, W. L. Zhu, S. H. Sun, Nanoscale
2016, 8, 2626-2631; b) J. Wang, Z. Wang, S. Li, R. Wang, Y. Song,
Nanoscale 2017, 9, 4066-4075; c) J. Liu, T. Xia, S. Wang, G. Yang,
B. Dong, C. Wang, Q. Ma, Y. Sun, R. Wang, Nanoscale 2016, 8,
11432-11440.
Commun. 2016, 52, 5985-5988.
a) Q. Chen, J. Zhang, Y. Jia, Z. Jiang, Z. Xie, L. Zheng, Nanoscale
2014, 6, 7019-7024; b) Y. Kang, J. B. Pyo, X. Ye, T. R. Gordon, C.
B. Murray, Acs Nano 2012, 6, 5642-5647.
A. Naitabdi, A. Boucly, F. Rochet, R. Fagiewicz, G. Olivieri, F.
Bournel, R. Benbalagh, F. Sirotti, J.-J. Gallet, Nanoscale 2018, 10,
6566-6580.
a) J. Zhu, X. Zheng, J. Wang, Z. X. Wu, L. L. Han, R. Q. Lin, H. L.
L. Xin, D. L. Wang, J. Mater. Chem. A 2015, 3, 22129-22135; b) Z.
X. Chen, K. M. Neyman, A. B. Gordienko, N. Rosch, Phys. Rev. B
2003, 68.
[17]
[18]
[7]
[8]
[19]
D. Chen, P. Sun, H. Liu, J. Yang, J. Mater. Chem. A 2017, 5,
4421-4429.
[20]
[21]
A. C. Chen, C. Ostrom, Chem Rev 2015, 115, 11999-12044.
T. Xia, J. Liu, S. Wang, C. Wang, Y. Sun, R. Wang, Sci. China
Mater. 2017, 60, 57-67.
a) Z. X. Chen, K. M. Neyman, A. B. Gordienko, N. Rosch, Phys.
Rev. B 2003, 68, 8; b) I. Pasti, S. Mentus, J. Alloy. Compd. 2010,
497, 38-45.
G. X. Chen, C. F. Xu, X. Q. Huang, J. Y. Ye, L. Gu, G. Li, Z. C.
Tang, B. H. Wu, H. Y. Yang, Z. P. Zhao, Z. Y. Zhou, G. Fu, N. F.
Zheng, Nat. Mater. 2016, 15, 564-+.
a) D. Bin, B. Yang, F. Ren, K. Zhang, P. Yang, Y. Du, J. Mater.
Chem. A 2015, 3, 14001-14006; b) X. Yan, X. Hu, G. Fu, L. Xu, J.
M. Lee, Y. Tang, Small 2018, 14, e1703940; c) J. J. Feng, X. X.
Lin, L. X. Chen, M. T. Liu, J. Yuan, A. J. Wang, J. Colloid Interface
Sci. 2017, 498, 22-30.
[22]
[23]
[24]
[9]
[10]
a) M. Tang, S. P. Luo, K. Wang, H. Y. Du, R. Sriphathoorat, P. K.
Shen, Nano Res. 2018, 11, 4786-4795; b) K. D. Gilroy, A.
Ruditskiy, H. C. Peng, D. Qin, Y. N. Xia, Chem Rev 2016, 116,
10414-10472; c) Y. N. Xia, X. H. Xia, Y. Wang, S. F. Xie, MRS Bull.
2013, 38, 335-344; d) Y. Peng, L. D. Li, R. Tao, L. Y. Tan, M. N.
Qiu, L. Guo, Nano Res. 2018, 11, 3222-3232.
[25]
T. Vidakovic, M. Christov, K. Sundmacher, Electrochim. Acta 2007,
52, 5606-5613.
[11]
Y. Xu, L. Chen, X. Wang, W. Yao, Q. Zhang, Nanoscale 2015, 7,
10559-10583.
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Author(s), Corresponding Author(s)*
Highly uniform bimetallic Pt3Zn alloy
nanocrystals were facilely fabricated with
unique geometries and well-defined
structure features with ascorbic acid (AA),
glucose (Glc) and sodium citrate (SC) as
the weaker reductants and structure
directing agents, which exhibited superior
electrocatalytic activity for methanol and
ethanol oxidation reaction. In addition, the
CO stripping measurement indicated that
the tolerance to CO poisoning has been
significantly improved by alloying PtZn.
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Title
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