Ultrathin Vein-Like Iridium–Tin Nanowires with Abundant Oxidized Tin as High-Performance Ethanol Oxidation Electrocatalysts

Article abstract of DOI:10.1002/smll.201701295

Iridium (Ir) holds great promise for ethanol oxidation reaction (EOR), while its practical applications suffer from the limited shape-controlled synthesis due to its low-energy barrier for nucleation. To overcome this limitation, the preparation of a new class of ultrathin vein-like Ir–tin nanowires (Ir?Sn NWs) with abundant oxidized Sn is reported. By tuning the ratio of Ir to Sn, the optimized Ir₆₇Sn₃₃/C exhibits the highest mass density of 95.6 mA mg^?1 Ir for EOR at low potential (0.04 V), which is 4.1-fold and 20-fold higher than that of Ir/C and the commercial Pt/C, respectively. It also exhibits the smallest Tafel slope of 153 mV dec^?1 and superior stability after 2 h chronoamperometric measurement. Electrochemical measurements and X-ray photoelectron spectra results confirm that the abundant oxidized Sn promotes a complete oxidization of ethanol into CO₂ at low potential. This work highlights the importance of non-noble metal on enhancing the EOR performance.

Full text of DOI:10.1002/smll.201701295

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Electrocatalysis
Ultrathin Vein-Like Iridium–Tin Nanowires with Abundant
Oxidized Tin as High-Performance Ethanol Oxidation
Electrocatalysts
Meiwu Zhu, Qi Shao, Yecan Pi, Jun Guo, Bin Huang, Yong Qian,*
and Xiaoqing Huang*
Iridium (Ir) holds great promise for ethanol oxidation reaction (EOR), while its
practical applications suffer from the limited shape-controlled synthesis due to its low-
energy barrier for nucleation. To overcome this limitation, the preparation of a new

class of ultrathin vein-like Ir–tin nanowires (Ir Sn NWs) with abundant oxidized
Sn is reported. By tuning the ratio of Ir to Sn, the optimized Ir67Sn33/C exhibits the
highest mass density of 95.6 mA mg−1 Ir for EOR at low potential (0.04 V), which is
4.1-fold and 20-fold higher than that of Ir/C and the commercial Pt/C, respectively.
It also exhibits the smallest Tafel slope of 153 mV dec−1 and superior stability after
2 h chronoamperometric measurement. Electrochemical measurements and X-ray
photoelectron spectra results confirm that the abundant oxidized Sn promotes a
complete oxidization of ethanol into CO2 at low potential. This work highlights the
importance of non-noble metal on enhancing the EOR performance.
Ethanol (CH3CH2OH) is an ideal energy source for fuel cells studied as the highly efficient catalysts toward EOR,[7–12]
because of its unique characteristics such as high availability especially the Pt-based catalysts, which is commonly consid-
from biomass production, low toxicity, and safety for storage ered as the optimal catalyst. However, during the complex
and transportation in liquid form.[1–6] However, ethanol oxi- EOR process, the generated intermediates such as CO can
dation reaction (EOR) in fuel cells is extremely hindered by poison Pt active sites on the surface, largely restricted its
the contemporary, low-efficient catalysts. To overcome these efficiency. Hence, developing the Pt-free catalysts for EOR
limitations, noble metal nanomaterials have been extensively is highly desirable. While various shape-controlled noble
metal-based catalysts have been well testified as highly active
and selective ones for EOR,[10,13–15] the iridium (Ir)-based
M. Zhu, Dr. B. Huang, Prof. Y. Qian
Jiangxi Province Key Laboratory
of Polymer Micro/Nano Manufacturing and Devices
East China University of Technology
Nanchang, Jiangxi 330013, China
E-mail: yqianecit@163.com
electrocatalysts for EOR have rarely been reported, despite
their appealing catalytic activities in many electrochemical
catalysis.[16–21]
The practical applications of Ir nanomaterials suffer
from not only their scarcity and high cost but also difficul-
ties in controlled synthesis, in which only small and irregular
Ir nanoparticles (NPs) can be obtained.[22] To address the
above challenges, introducing non-noble metal into Ir is
highly desirable.[20,23,24] Except for reducing the cost, experi-
mental results suggest that introducing the non-noble metal
promotes the formation of shape-controlled nanomate-
rials,[25–29] which may provide an alternative pathway for the
controlled synthesis. Furthermore, a complete C2H5OH oxi-
dation undergoes a 12-electron process to generate CO2 and
water, while most of the real EOR processes only produce
acetaldehyde or acetic acid via two or four electrons process
M. Zhu, Dr. Q. Shao, Y. Pi, Prof. X. Huang
College of Chemistry
Chemical Engineering and Materials Science
Soochow University
Jiangsu 215123, China
E-mail: hxq006@suda.edu.cn
Prof. J. Guo
Testing and Analysis Center
Soochow University
Jiangsu 215123, China
DOI: 10.1002/smll.201701295
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since the multiple poison intermediates such CO and CHx No distinct peak shift was observed compared to that of the
can poison the surface active sites and slow down the reac- (111) plane of pure Ir (2θ = 40.6°) (JCPDS No. 06-0598) and
tion kinetics.[30] The introduction of the oxidized non-noble no Sn (JCPDS No. 05-0390) peaks were found in the vein-
metal into noble metal catalysts is expected to boost the like Ir67Sn33 NWs, indicating the nonalloy phase of Ir67Sn33
EOR process,[13,30] since oxidized metals favor the develop- NWs that coincided with the result of SAED. The crystal-
ment of OH species from dissociative adsorption of water, line nature of the vein-like Ir67Sn33 NWs was further char-
which not only helps to clean the surface of noble metal cata- acterized by high-resolution TEM (HRTEM) (Figure 1e).
lyst by removing CO and CHx but also enhances the reac- A majority of the interplanar spacings of ≈0.230 nm were
[30]

tion kinetics and C C bond splitting ability. Therefore, it observed, which were consistent with the (111) plane of fcc
is highly desirable to design Ir nanomaterials with oxidized Ir (JCPDS No. 06-0598). As shown in the inset of Figure 1e,
metals for enhanced EOR catalysis.
it is obvious that a few exterior low coordination atoms and

Herein, ultrathin vein-like Ir–tin nanowires (Ir Sn NWs) defects adhere to the kinks, which can supply a number of
with controlled compositions were synthesized by a facile active sites for catalytic process.[31–34] In addition, we have
wet-chemical method, where Sn plays a critical role in the carefully collected the fast Fourier transform (FFT) patterns
formation of ultrathin vein-like structure. The ultrathin vein- in three different regions from HRTEM images (Figure S5,
like Ir-Sn NWs with different Ir/Sn ratios provide an ideal Supporting Information). The diffraction direction showed an
platform to pursue the best catalytic condition toward EOR, obvious shift that attributed to the discontinuous crystalline
in which the Ir67Sn33/C exhibited the highest mass activity, fringes in the NWs, revealing the polycrystalline structure of
lowest Tafel slope, and best durability for EOR, compared to the vein-like NWs. STEM-EDS elemental mapping analysis

the Ir/C and other Ir Sn/C with different Ir/Sn molar ratios. showed the composition distribution of vein-like Ir67Sn33

Significantly, Sn in Ir Sn NWs is in the form of oxidized Sn, NWs (Figure 1f), where both Ir and Sn were uniformly dis-
which is beneficial for promoting C2H5OH oxidation. The tributed over the whole vein-like NWs. In short, the above

electrochemical activities of Ir Sn/C improve with increasing characterizations confirm that the Ir67Sn33 NWs are com-
the concentration of oxidized Sn. It turns out that the opti- posed of a nonalloy bimetallic nanostructure with the crystal-
mized Ir67Sn33/C enabled oxidization of C2H5OH into CO2 line Ir and the amorphous Sn species.[35]
efficiently at low potential, which is 20 times higher in mass
Interestingly, introducing the non-noble metal Sn into
activity than the commercial Pt/C at 0.04 V. The successful Ir is necessary for the formation of the ultrathin vein-like
introduction of abundant oxidized Sn can boost the synthesis Ir67Sn33 NWs since only pure Ir NPs could be synthesized
and electrocatalysis of Ir-based nanomaterials, which paves a in the absence of Sn precursor while keeping the other
new avenue for the fabrication of the high-performance elec- parameters same (Figure S3, Supporting Information). After
trocatalysts with unique nanostructure for practical fuel cells acknowledging the important role of non-noble metal Sn in
and beyond.
the synthesis for ultrathin vein-like Ir67Sn33 NWs, we further

The synthesis of Ir Sn NWs was carried out by using studied the effect of the amount of Sn(Ac)2 on the synthesis
iridium(III) chloride hydrate (IrCl3) as Ir precursor, tin(II) of Ir67Sn33 NWs. Figures S6–S8 (Supporting Information)
acetate (Sn(Ac)2) as Sn precursor, citric acid (CA) as reducing show the compositional, morphological, and structural char-

agent, poly(vinylpyrrolidone) (PVP) as reducing agent, and acterizations of the three prepared Ir Sn NWs with dif-
ethylene glycol (EG) as solvent and reducing agent (see ferent molar ratios (Ir72Sn28, Ir67Sn33, and Ir61Sn39) in details,
the Experimental Section for details). Through optimizing a respectively. The SEM-EDS results consist of the supplied
variety of synthetic parameters, such as solvents, amount of molar ratios of Ir72Sn28, Ir67Sn33, and Ir61Sn39, respectively
reducing agent, and reaction time, we found that the com- (Figure S6, Supporting Information). The TEM images show
bined usages of CA, PVP, Sn(Ac)2, and EG were essential for that Ir72Sn28 NWs and Ir61Sn39 NWs have the similar ultrathin
the successful preparation of vein-like NWs (Figures S1–S4, vein-like morphology as Ir67Sn33 NWs (Figure S7, Sup-
Supporting Information). The typical high-angle annular dark porting Information). The XRD patterns of Ir72Sn28 NWs and
field STEM (HAADF-STEM) (Figure 1a) and transmission Ir61Sn39 NWs are similar to that of Ir67Sn33 NWs (Figure S8a,
electron microscopy (TEM) (Figure 1b) images clearly show Supporting Information), where one set of peaks fit well with
the ultrathin vein-like morphology with many kinks, which that of fcc Ir and no Sn peaks are observed, indicating these

were interwoven by ultrathin NWs. The selected area elec- Ir Sn NWs have nonalloy binary structure.
tron diffraction (SAED) pattern of the products in the inset
We then started to elucidate the growth mechanism of
of Figure 1a can be indexed to (111), (220), and (311) face- Ir67Sn33 NWs by collecting the TEM images (Figure 2) and
centered cubic (fcc) Ir (JCPDS No. 06-0598) with no diffrac- SEM-EDS spectra (Figure S9, Supporting Information) of
tion ring of Sn species can be found, indicating the formation the intermediates at different reaction time. As shown in
of crystalline Ir and absence of crystalline Sn. Since the molar Figure 2a,b of the intermediates obtained after the 1 h syn-
ratio of Ir to Sn in the NWs was determined to be 67:33 by thesis, only small NPs with the diameter of less than 2 nm were
scanning electron microscopy energy-dispersive spectrometer obtained.The atomic ratio of Ir in this intermediate was 75.70%.

(SEM-EDS) (Figure 1c), the product was termed as Ir67Sn33 As the reaction prolonged to 3 h, the size of Ir Sn NPs almost
NWs. Powder X-ray diffraction (XRD) pattern was used kept the same and a small proportion of short NWs appeared
to verify the crystalline nature of vein-like Ir67Sn33 NWs (Figure 2c,d). When the reaction time increased to 5 h, the
(Figure 1d).The broad peaks of (111),(220),and (311) planes of distinct vein-like NWs came out (Figure 2e,f). At this point,
fcc Ir give the evidence of the ultrathin feature of the NWs. a large number of convex/concave regions and kinks could
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Figure 1. a) HAADF-STEM image and SAED pattern in the inset, b) TEM image, c) SEM-EDS, d) XRD pattern, e) HRTEM image, and f) HAADF-STEM
element mappings image of the vein-like Ir67Sn33 NWs. Dashed lines in (e) indicate the defects and the white arrows in the inset point to the atom
steps (red dots).
be observed. Further extension of reaction time to 10 h, beneficial to the oxidation of C2H5OH molecules.[31] To this
the ultrathin vein-like NWs were finally obtained with the end, we chose the Ir67Sn33 NWs as electrocatalysts for EOR.
atomic ratio of Ir to Sn of 67.08:32.92 (Figure 2g,h). These The electrocatalysts were prepared by a surface-clean method

time-dependent morphological changes suggest an attached that directly grown Ir Sn NWs on carbon black without
process of the formation of vein-like NWs, where it started using any surfactants (Figure S11, Supporting Information).
from the initial small nanoparticles, then gradually grew The resultant electrocatalysts were dispersed in C2H5OH
into short NWs and finally lead to the ultrathin vein-like with 5% Nafion to form a uniform catalyst ink via 30 min

NWs (Figure 2i). The XRD patterns of Ir Sn intermediates sonication. 4 µL of catalyst ink was casted on the glassy
showed that all the peaks matched well with those of fcc Ir carbon electrode (GCE) (containing 20.4 µgIr cm−2 according
(JCPDS No. 06-0598), indicating the intermediates have the to the thermogravimetric analyses (TGA) (Figure S12, Sup-
same nonalloy crystalline phase as Ir67Sn33 NWs (Figure S10, porting Information) and SEM-EDS (Figure S13, Supporting
Supporting Information).
Information)).
The EOR activities of the pristine Ir Sn/C were inves-

The unique structures of the as-prepared Ir67Sn33 NWs,
such as ultrathin feature, plenty of defects and steps, exposed tigated by cyclic voltammetry (CV) (Figure S14, Supporting
large active surface area, and numerous active sites, are Information).Although mass current density of Ir67Sn33/C was
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Figure 2. TEM images of ultrathin vein-like Ir67Sn33 NWs intermediates obtained after proceeding the reaction for a,b) 1, c,d) 3, e,f) 5, and g,h) 10 h.

i) Schematic illustration of the growth mechanism of the ultrathin vein-like NWs. j) Atomic ratios of Ir and Sn in Ir Sn intermediates at different
reaction time.


slightly higher than other Ir Sn/C, the three Ir Sn/C exhib- activity among the four different catalysts, which is 1.6, 2.2,
ited low mass current density. Therefore, we thermally and 4.1 times higher than those of Ir72Sn28/C, Ir61Sn39/C, and

treated the Ir67Sn33/C at 200, 250, and 300 °C under H2/N2 Ir/C, respectively. Meanwhile, all the Ir Sn/C catalysts show
flow for 1 h to optimize the catalytic activities (Figure S15, similar oxidation peaks at low potential, which are much

Supporting Information). Among the Ir67Sn33/C(H2-200 °C), higher than that of the Ir/C, indicating that the Ir Sn/C cata-
Ir67Sn33/C(H2-250 °C), and Ir67Sn33/C(H2-300 °C), the lysts own better EOR activity than Ir/C. Figure 3c shows the
Ir67Sn33/C(H2-250 °C) displayed the highest mass current den- Tafel plots of the Ir72Sn28/C, Ir67Sn33/C, Ir61Sn39/C, and Ir/C.
−1
sity of 94.5 mA mg at 0.09 V. Catalytic durability was then The Ir67Sn33/C exhibits the lowest Tafel slope (153 mV dec−1)
Ir
tested at the low potential of 0.09 V by chronoamperometry. among the four catalysts, indicating the highest rate of
Figure 3a shows the concrete mass current densities of the C2H5OH electrooxidation. By comparing the CV curves and
catalysts in the durability measurements at 0.09 V for 2 h. Ini- Tafel plots of Ir72Sn28/C, Ir67Sn33/C, Ir61Sn39/C, and Ir/C, we
tially, the Ir67Sn33/C(H2-200 °C), Ir67Sn33/C(H2-250 °C), and find that the Ir67Sn33/C exhibits the best activity toward

Ir67Sn33/C(H2-300 °C) electrocatalysts display the mass cur- EOR. Obviously, all the Ir Sn/C show higher mass activity
−1
rent densities of 42.28, 82.65, and 25.20 mA mg , respectively. and reaction rate than Ir/C, suggesting the non-noble metal
Ir
After 1 h, mass current densities of Ir67Sn33/C(H2-200 °C), Sn may assist the EOR. In addition, the durabilities of the
Ir67Sn33/C(H2-250 °C), and Ir67Sn33/C(H2-300 °C) decrease Ir72Sn28/C, Ir67Sn33/C, Ir61Sn39/C, and Ir/C were also exam-
−1
to 4.33, 6.11, and 2.02 mA mg , respectively, and then slowly ined by applying a constant potential at 0.09 V for 2 h. As
Ir
−1
drop to 2.86, 3.32, and 0.98 mA mg until 2 h. It is obvious displayed in Figure 3d, the Ir67Sn33/C shows the best dura-
Ir

that thermal treatment at 250 °C can optimize the catalytic bility, and all Ir Sn/C catalysts present better durability than
activities of Ir67Sn33/C. We then started to explore the influ- the Ir/C. After the durability measurements, limited changes

ence of composition on Ir Sn/C in EOR. Detailed electro- in morphology and composition were found in Ir67Sn33/C
chemical results are represented in Figure 3b–d. As shown in (Figures S16 and S13d, Supporting Information), while plenty
Figure 3b, the mass current densities of Ir72Sn28/C, Ir67Sn33/C, of aggregations were observed in the Ir/C (Figure S17, Sup-
−1
Ir Sn /C, and Ir/C are 59.9, 95.6, 44.1, and 23.6 mA mg at porting Information), further highlighting the superior dura-
Ir
61
39
0.04 V, respectively. The Ir67Sn33/C exhibits the highest mass bility of the Ir67Sn33/C.
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Figure 3. Electrochemical performances of Ir72Sn28/C, Ir67Sn33/C, Ir61Sn39/C, and Ir/C in acidic condition in 0.5 m H2SO4 and 0.5 m CH3CH2OH
solution. a) Concrete mass current densities of the catalysts in the durability measurements at 0.09 V for 2 h; the error bars were recorded by three
independent tests. b) EOR curves from −0.1 to 0.35 V. c) Tafel plots were tested at the scan rate of 1 mV s−1 and d) durability measurements at
0.09 V of Ir72Sn28/C, Ir67Sn33/C, Ir61Sn39/C, and Ir/C after thermal treatment under H2/N2 flow at 250 °C.

Since Sn plays a significant role in the enhanced EOR catal- significantly, the activities of all the three Ir Sn/C are higher
ysis, we analyzed the chemical states of Ir and Sn of different than that of the Ir/C. Therefore, the oxidized Sn can promote

Ir Sn/C after thermal treatment at 250 °C under H2/N2 flow by the electrochemical activity of EOR for Ir-based binary metal
X-ray photoelectron spectroscopy (XPS). As shown in Figure 4, catalysts since oxidized Sn is propitious for the formation of
the surface atomic ratios of Ir/Sn in Ir72Sn28/C, Ir67Sn33/C, and OH species and helps to remove the adsorbed poison CO or
Ir61Sn39/C are 55.85/44.15, 50.52/49.48, and 48.92/51.08, respec- CHx intermediates, which efficiently promote the complete
tively. Furthermore, the XPS peaks of Ir in different catalysts oxidization of C2H5OH into CO2.[30] Considering the low

were divided into Ir 4f7/2 and Ir 4f5/2 peaks, which can be fur- EOR activity of the pristine Ir Sn/C, the surface states of the

ther splitted into two doublets, corresponding to Ir (0) (purple Ir Sn/C before thermal treatment were further studied by
line) and Ir (IV) (orange line) (Figure 4a). It was calculated that XPS (Figure S18, Supporting Information). Although the sur-

the Ir (0) fraction in Ir/C (55.01%) is slightly higher than those face atomic ratios of Ir/Sn in Ir Sn/C have no obvious changes
in Ir72Sn28/C (43.56%), Ir67Sn33/C (43.18%), and Ir61Sn39/C after the thermal treatment, the surface oxidized Ir distinctly
(40.83%) (Table S1, Supporting Information). As shown decreased while oxidized Sn had slightly changed (Tables S1–S4,
in Figure 4b, the Sn 3d peaks of Ir72Sn28/C, Ir67Sn33/C, and Supporting Information). Therefore, the EOR activities of

Ir61Sn39/C are composed of Sn 3d5/2 and Sn 3d3/2 peaks, both Ir Sn/C have distinctly increased after thermal treatment,
of which are split into two oxidized Sn peaks and one metallic which can be attributed to the reduction of surface-oxidized Ir
Sn peak. The oxidized Sn mainly involves Sn(II) (orange line) that consequently increased ethanol adsorption.[17]
and Sn(IV) (pink line). The metallic Sn (purple line) peaks are
EOR has been confirmed as an intricate reaction,
located at Sn(0) 3d5/2 484.9 eV and Sn(0) 3d3/2 493.3 eV.[36] For because it involves multiple reaction products, including CO2,
all Ir Sn/C, the peaks of Sn(II) and Sn(IV) are much higher CH3CHO, and CH3COOH.[37] Two parallel reactions can

than that of Sn(0), and the oxidized Sn accounts for over 98% be used to interpret the reaction process of EOR in acidic
(Table S2, Supporting Information), indicating that abundant solution:[23]

oxidized Sn on the surface of Ir Sn/C. Among these three

Ir Sn/C, Ir67Sn33/C has the highest content of oxidized Sn, and CH CH OH → CH CH OH → CH3CHO
[
]
3
2
3
2
ad
(1)
the content of oxidized Sn in Ir72Sn28/C is slightly higher than
that in Ir61Sn39/C. With increasing the content of oxidized Sn,
electrochemical mass activity and durability improve in three
Ir Sn/C, in which the Ir67Sn33/C with the highest amount of
oxidized Sn shows the best electrochemical performance. More
→ CH3 + CO → 2CO2 complete oxidation
(
)
CH CH OH → CH CH OH → CH3CHO
[
]
3
2
3
2
ad

(2)
→ CH CO → CH COOH partial oxidation
(
)
3
3
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Figure 4. a) Ir XPS spectra of Ir/C, Ir72Sn28/C, Ir67Sn33/C, and Ir61Sn39/C after thermal treatment under H2/N2 flow at 250 °C. b) Sn XPS spectra of
Ir72Sn28/C, Ir67Sn33/C, and Ir61Sn39/C after thermal treatment under H2/N2 flow at 250 °C. All data are corrected based on C1s at 284.6 eV.
During EOR, a complete oxidation into CO2 is more
To elucidate the EOR mechanism of Ir67Sn33/C, we
difficult than the partial oxidation into CH3CHO or further investigate possible intermediates of EOR for
CH3COOH,[17] because forming CO2 involves a 12-electron Ir67Sn33/C, Ir/C, and Pt/C. First, Ir67Sn33/C, Ir/C, and Pt/C
transfer via C C bond cleavage, while producing CH3CHO were activated for 300 cycles at 30 mV s−1 in 0.5 m H2SO4

or CH3COOH only needs two or four-electron transfer.[38] solution (Figure S19, Supporting Information) before car-

In other words, more energy is needed to split C C bond in rying out the electrochemical tests in a mixture of 0.5 m
order to generate CO2 in the complete oxidation.[30] There- C2H5OH, 0.5 m CH3CHO, or 0.5 m CH3COOH with 0.5 m
fore, exploring an excellent electrocatalyst for the complete H2SO4 at the rate of 30 mV s−1 from −0.1 to 0.35 V, respec-
oxidation is necessary, which could greatly improve the utili- tively (Figure 5). Only the Ir67Sn33/C has a high oxida-
zation of C2H5OH.
tion peak at potential less than 0.1 V, with the excellent
Figure 5. CVsofIr67Sn33/C(H2-250 °C), Ir/C, and Pt/Cwere collected in a mixture of0.5 m H2SO4 with 0.5 m. a) CH3CH2OH, b) CH3CHO, and c) CH3COOH,
respectively.
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−1
mass current density of 95.6 mA mg at 0.04 V, which is
Ir
4 and 20 times higher than Ir/C (23.5 mA mg−1) and Pt/C
(4.9 mA mg−1), respectively (Figure 5a). The durabilities
of the Ir67Sn33/C, Ir/C, and Pt/C were also conducted at a
constant potential of 0.09 V for 2 h, in which the Ir67Sn33/C
exhibited superior durability while Ir/C was nearly inac-
tive after 1 h, and Pt/C lost activity completely in a very
short time (Figure S20, Supporting Information). As
shown in Figures S17 and S21 (Supporting Information),
obvious aggregations were found in Ir/C and Pt/C, while
the Ir67Sn33/C had relatively few aggregations, further
suggesting that the Ir67Sn33/C is more stable than Ir/C
and Pt/C. In addition, the similar catalytic curves as the
measured EOR curves were observed in CH3CHO oxida-
tion reaction (Figure 5b), where only the Ir67Sn33/C had
an obvious oxidation peak from −0.1 to 0.1 V, suggesting
that the Ir67Sn33/C shows the best electrochemical activity
among the three electrocatalysts at low potential. These
phenomena show that CH3CHO is a necessary interme-
diate product of EOR, similar to the reported measure-
ment.[23] The CH3COOH oxidation reaction was further
carried out to check if CH3COOH is the ultimate product
of EOR (Figure 5c). Although Ir67Sn33/C had slightly
higher mass activity than Ir/C and Pt/C, all the three elec-
trocatalysts show negligible mass activity compared with
those in EOR and CH3CHO oxidation reaction, indicating
that CH3COOH is the ultimate product of partial oxida-
tion for EOR. Since a complete oxidation of ethanol into
CO2 involves a 12-electron transfer while partial oxida-
tion into CH3COOH involves a four-electron transfer as
mentioned above two parallel reactions;[38] higher mass
activities in both CH3CH2OH and CH3CHO oxidations
of the Ir67Sn33/C than those of the Ir/C and Pt/C indicate
that CO2 can be the major ultimate product of Ir67Sn33/C
for EOR. In a word, by comparing CH3CH2OH, CH3CHO,
and CH3COOH oxidation processes, we find that the abun-
dant oxidized Sn in Ir67Sn33/C could promote the complete
oxidation of CH3CH2OH molecules into CO2 rather than
CH3CHO or CH3COOH, which significantly enhances the
EOR performance of Ir67Sn33/C.
Supporting Information
Supporting Information is available from the Wiley Online Library
or from the author.
Acknowledgements
This work was financially supported by the Ministry of Science
and Technology (2016YFA0204100), the National Natural Science
Foundation of China (21571135, 21565002), Young Thousand Tal-
ented Program, the start-up fundings from Soochow University, the
Priority Academic Program Development of Jiangsu Higher Educa-
tion Institutions (PAPD), Young Scientist Foundation of Jiangxi Prov-
ince (20133BCB23020), and Most Foundation of Jiangxi Province
(20152ACB21018).
Conflict of Interest
The authors declare no conflict of interest.
[1] E. Antolini, Energy Environ Sci. 2009, 2, 915.
[2] I. Kim, O. H. Han, S. A. Chae, Y. Paik, S. H. Kwon, K. S. Lee,
Y. E. Sung, H. Kim, Angew. Chem. Int. Ed. 2011, 50, 2270.
[3] C. W. Xu, H. Wang, P. K. Shen, S. P. Jiang, Adv. Mater. 2007, 19,
4256.
[4] A. Chen, P. Holt-Hindle, Chem. Rev. 2010, 110, 3767.
[5] A. Rabis, P. Rodriguez, T. J. Schmidt, ACS Catal. 2012, 2,
864.
[6] L. Yang, S. Kinoshita, T. Yamada, S. Kanda, H. Kitagawa,
M. Tokunaga, T. Ishimoto, T. Ogura, R. Nagumo, A. Miyamoto,
M. Koyama, Angew. Chem. Int. Ed. 2010, 122, 5476.
[7] C. Bianchini, P. K. Shen, Chem. Rev. 2009, 109, 4183.
[8] Z. Fan, H. Zhang, Chem. Soc. Rev. 2016, 45, 63.
[9] C. Zhu, S. Guo, S. Dong, Adv. Mater. 2012, 24, 2326.
[10] W. Wang, F. Lv, B. Lei, S. Wan, M. Luo, S. Guo, Adv. Mater. 2016,
28, 10117.
[11] H. Wu, H. Li, Y. Zhai, X. Xu, Y. Jin, Adv. Mater. 2012, 24, 1594.
[12] C. Hu, H. Cheng, Y. Zhao, Y. Hu, Y. Liu, L. Dai, L. Qu, Adv. Mater.
2012, 24, 5493.
[13] A. Kowal, M. Li, M. Shao, K. Sasaki, M. B. Vukmirovic, J. Zhang,
N. S. Marinkovic, P. Liu, A. I. Frenkel, R. R. Adzic, Nat. Mater. 2009,
8, 325.
[14] F. Wu, D. Zhang, M. Peng, Z. Yu, X. Wang, G. Guo, Y. Sun, Angew.
Chem. Int. Ed. 2016, 55, 4952.
[15] A. L. Wang, X. J. He, X. F. Lu, H. Xu, Y. X. Tong, G. R. Li, Angew.
Chem. Int. Ed. 2015, 54, 3669.
In summary, the synthesis of a new class of ultrathin vein-
like Ir67Sn33 NWs is successfully demonstrated with abun-
dant oxidized Sn as high-performance EOR electrocatalysts
for C2H5OH electrooxidation. By upgrading the synthetic
method and tuning the amount of Sn precursors supplied, a

clean surface is readily obtained, vein-like Ir Sn NWs with
different Ir/Sn ratios. Interestingly, the abundant oxidized Sn

is found distributed uniformly in those unique Ir Sn NWs,
which plays an important role on enhancing the EOR pro-
[16] E. Antolini, ACS Catal. 2014, 4, 1426.

cess. The electrochemical performances of Ir Sn/C improve
[17] M. Li, D. A. Cullen, K. Sasaki, N. S. Marinkovic, K. More,
R. R. Adzic, J. Am. Chem. Soc. 2013, 135, 132.
[18] H. S. Oh, H. N. Nong, T. Reier, A. Bergmann, M. Gliech, J. Ferreira
de Araujo, E. Willinger, R. Schlogl, D. Teschner, P. Strasser, J. Am.
Chem. Soc. 2016, 138, 12552.
[19] Y. Pi, N. Zhang, S. Guo, J. Guo, X. Huang, Nano Lett. 2016, 16,
4424.
[20] H. N. Nong, H. S. Oh, T. Reier, E. Willinger, M. G. Willinger,
V. Petkov, D. Teschner, P. Strasser, Angew. Chem. Int. Ed. 2015,
54, 2975.
with increasing the content of the oxidized Sn. The opti-
mized Ir67Sn33/C can oxidize C2H5OH into CO2 efficiently
at low potential with the mass activity being 20 times higher
than that of Pt/C at 0.04 V, as well as enhance the durability.
This work highlights the important role of oxidized Sn in
synthesis and electrocatalysis of Ir-based nanomaterials, pre-
senting a promising candidate as efficient electrocatalyst for
EOR.
(7 of 8) 1701295
© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
small 2017, 1701295
www.small-journal.com

communications
www.advancedsciencenews.com
[21] L. C. Seitz, C. F. Dickens, K. Nishio, Y. Hikita, J. Montoya, A. Doyle, [31] N. Tian, Z. Y. Zhou, S. G. Sun, Y. Ding, Z. L. Wang, Science 2007,
C. Kirk, A. Vojvodic, H. Y. Hwang, J. K. Norskov, T. F. Jaramillo, Sci-
ence 2016, 353, 1011.
[22] X. Xia, L. Figueroa-Cosme, J. Tao, H.-C. Peng, G. Niu, Y. Zhu, Y. Xia,
J. Am. Chem. Soc. 2014, 136, 10878.
316, 732.
[32] Z.-Y. Zhou, N. Tian, J.-T. Li, I. Broadwell, S.-G. Sun, Chem. Soc. Rev.
2011, 40, 4167.
[33] Z. Niu, D. Wang, R. Yu, Q. Peng, Y. Li, Chem. Sci. 2012, 3, 1925.
[23] W. Du, Q. Wang, D. Saxner, N. A. Deskins, D. Su, J. E. Krzanowski, [34] P. Liu, R. Qin, G. Fu, N. Zheng, J. Am. Chem. Soc. 2017, 139,
A. I. Frenkel, X. Teng, J. Am. Chem. Soc. 2011, 133, 15172. 2122.
[24] T. Kwon, H. Hwang, Y. J. Sa, J. Park, H. Baik, S. H. Joo, K. Lee, Adv. [35] C. Zhu, Q. Shi, S. Fu, J. Song, H. Xia, D. Du, Y. Lin, Adv. Mater.
Funct. Mater. 2017, 27, 1604688.
2016, 28, 8779.
[25] D. Wang, Y. Li, Adv. Mater. 2011, 23, 1044.
[26] J. Wu, L. Qi, H. You, A. Gross, J. Li, H. Yang, J. Am. Chem. Soc.
2012, 134, 11880.
[36] W. Du, K. E. Mackenzie, D. F. Milano, N. A. Deskins, D. Su, X. Teng,
ACS Catal. 2012, 2, 287.
[37] I. Kim, O. H. Han, S. A. Chae, Y. Paik, S.-H. Kwon, K.-S. Lee,
Y.-E. Sung, H. Kim, Angew. Chem. Int. Ed. 2011, 50, 2270.
[27] J. Zhang, H. Yang, J. Fang, S. Zou, Nano Lett. 2010, 10, 638.
[28] C. Cui, L. Gan, M. Heggen, S. Rudi, P. Strasser, Nat. Mater. 2013, [38] Q. He, B. Shyam, K. Macounová, P. Krtil, D. Ramaker, S. Mukerjee,
12, 765.
J. Am. Chem. Soc. 2012, 134, 8655.
[29] S. Guo, D. Li, H. Zhu, S. Zhang, N. M. Markovic, V. R. Stamenkovic,
S. Sun, Angew. Chem. Int. Ed. 2013, 52, 3465.
[30] W. Du, G. Yang, E. Wong, N. A. Deskins, A. I. Frenkel, D. Su,
X. Teng, J. Am. Chem. Soc. 2014, 136, 10862.
Received: April 23, 2017
Revised: June 15, 2017
Published online:
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