Constructing hierarchical interfaces: TiO2-supported PtFe-FeOx nanowires for room temperature CO oxidation

Article abstract of DOI:10.1021/jacs.5b07011

In this communication, we report a facile approach to constructing catalytic active hierarchical interfaces in one-dimensional (1D) nanostructure, exemplified by the synthesis of TiO₂-supported PtFe-FeO_x nanowires (NWs). The hierarchical interface, constituting atomic level interactions between PtFe and FeO_x within each NW and the interactions between NWs and support (TiO₂), enables CO oxidation with 100% conversion at room temperature. We identify the role of the two interfaces by probing the CO oxidation reaction with isotopic labeling experiments. Both the oxygen atoms (Os) in FeO_x and TiO₂ participate in the initial CO oxidation, facilitating the reaction through a redox pathway. Moreover, the intact 1D structure leads to the high stability of the catalyst. After 30 h in the reaction stream, the PtFe-FeO_x/TiO₂ catalyst exhibits no activity decay. Our results provide a general approach and new insights into the construction of hierarchical interfaces for advanced catalysis.

Full text of DOI:10.1021/jacs.5b07011

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Constructing Hierarchical Interfaces: TiO -Supported PtFe-FeOx
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Nanowires for Room Temperature CO Oxidation
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*
, †
†,±
§
ǁ
#
†
Huiyuan Zhu, Zili Wu, Dong Su, Gabriel M. Veith, Hanfeng Lu, Pengfei Zhang, Songhai
‡
*,†,‡
Chai, and Sheng Dai
†
±
ǁ
Chemical Sciences Division, Center for Nanophase Materials Sciences, and Materials Science and Technology Di-
vision, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
‡
Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, United States
§
Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, United States
#
Institute of Catalytic Reaction Engineering, College of Chemical Engineering, Zhejiang University of Technology,
Hangzhou, Zhejiang 310014, China
Supporting Information Placeholder
surface energy dramatically increases. This often makes the
ABSTRACT: In this communication, we report a facile ap-
NPs highly active, and at the same time, unstable (NPs tend
to sinter or aggregate) when exposed to chemical and ther-
mal treatment. A more intriguing approach is to tailor the
atomic level interface directly on the surface of NPs. For in-
proach to constructing catalytic active hierarchical interfaces
in 1-dimensional (1D) nanostructure, exemplified by the syn-
thesis of TiO -supported PtFe-FeO nanowires (NWs). The
1
0
2
x
hierarchical interface, constituting of atomic level interac-
stance, Pt-FeNi(OH) interface can be created by integrating
tions between PtFe and FeO within each NW and the inter-
x
x
1
1
a submonolayer of FeNi(OH)x onto small Pt NPs. Even
though these strategies have advanced the fabrication of
metal-support interface, one paramount question remains
unanswered, that is, whether there is a catalyst motif which
could simultaneously provide the high active surface area
actions between NWs and support (TiO ), enables CO oxida-
2
tion with 100% conversion at room temperature. We identify
the role of the two interfaces by probing the CO oxidation
reaction with isotopic labeling experiments. Both the oxygen
atoms (Os) in FeO and TiO participate in the initial CO
x
2
(
small NPs) and good stability under thermal or chemical
oxidation, facilitating the reaction through a redox pathway.
Moreover, the intact 1D structure leads to the high stability
of the catalyst. After 30 h in the reaction stream, the PtFe-
FeO /TiO catalyst exhibits no activity decay. Our results
provide a general approach and new insights into the con-
struction of hierarchical interfaces for advanced catalysis.
treatment (large NPs) with abundant atomic level interfaces.
The ultra-thin 1-dimensional (1D) nanowires (NWs) with
the diameter less than 5 nm and the length larger than 20 nm
have emerged as a new class of nanocatalysts with impressive
activity and durability, demonstrated by their superior per-
x
2
1
2-13
formance in fuel cell reactions.
The structural anisotropy
of 1-D structure brings in a preferential exposure of low-
energy facets, minimizing the surface energy and conse-
quently, making the NWs more stable than NPs with the
same diameter. Meanwhile, 1-D motif possesses fewer de-
fects comparing with NPs and thereby a less tendency to be
The interfacial synergy, typically between metal nanoparti-
cles (NPs) and the supporting metal oxide, determines the
active site in heterogeneous catalysis. The critical role of the
interface between the oxide and metal has been spotlighted
14
1
4
passivated by reactants. Inspired by these recent synthetic
advances of the 1D nanocatalysts, we report a unique catalyst
based on 1D core-shell-like PtFe-FeOx NWs supported on
TiO (denoted as PtFe-FeO /TiO ) for room temperature CO
by many previous studies. For example, TiO and CeO are
2
2
reported to be active supports for Au and Pt in CO oxidation
by activating oxygen or supplying oxygen atoms at the metal
2
x
2
1
-5
NPs-support interface. The conventional approach to fabri-
cating such an interface is either in-situ growth or direct
assembly of metal NPs onto oxide supports, which provides
limited interfacial effects. Many efforts have been put to de-
sign and construct the interfaces at the atomic level to max-
imize the interfacial synergy and the catalytic performance. A
typical strategy is to use small NPs which provide high sur-
face area on each NP and abundant interfaces between NPs
oxidation. Figure 1A illustrates the synthetic route for PtFe-
FeO /TiO . The pre-made PtFe NWs were first assembled
x
2
onto TiO to form the interface between NWs and TiO . The
2
2
product was subsequently heated in air to diffuse Fe out onto
the surface, forming FeO domain. The hierarchical architec-
x
ture in PtFe-FeO /TiO creates two interfaces including: 1)
x
2
the atomic interface between the PtFe and metal oxide
(
(
FeO ), and 2) the interface between NWs and the support
x
6-9
and support. However, once the NPs’ size decreases, the
TiO ). Both interfaces are found to be highly effective in
2
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catalyzing CO oxidation through a combination of Mars-van
Krevelen (MvK) and Langmuir-Hinshelwood (L-H) reaction
mechanism.
The as-synthesized PtFe NWs (width: 4.5 nm) and Pt NPs
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were deposited on TiO (Degussa P25, surface area 48 m /g)
2
through a solution-phase adsorption-assisted assembly (SI).
The product, denoted as PtFe/TiO , was then annealed in air
2
o
at 200 C for 3h to remove the capping agents and to con-
struct PtFe-FeO interfaces. The 1D morphology of the NWs
x
maintained after air annealing, as tracked by the scanning
electron transmission microscopy (STEM) (Figure 1E). The
o
2
00 C annealing effectively removed the capping agents,
evidenced by the study of in-situ oxidation of PtFe/TiO NWs
2
on a thermogravimetric analyzer equipped with a mass spec-
trometer (TGA-MS) (Figure S2B). The steepest weight loss
from the TGA and the peak of CO and H O production from
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the MS, occurs at 200 C, corresponding to the thermal de-
composition of OAm and OA capped on the NW surface.
The removal of the capping agents is further confirmed by
Fourier transform infrared (FTIR) spectroscopy, as the strong
-
1
C-H stretches at 2921 and 2850 cm from OAm and OAc dis-
o
appear after 200 C annealing (Figure S3). During the anneal-
ing, Fe, with a strong O affinity, diffuses out onto the NW
2
surface, forming a thin FeO coating, similar to the synthesis
x
8
1
of core/shell Au/MnO NPs. The 2D high-angle annular dark
field (HAADF)-STEM-electron energy-loss spectroscopy
(
EELS) (Figure 2A and S4A) and EELS line scan (Figure S4B)
confirm the enrichment of Fe component on the surface at
both the tip and body of the NWs. But we should notice that
Figure 1. (A) Schematic illustration of the synthesis of TiO2-
supported PtFe-FeO NWs. TEM images of the 2.5 × 20-50
the FeO
while a portion of the Pt atoms are exposed. FeO
x
on PtFe does not form a compact shell (Figure S4),
x
nm PtFe NWs (B); 4.5 × 20-50 nm PtFe NWs (C). (D) HRTEM
of the 4.5 × 20-50 nm PtFe NWs. (E) STEM image of the 4.5 ×
x
formed on
PtFe surface is amorphous, characterized by the XRD pattern
obtained on the thermally-treated PtFe NWs (Figure S5).
Further, the X-ray photoelectron spectroscopy (XPS) spectra
2
0-50 nm PtFe-FeO NWs supported on TiO .
x
2
3+
of Fe2p show multiplet peaks of Fe at 710 eV (Figure 2B).
To prepare PtFe-FeO /TiO nanostructure, PtFe NWs with a
The O1s spectra suggest a small portion of metal (M)-OH
group and a large portion of M-O group, confirming the for-
x
2
width of 4.5 ± 0.3 nm and a length of 20-50 nm were synthe-
sized via a seed-mediated growth, according to a modified
mation of FeO with a Fe valence of 3+ on NW surface (Fig-
x
15-16
previous method (See supporting information (SI)).
The
ure 2C).
2.5 ± 0.2 × 20-50 nm PtFe NWs were first synthesized and
used as the seeds (Figure 1B). To generate the 4.5 ± 0.3 × 20-
5
0 nm PtFe NWs, an equal amount (0.25 mmol) of platinum
acetylacetonate (Pt(acac) ) and iron pentacarbonyl (Fe(CO) )
2
5
were added into the mixture of oleylamine (OAm), oleic acid
(
(
OA) and 1-octadecene (ODE) in the presence of PtFe seeds
SI). For comparison, 4 ± 0.4 nm Pt NPs were synthesized by
reducing Pt(acac) with borane tert-butylamine complex in
2
OAm (SI, Figure S1). Figure 1C shows a representative trans-
mission electron microscopy (TEM) image of the as-
synthesized 4.5 ± 0.3 × 20-50 nm PtFe NWs. A typical face
centered cubic (fcc) structure was observed in the X-ray dif-
fraction (XRD) patterns of both PtFe (width: 2.5 nm) and
PtFe (width: 4.5 nm) NWs with their (111) peak positions shift
to a higher angle compared with Pt NPs, indicating the in-
corporation of Fe into the crystalline lattice (Figure S2A).
Furthermore, PtFe (width: 4.5 nm) NWs have an increased
domain size and crystallinity, evidenced by the narrower and
sharper peaks, than that of PtFe (width: 2.5 nm) NWs (Figure
S2A). An interplanar distance of 0.22 nm was obtained from
the high-resolution TEM (HRTEM) image, corresponding to
the (111) crystalline plane in the fcc-PtFe (Figure 1D), similar
1
2, 17
to the observations in previous reports.
The Pt to Fe ratio
in the seed and final NWs was measured to be ~1 by induc-
tively coupled plasma optical emission spectroscopy (ICP-
OES), indicating a stoichiometric reaction during the synthe-
sis.
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Figure 2. (A) 2D EELS elemental mapping of Fe (red) and Pt
ated, the gas phase O starts to replenish the vacancies and
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(green). XPS spectra of Fe2p (B) and O1s (C).
react with CO.
The PtFe-FeO /TiO and Pt/TiO (ca. 18 mg) were packed
x
2
2
into a U-shaped quartz tube (i. d. = 4 mm) and sealed by
quartz wool. CO oxidation was then performed with a gas
stream consisting of 1% CO (balance air, < 4 ppm water) at a
-1
-1
space velocity (SV) of 1333 L g h for PtFe-FeO /TiO and
Pt
x
2
-1
-1
833 L g
h for Pt/TiO . The PtFe-FeO /TiO readily con-
Pt 2 x 2
o
verted 100% CO starting from room temperature (22 C),
while Pt/TiO displayed negligible CO oxidation activity at
2
O
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temperatures below 88 C and only achieved 100% conver-
O
sion starting from 118 C (Figure 3A). To explore the effect of
surface FeO , acid leaching was applied to PtFe-FeO /TiO by
x
x
2
immersing the sample in acetic acid (AA) (SI). The removal
of surface FeO , verified by ~40% Fe loss from ICP, reduced
x
the catalytic activity. Figure 3A shows that the acid-leached
o
NWs start to convert CO at 58 C and present 100% CO con-
o
version at 88 C. The CO oxidation activity of acid-leached
NWs is higher than that of Pt/TiO because of the Fe incor-
2
poration in the core region. This alloy effect is consistent
1
9
with the reported enhanced CO oxidation on NiPt catalyst.
The apparent activation energies (Ea) were derived with a SV
-1
-1
-1
-1
of 24000 L g h on PtFe-FeO /TiO and 7500 L g h on
Pt
x
2
Pt
-1
Pt/TiO . Pt/TiO had a Ea value of 49 kJ mol , in agreement
2
2
11
-1
with other reports. The Ea was reduced to 41 kJ mol (tem-
o
o
-1
perature range: 20 C to 70 C) and 29 kJ mol (temperature
o
o
range: 70 C to 85 C) on PtFe-FeO /TiO , proving that in-
x
2
corporation of Fe and FeO into Pt facilitates the CO oxida-
x
tion (Figure 3B). For comparison, PtFe-FeO /SiO , FeO /TiO
2
x
2
x
and PtFe-FeO NPs/TiO were prepared and tested accord-
x
2
20
ingly (SI). They were all less active than PtFe-FeO /TiO2
x
(Figure S6 and S7). The improved CO oxidation catalysis can
be attributed to two synergistic effects of Fe in PtFe-
FeO /TiO : 1) The surface FeO moiety acts as an active O
2
Figure 3. (A) CO oxidation light-off curves for the Pt/TiO2,
x
2
x
PtFe-FeO /TiO and acid-leached PtFe-FeO /TiO . (B) Acti-
x
2
x
2
reservoir to continuously supply O atoms to CO through a
vation energies of CO oxidation over PtFe-FeO NWs and Pt
x
redox mechanism and to replenish O from the bulk O lat-
2
21
NPs on TiO . QMS profiles collected during CO oxidation
2
tice. 2) The Fe and the FeO in the NW modify Pt d-band
x
18
16
16
16
18
9
, 22-24
with O over PtFe-Fe O /Ti O (C) and with O over O2
2 x 2 2
center to ease the strong CO adsorption on Pt.
pretreated PtFe/TiO (D) at various temperatures. (E) Sche-
matic illustration of two reaction regimes in PtFe-FeO /TiO .
2
To gain insights into the reaction mechanism on PtFe-
FeO /TiO , we performed isotopic labeling experiments by
x
2
x
2
monitoring the exiting stream during the light-off process of
CO oxidation via an online quadrupole mass spectrometer
To identify the origination of the lattice O, PtFe/TiO
2
was
18
18
treated with
O
to form Fe O
on the NW surface and then
at 60 C (SI). The product was also
2
x
16
16
o
(
QMS). The PtFe/TiO was first treated with O to produce
mixed with CO and
analyzed by QMS. Along with the signal of Ar and CO ,
2
O
2
2
2
16
18
o
44
PtFe-Fe O /TiO and then reacted with O at both 60 C
and 90 C (SI). At the beginning of the reaction, the QMS
signal of CO increases simultaneously with background Ar
signal, suggesting only lattice O participates in the reaction.
As the reaction goes on, the intensity of CO starts to de-
cline, while the signal of CO increases and becomes domi-
nant. Accompanying with the signal of CO2, CO signal
x
2
2
o
46
CO
participation of O in FeO
Figure 3E presents the schematic illustration of the proposed
CO oxidation mechanism on the PtFe-FeO /TiO surface.
Two active reaction regimes were observed: 1) The interface
between PtFe and FeO adopts both MvK mechanism by
transferring O atoms from gas phase O to CO through the O
vacancy in FeO (dash arrow) and L-H route by reacting CO
directly with adsorbed O from gas phase O (dot arrow). 2)
The interface between NWs and TiO follows mainly MvK
pathway with lattice O in TiO participating in the reaction
(solid arrow). In order to quantify the contribution percent-
age of each mechanism, the CO-O copulse and sequential
pulse were performed on PtFe-FeO /TiO (SI). In the sequen-
tial pulse, CO reacts only with lattice O due to the transient
exposure to gas phase O , providing the information for MvK
appears initially and gradually declines, confirming the
2
44
18
during CO oxidation (Figure 3D).
x
2
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2
x
2
4
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2
4
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48
2
x
gradually appears (Figure 3C). These results indicate that a
mixture of the MvK and L-H reaction mechanism proceeds
2
x
1
6
on PtFe-FeO /TiO surface at both temperatures. The O2-
2
2
x
2
1
8
treated PtFe/TiO2 reacted with CO and O2 was further
2
characterized by in-situ IR spectroscopy. As shown in Figure
2
-
1
S8, two parallel bands at 2356 and 2342 cm , associated with
4
4
CO , appear at the beginning of the reaction and decrease
2
2
in intensity during the reaction. On the other hand, the
x
2
-
1
46
bands at 2342 and 2324 cm , which are assigned to CO2
increase in intensity as the reaction proceeds. This is con-
sistent with the result from QMS that the lattice O reacts
first with CO and as the O vacancies are continuously gener-
2
route. Meanwhile, during the copulse, the total CO2 intensi-
ty can be attributed to the sum of MvK and L-H routes. As a
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result, MvK mechanism accounts for over 70 % of the gener-
ated CO , while ~ 25 to 30% of CO arises from L-H route at
observation that the strong CO adsorption is eased on PtFe-
FeO /TiO at a slightly elevated temperature. The high sta-
bility of the catalyst can be attributed to the intact 1D
nanostructure during prolonged reaction (Figure S14).
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both 60 and 90 C (Figure S9). To determine the contribu-
tion ratio of lattice O between FeO and TiO , CO was pulsed
x
2
1
8
onto O -treated PtFe-TiO and the produced CO was col-
lected. The isotopically-labeled CO ( CO + CO ) accounts
2
2
2
In summary, we have reported a facile synthesis of TiO2-
4
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48
2
2
2
upported PtFe-FeO NWs. The interfacial effects on catalysis
x
for 33.3% of the total CO2 production (Figure S10A). For
in PtFe-FeO /TiO have been studied with CO oxidation as a
x
2
1
8
comparison, Pt/TiO was also treated with O and reacted
2
2
prototype reaction. By taking the advantage of highly active
hierarchical interfaces and structural stability of 1D
nanostructure, these PtFe-FeO /TiO catalysts demonstrate
with CO. In this case, only 6.5% 0f the total produced CO2
was isotopically labeled (Figure S10B), confirming the isotop-
x
2
1
8
ically-labeled CO was mainly from Fe O . Considering part
2
x
the superior performance in CO oxidation and achieve 100%
CO conversion at room temperature. The strategy of prepar-
ing efficient hierarchical interfaces within supported 1D
nanostructure provides a unique and promising way to de-
sign and fabricate active sites for advanced catalysis.
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of the CO MvK production is from PtFe-FeO interface, and
2
x
L-H route contributes significantly at the same time, the
PtFe-FeO interface serves as a superior active site for CO
x
oxidation.
ASSOCIATED CONTENT
Supporting Information
Materials, PtFe nanowire, Pt, PtFe, FeO nanoparticles syn-
x
thesis, characterization and their catalytic measurements;
Figure S1-14. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
Figure 4. IR spectra of CO adsorbed on PtFe-FeO /TiO (A)
x
2
Pt/TiO (B) at room temperature and subsequent tempera-
2
ture-programmed desorption in He.
zhuh@ornl.gov.
dais@ornl.gov
The effect of Fe, to tune the electronic structure of Pt in
PtFe, has been demonstrated by intensive experimental and
2
4-27
Notes
theoretical studies.
Hence, the excellent tolerance to CO
28
The authors declare no competing financial interests.
poisoning can be achieved in Pt-Fe system. To study CO
adsorption/desorption behavior, temperature-programmed
ACKNOWLEDGMENT
x
desorption (TPD) of CO adsorbed on both PtFe-FeO /TiO2
and Pt/TiO was tracked by IR spectroscopy (Figure 4A-B).
2
H.Z. was supported by Liane B. Russell Fellowship sponsored
by the Laboratory Directed Research and Development Pro-
gram at the Oak Ridge National Laboratory, managed by UT-
Battelle, LLC, for the US Department of Energy. Z. W. and S.
D. were supported by the U. S. Department of Energy, Office
of Science, Chemical Sciences, Geosciences and Biosciences
Division. Part of the work, including the DRIFTS study, was
conducted at the Center for Nanophase Materials Sciences,
which is a DOE Office of Science User Facility.
-
1
Upon CO adsorption, an intensive band at 2090 cm , corre-
sponding to the linear CO-Pt, readily forms on both catalysts
(
Figure 4A-B). This CO-Pt species is not stable and starts to
desorb CO even at room temperature upon switching from
CO to inert gas (He) purging on PtFe-FeO /TiO (Figure 4A).
x
2
The desorption of CO accelerated with the temperature in-
crease (Figure 4). In comparison with Pt/TiO (Figure 4B),
2
PtFe-FeO /TiO adsorbs CO less strongly and CO desorbs at
x
2
a much lower temperature (Figure 4A). Figure S11 summariz-
es the CO TPD-MS profile of Pt/TiO and PtFe-FeO /TiO . A
2
x
2
o
maximum CO desorption was achieved at 54 C on PtFe-
FeO /TiO , while on Pt/TiO the peak intensity was obtained
REFERENCES
x
2
2
o
(1) Wang, Y.; Yoon, Y.; Glezakou, V.; Li, J.; Rousseau, R. J. Am.
Chem. Soc. 2013, 135, 10673.
at 70 C. This observation proves the incorporation of Fe and
FeO into Pt alleviates “CO-poisoning” on Pt and promotes
x
(
2) Widmann, D.; Behm, R. J. Angew. Chem. Int. Ed. 2011, 50,
0241.
CO oxidation. The decay of the room-temperature activity on
PtFe-FeO /TiO starts after 40 mins on stream (Figure S12A).
1
x
2
(3) Liu, K.; Wang, A.; Zhang, T. ACS Catal. 2012, 2, 1165.
(4) Kim, H. Y.; Lee, H. M.; Henkelman, G. J. Am. Chem. Soc.
2012, 134, 1560.
But upon purging with O for 1h at slightly heated condition
2
o
(
40 C), the room-temperature CO conversion arises back to
(
5) Liu, H. H.; Wang, Y.; Jia, A.; Wang, S.; Luo, M.; Lu, J. Appl.
Surf. Sci. 2014, 314, 725.
100% (Figure S12A). This “poisoning” and “recovering” behav-
ior indicates the activity decay is not due to the instability of
the catalyst. Instead, it is because that the active sites are
blocked by CO at the low temperature and can be reactivated
at mild conditions (Figure S12B). For long-term stability
study, a time-on-stream test was performed on PtFe-
FeO /TiO , and the catalyst maintained 100% conversion
(
6) Cargnello, M.; Doan-Nguyen, V. V. T.; Gordon, T. R.; Diaz, R.
E.; Stach, E. A.; Gorte, R. J.; Fornasiero, P.; Murray, C. B. Sci-
ence 2013, 341, 771.
(
7) Wu, Z.; Jiang, D.; Mann, A. K. P.; Mullins, D. R.; Qiao, Z.; Al-
lard, L. F.; Zeng, C.; Jin, R.; Overbury, S. H. J. Am. Chem. Soc.
2014, 136, 6111.
x
2
o
efficiency after 30 h at 40 C (Figure S13), consistent with the
ACS Paragon Plus Environment

Page 5 of 6
Journal of the American Chemical Society
(
8) Peterson, E. J.; DeLaRiva, A. T.; Lin, S.; Johnson, R. S.; Guo,
1
2
3
4
5
6
7
8
9
H.; Miller, J. T.; Kwak, J. H.; Peden, C. H. F.; Kiefer, B.; Allard,
L. F.; Ribeiro, F. H.; Datye, A. K. Nat. Commun. 2014, 5, 4885.
9) Qiao, B.; Wang, A.; Yang, X.; Allard, L. F.; Jiang, Z.; Cui, Y.;
Liu, J.; Li, J.; Zhang, T. Nat. Chem. 2011, 3, 634.
10) Li, D.; Wang, C.; Strmcnik, D. S.; Tripkovic, D. V.; Sun, X.;
Kang, Y.; Chi, M.; Snyder, J. D.; Vliet, D. v. d.; Tsai, Y.; Sta-
menkovic, V. R.; Sun, S.; Markovic, N. M. Energy Environ. Sci.
(
(
2014, 7, 4061.
(
11) Chen, G.; Zhao, Y.; Fu, G.; Duchesne, P. N.; Gu, L.; Zheng, Y.;
Weng, X.; Chen, M.; Zhang, P.; Pao, C.; Lee, J.; Zheng, N. Sci-
ence 2014, 344, 495.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(
(
(
12) Zhu, H.; Zhang, S.; Guo, J.; Su, D.; Sun, S. J. Am. Chem. Soc.
2013, 135, 7130.
13) Zhu, H.; Zhang, S.; Su, D.; Jiang, G.; Sun, S. Small 2015, 11,
3
545.
14) Koenigsmann, C.; Santulli, A. C.; Gong, K.; Vukmirovic, M.
B.; Zhou, W.; Sutter, E.; Wong, S. S.; Adzic, R. R. J. Am.
Chem. Soc. 2011, 133, 9783.
(15) Guo, S.; Li, D.; Zhu, H.; Zhang, S.; Markovic, N. M.; Stamen-
kovic, V. R.; Sun, S. Angew. Chem. Int. Ed. 2013, 52, 3465.
(
(
16) Guo, S.; Zhang, S.; Su, D.; Sun, S. J. Am. Chem. Soc. 2013, 135,
3879.
17) Guo, S.; Zhang, S.; Sun, X.; Sun, S. J. Am. Chem. Soc. 2011, 133,
5354.
1
1
(18) Zhu, H.; Sigdel, A.; Zhang, S.; Su, D.; Xi, Z.; Li, Q.; Sun, S.
Angew. Chem. Int. Ed. 2014, 53, 12508.
19) Mu, R.; Fu, Q.; Xu, H.; Zhang, H.; Huang, Y.; Jiang, Z.; Zhang,
S.; Tan, D.; Bao, X. J. Am. Chem. Soc. 2011, 133, 1978.
(
(
20) (a) Nakaya, M.; Kanehara, M.; Teranishi, T. Langmuir 2006,
2
2, 3485. (b) Zhang, S.; Jiang, G.; Filsinger, G. T.; Wu, L.; Zhu,
H.; Lee, J.; Wu, Z.; Sun, S. Nanoscale 2014, 6, 4852.
(21) Li, L.; Wang, A.; Qiao, B.; Lin, J.; Huang, Y.; Wang, X.; Zhang,
T. J. Catal. 2013, 299, 90.
22) Guo, X.; Fu, Q.; Ning, Y.; Wei, M.; Li, M.; Zhang, S.; Jiang, Z.;
Bao, X. J. Am. Chem. Soc. 2012, 134, 12350.
23) Fu, Q.; Li, W.; Yao, Y.; Liu, H.; Su, H.; Ma, D.; Gu, X.; Chen,
L.; Wang, Z.; Zhang, H.; Wang, B.; Bao, X. Science 2010, 328,
1141.
(
(
(
(
24) Xu, H.; Fu, Q.; Yao, Y.; Bao, X. Energy Environ. Sci. 2012, 5,
6
313.
25) Zhang, S.; Guo, S.; Zhu, H.; Su, D.; Sun, S. J. Am. Chem. Soc.
012, 134, 5060-5063.
2
(26) Zhang, S.; Zhang, X.; Jiang, G.; Zhu, H.; Guo, S.; Su, D.; Lu,
G.; Sun, S. J. Am. Chem. Soc. 2014, 136, 7734.
(
(
27) Stamenkovic, V. R.; Mun, B. S.; Arenz, M.; Mayrhofer, K. J. J.;
Lucas, C. A.; Wang, G.; Ross, P. N.; Markovic, N. M. Nat. Ma-
ter. 2007, 6, 241.
28) Chen, W.; Kim, J.; Sun, S.; Chen, S. Langmuir 2007, 23, 11303.
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