Replicating the Defect Structures on Ultrathin Rh Nanowires with Pt to Achieve Superior Electrocatalytic Activity toward Ethanol Oxidation

Article abstract of DOI:10.1002/adfm.201806300

Metal nanostructures with an ultrathin Pt skin and abundant surface defects are attractive for electrocatalytic applications owing to the increased utilization efficiency of Pt atoms and the presence of highly reactive sites. This paper reports a conformal, layer-by-layer deposition of Pt atoms on defective Rh nanowires for the faithful replication of surface defects (i.e., grain boundaries) on the Rh nanowires. The thickness of the Pt shell can be controlled from one monolayer up to 5.3 atomic layers. This series of Rh@Pt_nL (n = 1–5.3) core–sheath nanowires show greatly enhanced activity and durability in catalyzing the ethanol oxidation reaction in an acidic medium. Among others, the Rh?@?Pt_3.5L nanowires show the greatest mass activity (809 mA mg^?1_Pt) and specific activity (1.18 mA cm^?2) after loaded on carbon support, which are 3.7 and 3.4 times those of the commercial Pt/C, respectively. In situ Fourier transform infrared spectroscopy studies indicate an enhanced interaction between the outermost Pt layer and the Rh nanowire can promote C?C bond cleavage for complete oxidation of ethanol to CO₂ while depress the dehydrogenation of ethanol to acetic acid. As the Pt shell thickness is increased, the selectivity for the CO₂ pathway decreases while that for acetic acid is increased.

Full text of DOI:10.1002/adfm.201806300

FULL PAPER
Oxidation Catalysts
www.afm-journal.de
Replicating the Defect Structures on Ultrathin Rh Nanowires
with Pt to Achieve Superior Electrocatalytic Activity toward
Ethanol Oxidation
Kai Liu, Wei Wang, Penghui Guo, Jinyu Ye, Yuanyuan Wang, Pingting Li, Zixi Lyu,
Yongsheng Geng, Maochang Liu, and Shuifen Xie*
1. Introduction
Metal nanostructures with an ultrathin Pt skin and abundant surface
defects are attractive for electrocatalytic applications owing to the
Electrocatalytic energy conversions are
critical processes for facilitating the com-
increased utilization efficiency of Pt atoms and the presence of highly
mercially widespread application of
reactive sites. This paper reports a conformal, layer-by-layer deposition
proton exchange membrane fuel cells
of Pt atoms on defective Rh nanowires for the faithful replication
of surface defects (i.e., grain boundaries) on the Rh nanowires. The
thickness of the Pt shell can be controlled from one monolayer up to 5.3
atomic layers. This series of Rh@PtnL (n = 1–5.3) core–sheath nanowires
show greatly enhanced activity and durability in catalyzing the ethanol
oxidation reaction in an acidic medium. Among others, the Rh@Pt3.5L
nanowires show the greatest mass activity (809 mA mg−1Pt) and specific
activity (1.18 mA cm−2) after loaded on carbon support, which are 3.7
and 3.4 times those of the commercial Pt/C, respectively. In situ Fourier
transform infrared spectroscopy studies indicate an enhanced interaction
(PEMFCs). Intensive fundamental works
have been devoted to the design of effi-
cient and durable electrocatalysts.[1–5] To
date, nanostructured Pt-based materials
are admitted as the most effective electro-
catalysts for accelerating both the anode
and cathode reactions of fuel cells in
acidic mediums.[6–8] However, unsolved
issues, including side reactions, sluggish
reaction kinetics, intermedium poisons,
instabilities, etc., still need to be addressed
urgently through synthetic control of the
Pt-based nanocatalysts.[9–13] In particular,
ethanol offers a superior fuel source for
PEMFCs, due to its higher energy density
(8 kWh kg−1), lower toxicity, and repro-
ducibility from biomass, etc. However,
in the process of ethanol oxidation reac-
tion (EOR), commonly, three different
products, that is, acetaldehyde (CH3CHO),

between the outermost Pt layer and the Rh nanowire can promote C C
bond cleavage for complete oxidation of ethanol to CO2 while depress
the dehydrogenation of ethanol to acetic acid. As the Pt shell thickness
is increased, the selectivity for the CO2 pathway decreases while that for
acetic acid is increased.
acetic acid (CH3COOH), and CO2, were obtained on Pt catalysts
K. Liu, W. Wang, Y. Wang, P. Li, Z. Lyu, Y. Geng, Prof. S. Xie
College of Materials Science and Engineering
Huaqiao University
Xiamen 361021, P. R. China
E-mail: sfxie@hqu.edu.cn
releasing 2, 4, and 12 electrons, respectively.[14–17] The difficulty

in C C bond cleavage results in an incomplete oxidation of eth-
anol. To date, the efficiency of direct ethanol fuel cells (DEFCs)
is restricted by the lack of active anode materials which can effi-
W. Wang, Prof. S. Xie
Shenzhen Research Institute of Xiamen University
Shenzhen 518000, P. R. China

ciently catalyze the C C bond cleavage accomplishing ethanol
complete oxidation to CO2.
It has been universally recognized that the catalytic behavior of
metal nanocrystals is highly dependent on their surface compo-
sitions and structures.[18–20] Metallic nanocrystals with ultrathin
Pt skins exhibit extraordinary electronic structures which can
drastically improve their electrocatalytic performance.[21–23] For
example, dealloyed core–sheath metal nanocrystals, such as
PtCu@Pt core–sheath nanocrystals and PtPb@Pt core–sheath
nanoplates, were demonstrated to have extremely high activity
and endurance for catalyzing the oxygen reduction reaction
(ORR) owing to the geometric lattice strains and electronic
ligand effects.[24,25] On the other hand, metal nanocrystals with
high density of surface defects are superior candidates for highly
active electrocatalysts because the defect sites can act as reactive
P. Guo, Prof. M. Liu
International Research Center for Renewable Energy
State Key Laboratory of Multiphase Flow in Power Engineering
Xi’an Jiaotong University
Xi’an, Shaanxi 710049, P. R. China
Dr. J. Ye
State Key Laboratory of Physical Chemistry of Solid Surfaces
Department of Chemistry
College of Chemistry and Chemical Engineering
Xiamen University
Xiamen 361005, P. R. China
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/adfm.201806300.
DOI: 10.1002/adfm.201806300
©
Adv. Funct. Mater. 2018, 1806300
1806300 (1 of 9)
2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

www.advancedsciencenews.com
www.afm-journal.de
hot spots.[26–29] As a model study, the electrocatalytic activities for
formic acid oxidation catalyzed on twinned Pd nanocrystals that
enclosed with the identical crystal facets were demonstrated to
be gradually enhanced as the increasing of surface twin defect
number.[28] Based on above progresses, it is reasonable to deduce
that conformal coating of an ultrathin Pt skin with optimized
thickness on a second metal nanoseed equipped with high-den-
sity surface defects, to faithfully replicate the active defect sites
out on the Pt shells as well as engender appreciable geometric
lattice strain and electronic ligand effects, could offer a feasible
strategy toward highly active electrocatalysts.
the application of DEFCs. Compared to the state-of-the-art Pt/C
catalyst, the carbon-supported Rh@PtnL NWs exhibited great
enhancements in both the current density and durability, owing
to the integration of the active defect sites and the modulated
geometric lattice strains and electronic ligand effects. Electro-
chemical in situ Fourier transform infrared (FTIR) spectroscopy
indicated that the two pathways for the generation of CO2 and
acetic acid were fluctuant and closely correlated to the atomic
layer numbers of the Pt shells on these core–sheath NWs.
Ultrathin metal wavy nanowires (NWs), which are generated
from an oriented attachment process and thus possess rich
grain boundaries (GBs),[30,31] can serve as typical highly defec-
tive nanocores for coating Pt skins. Herein, we demonstrate a
facile route for conformally layer-by-layer coating of Pt atoms
on the surface of defective Rh wave NWs to fabricate shell
thickness controlled Rh@PtnL core–sheath NWs. The high-den-
sity surface GBs on the inner Rh NW were faithfully replicated
out on the surface of the Pt sheath. Moreover, the thicknesses
of the Pt sheaths can be precisely controlled from one atomic
monolayer (1L) up to 5.3 atomic layers (5.3L). These defective
Rh@PtnL core–sheath NWs were applied to catalyze EOR for
2. Results and Discussion
Ultrathin Rh wavy NWs with a diameter around 1.9 nm and
high-density GBs were initially synthesized in high yield
according to a previous report (Figure S1, Supporting Infor-
mation).[27] Later, Pt atomic layers were conformally coated
on the Rh NWs in an ethylene glycol (EG) solution using
H2PtCl6·6H2O as a Pt source. In order to regulate the atomic
layer numbers of the outer Pt shell, different amounts of
H2PtCl6·6H2O were added during the coating process (see
the Experimental Section in the Supporting Information).
Figure 1a schematically shows the conformal, layer-by-layer
Figure 1. a) Schematic illustrating the conformal, layer-by-layer deposition of Pt atoms on ultrathin, wavy NWs of Rh. b–e) TEM images and diameter
distributions of the Rh@PtnL core–sheath NWs: Rh@Pt1L, Rh@Pt2L, Rh@Pt3.5L, and Rh@Pt5.3L
.
©
Adv. Funct. Mater. 2018, 1806300
1806300 (2 of 9)
2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

www.advancedsciencenews.com
www.afm-journal.de
Figure 2. Structural characterizations of the as-prepared Rh@Pt3.5L core–sheath NWs: a) TEM; b) HRTEM (with the blue dashed lines marking the
domain boundaries along the NWs); c) STEM and the corresponding EDS elemental mapping; d) EDS line scan along the yellow arrow marked in (c);
e–g) HAADF-STEM showing the bright, outer Pt sheaths. The inset in (g) shows the corresponding FFT pattern of the dashed square region.
coating of Pt atoms on the defective Rh NWs for fabricating the
Rh@PtnL core–sheath NWs. The transmission electron micro-
scope (TEM) images show that the coated products all well
reserved the wavy NW structure (Figure 1b–e and Figure S2,
Supporting Information), indicating the success of conformal
coating. Statistically, the mean diameters for these Rh@PtnL
core–sheath NWs were thickened from 1.9 to 2.4, 2.8, 3.5, and
4.2 nm, respectively. Assuming the wavy NWs are dominated
by {111} facets,[27,31] the atomic layer numbers of the Pt sheath
can be calculated to be about 1L, 2L, 3.5L, and 5.3L, respectively.
Corresponding X-ray diffraction (XRD) patterns only show a
single pure face-centered cubic (fcc) phase for these Rh@PtnL
core–sheath NWs (Figure S3, Supporting Information), because
of the broadening of the diffraction peaks and the small devia-
tions in peak positions between Rh and Pt. As the increase of
the diameter of the Rh@PtnL core–sheath NWs, the positions of
the (111) diffraction peaks were gradually shifted from the Rh
phase close to the Pt phase, indicating the Pt fractions in the
core–sheath products are increased. Gradually increased Pt/Rh
molar ratios were also confirmed by the energy-dispersive X-ray
spectroscopy (EDS) and inductively coupled plasma mass spec-
trometry (ICP-MS) (Table S1, Supporting Information).
The structure and composition distribution of Rh@Pt3.5L
NWs were detailedly analyzed to visually illuminate the core–
sheath structure of the Pt coated NWs (Figure 2). The low-
magnification TEM image reveals the high yield production
of the wavy NWs after coating (Figure 2a). The blue dashed
lines in the high-resolution TEM (HRTEM) images evidently
highlight the high density of defect sites cross-sectioning the
Rh@Pt3.5L core–sheath NWs (Figure 2b and Figure S4, Sup-
porting Information). Figure 2c,d shows a scanning TEM
(STEM) image of an individual Rh@Pt3.5L core–sheath NW
and the corresponding EDS composition mapping and cross-
sectioning line scan. An enrichment of Rh at the central region
(red) and the presence of an outer Pt shell (green) can be dis-
tinctly observed, verifying the segregated Rh@Pt core–sheath
©
Adv. Funct. Mater. 2018, 1806300
1806300 (3 of 9)
2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

www.advancedsciencenews.com
www.afm-journal.de
Figure 3. a–d) Analysis of the Rh 3d and Pt 4d XPS spectra recorded from the as-prepared Rh@PtnL core–sheath NWs: Rh@Pt1L, Rh@Pt2L, Rh@Pt3.5L
,
and Rh@Pt5.3L
.
structure. The core–sheath structure can be further illuminated
through high-angle annular dark-field STEM (HAADF-STEM)
images due to the brighter Z-contrast of Pt atoms than that
of Rh (Figure 2e,f). The d-spacing between lattice planes that
paralleled to the surface of the NWs was 0.22 nm, indicating
the major surface of the core–sheath Rh@Pt3.5L core–sheath
NWs were indeed enclosed by {111} facets, which can also be
revealed by the corresponding fast Fourier transform (FFT)
pattern (Figure 2g).
The surface defect structures of the Rh@PtnL core–sheath
NWs were further intentionally inspected. As shown by the
TEM images (Figures S2 and S5, Supporting Information), all
the Rh@PtnL core–sheath NWs maintained extremely twisty
together with the presence of high-density GBs. The corre-
sponding statistic densities of GBs on the Rh NWs and the
Rh@PtnL core–sheath NWs (Figure S6, Supporting Information)
indicate only slight decline can be found on the samples with
thicker Pt coating (i.e., Rh@Pt3.5L and Rh@Pt5.3L NWs). To fur-
ther evaluate the surface defect and electronic characteristics,
X-ray photoelectron spectroscopy (XPS) was applied to character
the surface chemical states of these Rh@PtnL core–sheath
NWs. As shown in Figure 3, the intensities of the Pt 4d referred
to that of Rh 3d were gradually elevated as the increase of Pt
atomic layer numbers. Each individual peak assigned to the Rh
3d or Pt 4d can be further split into two doublets, associated
with Rh0/Rh3+ and Pt0/Pt2+, respectively. It has been indicated
that the structural defects could serve as possible channels for
oxygen incorporation.[32] The Rh3+ and Pt2+ chemical states can
be assigned to the oxidized species, which have been approved
to be favorably formed at the surface defect sites and increased
with the density of the surface defects.[27,33,34] Only little decline
of the Pt2+ fraction was observed from both the Pt 3d and Pt 4f
spectra with the thickening of Pt sheaths (Figure 3, Figure S7
and Table S2, Supporting Information), implying the density of
GBs was no distinctly decreased after the Pt coating. It is also
worth to mention that the binding energy (BE) of the Pt0 4f
on the Rh@Pt1L NWs positively shifted by 0.12 eV compared
to that of standard Pt. It was previously observed that the posi-
tive shift of Pt0 4f could weaken the surface Pt CO interac-

tion.[35,36] This upshifting was gradually faded as the increase
of Pt atomic layer numbers (Table S2, Supporting Information),
indicating the electronic ligand effects on the outermost Pt
layer was weakened as the increase of the Pt shell thickness.
Meanwhile, considerable compression strain is caused on the
outer Pt shells due to the lattice mismatch between Rh and Pt
(3.1%),[37] which can also be released as the increase of the Pt
atomic layer numbers.
It has been demonstrated that incorporation of Rh into Pt
forming alloys can efficiently improve the electrocatalytic
activity toward EOR as Rh has an infusive effect in promoting
[38–40]

the C C bond cleavage on PtRh bimetallic nanocrystals.
The electrocatalytic activity of the Rh@PtnL core–sheath
NWs for EOR in an acidic medium was evaluated in order to
correlate the Pt atomic layer number with the electrocatalytic
EOR polarization behavior. Before the electrocatalytic meas-
urements, Rh@PtnL core–sheath NWs were loaded on carbon
©
Adv. Funct. Mater. 2018, 1806300
1806300 (4 of 9)
2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

www.advancedsciencenews.com
www.afm-journal.de
Figure 4. a) CV curves normalized to the Pt mass and b) histogram of the corresponding mass activities and specific activities of the Rh@PtnL NW/C
and commercial Pt/C catalysts for EOR in 0.2 m ethanol and 0.1 m HClO4 at 50 mV s−1. c) Chronoamperometry measurements (i–t) of EOR recorded
at 0.64 V (vs SCE) with the Rh@PtnL NW/C and commercial Pt/C catalysts at room temperature in 0.2 m ethanol and 0.1 m HClO4. d) The values of
If1/If2 and If1/Ib derived from the EOR CV curves.
support (Vulcan XC-72, 25 wt% total metals, Figure S8, Sup-
porting Information). The commercial Pt/C (JM, 20%, Figure S9,
Supporting Information) was used as a benchmark catalyst for
the comparisons. The electrochemically active surface areas
(ECSAs) of all the catalysts were estimated by cyclic voltam-
metry (CV) in 0.1 m HClO4. By calculating the charge transfer
during the hydrogen adsorption/desorption (Figure S10, Sup-
porting Information), the ECSA of Rh@Pt1L NW/C, Rh@Pt2L
NW/C, Rh@Pt3.5L NW/C, Rh@Pt5.3L NW/C, and commercial
Pt/C is determined to be 38.7, 42.0, 44.6, 39.2, and 56.0 m2 g−1,
respectively.
We evaluated the EOR activity of the Rh@PtnL NW/C cata-
lysts in 0.1 m HClO4 and 0.2 m ethanol at 50 mV s−1. Figure 4a
and Figure S11 (Supporting Information) show the ethanol elec-
trooxidation curves of different electrocatalysts with the current
density normalized to the Pt mass and the ECSA, respectively.
The Rh wavy NWs are inactive for EOR (Figure S12, Supporting
Information), because Rh has much less capacity for dehydro-
genation than Pt.[41] Therefore, the activities for ethanol elec-
trooxidation on these Rh@PtnL NW/C catalysts are completely
stemmed from the outer Pt shells. At the forward scanning,
ethanol electrooxidation gives two peaks, the first peak (peak f1)
is commonly ascribed to the formation of acetaldehyde, acetic
acid, and CO2, whereas the second peak (peak f2) is almost
completely attributed to acetic acid.[39,42] The current den-
sity of peak f1 is commonly used to evaluate the activities of
diverse electrocatalysts for EOR.[16,43–47] Figure 4b shows a his-
togram of both the mass activity and specific activity in terms
of peak f1 on these catalysts. As shown, the carbon-loaded
Rh@Pt1L, Rh@Pt2L, Rh@Pt3.5L, and Rh@Pt5.3L NW/C catalysts
exhibit 628 mA mg−1Pt, 685 mA mg−1Pt, 809 mA mg−1Pt, and
574 mA mg−1Pt, respectively, which are all more active than the
commercial Pt/C catalysts (221 mA mg−1Pt). For specific activity,
as the Pt atomic layer numbers increased, the Rh@PtnL NW/C
gave 0.54, 0.77, 1.18, and 1.13 mA cm−2, respectively, which are
also much higher than that of the Pt/C (0.35 mA cm−2). Col-
lectively, the Rh@Pt3.5L NW/C shows the best performance in
both the mass activity and specific activity, which are 3.7 and
3.4 times those of the commercial Pt/C catalyst, respectively.
In order to evaluate the catalytic activities and the possible
poisoning of the Rh@PtnL NW/C catalysts under continuous
operation condition, we conducted chronoamperometric tests
(i–t) for the electrocatalysts at 0.64 V (vs saturated calomel
electrode (SCE)) and room temperature for 60 min. As shown
in Figure 4c, there was a sharp decline in current during the
initial several seconds, which has been ascribed to the adsorp-
tion of intermediates formed at the beginning of the oxidation
reaction.[47] As the reaction proceeded, the current gradually
reached a more stable state due to the intermediates adsorbing
and oxidizing rate approached a balance. It can be found that,
in comparison with Pt/C, all the Rh@PtnL NW/C showed a
much better capacity to overcome catalytic poisoning and,
hence, exhibited a continuous higher current density in dura-
tion measurements. In addition, Rh is highly resistant to
chemical corrosion and capable to stabilize the neighboring Pt
atoms, which can also enhance the catalytic durability in acidic
mediums.[48–50]
The current peak for the back scanning (Ib) indicates the
removal of the carbonaceous intermediates adsorbed on the
catalysts. The relative intensity of If1/Ib has been widely adopted
as an indicator for the amount of carbonaceous intermedium
accumulated on the catalyst surfaces due to the incomplete
©
Adv. Funct. Mater. 2018, 1806300
1806300 (5 of 9)
2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

www.advancedsciencenews.com
www.afm-journal.de
Figure 5. a–d) In situ FTIR spectra of the electrocatalysts for EOR in 0.2 m ethanol and 0.1 m HClO4 solution: Rh@Pt1L NW/C, Rh@Pt3.5L NW/C,
Rh@Pt5.3L NW/C, and commercial Pt/C. e,f) Integrated in situ FTIR band intensities (normalized by Pt mass) of CO2 (2342 cm−1) and CH3COOH
(1280 cm−1) from the compared electrocatalysts.
oxidation.[51] In addition, the value of If1/If2 signifies the
and promoting the cleavage of the C C bond of ethanol. This

[39]

capacity for the C C bond cleavage of ethanol. As shown
Pt atomic layer number dependent EOR behavior can be attrib-
uted to the variation of the geometric compression strain and
the electronic ligand effects balanced by the Pt thickness.[52]
In order to get deeper insights into the apparent activity and
the product selectivity during EOR at molecular level, elec-
trochemical in situ FTIR studies were carried out on these
Rh@PtnL NW/C catalysts with altered Pt shell thicknesses.
Figure 5a–d shows the in situ FTIR spectra on Rh@Pt1L
NW/C, Rh@Pt3.5L NW/C, Rh@Pt5.3L NW/C, and Pt/C catalysts
during EOR. A number of absorption bands appeared with the
increase of electrode potential (Table S4, Supporting Informa-
tion). According to previous studies,[53–56] the band at 2342 cm−1
was attributed to the asymmetric stretch vibration of CO2,
in Figure 4d and Table S3 (Supporting Information), both the
values of If1/Ib and If1/If2 on these Rh@PtnL NW/C derived
from the EOR CV curves are obviously higher than that of
the Pt/C, indicating the surface poisoning was inhibited and

the cleavage of the C C bond was promoted on these Rh@
PtnL NWs/C catalysts. In particular, Rh@Pt1L NW/C shows the
maximum values of both If1/Ib (2.46) and If1/If2 (1.12), which
are 3.2 and 1.6 times that of the commercial Pt/C, respectively.
Interestingly, these values were gradually decreased as the
atomic layer numbers of the Pt shells increased, implying the
closer interaction between the outermost Pt layers and the Rh
substrates is more effective in mitigating the surface poisoning
©
Adv. Funct. Mater. 2018, 1806300
1806300 (6 of 9)
2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

www.advancedsciencenews.com
www.afm-journal.de

which reflects the cleavage of the C C bond associated with
the complete oxidation of ethanol. The bipolar band at round
2050 cm−1 was ascribed to the linearly adsorbed CO (COL),
implying the CO adsorption on catalyst surfaces. The peak
located around 1718 cm−1 was assigned to the stretching vibra-
GBs of the Rh NW cores on the outermost Pt shells. When
loaded on carbon support, the Rh@PtnL NW catalysts show
greatly improved behaviors for catalyzing EOR in both activity
and durability. As the balance of compression strain and ligand
effects between the Rh nanowires and the Pt shells, the EOR
performances are highly dependent on the number of the outer
Pt atomic layers. Electrochemical in situ FTIR spectroscopy
indicated that thinner Pt shell (i.e., Rh@Pt1L NW/C catalysts)

tion of C O bond in both acetaldehyde and acetic acid. Another
band at 1280 cm−1 belongs to the C O stretching deformation

in CH3COOH, which can be applied to monitor the production
of CH3COOH.

has better capacity to break the C C bond for complete oxida-
The evolution of the band integrated intensities normalized
to the Pt mass as a function of electrode potential is shown in
Figure S13 (Supporting Information). It can be observed that
the Rh@PtnL NW/C catalysts’ selectivities toward CO2 and
CH3COOH are very sensitive to the atomic layer number of the
Pt shells, and are obviously improved compared to the commer-
cial Pt/C. Particularly, the Rh@Pt1L NW/C shows the highest
CO2 selectivity but poorer CH3COOH selectivity at the inves-
tigated potential windows (Figure 5e,f). With the increase of
the outer Pt atomic layer numbers, the selectivity toward CO2
was gradually decreased while the CH3COOH selectivity was
increased inversely. Also, the onset potential for generating
CO2 was lower on the catalysts with less Pt atomic layer num-
bers. In Rh-Pt bimetallic heterosystems, the strain and ligand
effects from the Rh subsurface is a key factor for weakening
tion of ethanol to CO2 but poorer ability for dehydrogenation
of ethanol to acetic acid. With the increase of the Pt shell thick-
ness, the CO2 pathway is weakened down and the formation of
acetic acid is boosted up on the core–sheath catalysts. Overall,
the Rh@Pt3.5L NWs show the best performance in both the
mass activity and specific activity.
4. Experimental Section
Chemicals: Sodium hexachlororhodate (III) dodecahydrate
(Na3RhCl6·12H2O) was purchased from Alfa Aesar. Chloroplatinic
≧
acid hexahydrate (H2PtCl6·6H2O, Pt
(HClO4, 70%) were purchased from Aladdin. Polyvinylpyrrolidone
37.5%) and perchloric acid
(PVP, MW ≈ 55 000) was purchased from Sigma-Aldrich. Sodium
≧
≧
iodide dihydrate (NaI·2H2O, 99.0%) and ethanol (C2H5OH, 99.7%)
were purchased from Xilong Chemical Co. Ltd. Sodium ascorbate

Pt–intermediate binding strength (such as Pt CO) to ease their
oxidation.[41] As the in situ FTIR spectra shown, no obvious COL
band can be observed on the Rh@Pt1L NW/C and Rh@Pt3.5L
NW/C catalysts, while a tiny COL signal and a larger one can be
found on the Rh@Pt5.3L NW/C and the Pt/C, respectively. This
result is well consistent with the chronoamperometric tests
and the aforementioned If1/Ib values, indicating an improved
anti CO-poisoning ability. Also, it has been demonstrated that
≧
≧
(NaAA), acetone (C3H6O, 99.5%), and ethylene glycol (EG, 99.0%)
were purchased from Sinopharm Chemical Reagent Co. Ltd. Ultrapure
water (18.2 MΩ) was used in all experiments. All reagents were used as
received, without further purification.
Synthesis of 1.9 nm Rh Wavy Nanowires: In a typical synthesis of the
1.9 nm Rh wavy nanowires, Na3RhCl6·12H2O (15.6 mg, 0.026 mmol),
NaI·2H2O (93 mg, 0.5 mmol), NaAA (40 mg, 0.2 mmol), and PVP
(160 mg) were mixed together with EG (5.0 mL) and H2O (1.0 mL)
in a 25 mL glass vial. After the vial was capped, the mixture was
ultrasonicated for around 6 min and then magnetically stirred at 360 rpm
for 10 min. The obtained mixture was heated at 170 °C in an oil bath
under magnetic stirring for 2 h. The products were cooled down to room
temperature and washed with ethanol/acetone four times, collected by
centrifugation and then redispersed in 10 mL EG.
Synthesis of Rh@PtnL Core–Sheath Nanowires: Typically, 2.0 mL
EG solution of the as-prepared Rh nanowires and 5.0 mL EG were
added together in a 25 mL glass vial. The mixture (Solution A) was
ultrasonicated for 7 min and then magnetically stirred at room
temperature for another 7 min to make sure the Rh NWs were well
dispersed. Solution A was then preheated in an oil bath at 120 °C for
10 min under magnetic stirring (360 rpm). The Pt precursor solution
(Solution B) was prepared by dissolving quantitative H2PtCl6·6H2O
(2.2 mg mL−1) and PVP (83 mg mL−1) together in EG. To obtain Rh@Pt1L
NWs, Rh@Pt2L NWs, Rh@Pt3.5L NWs, and Rh@Pt5.3L NWs, a series of
volumes of solution B, that is, 0.3, 0.6, 1.2, and 2.4 mL, were added into
the preheated Solution A, respectively. The total volumes of the reaction
solutions were all set to 10 mL by extra additions of EG. The reaction
solution was maintained at 120 °C in the oil bath with magnetic stirring
for 4 h. The final products were cooled down to room temperature,
collected by centrifugation (14 000 rpm, 10 min) and washed four times
with a mixture of ethanol and acetone.

the dehydrogenation process is favored on Pt sites, while C C
bond cleavage prefers Rh sites.[56] The less atomic layer number
of the Pt shell causes stronger Rh–Pt interaction compression
strain and larger electronic ligand effect on the outermost Pt
surface, which can dramatically alter the catalytic behavior of

the outermost Pt surface leading to the priority of C C bond
cleavage. When the Pt shell thickened, the strain effects and
ligand effects were gradually released, and the catalytic proper-
ties of outermost Pt shell tended to be the nature of pristine
Pt, as the geometric strain and ligand effect can only impact
surface reactivity over less than a few atomic layers.[20,24] Thus,
the Rh@Pt5.3L NW/C catalysts presented the highest capacity
for producing acetic acid but poor selectivity toward CO2. It has
been demonstrated that the CO2 current efficiency (a quantifica-
tion of the current generated form the CO2 pathway reported to
the EOR overall current) is generally found to be only between
5 and 20%.[57] The overall activity for EOR should integrate both
the CO2 and CH3CH2OH pathways into account. As a result,
the Rh@Pt3.5L NW/C catalysts possess the greatest mass activity
and specific activity in the scope of this study.
Characterizations: XRD analysis was performed using a Rigaku
Smar/SmartLa operating at 30 mA and 40 kV using a Cu Kα radiation
(λ = 1.541 Å), in a range of 2θ from 30° to 90° at a scan rate of
5° min−1. TEM images, EDS elemental mappings, and cross-sectional
compositional line scanning profiles were conducted with a Hitachi
H-7650 operated at 100 kV, an FEI Tecnai G2 F30 S-Twin at 300 kV,
and a JEOL ARM200 microscope with a STEM Cs corrector. The EDS
elemental analysis was also recorded on a Hitachi S4800 equipped with
3. Conclusion
In summary, this work demonstrates the successful synthesis
of ultrathin Rh@PtnL core–sheath NWs with controlled Pt
atomic layer number and faithful replication of the high-density
©
Adv. Funct. Mater. 2018, 1806300
1806300 (7 of 9)
2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

www.advancedsciencenews.com
www.afm-journal.de
an energy-dispersive X-ray spectrometer. The elemental contents of
Rh and Pt were analyzed by an Agilent 7800 ICP-MS. XPS analysis was
performed on a ThermoFisher ESCALAB250. The XPS spectra were all
corrected by C 1s peak (284.6 eV).
Foundation of Guangdong Province (2015A030310011), and the
Scientific Research Funds and Subsidized Project for Postgraduates’
Innovative Fund in Scientific Research of Huaqiao University. The authors
thank Dr. Lu Lu from the Jia-Lab for Interface and Atomic Structure
of Xi’an Jiaotong University for Cs-corrected STEM characterizations.
The authors also thank the Instrumental Analysis Center of Huaqiao
University for analysis support.
Electrocatalysis Measurements: Before the electrocatalytic tests, the
Rh@PtnL NWs were loaded on Vulcan XC-72 carbon (25 wt% of total
metals, determined by ICP-MS). Typically, 9.0 mg Vulcan XC-72 carbon
was dispersed in 9.0 mL ethanol and then ultrasonicated for 1 h. After
that, the dispersion of Rh@PtnL NWs in ethanol (containing 3.0 mg
of total metals, determined by ICP-MS) was dropwise added into the
homogeneous carbon solution under vigorously magnetic stirring. The
obtained solution was further ultrasonicated for 1 h and magnetically
stirred for 3 h. The loaded Rh@PtnL NW/C electrocatalysts were
collected by centrifugation and redispersed in 10 mL acetic acid, heated
at 60 °C for 12 h with magnetic stirring to clean the surface of the
Rh@PtnL NWs. The cleaned catalysts were washed thrice with ethanol,
dried under vacuum condition, and then annealed at 200 °C for 1 h.
The electrocatalyst inks were prepared by redispersing the Rh@PtnL
NW/C (4.8 mg) or the commercial Pt/C (6 mg, 20 wt%, JM) catalysts
in 2 mL mixed solution of ethanol and 5% Nafion (vol:vol = 1:0.005),
respectively. 5 µL of the ink was dropped on a glassy-carbon electrode
(GCE, diameter: 5 mm, area: 0.196 cm2, Tianjin Aida Co., China) and
then dried in room temperature naturally. Therefore, the loading
concentration of metal nanocatalysts for Rh@PtnL NW/C and
commercial Pt/C was 15.3 µgRh+Pt cm−2 and 15.3 µgPt cm−2, respectively,
according to the geometric electrode area.
Conflict of Interest
The authors declare no conflict of interest.
Keywords

C
C bond cleavage, core–sheath nanowire, ethanol oxidation, grain
boundary, PtRh bimetallic
Received: September 5, 2018
Revised: October 22, 2018
Published online:
[1] F. T. Wagner, B. Lakshmanan, M. F. Mathias, J. Phys. Chem. Lett.
2010, 1, 2204.
All electrochemical measurements were conducted on
a CHI
760E electrochemical workstation (Shanghai Chenhua Co., China).
A three-electrode system was used to conduct the electrochemical
measurements. The SCE was used as reference electrode, a Pt mesh
(1 × 1 cm2) was served as counter electrodes, and a catalyst-loaded GCE
(diameter: 5 mm) was served as working electrode. The ECSAs were
determined by integrating the hydrogen desorption/adsorption charge
on the cyclic voltammograms (CVs) recorded between −0.25 and 0.95 V
(vs SCE) at a sweep rate of 50 mV s−1 in N2-saturated 0.1 m HClO4
solution. Electrocatalytic oxidation of ethanol was recorded between
−0.25 and 1.20 V (vs SCE) at a sweep rate of 50 mV s−1 in N2-saturated
0.1 m HClO4 and 0.2 m ethanol solution.
Electrochemical In Situ FTIR Studies for Ethanol Oxidation: In order
to study the product selectivity and reaction mechanisms of ethanol
oxidation reaction for different catalysts, in situ FTIR spectroscopic
studies were carried out on a Nexus 870 FTIR spectrometer (Nicolet)
fitted out a MCT detector cooled with liquid nitrogen and an EverGlo
IR source. In this configuration, infrared radiation sequentially passed
through a CaF2 window and a thin-layer solution (≈10 µm), and then it
was reflected by the electrode surface, at a spectral resolution of 8 cm−1.
The resulting spectra were reported as relative change in reflectivity
[2] M. K. Debe, Nature 2012, 486, 43.
[3] P. Strasser, Science 2015, 349, 379.
[4] M. Shao, Q. Chang, J.-P. Dodelet, R. Chenitz, Chem. Rev. 2016, 116,
3594.
[5] Z. W. Seh, J. Kibsgaard, C. F. Dickens, I. Chorkendorff, J. K. Nørskov,
T. F. Jaramillo, Science 2017, 355, eaad4998.
[6] N. Tian, Z. Y. Zhou, S. G. Sun, Y. Ding, Z. L. Wang, Science 2007,
316, 732.
[7] N. S. Porter, H. Wu, Z. Quan, J. Fang, Acc. Chem. Res. 2013, 46, 1867.
[8] Y. J. Wang, W. Long, L. Wang, R. Yuan, A. Ignaszak, B. Fang,
D. P. Wilkinson, Energy Environ. Sci. 2018, 11, 258.
[9] Y. Sun, L. Zhuang, J. Lu, X. Hong, P. Liu, J. Am. Chem. Soc. 2007,
129, 15465.
[10] A. Chen, P. Holt-Hindle, Chem. Rev. 2010, 110, 3767.
[11] R. Lin, X. Cai, H. Zeng, Z. Yu, Adv. Mater. 2018, 30, 1705332.
[12] D. Y. Chung, J. M. Yoo, Y.-E. Sung, Adv. Mater. 2018, 30, 1704123.
[13] P. Rodriguez, Y. Kwon, M. T. M. Koper, Nat. Chem. 2012, 4, 177.
[14] E. Antolini, J. Power Sources 2007, 170, 1.
[15] H. F. Wang, Z. P. Liu, J. Am. Chem. Soc. 2008, 130, 10996.
[16] 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.
R E −R E
∆R
R
(
)
(
)
S
R
=
(1)
R E
(
)
R
[17] W. Zhu, J. Ke, S. B. Wang, J. Ren, H. H. Wang, Z. Y. Zhou, R. Si,
Y. W. Zhang, C. H. Yan, ACS Catal. 2015, 5, 1995.
[18] J. Gu, Y. W. Zhang, F. Tao, Chem. Soc. Rev. 2012, 41, 8050.
[19] Y. Xiong, H. Shan, Z. Zhou, Y. Yan, W. Chen, Y. Yang, Y. Liu, H. Tian,
J. Wu, H. Zhang, D. Yang, Small 2017, 13, 1603423.
[20] K. D. Gilroy, X. Yang, S. Xie, M. Zhao, D. Qin, Y. Xia, Adv. Mater.
2018, 30, 1706312.
[21] S. Xie, S.-I. Choi, N. Lu, L. T. Roling, J. A. Herron, L. Zhang, J. Park,
J. Wang, M. J. Kim, Z. Xie, M. Mavrikakis, Y. Xia, Nano Lett. 2014,
14, 3570.
where R(ES) and R(ER) are the single-beam spectra collected at sample
potential ES and reference potential ER, respectively. The ER was recorded
at −0.25 V (vs SCE).
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
[22] Y. Wang, W. Wang, F. Xue, Y. Cheng, K. Liu, Q. Zhang, M. Liu,
S. Xie, Chem. Commun. 2018, 54, 5185.
[23] B. W. Zhang, H. L. Yang, Y. X. Wang, S. X. Dou, H. K. Liu, Adv.
Energy Mater. 2018, 8, 1703597.
Acknowledgements
[24] P. Strasser, S. Koh, T. Anniyev, J. Greeley, K. More, C. Yu, Z. Liu,
S. Kaya, D. Nordlund, H. Ogasawara, M. F. Toney, A. Nilsson, Nat.
Chem. 2010, 2, 454.
This work was supported by the National Natural Science Foundation
of China (21771067), the Natural Science Foundation of Fujian Province
(Distinguished Young Investigator, 2017J06005), the Natural Science
©
Adv. Funct. Mater. 2018, 1806300
1806300 (8 of 9)
2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

www.advancedsciencenews.com
www.afm-journal.de
[25] L. Bu, N. Zhang, S. Guo, X. Zhang, J. Li, J. Yao, T. Wu, G. Lu,
J. Y. Ma, D. Su, X. Huang, Science 2016, 354, 1410.
[43] Z.-B. Wang, G.-P Yin, J. Zhang, Y.-C. Sun, P.-F. Shi, J. Power Sources
2006, 160, 37.
[26] C. W. Li, J. Ciston, M. W. Kanan, Nature 2014, 508, 504.
[27] X. Huang, Z. Zhao, Y. Chen, C.-Y. Chiu, L. Ruan, Y. Liu, M. Li,
X. Duan, Y. Huang, Nano Lett. 2014, 14, 3887.
[28] S.-I. Choi, J. A. Herron, J. Scaranto, H. Huang, Y. Wang, X. Xia, T. Lv,
J. Park, H.-C. Peng, M. Mavrikakis, Y. Xia, ChemCatChem 2015, 7, 2077.
[29] S. Xie, Q. Xu, X. Huang, ChemCatChem 2016, 8, 480.
[30] H. G. Liao, L. Cui, S. Whitelam, H. Zheng, Science 2012, 336, 1011.
[31] Y. Wang, S.-I. Choi, X. Zhao, S. Xie, H.-C. Peng, M. Chi, C. Z. Huang,
Y. Xia, Adv. Funct. Mater. 2014, 24, 131.
[44] X. Huang, Z. Zhao, J. Fan, Y. Tan, N. Zheng, J. Am. Chem. Soc. 2011,
133, 4718.
[45] Y. Shen, Z. Zhang, K. Xiao, J. Xi, ChemCatChem 2014, 6, 3254.
[46] J. Ding, L. Bu, S. Guo, Z. Zhao, E. Zhu, Y. Huang, X. Huang, Nano
Lett. 2016, 16, 2762.
[47] J. E. Sulaiman, S. Zhu, Z. Xing, Q. Chang, M. Shao, ACS Catal.
2017, 7, 5134.
[48] S. Xie, N. Lu, Z. Xie, J. Wang, M. J. Kim, Y. Xia, Angew. Chem., Int.
Ed. 2012, 51, 10266.
[32] R. Blume, H. Niehus, H. Conrad, A. Böttcher, J. Phys. Chem. B 2004,
108, 14332.
[33] Y. Yang, J. Zhang, Y. Wei, Q. Chen, Z. Cao, H. Li, J. Chen, J. Shi,
Z. Xie, L. Zheng, Nano Res. 2018, 11, 656.
[34] X. Sun, K. Jiang, N. Zhang, S. Guo, X. Huang, ACS Nano 2015, 9, 7634.
[35] M. Wakisaka, S. Mitsui, Y. Hirose, K. Kawashima, H. Uchida,
M. Watanabe, J. Phys. Chem. B 2006, 110, 23489.
[49] V. Beermann, M. Gocyla, E. Willinger, S. Rudi, M. Heggen,
R. E. Dunin-Borkowski, M.-G Willinger, P. Strasser, Nano Lett. 2016,
16, 1719.
[50] H. Huang, K. Li, Z. Chen, L. Luo, Y. Gu, D. Zhang, C. Ma, R. Si,
J. Yang, Z. Peng, J. Zeng, J. Am. Chem. Soc. 2017, 139, 8152.
[51] Z. Liu, X. Y. Ling, X. Su, J. Y. Lee, L. M. Gan, J. Power Sources 2005,
149, 1.
[36] J.-X. Tang, Q.-S. Chen, L.-X. You, H.-G. Liao, S.-G. Sun, S.-G. Zhou,
Z.-N. Xu, Y.-M. Chen, G.-C. Guo, J. Mater. Chem. A 2018, 6, 2327.
[37] E. W. Harak, K. M. Koczkur, D. W. Harak, P. Patton, S. E. Skrabalak,
ChemNanoMat 2017, 3, 779.
[38] J. P. I. de Souza, S. L. Queiroz, K. Bergamaski, E. R. Gonzalez,
F. C. Nart, J. Phys. Chem. B 2002, 106, 9825.
[52] D. Friebel, V. Viswanathan, D. J. Miller, T. Anniyev, H. Ogasawara,
A. H. Larsen, C. P. O’Grady, J. K. Nørskov, A. Nilsson, J. Am. Chem.
Soc. 2012, 134, 9664.
[53] N. Erini, R. Loukrakpam, V. Petkov, E. A. Baranova, R. Yang,
D. Teschner, Y. Huang, S. R. Brankovic, P. Strasser, ACS Catal. 2014,
4, 1859.
[39] L. Rao, Y. X. Jiang, B. W. Zhang, Y. R. Cai, S. G. Sun, Phys. Chem.
Chem. Phys. 2014, 16, 13662.
[40] J. Bai, X. Xiao, Y. Y. Xue, J. X. Jiang, J. H. Zeng, X. F. Li, Y. Chen, ACS
Appl. Mater. Interfaces 2018, 10, 19755.
[41] V. D. Colle, V. Grozovski, E. Herrero, J. M. Feliu, ChemCatChem
2013, 5, 1350.
[54] M. Heinen, Z. Jusys, R. J. Behm, J. Phys. Chem. C 2010, 114, 9850.
[55] E. A. de Souza, M. J. Giz, G. A. Camara, E. Antolini, R. R. Passos,
Electrochim. Acta 2014, 147, 483.
[56] N. Erini, V. Beermann, M. Gocyla, M. Gliech, M. Heggen,
R. E. Dunin-Borkowski, P. Strasser, Angew. Chem., Int. Ed. 2017, 56,
6533.
[42] Z. Y. Zhou, Z. Z. Huang, D. J. Chen, Q. Wang, N. Tian, S. G. Sun,
Angew. Chem., Int. Ed. 2010, 49, 411.
[57] A. B. Delpeuch, M. Chatenet, M. S. Rau, C. Cremers, Phys. Chem.
Chem. Phys. 2015, 17, 10881.
©
Adv. Funct. Mater. 2018, 1806300
1806300 (9 of 9)
2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim