PtPb/PtNi Intermetallic Core/Atomic Layer Shell Octahedra for Efficient Oxygen Reduction Electrocatalysis

Article abstract of DOI:10.1021/jacs.7b03510

Although explosive studies on pursuing high-performance Pt-based nanomaterials for fuel cell reactions have been carried out, the combined controls of surface composition, exposed facet, and interior structure of the catalyst remains a formidable challenge. We demonstrate herein a facile chemical approach to realize a new class of intermetallic Pt-Pb-Ni octahedra for the first time. Those nanostructures with unique intermetallic core, active surface composition, and the exposed facet enhance oxygen reduction electrocatalysis with the optimized PtPb_1.12Ni_0.14 octahedra exhibiting superior specific and mass activities (5.16 mA/cm² and 1.92 A/mg_Pt) for oxygen reduction reaction (ORR) that are ～20 and ～11 times higher than the commercial Pt/C, respectively. Moreover, the PtPb_1.12Ni_0.14 octahedra can endure at least 15 000 cycles with negligible activity decay, showing a new class of Pt-based electrocatalysts with enhanced performance for fuel cells and beyond.

Full text of DOI:10.1021/jacs.7b03510

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Article
PtPb/PtNi Intermetallic Core/Atomic Layer Shell Octahedra
for Efficient Oxygen Reduction Electrocatalysis
Lingzheng Bu, Qi Shao, Bin E, Jun Guo, Jianlin Yao, and Xiaoqing Huang
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.7b03510 • Publication Date (Web): 28 Jun 2017
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PtPb/PtNi Intermetallic Core/Atomic Layer Shell Octahedra for Ef-
ficient Oxygen Reduction Electrocatalysis
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Lingzheng Bu,† Qi Shao,† Bin E,† Jun Guo,‡ Jianlin Yao,† and Xiaoqing Huang*,†
†College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Jiangsu, 215123, China
‡Testing & Analysis Center, Soochow University, Jiangsu 215123, China
Supporting Information
ABSTRACT: Although explosive studies on pursuing highꢀperformance Ptꢀbased nanomaterials for the fuel cell reactions have
been carried out, the combined controls of surface composition, exposed facet and interior structure of the catalyst remains
formidable challenge. We demonstrate herein a facile chemical approach to realize a new class of intermetallic PtꢀPbꢀNi octahedra
for the first time. Those nanostructures with unique intermetallic core, active surface composition and the exposed facet enhance
oxygen reduction electrocatalysis with the optimized PtPb1.12Ni0.14 octahedra exhibiting superior specific and mass activities (5.16
mA/cm2 and 1.92 A/mgPt) for oxygen reduction reaction (ORR) that are ~ 20 and ~ 11 times higher than the commercial Pt/C,
respectively. Moreover, the PtPb1.12Ni0.14 octahedra can endure at least 15000 cycles with negligible activity decay, showing a new
class of Ptꢀbased electrocatalysts with enhanced performance for fuel cell and beyond.
can contribute greatly to the durability for Ptꢀbased intermetalꢀ
1. INTRODUCTION
lic NCs in the process of electrocatalysis.32ꢀ36 The strong interꢀ
The current global energy status urgently requires the efficient
and reliable conversion of fossil fuels or renewable sources to
generate electric power on large scale.1ꢀ5 In all different forms
of electric energies, fuel cells are highly expected to realize
widespread commercial applications in the fields of transporꢀ
tation, stationary, and portable power generations, due to their
obvious advantages of promising efficiency, lightness, conꢀ
venience, hardly pollution to the environment, and etc.4ꢀ6 As to
the cathodic oxygen reduction reaction (ORR) in fuel cells, Ptꢀ
based nanomaterials are considered as the most efficient elecꢀ
trocatalysts.7ꢀ9 However, the high cost associated with Pt based
action between the active PtNi shell and the PtM core will
greatly boost oxygen reduction catalysis. In this regard, the
rational combination of PtM intermetallic NCs as the core and
the active PtNi on the surface may come into being unique Ptꢀ
based electrocatalysts with simultaneously enhanced activity
and durability for ORR, while it is still a formidable challenge.
We show herein a facile chemical route to create unique inꢀ
termetallic NCs, namely bimetallic PtꢀPb octahedra and trimeꢀ
tallic PtꢀPbꢀNi octahedra. The successful creations of intermeꢀ
tallic PtꢀPb and PtꢀPbꢀNi octahedra with wellꢀdefined morꢀ
phology, composition, and size provide an ideal platform to
study the structural effects, especially the surface composition
and the exposed facets on ORR. It is shown that the PtꢀPbꢀNi
octahedra show outstanding activity and improved durability
for ORR relative to the commercial Pt/C, because of their orꢀ
dered structure, wellꢀdefined morphology and alloy effect. To
be specific, the intermetallic PtPb1.12Ni0.14 octahedra/C show
1.4, 1.9, 1.1, 2.7 and 11.4 times higher in mass activity, and
1.4, 1.9, 1.3, 2.9 and 19.6 times higher in specific activity than
those of PtPb1.07Ni0.10 octahedra/C, PtPb1.03Ni0.05 octahedra/C,
Pt1.21Pb octahedra/C, PtPb octahedra/C and Pt/C, respectively.
The intermetallic core structure and the unique core/shell
structure also make the PtPb1.12Ni0.14 octahedra highly durable
with negligible activity decay over 15000 potential sweeps.
electrocatalysts largely obstructs their practical applications.10ꢀ
12
So far, the widely used approach to deal with this signifiꢀ
cant challenge is to alloy the lowꢀcost transition metals with Pt
.
13ꢀ15 Indeed, the alloyed Ptꢀbased nanocrystals (NCs), especialꢀ
ly Ptꢀnickel (PtꢀNi) NCs with well controls in size, morpholoꢀ
gy, and composition, exhibit enhanced performance, where
substantial works have been done.16ꢀ22 Another ingenious reciꢀ
pe for reducing the content of scarce Pt and improving its utiꢀ
lization is to design core/shell nanostructure, because the
core/shell structure with ultrathin Pt shell is beneficial to the
enhancements of performance and lifetime for ORR.23ꢀ25 Howꢀ
ever, the reported core/shell structured PtM NCs with singleꢀ
component core and/or shell have large limitations in terms of
the ORR activity and durability enhancement,26ꢀ29 since the
multicomponent PtM usually exhibits higher ORR activity
than pure Pt.30,31 Considering the critical role of core in the
enhancements of ORR performance, the PtM core for activatꢀ
ing oxygen reduction catalysis should also be rationally selectꢀ
ed.28 Ptꢀbased intermetallic NCs, such as Ptꢀiron (PtꢀFe), Ptꢀ
copper (PtꢀCu), Ptꢀchromium (PtꢀCr), and the Ptꢀlead (PtꢀPb)
NCs, have been attracted great research attentions,32ꢀ36 mainly
due to their better modulate over their geometric, structural as
well as electronic effects. The chemical and structural stability
2. EXPERIMENTAL SECTION
2.1. Chemicals: Lead(II) acetylacetonate (Pb(acac)2, 99%),
nickel(II) formate dihydrate (Ni(HCO2)2·2H2O), and oleic acid
(C18H34O2, OA, > 85%) were obtained from SigmaꢀAldrich.
Lead(II) chloride (PbCl2, 99.99%), lead(II) acetate trihydrate
(Pb(Ac)2·3H2O, > 99%) and phloroglucinol (C6H6O3, ≥ 99%)
were purchased from Aladdin. Diphenyl ether (C12H10O, DPE,
analytical reagent, ≥ 99.0%) came from Sinopharm Chemical
Reagent Co., Ltd. (Shanghai, China). All the other chemicals
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used in this work were described in our previous works.37ꢀ39
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2.2. Synthesis of PtPb octahedra, PtPb1.03Ni0.05 octahedra,
PtPb1.07Ni0.10 octahedra, PtPb1.12Ni0.14 octahedra, and
Pt1.21Pb octahedra: To synthesize the PtPb octahedra, 17.8
mg AA, 8.0 mg Pb(acac)2, 10.0 mg Pt(acac)2, 2.5 mL OAm
and 2.5 mL ODE were mixed in a glass vial and heated at 160
ºC for 5 h. The products were collected by centrifugation. All
the synthetic parameters for PtPb1.03Ni0.05 octahedra,
PtPb1.07Ni0.10 octahedra and PtPb1.12Ni0.14 octahedra are similar
to those of PtPb octahedra but introducing additional
Ni(HCO2)2·2H2O (0.4, 0.8 and 1.2 mg, respectively) into the
synthesis. The Pt1.21Pb octahedra were obtained by adding 2.6
mg Pt(acac)2, 17.8 mg AA, 1.0 mL OAm, 1.0 mL ODE into
the PtPb octahedra mixture, and further heated at 160 ºC for 3
h.
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2.3. Characterization: Fast Fourier transform (FFT) was colꢀ
lected with an FEI Tecnai F20 transmission electron microꢀ
scope at 200 kV. All the other characterization techniques in
this work were described in our previous work.37ꢀ39
2.4. Electrochemical measurements: The loading amounts of
Pt for the PtPb octahedra/C, Pt1.21Pb octahedra/C, PtPb1.03Ni0.05
octahedra/C, PtPb1.07Ni0.10 octahedra/C, PtPb1.12Ni0.14 octaheꢀ
dra/C, and commercial Pt/C were all kept at 12.8 µg/cm2, as
calculated by ICPꢀAES measurement. The equation for the
calculation of electrochemically active surface area (ECSA) is
shown as follow.
ECSAPt, cat (m2/gPt) =
Q
(C)
2
H−adsorption
[
]×105
2
2
210ꢁC/cm L (mg /cm ) Ag (cm )
Pt
Pt
PtPb Octahedra. (a, b) TEM images, (c) PXRD pattern, (d)
In this equation, QHꢀadsorption (C) is the hydrogen adsorption
charge calculated from the cyclic voltammograms (CVs). 210
ꢁC/cm2 is used as the conversion factor. LPt (mgPt/cm2) is the
working electrode Pt loading. Ag (cm2) is the geometric surꢀ
face area of the glassy carbon electrode (i.e. 0.196 cm2).
TEMꢀEDS, (e) HRTEM image and the FFT pattern, (f) HAADFꢀ
STEM image and elemental mappings, and (g) corresponding
lineꢀscans of the PtPb octahedra. The inset in (a) is the 3D model
of the PtPb octahedra. The composition ratio of Pt/Pb is 50.9 ±
0.2/49.1 ± 0.2 as revealed by ICPꢀAES and 50.7 ± 0.5/49.3 ± 0.5
as confirmed by TEMꢀEDS.
For the ORR polarization curve of each catalyst, the current
value at 0.4 V (vs. RHE) was defined as the diffusion limited
current. All the other electrochemical measurements were
similar with our previous publication.37ꢀ39
Figure 1aꢀb and Figure S9aꢀb show the representative
TEM images of the PtꢀPb octahedra. TEM characterization
shows that the octahedra are the major products (nearly 100%).
Figure S9cꢀd are the HAADFꢀSTEM images, which further
3. RESULTS AND DISCUSSION
reveal the wellꢀdefined structure of the PtꢀPb octahedra, and
the corresponding 3D model has been shown in the inset in
Figure 1a. The PtꢀPb octahedra have narrow edge length disꢀ
tribution of around 18.0 nm (Figure S9e). As shown in Figure
1c, the distinct PXRD pattern of the PtꢀPb octahedra can
match well with the reflections of the intermetallic PtꢀPb maꢀ
terials (Joint Committee on Powder Diffraction Standards,
JCPDS, No. 06ꢀ0374). The composition ratio of Pt/Pb is 50.9
± 0.2/49.1 ± 0.2, as revealed by the ICPꢀAES, which is conꢀ
We prepared the PtꢀPb and/or PtꢀPbꢀNi NCs through a novel
wetꢀchemical approach, in which Pt(acac)2, Pb(acac)2 and/or
Ni(HCO2)2·2H2O were used as Pt, Pb and/or Ni precursors,
AA was chosen as reducing agent and OAm and ODE were
applied as mixed solvents and surfactants (see
EXPERIMENTAL SECTION for details). The synthetic paꢀ
rameters, such as the precursors, the species, the reducing
agents, and the solvents, have been explored in detail (Figures
S1-7). The formation of PtPb octahedra with relatively weak
anisotropy can be attributed to the equivalent growth along the
directions of three symmetry axes in the condition of relatively
low reducing capacity (17.8 mg AA), as compared with the
creation of hexagonal nanopaltes with high anisotropy in conꢀ
ditions of fast reducing rate (35.6 mg AA).36 Based on the relaꢀ
tionship between shape percentage and amount of AA (Figure
S8), we found the shape evolution from octahedra to nanoꢀ
plates with the increased amounts of AA.
sistent with the TEMꢀEDS (50.7 ± 0.5/49.3 ± 0.5) (Figure 1d
)
and SEMꢀEDS (50.4 ± 0.8/49.6 ± 0.8) results (Figure S9f).
The interplannar spacing displays 0.304 nm, in consistent with
the (101) plane of hexagonal phase PtPb (P63/mmc) intermeꢀ
tallic structure (Figure 1e & Figure S10a). The FFT pattern
of an individual PtPb octahedron reveals the singleꢀcrystalline
nature (inset in Figure 1e). The elements of Pt and Pb are
homogeneously distributed throughout the whole octahedron
(Figure 1f), as confirmed by the lineꢀscans (Figure 1g & Fig-
ure S10b), showing the alloyed structure of the PtPb octaheꢀ
Figure 1. Morphological and Structural Characterizations of
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The optimized synthetic parameters of PtꢀPbꢀNi octahedra,
dra.
1
such as the precursors, the species, the reducing agents, and
the solvents, have been also explored in details (Figures S12-
19). We found that the introduction of Ni(HCO2)2·2H2O into
the synthesis of PtPb hexagonal nanoplates cannot yield wellꢀ
defined PtPb/PtNi nanoplates (Figure S20). As shown in Fig-
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ure 3 & Figures S21
feature have the similar size and morphology as the PtPb octaꢀ
hedra. The PtPb1.03Ni0.05 octahedra (Figure 3a b & Figure
S21), PtPb1.07Ni0.10 octahedra (Figure 3c d & Figure S22) and
PtPb1.12Ni0.14 octahedra (Figure 3e f & Figure S23) were furꢀ
ꢀ23, PtꢀPbꢀNi NCs with monodisperse
ꢀ
ꢀ
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ꢀ
ther characterized by series of techniques, such as TEM,
STEM, EDS, and elemental mappings. It is worth mentioned
that the Ni mapping is slightly larger than Pb mapping in
PtPb1.03Ni0.05 octahedra (Figure 3b), PtPb1.07Ni0.10 octahedra
(Figure 3d) and PtPb1.12Ni0.14 octahedra (Figure 3f), indicatꢀ
ing that the Ni precursor was reduced after the formation of
PtPb octahedra.
Figure 2. Growth Mechanism of the PtPb Octahedra. (a-e)
TEM images of PtPb octahedra intermediates collected from (a)
0.5 h, (b) 1 h, (c) 3 h, (d) 5 h and (e) 6 h. (f) SEMꢀEDS of PtPb
octahedra intermediates collected from the reactions at different
reaction times. (g) The changes on the composition ratio of Pb to
Pt for the PtPb octahedra intermediates, as determined by ICPꢀ
AES measurements. (h) PXRD patterns of PtPb octahedra interꢀ
mediates collected from the reactions at different reaction times.
To uncover the growth mechanism, we have tracked the
PtPb octahedra intermediates collected from different reaction
times. At 0.5 h of the synthesis (Figure 2a), the product conꢀ
tains the smallꢀsize NCs. The SEMꢀEDS result shows the
Pt/Pb in the initial intermediate is 11.6/88.4, revealing high
content of Pb in the initial intermediate. They are the mixtures
of Pt (JCPDS No.04ꢀ0802), Pb3(CO3)2(OH)2 (JCPDS No.13ꢀ
0131) and PtPb (JCPDS No.06ꢀ0374), as revealed by the
PXRD analysis (Figure 2h & Figure S11). At the reaction
time of 1.0 h, the NCs became to be faceted (Figure 2b), and
the composition of Pt increased from 11.6% to 32.8% (Figure
2g). After the 3.0 hꢀreaction, the size and the Pt content
(42.7%) of the intermediates increased associated with presꢀ
Figure 3. Morphological and Structural Characterizations of
PtPb1.03Ni0.05 Octahedra, PtPb1.07Ni0.10 Octahedra and
PtPb1.12Ni0.14 Octahedra. (a) TEM image of PtPb1.03Ni0.05 octaꢀ
hedra. The inset in (a) is the HAADFꢀSTEM image of an individꢀ
ual PtPb1.03Ni0.05 octahedron, and the elemental mappings are
shown in (b). (c) TEM image of PtPb1.07Ni0.10 octahedra. The
inset in (c) is the HAADFꢀSTEM image of an individual
PtPb1.07Ni0.10 octahedron, and the elemental mappings are shown
in (d). (e) TEM image of PtPb1.12Ni0.14 octahedra. The inset in (e)
is the HAADFꢀSTEM image of an individual PtPb1.12Ni0.14 octaꢀ
hedron, and the elemental mappings are shown in (f).
ence of regular octahedra (Figure 2c
time was 5.0 h, the intermetallic PtPb octahedra with the Pt/Pb
ratio of about 1/1 (50.6/49.4) were obtained (Figure 2d f-h).
, fꢀg). When the reaction
,
When the reaction time was 6 h, there were hardly size, morꢀ
phology, composition, and phase changes of octahedra (Fig-
ure 2e-h). During the reaction time from 0.5 to 1.0 and to 3.0
h, there are obvious changes in both the PXRD pattern and the
structure of the intermediates. The dominant intermediate of
Pb3(CO3)2(OH)2 produced from the reaction time of 0.5 h was
transformed into intermetallic PtPb after 3.0 h (Figure 2h &
Figure S11).
The PXRD for PtꢀPb octahedra and PtꢀPbꢀNi octahedra was
also carried out (Figure S24). There is hardly difference
among the PXRD patterns for PtꢀPb and PtꢀPbꢀNi octahedra
To date, the most active ORR electrocatalysts are mainly PtꢀNi
nanomaterials.40ꢀ42 To this end, we prepared PtꢀPbꢀNi octaheꢀ
dra by introducing additional Ni precursor into the synthesis of
PtPb octahedra while keeping other parameters unchanged.
(Figure S24a), while the enlarged patterns reveal that the halfꢀ
peak width such as (110) facet for PtꢀPbꢀNi octahedra reduces
with increasing the Ni composition (Figure S24b). To further
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analyse PtꢀPbꢀNi nanostructure, HRTEM, lineꢀscan and XPS electrocatalysts are shown in Figure 5a. According to the CVs
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tests have been carried out (Figure 4 & Figure S25 & Figure
S26). We can see that the PtPb1.12Ni0.14 octahedra possess a
clearer core/shell structure than the PtPb1.07Ni0.10 octahedra and
curves, the ECSAs of these electrocatalysts were calculated to
be 37.2, 38.0, 37.6, 39.5, and 63.8 m2/g for the PtPb1.12Ni0.14
octahedra/C, PtPb1.07Ni0.10 octahedra/C, PtPb1.03Ni0.05 octaheꢀ
PtPb1.03Ni0.05 octahedra (Figure 4a
,
b
,
d
,
e,
g
,
h
), because the
dra/C, PtPb octahedra/C, and Pt/C (Figure 5b). The
former contains more Ni to form thicker PtNi shell. The PtNi
shell thicknesses were calculated to be around 0.3 nm for the
PtPb1.03Ni0.05 octahedra, around 0.5 nm for the PtPb1.07Ni0.10
octahedra, and around 0.8 nm for the PtPb1.12Ni0.14 octahedra.
It is evident that the PtNi shell locates outside the octahedra
and distributes homogeneously on the surface, revealed by the
PtPb1.12Ni0.14 octahedra/C has similar ECSA with the
PtPb1.07Ni0.10 octahedra/C, PtPb1.03Ni0.05 octahedra/C, and PtPb
octahedra/C, due to their similar size and morphology.
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lineꢀscans and the XPS spectra (Figure 4c, f, i & Figure S26).
As determined by XPS (Figure S26), the surface molar ratio
of Ni to Pb to Pt is 17.0/40.5/42.5, 18.3/38.3/43.4, and
23.6/34.1/42.3 for PtPb1.03Ni0.05 octahedra, PtPb1.07Ni0.10 octaꢀ
hedra and PtPb1.12Ni0.14 octahedra, respectively, higher than the
overall Ni/Pb/Pt compositions of different PtꢀPbꢀNi octahedra,
indicating the Niꢀrich surface of different PtꢀPbꢀNi octahedra.
The integration of strong tensile strain of PtPb to the Pt (110)
facet, the ordered intermetallic phase core,36 and the active
PtNi shell40ꢀ42 are highly beneficial for the enhancement of
ORR performance.
Figure 5. ORR Performances of PtPb1.12Ni0.14 Octahedra/C,
PtPb1.07Ni0.10 Octahedra/C, PtPb1.03Ni0.05 Octahedra/C, PtPb
Octahedra/C and Pt/C. (a) CVs of different electrocatalysts in
0.1 M HClO4 solution. (b) Histogram of ECSAs of different elecꢀ
trocatalysts. (c) ORR polarization curves of different electrocataꢀ
lysts. (d) Histogram of mass and specific activities of different
electrocatalysts. The activities and standard deviations were calꢀ
culated based on five parallel measurements after Ohmic drop
correction. The current densities in (c) were normalized to the
geometric area of a rotating disk electrode (RDE, 0.196 cm2).
Figure 5c shows the ORR polarization curves of various
electrocatalysts (O2ꢀsaturated 0.1 M HClO4, 10 mV/s and 1600
rpm at room temperature). The mass activity and specific acꢀ
tivity for the different electrocatalysts, based on Figure 5c
,
were presented in Figure 5d & Figure S32 & Table S1 (at
0.90 V vs. RHE). In general, the PtPb1.12Ni0.14 octahedra/C has
the largest highest mass activity of 1.92 A/mgPt among in these
five catalysts, which is 1.4, 1.9, 2.7, and 11.4 times larger than
the PtPb1.07Ni0.10 octahedra/C (1.40 A/mgPt), PtPb1.03Ni0.05 ocꢀ
tahedra/C (1.02 A/mgPt), PtPb octahedra/C (0.71 A/mgPt), and
the commercial Pt/C (0.17 A/mgPt), respectively, and about 4.4
times that of the 2020 U.S. Department of Energy target (0.44
A/mgPt).43 The ORR specific activity of the PtPb1.12Ni0.14 octaꢀ
hedra/C reaches to 5.16 mA/cm2, which is 1.4, 1.9, 2.9, and
19.6 times greater than the PtPb1.07Ni0.10 octahedra/C,
PtPb1.03Ni0.05 octahedra/C, PtPb octahedra/C, and Pt/C, respecꢀ
tively, all which show that the PtPb1.12Ni0.14 octahedra/C is one
of the best ORR electrocatalysts reported to date up to now
Figure 4. Structural Analyses of PtPb1.03Ni0.05 Octahedra,
PtPb1.07Ni0.10 Octahedra and PtPb1.12Ni0.14 Octahedra. (a, d, g)
TEM images, (b, e, h) HRTEM images, and (c, f, i) highꢀ
magnification HAADFꢀSTEM images and the corresponding lineꢀ
scans of (a, b, c) PtPb1.03Ni0.05 octahedra, (d, e, f) PtPb1.07Ni0.10
octahedra and (g, h, i) PtPb1.12Ni0.14 octahedra.
To investigate the ORR properties of different nanostrucꢀ
tures, the obtained PtPb octahedra, PtPb1.03Ni0.05 octahedra,
PtPb1.07Ni0.10 octahedra and PtPb1.12Ni0.14 octahedra were loadꢀ
ed onto a carbon black (C, Vulcan XCꢀ72R) and then extenꢀ
sively washed with the mixture of ethanol (9) /cyclohexane (1)
to remove the excess surfactant. Such treatments allowed the
NCs uniformly distributed on C (Figure S27-30). The resultꢀ
ing electrocatalysts, namely, PtPb octahedra/C (Figure S27a-
(
Table S2). We also compared the ORR activities of the
PtPb1.12Ni0.14 octahedra/C before and after washing treatment
Figure S33). The PtPb1.12Ni0.14 octahedra/C without washing
(
treatment shows much lower mass activity and specific activiꢀ
ty (0.81 A/mgPt and 2.17 mA/cm2 at 0.90 V vs. RHE) than
those of the catalyst after treatment, revealing the necessity of
severe washing treatment for the preparation of active ORR
catalysts. Additionally, the shape evolution of PtPb NCs from
nanoplates to octahedra as well as their corresponding electroꢀ
c
), PtPb1.03Ni0.05 octahedra/C (Figure S28a-c), PtPb1.07Ni0.10
octahedra/C (Figure S29a-c), and PtPb1.12Ni0.14 octahedra/C
Figure S30a-c), were selected as ORR electrocatalysts, and
compared with the Pt/C (Figure S31a-b). CVs of different
(
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catalytic performances have also been checked (Figure S4 &
show higher ECSA losses than that of the PtPb1.12Ni0.14 octaꢀ
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Figure S34). We found that the PtꢀPb NCs/Cꢀ22.3 mg AA
exhibits the mass activity of 1.04 A/mgPt and the specific acꢀ
tivity of 2.53 mA/cm2 at 0.90 V vs. RHE. While the PtꢀPb
NCs/Cꢀ26.8 mg AA (2.02 A/mgPt and 4.59 mA/cm2) and PtꢀPb
NCs/Cꢀ31.2 mg AA (2.57 A/mgPt and 5.19 mA/cm2) show
higher ORR activities than those of the PtꢀPb NCs/Cꢀ22.3 mg
AA, which is likely due to their higher yield of nanoplates in
the products in the presence of more AA.
hedra/C (Figure S35a-f). Moreover, The PtPb octahedra/C
exhibits larger ORR activity loss, about 27.3% in mass activity
and 12.9% in specific activity, and also the larger ECSA loss
(Figure 6c-d & Figure S35g-h). By contrast, the commercial
Pt/C shows as large as 39.9% loss in mass activity, but 26.6%
enhancement in specific activity along with the 52.4% ECSA
loss (Figure S35i-j & Figure S36e-f). All these electrocataꢀ
lysts after the 15000 cycles of ADTs were also investigated by
series of characterizations, such as TEM, HRTEM, EDS and
lineꢀscans. It reveals that there were limited changes in the
shapes, sizes, compositions, and structures of PtPb1.03Ni0.05
octahedra/C (Figure S28d-f), PtPb1.07Ni0.10 octahedra/C (Fig-
ure S29d-f), and PtPb1.12Ni0.14 octahedra/C (Figure S30d-f &
Figure S37 & Figure 6e-f) after 15000 potential cycles. For
the PtPb octahedra/C, after durability tests there was observaꢀ
ble composition change and the PtPb octahedra changed into
porous NCs (Figure S27d-f). On the sharp contrast, the nanoꢀ
particles on Pt/C became aggregated and larger after ADTs
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(Figure S31c-d), confirming the improved stability of the Ptꢀ
PbꢀNi octahedra/C.
The highlight in our work is the improved ORR activities of
PtꢀPbꢀNi octahedra compared with the PtPb octahedra.18,40ꢀ42
To understand the origin of enhanced performance of PtꢀPbꢀNi
octahedra with intermetallic core/atomic layer shell nanostrucꢀ
ture, we further carried out additional study to illustrate the
advantage of PtNi shell versus Pt shell on ORR catalysis (Fig-
ure S38-S40). We can see that the Pt1.21Pb octahedra/C with
PtPb/Pt core/shell nanostructure exhibits the specific activity
of 4.11 mA/cm2 and the mass activity of 1.72 A/mgPt, which is
lower than that of the PtPb1.12Ni0.14 octahedra/C, as well as the
higher ECSA and activity losses after the durability tests
(12.2 % ECSA loss, 19.8% mass activity loss, and 8.3% speꢀ
cific activity loss), further revealing the obvious advantage of
active PtNi shell versus Pt shell (Figure 5-6 & Figure S40).
Figure 6. ORR Durability of PtPb1.12Ni0.14 Octahedra/C and
PtPb Octahedra/C. (a) ORR polarization curves and (b) the
corresponding histogram of mass and specific activities of the
PtPb1.12Ni0.14 octahedra/C before and after different potential cyꢀ
cles. (c) ORR polarization curves and (d) the corresponding hisꢀ
togram of mass and specific activities for the PtPb octahedra/C
before and after different potential cycles. (e) HAADFꢀSTEM
image and (f) the corresponding elemental mappings of the
PtPb1.12Ni0.14 octahedra/C after 15000 cycles. The current densiꢀ
ties in (a) and (c) were normalized to the geometric area of a RDE
(0.196 cm2).
Therefore, the superior ORR performance of PtPb1.12Ni0.14
octahedra likely arises from their intimately interaction beꢀ
tween intermetallic PtPb core and atomic layers PtNi shell,
exposed active facets, and the synergistic effect between difꢀ
ferent components. Thanks to the addition of Ni, trimetallic
PtPb/PtNi nanostructures with atomic layers shell on the surꢀ
face have been created, resulting in the maximized Pt utilizaꢀ
tion, higher than those of PtPb octahedra. Consequently, the
PtPb1.12Ni0.14 octahedra exhibit more active than the Pt/C. Furꢀ
thermore, due to the stable PtPb intermetallic core and the
atomic PtNi layers, the intermetallic PtPb1.12Ni0.14 octahedra
exhibit outstanding durability, comparing with the commercial
Pt/C and the PtPb octahedra. All these superiorities ensure the
PtPb1.12Ni0.14 octahedra high ORR performance, even better
than many PtNiꢀbased ORR electrocatalysts (Table S2).
The durability is another important criterion for the electroꢀ
catalyst evaluation.17,39,44 An electrocatalyst with better duraꢀ
bility can exhibit a much longer lifetime, which is the key for
the practical applications. To determine ORR durability of the
catalysts, the ORR activities of different catalysts before and
after different cycles of accelerated durability tests (ADTs,
100 mV/s) were measured. As shown in Figure 6a-d & Fig-
ure S35-S36, after 15000 cycles of ADTs, the ECSA of
PtPb1.12Ni0.14 octahedra/C changed from 37.2 m2/g to 34.2 m2/g
with only 17.2% mass activity and 9.9% specific activity lossꢀ
es, respectively (Figure 6a-b & Figure S35a-b). While the
PtPb1.07Ni0.10 octahedra/C have 20.9% mass activity and 13.3%
specific activity losses, the PtPb1.03Ni0.05 octahedra/C show
21.6% and 13.3% losses in mass and specific activities, reꢀ
spectively (Figure S35-S36). Other PtꢀPbꢀNi octahedra/C also
4. CONCLUSIONS
To summarize, we have demonstrated a wetꢀchemical stratꢀ
egy to successfully synthesize PtPb, Pt1.21Pb, PtPb1.03Ni0.05
,
PtPb1.07Ni0.10, and PtPb1.12Ni0.14 intermetallic NCs with wellꢀ
defined shape, size, and composition. The PtPb1.12Ni0.14 octaꢀ
hedra with intermetallic PtPb core and active PtNi shell exhibꢀ
it superior activity for ORR with ~11 and ~20 times enhanceꢀ
ment on mass activity and specific activity than the Pt/C, reꢀ
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(18) Choi, S. ꢀI.; Xie, S. F.; Shao, M. H.; Odell, J. H.; Lu, N.; Peng,
spectively, as well as better than those of the PtPb octahedra,
even better than those of the PtPb/Pt core/shell octahedra,
making it among the most promising ORR electrocatalysts up
to now. Those PtPb1.12Ni0.14 octahedra are also very stable after
longꢀterm durability investigation. We anticipate the present
work will inspire the rational design of highꢀperformance Ptꢀ
based NCs with wellꢀcontrolled structure, phase, and surface
composition for heterogeneous reactions, fuel cells and beꢀ
yond.
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AUTHOR INFORMATION
Corresponding Author
hxq006@suda.edu.cn
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENT
This work was financially supported by the Ministry of Science
and Technology (2016YFA0204100), the National Natural Sciꢀ
ence Foundation of China (21571135), Young Thousand Talented
Program, the startꢀup supports from Soochow University, and the
Priority Academic Program Development of Jiangsu Higher Eduꢀ
cation Institutions (PAPD).
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