Enhanced methanol oxidation and CO tolerance using oxygen-passivated molybdenum phosphide/carbon supported Pt catalysts

Article abstract of DOI:10.1039/c6ta01319h

To improve the sluggish kinetics of the methanol oxidation reaction (MOR), one efficient way is to improve the properties of catalyst supports to enhance the activity and durability of Pt-based catalysts. In this study, molybdenum phosphide/porous carbon (MoP/C) composites as Pt-supports and co-catalysts for the MOR are prepared by varying the molar ratio of citric acid (CiA) to glucose (Glu). Pt-MoP/C-2 (CiA:Glu = 2) has far higher electro-catalytic activity (platinum electrochemical surface area and mass activity) and durability for the MOR than commercial Pt/C. Because of the close integration between MoP and carbon and the ligand effect of Mo-P bonds, MoP/C can maintain a commendable stability for facilitating the fast transport of electrons. A fast oxidative removal of CO can reduce the adsorption of poisoning species (CO and CHO) onto the surface active sites of Pt and lead to the regeneration of active sites in Pt-MoP/C. Furthermore, the surface of MoP/C contains abundant absorbed -OH (hydrophilic) and oxygen-containing functional groups originating from the O₂ passivation, which promotes the dispersion of deposited Pt and the mass transfer of fuel. This study provides useful information for the design and preparation of a state-of-the-art anodic electro-catalyst support with promising co-catalytic effects for the MOR.

Full text of DOI:10.1039/c6ta01319h

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Enhanced methanol oxidation and CO tolerance using oxygen-
passivated molybdenum phosphide/carbon supported Pt catalysts
Received 12th February 2016,
Accepted 00th xxxxxxxx 2016
Yaqiang Duana,b, Ye Suna, Lei Wanga, Ying Daia,c,*, Baibing Chena, Siyu Pana, Jinlong Zoua,b,
*
DOI: 10.1039/x0xx00000x
To improve the sluggish kinetics of methanol oxidation reaction (MOR), one efficient way is to improve the property of
catalyst support to enhance the activity and durability of Pt-based catalyst. In this study, molybdenum phosphide/porous
carbon (MoP/C) composites as Pt-supports and co-catalysts for MOR are prepared by varying the molar ratio of citric acid
(CiA) to glucose (Glu). Pt-MoP/C-2 (CiA: Glu=2) has far higher electro-catalytic activity (platinum electrochemical surface
area and mass activity) and durability for MOR than those of commercial Pt/C. Because of the close integration between
MoP and carbon and the ligand effect of Mo–P bonds, MoP/C can maintain a commendable stability for facilitating the fast
transport of electron. A fast oxidative removal of CO can reduce the adsorption of poisoning species (CO and CHO) onto the
surface active sites of Pt and lead to the regeneration of active sites in Pt-MoP/C. Furthermore, the surface of MoP/C
contains abundant absorbed –OH (hydrophilic) and oxygen-containing functional groups originating from the O2
passivation, which promotes the dispersion of deposited Pt and the mass transfer of fuel. This study provides useful
information for the design and preparation of a state-of-the-art anodic electro-catalyst support with promising co-catalytic
effect for MOR.
www.rsc.org/
comparing with the unsupported Pt catalysts, the supported Pt
catalysts have already shown promise for obtaining high
electrocatalytic activity and stability.14,15 However, several
1. Introduction
Direct methanol fuel cell (DMFC), which directly converts the
chemical energy of methanol fuel into electricity, is
grand challenges still need to be overcome.
a
To solve the above mentioned problems, the use of novel
synthetic carbon supports has attracted much more attention,
regarding the superiority of carbon support.6–8,16–18 The carbon
materials, with a sequential structure and high electrical
conductivity, can dramatically improve the performance of Pt-
based catalysts.8 The carbon materials including carbon
microspheres,17 hard carbon spherules, mesoporous carbons,18
carbon nanorods,6 carbon nanofibers (CNFs),19 carbon
nanotubes,7 carbon aerogels and xerogels have already shown
excellent performance for MOR.9,20 Zhang et al.21 synthesize
the Pt/mesoporous nitrogen-doped carbon composites by
using the silica nanoparticles as the template for obtaining the
honeycomb-like structure. Results demonstrate that the
improved electrochemical performance for MOR can be
attributed to the anchoring effect for Pt nanoparticles and the
enhanced electrical conductivity, which further improve the
electrocatalytic activity and stability of these catalysts.21
However, the Pt/carbon catalysts still show some
shortcomings for MOR and therefore the carbon-supported Pt
alloys are further studied. Calderón et al.19 investigate the
synergistic activity of CNFs-supported Pt-Ru catalysts, which
are prepared by the solution-reduction method using different
reducing agents. The Pt-Ru/CNF catalysts prepared by the
formate ions reduction method produce the highest CO
tolerance and current density for MOR, which can be
promising candidate for a portable electronic device.1–4 It
theoretically has the advantage of easy storage, rapid start-up,
low operation temperature and environmental compatibility.5–
7
So far, Pt-based materials are usually used as methanol
oxidation reaction (MOR) catalysts because of its relatively
high electrocatalytic activity for DMFC.1,2 However, because of
the sluggish MOR (which causes a large anode overpotential)
and low electrocatalytic stability (which results from CO
poisoning of Pt species and methanol crossover), DMFC
exhibits low energy density and conversion efficiency.8,9
Furthermore, the high cost of DMFC is another obstacle for its
industrialization due to the use of expensive Pt-based
catalysts.10,11 To overcome those limitations, for MOR catalysts,
the critical steps are to hinder the CO poisoning of Pt
nanoparticles and lower the amount of Pt loading.12,13 By
a.Key Laboratory of Functional Inorganic Material Chemistry, Ministry of Education
of the People's Republic of China, School of Chemistry and Materials Science,
Heilongjiang University, Harbin 150080, China. *E-mail: zjl_0308@126.com;
zoujinlong@aliyun.com
b.Key Laboratory of Chemical Engineering Process and Technology for High–
Efficiency Conversion, College of Heilongjiang Province, School of Chemistry and
Materials Science, Heilongjiang University, Harbin 150080, China.
c.School of Civil Engineering, Heilongjiang Institute of Technology, Harbin 150050,
China.
† Electronic Supplementary Information (ESI) available:. See
DOI: 10.1039/x0xx00000x
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attributed to the formation of crystalline Ru-oxides.19 in a water bath at 90 oC for 12 h. The mixture was stirred at 80
Moreover, metal nanoparticles,22 metal oxides,23 conducting oC to evaporate water and then a brown slurry was obtained.
polymers,24 composite materials and core-shell nano- The slurry was further dried at 100 oC in an oven to completely
structured materials are also reported as excellent catalysts or remove the water. The dried slurry was first carbonized from
catalyst supports for DMFC.11,25
room temperature to 350 oC (5 oC min–1) and then from 350 oC
The transition-metal compounds have been used to prepare to 900 oC (1 oC min–1) in flowing nitrogen (N2) atmosphere (50–
co-catalysts and/or catalyst supports, exhibiting high catalytic 60 mL min–1). The slurry was soaked at 900 oC for 2 h, followed
activity and Pt utilization for MOR.6,9,12 Transition-metal by naturally cooling to room temperature (approximately 25 oC)
phosphides have been used as electro-catalysts in many fields under the N2 gas. Then, the carbonized slurry was passivated
including photocatalysis,26 electro-catalysis,27 hydrogen in a mixture (60 mL min–1) of 0.5 % O2 and 99.5 % N2 for 4 h to
evolution reaction (HER),26,28 fuel cells,29 etc. Molybdenum prevent the pyrophoric oxidation of phosphide species upon
phosphide (MoP) is a promising one to substitute Pt catalyst exposure to air. The final samples were marked as MoP/C-x
for
HER,26,27,30
hydrodesulfurization
(HDS)
and (x=0, 1, 2, 3 and 4). The non-passivated samples used as the
hydrodenitrogenation (HDN).31 It is reported that the control samples were synthesized by the same method
supported-MoP can be used as active HER electro-catalysts, without passivation and marked as n-MoP/C-x (x=0, 1, 2, 3 and
exhibiting excellent activity and stability (similar to Pt) due to 4).
their high conductivity and low onset over-potential.26,32 The 2.2. Synthesis of Pt-MoP/C composites
prepared MoP/porous carbon has suffered from the
Pt-MoP/C and n-Pt-MoP/C composites with a nominal Pt
shortcomings of non-loading MoP for the lack of exposed
loading of 5 wt.% were prepared by using the modified
borohydride reduction method.15 100 mg of MoP/C composite
active sites and poor electrical conductivity, which originate
from the lack of specific surface areas and favorable charge
was suspended in deionized water to form a dispersed slurry in
carriers, respectively.33 The superiority of MoP for HER should
an ultrasonic bath. Then, H2PtCl6·6H2O aqueous solution with
be ascribed to the P atoms (active sites), which have a nearly
Pt concentration of 2 mM was added into the MoP/C slurry
zero Gibbs free energy.34 However, MoP is just used as the
with constant stirring. The suspension pH was adjusted to 10
electro-catalyst for HER, etc, and not as co-catalyst and
by adding 1 M NaOH solution, and then the Pt-species was
support for MOR, which deserves further study.
slowly reduced by excessive NaBH4 with vigorous stirring for 3
h at ambient temperature.37 The suspension was left to stand
In this study, for the first time, MoP/porous carbon (MoP/C)
composites are prepared as catalyst supports and MOR co-
overnight and was then centrifuged at 4000 rpm. The
catalysts via
a simultaneous synthesis method. After
precipitate was thoroughly rinsed with deionized water and
ethanol, and was then dried at 50 oC .
carbonization, the carbon sources of citric acid (CiA, also as a
chelating agent) and glucose (Glu) are converted into porous
carbon, while MoP nanoparticles are in situ formed in the
carbon skeleton, which are intimately incorporated with the
carbon phase. The mechanisms associated with the structure
and crystalline (Mo-species) evolution for MoP/C are explored.
By assisting with the surface properties of these supports (co-
catalysts), Pt nanoparticles are supposed to be well-dispersed
on the surface of MoP/C. The integration of Pt and MoP (or Pt
and C), which provides more exposed active sites, may
contribute to the easy charge-transfer from Pt to MoP/C and
the excellent durability for MOR. The Pt-MoP/C catalysts are
also expected to exhibit higher activity and stability for MOR
than those of commercial Pt/C.
2.3. Materials characterization
X-ray diffraction (XRD) patterns were obtained from a Rigaku
D/max 2500 diffractometer using Cu-Kα radiation (k=1.5406 Å,
40 Kv, 20 mA) at step scan of 0.02º. The Scherrer equation was
used to calculate the crystallite sizes of Pt using the diffraction
peaks of (220) planes. The N2 adsorption/desorption isotherms
were measured using a Micromeritics Tristar II at 77 K. Specific
surface area and pore size distribution were calculated using
the Brunauer-Emmett-Teller (BET) theory and the Barrett-
Joyner-Halenda
(BJH)
method,
respectively.
X-ray
photoelectron spectroscopy (XPS, Kratos-AXIS UL TRA DLD, Al
Ka X-ray source) was used to analyze the surface components
of the as-prepared catalysts, by deconvolution of C 1s, O 1s,
Mo 3d, P 2p and Pt 4f spectra. The ‘XPS peak’ software was
used to fit the data for each atom. Scanning electron
microscopy (SEM) analyses were conducted using an S-4800
scanning electron microscope (Japan) at an accelerating
voltage of 5.0 kV. Catalyst structure was studied by taking
transmission electron microscopy (TEM) images on a JEM-2100
electron microscope (JEOL) with an acceleration voltage of 200
kV.
2. Experimental
2.1. Synthesis of MoP/C composites
CiA as a chelating agent and carbon source was added into a
mixed
solution
of
ammonium
heptamolybdate
((NH4)6Mo7O24·4H2O, A.R.) and diammonium hydrogen
phosphate ((NH4)2HPO4, A.R.).35,36 Glu was added into the
solution to provide adequate amount of carbon source. To
keep a constant amount of carbon, the added amount (sum) of
CiA and Glu was four times to Mo or P species (molar ratio of 4:
1). The molar ratio of Mo: P: CiA: Glu was controlled as 1: 1: x:
(4-x) (x=0, 1, 2, 3 and 4). The mixture was continuously stirred
2.4. Electrochemical analysis
To investigate the electrochemical characteristics, the catalyst
ink was prepared by dispersing 5 mg of Pt-MoP/C in the
mixture of 100 μL of ethanol and 50 μL of Nafion solution (5
wt.%, Aldrich). Subsequently, the suspension was well
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adsorption/desorption (HAD) region is used to obtain the ESAPt,
which is normalized by Pt loading and calculated by the
a
MoP
following formula: ESAPt=QH/(m
charge for the HAD and QH=S/
hydrogen stripping peak (A·V) and
×
ν
0.21),17,39 where QH is the
, S is the integral area of
is 0.05 V s–1 meaning
MoP/C-0
MoP/C-1
MoP/C-2
MoP/C-3
ν
scanning speed; m is the platinum loading on the electrode
(mg), and 0.21 is the charge required to oxidize the H2
monolayer on a bright Pt (mC cm–2). The chronoamperometry
(CA) tests were performed for 3600 s to investigate long-term
durability of the catalysts in 1.0 M H2SO4 + 1.0 M CH3OH
solution at a constant potential of 0.6 V. Electrochemical
impedance spectroscopy (EIS) was conducted at 0.6 V over a
MoP/C-4
10
20
30
40
50
60
70
80
frequency range of 105 to 10–2 Hz with
a sinusoidal
2θ (Degrees)
perturbation of 10 mV amplitude.40,41 CO stripping
voltammetry was carried with a scan rate of 10 mV s–1 in 0.5 M
H2SO4 solution.41 All of the used electrolytes were saturated
with pure N2 to remove the dissolved oxygen, which was
tested by a portable oxygen sensing system (NeoFox sport,
Ocean Optics).
b
Pt (111)
Pt (200)
Carbon
Pt (220)
Pt-MoP/C-0
Pt-MoP/C-1
Pt-MoP/C-2
Pt-MoP/C-3
Pt-MoP/C-4
3. Results and Discussion
3.1. Composition and Structural Characterization of MoP/C
Composites
Pt/C
10
20
30
40
50
60
70
80
Fig. 1 presents the XRD patterns of MoP/C and Pt-MoP/C
composites with different molar ratio of CiA and Glu. As shown
in Fig. 1(a), all of as-synthesized MoP/C-x (x=0, 1, 2, 3 and 4)
show the typical crystalline phase of MoP (hexagonal, space
2θ (Degrees)
Fig. 1 XRD patterns of MoP/C (a) and Pt-MoP/C (b) composites.
group P
6
m2). The diffraction peaks at 27.8
º
, 31.9
º, 42.9º, 56.9
¯
, 57.5º, 64.5º, 66.8º, 67.3º and 73.8º are attributed to the
dispersed in an ultrasonic bath for 30 min to obtain the
homogeneous ink.38 2.5 μL of the as-prepared ink was dropped
onto a glassy carbon (GC) electrode (diameter of 3 mm) and
then the solvent was naturally evaporated to form a thin-film
as the working electrode. Before each use, the GC electrode
was polished with Al2O3 slurry and washed with deionized
water and ethanol. N-Pt-MoP/C and commercial Pt/C (10 wt.%)
were used as the control samples. The Pt loadings on the GC
electrode were 59.0 μgPt cm–2, 59.0 μgPt cm–2 and 118.0 μgPt
cm–2 for as-prepared Pt-MoP/C, n-Pt-MoP/C catalysts and
commercial Pt/C, respectively.
º
characteristic peaks of the (001), (100), (101), (110), (002),
(111), (200), (102), and (201) planes of MoP (JCPDS, No. 65-
6024), respectively.26,27 Noting that the crystallinity of MoP/C-x
(x=1, 2, 3 and 4) is far higher than that of MoP/C-0. It shows
that CiA plays an important role in the formation of well-
crystallized MoP in carbon skeleton. As shown in Fig. 1(b), the
typical diffraction peaks of Pt [(111), (200), and (220), JCPDS,
No. 65-2868] are distinctly observed at 39.8º, 46.2º and 67.5º,
respectively, implying that the deposited Pt crystals are existed
with the face-centered cubic (fcc) structure.12,20,21,29 Because of
the tiny difference in crystal lattice spacing and the strong
peak intensity of Pt (111), the main peak of MoP (101) cannot
be observed in XRD patterns. The average particle sizes of Pt
(220) for Pt-MoP/C-x (x=0, 1, 2, 3 and 4) calculated by Scherrer
equation are 4.1 nm, 3.7 nm, 2.3 nm, 2.6 nm and 3.9 nm,
o
Electrochemical measurements were conducted at 25 C on
an electrochemical workstation (CHI760E, Shanghai) with a
typical three-electrode testing system. The counter electrode
consisted of a 1 cm2 of platinum plate, while the reference
electrode was a saturated calomel electrode (SCE, +0.2415 V
vs standard hydrogen electrode, 3.0 M KCl). All of the
potentials reported in this work were versus the SCE. The
working electrode was pre-activated in 1.0 M H2SO4 + 1.0 M
CH3OH solution by cyclic voltammetry (CV) tests from -0.2 to
+1.0 V for 50 cycles at a scan rate of 50 mV s–1. Then, CV tests
were formally conducted from -0.2 to +1.0 V (50 mV s–1) in 1.0
Table 1 Textural properties of the MoP/C composites.
Pore
volume
(cm3 g–1)
0.06
Average pore
width
(nm)
Surface area
(m2 g–1)
Samples
M
H2SO4 + 1.0 M CH3OH solution to investigate the
MoP/C-0
MoP/C-1
MoP/C-2
MoP/C-3
MoP/C-4
24.70
117.28
300.39
195.86
127.13
8.74
electrocatalytic activity. The electrochemically active surface
area (ESAPt) of the catalyst layer was measured in the potential
range of -0.2 to +1.0 V at a scan rate of 50 mV s–1 in 1.0 M
H2SO4 solution. The integration of the hydrogen
0.13
5.88
0.22
2.96
0.19
4.17
0.16
5.20
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respectively.
at high temperature. The morphology of MoP/C-0 is quite
N2 adsorption/desorption isotherms and pore size different from others, exhibiting a smooth surface structure
distributions of MoP/C-x (x=0, 1, 2, 3 and 4) composites are with slight roughness, which is attributed to the absence of CiA
shown in Fig. S1 (ESI†). The remarkable hysteresis loops in the precursor.
indicate the mesoporous nature of MoP/C composites. All of To detect the valence states of each element and surface
the as-synthesized composites show the typical type-IV compositions of the Pt-MoP/C, XPS measurements are
isotherms with a sharp capillary condensation step and the H4- conducted (Fig. 2a). From the survey spectra, the predominant
type hysteresis loops at relative pressures (P/P0) of 0.4–0.8. As (narrow) C 1s peaks are located at around 284.6 eV, along with
shown in Table 1, the maximum BET surface area (SBET) is O 1s peaks at around 531.5 eV for the Pt-MoP/C-x (x=0, 1, 2, 3
obtained by MoP/C-2 (300.39 m2 g–1), which is much larger and 4) catalysts. The Mo 3d peaks and P 2p peaks appear at
than those of other samples. High porous structure (high SBET), around 232.7 and 133.5 eV, respectively. The Pt 4f peaks at
which originates from the interaction of CiA and Glu during the around 71.4 eV are also observed, confirming that Pt species
carbonization process, can provide sufficient active sites to are successfully deposited onto the MoP/C supports, in
support Pt nanoparticles. With the increase of Glu content, consistent with the XRD results.
SBET and pore volume of these composites firstly increase and
then decrease.
The Pt 4f spectra (Fig. 2b and Fig. S3 (ESI
†)) of Pt-MoP/C-x
(x=0, 1, 2, 3 and 4) can be deconvoluted into three pairs of
The morphology and structure (SEM) of as-synthesized doublets, which can be attributed to different valence states of
MoP/C-x (x=0, 1, 2, 3 and 4) are presented in Fig. S2 (ESI
). A Pt.20,21,42 In addition, as listed in Table 2, the binding energies
†
lot of spherical particles can be observed on the surface of of metallic Pt 4f of Pt-MoP/C catalysts have negative shifts of
carbon as shown in Fig. S2b-S2e, which show no significant 0.7–0.9 eV in comparison with that of commercial Pt/C. An
morphological difference. Those particles with relatively negative shift in the binding energy of metallic Pt nanoparticle
uniform diameters of approximately 10–50 nm are stacked means that less Pt (II) and/or Pt (IV) originating from the
with each other, and some particles are significantly oxidation of finely dispersed Pt particles are existed on the
agglomerated to form a huge agglomerates after carbonization surface of MoP/C.43 The Pt (0) proportions of the Pt-MoP/C-x
(x=0, 1, 2, 3 and 4) are higher than that of Pt/C, implying that
Pt-MoP/C catalysts may provide more stable Pt active sites
a
C 1s
available for methanol adsorption and oxidation. Moreover,
the uniform deposition of fine Pt particles and strong Pt-
supports interactions are also important for improving the
electrochemical activity of Pt-MoP/C catalysts.20,44
b
d
f
O 1s
Pt 4f
Mo 3d
Pt/MoPꢀPGCꢀ0
0
Pt
71.4, 74.7 eV
P 2p
4+
Pt
74.8, 78.1eV
Pt/MoPꢀPGCꢀ1
Pt/MoPꢀPGCꢀ2
2+
Pt
72.6, 75.9eV
As shown in Mo 3d spectra (Fig. 2c and Fig. S4 (ESI†)), the
Mo species in Pt-MoP/C-x (x=0, 1, 2, 3 and 4) can be
Pt/MoPꢀPGCꢀ3
Pt/MoPꢀPGCꢀ4
decomposed into two components originating from Mo 3d5/2
33,34
0
200
400
600
800
1000
1200
66
68
70
72
74
76
78
80
82
Binding Energy (eV)
and Mo 3d3/2
.
The Mo 3d3/2 peak at higher binding energy
Binding Energy (eV)
(around 235.9 eV) ascribes to the Mo6+ and Mo5+ species
(molybdenum oxides), while the Mo 3d5/2 peak at lower
binding energy (around 232.8 eV) corresponds to the Moδ+ in
MoP. It is not surprising that the peaks corresponding to
molybdenum oxides are existed in the spectra because all of
the samples have undergone O2 passivation. No metallic Mo0
peaks at approximately 227.4–227.8 eV can be found for Pt-
MoP/C-x, implying that except for the formation of
molybdenum oxides, Mo is mainly bound with P to form MoP
in the carbon skeleton. For Pt-MoP/C-0 and Pt-MoP/C-1, the
Moδ+ peaks have a slight shift toward higher binding energy by
comparing with those of Pt-MoP/C-x (x=2, 3 and 4). This shift
may be attributed to the decrease in the electron cloud
density of Mo atoms in MoP, which may be caused by the
higher degree of Mo oxidation (O2 passivation).
c
5+
P
, P O
2
5
δ+
Mo
Mo 3d
3/2
133.5 eV
Mo 3d
,
5/2
235.6 eV
232.4 eV
δꢀ
, MoP
P
129.8 eV
228
230
232
234
236
238
240
126
128 130
132
134
136
138
140
142
Binding Energy (eV)
Binding Energy (eV)
e
OꢀP
531.9 eV
C in graphtie
284.6 eV
CꢀN
CꢀOꢀC, CꢀOꢀH, CꢀOH
533.6 eV
286.2 eV
Oꢀphysically absorbed
or cabonated
CꢀO
530.4 eV
288.1 eV
Fig. 2d and Fig. S5 (ESI†) show the P 2p binding energy
regions for Pt-MoP/C-x (x=0, 1, 2, 3 and 4). In all of the curves,
there are two obvious bands, which correspond to the lower
energy (Pδ–) and higher energy (P5+) symmetric bands due to
the spin orbital splitting.26,33,45 The P 2p3/2 peak at 133.6 eV in
the XPS spectra is assigned to the typical peak of P5+ species
(P2O5), which surely originate from the O2 passivation. It is
280
282
284
286
288
290
292
294
526
528
530
532
534
536
538
540
Binding Energy (eV)
Binding Energy (eV)
Fig. 2 XPS survey spectra (a) for Pt-MoP/C-x (x=0, 1, 2, 3 and 4)
and high resolution XPS of Pt 4f (b), Mo 3d (c), P 2p (d), C 1s (e)
and O 1s (f) for Pt-MoP/C-2.
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Table 2 Binding energies and surface compositions for Pt 4f core level region of Pt-MoP/C-x.
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Pt (0)
Pt (II)
Pt (IV)
Sample
Binding
Relative
ratio (%)
65.1
Binding
Relative
ratio (%)
23.9
Binding energy Relative ratio
energy (eV)
71.4
energy (eV)
72.6
(eV)
74.8
78.1
74.9
78.1
74.8
78.1
74.9
78.1
74.9
78.1
74.8
79.8
(%)
Pt-MoP/C-0
Pt-MoP/C-1
Pt-MoP/C-2
Pt-MoP/C-3
Pt-MoP/C-4
10 wt.% Pt/C
11.0
74.8
75.9
71.4
69.8
62.5
66.5
68.0
58.3
72.6
21.8
23.5
22.5
25.0
22.8
8.4
14.0
11.0
7.0
74.7
75.9
71.4
72.6
74.7
75.9
71.5
72.6
74.8
75.9
71.5
72.9
74.9
75.9
72.0
73.2
18.9
75.6
77.6
proposed by us that the passivation of P can dramatically 4) catalysts are higher than that of Pt/C. Due to a weak “ligand
increase the amount of oxygen-containing functional groups, effect” of Mo-P bonds, the introduction of MoP can facilitate
because the formation of P–O bonds leads to the increase of the transport of electrons and accordingly enables an increase
the oxygen content (P–O, C–O, C–O–C, etc) in the structure of in the exposure of electro-active species (Pt).35 Generally, the
MoP/C.46 The P 2p3/2 peak at around 129.8 eV confirms the higher ESAPt of catalysts can usually provide more active sites
presence of Pδ– species in MoP.33 As indicated in the Mo 3d5/2 for MOR. Therefore, the MOR activity of Pt-MoP/C-x (x=1, 2, 3
and P 2p3/2 spectra, MoP is successfully formed in the skeleton and 4) catalysts may be better than that of Pt/C.
of carbon. Furthermore, note that the oxidization of MoP only
happens on its surface and not on the interior of the MoP.
CV (in methanolic acidic medium) results for Pt-MoP/C-x
(x=0, 1, 2, 3 and 4) and Pt/C are shown in Fig. 3b and Table 3.
As shown in Fig. 2e and Fig. S6 (ESI
†
1s peaks corresponds to three components originating from and 4) and Pt/C are shown in Fig. S8a (ESI
), the deconvolution of C For comparison, the CV curves for n-Pt-MoP/C-x (x=0, 1, 2, 3
). Typically, the
†
the C in graphite (around 284.6 eV), C–N (around 285.8 eV) methanol oxidation current peak appears at around 0.6 V in
and C–O (287.0 eV), respectively. The existence of the the positive scan direction, while the oxidation peak at around
graphitic C can significantly enhance the electrical conductivity 0.4 V in the negative scan direction is associated with
of the MoP/C supports. As shown in Fig. 2f and Fig. S7 (ESI†), oxidization of the residual carbon species (for COads and CHOads
by decomposing the O 1s peaks, three components can be intermediate products). As shown in Fig. 3b, the Pt-MoP/C-2
observed at around 530.7, 531.9 and 533.5 eV, which originate
from the physically absorbed O or carbonates, O–P and C–O–
60
800
a
C/C–O–H/C–OH, respectively. Existence of C–O–C/C–O–H/C–
OH means that the hydrophilicity of Pt-MoP/C-x (x=0, 1, 2, 3
and 4) is comparable, which is beneficial to the methanol-
absorption and mass transfer of the acidic electrolyte.47 The
O–P in the O 1s spectra implies that a small amount of
phosphorus oxides (P2O5) originating from the passivation
(oxidation) of P species is existed in shallow surface, in
consistent with the results of P 2p peaks.
b
Pt/C
700
600
500
400
300
200
100
0
40
20
Pt-MoP/C-0
Pt-MoP/C-1
Pt-MoP/C-2
Pt-MoP/C-3
Pt-MoP/C-4
0
ꢀ20
ꢀ40
ꢀ60
ꢀ80
Pt/C
Pt-MoP/C-0
Pt-MoP/C-1
Pt-MoP/C-2
Pt-MoP/C-3
Pt-MoP/C-4
ꢀ100
ꢀ200
ꢀ0.2
0.0
0.2
0.4
0.6
0.8
1.0
ꢀ0.2
0.0
0.2
0.4
0.6
0.8
1.0
Potential(V) vs SCE
Potential(V) vs SCE
120
100
80
60
40
20
0
240
210
180
150
120
90
c
Pt/C
3.2. Performance of anodes with different catalysts
d
Pt-MoP/C-0
Pt-MoP/C-1
Pt-MoP/C-2
Pt-MoP/C-3
Pt-MoP/C-4
The CV tests for Pt-MoP/C-x (x=0, 1, 2, 3 and 4) and Pt/C
catalysts in acidic medium (1.0 M H2SO4) are conducted to
analyze the numbers of effective catalytic sites for MOR (Fig.
3a). The ESAPt of Pt-MoP/C-x (x=0, 1, 2, 3 and 4) and Pt/C
catalysts are 40.80, 80.99, 103.90, 94.51, 77.16 and 54.81 m2
g–1Pt, respectively. It shows that Pt-MoP/C-2 catalyst exhibits
the highest ESAPt. Furthermore, the peak intensity of the HAD
of the Pt-MoP/C-2 electrode is higher than those of others,
indicating the presence of a larger number of available Pt
surface sites.16,37,39 All of the ESAPt of Pt-MoP/C-x (x=1, 2, 3 and
Pt/C
Pt-MoP/C-0
Pt-MoP/C-1
Pt-MoP/C-2
Pt-MoP/C-3
Pt-MoP/C-4
60
30
0
0
500
1000
1500
2000
2500
3000
3500
0
20
40
60
80
100 120 140 160
Time (s)
Zre (ꢁ)
Fig. 3 CV curves (a, in 1.0 M H2SO4 solution), CV curves (b), CA
curves (c) and Nyquist plots (d) of Pt-MoP/C and Pt/C catalysts
in methanolic acidic medium.
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Journal of Materials Chemistry A
Table 3 Electrochemical metrics for methanol oxidation on the
Pt-MoP/C-x (x=0, 1, 2, 3 and 4) and commercial Pt/C (10 wt.%)
catalysts.
suggest that Pt in close contact with MoP and/or carbon
substantially helps the electron transfer and subsequently
enhances the MOR activity.
Onset
potentials
(mV)
Peak
potentials
(mV)
Mass
EIS tests is conducted to examine the impedance of the
If/Ib working electrode with Pt-MoP/C-x (x=0, 1, 2, 3 and 4) and
Pt/C. All of the Nyquist curves (Fig. 3d) consist of arcs,
Sample
activity
–1
(mA mgPt
)
corresponding to the charge transfer resistances (Rct), which
\
Pt-MoP/C-0
Pt-MoP/C-1
Pt-MoP/C-2
Pt-MoP/C-3
Pt-MoP/C-4
10 wt.% Pt/C
411
382
383
392
376
373
596
609
598
594
610
581
96.1
reflect the electrocatalytic activity for MOR in the anodes.21,29
316.7
680.7
599.6
363.8
480.7
1.52
The Rct of Pt-MoP/C-2 and Pt-MoP/C-3 are 17.87 and 37.47
respectively, which are higher than that (10.21 ) of Pt/C. As
shown in Table S1 (ESI ), the solution resistances (Rs) of the
ꢀ,
1.78
2.01
1.35
0.81
ꢀ
†
Pt-MoP/C catalysts, which decrease as Glu ratio increases, are
also higher than that of Pt/C. Although the Pt-MoP/C-2 and Pt-
MoP/C-3 electrodes have higher Rct and Rs, their ESAPt and
mass activities for MOR are still higher than that of Pt/C. The
enhanced activity of Pt-MoP/C-x (x=2 and 3) may be ascribed
to the effect of P on the electronic state of Mo, the highly
uniform dispersion of Pt on the surface of MoP/C, the close
integration between MoP and carbon, and the high tolerance
to the carbonaceous species (CO and CHO). However, the high
Rct and Rs may inevitably discourage the improvement of
electrochemical activity and stability of Pt-MoP/C catalysts.
To further verify the CO tolerance of Pt-MoP/C catalysts, CO
stripping experiments were carried out. As shown in Fig. 4, Pt-
MoP/C-2 exhibits the lowest onset potential of CO oxidation at
around 0.48 V, which is more negative than that of Pt/C
(around 0.56 V). The negative shifting of the potential means
that Pt-MoP/C-2 is more effective than Pt/C in oxidation of the
COads on the active sites of Pt.48 The similar onset and peak
potentials of CO oxidation for Pt-MoP/C-x (x=1, 3, 4) and Pt/C
suggest that Pt-MoP/C-x (x=1, 3, 4) exhibits the same CO
oxidation activity as that of Pt/C. However, Pt-MoP/C-0
and Pt-MoP/C-3 catalysts for MOR show the mass current
density of 680.7 and 599.6 mA mgPt–1, respectively, which are
higher than that of commercial Pt/C (480.7 mA mgPt–1). Pt-
MoP/C-1 and Pt-MoP/C-4 also exert reasonable MOR activity
of 363.8 and 316.7 mA mgPt–1, respectively. The Pt-MoP/C-0
shows a low MOR activity (96.1 mA mgPt–1), attributing to the
low crystallinity of MoP (absence of CiA). In the forward scan,
Pt-MoP/C-x (x=0, 1, 2, 3 and 4) catalysts show higher onset
potentials and peak potentials than those of Pt/C, indicating
that as-prepared Pt-MoP/C catalysts may provide higher
catalytic activity for MOR. The high performance (high mass
activity and peak potentials) of Pt-MoP/C catalysts is
attributed to the particular electronic structure of MoP and
more available Pt surface sites. However, in Fig. S8a (ESI†), all
of the n-Pt-MoP/C catalysts exhibit lower activities than those
of Pt-MoP/C and Pt/C. As shown in Table 3, the ratios (If/Ib) of
the methanol oxidation current peak (If) to the backward one
(Ib) are calculated to preliminarily evaluate the tolerance of
7,11
poisoning species such as COads and CHOads
.
The If/Ib ratios
of Pt-MoP/C-x (x=2 and 3) are far higher that of Pt/C,
suggesting that more poisoning species may be adsorbed onto
(transferred to) the MoP structure other than the Pt surface
active sites during the forward scan. The higher tolerance to
CO-like intermediates is also attributed to the high removal
rate of the poisoning species on the Pt particles, which is
further verified by CO stripping experiments.
ꢀ0.2 0.0
0.2
0.4
0.6
0.8
1.0
Pt-MoP/C-0
20
10
0
ꢀ10
54 Pt-MoP/C-1
27
0
ꢀ27
76
The stability and durability of the as-prepared catalysts and
commercial Pt/C are evaluated by CA tests (Fig. 3c and Fig. S8b
Pt-MoP/C-2
38
0
ꢀ38
(ESI†)). For all of the n-Pt-MoP/C catalysts, the activities
64
32
0
Pt-MoP/C-3
Pt-MoP/C-4
Pt/C
rapidly drop at first and then keep at a relatively low level
(below 25 mA mgPt–1). While in the first 200 sec, the mass
activity of Pt-MoP/C decreases rapidly for all of the
electrocatalysts. As time increases, the minimum decline
(92.6 %) of mass activity is obtained by Pt-MoP/C-2, revealing
that the charge transfer in Pt-MoP/C-2 is the most efficient.
After 3600 sec, the retained mass activity for Pt-MoP/C-x (x=0,
1, 2, 3 and 4) and commercial Pt/C catalysts are 3.3 (96.6 %),
12.6 (96.0 %), 50.2 (92.6 %), 37.1 (93.8 %), 20.3 (94.4%), and
28.6 (94.1 %) mA mgPt–1, respectively. The Pt-MoP/C-2 exhibits
the best durability for MOR, which may be attributed to the
good dispersion of Pt species on the MoP/C surface and the
strong interactions amongst Pt, MoP and carbon. These results
ꢀ32
48
24
0
ꢀ24
38
19
0
ꢀ19
ꢀ0.2 0.0
0.2
0.4
0.6
0.8
1.0
Potential (V) vs SCE
Fig. 4 CO stripping voltammogram for Pt-MoP/C and Pt/C
catalysts.
6 | J. Mater. Chem.A, 2016, 00, 1-9
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ARTICLE
Pt/C. Moreover, because of the positive surface charge of the
carbon, the charge transfer between MoP and carbon skeleton
is easy to conduct, leading to a reproducible conductivity and a
significantly enhanced electro-catalytic activity for MOR. In a
conclusion, the MoP/C support with surface negative charges
and O-groups play an important role for MOR activity (high
ESAPt and mass activity).
900
750
600
450
300
150
0
MoꢀP, Mod+
PꢀO
MoꢀO
Mass Activity
PꢀMo, Pdꢀ
a
100
80
60
40
20
0
3.4. Detailed structure of Pt-MoP/C-x (x=2 and 3) and MOR
mechanism
TEM images and EDAX patterns of Pt-MoP/C-x (x=2 and 3) are
shown in Fig. 6. As shown in Fig. 6a and 6e, a large amount of
nanoparticles with relatively uniform sizes and excellent
dispersibility are tightly deposited on the carbon skeleton.
Smaller particles (Pt) with better dispersion and less
agglomeration can be observed on the surface of Pt-MoP/C-2.
As shown in Fig. 6a and 6e (the inlet figures), the average grain
diameters of Pt for Pt-MoP/C-2 and Pt-MoP/C-3 are
approximately 2.18 and 2.26 nm, respectively, which are
calculated from the fits (a Gauss function) of the measured
data. In the high-resolution TEM (HRTEM) images (Fig. 6b and
6f), MoP with particle sizes of approximately 21.5 and 15.4 nm
can be found on the surface of Pt-MoP/C-2 and Pt-MoP/C-3,
respectively. Meanwhile, the lattice spacing of 0.279 nm
corresponds to the (100) plane of MoP, which is surrounded by
the Pt nanoparticles with the exposed (111) plane. As shown in
Fig. 6c and 6g, the lattice spacing of 0.226 nm is ascribed to the
(111) plane of Pt.5,29 The average sizes of Pt for Pt-MoP/C-2
and Pt-MoP/C-3 are approximately 2.31 and 3.33 nm,
respectively, in consistent with the results in Gauss function
and Fig. 1b. In addition, the Pt particles are mainly deposited
on the boundary of MoP. The larger MoP particles in Pt-
MoP/C-2 can form the skeletal framework of the triple
junction structure (Pt-MoP-C), which can enhance the activity
and stability of the catalyst for methanol electrooxidation.49,50
4
3
0
1
2
120
100
80
60
40
20
0
absorbed O or carbonates
CꢀOꢀC/CꢀOꢀH/CꢀOH
OꢀP
ESA
b
60
50
40
30
20
10
0
4
1
3
0
2
Fig. 5 The relationship between the Mo and P species of Pt-
MoP/C-x (x=0, 1, 2, 3 and 4) and mass activity (a); and
relationship between the O-species of Pt-MoP/C and ESA (b).
exhibits the highest peak potential and the lowest CO
oxidation activity, which is consistent with the results of ESAPt.
3.3. Determination of the main active-constituents in Pt-MoP/C
In Fig. 5 and Fig. S9 (ESI†), the weight percentage of each Fig. 6d and 6h (EDAX) show that the Pt, Mo, P and C are the
component (Mo-P, Mo-O, P-O, etc) is calculated according to major elements of the two catalysts. The chemical composition
its area proportion in high resolution XPS spectra. The high of the two catalysts are listed in the inlet tables. The amounts
ESAPt and mass activity of Pt-MoP/C-2 can be attributed to the of Pt loaded on the MoP/C-2 and MoP/C-3 supports are 4.71 %
high content of Mo–P bonds and O-groups (C–OH, C–O–C, etc.) and 4.80 %, respectively, which are very near to the theoretical
deriving from the surface structure of carbon. The formation value of 5 wt.%. The higher content of O-species in Pt-MoP/C-2
of Moδ+ and Pδ– species in MoP is due to the electron transfer is related to the higher content of oxygen-containing
from Mo atoms to P atoms.43 Thus, Mo atoms have some functional groups, in consistent with the XPS results.
positive charge while P atoms have some negative charge in
Based on all of the above analyses, the possible
MoP. Considering the characteristics of Mo–P elementary electrochemical reaction mechanism for methanol oxidation
substance, the Mo species may change the state density of by Pt-MoP/C catalysts is illustrated in Fig. 7. The close contact
electrons in MoP with the introduction of electronic defects, between Pt and MoP/C (or Pt and C) is beneficial to conduct
which is favorable to the close contact between MoP and Pt. the synergistic effect among Pt, MoP and carbon and to
Because of the O2 passivation and the alkaline environment maintain the MOR activity and durability. The molybdenum
(pH=10) for Pt deposition, the abundant absorbed –OH and O- and phosphorus oxides originating from O2 passivation possess
groups are formed on the surface of Pt-MoP/C catalysts, which high ability to generate more active sites (O-groups) on the
are favorable to possess more negative charge on their surface shallow surface of MoP. Moreover, this structure can enhance
than that of Pt/C. The repulsive interactions originating from the electrical conductivity and stability of the MoP/C supports.
their negatively charged surfaces have a key role on facilitating The O-groups on the surfaces of MoP and/or carbon have the
the uniform dispersion of Pt and MoP particles. Therefore, the stronger adsorption capacity for CH3OH and CO, which play an
distribution of Pt nanoparticles (with a relatively narrow size important role in improving fuel mass transfer efficiency and
range) on the MoP/C support is more uniform than that of preventing the CO poisoning of the Pt active sites.
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Fig. 6 TEM images of Pt-MoP/C-x (x = 2 (a) and 3 (e)), HRTEM images of Pt-MoP/C-x (x = 2 (b, c) and 3 (f, g)) and EDAX patterns of
Pt-MoP/C-x (x = 2 (d) and 3 (h)).
electric-conductivity of the composites. These structure-
activity relationships provide new insights into the further
4. Conclusions
optimization of chemical and physical properties of the MoP/C
supports for Pt-based MOR catalysts.
By varying the molar ratio of CiA to Glu, MoP/C composites
with high SBET and stability are successfully obtained as the
electrocatalyst supports and co-catalysts for MOR. With the
chelating agent (CiA) in the precursor, the MoP particles have
Acknowledgements
highly crystalline structure, good dispersion and intimate We acknowledge the support by National Natural Science
contact with the carbon skeletons, which are energetic for Foundation of China (51578218, 51108162, 51210105014),
enhancing the electrocatalytic activity for MOR. After Natural Science Foundation of Heilongjiang Province (B201411,
deposition with 5 wt.% Pt, Pt-MoP/C-2 exhibits the highest QC2015009), Postdoctoral Science Foundation of Heilongjiang
ESAPt (103.90 m2 g–1Pt) and mass activity (680.7 mA mgPt–1), Province (LBH-Q14137), and Excellent Young Teachers Fund of
electro-catalytic durability and CO tolerance for MOR due to Heilongjiang University and Hundred Young Talents in
the particular structure and the integrated functionalities of Heilongjiang University.
MoP/C support. The embedded Mo and P species in the
carbon skeleton contribute to the high activity and stability of
Notes and references
the Pt (and/or MoP) surface sites. MoP/C also plays a crucial
role in anchoring Pt nanoparticles and strengthening the
1
2
3
R. K. Mallick, S. B. Thombre and N. K. Shrivastava, J. Power
Sources, 2015, 285, 510–529.
N. Kakati, J. Maiti, S. H. Lee, S. H. Jee, B. Viswanathan and Y.
S. Yoon, Chem. Rev., 2014, 114, 12397–12429.
S. Zinoviev, F. M. Langer, P. Das, N. Bertero, P. Fornasiero, M.
Kaltschmitt, G. Centi and Stanislav Miertus, ChemSusChem,
2010, 3, 1106–1133.
4
5
N. Armaroli and V. Balzani, ChemSusChem, 2011, 4, 21–36.
L. Nan, W. Yue and Y. Jiang, J. Mater. Chem. A, 2015, 3,
22170–22175.
6
J. Sanetuntikul, K. Ketpang and S. Shanmugam, ACS Catal.,
2015, 5, 7321–7327.
7
8
Z. Yang and N. Nakashima, ChemCatChem, 2016, 8, 600–606.
P. Joghee, S. Pylypenko, K. Wood, G. Bender and R. O’Hayre,
ChemSusChem, 2014, 7, 1854–1857.
9
P. Kolla and A. Smirnova, Electrochim. Acta., 2015, 182, 20–
30.
Fig. 7 Schematic of methanol oxidation by Pt-MoP/C catalysts.
This journal is © The Royal Society of Chemistry 2015
J. Mater. Chem.A, 2015, 00, 1-9 | 8
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry A
Page 9 of 10
View Article Online
DOI: 10.1039/C6TA01319H
Journal of Materials Chemistry A
ARTICLE
10 J. Wang, Y. Liu, I. Chen, Y. Yang, T. K. Yah, C. Lee, C. Hu, T. 41 P. P. Patel, M. K. Datta, P. H. Jampani, D. Hong, J. A. Poston,
Wen, T. Chen and T. Lin, J. Phys. Chem. C, 2014, 118, 2253–
2262.
A. Manivannan and P. N. Kumta, J. Power Sources, 2015, 293,
437–446
11 A. Serrà, E. Gόmez and E. Vallés, Electrochim. Acta, 2015, 42 C. Santoro, A. Serov, C. Villarrubia, S. Stariha, S. Babanova, A.
174, 630–639.
Schuler, K. Artyushkova and P. Atanassov, ChemSusChem,
2014, 8, 828–834.
43 D. Higgins, M. Hoque, M. Seo, R. Wang, F. Hassan, J. Choi, M.
Pritzker, A. Yu, J. Zhang and Z. Chen, Chen. Adv. Func. Mater.,
2014, 24, 4325–4336.
12 M. E. Scofield, C. Koenigsmann, L. Wang, H. Liu and S. S.
Wong, Energy Environ. Sci., 2015, 8, 350–363.
13 J.C. Calderón, G. García, L. Calvillo, J.L. Rodríguez, M.J. Lázaro
and E. Pastor, Appl. Catal. B: Environ., 2015, 165, 676–686.
14 S. Sun, G. Zhang, N. Gauquelin, N. Chen, J. Zhou, S. Yang, W. 44 J. Zheng, D. Cullen, R. Forest, J. Wittkopf, Z. Zhuang, W.
Chen, X. Meng, D. Geng, M. N. Banis, R. Li, S. Ye, S. Knights, Sheng, J. Chen and Y. Yan, ACS Catal., 2015, 5, 1468–1474.
G. A. Botton, T. K. Sham and X. Sun, Sci. Rep., 2013, 3, 1775– 45 Y. Teng, A. Wang, X. Li, J. Xie, Y. Wang and Y. Hu, J. Catal.,
1784. 2009, 266, 369–379.
15 Y. Liu, H. Yan, X. Zhou, M. Li and H. Fu, Chem. Eur. J., 2015, 46 Y. Gassenbauer and A. Klein, J. Phys. Chem. B, 2006, 110,
21, 18345–18353. 4793–4801.
16 H. D. Jang, S. K. Kim, H. Chang, J. H. Choi, B. G. Cho, E. H. Jo, J. 47 H. An, G. An and H. Ahn, J. Alloy. Compd., 2015, 645, 317–
W. Choi and J. Huang, Carbon, 2015, 93, 869–877. 321.
17 P. Liu, D. Yang, H. Chen, Y. Gao and H. Li, Electrochim. Acta, 48 A. H. Duffy, D. J. Chen, S. G. Sun and Y. J. Tong, J. Mater.
2013, 109, 238–244. Chem., 2012, 22, 5205–5208.
18 C. Hung, Z. Liou, P. Veerakumar, P. Wu, T. Liu and S. Liu, 49 Y. Qu, Y. Gao, F. Kong, S. Zhang, L. Du and G. Yin, Int. J.
Chinese J. Catal., 2016, 37, 43–53. Hydrogen Energy, 2013, 28, 12310–12317.
19 J.C. Calderón, G. García, L. Calvillo, J.L. Rodríguez, M.J. Lázaro 50 R. Kou, Y. Shao, D. Mei, Z. Nie, D. Wang, C. Wang, V.
and E. Pastor, Appl. Catal. B: Environ., 2015, 165, 676–686.
20 C. Alegre, M. E. Gálvez, E. Baquedano, R. Moliner, E. Pastor
and M. J. Lázaro, J. Phys. Chem. C, 2013, 117, 13045–13058.
21 L. Zhang, Z. Wang, J. Zhang, X. Sui, L. Zhao and D. Gu, Carbon,
2015, 93, 1050–1058.
Viswanathan, S. Park, I. Aksay, Y. Lin, Y. Wang and J. Liu, J.
Am. Chem. Soc., 2011, 133, 2541–2547.
22 H. Liu, F. Ye, Q. Yao, H. Cao, J. Xie, J. Lee and J. Yang, Sci.
Rep., 2014, 4, 3969–3976.
23 M. Yu, S. Wang, J. Hu, Z. Chen, Y. Bai, L. Wu, J. Chen and X.
Weng, Electrochim. Acta, 2014, 145, 300–306.
24 H. Gao, J. He, Y. Wang and N. Deng, J. Power Sources, 2012,
205, 164–172.
25 W. Huang, H. Wang, J. Zhou, J. Wang, P. N. Duchesne, D.
Muir, P. Zhang, N. Han, F. Zhao, M. Zeng, J. Zhong, C. Jin, Y.
Li, S. Lee and H. Dai, Nat. Commun., 2015, 6, 10035–10043.
26 Q. Yue, Y. Wan, Z. Sun, X. Wu, Y. Yuan and P. Du, J. Mater.
Chem. A, 2015, 3, 16941–16947.
27 X. Chen, D. Wang, Z. Wang, P. Zhou, Z. Wu and F. Jiang,
Chem. Commun., 2014, 50, 11683–11685.
28 H. Du, Q. Liu, N. Cheng, A. M. Asiri, X. Sun and C. Li, J. Mater.
Chem. A, 2014, 2, 14812–14816.
29 J. Chang, L. Feng, C. Liu and W. Xing, ChemSusChem, 2015,
10, 3340–3347.
30 T. Wang, K. Du, W. Liu, Z. Zhu, Y. Shao and M. Li, J. Mater.
Chem. A, 2015, 3, 4368–4373.
31 M. Peroni, G. Mancino, E. Baráth, O. Y. Gutiérrez and J. A.
Lercher, Appl. Catal. B: Environ., 2016, 180, 301–311.
32 L. Wang, A. Lai, C. Lin, Q. Zhang, A. Zhu and Q. Liu, J.
Membrane Sci., 2015, 492, 58–66.
33 S. Han, Y. Feng, F. Zhang, C. Yang, Z. Yao, W. Zhao, F. Qiu, L.
Yang, Y. Yao, X. Zhuang and X. Feng, Adv. Funct. Mater.,
2015, 25, 3899–3906.
34 P. Xiao, M. A. Sk, L. Thia, X. Ge, R. J. Lim, J. Wang, K. H. Lim
and X. Wang, Energy Environ. Sci., 2014, 7, 2624–2629.
35 J. Kibsgaard and T. F. Jaramillo, Angewandte. Chemie., 2014,
126, 14661–14665.
36 R. Cheng, Y. Shu, M. Zheng, L. Li, J. Sun, X. Wang and T.
Zhang, J. Catal., 2007, 249, 397–400.
37 M.D. Obradović, U.Č. Lačnjevac, B.M. Babić, P. Ercius, V.R.
Radmilović, N.V. Krstajić and S.L. Gojković, Appl. Catal. B:
Environ., 2015, 170–171, 144–152.
38 K. Wang, Y. Wang, Z. Liang, Y. Liang, D. Wu, S. Song and P.
Tsiakaras, Appl. Catal. B: Environ., 2014, 147, 518–525.
39 H. D. Jang, S. K. Kim, H. Chang, J. Choi, B. G. Cho, E. H. Jo, J.
W. Choi and J. Huang, Carbon, 2015, 93, 869–877.
40 L. Wang, C. G. Tian, H. Wang, Y. G. Ma, B. L. Wang and H. G.
Fu, J. Phys. Chem. C, 2010, 144, 8727–8733.
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