Low Pt-Loaded Mesoporous Sodium Germanate as a High-Performance Electrocatalyst for the Oxygen Reduction Reaction

Article abstract of DOI:10.1002/cssc.201600785

Although Pt/C catalysts show relatively high activities for the oxygen reduction reaction (ORR) and great potential for use in polymer electrolyte membrane fuel cells, the large amount of Pt required and the poor stability of Pt/C-based catalysts remain big challenges. Herein, mesoporous Na₄Ge₉O₂₀ micro-crystals have been successfully synthesized to serve as a new kind of electrocatalyst support owing to its special structural characteristics and high structural stability. After loading a low amount of Pt (5 wt %) nanoparticles of 2–5 nm in diameter, the obtained mesoporous Pt/Na₄Ge₉O₂₀ composite shows not only high electrocatalytic activity for ORR in both acidic and alkaline electrolyte media, which are comparable to those of conventional 20 wt % Pt/C, but also remarkably enhanced Pt mass-specified ORR current density and durability. Synergetic catalytic effects between loaded Pt and the support for the ORR activity has been proposed.

Full text of DOI:10.1002/cssc.201600785

DOI: 10.1002/cssc.201600785
Communications
Low Pt-Loaded Mesoporous Sodium Germanate as a High-
Performance Electrocatalyst for the Oxygen Reduction
Reaction
[
a]
[a]
[a]
[a]
[a]
[a, b]
Xiaoxia Zhou, Lisong Chen, Gang Wan, Yu Chen, Qinglu Kong, Hangrong Chen,*
[a, b]
and Jianlin Shi*
Although Pt/C catalysts show relatively high activities for the
oxygen reduction reaction (ORR) and great potential for use in
polymer electrolyte membrane fuel cells, the large amount of
Pt required and the poor stability of Pt/C-based catalysts
remain big challenges. Herein, mesoporous Na Ge O micro-
also show better electrochemical stability as well as good ORR
activity. Additionally, it is noted that the spinels as an alterna-
tive low-cost bifunctional electrocatalyst have been developed
rapidly in the recent years [e.g., M Mn O4 (M=divalent
x
3ꢀx
[17]
[16]
metals) and MMoO (M=Co, Ni, or Fe) ] and exhibits excel-
4
9
20
4
crystals have been successfully synthesized to serve as a new
kind of electrocatalyst support owing to its special structural
characteristics and high structural stability. After loading a low
amount of Pt (5 wt%) nanoparticles of 2–5 nm in diameter, the
obtained mesoporous Pt/Na Ge O composite shows not only
lent oxygen reduction and/or evolution reaction (ORR/OER) ac-
tivity.
A series of germanate crystals M Ge O (M=Na, K) as a po-
4
9
20
tential and important semiconductor and infrared material,
were usually synthesized under harsh hydrothermal conditions
(i.e., under a pressure of 0.05 GPa and at a high temperature
4
9
20
high electrocatalytic activity for ORR in both acidic and alkaline
electrolyte media, which are comparable to those of conven-
tional 20 wt% Pt/C, but also remarkably enhanced Pt mass-
specified ORR current density and durability. Synergetic catalyt-
ic effects between loaded Pt and the support for the ORR ac-
tivity has been proposed.
[18]
of 3508C). The M Ge O crystal contains tetrahedral [GeO4]
4
9
20
and octahedral [GeO ] units, indicating that germanate has
6
richer topology structure than silicate. As far as we know, the
M Ge O crystal as an electrocatalyst support has never been
4
9
20
reported. Compared with carbon-based materials, M Ge O
20
4
9
features the following structural characteristics favoring its use
as a support for ORR: 1) the rich topology structure as well as
the porous structure enables fast diffusion and transport of the
reactants and products, 2) the highly crystalline framework of
M Ge O endows the material with higher tolerance to acid
Polymer electrolyte membrane fuel cells (PEMFCs) have been
becoming one of the most promising green energy sources to
[
1,2]
replace traditional ones on a large scale.
However, extensive
4
9
20
application of fuel cells is hindered owing to electrochemical
stability and high Pt loading required for the commercial Pt/C
catalyst used for the oxygen reduction reaction (ORR) at the
cathodes. Therefore, the exploration of highly active and elec-
trochemically stable catalysts with minimal Pt loading for ORR
has received much attention in recent years. Many kinds of
active Pt-based metal alloys have been developed to reduce
and basic corrosion than commercial carbon materials, and
3) the germanate M Ge O possesses abundant vacancies
4
9
20
owing to the doping of the low valence heteroatom M, which
is helpful to the adsorption and activation of O . Additionally,
2
it has also been found that nanocomposites of semiconductors
and precious metals can bring about unique physical and
chemistry features through strong metal–substrate coupling
[
3,4]
[19,20]
the Pt usages, such as the Pt-Ni,
core-shell Pd@PtNi nano-
interactions,
which may create opportunities in the devel-
[
5]
[6,7]
[8,9]
particles, Pt skin-layer,
and thin films,
which shows the
opment of functionalized catalytic materials for applications in
[21–23]
unique electrocatalytic activity toward ORR. Besides, carbon-
clean energy and environmental protections.
Therefore, it
[
10,11]
based electrocatalysts (i.e., N/B-doped carbon nanotubes,
is possible to achieve substantially improved ORR performan-
ces by designing and fabricating a nanocomposite of precious
metal-loaded germanate crystal M Ge O .
[
12]
[13–15]
Co O loaded graphene and N/S/P-doped graphene
) are
3
4
promising alternatives to Pt-based catalysts for ORR, which
4
9
20
Herein, mesoporous Na Ge O is used as an electrocatalyst
4
9
20
[
a] X. Zhou, L. Chen, G. Wan, Y. Chen, Q. Kong, Prof. Dr. H. Chen, Prof. Dr. J. Shi
State Key Laboratory of High Performance Ceramics and Superfine Micro-
structures
Shanghai Institute of Ceramics
Chinese Academy of Science
No. 1295 Ding-xi Road, Shanghai 200050 (P.R. China)
Fax: (+86)21-5241-3122
E-mail: hrchen@mail.sic.ac.cn
support for ORR, for the first time. The material was successful-
ly synthesized under mild hydrothermal conditions assisted by
tetraethylammonium hydroxide. Then, a highly active and
stable electrochemical catalyst was obtained by further loading
a low amount of Pt nanoparticles on the synthesized support.
The obtained nanocomposite Pt(5 wt%)/Na Ge O exhibits ex-
4
9
20
cellent catalytic activity and high durability for ORR in both
acidic and alkaline electrolyte solutions, which are comparable
to the commercial carbon-supported Pt catalyst (20 wt% Pt/C).
XRD patterns shown in Figure S1 confirm that the prepared
catalyst support well corresponds to the Na Ge O crystals
jlshi@mail.sic.ac.cn
[b] Prof. Dr. H. Chen, Prof. Dr. J. Shi
Jiangsu National Synergetic Innovation Center for Advanced Materials
Supporting Information for this article can be found under:
http://dx.doi.org/10.1002/cssc.201600785.
4
9
20
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(
JCPDS: 80-0703). After loading the Pt, the Pt/Na Ge O
ductively coupled plasma atomic emission spectroscopy (ICP-
AES). The corresponding energy dispersive X-ray spectroscopy
(EDX) spectrum and its quantitative result confirm the exis-
tence of Pt and give a similar Pt content to the ICP-AES result
(Figure 1 f).
4
9
20
sample shows the Na Ge O characteristic diffraction with
4
9
20
a little lower intensity, and no Pt diffraction peaks can be de-
tected, suggestive of low loading amount of Pt and/or small Pt
particle sizes with weak crystallization. The N adsorption iso-
2
therms for Na Ge O and Pt/Na Ge O are shown in Figure S2
The UV/Vis diffuse reflectance spectrum of Na Ge O shows
4
9
20
4
9
20
4
9
20
and the corresponding pore structure parameters are summar-
ized in Table S1. Two samples exhibit typical type IV isotherms,
confirming the presence of mesoporous structure owing to ag-
gregation of Na Ge O nanoparticles. The pore structure pa-
typical optical characteristics of semiconductors. Figure S3 sug-
gests that the absorption edge for the Na Ge O is about
4
9
20
359 nm, and the indirect bandgap is 2.75 eV.
Figure S4 shows the XPS analysis results of the sample Pt/
Na Ge O . The O1s XPS peak of Pt/Na Ge O can be deconvo-
4
9
20
rameters of the Na Ge O are nearly unchanged after loading
4
9
20
4
9
20
4
9
20
the Pt species, and the Brunauer–Emmett–Teller (BET) surface
luted into two components at 530.5 and 532.2 eV after Gaussi-
2
ꢀ1
area, mesoporous volume, and pore size are 69 m g ,
an fitting, which can be ascribed to lattice oxygen O and sur-
L
3
ꢀ1
0
.06 cm g , and 3.4 nm, respectively. The field emission SEM
FE-SEM) and low-magnification TEM images, shown in Fig-
ure 1a–b, reveal that the Na Ge O is composed of microme-
face adsorbed oxygen O , respectively. Besides, as high as
C
(
59.5% (Table S2) of surface adsorbed oxygen O is seen in the
C
Pt/Na Ge O sample, which is related to PtꢀO or GeꢀO spe-
4
9
20
4
9
20
[
24,25]
ter-sized and irregularly shaped crystals, and the FE-SEM image
further indicates that the mesopore structure comes from the
accumulation of nanocrystals. The high-resolution TEM (HR-
TEM) image (Figure 1c) clearly exhibits the lattice fringes of
crystals Na Ge O , and the corresponding selected area elec-
cies.
The binding energy of the Pt4f7 at 71.3 and 72.2 eV
/2
[24,26]
can be assigned to the Pt and PtO signals,
which accounts
for 32.5% and 67.5% of the total Pt content, respectively (Fig-
ure S4b and Table S2). It is believed that the co-existence of Pt
and PtO in the sample Pt/Na Ge O would be favorable in ele-
4
9
20
4
9
20
tron diffraction (SAED) pattern in the inset of Figure 1c con-
firms that the prepared Na Ge O has a single crystalline char-
vating the ORR catalytic activity. It is noted that compared to
the bulk metal Pt at 70.8 eV, Pt/Na Ge O shows a slight shift
4
9
20
4
9
20
acter. The typical FE-SEM and HR-TEM images of Pt/Na Ge O
20
to higher energy, which can be ascribed to the interaction be-
tween the catalyst support and the loading Pt species.
4
9
are shown in Figure 1d–e; it can be found that Pt nanoparti-
cles are uniformly dispersed onto the support Na Ge O with-
The ORR eletrocatalytic activity of prepared support
Na Ge O was investigated in N - and O -saturated 0.1m KOH
4
9
20
out apparent aggregation (Figure 1d) and the diameter of Pt is
smaller than 5 nm. In addition, the Pt nanoparticles are found
in the HR-TEM image (Figure 1e), as indicated by the yellow
arrows. The Pt loading amount is 5.0 wt% measured by the in-
4
9
20
2
2
electrolyte solution using cyclic voltammetry (CV), as shown in
Figure S5a. The CV curve of Na Ge O shows a featureless vol-
4
9
20
tammetric profile in N -saturated KOH electrolyte solution in
2
4 9 4 9
Figure 1. a) Typical FE-SEM. b) Low-magnification and c) HR-TEM images of Na Ge O20. d–e) FE-SEM and HR-TEM images of the Pt/Na Ge O20. f) The corre-
sponding EDX spectrum to the selected area in d and its quantitative result.
&
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the potential range of ꢀ1.0 to 0 V. In contrast, the electrodes
transfer pathway and the half-wave potential is ꢀ0.20 V vs.
Ag/AgCl at 1600 rpm (Figure 2b), similar to that of 20 wt% Pt/
C (ꢀ0.16 V, Figure S6a). The results of the Tafel plot (Figure 2c),
based the analysis the LSV curves, indicate a higher slope for
exhibit a dramatic increase in voltammetric current in O -
2
saturated alkaline solution, with a relatively positive ORR onset
potential (ꢀ0.29 V vs. Ag/AgCl) and a high cathodic current
ꢀ
2
ꢀ1
density (ꢀ0.72 mAcm ). The linear sweep voltammograms
the Pt/Na Ge O (83 mVdec ) in the lower overpotential
4
9
20
ꢀ1
(
LSV) of Na Ge O in alkaline medium using a rotating disk
region than the reference Pt/C (60 mVdec ), suggesting the
relatively slow kinetics for ORR in alkaline electrolyte solution,
which is related to the relatively weak conductivity of the sup-
port Na Ge O However, the corresponding Koutecky–Levich
4
9
20
electrode (RDE) are shown in the Figure S5b, and a two-step
ꢀ
transfer pathway by producing HO2 as intermediates is ob-
served. Furthermore, the rotating ring-disk electrode (RRED)
measurements (Figure S5c) also show high ring currents of the
Na Ge O . The electron transfer number (n) is 2.2–2.5 for
4
9
20.
(K–L) plots at different potentials exhibit good linearity (Fig-
ure 2d), and the slopes keep constant from ꢀ0.60 to ꢀ0.90 V
vs. Ag/AgCl, implying the similar n. Moreover, the n is 3.8 by
calculating from the K–L equation, indicating the catalyst Pt/
Na Ge O follows the four-electron reduction mechanism in
4
9
20
Na Ge O from ꢀ0.3 to ꢀ1.0 V on the basis of the ring and
4
9
20
disk currents (Figure S5d), indicating a dominant two-electron
process.
4
9
20
Interestingly, the ORR performance of the Na Ge O by load-
the ORR. In addition, the n of the Pt/Na Ge O in alkaline elec-
4 9 20
4
9
20
ing a low amount of precious metal (5 wt% Pt) can be greatly
enhanced in 0.1m KOH electrolyte solution, and the CV curve
of Pt/Na Ge O shows a more positive ORR onset potential
trolyte solution is 3.6–3.8 over the potential range of ꢀ0.6 to
ꢀ0.9 V vs. Ag/AgCl (inset in Figure 2e) based on the corre-
sponding RDE dates, which is basically consistent with the re-
sults of K–L plots analysis. The RDE measurements (Figure 2e)
are conducted to verify the formation of the intermediates
4
9
20
(
(
ꢀ0.04 V vs. Ag/AgCl) and
a
higher current density
ꢀ
2
ꢀ1.02 mAcm ) than that of support Na Ge O , as shown in
4
9
20
ꢀ
ꢀ
Figure 2a. RDE measurement results indicate a four-electron
HO2 , and the HO2 yield is as low as 3% for Pt/Na Ge O , as
4 9 20
ꢀ
1
Figure 2. The electrocatalytic activity for ORR in KOH electrolyte solutions (0.1m). a) CV traces of Pt/Na
4
Ge
9
O
20 at a scan rate of 100 mVs . b) LSV scans on Pt/
ꢀ
1
Na
4
Ge
9
O
20 in O
2
-solution at a scan rate of 10 mVs and different rotation rates. c) Tafel plots of Pt/Na
Ge
was scanned at 10 mVs while the ring potential was fixed at 0.5 V vs. Ag/AgCl during the tests (I
4
Ge
9
O
20 and Pt/C at a rotation rate of 1600 rpm. d) K–L
plots at different potentials. e) RRED test of the ORR on the Pt/Na
4
9
O
20 in O
2
-saturated electrolyte solution at a rotation rate of 1600 rpm. The dark potential
: ring current; I : disc current). inset) The n of Pt/Na Ge
Ge 20 and commercial Pt/C at an electrode
ꢀ
1
r
d
4
9 20
O
at varied potentials based on the corresponding RRED dates. f) Mass-specified ORR current density (jmass) of Pt/Na
rotating rate of 1600 rpm and a potential of ꢀ0.1 V vs. Ag/AgCl.
4
9
O
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shown in Figure S7a, indicating a dominant four-electron pro-
cess. More importantly, the mass-specified kinetic current den-
By the polarization curves, several potential points from 0.00–
0.50 V vs. Ag/AgCl are also chosen to determine the K–L slope
and calculate n (Figure 2d). The n was determined to be 3.9,
confirming a highly desirable four-electron reduction pathway
in the ORR. In addition, the RRED measurements (Figure 3c)
are also performed to determine the ORR catalytic pathway
and monitor the formation of H O of the Pt/Na Ge O
20
ꢀ
1
ꢀ1
sities (jmass) are 0.38 Amg Pt and 0.20 Amg Pt for the
sample Pt/Na Ge O and the commercial Pt/C at ꢀ0.1 V vs.
4
9
20
Ag/AgCl, respectively. The former is twice that of the later, as
shown in Figure 2 f, which is highly encouraging for the future
PEMFC application of the synthesized Pt/Na Ge O .
4
9
20
2
2
4
9
[27]
More encouragingly, the Pt/Na Ge O sample also shows an
sample in the ORR process.
It is noted that the amount
4
9
20
excellent ORR performance in acidic electrolyte solution (0.1m
of produced H O species is lower than 2% (Figure S7b) over
2
2
HClO ). The CV curve of Pt/Na Ge O exhibits a more positive
the sample Pt/Na Ge O , giving a n of 3.9 (inset in Figure 3c)
4 9 20
4
4
9
20
ORR onset potential (0.62 V) and
a
higher current
in acidic electrolyte solution, which is consistent with the
analysis of K–L plots, indicating a dominant four-electron
process. More importantly, the mass activity of Pt/Na Ge O
20
ꢀ
2
(
ꢀ1.23 mAcm ) in the O -saturated HClO electrolyte solution,
2
4
as shown in Figure 3a. Compared to the commercial 20 wt%
Pt/C (Figure S6b), the half-wave potential for the Pt/Na Ge O
20
4
9
ꢀ
1
has been calculated to be 0.15 Amg Pt at 0.6 V vs Ag/AgCl,
which is remarkably higher than that of the commercial
4
9
has a slight shift of 10 mV towards the positive direction [i.e.,
.46 V vs. Ag/AgCl at 1600 rpm (Figure 3b)], suggesting largely
ꢀ
1
0
catalyst Pt/C (0.035 Amg Pt), indicating a great enhancement
of electrochemical ORR activity in the acidic electrolyte solu-
tion.
accelerated ORR reaction kinetics. The ORR kinetics investiga-
tion of the Pt/Na Ge O by Tafel analysis in the low overpoten-
4
9
20
ꢀ
1
tial region indicates a comparable ORR activity (104 mdec )
To better understand the transport property of electrons on
Pt/Na Ge O , electrochemical impedance spectroscopy (EIS)
ꢀ
1
compared to the Pt/C (102 mVdec ), as shown in Figure 3c,
suggesting a quick ORR kinetics in acidic electrolyte solution.
4
9
20
characterization was performed under dark conditions, as
Figure 3. The electrocatalytic activity for ORR in 0.1m HClO
4
electrolyte solution. a) CV scans of Pt/Na
4
Ge
9
O
20 in N
2
- and O
2
-saturated solutions at a scan rate
ꢀ1
ꢀ1
of 100 mVs . b) LSV scans on the Pt/Na
Na Ge
electrolyte solution (0.1m) at a rotation rate of 1600 rpm. The dark potential was scanned at 10 mVs while the ring potential was fixed at 0.5 V vs. Ag/AgCl
during the tests. inset) The n of Pt/Na Ge 20 at varied potentials based on the corresponding RRED data. f) Pt mass-specified ORR current density (jmass) of Pt/
Na Ge 20 and commercial Pt/C with the rotating rate of 1600 rpm at 0.6 V vs. Ag/AgCl.
4
Ge
9
O20 in O
2
-saturated electrolyte solution at a scan rate of 10 mVs and different rotation rates. c) Tafel plots of Pt/
4
9 4 9 2 4
O20 and Pt/C at a rotation rate of 1600 rpm. d) K–L plots at different potentials. e) RRED tests of the ORR on the Pt/Na Ge O20 in O -saturated HClO
ꢀ
1
4
9
O
4
9
O
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shown in Figure S8. It is found that both the Na Ge O and Pt/
Scheme 1. Firstly, a large amount of intrinsic oxygen vacancies
can be generated in the lattice of the support Na Ge O
20
4
9
20
Na Ge O show a semicircle in the high frequency region at
4
9
20
4
9
1
.2 V, and the diameter of the semicircle of Pt/Na Ge O is
owing to the doping of the heteroatom Na among [GeO ] and
4
9
20
4
smaller than that of Na Ge O , which indicates that the elec-
[GeO ] groups, as shown in step 1 in Scheme 1. Therefore, O
2
4
9
20
6
tron/charge transfer resistance of Pt/Na Ge O is much smaller
molecules in the electrolyte solution can be adsorbed quickly
(Oads) onto the surface of the support and then further activat-
ed to form the activated oxygen (O*). The O* species will mi-
grate to Pt nanoparticles along the surface of the Na Ge O
20
4
9
20
than the support Na Ge O and the higher electrical conduc-
4
9
20
tance of Pt/Na Ge O can lead to the faster reaction rate in
4
9
20
the ORR.
The long-term durability of Pt/Na Ge O was evaluated by
4
9
ꢀ
and be reduced to OH in alkaline media through the four-
4
9
20
ꢀ
ꢀ
stability tests, as shown in Figure S9. The results demonstrate
that the new Pt/Na Ge O electrocatalyst displays excellent
electron ORR reaction 2PtꢀO*+2H O+4e !2Pt+4OH , or
2
+
ꢀ
H O in acidic media through 2PtꢀO*+4H +4e !2Pt+
4
9
20
2
long term stability not only in the alkaline solution also in the
acidic medium. It is found that the half-wave potential for the
Pt/Na Ge O remains almost unchanged both in the alkaline
2H O, under the Pt active species and electric field of the cell,
2
as shown in route 1 in step 2 (Scheme 1). In addition to the
above surface route, an alternative lattice route could also be
possible. There is abundant lattice oxygen presented in the
support Na Ge O , as proved by the XPS results (Figure S4a).
4
9
20
th
and acidic electrolyte solutions at the 2000 LSV cycle at
ꢀ
1
5
0 mVs . Additionally, the half-wave potentials for the Pt/
4
9
20
Na Ge O decay by only 15 (Figure S9a) and 20 mV (Fig-
Those lattice oxygen close to Pt nanoparticles could interact
with the surface Pt atoms and thus form the low valence PtO
species, as proved by the XPS results (Figure S4b), which can
4
9
20
ure S9b) in the alkaline and acidic electrolyte solutions at the
th
5
000 cycle, respectively. For comparison, the commercial Pt/C
ꢀ
ꢀ
shows 15 and 21 mV negative shifts in the alkaline electrolyte
solution, and 20 and 60 mV in the acidic electrolyte solution, in
generate OH in alkaline media through 2PtO+2H O+4e !
2
ꢀ
+
2Pt+4OH , or H O in acidic media through 2PtO+4H +
2
th
th
ꢀ
the half-wave ORR potentials at 2000 and 5000 cycles, re-
spectively, as shown in Figure S10. The above durability tests
confirm the extremely promising electrochemical stability of
such a novel kind of electrocatalyst Pt/Na Ge O in both alka-
4e !2Pt+2H O, under the effect of an electric field. Mean-
2
while, the O
on the support surface from the external
ads
oxygen supply will migrate into the lattice and take the posi-
tion of initial lattice oxygen (Oads!Olattice) through the micro-
pore and mesoporous channels of the crystals Na Ge O , as
4
9
20
line and acidic media, resulting from the high structural stabili-
ty of the Pt/Na Ge O and high dispersion of nanoparticles Pt
4
9
20
demonstrated in route 2 in the step 2 (Scheme 1). The two
ORR routes indicate that both Pt and PtO as active sites can ac-
celerate the ORR, and the efficient diffusion and migrate of O2
owing to the special porous structure of the sodium germinate
support can also improve the electrocatalysis activity.
4
9
20
in the support Na Ge O .
4
9
20
A possible catalytic mechanism toward ORR over the Pt/
Na Ge O in alkaline and acidic media is proposed, and two
4
9
20
possible four-electron reaction pathways are shown in
Scheme 1. Schematics for the possible catalytic pathways of ORR on Pt/Na
4
Ge
9
O
20 in the alkaline media (A) and acidic media (B). Step 1: the generation of
oxygen vacancies and PtO species; Step 2: two routes of the reduction of O
2
in the alkaline media: Route 1 is the surface route in which ambient oxygen mol-
ecules are activated to active O* on the support and then form PtꢀO* species on Pt NPs, favoring the oxygen reduction; Route 2 is the lattice route in which
lattice oxygen migrate to Pt and form PtO species, then the ambient oxygen molecules will be reduced and take the initial positions of latticed oxygen.
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Communications
Compared to the commercial Pt/C, this new type of electro-
catalyst Pt/Na Ge O shows approximately 4 and 2-fold in-
Keywords: electrocatalyst · fuel cells · oxygen reduction
reaction · platinum · sodium germanate
4
9
20
creases in the mass activity in acidic and alkaline media, re-
spectively. The excellent catalytic activity can be ascribed to
the following aspects: 1) much improved adsorption of ambi-
ent O by Na Ge O owing to the oxygen vacancies in its lat-
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[
28]
nanoparticles; 2) the efficient diffusion of O related to the
2
[
special porous structure characters of the support; and 3) pro-
moted PtO formation by the lattice oxygen species, through
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ꢀ
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2
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+
between H O/H and oxygen from PtO. In addition, the uni-
2
form and stable dispersion of Pt nanoparticles, the binding of
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high structure stability of the Na Ge O matrix are also be-
[7] Y. S. Kim, S. H. Jeon, A. Bostwick, E. Rotenberg, P. N. Ross, V. R. Stamen-
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4
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[
lieved to contribute to the excellent durability of the Pt/
Na Ge O electrocatalyst.
2
4
9
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In conclusion, a novel type of low Pt-loaded semiconductor,
Pt/Na Ge O electrocatalyst, has been synthesized through
[
[
4
9
20
a facile process, and its electrocatalytic activity toward ORR in
both acidic and alkaline electrolyte solutions has been ex-
plored for the first time. Such a catalyst with 5 wt% Pt loading
shows comparable ORR activities to commercial 20 wt% Pt/C
catalyst and follows a four-electron pathway in the acidic and
alkaline media (i.e., the ORR mass activity of the Pt/Na Ge O
20
[12] Y. Liang, Y. Li, H. Wang, J. Zhou, J. Wang, T. Regier, H. Dai, Nat. Mater.
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2
[
[
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1908.
4
9
is four times and twice that of the commercial 20 wt% Pt/C in
acidic and alkaline electrolyte solutions, respectively). More im-
portantly, Pt/Na Ge O demonstrates excellent electrochemical
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4
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durability in the ORR, with its half-wave potentials decayed by
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th
only 15 and 20 mV up to 5000 cycle in the alkaline and acidic
[
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electrolyte solutions, respectively, in contrast to the commer-
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highly dispersed Pt and PtO on the support Na Ge O in this
5, 3924.
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catalyst system should be responsible for the enhanced cata-
lytic activity and excellent durability. The study is also benefi-
cial for the exploration of highly efficient, low Pt loading and
non-carbonaceous electrocatalysts.
[
[
[
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[
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This research was sponsored by the National Key Basic Research
Program of China, (2013CB933200), China National Funds for
Distinguished Young Scientists (51225202) and National Natural
Science Foundation of China (51502330).
Received: June 12, 2016
Revised: July 2, 2016
Published online on && &&, 0000
&
ChemSusChem 2016, 9, 1 – 7
www.chemsuschem.org
6
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

COMMUNICATIONS
Less Pt, higher activity: A Pt(5 wt%)/
X. Zhou, L. Chen, G. Wan, Y. Chen,
Q. Kong, H. Chen,* J. Shi*
Na Ge O composite shows not only
4
9
20
high electrochemical catalytic activity
for the oxygen reduction reaction (ORR),
but also remarkably enhanced Pt mass-
specified ORR current density in both
acidic and alkaline electrolyte media,
which are comparable to those of the
commercial Pt/C catalyst.
&
& – &&
Low Pt-Loaded Mesoporous Sodium
Germanate as a High-Performance
Electrocatalyst for the Oxygen
Reduction Reaction
ChemSusChem 2016, 9, 1 – 7
www.chemsuschem.org
7
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
These are not the final page numbers! ÞÞ