In situ growth of Co0.85Se and Ni0.85Se on conductive substrates as high-performance counter electrodes for dye-sensitized solar cells

Article abstract of DOI:10.1021/ja303034w

We present herein a facile one-step low-temperature hydrothermal approach for in situ growth of metal selenides (Co_0.85Se and Ni _0.85Se) on conductive glass substrates. The as-prepared metal selenides on conductive substrates can be used directly as transparent counter electrodes for dye-sensitized solar cells (DSSCs) without any post-treatments. It is found that graphene-like Co_0.85Se exhibits higher electrocatalytic activity than Pt for the reduction of triiodide. As a consequence, the DSSC with Co_0.85Se generates higher short-circuit photocurrent and power conversion efficiency (9.40%) than that with Pt.

Full text of DOI:10.1021/ja303034w

Article
pubs.acs.org/JACS
In Situ Growth of Co Se and Ni Se on Conductive Substrates as
0.85
0.85
High-Performance Counter Electrodes for Dye-Sensitized Solar Cells
Feng Gong, Hong Wang, Xin Xu, Gang Zhou, and Zhong-Sheng Wang*
Department of Chemistry, Laboratory of Advanced Materials, Fudan University, 2205 Songhu Road, Shanghai 200438, P.R. China
*
S Supporting Information
ABSTRACT: We present herein a facile one-step low-temperature hydrothermal approach for
in situ growth of metal selenides (Co0.85Se and Ni0.85Se) on conductive glass substrates. The
as-prepared metal selenides on conductive substrates can be used directly as transparent
counter electrodes for dye-sensitized solar cells (DSSCs) without any post-treatments. It is
found that graphene-like Co0.85Se exhibits higher electrocatalytic activity than Pt for the
reduction of triiodide. As a consequence, the DSSC with Co0.85Se generates higher short-
circuit photocurrent and power conversion efficiency (9.40%) than that with Pt.
INTRODUCTION
conductive substrates for use in DSSCs as electrocatalysts has
been reported so far.
■
As one of the most promising alternatives for traditional silicon
solar cells, dye-sensitized solar cells (DSSCs) have attracted
tremendous scientific and industrial attention in the past two
decades, owing to their low cost, environmental friendliness,
simple production processes, and high efficiency. A typical
DSSC has a sandwich structure with a photoanode comprising
Herein, we propose a facile one-step strategy to synthesize
cobalt selenide (Co0.85Se) and nickel selenide (Ni0.85Se) in situ
on conductive glass substrates and use them directly as CEs to
assemble DSSCs without any post-treatments such as heating
or coating with other ancillary materials. When applied as the
CE in DSSCs, graphene-like Co0.85Se achieved a power
conversion efficiency (PCE) of 9.40% versus 8.64% for Pt
under the same conditions. To the best of our knowledge, this
1
TiO nanocrystals sensitized by dye molecules, an electrolyte
2
−
−
containing the iodide/triiodide (I /I ) redox couple, and a
3
−
−
counter electrode (CE) catalyzing the reduction of I3 to I .
Usually, platinum is the preferred material for catalyzing the
reduction of I3− due to its superior conductivity, electrocatalytic
activity, and stability. However, as a noble metal, low
abundance ratio and high cost prevent Pt from being used
for large-scale manufacturing of DSSCs, which has stimulated
great efforts to exploit substitutes for Pt in order to reduce the
overall cost and simultaneously keep the performance of
−
−
is the highest PCE for I /I3 redox couple based DSSCs with
Pt-free cathodes under AM1.5G simulated solar light (100 mW
−2
cm ).
EXPERIMENTAL SECTION
■
Preparation of Selenide and Pt Electrodes. Se powder (0.024
mmol, 99.999%, Aladding) and CoCl ·6H O (0.02 mmol, 99.9%, Alfa
2
2
Aesar) or NiCl ·6H O (0.02 mmol, 99.9%, Alfa Aesar) dissolved in 5.5
2
2
2
DSSC.
mL of deionized water were added to a 10 mL Teflon-lined autoclave
in sequence, and then 1.5 mL of N H ·H O (85 wt %, Sinopharm) was
3
4
Carbonaceous materials and conductive polymers have
been proposed as CEs to replace Pt in DSSCs, but their
stabilities and catalytic activities are not satisfactory. To
improve the catalytic activity, a self-assembled graphene/Pt
monolayer film with an extremely low loading amount of Pt
was developed, and good performance was achieved using this
ultrathin film as CE for a DSSC. Recently, some inorganic
compounds have also been introduced into DSSCs as
electrocatalysts, such as sulfides, nitrides, and carbides,
2
4
2
added with vigorous stirring for 10 min. Transparent conductive glass
(
F-doped SnO , FTO, 15 Ω/square, transmittance of 80%) was
2
received from Nippon Sheet Glass Co., Japan. A piece of cleaned FTO
substrate was put in the autoclave and placed at an angle against the
wall of the Teflon liner with the conducting side facing down. The
autoclave was sealed and maintained at 120 °C for 12 h. To prepare Pt
5
2
CEs, 50 μL of H
PtCl
in ethanol was drop-cast on 1.5 × 1.5 cm FTO
2
6
glass substrates, followed by heat treatment at 380 °C for 30 min.
Fabrication of DSSCs. TiO2 films (15 μm thick) containing
2
,6
7
8
transparent (11 μm) and scattering (4 μm) layers were prepared
which show good catalytic activity as CE materials. Lately, the
need for low-cost, scalable, and solution-processable photo-
voltaic materials gives great impetus to the research on the
11
according to a previous report. TiO films were soaked overnight in
2
cis-di(isothiocyanato)-bis-(2,2′-bipyridyl-4,4′-dicarboxylato)ruthenium-
(
II) bis-tetrabutylammonium (so-called N719, used as received from
Solaronix SA) solution (0.3 mM in a mixed solvent of acetonitrile and
tert-butanol in a volume ratio of 1:1). The dye-sensitized TiO
9
synthesis of semiconductor nanocrystals. As an important class
of chalcogenides, semiconducting selenides have drawn
enormous attention due to their distinctive electronic proper-
ties, interesting chemical behaviors, and wide variety of
2
photoanode and the CE were separated by a hot-melt Surlyn film
1
0
potential applications. To the best of our knowledge, no
research on in situ growth of binary metal selenides on
Received: April 5, 2012
Published: June 1, 2012
©
2012 American Chemical Society
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Journal of the American Chemical Society
Article
(
(
30 μm thick) and sealed through hot-pressing. The redox electrolyte
0.1 M LiI, 0.05 M I , 0.6 M 1,2-dimethyl-3-n-propylimidazolium
2
iodide, and 0.5 M 4-tert-butylpyridine in anhydrous acetonitrile) was
injected into the interspace between the photoanode and CE. Finally,
the holes on the back of the CE were sealed with a Surlyn film covered
with a thin glass slide under heat.
Characterizations. X-ray diffraction (XRD) profiles of the
obtained selenides were recorded on an X-ray powder diffractometer
(
D8 Advance, Bruker) with Cu Kα radiation (λ = 0.154 nm). The
optical transmittance spectra of as-prepared selenide cathodes were
measured on a Shimadzu UV-2550 UV−vis spectrometer. The
morphology and microstructure of the selenide CEs were examined
by field emission scanning electron microscopy (FESEM, S-4800,
Hitachi) and high-resolution transmission electron microscopy
(
HRTEM, JEM-2100F, JEOL). The composition and loading amount
of selenides on substrates were detected by inductively coupled
plasma−atomic emission spectra (ICP−AES, Thermo Electron Corp.
Adv. ER/S). Before the ICP measurements, the selenide CEs were
immersed in concentrated nitric acid with agitation for 12 h to dissolve
the compounds from the substrate. The specific surface area was
measured with a Micromeritics ASAP2020 nitrogen adsorption−
desorption apparatus. Cyclic voltammetry (CV) was carried out in a
three-electrode system containing an anhydrous acetonitrile solution
Figure 1. XRD patterns of the selenide products.
−1
of 0.1 M LiClO , 10 mM LiI, and 1 mM I at a scan rate of 50 mV s ,
4
2
+
using a Pt wire as the CE, an Ag/Ag electrode as the reference
electrode, and the as-prepared CE as the working electrode. For
electrochemical impedance spectroscopy (EIS) and polarization
measurements, the symmetrical dummy cells were assembled with
two identical CEs filled with the same electrolyte as used in the
2
DSSCs. The active apparent area of the dummy cell was 0.36 cm . In
EIS tests, the samples were scanned from 0.1 Hz to 500 kHz at 0 V
bias and ac amplitude of 10 mV. The polarization measurements were
performed at a scan rate of 50 mV s . All the electrochemical
characterizations were performed on an electrochemical workstation
−1
Figure 2. Optical transmittance spectra of Co0.85Se, Ni0.85Se, and Pt
CEs.
(
ZAHNER ZENNIUM CIMPS-1, Germany). The photocurrent
−
2
density−voltage curves of DSSCs were recorded on a Keithley 2400
source meter under the illumination of AM1.5G simulated solar light
coming from an AAA solar simulator (Newport-94043A) equipped
with a Xe lamp (450 W) and an AM1.5G filter. The light intensity was
calibrated using a reference Si solar cell (Oriel-91150). A black mask
5
1
.3, and 23.0 μg cm , respectively. Specific surface areas of
2
−1
1.8, 16.7, and 5.8 m g were measured for Co0.85Se, Ni0.85Se,
and Pt, respectively.
Figure 3 shows the FESEM images of Co0.85Se and Ni0.85Se
grown in situ on FTO substrates with different magnifications.
2
with an aperture area of 0.2304 cm was applied on the surface of
DSSCs to avoid stray light completely.
RESULTS AND DISCUSSION
■
Characterizations of the Selenides and As-Prepared
CEs. The metal selenides could grow in situ on well-cleaned
FTO glass substrates from a precursory mixture solution (see
Experimental Section) in a Teflon-lined autoclave through a
10
hydrothermal reaction. The best metal selenide CEs in terms
of solar cell performance were obtained at reaction temperature
of 120 °C for 12 h. The XRD patterns of the selenide products
are shown in Figure 1. The peak positions can be well indexed
to Co0.85Se (JCPDS No. 52-1008) and Ni0.85Se (JCPDS No.
1
8-0888), as shown in Figure 1. After the hydrothermal
procedure, FTO glass turned shallow black but still kept high
optical transparency (>85% in the visible region), as shown in
Figure 2. The transparency of the CE provides added value for
many practical applications such as windows, roof panels, or
various decorative installations, although it is not critical for the
function of DSSCs. In addition, transparent CE is useful to
construct tandem solar cells.
Figure 3. FESEM images of Co0.85Se (a,b) and Ni0.85Se (c,d) grown in
situ on FTO glass at different magnifications.
3d
The compositions of the selenides and loading amounts on
FTO were determined by ICP−AES. The results show that the
atomic ratios are 0.845:1.000 for Co:Se and 0.841:1.000 for
Ni:Se, which are close to the stoichiometry of Co0.85Se and
Ni0.85Se, respectively. The loading amounts of Co0.85Se,
Ni0.85Se, and Pt on the substrate were determined to be 8.7,
Co0.85Se and Ni0.85Se with different morphologies were
successfully grown on FTO substrates, but the FTO surface
was not covered fully by the selenides, as revealed by the clear
observation of scalelike FTO layer. The relatively low surface
coverage of Co0.85Se and Ni0.85Se is responsible for their high
transparency. Moreover, Co0.85Se has a higher surface coverage
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Article
and loading than Ni0.85Se, which supports that the former has a
lower transparency than the latter (Figure 2). The as-prepared
Co0.85Se exhibits a foliate structure (Figure 3a,b) just like
graphene, which is similar to a recent report. By contrast,
spherical nanoparticles are observed for Ni0.85Se grown on FTO
remarkable PCE of 9.40% (short-circuit photocurrent density
−2
(J ) = 16.98 mA cm , open-circuit photovoltage (V ) = 738
sc
oc
mV, fill factor (FF) = 0.75), while the DSSC with Ni0.85Se CE
12
−2
produced a PCE of 8.32% (J = 15.63 mA cm , V = 739 mV,
sc oc
FF = 0.72). For reference, the Pt-coated CE-based DSSC was
also measured under the same condition, giving a PCE of 8.64%
(
Figure 3c,d). Energy dispersive spectroscopy (EDS, Figure S1
−2
in Supporting Information) analysis demonstrates the presence
of Co and Se for Co0.85Se and Ni and Se for Ni0.85Se with
atomic ratios close to their stoichiometry.
The morphologies of the formed metal selenides are further
characterized through HRTEM, as depicted in Figure 4.
(
J = 16.03 mA cm , V = 738 mV, FF = 0.73). J increased
sc oc sc
in the order of Ni0.85Se < Pt < Co0.85Se, and PCE increased in
the same order. Evidently, Co0.85Se performs better than Pt as
the CE in DSSCs. The obtained efficiency is impressive for a
Pt-free electrochemical catalyst. To the best of our knowledge,
−
−
this is the highest PCE for I /I3 redox couple based DSSCs
with Pt-free cathodes under AM1.5G simulated solar light (100
−2
mW cm ). As the CEs are transparent, PCE can be further
improved by putting a reflective mirror on the back of the CE.
Electrochemical Behaviors. To interpret the J difference,
sc
the electrocatalytic activity of various CEs, which has a positive
correlation with the photocurrent generation, was evaluated by
CV. Figure 6 gives the CV curves of iodide/triiodide redox
species using Co0.85Se, Ni0.85Se, and Pt electrodes, respectively.
For all the three electrodes, two pairs of oxidation and
reduction peaks (Ox-1/Red-1, Ox-2/Red-2) are well resolved,
as labeled in Figure 6. The left and right pairs are described by
eqs 1 and 2, respectively.
I3 + 2e ↔ 3I−
−
−
(1)
−
−
3
I + 2e ↔ 2I
(2)
2
3
Figure 4. HRTEM images of as-synthesized Co0.85Se (a,c) and Ni0.85Se
(
b,d).
Since the CE of a DSSC is responsible for catalyzing the
reduction of I3− to I , the characteristics of peaks Ox-1 and
Red-1 are at the focus of our analysis. The peak currents and
−
Co0.85Se presents a graphene-like structure, possessing large
surface area. On the other hand, Ni0.85Se obtained by
hydrothermal reaction mainly exhibits particulate shape with
aggregation. The clear observation of lattice fringes (Figures
the peak-to-peak separation (E ), which is negatively
pp
correlated with the standard electrochemical rate constant of
a redox reaction, are two important parameters for comparing
4
c,d) for the metal selenides indicates that the formed Co0.85Se
13
catalytic activities of different CEs. The higher peak current
and Ni0.85Se have good crystallinity. The interplanar spacings of
d101 derived from the lattice fringes are 2.7 ± 0.1 Å for both
Co0.85Se and Ni0.85Se, which are in good coincidence with the
theoretical values (d101 = 2.69 Å for Co0.85Se and d101 = 2.70 Å
for Ni0.85Se).
Photovoltaic Performance. Figure 5 compares the
photovoltaic performance of N719-sensitized solar cells
assembled with various cathodes, and the corresponding
photovoltaic performance parameters are summarized in
Table 1. The DSSC with Co0.85Se-loaded CE yielded a
densities and lower E value (Table 1) reveal that Co Se is a
pp
0.85
−
remarkable electrochemical catalyst for the reduction of I ,
3
even better than the Pt electrode. Judged from the lower peak
currents and larger E , Ni0.85Se is inferior to Pt and Co0.85Se,
pp
but still exhibits good electrocatalytic activity.
To further elucidate the catalytic activities of different CEs
on the reduction of triiodide, EIS experiments were carried out
using symmetric cells fabricated with two identical electrodes
(
CE/electrolyte/CE). The Nyquist plots (Figure 7) for
symmetric cells with different CEs illustrate impedance
characteristics, in which two semicircles are observed in the
higher (left) and lower (right) frequency regions. According to
the Randles-type circuit (inset of Figure 7), the high-frequency
intercept on the real axis represents the series resistance (Rs).
The left arc arises from the charge-transfer resistance (R ) at
ct
the CE/electrolyte interface, which changes inversely with the
catalytic activity of different CEs on the reduction of triiodide,
and the corresponding constant phase element (CPE), while
the right one stems from the Nernst diffusion impedance (Z )
N
−
−
3d
of the I /I3 redox couple in the electrolyte. These
parameters were determined by fitting the impedance spectra
using the Z-view software, and good agreement between the
measured and the fitted data was achieved in all cases. The
resistance and impedance shown in Table 1 were calculated
using the total surface area of catalysts on the electrode of the
dummy cell. The total surface area obtained by the production
Figure 5. Photocurrent density−voltage characteristics of DSSCs with
−2
different CEs, measured at AM1.5G illumination (100 mW cm ).
1
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Table 1. Photovoltaic and Electrochemical Performance Parameters for Different CEs
J /mA cm−
2
FF
PCE/%
Rs/Ω cm
2
Rct/Ω cm
2
ZN/Ω cm
2
Epp/mV
CE
Voc/mV
sc
Co0.85Se
Ni0.85Se
Pt
738
739
738
16.98
15.63
16.03
0.75
0.72
0.73
9.40
8.32
8.64
2.1
1.8
2.6
0.6
1.8
1.1
0.5
1.4
0.9
342
581
414
2
2
the graphene-like (0.6 Ω cm ) to particulate (1.7 Ω cm )
morphology for the Co0 Se sample, the graphene-like (or
.85
sheet) morphology should be favorable for high electrocatalytic
activity.
It can be found that Z for the three symmetric cells also
N
2
2
increases in the order of Co0 Se (0.5 Ω cm ) < Pt (0.9 Ω cm )
.85
2
<
Ni0.85Se (1.4 Ω cm ), which means that the diffusion
coefficients (D) of triiodide for the cells vary in the inverse
order, judged from eq 3, where k is the Boltzmann constant, T
⎛
tanh⎜
⎝
⎞
kT
iω
Z =
δ⎟
N
2
2
n e cA iωD
D ⎠
(3)
0
Figure 6. CV curves of iodide/triiodide redox species for Co0.85Se,
Ni0.85Se, and Pt electrodes, respectively.
is the absolute temperature, n is the number of electrons
involved in the electrochemical reduction of I3− at the electrode
(
here n = 2), e is the elementary charge, c is the concentration
0
−
of I , A is the electrode area, ω is the angular frequency, and δ
3
14
is the thickness of the diffusion layer. This result indicates
that D increases with increasing electrocatalytic activity of the
CE.
Figure 8 shows the Tafel polarization curves measured on the
symmetrical cells used in EIS experiments. The slopes for the
Figure 7. Nyquist plots for symmetric cells fabricated with Co0.85Se,
Ni0.85Se, and Pt CEs. The lines express fit results for corresponding
EIS data, and the inset gives the equivalent circuit.
of specific surface area, loading amount, and the active apparent
2
2
area (0.36 cm ) of the electrode is 0.37, 0.32, and 0.48 cm for
Co0.85Se, Ni0.85Se, and Pt, respectively.
As the three CEs have nearly the same absolute R , the effect
s
Figure 8. Tafel polarization curves of symmetrical cells fabricated with
different CEs that are same as the ones used in EIS experiments.
of various CEs caused by R on photovoltaic performance can
s
be omitted. The R increases in the order of Co Se (0.6 Ω
ct
0.85
2
2
2
cm ) < Pt (1.1 Ω cm ) < Ni Se (1.8 Ω cm ), indicating an
inverse order of catalytic activity. The smallest R for Co Se
0
.85
anodic or cathodic branches are in the order of Co0.85Se > Pt >
Ni0.85Se. A larger slope in the anodic or cathodic branch
ct
0.85
implies that it has eximious catalytic activity on the reduction of
triiodide and supersedes the expensive Pt as the CE in DSSCs.
The conclusions for the catalytic activity derived from the EIS
and CV data are consistent.
As the electrocatalytic activity may depend on the
morphology, we prepared particulate Co0.85Se in a mixed
solvent of acetonitrile and water (volume ratio of 3.5:2.0),
which was characterized with HRTEM (Figure S2a,b), FESEM
indicates a higher exchange current density (J ) on the
0
6a
electrode. J can be also calculated by eq 4, where R is the
0
ct
RT
nFRct
J0 =
(4)
charge-transfer resistance obtained from EIS spectra (Figure 7),
(
Figure S2c), and XRD (Figure S3) as detailed in the
R is the gas constant, T is the absolute temperature, and F is
Supporting Information, in order to compare the electro-
Faraday’s constant. Apparently, the calculated J also follows
0
catalytic activity of the two selenides with the same
the order of Co0.85Se > Pt > Ni0.85Se, which is consistent with
2
morphology. The R was 1.7 and 1.8 Ω cm for particulate
the J order. In addition, the Tafel polarization curves contain
ct
sc
Co Se and Ni Se, respectively, as estimated from Figure S4,
the information about limiting current density (J ), which can
0.85
0.85
lim
suggesting that the two selenides with the same morphology
be expressed by eq 5, where N is the Avogadro constant, l is
the spacer thickness, and other parameters have been defined
A
had comparable electrocatalytic activity. As R increased from
ct
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Journal of the American Chemical Society
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Jlim = 2ne DcNA
0
(5)
l
1
4
previously. As the value of Jlim increases in the order of
Co0.85Se > Pt > Ni0.85Se and is directly proportional to the D,
the latter should vary in the order of Co0.85Se > Pt > Ni0.85Se,
which is fairly consistent with the EIS analysis about the Z and
N
D. Consequently, we conclude from the electrochemical and
EIS results that graphene-like Co0.85Se has a higher electro-
catalytic activity than Pt, and the latter is more active than
particulate Ni0.85Se. The order of electrocatalytic activity well
explains the order of Jsc.
The electrochemical stability of the CEs was examined by
repeated EIS measurements after aging or a pretreatment of CV
scanning before each EIS measurement. Figure 9 shows the
Figure 10. Nyquist plots of EIS for the symmetrical cells with Co0.85Se
(a), Ni0.85Se (b), and Pt (c) electrodes. The cell was first subjected to
CV scanning from 0 to 1 V and then from −1 to 0 V with a scan rate
−1
of 100 mV s , followed by 20 s relaxation at 0 V, and then EIS
measurement at 0 V from 0.1 Hz to 500 kHz was performed. This
sequential electrochemical test was repeated 10 times.
ohmic resistance and the mass transport in the redox electrolyte
solution.
The electrochemical stability of the particulate Co0.85Se
against aging (Figure S5) and potential cycling (Figure S6) was
also tested. Based on the stability data, the particulate Co0.85Se
has an electrochemical stability comparable to that of
particulate Ni0.85Se but poorer than that of graphene-like
Co0.85Se.
CONCLUSIONS
Figure 9. Nyquist plots of EIS for the symmetrical cells with Co0.85Se
■
(
a), Ni0.85Se (b), and Pt (c) electrode subjected to aging for some days
In summary, metal selenides, Co0.85Se and Ni0.85Se, have
successfully in situ grown on the surface of conductive glass
through a facial one-step hydrothermal reaction at low
temperature and shown to efficiently act as transparent counter
electrodes in DSSCs without any post-treatments. Co0.85Se
at room temperature and open circuit.
impedance spectra for the fresh and aged dummy cells at room
temperature and open circuit. For all the samples, R and Z
exhibits amazing electrocatalytic activity for the reduction of
s
N
−
hardly changed, indicating that the cell aging had almost no
I
3
, and the DSSC with it produces a higher short-circuit
influence on the series ohmic resistance and the mass transport
photocurrent and power conversion efficiency than the DSSC
with a Pt CE. In consideration of this mild and facile approach,
optical transparency, and low cost, selenide-based electro-
chemical catalysts have vast potential in scalable production of
DSSCs. This finding paves the way for preparing cheap and
highly efficient counter electrodes for DSSCs.
in the redox electrolyte solution. By contrast, the R increased
ct
2
2
from 0.6 to 0.7 Ω cm for Co Se, from 1.8 to 4.0 Ω cm for
0
.85
2
Ni Se, and from 1.1 to 1.3 Ω cm for Pt after aging for 10
0.85
days. This indicates that Co Se and Pt had better electro-
0
.85
chemical stability against aging than Ni0.85Se.
Figure 10 shows the evolution of impedance spectra for the
dummy cells subjected to sequential scans of CV and EIS for 10
cycles. After 10 cycles of scanning, there was negligible change
in R for Co Se and Pt, while R increased from 1.8 to 3.0 Ω
ASSOCIATED CONTENT
Supporting Information
EDS analysis of Co0.85Se and Ni0.85Se products obtained by
hydrothermal reaction, HRTEM and FESEM images and XRD
patterns for the particulate Co0.85Se, comparison of the EIS for
particulate Co0.85Se and Ni0.85Se electrodes, and electro-
chemical stability against aging or potential cycling of the
■
*
S
ct
0.85
ct
2
cm for Ni0 Se. This indicates that Co Se and Pt had better
.85
0.85
electrochemical stability against potential cycling than Ni0.85Se.
For all the samples, there was almost no change of R and Z ,
s
N
meaning that the potential cycling hardly influenced the series
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Journal of the American Chemical Society
Article
particulate Co0.85Se electrode. This material is available free of
charge via the Internet at http://pubs.acs.org.
(13) Roy-Mayhew, J. D.; Bozym, D. J.; Punckt, C.; Aksay, I. A. ACS
Nano 2010, 4, 6203−6211.
(
14) Hanch, A.; Georg, A. Electrochim. Acta 2001, 46, 3457−3466.
AUTHOR INFORMATION
Corresponding Author
zs.wang@fudan.edu.cn
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was financially supported the National Basic
Research Program (2011CB933302) of China, the National
Natural Science Foundation of China (20971025, 90922004,
and 50903020), Shanghai Leading Academic Discipline Project
(
B108), and Jiangsu Major Program (BY2010147).
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