Synthesis of hierarchical rippled Bi2O3 nanobelts for supercapacitor applications

Article abstract of DOI:10.1039/c002126a

Hierarchical rippled Bi₂O₃ nanobelts were successfully synthesized by an electrodeposition route and tested as promising materials for supercapacitor applications.

Full text of DOI:10.1039/c002126a

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Synthesis of hierarchical rippled Bi O nanobelts for supercapacitor
2
3
applicationsw
Fu-Lin Zheng, Gao-Ren Li,* Yan-Nan Ou, Zi-Long Wang, Cheng-Yong Su and
Ye-Xiang Tong*
Received 2nd February 2010, Accepted 4th May 2010
First published as an Advance Article on the web 7th June 2010
DOI: 10.1039/c002126a
2 3
Hierarchical rippled Bi O nanobelts were successfully synthe-
sized by an electrodeposition route and tested as promising
materials for supercapacitor applications.
Recently supercapacitors have become attractive electrochemical
energy-storage devices because they have greater power density
than batteries and can be deeply discharged without any deleterious
1
effect on their lifetime. Among various electrode materials, RuO
2
has been considered as one of most promising materials for
2–4
Fig. 1 The illustration for the electrode potential oscillations when
supercapacitors with high-power and high-energy densities.
Unfortunately, the expensive nature of RuO has limited its
the current density exceeds the diffusion-limited one in solution of
3 3 2
0.005 M Bi(NO ) + 0.05 M Na EDTA + 0.1 M sucrose.
2
technological viability. Therefore, there is a strong appetency to
develop cost-effective supercapacitors based on non-noble
one. Here, by using the electrode potential oscillations, we success-
fully realize the hierarchical rippled surface growth during the
synthesis of nanobelts. When the electrode potential periodically
decreases and increases as shown in Fig. 1, the thicknesses of
nanobelts will also decrease and increase periodically, and
accordingly the hierarchical rippled nanobelts will be formed, as
illustrated in Fig. 2(1). When the electrode potential oscillations do
not happen, nanobelts with flat shapes will be formed because of
no thickness change, as shown in Fig. 2(2). Herein, these prepared
5
6
7
8
transition metal oxides, e.g. Co
3
O
4
, TiO
Recent research has focused on the nanoscale electrode
materials to improve their electrochemical performances.
2 2 2
, MnO , SnO , and
9–10
2 3
Bi O
11
1
D Nanostructured materials, such as nanorods, nano-
13
and nanotubes, have stimulated great interest for the
7,12
wires,
next generation of supercapacitors because they provide high
surface-to-volume ratio and short diffusion path lengths for ions,
leading to high charge/discharge rates. However, 1D nanobelts
are rarely reported for supercapacitor applications, although their
application is strongly desired. Nanobelts have attracted much
attention because of their high surface-to-volume ratio, excellent
2 3
hierarchical rippled Bi O nanobelts are expected to make a
significant contribution for the advancement of supercapacitors
because of their predominant electrochemical behaviors.
Electrochemical deposition of Bi O was carried out in solution of
2 3
14
surface activities, and crystallographic orientation. Up to now,
the majority of the reported 1D nanobelts are only limited to the
smooth surfaces, and the synthesis of 1D nanobelts with
hierarchical rippled surfaces is rarely reported. In addition, for
0
.005 M Bi(NO ) + 0.05 M Na EDTA + 0.1 M sucrose with a
3 3 2
À2
current density of 4.0 mA cm for 60 min. (Here the electrode
potential oscillations happened as shown in Fig. 1.) Fig. 3(a) and (b)
showed SEM images of Bi
It can be clearly observed that the hierarchical rippled Bi
nanobelts have been successfully synthesized. Generally, the obtained
Bi nanobelt has a width of 250–300 nm, a thickness of 10–30 nm,
and a length of 1–5 mm. The intervals between the ripples are about
5–30 nm. The thickness of ripples is about 15 nm. Fig. 3(c) shows a
2 3
O deposits with different magnifications.
15
Bi O , 1D nanostructures are also rarely reported. Herein, we
2
3
2 3
O
firstly reported a facile synthetic strategy to prepare novel hier-
archical rippled Bi O nanobelts for supercapacitor applications.
2
3
2 3
O
It is well known that the surface morphologies of crystals are
generally correlative to the formation conditions from the thermo-
1
16
dynamic equilibrium or driving force for crystallization. During
the electrodeposition under galvanostatic conditions, the electrode
potential oscillations can be observed as shown in Fig. 1 when the
current density is sufficiently high and exceeds the diffusion-limited
representative TEM image of a single hierarchical rippled Bi O
2
3
nanobelts with widths of about 200 nm. The periodic rippled
structures were clearly observed. The typical HRTEM image of
2 3
hierarchical rippled Bi O nanobelts is shown in Fig. 3(d), which
indicates the single crystal nature. The fringe spacing is determined to
MOE Laboratory of Bioinorganic and Synthetic Chemistry/School of
Chemistry and Chemical Engineering/Institute of Optoelectronic and
Functional Composite Materials, Sun Yat-sen University, Guangzhou,
510275, P. R. China. E-mail: ligaoren@mail.sysu.edu.cn,
chedhx@mail.sysu.edu.cn; Fax: +86-20-84112245;
Tel: +86-20-84110071
w Electronic supplementary information (ESI) available: Experimental
details, XRD pattern, EDS pattern, XPS spectra, SEM images, and
TEM image, and calculation method of specific capacitance. See DOI:
Fig. 2 The illustration for (1) the formation of rippled nanobelt
because of thickness change and (2) the formation of nanobelt with
smooth surface because of no thickness change. (The Figures are the
side views of nanobelts.)
10.1039/c002126a
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Chem. Commun., 2010, 46, 5021–5023 | 5021

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superoxide Bi
pure Bi was successfully obtained.
In the case of hierarchical rippled Bi O nanobelts, their surface
2
O
5
phases existed in Bi
2
O
3
products, and highly
2 3
O
2
3
areas are much larger than those of Bi O nanobelts with smooth
2
3
surfaces, leading to higher efficiency of Bi O utilization. In order
2
3
to examine the surface properties of these two kinds of Bi O
2
3
nanobelts, their porosities were characterized by nitrogen sorption
analysis using standard Brunauer–Emmett–Teller (BET)
techniques. The nitrogen adsorption and desorption isotherms
2 3
and the resulting pore size distributions of Bi O hierarchical
rippled nanobelts and nanobelts with smooth surfaces are shown
in Fig. 4(a) and (b), respectively. They both displayed the typical
Type I adsorption isotherms and yield specific surface areas of
2
À1
1
96 and 24 m g , respectively. Their pore diameters are around
and 13 nm, respectively. Thus, the specific surface area of
hierarchical rippled Bi O nanobelts increased up to 8 times
8
2
3
compared with that of Bi O nanobelts with smooth surfaces.
2 3
Fig. 3 SEM images of hierarchical rippled Bi
2
O
3
nanobelts: (a)Â20 000;
2 3
The supercapacitive performance of Bi O nanobelts with
(b)Â50 000; (c) TEM image; (d) HRTEM image and SAED pattern (inset).
hierarchical rippled surfaces was investigated by means of cyclic
voltammetry. Fig. 5(a)(1) shows the cyclic voltamogramm of
be about 0.32 nm, which is very close to the (201) lattice spacing of
Bi , indicating the crystal growth of the hierarchical rippled
Bi nanobelt is preferential in the [101] direction. The selected
2 3
O
the prepared hierarchical rippled Bi
.0 M Na SO
2
O
3
nanobelt electrode in
À1
2
O
3
1
2
4
solution at a scan rate of 100 mV s . One pair
area electron diffraction (SAED) pattern is shown in the inset in
Fig. 3(d), which also indicates a single-crystal structure. The XRD
pattern of hierarchical rippled Bi O nanobelts is shown in Fig. S1.
of redox peaks on this cyclic voltammogram distinctly
appeared, indicating good redox transitions of these Bi
2 3
O
2
3
nanobelts between different valence states. Therefore, these
prepared Bi O nano-belts can be used as electrode materials
All the peaks in the XRD can be indexed to Bi O3 phases,
2
2
3
revealing that pure Bi O is obtained. The results of EDS
2
3
for electrochemical supercapacitors. In addition, the highly
symmetrical CV characteristics in the forward and reverse
sweeps are also observed. These results exhibit a good
(
Fig. S2) also demonstrated that pure Bi
2
O
3
was obtained. When
À2
the current density was decreased to 2.0 mA cm , Bi
2
O
3
nanobelts with blurry ripples were observed, as shown in
Fig. S3(b). This may be attributed to the weak electrode potential
oscillations (Fig. S3(d)(2)). However, when a small current density
2 3
capacitive response from Bi O nanobelts with hierarchical
9
rippled surfaces. Based on the above results, it is obvious that
this is a redox supercapacitor, which utilizes the charge-transfer
pseudocapacitance arising from reversible Faradaic reactions
occurring on the electrode surface. When a potential difference
is applied across the electrode, the redox transitions of bismuth
oxide between different valence states will occur and the charge
will build up on the surface of electrode. As the charge on the
surface of electrode changes, the ions in the solution, i.e.,
protons will be transferred to the surface of the electrode under
the influence of electrostatic interactions to counter-balance the
charge on the electrode. At the same time the electron transfer
will happen through the current source or the external load.
Therefore, a pair of symmetric redox peaks in the cyclic
voltammogram was observed. The average specific capacitance
À2
of 1.0 mA cm was used for electrodeposition, the electrode
potential kept stable all along and the oscillation was not observed
(Fig. S3(d)(3)), and accordingly Bi O nanobelts with smooth
2 3
surfaces were synthesized as shown in Fig. S3(c).
The direct electrochemical reactions corresponding to the
formation of Bi O were described as follows. The electro-
2
3
À
À
chemical reduction of the nitrate ions (NO
3
to NO
2
) in
À
deposition solution directly results in the formation of OH
1
via reaction (1). These produced OH ions will react with
7
À
3
+
+ 18
,
Bi
ions to form Bi(OH)
2
which is crucial for the
formation of Bi
2
O
3
(reaction (2)). Finally, Bi
+
2
O
3
will be
produced from Bi(OH)
2
via reaction (3).
À1
3À
2À
À
is about 250 F g , which is much larger than that reported for
À1
NO + H
2
O + 2e - NO + 2OH
(1)
(2)
(3)
9
2 3
Bi O nanocrystals (68 F g ).
3
+
À
+
Bi + 2OH - Bi(OH)
2
+
2
À
2 3 2
+ 2OH - Bi O k + 3H O
2
Bi(OH)
2 3
The XPS spectra of Bi O nanobelts are shown in Fig. S4(a) and
(b). The existence of a carbon peak is associated with carbon that
was used as an internal reference to determine the binding energy
of the XPS spectra. Fig. S4(a) shows the high resolution spectra
2 3
of Bi O for Bi4f7/2 and Bi4f5/2 photolines. The Bi4f7/2 and Bi4f5/2
peaks are centered, respectively, at about 158.58 and 163.61 eV,
1
9
2 3
which is close to the reported values for crystalline Bi O . The
shoulder on the Bi4f7/2 peak, related to either bivalent or
tetravalent or pentavalent states in Bi O nanobelts, did not
Fig. 4 Adsorption–desorption isotherms and pore size distributions
2
3
(the inset) of (a) hierarchical rippled Bi O nanobelts and (b) Bi O
3
2
3
2
19–20
appear.
Therefore, no unoxidized Bi, suboxide BiO and
nanobelts with smooth surfaces.
5
022 | Chem. Commun., 2010, 46, 5021–5023
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Notes and references
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2 3
4
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2 3
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2
3
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3
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O
2 3
O
2 3
O
8
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over 1000 cycles without any significant decrease in the specific
capacitance. Therefore, the hierarchical rippled Bi O nanobelts
1
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as electrodes show very high electrochemical stability for
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O
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1
2 3
those of hierarchical rippled Bi O nanobelts. Therefore, the
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2 3
hierarchical rippled Bi O nanobelts show a potential application
for electrochemical supercapacitors.
In summary, electrode potential oscillations have been used
for the synthesis of hierarchical rippled nanobelts. The
hierarchical rippled Bi O nanobelts showed a much bigger
2
3
specific surface area than that of nanobelts with smooth
surfaces. These deposited hierarchical rippled Bi nanobelts
1
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O
3
(
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have been successfully employed as supercapacitor electrodes,
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stability were obtained. It is believed that this study will open
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supercapacitor applications because of the low cost associated
with the precursor and the simplicity in the preparation of this
novel nanobelt structure.
1
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and 90923008), Guangdong Province (2008B010600040 and
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251027501000002), and Sun Yat-sen University (09lgpy17).
This journal is ꢀc The Royal Society of Chemistry 2010
Chem. Commun., 2010, 46, 5021–5023 | 5023