Synthesis and electrochemical properties of two types of highly ordered mesoporous MnO2

Article abstract of DOI:10.1016/j.electacta.2009.10.049

Mesoporous MnO₂ with uniform nanorod morphology and mesoporous β-MnO₂ were prepared using SBA-15 and KIT-6 as the templates, respectively. XRD, nitrogen adsorption analysis, SEM, TEM and EDX techniques were used for the structural characterization. The electrochemical properties of the MnO₂ samples were studied using alkaline Zn/MnO₂ batteries in a 9 M KOH electrolyte solution. Compared to the commercial electrolytic manganese dioxide (EMD), the discharge capacity of the mesoporous MnO₂ nanorods increased by 74.98%, 119.74% and 146.19% at constant currents of 50, 250 and 500 mA g^-1, respectively, while the discharge capacity of the mesoporous β-MnO₂ increased by 63.58%, 95.14% and 100.23%.

Full text of DOI:10.1016/j.electacta.2009.10.049

Electrochimica Acta 55 (2010) 1682–1686
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Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Synthesis and electrochemical properties of two types of highly ordered
mesoporous MnO2
Lianxia Lia, Ping Huaa, Xike Tiana,∗, Chao Yanga,b, Zhenbang Pia
a Faculty of Material Science and Chemistry Engineering, China University of Geosciences, Lumo Road 388#, Wuhan 430074, Hubei, PR China
b School of Environmental Studies, China University of Geosciences, Wuhan 430074, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 23 June 2009
Received in revised form 15 October 2009
Accepted 20 October 2009
Available online 29 October 2009
Mesoporous MnO2 with uniform nanorod morphology and mesoporous ␤-MnO2 were prepared using
SBA-15 and KIT-6 as the templates, respectively. XRD, nitrogen adsorption analysis, SEM, TEM and EDX
techniques were used for the structural characterization. The electrochemical properties of the MnO2
samples were studied using alkaline Zn/MnO2 batteries in a 9 M KOH electrolyte solution. Compared to
the commercial electrolytic manganese dioxide (EMD), the discharge capacity of the mesoporous MnO2
nanorods increased by 74.98%, 119.74% and 146.19% at constant currents of 50, 250 and 500 mA g−1
,
Keywords:
respectively, while the discharge capacity of the mesoporous ␤-MnO2 increased by 63.58%, 95.14% and
100.23%.
Mesoporous structure
Manganese dioxide
Alkaline Zn/MnO2 battery
Electrochemical capacity
© 2009 Elsevier Ltd. All rights reserved.
1. Introduction
specific surface areas. Furthermore, several techniques have been
developed for the preparation of nanosized manganese dioxide, and
In modern society, the complexity of electronic equipment con-
tinues to increase and, simultaneously, portability of these devices
is becoming more important (e.g., computers, digital cameras,
phones, and mp3 players). As such, an increasing demand is being
placed on the batteries that are used to power these devices. The
alkaline Zn/MnO2 battery is a popular choice as a portable power
supply due to its good electrochemical properties, favorable cost
structure and low toxicity [1,2]. Despite this popularity, the alkaline
Zn/MnO2 battery exhibits performance limitations. The discharge
efficiency of an alkaline Zn/MnO2 battery is limited by many ele-
ments, such as the ionic diffusion rate and the proton diffusion rate
in the MnO2 cathode [3,4] and the passivation and the corrosion
of the zinc anode [5]. In addition, the low utilization rate of the
manganese dioxide cathode is one of the main factors responsible
for these performance limitations. For example, only 30–40% of the
active material in an alkaline Zn/MnO2 battery is utilized in a high
power electronic device such as a digital camera [6]. Therefore, it
is extremely important to make the traditional alkaline Zn/MnO2
batteries more effective at high discharge rates.
significant progress has been reported [5,7–23].
Nanosized manganese dioxides for electrode materials typi-
cally are fabricated via electrochemical and chemical routes. For
example, Li and co-workers [7,8] have reported the hydrothermal
preparation of ␣-MnO2 nanowires by oxidizing MnSO4 in either
KMnO4 or (NH4)2S2O8. Yuan et al. [11] reported that ␥-MnO2
nanowires can be prepared by facile hydrothermal treatment of
commercial granular ␥-MnO2 crystals. Hu et al. [18,19] reported the
synthesis of hydrated MnOx nanostructured films via a galvanos-
tatic electrodeposition, showing a specific capacitance of 230 F g−1
,
as measured by cyclic voltammetry at 25 mV s−1. Ghaemi et al. [23]
prepared ␥-MnO2 nanowires by employing a galvanostatic tech-
nique in the presence of a surfactant, and these nanowires showed
enhanced rechargeability in alkaline Zn/MnO2 batteries.
However, to the best of our knowledge, few attempts have been
made at investigating the use of mesoporous MnO2 in alkaline
Zn/MnO2 batteries. In this paper, we report the synthesis of two
types of highly ordered mesoporous MnO2 by using mesoporous
silica as a hard template. The mesoporous MnO2 obtained was
directly used in alkaline Zn/MnO2 batteries.
Nanoscale materials exhibit peculiar and fascinating properties
superior to their bulk counterparts. Electrode active materials with
small crystalline particle sizes usually show high electrochemi-
cal activities and good discharge performances due to their high
2. Experimental procedures
2.1. Synthesis of materials
∗
The SBA-15 template was prepared according to earlier
report using non-ionic triblock copolymer [Pluronic P123,
Corresponding author. Tel.: +86 27 67884574; fax: +86 27 67884574.
E-mail address: xktian@cug.edu.cn (X. Tian).
0013-4686/$ – see front matter © 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2009.10.049

L. Li et al. / Electrochimica Acta 55 (2010) 1682–1686
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(EO)20(PO)70(EO)20, EO = ethylene oxide, PO = propylene oxide] as
a surfactant and tetraethoxysilane as a silica source [24]. In a typ-
ical synthesis, Pluronic P123 (4 g) was dissolved in distilled water
(30 g) and 2 M HCl (120 mL) with stirring, followed by the addi-
tion of tetraethoxysilane (TEOS, 8.8 g) at 40 ◦C. This gel was stirred
continuously for 24 h and then was crystallized in a Teflon-lined
autoclave at 120 ◦C for 48 h. After crystallization, the solid product
was filtered and was washed with distilled water. The product then
was dried in air at 100 ◦C for 6 h and finally was calcined at 550 ◦C
for 5 h, which yielded the mesoporous silica SBA-15 powder.
The mesoporous MnO2 with uniform nanorod morphology was
synthesized using SBA-15 as the hard template and manganese
nitrate solution [Mn(NO3)2, 50 wt%] as the manganese source, fol-
lowed by removal of the silica template using a hot solution of 1 M
NaOH. In a typical synthesis, SBA-15 powder (0.2 g) was dispersed
in deionized water (5 mL), and then Mn(NO3)2 (0.5 g, 50 wt%) was
added. The solution was held at room temperature with continu-
ous stirring for at least 4 h. Afterwards, the resulting composite was
dried at 100 ◦C for at least 12 h and finally was calcined at 350 ◦C
for 5 h. The silica template in the composite was carefully removed
by washing twice with heated 1 M NaOH solution for 30 min. The
mesoporous MnO2 with uniform nanorod morphology was col-
lected by filtration and was washed with deionized water until the
pH value of the filtrate was close to 7. The product then was dried
at 110 ◦C for 12 h.
Fig. 1. The powder XRD patterns of (a) mesoporous MnO2 nanorods and (b) meso-
porous ␤-MnO2. Insets (c) and (d) show the corresponding low-angle XRD patterns.
The ␤-MnO2 with regular mesoporosity was synthesized using
mesoporous silica KIT-6 as a template. Mesoporous silica KIT-6
was prepared according to the reported procedure [25,26]. In a
typical synthesis, Mn(NO3)2 (3 g, 50 wt%) was dissolved in ethanol
(12.5 mL), and then KIT-6 (0.5 g) was added to the solution. The mix-
ture was stirred overnight. Then, a powder specimen was obtained,
and the solid was calcined at 350 ◦C for 5 h. The silica template
in the composite was carefully removed by washing twice with
a heated 1 M NaOH solution. The ␤-MnO2 (with an ordered meso-
porous structure) was obtained by filtration followed by sequential
washing with deionized water and ethanol.
working electrodes were punched into plates with a typical
area of 1 cm2 (1 cm × 1 cm). The typical mass load of the active
materials is about 10 mg/cm2. All electrochemical measurements
were carried out at room temperature and at atmospheric pres-
sure.
Cyclic voltammograms were obtained by sweeping the working
electrodes within a potential window of −800 mV to 400 mV using
a scan rate of 0.25 mV s−1
.
In the discharge performances, the working electrodes were
stepped from their open-circuit voltages (OCV) to a cut-off voltage
of −1.0 V at different constant currents of 50, 250 and 500 mA g−1
.
2.2. Characterization of materials
The phase structure and purity of the products were charac-
terized by powder X-ray diffraction (XRD) taken on a Philips XRD
X’PERT PRO diffractometer with Cu K␣ radiation (ꢀ = 1.5418 Å).
Scanning electron micrographs (SEM) and energy-dispersive X-ray
spectroscopy (EDX) measurements were taken on a field emis-
sion scanning electron microscope (FE-SEM) (JEOL JSM-6700F SEM)
equipped with an EDX spectrometer. Transmission electron micro-
graphs (TEM) and the electron diffraction (ED) patterns were
obtained using a JEOL 2010 electron microscope operated at an
acceleration voltage of 200 kV. Nitrogen adsorption and desorp-
tion experiments were carried out on a Micromeritics Tristar
3000 system at 77.3 K. The surface area was calculated using the
Brunauer–Emmett–Teller (BET) equation. Pore size distributions
were calculated by the Barrett–Joyner–Halenda (BJH) method.
3. Results and discussion
Fig. 1a shows the wide-angle X-ray diffraction (XRD) pattern of
the MnO2 prepared using SBA-15 as the template. The very broad
peaks demonstrate that the material is amorphous. The low-angle
XRD pattern (Fig. 1c, inset) exhibits three diffraction peaks; this pat-
tern is characteristic of a 2D hexagonal (p6m) structure, indicating
that the MnO2 prepared using SBA-15 as the template consists of
ordered mesostructured arrays and is a perfect replica of hexag-
onally channeled mesoporous silica (SBA-15). Fig. 1b shows the
wide-angle XRD pattern of the MnO2 prepared using KIT-6 as the
template. Slight broadening of the peaks is likely due to the very fine
grain size and to defects along the channel that were produced dur-
ing the decomposition process. The diffraction peaks are consistent
with the pure tetragonal phase of ␤-MnO2 [space group D42/mnm].
No peaks from other phases have been detected, indicating that the
products are of high purity. Fig. 1d (inset) shows the low-angle XRD
pattern of the ␤-MnO2. The characteristic diffraction peaks of the
Ia3d cubic structure of the mesoporous ␤-MnO2 can be observed,
although the higher-order reflections are neither very pronounced
nor well-resolved.
2.3. Electrochemical measurements
Cyclic voltammetry (CV) experiments and discharge perfor-
mances were both performed in a 9 M KOH electrolyte solution,
with the aid of the electrochemical workstation (CHI660C, CH
Instruments, USA) using a three-electrode arrangement that con-
sisted of a working electrode, a Pt-wire counter electrode and
The SEM image of the prepared mesoporous MnO2 with uniform
nanorod morphology can be found in Fig. 2a. This material exhibits
an interesting micro-scale network of interlocked rods with
macropores of several hundred nanometers. Fig. 2b shows a typ-
ical SEM image of the pure mesoporous SBA-15; it is clear that the
prepared mesoporous MnO2 with uniform nanorod morphology
a
Hg/HgO reference electrode. The working electrodes were
fabricated by compressing a mixture of the active materials
(the mesoporous MnO2 or EMD), conductive material (AB), and
binder [poly(tetrafluorethylene) (PTFE)] in
a weight ratio of
MnO2/AB/PTFE = 75:20:5 onto the nickel foam at 10 MPa. The

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L. Li et al. / Electrochimica Acta 55 (2010) 1682–1686
Fig. 2. The SEM images of the (a) mesoporous MnO2 nanorods, (b) SBA-15, and (c) mesoporous ␤-MnO2.
Fig. 3. The TEM images of the (a) mesoporous MnO2 nanorods and (b) mesoporous ␤-MnO2.
has inherited the rod-like morphology of the SBA-15 template. A
typical SEM image of the mesoporous ␤-MnO2 is shown in Fig. 2c.
Fig. 3 shows typical transmission electron microscopy (TEM)
images of the mesoporous MnO2. Fig. 3a features highly ordered
MnO2 nanorods viewed from the [1 0 0] direction, and these
nanorods are in the same perfect hexagonally mesostructured
arrays as the channels of the SBA-15 mother mold. Energy-
dispersive X-ray spectroscopy (EDX) measurements (not shown)
reveal that the silica host had been completely removed, and there-
fore, the nanorods constitute a self-supported superlattice. The
diameter of the nanorods is ca. 5–6 nm, and this value is similar to
(but slightly smaller than) the pore diameter of SBA-15, which has
a pore diameter of ca. 6–7 nm. This similarity in size indicates that
the MnO2 nanorods have been formed within the pore channels
of SBA-15. When employing KIT-6 (a Ia3d cubic mesoporous silica
material) as an alternative hard template, highly ordered spherical
nanoarrays can be formed. Fig. 3b reveals the [1 1 1] plane of the
Ia3d cubic structured ␤-MnO2 nanospheres. The diameter of the
spheres is similar to that of KIT-6, and these measurements are in
good agreement with the low-angle XRD in Fig. 1d.
Fig. 4 shows the nitrogen adsorption–desorption isotherms and
the pore size distribution curves of the mesoporous MnO2 nanorods
(Fig. 4a) and the mesoporous ␤-MnO2 (Fig. 4b). The isotherms
of these samples are of typical IV classification and exhibit clear
H1-type hysteresis loops, which are characteristic of mesoporous
materials. The mesoporous MnO2 nanorods have a surface area
of 112 m2 g−1, which is much larger than that (23.8 m2 g−1) of
the MnO2 nanorods reported by Kijima et al. [27]. The pore
size distribution of mesoporous MnO2 nanorods averages 3.81 nm
(Fig. 4a, inset), which is slightly smaller than the wall thickness
(3.83 nm) of SBA-15. This data further confirms the replication of
the mesoporous MnO2 nanorods from SBA-15. The mesoporous
Fig. 4. The nitrogen adsorption–desorption isotherms and pore size distributions
(inset) of (a) mesoporous MnO2 nanorods and (b) mesoporous ␤-MnO2.

L. Li et al. / Electrochimica Acta 55 (2010) 1682–1686
1685
Fig. 5. The cyclic voltammograms of (a) commercial EMD, (b) mesoporous MnO2
nanorods and (c) mesoporous ␤-MnO2 in 9 M KOH solution at a scan rate of
0.25 mV s−1
.
␤-MnO2 sample has a surface area of 83 m2 g−1 and a pore vol-
ume of 0.38 cm3g−1; both of these measurements are much larger
than those of conventional ␤-MnO2, which has a surface area of
0.6 m2 g−1 and a pore volume of 0.01 cm3 g−1. Mesoporous ␤-MnO2
has two pore size averages at 4.9 and 18.2 nm (Fig. 4b, inset); the
first number reflects the minimum wall thickness of KIT-6, and the
second corresponds either to the wall junctions in KIT-6 or to the
pores between the particles.
The surface area of our mesoporous MnO2 is low compared with
the templates of SBA-15 and KIT-6, and this attribute is likely due
to the collapsing of large pores during the template etching step.
3.1. Electrochemical properties
Fig. 5 presents cyclic voltammograms of commercial elec-
trolytic manganese dioxide (EMD), mesoporous MnO2 nanorods,
and mesoporous ␤-MnO2 in the potential window of −800 to
400 mA versus Hg/HgO in 9 M KOH. The cyclic voltammogram of
EMD is shown in Fig. 5a; a broad cathodic shape appears at around
−40 mA, and this peak may be composed of two overlapping peaks
that correspond to the reduction of the surface and the interior
manganese dioxide. Alternatively, two anodic peaks at the poten-
tials −220 and 210 mA are probably due to the oxidation of the
surface and the interior MnOOH [28]. The area of the oxidation
peak is smaller than that of the reduction peak, which suggests
that the reversibility of EMD is poor [29]. Cyclic voltammograms of
mesoporous MnO2 nanorods and mesoporous ␤-MnO2 are shown
in Fig. 5band c, respectively. Twocathodic peaksappear in the range
between 100 and −300 mA, and two anodic peaks are observed at
potentials of −480 and 220 mA. Compared to the spectrum of EMD,
the cathodic peaks are shifted to more positive values. In addition,
the area of the oxidation peak is larger than that of the reduc-
tion peak, which suggests that the reversibility of the two types
of mesoporous MnO2 is better.
The discharge performances of the two types of meso-
porous MnO2 were characterized with chronopotentiometric
measurements. The working electrodes were stepped from their
open-circuit voltages (OCV) to a cut-off voltage of −1.0 V in a 9 M
KOH electrolyte solution at different constant currents.
Fig. 6 shows the discharge curves of the mesoporous MnO2
nanorods, mesoporous ␤-MnO2 and commercial electrolytic man-
ganese dioxide (EMD) (surface area of 31 m2 g−1, pore volume of
0.048 cm3 g−1, pore size distribution at 0.7 and 1.5 nm) at room
temperature and at different constant currents of 50, 250 and
Fig. 6. The discharge curves of (a) mesoporous MnO2 nanorods, (b) mesoporous ␤-
MnO2 and (c) commercial EMD in 9 M KOH solution at constant currents of 50, 250
and 500 mA g−1, respectively.
500 mA g−1. From Fig. 6, it is clear that all electrodes exhibit smooth
discharge curves. The mesoporous MnO2 nanorods have an open-
circuit voltage of ca. 0.12 V and a discharge plateau at ca. −0.4 V
at a constant current of 50 mA g−1 (Fig. 6a). The discharge capacity
reaches 430.32 mAh g−1 to a cut-off voltage of −1.0 V. In addition,
the discharge plateaus of mesoporous MnO2 nanorods decrease
to −0.41 and −0.415 V when the constant currents are increased
to 250 and 500 mA g−1, respectively. Accordingly, their discharge
capacities decrease to ca. 344.26 and 291.76 mAh g−1, respectively.
In contrast, the commercial EMD has an open-circuit voltage of
ca. −0.06 V and a discharge plateau at around −0.42 V at a con-
stant current of 50 mA g−1 (Fig. 6c). Its discharge capacity reaches
245.92 mAh g−1, which is lower than that of mesoporous MnO2
nanorods. In addition, the commercial EMD exhibits much poorer
discharge characteristics compared to the mesoporous MnO2
nanorods at high discharge current density. The discharge capaci-
ties of the commercial EMD are merely 156.67 and 118.50 mAh g−1
at constant currents of 250 and 500 mA g−1, respectively. Thus, the
discharge capacity of the mesoporous MnO2 nanorods increased
by 74.98%, 119.74% and 146.19% at constant currents of 50, 250
and 500 mA g−1, respectively, compared to the commercial elec-

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L. Li et al. / Electrochimica Acta 55 (2010) 1682–1686
trolytic manganese dioxide (EMD). However, mesoporous ␤-MnO2
has an open-circuit voltage of ca. −0.04 V and a discharge plateau
at −0.42 V at a constant current of 50 mA g−1 (Fig. 6b). The dis-
charge capacity reaches 402.28 mAh g−1 to a cut-off voltage of
−1.0 V. In addition, the discharge plateaus of mesoporous ␤-MnO2
decrease to −0.425 and −0.43 V when the constant currents are
increased to 250 and 500 mA g−1, respectively. Accordingly, their
and 100.23%, compared to the commercial electrolytic manganese
dioxide (EMD), at constant currents of 50, 250 and 500 mA g−1
respectively. Therefore, the ordered mesoporous MnO2 is
promising cathode material in alkaline Zn/MnO2 batteries. The
mesoporous structure may also provide a new approach for
improving the reactivity of the materials.
,
a
discharge capacities decrease to ca. 305.73 and 237.3 mAh g−1
,
Acknowledgment
respectively. Therefore, the discharge capacity of the mesoporous
␤-MnO2 increased by 63.58%, 95.14% and 100.23% at constant cur-
rents of 50, 250 and 500 mA g−1, respectively, compared to the
commercial electrolytic manganese dioxide (EMD).
We are grateful to the National Natural Science Foundation of
China (Grant No. 50904054) for financial support.
Davis et al. [30] concluded that high power MnO2 performance
is linked to both the BET area and the micropore area. The micro-
pore is associated with both high OCV and fast discharge kinetics,
i.e., with a high power capability, since a high micropore area is
a requirement for high power MnO2. In this paper, the synthe-
sized mesoporous MnO2 has a high micropore area. Therefore,
of the three electrodes, the electrode made of mesoporous MnO2
nanorods exhibits the highest open-circuit voltage, and the EMD
electrode exhibits the lowest.
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4. Conclusion
In summary, two types of mesoporous MnO2 were successfully
synthesized. Electrochemical measurements of alkaline Zn/MnO2
battery showed that the discharge capacity of the mesoporous
MnO2 nanorods increased by 74.98%, 119.74% and 146.19% and
that of the mesoporous ␤-MnO2 increased by 63.58%, 95.14%