Facile preparation of Mn3O4 hollow microspheres via reduction of pentachloropyridine and their performance in lithium-ion batteries

Article abstract of DOI:10.1039/c6ra24803a

Mn₃O₄ hollow microspheres have been facilely prepared via a green synthesis of 2,3,5,6-tetrachloropyridine reduced from pentachloropyridine by manganese. The specific hollow microspheres were made by a H₂ gas bubble-templating method presenting a high specific surface area (87.1 m² g^-1) and a big total pore volume (0.2030 cm³ g^-1). The Mn₃O₄ hollow microspheres as an anode material demonstrate a good electrochemical performance, with a high reversible capacity of 646.9 mA h g^-1 after 240 cycles at a current density of 200 mA g^-1. The good cycling performance is attributed to numerous mesopores, high specific surface area and big total pore volume, which can offer good electrical contact and conductivity as well as accommodate the mechanism strains. In addition, the yield and selectivity of 2,3,5,6-tetrachloropyridine achieved up to 99.2% and 99.5%, respectively.

Full text of DOI:10.1039/c6ra24803a

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Facile preparation of Mn O hollow microspheres
3
4
via reduction of pentachloropyridine and their
Cite this: RSC Adv., 2017, 7, 8264
performance in lithium-ion batteries
Zhan Jiang, Kaihua Huang, Dian Yang, Shuai Wang, Hong Zhong*ab
ab
a
a
ab
and Chongwen Jiang*a
3 4
Mn O hollow microspheres have been facilely prepared via a green synthesis of 2,3,5,6-tetrachloropyridine
reduced from pentachloropyridine by manganese. The specific hollow microspheres were made by a H
2
2
ꢀ1
gas bubble-templating method presenting a high specific surface area (87.1 m
g
) and a big total pore
3
ꢀ1
volume (0.2030 cm
g
3 4
). The Mn O hollow microspheres as an anode material demonstrate a good
ꢀ1
electrochemical performance, with a high reversible capacity of 646.9 mA h g after 240 cycles at
Received 6th October 2016
Accepted 22nd November 2016
ꢀ1
a current density of 200 mA g . The good cycling performance is attributed to numerous mesopores,
high specific surface area and big total pore volume, which can offer good electrical contact and
conductivity as well as accommodate the mechanism strains. In addition, the yield and selectivity of
2,3,5,6-tetrachloropyridine achieved up to 99.2% and 99.5%, respectively.
DOI: 10.1039/c6ra24803a
www.rsc.org/advances
ꢀ
1
16
4
00 mA h g at 0.1C. Wang and Du prepared an order-aligned
1
. Introduction
ꢀ1
3 4
Mn O anode retaining a capacity of 494 mA h g over 100
have drawn considerable interest in many cycles. Gao found that sponge-like Mn
catalysis, ion exhibited a high capacity of 800 mA h g aer 40 charge/
exchange, molecular adsorption, magnetic applications and discharge cycles. Despite achieving better performance, it
3
Recently, Mn
3
O
4
3
ꢀ
O
4
nanomaterial
1
1
–4
5,6

elds including lithium-ion battery (LIB),
7
8
4
9
supercapacitors, etc. Particularly in LIBs applications, Mn
3
O
4
should be noted that the methods used to prepare mesoporous
nanomaterials are coprecipitation, elec-
owing to its relatively low cost, environmentally friendly nature, trospinning, hydrothermal/solvothermal and sol–gel tech-
3 4
has been regarded as a remarkably attractive anode material, architectures Mn O
3,4
1–4,13–18
and abundant natural reserves. Hence, Mn O with various niques, etc.,
which always include high-temperature
3
4
nanostructures have been explored through different routes to processing and excessive consumption of organic agents
improve the electrochemical performance of LIBs. Conse- leading to low yields. On the other hand, high purity Mn source
quently, engineering hollow nanostructure or mesoporous used in these methods, such as MnCl
architectures have been proposed as an effective approach for KMnO , are obtained aer certain processes from manganese
enhancing electrochemical performance because of its unique metal, which will increase the cost of Mn production to
advantages. For instance, the large surface area contributes to some extent. In consideration of practical applications, it is
a large electron/Li-ion contact area between the electrolyte and highly desirable to explore a simple method to produce Mn
, Mn(CH COO) , and
2
3 2
4
O
3 4
3 4
O
electrode solid; the pores provide exible and fast transport from manganese metal with good control of morphology, mild
pathways for the electrolyte ions and free space to alleviate the operating conditions, lower cost and high through-put.
strains caused by signicant volume change from lithium-ion
Even directly using manganese metal as raw materials
to produce Mn , the costs are still too high. To solve this
which have a capacity of 200 mA h g , and a cobalt-doped problem, we turned our attention to better utilization of the
10–13
insertion/extraction.
D. Pasero synthesized pure Mn
3
O
4
O
3 4
ꢀ1
ꢀ
1
14
sample of Mn
Wang synthesized carbon layer coated Mn
3
O
4
exhibited a capacity of 400 mA h g
nanorods which will the cost signicantly be reduced by the generation of high-
retained a capacity of 473 mA h g aer 50 cycles at a current value by-product. The reducibility of manganese is stronger
.
high-grad chemical energy in metallic manganese, in which way
3 4
O
ꢀ
1
ꢀ
1
15
density of 40 mA g .
Deepak P. Dubal reported a mesoporous than that of zinc attributing to higher reduction potential of
stacked Mn O4 nano sheets exhibited a capacity of about Mn/Mn with 1.185. Zinc is widely applied in organic reduction
2
+
3
19–21
such as hydrodeoxygenation and hydrodechlorination.
Additionally, plenty of developed theories on the mechanism of
these organic reductions have suggested that zero valent metal
a
College of Chemistry and Chemical Engineering, Central South University, Changsha
4
b
10083, China. E-mail: zhongh@csu.edu.cn; jcwcsu@csu.edu.cn
just serves as a donor of electrons (reducing agent) to reduce
Hunan Provincial Key Laboratory of Efficient and Clean Utilization of Manganese
+
H
into active hydrogen which is the primary to nish the
Resources, Central South University, Changsha 410083, China
8264 | RSC Adv., 2017, 7, 8264–8271
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22–25
reduction process.
Guided by the above theories and prac- and ltering. The acetate in washing water was then recovered
tical application, it is considered feasible to substitute zinc with and recycled.
manganese as reductant in hydrodechlorination. For example,
it can be used in hydrodechlorination of pentachloropyridine
PCP) for preparing 2,3,5,6-tetrachloropyridine (TECP), a valu-
2
.2 Characterization and analysis
(
Transmission electron microscopy (TEM), high resolution
transmission electron microscopy (HR-TEM), and selected area
electron diffraction (SAED) measurements were obtained from
a JEOL-2100F instrument at an acceleration voltage of 200 kV.
Field emission scanning electron microscopy (FE-SEM) is per-
formed with an JSM-7800F. X-ray diffraction (XRD) analyses
were carried out on Bruker D8 diffractometer. Diffraction
able commercial product as an important intermediate which is
2
6
27
useful in manufacture agrochemical, such as chlorpyriphos,
28
29,30
triclopyricarb, triclopyr and their derivatives.
Meanwhile,
common problems in organic reductions using zinc dust as
31
reducing agent, such as poisonous solvent (acetonitrile) used,
equipment corrosion by using concentrated hydrochloric acid,
2
+
mass of concentrated acid wastewater containing Zn yielded,
ꢁ
ꢀ1
patterns were collected in the range of 2Q ¼ 10–80 under
2
+
can also be hopefully solved. Moreover, generated Mn can
ꢁ
ambient conditions with a scanning rate of 8 min . X-ray
photoelectron spectroscopy (XPS) analysis was conducted by
an ESCALAB 250 with Al K alpha radiation. Nitrogen adsorp-
tion–desorption isotherms were measured on a ASAP 2020
adsorption analyser.
16
easily transform into Mn
3
O
4
.
And the organic solvents,
necessarily used in organics involved reaction, is possibly
benecial to the formation of mesoporous architectures,
32,33
because of their dispersion effect on nanocrystals.
Herein, a facile preparation of two products Mn O hollow
3
4
Chloride pyridine were analysed by a high-performance
liquid chromatography (HPLC) equipped with a C18-WR
column (250 ꢂ 4.6 mm, 5 mm) and an UV detector. The
mobile phase composed 90% methanol (HPLC-grade) and 10%
ultrapure water, and the detective wavelength was 298 nm, with
microspheres material and TECP reduced from PCP by
manganese with a low temperature reaction using water as
hydrogen source and ethanol as inexpensive, non-toxic solvent
followed by a simple aeration step in the same pot, is reported.
The specic hollow microspheres, consisted of Mn
particles possessing high specic surface area of about 87.1 m
3 4
O nano-
ꢀ
1
a ow rate of 1.0 mL min and an injection volume of 20 mL.
2
ꢀ1
g
, self-assembled around the H
macro- and mesoporous structures. In addition, the as-prepared
Mn O hollow microspheres were used as an anode material for The electrodes for electrochemical studies were prepared with
2
gas bubble templates into
2.3 Electrochemical investigation
3
4
a lithium-ion battery to investigate its electrochemical proper- 70 wt% active material of Mn
ties, such as capacity, rate capability, cycle life, etc. Detailed polyvinylideneuoride (PVDF), 20 wt% conducting acetylene
characterization conrms that the Mn
hollow spheres shows black binder in N-methyl pyrrolidinone, grinded for 30 min in
a comparable performance. The strategy of Mn
3 4
O hollow microspheres, 10%
3 4
O
3
O
4
preparation, an agate mortar, thus the slurry was coated on a piece of Cu foil,
substituting zinc with manganese can possibly be extended to and the plate was dried at 80 C under vacuum for 12 hours, the
ꢁ
other organic reductions using zinc dust as reducing agent.
cells were fabricated by using lithium foil as the counter elec-
trode and the reference electrode, Celgard 2300 microporous
membrane as separator, and a solution of 1 mol L LiPF6 in
a mixture of ethylene carbonate (EC) and dimethyl carbonate
ꢀ1
2. Experimental
2
.1 Synthesis of Mn O hollow microspheres and 2,3,5,6-
3 4
(DMC) with volume ratio of 1 : 1 as electrolyte. The assembly of
tetrachloropyridine
the cell was prepared in an argon-lled humidity-free glove box.
In a typical process, 2 g pentachloropyridine (PCP) (Aladdin, And the cells were cycled galvanostatically from 0.01 to 3.00 V at
reagent grade, 98%) was dissolved in 200 mL ethyl alcohol different current rates (Land CT2001A). Cyclic voltammograms
(
Sinopharm Chemical Reagent Co., Ltd, analytic grade, 99%) (CV) were performed on a CHI-760 electrochemical workstation
ꢁ
with vigorously stirring in 40 C. Then 0.6 g pure metallic over a potential range 0.01 to 3.00 V at a scan rate of 0.40 mV
ꢀ
1
manganese (Mn) dust (Aladdin, reagent grade, 99%, 200
meshes) was added into the mixture. Solution of 1.3 g ammo-
s .
4
nium acetate (NH Ac) (Sinopharm Chemical Reagent Co., Ltd,
analytic grade, 99%) dissolved in 5 g water was added drop-wise
3
. Results and discussion
3 4
3.1 Characterization of Mn O hollow microspheres
over a 2 hours' period. Aer agitation for about 4 hours under
ꢁ
the protection of nitrogen, the slurry was heated up to 65 C and As shown in Fig. 1, all the diffraction peaks of the XRD pattern
adjusted the pH value close to 8.0 by addition 20% ammonia- should be indexed to the spinel structure of Mn
que (NH O) solution. At the same time, fresh air was blown of 24-0734, space group of I4
/amd, a ¼ 5.762, b ¼ 5.762, c ¼
into the reaction for 1 h. 9.47), which conrms that these products are pure Mn
Then the mixture was centrifuged and the solids portion was Relatively broad diffraction peaks indicate that Mn crystals
3 4
O (JCPDS card
3
H
2
1
3 4
O .
3 4
O
washed several times with absolute ethanol to remove impuri- are in small sizes. From the width of diffraction peaks and
ꢁ
ties and dried at 60 C for 5 h in air to get the Mn O hollow calculation by the Debye–Scherrer formula, an average particle
3
4
microspheres. 2,3,5,6-Tetrachloropyridine products was ob- size of Mn O is around 9.7 nm.
3
4
tained by decompressing and distilling the centrifugal liquid,
recovering the solvent, washing the residual in the cold water FE-SEM and TEM. The typical SEM image of the Mn
The morphology of the Mn
3
O
4
product was investigated by
product
3 4
O
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concordant with the value obtained from the XRD measure-
ment. Also, there are some defects and vacancies on the surface
of the sphere. Thus, it appears to be unsmooth. The vacancies
and defects are benecial to the Li-ion transport and redox
reaction, which can improve the electrochemical performance
11
of Mn
As high-resolution transmission electron microscopy (HR-TEM)
image of the Mn nanoparticles is shown in Fig. 2e, the lattice
fringes exhibited different crystal planes, which can be identi-
ed in (103), (112), (211) and (200) planes with matching d-
3 4
O as the lithium-ion battery material to some extent.
3 4
O

spacing of 0.2784, 0.3084, 0.2495 and 0.2910 nm, respectively.
Fig. 2f is ring pattern of selected-area electron diffraction
(
(
(
SAED), the rings matched well with (101), (112), (103), (211),
220), (105), (224) planes, as reference to the JCPDS database
card of 27-0734) further demonstrate the tetragonal structure
3 4
Fig. 1 XRD pattern of Mn O hollow microspheres.
of Mn
The specic surface area and pore size distribution of the
synthesized Mn O hollow microspheres were further investi-
3 4
O nanoparticles.
shown in Fig. 2a displays that the crystals are formed in large
scale with good dispersion and uniform diameter of about
3 4
gated by N adsorption–desorption measurements. The adsorp-
2
tion isotherms proles are displayed in Fig. 3. It shows that
Mn O hollow microspheres have a type isotherm of IV adsorp-
3 4
tion–desorption curve with a capillary condensation step and
hysteresis loop which is characteristic of mesoporous materials.
5
00 nm. Moreover, observing from some broken microspheres
shown in the partial enlarged detail in Fig. 2b, it is evident that
these Mn microspheres are in hollow structure. Further-
more, the Mn O microspheres were characterized with TEM to
3 4
O
3
4
3 4
The BET surface area of the Mn O sample is measured to be 87.1
examine their ne structures. Fig. 2c shows that the Mn O
3
4
2
ꢀ1
3
ꢀ1
m g and a total pore volume of 0.2030 cm g , much higher
than the previous reports. For example, the nanotube Mn O
microspheres present a clear hollow structure with loose shell.
A low magnication TEM image of the Mn hollow sphere
shell is shown in Fig. 2d, which manifest that Mn nano-
3
O
4
3 4
2
ꢀ1
present BET surface area about 48.83 m g and a total pore
3 4
O
3
ꢀ1 13
volume of 0.08 cm g
, the mesoporous Mn O has a total pore
3 4
. The pore-size distribution curve (the
crystals were partially aggregated together. Measurement of
about 100 nanocrystals from more HR-TEM images indicates
that most nanocrystal sizes range from 7 to 15 nm, which is
3
ꢀ1 34
volume of 0.150 cm g
inset in Fig. 4), obtained by the Barrette–Joynere–Halenda (BJH)
method, shows the pore size distribution located around at 5 nm.
From the TEM photos in Fig. 2, such pores were formed mainly
by the stacking of nanoparticles. The narrow pore size distribu-
tion and big volume will contribute much to the effective trans-
port and storage of ion at the interface of electrode/electrolyte,
which shows the tremendous potential applications in LIBs,
sensors and electrochemical super capacitors.
Although it is easy to see the hollow sphere product is pure
Mn O with hausmannite crystal structure from the XRD anal-
3 4
ysis and has clean and neat crystal faces from HR-TEM photos,
we further characterized the sample by X-ray photoelectron
spectroscopy (XPS) and analysed with liquid-phase micro
extraction high performance liquid chromatography (LPME-
HPLC) analysis procedure, to investigate if there is chloride
pyridine composition remnant on the surface or wrapped inside
the Mn
of the Mn
3
O
4
nanocrystals. Fig. 4a shows a typical over XPS spectra
3 4
O hollow microspheres, suggesting that the hollow
microspheres test samples are composed of Mn 2p, 3s, 3p, O 1s
and 2s, respectively, as well as a weaker C 1s peak at 284.8 eV
always come from environmental carbon pollution used for the
XPS curve correction. It is clear that N and Cl not detected in the
curve, which substantiates almost no existence of chloropyridine
components in surface of hollow spheres aer washing process.
Fig. 4c depicts the XPS spectrum of Mn 2p, where two peaks
located at 642.19 eV and 653.19 eV can be respectively attributed
to Mn 2p3/2 and Mn 2p1/2 levels. In the Mn 3s spectra (Fig. 4d),
two peaks at 83.40 eV and 89.04 eV with a separation of 5.64 eV
Fig. 2 (a) Representative FE-SEM images of Mn
image of partial enlarged detail (c) TEM image of Mn
3
O
4
and (b) FE-SEM
4
; (d) TEM image
3
O
of partial enlarged detail; (e) HR-TEM image of partial enlarged detail;
f) SAED image of Mn
(
3 4
O .
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Fig. 3
2 3 4
N adsorption isotherms and pore size distribution (insets) of Mn O hollow microspheres.
were observed, which agree well with that of reported for
In the LPME-HPLC analysis procedure, 0.1 g as-synthesis
As for the O 1s spectra shown in Fig. 4b, the asym- Mn sample dissolved in hydrochloric acid, and then the
metric peak was obviously superposed by two peaks a main at transparent solution was transferred into a 10 mL volumetric
29.89 eV and weaker 531.49 eV one, which could be attributed ask and diluted with puried water. 0.5 mL toluene was added
to lattice oxygen (Olatt) and adsorbed oxygen (Oads), respec- to extract the organic compounds for analysing. The result
35,36
3 4
Mn O .
3 4
O
5
3
7
ꢀ7
tively. Adsorbed oxygen (Oads) can be associated with many showed that the residue of TECP was lower than 2.0 ꢂ 10 g in
kinds of species including low coordination situation, oxygen- every one gram Mn O sample and other chloride pyridine
3
4
containing surface contamination and surface chemisorbed compositions were not detected.
oxygen. A higher ratio of Oads/Olatt (in our work is 0.4) could
38
indicate a larger amount of chemisorbed oxygen species, which 3.2 Reaction mechanism and formation processes of hollow
could explain that the as-prepared Mn
have a good interfacial activity.
O
3 4
hollow microspheres microspheres
To study the reaction mechanism and formation process of
Mn hollow microspheres, the source material and interme-
diates were tested by XRD and SEM. The intermediate samples
3 4
O
Fig. 4 XPS spectra of the Mn
3 4
O hollow microspheres (a) survey scan,
2 3 3 4
Fig. 5 XRD pattern of (a) Mn; (b) Mn (OH) Cl; (c) Mn O .
(
b) O 1s, (c) Mn 2p (d) Mn 3s spectra.
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were taken 4 hours aer NH
4
Ac solution were added dropwise at Mn
2
(OH)
3
Cl crystal as shown in reaction (4). Consequently, by
ꢁ
the temperature of 40 C. Fig. 5a shows the XRD pattern of the using manganese powder as reducing agent, water as the
metallic manganese source, which suggests that the source is hydrogen donor, NH Ac as catalyst, alcohol as solvent and in an
4
ꢁ
ꢀ
pure Mn (JCPDS card of 32-0637, space group of I43m, a ¼ 8.912, eco-friendly temperature of 40 C, the yield and selectivity of
b ¼ 8.912, c ¼ 8.912). Fig. 5b shows the XRD pattern of the TECP achieved up to 99.2% and 99.5%, respectively. As the pH
2
+
intermediates, which indicates that the intermediate has value adjusted to 8.0 with NH
3
H
2
O solution, all the Mn
white precipitation. When the air
¼ 7.12). Fig. 5c shows the XRD owed in, its colour apparently turned to brown quickly, which
. Based on the test results, the is the specic phenomenon of Mn(OH) out of all the manga-
possible reaction mechanism of the rst reaction step for nese compounds. Mn(OH) will then dehydrate and generate
a Mn
pnam, a
pattern of nal product Mn
2
(OH)
3
Cl crystal structure (JCPDS card 25-1158 space group transformed into Mn(OH)
2
0
¼ 6.490, b
0
¼ 9.52, c
0
3
O
4
2
39
2
obtaining TECP is described as follows.
Mn O . The reactions can be expressed as eqn (6)–(8).
3
4
+
2+
2
2NH
4
+ Mn / Mn(NH
3
)
+ 2Hc
(1)
Mn
2
(OH)
3
Cl + NH
3
$H
+ 2H O / Mn(OH)
Mn(OH) + O / 2Mn
2
O / 2Mn(OH)
2
+ NH Cl
4
(6)
(7)
(8)
2
2
+
+
Mn(NH
3
)
2
2
+ 2NH
4
(2)
6
2
2
3
O
4
+ 6H
2
O
To explain formation processes of hollow microspheres
clearly, a plausible conjecture involving bubble-templating
process was described in Scheme 1, where the by produced H2
plays the role of bubble templates. Actually, the gas bubble-
templating method has been proved to be a facile process to
2
+
ꢀ
2
Clc + Mn / Mn + 2Cl
(3)
(4)
2
+
ꢀ
+
4
2
Mn(NH
3
)
2
+ 3H
2
O + Cl / Mn
2
(OH)
3
Cl + 4NH
2
Hc / H
2
[
(5) fabricate hollow microspheres of inorganic materials, such as
40
41
42
43
Fe, ZnO, ZnSe, CoOOH, CaCO
rGO. As illustrated in Scheme 1, a certain concentration of H
3
(ref. 44) and Cu2xSe
y
S
1y
/
45
2
+
In reaction (1), catalyst NH
metallic Mn as a hydrogen carrier, where electron transferred
and reactive hydrogen and Mn(NH )
4 3 2
generated. Then, Mn could easily transfer from the surface of
4
attaches on the surface of
was generated by reaction (5) and formed sub-microbubbles. At
the same time, a large amount of Mn (OH) Cl nuclei was
2
3
+
2+
from Mn (0) to NH
produced in solution through the relatively low nucleation
process by reaction (4), leading to a relatively high local
concentration of Mn (OH) Cl. Thus, it inevitably resulted in
2
+
2
+
3 2
manganese powder into the solution in the form of Mn(NH )
2
3
complexes, which is very important for the exposure of intimal
Mn. As in reaction (2) and (3), the reactive hydrogen replaces p-
Cl from PCP selectively, which is a typical hydrodechlorination
Mn
between H
OH) Cl nuclei grow into small size nanocrystals with the
dispersion effect of ethyl alcohol. Additionally, small size H
2
(OH)
3
Cl nuclei diffusing to the gas–liquid interfaces
2
bubbles and liquid solution. Then these Mn -
2
(
3
2
by SN reaction process. At the meantime, substituted Cl gains
2
another electron on the surface of metallic Mn and turned to
bubbles come into collisions in the dispersion system and
coagulate to generate bigger H bubbles, while the Mn (OH) Cl
ꢀ
1
Cl . Unavoidably, reactive hydrogens can easily combine to H
2
2
2
3
2
+
as shown in reaction (5). Mn(NH
3
)
2
will hydrolyse into
nanocrystals on the surface of bubbles assembled into hollow
Scheme 1 Possible mechanism for hydrodechlorination reaction process and formation processes of hollow microspheres.
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2 3
microspheres. Other Mn (OH) Cl nanocrystals may also accu-
mulate on the surface, forming the hollow sphere Mn (OH) Cl
2
3
with a thick shell, which is conrmed by the SEM photo of
Mn (OH) Cl with hollow structure as shown in Scheme 1.
2
3
Driven by reaction (6)–(8), these nanocrystals generated smaller-
volume Mn nanocrystals and le some space or pores
3 4
between nanocrystals in the shell, forming as-prepared Mn O
3 4
O
hollow microspheres with macro- and mesoporous structures.
As a summary, two products 2,3,5,6-tetrachloropyridine and
Mn O hollow microspheres material were prepared in one pot
3
4
via two simple steps with Mn, water, ethyl alcohol and air as
inexpensive, non-toxic reductive agent, hydrogen source, solvent
and oxidizing agent, respectively. With several advantages,
including low temperature, low corrosion to equipment, good
atom economy, organic-free template, low-cost, high conversion
3 4
rate and selectivity, this hollow Mn O microspheres prepara-
tion method was much better than those were previously re-
ported. For example, Jian reported a method based on an in situ
gas blowing mechanism in single aerosol droplets, in which
Mn(NO ) , sucrose and H O used as raw material to synthesize
3
2
2 2
17
hollow Mn
CNSs) as a template and reagent to reduce KMnO
MnO nanospheres, and then the hollow MnO
3 4
were reduced under an atmosphere of H /Ar into hollow Mn O
O
3 4
microspheres. Yue used carbon nanospheres
into hollow
nanospheres
(
4
2
2
2
ꢁ
46
microspheres at 280 C for 3 h. Sun reported a surface-layer-
adsorption and calcination (SLA-C) method for the fabrication
of hollow Mn O microspheres by templating carbonaceous
3
4
47
microspheres. Thus, it can be considered as a facile and green
synthesis technology, as is summarized in reaction (9).
(9)
3.3 Electrochemical performance
st
nd
th
th
Fig. 7 (a) The 1 , 2 , 37 and 200 voltage profiles of the Mn
3
O
4
The electrochemical properties of the as-synthesized Mn O
hollow microspheres were evaluated by cyclic voltammetry (CV)
3
4
ꢀ
1
electrode between 0.01 and 3.00 V at a current density of 200 mA g
b) Cycle performance and coulombic efficiency versus cycle number
.
(
ꢀ
1
of Mn O
3 4
hollow spheres at a current density of 200 mA g . (c) Rate
capabilities with increasing current density.
conducted in the range of 0.01 and 3.00 V at a scan rate of
ꢀ1
0
.40 mV s , which is shown in Fig. 6. During the rst cathodic
process, there was a broad weak peak located at 1.10 V which
disappeared aerwards. This peak can mainly be attributed to
the formation of a solid electrolyte interphase (SEI) layer
because of the decomposition of the electrolyte and formation
of solid-state interface of the Mn
3 4
O hollow microspheres. The
intensive peak which appeared in the low potential is ascribed
0
3 4
to the reduction of Mn O into Mn accompanied by the
generation of Li O. In the following anodic process, it can be
2
0
observed at around 1.3 V that Mn is oxidized to Mn O and
st nd
rd
3 4
Fig. 6 Cyclic voltammetry (CV) curves of the 1
the Mn hollow microspheres at a scan rate of 0.40 mV s between
.01 and 3.00 V.
2
and 3 cycles for
ꢀ
1
Li O is decomposed in the meantime. In the following cycles,
2
3 4
O
the reduction peak shied to a higher voltage about 0.3 V, which
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is primarily due to an irreversible structure change related to the efficient utilization of active material and allow lithium ions
the lithium insertion. Aer the second cycle, the CV curves to transfer easily in and out. The unique structure is also able to
demonstrate good reversibility and stability of the Mn O
hollow microspheres.
accommodate the strain by volume change during conversion
process and maintain the integrity in the reversible growth
3
4
Fig. 7a shows the cycling stability curve of the Mn
3
O
4
hollow process of polymeric gel-like lm.
We also investigated the rate capability of Mn
and 0.01 V at a current density of 200 mA g over 240 cycles. microspheres at increased stepwise current densities from 100
microspheres, examined by charging/discharging between 3.00
3 4
O hollow
ꢀ
1
ꢀ1
ꢀ1
The electrode has a large initial discharge capacity of about mA g to 1500 mA g between 0.01 and 3.00 V with each
ꢀ
1
1
577.8 mA h g . However, the coulombic efficiency for the rst current density tested for 8 cycles (Fig. 7c). At current density of
ꢀ1
ꢀ1
cycle was 46% with the rst charge capacity of 720.48 mA h g
,
100 mA g , it delivered an initial capacity of about 955 mA h
ꢀ1
ꢀ1
then the discharge capacity gradually dropped to 448.2 mA h
g
g
, then reduced to 718 mA h g gradually. Even at 1500 mA
ꢀ
1
th
ꢀ1
g
at the 38 cycle, while the coulombic efficiency increased
the Mn O hollow microspheres can still deliver a specic
3
4
ꢀ1
to 93% sharply at the second cycle, then gradually increased to capacity of nearly 200 mA h g . When the test current density
and maintained at between 95–100% in the following several returns to 100 mA g again, the capacity recovered to 645 mA h
ꢀ
1
ꢀ
ꢀ1
1
hundred cycles (Fig. 7b). The capacities of Mn
3
O
4
exhibited
g
g
, which was close to the capacity at the initial rate of 100 mA
th
a rising trend from the 39 cycle, and the electrode retains an
, indicating a good reversibility of the Mn
hollow microspheres
cycle to the 240 cycle. The Mn O hollow microspheres elec- showed good electrochemical properties and huge application
3 4
O hollow
ꢀ1
th
average reversible capacity of 637.2 mA h g during the 130
3 4
microspheres. Thus, as-prepared Mn O
th
3
4
ꢀ
1
trode still retains a reversible capacity of 646.9 mA h g aer potential in high capacity LIB anode materials.
th
total around 240 cycles. Such a rising trend of capacity
th
th
between the 38 –130 is normally observed in transition metal
1,48–51
4. Conclusions
oxides and is well-documented in literatures.
It is
considered to be attributed to the reversible growth process of
a polymeric gel-like lm resulting from kinetically activated
electrolyte degradation. In terms of discharge capacity and
cycling stability, our electrode performs better than some
previously reported Mn O electrode.
In summary, a new facile and green route for the preparation of
Mn O hollow microspheres and 2,3,5,6-tetrachloropyridine in
3 4
one pot via two simple steps was developed using Mn, water,
ethyl alcohol and air as inexpensive non-toxic reductive agent,
hydrogen source, solvent and oxidizing agent, respectively.
3
4
The charge/discharge proles of the hollow Mn O micro-
3
4
3 4 2
Mn O hollow microspheres was made by H gas bubble-
th
th
spheres in the 1st, 2nd, 37 , and 200 cycles for the Mn
3 4
O
templating method presenting a high specic surface area
hollow microspheres electrode cycled between 3.00 and 0.01 V
2
ꢀ1
3
ꢀ1
(
87.1 m g ) and a big a total pore volume (0.2030 cm g ). The
ꢀ
1
at a current density of 200 mA g are shown in Fig. 6a. In the
rst discharge curve, it is observed a sloping voltage from 2.00
to 0.35 V is attributed to the generation of solid-electrolyte
Mn O hollow microspheres electrode shows a good electro-
3
4

chemical performance with a reversible specic capacity of
ꢀ1
ꢀ1
6
46.9 mA h g at a current density of 200 mA g aer 240
3
+
2+
interphase (SEI) lm and the reduction of Mn to Mn . The
well-dened voltage plateau at 0.35 V is related to the main
cycles. In addition, the yield and selectivity of 2,3,5,6-tetra-
chloropyridine achieved up to 99.2% and 99.5%, respectively.
Above all, the whole process has several advantages, including
low temperature, low corrosion to equipment, good atom
economy, surfactant and/or solid free template, low-cost, high
conversion rate and selectivity and short reaction process. The
2
+
0
reduction of Mn to Mn . In the charge curve, the Mn O
3
4
hollow microspheres electrode shows a gentle incline in the
voltage range between 1.0 and 1.5 V, which is associated with
0
2+
3+
the oxidation from Mn to Mn /Mn . In comply with the CV
results, in the second cycle the lithiation plateau moves to
a higher voltage of about 0.65 V and the sloping voltage rapidly
decreased from 1.75 V to 1.00 V which are attributed to an
irreversible capacity loss of 54%, resulted from the phase
transformation in the rst cycle. As the cycle times increase
2,3,5,6-tetrachloropyridine will signicantly reduce the
production costs of Mn product. The strategy of Mn
3
O
4
3 4
O
preparation, substituting zinc with manganese can possibly be
extended to other organic reductions using zinc dust as
reducing agent.
nd
th
from 2 cycle to 37 cycle, the lithiation plateau continue
decreasing to a lower voltage of about 0.5 V, which is attributed
to the continuing phase transformation occurred in the Acknowledgements
th
conversion process. The lithiation plateau of the 200 cycle
hardly changed compared with the 37 cycle, but the voltage
th
This work was nancially supported by National Science and
Technology Support Plan of China (2015BAB17B01) National
Natural Science Foundation of China (21376273) and the
Hunan Provincial Science and Technology Plan Project, China
decrease from 2.00 V to 0.50 V is much slower, which contrib-
utes a lot to the increase of the reversible capacity, and it also
conrms the dominant inuence on Mn O /Li cell capacity
3
4
(No. 2016TP1007).
from the reversible growth of polymeric gel-like lm.
The perfect electrochemical performance of the synthesized
3 4
Mn O hollow microspheres could be associated with the big
specic surface area and the big total pore volume of the macro-
Notes and references
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