Carbon nanotubes chemically modified by metal phthalocyanines with excellent electrocatalytic activity to Li/SOCl2 battery

Article abstract of DOI:10.1149/2.0611706jes

Carbon nanotubes (CNTs)-templated metal phthalocyanines (MPc) (M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II)) assemblies (CNTs-CONH-MPc) were synthesized and characterized by IR, XRD, SEM, XPS. The lithium-thionyl chloride (Li/SOCl2) cells using CNTs

Full text of DOI:10.1149/2.0611706jes

A1140
Journal of The Electrochemical Society, 164 (6) A1140-A1147 (2017)
0
013-4651/2017/164(6)/A1140/8/$37.00 © The Electrochemical Society
Carbon Nanotubes Chemically Modified by Metal Phthalocyanines
with Excellent Electrocatalytic Activity to Li/SOCl Battery
2
a
a
a
a
b
c
Yan Gao, Siwen Li, Xiao Wang, Ronglan Zhang, Gai Zhang, Ying Zheng,
a,z
and Jianshe Zhao
aKey Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, Shaanxi Key
Laboratory of Physico-Inorganic Chemistry, College of Chemistry & Materials Science, Northwest University,
Xi’an 710069, People’s Republic of China
b
School of Materials and Chemical Engineering, Xi’an Technological University, Xi’an 710021,
People’s Republic of China
c
Department of Chemical Engineering, University of New Brunswick, Fredericton, New Brunswick E3B 5A3, Canada
Carbon nanotubes (CNTs)-templated metal phthalocyanines (MPc) (M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II)) assemblies
(CNTs-CONH-MPc) were synthesized and characterized by IR, XRD, SEM, XPS. The lithium-thionyl chloride (Li/SOCl2) cells
using CNTs-CONH-MPc as catalysts showed excellent performance, which the capacities increased by 15.44–88.49%, and the initial
voltages improved to 3.09–3.22 V. The sequence of the electrochemical catalytic performance of CNTs-CONH-MPc was ranked
by central metal ion: Co > Ni > Mn > Fe > Cu > Zn. Based on cyclic voltammetry measurements, the reasonable mechanism
is proposed and the role of catalyst is verified. The modified CNTs by MPc greatly promoted the electronic transmission, which
significantly improved the performance and the initial voltage of Li/SOCl2 battery.
©
2017 The Electrochemical Society. [DOI: 10.1149/2.0611706jes] All rights reserved.
Manuscript submitted December 28, 2016; revised manuscript received February 21, 2017. Published March 31, 2017.
In the 1970s, thionyl chloride battery as a new type of efficient
chemical power causes the wide attention of scientific research work-
In this paper, metal phthalocyanines modification of carbon nan-
otubes are synthesized and used as electrocatalysts for the Li/SOCl
battery. The results show that CNTs and metal phthalocyanines are
linked covalently and the modified CNTs possess high electrocatalytic
2
ers. Li/SOCl
2
battery possesses several prominent characteristics such
as high specific energy, high voltage and low temperature performance
as well as long life in the storage, which makes this type of batteries
2
effect on Li/SOCl battery. The modified CNTs cannot only lengthen
1
exclusive in some extreme conditions. Due to its many unique char-
the discharge time, but also improve the initial voltage of the bat-
tery. In addition, the catalysis mechanism of the CNTs-CONH-MPc
is speculated and demonstrated by the cyclic voltammetry results.
acteristics, Li/SOCl
sea exploration and consumer industry. However, one of limitations
of Li/SOCl battery is that the actual voltage value is far less than
the theory value (3.65 V). Extensive works have been done to in-
crease the practical energy of Li/SOCl battery by adding catalysts
2
battery is widely applied in petroleum mining,
2
,3
2
2
Experimental
4
–8
into electrolyte.
Materials and characterizations.—Carboxylic multi-walled car-
bon nanotubes was purchased from Chengdu Institute of Organic
Chemistry, Chinese Academy of Sciences. All other reagents were of
analytical grade without further purification.
Carbon nanotubes (CNTs), a new carbon derivatives, possess high
specific surface, prominent electrical conductivities and unique chem-
9
ical properties. In addition, CNTs have conjugated structure, thermal
stability and electrochemical property, which attract widespread at-
tention. Recently, Carbon nanotube is widely used in electrochemical
IR spectra were recorded by using a Germany BRUKER VECT022
−
1
10
analyzer with KBr pellets in the infrared region of 400–4000 cm
SEM spectra were tested on a Holland ESEM-FEG, Quanta
00FEG.
XRD patterns were employed by using a Bruker D8 Advance
.
materials, due to its unique structure and excellent performance.
Furthermore, metal phthalocyanine compounds as functional organic
materials are widely used in different fields such as solar cell, sensor,
4
light-emitting device and nonlinear optical material.1
1,12
Phthalocya-
diffractometer equipped with Cu-Kα radiation in the 2θ range
nine compounds present certain unique characteristics derived from
having two-dimensional conjugated π-electronic structure. For in-
stance, phthalocyanines can form complex with different metal ele-
ments by accommodating metal elements in the center of the ring; n ad-
dition to good chemical stability, Phthalocyanines are both good elec-
tron donors and good electron acceptors. Besides, metal phthalocya-
◦
of 5–80 .
The XPS spectra were measured on an American PE company
HI-540 X-ray photoelectron spectrometer.
The Cyclic Voltammetry was performed on a Chinese Zhengzhou
Shiruisi Technology Co. Ltd. RST5000 electrochemical workstation.
1
3
14
nines show excellent catalytic chemistry, photodynamic therapy,
electrochemical and photosensitizing properties.1
5–17
Over decades,
Catalyst preparation.—The chemically modified CNTs by met-
all phthalocyanines (MPc) were prepared as following the method
outlined in Scheme 1.
many research efforts have been focused on the phthalocyanine com-
pounds. Yun Sung Lee and Kee Suk Nahm has studied the influence
of phthalocyanine metal complexes to Lithium-Air battery. It is found
that the phthalocyanine metal complexes have better battery catalytic
18
activities. Chen et al. have studied the carbonyl-substituted phthalo-
cyanine compounds, they found that materials with high specific ca-
pacity for lithium-ion battery.19 In recent years, our group has studied
Synthesis of 2,9,16,23-tetranitro-metallophthalocyanine.—The
2,9,16,23-tetranitro-metallophthalocyanines {MTnPc [M = Mn(II),
Fe(II), Co(II), Ni(II), Cu(II), Zn(II)]} were synthesized by sol-
vent method. As a route to synthesize FeTnPc, a mixture of 3.00
g 4-nitrophthalimide, 1.20 g FeCl · 4H O, 3.00 g urea, 0.10 g
the influence of different phthalocyanine compounds on Li/SOCl
battery, and we found that the phthalocyanine compounds show good
2
2
2
20,21
catalytic performance to Li/SOCl
2
battery.
The main reason is that
4 2 2 7 4
(NH ) Mo O , 1.50 g NH Cl was blended and grinded fully in a
the delocalized and weakly bound character of π electron clouds in
agate mortar. The grinded mixture was added into a 250 mL three-
necked flask with 30 mL jet fuel. The mixture was continually stirred
ligand phthalocyanine rings and the d electrons in central transition
metal ions can promote electronic gain and loss.2 Thus, phthalocya-
2
◦
at 185 C for 4 h, and then the dark blue solid was generated.
nines can improve electron transfer as catalysts.
Purification: When cooling to ambient temperature, the original
product was refluxed in 2% HCl solution for 8 h, then the solid was
filtered off using G4 funnel under vacuum. The product was refluxed
zE-mail: jszhao@nwu.edu.cn
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Journal of The Electrochemical Society, 164 (6) A1140-A1147 (2017)
A1141
Scheme 1. The synthetic reaction of the MTnPc, MPc and CNTs-CONH-MPc.
in petroleum ether, acetone and dichloromethane for 4 h, respectively.
And the precipitate was filtered off using G4 funnel, then the filter
cake was washed with 2% NaOH solution until the filtrate became
neutral. Finally, the product was refluxed in distilled water and ethyl
ZnTnPc - blue green powder, yield 2.30 g (20.26%), and m.p.
>300 C, IR (KBr pellet, cm ): 1333, 1517, 1407, 1598, 1104, 1038,
750.
◦
−1
MnTnPc - blue green powder, yield 2.40 g (20.87%), and m.p.
◦
◦
−1
alcohol, respectively. After filtered, the filter was dried at 100 C for
>300 C, IR (KBr pellet, cm ): 1340, 1518, 1407, 1605, 1126, 1089,
8
h, then dried under vacuum for 24 h to obtained the powder FeTnPc.
Other compounds were synthesized by the same method, only the
FeCl O was replaced.
723.
2
· 4H
2
Synthesis of tetraamino-metallophthalocyanine.—Tetraamino-
metallophthalocyanines were synthesized by means of the gen-
eral method. The general synthesis method of tetraamino-
metallophthalocyanine was as follows: 1.50 g FeTnPc was dissolved
in 15mL DMF in a three-necked bottle and heated under stirring.
The results of basic information of the compounds listed as follows
provide evidence to the structure of the proposed complexes.
FeTnPc - blue green powder, yield 2.51 g (22.37%), and m.p.
◦
−1
>
7
300 C, IR (KBr pellet, cm ): 1340, 1524, 1487, 1613, 1134, 1082,
21.
CoTnPc - blueviolet powder, yield 2.70 g (23.98%), and m.p.
◦
When the mixture was heated to 60 C, 5.8 g sodium sulfide nonahy-
drate was added to the solution, and refluxed for 24 h. The mixture
was poured into 150 mL distilled water after the product cooled to
the room temperature. The resulting product was filtered off using G4
funnel. The precipitate was repeatedly washed with 2% HCl solution
and 2% NaOH solution, respectively. Then, the product was refluxed
again in distilled water and ethyl alcohol for 4 h, respectively. The
◦
−1
>
7
300 C, IR (KBr pellet, cm ): 1347, 1510, 1498,1606, 1155, 1097,
36.
NiTnPc - blue violet powder, yield 3.20 g (28.42%), and m.p.
◦
−1
>
7
300 C, IR (KBr pellet, cm ): 1353, 1536, 1457, 1619, 1110, 1037,
56.
CuTnPc - azure powder, yield 3.60 g (31.86%), and m.p. >300 C,
◦
◦
filtered product was dried at 100 C for 8 h, and dried in vacuum
desiccator for 24 h. Finally, the product was obtained.
−
1
IR (KBr pellet, cm ): 1355, 1532, 1421, 1605, 1155, 1082, 728.
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Journal of The Electrochemical Society, 164 (6) A1140-A1147 (2017)
The results of IR spectra of the compounds listed as follows provide
evidence to the structure of the proposed complexes.
FePc–atrovirens powder, yield 0.42 g (35.01%), and m.p. >300 C,
◦
−
1
IR (KBr pellet, cm ): 729, 1041, 1123, 1612, 1441, 3346,
456.
CoPc–atrovirens powder, yield 0.40 g (31.75%), and m.p. >300 C,
3
◦
−
1
IR (KBr pellet, cm ): 753, 1089, 1141, 1621, 1434, 3329, 3421.
◦
NiPc–atrovirens powder, yield 0.60 g (47.62%), and m.p. >300 C,
−
1
IR (KBr pellet, cm ): 744, 1064, 1179, 1631, 1419, 3329, 3419.
◦
CuPc–atrovirens powder, yield 0.39 g (30.95%), and m.p. >300 C,
−
1
IR (KBr pellet, cm ): 747, 1078, 1145, 1619, 1427, 3339, 3486.
◦
ZnPc–atrovirens powder, yield 0.37 g (29.37%), and m.p. >300 C,
−
1
Figure 1. The structure diagram of cyclic voltammetry.
IR (KBr pellet, cm ): 736, 1037, 1165, 1627, 1436, 3357, 3428.
MnPc–atrovirens powder, yield 0.25 g (19.84%), and m.p.
300 C, IR (KBr pellet, cm ): 718, 1051, 1077, 1624, 1482, 3369,
◦
−1
Results and Discussion
>
3
487.
IR Spectra.—IR spectra of CNTs (a), CNTs-CONH-CuPc (b),
CuPc/CNTs (mixed) (c) and CuPc (d) are carried out (Fig. 2). It can
be seen from 2a that the absorption peaks of CNTs are not obvious,
which is coincide with previous report. As seen from 2d, the double
peaks corresponding to amino group are in the region of 3428–3490
Synthesis of CNTs-CONH-MPc.—0.2 g CNTs and 10 mL DMF
were added into the 100 mL three-necked bottle with stirring and
heated under the N atmosphere. When the temperature reached 76 C,
23
◦
2
−
1
5
mL SOCl
2
was added dropwise into the solution within 1 h. The
cm . Combining with the characteristic peaks of phthalocyanine,
◦
−1
mixture was reacted for 24 h at 76 C, and then evaporated the resid-
such as the C=N and C=C stretching vibration peaks at 1400 cm
◦
−1
ual SOCl
2
. When the temperature reduced to 60 C, 0.4 g MPc was
and 1600 cm , respectively, the strong peaks of the backbone ring of
−1 −1 −1
poured to the mixture, and then 1 mL triethylamine was dropped to the
solution with a dropping funnel. After 48 h, the mixture was cooled, fil-
tered, refluxed with acetone, dried at 100 C for 8 h, and dried for 24 h
in vacuum. Finally, the product of CNTs-CONH-MPc was gained.
The result of IR spectra of CNTs-CONH-MPc and basic information
provide evidence for the formation.
MPc at 1120 cm , 1050 cm , 750 cm , it confirms that the CuPc is
24
−1
−1
synthesized. The new stretches at 1697 cm and 3341 cm in 2b
can be assigned to the amido bond stretching vibration, and the FT-IR
spectra of 2c do not contain signals associated with the amido bond,
which proves the CNTs chemically modified by CuPc.
◦
CNTs-CONH-FePc–dark blue powder, yield 0.43 g (31.75%), IR
XRD analysis.—The XRD patterns of CNTs, CNTs-CONH-CuPc,
CuPc/CNTs (mixed) and pure CuPc are showed in Fig. 3. The diffrac-
tion patterns of pure CNTs exhibits two weak and broad peaks at
−
1
(
(
(
(
(
(
KBr pellet, cm ): 1650, 3426, 1436, 1605, 1112, 1031, 736.
CNTs-CONH-CoPc–dark blue powder, yield 0.38 g (63.33%), IR
−
1
◦
◦
KBr pellet, cm ): 1701, 3431, 1413, 1613, 1134, 1082, 773.
CNTs-CONH-NiPc–dark blue powder, yield 0.73 g (81.11%), IR
2θ = 25.2 and 44.6 , which correspond to the (002) and (101) re-
flections, respectively. As for the pattern of CuPc, six characteristic
−
1
◦
◦
◦
◦
◦
◦
KBr pellet, cm ): 1698, 3393, 1407, 1607, 1163, 1079, 728.
CNTs-CONH-CuPc–dark blue powder, yield 0.32 g (56.14%), IR
peaks are at 2θ = 17.2 , 22.3 , 27.2 , 28.8 , 30.1 and 32.5 , respec-
tively. All diffraction peaks appeares in the low angle range, which
conforms to the complex characteristic peak. The diffraction pat-
−
1
25
KBr pellet, cm ): 1697, 3341, 1413, 1613, 1155, 1089, 756.
CNTs-CONH-ZnPc–dark blue powder, yield 0.32 g (57.14%), IR
terns of CNTs-CONH-CuPc show both characteristic peaks of CuPc
and the CNTs, which further confirms that CuPc bonding with CNTs.
For CuPc/CNTs (mixed), five diffraction peaks can be observed at
−
1
KBr pellet, cm ): 1716, 3426, 1413, 1610, 1134, 1031, 7158.
CNTs-CONH-MnPc–dark blue powder, yield 0.29 g (76.32%), IR
−
1
◦
◦
◦
◦
◦
KBr pellet, cm ): 1707, 3345, 1473, 1618, 1097, 1031, 713.
2θ = 6.5 , 7.3 , 9.1 , 27.3 , 31.8 . The XRD results manifest that
CNTs and CuPc form CNTs-CONH-CuPc.
Electrochemistry testing.—The whole experiment process was
SEM analysis.—SEM images of CNTs, CNTs-CONH-CuPc,
CuPc/CNTs (mixed) and pure CuPc are showed in Fig. 4. SEM
conducted in the glove box with argon gas, in which the relative hu-
midity of atmosphere was less than 2%, and the temperature was kept
◦
at 20–23 C. All experimental equipment was kept dry. Carbon film,
lithium plate and diaphragm were combined to make experimental
battery. 2 mg catalyst (CNTs-CONH-MPc) was added to 2 mL elec-
trolyte, and the mixture was injected into the battery. The discharge
test for the assembled battery was evaluated with a constant resistance
of 40 ꢀ until the voltage reached to 2 V. The blank experiment was
conducted without any catalyst. In this progress, the relation between
the output voltage (U) and the discharge time (t) was measured.
Cyclic voltammetry.—The cyclic voltammetry measurement was
conducted on RT5000 electrochemical workstation. The structure di-
agram of cyclic volammetry was showed in Fig. 1. The test was
carried out with three-electrode system: glassy carbon electrode as
the working electrode, two lithiums acted as the reference electrode
and auxiliary electrode, respectively. Before the tests started, copper
wire was handled with sandpaper, glassy carbon electrode was pol-
2 3
ished with Al O powder and then washed with alcohol. The whole
experiment process was conducted in the glove box, in which the rel-
ative humidity of atmosphere was less than 2%, and the temperature
◦
was kept at 20–23 C.
Notes: 1-working electrode, 2-reference electrode, 3-auxiliary
electrode, 4-SOCl
2
/LiAlCl
4
electrolyte, 5-glass container, 6-lithium
Figure 2. IR spectra of a: CNTs, b: CNTs-CONH-CuPc, c: CuPc/CNTs
plate, 7-copper wire.
(mixed), d: CuPc.
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Journal of The Electrochemical Society, 164 (6) A1140-A1147 (2017)
A1143
Figure 3. X-ray diffraction spectra of a: CNTs, b: CuPc, c: CNTs-CONH-
CuPc, d: CuPc/CNTs (mixed).
Figure 4. SEM image of a: CNTs, b: CNTs-CONH-CuPc, c: CuPc/CNTs
(
mixed), d: CuPc.
examination of CNTs reveals that the morphology of CNTs is tubular
(
Fig. 4a). The morphology analysis on the CNTs-CONH-CuPc shows
that the CuPc is linked to the CNTs (Fig. 4b), and no obvious gap
between them. Compared Fig. 4c with Fig. 4b, the CuPc particle is
suspended in the CNTs surface, not formed bond between CNTs and
CuPc. The SEM of CuPc shows irregular bulk morphology (Fig. 4d).
SEM study indicates that the CuPc bonds with CNTs and forms target
product.
X-ray photoelectron spectroscopy analysis.—In order to obtain
chemical state information of CNTs-CONH-CuPc, XPS analysis has
been conducted (Fig. 5). The diffraction signals of carbon, nitrogen,
oxygen and copper exist in the whole scanning spectrum, which the
diffraction peaks locating at about 290 eV, 400 eV, 532 eV, 940 eV
are assigned to the C1s, N1s, O1s, Cu2p, respectively (Fig. 5a). The
Figure 5. a: XPS whole scanning spectra in CNTs-CONH-CuPc, b: core level spectra of Ni2p, c: core level spectra of C1s, d: core level spectra of N1s.
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A1144
Journal of The Electrochemical Society, 164 (6) A1140-A1147 (2017)
Figure 7. The cell capacity of Li/SOCl2 battery CNTs-CONH-MPc
(M = Mn,Fe, Co, Ni, Cu, Zn).
Figure 6. The U-t curves of Li/SOCl2 battery.
expended Cu2p region reveals two strong peaks with binding energies
at 954.6 eV (2p1/2) and 934.8 eV (2p2/3) (Fig. 5b). The analysis of
the C1s region manifests one characteristic peak at 285.4 eV, which is
corresponding to the C-N bond (Fig. 5c). The N1s energy level signal
is located at 398.58 eV, which is attributed to the nitrogen atoms of
the C=N in phthalocyanine ring (Fig. 5d). The XPS results further
certify that the CNTs are chemical modified by the CuPc through the
covalent bond.
Electrocatalytic performance.—Fig. 6 shows the discharge curves
of Li/SOCl battery electrocatalyzed by CNTs and CNTs-CONH-
2
MPc (M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II)). The blank
represents the battery in absence of catalyst, and the initial voltage
and the discharge time of blank experiment are 3.13 V and 607 s,
respectively. It shows that the battery performances of CNTs-CONH-
MPc and CNTs are better than that of blank. The different center metal
ions of CNTs-CONH-MPc lead to the different catalytic activities. The
results show that the electrocatalytic performance is relate to the metal
ions. The reason is that the electrons of the metal ions are shifted into
phthalocyanine rings, resulting in acceleration of the catalytic reaction
rate. In comparison to the different central metal ions, the discharge
time of the battery with CNTs-CONH-CuPc is the longest among the
tests (1342 s), and the initial voltage of the battery with CNTs-CONH-
CuPc is the maximum among the measurements (3.22 V).
Figure 8. The cell capacity increasing rate of Li/SOCl2 battery CNTs-CONH-
MPc (M = Mn, Fe, Co, Ni, Cu, Zn).
15.44–88.49%, and the cell capacity of CNTs-CONH-CoPc is ex-
tended to 95.84 mA · h.
The capacity and the rate capability of the battery are used to eval-
All the data indicate that the catalysts can improve the performance
uate performance of Li/SOCl
2
battery electrocatalyzed by catalyst.
of Li/SOCl battery. The main reason is that the carbon nanotube can
2
The cell capacity of Li/SOCl
2
battery is:
promote the electronic transmission, and the phthalocyanine has good
ꢀ
ꢀ
conjugative effect and enough number of catalytic active sites. When
CNTs is bonding with MPc, the synergistic effect between CNTs and
MPc can greatly enhance the performance of the Li/SOCl battery.
2
C = ∫ Idt = ∫ U/Redt =
U/Redt = 1/Re
Uꢁt
[1]
Where I is the discharge current, U stands for the output voltage, Re
stands for the electrical resistance, ꢁt represents the time of discharge.
The cell capacity increasing rate of Li/SOCl
X = (C C )/C · 100
are the capacity of the Li/SOCl
2
battery is:
Table I. The Performance of CNTs-CONH-MPc to Li/SOCl2.
battery battery capacity
0
0
[2]
battery and the blank
Where C and C
experiment, respectively.
0
2
initial
discharge capacity
increase
rate (%)
CNTs-CONH-MPc voltage(V) time(s) (mA · h)
The capacity of the battery electrocatalyzed by CNTs-CONH-
CoPc is 95.84 mA · h, which is higher than that of the blank (50.68
mA · h) by the rate of 88.49% (Fig. 7 and Fig. 8).
Blank
CNTs
Co(II)
Cu(II)
Fe(II)
Mn(II)
Ni(II)
Zn(II)
3.09
3.17
3.20
3.22
3.18
3.20
3.19
3.19
810
773
1342
919
1028
1049
1196
817
50.68
57.67
95.84
73.98
73.09
74.23
86.46
58.54
13.79
88.49
34.43
42.39
46.45
69.02
15.44
The electrical testing results are listed in Table I. The maximum
2
initial voltage of Li/SOCl battery catalyzed by CNTs-CONH-CuPc
can reach 3.22 V, and the discharge time of CNTs-CONH-CoPc
is increased to 1342 s. Compared with blank test, the cell capac-
2
ities of Li/SOCl battery catalyzed by CNTs-CONH-MPc rise by
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Journal of The Electrochemical Society, 164 (6) A1140-A1147 (2017)
A1145
Figure 10. Comparative cyclic voltammetries of a: blank, b: CuPc, c: CNTs-
CONH-CuPc, d: CNTs e: CuPc/CNTs (mixed).
Figure 9. Cyclic voltammogram of the Li/SOCl2 battery. Scan rate was
−
1
1
00 mV s
.
Cyclic voltammetric analysis.—Cyclic voltammograms are con-
ducted to further investigate the electrocatalytic behavior and the elec-
trocatalytic mechanism. The CVs of bare and CNTs-CONH-MPc in
nine has good conjugative effect and abundant catalytic active sites.
So, the electrocatalytic performances of the CNTs bonding with MPc
performs best among them.
1
.47 mol/L electrolyte are showed in Fig. 9. Two current peaks are
observed at 2.6 V and 3.6 V, which are assigned to reductions of
SOCl and SCl , respectively. That is, two reduction reactions occur
In order to investigate the function between the phthalocyanine
and the CNTs, the cyclic voltammetric curves are also recorded by
different scan rates. Fig. 11 shows CV curves at different scanning
rates (40 ∼ 100 mV/s) in LiAlCl /SOCl solution containing CNTs-
2
2
in battery system (shown in Eqs. 3 and 4). And The high current peak
at 2.6 V, which means that Eq. 3 is the rate-controlling step for the
4
2
CONH-CuPc. It can be seen that the reduction peaks are enhanced
with the raise of the scanning rate. A linear equation is obtained by
reductive reaction of SOCl
of battery is irreversible.
2
. Due to no oxidation peak, the reaction
fitting the data (log ipc vs log v (i : current of the rate-controlling step,
pc
+ Cl−
v: scan rate)) (Fig. 12). The obtained linear equation is y = 36.654x
SOCl
2
+ e → 1/2 SCl
2
+ 1/2 SO
2
[3]
−
101.97, with the correlation coefficient of 0.9845, which indicates
the function of electrode surface is mainly diffusion control.
1
/2 SCl
2
+e → 1/2 S + Cl−
[4]
Catalytic mechanism.—Other group has studied the cat-
alytic mechanism of the Li/SOCl
phthalocyanines.
2
battery catalyzed by metallo-
On the basis of the previous study and CV the
result, the process of the reduction of SOCl catalyzed by CNTs-
CONH-MPc may undergo three steps (Fig. 13):
The shift of the reduction potential and the peak height can testify
the electrocatalytic activity of the catalysts. That is, excellent catalyst
has bigger reduction potential and higher reduction peak. It can be
29,30
2
2
+
2+
2+
seen that the order of the peak height is: Co > Ni > Mn >
2
+
2+
2+
Cu > Fe > Zn , which means that the CNTs-CONH-CoPc has
the higher electrocatalytic activity to the Li/SOCl battery. The result
is in accordance with results of electrocatalytic performance.
CNTs-CONH-MPc + SOCl → CNTs-CONH-MPc · SOCl
2
2
[5]
2
2
6–28
In the metal Phthalocyanines, the ligands and the central metal ions
are both the electrocatalytic active sites. By comparing electrocatalytic
activity of catalysts with the different central metal ions, it is found
that the electrocatalytic activity relates to the electronic configurations
of the central metal ions. Among all catalysts, the electrocatalytic
performance of Co phthalocyanine is excellent, because the d orbital
of Co ion can participate in the electron transition, and the catalytic
active sites can achieve an appropriate state through the synergistic
effect of the ligands and the central metal ion. Combine with the
advantages of CNTs, the CNTs-CONH-CoPc possess the wonderful
+ e−
CNTs-CONH-MPc · SOCl
2
−
→ CNTs-CONH-MPc · SOCl + Cl
[6]
electrocatalytic performance to Li/SOCl
In order to further verify the electrocatalytic performance of
CNTs-CONH-MPc to the Li/SOCl battery, the cyclic voltammet-
2
battery.
2
ric curves of battery catalyzed by CuPc, CNTs, CNTs-CONH-CuPc
and CuPc/CNTs (mixed) are investigated at 100 mV/s (Fig. 10). The
reduction peaks potentials and currents of fast reaction step for all
samlpes are higher than that of bare, which means that all sam-
ples can improve the reaction speed of the fast reaction step. The
catalytic activity order is showed as follows: CNTs-CONH-CuPc >
CuPc/CNTs(mixed) > CNTs > CuPc > blank. The results show that
all the catalysts can improve the electrocatalytic performance to the
2
Li/SOCl battery. Obviously, the modified CNTs-CONH-CuPc is su-
perior to others. The main reason is that there are synergistic effect
between the phthalocyanine and the CNTs. CNTs can enhance the
surface area and accelerate the electron transfer, and the phthalocya-
Figure 11. Representative cyclic voltammograms for CNTs-CONH-CuPc at
different scan rates.
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A1146
Journal of The Electrochemical Society, 164 (6) A1140-A1147 (2017)
·
−
CNTs-CONH-MPc · SOCl + e
−
→
1/2 S + 1/2 SO
2
+ Cl + CNTs-CONH-MPc
[7]
The first step is that the SOCl
2
bonds with catalyst to form an
adduct CNTs-CONH-MPc · SOCl
2
. In the second step, the adduct
−
gains one electron and decomposes into MPc-CNTs · SOCl and Cl .
In the finally step, CNTs-CONH-MPc · SOCl gain another electron
by the fast electron transfer reaction, accompanying with the return of
−
the catalyst and forming S, SO
2
and Cl . CNTs is a good conductor of
electronic, and metal phthalocyanines possess good electrochemical
properties. The CNTs-CONH-MPc has beneficial effects on electron
shift in the electrocatalysts, due to their excellent electrochemical
properties and the synergistic effect of CNTs and metal phthalocya-
nines. The For these reasons, the CNTs-CONH-MPc possess excellent
catalytic activity.
Conclusions
In this paper, chemically modified CNTs were synthesized by
bonding with metal phthalocyanines, and the electrical performance
of Li/SOCl battery catalysed by CNTs-CONH-MPc were studied.
2
The results manifested that metal phthalocyanines are bonding with
CNTs by chemical bond, and the obtained CNTs-CONH-MPc catalyst
shows excellent catalytic activity. The experiment results show that all
Figure 12. Plot of scan rate versus root of the sweep rate for CNTs-CONH-
CuPc.
catalysts can enhance the electrical performance to Li/SOCl
2
battery,
especially, the cell capacity of Li/SOCl battery catalyzed by CNTs-
2
CONH-CoPc can extended to 95.84 mA · h, with increase by 88.49%.
Besides, it is found that the synergistic effect between the CNTs and
Figure 13. The catalytic mechanism of the CNTs-CONH-MPc to Li/SOCl2 battery.
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Journal of The Electrochemical Society, 164 (6) A1140-A1147 (2017)
A1147
¨
the phthalocyanine is the main reason for improve the performance of
Li/SOCl battery.
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metallo-phthalocyanines/polymer composite films,” Optics & Laser Technology, 43,
92 (2011).
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9
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study,” Nanoscale, 7, 11633 (2015).
Acknowledgments
The authors thank the National Natural Science Foundation of
China (Nos. 21371143, 21671157 and 21501139) for the financial
support of this work.
17. Y. H. Bian, J. S. Chen, S. T. Xu, Y. L. Zhou, L. J. Zhu, and Y. Z. Xiang, “The effect
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metal-free benzoxazole-substituted phthalocyanines,” New Journal of Chemistry, 39,
5750 (2015).
1
8. A. Arul, M. Christy, Y. Oh M., S. Lee Y., and S. Nahm K., “Nanofiber Carbon-
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