Composite of CoOOH Nanoplates with Multiwalled Carbon Nanotubes

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Composite of CoOOH Nanoplates with Multi-Walled Carbon Nanotubes as Superior Cathode Material for Supercapacitors Lei Zhu, Wenyi Wu, Yusong Zhu, Weiping Tang, and Yuping Wu J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.5b01498 • Publication Date (Web): 27 Feb 2015 Downloaded from http://pubs.acs.org on March 14, 2015

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The Journal of Physical Chemistry

Composite of CoOOH Nanoplates with Multi-walled Carbon Nanotubes as Superior Cathode Material for Supercapacitors Lei Zhu, †,‡ Wenyi Wu#, Yusong Zhu*,†,#, Weiping Tang*,‡ and Yuping Wu*,†,#

†

College of Energy, Nanjin Tech University, Nanjing 211816, Jiangsu Province, China

‡

Shanghai Institute of Space Power-Sources (SISP), Shanghai Academy of Spaceflight

Technology, Shanghai 200245, China #

New Energy and Materials Laboratory (NEML), Department of Chemistry and Shanghai Key

Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433, China ABSTRACT: A hydrothermal-oxidation two-step method has been employed to fabricate a composite of CoOOH nanoplates with conducting MWCNTs, which present excellent electrochemical performance as a cathode material for supercapacitor. The conductive nanostructure network of MWCNTs not only provides effective surface area for the contact between the electrode material and the electrolyte, but also shortens the diffusion distances for ions and electrons and buffers the volume change, resulting in higher capacitance, faster redox reaction kinetics and outstanding cycling stability. The maximum specific capacitance of the composite can achieve 270 F g-1 at a current density of 1 A g -1 in 0.5 mol L-1 KOH aqueous solution. It also exhibits good rate capability with a capacitance of 169 F g -1 even at a high current density of 10 A g-1 and outstanding long-term cycling stability, almost 100% retention of its initial capacitance after 10 000 full cycles. In contrast, the virginal CoOOH shows a capacitance of only 124 and 100 F g-1 at 1 and 10 A g-1 , respectively, and its capacitance retention is only 79.4% after 10 000 full cycles. These results, for the first time, indicate that the composite of CoOOH nanoplates with MWCNTs is a promising cathode material for high-performance aqueous supercapacitors.

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Introduction Supercapacitors have attracted great attention as a new energy storage device due to its virtues of high power performance, excellent reversibility, long cycling life, and the possibility to gain high energy and high power densities at the same time. 1-5 In the way of charge storage mechanism, supercapacitors have been divided into electrical double layer capacitors and pseudocapacitors.

Electrical

absorption/desorption.6,

7

double

layer

capacitors

store

electrical

energy

by

Porous carbon materials are considered as the most representative

electrode materials for electrical double layer capacitors with excellent cycling performance. Nevertheless, their commercial application is limited due to its low capacitance and energy density.8, 9 On the other hand, pseudocapacitors, which involves reversible Faradaic reactions, behaves like a capacitor rather than a battery. Transitional metal oxides/hydroxides like RuO210, 11

, V2O512, and some conducting polymers are considered as ideal electrode materials, which

have much larger specific capacitances than those of carbon based materials. However, their widely commercial applications are limited for higher cost and environmental unfriendliness.13, 14 Hence, in an effort to adapt the market demand, inexpensive alternatives should be found. On this account, transition metal oxides/hydroxides like TiO2,15 SnO2,16 Co3O4,17 MoO3,18 MnO219 and NiO20 were recently explored. Specifically, CoOOH has been considered as one of the most promising candidates for developing electrodes for supercapacitors because of comparatively lower material costs. However, its practical capacitance is less than 200 F g-1 because of the relatively low conductivity,21 causing the little possibility in market application. A lot of efforts have been made to overcome this disadvantage. One of the most effective strategies is to coat other positive materials like MnO2 to enlarge their narrow potential windows.22 In the meanwhile, a series of nanostructured cobalt hydroxide and cobalt oxyhydroxide materials have been prepared as electrode materials, to increase their surface areas for the contact between the positive materials and the electrolyte.23,24 At the same time, some fine conductive materials like nickel foam,21 indium tin oxide-coated glass,22and graphene membrane25 have been introduced to these nanomaterials as substrates to increase their electrical conductivity, leading to the capacitance

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enhancement. However, during the charging/discharging process, inevitably, the positive materials will be separated from the substrate, resulting in poor cycling performance. It is known that carbon nanotubes (CNTs) are outstanding in terms of high electronic conductivity and excellent stability.26,27 As a result, CNTs are intensively used with electrode materials like MnO2 28 and RuO2 29 to form nanocomposites to lead to much enhanced capacitive performance. Here, we prepared a composite consisted of CoOOH nanoplates and conductive multi-walled CNTs (MWCNTs) as the cathode material for suepercapacitors with 0.5 mol L-1 KOH aqueous solution as the electrolyte. The addition of MWCNTs can markedly increase the electrical conductivity to accelerate the transfer of ions and electrons, leading to an increased maximum capacitance of 270 F g-1 at the current density of 1 A g-1, and the porous network structure constructed by CoOOH nanoplates and the MWCNTs can buffer or resist to the volume change and strains, leading to an excellent cycling performance. This shows great promise for the application of this composite for supercapacitors. EXPERIMENTAL SECTION Synthesis of the composite of CoOOH nanoplates with MWCNTs. Firstly, MWCNTs were treated by 6 M HNO3 to remove the impurities, after two hours’ sonication, the MWCNTs were collected by filtration, and then washed by deionized water and ethanol, dried at 60 °C for 12 h in vacuum. Secondly, a certain amount of acid-treated MWCNTs were dispersed into a 30 mL aqueous solution of CoCl2 (0.04 mol L-1) with sonication and agitation for 2 h, separately. Lastly, 3.75 mmol NaOH was added into the mixture. After 10 min stirring, a dark green precipitate was obtained, and then the suspension was transferred into 40 mL Teflon-lined stainless steel autoclave and maintained at 120 °C for 3 h. After cooling to room temperature, the suspension (the composite of MWCNT and Co(OH)2) was oxidized by adding H2O2 drop by drop under magnetic stilling at 90 oC for 4 h, and then the composite of CoOOH nanoplates with MWCNTs has been prepared. The pristine CoOOH nanoplates were also prepared as a contrast sample by the same prepared method without the addition of MWCNTs.30

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Materials characterization. The crystallographic information of the pristine CoOOH nanoplates and the composite was collected by a Rigaku D/MAX-IIA X-ray diffractometer (XRD) with Cu-Kα radiation at a current density of 2° min-1. The morphologies both of the pristine CoOOH nanoplates and the composite were characterized on a Hitachi S4300 field emission scanning electron microscope (FESEM) and a JEOL JEM-2010 transmission electron microscope (TEM). The contents of the MWCNTs of the composite were determined by a Shimadzu DTG-60H thermogravimetric analysis (TGA). Electrochemical tests. The three-electrode system was applied to measure the electrochemical performance and the electrolyte is 0.5 mol L-1 KOH aqueous solution. The working electrode consists of the composite of CoOOH nanoplates with MWCNTs, acetylene black and polytetrafluoroethylene (PTFE, binder) in a weight ratio of 8:1:1. In addition, a nickel foil was used as the counter electrode while a saturated calomel electrode (SCE) as the reference electrode. A CHI 660D electrochemical station was employed to investigate the cyclic voltammetric (CV) curves at different scan rates in the range of 1 to 100 mV s-1. The galvanostatic charge/discharge curves at various current densities from 1 to 10 A g-1 were achieved by the LAND battery test system. The potential window selected for all the electrochemical tests was from 0 to 0.5 V. The cycling performance was measured by the galvanostatic charge/discharge measurement at the current density of 10 A g-1.

Results and discussion Figure 1a presents the XRD patterns of the pristine CoOOH and the composite of CoOOH nanoplates with MWCNTs. According to JCPDS 07-0169, the hexagonal rhomb-centered phase of CoOOH can be found without any impurities.31 As to that for the composite of CoOOH nanoplates with MWCNTs, except the peaks belong to CoOOH, there are two peaks appearing at 26.2° and 43.2°, corresponding to the (002) and (100) planes of MWCNTs, respectively.32 By the way, there is a minor impure phase at 34°, and this is perhaps due to the remained Co(OH)2, which is not completely oxidized. In spite of this, it will not affect the overall crystallinity.

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(a)

100

CNT CoOOH

(b)

CNT/CoOOH

90

Weight (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


CNT/CoOOH (003) (012) (101) (015)

(110)(113)

30

40

50

60

53.90%

70 60 50

CoOOH 20

80

40 0

70

100

200

300

400

500

600

700

800

Temperature (oC)

2 Theta (degree)

Figure 1. (a) XRD patterns of the composite of CoOOH nanoplates with MWCNTs (bottom) and the pristine CoOOH (top), and (b) TGA curve of the composite of CoOOH nanoplates with MWCNTs. Thermogravimetric analysis (TGA) (Figure 1b) of the composite presents two weight loss peaks. The first one appears at approximately 300 °C, which is attributed to the decomposition of CoOOH to Co3O4.33 The second weight loss takes place at approximately 400 °C, corresponding to the oxidation of MWCNTs. After the TGA measurement, the weight percentage of the final product is 46.1 wt.%, mostly the amount of the pure Co3O4, so it can be calculated that the CoOOH content in the composite is approximately 52.8 wt.%, with the rest being the MWCNTs.

Figure 2. FESEM micrographs of (a) the precursor Co(OH)2 nanoplates, (b) the pristine CoOOH nanoplates and (c) the composite of CoOOH nanoplates with MWCNTs. Figure 2a and 2b show the field emission scanning electron micrographs (FESEMs) of the precursor Co(OH)2 nanoplates, the pristine CoOOH nanoplates. It is clear that there is no significant change of the morphology during the oxidation process from Co(OH)2 to CoOOH except that there is a little excessive penetration, which is negligible to overall morphology. Both of the as-prepared Co(OH)2 and CoOOH exist in well-defined plate-like nanostructure, and many of them are regular hexagons with the angles of adjacent edges of 120o. In addition, some buds 5



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are found on the surface of CoOOH nanoplates. After decorated by MWCNTs, it can be seen from Figure 2c that the MWCNTs have been incorporated into the CoOOH nanoplates and form a conductive network structure to interconnect every independent nanoplates, which is in favor of the fast transfer of electrons. By the way, a very interesting phenomenon appears in Figure 2b and Figure 2c, where both of the size and the thickness of CoOOH nanoplates are decreased slightly after adding the MWCNTs. The smaller CoOOH nanoplates came into being during the nucleation process, where the reunion of nanoparticles is probably hindered by the conductive nanostructure network. TEM micrographs of the composite of CoOOH nanoplates with MWCNTs and the pristine CoOOH nanoplates are shown in Figure 3. In the inset of Figure 3a the selected area electron diffraction (SAED) pattern recorded on the edge of the products suggests that the individual nanoparticles also exist in single crystalline, which belongs to CoOOH. On the basis of the XRD pattern and SAED, the phase structures of both the nanoplates and the buds are CoOOH. The TEM micrograph (Figure 3a) of the pristine CoOOH nanoplates shows that they are composed of hexagonal plates at nanoscale with the size in the range of 100-120 nm. Besides, some rod-like nanostructures can also be found, which should be some nanoplates that lie on their sides, it could be concluded that the thickness of the plates is approximately 10-20 nm. The TEM micrograph of the composite (Figure 3b) presents that the MWCNTs and the CoOOH nanoplates have been inseparably intertwined to form a conductive network structure to shorten the transport pathway of electrons. Furthermore, it is more obvious to see that the CoOOH nanoplates become thinner, which is in consistent with the FESEM micrographs. The smaller nanoplates mean more adequate areas for the connection of the electrolyte and active materials, in favor of the fast transport of ions. The probable growth process is schematically shown in Figure 4.

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Figure 3. TEM micrographs of (a) the pristine CoOOH nanoplates and (b) the composite of CoOOH nanoplates with MWCNTs.

Figure 4. Schematic illustration of the growth process for the composite of CoOOH nanoplates with MWCNTs.

The CV curves for the composite and the pristine CoOOH samples are shown in Figure 5. Since the Co atoms are converted into higher/lower valence states, as shown in Figure 5a, there are two pairs of redox peaks in the CV curve for the pristine CoOOH at 1 mV s-1, corresponding to the transformation of Co(II)/Co(III) (0.15/0.21 V) and Co(III) V)/Co(IV) (0.35/0.42 V), indicating the

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Faradaic reactions behavior. According to electrochemical redox reactions of Co(OH)2 and Co3O4 reported 34, the possible reactions during the CV test are presented as follows:

0.0004

CoOOH + H2O + e- ↔ Co(OH)2 + OH-

(lower potential)

(1)

CoO2 + H2O + e- ↔ CoOOH + OH-

(higher potential)

(2)

(a)

3+

Co

Co

(b)

CoOOH

4+

0.012

0.0002

Co

0.0001

2+

Co

3+

0.0000 -0.0001

Co

3+

Co

2+

Co 0.0

0.1

0.2

0.004 0.000 -0.004 -0.008

-0.0002 -0.1

CoOOH 1mV/s 2mV/s 5mV/s 10mV/s 20mV/s 50mV/s 100mV/s

0.008

Current density = 1mV/s

Current / A

Current / A

0.0003

0.3

4+

0.4

Co

3+

0.5

-0.012 0.6

0.0

0.1

0.2

0.0010

0.024

(c)

0.020

CoOOH CNT/CoOOH

0.0008

(d)

0.4

0.5

Current / A

Current density = 1mV/s

0.0002 0.0000

CNT/CoOOH

1mV/s 2mV/s 5mV/s 10mV/s 20mV/s 50mV/s 100mV/s

0.016

0.0006 0.0004

0.3

Potential / V

Potential / V

Current / A

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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0.012 0.008 0.004 0.000 -0.004 -0.008

-0.0002

-0.012 -0.0004 0.0

0.1

0.2

0.3

0.4

0.5

0.0

Potential / V

0.1

0.2

0.3

0.4

0.5

Potential / V

Figure 5. Cyclic voltammetric (CV) curves: (a) the pristine CoOOH nanoplates at the scan rate of 1 mV s-1, (b) the pristine CoOOH nanoplates at different scan rates, (c) comparison between the pristine CoOOH nanoplates and the composite at the scan rate of 1 mV s-1, and (d) the composite of CoOOH nanoplates with MWCNTs at different scan rates. Figure 5c compares the CV curves of the pristine CoOOH with those of the composite in the same weight of the active materials in the electrode. In the CV curves of the composite at the current density of 1 mV s-1 the pseudo-capacitance behaviour is also observed. However, compared to the pristine CoOOH, after decorating with the MWCNTs, the redox pair peaks at lower potential becomes more distinct. In addition, the area of the CV curves of the composite electrodes drastically expanded, which is a sign of larger capacitance. In other words, this 8


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composite has a promoted Faradaic reactions for CoOOH due to the faster electron and ion transfer, profiting from the penetration of CNTs into the CoOOH nanoplates to form a network structure, promoting the electronic conductivity of the electrode and accelerating the ion diffusion. By the way, the phenomenon is in agreement with the previous FESEM and TEM measurements. Compared Figure 5b with Figure 5d, it is found that at different scan rates of 1, 2, 5, 10, 20, 50, and 100 mV s-1, the composite shows even larger area than that of the pristine CoOOH, indicating higher specific capacitance and higher utilization of CoOOH in the composite. In addition, the symmetric shape in the CV curves of both electrodes proves the better reversibility of the redox reactions. Significantly, with the increase of the current density, even at a high current density of 100 mV s-1, the potential difference between the oxidation and reduction peaks is not much increased, implying that the polarization is very small for the composite which attributes to the excellent reversibility of the as-prepared CoOOH nanoplates.

0.5

0.5

(a)

(b)

0.4

CoOOH

Voltage / V

Voltage / V

0.4 0.3

1 A/g 2 A/g 5 A/g 8 A/g

0.2 0.1

CNT/CoOOH

0.3 0.2

1 A/g 2 A/g 5 A/g 8 A/g

0.1

0.0

0.0 0

20

40

60

80

100

120

0

40

80

280

220

(c) -1

CNT/CoOOH CoOOH

240 200 160 120

1

2

3

80 40

1

1 A/g

4

5

Current d ensity: A g

6

7

8

9

10

-1

0 0

10

20

120

160

t / sec

Specific Capacitance F g

-1

t / sec

Specific Capacitance F g

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


30

40

50

(d) CNT/CoOOH

200 180 160 140

CoOOH

120 100 80 60

Current density = 10 A g

40 20 0

Cycle number

-1

2000

4000

6000

8000

10000

Cycle number

Figure 6. Galvanostatic charge/discharge curves of (a) the pristine CoOOH nanoplates and (b) the composite of CoOOH nanoplates with MWCNTs at different current densities, (c) comparison 9



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of their capacities at different current densities, and (d) their cycling performance at the current density of 10 A g-1. Figure 6a and Figure 6b show the galvanostatic charge/discharge curves of the pristine CoOOH and the composite between 0 and 0.5 V, respectively. It can be seen that the charging time is the same as the discharging one, implying high reversibility, too. However, there are two obvious stages at 0.1-0.2 V and 0.4-0.5 V in the discharge curves of the composite, in response to the reactions (1) and (2), respectively. Significantly, the discharge stage at lower potential emerged with the assist of MWCNTs. Besides, as expected, compared with the pristine CoOOH nanoplates, the composite demonstrates longer discharging time. It means that the composite of CoOOH nanoplates with MWCNTs exhibits higher specific capacitances than the pristine CoOOH, which is also consistent with the former results. The outstanding performance of the composite of CoOOH nanoplates with MWCNTs in supercapacitors is also confirmed at different current densities. As shown in Figure 6c, the composite exhibits a specific capacitance of 270 F g-1 at the current density of 1 A g-1 while that of the pristine CoOOH electrode is just 150 F g-1. The specific capacitance is calculated according to the following equation: 35 C = I ∆t/ (m∆V)

(3)

where I (mA) is discharge current, ∆t(s) is discharge time, m (mg) is mass of the active material and ∆V(V) is the potential window. Significantly, there is a decrease in specific capacitance with the increase in current density for both samples due to a decrease in utilization efficiency of active material at high current density, where only the outer surface of the electrode material can contact quickly with ions, resulting in decreased sites for ions diffusion.36 However, under these circumstances, in the case of the composite, even at a high current density of 10 A g-1, its specific capacitance still maintains 169 F g-1 Furthermore, as the current density is back to 1 A g-1, the capacitance of the composite returns to 270 F g-1, suggesting good rate capability and structure stability of the composite active material.

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Another important requirement for supercapacitor applications is the cycling stability. As shown in Figure 6d, it can be clearly seen that the specific capacitances of both the pristine CoOOH nanoplates and the composite of CoOOH nanoplates with MWCNTs gradually increase initially and then slightly decrease. It has been reported that there is an activation process in initial cycles. 37

At the beginning of the charge/discharge processes, the contact between the electrolyte and the

inner of the active materials becomes more complete. Besides, the electrode will be completely activated through the intercalation and de-intercalation of ions, resulting in the increase of active sites inside the electrode materials and a consequent increase in the specific capacitance. In addition, it is interesting that the activation process of the composite lasts for 200 cycles. However, this process for the pristine CoOOH electrode continues for 2000 cycles. From here it can be seen that the combination of the CoOOH nanoplates with MWCNTs enables a much easier transferring of electrons and ions at the interface between the electrode and electrolyte, as well as accelerates the activation process of the electrode. On the other hand, there is a significant improvement of cycling stability by the introduction of MWCNTs. After stabilizing, the overall specific capacitance retention for the composite of CoOOH nanoplates with MWCNTs is almost 100 % after 10 000 cycles, while that of the pristine CoOOH sample is about 79.4 % after 10 000 cycles (101 F g-1). The dramatic performance improvement of the composite illustrates that the configuration become more stable by the modification of MWCNTs, which is favour of the long-term cycling stability.

(a)

120

160

100

140

80

120

60

100

40

Current density=1 A/g

80 60 0

400

800

1200

1600

20

0.5

(b)

0.4

Voltage / V

Specific Capacitance F/g

180

Coulumbic Efficiency / %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.3 0.2

Current density=1 A/g

0.1

0 2000

0.0 0

20

40

60

80

100

120

t / sec

Cycle number

Figure 7. (a) The cycling performance and (b) galvanostatic charge/discharge curves of the mixture of CoOOH nanoplates with MWCNTs at the current density of 1 A g-1. 11



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In addition, we simply mixed pristine CoOOH and MWCNTs together as active materials with the same amount of CoOOH 52.8 wt.% according to the TGA measurement. The electrochemical performance of the mixture was also measured under the same condition. The cycling performance of the mixture at the current density of 1 A g-1 is shown in Figure 7a. It delivers a specific capacity of 125 F g-1, which is almost equal to the pristine CoOOH but much smaller than that of the composite of CoOOH nanoplates with conductive MWCNTs, indicating that CNT plays very little part in the capacitance of the mixture of CoOOH with MWCNTs. This demonstrates that the superior capacitance of the composite is mainly attributed to the CoOOH while the MWCNTs acts as a role of enhancing the conductivity. Furthermore, after 2000 cycles, the specific capacity of the mixture decays fast and only 110 F g-1 is remained, indicating the poor cycling performance without the flexible MWCNTs inlayed, which is helpful to buffer the volume expansion. Also, the galvanostatic charge and discharge curves of the mixture tested at the current density of 1 A g-1 is shown in Figure 7b, the discharge curve of the mixture is similar to the pristine CoOOH. However, the discharge time is less than 60 s, much lower than that for the composite (80 s). This further confirms that there is a synergistic action between CoOOH and the MWCNTs. The superior electrochemical performance of the composite can be attributed to the unique conductive network structure comprised of smaller and thinner CoOOH nanoplates and the conductive MWCNTs, increasing more contact areas for the reversible redox reactions of CoOOH. Furthermore, the CNTs with high surface area and good flexibility could accommodate large volume expansion during the charging and discharging processes, ensuring an excellent cycling performance.38 On the other hand, the composite can shorten the pathway for rapid electron transference because of the good conductivity from the MWCNTs, resulting in a significant improvement of high rate performance. CONCLUSIONS A composite of CoOOH nanoplates with MWCNTs and pristine CoOOH nanoplates have been successfully fabricated by a hydrothermal-oxidation two-step method. MWCNTs have been 12


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distributed into the CoOOH nanoplates, forming an interconnected conductive network. As the positive material for aqueous supercapacitors, the pristine CoOOH electrode exhibits specific capacitance of nearly 126 F g-1 at a current density of 1 A g-1 due to its poor electronic conductivity. In contract, the specific capacitance is remarkably increased when for the composite, nearly 270 F g-1 at 1 A g-1. In addition, the composite shows excellent rate performance and its capacitance can be 169 F g-1 at a high current density of 10 A g-1. Besides, the composite presents an excellent cycling stability, almost 100 % capacitance retention after 10 000 full cycles, much better than the pristine CoOOH. It is clear that the introduction of MWCNTs into the composite can significantly enhance the electronic conductivity, the charge transfer process, the electrode reaction kinetics and structure stability, directly leading to the improvements of the specific capacitance and cycling performance in comparison to the pristine CoOOH. Therefore, the composite of CoOOH nanoplates with MWCNTs made from environmentally friendly and low cost materials would be a promising cathode material for supercapacitor applications. AUTHOR INFORMATION Corresponding Author E-mail: [email protected]. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT The financial support of this research is from China National Distinguished Young Scientists Project (NSFC No. 51425301).

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Table of content:

Composite of CoOOH Nanoplates with Multi-walled Carbon Nanotubes as Superior Cathode Material for Supercapacitors Lei Zhu, Wenyi Wu, Yusong Zhu, Weiping Tang and Yuping Wu A composite of CoOOH nanoplates with MWCNTs have been successfully fabricated by a hydrothermal-oxidation two-step method, exhibiting high specific capacitance, good rate capability and excellent cycling performance.

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Composite of CoOOH Nanoplates with Multiwalled Carbon Nanotubes

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