Asymmetric Supercapacitors Using 3D Nanoporous Carbon and ...
Supplementary Information
Asymmetric Supercapacitors Using 3D Nanoporous Carbon and Cobalt Oxide Electrodes Synthesized from a Single Metal-Organic Framework Rahul R. Salunkhe,1 Jing Tang, 1,2 Yuichiro Kamachi, 1,3 Teruyuki Nakato,3 Jung Ho Kim*,4 and Yusuke Yamauchi*,2
[1]
World
Premier
International
(WPI)
Research
Center
for
Materials
Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan. [2]
Faculty of Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan.
[3]
Department of Applied Chemistry, Graduate School of Engineering, Kyushu Institute of Technology, 1-1 Sensui-Cho, Tobata, Kitakyushu, Fukuoka 8048550, Japan.
[4]
Institute for Superconducting and Electronic Materials, University of Wollongong, North Wollongong, New South Wales 2500, Australia.
Keywords: nanoporous materials; coordination polymers; metal-organic frameworks; cobalt oxide; carbon; supercapacitors
*Corresponding authors: [email protected] (J.H. Kim); [email protected] (Y. Yamauchi)
S1
Table S1 Comparison of surface area of our Co3O4 polyhedra with previously reported Co3O4 nanostructures produced by different synthetic routes. Method
Morphology
Hydrothermal method Chemical precipitation
Ultralayered Co3O4 Co3O4 Nanosheets Co3O4 nanorod/Ni foam Co3O4 nanosheets Co3O4 microsheets Co3O4 nanosheets Co3O4 nanotubes Co3O4 Nanosheet Co3O4 Nanobelt Co3O4 Nanocubes Co3O4 porous agglomerates Co3O4 polyhedrons
Hydrothermal method Controlled precipitation MOF templated method Solution method Topotactic transfer approach Hydrothermal method MOF templated method MOF templated method
Surface area (m2∙g1 ) 97 127
Ref. S1 S2
14.74
S3
75.9 0.21 25.12 7.6 17.8 20.1 22.6
S4 S5 S6 S7
47.12
S9
148
Our work
S8
S2
Table S2 Comparison of electrochemical performance of our Co3O4 sample with previous reports using standard three-electrode system. Method Hydrothermal method Hydrothermal method Controlled precipitation method Hydrothermal method Hydrothermal method Hydrothermal method MOF templated method MOF templated
Scan rate (mV∙s-1)
Current density (A∙g-1)
Ref.
-
1
S10
Electrolyte
Morphology
Capacitance (F∙g-1)
KOH (6M)
Nanorod
456
KOH (1M)
Ultra layer
548
8
S1
KOH (2M)
Layered
202
1
S4
NaOH (1M)
Net-like
1090
10
-
S11
KOH (2M)
Nanowire
754
-
2
S12
KOH (6M)
Flakes
263
-
1
S13
KOH (6M)
Sheets
208
-
1
S5
KOH (6M)
Porous polyhedron
504
5
-
Our work
S3
method
Table S3 Various performance parameters for our ASC supercapacitor. Current density -1
(A∙g )
Discharge time
Specific capacitance -1
Specific energy -1
Specific power
(F∙g )
(W∙h∙kg )
(W∙kg-1)
(s) 2
81
101.2
36
1600
3
40
75
27
2430
4
25
63
23
3312
5
19
60
22
4042
7
10.2
44.62
16.9
5964
10
7
44
15.4
7920
S4
Table S4 Comparison of our ASC performance of different metal oxides/hydroxides. Materials
Counter
Electrolyte
KOH (6M)
Operating voltage (V) 1.8
Energy density (W∙h∙kg-1) 13.4
Power density (W∙kg-1) 85000
Ni(OH)2@Ni foam Co (OH)2 nanorods MoO3 MnO2
a-MEGO
MnO2
AC
Ni(OH)2 Co3O4
AC Nanoporous carbon
Ref.
GO
KOH (1M)
1.2
11.94
2540
S15
AC AC
LiSO4 K2SO4 (0.5 M) Na2SO4 (0.5 M) KOH (1 M) KOH (6 M)
1.8 1.8
45 28.4
450 150
S16 S17
1.8
10.4
14700
S18
1.3 1.6
35.7 36
490 1600
S19 Our work
S14
GO: graphene oxide a-MEGO: activated microwave exfoliated graphite oxide AC: activated carbon (Note: The comparison has been made with bare metal oxides/hydroxides that used as positive electrode only and ASC calculation based on weight of active electrode materials.)
S5
Figure S1
Figure S1. Wide angle XRD pattern of ZIF-67 crystals.
Note for Figure S1: The topological information of the prepared crystals is revealed by the powder X-ray diffraction (XRD) patterns. As shown in the Figure S1, the diffraction peaks of the prepared crystals are identical to simulated crystal structure of the ZIF-67 crystals,S20 indicating the successful formation of ZIF-67 crystals.
6
Figure S2
Figure S2. EDS elemental mapping images of nanoporous carbon (top) and nanoporous Co3O4 (bottom). Both samples contain carbon, cobalt, oxygen, and nitrogen as the main elements. (All scale bars shown are 1 μm in length.)
7
Figure S3
Figure S3. (a, c) Nitrogen adsorption-desorption isotherms for (a) nanoporous carbon and (c) nanoporous Co3O4. (b, d) Pore size distributions of (b) nanoporous carbon and (d) nanoporous Co3O4. Inset of b shows magnified view of mesopores distribution.
8
Figure S4
Figure S4 (a) CV curves of Co3O4//carbon ASC. The device was cycled by varying the upper cell voltage from 1 V to 1.6 V. (b) Stability study of ASC up to 2000 repeated charge-discharge cycles. Inset of (b) shows the 10 charge-discharge cycles.
9
Figure S5
Figure S5 SSC tests based on nanoporous carbon electrodes. (a) CV curves of carbon//carbon SSC, with the device cycled by varying the upper cell voltage from 1 V to 1.6 V; (b) galvanostatic discharge curves of the carbon//carbon SSC cell at various current densities from 1-5 A∙g-1; and (c) dependence of the specific capacitance on the applied current density.
10
Figure S6
Figure S6 SSC tests based on nanoporous cobalt oxide electrodes. (a) CV curves of Co3O4//Co3O4 SSC, with the device cycled by varying the upper cell voltage from 0.5 V to 0.9 V; (b) galvanostatic discharge curves of Co3O4//Co3O4 SSC cell at various current densities from 1-5 A∙g-1; and (c) dependence of the specific capacitance on the applied current density.
11
Note for Figure S5 and Figure S6: Symmetric supercapacitor (SSC) studies were carried out for the nanoporous carbon and the Co3O4. Each type of electrode, with size of 1 × 1 cm2, was used as both the positive and negative working electrodes. In case of the SSCs, the total mass of both electrodes was adjusted to 2 mg∙cm-2. Figure S5a shows the CV curves of the carbon//carbon SSC at various potential windows ranging from 1.0 V to 1.6 V. It exhibits a rectangular shape, however, and after 1.6 V, a steep peak is observed, which might be due to some irreversible chemical reactions, so the maximum working potential of this material is up to 1.6 V. The capacitance of the SSC was evaluated by galvanostatic charge-discharge measurements (Figure S5b). For this purpose, the applied current density was varied from 1 to 5 A∙g-1. The absence of any initial voltage loss (i.e. IR drop) indicates a fast current response with low internal resistance. The variation of specific capacitance with applied current density is shown in Figure S5c. The maximum capacitance value obtained for the symmetric carbon//carbon supercapacitor was 20 F∙g-1 at a current density of 1 A∙g-1. Similar to the tests for the carbon-based SSC, Co3O4 SSC tests were carried out (Figure S6a-c). The CV studies show that the maximum working potential for the Co3O4-based supercapacitor is 0.9 V. The SSC cell shows a very rectangular shape. The maximum capacitance value of the SSC was found to be 66 F∙g-1 at a current density of 1 A∙g-1.
12
Figure S7
Figure S7 Heating of Co3O4 samples without preliminary nitrogen heat treatment at (a) 400 ºC and (b) 350 ºC, respectively.
13
References S1 Meher, S. K.; Rao, G. R., Ultralayered Co3O4 for high performance supercapacitor applications. J. Phys. Chem. C 2011, 115, 15646-15654. S2 Wang, Y.; Zhong, Z.; Chen, Y.; Ng, C. T.; Lin, J., Controllable synthesis of Co 3O4 from nanosize to microsize with large-scale exposure of active crystal planes and their excellent rate capability in supercapacitors based on the crystal plane effect. Nano Res. 2011, 4, 695-704. S3 Tang, C. H.; Yin, X.; Gong, H., Superior performance asymmetric supercapacitors based on a directly grown commercial mass 3D Co3O4@Ni(OH)2 core-shell electrode. ACS Appl. Mater. Interfaces 2013, 5, 10574-10582. S4 Wang, D.; Wang, Q.; Wang, T., Morphology controllable synthesis of cobalt oxalates and their conversion to mesoporous Co3O4 nanostructures for application in supercapacitors. Inorg. Chem. 2011, 50, 6482-6492. S5 Zhang, F.; Hao, L.; Zhang, L.; Zhang, X., Solid-state thermolysis preparation of Co3O4 nano/micro superstructures from metal-organic framework for supercapacitors. Int. J. Electrochem. Sci. 2011, 6, 2943-2954. S6 Xiong, S.; Yuan, C.; Zhang, X.; Xi, B.; Qian, Y., Controllable synthesis of mesoporous Co3O4 nanostructures with tunable morphology for application in supercapacitors. Chem. Eur. J. 2009, 15, 5320-5326. S7 Lou, X. W.; Deng, D.; Lee, J. Y.; Feng, J.; Archer L. A., Self-supported formation of needlelike Co3O4 nanotubes and their application as lithium-ion battery electrodes. Adv. Mater. 2008, 20, 258-262. S8 Hu, L.; Peng, Q.; Li, Y., Selective synthesis of Co3O4 nanocrystal with different shape and crystal plane effect on catalytic property for methane combustion. J. Am. Chem. Soc. 2008, 130, 16136-16137. S9 Meng, F.; Fang, Z.; Li, Z.; Xu, W.; Wang, M.; Liu, Y.; Zhang, J.; Wang, W.; Zhao, D.; Guo, X., Porous Co3O4 materials prepared by solid-state thermolysis of a novel Co-MOF crystal and their superior energy storage performances for supercapacitors, J. Mater. Chem. A 2013, 1, 7235-7241. S10 Cui, L.; Li, J.; Zhang, X. G., Preparation and properties of Co3O4 nanorods as supercapacitor material. J. Appl. Electrochem. 2009, 39, 1871-1876. S11 Wang, H.; Zhang, L.; Tan, X.; Holt, C. M. B.; Zahiri, B.; Olsen, B. C.; Mitlin, D., Supercapacitive properties of hydrothermally synthesized Co3O4 nanostructures. J. Phys. Chem. C 2011, 115 (35), 17599-17605. S12 Xia, X. H.; Tu, J. P.; Zhang, Y. Q.; Mai, Y. J.; Wang, X. L.; Gu, C. D.; Zhao, X. B., Freestanding Co 3O4 nanowire array for high performance supercapacitors. RSC Adv. 2012, 2, 1835-1841. S13 Xie, L.; Li, K.; Sun, G.; Hu, Z.; Lv, C.; Wang, J.; Zhang, C., Preparation and electrochemical performance of the layered cobalt oxide (Co3O4) as supercapacitor electrode material. J. Solid State Electrochem. 2012, 17, 55-61. S14 Ji, J.; Zhang, L. L.; Ji, H.; Li, Y.; Zhao, X.; Bai, X.; Fan, X.; Zhang F.; Ruoff, R. S., Nanoporous Ni(OH)2 thin film on 3D ultrathin graphite foam for asymmetric supercapacitor. ACS Nano 2013, 7, 6237-6243. S15 Salunkhe, R. R.; Bastakoti, B. P.; Hsu, C. T.; Suzuki, N.; Kim, J. H.; Dou, S. X.; Hu, C. C.; Yamauchi, Y., Direct growth of cobalt hydroxide rods on nickel foam and its application for energy storage. Chem. Eur. J. 2014, 20, 3084-3088. S16 Tang, W.; Liu, L.; Tian S.; Li, L.; Yue, Y.; Wu, Y.; Zhu, K., Aqueous supercapacitor of high energy density based on MoO3 nanoplates as anode material. Chem. Commun. 2011, 47, 10058-10060. S17 Qu, Q.; Zhang P.; Wang, B.; Chen Y.; Tian, S.; Wu, Y.; Holze, Y., Electrochemical performance of MnO2 nanorods in neutral aqueous electrolytes as a cathode for asymmetric supercapacitors. J. Phys. Chem. C 2009, 113, 14020-14027. S18 Wang, Y. T.; Lu, A. H.; Zhang, H. L.; Li, W. C., Synthesis of nanostructured mesoporous manganese oxides with three-dimensional frameworks and their application in supercapacitors. J. Phys. Chem. C 2011, 115, 5413-5421. 14
S19
S20
Li, H. B.; Yu, M. H.; Wang, F. X.; Liu, P.; Liang, Y.; Xiao, J.; Wang, C. X.; Tong, Y. X.; Yang, G. W., Amorphous nickel hydroxide nanospheres with ultrahigh capacitance and energy density as electrochemical pseudocapacitor materials. Nat. Commun. 2013, 4, Article number: 1894. Banerjee, R.; Phan, A.; Wang, B.; Knobler, C.; Furukawa, H.; O’Keeffe, M.; Yaghi, O. M., Highthroughput synthesis of zeolitic imidazolate frameworks and application to CO2 capture. Science 2008, 139, 939-943.
15
Asymmetric Supercapacitors Using 3D Nanoporous Carbon and Cobalt Oxide Electrodes Synthesized from a Single Metal-Organic Framework Rahul R. Salunkhe,1 Jing Tang, 1,2 Yuichiro Kamachi, 1,3 Teruyuki Nakato,3 Jung Ho Kim*,4 and Yusuke Yamauchi*,2
[1]
World
Premier
International
(WPI)
Research
Center
for
Materials
Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan. [2]
Faculty of Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan.
[3]
Department of Applied Chemistry, Graduate School of Engineering, Kyushu Institute of Technology, 1-1 Sensui-Cho, Tobata, Kitakyushu, Fukuoka 8048550, Japan.
[4]
Institute for Superconducting and Electronic Materials, University of Wollongong, North Wollongong, New South Wales 2500, Australia.
Keywords: nanoporous materials; coordination polymers; metal-organic frameworks; cobalt oxide; carbon; supercapacitors
*Corresponding authors: [email protected] (J.H. Kim); [email protected] (Y. Yamauchi)
S1
Table S1 Comparison of surface area of our Co3O4 polyhedra with previously reported Co3O4 nanostructures produced by different synthetic routes. Method
Morphology
Hydrothermal method Chemical precipitation
Ultralayered Co3O4 Co3O4 Nanosheets Co3O4 nanorod/Ni foam Co3O4 nanosheets Co3O4 microsheets Co3O4 nanosheets Co3O4 nanotubes Co3O4 Nanosheet Co3O4 Nanobelt Co3O4 Nanocubes Co3O4 porous agglomerates Co3O4 polyhedrons
Hydrothermal method Controlled precipitation MOF templated method Solution method Topotactic transfer approach Hydrothermal method MOF templated method MOF templated method
Surface area (m2∙g1 ) 97 127
Ref. S1 S2
14.74
S3
75.9 0.21 25.12 7.6 17.8 20.1 22.6
S4 S5 S6 S7
47.12
S9
148
Our work
S8
S2
Table S2 Comparison of electrochemical performance of our Co3O4 sample with previous reports using standard three-electrode system. Method Hydrothermal method Hydrothermal method Controlled precipitation method Hydrothermal method Hydrothermal method Hydrothermal method MOF templated method MOF templated
Scan rate (mV∙s-1)
Current density (A∙g-1)
Ref.
-
1
S10
Electrolyte
Morphology
Capacitance (F∙g-1)
KOH (6M)
Nanorod
456
KOH (1M)
Ultra layer
548
8
S1
KOH (2M)
Layered
202
1
S4
NaOH (1M)
Net-like
1090
10
-
S11
KOH (2M)
Nanowire
754
-
2
S12
KOH (6M)
Flakes
263
-
1
S13
KOH (6M)
Sheets
208
-
1
S5
KOH (6M)
Porous polyhedron
504
5
-
Our work
S3
method
Table S3 Various performance parameters for our ASC supercapacitor. Current density -1
(A∙g )
Discharge time
Specific capacitance -1
Specific energy -1
Specific power
(F∙g )
(W∙h∙kg )
(W∙kg-1)
(s) 2
81
101.2
36
1600
3
40
75
27
2430
4
25
63
23
3312
5
19
60
22
4042
7
10.2
44.62
16.9
5964
10
7
44
15.4
7920
S4
Table S4 Comparison of our ASC performance of different metal oxides/hydroxides. Materials
Counter
Electrolyte
KOH (6M)
Operating voltage (V) 1.8
Energy density (W∙h∙kg-1) 13.4
Power density (W∙kg-1) 85000
Ni(OH)2@Ni foam Co (OH)2 nanorods MoO3 MnO2
a-MEGO
MnO2
AC
Ni(OH)2 Co3O4
AC Nanoporous carbon
Ref.
GO
KOH (1M)
1.2
11.94
2540
S15
AC AC
LiSO4 K2SO4 (0.5 M) Na2SO4 (0.5 M) KOH (1 M) KOH (6 M)
1.8 1.8
45 28.4
450 150
S16 S17
1.8
10.4
14700
S18
1.3 1.6
35.7 36
490 1600
S19 Our work
S14
GO: graphene oxide a-MEGO: activated microwave exfoliated graphite oxide AC: activated carbon (Note: The comparison has been made with bare metal oxides/hydroxides that used as positive electrode only and ASC calculation based on weight of active electrode materials.)
S5
Figure S1
Figure S1. Wide angle XRD pattern of ZIF-67 crystals.
Note for Figure S1: The topological information of the prepared crystals is revealed by the powder X-ray diffraction (XRD) patterns. As shown in the Figure S1, the diffraction peaks of the prepared crystals are identical to simulated crystal structure of the ZIF-67 crystals,S20 indicating the successful formation of ZIF-67 crystals.
6
Figure S2
Figure S2. EDS elemental mapping images of nanoporous carbon (top) and nanoporous Co3O4 (bottom). Both samples contain carbon, cobalt, oxygen, and nitrogen as the main elements. (All scale bars shown are 1 μm in length.)
7
Figure S3
Figure S3. (a, c) Nitrogen adsorption-desorption isotherms for (a) nanoporous carbon and (c) nanoporous Co3O4. (b, d) Pore size distributions of (b) nanoporous carbon and (d) nanoporous Co3O4. Inset of b shows magnified view of mesopores distribution.
8
Figure S4
Figure S4 (a) CV curves of Co3O4//carbon ASC. The device was cycled by varying the upper cell voltage from 1 V to 1.6 V. (b) Stability study of ASC up to 2000 repeated charge-discharge cycles. Inset of (b) shows the 10 charge-discharge cycles.
9
Figure S5
Figure S5 SSC tests based on nanoporous carbon electrodes. (a) CV curves of carbon//carbon SSC, with the device cycled by varying the upper cell voltage from 1 V to 1.6 V; (b) galvanostatic discharge curves of the carbon//carbon SSC cell at various current densities from 1-5 A∙g-1; and (c) dependence of the specific capacitance on the applied current density.
10
Figure S6
Figure S6 SSC tests based on nanoporous cobalt oxide electrodes. (a) CV curves of Co3O4//Co3O4 SSC, with the device cycled by varying the upper cell voltage from 0.5 V to 0.9 V; (b) galvanostatic discharge curves of Co3O4//Co3O4 SSC cell at various current densities from 1-5 A∙g-1; and (c) dependence of the specific capacitance on the applied current density.
11
Note for Figure S5 and Figure S6: Symmetric supercapacitor (SSC) studies were carried out for the nanoporous carbon and the Co3O4. Each type of electrode, with size of 1 × 1 cm2, was used as both the positive and negative working electrodes. In case of the SSCs, the total mass of both electrodes was adjusted to 2 mg∙cm-2. Figure S5a shows the CV curves of the carbon//carbon SSC at various potential windows ranging from 1.0 V to 1.6 V. It exhibits a rectangular shape, however, and after 1.6 V, a steep peak is observed, which might be due to some irreversible chemical reactions, so the maximum working potential of this material is up to 1.6 V. The capacitance of the SSC was evaluated by galvanostatic charge-discharge measurements (Figure S5b). For this purpose, the applied current density was varied from 1 to 5 A∙g-1. The absence of any initial voltage loss (i.e. IR drop) indicates a fast current response with low internal resistance. The variation of specific capacitance with applied current density is shown in Figure S5c. The maximum capacitance value obtained for the symmetric carbon//carbon supercapacitor was 20 F∙g-1 at a current density of 1 A∙g-1. Similar to the tests for the carbon-based SSC, Co3O4 SSC tests were carried out (Figure S6a-c). The CV studies show that the maximum working potential for the Co3O4-based supercapacitor is 0.9 V. The SSC cell shows a very rectangular shape. The maximum capacitance value of the SSC was found to be 66 F∙g-1 at a current density of 1 A∙g-1.
12
Figure S7
Figure S7 Heating of Co3O4 samples without preliminary nitrogen heat treatment at (a) 400 ºC and (b) 350 ºC, respectively.
13
References S1 Meher, S. K.; Rao, G. R., Ultralayered Co3O4 for high performance supercapacitor applications. J. Phys. Chem. C 2011, 115, 15646-15654. S2 Wang, Y.; Zhong, Z.; Chen, Y.; Ng, C. T.; Lin, J., Controllable synthesis of Co 3O4 from nanosize to microsize with large-scale exposure of active crystal planes and their excellent rate capability in supercapacitors based on the crystal plane effect. Nano Res. 2011, 4, 695-704. S3 Tang, C. H.; Yin, X.; Gong, H., Superior performance asymmetric supercapacitors based on a directly grown commercial mass 3D Co3O4@Ni(OH)2 core-shell electrode. ACS Appl. Mater. Interfaces 2013, 5, 10574-10582. S4 Wang, D.; Wang, Q.; Wang, T., Morphology controllable synthesis of cobalt oxalates and their conversion to mesoporous Co3O4 nanostructures for application in supercapacitors. Inorg. Chem. 2011, 50, 6482-6492. S5 Zhang, F.; Hao, L.; Zhang, L.; Zhang, X., Solid-state thermolysis preparation of Co3O4 nano/micro superstructures from metal-organic framework for supercapacitors. Int. J. Electrochem. Sci. 2011, 6, 2943-2954. S6 Xiong, S.; Yuan, C.; Zhang, X.; Xi, B.; Qian, Y., Controllable synthesis of mesoporous Co3O4 nanostructures with tunable morphology for application in supercapacitors. Chem. Eur. J. 2009, 15, 5320-5326. S7 Lou, X. W.; Deng, D.; Lee, J. Y.; Feng, J.; Archer L. A., Self-supported formation of needlelike Co3O4 nanotubes and their application as lithium-ion battery electrodes. Adv. Mater. 2008, 20, 258-262. S8 Hu, L.; Peng, Q.; Li, Y., Selective synthesis of Co3O4 nanocrystal with different shape and crystal plane effect on catalytic property for methane combustion. J. Am. Chem. Soc. 2008, 130, 16136-16137. S9 Meng, F.; Fang, Z.; Li, Z.; Xu, W.; Wang, M.; Liu, Y.; Zhang, J.; Wang, W.; Zhao, D.; Guo, X., Porous Co3O4 materials prepared by solid-state thermolysis of a novel Co-MOF crystal and their superior energy storage performances for supercapacitors, J. Mater. Chem. A 2013, 1, 7235-7241. S10 Cui, L.; Li, J.; Zhang, X. G., Preparation and properties of Co3O4 nanorods as supercapacitor material. J. Appl. Electrochem. 2009, 39, 1871-1876. S11 Wang, H.; Zhang, L.; Tan, X.; Holt, C. M. B.; Zahiri, B.; Olsen, B. C.; Mitlin, D., Supercapacitive properties of hydrothermally synthesized Co3O4 nanostructures. J. Phys. Chem. C 2011, 115 (35), 17599-17605. S12 Xia, X. H.; Tu, J. P.; Zhang, Y. Q.; Mai, Y. J.; Wang, X. L.; Gu, C. D.; Zhao, X. B., Freestanding Co 3O4 nanowire array for high performance supercapacitors. RSC Adv. 2012, 2, 1835-1841. S13 Xie, L.; Li, K.; Sun, G.; Hu, Z.; Lv, C.; Wang, J.; Zhang, C., Preparation and electrochemical performance of the layered cobalt oxide (Co3O4) as supercapacitor electrode material. J. Solid State Electrochem. 2012, 17, 55-61. S14 Ji, J.; Zhang, L. L.; Ji, H.; Li, Y.; Zhao, X.; Bai, X.; Fan, X.; Zhang F.; Ruoff, R. S., Nanoporous Ni(OH)2 thin film on 3D ultrathin graphite foam for asymmetric supercapacitor. ACS Nano 2013, 7, 6237-6243. S15 Salunkhe, R. R.; Bastakoti, B. P.; Hsu, C. T.; Suzuki, N.; Kim, J. H.; Dou, S. X.; Hu, C. C.; Yamauchi, Y., Direct growth of cobalt hydroxide rods on nickel foam and its application for energy storage. Chem. Eur. J. 2014, 20, 3084-3088. S16 Tang, W.; Liu, L.; Tian S.; Li, L.; Yue, Y.; Wu, Y.; Zhu, K., Aqueous supercapacitor of high energy density based on MoO3 nanoplates as anode material. Chem. Commun. 2011, 47, 10058-10060. S17 Qu, Q.; Zhang P.; Wang, B.; Chen Y.; Tian, S.; Wu, Y.; Holze, Y., Electrochemical performance of MnO2 nanorods in neutral aqueous electrolytes as a cathode for asymmetric supercapacitors. J. Phys. Chem. C 2009, 113, 14020-14027. S18 Wang, Y. T.; Lu, A. H.; Zhang, H. L.; Li, W. C., Synthesis of nanostructured mesoporous manganese oxides with three-dimensional frameworks and their application in supercapacitors. J. Phys. Chem. C 2011, 115, 5413-5421. 14
S19
S20
Li, H. B.; Yu, M. H.; Wang, F. X.; Liu, P.; Liang, Y.; Xiao, J.; Wang, C. X.; Tong, Y. X.; Yang, G. W., Amorphous nickel hydroxide nanospheres with ultrahigh capacitance and energy density as electrochemical pseudocapacitor materials. Nat. Commun. 2013, 4, Article number: 1894. Banerjee, R.; Phan, A.; Wang, B.; Knobler, C.; Furukawa, H.; O’Keeffe, M.; Yaghi, O. M., Highthroughput synthesis of zeolitic imidazolate frameworks and application to CO2 capture. Science 2008, 139, 939-943.
15
