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NiO-Microflower Formed by Nanowire-weaving Nanosheets with. 3. Interconnected Ni-network Decoration as Supercapacitor Electrode. 4. 5. Suqin Ci, Zhenhai ...

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Supporting Information for:

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NiO-Microflower Formed by Nanowire-weaving Nanosheets with

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Interconnected Ni-network Decoration as Supercapacitor Electrode

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Suqin Ci, Zhenhai Wen,* Yuanyuan Qian, Shun Mao, Shumao Cui, and Junhong Chen,*

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Department of Mechanical Engineering, University of Wisconsin-Milwaukee, Milwaukee,

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Wisconsin 53211, United States

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Corresponding Author* E-mail: [email protected], [email protected]

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Fig. S1. Schematic of the synthesis of Ni-NiO nanocomposites: (1) hydrothermal synthesis; (2)

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annealing of the hydrothermal products; (3) partial reduction of NiO under an H2/Ar

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atmosphere.

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2

NiCO3 ·Ni(OH)2 ·xH2O

Diffraction Intensity (a.u.)

a

10

20

30

1

40 2 theta

50

60

100

70

b

Weight loss (%)

90

80

70

NiCO3 Ni(OH)2

  xH2O 

NiO + H2O + CO2

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In air 50 0 2 3

100

200 300 400 Temperature (C)

500

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Fig. S2. (a) XRD patterns of the as-prepared hydrothermal product, i.e., NiCO3 Ni(OH)2 xH2O; (b)

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Thermal gravimetric analysis (TGA) curve of the as-prepared NiCO3 Ni(OH)2 xH2O.

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Fig. S3. SEM images of the NiO products obtained with a ratio of NiCl2/Urea: (a, b) 5:1; (c, d)

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3:1; (e, f) 1:1; the amount of NiCl2 was fixed at 5 mmol and the reaction temperature was 150

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ºC.

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Fig. S4. SEM images of the NiO products obtained with a ratio of NiCl2/Urea: (a, b) 1:2, (c, d)

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1:10; the amount of NiCl2 was fixed at 5 mmol and the reaction temperature was 150 ºC.

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Fig. S5. SEM images of the NiO products synthesized by adding 0.1 g SDS (a-c): (a) the

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general morphology, (b) the magnified image of porous microspheres constructed from

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nanowires, and (c) the magnified image of ‘microflowers’ constructed from nanosheets; SEM

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images of the NiO products synthesized by adding 0.3 g SDS (d-f): (d) the general morphology,

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(e) the magnified image of porous microspheres constructed from nanowires, and (f) the

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magnified image of ‘microflowers’ constructed from nanosheets; the amount of NiCl2 and urea

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was fixed at 5 mmol and the reaction temperature was 150 ºC.

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Fig. S6. SEM images of the NiO products obtained when adding 1.0 g SDS; the amount of

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NiCl2 and urea was fixed at 5 mmol and the reaction temperature was 150 ºC.

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Fig. S7. SEM images of the NiO products obtained with a hydrothermal reaction time of: (a) 1

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hour; (b) 5 hours; (c) 10 hours; and (d) 20 hours. (Note: 0.6 g SDS; the amount of NiCl2 and

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urea was fixed at 5 mmol and the reaction temperature was 150 ºC)

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Fig. S8. SEM images of the NiO products obtained with a hydrothermal reaction temperature of:

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(a) 120 ºC; (b) 180 ºC.

(Note: 0.6 g SDS; the amount of NiCl2 and urea was fixed at 5 mmol)

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850 852 854 856 858 860 862 864 866 Binding Energy (eV)

532 534 Binding Energy (eV)

528

530 532 534 Binding Energy (eV)

e

Survey NiO

O 1s

536

0

Ni 2p3/2 Ni 2p1/2

d

NiO

536

O KLL

530

Ni LMM2

Satellite

528

Ni LMM1

c

866

O 1s

NiO

Ni 2p3/2

864

Ni LMM

856 858 860 862 Binding Energy (eV)

Relative Intensity (a. u.)

854

C 1s

0

Ni

Relative Intensity (a. u.)

Relative Intensity (a. u.)

NiO

Satellite

852

b

O 1s

Ni 3p Ni 3s

Relative Intensity (a. u.) 850

1

Ni-NiO-5min

a

NiO

Ni 2p3/2

Relative Intensity (a. u.)

Ni-NiO-5min

200

400 600 800 Binding Energy (eV)

1000

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Fig. S9. High resolution XPS spectra of the Ni 2p3/2 (a) and O 1s (b) in Ni-NiO-5min after

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Shirley background removal; High resolution XPS spectra of the Ni 2p3/2 (c) and O 1s (d) in

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the pristine NiO after Shirley background removal, and survey XPS spectrum of the pristine

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NiO. The fitted peak with a binding energy at 531.0 eV is assigned to NiO and the peak at

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532.6 eV is assigned to hydrous species.5

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10

160 140

400

103

98

100

Weight change Temperature

97 96

Ar

80 60

101

Ar

99

20 40

98

300

Air Weight change Temperature

100

40

350

5.0 %

102

T (°C)

120

Weight (%)

99

T (°C)

Weight (%)

450

b

104

a

100

250 200 150

95 0

1 2

5

10

15

20

25

30

35

0

Time (min)

50

100

150

200

250

Time (min)

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Fig. S10. TGA curve of the as-prepared Ni-NiO-5min upon heating to 160 oC under Ar

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atmosphere with a heating rate of 5 oC/min (a), and subsequent heating to 300 oC with a heating

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rate of 5 oC/min and maintaining at 300 °C for 30 minutes under Ar protection to eliminate the

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effect of adsorbed water; the sample was then heated to 450 oC in air to investigate the

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oxidation reaction of metallic Ni (b).

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The Ni content in Ni-NiO-5min was calculated based on the reaction below: Ni + 1/2 O2 = NiO 59 75 x (g) 75x/59 (g) The mass increase is 16x/59, in which 59 and 75 are molecular weights of Ni and NiO, respectively.

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Assuming that there is x (g) metallic Ni in 1 g Ni-NiO-5min sample, which would convert to

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75x/59 (g) NiO after fully oxidizing to NiO. This means the total weight should increase by

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16x/59; i.e., the total weight increases from 1 to 1+16x/59.

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weight increases by 5.0% after heating to 450 oC. Therefore (75x/59-x)/1 = 16x/59 = 5.0%, and

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x is calculated as 0.184, suggesting that there is 18.4 wt.% Ni in the Ni-NiO-5min samples.

The TGA test indicated the total

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0.005

a

NiO

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Pore Volume (cm g Å )

0.004

0.003

0.002

0.001

0.000 0

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10 15 20 Pore Diameter (nm)

1

25

30

0.005

b

Ni-NiO-5min

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Pore Volume (cm g Å )

0.004

0.003

0.002

0.001

0.000 0

2 3

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20 15 10 Pore Diameter (nm)

25

30

Fig. S11. The pore size distribution of the NiO and the Ni-NiO-5min samples.

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Fig. S12. SEM and TEM images of (a-c) Ni-NiO-2min and (d-f) Ni-NiO-10min.

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1 2

Fig. S13. HRTEM images of edge area from two different nanosheets in the Ni-NiO-5min

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samples.

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15

5

0

-5

40 20

b

Ni-NiO-2min mV S-1

0

-40

2

1 2 5 10 20 50 100

0.6

Ni-NiO-10 min

c

mV S-1

0 -2 -4 0.1

0.2

0.3 0.4 0.5 0.6 Potential (V) vs. NHE

-60 0.1

0.7

-1

4

0.3 0.4 0.5 Potential (V) vs. NHE

Specific capacitance (F g )

0.2

1

Current density (A g-1)

1 2 5 10 20 50 100

-20

-10 0.1

2

Current density (A g-1)

-1

Current density (A g )

NiO

10

60

a

1 2 5 -1 10 mV S 20 50 100

0.7

0.2

0.3 0.4 0.5 Potential (V) vs. NHE

0.6

d

NiO Ni-NiO-2 min Ni-NiO-5 min Ni-NiO-10 min

1500 1200

0.7

900 600 300 0 0

20

40 60 -1 Scan rate (mV S )

80

100

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Fig. S14. CVs of different electrodes at different scan rates: (a) NiO; (b) Ni-NiO-2min; (c)

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Ni-NiO-10min; (d) specific capacitance versus CV scan rate for different NiO-based electrodes.

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0.7

0.7

a

NiO 0.5 0.4

1 2 4 10 20 40 100

0.3 0.2 0.1 0

1

50

100

150 Time (s)

-1

Ag

0.4

0.2 0.1

200

250

300

0

0.7

400

600 Time (s)

800

0.7

Potential (V) vs. NHE

Potential (V) vs. NHE

200

-1

Ag

Ni-NiO-5min

0.5 0.4

1 2 4 10 20 40 100

0.3 0.2

0

500

1000

-1

Ag

1500 Time (s)

2500

1200

Ni-NiO-10 min 0.5 1 2 4 10 20 50 100

0.4 0.3 0.2 0.1

2000

1000

d

0.6

0.1

4

1 2 4 10 20 40 100

0.3

0.6

3

Ni-NiO-2min

0.5

c

2

b

0.6 Potential (V) vs. NHE

Potential (V) vs. NHE

0.6

0

50

100

150 Time (s)

A g-1

200

250

Fig. S15. Galvanostatic charge/discharge curves at different current densities: (a) NiO; (b) Ni-NiO-2min; (c) Ni-NiO-5min; (d) Ni-NiO-10min.

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a

300

0.2

200 100 1 2 5 10 20 50 100 200 500

0 -100 -200 -300 -400 -500 -0.4

-0.2

0.0

0.2

0.0 -0.2 -0.4

0.4

0

Potential (V)

1

50

100

150

200

250

Time (s) 2.0

NiO Ni-NiO-5min

c

1500

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Energydensity Power density

Energy density (Wh kg-1)

2000

Specific Capacity (F g-1)

b

0.5 1 2 5 10 20

0.4

d

1.5

1000

4

1.0

500

2

0.5

0

0.0 0

2

5

10 15 Current density (A g-1)

20

Power density (KW Kg-1)

400

Potential

Specific capacitance (F g-1)

500

0 0

5 10 15 Current density (A g-1)

20

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Fig. S16. (a) CVs of two-electrode cell based on pristine NiO at different scan rates; (b)

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galvanostatic charge/discharge curves at different current densities; (c) specific capacitance

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versus current density for NiO- and Ni-NiO-5min based symmetrical supercapacitors; and (d)

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energy and power densities versus current density for NiO symmetrical supercapacitor.

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Fig. S17. Schematic of the formation mechanism of the Ni-NiO microflower.

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10

4

0 2 5 10 -1 20 mV s 50 MnO2 100

-2 -4 -6 0.0

0.1

1 2.5

1.5 1.0

-1.0 0.1

Current density (A g-1)

0.2

0.2 0.3 0.4 0.5 Potential (V) vs. Ag/AgCl

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-0.1

0.1

2 5 10 mV s-1 20 50 100

0.2 0.3 0.4 0.5 Potential (v) vs. Ag/AgCl

0.6

0.6

d

-2 -4

1.5 1.0

r-CuO 0.1

0.2 0.3 0.4 0.5 Potential (V) vs. Ag/AgCl

2 5 10 mV s-1 20 50 100

0.6

f

0.5 0.0 -0.5

Fe2O3 0.1

0.2 0.3 0.4 0.5 Potential (V) vs. Ag/AgCl

0

e

0.0

r-MnO2

2

2.0 2 5 10 mV s-1 20 50 100

0.1

-0.2 0.0

0

-6 0.0

0.6

b

2 5 10 mV s-1 20 50 100

2

8

CuO

2

3

c

-0.5

0.3

4

10 2 5 10 -1 20 mV s 50 100

0.0

0.4

6

-4 0.0

0.6

0.5

-1.5 0.0

8

-2

Current density (A g-1)

Current density (A g-1)

2.0

0.2 0.3 0.4 0.5 Potential (V) vs. Ag/AgCl

Current density (A g-1)

2

Current density (A g-1)

Current density (A g-1)

a

-1.0 0.0

r-Fe2O3 0.1

0.2 0.3 0.4 0.5 Potential (v) vs. Ag/AgCl

0.6

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Fig. S18. CVs of different electrodes at different scan rates: (a) MnO2; (b) r-MnO2; (c) CuO; (d)

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r-CuO; (e) Fe2O3; (f) r- Fe2O3.

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We also investigated the effect of metal oxides (such as r-CuO, r-MnO2, and r-Fe2O3) on the

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supercapacitive behavior. CuO (Nanopowder,