*Corresponding author. Tel.: +86 931 7973255; Fax: +86 931 8859764.E-mail address: zhongai@nwnu.edu.cn (Zhong-ai Hu)

1

Electronic Supplementary Information (ESI) Nitrogen-doped heterostructure carbon functionalized by electroactive

organic molecules for asymmetric supercapacitors with high energy

density

Bingshu Guo, Zhongai Hu*, Yufeng An, Ning An, Pengfei Jia, Yadi Zhang, Yuying

Yang, Zhimin Li.

Key Laboratory of Eco-Environment-Relatged Polymer Materials of Ministry of

Education, Key Laboratory of Polymer Materials of Gansu Province, College of

Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou

730070, PR China

1. Introduction

In order to prove the unzipped carbon nanotubes have good dispersion, we have

prepared the aqueous dispersions of the Multi-walled carbon nanotubes (MWCNTs)

and heterostructure carbon nanotubes (HCNTs) with same concentration (0.1 mg mL-

1). After sonication for 30 min, the HCNTs were homogeneously dispersed to form a

black solution, while the pristine MWCNTs suspended themselves in the water (Fig.

S1a). After a week, the dispersed solution still keeps homogeneous for the HCNTs

while the sedimentation is obviously seen for the MWCNTs (Fig. S1b). For

comparing the hydrophilicity, the contact angle measurements of MWCNTs and

HCNTs were also provided. Seen from Fig S1c and Fig S1d, the corresponding

contact angle for the MWCNTs is about 131.7˚ indicating that the MWCNTs are

hydrophobic material. But for HCNTs, the contact angle is nearly 0˚. This suggests

Electronic Supplementary Material (ESI) for RSC Advances.This journal is © The Royal Society of Chemistry 2016

2

that the HCNTs are completely hydrophilic, which is propitious to the accessibility of

electrolyte ions to active sites during the electrochemical process. Moreover, in order

to certify the specific surface area of HCNTs were increased, we have performed the

BET measurement (Fig. S1e). It inferred from the BET analysis that the specific

surface area of HCNTs (185.3 m2 g-1) is really larger than that of MWCNTs (102.3 m2

g−1), which is consistent with the relevant literatures as shown in Table S1

2. Structure characterization

2.1. FT-IR

Fig S2 shows the FT-IR spectrum of NHC. The broad and intense absorption

band at around 3430 and 1608 cm-1 could be interpreted as O-H stretching vibrations

and deformation vibrations of the water molecules.15 However, the N-H stretching

vibration band at about 3300 cm-1 becomes inconspicuously, which may be covered

by the absorption bond of O-H stretching vibrations. The bands at about 2925, 1398

and 1262 cm-1 are assigned to C-H stretching vibration, C-O-C (epoxy) stretching

vibration and C-N stretching vibration of a secondary amine from NHC,

respectively.16 Besides, the bond near 802 cm-1 corresponds to aromatic C-H out-of-

plane deformation vibration.

3. Electrochemical Characterization

3.1 Contents calculation

A segment of the cyclic voltammogram at a scan rate of 20 mV s-1 was

integrated according to the equation (1) and (2):

3

(1)1b b

a a

V V

V V

IQ Idt dV IdVdV vdt

(2)A A A AQm n M MzF

where Q (C), V (V), I (A), t (s), mA (g), nA (mol), MA (mol g-1), F and z represent

voltammetric charge, potential, instantaneous anodic (cathodic) current, sampling

time, mass of the material that takes part in redox reactions, amount of substance,

molar mass, Faraday constant and stoichiometric coefficient of electron transport in

the electrochemical processes, respectively. The Va (V) and Vb (V) are defined as the

selected boundaries of potential range. The Q is numerically equal to the integral area

of the dash area as shown in Fig S5 (a and b). The calculations indicated that the

contents of TCBQ and AQ are about 22.1% and 18.6% of the total mass in the

optimal sample, respectively.

Fig. S6a displays the CV curves of TCBQ-NHC with different mass ratio at a

scan rate of 10 mV s-1. When the content of TCBQ-NHC is relatively low (1:4 and

1:5), the CV curves show a single redox couple at the potential about 0.5 V. With

increasing of the content of TCBQ (1:3), the CV curve appears the other pair of

shoulder peaks at the potential around 0.4 V. At this point, the electrode has a

maximum specific capacitance of 365 F g-1 with the current density at 1 A g-1. As the

TCBQ content continues increase (1:2), the peak intensity of TCBQ-NHC is gradually

weakened. The specific capacitances of TCBQ-NHC with different mass ratio are

shown in Fig S6b. For AQ-NHC, with increasing of the content of AQ-NHC (1:4 to

1:2), the shapes of the CV curve have almost no obverse change (Fig S6c).

4

Meanwhile, the specific capacitances of AQ-NHC with different mass ratio are

presented in Fig S6d. Among them, the maximum specific capacitance of 331 F g-1 is

achieved when the AQ-NHC content is 1:4.

In addition, we also directly used HCNTs as substrate to absorb AQ through

refluxing to achieve AQ functionalized HCNTs (AQ-HCNTs). Fig S7 shows a series

results of electrochemical measurements. As shown in Fig S7a, the CV curves display

a couple of redox peaks with oxidation and reduction peaks locating at the potential

near -0.09 and -0.11 V, respectively. Fig. S7b gives the galvanostatic charge-

discharge (GCD) curves of the HCNTs and AQ-HCNTs at the current density of 1A

g-1. Based on calculation, the HCNTs show the specific capacitance of 165 F g-1,

which is approximately 10 times larger than the pristine MWCNTs (12 F g-1). After

modifying, the specific capacitance of AQ-HCNTs is 285 F g-1. When the current

density is 20 A g-1, the specific capacitance retentions of MWCNTs, HCNTs and AQ-

HCNTs are 51.4%, 71.5% and 71.2% of the initial value at 1 A g-1.

5

0.0 0.2 0.4 0.6 0.8 1.00

500

1000

1500

2000

2500

Qua

ntity

ads

orbe

d (c

m3 /g

)

Relative pressure (P/P0)

HCNTs MWCNTs

e

Fig. S1 Photographs of aqueous dispersions of MWCNTs and HCNTs (a, b) at a

concentration of 0.1 mg mL-1, contact angle measurements of MWCNTs (c), and

HCNTs (d), Nitrogen adsorption/desorption isotherms of MWCNTs and HCNTs (e).

6

Table S1. Specific surface area and specific capacitance comparison of different

materials.

Pristine

MWCNTs

(m2 g−1)

Dissected

MWCNTs

(m2 g−1)

Specific

capacitance

(F g-1)

Ref

(year)

Porous

carbon

(m2 g-1)

Specific

capacitance

(F g-1)

Ref

(year)

47 85 256@0.3 A g-1 1 (2012) 1084 308@1 A g-1 8 (2015)

17.6 ± 2.4 33.1 ± 0.3 232.9@1A g-1 2 (2013) 1580 855 @1 A g-1 9 (2015)

172 391 152 @ 1 A g-1 3 (2011) 2572 228 @1 A g-1 10 (2015)

291 511 _ 4 (2010) 1938 254 @1 A g-1 11 (2015)

47.3 321.6 _ 5 (2014) 1749 313 @1 A g-1 12 (2015)

93 120 _ 6 (2014) 2080 304 @ 1 A g-1 13 (2014)

30 161 _ 7 (2014) 2988 306 @1 A g-1 14 (2015)

102.1 185.3 165 @ 1A g-1 This work 1454 251 @ 1A g-1 This work

4000 3500 3000 2500 2000 1500 1000 500

802

2925 12

6211

18

1398

1608

3430

Tran

smitt

ance

(a.u

.)

Wavenumber (cm-1)

Fig. S2 FT-IR spectrum of NHC

7

282 284 286 288 290Banding energy (eV)

Inte

nsity

(a.u

.)

N-sp3 C/C=O

N-sp2 C/C-O

sp2-sp2 C C1s NHCa

282 284 286 288 290

b

N-sp3 C/C=O

sp2-sp2 C

N-sp2 C/C-O

C 1s TCBQ-NHC

Banding energy (eV)

Inte

nsity

(a.u

.)

282 284 286 288 290

c

N-sp3 C/C=O

N-sp2 C/C-O

sp2-sp2 C

Banding energy (eV)

Inte

nsity

(a.u

.)

C 1s AQ-NHC

528 530 532 534 536 538

d

Banding energy (eV)

Inte

nsity

(a.u

.)C=O

O 1s NHC

C-O-CC-OH

528 530 532 534 536 538

e

Banding energy (eV)

Inte

nsity

(a.u

.)

C=OC-OH C-O-C

O 1s TCBQ-NHC

528 530 532 534 536 538

f

Banding energy (eV)

Inte

nsity

(a.u

.) C-O-CC-OH

C=O

O 1s AQ-NHC

Fig. S3 C 1s regions of NHC, TCBQ-NHC and AQ-NHC (a-c), O 1s regions of NHC,

TCBQ-NHC and AQ-NHC (d-f).

8

0.0 0.2 0.4 0.6 0.8 1.040

80

120

160

200

240

Q

uant

ity a

dsor

bed

(cm

3 /g)

Relative Pressure (p/p0)

BET Surface Area: 234.5 m2 g-1

Fig. S4 Nitrogen adsorption/desorption isotherms of carbonized PANI/HCNTs.

0.0 0.2 0.4 0.6 0.8 1.0-30

-20

-10

0

10

20

30

VbVa

Vb

Potential (V vs. SCE)

Spec

ific c

urre

nt (A

g-1)

NHC TCBQ-NHC

a

Va

-0.4 -0.2 0.0 0.2 0.4 0.6-40

-30

-20

-10

0

10

20

30

40

AQ-NHC NHC

VbVa

Vb

Spec

ific

curr

ent (

A g

-1)

Potential (V vs. SCE)

b

Va

Fig. S5 CV curves of TCBQ-NHC (a) and AQ-NHC (b) at 20 mV s-1.

9

0.0 0.2 0.4 0.6 0.8 1.0

-12

-8

-4

0

4

8

12

Spec

ific c

urre

nt (A

g-1)

Potential (V vs. SCE)

1:5 1:4 1:3 1:2

aTCBQ-NHC

0

60

120

180

240

300

360

420

1:21:31:4

260

365

304

Spec

ific c

apac

itanc

e (F

g-1)

278

TCBQ-NHCb

1:5

-0.4 -0.2 0.0 0.2 0.4 0.6-20

-15

-10

-5

0

5

10

15

20

1:2

1:4

cAQ-NHC

Spec

ific

curr

ent (

A g

-1)

Potential (V vs. SCE)

1:3

0

50

100

150

200

250

300

350

1:21:31:4

287331 310d AQ-NHC

Spec

ific c

apac

itanc

e (F

g-1)

Fig. S6 the CV curves of TCBQ-NHC (a) and AQ-NHC (b) with different mass ratio

at a scan rate of 10 mV s-1, the specific capacitance of TCBQ-NHC (c) and AQ-NHC

(d) with different mass ratio at the current of 1 A g-1.

10

-0.4 -0.2 0.0 0.2 0.4 0.6-100-80-60-40-20

020406080

100a

Spec

ific

curr

ent (

A g

-1)

Potential (V vs. SCE)

100 mV s-1

50 mV s-1

30 mV s-1

20 mV s-1

10 mV s-1

5 mV s-1

0 100 200 300 400 500-0.4

-0.2

0.0

0.2

0.4

0.6

Po

tent

ial (

V v

s. SC

E)

Time (s)

AQ-HCNTs rHCNTs

b

0 5 10 15 200

50

100

150

200

250

300

350

54.1%

71.5%

Spec

ific

capa

cita

nces

(F g

-1)

Current density (A g-1)

AQ-HCNTs rHCNTs MWCNTs

71.2%

c

Fig. S7 the CV curves of AQ-HCNTs (a) at different scan rates, GCD curves of AQ-

HCNTs (b) at current density of 1 A g-1 and specific capacitances of AQ-HCNTs (c)

at various current density.

11

References

1 H. Wang, Y. Wang, Z. Hu, X. Wang, ACS applied materials & interfaces, 2012,

4, 6827-6834.

2 L. Lin, M. Yeh, J. Tsai, Y. Huang, C. Sun and K. Ho, Journal of Materials

Chemistry A, 2013, 1, 11237.

3 G. Wang, Y. Ling, F. Qian, X. Yang, X. Liu and Y. Li, Journal of Power

Sources, 2011, 196, 5209-5214.

4 M. Rafiee, W.Lu, A. Thomas, A. Zandiatashbar, J. Rafiee, J. Tour and N. Koratkar,

Acs Nano, 2010, 4, 7415-7420.

5 B. Xiao, X. Li, X. Li, B. Wang, C. Langford, R. Li and X. Sun, The Journal of

Physical Chemistry C, 2014, 118, 881-890.

6 J. Zhang, Y. Wang, J. Zang, G. Xin, H. Ji, Y. Yuan, Materials Chemistry and

Physics, 2014, 143, 595-599.

7 J. Hernández, P. Laporta, F. Gutiérrez, M. Rubianesb, G. Rivasb, M. Martínez,

Electrochemistry Communications, 2014, 39, 26-29.

8 Q. Zhao, X. Wang, H. Xia, J. Liu, H. Wang, J. Gao, Y. Zhang, Electrochimica Acta,

2015, 173, 566-574

9 T. Lin, I. Chen, F. Liu, C. Yang, H. Bi, F.Xu, F. Huang, Science, 2015, 350, 1508-

1513.

10 C. Zhong, S. Gong, Li. Jin, P. Li, Q. Cao, Materials Letters, 2015, 156, 1-6.

11 M. Yeh, L. Lin, C. Sun, Y. Leu, J. Tsai, C. Yeh, R. Vittal and K. Ho, The

Journal of Physical Chemistry C, 2014, 118, 16626-16634

12

12 J. Zhao, H. Lai, Z. Lyu, Y. Jiang, K. Xie, X. Wang, Q. Wu, L. Yang, Z. Jin, Y.

Ma, J. Liu and Z. Hu, Advanced materials, 2015, 27, 3541-3545.

13 Y. Zhao, M. Liu, X. Deng, L. Miao, P. Tripathi, X. Ma, D. Zhu, , Z. Xu, Z. Hao, L.

Gan, Electrochimica Acta, 2015, 153, 448-45.

14 F. Zheng, Y. Yang and Q. Chen, Nature communications, 2014, 5, 5261.

15 H. Wang, H. Yi, X. Chen, X. Wang, Journal of Materials Chemistry A, 2014, 2,

1165-1173.

16 C. Wu, X. Wang, B. Ju, L. Jiang, H. Wu, Q. Zhao, Journal of Power Sources, 2013,

227, 1-7.