Nitrogen-enriched Nanoporous Polytriazine for High Performance

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Nitrogen-enriched Nanoporous Polytriazine for High Performance Supercapacitor Application Monika Chaudhary, Arpan Kumar Nayak, Raeesh Muhammad, Debabrata Pradhan, and Paritosh Mohanty ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b04254 • Publication Date (Web): 20 Mar 2018 Downloaded from http://pubs.acs.org on March 22, 2018

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ACS Sustainable Chemistry & Engineering

1

Nitrogen-enriched Nanoporous

Polytriazine

for

High

Performance

2

Supercapacitor Application

3

Monika Chaudhary,† Arpan Kumar Nayak,‡ Raeesh Muhammad,† Debabrata Pradhan‡ and

4

Paritosh Mohanty†*

5

†

6

Uttarakhand-247667, INDIA

7

‡

8

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

Functional Materials Laboratory, Department of Chemistry, IIT Roorkee, Roorkee,

Materials Science Centre, IIT Kharagpur, West Bengal-721302, INDIA

9 10

ABSTRACT: Polytriazine with high nitrogen content (c.a. 50.5 wt%) has been

11

synthesized by an ultrafast microwave assisted method using melamine and cyanuric

12

chloride. The nitrogen enriched nanoporous polytriazine (NENP-1) has exhibited high

13

specific surface area (maximum SABET of 838 m2 g-1) and narrow pore size

14

distribution. The NENP-1 has been employed as electrode materials for supercapacitor

15

applications. A maximum specific capacitance (Csp) of 1256 F g-1 @1 mV s-1 and 656

16

F g-1 @1 A g-1 estimated from the cyclic voltammetry (CV) and galvanostatic

17

charge/discharge

18

configuration. This Csp value is considered as very high for non-metallic system

19

(organic polymer). Superior capacitance retention of 87.4 % of its initial Csp was

20

observed after 5000 cycles at a current density of 5 A g-1 demonstrates its potential as

21

efficient electrode material for practical applications. To test this claim, an asymmetric

22

supercapacitor device (ASCD) was fabricated. The Csp of the device in the two

23

electrode configuration are 567 F g-1 @5 mV s-1 and 287 F g-1 @4 A g-1 in the CV and

24

GCD measurements, respectively. The ASCD has shown superior energy density and

25

power density of 102 Wh kg-1 and 1.6 kW kg-1, respectively, at the current density of 4

(GCD)

measurements,

respectively,

1 ACS Paragon Plus Environment

in

a

three

electrodes

ACS Sustainable Chemistry & Engineering 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

1

A g-1. The energy density is much higher than the best reported supercapacitors and

2

also close to the commercial batteries. This indicates the material could bridge the gap

3

between the commercial batteries and supercapacitors.

4

Keywords: Nitrogen enriched polymer, Polytriazine, Microwave-assisted synthesis, Energy

5

density, Supercapacitor, Ragone plot

6

Introduction

7

High surface area nanoporous organic polymers with high nitrogen content have got

8

tremendous interest of late because of their applications in gas storage, energy storage,

9

semiconductors, catalysis, photocatalysis, and electrocatalytic properties.1-6 These nitrogen

10

enriched framework materials have shown great potential to tune the applications, especially,

11

in the gas storage and electrochemical supercapacitors.1,2 The lone pair of electrons in

12

nitrogen can act as Lewis base and plays very important role in electrochemical applications

13

by manipulating the formation of the electrical double layers.7-10 It remains a great challenge

14

to synthesize nitrogen enriched nanoporous polymers (NENPs) with the high surface area by

15

rationally designing at molecular scale using cheap reagents.11 The major challenges for

16

synthesizing these materials being finding appropriate precursors and reaction conditions so

17

that thermodynamically unfavorable high surface area nanoporous materials could be

18

produced.12 Some of the notable synthetic strategies adopted were condensation method,

19

solvothermal synthesis and cyclotrimerization approaches.13-15

20

The high power density, excellent reversibility, operation at wide temperature ranges

21

by supercapacitors have attracted numerous research groups to explore the research area with

22

various objectives, such as; (i) designing the electrode materials starting from molecular

23

architecture, (ii) find out appropriate electrolytes and (iii) designing the devices.16-18 Among

24

these, the research on electrode materials is in the forefront.16,19 Carbonaceous electrode

25

materials are considered as most widely explored electrode materials, however, the low 2 ACS Paragon Plus Environment

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1

energy density limited their applications.20 In order to improve the energy density issue,

2

emphasis was given to enhance the capacitance of supercapacitors.21 As most of the modern

3

day supercapacitors are based on the electric double layer capacitor (EDLC) concept,

4

synthesizing materials with superior textural properties such as high specific surface area

5

(SA) and controlled pore size distribution (PSD) is desirable.22-24 Moreover, the introduction

6

of heteroatoms, such as N, S and P etc. in the high surface area materials is an additional

7

advantage.2,25,26 Many of the above expected properties could be realized by synthesizing

8

NENPs with controlled PSD and high SA. Some of the recently explored porous organic

9

polymers (POPs) showing good supercapacitor applications are HCPANIs, TaPa-Py COF,

10

DAAQ-TFP COF, TpDAB and Aza-CMPs.25-30 Among these POPs, high surface area

11

polytriazines stand out due to their high nitrogen content. The highest N content reported in

12

the NENPs so far is 53.27 wt%.31 In some of the recent reports, N was also doped in the

13

porous carbon frameworks to enhance the supercapacitor applications.32

14

In this investigation, the condensation of inexpensive melamine and cyanuric chloride

15

is carried out keeping in mind the high nitrogen content in both due to the presence of triazine

16

rings and their ability to form three dimensional frameworks.33-36 An additional advantage

17

being the ease of condensation due to the facile nucleophilic substitution reaction between

18

cyanuric chloride and melamine owing to the presence of easily removable chloride groups in

19

cyanuric chloride.36 The synthesized NENP-1 was employed as an electrode material for

20

supercapacitor application.

21

Experimental Section

22

Equimolar mixture of melamine (99 %, Sigma Aldrich, India) and cyanuric chloride (99 %,

23

Sigma Aldrich, India) were condensed in DMSO using a microwave reactor in the presence

24

of triethylamine (Fisher Scientific, India) as proton absorber. Typically, 1 mmol of each of the

25

reactants condensed at 140 °C in 20 ml of DMSO with a microwave power of 400 W and



1

reaction time of 30 min. The synthesized white fluffy product was filtered and washed with

2

distilled water and dried. The specimen was designated as NENP-1.

3

The obtained specimen was investigated by FTIR (Perkin Elmer SpectrumTwo

4

spectrophotometer) and cross polarization magic angle spinning (CP-MAS) 13C NMR spectra

5

(JEOL Resonance JNM-ECX-400II). XPS analysis was conducted on PHI 5000 Versa Probe

6

III. XRD pattern was obtained using Rigaku Ultima IV with CuKα source. The microstructure

7

of the specimen was studied by FESEM (TESCAN MIRA3) and TEM (TECNAI G2S-

8

TWIN). The elemental analysis (C/H/N/S) was conducted using Thermo Flash 2000. TGA

9

was performed on EXSTAR TG/DTA6300. The N2 sorption was carried out using Autosorb-

10

iQ2 (Quantachrome Instruments, USA).

11

The conductivity measurement was carried out using Nanomagnetics ezHEMS. The

12

electrochemical analysis was performed by cyclic voltammetry (CV), galvanostatic charge-

13

discharge (GCD) and electrochemical impedance spectroscopy (EIS) techniques in CHI 760D

14

electrochemical workstation. A three-electrode configuration mode with active material

15

modified glassy carbon electrode (GCE), Pt wire, and saturated calomel electrode were used

16

as working, counter and reference electrodes, respectively. 0.1 M H2SO4 was used as an

17

electrolyte for the electrochemical studies. Prior to preparation of the working electrode, the

18

GCE surface was cleaned using a slurry of alumina powder and performing ultrasonication

19

for 30 min. The active material slurry was prepared by dispersing 5 µl of PTFE (5 wt% of

20

ethanol) and 5 mg of NENP-1 in ethanol (5 mg ml−1) through ultrasonication for 30 min. 50

21

µl of the slurry was drop casted on the GCE surface and allowed to dry for overnight at 60 °C

22

for the electrochemical investigation. Asymmetric supercapacitor device (ASCD) was

23

fabricated using commercially available Whatman 54 filter paper, active material, and

24

activated carbon, as separator, negative and positive electrode material, respectively. First, the

25

active material slurry was prepared by mixing either active material or activated carbon and 5


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1

µl of PTFE (5 wt% of ethanol) in 9:1 mass ratio using ethanol (5 mg ml−1) with the help of

2

ultrasonication for 30 min. The as-prepared slurries were then drop casted individually on the

3

graphite sheet of 0.5×0.5 cm2 area and dried at 60 °C for overnight. The graphite sheet coated

4

with active material and activated carbon was used as negative and positive electrodes,

5

respectively. The specific capacitance (Csp) was calculated from CV curves measured at

6

various scan rates using equation: ∫

= ν ∆

7

(1)

8

where, Csp is specific capacitance (F g−1), I is current (A), m is the mass of active

9

material (g), ν is the scan rate (mV s−1), and ∆V is the potential window (V).

10

The Csp from GCD curve was calculated using the below given equation (2): =

11

∆

(2)

∆

12

where I stand for applied current, ∆V represents the potential window and ∆t signifies

13

discharge time (s) and m denotes the mass of active material (g).

14

The energy density and power density of ASCD was calculated using equation (3)37,38 and

15

(4)7,39,40

16

=

17

= ∆

(3)

(4)

18

where, E is the energy density (Wh kg−1), Csp is specific capacitance (F g−1), ∆V is the

19

potential window (V), P is power density (kW kg−1) and ∆t is the discharge time.

20

Results and Discussion

21

Successful condensation of melamine and cyanuric chloride under the irradiation of

22

microwave yields product as per the Scheme S1, which has been confirmed by the

23

MAS NMR and FTIR spectroscopic investigation. A strong signal at 166.7 ppm in the

24

CP-MAS NMR spectrum in Figure 1a originated from the carbon of the triazine ring 5 ACS Paragon Plus Environment

13

C CP13

C


1

confirms the condensation. Observation of a small signal at 153 ppm may be attributed to the

2

side group functionalities originated from cyanuric chloride (Figure S1). Further, the

3

observation of only broadband (instead of multiple bands observed for primary amine) above

4

3350 cm-1 in the FTIR spectrum (Figure 1b) along with the absence of the band at 850 cm-1

5

due to the C-Cl stretching vibration further corroborate the NMR results. The elemental

6

composition estimated from the CHNSO analysis reveals the high nitrogen content of 50.5

7

wt% in the specimen (C:37.9, N:50.5, H:2.4, S:1.6). Further, the chemical environment of the

8

elements present in the specimen was studied using XPS (Figure S2). To analyse the detailed

9

chemical states of C and N elements, their high resolution XPS scan were also recorded. The

10

high-resolution C 1s scan given in Figure 1(c) shows the peaks at 284.7, 285.7 and 288.1 eV.

11

The peak at 285.7 eV is assigned to sp2-C of the triazine ring.32,41-43 The peaks at 284.7 and

12

288.1 eV are ascribed to trapped DMSO, oxidized carbon and graphitic impurity arises from

13

the carbon tape used for XPS investigation (Figure S3).42,43 The high-resolution N 1s XPS

14

spectra shown in Figure 1d reveals the peaks at 398.4 and 399.7 eV originated primarily due

15

to pyridine (N6) and pyrrolic (N5) types of nitrogen, respectively (Figure 1d).32,41-43 As

16

documented earlier, the higher N contents enhance the chemical wettability of the electrode

17

materials. The N5 type of nitrogen provides higher pseudo-capacitance by participating in

18

redox reaction as compared to other types of nitrogen.41-43 The high nitrogen content of 50.5

19

wt% along with the higher N5 (62.4 at%) type as compared to N6 (32.7 at%) type could be a

20

direct bearing on the electrochemical supercapacitor applications.

21

Nearly spherical inter-grown nanoparticles of the average size of 220 nm could be

22

seen in the FESEM image (Figure 1e). The TEM image (Figure 1f) further reveals the porous

23

nature of the specimen with the pore size in the range of 2 to 6 nm. The XRD (Figure S4) and

24

SAED pattern inset of Figure 1d confirm the amorphous nature of the specimen. NENP-1

25

shows good thermal stability upto 350 °C in air (Figure S5). 6 ACS Paragon Plus Environment

Page 6 of 23

(a)

166.7 HN

# - Triethylamine

NH

N N

N #

HN

∗- Side bands

55.6

∗

∗

153

250

200

150

100

#

(b) NENP-1 Triazine ring

Melamine

Cyanuric chloride

39.6 15.1 50

C-Cl str

4000

0

3500

(c)

C1s Intensity (a.u.)

-C=N -C-O

290

289

288

287

286

285

284

283

2500

2000

1500

1000

-1

500

N1s

(d)

C-C

282

H N

C

404

402

N

398.4 eV

399.7 eV

400

398

396

394

Binding energy (eV)

Binding energy (eV)

2

3000

Wavenumber (cm )

Chemical shift (ppm)

1

Intensity (a.u.)

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


Transmittance (a.u.)

Page 7 of 23

3 13

4

Figure 1. (a)

C CPMAS NMR spectrum, (b) FT-IR spectra (c) High resolution C1s XPS

5

spectra (d) High resolution N1s XPS spectra (e) FE-SEM image and (f) HRTEM images of

6

NENP-1 (inset: SAED).

7

The N2 sorption isotherm measured at 77 K as shown in Figure 2(a) is a type-I

8

isotherm with sharp uptake at low-pressure region indicate the microporous nature of the

9

specimen. Additionally, narrow hysteresis was extended from low to high-pressure range

10

infers a hierarchical pore structure with the presence of both micro and mesopores, which

11

was further confirmed from the PSD [Figure 2(b)]. The nanopores centered at 1.6 nm

12

(micropore) and 3.8 nm (mesopore) can be seen in the PSD. The BET (SABET) and Langmuir 7 ACS Paragon Plus Environment


1

(SALang) specific surface areas were estimated to be 838 and 1102 m2 g-1, respectively (Figure

2

S6), with a total pore volume of 0.65 cm3 g-1. 25 20 15 10

Adsorption Desorption

5 0 0.0

3

(a)

Surface Area (m 2 g -1 )

Gas Uptake (mmol g -1)

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

Page 8 of 23

0.2

0.4

0.6

Relative Pressure (P/P0)

0.8

1.0

150

(b)

100

50

0 0

4

8

12

Pore width (nm)

16

20

4

Figure 2. Gas sorption studies of NENP-1: (a) N2 sorption isotherm measured at 77 K, (b)

5

DFT pore size distribution estimated from N2 isotherm.

6

The observation of large specific surface area, narrow PSD and high N content in

7

NENP-1, has encouraged us to investigate the electrochemical supercapacitor application. It

8

has already been documented in some of the recent literatures that not only the superior

9

textural properties but also the electrical conductivity of electrode material plays important

10

role in tuning the electrochemical performance of supercapacitors.8,9,16,30 The electrical

11

conductivity of 0.95 S cm-1 at RT was estimated in the NENP-1 measured using a four point

12

probe method. This value of conductivity is high considering the nature of the materials and

13

the textural properties. In general, the electrical conductivity of some of the polymeric

14

materials have value in the range of 104 to 10-7 S cm-1. However, the introduction of

15

nanopores in the material could substantially reduce the electrical conductivity.8,30

16

Considering the high specific surface area and large pore volume, the estimated electrical

17

conductivity for this nanoporous NENP-1 could be beneficial for enhancing the capacitance

18

and charge storage capacity of the electrode.

19

The NENP-1 was subjected to CV and GCD measurements in a three electrodes

20

configuration using 0.1 M H2SO4 as electrolyte. The CV curves of NENP-1 [Figure 3(a)]

21

measured at different scan rates in the range of 1 to 100 mV s-1 exhibited nearly rectangular 8 ACS Paragon Plus Environment

Page 9 of 23

1

profile with a pair of minor reversible humps, which remain similar even at high scan rate up

2

to 100 mV s-1. Thus, the capacitive response for NENP-1 originates from the combination of

3

electrical double layer (EDL) capacitance and pseudo-capacitance. The EDL feature is

4

mainly due to the high SABET of nanoporous polytriazine and the reversible redox

5

transformation of N functionality of bridged amine and triazine ring contributed the pseudo-

6

capacitance feature.41 As discussed above in XPS, the higher N5 (62.4 at%) type of nitrogen

7

compared to N6 (32.7 at%) type has a direct bearing on the higher contribution of pseudo-

8

capacitance.41-43 The specific capacitance (Csp) of 1256 F g-1 at the scan rate of 1 mV s-1

9

estimated for NENP-1 is on the higher side. It is worth mentioning that the Csp of NENP-1 is

10

comparable with many of the recently reported materials such as Aza-CMP@450 (946 F g-1

11

@0.1 A g-1),29 and even better than TpDAB (432 F g-1 @0.5 A g-1),28 TaPa-Py COF (102 F g-

12

1

@0.5 A g-1)26 and DAAQ-TFP COF (48 ± 10 F g-1 @0.1 A g-1) 27. -1

(i) 1 mV s -1 (ii) 5 mV s -1 (iii) 10 mV s -1 (iv) 20 mV s -1 (v) 40 mV s -1 (vi) 60 mV s -1 (vii) 80 mV s -1 (viii) 100 mV s

29

(a)

Potential (V vs SCE)

-1

Current density (A g )

58

(i) . . . . (viii)

0

-29

-0.4

0.0

0.4

-1

(i) 1 A/g - 656 F g -1 (ii) 2 A/g - 580 F g -1 (iii) 3 A/g - 540.4 F g -1 (iv) 4 A/g - 509.1 F g -1 (v) 8 A/g - 362.7 F g

(b)

1.06

0.53

0.00

-0.53

-0.8

(v) (iv) (iii) 0

0.8

(ii)

500

(i)

1000

1500

2000

Time (s)


13

-1

14

20

40

60

80

500

100

(c)

1200 1000 800

CV

600 400

CD

200 0 0

4

6

-1


8

10

(d)

400

300

200

0.8

0.4

0.0 st

1 cycle th 5000 cycle

-0.4

100 0

50

100

150

200

250

Time (s)

0

2

−1

Current density = 5 A g


Scan rate (mV s )

0

-1

1400

Specific capacitance (F g )

Specific capacitance (F g -1)

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

1000


2000

3000

Cycle number

4000

5000


1

Figure 3. (a) CV curves at different scan rates, (b) GCD curves at various current densities,

2

(c) Specific capacitance vs scan rate/current density and (d) Cyclic stability of NENP-1 tested

3

using GCD.

4

It is interesting to note that even at higher scan rate of 5, 10, 20, 80 and 100 mV s-1,

5

NENP-1 has exhibited Csp of 1064, 975, 866, 625 and 497 F g-1, respectively. A small

6

decrease in the Csp values with the increased scan rate is believed to be due to the hierarchical

7

pore structure, which facilitates the smooth transfer of ions, at higher scan rates. Moreover,

8

the smallest pores in the sample is also on the higher side of the micropore range that

9

facilitates the ion transport.44 In order to further understand the electrochemical

10

supercapacitor behavior, the NENP-1 was further employed for GCD analysis. The GCD

11

curves [Figure 3(b)] measured at different current densities between 1 to 8 A g-1 have

12

exhibited regular triangular shapes with minor kink, which suggests reversible redox reaction

13

during charging discharging processes. Almost inconspicuous IR drop was observed in GCD

14

curve indicating a minute ohmic resistance and good capacitive performance. The maximum

15

Csp calculated to be 656 F g-1 at the current density of 1 A g-1 [Figure 3(c)]. As expected, the

16

drop in Csp is not sharp on increasing the current density (580 F g-1 @2 A g-1, 540 F g-1 @3 A

17

g-1, 509 F g-1 @4 A g-1 and 362 F g-1 @8 A g-1), which could be attributed to the facile

18

diffusion of proton, due to which most of the active sites on electrode surface are accessible

19

to electrolyte.44,45

20

The cyclic stability of the prepared electrode has been tested using GCD. Almost

21

87.4% of retention from its initial Csp was observed even after 5000 cycles at a current

22

density of 5 A g-1 [Figure 3(d)], further reveals its importance as electrode material for

23

supercapacitor application.


Page 10 of 23

(a)

NENP-1 Activated carbon

4

0

-8

-0.5

-1

-1

Current density (A g

-1

)

8

-4

0.0

0.5

1.0

0.0

(i) 4 A/g - 287.5 F g -1 (ii) 5 A/g - 287.5 F g -1 (iii) 6 A/g - 255.2 F g -1 (iv) 7 A/g - 229.7 F g -1 (v) 8 A/g - 209.5 F g -1 (vi) 9 A/g -191.3 F g

1.0

0.5

0.0

(vi) (v) (iv) (iii) 0

0

-1

(c)

200

(ii) 400

0.8

1.2

(i) 600

20

Scan rate (mV s 40

60

-1

)

80

1.6

100

(d)

600

400

CV 200

CD 0

800

Time (s)

2

0.4


Specific capaitance (F g -1 )


1.5

(b)

24 (i) 5 mV s -1 (ii) 10 mV s -1 (iii) 20 mV s -1 (iv) 40 mV s 12 -1 (v) 60 mV s -1 (vi) 80 mV s -1 (vii)100 mV s 0 (i) . . . -12 . (vii)


1

4

5

6

7

-1


8

9

80

(e) 2.0

(f)

60 1.5

Z'' (ohm)

Energy 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



Page 11 of 23

40

0-1.6 V 20

4

5

6

7

8

1.0

0.5

9

0.0

6

-1

3


8

10

Z' (ohm)

4

Figure 4. (a) Cyclic voltammograms of NENP-1 and activated carbon recorded using three

5

electrode system at 10 mV s-1, (b) CV curves at different scan rates, (c) GCD curves at

6

various current density, (d) Specific capacitance vs. scan rate/current density of NENP-1

7

ASCD, (e) Energy efficiency vs. current density and (f) Nyquist plot of NENP-1 (inset:

8

equivalent circuit diagram).

9

The high Csp estimated both from the CV and GCD studies of the three electrodes

10

configuration have encouraged us to further investigate the device behavior of NENP-1 in

11

two electrodes asymmetric configuration. An asymmetric supercapacitor device (ASCD) was

12

fabricated, using NENP-1 and activated carbon as negative and positive electrodes, 11 ACS Paragon Plus Environment


1

respectively. Commercially available Whatman 54 filter paper was used as a separator. The

2

electrochemical performance of the ASCD was studied in 0.1 M H2SO4 as electrolyte. To

3

observe the maximum performance of the NENP-1//AC based ASC device, mass ratio of

4

negative to positive electrode was measured using the charge balance theory (Q+ = Q−).

5

According to charge balance theory,

6

Q+ = Q−

(5)

7

m+ × C sp + × ∆ V + = m− × C sp − × ∆ V −

(6)

8

m+ Csp − × ∆V− = m− Csp + × ∆V+

(7)

9

m+ 975 × 1.6 = = 3.00 m− 325 × 1.6

(8)

10

where Csp refers to the specific capacitance (F g−1) at 10 mV s−1 scan rate, ∆V is the potential

11

window (V), and m stands for mass of the electrode (g). From the CV profile [Figure 4(a)],

12

the specific capacitance of NENP-1 and AC was calculated to be 975 F g−1 and 325 F g−1,

13

respectively at 10 mV s−1. The mass ratio of NENP-1 and AC was 0.33 in the ASC device.

14

The mass of NENP-1 and AC used in the fabrication of ASC device is 6.0 and 2.0 mg,

15

respectively. Hence the total mass of the ASCD is 8 mg. The individual voltammograms of

16

NENP-1 and AC was recorded [Figure 4(a)] by three electrode system at 10 mV s-1 in 0.1 M

17

H2SO4 electrolyte. The AC and NENP-1 has the potential window from −0.6 to 1.0 V. Thus,

18

the total potential window was found to be 1.6 V in 0.1 M H2SO4, suggesting that the

19

operating cell voltage could be extended up to 1.6 V for two-electrode ASCD device.

20

The CV [Figure 4(b)] and GCD [Figure 4(c)] profiles have shown a similar trend to

21

three electrode configuration. The Csp was estimated to be 567 F g-1 at 5 mV s-1 and 287 F g-1

22

at 4 A g-1, from CV and GCD analysis, respectively [Figure 4(d)]. As expected, the Csp of the

23

ASCD is lower compared to the three electrodes configuration. To the best of our knowledge,


Page 12 of 23

Page 13 of 23 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


1

the calculated values of Csp are much higher compared to many of the recently reported

2

materials based ASCD such as SPANI/G-1 (157 F g-1 @1.5 A g-1),45 HFAC (114 F g-1 @0.5

3

A g-1)46 and also better than many of the metal oxide based ASCD such as Co3O4/carbon

4

(101 F g-1 @2 A g-1),47 Ni(OH)2/graphene (218.4 F g-1 @1 mV s-1),48 Ni(OH)2/AC (218.4 F g-

5

1

6

Moreover, the ASCD shows remarkable energy efficiency with the maxima reaches as high

7

as 71.4 % at a current density of 8 A g-1, further reveals that the applied potential window is

8

efficient enough to provide good performance [Figure 4e].52

@5 mV s-1),49 MnO2/P-GA (108.9 F g-1 @5 mV s-1),50 MWS/MWV (198 F g-1 @1 A g-1).51

9

It is very important to note that the energy density of 102 Wh kg-1 calculated at the

10

power density of 2.0 kW kg-1 in the ASCD was far better than the previously reported

11

materials such as SPANI/G-1 (31.4 Wh kg-1 @14 kW kg-1),45 Ni(OH)2/graphene (77.8 Wh kg-

12

1

13

@0.270 kW kg-1),53 AC/MnO2 (21 Wh kg-1 @0.300 kW kg-1),54 and lower than Li-ion battery

14

(270 Wh kg-1).55 The remarkable energy density of 74 Wh kg-1 even at high power density of

15

3.6 kW kg-1 is estimated, further indicates its applicability as the future generation electrode

16

materials for supercapacitor applications. To further understand the charge transfer behaviour

17

and estimate the internal resistance, the EIS was measured in the frequency range of 1 Hz to 1

18

MHz and amplitude between 0.005 and 0.03 V [Figure 4(f)]. An equivalent simulated circuit

19

diagram of the experimental data consisting of solution resistance (Rs), charge transfer

20

resistance (Rct), Warburg element (W) and capacitor (C) was fitted. The obtained Nyquist

21

plot has a semicircle in high frequency region and a straight line in the medium to low

22

frequency region. The diameter of the semicircle provides the Rct of electrode-electrolyte

23

interface and the straight line is due to the diffusion of ions from the electrolyte to the

24

electrode surface. The estimated Rct value for NENP-1 electrode was 2.471 Ω along with Rs

25

of 4.679 Ω obtained from the fitting of the equivalent circuit model as shown in the inset of

@0.174 kW kg-1),48 Ni(OH)2/AC (12.6 Wh kg-1 @1.6 kW kg-1),49 RGO-MnO2 (47.9 Wh kg-1



1

Figure 4b. The low Rct value is beneficial as it is responsible for the quick charge transfer and

2

fast ions diffusion resulting in the improved electrochemical performance.

3

Further to compare the energy storage and power delivery rate of fabricated ASCD

4

with reported energy storage devices, Ragone plot was plotted [Figure 5(a)]. The Ragone plot

5

indicates that the NENP based ASCD could store the energy comparable to batteries while

6

keeping its power density performance comparable to supercapacitors.48,49,55-57

7

The observation of the superior supercapacitive performance of the investigated

8

material could be attributed to the high nitrogen content (50.5 wt%) and hierarchical pore

9

structure. The nitrogen functionality in the framework provides the active sites for the redox

10

reaction, whereas the hierarchical pore structure helps in the kinetics of the electrolytic ion

11

movements. The ASCD was further tested as a power source to lit a 1.5 V red and green

12

LEDs, and 3.0 V blue LED [Figure 5(b)]. On charging for 30 s with an input potential of 3.0

13

V, the red, green and blue LEDs could be lit up to 11, 4 and 0.5 min, respectively. Li ion Battery [55]

se

nt

w

or k]

[5 8

]

(a)

B at te ry

nO 2 /P SP -G AN A [ Ni 50 (O H I/G1 ] )2 / [4 gr ap 5] he ne [4 8]

M

/A C 4

O 3

Co

[5 7] Ni (O H )2 / A C

[4 6

[4 7]

]

100

N EN

N i-Z

n

-1

[P

re

B Ni-M at te H ry Ba [5 tt 6] er P y

) -1

Energy Density (Wh kg

200

0

14 15

Ni -C d

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

5 10 -1 15 Power Density (kW kg )

20

16

Figure 5. (a) Ragone plot of NENP-1 ASCD and its comparison with some reported energy

17

storage devices, (b) Snapshot of different LEDs.

18

Conclusions

19

Nitrogen-enriched nanoporous polytriazine frameworks have been synthesized by an ultrafast

20

microwave-assisted method. The excess nitrogen content and the hierarchical pore structure

21

helped to achieve superior electrochemical supercapacitor performance (1256 F g-1 @1 mV 14 ACS Paragon Plus Environment

Page 14 of 23

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1

sec-1). The fabricated ASCD demonstrates excellent performance (567 F g-1 @5 mV sec-1)

2

and could deliver the energy density of 102 Wh kg-1 at 1.6 kW kg-1. All these above observed

3

physicochemical properties make it a front-runner for the future generation energy materials.

4 5

ASSOCIATED CONTENT

6

Supporting Information. Reaction scheme, NMR, XRD, TGA, BET and Langmuir plot, and

7

tables of energy density and power density at various current density in two electrode

8

configurations.

9

AUTHOR INFORMATION

10

Corresponding Author

11

E-mail: [email protected], [email protected]

12

Phone: +91-1332-284859; Fax: +91-1332-286202

13

ORCID ID:

14

Paritosh Mohanty: 0000-0003-2765-0129

15 16

ACKNOWLEDGMENT

17

The work was financially supported by SERB, DST New Delhi, Govt. of India with Grant

18

code: EMR/2016/001693.

19

References

20

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57. Gao, X. P.; Yang, H. X. Multi-electron Reaction Materials for High Energy Density Batteries. Energy Environ. Sci. 2010, 3, 174-189. 58. Liu, Y.; Pan, H.; Gao, M.; Wang, Q. Advanced Hydrogen Storage Alloys for Ni/MH Rechargeable Batteries. J. Mater. Chem. 2011, 21, 4743-4755.

5 6 7 8 9 10 11

“For Table of Contents Use Only”

12

The performance of nanoporous polytriazine as electrode material for electrochemical

13

supercapacitor has shown its potential to bridge the gap between the supercapacitors

14

and batteries.

15 16 17 18 19 20 21 22


Nitrogen-enriched Nanoporous Polytriazine for High Performance

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