Biotemplate preparation of multilayered TiC nanoflakes for high performance symmetric supercapacitor

Journal Pre-proof Biotemplate preparation of multilayered TiC nanoflakes for high performance symmetric supercapacitor Tao Chen, Man Li, Seunghyun Song, Pangil Kim, Joonho Bae PII:

S2211-2855(20)30106-3

DOI:

https://doi.org/10.1016/j.nanoen.2020.104549

Reference:

NANOEN 104549

To appear in:

Nano Energy

Received Date: 19 December 2019 Revised Date:

28 January 2020

Accepted Date: 28 January 2020

Please cite this article as: T. Chen, M. Li, S. Song, P. Kim, J. Bae, Biotemplate preparation of multilayered TiC nanoflakes for high performance symmetric supercapacitor, Nano Energy, https:// doi.org/10.1016/j.nanoen.2020.104549. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier Ltd.

100

Energy Density(Wh/kg)

This work hollow graphene

10

TiC NWs PEDOT/MWCNT porous carbon nanofibers porous carbon

1

0.1 101

graphene aerogel 10

2

103

Power Density(W/kg)

104

105

Biotemplate preparation of multilayered TiC nanoflakes for high performance symmetric supercapacitor Tao Chen, Man Li, Seunghyun Song, Pangil Kim, Joonho Bae* Department of Nano-physics, Gachon University, Seongnam-si, Gyeonggi-do 461-701, Republic of Korea Email address:[email protected](J.Bae)

Abstract：Designing and developing more efficient electrode materials with high performance remains a great challenge in energy storage system. Recently, transition metal carbide materials have attracted a lot of attentions to next generation energy storage device. In this work, TiC nanoflakes were successfully prepared by a simple and highly effective biotemplate method using a cotton towel as a carbon source and sacrificial template. The phases and structures of asobtained samples were measured by X-ray powder diffraction (XRD), Raman analysis, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) techniques. The results demonstrated that layered TiC nanoflakes were strongly influenced by the sintering time at high temperature. The TiC nanoflakes electrode showed a highest specific capacitance of 276.1 Fg-1 at 5 mVs-1 and capacitance retention of 94% over 1000 cycles at the current density of 10 Ag-1. Then, the symmetric supercapacitors based on TiC nanoflakes electrodes (276.1 Fg-1) were fabricated and their electrochemical properties fully investigated. The results illustrated that the prepared symmetric TiC//TiC supercapacitor has a maximum specific capacitance of 194.5 Fg-1 and a capacitance retention of 80.5% after 20000 cycles. To the best of our knowledge, it is the highest capacitance from TiC-based symmetric supercapacitor in the literature. Moreover, the TiC//TiC symmetric supercapacitor in series with a superior energy density of 41 Whkg-1 at a power density of 2.3 KWkg-1 and outstanding cycling stability is demonstrated to light up a

white LED indicator for 10 min, highlighting the promising potential of TiC for next generation energy storage system. Keywords: Biotemplate; TiC nanoflakes; supercapacitor.

Introduction To date, the consumption of fossil fuel resource and global pollution issue of the environment have attracted a lot of attention in developing advanced renewable energy storage and conversion technologies to replace and supplement the traditional energy source, which are required for the emerging biomedical device, consumer electronics and electric vehicles [1-3]. Among numerous promising technologies available, supercapacitor with high power density, good capability, and outstanding cycling stability has been considered as the most promising candidate for the next generation energy storage and conversion device. It is well known that typical supercapacitors consist of electrical double layer capacitors and pseudocapacitors, which are resulted from ion adsorption and surface Faradic redox reactions, respectively [4-6]. In particular, the performances of electrode materials as the important component determine the overall properties of supercapacitors. Therefore, it is critical to explore excellent electrode materials by developing and designing new materials or surface modification [7-9]. By now, researchers have focused on studying new materials such as transition metal carbide for supercapacitors owing to their good chemical stability and high electrical conductivity [10-12]. Among various transition metal carbides, titanium carbide (TiC) is of special interest due to its outstanding features such as high hardness, high melting point (3067

), good thermal stability,

excellent anti-corrosion and anti-oxidation ability, and low electrical resistivity (6.8*10-5 Ωcm) [13]. Compared with Ti3C2 (MXene) prepared by chemical etching Ti3AlC2, TiC synthesized via

physical and chemical methods exhibits much higher electrical conductivity (105-106 s/m, close to that of metals)，which makes it suitable for high performance EDLCs [14]. These advantages lead to potential applications of TiC in the field of electrochemical catalysis [12] and electrochemical energy storage and conversion [14]. Recently, several techniques based on carbon nanotube (CNT) confined reaction [15], chemical vapor deposition [16], and carbon thermal reduction [17] have been employed to prepare TiC. All the methods used CNTs, graphite, activated carbon, carbon black, and biomaterials as the carbon source have been illustrated that the morphology and structure of prepared TiC products are highly attributed to the added carbon source [17-19]. Among these carbon sources, the porous and commonly used cotton is constructed from polysaccharide chains arranged into amorphous and crystalline regions, which are preferable for the synthesis of TiC electrode [20]. Up to now, while different types of TiC structures have been prepared, there are rare report on integrated TiC electrodes for electrochemical energy storage and conversion system. Herein, multilayered TiC nanoflakes were successfully synthesized by a simple, low-cost and highly effective biotemplate method using cotton towel as carbon resource and sacrificial template. As the electrode active materials, TiC nanoflakes were grown from TiO2 nanopartices and carbon source with sintering at high temperature in argon atmosphere. In order to further demonstrate their performance as electrode, the symmetric supercapacitor using TiC nanoflakes as electrodes were fabricated, and their electrochemical characteristics were fully investigated. The results of electrochemical measurements clearly illustrated that the symmetric TiC//TiC supercapacitor has a maximum specific capacitance of 194.5 Fg-1 at scan rate of 5mV/s with good capability and an excellent cycling stability with a capacitance retention (80.5% after

20000 cycles). Moreover, the maximum energy density is 41 Whkg-1 at the power density of 2.3 kWkg-1, which demonstrates the TiC could be potential next-generation electrode materials for high-performance energy storage and conversion system.

Experimental sections 1 Material TiO2 powders, NaCl, Ni(NO3)2·6H2O, ethanol and graphite were purchased from Samchun Chemical Corporation (South Korea). The yellow cotton towel was obtained from Zhe Jiang Grace Company (China). Deionized water was used for all experiments. All reagents were analytical grade and used without further purification. 2 Preparation of TiC nanoflakes Multilayered TiC nanoflakes were successfully synthesized by a simple, low-cost and high effective biotemplate method using cotton textile as carbon resource and biotemplate [11]. Firstly, 0.8 g of TiO2 powders, 0.29 g of NaCl and 0.15 g of Ni(NO3)2·6H2O were dissolved into 50 mL of ethanol to form a Ti-Cl-Ni emulsion under stirring for 1 h. Then, a small piece of cotton towel with a weight of 0.8 g was cut and immersed into above mixed emulsion. After stirring for 2 h at 400 rmp, the yellow cotton textile was dried at 110

for 5 h. Subsequently, the

cotton textile- loaded Ti-Cl-Ni precursors was placed in a sealed graphite crucible and then sintered at 1150

for 96 h under argon atmosphere. In order to remove the impurities such as

Na, Cl, Ni, N, etc. from the reagents, the synthesized sample was immersed into 5% HCl solution for 1 h after the tube furnace was turned off and cooled down to room temperature. Finally, the

black precipitate was obtained by washing and centrifugating several times with deionized water before drying at 100

for 10 h in a vacuum oven.

3 Characterizations The morphology and structure of the TiC samples were characterized by using scanning electron microscopy (SEM, Hitachi, S-4800). The phase and composition were measured by roman spectroscopy and X-ray diffraction (XRD) using Rigaku X-ray diffractometer with Cu ka radiation (0.15418). Raman analysis was test by Thermo Fisher Scientific DXR Raman microscope using laser excitation at 532nm. X-ray photoelectron spectroscopy (XPS) measurement was employed to investigate the chemical state analysis of as-prepared sample. 4 Electrochemical measurements The electrochemical properties of as-synthesized TiC were investigated though three electrodes system in a 3 M KOH electrolyte, where Ag/AgCl was used as reference and Pt as counter electrodes. The working electrode for supercapactor test was prepared via mixing TiC active materials, carbon materials and polyvinylindene fluoride (PVDF) in N-methyl-2pyrrolidene (NMP) at a mass ratio of 80:10:10. The resulting slurry was uniformly coated on nickel foam and dried under vacuum oven at 80

overnight. Cyclic voltammetry (CV) and

galvanostatic charge and discharge (GCD) test were carried out on an electrochemical working station (Princeton applied research). Electrochemical impedance spectroscopy (EIS) was measured in frequency range from 10 MHZ to 20 KHZ. The specific capacitance (Cm) of the prepared electrodes was calculated from the CV and GCD curves according to following two equations:

(1) Cm=(∫IdV)/(m*∆V*v), Where I, m, △V and v represent working current, mass of active materials, potential window and scanning rate, respectively; (2) C=I*△t/m, Where I is the discharge current, △t is the discharge time, m represents the mass of active materials in the electrode, △V represents potential window. 5 Fabrication of symmetric supercapacitor All the electrochemical measurements of symmetric supercapacitors were conducted using two-electrode system. The active materials loading of two electrodes were adjusted to reach a matching capacitance. Symmetric supercapacitors based on TiC were assembled by using TiC nanoflakes as positive and negative electrodes in 3 M KOH electrolyte, respectively. A cellulosic paper was used as the separator. The TiC//TiC symmetric supercapacitors were employed to CV, GCD, and EIS measurements. Then, the cycling stability of the symmetric supercapacitor was measured over 20000 charge and discharge cycles at a current density of 20 Ag-1.

Results and discussion

Fig. 1 Schematic display of the synthesis process of layered TiC nanoflakes by using biotemplate method as the electrode materials for symmetric supercapacitor.

The general process for synthesis of layered TiC nanoflakes materials by biotemplate method was illustrated in Fig. 1. TiO2 powders were used as the raw materials and the cotton towel was employed as the carbon resource to prepare the layered TiC nanoflakes via biotemplate method. Firstly, TiO2 powders, NaCl and Ni(NO3)2·6H2O were dissolved into ethanol to form a TiO2based emulsion. Then, a small piece of cotton towel was cut and immersed into above mixed

(111)

(002)

emulsion. Subsequently, the cotton textile loaded with Ti precursors was placed in a sealed (a) TiC nanoflakes graphite crucible and sintered at high temperature(b)under argon atmosphere. Commercial TiO2 TiO2 powders

263

417

TiC

603

630

Intensity(a.u.)

Intensity(a.u.)

nanoparticles were reduced to TiC nanoflakes with good conductivity. JCPD Finally, the TiC No. 65-0242

(200)

nanoflakes electrodes were used to fabricate the symmetric supercapacitor for powering up the

(111)

(222)

(311)

263

(311)

630 400

600

795

TiO2JCPD No. 65-0242

800

1000

1200

Raman Shift (cm-1)

1400

1600

520

(222)

(200) (215)

(116) (220)

(101)

(101) (004) (111)

(110)

TiC

603

JCPD No.71-1166

20 25 30 35 40 45 50 55 60 65 70 75 80 200

2theta(deg)

417

JCPD No.71-1166

Intensity(a.u.)

(215)

(116) (220)

(101)

(110)

(101)

2theta(deg)

520

(b)

TiC nanoflakes TiO2 powders

20 25 30 35 40 45 50 55 60 65 70 75 80 200

(101)

Intensity(a.u.)

(a)

(101) (004) (111)

(002)

light.

400

600

795

TiO2

800

1000

1200

Raman Shift (cm-1)

1400

1600

Fig. 2 (a) XRD and (b) raman patterns of the raw materials TiO2 powders and the TiC products prepared by biotemplate method.

The phases and structures before and after sintering by tube furnace under high temperature were measured by X-ray powder diffraction (XRD) and Raman analysis. The typical XRD

patterns of the TiO2 powders and TiC products were shown in Fig. 2a. In the black curve (TiO2 powders), the corresponding diffraction peaks of precursor powders could be readily indexed to the anatase TiO2, which agree with the standard XRD databases (JCPDS, Card NO.71-1166) (a) (c) to the (002), (111), (200), [21]. The peaks located at 36°, 42(b) °, 61°, 73°, and 76° can be assigned

(311), and (222) planes of TiC phase [13]. No impurities such as Ti metal TiOC and TiO phases were detected, illustrating that TiO2 have been fully transformed to TiC, and the purity of h as carbon source can 0 h is high [17]. The formation24ofhTiC nanoflakes using cotton48towel products 500 nm 500 nm 500 nm h h also be investigated by Raman spectra (Fig. 2b). The sharp peaks at 264, 416, and 602 cm-1 (d) (e) Ti (f) C

correspnded to the TiC phase (JCPD No. 65-0242), confirming the formation of TiC products [17, 22]. mapping 96 h 500 nm

Fig. 3 SEM images of as-prepared TiC nanoflakes via biotemplate method at different sintering time: (a) 0 h; (b) 24 h; (c) 48 h; (d) 96 h, and EDS elements mapping of d; (e) Titanium; (f) Carbon.

Fig. 3 presented SEM images of as-synthesized TiC samples at various sintering time and the

elements distribution of TiC samples. The typical SEM images of the TiO2 raw materials without sintering were exhibited in Fig. 3a. The SEM images show that the morphology of TiO2 powders was uniform nanoparticle with the diameter distribution of 100-200 nm. Fig.3b displayed the SEM images of the sample sintered at 1150

for 24 h by biotemplate method. It was obviously

seen that there were some small bulks without layers assembling on the surface of carbon fiber, which demonstrated that the TiO2 precursors were coated on the surface of cotton towel during the immersing process and the cotton textiles have been successfully transformed to carbon materials after sintering at high temperature. After reaction for 48 h (Fig. 3c), two-dimensional multilayered products with large surface area were observed, which gradually grew from spherical TiO2 nanoparticles to layered structure. As the high reaction time prolonged to 96 h

Ti2p3 Ti2p1 Ti2p

(a) the layered TiC nanoflakes were obtained, (b)along with the disappearance of carbon fibre. (Fig.3d), C1s

Intensity(a.u.)

Ti2s

Intensity(a.u)

O1s

The results demonstrated that layered TiC nanoflakes were successfully synthesized and the morphology and structure of products were strongly influenced by the sintering time at high C-C

C1s

temperature. The photographs of EDS elements mapping were shown in Fig.3e and 3f, the C-C

Ti-C

Ti3s Ti3p

C-O results indicated titanium and carbon elements were uniformly distributed in the TiC nanoflakes.

Moreover, to further validate the composition, the sample was investigated by EDS analysis (SI 800 600 400 200 0 288 287 286 285 284 283 282 281 280 Binding Energy(eV)

Binding Energy(eV)

Fig.1)(c)associated with above SEM observations, Ti(d)and C elements could be detected. Therefore, O1s

Ti2p

Intensity(a.u.)

Intensity(a.u.)

the biotemplate method can be considered as an effective and promising way to prepare metal transition carbides.

OH/O-Ti Ti-O OH/Ox

Ti-O2 Ti-O2-x Ti-C +4-x Ti2p1/2 Ti+42p3/2 Ti 2p3/2

Ti-O2 Ti2p1/2

466

464

462

460

458

456

Binding Energy(eV)

Ti+42p3/2 Ti-C Ti02p3/2

454

452

534

532

530

528

526

Binding Energy(eV)

524

Fig. 4 XPS spectrum of TiC sample: (a) survey spectrum; (b) C1s; (c) Ti2p; (d) O1s.

The corresponding XPS spectra of the obtained TiC samples prepared by biotemplate method was displayed in Fig. 4, indicating the chemical bond on the TiC nanoflakes [23]. The full survey spectrum (Fig. 4a) of the TiC samples presents the existence of Ti, O, C elements. Fig. 4b showed the

bind energy of C1s, the observed peaks at 281.9 eV and 286.7 eV were ascribed to the Ti-C and C-O bond [24]. Fig. 4c represented the Ti2p spectrum, which were consisted of six peaks. The peaks at 454.9 eV and 40.1 eV corresponded to the Ti-C bond, which illustrated the presence of TiC [25]. The other three peaks corresponded to the Ti-O bond, suggesting the existence of TiO, which was attributed to the small amount of TiO2 impurities. O1s spectrum was exhibited in Fig. 4d, the peak at 532.6 eV was usually assigned to the O-H group on the surface of TiC sample, the peaks at 528.3 eV and 529.5 eV originated from the O-Ti bond, which were consistent with the corresponding bond in Fig. 4c. The results of XPS measurements further confirm that the TiC products were successfully synthesized by biotemplate method.

2

(a)

(b)

8 4 0 -4 -8

-16 -20 -1.0

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-3 -4

-0.2

-1.0

-0.1

(c) 276.1Fg

Potential(V)

160 120

-0.3

-0.2

(d)

5 Ag-1 10Ag-1 20Ag-1 40Ag-1

-1.0

0 10

20

30

40

50

60

70

Scan Rate(mVs-1)

80

90

100 110

0 210

(e) 94%

5

10

15

150

(f) 3.0 2.5

120 90

20

25

Elapsed Time(s)

180

Zim(ohm)

0

60

-0.4

-0.7

-0.9

70

-0.5

-0.6

40

80

-0.6

-0.5

-0.8

90

-0.7

Potential vs Ag/AgCl(V)

-0.4

80

100

-0.8

-0.3

200

110

-0.9

-0.2

-1

240

ance Retention(%)

0

-2

Potential vs Ag/AgCl(V)

280

1

2.0

im(ohm)

320

-0.9

5mVs-1

-1

80mVs-1 -1 60mVs 40mVs-1 20mVs-1 -1 10mVs -1 5mVs

-12

Specific Capacitance(Fg-1)

Current Density(Ag-1)

Current Density(Ag-1)

12

1.5

30

35

40

Fig. 5 Electrochemical performance of TiC nanoflakes electrode in 3M KOH in a three-electrode system: (a) CV curves at different scan rates from 5 to 80 mVs-1; (b) enlarged CV curve at scan rate of 5 mVs-1; (c) specific capacitance at various scan rates from 5 to 100 mVs-1; (d) galvanostatic charge and discharge curves at different current densities from 5 to 40 Ag-1; (e) cycling stability over 1000 cycles at a current density of 10 Ag-1; (f) Nyquist plots.

The electrochemical behaviors of the prepared TiC nanoflakes working electrode were evaluated by using cyclic voltammetry (CV), galvanostatic charge and discharge (GCD), and electrochemical impedance spectroscopy (EIS) measurements in 3 M KOH electrolyte. Fig. 5a and 5b show the CV curves of TiC electrode at different scan rates from 5-80 mVs-1. Obviously, the TiC electrode shows good EDLCs behavior with the rectangular shape CV curves, rather than pseudocapacitive process. The increase in current density with the scan rate highlights ionic charge transport even at higher scan rate, indicating the improved capability and decreased resistance of electrode [26]. The mass specific capacitance verse scan rate of TiC nanoflakes electrode was exhibited in Fig. 5c. The TiC nanoflakes electrode shows a highest specific capacitance of 276.1 Fg-1 at 5 mVs-1. Even though the scan rate reached up to 80 mVs-1, the electrode still has a specific capacitance of 170 Fg-1. The galvanostatic cycling performance for TiC nanoflakes electrode was presented in Fig. 5d. The GCD curves at current densities varying from 5 to 40 Ag-1shows a good linear potential-time performance, suggesting the TiC nanoflakes electrode has EDLCs characteristics. Due to the nanoflake layered structure of TiC samples, the

prepared electrode displays that the capacitance retention is as high as 94% over 1000 cycles a current density of 10 Ag-1 (Fig. 5e). The resistance of the TiC sample tested by electrochemical impedance spectroscopy measurement is also an important parameter for determining the electrochemical characteristic of electrode for supercapacitor. Fig. 5f displays Nyquist plot for TiC nanoflakes electrode. The x-intercept of Nyquist plot represents the resistance for the electrode (0.55 Ω), which demonstrates that the TiC nanoflakes sample with a low resistance has a promising potential in application for supercapacitors.

Current Density(Ag-1)

10

4

(a)

6 4 2 0 -2 -4

-1

-1

80mVs 40mVs-1 10mVs-1

-6 -8

60mVs 20mVs-1 5 mVs-1

2

5 mVs-1

1 0

-1

-10

-2 0.0

240

(b)

3

8

Current Density(Ag-1)

12

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0.0

Potential vs Ag/AgCl(V)

0.2

0.4

0.6

0.8

1.0

(d)

(c) 194.5 Fg-1

Potential(V)

120 80

1.6

1.0 0.8 0.6 0.4

40

0.2 0.0

0

120

10

20

30

40

50

60

70 -1

80

90

Scan Rate(mVs )

140

(e) 80.5%

60 40

10 20 30 40 50 60 70 80 90 100 110 120 130 140

Elapse Time(s) (f)

120

100 80

0

100 110

3.0

100

Zim(ohm)

0

itance Retention(%)

1.2

2.5

80 60 40

Zim(ohm)

Specific Capacitance(Fg-1)

1.4

160

1.4

5 Ag-1 10Ag-1 20Ag-1 40Ag-1

1.6 200

1.2

Potential vs Ag/AgCl(V)

1.8

2.0 1.5 1.0

Fig. 6 Electrochemical performance of TiC//TiC symmetric supercapacitor: (a) CV curves at various scan rates from 5 to 80 mVs-1; (b) magnified CV curve at scan rate of 5 mVs-1; (c) specific capacitance at different scan rates from 5 to 100 mVs-1; (d) GCD curves at various current densities from 5 to 40 Ag-1; (e) cycling stability over 1000 cycles at a current density of 10 Ag-1; (f) Nyquist plots.

Up to now, the electrochemical performance of single TiC nanoflakes electrode in a threeelectrode system was only discussed. To further evaluate the electrode for real application, symmetric supercapacitors were fabricated by conforming TiC nanoflakes electrodes as positive and negative electrodes (after 1000 cycles), and a cellulose paper as the separator in 3 M KOH electrolyte. The electrochemical properties of the TiC nanoflakes-based symmetric supercapacitors were investigated in a two-electrode configuration as introduced in the previous experimental section. It is noticed that the op timum working voltage of 1.6 V was obtained due to the symmetric device which combines the potential window of the two electrodes to maximum the overall cell voltage [27]. Fig. 6a and 6b gave the CV curves of as-fabricated TiC//TiC symmetric supercapacitors at different scan rates from 5-80 mVs-1, the curves displayed a typical rectangular shape, suggesting the obvious capacitive behavior of EDLCs in a voltage of 0-1.6 V. As the scan rate increased, the shapes of CV curves still keep unchangeable, which indicates a nice rate capability [28]. The mass specific capacitance of the TiC//TiC symmetric supercapacitor at varied scan rates calculated from the CV curves was shown in Fig. 6c. The highest specific capacitance can be up to 194.5 Fg-1 at scan rate of 5 mVs-1. Fig. 6d exhibits

galvanostatic charge and discharge curves of as-synthesized device at current densities varying from 5-40 Ag-1. The curves display triangular shape characteristic of EDLC [26]. The specific capacitance can also be determined by the GCD curves using the equation (Cm=I*△t/m) as mentioned before. The specific capacitance reaches a maximum of 110 Fg-1 at low current density of 5 Ag-1 and remains 60 Fg-1 at 40 Ag-1, which was resulted from the good conductivity and nanoflake structure of TiC sample. In particular, the value (110 Fg-1) at 5 Ag-1 lies within the range of the capacitance (100-194.5 Fg-1) calculated from CV curves, demonstrating the

Energy Density(W h/kg)

100

(a)

(b)

capacitance from the two different curves This work

match with each other. Additionally, the

ref32, hollow graphene ref27, TiC NWs ref29, PEDOT/MWCNT ref31, porous carbon nanofibers

10

cycling life was also a significant feature of supercapacitors, as shown in Fig. 6e, the

ref28, porous carbon 1

capacitance retention was maintained at 80.5% after 20000 0cycles minat a relative high

ref30, graphene aerogel

0.1 10

out

1

a

10

deeper

(c)

2

10

3

Power Density(W/kg)

10

4

10

5

current density of 20 Ag-1. In order to carry

investigation of electrochemical characteristics of

(d)

TiC//TiC symmetric device, the electrochemical impedance spectroscopy (EIS) test was employed to measure the resistance. The Nyquist plots of TiC//TiC nanoflake-based supercapacitors were shown in Fig. 6f. The small charge transfer resistance at high frequencies illustrates the simple capacitive feature of as-prepared configuration. The intercept at x-axis is only 1.4 Ω, demonstrating 5 themin low internal resistance of the device.

10 min

Fig. 7 (a) Ragone plots of as-fabricated TiC//TiC symmetric supercapacitor and other results from the literature; (b,c and d) photographs showing the symmetric supercapacitor can light up the yellow LED indicator during different time: (b) 0 min; (c) 5 min; (d) 10 min.

Power density and energy density are regarded as the two main parameters to investigate the characterizations of supercapacitors. The corresponding energy density (E) and power density (P) were obtained from the following two equations: (1) E=Cm*(△V)2/2/3.6, where Cm is specific capacitance and △V represents working potential; (2) P= 3600*E/△t, where △t is the discharge time of the symmetric supercapacitors. In order to demonstrate the advantages of our TiC//TiC symmetric supercapacitor, Ragone plots of power density and energy density were obtained and compared with previously work, as shown in Fig. 7a. The maximum energy density of the symmetric supercapacitor decreases from 41 to 21 Whkg-1 as the power density is 2.3 KWkg-1 which increases to 29 KWkg-1. These value

is superior to those of symmetric energy storage devices reported in the literature such as TiC//TiC NWs (18.2 Whkg-1) [29], porous carbon//porous carbon (3 Whkg-1) [30], PEDOT/MWCNT//PEDOT/MWCNT (11.3 Whkg-1) [31], graphene aerogel//graphene aerogel (0.26 Whkg-1) [32], porous carbon nanofibers//porous carbon nanofibers (3.22 Whkg-1) [33], and hollow graphene//hollow graphene (35 Whkg-1) [34]. Fig. 6b-d displayed a simple and quick illustration for the viability of TiC//TiC symmetric supercapacitor for practice applications. In the typical process, the symmetric supercapacitor successfully lighted up a white round lightemitting diode (LED) indicator for almost 10 min.

Conclusion In this work, multilayered TiC nanoflakes were successfully synthesized by a simple, lowcost and highly effective biotemplate method using cotton towel as a carbon resource and sacrificial template. As the electrode materials, TiC nanoflakes products were grown from TiO2 nanopartices and carbon source under sintering at high temperature in argon atmosphere. The morphology and structure of products were strongly influenced by the sintering time at high temperature. The TiC nanoflakes electrode showed a highest specific capacitance of 276.1 Fg-1 at 5 mVs-1 and capacitance retention of 94% over 1000 cycles at the current density of 10 Ag-1. In order to further demonstrate, the symmetric supercapacitor based on TiC nanoflakes electrodes were fabricated and their electrochemical characteristics were fully investigated. The results of electrochemical measurements clearly illustrated that the prepared symmetric TiC//TiC supercapacitor has a maximum specific capacitance of 194.5 Fg-1 at scan rate of 5 mVs-1 with good capability and an excellent cycling stability with a capacitance retention kept at 80.5% after 20000 cycles at a current density of 20 Ag-1. To the best of our knowledge, it is the highest

capacitance from TiC-based symmetric supercapacitor in the literature. Moreover, the symmetric supercapacitors assembled by TiC nanoflakes have a maximum energy density of 41 Whkg-1 at power density of 2.3 KWkg-1 and light up a white LED indicator for 10 min, which demonstrating the titanium carbide could be potential next-generation electrode materials for high-performance energy storage system.

Acknowledgement This research was supported by Basic Science Research Program through the National Research

Foundation

of

Korea

(NRF)

funded

by

the

Ministry

of

Education

(2017R1D1A1B03032466).

Reference [1] Z.Y. Zhang, M.L. Liu, X. Tian, P. Xu, C.Y. Fu, S. Wang, Y.Q. Liu, Scalable fabrication of ultrathin free-standing graphene nanomesh films for flexible ultrafast electrochemical capacitors with AC line-filtering performance, Nano Energy 50 (2018) 182-191. [2] C. Liu, F. Li, L.P. Ma, H.M. Cheng, Advanced materials for energy storage, Adv. Mater. 22 (2010) E28-E62. [3] C. Hu, L. Song, Z. Zhang, N. Chen, Z. Feng, L. Qu, Tailored graphene systems for unconventional applications in energy conversion and storage devices, Energy Environ. Sci, 8 (2015) 31-54. [4] G.P. Wang, L. Zhang, J.J. Zhang, A review of electrode materials for electrochemical supercapacitor, Chem. Soc. Rev. 41 (2012) 797-828.

[5] V. Augustyn, P. Simon, B. Dunn, Pseudocapacitive oxide materials for high-rate electrochemical energy storage, Energy Environ. Sci. 7 (2014) 1597-1614. [6] R.S. Devan, R.A. Patil, J.H. Lin, Y.R. Ma, One-dimensional metal-oxide nanostructure: recent development in synthesis, characterization, and applications, Adv. Funct. Mater. 22 (2012) 3326-3370. [7] Y.Y. Wang, T.E. Rufford, X.Z. Chen, N. Li, M.Q. Lyu, L.M Dai, L.Z Wang. Nitrogen-doped Ti3C2Tx MXene electrodes for high-performance supercapacitor, Nano Energy 38 (2017) 368376. [8] J. Bae, M.K. Song, Y.J. Park, J.M. Kim, M.L. Liu, Z.L. Wang, Fiber Supercapacitors Made of Nanowire‐Fiber Hybrid Structures for Wearable/Flexible Energy Storage, Angew. Chem. Int. Ed. 50 (2011) 1683-1687. [9] Y. Xue, T. Chen, S. Song, P. Kim, J. Bae. DNA-directed fabrication of NiCo2O4 nanoparticles

on

carbon

nanotubes

as

electrodes

for

high-performance

battery-like

electrochemical capacitive energy storage device, Nano Energy 56 (2019) 751-758. [10] M. Naguib, J. Halim, J. Lu, K.M. Cook, L. Hultman, Y. Gogotsi, M.W. Barsoum, New twodimensional Niobium and Vanadium Carbides as promising materials for Li-ion batteries, J. Am. Chem. Soc. 135 (2013) 15966-15969. [11] S.T. Hunt, T. Nimmanwudipong, Y. Romanleshkov, Engineering non-sintered, metalterminated Tungsten Carbide nanoparticles for catalysis, Angew. Chem. Int. Ed. 53 (2014) 51315136.

[12] Y. Liu, T.G. Kelly, J.G. Chen, W.E. Mustain, Metal Carbides as alternative electrocatalyst support, ACS Catal. 3 (2013) 1184-1194. [13] Z. Qiu, H. Huang, J. Du, X.Y. Tao, Y. Xia, T. Feng, Y.P Gan, W.K. Zhang, Biotemplated synthesis of bark-structure TiC nanowires as Pt catalyst supports with enhanced electrocatalytic activity and durability for methanol oxidation, J. Mater. Chem. A 2 (2014) 8003-8008. [14] Y. Cao, V. Presser, L.F. Zhang, J.J. Niu, J.K. McDonough, C.R. Perez, H.B. Lin, H. Fong, Y. Gogotsi, High power supercapacitor electrodes based on flexible TiC-CDC nano-felts, J. Power Source 201 (2012) 368-375. [15] T. Taguchi, H. Yamamoto, S. Shamoto, Synthesis and characterization of single-phase TiC nanotubes, TiC nanowires, and carbon nanotubes equipped with TiC nanoparticles, J. Phy. Chem. C 111 (2007) 18888-18891. [16] C.H. Liang, G.W. Meng, W. Chen, Y.W. Wang, L.D. Zhang, Growth and characterization of TiC nanorods activated by nickel nanoparticles, Journal of Crystal Growth 220 (2000) 296300. [17] X.H. Xia, Y.Q. Zhang, D.L. Chao, Q.Q. Xiong, Z.X. Fan, X.L. Tong, J.P. Tu, H. Zhang, H.J. Fan. Tubular TiC fibre nanostructure as supercapactor electrode materials with stable cycling life and wide-temperature performance, Energy Environ. Sci. 8 (2015) 1559-1568. [18] X.K. Li, A. Westwood, A. Brown, R. Brydson, B. Rand, A convenient, general synthesis of carbide nanofibers via template reactions on carbon nanotubes in molten salt media, Carbon, 47 (2009) 201-208.

[19] H. Zhang, T. Feng, Y.P. Gan, M.Y. Fang, Y. Xia, C. Liang, X.Y. Tao. W.K. Zhang, TiC/NiO core/shell nanoarchitecture with battery-capacitive synchronous lithium storage for high-performance lithium-ion battery, ACS Appl. Mater. Interface 7 (2015) 11842-11848. [20] X.Y. Tao, J. Du, Y.C. Yang, Y.P. Li, Y. Xia, Y.P. Gan, H. Huang, W.K. Zhang, X.D. Li, TiC nanorods derived from cotton fibers: Chloride-assisted VLS growth, structure, and mechanical properties, Cryst. Growth Des. 11 (2011) 4422-4426. [21] T.G. Deepak, D.E. Subash, G.S. Anjusree, K.R.N. Pai, S.V. Nair, A.S. Nair, Photovoltaic property of anatase TiO2 3-D mesoflowers, ACS Sustainable Chem. Eng. 2 (2014) 2772-2780. [22] Q. Peng, J. Guo, Q. Zhang, J. Xiang, B. Liu, A. Zhou, R. Liu, Y. Tian, Unique lead adsorption behavior of activated hydroxyl group in two-dimensional titanium carbide, J. Am. Chem. Soc. 136 (2014) 4113-4116. [23] R. Zhang, X.B. He, Q. Liu, X.H. Qu, Improvement in Mechanical and thermal properties of graphite flake/Cu composites by introducing TiC coating on graphite flake surface, Metals. 5 (2019) 519. [24] E. Benko, T. Barr, S. Hardcastle, E. Hoppe, A. Bernasik, J. Morgiel, XPS study of the cBNTiC system, Ceram. Int. 27 (2001) 637-643. [25] X.H. Gao, Z.M. Guo, Q.F. Geng, P.J. Ma, G. Liu, Structure, optical properties and thermal stability of TiC-based tandem spectrally selective solar absorber coating, Sol. Energy Mater. Sol. Cells 157 (2016) 543-549. [26] Y. Gogotsi, R.M. Penner, Energy storage in nanomaterials-capacitive, pseudocapacitive, or battery-like, ACS Nano 12 (2018) 2081-2083.

[27] A. Pendashteh. S.E. Moosavifard, M.S. Rahmanifar, Y. Wang, M.F.E. Kady, R.B. Kaner, M.F. Mousavi, Highly ordered mesoporous CuCo2O4 nanowires, a promising solution for highperformance supercapacitors, Chemistry of Materials 27 (2015) 3919-3926. [28] H.Y. Liang, J.H. Lin, H.N. Jia, J.L. Qi, J. Cao, T.S. Lin, Hierarchical NiCo-LDH@NiOOH core-shell heterostructure on carbon fiber cloth as battery-like electrode for supercapacitor, J. Power Source 378 (2018) 248-254. [29] X.H. Xia, J.Y. Zhan, Y. Zhong, X.L. Wang, J.P. Tu, H.J. Fan, Single-crystalline, metallic TiC nanowires for highly robust and wide-temperature electrochemical energy storage, Small 13 (2017) 1602742. [30] J.A. Fernandez, T. Morishita, M, Toyota, M. Inagaki, F. Stoeckli, T.A. Centeno, Performance of mesoporous carbon derived from poly(vinly alcohol) in electrochemical capacitors, J. Power Source 2008, 175, 675-679. [31] X.X. Bai, X.J. Hu, S.Y. Zhou, J. Yan, C.H. Sun, P. Chen, L.F. Li, In situ polymerization and characterization of grafted poly(3,4-ethylenedioxythiophene)/multiwalled carbon nanotubes composite with high electrochemical performance, Electrochim Acta 87 (2013) 394-400. [32] C. Zhu, T. Liu, F. Qian, T.Y.J. Han, E.B. Duoss, J.D. Kuntz, C.M. Spadaccini, M.A. Worsley, Y. Li, Supercapacitors based on three-dimensional hierarchical graphene aerogel with periodic macropores, Nano Lett. 16 (2016) 3488-3456. [33] L.S. Zhang, Q.W. Ding, Y.P. Huang, H.H. Gu, Y.E. Miao, T.X. Liu, Flexible hybrid membranes with Ni(OH)2 nanoplatelets vertically grown on electrospun carbon nanofibers for high performance supercapacitors, ACS Appl Mater Interface 7 (2015) 23515-23520.

[34] Y.X. Xu, Z.Y. Lin, X. Zhong, X.Q. Huang, N.O. Weiss, Y. Huang, X.F. Duan, Holey graphene frameworks for highly efficient capacitive energy storage, Nat Commun. 5 (2014) 4554.

Brief introduction of authors Tao Chen received his master degree in chemical engineering from school of petrochemical engineering, Changzhou University in 2016. He is currently a Ph.D. candidate under supervision of Professor Joonho Bae at Gachon University, South Korea. His research focuses on electrode materials for supercapacitor and batteries.

Li Man is currently a Ph.D. candidate in the department of Nano-Physics, Gachon University, Korea, under the supervision of Prof. Joonho Bae. She received her B.S. and M.S. from Yan Tai University and Chinese Academy of Forestry, respectively. Her research interests include of DNA functionalized MOF synthesis, solid-state electrolytes and electronic devices.

Seunghyun Song received her B.S. degree in Department of Nano Physics from Gachon University, Korea. She is working on carbon-based materials and energy storage and harvesting devices. Her research focuses on synthesis and applications of the zero dimensional carbon nanomaterials.

Pangil Kim received his B.S degree in Department of Nanophysics from Gachon University, Korea. He is currently a master student under the supervision of Professor Joonho Bae. His research interest includes electrochemical energy storage materials.

Prof. Joonho Bae received his B.S. and M. S. degrees from Seoul National University in 1996 and 1998, respectively. He was awarded Ph. D. by the University of Texas at Austin in 2007 under supervision of Prof. C. K. Shih, and carried out postdoctoral research at Georgia Institute of Technology under supervision of Prof. Z. L. Wang until 2011. After the postdoctoral research, he worked in Samsung electromechanics as a senior researcher. He joined department of nano-physics at Gachon University in 2013. His recent research interests include synthesis of nanomaterials for energy harvestings and storage devices including supercapacitors and lithium ion batteries.

Multylayered TiC nanoflakes were successfully prepared by a simple and high effective biotemplate method. During the sintering process under high temperature, cotton towel was used as carbon resource and a sacrificial template to reduce TiO2 nanoparticles to TiC nanoflakes. To the best of our knowledge, it is the highest capacitance from TiC-based symmetric supercapacitor in the literature. Symmetric supercapacitor based on as-prepared TiC nanoflakes electrodes shows electrochemical performance with excellent cycling stability and high energy density.

Declaration submission This work has not been published previously, that it is not under consideration for publication elsewhere, that its publication is approved by all authors and tacitly or explicitly by the responsible authorities where the work was carried out, and that, if accepted, it will not be published elsewhere in the same form, in English or in any other language.