Electronic Supplementary Material

Multi-dimensional Carbon Nanofibers

for Supercapacitor Electrodes

Byung Gwan Hyun,a Hye Jeong Son,b Sangyoon Ji,a Jiuk Jang,a Seung-Hyun Hur,*b and Jang-Ung Park* a

a School of Materials Science and Engineering, Wearable Electronics Research Group, Ulsan

National Institute of Science and Technology (UNIST), Ulsan Metropolitan City, 44919,

Republic of Korea.

[*] E-mail: jangung@unist.ac.kr

b Department of Chemical Engineering, University of Ulsan, Ulsan Metropolitan City, 44919,

Republic of Korea.

[*] E-mail: shhur@unist.ac.kr

This Supplementary data includes:

Methods

Supporting Fig. S1-S5

Table S1

Methods

Electrospinning.

Plain and MC CNF precursors were electrospun for preparing the plain and MC CNFs. The distance

between the tip of the needle (21 gauge needle from NanoNC) and the grounded liquid collector

(water) was 15 cm, and the voltage of 10 kV was used to obtain a stable Taylor cone. The flow rate

was constantly kept in 0.4 mL/h. A dual concentric nozzle (17 and 23 gauge, purchased from

NanoNC) was used in this experiment. The core solution was hollow CNF precursor solution and

shell solutions were plain CNF precursor (hollow CNF) and MC CNF precursor (hollowed MC)

solutions, respectively. Two plastic syringes were loaded each solution to form the core (high-MW

PMMA)-shell (PAN or PAN/low-MW PMMA) electrospun nanofibers. Coaxial electrospinning was

carried out at 10 kV at the 18 cm distance from the liquid collector to the end of the dual nozzle. Inner

solution feed rate was 0.2 mL/h and outer solution feed rate was 1.0 mL/h, respectively. All processes

were conducted at room temperature with humidity below 30%.

Synthesis of carbon nanofiber.

Electrospun PAN-based nanofibers were placed in a furnace and heated for 2 hours at 280 °C in air.

This process is oxidized stabilization and ramp rate was 1 °C/min. After then, stabilized PAN-based

nanofibers were heated for 1 hours at 850 °C in argon. This process is carbonization and ramp rate

was 5 °C/min. Finally, we obtained the carbon nanofibers and we did not conduct the activation

process.

Characterizations.

The surface morphology of electrospun nanofiber mats was characterized using scanning electron

microscopy (SEM, Hitachi, S-4800). The physical adsorption properties were determined by N 2

adsorption-desorption measurements (Micrometrics Instruments, ASAP-2020). The Brunauer-Emmet-

Teller (BET) method was utilized to calculate the specific surface area and pore size distribution; the

pore size distribution curves were calculated from the analysis of the desorption branch of the

isotherm based on the Barrett-Joyner-Halenda (BJH) model.

Electrode preparation

The CNF mats were pulverized using agate mortal and we weighed 1 mg of pulverized CNF powder

with 1 µg resolution electronic scale (XS3DU micro balance, METTLER TOLEDO). The CNF

solution (1 mg/ml in ethanol) was prepared and sonicated in a sonication bath for 3 min. We made

two CNF coated glass filter paper by dropping 0.5 ml CNF solution on the 10 mm diameter punched

glass filter papers. As shown in Fig. S4, stainless steel (SS) electrode, CNF-coated glass filter, and

glass filter were assembled in PTFE union fitting. 5 µl of H2SO4 aqueous electrolyte was dropped in

the fitting and then, opposite side was sealed using same materials (CNF-coated glass filter and SS

electrode).

Electrochemical properties characterizations.

Cyclic voltammetry (CV) measurements were carried out using 1 M H2SO4 solution and the sweep

potential range was adjusted from 0 V to 1.0 V in the electrochemical cell. A two-electrode system

was used: Stainless steel disk as the current collector, synthesized CNFs as the active materials, and

glass fiber filter as a separator. The two current collectors were served to convey the electrical current

from one electrode to the other. CV and galvanostatic charge-discharge constant-current test were

used to characterize the electrochemical performance of the supercapacitor cells. During the process,

the CV and galvanostatic charge-discharge curves were recorded using an electrochemical interface

(Solartron, SI 1287) and used for evaluating the capacitive behavior and calculating the specific

capacitance of the nanostructured CNF electrodes. The electrochemical impedance test was performed

on an impedance/gain-phase analyzer (Solartron, SI 1260) with a frequency in the range of 0.01 Hz ~

100 kHz and 10 mV amplitude.

Calculation of the specific capacitance from CV measurements

The specific capacitance was calculated from CV curve by following equation. [1]

Specific capacitance= ∫ i dV2×m ×∆ V × S

Where ∫ i dV is the integrated area of the CV curve, m is the mass of the single electrode, ∆ V is the

potential range and S is the scan rate, respectively.

Calculation of the energy density and the power density

The internal resistance, the energy density and power density was calculated by following equations.

Internal resistance=∆ V IRdrop

i

Energy density=C U 2

2

Power density= U2

4 R

Where ∆ V IRdrop is the slop of the discharge curve after IR drop, i is applied current, C is the specific

capacitance [F/g], U is the applied voltage and R is the internal resistance.

[1] A. Yu, I. Roes, A. Davies, Z. Chen, Appl. Phys. Lett., 2010, 96, 253105.

Supp lementary Figures and Tables

Fig. S1. The thickness of PAN-based nanofibers network on the metal and the liquid collector

as a function of electrospinning time.

Fig. S2. CV curves of both punched CNFs electrode and pulverized CNFs electrode at 50

mV/s.

Fig. S3. Schematic of two-electrode assembled electrochemical cell in union connector

fitting.

Fig. S4. OM image of dispersed low-MW PMMA solutions in the PAN solution. The scale

bar is 100 μm

.

Fig. S5 Schematics of hollow carbon nanofiber synthesis process.

Table S1. Electrospun non-activated carbon nanofiber as supercapacitor electrode materials.

Structures Specific surface area(m2/g)

Specific capacitance(F/g)

Reference

Plain 20 20 [2]

Plain - 50 [3]

Plain 48 118 [4]

Plain 17 63 [5]

Plain 502.5 60 [6]

Plain - 150 [7]

Plain 359 42 This work

Hollow 438 99 This work

Multi-channel (MC) 491 133 This work

Hollowed MC 549 129 This work

[2] J. S. Im, S. -W. Woo, M. -J. Jung, Y. -S. Lee, J. Colloid Interface Sci. 2008, 327, 115-119. [3] J. Li, E. -H. Liu, W. Li, X. -Y. Meng, S. -T. Tan, J. Alloys Compd. 2009, 478, 371-374.[4] X. Yan, Y. Liu, X. Fan, X. Jia, Y. Yu, X. Yang, J. Power Sources 2014, 248, 745-751.[5] A. G. El-Deen, N. A. Barakat, K. A. Khalil, H. Y. Kim, New J. Chem. 2014, 38, 198-205.[6] B.-H. Kim, K. S. Yang, Y. A. Kim, Y. J. Kim, B. An, K. Oshida, J. Power Sources 2011, 196, 10496-10501[7] H. He, L. Shi, Y. Fang, X. Li, Q. Song, L. Zhi, Small 2014, 22, 4671-4676