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: [email protected]
b Department of Chemical Engineering, University of Ulsan, Ulsan Metropolitan City, 44919,
Republic of Korea.
[*] E-mail: [email protected]
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
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