Conference Full Paper template
Proceedings of the 3rd Applied Science for Technology
Application, ASTECHNOVA 2014International Energy
ConferenceYogyakarta, Indonesia, 13-14 August 2014Performance of
Electric Double Layer Capacitor Electrode from Reduced Graphene
Oxide Material Prepared by Zn Reduction Following by Hydrothermal
Process
Haniffudin Nurdiansah #, Diah Susanti #,*, Dah Shyang
Tsai^Hariyati Purwaningsih#, Lukman Noerochiem#
#Materials and Metallurgical Engineering Department, Institut
Teknologi Sepuluh Nopember Kampus ITS, Keputih, Sukolilo, Surabaya,
Indonesia^Chemical Engineering Department, National Taiwan
University of Science and Technology43, Section 4, Keelung Road,
Taipei, Taiwan*Corresponding Author : [email protected]
ABSTRACTReduced graphene oxide (rGO) has been succesfully
synthesized from graphite powder via Hummer's method, followed by
ultrasonication at different time (1.5, 2, and 2.5 h ), continued
by Zn reduction in acidic conditions, and finally thermally treated
by hydrothermal process at 1600C. These synthesized materials have
been characterized by XRD, SEM, FTIR, EDS, and Raman Spectroscopy.
From the XRD result, it appears that the peak of Graphite Oxide
(GO) (~9.80) has fully dissappeared, and broad peak at ~23-240 has
appeared. FTIR spectra indicate that the intercalated H2O molecules
and most of the oxide groups of GO are removed. The % weight of C
and O around 81.98% and 18.02 %, concluded from EDS Testing. From
Raman Spectroscopy Testing, shows that the curve consists of two
dominant peaks at 1350 cm-1 and 1590 cm-1 along with a wide band
extending from about 26003300 cm-1. Furthermore, the
electrochemical performance investigated by using electrode
prepared by dipping a piece of Nickel Foam into a rGO solution, and
then dried it and press it. The CV Testing shows a rectangular
shape and a high capacitance up to 350.37 F/gr at scan rate 2mV/s
in the Na2SO4 solution 1M. Galvanostatic charge discharge shows the
capacitance 368 F/gr at the current density 2 A/g. We concluded
that the best result was obtained by sample with ultrasonication
time 1.5 hour.
KEYWORDS: Reduced graphene oxide, Zn reduction, Hydrothermal,
Capacitance
INTRODUCTIONThe traditional synthesis of rGO from GO involves
harmful chemical reducing agents and is undesirable for practical
applications. Using Zn as a reductor to acquire rGO from GO under
acidic condition has been carried out, and it offers a potential
for cost-effective, environmentally friendly, and large-scale
production of rGO (Panbo Liu, et al, 2013).Several methods have
recently been reported to synthesize rGO, such as chemical vapor
deposition, thermal annealing graphene oxide with NH3, and arc
discharge method, but this process need rigorous conditions or
special instruments. Compared with these methods, the hydrothermal
method has merits of mild conditions and scale-up synthesis (Ping
Chen, et al, 2013).Electric double-layer capacitors (EDLCs), are
used in a wide range of energy capture and storage applications,
which are believed to provide clean energy with almost zero waste
emission. Carbon materials can meet the request of EDLC electrodes.
The commonly material used was activated carbon. Although activated
carbons always have high BET surface areas, only parts of the
surface can contribute to the specific.capacitance. Hence the
specific surface capacitance was lower than graphite (Xian Du, et
al, 2010).In recent years, graphene has been extensively explored
as an electrode material for EDLC because of its high conductivity,
large specific surface area (SSA), and excellent electrochemical
stability. For this purpose, reduced graphene oxide (rGO) has been
paid the most intensive attention, mainly because it can be cheaply
produced on a large scale from graphite oxide (GO). Graphene
materials for supercapacitors seem to be extremely attractive for
the present. Stoller et al, (2008) fabricated a symmetric
supercapacitor based on chemically reduced graphene oxide (rGO) to
give a specific capacitance of 135 F/gr in KOH and 99 F/gr in an
organic electrolyte . Xian Du et al, (2010) fabricated a
supercapacitor graphene nanosheet by coated into a piece of nickel
foam, which has a specific capacitance up to 150 F/gr in Na2SO4
electrolyte.In this work, rGO was prepared by Zn reduction under
acidic conditions. The ultrasonication was conducted at different
time (1.5, 2, and 2.5 h). Compared to other synthesis methods, the
advantages of our strategy is that this reduction process is very
fast, and environmentally friendly. In addition, the hydrothermal
process gave a rGO paper which has a good quality and can be
obtained at a lower temperature process (1600C). Therefore, the
resulting rGO paper exhibits excellent electrochemical capacitive
properties in neutral electrolyte, Na2SO4.Experimental
procedure
Preparation of rGOGraphite oxide was synthesized using graphite
flakes by the Hummers method . In a typical synthesis, 2.0 g of
graphite powder was added to 80 mL of cold (00C) concentrated H2SO4
in an ice bath. Then, NaNO3 (4.0 g) and KMnO4 (8.0 g) were added
gradually under stirring and the temperature of the mixture was
kept to be below 100C. The reaction mixture was continually stirred
for 4 h at temperature below 100C. Next step, the mixture was
stirred at 350C for 4 h, and then diluted with 200 mL of deionized
(DI) water. After adding all of the 200 mL of DI water, the mixture
was stirred for 20 h. The reaction was terminated by adding 15 mL
of 30% H2O2 solution. The solid product was separated by
centrifugation, washed repeatedly with 5% HCl solution until
sulfate could not be detected when titrated with BaCl2. For further
purification, the resulting solid was re-dispersed in DI water and
then was washed several times until the pH was neutral. Finally,
the resulting solid was dried at 1100C for 12 h to obtain graphite
oxide (GO) paper. Graphene oxide was achieved by ultrasonication of
graphite oxide paper in water for different time (1.5, 2, and 2.5
h). For the reduction process, 1.6 gr Zn powder and 10 mL HCl
(35wt%) were added into 40 mL graphene oxide solution (1 mg/mL)
solution. The mixture was stirred for 30 min. After that, 10 mL HCl
(35wt%) was added into the above solution and then maintained for a
period of time to remove excess Zn powder. Finally, the resulting
rGO was collected, washed with pure water several times, and put
into an autoclave and then dried at hydrothermal temperature
(1600C) for 12 h in a muffle furnace.
Characterization of Graphite Oxide Paper and rGO paperThe
morphologies and structures of the samples were observed by
scanning electron microscope (SEM, Inspect S50). The ratio of C/O
measure by EDS testing on SEM Jeol JSM-7001F with INCA software.
Chemical compositions and crystallite structures of the samples
were determined by XRD (X Pert Pro PANalytcal, Philips) using Cu K
radiation from 10 to 900 angles. The information of functional
groups was measured by Fourier transform infrared spectroscopy
instrument (FTIR, Nicolet Nexus 670). Raman spectra were recorded
on Renishaw Invia Raman Microscope, with WiRE 2.0 software.
Electrode Preparation and Electrochemical MeasurementsEDLCs
electrode was prepared by dipping a piece of nickel foam (10cm x
1cm) in a suspension of rGO (1 mg/ml) under stirring, without any
binders . The area which contact with the solution was 1cm2. After
30 minutes dipping, the bath was ultrasonication for 10 minutes.
Nickel foam rod then dried at 1100C for 12 h in a muffle furnace,
and then pressed using pressure machine for 1 minutes. Finally, the
electrode was dipping into the electrolyte for 5 hours, prior to be
used.All electrochemical measurements were carried out in a
conventional glass electrochemistry cell with a three-electrode
system in 1 M Na2SO4 aqueous solution. All measurements conducted
using set up 3 electrode system. A platinum wire used as a counter
electrode and a saturated calomel electrode (SCE) as reference
electrode. The cyclic voltammetry (CV) measurements were conducted
at different scan rates ranging from 2 to 100 mV with a potential
window from -0.2 V to -0.7 V in 1 M Na2SO4, respectively.
Galvanostatic charge/discharge measurements were run on from -0.2
to -0.7 V (in 1 M Na2SO4 electrolyte) at different current
densities. All measurements were carried out on a Jiehan 5000
Electrochemical Workstation Instrument.
3RESULT AND DISCUSSION
3.1 Morphologies and Structures of rGO
The morphologies of the graphite, graphite oxide and obtained
rGO were observed by SEM and their images are shown in Fig. 1. Fig
1 exhibits the different morphologies of graphite (A), graphite
oxide (B), and rGO (C-D). Graphite has a flakes structure, and
opaque. On the other hands, graphite oxide and rGO exhibits almost
transparent paper structure. rGO at the high magnification shows
the structure of layer by layer, someplace shows almost single
layer structure, which is very thin and transparent. It can be seen
the thin wrinkled structure and folding structure that graphene
owns intrinsically.
Figure 1 SEM images of Graphite (A), graphite oxide (B), and rGO
(C-D)The structural changes from graphite to graphite oxide and
finally to rGO were investigated by XRD measurement, and the
patterns are shown in Fig. 2 (a). The interlayer distance in
graphite is about 0.336356 nm, in 2= 26.50030. This is markedly
expanded to 0.830268 nm, 2= 10.65560 in GO due to the formation of
intercalated moieties and oxygen functional groups between the
layer of GO. In rGO, at 2= 23.71180, with the interlayer distance
about 0.370995 nm peak has appeared, which indicates that most of
intercalated water and oxygen fuctionalities are removed. Figure 2
(b) show the typical XRD pattern of rGO at different
ultrasonication time. It clearly seen that the broad peak of (002)
decreasing with the increasing of ultrasonication time. Also, the
value of intensity also increasing with the increasing of
ultrasonication time, as seen on figure 2 (c).
Figure 2 (a) XRD pattern of graphite, graphite oxide and rGO.
(b) XRD pattern of rGO at different ultrasonication time. (c)
Intensity pattern of rGO at different ultrasonication time.
Raman technology was performed to indicate the structures of
graphite, graphite oxide and rGO by the resulting characteristic G
and D bands sensitive to defects and disorder, respectively. From
the result, it clearly seen at the figure 3 (a) that all of the
material consists of two dominant peaks at 1350 cm-1 and 1590 cm-1
along with a wide band extending from about 26003300 cm-1. The peak
at around 1350 cm-1 is the D band. The D band is attributed to the
presence of defects, like disruption in the sp2 bonding (because of
vacancies, heptagon and pentagon rings, edge effect, etc.), wrinkle
formation and the presence of functional groups.The peak at around
1590 cm-1 is the G band. The G band is a characteristic of all
graphitic structures, arising due to the inplane bond-stretching
motion of sp2 hybridized carbon atoms. The peak at around 2600 cm-1
is known as the 2D (or G) band since it is an overtone of the D
band. The peak around 2930 cm-1 is a combination mode of G and D
bands, often referred to as the D + G band. The hump at about 3170
cm-1 is due to an overtone of the D band (2D).
Figure 3 (a) Raman pattern of graphite, graphite oxide and rGO.
(b) Raman pattern of rGO at different ultrasonication time
Graphite has a nearly perfect structure, indicates by small weak
peak of D band, and the sharp peak of 2D. Its also supported by the
ID/IG ratio value, which is 0.16, nearly 0. Graphite oxide and rGO
has similar pattern, large D band and small weak 2D band. The ID/IG
ratio is increased from 0.74 in graphite oxide to 1.70 in rGO,
which suggests that more sp2 domains are formed, indicating that
reduction of GO takesplace. It also shows that the defect on the
structure of rGO is increasing. Figure 3 (b) shows raman pattern of
rGO at different ultrasonication time. All sampel shows the same
pattern. The value of ID/IG is increasing from the ultrasonication
time 1.5 hour to 2 hour, and then decrease again at 2.5 hour.
Increasing of ID/IG value corresponding to the increasing level of
defect on material.
Figure 4 (a) FTIR pattern of graphite oxide and rGO. (b) FTIR
pattern of rGO at different ultrasonication time
Another confirmation of the reduction mechanism is obtained by
the FTIR spectra. FTIR spectra indicate that the intercalated H2O
molecules and most of the oxide groups of graphite oxide are
succesfully removed at the structure of rGO. However, a small
number of the epoxide groups remain after reductions, as shown in
the FTIR spectra at figure 4 (a). Figure 4 (b) shows the FTIR
pattern at different ultrasonication time. Increasing the
ultrasonication time caused almost all of the oxide group has been
succesfully removed. EDS analysis at figure 5 also indicates that
the contain smaller amounts of oxygen. The % weight of C and O
around 81.98% and 18.02 %, as shows at figure 5. So, the ratio of
C/O for rGO is 4.54.
ElementWeight % Atomic %
C K81.9885.84
O K18.0214.16
Totals100
Figure 5 EDS result of rGO, contain C and O element.
3.2Electrochemical Performance of rGOFigure 6 (a-c) shows CV
curves of rGO sample with various scan rates in the range of -0.2
to -0.7 V in 1 M Na2SO4 aqueous solution , and rGO electrode
exhibited fairly rectangular CV curves which is indicative of
double layer capacitor behavior. Also, the current density response
gradually increased with the increase of the voltage sweep
rate.
Figure 6 CV curve pattern of rGO at scan rates varying from
2mV/s until 20mV/s for different ultrasonication time (a) 1.5 hour
(b) 2 hour (c) 2.5 hour and (d) comparison of capacitance values
with increasing scan rates
The best value of capacitance is 350.37 F/gr at scan rate 2mV/s,
higher than Xian Du, et all, (2010). Figure 6 (d) shows the value
of capacitance at different scan rate. It appear that the
capacitace is decreasing with the increasing of scan rates. It also
shows that the capacitance is decreasing with the increasing of
ultrasonication time.Fig. 7 (a-c) shows the galvanostatic
charge/discharge curves of rGO tested at different current
densities for sampel from different ultrasonication time. At sampel
with ultrasonication time 1.5 h, rGO exhibits a nearly linear and
symmetric charge/discharge profile at different current densities,
giving capacitance as big as 368 F/gr. A small portion of IR drop
happens at beginning of discharge curve, IR drop occurs from the
accumulation of DC internal resistance and the electric current.
For sampel with ultrasonication time 2 (b) and 2.5 hour (c), the
profile not really shows triangle, indicating that charging and
discharging process occurs with different time. From the curve, its
easy to look, the charging time is much longer than dicharging
time, which indicate that the performance is not so good, and it
proven by the value of capacitance, which is much lower than sampel
with ultrasonication time 1.5 hour.
Figure 7 Charge-Discharge curve pattern of rGO at at different
ultrasonication time (a) 1.5 hour (b) 2 hour (c) 2.5 hour and (d)
comparison of capacitance values with increasing scan rates
The value of capacitance is almost contiguous with the result
from CV testing. The behaviour of decreasing capacitance with the
increasing of current densities also occurs at charge discharge
testing for all sampel, as shows at figure 7 (d).4conclusionReduced
graphene oxide (rGO) has been succesfully synthesized from graphite
powder via Hummer's method, followed by ultrasonication at
different time (1.5, 2, and 2.5 h ), continued by Zn reduction in
acidic conditions, and finally thermally treated by hydrothermal
process at 1600C. It result a transparent structure of rGO sheet,
has structure of rGO from XRD test, with almost all of the oxygen
containing functional group was removed. The paper contain only C
and O element, indicates doesnt have any impurities. Raman spectra
shows that rGO structure has two dominant peak, D band and G band,
with various value of ID/IG, indicate the level of defect on
materials. Electrochemical test shows that rGO exhibits high rate
supercapacitive performance. The CV Testing shows a rectangular
shape as the characteristic of EDLC, shows a high capacitance up to
350.37 F/gr at scan rate 2mV/s in the Na2SO4 solution 1M.
Galvanostatic charge discharge shows the pattern almost triangular,
with the capacitance 368 F/gr at the current density 2 A/g. Both CV
and Charge Discharge test shows that increasing the ultrasonication
time will decreased the capacitance of rGO. Hence, we concluded
that the best result was obtained by sample with ultrasonication
time 1.5 hour.5ACKNOWLEDGEMENTSThis work was supported by Institut
Teknologi Sepuluh Nopember and Prof Dah Shyang Tsai from NTUST,
Taiwan.
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