This document summarizes a study that tested different mass ratios of graphene and functionalized carbon black (FCB) as electrode materials for supercapacitors. The study found that a 1:1 mass ratio of graphene to FCB produced the best performance. Specifically, cyclic voltammetry tests showed that an electrode with a 1:1 graphene to FCB ratio had the highest specific capacitance of 178.48 F/g at a scan rate of 2 mV/s, and maintained 75.26% of its capacitance as the scan rate increased. In contrast, electrodes with higher or lower FCB content showed lower specific capacitances and poorer capacitance retention at higher scan rates. Therefore, the 1:1 graphene to F

1. Graphene-based Electrochemical Supercapacitors Using Different Mass Ratios
of FCB Spacer
Kailiang Chen, Bingcheng Zhou
Department of Mechanical Engineering, Purdue School of Engineering and Technology
1. Abstract
A test, which is based on cyclic voltammetry method[1]
, has been developed to find out the
best mass ratio between graphene and functionalized carbon black (FCB) spacer for
supercapacitor application. As one of the promising future materials, graphene has a very high
theoretical specific surface area (2630m2
/g) which is ideal material for supercapacitors that
require porous structure[2]
. However, the pure graphene sheets restack to each other and
significantly reduce the specific surface area and lead to a bad performance of graphene as
electrode material. To solve this problem, FCB spacers can be added to graphene sheets to
form a sandwiched structure between the stacks[3]
. And the best mass ratio between graphene
and FCB Spacer to form the composite material turns out to be 1:1.
Mentors: Prof. Jian Xie, Department of Mechanical Engineering, Purdue School of
Engineering and Technology, IUPUI
Co-mentors: Dr. Zhe-Fe Li, Postdoctoral Research Associate, Department of Mechanical
Engineering, School of Engineering and Technology and Prof. Lei Li, Assistant Professor,
Department of Chemistry, School of Science.

2. 2. Introduction
One of the biggest and most urgent problems in our society today is the storage and efficient
usage of energy. For over a century, fossil fuels are dominant energy consumption types, and
dominant energy storage types for their relatively easy storage, high power density and cheap
price. However, it also has fatal disadvantages as non-renewable, high environmental cost,
and low efficiency. On the contrary, energy storage in electrochemical method has its own
pros and cons. As a clean, renewable and efficient energy source, electrochemical storage
such as battery and capacitor have different characteristic. Battery has relatively high energy
density, stable discharging voltage, but a low charging and discharging rate, and a bad
tolerance for charging and discharging cycles. Capacitors, which are widely used in
controlling circuit, have good tolerance, high rate, but relatively low energy density, and
unstable voltage. Their characteristics highly restrict their ability in replacing the fossil fuels
as a clean energy source.
Supercapacitors, which is high-capacity capacitors, get both the advantages of battery and
capacitor for its high power density and high voltage[4]
. On the other hand, graphene, which is
a two-dimentional carbon based nanoparticle, has a large specific surface area (2630m2
/g) and
is rife with porous structures, that are perfect for adsorption of electric charges.
Although graphene is a very promising material in electrochemical industry, other problems
arouse. Pure graphene tends to restack to each other and significantly reduce the specific
surface area and lead to a bad performance[3]
. Consequently, researchers start to use spacers to
isolate and separate the stacks between graphene sheets. As one of the spacer, functionalized
carbon black (FCB) can insert to the graphene sheets to form a composite material as a
sandwich. FCB has excellent electrical conductibility, a similar structure as graphene for their
carbon based material characteristic, while its nanoscale solid can fit in the porous structure
of graphene. So it makes FCB a good spacer in theory.
In this project, graphene/FCB nanocomposites with different ratios were prepared and studied
their application as supercapacitor. Since it’s very troublesome and high cost to confirm the
structure of the composite material, a chemical test has been set up to figure out the best mass
ratio for the graphene and FCB to form the electrode material.

3. 3. Theory and Experimental Method
3.1 Preparation of FCB
2 g of EC600 carbon black was treated with 100 mL 0.5M HCl solution.
Add 3.5 g sulfanilic acid to the solution.
Stir the dispersion for 30mins and then add 3.6g sodium nitrite.
The resulting dispersion was stirred for 4 hours and then heated up to 70℃for another 3
hours.
The final dispersion was filtrated using suction filtration method with DI water.
3.2 Preparation of Graphene-FCB composite material
One of the most time consuming experiment in this test is the preparation of graphene.
The preparation of graphene include the process of pre-oxidation of graphite, turning
from pre-oxidized graphite to graphene oxide, and the reduction of GO with FCB, as well
as the final desiccation process.
(Materials list: Graphite flake,sulfuric acid, NaNO3, KMnO4, FCB,H2O)
3.2.1Pre-oxidation ofgraphite
Prior to the Hummer's method, an additional graphite oxidation procedure was carried
out.
10 g of graphite flakes were mixed with 50 mL concentrated H2SO4, 10 g K2S2O8, and
10 g P2O5.
The resulting mixture heated at 80 ºC and slowly cooled down for 4 h under constant
stirring.
The mixture was then filtered and washed with DI water. The product was dried in an
oven at 80 ºC.
3.2.2Synthesis ofgraphene oxide by modified Hammer’s method[6]
.
2g of pre-oxidized graphite and 1g of sodium nitrate was added into 46 mL of
concentrated sulfuric acid.
After stirring for 30 min, 6 g of KMnO4 was slowly added into the above suspension in
an ice bath.
Then the ice bath was removed and the suspension was maintained at 35 ℃for another
30 mins.
92 mL of water was dropwise added into the suspension, and the temperature was
increased to around 95-100 ℃. The suspension was kept stirring for 15 mins.
Then the suspension was diluted by 280 mL of water and treated with 10 mL H2O2.
The above suspension was washed a few times by centrifuge at 10000 rpm for 30 mins.
Use a ultrasonic bath to treat the solid for 1 hour to get the pure graphene oxide.

4. 3.2.3Reduction ofgraphene oxide with different mass ratio ofFCB[7]
(Procedure
example ofmass ratio between graphene and FCB equals to 1:1)
Weigh 100 mg FCB in the round flask, mixed it with DI water, stir it for a while.
Weigh 100 mg GO and mix it in the round flask with FCB, add DI water into a 100ml
turbid liquid.
Stir the solution using an ultrasonic bath for 1 hour.
An amount of 0.5 μL hydrazine solution was added into the mixture.
The mixture was stirred and heated treated with an oil field for 8 hours at about 90℃.
The dispersion solution is ready for desiccation process.
Fig 1. (a)Demonstration of the experiment process, functionlized carbon black(FC in
graph), graphene oxides(GO) to process into Graphene-FCB Composite; (b)Cryo-TEM
image of the material before reduction. Green arrows point to the FC particles and yellow
arrow to the graphene edge; (c)Cryo-TEM image of the material after reduction. Blue and
red arrows point to sandwiched graphene layers, and green arrow point to FCB particles[3].
3.2.4Desiccation ofgraphene dispersion solution with other soluble impurities
Preparing for a set of suction filtration equipment, using a filter paper with bore diameter
of 400 nm.
Wetting the filter paper with DI water, and turn on the air exhaust machine.
Filtrate the dispersion solution, making sure the composite grains will not dry out.
After the filtration of dispersion solution, add DI water for several times.
After the filtration of DI water,collect the solid and put it in the freeze-dying for 24

5. hours.
Heat-dying it for 1 hour using a vacuum at 80℃.
The resulting solid becomes the composite material and ready for testing.
3.3 Cyclic Voltammetry(CV) Method
In the cyclic voltammetry method, a series of time based controlled voltage with a specific
rate are applied to the tested object, and the corresponding current quantities are measured.
By the data collected, one could build up graphs in current vs. time, voltage vs. time, and
current vs. voltage. The voltage is the driving force of different kinds of oxidation and
reduction reaction, and the corresponding current value and graph shape can be used to
determine the reversibility, performance of electrode material, adsorption rate, storing ability
of material, etc[1]
. In the experiment, all the electrode materials were tested in the aqueous 1
mol/L 𝑁𝑎2 𝑆𝑂4 electrolyte.
We can use the CV method for performance test by calculation of average capacitance of
the tested object[5]
:
𝐶 =
𝑄
𝑉
=
∫ 𝑑𝑞
𝑉
=
∫ 𝐼𝑑𝑡
𝑉
=
1
𝑉
× ∫
𝐼
𝜇
× 𝑑𝑉 =
1
𝑉𝜇
∫ 𝐼𝑑𝑉
where C=capacitance,Q=total charges, V=voltage, I=current, μ=scan rate
𝐶 𝑚 =
1
2𝑚∆𝑉𝜇
∫ | 𝐼|
𝑉𝑓𝑖𝑛𝑎𝑙
𝑉𝑖𝑛𝑖𝑡𝑖𝑎𝑙
𝑑𝑉
where Cm=specific capacitance,m=mass of one electrode, ∆𝑉=𝑉𝑓𝑖𝑛𝑎𝑙 − 𝑉𝑖𝑛𝑖𝑡𝑖𝑎𝑙, μ
=scan rate, V=voltage, I=current

6. 4. Results and Conclusion
4.1 Graphene in comparison to activated carbon as an electrode material
One of the characteristic properties of graphene is its relatively large surface area. This
character and its high conductivity are our initiatives to study its application in
supercapacitors. In this set of experiment, commercially available activated carbon, which has
a loose structure, was used as the reference for the large surface area material. The
electrochemical capacitance was collected by measuring the cells, which used nearly identical
materials on both electrodes.All the cells used Ni foil as the current collector.
Fig 3. Graphene and activated carbon performance in coin cell (Cyclic voltammograms of
two samples obtained in 1 mol/L 𝑁𝑎2 𝑆𝑂4at scan rate of 5mV/s (a) and overall specific
capacitance at different scan rates (b)).
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0.25
0 0.2 0.4 0.6 0.8 1
Current(A/g)
Voltage(V)
AC-cell-5mVs
G-cell-5mVs
a
0
10
20
30
40
50
60
70
80
0 10 20 30 40
F/g
Scan rate(mV/s)
Graphene
Activated carbon
b

7. From the Fig 3, it can be observed at scan rate of 2 mV/s, the graphene have a higher specific
capacitance (69.59 F/g) than the activated carbon (48.98 F/g). And at each scan rate, the
graphene has better performance. This phenomenon may be explained from two reasons. On
one hand, the electron in the activated carbon still need to overcome the gap between different
band energy, thus its conductivity is smaller. On the other hand, a large part of the surface of
the activated carbon may not be effectively used. The blocks inside its structure can prevent
some of its area get in touch with the electrolyte. Thus, the graphene has the high potential in
the cell industry as an electrode.
4.2 The ideal value for the graphene performance
To find out the optimum performance of graphene, a RDE test is conducted in a
three-electrode system in 1 M Na2SO4 using Ag/AgCl electrode as a reference electrode and
platinum wire as the counter electrode. In the test, a thin graphene layer (20 μg) was
deposited on the working electrode by drop casting method. Since the material is mostly
presented in a uniform thin layer, the effect of the particle agglomeration can be excluded to
some extent.
Fig 4 Specific capacitance at different scan rates for graphene and activated carbon
in RDE device and graphene cell.
Fig 4 shows that the results from the RDE test are always larger than the values in the actual
coin cells. This points out that in real world practice, several factors, like the quality of the ion
exchange membrane, contact between the current collector and the electrode, as well as the
electrolyte transport, can largely reduce the specific capacitance that one material can
perform.
4.3 The best proportion
It has been discovered that pure graphene has many disadvantages that limits its further
application. Semiconductor transistors have a band gap: a transition point that allows an
0
20
40
60
80
100
120
140
160
180
0 5 10 15 20 25 30 35
Title
Title
Graphene RDE
Graphene cell
AC-RDE

8. asymmetric flow of charge through circuits. Pure graphene lacks a band gap[8]
, which needs to
be addressed. Its susceptibility to oxidative environments also influences the usage in high
voltage condition. Finally, the graphene works poorly in the aqueous environment. One of the
solutions is to functionalize it. After adding some functional groups on its surface, the
material is expected to have a higher performance. In this experiment, the samples contain
graphene nanosheets mixed with different amounts of functionalized carbon. The sample is
symbolled as in the pattern of “G/F=weight ratio”, in which “G” stands for graphene, “F”
stands for functionalized carbon. All the following results in this section are collected from
RDE test, which use Ag/AgCl electrode as a reference electrode. This is environmentally
friendly way to judge the property of a single material because each cycle only cost a tiny
amount of the ink to discover the ideal value.
4.4 Result Tables and Graph
Specific capacitances (𝐶 𝑚) obtained in 1 mol /L 𝑁𝑎2 𝑆𝑂4 from CV method and capacitance
retentions from 5mV/s to 30 mV/s for the samples.
Sample name 𝐶 𝑚(𝐹/𝑔) at different scan rate Capacitance
retention (%)2mV/s 5mV/s 10mV/s 20mV/s 30mV/s
G 97.75 88.34 82.66 77.79 76.85 78.62%
G/F=5/1 115.34 107.09 103.21 96.15 93.47 66.47%
G/F=3/1 145.94 127.55 118.77 115.38 110.54 75.74%
G/F=2/1 166.37 138.27 130.12 124.32 118.98 71.52%
G/F=1/1 178.48 158.37 149.09 142.84 134.33 75.26%
G/F=1/2 70.46 64.21 61.14 61.91 56.95 80.83%
F 61.46 55.54 52.54 50.80 49.34 80.26%

9. Fig. 5 Graphene composite performance in coin cell (Cyclic voltammograms of all
samples obtained in 1 mol/L 𝑁𝑎2 𝑆𝑂4 at scan rate of 5 mV/s (1)
Fig. 6 Graphene composite performance in coin cell (Cyclic voltammograms of all
samples obtained in 1 mol/L 𝑁𝑎2 𝑆𝑂4 at scan rate of 5 mV/s (2)
In general, it is shown that when graphene and FCB were mixed by half and half, the device
showed the best outcome at each scan rate. The following CV diagrams give visualized
support to the results. From the diagrams, the sample G/F=1/1 has the largest area in one
cycle. This give the largest value of ∫ | 𝑖|
𝑉𝑓𝑖𝑛𝑎𝑙
𝑉𝑖𝑛𝑖𝑡𝑖𝑎𝑙
𝑑𝑉, thus provide the largest 𝐶 𝑚.
-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
-0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6
Current(A/g)
Voltage(V)
G G/F=5/1
G/F=1/2 F
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
-0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6
Current(A/g)
Voltage(V)
G G/F=1/1
G/F=3/1 G/F=2/1

10. Furthermore, the trend with different mass ratio in this composite material are more obvious
when taking out the data at a scan rate of 2 mV/s, the curve’s peak can be easily pointed out
to 50% proportion of the graphene in the electrode material.
Fig.7 𝐶 𝑚 of samples at 2mV/s
Thus, the addition of the factionalized groups can efficiently improve the property of the
graphene by 60 F/g at most. One possibility is that this can be largely owed to expansion of
the surface. Even a single layer of the graphene is smooth at every point. It can fold and
contains impurities. The FCB pull out the space between surfaces and allow more surface
conduct electrons. But FCB itself has low conductivity compared to other electrical materials.
So when the proportion of the FCB keeps getting higher, like the sample G/F=1/2, the FCB
begins to conduct the most of the electrons instead of improving graphene’s performance, and
it comes out that the 𝐶 𝑚 drops.
4. Using new composite in actual cells
0
20
40
60
80
100
120
140
160
180
200
0.00% 10.00% 20.00% 30.00% 40.00% 50.00% 60.00% 70.00% 80.00% 90.00% 100.00%
F/g
graphene porportion
0
20
40
60
80
100
120
140
160
180
200
0 5 10 15 20 25 30 35
F/g
Scan rate(mV/s)
Graphene/FCB=1/1
Graphene/FCB=1:1 cell

11. Fig. 8 The comparison between the outcome of the G/F=1/1 composite fromRDE device and
coin cell
Fig. 9 Impedance plotsmeasured from1000 kHz to 0.1 Hz of the sample G/F=1/1 in 1 mol /L
𝑁𝑎2 𝑆𝑂4
At low scan rates, the cell works in an ideal condition. But when the scan rate gets higher, the
cell performance drops significantly. It is mainly due to the large internal resistance of the cell.
The radius of our semicircle is about 1.5 ohm, which may cause some energy loss when
charge and discharge in cycles.
-20
0
20
40
60
80
100
120
140
0 50 100 150 200 250
Z''(ohm)
Z'(ohm)
G/F=1/1
0
0.5
1
1.5
6
Z''(ohm)
Z'(ohm)

12. 5. Conclusion
After a series of experiments, we have got to some results. Although both pure
graphene and activated carbon have a high specific surface area, the performance of pure
graphene is about 20F/g (40%) better than the activated carbon in coin cell. Moreover, it is
concluded that the RDE test will provide a better value than the real application in coin cells
just as we expect. Finally, adding certain amount of FCB into the graphene will improve its
performance. The improvement of the property can be observed in every sample from
G/F=5/1(115.34F/g at scan rate 2mV/s) to G/F=1/1(178.48F/g at scan rate 2mV/s), and the
best mass ratio between graphene and FCB is 1:1 according to our tests. All in all,
graphene-spacer composite material groups (in our case: FCB) perform a lot better than
activated carbon.

13. Reference
[1]Heinze, J., 1984, “Cyclic Voltammetry—‘Electrochemical Spectroscopy’. New Analytical
Methods (25),” Angew. Chem. Int. Ed. Engl., 23(11), pp. 831–847.
[2]2015, “Graphene,” Wikipedia, the free encyclopedia.
[3]Wang, M., Liu, Q., Sun, H., Stach, E. A.,Zhang, H., Stanciu, L., and Xie, J.,2012,
“Preparation of high-surface-area carbon nanoparticle/graphene composites,” Carbon,
50(10),pp. 3845–3853.
[4]Zhang, L. L., and Zhao, X. S., 2009, “Carbon-based materials as supercapacitor electrodes,”
Chem. Soc. Rev., 38(9),pp. 2520–2531.
[5]Du,Q.,Zheng,M.,Zhang,L.,Wang,Y.,Chen,J., Xue,L.,Dai,W.,Ji, G.,and Cao,J.,2010,
“Preparation of functionalized graphene sheets by a low-temperature thermal exfoliation
approach and their electrochemical supercapacitive behaviors,” Electrochimica Acta,
55(12),pp. 3897–3903.
[6]Hummers,W. S.,and Offeman,R. E., 1958,“Preparation of Graphitic Oxide,” J. Am. Chem.
Soc., 80(6),pp. 1339–1339.
[7]Stankovich, S., Dikin, D. A., Piner, R. D., Kohlhaas, K. A.,Kleinhammes, A., Jia, Y., Wu,
Y., Nguyen, S. T., and Ruoff, R. S., 2007, “Synthesis of graphene-based nanosheets via
chemical reduction of exfoliated graphite oxide,” Carbon, 45(7),pp. 1558–1565.
[8]Singh, V.,Joung, D.,Zhai, L.,Das, S., Khondaker, S. I., and Seal, S., 2011, “Graphene
based materials: Past,present and future,” Progress in Materials Science, 56(8),pp. 1178–
1271.