Introduction and Purpose

Conclusions

Acknowledgements

GRAPHENE SYNTHESIS VIA CHEMICAL VAPOR DEPOSITION

FOR USE IN SUPERCAPACITOR ElECTRODES

Michael Curtin, Jian Liu,William E. Bernier, and Wayne E. Jones, Jr

Department of Chemistry, Binghamton University - State University of New York, NY, 13902

Research Experiences For Undergraduates Poster Session, JULY 31, 2014

References 1 Wonbong Choi, et al., Critical Reviews in Solid State and Materials Sciences, 35:1 (2010) 52-71

2 Chenguang Liu, et al., Nano Letters, 10 (2010) 4863–4868

3 Xuesong Li, et al., Science Express, 324 (2009) 1312

4 A.M. Awad, et al., Applied Surface Science 256 (2010) 4370–4375

5 Ajay Kumar and Chee Huei Lee (2013). Synthesis and Biomedical Applications of Graphene:

Present and Future Trends, Advances in Graphene Science, Dr. M. Aliofkhazraei (Ed.), ISBN:

978-953-51-1182-5, InTech, DOI: 10.5772/55728.

Results

Graphene, a mono-layer sheet of carbon atoms oriented in a honeycomb crystal lattice has

captured considerable attention due to its exceptional electronic and optoelectronic

properties. With its high electrical conductivity, optical transparency, and superb thermal

properties, graphene has generated extensive research for use in supercapacitor

applications.[1] Supercapacitors are electrical energy storage devices that can store and

release energy, quite similar to electrochemical batteries. Unlike batteries, supercapacitors

are able to charge and discharge rapidly, generating an extremely large amount of power

upon discharge. Batteries however remain to have a higher energy density, allowing for

extended storage and discharge of energy.[2] Graphene has the capability of enhancing the

energy density of a supercapacitor primarily due to its large surface-to-volume ratio. When

paired with the electrodes of a supercapacitor cell, graphene’s surface area and high

electron mobility create a tremendous amount of space for efficient electrical charge

storage.

According to the Raman spectroscopy analysis, the (2D/G) ratio increases with an

increasing flow rate of H2 gas, which indicates mono-layer graphene results from increased

H2. Also when shortening the growth time, the (2D/G) ratio increased as well. When

running an experiment with a much lower concentration of hydrogen under the same

conditions, there was no detection of carbon deposition, concluding the pivotal role of

hydrogen involved in the chemical vapor deposition of graphene films.

This work was supported by the Research Experiences for Undergraduates (REU) program

of the National Science Foundation under Award Number 1263004. This work could not

have been completed without the help of the professional and graduate personnel at the

Binghamton University Department of Chemistry. Also special thanks to the CASP Lab at

Binghamton University for providing the resources necessary for this work to be

completed.

The graphene films were prepared using the chemical vapor deposition (CVD) method.

Chemical vapor deposition is an efficient deposition process where chemical precursors are

transported in the vapor phase to decompose on a heated substrate to form a film [3]. This

growth technique was used to produce high-purity, high-performance solid materials. The target substrate for graphene growth included a thin piece of copper foil. The precursor

gases used involved both hydrogen (H2) and methane (CH4). The methane gas provides the

carbon source for deposition and the hydrogen supply plays the role of a carrier gas for

deposition of carbon. Both gases are carefully controlled using digital monitors and gauges

that regulate their flow rate and pressure. The process begins with loading the copper

sample into a tube furnace and evacuating any air inside to create a vacuum. The furnace is

then heated to approximately 1000 °C while the hydrogen gas enters the chamber. Once the

temperature reaches1000 °C the copper is annealed for 15 minutes, after which methane is

introduced for a desired period of time.[3] This is the effective growth time for the graphene

layer. The furnace is rapidly cooled to room temperature, while the remaining waste gas is

evacuated through an external pump.

Diagram 1: Double Layer Supercapacitor with Graphene-Coated Aluminum Electrodes

Experiment A

Results and Discussion

Diagram 2: Chemical Vapor Deposition Process

H2

CH4

Flow Rate

Controller

Tube Furnace

Copper

Pump/

Evacuation

Pressure Gauge

Carbon

Deposition

Heat Flow

Pressure Gauge

Flow Rate (sccm)

Gas Ratio (H2/CH4)

Growth Time (min)

Hydrogen Supply

Sample

#

H2 CH4

1 2 35 0.0571 30 Pure Hydrogen

2 10 35 0.286 30 Pure Hydrogen

3 20 35 0.571 30 Pure Hydrogen

4 2 35 0.0571 15 Pure Hydrogen

9 20 35 0.571 30 5% Hydrogen

Figure 1: Raman spectrum for graphene varying H2

concentration

Figure 2: Raman spectrum for graphene varying

growth time

Figure 3: Peak intensity ratios for increasing H2 concentration

Table 1: Growth parameters for CVD trials

Running parallel to the cvd experiment included an exploration into the surface morphology

of the target substrate Cu, and potential methods for developing a cleaner and smoother

surface. The electrochemical technique of electropolishing was further investigated. This

process involves removing metal ion by ion from the surface material, leaving behind a

microscopically featureless and smooth surface.

Experiment B

The electropolishing process involves making the workpiece anodic by negatively biasing

the two electrodes. When an electric potential is applied, a current will travel through a

conductive electrolyte and remove ions from the surface of the metal workpiece. To run a

successful electropolish, parameters including current density, current duration, concentration

of acidic electrolyte and electrode positioning must be carefully chosen and monitored.[4]

Diagram 3: Electropolishing Mechanism

Figure 6: AFM image of Copper sample surface profile before electropolish

Figure 7: AFM image of Copper sample surface profile after electropolish

Experiment C

Although less studied than the graphene growth process, the transfer of graphene from the

Copper substrate to another target substrate for use in supercapacitor electrodes has

generated interest and investigation. This tricky and delicate process has the potential for

developing convenient and much cheaper supercapacitors on an industrial scale

Diagram 4: Graphene transfer process [5]

Figure 5: Raman spectrum for graphene with a varying H2 supply

Figure 4: Peak intensity ratios for varying growth time

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

H2 =2 CH4 =35 H2 =10 CH4 =35 H2 =20 CH4 =35

Inte

nsi

ty

(2D/G) Ratio

(D/G) Ratio

0

0.2

0.4

0.6

0.8

1

1.2

Growth =30 min Growth = 15 min

Inte

nsi

ty

(2D/G) Ratio

(D/G) Ratio

-1.00E+02

0.00E+00

1.00E+02

2.00E+02

3.00E+02

4.00E+02

5.00E+02

6.00E+02

1.00E+03 1.50E+03 2.00E+03 2.50E+03 3.00E+03

Ra

ma

n I

nte

nsi

ty

Wavenumber (cm-1)

5% Hydrogen Supply

Pure Hydrogen Supply

According to the AFM images, the the copper sample appears to have an

increased surface roughness than before the polish. This could be the result of a

very aggressive acid concentration.

-1.00E+02

-5.00E+01

0.00E+00

5.00E+01

1.00E+02

1.50E+02

2.00E+02

1.20E+03 1.70E+03 2.20E+03 2.70E+03

Ra

ma

n I

nte

nsi

ty

Wavenumber (cm-1 )

H2=2 CH4=35

H2=10 CH4=35

H2=20 CH4=35

2D

G

D

-1.00E+02

-5.00E+01

0.00E+00

5.00E+01

1.00E+02

1.50E+02

2.00E+02

1.00E+03 1.50E+03 2.00E+03 2.50E+03 3.00E+03

Ra

ma

n I

nte

nsi

ty

Wavenumber (cm-1 )

Growth Time =30 min

Growth Time = 15 min