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Synthesis and Electrochemical
Properties of GUITAR: A Breakthrough
Material for Energy Storage.IAS Meeting, Moscow ID March 21, 2014
I. Francis (Frank) Cheng, Isaiah Gyan, Haoyu Zhu
Department of Chemistry
University of Idaho
Moscow, ID 83844-2343
208-885-6387
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Outline
• Discovery
- Thermolyzed Asphalt Reaction (TAR)
– Graphene from UI-TAR (GUITAR)
• Comparison of GUITAR with Literature
– What is it?
– Not Graphene nor Ordinary Graphite
• Electrochemical Characteristics
- Energy storage applications
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Porcelain
Crucible
Heat
Porcelain
Cover
Inner Crucible
with precursors
Flames from
precursor
combustion
Brownish
Fumes
Figure 2.0.1 (Left) Pyrolysis of roofing tar, (Middle) schematic of the process, (Right) finished product.
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University of Idaho Thermolyzed Asphalt Reaction
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Figure 2.0.2 GUITAR graphene, A – a photograph of a flake approximately 25 mm in
diameter. B – an optical micrograph (400x) in water. C – graphene layers (400x). D –
9.45K x SEM of microtomed layers on Si. E – 23.08K x SEM showing layered
characteristics. F – A TEM showing layered characteristics on the nanometer scale.
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UITAR-University of Idaho
Thermolyzed Asphalt Reaction
• Successful Reagents– Shale Oil
– Crude Oil
– Roofing Tar (Ace Hardware)
– Taco Chips
– Some Candy Bars
• Failed– Motor Oil, 5W-20
– Paraffin
– Pyrene
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Mechanism of Formation
• First Hunch – Sulfur is Involved
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cyclohexanol and Sulfur
cyclohexanol only
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Thermogravimetric analysis
7
Cycohexanol (40 mg)
Element sulfur (1 mg)
Final temperature
600 0C
Temperature ramp
100C/min
Under N2 purge
I.F. Cheng, et al. J. Mater. Chem. 2012, 22, 5723-29
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Raman indicates an intermediate at 1450 cm-1
8
Minimum temperature 6000C
O2 not affect graphene
formation
Graphene forms under N2
1450 cm-1 intermediate at 4000C
Y. Xie, I.F. Cheng, et al. Submitted
1300
1350
1400
1450
1500
1550
1600
500 1000 1500 2000 2500 3000
4000C
1450
835
840
845
850
855
860
500 1000 1500 2000 2500 3000
5500C
G15841444
D1350
1400
1500
1600
1700
1800
1900
2000
500 1000 1500 2000 2500 3000
6000C
Wavenumber(cm-1)
G1594D1350
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Summary of Formation
• TGA and Raman Evidence – Intermediates formed with S between 120 – 450 0C
– Graphene/Graphite formation at 600 0C
• Reagents– Organic BP – MP 100-250 0C
– Elemental Sulfur, Organic Sulfur
• Conformal Coatings
– Unique to TAR
– Deposition onto silica nanostructures
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Hypothesized TAR MechanismCheng et al, J. Mater. Chem. 2012, 22, 5723-29
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What is that Material?
• Graphene (l) vs. GUITAR (r)
– Graphene is a monolayer
– GUITAR is multilayer
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Graphene Paper and Highly Oriented
Pyrolytic Graphite
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• Is it multilayer-graphene?• Graphene Paper (GP) Left• Highly Oriented Pyrolytic Graphite (HOPG)? Right
http://users.monash.edu.au/~lidan/http://www.hqgraphene.com/NaturalGraphiteFlakes.php
GUITAR
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14
Geim, Science, 2009, 324, 1530-4
GUITAR
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Graphene Paper (GP)
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Morphological Differences GP – GUITAR
15
Ruoff, et al. Nature, 2007, (448), 457-460
GUITAR
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UI Material is Nearly Atomically Flat
16
Micron Scale AFM of UI Carbon
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HOPG and UI Carbon
17
http://www.theodoregray.com/periodictable/Elements/006/index.s14.html#sample31
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HOPG
GUITAR
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Physical Characterization
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Material XPS Raman (cm-1)
GUITAR Nearly Pure sp2
CarbonG-band 1593D-band 1350
Defective graphene structure
HOPG Same G-band only Nearly Defect Free
GraphenePapers
Same G-band (obs)D-band (obs)
Defective graphene structure
IR - 861 and 1576 cm-1 peaks intralayer graphene stretchesNo other surface functionalities
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UI Carbon
• SEM and AFM– Flat, layered morphology Resembles Highly Ordered
Pyrolytic Graphite (HOPG)
– Does Not Appear to be literature GP or r-GO paper
• Raman Studies– Grain Size 5.3 nm (Raman) with GP/r-GO parameters 3-
6 nm
– Closer to GP than HOPG
Neither HOPG or GP -- just graphite?
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UI Carbon - Structure
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Graphene Paper UI Material (Proposed) HOPG
Textured surface Flat Flat
Ferrari, Robertson. Phys Rev. 2000, (B61), 14095-14107
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GUITAR Electrochemistry
• Electrochemical Characterization
– Indicates that GUITAR is a unique graphitic material.
–Graphene and HOPG are terrible electrodes
–GUITAR is an excellent electrode
– Excellent corrosion stability
–High H2 overpotential
– Proposed Applications
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23
GUITAR electrode fabricationDeposit GUITAR onto silicon wafer
Transfer the GUITAR flakes onto mica by vacuum
grease or 3M double sided conductive tape
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1 cm2, 0.1 M KCl(aq) at 0.1 V/s.
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Cyclic Voltammetry Indicates that GUITAR has excellente- transfer rates with dissolved redox couples.
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Fe(CN)6 3-/4-
k0 (cm/s)
Ru(NH3)63+/2+
k0 (cm/s)
GUITAR
1 x 10-2 2 x 10-2
Graphene (Basal Plane)
3 x 10-10 5 x 10-3
HOPG (Basal Plane)
10-6 10-3
HOPG (edge plane)
10-1 --
Glassy Carbon
1 x 10-2 2 x 10-2
𝑂𝑥 + 𝑒−𝑘0
𝑅𝑒𝑑
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e- Transfer at Graphitic Electrodes
Edge vs. Basal Planes
• Electron transfer rates on
HOPG/Graphenes
– Edge >> Basal Plane
• GUITAR electrodes have only Basal
Planes exposed
• GUITAR Basal Planes has fast e-
transfer
– More like disordered systems
Jan. 13, 2014 26
Edge
Basal
slowOx + ne-
Red
FastOx + ne-
Red
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Electron Transfer Rate Trends
• Fastest Left Right
GUITAR ≈ Glassy Carbon ≈ Graphite (edges)
> Boron Doped Diamond ≈ DLC
> HOPG (basal Plane) ≈ Graphene (basal plane)
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σ+ π+ σ-π-
EFermi
DOS
EFermi
Energy (eV)
Crystalline Graphite Disordered Graphite
McCreery et al, J. Phys. Chem. 1994, 98, 5314-5319
From McCreeryTable 5
Free e- density (cm-3)
DOS at Fermi Level states/atom/eV
Au 6 × 1022 0.28
HOPG 5 × 1018 2.2 x 10-3
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ValenceBand
ConductionBand
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GUITAR Electrodes
• Higher DOS along Structural Defects?
• Structural Defects
– Sites for fast e- transfer?
– Nano-crystals 5 nm
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Defects
Defects
Defects
e-
e-
e-
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More Evidence that GUITAR is not a
just another graphite - Anodic Limits• Potential “Window”
• Anodic Limits– Water breakdown
– 2H2O O2 + 4H+ + 4e- E0 = 1.23 volts
– Corrosion– C + 2H2O CO2 + 4H+ + 4e- E0 = 0.207 V
• Cathodic Limit– Water breakdown
• 4H+ + 4e- 2H2 E0 = 0.00 volts
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E, potential (Volts)
More oxidizing
Current
1.23 V
Oxygen overpotential
0 V
Hydrogen overpotential
No reaction
2H2O O2 + 4H+ + 4e-
4H+ + 4e- 2H2
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-500
-400
-300
-200
-100
0
100
200
Cu
rre
nt
(µA
/cm
2)
-10
-5
0
5
10
-1 0 1 2 3
Potential (V) vs Ag/AgCl
Cu
rre
nt
( m
A/c
m2
)
Cyclic voltammograms of a
GUITAR electrode 1M H2SO4
υ = 50 mV/s, under Ar.
The anodic limit at 200
µA/cm2 is 2.1 volts.
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Figure2.6.2Cyclicvoltammogramsofa1cm2GUITARelectrodeinvariouselectrolytesat50mV/s.AllthesolutionswerepurgedwithAr.
KNO3
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34
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Material Anodic Limit (V)
CathodicLimit (V)
Total window (V)
reference
GUITAR 2.10 ± 0.03 (15) -0.90 ± 0.08 ( n = 15) 3.00
This workPyrolytic Graphite 1.88 ± 0.03 (12) -0.44 ± 0.08 (12) 2.32
Graphite Foil 1.45 ± 0.01 (10) -0.51 ± 0.05 (10) 1.96
HOPG 1.67 -0.41 2.08 Literature
HOPG 1.60 -0.40 2.00 Literature
Exfoliated Graphite 1.71 -0.50 2.21 Literature
Potentials are referenced to the standard hydrogen electrode (SHE).
GUITAR has a much larger potential window than literature Graphite and HOPG
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Anodic limits comparison of the GUITAR anode to boron doped diamond and HOPG in various electrolytes.
Electrode
Electrolyte
Anodic
Limits
vs. SHE (V)
Current
density
(µA/cm2)
Ref.
GUITAR
1 M H2SO4
2.1 200 This
work
BDD 1.9 - 2.5 200 1,2,3
HOPG 1.7 200* 4
N-Doped
Diamond-
Like Carbon
0.5 M
H2SO4
2.6 V 200 7
*Current density estimated from an average of 0.1 cm2.
Reference 4 reports electrodes varied from 0.05 to 0.2 cm2
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Anodic Limits of GUITAR and other Dimensionally Stable
Anodes.
Material
Anodic Limit
(V) vs. SHE
Conditions Reference
GUITAR 2.7 1 M H2SO4 This work
Graphite 1.7 0.5 M H2SO4 1,2,3
Ruthenium
Oxide
1.47 0.5 M H2SO4
4,5,6
Iridium Oxide 1.52 0.5 M H2SO4
Platinum 1.6 0.5 M H2SO4 7,8,9
Tin Dioxide 1.9 0.05 M H2SO4 10,11,12
Lead Dioxide 1.9 1 M H2SO4 13,14,15
!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
[1] Canizares, P. Dominguez, J. A. Rodrigo, M. A. Villasenor, J. Rodriguez, Effect of the
Current Intensity in the Electrochemical Oxidation of Aqueous Phenol Wastes at an Activated Carbon and Steel Anode, J. Ind. Eng. Chem. Res. 1999, 38, 3779.
[2 ] Polcaro, A. M. Palmas, S. Electrochemical Oxidation of Chlorophenols, Ind. Eng. Chem.
Res. 1997, 36, 1791.
[3] Polcaro, A. M. Palmas, S. Renoldi, F. Mascia, M. Three-dimensional electrodes for the
electrochemical combustion of organic pollutants, Electrochim. Acta 2000, 46, 389.
[4] Panizza, M. Cerisola, G. Influence of anode material on the electrochemical oxidation of 2-
naphthol: Part 1. Cyclic voltammetry and potential step experiments, Electrochim. Acta 2003, 48, 3491.
3/21/14 37
2.1
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Anodic Stability Trends
• BDD ≈ DLC > GUITAR > HOPG = Graphite =
Glassy Carbon ≈ Metal Oxides > Pt > Metals
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GUITAR vs. HOPG Anodic Limits
• HOPG limit = +1.7 V– Murray et al, Anal. Chem.1995, 67, 2201– Can’t do methylene blue degradation @ 2.0 V
• GUITAR limit = 2.1 V
• Anodic Limit– GUITAR > HOPG– Cheng et al, RSC Advances 2013, 3, 2379
• Why?
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Jan. 13, 2014 40
HOPG anodic limit 1.7 VMicron size grainsGaps between grain boundaries
Electrolytic penetration
Corrosion on HOPG is initiated with electrolyte intercalation. Murray et al, Analytical Chemistry, 1995, 67, 2201-2206
gasO2 Gas EvolutionBlister and Pit Corrosion Formation
O2
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Defects HOPG vs. GUITAR
• Highly Ordered Pyrolytic Graphite (HOPG)
– Grain Defects with Holes, Crevasses
– Nearly Flawless Structure
• Raman G-Band only
• GUITAR
– Structural Defects with No Holes
• Raman D/G band
• No Electrolyte Intercalation – Cyclic Voltammetry
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gas
Gas Evolution, Blister and Pit Formation
Murray et al, Analytical Chemistry, 1995, 67, 2201-2206
2H2O O2(g) + 4H+ + 4e- forward scan
2O2 + 4H+ + 4e- 2H2O reverse scan
Forward scan
Reverse scan
Blister formation on pyrolytic graphite anodes
More oxidizing potentials
Ianode
Icathode
O2
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Cyclic voltammograms of a 1 cm2 GUITAR electrode in various electrolytes at 50 mV/s. All the solutions were purged with Ar.
1MH2SO4
HClO4
KNO3
-1 0 1 2 3
Poten alvs.Ag/AgCl
1MNa2SO4
1MKNO3
0.1MHClO4
400μA/cm2
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GUITAR anodes do not exhibit electrolytic intercalation
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Current Model
44
HOPG anodic limit 1.7 VGUITAR anodic limit 2.1 V
Electrolytic penetration
Micron size grainsPin-Holes-Fewer DOS
Nano-size Grains w/Structural DefectsPin-Hole Free?-Higher DOS
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GUITAR Has the Highest Measured H2
Overpotential of Graphitic Materials
• Aqueous Media– 2H+ + 2e-
H2 E0 = 0.00 V
• Overpotentials– Metal electrodes 0.1 to 0.5 V
– Carbon electrodes 0.2 to 0.6 V
– GUITAR 1 V
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400 µA/cm2
-2 -1.5 -1 -0.5 0
E (V) vs Ag/AgCl
H2SO4
KNO3
H3PO4
LiClO4
(NH4)2SO4
400 µA/cm2
Figure 3. Cyclic voltammograms at GUITAR at 50mV/s in the indicated electrolytes (1M). Starting potential was zero and scan direction was towards more negative potentials. Counter and reference electrodes were graphite rod and Ag/AgCl respectively. Potentials for hydrogen evolution were extrapolated at 200µA/cm2 from these voltammograms.
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1 M H2SO4
GUITAR potential Limits (V) (n = 15)
Anodic ± σ Cathodic ± σ ΔEp 1mM Fe(CN)64-/3- , 1 M KCl
2.10 V ± 0.03 -0.90 V ± 0.11 73 mV ± 5
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GUITAR electrodes have a • 3 V potential window in 1 M H2SO4 and • Excellent electron transfer kinetics
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material condition cathodic anodic Total window
Ref.
GUITAR1M H2SO4, ± 0.2mA/cm2, SHE
-0.9 2.1 3.0 V This work
Platinum -0.1 1.4 1.5
HOPG
0.1M H2SO4, ± 0.2mA/cm2, SHE
-0.4 1.7 2.1
1GC -0.5 1.5 2.0
BDD -0.5 2.1 2.5
DLC -0.9 2.0 3.0
GUITAR electrodes have the largest reported aqueous potential windows
• HOPG and graphene are not good electrodes • Fe(CN)6
4-/3- ΔEp > 500 mV
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Ultracapacitors & Energy Storage
• E = ½ CV2
• Energy Storage
– Increased Capacitance
– Increase Cell Voltage, V
– Aqueous Systems Preferred
• H2SO4(aq)
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Capacitance Studies
• GUITAR has much higher capacitance than other materials - DOS ?
• Capacitors Applications Require Zero Faradaic current
- Narrower potential window than 200 A/cm2 limits
• Cyclic voltammetric measurements
𝐶 =𝑖
𝑑𝑉𝑑𝑡
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Proposed capacitive window -0.8 to 1.2 V
640 μF / cm2
Capacitors Applications Require Zero Faradaic Current
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-1.50E-05
-1.00E-05
-5.00E-06
0.00E+00
5.00E-06
1.00E-05
1.50E-05
-0.800 -0.600 -0.400 -0.200 0.000 0.200 0.400 0.600 0.800 1.000
Cu
rren
t d
ensi
ty(u
A/c
m2
)
potential vs Ag/AgCl
Capacitance of Glassy Carbon electrode in 1M H2SO4, dV/dt = 50mV/s
5µA/cm2
@0.1V, Δi=4.93 µA/cm2 , C=49.3µF/cm2
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-1.50E-06
-1.00E-06
-5.00E-07
0.00E+00
5.00E-07
1.00E-06
1.50E-06
2.00E-06
-0.400 -0.200 0.000 0.200 0.400 0.600 0.800
CU
RR
ENT
DEN
SITY
(U
A/C
M2)
POTENTIAL VS AG/AGCL (V)
0.5µA/cm2
@0.1V, Δi = 0.66 µA/cm2, C = 6.6µF/cm2
Capacitance of pyrolytic graphite
electrode in 1M H2SO4, dV/dt = 50mV/s
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Material Cathodic Limit (Volts)
Anodic Limit (Volts)
Capacitive Window (Volts)
Capacitance (F/cm2) @ 0.1 V
GUITAR -0.8 1.2 2 640
Glassy Carbon
(Bioanalytical Systems)
-0.6 0.7 1.3 50
PyrolyticGraphite
-0.1 0.65 0.75 7
• GUITAR has more capacitance per unit than other carbon electrodes• GUITAR has a wider capacitive window than other carbon electrodes
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GUITAR vs. Activated Carbon (AC)
• AC -- the predominate material in UC’s. Low Cost & High Surface Area
• Potential Window, & Capacitance,• C = 10 μF/cm2
• V = 0.8 V
• Expected Performance:
• AC) Energy = ½ CV2 = 3 μJ/cm2
• GUITAR) Energy = 1300 μJ/cm2
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GUITAR vs. Activated Carbon (AC)
• AC surface area 1000 m2/g
– Specific Energy = 30 J/g
• GUITAR – produces conformal coatings
– On McIlroy Nanosprings, surface area = 200 m2/g
– Specific Energy = 2600 J/g
– Excluding nanospring mass
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200 nmA – Bare silica McIlroy nanosprings. B – D Silica nanosprings coated with G-UI-TAR.
AB
C D
200 nm
200 nm
D
2 µm
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High Surface Area GUITAR Electrodes
– Water Purification• Wide potential and excellent electrode
• Hydrophobic surface adsorption
– Ultra-capacitors• Aqueous Ucaps limited to 1.5 volts
• GUITAR Ucaps > 2.0 V
• Higher capacitance based on DOS?
– V Redox Flow Batteries• Requires high H2 overpotential and, e- transfer kinetics
– Enhancing Lead-Acid Battery• Requires corrosion resistance, high O2 and H2 overpotential,
conformal coatings on microporous materials, and electrochemical conductivity.
– CNT Replacement in Fuel Cells• GUITAR on nanosprings
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Summary - GUITAR
• A new material– Not HOPG, Graphene Paper
– Sulfur a key component to formation• Low T (800 0C), economical
– Atomically Smooth with nano-size grains
• Fast Electron Transfer• High DOS?
• Large Aqueous Potential Window• 3 Volts in 1 M H2SO4 exceeds almost all other electrode
materials.
• Ability to create conformal coatings
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Future
• 1450 cm-1 intermediate
• Electrical and Thermal Conductivities
• Hypotheses for• Anodic Limit
• Cathodic limit (hydrophobicity)
• Pursue Applications
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Conformal coatings on high surface area substrates.NanospringsHalloysite nanotubesDiatomitesPorous hollow glass microspheres
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63
AcknowledgementsYuqun XieIsaiah GyanHaoyu ZhuDr. Nolan NicholasJeremy FoutchProf. David McIlroy UI-PhysicsProf. Peter Griffiths UI-ChemistryProf. Eric Aston UI-Chem. E.
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Raman Spectrum of UI Carbon
13541593
1260
1270
1280
1290
1300
1310
Int
1000 2000 3000
Wavenumbers (cm-1)
I.F. Cheng, et al. Carbon. 2011,(49), 2852-2861S. Stankovich, et,al. Carbon. 2007, (45), 1558-1565
64
D 1354 G 1593
1000 2000 3000
UI Carbonr-GO Paper
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Ferrari Amorphization
Trajectory
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Figure 10 from Ferrari, Robertson. Phys Rev. 2000, (B61), 14095-14107
1594
0.93
Between Graphite to NC-
graphite
0% sp3 hybridization
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XPS – GP and UI Material are Nearly Pure
Carbon
66
C=C sp2
C=N sp2
C-O
Reduced Graphene Oxide Paper Pei, et al. Carbon. 2010, (48), 4466-4474
UI Carbon Cheng, et al. Carbon. 2011,(49),
2852-2861
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