Transcript The Production, Purification and Characterization of

The Production, Purification and
Characterization of Carbon
Nanotubes for Hydrogen Storage
By
Jorge Ivan Salazar Gomez
Main Supervisor:
Prof. Peter J. Hall
Second Supervisor:
Dr. Len Belouis
INTRODUCTION
• The discovery of the fullerenes [1] and the carbon nanotubes [2]
opened a new area of research in both the theoretical and the
experimental field. Since the discovery of the single wall carbon
nanotubes SWNTs, many chemical and physical properties have been
predicted.
• Different techniques have been applied to produce carbon nanotubes:
electric arc discharge [2,3,4], laser ablation [5,6], chemical vapor
deposition (CVD) [7,8,9], being the last one the method that shows
large scale production, but with the disadvantage of the formation of
amorphous carbon and other impurities, which must be removed by
physical or chemical methods. Therefore, the purification process
[10,11] is a key step in the production of carbon nanotubes addressed
toward hydrogen storage [12] or other applications.
• The characterization [13] becomes an important part of the
process because it gives information about the catalyst and the
carbon samples before and after purification, so giving
information about the actual nature of the samples produced and
how to control and improve them.
AIM
• The aim of this project focuses on achieving the best conditions
for the production of carbon nanotubes by the CVD method,
directed towards hydrogen storage. The storage of hydrogen by
physical adsorption or by electrochemical methods is one of the
most promising applications of carbon nanotubes due to their
possible use in fuel cells, especially for the transportation sector,
implying a clean process and therefore reducing the global
contamination from CO2.
OBJECTIVES
1) To evaluate the effect of:
• Catalyst composition
• Temperature
• Time
• Flow rate of feed gas
• Particle size
2) To elucidate the impact of the processes of washing,
graphitization and activation on the properties of the nanotubes.
3) To characterize the catalysts and the carbons using different
techniques that permit to understand the structure and properties
of these materials.
4) To evaluate the physical and electrochemical hydrogen storage.
EXPERIMENTAL
Catalyst preparation
sol-gel method
Calcination Cu:Ni
Calcination Cu:Ni:Mg
CVD (DEON)
CVD (SP, CAT)
C2H4, 600oC
C2H4, CH4,
600oC, 800oC
CATALYST REMOVAL
Washing with acids
Passing acid through
the samples (filtering)
Adding acid and stirring
For minimum 4 h and filtering
To rinse with deionized
Water until pH 7
To dry in vacuum
GRAPHITIZATION
To put an amount of sample in an
horizontal furnace and purge 30 min.
To heat at 10oC/min until 1500oC
in inert atmosphere (Ar 100 ml/min)
To leave the samples 2h
To cool until room temperature
ACTIVATION (CO2)
To put an amount of the samples in an
horizontal furnace
To purge 30 min. with Ar
To heat at 10oC/min from room
temperature until 850oC
To change the gas by CO2 and
to leave the sample for 1-4 h.
To cool until room
temperature with Ar
CVD REACTION APPARATUS
RESULTS
8
Yield (g/g)
DEON: Cu:Ni = 40:60
7
6
SP: Cu:Ni:Mg = 10:20:70
Yield (g/g)
CAT: Cu:Ni:Mg = 0.3:0.7:3.0
5
4
3
2
1
70
0
0
20
40
Yield of Carbon (g/g)
60
60
80
100
W eight % Ni
No termination time observed
50
40
Catalyst still active
30
Constant Reaction rate
20
No diffusional effects
10
0
20
40
60
R ea ction Tim e (m in)
80
100
120
4
70
2
y = 14.36 - 9287.1x R = 0.99964
3.5
60
2.5
40
ln(k)
Yield of Carbon (g/g)
3
50
2
30
1.5
20
1
10
0.5
2
y = 35.33 - 25490x R = 0.99892
0
0
450
500
550
0 .0 011
600
0.00 115
0 .0 012
0.00 125
1 /T (1/K )
o
R eac tion Tem pera ture ( C )
Below 500oC Ea = 211.924 kJ.mol-1
Above 500oC Ea = 77.213 kJ.mol-1
SAMPLES
DEON 011(i)a
PARTICLE SIZE (µm)
x < 150
YIELD (g/g)
40.36
DEON 011(ii)a
212 > x > 150
31.01
DEON 011(iii)a
x > 212
33.89
DEON 011(i)b
x < 150
41.14
0 .0 013
0.00 135
0 .0 014
BET Surface Area
W
C

Wm  P0  
 P   1
350
n
n 1




 
1  n  1 P P   n P P  
 0
 0 

n 1


 
1  C  1 P P  C  P P  
0
 0 

250
100
a)
o
o
b)
raw
300
010a(600 C-80ml/min)
010a(Activated)
washed
o
09d(600 C-80m l/min)
o
Graphitised
010e(600 C-80ml/min)
010e(W ashed)
80
200
150
100
010f(600 C-80ml/min)
010f(Graphitized)
Adsorption am ount (cc/g)
Adsorption Am ount (cc/g)
250
o
200
o
Adsorption am ount (cc/g)
09e(500 C-10m l/min)
c)
60
40
09c(600 C-57m l/m in)
09c(Graphitized)
o
09b(600 C-33m l/min)
o
09a(600 C-10m l/min)
150
100
50
20
50
0
0
0
0
0.2
0.4
0.6
R elative pressure
0.8
1
0
0.2
0.4
0.6
Relative Pressure
0.8
1
0
0.2
0.4
0.6
R elative pres sure
0.8
1
X-Ray Diffraction
1 200
a)
b)
DE ON 01a (Raw)
DE ON 01a (W )
1 000
4000
Cat. SP1
Cat. SP2
SP1a
3500
DEON01a (G)
SP2a
SP2b
3000
Intensity/a.u.
Counts
800
600
2500
2000
1500
400
1000
200
500
0
0
10
20
30
40
50
60
70
80
20
30
40
50
90
2 Theta
2 TH ETA
nl  2d sinq
SAMPLE
DEON 09a
DEON 09b
DEON 09c
DEON 09d
DEON 09e
DEON 09f
SP1a
SP2a
SP2b
TEMPERATURE
(oC)
600
600
600
600
500
700
600
600
700
C2H4 FLOW RATE
(ml/min)
10
33
57
80
10
10
80
80
80
d-SPACING
(nm)
0.3437
0.3405
0.3418
0.3405
0.3445
0.3406, 0.3427
3.441
3.426
3.422
60
70
80
90
TGA
Graphitized more stable
Raw carbon is more reactive
Washed carbons have
medium reactivity
100
1000
o
SP1a (600 C-90 m in)
80
800
o
SP2a (600 C-90 m in)
o
o
SP2e (700 C-90 m in)
60
600
o
S P2f (600 C-30 m in)
o
SP2g (700 C-30 m in)
400
o
40
Temperature ( C)
W eight loss (%)
SP2d (700 C-90 m in)
Tem peratu
Tem peratu
20
200
Tem peratu
Tem peratu
Tem peratu
0
0
0
10
20
30
40
50
60
Tim e (m in)
SAMPLE
SP1a-2
SP2a-1
SP2d-1
SP2e-1
SP2f-1
SP2g-1
VOLATILES
(%)
5.01
6.48
6.90
5.06
17.36
9.63
PURE CARBON
ASHES (%)
(%)
93.06
93.01
92.17
94.52
79.10
89.76
1.95
0.58
0.82
0.39
3.57
0.56
Tem peratu
ELECTROCHEMICAL STORAGE
DEON 09d-1
DENSITY
DELOADING
(mA/g)
100
0.2
DEON 09d-2
0
DEO N 09d
POTENTIAL (V)
0.4
CYCLE
Cycle 10
Cycle1
-0.2
-0.4
-0.6
-0.8
-1
-1.2
100
110
120
130
140
CAPACITY
(mAh/g)
H:C
ratio
WEIGHT
(%)
34.94
1:64
0.130
50
10.27
1:124
0.067
DEON 09d-3
100
15.07
1:104
0.080
DEON 09d-4
50
14.09
1:158
0.053
DEON 09d-5
5
8.82
1:160
0.052
DEON 09d-6
20
13.64
1:172
0.048
DEON 09d-7
20
13.99
1:171
0.049
DEON 09d-8
50
19.60
1:114
0.073
DEON 09d-9
23
13.93
1:163
0.051
DEON 09d-10
100
20.53
1:109
0.076
DEON 09d-11
50
38.39
1:125
0.066
DEON 09d-12
23
8.24
1:129
0.065
CA-01
100
57.33
1:39
0.210
CA-02
200
69.05
1:32
0.260
C APAC ITY (m Ah/g)
Discharging process after 1 and 10 cycles for the sample DEON 09d previously
loaded electrochemically with hydrogen at a current density of 1000 mA/g for 1h
in a 6M KOH solution.
MS-TPD
D E O N 09d He (2nd cycle)
D EO N 09d under H e
3.5 10
4 10
-9
-9
M ass 1
M ass 2
3 10
-9
3.5 10
Mass 16
Mass 17
2.5 10
2 10
1.5 10
1 10
5 10
Partial Pressure (Torr)
Partial Pressure (Torr)
3 10
-9
-9
-9
-9
2.5 10
2 10
1.5 10
1 10
-10
5 10
-9
-9
M ass 1
M ass 2
-9
Mass 16
Mass 17
-9
-9
-9
-10
0
0
50
100
150
200
250
300
350
50
o
Tem pe rature ( C )
100
150
200
250
o
Tem pe rature ( C)
Adsorption at 10 bar for 24h at room temperature.
Desorption at 20oC/min in He as carrier.
300
350
400
450
RAMAN SPECTROSCOPY
CAT 3B
G-Band at 1575
cm-1
D-Band at 1312
cm-1
6000
406 nm
517nm
632 nm
5000
G/D = 3.87
Mainly Semiconducting
Intensity/a.u.
4000
3000
2000
1000
2500
011(ii)a-1
011(ii)a-3
011(ii)a-3
0
400
2000
Intensity/a.u.
800
1200
1600
2000
457 nm
Raman Shift/cm
1500
1000
406 nm
500
785 nm
0
800
1200
1600
2000
2400
Raman Shift/cm
-1
2800
3200
2400
-1
G-Band at 1589 cm-1 (shoulder
at 1546 cm-1)
D-Band at 1351 cm-1
G/D = 1.19
Metallic and Semiconducting
2800
Small-Angle Neutron Scattering (SANS)
PJH1416-1436m-09d-Dry
PJH1414-1434m-SP2a-Dry
DEON 09d Dry
DEON 09d CM
1000
100
100
-1
dS/dWQ)(cm )
1000
-1
dS/dWQ)(cm )
SP2a Dry
SP2a CM
10
1
10
1
0.1
0.1
0.01
0.001
0.01
0.1
-1
Q (Å )
1
0.001
0.01
0.1
-1
Q (Å )
Raw data for time-of-flight technique with corrections for
instrument background and transmission.
1
TEM
5nm
250nm
100nm
5nm
CONCLUSIONS
•The best catalyst composition for the synthesis of the carbon nanofibers is
Cu:Ni=40:60 and the optimum temperature is 600oC, at higher temperature catalyst
deactivation appears.
• The washing process with nitric acid was effective in the removal of catalyst
particles and induced some ordering. It had little effect on the surface area.
• The graphitization process enhances the chemical stability of the nanofibres and
induces more order (formation of bundles and reduction of aggregated pores) and
enhances crystallinity, but it decreases the capacity of adsorption.
• The activation process with CO2 opens some of the tubes, but it does not apparently
remove the amorphous carbon. The selectivity though appears to be better than
oxygen.
•The Raman results indicate that the nanotubes formed are mainly semiconducting,
but a high proportion of nanofibers and impurities are present.
• The capacity of adsorption for hydrogen is very low for the raw samples, but higher
uptakes are expected for purified samples.
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