Carbon nanotubes have the potential for solid state hydrogen storage if modified with heteroatoms. Theoretical studies show that heteroatoms like nitrogen can facilitate hydrogen activation and storage in carbon nanotubes. For effective storage, heteroatoms must be incorporated geometrically and chemically into the carbon structure. Boron-substituted carbon nanotubes were synthesized using template methods and exhibited up to 2% hydrogen storage capacity, depending on the boron configuration within the nanotube structure. Heteroatom substitution in carbon nanotubes provides a promising approach for developing hydrogen storage materials.

1. Arunai Engg. college

2. →It comprises any technological developments on
the nanometer scale, usually 0.1 to 100 nm.
→ One nanometer equals one thousandth of a
micrometer or one millionth of a millimeter.
→ It is also referred as microscopic
technology.

3. CNT is a tubular form of carbon with diameter as
small as 1 nm.
Length: few nm to microns.
CNT is configurationally equivalent to a two
dimensional graphene sheet rolled into a tube (single
wall vs. multiwalled).
CNT exhibits extraordinary mechanical
properties: Young’s modulus over
1 Tera Pascal, as stiff as diamond, and
tensile strength ~ 200 GPa.
CNT can be metallic or semiconducting,
depending on (m-n)/3 is an integer
(metallic)
or not (semicon).

4. History of nanotubes
1991 carbon nanotubes discovered
“graphitic carbon needles ranging from 4 nm
– 30 nm and up to 1 micron in length”
( Sumino Iijima)
Just wait, the next century is going to be
incredible. We are about to be able to
build things that work at the smallest
possible length scales, atom by atom .
These little nanothings will revolutionize
our industries and our lives.”

5. • The strongest and most flexible molecular material because of C-C
covalent bonding and seamless hexagonal network architecture
• Strength to weight ratio ~500 times greater than Al, steel,
titanium; one order of magnitude improvement over
graphite/epoxy
• Maximum strain ~10%; much higher than any material
• Thermal conductivity ~ 3000 W/mK in the axial direction
with small values in the radial direction
• Very high current carrying capacity
• Excellent field emitter; high aspect ratio and small
tip radius of curvature are ideal for field emission
• Other chemical groups can be attached
to the tip or sidewall (called ‘functionalization’)

6. A fuel cell is an electromechanical energy
conversion device which produces electricity
with an oxidant and a fuel source.
Net reaction H2 + 1/2O2 → H2O

7.  Fuel cells have been around since the middle of the
nineteenth century, but their use has been limited to the
space industry .
 Recently, companies have been looking for a more
efficient, reusable energy source, and fuel cells are a
likely candidate.
 Two factors inhibiting the use of fuel cells in consumer
application are efficiency and size.

8.  1839- First fuel cell designed by Sir William
Robert Grove.
 1889-The term fuel cell was coined by Ludwig
Mond and Charles Langer.
 1913- Dr. Francis Thomas Bacon created the
first alkaline fuel cell which he termed the
“Bacon Cell”.
 1960’s- NASA uses fuel cells to power their
manned space missions [2].

9.  The automotive industry hopes to utilize fuel cells as either a sole
power source or in conjunction with fossil fuels or ethanol in hybrid
vehicles.
 All major automobile manufacturers from GM to Honda have a
prototype fuel cell car fully developed in testing on city roads [2].
 Research focus:
◦ Safe storage of hydrogen
◦ Reduction of size of fuel cells

10. (i) Are the carbon materials appropriate for solid state
hydrogen storage?
(ii) If this were to be true, what type of carbon materials or
what type of treatments for the existing carbon materials
are suitable to achieve desirable levels of solid state
hydrogen storage?
(iii) What are the stumbling blocks in achieving the desirable
solid state hydrogen storage?
(iv) Where does the lacuna lie? Is it in our theoretical
foundation of the postulate or is it in our inability to
experimentally realize the desired levels of storage?

11. Why carbon materials for solid state hydrogen storage?
 Coordination number is variable/expandable
 Promote new morphologies
 Covalent character retention
 Variable hybridization possible
 Geometrical possibilities/size considerations
 Meta-stable state
 Similar to biological architectures “Haeckelites”
 Boron and nitrogen doped graphitic
arrangements promise important applications.

12. Objectives
Necessity of active sites
Heteroatom containing carbon materials -
appropriate candidates?
Gradation of the carbon materials containing
various heteroatoms
Geometrical positions of the heteroatoms
12

13. Energy profile for hydrogen interaction with heteroatom substituted CNT clusters
10
TS I N
P
8 S
C
Energy (eV)
6
TS II
4
TS I
2
0 + H2
Reaction coordinate
Ea I Ea II H1-H2 X-H C-H1* C-H2*
Substitution
(eV) (eV) (Å) (Å) (Å) (Å)
CNT 10.02 - 0.71 - - -
N CNT 3.84 4.58 1.45 1.11 1.70 1.94
P CNT 3.81 3.99 1.51 1.61 1.27 2.33
S CNT 3.65 4.85 1.50 1.75 1.24 2.40
Ea = E (transition state) – E (reactant) * Shortest C-H bond distance 13

14. Energy profile of boron substituted CNT clusters
Alternative position
Ea I Ea II H1-H2 X-H C-H1∗ C-H2*
Substitution
(eV) (eV) (Å) (Å) (Å) (Å)
CNT 10.02 - 0.71 - - -
2B CNT (adjacent) 2.22 2.98 1.95 1.31 2.59 2.72
2B CNT (alternate) 1.5 2.33 2.95 1.47 1.47 2.34
Ea = E (transition state) – E (reactant) * Shortest C-H bond distance
Adjacent position 14

15. Outcome
 Substituted heteroatom acts as an active
centre for hydrogen activation
 For the effective hydrogenation and
hydrogen storage, the heteroatoms should
be incorporated geometrically and
chemically into the carbon network

16. Boron substituted carbon nanotubes- synthesis,
characterization and hydrogen absorption activity

17. Template Carbon Technique Morphology
Source
Alumina Polymer In-situ Tubular
membrane (hydroborane) polymerization
(BCNT1)
Zeolite Hydrocarbon Chemical Tubes and
(BCNT2) (Acetylene + vapor Fibers
borane gas) deposition
Clay Hydrocarbon Chemical Tubes and
(pillared) (Acetylene + vapor Fibers
(BCNT3) borane gas) deposition
17

18. Boron containing carbon nanotubes prepared using alumina
membrane
Alumina membrane Borane (BH3.THF)
(0.2μm pore size) in THF
Divinyl benzene
Stirred 273 K
Polymerization at RT 3h
Polymer /Alumina
Carbonization 1173K Ar,4h
Carbon / Alumina
48% HF 24h Carbon nanotubes (BCNT1)
0°C n
B
THF n
+ BH3:THF solvent n
B
N2 atm
using hydroborane polymers
n 18

19. Preparation of boron containing carbon nanomaterials using
zeolite and pillared clay
Tubular furnace
H-Y Zeolite or
pillared clay in
Mass flow meter quartz boat
After carbonization
Conc. H2SO4 treated wit 48% HF to
Acetylene gas remove the template
Ar gas
Ice bath
BCNT 2 (Zeolite)
Magnetic stirrer
NaBH4 + THF BCNT 3 (Clay)
Chemical vapor deposition of borane gas + acetylene
mixture over template
19

20. Hydrogen absorption activity of boron containing carbon
nanomaterials at 1 atm
Amount of hydrogen absorbed
(cm3/g) at 1 atm & at various
Carbon Surface temperatures (°C)
area
nanomaterial (m2/g)
-196 25 100 150
BC 11.9 3.63 0.6 3.63 4.68
PBC 429.9 73 - 2.90 3.02
BCNT1 523 127 - 16.5 14.8
BCNT2 62.3 3.22 - 2.38 4.73
BCNT3 32.7 1.09 - 1.7 -
20

21. Hydrogen storage capacity of boron containing carbon
nanotubes
Boron containing carbon nanotubes prepared with polymer precursor,
show different boron chemical environments and structural morphology.
This configuration has a bearing on hydrogen sorption characteristics.
21

22. Conclusions
 Theoretical studies have shown that the effective hydrogenation of
CNTs is possible with activation centers and the heteroatom
containing CNTs are able to activate the hydrogen in a facile manner
compared to pure CNTs.
 For effective hydrogenation and hydrogen storage heteroatom
should be incorporated geometrically and chemically into the carbon
network.
 Nitrogen containing CNTs are amenable for hydrogen absorption
than other carbon materials. However, these active sites should be
made catalytic in nature by various preparation methods and
surface engineering so that necessary hydrogen storage may be
achieved.
 Boron containing carbon nanotubes have been produced successfully
by template synthesis method. For boron atoms two different
environments in the carbon nanotubes have been prepared and the
maximum hydrogen storage capacity of 2 Wt % has been realised.
This configuration has a bearing in hydrogen sorption
characteristics.
 The heteroatom substitution in the carbon nanotubes opens up
another avenue in the search for materials for hydrogen storage.
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