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Thesis Defense
1. STUDY OF SOFT AMMONIA
BORANE-POLYVINYLPYRROLIDONE
HYDROGEN STORAGE COMPOSITES
Sahithya Pati
Master of Science
in Chemistry
Thesis defense
Lamar University
August 2016
2. Outline
• Introduction
Hydrogen as a Fuel Source
Background of Ammonia Borane
Ammonia Borane has Hydrogen Storage
Ammonia borane with polymers (polyvinylpyrrolidone)
• Goal and Objective
• Experimental Details
• Results & Discussion
Thermal studies: Structural properties (180 - 300 K)
Kinetic studies of Dehydrogenation above 350 K
Room temperature IR-studies of AB and the composites
IR- studies of the decomposition mechanism
• Conclusion
• Acknowledgement
2
3. Hydrogen as Fuel Source
• The world’s increasing demands for energy and the need for
the reduction of the air pollution have led to the quest of new
alternative energy source that would also be environmental
friendly.
• Hydrogen has been considered as one of the best alternative
energy carriers to satisfy the increasing demand.
• Hydrogen as an efficient and clean energy supply because of
its abundance and high energy density.
• Hydrogen can be stored in different forms
4. Hydrogen Storage
• Improved hydrogen storage materials are required to enable the hydrogen
economy.
• For use in auto-mobile applications, potential storage materials must
exhibit high capacity, rapid rate and reversible sorption under reasonable
operating conditions for thousands of cycles.
• Hydrogen storage materials should be light weight, compact, safe,
inexpensive, long-range, rapidly refuelable and the Energy carrier should
have a high energy content in as small volume
• The hydrogen storage materials are divide into three categories in terms of
the strength of hydrogen bonding, 1. sorbent materials
2.complex hydrides
3.nanostructured materials
5. Unusual properties of H-bonded solids:
Phase Transitions
• Hydrogen-bonded compounds exhibit structural phase transitions
with accompanying anomalous changes in many thermodynamic,
dielectric and lattice-dynamical properties.
• The mechanisms of the phase transitions are not fully understood.
• Ammonia Borane, NH3BH3 is one of the model for H-bonded solids.
6. Why study Ammonia Borane?
• Ammonia Borane (NH3BH3) is a model H-bonded material.
Dipole moment = 5.216 debye
• NH3BH3 is a classic donor-acceptor complex which makes it a
good candidate for becoming a ferroelectric or
antiferroelectric below a certain temperature, Tp.
• AB is a potential hydrogen storage system, because of its high
gravimetric H2 density of 19.6% and is a nonflammable,
nonexplosive solid at ambient conditions.
6
7. Ammonia Borane
• Ammonia Borane crystallizes in the tetragonal, at room
temperature and undergoes a phase transition at Tp~223 K
below which it becomes orthorhombic and displays an order-
disorder behavior.
• There is also a possible existence of a dihydrogen bond
(N-H…H-B) at NH3 sites and dipole-dipole interaction ,
which explains the high melting point of AB (114 0C)
7
Conformation of the closest N-
H…H-B contact from the
neutron diffraction structure of
NH3BH3 at room temperature.
8. Ammonia Borane: H2 release
• AB decomposes in three sequential steps ,during this steps AB
transforms progressively into polyamidoborane (PAB),
polyimidoborane (PIB) and finally boron nitride (BN) at
temperature range of 80 to 1500 0C, with about 6.5 wt. % H2
liberated in each step which is relatively low in this
temperature range.
• NH3BH3 (NH2BH2) n + H2 (90 - ~ 120 0C)
(NH2BH2)n (NHBH) n + nH2 (120 - ~160 0C)
(NHBH)n BN + nH2 (>500 0C)
8
9. Ammonia borane with polymers
• Polymers were found to be effective in improving the practical
applications of Ammonia Borane by inducing changes in its
structural properties.
• Polymer bulk composites such as poly(methyl acrylate)
(PMA) and fibers of poly(vinylpyrrolidone) showed a
significant results in decreasing the boracic impurities and
decomposition kinetics of AB.
• In the present work AB is blended with
poly(vinylpyrrolidone) (PVP) (Mw-40,000-360,000)
(AB:PVP) in various proportions, through a simple sol-mixing
preparation and investigated for thermal and kinetic properties.
9
10. AB/ Polyvinylpyrrolidone
• In the present work AB is blended with polyvinylpyrrolidone
(PVP) (Mw-40,000-360,000) (AB:PVP) in various proportions,
through a simple sol-mixing preparation and investigated for
thermal and kinetic properties.
Structure of polyvinylpyrrolidone
• PVP is a water soluble polymer . When dry it is a light
flaky hygroscopic powder, readily absorbing up to 40% of its weight in
atmospheric water.
• It shows a significant results in decreasing the boracic impurities and
decomposition kinetics of AB.
10
11. Goal and Objectives
• To understand the thermal behavior of Ammonia Borane/
polyvinylpyrrolidone (AB:PVP) bulk composites around the Phase
Transition Temperature Tp (223 K).
• We also study the high temperature behavior to quantify the enhanced
kinetics of the composites at high temperatures where the hydrogen
release was observed (>350 K).
• Investigate the structural properties as well as the decomposition
mechanism to understand the use of ammonia borane (AB) as a
potent solid system for hydrogen storage.
• To understand the chemical interaction between AB and PVP
composites in bulk form at room temperature and also after
decomposition temperatures.
11
12. Experimental details
• 97 % pure Ammonia Borane and Polyvinylpyrrolidone (Mw-
40,000& 360,000) were purchased from Sigma Aldrich.
• Ammonia borane/Polyvinylpyrrolidone composites were
prepared by sol-mixing technique.
• TA instruments differential scanning calorimetry (DSC) Q20
was used for thermal studies.
• Nicolet iS10 FT-IR was used to study the molecular
interaction.
12
13. Preparation of Ammonia
Borane/Polyvinylpyrrolidone composites
• AB:PVP composites with various mass ratios of 1:1, 1:2 were
prepared by decreasing the amount of AB and keeping the
PVP (Mw-40,000 & 360,000) part constant.
• Polyviylpyrrolidone and ammonia borane were mixed in
distilled water and stirred well to get a white semi transparent
rubbery material.
• This mixture is vacuum dried using a vacuum pump for three
days and then the sample is transferred into a clean vial and
purged with nitrogen gas.
13
14. Differential Scanning Calorimetry
• TA instruments differential scanning calorimetry (DSC) Q20
was used to determine the phase transition temperature,
enthalpy, entropy and decomposition of the AB, AB/PVP bulk
composites.
• Modulated mode with Tzero pans were used for low
temperature studies to measure heat capacity, determine phase
transition, enthalpy and entropy.
• Standard mode with classic pans were used to determine the
heat flow for dehydrogenation studies at high temperatures.
14
15. Thermal studies: Structural properties
(180 - 300 K)
• Heating runs at low temperatures from 180 K to 300 K were
performed using modulation mode at 1K/min heating rate.
• After performing multiple runs with 1K/min heating rate, there
is no noticeable change in the phase transition temperature
(Tp).
• The values are within the errors limits i.e., 223±0.5 K for bulk
AB and the AB/PVP composites.
15
16. Phase Transition Temperature (Tp)
Heat capacity vs Temperature plot, showing Tp of AB, AB:PVP(40,000) composites at
Ramp 1 K/min
190 200 210 220 230 240 250 260 270 280
1
2
3
4
5
6
7
8
9
Cp(J/gK)
Temperature (K)
Tp = 222.8 K
Tp = 223.0 K
Tp = 222.8 K
(AB)
(1:1)
(1:2)
17. Enthalpy and Entropy
• Enthalpy (ΔH) is the amount of heat content used or released
in a system at constant pressure. Enthalpy is usually expressed
as the change in enthalpy.
∆H=∫CpdT
• Entropy (∆S) is a measure of the number of specific ways in
which a thermodynamic system may be arranged, commonly
understood as a measure of disorder.
∆S = ∫(Cp/T)dT
17
18. 200 210 220 230 240 250 260
100
200
300
400
500
600
700
800
Cp
(J/molK)
Temperature (K)
222.81 K
1000
2000
3000
4000
5000
Enthalpy(J/mol)
200 210 220 230 240 250 260
0.4
0.8
1.2
1.6
2.0
2.4
2.8
3.2
Cp/T(J/molK2
)
Temperature (K)
5
10
15
20
25
Entorpy(J/molK)
Tp
= 222.81 K
Temperature dependence of
heat capacity and enthalpy
of bulk ammonia borane.
Temperature dependence of
Cp/T and entropy of bulk
ammonia borane.
Bulk Ammonia Borane
24. Kinetic Studies of Decomposition above
350 K
• Activation energy (Ea) is the minimum energy required to
start a chemical reaction.
• Two methods were used for calculating kinetic energy
(a) Ozawa method lnβ = -Ea/RTd + C
(b) Kissinger's method ln(β/Td
2) = -Ea/RTd + C
• These equations are derived from Arrhenius expression
k = Ae-Ea/RT
24
25. Dehydrogenation above 350 K
25
Decomposition of bulk AB, AB:PVP (1:1),
AB:PVP(1:2)(40,000) with melting and first hydrogen
release temperatures at Ramp 5 K/min
300 350 400 450 500 550
-8
-6
-4
-2
0
2
4
6
8Heatflow
Temperature
AB-391 K
AB:PVP(1:1)-364 K
PVP
AB:PVP (1:2)-364 K
AB-387 K
AB:PVP(1:1)-350 K
AB:PVP(1:2)-350 K
26. Decomposition of bulk AB
320 340 360 380 400 420 440 460 480 500 520
-30
-20
-10
0
10
20
30
HeatFlow(W/g)
Temperature (K)
Ramp 1-380.78 K
Ramp 3-388.92 K
Ramp 5-392.97 K
Ramp 15-402.81 K
Ramp 20-406.53 K
Increase in the thermal decomposition temperatures of AB with
increase in heating rates (β K/min)
27. Decomposition of AB:PVP (1:1) composite
340 360 380 400 420 440 460 480 500
-2
0
2
4
6
8
Heatflow(W/g)
Temperature (K)
Ramp 3 - 372.6 K
Ramp 5 - 381.5 K
Ramp 15 - 387.7 K
Peaks from bulk AB
Increase in the thermal decomposition temperatures of AB:PVP(1:1)
(40,000) with increase in heating rates (β K/min)
28. Decomposition of AB:PVP (1:2) composite
340 360 380 400 420 440 460 480 500
-1
0
1
2
3
4
Heatflow(W/g)
Temperature (K)
Ramp 3 - 370.6 K
Ramp 5 - 377.3 K
Ramp 15 - 386.6 K
Increase in the thermal decomposition temperatures of AB:PVP(1:2)
(40,000) with increase in heating rates (β K/min)
29. Activation Energy by Ozawa method
lnβ = -Ea/RTd+ C
β – heating rate
Ea – Activation Energy
R – rate constant
Td – decomposition
temperature
Activation energy fits of the decomposition temperature peaks and
heating rates of AB, AB:PVP (1:1), AB:PVP (1:2)(40,000)
composites according to the Ozawa method.
2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Inbeta
1000/Tp
AB 153.38
AB:PVP(1:1) 125.80
AB:PVP(1:2) 118.81
30. Activation Energy by Kissinger’s method
ln(β/Td
2) = -Ea/RTd + C
β – heating rate
Ea – Activation Energy
R – rate constant
Td – decomposition
temperature
Activation energy fits of the decomposition temperature peaks and
heating rates of AB, AB:PVP (1:1), AB:PVP (1:2)(40,000) composites
according to the Kissinger’s method.
2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9
-12.5
-12.0
-11.5
-11.0
-10.5
-10.0
-9.5
-9.0
-8.5
ln(b/Tp2)
1000/Tp
AB 145.75
AB:PVP(1:1) 119.76
AB:PVP(1:2) 112.76
31. Thermogravimetric Analysis (TGA)
• Thermogravimetric Analysis (TGA) measures the amount and
rate of change in the weight of a material as a function of
temperature or time in a controlled atmosphere and inert
environment.
• This is a technique used for decomposition studies and kinetic
analysis.
• 5-10 mg of samples were allowed to run at 5 K/min and the
weight loss% of the AB, AB:PVP bulk composites were
calculated.
31
32. 50 100 150 200 250
40
50
60
70
80
90
100
Weightloss(wt%)
Temperature
AB
AB:PVP(1:1)
AB:PVP(1:2)
Thermogravimetric Analysis (TGA)
Weight loss due to the
emission of borazine
and diborane gases by
AB
TGA curve of AB, AB: PVP (1:1),AB: PVP (1:2)(40,000) bulk
composites
The total weight losses
for AB: PVP (1:1), AB:
PVP (1:2) was
composites were found
to be about 17.88 and
4.25 wt%,
33. 50 100 150 200 250
40
50
60
70
80
90
100
WeightLoss(wt%)
Temperature
AB
AB:PVP(1:1)
AB:PVP(1:2)
Thermogravimetric Analysis (TGA)
Weight loss due to the
emission of borazine and
diborane gases by AB
TGA curve of AB, AB: PVP (1:1), AB: PVP (1:2)(360,000) bulk
composites
The total weight losses for
AB: PVP (1:1), AB: PVP (1:2)
composites were found to be
about 16.38 and 8.79 wt%
34. Fourier Transform Infrared (FTIR)
• Molecular interactions at room temperature and after
dehydrogenation process at high temperatures were
investigated.
• Nicolet iS10 FT-IR was used and operated with resolution of 2
cm-1 using 32 scans.
• KBr pellets were prepared for the decomposed samples and
their absorbance were calculated.
34
35. Room temperature IR-studies of AB and
the composites
4000 3500 3000 2500 2000 1500 1000
0
50
100
150
200
250
300
350
Transmittance
Wave Number (cm-1
)
2206 cm-1
2273 cm-12313 cm-1
3186 cm-1
3239 cm-1
3305 cm-1
1280 cm-11651 cm-1
AB:PVP(1:2)
AB:PVP(1:1)
N-H bond
B-H and B-H2
strech
N-H,N-H2
and N-H3
strech AB
PVP
FT-IR spectra of PVP, AB and AB:PVP bulk composites with
mass ratios 1:1, 1:2(40,000) .
36. Chemical Interactions - IR
1900 1850 1800 1750 1700 1650 1600 1550 1500
30
40
50
60
70
80
90
100
Transmittance
Wavenumber (cm-1
)
1650 cm-1
1597 cm-1
1600 cm-1
1645 cm-1
1647 cm-1
C=O stretch
N-H deformationAB:PVP (1:1)
AB:PVP (1:2)
AB PVP
FT-IR spectra of PVP, AB and the polymeric composites (AB:PVP)
with mass ratios 1:1 and 1:2(40,000)
1650 1600
40
50
60
70
Transmittance
Wavenumber (cm-1
)
1650 cm-1
1600 cm-1
1645 cm-1
1647 cm-1
C=O stretch
N-H deformation
AB:PVP (1:1)
AB:PVP (1:2)
PVP
37. IR- studies of the decomposition
mechanism
• Hydrogen release during the decomposition at various
temperatures is confirmed by FTIR analysis performed for the
decomposed AB, AB:PVP(40,000) bulk composites
• Broadening of N-H stretch in the range of 3400 to 3100 cm-1
and B-H stretch at 2300 cm-1, indicates the decomposition and
release of hydrogen.
• There is an early start in the hydrogen release with polymer
composites when compared to bulk AB.
37
38. Ammonia Borane Decomposition
38
FTIR curves of bulk AB before and after the
decomposition at 353 K.
Bulk AB before
decomposition
(RT)
Bulk AB after
decomposition
at 353K (80 0C)
4000 3500 3000 2500 2000 1500 1000 500
Absorbance
Wave number (cm-1
)
bulk AB before decomposition
bulk AB after decomposition at 800
C (350 K)
N-H, N-H
2
and N-H
3
strectch B-H and B-H
2
strectch N-H bend
B-H
2
torsion
B-H
2
bend
B-N bend
39. Ammonia Borane Decomposition
39
FTIR curves of bulk AB before and after the
decomposition at 433 K.
Bulk AB before
decomposition
Bulk AB after
decomposition at
433 K (160 0C)
4000 3500 3000 2500 2000 1500 1000 500
bulk AB after decomposition at 1600
C (430 K)
bulk AB before decomposition
B-N bend
B-H
2
bend
B-H
2
torsionN-H bendB-H and B-H
2
strectchN-H, N-H
2
and N-H
3
strectch
Absorbance
Wave number (cm-1
)
0 2 4 6 8 10
40. Ammonia Borane Decomposition
40
FTIR curves of AB decomposition at 353 K
and 433 K.
Bulk AB
decomposition
at 353 K (80 0C)
Bulk AB
decomposition at
433 K (160 0C)
4000 3500 3000 2500 2000 1500 1000 500
B-N bend
B-H
2
bend
B-H
2
torsionN-H bendB-H and B-H
2
strectch
N-H, N-H
2
and N-H
3
strectch
AB decomposition at 1600
C
AB decomposition at 800
C (350 K)
Absorbance
Wave number (cm-1
)
41. Ammonia Borane Decomposition
41
FTIR curves for dehydrogenated samples of
bulk AB at various temperatures
4000 3500 3000 2500 2000 1500 1000 500
B-H
2
bend
B-N bend
B-H
2
torsion
N-H bend
B-H and B-H
2
strectchN-H, N-H
2
and N-H
3
strectch
(800
C)
(1000
C)
(1200
C)
(1400
C)
(1600
C)
(1800
C)
Absorbance
Wave number (cm-1
)
42. AB:PVP composite decomposition
FTIR curves of AB:PVP (1:1) (40,000) before and after the
decomposition at 353 K.
AB:PVP (1:1) after
decomposition 353 K (80 0C)
AB:PVP (1:1) before
decomposition (RT)
4000 3500 3000 2500 2000 1500 1000
B-N bend
N-H bend
B-H and BH2
stretchN-H,N-H2
,N-H3
stretch
Absorbance(a.u)
Wavenumber
43. AB:PVP (1:1) after
decomposition 433 K (160 0C)
AB:PVP (1:1) before
decomposition (RT)
AB:PVP composite decomposition
FTIR curves of AB:PVP (1:1)(40,000) before and after the
decomposition at 433 K.
4000 3500 3000 2500 2000 1500 1000
B-N bend
N-H bendB-H and BH2
stretch
N-H,N-H2
,N-H3
stretch
Absorbance(a.u)
Wavenumber
44. AB:PVP composite decomposition
AB:PVP (1:2) after
decomposition 353 K (80 0C)
AB:PVP (1:2) before
decomposition (RT)
FTIR curves of AB:PVP (1:2)(40,000) before and after the
Decomposition at 353 K.
4000 3500 3000 2500 2000 1500 1000
B-N bendN-H bendB-H and BH2
stretch
N-H,N-H2
,N-H3
stretch
Absorbance(a.u)
Wavenumber
45. AB:PVP composite decomposition
AB:PVP (1:2) after
decomposition 433 K (160 0C)
AB:PVP (1:2) before
decomposition (RT)
FTIR curves of AB:PVP (1:2) (40,000) before and after the
decomposition at 433 K.
4000 3500 3000 2500 2000 1500 1000
B-N bendN-H bendB-H and BH2
stretchN-H,N-H2
,N-H3
stretch
Absorbance(a.u)
Wavenumber
46. AB:PVP composite decomposition
AB:PVP (1:1) after
decomposition 353 K (80 0C)
AB:PVP (1:1) after
decomposition 433 K (160 0C)
FTIR curves of AB:PVP (1:1)(40,000) decomposition at
353K and 433 K
4000 3500 3000 2500 2000 1500 1000
B-N bendN-H bend
B-H and BH2
stretch
N-H,N-H2
,N-H3
stretch
Absorbance(a.u)
Wavenumber
47. AB:PVP composite decomposition
4000 3500 3000 2500 2000 1500 1000
B-N bendN-H bend
B-H and BH2
stretch
N-H,N-H2
,N-H3
stretch
Absorbance(a.u)
Wavenumber
AB:PVP (1:2) after
decomposition 433 K (160 0C)
AB:PVP (1:2) after
decomposition 353 K (80 0C)
FTIR curves of AB:PVP (1:2) (40,000) decomposition at 353K and
433 K
48. Conclusion
• Phase transition temperatures (Tp) of AB and AB:PVP
composites are found to be similar around Tp~223.0 (±0.7) K
• Decrease in the enthalpy and entropy values with the increase
in the polymer proportion in the AB:PVP(40,000 & 360,000)
composite could be due to interaction between the polymer
and ammonia borane.
• There is a decrease in the melting and hydrogen release
temperatures with the AB:PVP(40,000) composites compared
to the bulk AB.
• The activation energies are also quantified and a significant
enhancement in kinetics was found with polymer composites.
48
49. Conclusion
• FT-IR investigations for bulk AB, PVP and AB:PVP (40,000)
composites before decomposition showed that there is a
possible interaction between the O atom of the carbonyl group
in PVP and B atom in AB.
• FT-IR of dehydrogenated bulk AB and AB:PVP(40,000)
composites indicates the release of hydrogen from various N-
H and B-H bonds, which can be seen from the difference in the
absorption characteristics by broadening of N-H and B-H
peaks at various wavelength region.
49
50. Future Studies
• Further studies are carried out with different polymers such as
PEO, and PVA by preparing bulk composties and fibers with
different molecular weights.
• VT-IR studies need to be carried for change in chemical
interactions and effect of PVP on dihydrogen bond present in
AB.
• Electro spinning fibers with AB:PVP.
• High resolution solid state NMR 15N, 11B, 1H will be carried
out in order to investigate the decomposition mechanism and
observe how boding is affected.
50
51. Future Studies
• X-ray diffraction studies to study the crystalline structure and
properties are need to be carried out.
• Mass spectra and volumetric measurements are going to be
studied.
52. Acknowledgements
52
• Dr. Ozge Gunaydin Sen
• Dr. Paul Bernazzani
• Dr. Perumalreddy Chandrasekaran
• Adarsh Bafana
• Lamar University
• Welch Foundation
• My Family
• Friends
