Thesis Defense

STUDY OF SOFT AMMONIA BORANE-POLYVINYLPYRROLIDONEHYDROGEN STORAGE COMPOSITES

Sahithya PatiMaster of Science

in ChemistryThesis defense

Lamar UniversityAugust 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

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

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

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.

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)

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)

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.

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.

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.

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.

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.

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.

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/g

K)

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

200 210 220 230 240 250 260

100

200

300

400

500

600

700

800

Cp (

J/m

olK

)

Temperature (K)

222.81 K

1000

2000

3000

4000

5000

Ent

halp

y (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

/mol

K2 )

Temperature (K)

5

10

15

20

25

Ent

orpy

(J/m

olK

)

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

190 200 210 220 230 240 250 260

1

2

3

4

5

6

7

8

9

Cp (

J/gK

)

Temperature (K)

20

40

60

80

100

Ent

halp

y (J

/g)

Tp = 223.00 K

(a)

190 200 210 220 230 240 250 260

1.25

1.50

1.75

2.00

2.25

2.50

2.75

3.00

Cp (

J/gK

)

Temperature

20

40

60

80

100

Ent

halp

y (J

/g)

Tp = 222.81 K

(b)

Ammonia Borane/Polyvinylpyrrolidone(Mw-40,000) Composites

Temperature dependence of Heat Capacity and Enthalpy (a) 1:1 AB:PVP (b) 1:2 AB:PVP(40,000)

Ammonia Borane/Polyvinylpyrrolidone (Mw-360,000) Composites

200 220 240 260 280

1

2

3

4

5

6

7

8

Temparature K

Cp (

J/gK

)

223.03 K

0

40

80

120

160

Ent

hapl

y J/

g

Temperature dependence of Heat Capacity and Enthalpy (a) 1:1 AB:PVP (b) 1:2 AB:PVP(360,000)

200 220 240 260 2801.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Temperature k

Cp(

J/gK

)

0

30

60

90

120

150

Enth

alpy

J/g

222.85 K

190 200 210 220 230 240 250 260 270

0.008

0.012

0.016

0.020

0.024

0.028

Cp/

T (J

/gK

2 )

Temperature (K)

Tp = 223.00 K

(a)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Ent

ropy

(J/g

K)

190 200 210 220 230 240 250 260 270

0.006

0.008

0.010

0.012

0.014

0.016

Cp/

T (J

/gK

2 )

Temperature (K)

0.1

0.2

0.3

0.4

0.5

Ent

ropy

(J/g

K)

Tp = 222.81 K

(b)

Ammonia Borane/Polyvinylpyrrolidone(Mw-40,000) Composites

Cp/T and Entropy against temperature (a) 1:1 AB:PVP (b) 1:2 AB:PVP(40,000)

Ammonia Borane/Polyvinylpyrrolidone (Mw-360,000) Composites

Cp/T and Entropy against temperature (a) 1:1 AB:PVP (b) 1:2 AB:PVP(360,000)

200 220 240 260 280

0.006

0.008

0.010

0.012

0.014

0.016

0.018

0.020

0.022

Temperature k

Cp/

T J/

gk2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Entro

py J

/gK

222.85

200 220 240 260 2800.004

0.008

0.012

0.016

0.020

0.024

0.028

Temperature K

Cp/

T J/

gk2

0.00

0.15

0.30

0.45

0.60

0.75

Entro

py J/

gK

222.85

SAMPLE ΔH (J/g) ∆S(10-3J/gK) Tp (K)

AB 31.81 105.6 222.81

AB:PVP(1:1)(40,000) 9.01 65.3 222.89

AB:PVP(1:1)(360,000) 8.65 33.6 222.85

AB:PVP(1:2)(40,000)9.46 33.9 222.76

AB:PVP(1:2)(360,000) 6.51 33.1 222.85

Ammonia Borane/Polyviylpyrrolidone Composites

ΔH, ΔS and Tp values of AB,AB:PVP composites at 1 K/Min heating rates.

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

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Dehydrogenation above 350 K

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

8H

eatf

low

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

Decomposition of bulk AB

320 340 360 380 400 420 440 460 480 500 520-30

-20

-10

0

10

20

30H

eat F

low

(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)

Decomposition of AB:PVP (1:1) composite

340 360 380 400 420 440 460 480 500-2

0

2

4

6

8

Hea

t flo

w (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)

Decomposition of AB:PVP (1:2) composite

340 360 380 400 420 440 460 480 500

-1

0

1

2

3

4

Hea

t flo

w (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)

Activation Energy by Ozawa method

lnβ = -Ea/RTd+ C

β – heating rateEa – Activation EnergyR – rate constantTd – 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

In b

eta

1000/Tp

AB 153.38

AB:PVP(1:1) 125.80

AB:PVP(1:2) 118.81

Activation Energy by Kissinger’s method

ln(β/Td2) = -Ea/RTd + C

β – heating rateEa – Activation EnergyR – rate constantTd – 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

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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.

50 100 150 200 250

40

50

60

70

80

90

100

Wei

ght l

oss

(wt%

)

Temperature

AB

AB:PVP(1:1)

AB:PVP(1:2)


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%,

50 100 150 200 250

40

50

60

70

80

90

100

Wei

ght L

oss(

wt%

)

Temperature

AB

AB:PVP(1:1)

AB:PVP(1:2)


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%

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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.

Room temperature IR-studies of AB and the composites

4000 3500 3000 2500 2000 1500 10000

50

100

150

200

250

300

350

Tran

smitt

ance

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) .

Chemical Interactions - IR

1900 1850 1800 1750 1700 1650 1600 1550 1500

30

40

50

60

70

80

90

100

Tran

smitt

ance

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

Tran

smitt

ance

Wavenumber (cm-1)

1650 cm-1

1600 cm-1

1645 cm-1

1647 cm-1C=O stretch

N-H deformationAB: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.

38

Ammonia Borane Decomposition

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

Abs

orba

nce

Wave number (cm-1)

bulk AB before decomposition

bulk AB after decomposition at 800C (350 K)

N-H, N-H2 and N-H3 strectch B-H and B-H2

strectch N-H bendB-H

2 torsion

B-H2 bend

B-N bend

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 1600C (430 K)

bulk AB before decomposition

B-N bend

B-H2

bendB-H2 torsion N-H bendB-H and B-H2 strectchN-H, N-H

2 and N-H

3 strectch

Abs

orba

nce

Wave number (cm-1)

0 2 4 6 8 10

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-H2

bend

B-H2 torsion N-H bendB-H and B-H2 strectchN-H, N-H

2 and N-H

3 strectch

AB decomposition at 1600C

AB decomposition at 800C (350 K)Abs

orba

nce

Wave number (cm-1)

41


FTIR curves for dehydrogenated samples of bulk AB at various temperatures

4000 3500 3000 2500 2000 1500 1000 500

B-H2

bend

B-N bendB-H2 torsion

N-H bendB-H and B-H2 strectchN-H, N-H2 and N-H3 strectch

(800C)

(1000C)

(1200C)

(1400C)

(1600C)

(1800C)

Abs

orba

nce

Wave number (cm-1)

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 bendB-H and BH2 stretchN-H,N-H2,N-H3 stretch

Abs

orba

nce

(a.u

)

Wavenumber




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 stretchN-H,N-H2,N-H3 stretch

Abs

orba

nce

(a.u

)

Wavenumber




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 stretchN-H,N-H2,N-H3 stretch

Abs

orba

nce

(a.u

)

Wavenumber




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

Abs

orba

nce

(a.u

)

Wavenumber




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 bendB-H and BH2 stretch

N-H,N-H2,N-H3 stretch

Abs

orba

nce

(a.u

)

Wavenumber


4000 3500 3000 2500 2000 1500 1000

B-N bendN-H bendB-H and BH2 stretch

N-H,N-H2,N-H3 stretch

Abs

orba

nce

(a.u

)

Wavenumber



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.

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.

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.

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

• Dr. Ozge Gunaydin Sen • Dr. Paul Bernazzani • Dr. Perumalreddy Chandrasekaran• Adarsh Bafana• Lamar University• Welch Foundation• My Family• Friends

53

Thank you

Thesis Defense

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