Abstract Results and discussions

Behavior of Ammonia borane under high pressure up to 20 GPa and temperature from 80 – 350K has been studied using Raman spectroscopy/x-ray diffraction and a diamond anvil cell (DAC). Abundant phases are found in this molecular crystal at this pressure and temperature range. More changes in the feature of Raman spectroscopy are observed than the crystal structure changes identified by x-ray diffraction, indicating Raman spectroscopy may identify bonding changes in addition to crystal structural transitions. Based on Raman spectra of ammonia borane, four new phases are observed for the first time at high pressure and low temperature. Confining the sample into mesopores of nano-scaffold (SBA-15 with 1:1 ratio to sample) shifts the pressure induced phase transitions at ~0.9 GPa and ~10.2 GPa to ~0.5GPa and ~9.7GPa respectively, and the temperature induced transformation from 217K to 195K in ammonia borane. Raman spectroscopy study has also been conducted on lithium amidoborane at high pressures up to 19 GPa and room temperature. Two new high pressure phases are observed.

Experimental Method

Ammonia Borane under High Pressure

Jiuhua Chen, Yongzhou Sun, Shah Najiba, Jennifer Girard, Vadym Drozd, Wendy Mao1 CeSMEC, Department of Mechanical and Materials Engineering

Florida International University, Miami, FL 33199 1Stanford University, Stanford, CA 94305-2115

• Expand the in situ high pressure study of the ammonia borane derivative, lithium amidoborane, from ambient temperature to both elevated temperature and low temperature.

• Study pressure influence on dehydrogenation and rehydrogenation of lithium amidoborane. Apply the same experimental protocol used in ammonia borane system to lithium amidoborane system to explore reversibility of its thermolysis process through pressure.

• Synthesize and characterize aluminum amidoborane.

Publications: Jiuhua Chen, Helene Couvy, Haozhe Liu, Vadym Drozd, Luke L.

Daemen, Yusheng Zhao and Chi-Chang Kao, In situ x-ray study of ammonia borane at high pressures, International Journal of Hydrogen Energy, 35 (20), October 2010,11064-11070, doi:10.1016/j.ijhydene.2010.07.085.

Shah Najiba, Jiuhua Chen, Vadym Drozd, Andriy Durygin, Yongzhou Sun, Tetragonal to orthorhombic phase transition of ammonia borane at low temperature and high pressure, Journal of Applied Physics, 2012 in print.

Shah Najiba, Jiuhua Chen, Vadym Drozd, Andriy Durygin, Yongzhou Sun, Raman spectroscopy study of ammonia borane at low temperature and high pressure, in Energy Technology 2012: Carbon Dioxide Management and Other Technologies, Edited by Maria D. Salazar-Villalpando, Neale R Neelameggham, Donna Post Guillen, Soobhankar Pati, and Gregory K. Krumdick, TMS (The Minerals, Metals & Materials Society), 2012, pp 339-346

Ali Hadjikhani, J. Chen, S. Das, W. Choi, Raman spectroscopy of graphene and plasma treated graphene under high pressure, 2012 TMS Proceedings: Volume 2: Materials Properties, Characterization, and Modeling, TMS (The Minerals, Metals & Materials Society), 2012, pp 75-79

Yu Lin, Hongwei Ma, Charles Wesley Matthews, Brian Kolb, Stanislav Sinogeikin, Timo Thonhauser, and Wendy L. Mao, Experimental and Theoretical Studies on a High Pressure Monoclinic Phase of Ammonia Borane, Journal of Physical Chemistry C, 116, 2172–2178 (2012).

Support and facility: DE-FG02-07ER46461

Diamond anvil cell (DAC) for high pressure generation

High Pressure Raman Spectra of Ammonia Borane. Numbers next to the spectra indicate the pressure (difference colors represent phase change, blue: : I4mm , red and pink: Cmc21, black: P21, phase change between red and pink is a second order transition)

Above: Phase boundary of ammonia borane at high pressure and elevated temperature. Solid and open circles represent I4mm and Cmc21 phases respectively, determined by x-ray diffraction. Solid triangles and squares represent I4mm and P21 phases respectively, determined by Raman spectroscopy. Open symbols between I4mm and P21 phases represent Cmc21 phase.

Inte

nsity

Raman spectra of neat ammonia borane (2250cm-1 - 4750cm-1) during heating and subsequent compression

Dehydrogenation and rehydrogenation of ammonia borane with and without nanoconfinement

Future Direction

Raman spectroscopy system and Cryostat that houses the DAC for high pressure and low temperature experiments.

X-ray diffraction system at National Synchrotron Light Source of Brookhaven National Lab and high pressure cell assembly used in the multi anvil press.

In situ x-ray diffraction patterns of ammonia borane in DAC (left) and MAP (right) at ambient temperature. Black and red colors represent the patterns from the I4mm phase and the Cmc21 phase, respectively.

10.38 10.01 8.20 7.86 5.70 5.34

4.98 4.61 4.25 3.92 2.84 2.48

2.12 1.79

1.07 0.70 0.35 0

10.38 10.01 8.20 7.86 5.70 5.34

4.98 4.61 4.25 3.92

2.84 2.48

2.12 1.79

1.07 0.70

0.35 0

Pre

ssur

e (G

Pa)

Pre

ssur

e (G

Pa)

500 1000 1500 2000

19 GPa

16.4

12.8

12.7

10.6

9.9

9.3

7.3

5.9

4.6

3.9

2.4

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(arb

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Raman shift (cm-1)

1.7

(a)

3200 3300 3400 3500

1.7

2.4

3.9

4.6

5.9

7.3

9.3

9.910.6

12.7

12.8

16.4

19 GPa

Inte

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(arb

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y un

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Raman shift (cm-1)(b)

High Pressure Raman Spectra of lithium amidoborane. Numbers next to the spectra indicate the pressure in GPa. Two phase transitions are observed at about 3 GPa and 12 GPa respectively.

0 5 10 15 202100

2150

2200

2250

2300

2350

2400

Ram

an s

hift

(cm

-1)

Pressure (GPa)5 10 15 20

3300

3350

3400

3450

3500

Ram

an s

hift

(cm

-1)

Pressure (GPa)

Pressure dependence of Raman peaks of lithium amidoborane. The first phase transition is observed about 3 GPa for peak splitting at 2175 cm-1 and peak merging at 2300 cm-1. The second phase transition is observed at about 12GPa for peak splitting at 3375 cm-1 and 3450 cm-1.

Left: Phase boundary of ammonia borane at high pressure and low temperature determined by Raman spectroscopy

600 800 1000 1200 1500 1600 1700

10B-N st.11B-N st.

NBH Rock

Sym. BH3 def.

Asym. BH3 def.Asym. NH3 def.

226

223

220

217

Inte

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(arb

. uni

t)

Raman shift (cm-1)

90 K

210

2300 2400 3200 3300 3400

Sym. BHst

Asym. BHst Sym. NHst

Asym. NHst

90 K

210

217

220

223Inte

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(arb

. uni

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Raman shift (cm-1)

226

200 400 600 800 1000 1200 1600

226

223

220

217

210

205

200

195

180

Inte

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(arb

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Raman shift (cm-1)

90 K

130

2400 3200 3400

90 K

130

180

195

200

205

210

217

220

223

Inte

nsity

(arb

. uni

t)

Raman shift (cm-1)

226

Raman spectra of ammonia borane as a function of temperature

Raman spectra of ammonia borane confined in SBA15 nanoscaffold as a function of temperature

Confining ammonia borane in mesoporous confinement (i.e. SBA15 silica nanoscaffold) not only change its dehydrogenation temperature and kinetics but also influence its phase equilibrium. Comparative study using Raman spectroscopy was conducted to observed such influence on the temperature induced body centered tetragonal (I4mm) structure to low temperature orthorhombic (Pmn21) structure. Nanoconfinement shifts the phase transition from 217 K to 195 K (see figures on the left). A similar influence of the nanoconfiement on pressure induced phase transitions is also observed using Raman spectroscopy. The phase boundary between the phase and high pressure Cmc21 phase at ambient temperature is shifted from 0.9 GPa to 0.5 GPa; and that between the Cmc21 phase and higher pressure P21 phase is shifted from 10.2 GPa to 9.7 GPa. More remarkably, confining ammonia borane makes it possible to reverse its thermolysis process by applying high pressure to the system. Figures below show the comparison of behaviors of neat and confined ammonia borane during heating and subsequent compression.

Raman spectra of ammonia borane confined in SBA15 (2250cm-1 - 4150cm-1) during heating and subsequent compression. NH stretching peaks of ammonia borane reappear during the subsequent compression (after

dehydrogenation) to 6 GPa. This presentation does not contain any proprietary, confidential, or otherwise restricted information

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