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Title: Methods to Stabilize and Destabilize Ammonium Borohydride

Abstract

Ammonium borohydride, NH4BH4, has a high hydrogen content of ρm = 24.5 wt% H2 and releases 18 wt% H2 below T = 160 °C. However, the half-life of bulk NH4BH4 at ambient temperatures, ~6 h, is insufficient for practical applications. The decomposition of NH4BH4 (ABH2) was studied at variable hydrogen and argon back pressures to investigate possible pressure mediated stabilization effects. The hydrogen release rate from solid ABH2 at ambient temperatures is reduced by ~16 % upon increasing the hydrogen back pressure from 5 to 54 bar. Similar results were obtained using argon pressure and the observed stabilization may be explained by a positive volume of activation in the transition state leading to hydrogen release. Nanoconfinement in mesoporous silica, MCM-41, was investigated as alternative means to stabilize NH4BH4. However, other factors appear to significantly destabilize NH4BH4 and it rapidly decomposes at ambient temperatures into [(NH3)2BH2][BH4] (DADB) in accordance with the bulk reaction scheme. The hydrogen desorption kinetics from nanoconfined [(NH3)2BH2][BH4] is moderately enhanced as evidenced by a reduction in the DSC decomposition peak temperature of ΔT = -13 °C as compared to the bulk material. Finally, we note a surprising result, storage of DADB at temperature < -30 °C transformed,more » reversibly, the [(NH3)2BH2][BH4] into a new low temperature polymorph as revealed by both XRD and solid state MAS 11B MAS NMR. TA & AK are thankful for support from the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. A portion of the research was performed using EMSL, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated by Battelle.« less

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
1060106
Report Number(s):
PNNL-SA-89183
39979; KC0302010
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Dalton Transactions, 42(3):680-687
Additional Journal Information:
Journal Name: Dalton Transactions, 42(3):680-687
Country of Publication:
United States
Language:
English
Subject:
ammonium borohydride; hydrogen; Environmental Molecular Sciences Laboratory

Citation Formats

Nielsen, Thomas K., Karkamkar, Abhijeet J., Bowden, Mark E., Besenbacher, Fleming, Jensen, Torben R., and Autrey, Thomas. Methods to Stabilize and Destabilize Ammonium Borohydride. United States: N. p., 2013. Web. doi:10.1039/C2DT31591B.
Nielsen, Thomas K., Karkamkar, Abhijeet J., Bowden, Mark E., Besenbacher, Fleming, Jensen, Torben R., & Autrey, Thomas. Methods to Stabilize and Destabilize Ammonium Borohydride. United States. doi:10.1039/C2DT31591B.
Nielsen, Thomas K., Karkamkar, Abhijeet J., Bowden, Mark E., Besenbacher, Fleming, Jensen, Torben R., and Autrey, Thomas. Mon . "Methods to Stabilize and Destabilize Ammonium Borohydride". United States. doi:10.1039/C2DT31591B.
@article{osti_1060106,
title = {Methods to Stabilize and Destabilize Ammonium Borohydride},
author = {Nielsen, Thomas K. and Karkamkar, Abhijeet J. and Bowden, Mark E. and Besenbacher, Fleming and Jensen, Torben R. and Autrey, Thomas},
abstractNote = {Ammonium borohydride, NH4BH4, has a high hydrogen content of ρm = 24.5 wt% H2 and releases 18 wt% H2 below T = 160 °C. However, the half-life of bulk NH4BH4 at ambient temperatures, ~6 h, is insufficient for practical applications. The decomposition of NH4BH4 (ABH2) was studied at variable hydrogen and argon back pressures to investigate possible pressure mediated stabilization effects. The hydrogen release rate from solid ABH2 at ambient temperatures is reduced by ~16 % upon increasing the hydrogen back pressure from 5 to 54 bar. Similar results were obtained using argon pressure and the observed stabilization may be explained by a positive volume of activation in the transition state leading to hydrogen release. Nanoconfinement in mesoporous silica, MCM-41, was investigated as alternative means to stabilize NH4BH4. However, other factors appear to significantly destabilize NH4BH4 and it rapidly decomposes at ambient temperatures into [(NH3)2BH2][BH4] (DADB) in accordance with the bulk reaction scheme. The hydrogen desorption kinetics from nanoconfined [(NH3)2BH2][BH4] is moderately enhanced as evidenced by a reduction in the DSC decomposition peak temperature of ΔT = -13 °C as compared to the bulk material. Finally, we note a surprising result, storage of DADB at temperature < -30 °C transformed, reversibly, the [(NH3)2BH2][BH4] into a new low temperature polymorph as revealed by both XRD and solid state MAS 11B MAS NMR. TA & AK are thankful for support from the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. A portion of the research was performed using EMSL, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated by Battelle.},
doi = {10.1039/C2DT31591B},
journal = {Dalton Transactions, 42(3):680-687},
number = ,
volume = ,
place = {United States},
year = {2013},
month = {1}
}