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Title: MODIFIED BOROHYDRIDES FOR REVERSIBLE HYDROGEN STORAGE

Abstract

This paper reports the results in the effort to destabilize lithium borohydride for reversible hydrogen storage. A number of metals, metal hydrides, metal chlorides and complex hydrides were selected and evaluated as the destabilization agents for reducing dehydriding temperature and generating dehydriding-rehydriding reversibility. It is found that some additives are effective. The Raman spectroscopic analysis shows the change of B-H binding nature.

Authors:
Publication Date:
Research Org.:
SRS
Sponsoring Org.:
USDOE
OSTI Identifier:
891521
Report Number(s):
WSRC-CP-2006-00017
Journal ID: ISSN 1089-5647; JPCBFK; TRN: US200622%%75
DOE Contract Number:
DE-AC09-96SR18500
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN; ADDITIVES; BOROHYDRIDES; CHLORIDES; HYDRIDES; HYDROGEN STORAGE; LITHIUM

Citation Formats

Au, Ming. MODIFIED BOROHYDRIDES FOR REVERSIBLE HYDROGEN STORAGE. United States: N. p., 2006. Web. doi:10.1021/jp065490h.
Au, Ming. MODIFIED BOROHYDRIDES FOR REVERSIBLE HYDROGEN STORAGE. United States. doi:10.1021/jp065490h.
Au, Ming. Wed . "MODIFIED BOROHYDRIDES FOR REVERSIBLE HYDROGEN STORAGE". United States. doi:10.1021/jp065490h. https://www.osti.gov/servlets/purl/891521.
@article{osti_891521,
title = {MODIFIED BOROHYDRIDES FOR REVERSIBLE HYDROGEN STORAGE},
author = {Au, Ming},
abstractNote = {This paper reports the results in the effort to destabilize lithium borohydride for reversible hydrogen storage. A number of metals, metal hydrides, metal chlorides and complex hydrides were selected and evaluated as the destabilization agents for reducing dehydriding temperature and generating dehydriding-rehydriding reversibility. It is found that some additives are effective. The Raman spectroscopic analysis shows the change of B-H binding nature.},
doi = {10.1021/jp065490h},
journal = {Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical},
number = ,
volume = ,
place = {United States},
year = {Wed May 10 00:00:00 EDT 2006},
month = {Wed May 10 00:00:00 EDT 2006}
}
  • In attempt to develop lithium borohydrides as the reversible hydrogen storage materials with the high capacity, the feasibility to reduce dehydrogenation temperature of the lithium borohydride and moderate rehydrogenation condition has been explored. The commercial available lithium borohydride has been modified by ball milling with metal oxides and metal chlorides as the additives. The modified lithium borohydrides release 9 wt% hydrogen starting from 473K. The dehydrided modified lithium borohydrides absorb 7-9 wt% hydrogen at 873K and 7 MPa. The additive modification reduces dehydriding temperature from 673K to 473K and moderates rehydrogenation conditions to 923K and 15 MPa. XRD and SEMmore » analysis discovered the formation of the intermediate compound TiB{sub 2} that may plays the key role in change the reaction path resulting the lower dehydriding temperature and reversibility. The reversible hydrogen storage capacity of the oxide modified lithium borohydrides decreases gradually during hydriding-dehydriding cycling due to the lost of the boron during dehydrogenation. But, it can be prevented by selecting the suitable additive, forming intermediate boron compounds and changing the reaction path. The additives reduce dehydriding temperature and improve the reversibility, it also reduces the hydrogen storage capacity. The best compromise can be reached by optimization of the additive loading and introducing new process other than ball milling.« less
  • Borohydrides such as LiBH{sub 4} have been studied as candidates for hydrogen storage because of their high hydrogen contents (18.4 wt% for LiBH{sub 4}). Limited success has been made in reducing the dehydrogenation temperature by adding reactants such as metals, metal oxides and metal halides. However, full rehydrogenation has not been realized because of multi-step decomposition processes and the stable intermediate species produced. It is suggested that adding second cation in LiBH{sub 4} may reduce the binding energy of B-H. The second cation may also provide the pathway for full rehydrogenation. In this work, several bimetallic borohydrides were synthesized usingmore » wet chemistry, high pressure reactive ball milling and sintering processes. The investigation found that the thermodynamic stability was reduced, but the full rehydrogenation is still a challenge. Although our experiments show the partial reversibility of the bimetallic borohydrides, it was not sustainable during dehydriding-rehydriding cycles because of the accumulation of hydrogen inert species.« less
  • The Group II alkaline earth metal borohydrides, Mg(BH4)2 and Ca(BH4)2 are among the most promising materials for light-weight, high-capacity hydrogen storage. Five years ago, little were known about the potential of these materials for reversible hydrogen storage, except for their high hydrogen content of 14.9wt% and 11.6wt% respectively. Theory predicted nearly ideal thermodynamics, but competing decomposition pathways. Solid state synthesis routes have been developed and crystal structures and decomposition products have been identified as well as methods to improve hydrogen sorption performance including catalysis and nanoscience. Reversibility was demonstrated for both materials, but at high pressures and temperatures. We willmore » here review recent progress and discuss challenges and future pathways towards applications.« less
  • One of the challenges of implementing the hydrogen economy is finding a suitable solid H{sub 2} storage material. Aluminium (alane, AlH{sub 3}) hydride has been examined as a potential hydrogen storage material because of its high weight capacity, low discharge temperature, and volumetric density. Recycling the dehydride material has however precluded AlH{sub 3} from being implemented due to the large pressures required (>10{sup 5} bar H{sub 2} at 25 C) and the thermodynamic expense of chemical synthesis. A reversible cycle to form alane electrochemically using NaAlH{sub 4} in THF been successfully demonstrated. Alane is isolated as the triethylamine (TEA) adductmore » and converted to unsolvated alane by heating under vacuum. To complete the cycle, the starting alanate can be regenerated by direct hydrogenation of the dehydrided alane and the alkali hydride (NaH) This novel reversible cycle opens the door for alane to fuel the hydrogen economy.« less
  • Hydrides of period 2 and 3 elements are promising candidates for hydrogen storage, but typically have heats of reaction that are too high to be of use for fuel cell vehicles. Recent experimental work has focused on destabilizing metal hydrides through mixing metal hydrides with other compounds. A very large number of possible destabilized metal hydride reaction schemes exist, but the thermodynamic data required to assess the enthalpies of these reactions are not available in many cases. We have used density functional theory calculations to predict the reaction enthalpies for more than 300 destabilization reactions that have not previously beenmore » reported. The large majority of these reactions are predicted not to be useful for reversible hydrogen storage, having calculated reaction enthalpies that are either too high or too low, and hence these reactions need not be investigated experimentally. Our calculations also identify multiple promising reactions that have large enough hydrogen storage capacities to be useful in practical applications and have reaction thermodynamics that appear to be suitable for use in fuel cell vehicles and are therefore promising candidates for experimental work.« less