2006 APS March Meeting
Monday–Friday, March 13–17, 2006;
Baltimore, MD
Session A16: Focus Session: Hydrogen Storage I
8:00 AM–10:12 AM,
Monday, March 13, 2006
Baltimore Convention Center
Room: 312
Sponsoring
Unit:
FIAP
Chair: Louis G. Hector, General Motors
Abstract ID: BAPS.2006.MAR.A16.1
Abstract: A16.00001 : Quaternary Li-B-N-H Hydrides: New Hydrogen-Rich Storage Materials
8:00 AM–8:36 AM
Preview Abstract
Abstract
Author:
Frederick Pinkerton
(General Motors Research and Development Center)
We have synthesized light metal Li-B-N-H quaternary hydrides by ball milling
mixtures of LiNH$_{2}$ and LiBH$_{4}$ for a series of compositions
(LiNH$_{2})_{x}$(LiBH$_{4})_{1-x}$ (x = 0.33 to 0.8). We discovered a
new quaternary hydride phase, referred to here as $\alpha $ Li-B-N-H, as the
primary constituent for amide-rich (x $>$ 0.6) compositions. Although
previously tentatively identified as Li$_{3}$BN$_{2}$H$_{8}$, its true
equilibrium composition is Li$_{4}$BN$_{3}$H$_{10}$ as determined by single
crystal x-ray diffraction (XRD). Li$_{4}$BN$_{3}$H$_{10}$ has a
body-centered cubic crystal structure, space group I2$_{1}$3 ({\#} 199) with
a = 10.68 {\AA}. In situ XRD data demonstrate that the $\alpha $-phase also
forms without ball milling by reacting mixed LiNH$_{2}$ and LiBH$_{4}$
powders at temperatures above about 95$^{o}$C. The $\alpha $ phase melts at
about 190\r{ }C and releases hydrogen from the liquid above 250\r{ }C,
forming solid Li$_{3}$BN$_{2}$. Using mass spectrometry residual gas
analysis (RGA) we observe that NH$_{3}$ is released concurrently, and the
quantity of NH$_{3}$ released is strongly dependent on the composition x.
Maximum hydrogen release, exceeding 10 wt{\%}, with minimum NH$_{3}$ release
(1-3 mole {\%} of the evolved gas) occurs for compositions near
LiNH$_{2}$:LiBH$_{4}$ = 2:1 (x = 0.667). Small additions of Ni, Pt, or Pd as
powder or metal chloride reduce the dehydrogenation temperature by as much
as 112\r{ }C, and also reduce the quantity of NH$_{3}$ released by about an
order of magnitude. Differential scanning calorimetry shows an endothermic
melting peak above 190\r{ }C, followed by substantial exothermic heat flow
above 250\r{ }C associated with hydrogen release and solidification of
Li$_{3}$BN$_{2}$. The exothermic hydrogen release suggests that the reverse
reaction is not thermodynamically favored. This new quaternary compound and
its derivatives nonetheless represent promising research candidates in the
search for practical on-board hydrogen storage materials.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2006.MAR.A16.1