Journal of Alloys and Compounds
Preparations and de/re-hydrogenation properties of Li Na AlH
6
x
3-x
(
x¼0.9e1.3) non-stoichiometric compounds
a
a,
c
,
* , **
b
,
c
d
a
Xiaolu Fan , Yao Zhang
Jian Chen , Zengmei Wang , Liquan Li
, Yunfeng Zhu
, Cassandra Phillips , Xinli Guo ,
a
a
b, c
a
School of Materials Science and Engineering, Jiangsu Key Laboratory of Advanced Metallic Materials, Southeast University, Nanjing 211189, China
College of Materials Science and Engineering, Nanjing Tech University, 5 Xinmofan Road, Nanjing 210009, China
Jiangsu Collaborative Innovation Center for Advanced Inorganic Function Composites, Nanjing Tech University, Nanjing 210009, China
Department of Physics and Astronomy, Washington State University, Pullman, WA 99163, USA
b
c
d
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 27 June 2017
Received in revised form
Mixed alkali alanates Li Na3-xAlH6 have been successfully synthesized by means of grinding mixtures of
x
Li
perovskite-type structures (space group Fm-3m) can be formed only within the composition range of
exhibits superior hydrogen storage properties over other Li Na3-xAlH com-
3 6 3 6 x 6
AlH and Na AlH in specific molar ratios. Non-stoichiometric Li Na3-xAlH compounds with single
18 September 2017
x ¼ 0.9e1.3. Li1.3Na1.7AlH
6
x
6
Accepted 19 September 2017
Available online 21 September 2017
pounds. Its onset dehydrogenation temperature (~423 K) was lowered by more than 40 K from other
samples in temperature programmed dehydrogenation (TPD) curves. Also, the dehydrogenation capacity
of Li1.3Na1.7AlH
of Li Na3-xAlH
composition (PCI) curves and van't Hoff plots. It shows that the dehydrogenation Li1.3Na1.7AlH
6
(3.45 wt.%) is the highest among the compounds. The dehydrogenation enthalpy values
decreased as x increased from 0.9 to 1.3 according to the results by isothermal pressure-
Keywords:
x
6
Mixed alkali metals alanates
Hydrogen storage performances
Thermal stability
6
ꢀ
1
ꢀ1
(49.7 kJ mol H
apparent activation energy of dehydrogenation for Li1.3Na1.7AlH
ered from that of LiNa AlH . This illustrates that Li1.3Na1.7AlH
netics from that of LiNa AlH
2
) was greatly destabilized from that of LiNa
2
AlH
6
(68.1 kJ mol H
(138.1 kJ mol ) was remarkably low-
6
exhibits enhanced dehydrogenation ki-
2
). Furthermore, the
ꢀ1
Kinetics
6
2
6
2
6
.
©
2017 Elsevier B.V. All rights reserved.
1. Introduction
2 6 2 6
LiK AlH , and K NaAlH etc. People have already synthesized
these materials and investigated their hydrogen storage perfor-
As well known, hydrogen is very important as a new source of
mances extensively [17e32].
renewable energy [1]. However, the emerged hydrogen storage
materials cannot fully meet the standards of utilizations [2].
Among these compounds, LiNa
genation capacity. Approximately 6.7 wt.% H
2
AlH
6
exhibits a large dehydro-
can be evolved from
2
Some complex hydrides, such as NaAlH
target of both gravimetric and volumetric densities [3e11]. It's
possible for the de/re-hydrogenation capacity of NaAlH to attain
more than 4.5 wt.% H at a temperature below 473 K using Ti-
based additives [12e16]. In recent years, studies have been
6
expanded to include mixed alkali alanates such as LiNa AlH ,
4
, potentially reach the
the compound through a three-step reaction within the tempera-
ture range from 463 K to 753 K [31]. Many methods to synthesize
4
LiNa
obtained LiNa
NaAlH at a ratio of 1:1:1. Nearly 3.35 wt.% H
during the first stage of dehydrogenation [31,32]. Claudy et al. [17]
combined LiAlH with NaH to achieve LiNa AlH via either toluene
or a solid-state reaction at high temperatures and under high
hydrogen pressures. Huot et al. [20] obtained LiNa AlH by means
2
AlH
6
have been developed during the last decades. Wang et al.
AlH by solid-state reaction among LiH, NaH, and
can be released
2
2
6
4
2
2
4
2
6
2
6
*
Corresponding author. School of Materials Science and Engineering, Jiangsu Key
of mechanochemical method without any solvent, which supplied
a facile way to yield the product. Since then, the ball milling method
has been extensively used in many combinations such as 2NaH-
Laboratory of Advanced Metallic Materials, Southeast University, Nanjing 211189,
China.
** Corresponding author. College of Materials Science and Engineering, Nanjing
LiAlH
4
[26,27], NaH-LiAlH
4
[23], 2NaAlH
AlH
4 4
-LiH [22], and NaAlH -
NaH-LiH [25] for synthesizing LiNa
2
6
.
(
Y. Zhu).
925-8388/© 2017 Elsevier B.V. All rights reserved.
0