DOI: 10.1002/cssc.201500990
Communications
Ternary Amides Containing Transition Metals for Hydrogen
Storage: A Case Study with Alkali Metal Amidozincates
Hujun Cao,*[a] Theresia M. M. Richter,[b] Claudio Pistidda,[a] Anna-Lisa Chaudhary,[a]
Antonio Santoru,[a] Gçkhan Gizer,[a] Rainer Niewa,[b] Ping Chen,[c] Thomas Klassen,[a] and
Martin Dornheim[a]
The alkali metal amidozincates Li4[Zn(NH2)4](NH2)2 and
K2[Zn(NH2)4] were, to the best of our knowledge, studied for
the first time as hydrogen storage media. Compared with the
LiNH2–2 LiH system, both Li4[Zn(NH2)4](NH2)2–12 LiH and
K2[Zn(NH2)4]–8 LiH systems showed improved rehydrogenation
performance, especially K2[Zn(NH2)4]–8 LiH, which can be fully
hydrogenated within 30 s at approximately 230 8C. The absorption properties are stable upon cycling. This work shows that
ternary amides containing transition metals have great potential as hydrogen storage materials.
Hydrogen is a clean, renewable, efficient and environmentally
friendly energy carrier, regarded as a potential candidate for replacing fossil fuels. To utilize H2 for mobile applications, storage materials must exhibit high gravimetric and volumetric H2
capacities and rapid rates of reversible de-/rehydrogenation at
moderate temperatures and suitable pressures.[1] Amide–hydride systems have received a lot of attention as potential candidates for on-board applications due to their high gravimetric
and volumetric H2 capacities.[2] For example, the LiNH2–2 LiH
system can store more than 10.0 wt % of H2 reversibly (LiNH2 +
2 LiHÐLi2NH + LiH + H2ÐLi3N + 2 H2). However, the LiNH2–2 LiH
system cannot meet the required performance criteria for
proton exchange membrane fuel cells (PEMFCs), owing to its
high thermodynamic stability and slow dehydrogenation kinetics. According to Chen et al.,[2a] the plateau pressure of the first
[a] Dr. H. Cao, Dr. C. Pistidda, Dr. A.-L. Chaudhary, A. Santoru, G. Gizer,
Prof. T. Klassen, Prof. M. Dornheim
Institute of Materials Research
Materials Technology
Helmholtz-Zentrum Geesthacht
Max-Planck-Straße 1
Geesthacht 21502 (Germany)
Fax: ( + 49) 04152/87-2625
Phone: ( + 49) 4152/87-2643
E-mail: [email protected]
[b] Dr. T. M. M. Richter, Prof. R. Niewa
Institute of Inorganic Chemistry
University of Stuttgart
Pfaffenwaldring 55
70569 Stuttgart (Germany)
[c] Prof. P. Chen
Dalian Institute of Chemical Physics
Chinese Academy of Sciences
Dalian 116023 (P.R. China)
Supporting Information for this article is available on the WWW under
http://dx.doi.org/10.1002/cssc.201500990.
ChemSusChem 2015, 8, 3777 – 3782
step of desorption for LiNH2–2 LiH is 1 bar at circa 285 8C. To
utilize amide–hydride systems for practical applications, a considerable amount of work has been done to improve thermodynamic and kinetic behavior. Varieties of amide–hydride systems with different thermodynamic and kinetic properties
(e.g., Ca-N-H,[2a] Mg-N-H,[3] Li-Mg-N-H,[4] Li-Ca-N-H,[4a] Li-Al-N-H,[5]
Li-B-N-H[6]) have been developed and studied. For example, the
substitution of LiNH2 by Mg(NH2)2 or the replacement of 2 LiH
with MgH2 in the LiNH2–2 LiH system led to the development
of
Mg(NH2)2–2 LiH/2 LiNH2-MgH2
(2 LiNH2 + MgH2 !
Li2Mg(NH)2 + 2 H2ÐMg(NH2)2 + 2 LiH),[4a,b] which has a much
more favorable thermodynamic stability in the range of DH
… 40 kJ (mol-H2)¢1 while maintaining a high H2 storage capacity
(5.6 wt %).[7] In addition, introducing additives/catalysts was
proven to be an effective way to improve the H2 storage performance of amide–hydride systems. Transition metals such as
Sc, Ti, V, Ta, Ni, and their compounds were found to be efficient
additives for improving the properties of amide–hydride systems.[8] Ichikawa et al.[8a] reported that the LiNH2–LiH system
doped with nanosized Ti additives can desorb roughly 5.5 wt %
H2 within a temperature range of 150 to 250 8C, which is better
than the pristine LiNH2–LiH system.
Zn has some chemical properties similar to those of Ni,
which is an effective additive for these systems.[9] The use of
Li- and Zn-containing compounds could have a similar affect
compared to conventional “alloying” and “multi-cation” methods for H2 storage under more moderate pressure and temperature conditions.[10] The synthesis of ternary amides containing
alkali metals and transition metals might be an important step
towards the development of novel H2 storage systems with improved thermodynamic and kinetic properties.
In this work, the H2 sorption properties of alkali metal amidozincates, as far as we know, were studied for the first time.
The study draws attention to the great potential of ternary
amides containing transition metals as H2 storage material. In
the presented case, the K2[Zn(NH2)4]–8 LiH system can be fully
hydrogenated at circa 230 8C within 30 s. These excellent absorption properties are maintained upon cycling. Interestingly,
when performing a rehydrogenation measurement at 222 8C,
the
dehydrogenated
Li4[Zn(NH2)4](NH2)2–12 LiH
and
K2[Zn(NH2)4]–8 LiH mixtures were able to absorb roughly 2.0
and 1.5 wt % H2, respectively, within 30 s. Under the same temperature and H2 pressure conditions, almost no H2 was absorbed by the dehydrogenated LiNH2–2 LiH.
The studied systems were prepared by ball milling
Li4[Zn(NH2)4](NH2)2, K2[Zn(NH2)4], and LiNH2 with LiH in a molar
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Communications
ratio of 1:12, 1:8, and 1:2, respectively. Thermogravimetric (TG)
combined with differential thermal analysis (DTA) and mass
spectrometry (MS), namely, TG–DTA–MS, was employed to investigate the thermal decomposition performances. A Sievertstype apparatus (HERA, Quebec, Canada) was used to test the
de-/rehydrogenation properties. The structural evolution of the
crystalline phases was studied by powder X-ray diffraction
(PXRD).
TG–DTA–MS was employed to investigate the thermal decomposition performance of Li4[Zn(NH2)4](NH2)2, K2[Zn(NH2)4]
and LiNH2 (Figure 1). Different from the reference material (i.e.,
Figure 1. TG (a), DTA (b), and MS (c) measurements of LiNH2,
Li4[Zn(NH2)4](NH2)2, and K2[Zn(NH2)4] after grinding for 2 min using an agate
mortar and pestle.
LiNH2), Figure 1 a and b clearly shows the multi-step nature of
the
thermal
decomposition
reactions
of
both
Li4[Zn(NH2)4](NH2)2 and K2[Zn(NH2)4].[11, 12] After heating the
specimens to circa 500 8C, TG showed that K2[Zn(NH2)4],
Li4[Zn(NH2)4](NH2)2, and LiNH2 had lost 27.5, 31.7, and
37.2 wt %, respectively. As reported earlier,[12] upon heating to
500 8C, Li4[Zn(NH2)4](NH2)2 released 31.5 wt % NH3 using the decomposition pathways shown in Reactions (1) and (2), which
correlates well with the result presented here (31.7 wt %).
Li4 ½ZnðNH2 Þ4 ¤ðNH2 Þ2 ! 3 LiNH2 þ LiZnN þ 2 NH3
ð1Þ
6 LiNH2 ! 3 Li2 NH þ 3NH3
ð2Þ
Figure 1 c shows that the onset and maximum peak temperatures of Li4[Zn(NH2)4](NH2)2 decomposition to ammonia are at
approximately 260 and 300 8C, which are more than 60 8C
lower than that of the pristine LiNH2. However, K2[Zn(NH2)4] decomposed to ammonia at a much higher temperature (circa
ChemSusChem 2015, 8, 3777 – 3782
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350 8C) and the reaction quickly reached a peak temperature
at 360 8C. It should be pointed out that the sudden “jump” visible in the MS signals of Figure 1 c is due to the low sensitivity
of the used MS towards NH3.
The hydrogen storage properties of Li4[Zn(NH2)4](NH2)2–
12 LiH, K2[Zn(NH2)4]–8 LiH, and LiNH2–2 LiH were studied using
TG–MS and a Sieverts-type apparatus (Figure 2). Figure 2 a
shows material weight losses for both Li4[Zn(NH2)4](NH2)2–
12 LiH and LiNH2–2 LiH equal to 6.1 wt % after heating to
400 8C. However, the TG onset temperature for
Li4[Zn(NH2)4](NH2)2–12 LiH is below 100 8C, which is roughly
70 8C lower than that of the LiNH2–2 LiH sample. The TG onset
temperatures of K2[Zn(NH2)4]–8 LiH and LiNH2–2 LiH are almost
the same; however, K2[Zn(NH2)4]–8 LiH loses approximately
4.2 wt % when heated to 400 8C. The weight loss of
K2[Zn(NH2)4]–8 LiH significantly increases when the sample is
heated above 425 8C. To compare the effect of ball milling time
on the investigated samples, TG–DTA curves of
Li4[Zn(NH2)4](NH2)2–12 LiH and K2[Zn(NH2)4]–8 LiH mixtures after
grinding for 2 min using an agate mortar and pestle are shown
in Figure S1 in the Supporting Information. The NH3 and H2 MS
traces recorded during the TG of Li4[Zn(NH2)4](NH2)2–12 LiH,
K2[Zn(NH2)4]–8 LiH and LiNH2–2 LiH are summarized in Figure 2 b and c. Based on these analyses, it appears that the materials release mostly H2 upon decomposition. For
K2[Zn(NH2)4]–8 LiH and LiNH2–2 LiH, the amount of released
NH3 is almost undetectable. This could be due to the fact that
the formed NH3 is immediately captured by LiH[13] or that H2 is
released as a consequence of the direct reaction of amides
with LiH.[14] For the Li4[Zn(NH2)4](NH2)2–12 LiH sample, a small
amount of NH3 seems to be released at approximately 190 8C.
In addition, the
dehydrogenation
performance
of
Li4[Zn(NH2)4](NH2)2–12 LiH is similar to that of LiNH2–2 LiH
sample after circa 250 8C. This could be due to LiNH2, NH3, and
LiZnN being formed in the first step of the reaction of
Li4[Zn(NH2)4](NH2)2 decomposition, which can be described according
to
Reaction (1).
According
to
Figure 2 b,
Li4[Zn(NH2)4](NH2)2–12 LiH starts to release H2 at circa 100 8C,
which is around 72 8C lower than the onset temperature
(172 8C) of the reference LiNH2–2 LiH (with regard to the H2 release signal). Except for the shift to lower temperatures of the
dehydrogenation temperatures, the shapes of the H2 signals of
Li4[Zn(NH2)4](NH2)2–12 LiH and LiNH2–2 LiH measured by means
of MS are similar. This suggests that the reaction mechanism
for the second step of the decomposition reaction of
Li4[Zn(NH2)4](NH2)2–12 LiH involves the interaction of LiNH2
(which is formed during the first decomposition step) with LiH.
The catalytic effects of Zn and LiZnN may be the reason for
the apparent shift of the dehydrogenation temperature of
Li4[Zn(NH2)4](NH2)2–12 LiH to lower temperatures, as observed
in the ZnCl2-nLiNH2-yLiH system.[15] Sometimes, the H2 desorption behavior of an amide–hydride system, in an open system
(e.g., TG), is different from that of a closed system (e.g., Sieverts apparatus). That is because H2 desorption in amide–hydride systems involve two different mechanisms. One is
a solid–solid reaction mechanism[14] and the other is an ammonia-mediated mechanism.[16] Dehydrogenation properties of
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Communications
Figure 2. TG (a), hydrogen (b) and ammonia (c) mass spectra and H2 absorption curves (d) of LiNH2–2 LiH, Li4[Zn(NH2)4](NH2)2–12 LiH, and K2[Zn(NH2)4]–8 LiH.
The insert shows the relationship of time and hydrogen absorption capacity of LiNH2–2 LiH, Li4[Zn(NH2)4](NH2)2–12 LiH, and K2[Zn(NH2)4]–8 LiH with a heating
rate of 3 8C min¢1 and 50 bar H2.
Li4[Zn(NH2)4](NH2)2–12 LiH, K2[Zn(NH2)4]–8 LiH, and LiNH2–2 LiH
measured in a Sieverts type apparatus (HERA, Quebec, Canada)
are summarized in Figure S2. Despite the fact that the dehydrogenation capacities measured in a closed system are slightly different to an open system, the onset temperatures and dehydrogenation shapes of the desorption curves shown in Figures S2 and 2 a are similar. The lower H2 contents measured for
the investigated materials in a closed system could be due to
the formation of a H2 back-pressure that might slow down
and/or hinder the further release of H2 from the material. A detailed analysis of the thermodynamic properties of the alkali
metal amidozincates and LiH mixtures will be given in a separate publication.
To investigate the hydrogenation behavior of the system
outlined here, the desorbed Li4[Zn(NH2)4](NH2)2–12 LiH,
K2[Zn(NH2)4]–8 LiH and LiNH2–2 LiH, were hydrogenated at
300 8C and 50 bar H2 ; the results are summarized in Figure 2 d.
It is shown that the absorption behavior of both
Li4[Zn(NH2)4](NH2)2–12 LiH and K2[Zn(NH2)4]–8 LiH are better
than that of LiNH2–2 LiH. The hydrogenation onset temperatures of the three samples are roughly 190 8C; however, the absorption rates of Li4[Zn(NH2)4](NH2)2–12 LiH and K2[Zn(NH2)4]–
8 LiH are higher than that of LiNH2–2 LiH. The amount of H2 absorbed
is
4.0 wt %
for
LiNH2–2 LiH,
4.3 wt %
for
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Li4[Zn(NH2)4](NH2)2–12 LiH, and 3.1 wt % for K2[Zn(NH2)4]–8 LiH.
It should be noted that the plateau and further absorption
shown for Li4[Zn(NH2)4](NH2)2–12 LiH at circa 280 8C is due to
a nonlinear temperature change of the furnace (shown in Figure S3). Interestingly, a sharp increase in the amount of H2 absorbed in the K2[Zn(NH2)4]–8 LiH system occurs at about 230 8C.
This implies an extremely fast hydrogenation rate for the
K2[Zn(NH2)4]–8 LiH sample in the dehydrogenated state. The
insert in Figure 2 d shows that most of the absorbed H2 (i.e.,
2.5 wt %) is charged within 30 s for the K2[Zn(NH2)4]–8 LiH
system. To the best of our knowledge, the hydrogenation rate
shown by the desorbed K2[Zn(NH2)4]–8 LiH is the fastest reported in literature for amide–hydride systems.
Isothermal de-/rehydrogenation experiments were employed
to investigate the H2 properties of the studied systems. Figures S4 and 3 summarize the H2 properties of these materials for
the dehydrogenation process measured at 192 8C and the rehydrogenation process at 222 8C. After 7 h, the amount of H2
released by the materials were 2.4, 2.3, and 1.4 wt % for LiNH2–
2 LiH, Li4[Zn(NH2)4](NH2)2–12 LiH, and K2[Zn(NH2)4]–8 LiH, respectively (Figure S4). The sorption kinetics of Li4[Zn(NH2)4](NH2)2–
12 LiH and K2[Zn(NH2)4]–8 LiH are remarkably faster compared
to that of the reference LiNH2–2 LiH system. The insert in
Figure 3 shows that both Li4[Zn(NH2)4](NH2)2–12 LiH and
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Figure 3. Isothermal rehydrogenation at 222 8C and 50 bar H2 for post-isothermal 192 8C
dehydrogenated LiNH2–2 LiH, Li4[Zn(NH2)4](NH2)2–12 LiH and K2[Zn(NH2)4]–8 LiH samples.
The insert shows the relationship of time and isothermal rehydrogenation capacity of
LiNH2–2 LiH, Li4[Zn(NH2)4](NH2)2–12 LiH and K2[Zn(NH2)4]–8 LiH systems at 222 8C and
50 bar H2.
compared to the LiNH2–2 LiH system. The results of
this investigation are summarized in Figure 5 together with the PXRD patterns of the as-milled
Li4[Zn(NH2)4](NH2)2–12 LiH,
K2Zn(NH2)4–8 LiH,
and
LiNH2–2 LiH. The structural changes of the LiNH2–
2 LiH system are the same as reported previously.[2a]
Upon dehydrogenation, LiNH2–2 LiH converts into
Li2NH and LiH, which after hydrogenation, changes
back to LiNH2–2 LiH (Figure 5 a). Only LiNH2 and LiH
appear in the post-ball-milled Li4[Zn(NH2)4](NH2)2–
12 LiH sample (Figure 5 b; Zn appeared to be PXRD
amorphous as shown in Figure S5), which indicates
that the first step of the decomposition reaction of
Li4[Zn(NH2)4](NH2)2 could occur during ball milling.
After treating the Li4[Zn(NH2)4](NH2)2–12 LiH mixture
at 350 8C, Li2NH and LiZn13 formed. The materials rehydrogenated at 300 8C and 90 bar H2, showing the
conversion of Li2NH into LiNH2 and LiH; however,
LiZn13 is still present. This suggests that the desorp-
K2[Zn(NH2)4]–8 LiH can be charged within 30 s. However, in the
same range of time almost no H2 was absorbed by the LiNH2–
2 LiH system.
Temperature-programmed volumetric desorption and subsequent absorption measurements on the K2[Zn(NH2)4]–8 LiH
sample were performed for three cycles to investigate the reversibility (Figure 4). The results indicate that roughly 3 wt % H2
can be reversibly desorbed and absorbed in K2[Zn(NH2)4]–8 LiH.
It is interesting that the quick “absorption jump” at about
230 8C was present in all the absorption tests. In addition, de-/
rehydrogenation properties of the third cycle are better than
that of the second one, which could be due to phase segregation and not perfect intermixing of the reactants.
To shed some light on the reaction mechanism of the de-/rehydrogenation of Li4[Zn(NH2)4](NH2)2–12 LiH and K2[Zn(NH2)4]–
8 LiH, de-/absorption products were investigated by PXRD and
Figure 5. PXRD patterns of LiNH2–2 LiH (a), Li4[Zn(NH2)4](NH2)2–12 LiH (b), and
K2[Zn(NH2)4]–8 LiH (c) after ball milling (BM) 12 h under 50 bar H2, full dehydrogenation (Des) at 350 8C and vacuum, and full absorption (Abs) at 300 8C
and 90 bar H2.
Figure 4. First three temperature-programmed volumetric desorption and
absorption cycles of K2[Zn(NH2)4]–8 LiH. Desorption from room temperature
to 400 8C with a heating rate of 3 8C min¢1 and vacuum; absorption from
room temperature to 300 8C with a heating rate of 3 8C min¢1 and 50 bar H2.
ChemSusChem 2015, 8, 3777 – 3782
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tion process of Li4[Zn(NH2)4](NH2)2–12 LiH is not fully reversible
under these conditions. Upon cycling, K2[Zn(NH2)4]–8 LiH maintains a good degree of reversibility (Figure 4). An “unknown
compound” as well as LiH can be observed in the PXRD patterns of the as-milled and rehydrogenated K2[Zn(NH2)4]–8 LiH
samples. After dehydrogenation, the “unknown compound”
and LiH transformed to form LiZn13 and KH (Figure 5 c). The
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possible reasons for the fast rehydrogenation kinetics of
K2[Zn(NH2)4]–8 LiH could be as follows: 1) Changes in sample
morphology of K2[Zn(NH2)4]–8 LiH before and after dehydrogenation indicate the sample could have been in a molten
state at circa 230 8C (Figure S6). This molten state could aid in
mass transportation during the hydrogenation process due to
the Zn2 + sites becoming more readily available, increasing the
likelihood of H2 dissociation, which will accelerate the rate of
hydrogenation. 2) An unknown compound was observed
during the desorption and absorption processes (Figure 5 c),
this unknown compound could act as a “catalyst” during absorption, thereby increasing the reaction kinetics. A detailed investigation of de-/rehydrogenation mechanisms and reversibility of Li4[Zn(NH2)4](NH2)2–12 LiH and K2[Zn(NH2)4]–8 LiH samples
are currently underway and will be reported in a future work.
In summary, ternary amides containing alkali and transition
metals were studied for the first time as H2 storage materials.
After mixing Li4[Zn(NH2)4](NH2)2 and K2[Zn(NH2)4] with LiH, they
released 6.1 and 4.2 wt % H2 below 400 8C, respectively. Compared to the reference LiNH2–2 LiH, both Li4[Zn(NH2)4](NH2)2–
12 LiH and K2[Zn(NH2)4]–8 LiH showed improved rehydrogenation performance. Moreover, the desorbed K2[Zn(NH2)4]–8 LiH
sample can be hydrogenated within 30 s at 230 8C and 50 bar
H2 with a maximum rehydrogenation rate of approximately
6.0 wt % min¢1; this is, to the best of our knowledge, the fastest
rehydrogenation rate observed to date in amide–hydride systems. In addition, the extremely good absorption properties of
K2[Zn(NH2)4]–8 LiH are stable upon cycling. It should be pointed
out that the gravimetric and volumetric H2 capacities and operating temperature of alkali metal amidozincates still do not
meet the targets for on-board vehicular application; however,
the large variety of ternary amides that can be prepared opens
new perspectives for the development of an amide-based H2
storage material for mobile applications.
using a Netzsch STA 409 C (Germany) and a Hiden Analytical HAL
201 Mass-Spectrometer (United Kingdom) combined system in
50 mL min¢1 Ar flow. The samples were investigated in the range
of 20–500 8C using a heating rate of 5 8C min¢1. In addition, the
gases had to flow through a capillary (circa 2 m) connecting the
TG with the MS before reaching the MS.
De-/rehydrogenation experiments were performed using a Sieverts-type apparatus (HERA, Quebec, Canada). Absorption was
heated up to the final temperature of 300 8C under a H2 pressure
of 50 bar using a heating rate of 3 8C min¢1. Desorption experiments were performed from room temperature to 400 8C under
vacuum at a heating rate of 3 8C min¢1. Isothermal de-/rehydrogenation experiments were performed using a Sieverts-type apparatus (HERA, Quebec, Canada) at a temperature of 192 and 222 8C
and vacuum and 50 bar H2, respectively.
PXRD tests were carried out using a Bruker D8 discover X-ray diffractometer (Germany) with Cu radiation (l = 0.154 nm, 50 kV,
1000 mA) at a scanning rate of 0.05 degree s¢1. Air-tight sample
holders were used (Bruker, Germany) to prevent contamination of
the sample. All de-/rehydrogenated samples were heated to 350 8C
in vacuum and 300 8C under 90 bar H2 overnight before the PXRD
test.
Acknowledgements
The work was supported by the project of Chinese Academy of
Science–Helmholtz-Zentrum Geesthacht (CAS-HZG) collaborative
programme “RevHy”-“Study on the synthesis, structures and performances of complex hydrides systems for Reversible high capacity Hydrogen storage at low temperatures”, the Seventh
Framework Programme of the European Union, The Fuel Cells
and Hydrogen Joint Undertaking (FCH JU), and the German Research Foundation (DFG) within the research group FOR1600
Chemistry and Technology of Ammonothermal Synthesis of Nitrides.
Keywords: hydrides · hydrogen storage · sorption kinetics ·
ternary amides · transition metals
Experimental Section
LiNH2 (95 % purity) and LiH (97 % purity) were purchased from
Strem and Alfa, respectively. Li4[Zn(NH2)4](NH2)2 and K2[Zn(NH2)4]
were synthesized in supercritical ammonia in custom-built Alloy
718
(austenitic
Ni-Cr-based
superalloy)
autoclaves.
Li4[Zn(NH2)4](NH2)2 was grown in the cold temperature zone of the
autoclave under ammonothermal conditions (500 8C furnace temperature and 110 MPa NH3) from Zn, Li (molar metal ratio 1:4) and
supercritical ammonia. K2[Zn(NH2)4] was obtained in the cold temperature zone of the autoclave from Zn powder and K amide
(molar metal ratio 1:2) under ammonothermal conditions (300 8C
furnace temperature, 150 MPa NH3). Powder X-ray diffraction analyses (PXRD) of the as-synthesized Li4[Zn(NH2)4](NH2)2, K2[Zn(NH2)4]
and the commercial LiNH2 are summarized in Figure S7. LiNH2–
2 LiH, Li4[Zn(NH2)4](NH2)2–12 LiH, and K2[Zn(NH2)4]–8 LiH samples
were ball milled for 12 h at 250 rpm using a Fritsch Pulverisette 6
(Germany) classic line planetary mill, with a ball-to-powder ratio of
circa 40:1 in a high-pressure vial with 50 bar H2. All powder handling and milling were performed in an MBraun (Germany) Ar glovebox with H2O and O2 levels below d = 10 ppm to prevent contamination.
Thermogravimetric analysis (TG), differential thermal analysis (DTA)
as well as mass spectrometry (MS) measurements were carried out
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Received: July 22, 2015
Published online on October 14, 2015
3782
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