Investigation of hydrogen desorption from CaSiH by means of calorimetric method

Article abstract of DOI:10.1007/s10973-014-3920-2

The present work deals with the study of the reaction of hydrogen desorption from the CaSiH_X hydride by means of the calorimetric method. The dehydrogenation of the CaSiH_X hydride was carried out at 548 K. For a calorimetric study, the installation composed of the differential heat-conducting Tian-Calvet type calorimeter connected with a conventional Sieverts-type apparatus was employed. Such installation permitted us to obtain simultaneously the P-X isotherms (P - equilibrium hydrogen pressure, X = H/CaSi) and variation of the partial molar enthalpies of the reaction of hydrogen desorption from CaSiH_X with the hydrogen concentration in the metallic matrix. It was ascertained that in the CaSi-H₂ system there was one region where values of the partial molar enthalpy of the reaction of hydrogen desorption from the CaSiH_X hydride remained constant. This means that formation of one hydride phase in the CaSi-H₂ system took place. The enthalpy and entropy values for the reaction of hydrogen desorption from the CaSiH_X in the plateau range are ΔH _des = 53.8 ± 1.2 kJ mol^-1 H₂ and ΔS _des = 94.2 ± 2.7 J mol^-1 H₂ K^-1 (ΔH _des and ΔS _des - the differential molar enthalpy and entropy desorption, respectively).

Full text of DOI:10.1007/s10973-014-3920-2

J Therm Anal Calorim (2014) 118:801–805
DOI 10.1007/s10973-014-3920-2
Investigation of hydrogen desorption from CaSiH
by means of calorimetric method
•
E. Yu Anikina V. N. Verbetsky
Received: 30 October 2013 / Accepted: 4 June 2014 / Published online: 20 July 2014
´
´
Ó Akademiai Kiado, Budapest, Hungary 2014
Abstract The present work deals with the study of the
reaction of hydrogen desorption from the CaSiHX hydride by
means of the calorimetric method. The dehydrogenation of
the CaSiHX hydride was carried out at 548 K. For a calori-
metric study, the installation composed of the differential
heat-conducting Tian–Calvet type calorimeter connected
with a conventional Sieverts-type apparatus was employed.
Such installation permitted us to obtain simultaneously the
P-X isotherms (P—equilibrium hydrogen pressure, X = H/
CaSi) and variation of the partial molar enthalpies of the
reaction of hydrogen desorption from CaSiHX with the
hydrogen concentration in the metallic matrix. It was ascer-
tained that in the CaSi-H2 system there was one region where
values of the partial molar enthalpy of the reaction of
hydrogen desorption from the CaSiHX hydride remained
constant. This means that formation of one hydride phase in
the CaSi-H2 system took place. The enthalpy and entropy
values for the reaction of hydrogen desorption from the
CaSiHX in the plateau range are DHdes = 53.8 1.2 -
kJ mol-1 H2 and DSdes = 94.2 2.7 J mol-1 H2 K-1
(DHdes and DSdes—the differential molar enthalpy and
entropy desorption, respectively).
Introduction
The economic advancement raised two burning problems
in front of humanity, which are necessary to determine: the
first is the ecological problem, associated with burning of
large amount of hydrocarbon fuel and discharge into the air
of CO2, and the second one is the exhaustion of world
resources of fossil energy carrier (petroleum, coal and
natural gas). The use of hydrogen as an ecologically pure
energy carrier could permit to decide these problems.
Therefore, scientists deal with the development of hydro-
gen energy, search of new compounds, which could be
used for reversible hydrogen storage.
Libowitz et al. [1] in 1958 showed that the ZrNi com-
pound easily and reversibly interacted with hydrogen that
led to the formation of the ZrNiH3 hydride. Later, the
structure of the ZrNi hydride was studied by means of
X-ray and neutron diffraction methods [2–9], and it was
determined that ZrNi and ZrNiHX crystallized into the
orthorhombic structure CrB (space group Cmcm). As well,
there are few works in which the thermodynamic properties
of the ZrNi hydride were calculated using the van’t Hoff
equation [10, 11] and measured directly by reaction calo-
rimetry [11–13]. Besides that in the works [5, 10, 14], it
was ascertained that intermetallic compounds (IMC) such
as HfNi, HfCo and ZrCo reversibly absorb hydrogen too.
Nemirovskaya and Lunin studied [14] phase transforma-
tions in the IMC having CrB-type structure such as ZrNi,
HfNi, ZrCo and HfCo during hydrogen sorption–desorp-
tion. And the reaction of hydrogen interaction with each of
these IMC was studied by thermodynamic methods [15]. In
the recent work, Jat et al. [16] studied the hydrogen
interaction with ZrCo plotting PCI’s and calculated the
thermodynamic parameters according to van’t Hoff equa-
tion. In addition, the authors found the activation energy
Keywords CaSi ꢀ Hydride ꢀ Calorimetry ꢀ
Thermodynamic ꢀ Desorption
E. Y. Anikina (&) ꢀ V. N. Verbetsky
Chemistry Department, Lomonosov Moscow State University,
Leninskie Gory, 1, Moscow 119991, Russia
e-mail: anikina@hydride.chem.msu.ru
123

802
E. Y. Anikina, V. N. Verbetsky
for the absorption of hydrogen by ZrCo (120 5 kJ mol-1
H2).
hydrogenation of CaSi took place under smaller values of
the hydrogen pressure, then CaSiH1 is obtained.
In the present work, we hydrogenated the CaSi sample
at 548 K and hydrogen pressure of 52 atm for 1 day before
each experiment.
The development of hydrogen storage materials makes
expert community to analyse the cost of materials from
which the sorbent is produced and its molecular weight
though scientists drew attention on alkaline-earth silicides.
It was found out that CaSi, SrSi and BaSi also crystallized
in the CrB-type structure [17–22] and reversibly reacted
with hydrogen [23, 24].
Results and discussion
Japanese scientists [25–27] hydrogenated CaSi simul-
taneously to Swiss ones [28, 29] and for the first time
studied hydrogen absorption by CaSi, and ascertained that
CaSi reversibly absorbed hydrogen. Japanese scientists
[25, 26] hydrogenated CaSi at 473 K and hydrogen pres-
sure of 9 MPa and then they desorbed hydrogen from the
obtained hydride CaSiH1.3 on a Seiverts-type apparatus at
three different temperatures.
X-ray analysis
According to XRD data, the synthesized CaSi sample had
the CrB-type structure (space group Cmcm). Small
amounts of CaO (0.82 mass%) and Ca14Si19 (1.77 mass%)
were found as minor phases. In addition, the X-ray analysis
of the CaSiHX sample was carried out after five cycles of
hydriding/dehydriding. The refined unit lattice parameters
for both samples are presented in Table 1 along with ref-
erence data.
The present work is devoted to the study of hydrogen
interaction with CaSi by the calorimetric method.
As one can see from Table 1, the results obtained in the
present work are in good agreement with the reference
data. A small expansion of lattice parameters of the sample
after five cycles of hydriding/dehydriding is due to the fact
that a part of hydrogen remained in the matrix of CaSi after
desorption, as hereof wrote in [25]. The crystal structure of
CaSi after five cycles hydriding/dehydriding remained
unchanged.
Experimental
A CaSi sample was prepared by melting a starting mixture
with the stoichiometric composition of Ca (purity 99.5 %)
and Si (purity 99.999 %) in a high-frequency induction
furnace under argon pressure of 2.0 atm. Then, the CaSi
sample was subjected to homogenization in a fused quartz
tube under residual argon pressure of 0.1 atm at 1,073 K
for 240 h and finally quenched in cold water.
Hydrogen interaction with CaSi
The sample of CaSi was examined by a powder X-ray
diffraction analysis with a DRON-4 diffractometer at room
temperature using monochromatic Cu Ka radiation, and the
diffraction patterns were analysed by the Rietveld method
with the computer program RIETAN [30].
In Fig. 1, the dependences of P-X-T (T—temperature of an
experiment) are presented for the reaction of hydrogen
desorption from the CaSiHX hydride for four different runs
of determination. As one can see from Fig. 1, the CaSi
sample absorbs 1.49 mass% hydrogen (548 K and 52 atm)
that corresponds to the stoichiometric ratio of
H/CaSi = 1.04 and formation of the CaSiH1.04 hydride (as
pointed out in Fig. 1). In the a-region during dehydroge-
nation, the equilibrium hydrogen pressure sharply decrea-
ses with decreasing of the hydrogen concentration in the
metallic matrix (see Fig. 1). At 548 K, hydrogen did not
desorb completely from the sample. Really in the work
[25], the authors showed the data according to which the
hydrogen concentration on the CaSi sample under study
after evacuation it at 473 K, and the hydrogen pressure
below 1 9 10-1 Pa was 0.2 mass%, that corresponded to
formation of the CaSiH0.13 composition.
In our work, we studied the reaction of hydrogen
desorption from the CaSiHX hydride by the calorimetric
method using the differential heat-conducting Tian–Calvet
type calorimeter connected with the conventional Sieverts-
type volumetric apparatus that permitted us to measure
simultaneously the P-X isotherms (P—equilibrium hydrogen
pressure, X = H/CaSi) and the relationship of the differen-
tial molar enthalpy versus the hydrogen concentration in the
metallic matrix (DHdes. = f(X)) of desorption reaction of
hydrogen with the sample under investigation. The appara-
tus scheme, the experimental procedure and the treatment of
obtained results were described elsewhere [31].
Previously, it was established [32] that according to the
conditions of hydrogen reaction with CaSi, two hydride
On the P-X isotherms obtained at 548 K, one can sep-
arate three regions: the a-solid solution of hydrogen in
CaSi (0 \ X \ 0.35), the region of two-phase coexistence
or ‘‘plateau’’ where the a $ ß transition takes place
(0.35 \ X \ 0.80) and the region of hydrogen solid solu-
tion in the ß-hydride of CaSiHX (X [ 0.80). For the first
phases may be obtained, namely, CaSiH1 and CaSiH1.2
,
which have different structures. The CaSiH1.2 hydride was
obtained when hydrogenation of the CaSi sample was
carried out at hydrogen pressure of 90 atm. If
123

Investigation of hydrogen desorption from CaSiH
803
Table 1 Lattice parameters (a, b, c) and cell volumes (V) of CaSi and CaSiHX with CrB-type structure (space group Cmcm)
3
˚
a/A
˚
b/A
˚
c/A
˚
V/A
Reference
CaSi
4.556(0)
4.5589(1)
4.5594(9)
4.559(1)
4.531(6)
4.5336(7)
10.74(0)
3.892(5)
3.8930(1)
3.8900(7)
3.890(1)
3.890(2)
3.8913(6)
190.44
190.35
190.33
189.67
191.31
191.22
This work
[24]
CaSi
10.7250(2)
10.731(1)
10.731(1)
10.854(1)
10.839(2)
CaSi
[21]
CaSi
[23]
CaSiH0.19 (after 5-th desorption)
CaSiH0.26 (after desorption)
This work
[24]
100
1
160
140
120
100
80
2
1
2
3
4
3
10
4
1
0
0.2
0.4
0.6
0.8
1
1.2
60
H/CaSi
0.1
40
20
0.01
0
0
0.2
0.4
0.6
0.8
1
1.2
Fig. 1 Desorption isotherms for the CaSi-H2 system at 548 K for
four runs
H/CaSi
Fig. 2 Desorption enthalpies versus composition for the CaSi-H2
system at 548 K for four runs
two runs of the hydrogen desorption, plateau on the
P-X isotherm is well defined and in practice there is no
slope (see Fig. 1). However, one peculiarity of the mea-
sured P-X-T dependence should be noticed, notably, every
new process of hydrogen desorption from the CaSiHX
hydride results in a slight increase of the plateau slope and
the length of plateau reduces, that is the a-region length
widens. In whole, the presented plot of the P-X-T is in good
agreement with the reference data [25, 26].
350
300
250
200
2
3
4
In Fig. 2, the plot of the DHdes = f(X) function (DHdes
—
150
100
the differential molar enthalpy of the reaction of hydrogen
desorption from the CaSiHX hydride) is obtained directly
by calorimetric measurements for four runs of experiments.
As one can see from the presented plot, there is one region
where the enthalpy values are constant that correlates with
the process of the hydride formation. The behaviour of the
curve of the DHdes = f(X) dependence in the a-region
should be noticed. For the first two runs of experiments, the
decrease of the hydrogen concentration in the metallic
matrix results in reduction of the enthalpies values in the
interval 0.10 \ X \ 0.15, while for the third and fourth
runs, the decrease of the hydrogen concentration in the
a-region results in the increase of the enthalpy values in the
interval 0.16 \ X \ 0.30. It may be assumed that during
the absorption/desorption process in the sample under
investigation, ‘‘traps’’ form. These traps have greater
affinity for hydrogen than the normal interstitial sites.
50
0
0
0.2
0.4
0.6
0.8
1
1.2
H/CaSi
Fig. 3 Desorption entropies versus composition for the CaSi-H2
system at 548 K for three runs
Flanagan et al. [33] suppose that the trapping sites most
probably arise from the imperfect nature of intermetallic
structure, i.e. metal atoms in wrong positions. The same
trapping phenomenon is observed for LaNi5 [34] and ZrNi
[35]. In the range of the hydrogen solution in the ß-hydride,
the enthalpy values sharply decrease with the rise of the
hydrogen concentration in the metallic matrix.
123

804
E. Y. Anikina, V. N. Verbetsky
Fig. 4 The shape of curves of
heat generation for hydrogen
desorption from the CaSi-H2
system obtained in different
parts of this system: a hydrogen
solid solution in the b-hydride,
b a-region, c plateau region
(a $ b)
a
b
V/mV
V/mV
0
0.5
1.0
0
0.5
1.0
1.5
Time/h
Time/h
c
V/mV
0
0.5
1.0
1.5
2.0
2.5
3.0
Time/h
Figure 3 shows the DSdes-X dependence (DSdes—the
differential molar entropy of hydrogen desorption from the
CaSiHX hydride). The values of DSdes were calculated on
the basis of the calorimetric data and the data obtained
from the P-X measurements according to the following
equation:
formation of CaSiH1.3 was estimated as -42 kJ mol-1 H2
from the calculation based on crystal structure symmetry
determined by the Rietveld refinements of synchrotron
X-ray diffraction data and -27 kJ mol-1 H2 for the for-
mation of monohydride CaSiH. It may be connected with
either the past history of the sample or the feature behav-
iour of the hydrogen absorption–desorption reaction.
It is worthwhile to draw attention to one feature that we
noticed during our calorimetric study of the hydrogen
desorption from CaSiHX. The duration of the experiment
was different depending on which part of the CaSi-H2
system the reaction of hydrogen desorption took place,
namely, if hydrogen was desorbed from the dilute a-solu-
tion, the reaction would finish in 1.0–1.5 h; the reaction of
hydrogen desorption from the hydrogen solid solution in
the b-hydride finished in 0.5–1.0 h after removing the next
portion of hydrogen. If the reaction of the hydrogen
desorption takes place in the plateau region, then it would
finish in 2.5–3.0 h. To illustrate the above-described situ-
ation in Fig. 4, the shape of curves of heat generation is
presented for three parts we mentioned. It should be noted
that on the shape of curve corresponding to the reaction in
the plateau region, there is some inflection that testifies
about the complex character of reaction of the hydrogen
desorption from the CaSi-H2 system in the current region.
DHdes
DSdes
¼
þ R ln PH2des
:
ð1Þ
T
In the Fig. 3, the plots of the DSdes-X dependences were
presented for three runs of the carried out desorption
experiments (for 2nd, 3rd and 4th). As seen from Fig. 3,
there is one region with the constant entropy values on the
plot of the DSdes-X dependence (0.25 \ X \ 0.85). The
increase in the hydrogen concentration (X [ 0.85) leads to
a sharp decrease of the entropy values. In the a-region, the
same picture as for the DHdes = f(X) is observed, namely,
the entropy values of the second run decrease with the
decreasing hydrogen concentration in the range
0.10 \ X \ 0.15 in the metallic matrix, and on the con-
trary, the entropy values collected in the third and forth
runs increase with the decreasing hydrogen concentration
in the range 0.16 \ X \ 0.30.
The average values of enthalpy and entropy desorption
in the plateau region at 548 K are equal to
53.7 1.2 kJ mol-1 H2 and 94.2 2.7 J mol-1 H2 K-1
,
respectively. These results differ from those obtained from
earlier studies—in Aoki et al. [25, 26] for CaSiH1.3 the
authors calculated the enthalpy and entropy of the hydride
formation using the van’t Hoff plot and obtained the data as
-62 kJ mol-1 H2 and -116 mol-1H2 K-1, respectively,
and in Ohba et al. [27], the enthalpy of the hydride
Conclusions
1. For the first time, the hydrogen interaction with CaSi
was studied by the calorimetric method.
123

Investigation of hydrogen desorption from CaSiH
805
16. Jat RA, Parida SC, Nuwad J, Agarwal R, Kulkarni SG. Hydrogen
sorption-desorption studies on ZrCo-hydrogen system. J Therm
Anal Calorim. 2013;112:37–44. doi:10.1007/s10973-012-2783-7.
17. Hellner E. Die Kristallstrukture des CaSi. Z Anorg Allgen Chem.
1950;261:226–36.
2. The dependences of P-X, DHdes-X and DSdes-X were
obtained at 548 K for the CaSi-H2 system. The average
values of the enthalpy and entropy for the reaction of
the hydrogen desorption in the plateau region are
DHdes = 53.7 1.2 kJ mol-1 H2 and DSdes = 94.2
2.7 J mol-1 H2 K-1, respectively.
¨
18. Rockaschel G, Weiss A. ZurKenntnis der Strontiumsilicide.
Z Anorg Allg Chem. 1962;316:231–6.
19. Burnasheva VV, Gladyshevskii EI. Crystal structures of the BaSi
and BaGe compounds. Izv Nauk SSSR Neorg Mat. 1966;2:944–5.
20. Merlo F, Fornasini ML. CrB-type equiatomic compounds of
europium, ytterbium and alkaline-earth metals with Si, Ge, Sn,
Pb. J Less Common Met. 1967;13:603–10.
3. It was established on the basis of the obtained curves
of the heat generation that the process of the hydrogen
desorption from the CaSi-H2 system in the plateau
region has a complex character.
´
21. Rieger W, Parthe E. Alkaline earth silicides, germanides and stan-
nides with CrB structure type. Acta Crystallogr. 1967;22:919–22.
22. Currao A, Corda J, Nesper R. Can one design zintl anions?
Contributions from the system Sr/Mg/Si to the topic Si2-
Z Anorg Allg Chem. 1996;622:85–94.
.
References
¨
23. Armbruster M, Worle M, Krumeich F, Nesper R. Hydrogen
uptake in binary CrB-type silicides of Ca, Sr, Ba and Eu. In:
Proceedings of the 16th World Hydrogen Energy Conference.
Lyon, France, 13–16 June 2006.
1. Libowitz GG, Hayes HF, Gibb TRP. The system zirconium-
nickel and hydrogen. J Phys Chem. 1958;62:76–9.
2. Korst WL. The crystal structure of ZrNiH3. J Phys Chem.
1962;66:370–2.
¨
24. Armbruster M, Worle M, Krumeich F, Nesper R. Structure and
properties of hydrogenated Ca, Sr, Ba and Eu silicides. Z Anorg
Allg Chem. 2009;635:1758–66. doi:10.1002/zaac.200900220.
25. Aoki M, Ohba N, Noritake T, Towata S. Reversible hydriding
and dehydriding properties of CaSi: potential of metal silicides
for hydrogen storage. J Appl Phys Lett. 2004;85:387–8. doi:10.
1063/1.1773930.
26. Aoki M, Ohba N, Noritake T, Towata S. Hydriding and dehyd-
riding properties of CaSi. J Alloy Compd. 2005;404–6:402–4.
doi:10.1016/j.jallcom.2004.11.104.
3. Peterson SW, Sadama VN, Korst WL. Neutron diffraction study
of nickel zirconium hydride. J Phys (Paris). 1964;25:451–3.
4. Kirkpatrick ME, Bailey DM, Smith JE. The structures of NiZr2,
NiZr and their hafnium analogs. Acta Crystallogr. 1962;15:252–5.
5. Van Essen RM, Buschow KHJ. Hydrogen absorption in various
zirconium-and hafnium-based intermetallic compounds. J Less
Common Met. 1970;64:277–84.
6. Westlake GD. Stoichiometries and interstitial site occupation in
the hydrides of ZrNi and other isostructural intermetallic. J Less
Common Met. 1980;75:177–85.
7. Westlake DG, Shaked H, Mason PR, McCart BR, Mueller MH,
Matsumoto T, Amano M. Interstitial site occupation in ZrNiH.
J Less Common Met. 1982;88:17–23.
8. Jacob I, Bloch JM. Interstitial site occupation of hydrogen atoms
in intermetallic hydrides: ZrNiHX case. Solid State Commun.
1982;42:541–5.
27. Ohba N, Aoki M, Noritake T, Miwa K, Towata S. First-principles
study of a hydrogen storage material CaSi. J Phys Rev B.
2005;72:075104. doi:10.1103/PhisRevB.72075104.
28. Reinoso M. Untersuchungenzu Wasserstoffspeicherung in aus-
¨
gewahltenanorganischen Materialien. ETH, Zurich, Dissertation,
No. 15781, 2005.
¨
¨
29. Armbruster M, Worle M, Krumeich F, Nesper R. Binary CrB-type
silicides as hydrogen storage materials. Chimia. 2006;60:409.
30. Izumi F. Rietveld analysis and MEM-based whole-pattern fitting
under partial profile relaxation. J Rigaku. 2000;17–1:34–45.
31. Anikina EY, Verbetsky VN. Calorimetric investigation of the
hydrogen interaction with Ti0.9Zr0.1Mn1.1V0.1. J Alloy Compd.
2002;330–332:45–7.
9. Benham MJ, Browne JD, Ross DK. Inelastic neutron scattering
from ZrNiHX. J Less Common Met. 1984;103:71–80.
10. Kost ME, Padurets LN, Chertkov AA, Mikheeva VI. Isotherms of
dissociation in the ZrNi-H2(D2) and ZrCo-H2(D2) systems. Russ J
Inorg Chem. 1980;25:471–3.
11. Luo W, Craft A, Kuji T, Chung HS, Flanagan TB. Thermody-
namic characterization of the Zr-Ni system by reaction calorim-
32. Wu H, Zhou W, Udovic TJ, Rush JJ, Yildirim T. Structure and
hydrogen bonding in CaSiD1?X: issues about covalent bonding.
Phys Rev B. 2006;74:224101. doi:10.1103/PhysRevB.74.224101.
33. Flanagan TB, Wulff CA, Bowerman BS. Thermodynamics of
hydrogen trapping in intermetallic compounds: application to
LaNi5/H. J Solid State Chem. 1980;34:215–21.
34. Murray JJ, Post ML, Taylor JB. The thermodynamics of the
LaNi5-H2 system by differential heat flow calorimetry 1: tech-
niques; the a ? ß two-phase region. J Less Common Met.
1981;80:201–9.
etry and p-c-T measurements.
1990;162:251–66.
J
Less Common Met.
12. CantrellJS, Bowman RCJr, Wade LA, Luo S, Clewley JD, Flanagan
TB. Thermodynamic properties and the degradation of ZrNiHX at
elevated temperatures. J Alloy Compd. 1995;231:518–23.
13. Danzer P, Millet P, Flanagan TB. Thermodynamic characteriza-
tion of hydride phase growth in ZrNi-H2. Metall Mater Trans A.
2001;32:29–38.
14. Nemirovskaya IE, Lunin VV. Phase transitions in intermetallic
compounds of CrB-type structure during hydrogen sorption.
J Alloy Compd. 1994;209:93–7.
35. Flanagan TB, Clewley JD, Kuji T, Park C-N, Everett DH. Iso-
baric and isothermal hysteresis in metal hydrides and oxides.
J Chem Soc Faraday Trans. 1986;1(82):2589–604.
15. Nemirovskaya IE, Alekseev AM, Lunin VV. Thermodynamics of
processes of hydrogen sorption by hydrides of intermetallic of
CrB structural type. J Alloy Compd. 1991;177:1–15.
123