Thin film nanopores (V, 10Ti)NxHy hydrogen storages
This scientific paper delves into the findings of the investigation carried out to determine the adsorption and electrophysical characteristics of nanoporous (V, 10 at.% Ti)Nx films obtained using the ion beam-assisted deposition technique (IBAD). It has been shown that these films can accumulate mo...
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Guglya, A.G. Marchenko, Yu.A. Melnikova, E.S. Vlasov, V.V. Zubarev, E.N. 2015-04-09T12:35:14Z 2015-04-09T12:35:14Z 2014 Thin film nanopores (V, 10Ti)NxHy hydrogen storages / A.G. Guglya, Yu.A. Marchenko, E.S. Melnikova, V.V. Vlasov, E.N. Zubarev // Вопросы атомной науки и техники. — 2014. — № 2. — С. 162-166. — Бібліогр.: 15 назв. — англ. 1562-6016 PACS: 81.15Jj;72.15 Eb;81.07Bc https://nasplib.isofts.kiev.ua/handle/123456789/79964 This scientific paper delves into the findings of the investigation carried out to determine the adsorption and electrophysical characteristics of nanoporous (V, 10 at.% Ti)Nx films obtained using the ion beam-assisted deposition technique (IBAD). It has been shown that these films can accumulate more than 7 wt.% hydrogen at a relatively low pressure of 0,5 MPa. One part of it is accumulated in the grain boundaries and pores but another one forms the hydride phase. A complete release of hydrogen occurs at a temperature of 250 °C. During the hydrogen desorption the specific resistivity of (V, 10Ti)NxHy films is roughly increased by a factor of 10⁷. Приведены результаты исследований адсорбционных и электрофизических характеристик нанопористых пленок (V, 10 ат.% Ti)Nx, полученных с применением технологии ионно-стимулированного осаждения. Использование данной технологии позволило получить нанокристаллическую структуру, межзеренное пространство в которой заполнено порами размером менее 6 нм. Показано, что при относительно низком давлении (0,5 МПа) такие объекты могут аккумулировать более 7 вес.% водорода. Одна часть его накапливается в межзеренных границах и порах, другая часть – в виде гидридной фазы. Полное выделение водорода происходит при температуре 250 ºС. В процессе десорбции водорода удельное электросопротивление (V, 10Ti)NxHy-пленок увеличивается примерно в 10⁷ раз. Приведено дані досліджень адсорбційних та електрофізичних характеристик (V, 10 ат.% Ti)Nx нанопорових плівок, здобутих за допомогою технології іонно-стимульованого осадження. Використання даної технології дозволило створити нанокристалічну структуру, міжзеренних простір в якій заповнений порами розміром не більше 6 нм. Виявлено, що при відносно низькому тиску (0,5 МПа) такі об’єкти можуть акумулювати більш ніж 7 ваг.% водню. Одна його частина накопичується у міжзеренному просторі, а інша – у вигляді гідридної фази. Повне виділення водню має місце при температурі 250 ºС. У процесі десорбції водню питомий електроопір (V, 10Ti)NxHy-плівок збільшується приблизно у 10⁷ разів. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Физика радиационных и ионно-плазменных технологий Thin film nanopores (V, 10Ti)NxHy hydrogen storages Тонкопленочные нанопористые (V, 10Ti)NxHy-накопители водорода Тонкоплівкові нанопорові (V, 10Ti)NxHy-накопичувателі водню Article published earlier |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| title |
Thin film nanopores (V, 10Ti)NxHy hydrogen storages |
| spellingShingle |
Thin film nanopores (V, 10Ti)NxHy hydrogen storages Guglya, A.G. Marchenko, Yu.A. Melnikova, E.S. Vlasov, V.V. Zubarev, E.N. Физика радиационных и ионно-плазменных технологий |
| title_short |
Thin film nanopores (V, 10Ti)NxHy hydrogen storages |
| title_full |
Thin film nanopores (V, 10Ti)NxHy hydrogen storages |
| title_fullStr |
Thin film nanopores (V, 10Ti)NxHy hydrogen storages |
| title_full_unstemmed |
Thin film nanopores (V, 10Ti)NxHy hydrogen storages |
| title_sort |
thin film nanopores (v, 10ti)nxhy hydrogen storages |
| author |
Guglya, A.G. Marchenko, Yu.A. Melnikova, E.S. Vlasov, V.V. Zubarev, E.N. |
| author_facet |
Guglya, A.G. Marchenko, Yu.A. Melnikova, E.S. Vlasov, V.V. Zubarev, E.N. |
| topic |
Физика радиационных и ионно-плазменных технологий |
| topic_facet |
Физика радиационных и ионно-плазменных технологий |
| publishDate |
2014 |
| language |
English |
| container_title |
Вопросы атомной науки и техники |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| format |
Article |
| title_alt |
Тонкопленочные нанопористые (V, 10Ti)NxHy-накопители водорода Тонкоплівкові нанопорові (V, 10Ti)NxHy-накопичувателі водню |
| description |
This scientific paper delves into the findings of the investigation carried out to determine the adsorption and electrophysical characteristics of nanoporous (V, 10 at.% Ti)Nx films obtained using the ion beam-assisted deposition technique (IBAD). It has been shown that these films can accumulate more than 7 wt.% hydrogen at a relatively low pressure of 0,5 MPa. One part of it is accumulated in the grain boundaries and pores but another one forms the hydride phase. A complete release of hydrogen occurs at a temperature of 250 °C. During the hydrogen desorption the specific resistivity of (V, 10Ti)NxHy films is roughly increased by a factor of 10⁷.
Приведены результаты исследований адсорбционных и электрофизических характеристик нанопористых пленок (V, 10 ат.% Ti)Nx, полученных с применением технологии ионно-стимулированного осаждения. Использование данной технологии позволило получить нанокристаллическую структуру, межзеренное пространство в которой заполнено порами размером менее 6 нм. Показано, что при относительно низком давлении (0,5 МПа) такие объекты могут аккумулировать более 7 вес.% водорода. Одна часть его накапливается в межзеренных границах и порах, другая часть – в виде гидридной фазы. Полное выделение водорода происходит при температуре 250 ºС. В процессе десорбции водорода удельное электросопротивление (V, 10Ti)NxHy-пленок увеличивается примерно в 10⁷ раз.
Приведено дані досліджень адсорбційних та електрофізичних характеристик (V, 10 ат.% Ti)Nx нанопорових плівок, здобутих за допомогою технології іонно-стимульованого осадження. Використання даної технології дозволило створити нанокристалічну структуру, міжзеренних простір в якій заповнений порами розміром не більше 6 нм. Виявлено, що при відносно низькому тиску (0,5 МПа) такі об’єкти можуть акумулювати більш ніж 7 ваг.% водню. Одна його частина накопичується у міжзеренному просторі, а інша – у вигляді гідридної фази. Повне виділення водню має місце при температурі 250 ºС. У процесі десорбції водню питомий електроопір (V, 10Ti)NxHy-плівок збільшується приблизно у 10⁷ разів.
|
| issn |
1562-6016 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/79964 |
| citation_txt |
Thin film nanopores (V, 10Ti)NxHy hydrogen storages / A.G. Guglya, Yu.A. Marchenko, E.S. Melnikova, V.V. Vlasov, E.N. Zubarev // Вопросы атомной науки и техники. — 2014. — № 2. — С. 162-166. — Бібліогр.: 15 назв. — англ. |
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162 ISSN 1562-6016. ВАНТ. 2014. №2(90)
THIN FILM NANOPORES (V, 10Ti)NxHy HYDROGEN STORAGES
A.G. Guglya, Yu.A. Marchenko, E.S. Melnikova, V.V. Vlasov, E.N. Zubarev*
National Science Center “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine;
*National Technical University “Kharkov Polytechnic Institute”, Kharkov, Ukraine
E-mail: guglya@kipt.kharkov.ua
This scientific paper delves into the findings of the investigation carried out to determine the adsorption and
electrophysical characteristics of nanoporous (V, 10 at.% Ti)Nx films obtained using the ion beam-assisted
deposition technique (IBAD). It has been shown that these films can accumulate more than 7 wt.% hydrogen at a
relatively low pressure of 0,5 MPa. One part of it is accumulated in the grain boundaries and pores but another one
forms the hydride phase. A complete release of hydrogen occurs at a temperature of 250 °C. During the hydrogen
desorption the specific resistivity of (V, 10Ti)NxHy films is roughly increased by a factor of 107.
PACS: 81.15Jj;72.15 Eb;81.07Bc
INTRODUCTION
Development of storage devices for the fuel cells
of battery-driven vehicles requires the use of compact
and lightweight materials with high hydrogen
capacity. Therefore, single-component and complex
hydrides based on lightweight metals (Mg, Ca, Na,
Al, Be) provoke interest not only because of their
tendency to accumulate a considerable amount of
hydrogen but also because of substantial weight
percentage of hydrogen contained in hydrides of
these metals. It is also known that vanadium is a
relatively light transition metal and the vanadium-
based hydride can also be used for the fabrication of
hydrogen storage devices. It has low hydrogen
desorption temperature (~ 40 °C) and accumulates it
in amounts comparable with those accumulated by
porous and metal-organic structures. In addition, it is
very important that the amount of absorbed hydrogen
atoms (in the unit of volume) in VH2 is considerably
higher than, for example, in MgH2.
The V-H system is characterized by availability of
the following phases: α, ά is the solid solution,
β-(VH0.45-VH0.95) and γ-VH2. In the region of the
VH1,0-VH2,0 concentrations there is a mixture of
β+γ-phases. In the homogeneity region of β-phase the
ordered structures of V2H, V3H2, and V4H3 have been
revealed. The VH2-phase is less stable than the
β-phase. The hydrogen adsorption/desorption reacti-
on VH + 1/2H2 ↔ VH2 occurs at moderate tempera-
ture and pressure. As a result only half of hydrogen
adsorbed by vanadium can roughly be used for the
reverse adsorption/desorption process.
A diffusion mobility of hydrogen in metals with
the bcc lattice is much higher than in metals with fcc
and face-centered close-packed lattices. Moreover,
the hydrogen mobility is higher in vanadium than in
niobium and tantalum with the fcc lattice. According
to the data given in the paper [1] diffusion activation
energy in ά-VHx at х = 0.17-0.38 varies in the range
of 0.087…0.132 eV/at. (10…15.2 kJ/mole). In the
0.486<х<0.736 range, where the β-phase exists
energy remains virtually unchanged, i.e.
0.230…0,240 eV/аt. [2].
The data given above refer only to traditional
polycrystalline materials. Orimo S. et al. [3] showed
in what way the absorption kinetics of hydrogen in
vanadium can be improved for nanocrystalline films.
Vanadium was milled in the ball mill in the hydrogen
atmosphere during 5, 10 and 60 min. As a result were
obtained specimens with the grain size of 80, 30 and
10 nm, respectively. Mass-spectrometry and nuclear
magnetic resonance data showed that a decrease in
the grain size results in the cardinal enthalpy
reduction of diffusion processes.
The situation can still be improved if the VHх
hydride is altered to the nitrogen – containing VNхHу
hydride through the addition of nitrogen in the
amount required for the formation of such a chemical
compound as VNx. Vanadium nitride has the fcc
lattice which is more close-packed in comparison
with the bcc lattice, and this would improve nitride
phase stability. The paper [4] showed that the
bonding energy between the vanadium atoms and the
NH2 compound was equal to 142 kJ/mole, which is
sufficient to provide the nitride phase stability.
However, the complex hydride of a stochiometric
composition won’t be able to provide accumulation
of the required amount of hydrogen alone and release
it at low temperatures. Using the Ti-C compound as
an example, the authors of the paper [5] showed that
the TiC0.6 ceramics has the highest gravimetric
capacity (up to 2.9 wt.%) and acceptable kinetics of
hydrogen desorption. The lattice sites that were not
occupied by carbon atoms create the required
vacancy super saturation, which provides a high
hydrogen diffusion coefficient. In addition, such
“carbon” vacancies are capable of retaining up to 4
hydrogen atoms [6], which permits to accumulate a
large quantity of hydrogen at room temperature.
Therefore, in order to get a material capable of ad-
sorbing at least 6 wt.% H2 it is insufficient to design
nitride or carbide ceramics with under saturated
nitrogen or carbon bonds. It is necessary to form such
a nanocrystalline structure whose intergranular space
would contain additional pore-like traps that would
adsorb hydrogen in its molecular state. The intergra-
nular boundaries should provide a reasonable
hydrogen adsorption and desorption kinetics.
1. EXPERIMENT STATEMENT
Traditional equilibrium methods used for the
creation of nitrogen-containing complex hydrides
include the production of material powders or their
hydrides with their further milling in hydrogen or
ISSN 1562-6016. ВАНТ. 2014. №2(90) 163
ammonia atmospheres for many hours. Such
materials consist of crystallites that originate, in their
turn, from grains whose size varies in the range of
several microns to 10 nm. The intergranular
boundaries have a width of approximately 1nm.
The previous papers [7, 8] showed that using
IBAD we can produce VNxHy and (V, Ti)NxHy
nanoporous films that can adsorb up to 7.4 wt.%
hydrogen. In addition, the methods of neutron
spectroscopy showed that most pores have relatively
large size of 7 to 14 nm. These pores are not of vacuum
type and have been partially filled with nitrogen. It has
been established that the kinetics and thermodynamics
of hydrogen desorption from such pores still require
improvement. Thus, the size of 7 to 14 nm characterizes
not so much hydrogen capacity of nanoporous complex
vanadium hydrides as the amount of the excess nitrogen
in the material. During the adsorption of hydrogen in
such a structure a certain portion of it fills free space
inside the pores occupied by nitrogen. A certain portion
dissociates on the pore surface and forms the hydride
VNxHy-phase. Naturally, if the pores having such a size
were of a vacuum type we could hardly expect the
retention of such an amount of hydrogen from them at
room temperature.
In order to improve kinetic and thermodynamic
characteristics of hydrogen desorption we deposited
(V, 10 at.%Ti)Nх films of 1 μm thick with the grain size
of 15 to 20 nm in ion bombardment conditions. The
plates made of polished sapphire monocrystal of 1 mm
thick were used as the substrates.
The pore size was determined using the data of
transmission electron microscopy. Fig. 1 gives the
images of (V, 10Ti)Nх films at the initial growth stage
(a) and at the final growth stage (b). In the latter case
the film was thinned to a required thickness using the
ion beam. The estimated size of pores did not exceed
6 nm. The pores are mainly located at intergranular
junctions. They mainly have a shape elongated along
the boundaries, as a result the width of most boundaries
is increased (see Fig. 1,a). The grain boundary structure
of the formed film is slightly different. However, the
boundary width is virtually the same across the grain
perimeter. Notably, we can assert that the porous zone
envelops almost the entire space around the grains.
a b
Fig. 1. (V, 10Ti)Nx film structure: a – at the initial deposition stage (estimated film thickness of 20 nm),
b – at the final stage (of 1 μm thick)
It is known [9-11] that the definition of the
adsorption capacity of materials with a bcc lattice that
can capture oxygen-containing molecules requires their
obligatory preliminary activation. Usually this is
realized through the heating of a specimen in a vacuum
up to a temperature of 400 to 450 °С during 1 to
2 hours, with injection of hydrogen into the chamber
and subsequent cooling. Such a procedure is repeated
until the specimen starts to intensively adsorb hydrogen,
which is controlled by a change in pressure inside the
specimen-containing chamber.
This method is used in the case when the volume of
the test material allows for the accumulation of
hydrogen in amounts sufficient for the measurement by
available sensors. The volume of films studied by us is
rather low; therefore ordinary manometers fail to
reliably register a change in pressure caused by
hydrogen adsorption. Therefore, in order to control the
activation process we measured the resistivity value of
(V, 10Ti)Nх films during their annealing and hydrogen
saturation. In nanocrystalline films whose intergranular
boundaries contain pores the resistivity value depends
not only on the size of grains and pores, but also on the
amount of gas captured by the pores during their
formation or saturation. In our case the main gas
component in non activated films is nitrogen [7].
Therefore, the change of this value during annealing and
exposure to hydrogen environment can be used as a
parameter that defines the degree of activation of this
material. The availability of interrelation between the
change in the resistivity of thin “dense” films and
hydrogen adsorption kinetics was repeatedly noticed
earlier [12, 13].
In our experiments the start time of the activation of
nonporous (V, 10Ti)NхHу films was recorded by a
change in their resistivity after their heating up to
400 ºС and hydrogen injection up to 0.8 MPa. The
purpose of this experiment was to remove nitrogen
(oxygen) molecules from the intergranular boundaries
and replace them with hydrogen molecules.
Fig. 2 shows the change in the value of specific
resistivity of (V, 10Ti)NхHу films during their annealing
and injection of hydrogen into the chamber. It can be
seen that an increase in the annealing temperature
results in a slight decrease in the specific resistivity
(negative temperature coefficient of resistance). During
the injection of hydrogen at 400 °С up to the pressure of
0.8 MPa an insignificant increase in resistance is
164 ISSN 1562-6016. ВАНТ. 2014. №2(90)
observed. At a pressure of 0.8 MPa a stepwise more
than 102 times increase in resistance is observed. During
further cooling of the sample its resistance is reduced to
the initial value. At the repeated annealing a decrease in
resistance occurs only up to a temperature of 50 °С.
Starting from this temperature value a sequential
increase in resistance is observed. At a temperature of
300 °С the specific resistance in films exceeds its initial
value 105 times (not show on the Fig. 2).
0 100 200 300 400 500 600 700
0
20
40
60
80
100
120
140
160
180
200
R
, х
10
-4
oh
m
⋅cm Н
2
puffing
t, min
60
T, оС
0 2 2,5 4 6 10 16 17 21 55 60
60 20 20
Fig. 2. The changing in the value of specific resistivity
of (V,10Ti)NхHу films during their annealing and
injection of hydrogen into the chamber
After the activation (V, 10Ti)Nх films were saturated
by hydrogen in the chamber preliminary evacuated to
the pressure of ~ 10-5 mm Hg, at 200 °С and a pressure
of 0.5 MPa (1 hour).
2. RESEARCH RESULTS
2.1. HYDROGEN DESORPTION
To study the hydrogen desorption we fabricated
special stand that represents a system of two vacuum
chambers separated from each other by the valve whose
volumes are correlated as 1:10. The chamber of a
smaller size was used for the saturation of specimens
with hydrogen, and also for annealing and resistivity
measurement. While studying the hydrogen desorption
the valve between the chambers was opened and both of
them were evacuated to the pressure not worse than
10-4 mm Hg. After that the valve connecting both
chambers with the high-vacuum pump was closed and
the specimens were exposed to annealing. The amount
of hydrogen released during the annealing was recorded
with a change in pressure, which, in its turn, was
measured by the vacuum sensor. A total volume of
chambers and film mass were selected so as to ensure
the harmony of the entire pressure range measured by
the sensor, in terms of the number of hydrogen
molecules, with the hydrogen weight percentage range
of 0.5 to 10.
Fig. 3 (curve 1) gives the released hydrogen amount
versus annealing temperature curve. It is seen that the
hydrogen desorption starts already at 30 °С. At 200 °С
the number of the molecules of the desorbed hydrogen
reaches1.5·1019 Н2 (3.5 wt.%). A further increase in
temperature results in the marked increase in hydrogen
release rate (3.5 wt.%). On reaching 250 оС the total
mass of the released hydrogen exceeds 7 wt.%.
While cooling the specimen (curve 2) a decrease in
pressure inside the working chamber is observed
starting from 130 °С, which is indicative of that the
portion of released hydrogen is readsorbed by the
(V, 10Ti)Nх film. Total decrease in pressure inside the
chamber during cooling to 20 °С corresponds to the
absorption of 8·1018 hydrogen molecules, which
corresponds to 2 wt.% Н2.
0 25 50 75 100 125 150 175 200 225 250 275 300
0
4
8
12
16
20
24
28
32
H
2,
x
1
018
ToC
3
2
1
4
0
1
2
3
4
5
6
7
8
W
t.
%
H
2
Fig. 3. The relationship of the change in the amount of
hydrogen in the annealing chamber during heating (1)
and cooling (2) of the (V, 10Ti)NxHy film.
The repeated heating (3) and cooling (4)
To prove this statement we exposed the films to
repeated annealing. Fig. 3 (curve 3, 4) shows the change
in the pressure in the annealing chamber during the
repeated heating and cooling of the films. It can be seen
that the amount of released hydrogen is close to the
value of 2 wt.%. During the cooling the film reabsorbs
hydrogen.
It should be noted that during the repeated cooling of
the films (without previous hydrogen saturation)
hydrogen absorption in amount of 2 wt.% takes place at
a total pressure in the chamber not more than
2·10-1 mm Hg. The adsorption of hydrogen in such
amount at such a low pressure can be indicative of that
the film surface and the system of intergranular
channels and pores have not been “poisoned” by
oxygen-containing molecules. At such conditions the
absorption of molecular hydrogen by open intergranular
porosity can occur at partial hydrogen pressures lower
than 2·10-1 mm Hg.
2.2. RESISTIVITY
Taking into consideration uncommon structure state
of hydrogen storages based on complex vanadium
hydride the change of such parameter as the resistivity
value during heating can provide additional information
about the gas release kinetics. For the multicomponent
materials the polycrystalline-to-nanocrystalline state
transition is usually accompanied by a decrease in the
value of the temperature coefficient of resistance (TCR).
The availability of intergranular pores in such a
structure results in the origination of a tunneling
conduction mechanism and as a consequence TCR
changes its positive sign for negative. In nanocrystalline
VNхHу materials interganular boundaries and nanopores
absorb and release hydrogen in large amounts. The
resistivity value of such a material can be a function not
only of the grain size and pores but also of the amount
of gas adsorbed by the pores.
ISSN 1562-6016. ВАНТ. 2014. №2(90) 165
The resistance of the complex hydrides studied in
the paper [7] was within (4·103 ± 200) μΩ·cm, which is
much higher in comparison with that of a powder
material (85 μΩ·cm). TCR has a negative value equal to
– (2…3)·10-4 degrees-1 in the temperature range up to
600 °С. During the hydrogen saturation of the material
the resistance increased to (6.5…7.0)·103 μΩ·cm, and
during the annealing at a temperature of up to 500 °С a
decrease in resistance ([7], Fig. 5) was observed. The
authors arrived at a conclusion that hydrogen is
absorbed by the pores and it also forms a hydride phase.
During the annealing hydrogen is released only from the
pores. The occupancy of the pores with nitrogen is not
changed.
A decrease in the grain size and pore diameter in the
(V, 10Ti)Nх films that were investigated in this paper
resulted in the resistivity increase up to
(5…6)·104 μΩ·cm and TCR decreased to
(3…4)·10-5 degrees-1. In addition, the film resistance
versus annealing temperature curve of hydrogen
absorbed (200 ºC, 0.5 MPa, 1 hour) films has also
changed (Fig. 4). (Resistivity and hydrogen pressure
were measured simultaneously during the annealing).
0 50 100 150 200 250 300
0,01
0,1
1
10
100
1000
10000
100000
1000000
R
, o
hm
⋅c
m
T, oC
HeatingCooling
Fig. 4. The change in the (V, 10Ti)NхНу film resistivity
during its heating and cooling
The Figure shows that the negative sign of TCR
exists only until the temperature of ~ 40 °С. In the
temperature range of 40 to 150 ºС approximately a two-
fold increase in resistivity is observed. A further
increase in temperature resulted in giant resistivity
jumps. At 300 °С the resistivity of the (V, 10Ti)NхНу
film exceeded the value of 105 Ω·cm. During the
specimen cooling the resistance practically acquires its
initial value. We can explain this by the adsorption of
hydrogen from the chamber volume.
The increasing of the resistivity of the
(V, 10Ti)NхНу film is correlated with increasing of
hydrogen desorption (see Fig. 3). From our point of
view it is indicated that an increase in the annealing
temperature results in the complete evacuation of
hydrogen from the intergranular boundaries and pores.
As a result, the space between the grains becomes
practically impassable for conductivity electrons, which
results in the giant increase in the resistivity. During the
cooling the conduction of the (V, 10Ti)Nх Ну film is
virtually restored due to the reverse hydrogen
absorption from the chamber.
3. DISCUSSING OF THE RESULTS
Thin-film structures based on vanadium complex
hydrides are not just porous or “bulk”. In spite of the
fact that heir density is very close to that of the bulk
vanadium nitride (4.5…5.0 g/cm3) the level of porosity
reaches 30% and the specific area of the pore surface
reaches 15…2 m2/g. This is possible due to the fact that
the materials used by us combine small grain size with a
high density of intergranular pores. The density of such
pores exceeds 1018 сm-3. Actually all intergranular joints
contain pores.
The configuration of intergranular pores in our film
structures is not just a system of voids that directly
traverse each other (it is peculiar for metal-&-organic
and carbon film structures). In our case the pores are
interconnected by relatively long (~ 10 nm)
intergranular boundaries, whose width does not exceed
1 nm. This value is very closely related to the most
optimal (0.6 nm) design size at which hydrogen will be
retained in its molecular state [14]. The availability of
such branched pore system connected by narrow and
long channels provides fast delivery of molecular
hydrogen to the film volume and its retention at room
temperature.
The next stage, i.e. when the pores and intergranular
boundaries turn out to be filled with molecular
hydrogen, originates the second step of hydrogen
adsorption. The dissociation of hydrogen molecules, the
diffusion of atomic hydrogen and the formation of
hydride phase VNxHy occur at the pore-grain
boundaries. Thanks to the small grain size this process
passes rather quickly and at low pressures.
It is known [4] that the stability of such complex
hydrides as VNH2 and TiNH2 is rather high (142 and
121 kJ/mole) therefore the hydrogen desorption can
hardly be expected in that temperature range, in which it
occurs in our experiments. In addition the coefficient of
hydrogen diffusion in such nitrides of stochiometric
composition is very low. However, these statements are
related to polycrystalline structures. When the grain size
is 20 to 25 nm the thermodynamically balanced
concentration of vacancies in the major portion of the
volume of grains is much higher than that in “bulk”
materials [15]. Therefore, the structures of such
nanocrystalline films are far from being stochiometric.
The availability of a large amount of vacancies that are
not filled with nitrogen atoms provides a high
coefficient of hydrogen diffusion at relatively low
temperatures; this can explain a good kinetics of its
adsorption and desorption.
In addition some scientific papers show that vacant
positions in nitrides/carbides on sites that contain no
nitrogen/carbon atoms can retain up to 4 hydrogen
atoms. That is, a high equilibrium concentration of
vacancies in the nanocrystalline grains of
vanadium/titanium nitrides provides not only an optimal
kinetics of hydrogen adsorption, but also high
gravimetric characteristics of such film structures.
Thus, the combination of the developed system of
open intergranular nanoporosity with nanocrystalline
grains of nonstoichiometric vanadium/titanium nitrides
should provide acceptable thermodynamic, kinetic and
gravimetric characteristics for the materials of such a
R
, Ω
·c
m
166 ISSN 1562-6016. ВАНТ. 2014. №2(90)
kind. Hydrogen will be retained both in the form of
molecules and in hydride phase.
CONCLUSIONS
The results given in this paper show that the use of
IBAD allows not only for the controlled formation of
nanoporosity with prescribed parameters but also for the
embedment of this nanoporosity into the nanocrystalline
structure of a matrix. The material produced in such a
way is capable of accumulating hydrogen at low
pressures and room temperature in amounts required for
practical use. The availability of narrow channels in the
form of grain boundaries provides high diffusion
mobility, which allows hydrogen to accumulate and
release from the material within a short period of time
and also creates conditions for the retention of
molecular hydrogen in the pores at room temperature.
Varying the basic parameters of the ion beam-assisted
process and first of all its radiation component it is
possible to produce nanocrystalline porous structures in
which the grain size can be both higher and lower than
the pore diameter. Just the wanted relationship between
the sizes of these elements of the crystalline structure
will allow for the fabrication of solid-state hydrogen
storages with appropriate characteristics.
REFERENCES
1. J. Kleiner, E. Sevilla, R. Cotts. Diffusion of
hydrogen in ά-VHx // Phys. Rev. B. 1986, v. 33, p. 6662.
2. Y. Fukai, S. Kasama. Nmr studies of anomalous
diffusion of hydrogen and phase transition in vanadium-
hydrogen alloys // Acta Metall. 1977, v. 25, p. 59-70.
3. S. Orimo, F. Kimmerle, G. Majer. Hydrogen in
nanosrtuctured vanadium-hydrogen systems // Phys.
Rev. B. 2001, v. 63, p. 094307-10.
4. S. Kapellos, A. Mavridis, J. Harrison. Electronic
structure of transition-metal amide ions +TiNH2, +VNH2,
+CrNH2, and +MnNH2 // J. Phys. Chem. 1991, v. 95,
p. 6860-6865.
5. A. Gringoz, N. Glandut, S. Valette. Electro-
chemical hydrogen storage in TiC0.6 not in TiC0.9 //
Electrochemistry Communications. 2009, v. 11,
issue 10, p. 2044-2047.
6. H. Ding, X. Fan, X. Li, et al. First-principles
study of hydrogen storage in non-stoichiometric TiCx
// J. of Alloys&Comp. 2013, v. 551, p. 67-71.
7. V. Bryk, R. Vasylenko, А. Goncharov, et al.
Formation Mechanism, Structural and Adsorption
Characteristics of Microporous Nonacrystalline (V,Ti)-
N-He Thin Film Composites // Surface: X-ray,
Synchrotron and Neutron Investigations. 2011, v. 6,
p. 66-75.
8. А. Goncharov, A. Guglya, E. Melnikova. On the
feasibility of developing hydrogen storages capable of
adsorption hydrogen both in its molecular and atomic
states // J. of Hydrogen Energy. 2012, v. 37, p. 18061-
18073.
9. J.J. Reilly, R.H. Wiswall. The higher hydrides of
vanadium and niobium // Inorganic Chemistry. 1970,
v. 9, N 7, p. 1678-1682.
10. J.F. Lynch, J.J. Reilly, F. Millot. The absorption
of hydrogen by binary vanadium-chromium alloys // J.
Phys. Chem. Solids. 1978, v. 39, p. 883-890.
11. D. Plante, C. Raufast, S. Miraglia, et al. Impro-
vement of hydrogen sorption properties of compounds
based on vanadium “bcc” alloys by mean of
intergranular phase development // J. of Alloys&
Compounds. 2013, v. 580, p. S192-S196.
12. A. Kagawa. Absorption of hydrogen by vana-
dium-titanium alloys // Reports of the faculty of
engineering, Nagasaki University. 1995, v. 25, N 45,
p. 233-239.
13. G. Andersson, K. Aits, B. Hjorvarsson. Hydro-
gen uptake of thin epitaxial vanadium (001) films // J. of
Alloys & Compounds. 2002, v. 334, p. 14-19.
14. I. Carbia, M. Lopez, J. Alonso. The optimum
average nanopore size hygrogen storage in carbon
nanoporous materials // Carbon. 2007, v. 45, p. 2649.
15. N. Gladkikh, S. Durakov, A. Kryshtal, et al.
Poverhnostnie yavleniya i fazoviye prevratsheniya v
kondensirovannih plenkah. Kharkov: V.N. Karazin
Kharkiv National University, 2004. 286 p. (in Russian).
Статья поступила в редакцию 05.02.2014 г.
ТОНКОПЛЕНОЧНЫЕ НАНОПОРИСТЫЕ (V, 10Ti)NxHy-НАКОПИТЕЛИ ВОДОРОДА
А.Г. Гугля, Ю.А. Марченко, Е.C. Мельникова, В.В. Власов, Е.Н. Зубарев
Приведены результаты исследований адсорбционных и электрофизических характеристик нанопористых
пленок (V, 10 ат.% Ti)Nx, полученных с применением технологии ионно-стимулированного осаждения.
Использование данной технологии позволило получить нанокристаллическую структуру, межзеренное
пространство в которой заполнено порами размером менее 6 нм. Показано, что при относительно низком
давлении (0,5 МПа) такие объекты могут аккумулировать более 7 вес.% водорода. Одна часть его накапливается в
межзеренных границах и порах, другая часть – в виде гидридной фазы. Полное выделение водорода происходит
при температуре 250 ºС. В процессе десорбции водорода удельное электросопротивление (V, 10Ti)NxHy-пленок
увеличивается примерно в 107 раз.
ТОНКОПЛІВКОВІ НАНОПОРОВІ (V, 10Ti)NxHy-НАКОПИЧУВАТЕЛІ ВОДНЮ
О.Г. Гугля, Ю.О. Марченко, О.C. Мельникова, В.В. Власов, Є.М. Зубарєв
Приведено дані досліджень адсорбційних та електрофізичних характеристик (V, 10 ат.% Ti)Nx нанопорових
плівок, здобутих за допомогою технології іонно-стимульованого осадження. Використання даної технології
дозволило створити нанокристалічну структуру, міжзеренних простір в якій заповнений порами розміром не
більше 6 нм. Виявлено, що при відносно низькому тиску (0,5 МПа) такі об’єкти можуть акумулювати більш ніж
7 ваг.% водню. Одна його частина накопичується у міжзеренному просторі, а інша – у вигляді гідридної фази.
Повне виділення водню має місце при температурі 250 ºС. У процесі десорбції водню питомий електроопір
(V, 10Ti)NxHy-плівок збільшується приблизно у 107 разів.
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