DESCRIPTION
NbON FILM, METHOD FOR PRODUCING NbON FILM, HYDROGEN
GENERATION DEVICE, AND ENERGY SYSTEM PROVIDED WITH SAME
5
TECHNICAL FIELD
[0001] The present invention relates to a NbON film, a method for producing a
NbON film, a hydrogen generation device using the NbON film, and an energy
system including the hydrogen generation device.
10
BACKGROUND ART
[0002] There are conventionally known techniques for decomposing water into
hydrogen and oxygen by irradiating a semiconductor material serving as an optical
semiconductor with light (see, for example, Patent Literature 1). Patent Literature
1 discloses a technique in which an n-type semiconductor electrode and a counte15 r
electrode are disposed in an electrolyte and the surface of the n-type semiconductor
electrode is irradiated with light to obtain hydrogen and oxygen from the surfaces of
these electrodes. Specifically, the use of a TiO2 electrode or the like as the n-type
semiconductor electrode is described therein.
20 [0003] However, the sunlight utilization efficiency of the n-type semiconductor
electrode disclosed in Patent Literature 1 is still not high enough. For example,
since an anatase type TiO2 electrode has a band gap of 380 nm, only about 1% of
sunlight can be utilized.
[0004] In order to solve the above problem, it is proposed, for example, to use
25 optical semiconductor materials with smaller band gaps. For example, Patent
Literature 2 proposes the use of a NbON optical semiconductor obtained by
calcining Nb2O5 in a high-temperature ammonia atmosphere. Since the NbON
optical semiconductor has a smaller band gap of about 600 nm, the sunlight
utilization efficiency can be increased. Patent Literature 3 discloses an electrode
30 (electrode catalyst) containing a NbON optical semiconductor attached thereto.
This electrode can also be used for photolysis of water.
CITATION LIST
Patent Literature
35 [0005] Patent Literature 1 JP 51(1976)-123779 A
Patent Literature 2 JP 2002-066333 A
Patent Literature 3 JP 2005-161203 A
3
SUMMARY OF INVENTION
Technical Problem
[0006] However, there is still a demand for further improvement of conventional
NbON optical semiconductors to achieve better optical semiconductor propertie5 s
(higher quantum efficiency) for hydrogen production by decomposition of water.
[0007] It is therefore an object of the present invention to provide a NbON optical
semiconductor in the form of a film having further improved optical semiconductor
properties (quantum efficiency) for hydrogen production by decomposition of water
10 compared to conventional NbON optical semiconductors.
Solution to Problem
[0008] The present invention provides a NbON film in which a photocurrent is
generated by light irradiation.
15
Advantageous Effects of Invention
[0009] According to the present invention, NbON and a NbON film having
improved optical semiconductor properties (quantum efficiency) for hydrogen
production by decomposition of water can be provided by a simpler method.
20
BRIEF DESCRIPTION OF DRAWINGS
[0010] FIG. 1 is a schematic diagram showing an example of an apparatus for
carrying out a NbON production method of a second embodiment of the present
invention.
25 FIG. 2 is a diagram illustrating a NbON synthesis mechanism in the NbON
production method of the second embodiment.
FIG. 3 is a schematic diagram showing an example of an apparatus for
carrying out a NbON film production method of a third embodiment of the present
invention.
30 FIG. 4 is a diagram illustrating a NbON film synthesis mechanism in the
NbON film production method of the third embodiment.
FIG. 5 is a schematic diagram showing a configuration of a hydrogen
generation device of a fourth embodiment of the present invention.
FIG. 6 is a schematic diagram showing a configuration of a hydrogen
35 generation device of a fifth embodiment of the present invention.
FIG. 7 is a schematic diagram showing a configuration of an energy system
of a sixth embodiment of the present invention.
4
FIG. 8 shows TG-DTA (Thermogravimetry-Differential Thermal Analysis)
data of a raw material used for NbON synthesis in Example 1.
FIG. 9 shows XRD (X-ray Diffraction) data of a single-phase NbON powder
1 for comparison and XRD simulation data of NbON.
FIG. 10 shows UV-Vis (Ultraviolet Visible Absorption Spectroscopy) data of 5 a
film 1 of Example 1.
FIG. 11 shows XPS (X-ray Photoelectron Spectroscopy) data of Nb3d of the
single-phase NbON powder 1 for comparison and that of the film 1.
FIG. 12 shows UV-Vis data of a film 2 of Example 2.
10 FIG. 13 shows XPS data of Nb3d of the film 2 of Example 2.
DESCRIPTION OF EMBODIMENTS
[0011] It is proposed to use optical semiconductor materials with smaller band gaps
in a technique for producing hydrogen by decomposition of water under light
15 irradiation. The present inventors have found that the conventionally proposed
optical semiconductor materials described in Background Art have the following
disadvantages.
[0012] For example, the NbON disclosed in Patent Literatures 2 and 3 has the
disadvantage of being easily reduced when it is synthesized by the synthesis
20 methods disclosed in Patent Literatures 2 and 3. Since not only NbON is produced
but also NbN, a reduced species of Nb, is produced as a by-product in these
synthesis methods, a single-phase or almost single-phase NbON material cannot be
obtained. Therefore, it is difficult to make the NbON obtained by the synthesis
methods disclosed in Patent Literatures 2 and 3 exhibit optical semiconductor
25 properties sufficiently (high quantum efficiency) for hydrogen production by
decomposition of water under light irradiation. Thus, the by-products such as NbN
need to be dissolved in acid for removal from the resulting NbON.
[0013] In addition, even if a single-phase or almost single-phase NbON material is
obtained by dissolving the by-products such as NbN in acid for removal from the
30 NbON synthesized by the methods disclosed in Patent Literatures 2 and 3, a
single-phase or almost single-phase NbON film cannot be obtained by the same
methods. For example, when a commonly used film forming method was carried
out using a single-phase or almost single-phase NbON material, a single-phase or
almost single-phase NbON film could not be formed because impurities such as
35 NbN were again produced from NbON in the film forming process. Specifically, the
present inventors tried to form a film by sputtering using a single-phase or almost
single-phase NbON material as a sputtering target. However, a single-phase or
5
almost single-phase NbON film could not be obtained because NbON was
decomposed by the energy applied to the NbON as the sputtering target during
sputtering and thus by-products were produced. As another specific example, the
present inventors prepared a suspension using a single-phase or almost
single-phase NbON powder material, sprayed the suspension on a substrate to for5 m
a film, and calcined the film. However, NbON was oxidized during calcination, and
thus a NbON film could not be obtained.
[0014] As a result of intensive studies, the present inventors have found a method
for producing a NbON film containing a reduced amount of impurities such as
10 by-products, and consequently provided a NbON film having improved optical
semiconductor properties (quantum efficiency) for hydrogen production by
decomposition of water under light irradiation and a method for producing the
NbON film. In addition, the present inventors have provided a hydrogen
generation device and an energy system each using this NbON film.
15 [0015] A first aspect of the present invention provides a NbON film in which a
photocurrent is generated by light irradiation. In the present description, the
phrase a photocurrent is generated by light irradiation means that a
photocurrent is generated at a photocurrent density of 0.1 mA/cm2 or more by
irradiation with sunlight .
20 [0016] Since the amount of impurities such as by-products mixed in the NbON film
according to the first aspect is reduced, the NbON film allows NbON to exhibit
optical semiconductor properties sufficiently (high quantum efficiency) for hydrogen
production by decomposition of water under light irradiation.
[0017] A second aspect of the present invention provides a NbON film as set forth
25 in the first aspect, wherein the NbON film is a single-phase film. According to the
second aspect, a single-phase NbON film that has not been obtained before can be
provided. Therefore, it is further ensured that this NbON film allows NbON to
exhibit optical semiconductor properties sufficiently (high quantum efficiency) for
hydrogen production by decomposition of water under light irradiation.
30 [0018] A third aspect of the present invention provides a NbON film as set forth in
the first or second aspect, wherein the NbON film is formed by bringing, into
contact with a heated substrate, vaporized R1N=Nb(NR2R3)3 (where R1, R2, and R2
are each independently a hydrocarbon group) and at least either one selected from
oxygen and water vapor. The amount of impurities such as by-products in the
35 NbON film formed in this manner is sufficiently reduced. Therefore, it is further
ensured that this NbON film allows NbON to exhibit optical semiconductor
properties sufficiently (high quantum efficiency) for hydrogen production by
6
decomposition of water under light irradiation.
[0019] A fourth aspect of the present invention provides a NbON film as set forth in
the third aspect, wherein R1 is a tertiary butyl group ( C(CH3)3), and R2 and R3 are
each independently a straight-chain alkyl group (n CnH2n+1, where n is an integer of
1 or more). This NbON film is highly crystalline and thus can exhibit much bette5 r
optical semiconductor properties.
[0020] A fifth aspect of the present invention provides a method for producing a
NbON film. This method includes the steps of: (I) vaporizing R1N=Nb(NR2R3)3
(where R1, R2, and R3 are each independently a hydrocarbon group); and (II)
10 bringing, into contact with a heated substrate, the vaporized R1N=Nb(NR2R3)3 and
at least either one selected from oxygen and water vapor.
[0021] According to the production method according to the fifth aspect, a NbON
film containing a reduced amount of impurities such as by-products can be
synthesized by fewer steps than conventional methods. Therefore, this production
15 method makes it possible to provide a NbON film having improved optical
semiconductor properties (quantum efficiency) for hydrogen production by
decomposition of water by a simpler method.
[0022] A sixth aspect of the present invention provides a method for producing a
NbON film as set forth in the fifth aspect, wherein in the step (II), the substrate is
20 heated to a temperature that is equal to or higher than a boiling point of the
R1N=Nb(NR2R3)3 and is equal to or lower than a decomposition temperature of the
R1N=Nb(NR2R3)3. Heating of the substrate at temperatures in this range makes it
possible to synthesize NbON with the production of by-products reduced, and
therefore makes it easier to synthesize a single-phase NbON film. Thus, according
25 to this production method, a single-phase NbON film can be obtained without
carrying out a step of removing impurities.
[0023] A seventh aspect of the present invention provides a method for producing a
NbON film as set forth in the fifth or sixth aspect, wherein R1 is a tertiary butyl
group ( C(CH3)3), and R2 and R3 are each independently a straight-chain alkyl
30 group (n CnH2n+1, where n is an integer of 1 or more). Since the material in which
R1 is a tertiary butyl group ( C(CH3)3), and R2 and R3 are each independently a
straight-chain alkyl group (n CnH2n+1, where n is an integer of 1 or more) is easily
vaporized and has high heat resistance, it can be synthesized at higher
temperatures. As a result, a highly crystalline single-phase NbON film having
35 much better optical semiconductor properties can be synthesized more easily.
[0024] An eighth aspect of the present invention provides a hydrogen generation
device including an optical semiconductor electrode including a conductor and the
7
NbON film according to any one of the first to fourth aspects disposed on the
conductor; a counter electrode connected electrically to the conductor; a
water-containing electrolyte disposed in contact with a surface of the NbON film
and a surface of the counter electrode; and a container containing the optical
semiconductor electrode, the counter electrode, and the electrolyte. In this device5 ,
hydrogen is generated by irradiating the NbON film with light.
[0025] The hydrogen generation device according to the eighth aspect uses the
NbON film according to any one of the first to fourth aspects having excellent
optical semiconductor properties. Therefore, the hydrogen generation device
10 according to the eighth aspect can also use light in the longer wavelength region,
and thus the sunlight utilization efficiency can be increased.
[0026] A ninth aspect of the present invention provides an energy system
including: the hydrogen generation device according to the eighth aspect; a
hydrogen storage connected to the hydrogen generation device by a first pipe and
15 configured to store the hydrogen generated in the hydrogen generation device; and a
fuel cell connected to the hydrogen storage by a second pipe and configured to
convert the hydrogen stored in the hydrogen storage into electricity and heat.
[0027] The energy system according to the ninth aspect includes the hydrogen
generation device using the NbON film according to any one of the first to fourth
20 aspects having excellent optical semiconductor properties. Therefore, the energy
system according to the ninth aspect can also use light in the longer wavelength
region, and thus the sunlight utilization efficiency can be increased.
[0028] Hereinafter, embodiments of the present invention are described in detail
with reference to the drawings. The following embodiments are merely examples,
25 and the present invention is not limited to these embodiments. In the following
embodiments, the same parts are designated by the same numerals, and the same
description may be omitted.
[0029] (First Embodiment)
An embodiment of the NbON film of the present invention is described.
30 The NbON film of the present embodiment is a NbON film in which a photocurrent
is generated by light irradiation. As described above, the phrase a photocurrent is
generated by light irradiation means that a photocurrent is generated at a
photocurrent density of 0.1 mA/cm2 or more by irradiation with sunlight .
[0030] The NbON film of the present embodiment is a film containing less
35 impurities mixed, that is, a single-phase or almost single-phase NbON film.
Therefore, the NbON film allows NbON to exhibit optical semiconductor properties
sufficiently (high quantum efficiency) for hydrogen production by decomposition of
8
water under light irradiation. It is desirable that the NbON film be a single-phase
film to achieve high quantum efficiency more reliably.
[0031] Here, in the present description, the phrase a NbON film is a single-phase
film means that the NbON film consists essentially of a NbON compound phase or
the NbON film consists of a NbON compound phase. The phrase the NbON fil5 m
consists essentially of a NbON compound phase means that the content of
compound phases other than the NbON compound phase in the NbON film is 10
at.% or less, desirably 5 at.% or less, and more desirably 3 at.% or less. Even if the
NbON film of the present embodiment is a single-phase film, it may contain a
10 doping level of carbon atoms derived from hydrocarbon groups contained in the
starting material used for the formation of the NbON film, but this causes no
problem. As used herein, a single phase film containing a doping level of other
elements refers to a single phase film containing the other elements at a
concentration of 1 at.% or less in addition to the constituent elements of the single
15 phase. An easy means for determining whether the NbON film is a single-phase
film or not is, for example, to regard, as a single-phase film, a film having a
single-phase NbON spectrum in the XPS spectrum of Nb3d. When the film is
regarded as a single-phase film through the means, the film is made of single-phase
NbON in terms of a Nb compound, but carbon derived from the starting material
20 may be detected therein as long as the carbon content is in the above range.
[0032] The NbON film of the present embodiment may be a film formed by, for
example, bringing, into contact with a heated substrate, vaporized R1N=Nb(NR2R3)3
(where R1, R2, and R3 are each independently a hydrocarbon group) and at least
either one selected from oxygen and water vapor. In this case, R1 may be a tertiary
25 butyl group ( C(CH3)3), and R2 and R3 may each independently be a straight-chain
alkyl group (n CnH2n+1, where n is an integer of 1 or more).
[0033] The production method of the NbON film of the present embodiment is not
particularly limited, and the NbON film can be produced in a simple manner by a
production method described later.
30 [0034] (Second Embodiment)
An embodiment of the NbON production method of the present invention is
described below.
[0035] The NbON production method of the present embodiment includes a step of
heating R1N=Nb(NR2R3)3 (where R1, R2, and R3 are each independently a
35 hydrocarbon group) in an atmosphere containing at least either one selected from
oxygen and water. This step can be carried out using, for example, an apparatus
100 as shown in FIG. 1.
9
[0036] The apparatus 100 includes a tube furnace 111, a tube 112 penetrating the
tube furnace 111, and a boat 113 placed in the tube 112. NbON (NbON powder)
can be synthesized by heating a raw material (R1N=Nb(NR2R3)3) 101 set in the boat
113 in the tube 112, with an oxygen- and/or water-containing inert gas flow 102 in
the tube 112. This method makes it possible to synthesize NbON having a reduce5 d
content of by-products such as NbN and thus to obtain a single-phase NbON
material.
[0037] In the present embodiment, it is desirable that the raw material
R1N=Nb(NR2R3)3 be heated at a temperature that is equal to or higher than a
10 boiling point of the R1N=Nb(NR2R3)3 and is equal to or lower than a decomposition
temperature of the R1N=Nb(NR2R3)3. Heating of the raw material in this
temperature range makes it possible to synthesize NbON with the production of
by-products reduced, and thus makes it easier to synthesize a single-phase NbON
material (single-phase NbON powder). Therefore, a single-phase NbON material
15 can be obtained without carrying out a step of removing impurities. The
decomposition temperature of the material can be determined by TG-DTA
measurement using an inert gas flow, DSC measurement in a sealed container, or
the like.
[0038] In the R1N=Nb(NR2R3)3 used as the starting material, R1, R2, and R3 are
20 each independently a hydrocarbon group. Therefore, self-condensation reaction is
inhibited in the R1N=Nb(NR2R3)3. As R1, a branched-chain hydrocarbon group is
suitable because the resulting material is a liquid and thus is easy to handle, is
easily vaporized, easily undergoes a homogeneous reaction, and further has a higher
decomposition temperature. In particular, a tertiary butyl group ( C(CH3)3) is
25 desirable. As R2 and R3, straight-chain hydrocarbon groups are suitable because
the resulting material has a higher decomposition temperature. Straight-chain
alkyl groups (n CnH2n+1, where n is an integer of 1 or more) like CH3 and C2H5 are
desirable. Since a too long carbon chain causes the decomposition temperature to
become too high, the carbon number is desirably 3 or less (n 3). Since the
30 material in which R1 is a tertiary butyl group ( C(CH3)3), and R2 and R3 are each
independently a straight-chain alkyl group (n CnH2n+1, where n is an integer of 1 or
more) is easily vaporized and has high heat resistance, it can be synthesized at
higher temperatures. As a result, highly crystalline single-phase NbON having
better optical semiconductor properties can be synthesized more easily. It should
35 be noted that the starting material used in the present embodiment is highly
reactive with oxygen and water. Therefore, the content of oxygen and water in the
starting material is desirably 1 mol ppm or less of the total amount of the starting
10
amount, and more desirably 0.1 mol ppm or less.
[0039] As used in this description, the term single-phase NbON refers to a
substance consisting essentially of a NbON compound phase or a substance
consisting of a NbON compound phase. The phrase the substance consists
essentially of a NbON compound phase means that the content of by-product5 s
other than the NbON compound phase in the substance is 10 at.% or less, desirably
5 at.% or less, and more desirably 3 at.% or less. Even if the substance obtained in
the present embodiment is single-phase NbON, it may contain a doping level of
carbon atoms derived from hydrocarbon groups contained in the starting material,
10 but this causes no problem. As used herein, a substance containing a doping level
of other elements refers to a substance containing the other elements at a
concentration of 1 at.% or less in addition to the constituent elements of the single
phase. An easy means for determining whether the NbON obtained by the
production method of the present embodiment is a single-phase substance or not is,
15 for example, to regard, as a single-phase substance, a substance having a
single-phase NbON spectrum in the XPS spectrum of Nb3d. When the substance
is regarded as a single-phase through the means, the substance is made of
single-phase NbON in terms of a Nb compound, but carbon derived from the
starting material may be detected therein as long as the carbon content is in the
20 above range.
[0040] The inert gas used may be not only a so-called rare gas such as He, Ne, Ar,
Kr, or Xe but also nitrogen gas. It is desirable to use a gas having a low content of
oxygen and water. Therefore, the content of oxygen and water in the inert gas is
desirably 10 vol. ppm or less, and more desirably 1 vol. ppm or less.
25 [0041] Any tube and any boat may be used as the tube 112 and the boat 113 in the
tube furnace 111 as long as they withstand the operating temperatures and
environments. However, since oxygen and/or water is introduced into the tube,
quartz is suitably used for them because oxygen and water are less likely to be
adsorbed on or desorbed from quartz.
30 [0042] Next, the NbON synthesis mechanism in the production method of the
present embodiment is described with reference to FIG. 2. Here, the case where
tertiary butylimino tris(ethylmethylamino) niobium (tBuN=Nb(NMeEt)3), where R1
is a tertiary butyl group, R2 is a methyl group, and R3 is an ethyl group, is used as a
raw material 101 is described as an example. A compound produced by binding of
35 oxygen (O2) or water (H2O) to this raw material (R1N=Nb(NR2R3)3) 101 acts as an
initiator and causes addition polymerization of R1N=Nb(NR2R3)3. Next, NR2R3
reacts with oxygen or water and then is condensation polymerized. Thus, a NbON
11
powder is obtained. Since the production method of the present embodiment has
such a reaction scheme, much less by-products are produced compared to partial
nitridation of Nb2O5 with ammonia.
[0043] According to the production method of the present embodiment, NbON
containing very little by-products or NbON containing no by-products can 5 be
synthesized. This means that there is no need to carry out a step of removing
by-products, etc., and therefore single-phase NbON can also be produced by a
simple one-step method. As a result, NbON having improved optical
semiconductor properties (quantum efficiency) for hydrogen production by
10 decomposition of water can be produced easily and inexpensively.
[0044] (Third Embodiment)
An embodiment of the NbON film production method of the present
invention is described below.
[0045] The production method of the present embodiment includes the steps of: (I)
15 vaporizing R1N=Nb(NR2R3)3 (where R1, R2, and R3 are each independently a
hydrocarbon group); and (II) bringing, into contact with a heated substrate, the
vaporized R1N=Nb(NR2R3)3 and at least either one selected from oxygen and water
vapor. These steps can be carried out using, for example, a MOCVD
(Metal-Organic Chemical Vapor Deposition) apparatus 300 as shown in FIG. 3.
20 This method makes it possible to synthesize a NbON film having a reduced content
of impurities such as NbN and thus to obtain a single-phase NbON film. Therefore,
the NbON film described in the first embodiment can be produced by this method.
In addition, this method makes it possible to produce a NbON film fixed to a
substrate by chemical bonding. For example, in the case where a NbON film is
25 formed by attaching NbON powder to an electrode, like the electrode catalyst
described in Patent Literature 3, the NbON powder is only in contact with the
electrode and is not attached firmly enough, which makes it difficult to obtain
desired optical semiconductor properties (high quantum efficiency). In contrast, in
the NbON film obtained by the method of the present embodiment, the NbON film
30 is well fixed to the substrate, and thus this film allows NbON to exhibit its excellent
optical semiconductor properties.
[0046] It is desirable that, in the step (II), the substrate be heated to a temperature
that is equal to or higher than the boiling point of the R1N=Nb(NR2R3)3 as a raw
material and is equal to or lower than the decomposition temperature of the
35 R1N=Nb(NR2R3)3. Heating of the substrate at temperatures in this range makes it
possible to synthesize NbON with the production of by-products reduced, and thus
makes it easier to synthesize a single-phase NbON film. As a result, a
12
single-phase NbON film that has not been obtained before can be obtained. It is
desirable that, in the step (I), the raw material be vaporized at a temperature equal
to or lower than the decomposition temperature thereof.
[0047] R1N=Nb(NR2R3)3 used as the starting material is the same as that described
in the second embodiment. Therefore, detailed description thereof is omitted5 .
[0048] The MOCVD apparatus 300 includes a vaporizer 311, an inlet pipe 312, a
reaction chamber 313, a shower head 314, and a susceptor 315. The vaporizer 311
vaporizes the raw material. The reaction chamber 313 is a chamber into which a
source gas obtained by vaporizing the raw material in the vaporizer 311 is supplied
10 to grow a crystal on the treatment surface of the substrate. The inlet pipe 312
supplies a gas such as a source gas to the reaction chamber 313 from the vaporizer
311. The shower head 314 is connected to the end of the inlet pipe 312. It is
placed inside the reaction chamber 313 and injects a source gas, a reactant gas, etc.
to the substrate to grow a crystal thereon. The susceptor 315 supports the
15 substrate on which the crystal is to be grown and heats the substrate.
[0049] An inert gas 302 containing the raw material (R1N=Nb(NR2R3)3) 301 heated
(desirably heated at a temperature equal to or lower than the decomposition
temperature thereof) and vaporized in the vaporizer 311 is mixed with at least
either one reactant gas 303 selected from oxygen and water vapor using the
20 MOCVD apparatus 300. The mixed gas is injected from the shower head 314 to
the substrate 321 heated by the susceptor 315. The temperature of the heated
substrate 321 is desirably in the range of temperatures that are equal to or higher
than the boiling point of the raw material 301 and are equal to or lower than the
decomposition temperature thereof. In this temperature range, NbON can be
25 deposited in the crystalline form on the substrate 321 so as to form a NbON film.
The specific examples of the inert gas 302 used herein are the same as those of the
inert gas used in the second embodiment.
[0050] It is desirable that the chamber wall of the MOCVD apparatus 300 be made
of stainless steel because water and oxygen are less likely to be adsorbed on or
30 desorbed from stainless steel. In order to prevent the attachment of
R1N=Nb(NR2R3)3 on the chamber wall, a solution of the R1N=Nb(NR2R3)3 and an
organic solvent may be vaporized. In this case, a nonaqueous solvent such as
hydrocarbon, of which vaporization properties are similar to those of
R1N=Nb(NR2R3)3 and in which R1N=Nb(NR2R3)3 dissolves, is suitable as the organic
35 solvent. For example, ethylcyclohexane is suitably used.
[0051] Next, the NbON film synthesis mechanism in the production method of the
present embodiment is described with reference to FIG. 4. Here, the case where
13
tertiary butylimino tris(ethylmethylamino) niobium (tBuN=Nb(NMeEt)3), where R1
is a tertiary butyl group, R2 is a methyl group, and R3 is an ethyl group, is used as a
raw material 301 is described as an example. A compound produced by binding of
this raw material (R1N=Nb(NR2R3)3) 301 to hydroxyl groups on the surface of the
substrate 321 acts as an initiator and causes addition polymerization o5 f
R1N=Nb(NR2R3)3. Next, NR2R3 reacts with oxygen or water and then is
condensation polymerized. Thus, a NbON film is obtained. Since the production
method of the present embodiment has such a reaction scheme, much less
by-products are produced compared to partial nitridation of Nb2O5 with ammonia.
10 [0052] The production method of the present embodiment makes it possible to
synthesize a NbON film containing very little by-products or containing no
by-products. This means that there is no need to carry out a step of removing
by-products, etc., and therefore a single-phase NbON film can also be produced by a
simple method. As a result, a NbON film having improved optical semiconductor
15 properties (quantum efficiency) for hydrogen production by decomposition of water
can be produced easily and inexpensively. In the case of a film, even if a step of
removing impurities such as by-products is carried out additionally, it is difficult to
remove by-products contained in the film. Therefore, even if a film containing
NbON is produced by a commonly-used film formation method and a step of
20 removing impurities from the film is carried out, it is difficult to obtain a NbON film
containing very little or no by-products, such that a photocurrent is generated by
light irradiation.
[0053] (Fourth Embodiment)
An embodiment of the hydrogen generation device of the present invention
25 is described below with reference to FIG. 5.
[0054] A hydrogen generation device 500 of the present embodiment includes a
water-containing electrolyte 510 in which the NbON material produced by the
method described in the second embodiment is suspended, and a container 511
containing the electrolyte 510. This hydrogen generation device 500 decomposes
30 water by irradiating the electrolyte 510 with light so as to generate hydrogen.
[0055] At least a portion (herein referred to as a light incident portion 512) of the
container 511 is made of a material that transmits light such as sunlight so as to
allow light such as sunlight to reach the inside of the container 511. The container
511 is further provided with an outlet 514 for discharging hydrogen and oxygen
35 generated in the container 511 and an inlet 513 for supplying water to be
decomposed into the container 511. The hydrogen generation device 500 further
includes a hydrogen separation membrane 515, an oxygen outlet 516, and a
14
hydrogen outlet 517. The hydrogen separation membrane 515 separates hydrogen
from the gas discharged from the outlet 514. The hydrogen thus separated is
discharged from the hydrogen outlet 517. After the hydrogen is separated, the
remaining oxygen is discharged from the oxygen outlet 516.
[0056] Next, the operation of the hydrogen generation device 500 of the presen5 t
embodiment is described with reference to FIG. 5.
[0057] The water-containing electrolyte 510 which is contained in the container 511
and in which the single-phase NbON material is suspended is irradiated with
sunlight through the light incident portion 512 of the container 511 in the hydrogen
10 generation device 500. In this case, electrons are generated in the conduction band
of the NbON material in the electrolyte 510 and holes are generated in the valence
band thereof. The holes thus generated decompose water and causes oxygen to be
generated according to the reaction formula (1) below. On the other hand, the
electrons causes hydrogen to be generated according to the reaction formula (2)
15 below.
[0058]
[0059] The hydrogen and oxygen thus generated are discharged from the outlet 514
20 and then separated from each other through the hydrogen separation membrane
515. The oxygen and hydrogen are discharged from the oxygen outlet 516 and the
hydrogen outlet 517, respectively. Water is supplied into the container 511 through
the inlet 513 to replenish the water used for decomposition.
[0060] Since the NbON material used in the present embodiment is a material
25 having excellent optical semiconductor properties, the probability of recombination
of holes and electrons is low. Therefore, in the hydrogen generation device 500 of
the present embodiment, the quantum efficiency of the hydrogen evolution reaction
by light irradiation can be increased. In addition, since the NbON material used in
the present embodiment has a small band gap, it is also responsive to visible light in
30 sunlight. As a result, the hydrogen generation device 500 of the present
embodiment can generate more hydrogen than a device using a conventional optical
semiconductor material.
[0061] (Fifth Embodiment)
An embodiment of another hydrogen generation device of the present
35 invention is described below with reference to FIG. 6.
15
[0062] A hydrogen generation device 600 of the present embodiment includes an
optical semiconductor electrode 620 including a NbON film 622 described in the
first embodiment, a counter electrode 630 that is an electrode paired with the
optical semiconductor electrode 620, a water-containing electrolyte 640, and a
container 610 containing the optical semiconductor electrode 620, the counte5 r
electrode 630, and the electrolyte 640.
[0063] The optical semiconductor electrode 620 includes a conductive substrate
(conductor) 621 and the NbON film 622 formed on the conductive substrate 621.
[0064] In the container 610, the NbON film 622 of the optical semiconductor
10 electrode 620 and the counter electrode 630 are disposed so that the surfaces thereof
are in contact with the electrolyte 640. A portion of the container 610 that faces
the NbON film 622 of the optical semiconductor electrode 620 disposed inside the
container 610 (hereinafter, abbreviated as a light incident portion 611) is made of a
material that transmits light such as sunlight.
15 [0065] The conductive substrate 621 of the optical semiconductor electrode 620 is
connected electrically to the counter electrode 630 by a conducting wire 650. As
used herein, the counter electrode refers to an electrode that can exchange electrons
with an optical semiconductor electrode without an electrolyte. Accordingly, in the
present embodiment, there is no particular limitation on the positional relationship,
20 etc. of the counter electrode 630 with the optical semiconductor electrode 620, as
long as the counter electrode 630 is connected electrically to the conductive
substrate 621 that constitutes the optical semiconductor electrode 620. It should
be noted that since the NbON film 622 used in the present embodiment is an n-type
semiconductor, the counter electrode 630 serves as an electrode that receives
25 electrons from the optical semiconductor electrode 620 without the electrolyte 640.
[0066] As shown in FIG. 6, the hydrogen generation device 600 of the present
embodiment further includes a separator 606. The separator 606 separates the
inside of the container 610 into two regions: a region in which the optical
semiconductor electrode 620 is disposed; and a region in which the counter electrode
30 630 is disposed. The electrolyte 640 is contained in both of these regions. The
container 610 is provided with an oxygen outlet 613 for discharging oxygen
generated in the region in which the optical semiconductor electrode 620 is disposed,
and a hydrogen outlet 614 for discharging hydrogen generated in the region in
which the counter electrode 630 is disposed. The container 610 is further provided
35 with a water inlet 612 for supplying water into the container 610.
[0067] Next, the operation of the hydrogen generation device 600 of the present
embodiment is described with reference to FIG. 6.
16
[0068] When the NbON film 622 of the optical semiconductor electrode 620
disposed in the container 610 is irradiated with sunlight through the light incident
portion 611 of the container 610 in the hydrogen generation device 600, electrons
are generated in the conduction band and holes are generated in the valence band,
respectively, in the portion of the NbON film 622 irradiated with light. Since th5 e
NbON film 622 is an n-type semiconductor, the potential of the surface of the NbON
film 622 is higher than the potential of the inside of the NbON film 622. Therefore,
the holes generated at this time move to the surface of the NbON film 622 along the
band edge of the valence band. Thus, water is decomposed on the surface of the
10 NbON film 622 according to the above reaction formula (1), so that oxygen is
generated. On the other hand, the electrons move from the surface near-field
region of the NbON film 622 to the conductive substrate 621 through the inside of
the single-phase NbON film along the band edge of the conduction band. When the
electrons reach the conductive substrate 621, they are transferred, through the
15 conducting wire 650, to the side of the counter electrode 630 connected electrically to
the conductive substrate 621. Thus, hydrogen is generated on the surface of the
counter electrode 630 according to the above reaction formula (2).
[0069] The oxygen and hydrogen thus generated are discharged from the oxygen
outlet 613 and the hydrogen outlet 614, respectively. Water is supplied into the
20 container 610 through the inlet 612 to replenish the water used for decomposition.
[0070] Since the NbON film used in the present embodiment is a material having
excellent optical semiconductor properties, the probability of recombination of holes
and electrons is low. Furthermore, the hydrogen generation device 600 of the
present embodiment is a so-called photoelectrochemical cell using, as an electrode, a
25 NbON film serving as an optical semiconductor. Therefore, in the hydrogen
generation device 600, efficient charge separation between holes and electrons is
achieved, and thus the quantum efficiency of the hydrogen evolution reaction by
light irradiation is increased. In addition, since the single-phase NbON material
has a small band gap, it is also responsive to visible light in sunlight. As a result,
30 the hydrogen generation device 600 of the present embodiment can generate more
hydrogen than a device using a conventional optical semiconductor material.
Moreover, in the hydrogen generation device 600, hydrogen and oxygen can be
generated separately, and thus it is easy to collect hydrogen and oxygen separately.
[0071] It is desirable that the portion of the conductive substrate 621 that is not
35 covered with the NbON film 622 be covered, for example, with an insulating
material such as resin. This covering prevents the uncovered portion of the
conductive substrate 621 in the optical semiconductor electrode 620 from being
17
dissolved in the electrolyte 640.
[0072] It is desirable to use a material with a low overvoltage for the counter
electrode. For example, it is desirable to use a metal catalyst such as Pt, Au, Ag,
Fe, or Ni as the counter electrode because the use thereof increases the reaction
activity of the counter electrode. Any electrolyte can be used for the electrolyte 645 0
as long as it contains water. The water-containing electrolyte may be acidic or
alkaline. In the case where a solid electrolyte is disposed between the optical
semiconductor electrode 620 and the counter electrode 630, the electrolyte 640 in
contact with the surface of the NbON film 622 of the optical semiconductor electrode
10 620 and the surface of the counter electrode 630 can be replaced by pure water for
electrolysis.
[0073] (Sixth Embodiment)
The configuration of an energy system of the fifth embodiment of the
present invention is described with reference to FIG. 7. FIG. 7 is a schematic view
15 showing the configuration of the energy system of the present embodiment.
[0074] As shown in FIG. 7, an energy system 700 of the present embodiment
includes a hydrogen generation device 710, a hydrogen storage 720, a fuel cell 730,
and a storage battery 740.
[0075] The hydrogen generation device 710 is the hydrogen generation device 500
20 of the fourth embodiment or the hydrogen generation device 600 of the fifth
embodiment, and specific configurations of these devices are as shown in FIG. 5 and
FIG. 6, respectively. Therefore, detailed description thereof is omitted here.
[0076] The hydrogen storage 720 is connected to the hydrogen generation device
710 by a first pipe 751. The hydrogen storage 720 can be composed of, for example,
25 a compressor for compressing hydrogen generated in the hydrogen generation
device 710 and a high-pressure hydrogen tank for storing the hydrogen compressed
by the compressor.
[0077] The fuel cell 730 includes a power generator 731 and a fuel cell controller
732 for controlling the power generator 731. The fuel cell 730 is connected to the
30 hydrogen storage 720 by a second pipe 752. The second pipe 752 is provided with a
block valve 753. For example, a solid polymer electrolyte fuel cell can be used as
the fuel cell 730.
[0078] The positive electrode and the negative electrode of the storage battery 740
respectively are connected electrically to the positive electrode and the negative
35 electrode of the power generator 731 in the fuel cell 730 by a first line 754 and a
second line 755. The storage battery 740 is provided with a capacity meter 756 for
measuring the remaining capacity of the storage battery 740. For example, a
18
lithium ion battery can be used as the storage battery 740.
[0079] Next, the operation of the energy system 700 of the present embodiment is
described by taking, as an example, the case where the hydrogen generation device
600 of the fifth embodiment is used as the hydrogen generation device 710, and also
with reference to FIG. 65 .
[0080] When the surface of the NbON film 622 of the optical semiconductor
electrode 620 disposed inside the container 610 is irradiated with sunlight through
the light incident portion 611 of the hydrogen generation device 600, electrons and
holes are generated inside the NbON film 622. The holes generated at this time
10 move to the surface side of the NbON film 622. Thus, water is decomposed on the
surface of the NbON film 622 according to the above reaction formula (1), so that
oxygen is generated.
[0081] On the other hand, the electrons move to the conductive substrate 621 along
the bending of the band edge of the conduction band at the interface between the
15 NbON film 622 and the conductive substrate 621. When the electrons reach the
conductive substrate 621, they are transferred to the side of the counter electrode
630 through the conducting wire 650. Thus, hydrogen is generated on the surface
of the counter electrode 630 according to the above reaction formula (2). As
described in the fifth embodiment, in the hydrogen generation device 600, the
20 quantum efficiency of the hydrogen evolution reaction by light irradiation is
increased.
[0082] The oxygen thus generated is discharged from the oxygen outlet 613 to the
outside of the hydrogen generation device 600. On the other hand, the hydrogen
thus generated is supplied into the hydrogen storage 720 through the hydrogen
25 outlet 614 and the first pipe 751.
[0083] In generating power in the fuel cell 730, the block valve 753 is opened
according to signals from the fuel cell controller 732, so that the hydrogen stored in
the hydrogen storage 720 is supplied to the power generator 731 of the fuel cell 730
through the second pipe 752.
30 [0084] The electricity generated in the power generator 731 of the fuel cell 730 is
stored in the storage battery 740 through the first line 754 and the second line 755.
The electricity stored in the storage battery 740 is supplied to home and business
users through a third line 757 and a fourth line 758.
[0085] In the hydrogen generation device 600, the quantum efficiency of the
35 hydrogen evolution reaction by light irradiation can be increased. Thus, the energy
system 700 including this hydrogen generation device 600 can supply electric power
efficiently.
19
[0086] In the present embodiment, the example of the energy system using the
hydrogen generation device 600 described in the fifth embodiment is shown.
However, even if the hydrogen generation device 500 described in the fourth
embodiment is used, an energy system having the same effects can be obtained.
5
EXAMPLES
[0087] Hereinafter, examples of the present invention will be described in more
detail.
[0088] (Example 1)

As a raw material (R1N=Nb(NR2R3)3), tertiary butylimino
tris(ethylmethylamino) niobium ((CH3)3CN=Nb(N(CH3)C2H5)3) was used. FIG. 8
shows TG-DTA data of this raw material under an Ar flow. The boiling point of the
material was about 181ºC. The decomposition temperature of the residue of the
15 material, which was believed to be the film of the material, was about 303ºC.
Next, a single-phase NbON film was synthesized using the MOCVD
apparatus 300 shown in FIG. 3. An ethylcyclohexane solution of the raw material
301 at 3.38 × 10 5Pa m3s 1 ( 0.2 sccm) was vaporized at 150 ºC in the vaporizer 311.
Nitrogen gas 302 was used as an inert gas. Oxygen 303 at 1.69 × 10 4Pa m3s 1 (1
20 sccm) was mixed with a mixed gas at 1.69 × 10 1Pa m3s 1 (1000 sccm) containing
the source gas (vaporized material 301) and the nitrogen gas 302. The resulting
gas mixture was injected for 6 hours from the shower head 314 to the substrate 321
(ITO film (with a thickness of 150 nm) / glass substrate) heated at 300ºC by the
susceptor 315. Thus, a film 1 with a thickness of 160 nm was obtained.
25 [0089]
A reference NbON powder was synthesized using the apparatus shown in
FIG. 1. 2 g of Nb2O5 as the raw material 101, instead of R1N=Nb(NR2R3)3, was set
in the quartz boat 113 in the quartz tube 112 with an inner diameter of 25 mm of
the tube furnace 111. This was heated at 650 ºC for 4 hours under a NH3 flow at
30 1.69 × 10 1Pa m3s 1 (1000 sccm). NbN as an impurity was dissolved in 1N sulfuric
acid so as to remove NbN from the resulting material. Thus, the powder 1 was
obtained. FIG. 9 shows XRD data of the powder 1 (upper) and XRD simulation
data of NbON (lower). As a result of a comparison of these XRD data, it was
confirmed that the powder 1 was an almost single-phase NbON powder.
35 [0090]
FIG. 10 shows the UV-Vis spectrum of the film 1. FIG 10 indicates that the
band gap of the film 1 is 600 nm. This band gap almost coincides with the band
20
gap of NbON reported in various documents. FIG. 11 shows the XPS spectrum of
Nb3d of the film 1 and that of the powder 1 identified as a single-phase NbON
material. FIG. 11 reveals that these spectra almost coincide with each other. As a
result, it was confirmed that the film 1 was an almost single-phase NbON film.
[0091] In this example, the flow rate of oxygen during the synthesis of th5 e
single-phase NbON film was 1.69 × 10 4Pa m3s 1 (1 sccm), and the gas
concentration of oxygen with respect to nitrogen (inert carrier gas) was 0.1%.
However, the synthesis of single-phase NbON films was also confirmed when the
oxygen concentration was in the range of 0.01 to 1%.
10 [0092] (Example 2)
A NbON film was produced in the same manner as in Example 1 except that
the temperature of the susceptor 315 was changed from 300ºC to 350ºC. The
thickness of the resulting NbON film (film 2) was 800 nm.
[0093] FIG. 12 shows the UV-Vis spectrum of the film 2. Absorption was observed
15 at all wavelengths and no band gap was found.
[0094] FIG. 13 shows the XPS spectrum of Nb3d of the film 2. The fact that the
binding energy of the film 2 is 203.5 eV, which is different from the binding energy
206.8 eV of the film 1 (NbON), indicates that the film 2 contains NbN. However,
the fact that a shoulder peak is also observed at 206.8 eV, which is the binding
20 energy of the film 1, indicates that the film 2 also contains NbON.
[0095] (Example 3)
A single-phase NbON powder was synthesized using the apparatus 100
shown in FIG. 1. The raw material 101 was set in the quartz boat 113 in the
quartz tube 112 with an inner diameter of 25 mm of the tube furnace 111. As the
25 raw material 101, the same material as used in Example 1, i.e., tertiary butylimino
tris(ethylmethylamino) niobium ((CH3)3CN=Nb(N(CH3)C2H5)3) was used. This raw
material 101 was heated at 300ºC for 4 hours under a flow of a gas mixture of
nitrogen at 1.69 × 10 1Pa m3s 1 (1000 sccm) and oxygen at 1.69 × 10 4Pa m3s 1 (1
sccm). Thus, a powder 2 was obtained.
30 [0096] The XRD data of this powder 2 was compared with that of the powder 1 of
Example 1. As a result, it was confirmed that these data almost coincided with
each other. It was thus confirmed that the powder 2 was single-phase NbON
powder.
[0097] In this example, the flow rate of oxygen during the synthesis of the
35 single-phase NbON powder was 1.69 × 10 4Pa m3s 1 (1 sccm), and the gas
concentration of oxygen with respect to nitrogen (inert carrier gas) was 0.1%.
However, the synthesis of single-phase NbON powders was also confirmed when the
21
oxygen concentration was in the range of 0.01 to 1%.
[0098] (Example 4)
A NbON film was synthesized in the same manner as in Example 1 except
that water vapor was used instead of oxygen used in Example 1. The thickness of
the resulting NbON film (film 3) was 700 nm5 .
[0099] The XPS spectrum of Nb3d of this film 3 was measured. The measured
spectrum was almost the same as that of the film 1. As a result, it was confirmed
that the film 3 was a single-phase NbON film.
[0100] In this example, the flow rate of water vapor during the synthesis of the
10 single-phase NbON film was 1.69 × 10 4Pa m3s 1 (1 sccm), and the gas
concentration of water vapor with respect to nitrogen (inert carrier gas) was 0.1%.
However, the synthesis of single-phase NbON films was also confirmed when the
water vapor concentration was in the range of 0.01 to 1%.
[0101] (Example 5)
15 As a raw material (R1N=Nb(NR2R3)3), tertiary butylimino
tris(di-ethylamino) niobium ((CH3)3CN=Nb(N(C2H5)2)3) was used. The
decomposition temperature of this material was determined based on the TG-DTA
data thereof under an Ar flow. As a result, the decomposition temperature of this
raw material was about 410ºC.
20 [0102] Next, a single-phase NbON film was synthesized using the MOCVD
apparatus 300 shown in FIG. 3. An ethylcyclohexane solution of the raw material
301 at 3.38 × 10 5Pa m3s 1 (0.2 sccm) was vaporized at 150ºC in the vaporizer 311.
Nitrogen gas 302 was used as an inert gas. Oxygen 303 at 1.69 × 10 4Pa m3s 1 (1
sccm) was mixed with a mixed gas at 2.87 × 10 1Pa m3s 1 (1700 sccm) containing
25 the source gas (vaporized material 301) and the nitrogen gas 302. The resulting
gas mixture was injected for 6 hours from the shower head 314 to the substrate 321
(ITO film (with a thickness of 150 nm) / glass substrate) heated at 400ºC by the
susceptor 315. Thus, a film 4 with a thickness of 300 nm was obtained.
[0103] The XPS spectrum of Nb3d of this film 4 was measured. The measured
30 spectrum was almost the same as that of the film 1. As a result, it was confirmed
that the film 4 was an almost single-phase NbON film.
[0104] (Example 6)
As a raw material (R1N=Nb(NR2R3)3), tertiary butylimino
tris(di-methylamino) niobium ((CH3)3CN=Nb(N(CH3)2)3) was used. The
35 decomposition temperature of this material was determined based on the TG-DTA
data thereof under an Ar flow. As a result, the decomposition temperature of this
raw material was about 250ºC.
22
[0105] Next, a single-phase NbON film was synthesized using the MOCVD
apparatus 300 shown in FIG. 3. An ethylcyclohexane solution of the raw material
301 at 3.38 × 10 5Pa m3s 1 (0.2 sccm) was vaporized at 150ºC in the vaporizer 311.
Nitrogen gas 302 was used as an inert gas. Oxygen 303 at 1.69 × 10 4Pa m3s 1 (1
sccm) was mixed with a mixed gas at 2.87 × 10 1Pa m3s 1 (1700 sccm) containin5 g
the source gas (vaporized material 301) and the nitrogen gas 302. The resulting
gas mixture was injected for 6 hours from the shower head 314 to the substrate 321
(ITO film (with a thickness of 150 nm) / glass substrate) heated at 240ºC by the
susceptor 315. Thus, a film 5 with a thickness of 300 nm was obtained.
10 [0106] The XPS spectrum of Nb3d of this film 5 was measured. The measured
spectrum was almost the same as that of the film 1. As a result, it was confirmed
that the film 5 was an almost single-phase NbON film.
[0107] (Example 7)

15 As an example of the hydrogen generation device of the present invention, a
hydrogen generation device having the same configuration as that of the hydrogen
generation device 600 shown in FIG. 6 was produced. The configuration of the
hydrogen generation device of the present embodiment is described with reference
to FIG. 6.
20 As shown in FIG. 6, the hydrogen generation device 600 of Example 7
included a rectangular glass container 610 with an opening in the upper part, a
semiconductor electrode 620 and a counter electrode 630. The glass container 610
contained 1 molL 1 of H2SO4 aqueous solution as the electrolyte 640. As the optical
semiconfuctor electrode 620, a 1-cm-square electrode having the substrate 321 (ITO
25 film (with a thickness of 150 nm) / glass substrate) (corresponding to the conductive
substrate 621) produced in Example 1, and the 160-nm-thick film 1 (corresponding
to the NbON film 622) provided thereon was used. The optical semiconductor
electrode 620 was disposed so that the surface of the NbON film 622 faced the light
incident surface 611 of the glass container 610. A platinum plate was used as the
30 counter electrode 630. The conductive substrate 621 of the optical semiconductor
electrode 620 and the counter electrode 630 were electrically connected by the
conducting wire 650. The current flowing between the optical semiconductor
electrode 620 and the counter electrode 630 was measured with an ammeter 660.
[0108]
35 A solar simulator manufactured by SERIC Ltd. was used to apply simulated
sunlight. The surface of the optical semiconductor electrode 620 was irradiated
with light at an intensity of 1 kWm 2 through the light incident portion 611 of the
23
hydrogen generation device 600 of Example 7. The gas generated on the surface of
the counter electrode 630 was collected for 60 minutes, and the components of the
collected gas were analyzed and the amount of gas produced was measured by gas
chromatography. The photocurrent flowing between the optical semiconductor
electrode and the counter electrode was measured with the ammeter 660. Th5 e
apparent quantum efficiency was calculated using the amount of gas produced in
the counter electrode 630. About 30 L of oxygen was generated from the optical
semiconductor electrode 620, and about 60 L of hydrogen was generated from the
counter electrode 630. About 0.1 mA photocurrent was observed, and thus the
10 calcualted apparent quantum efficiency was about 1%.
[0109] It was confirmed from these results that the single-phase NbON film used
in this example had optical semiconductor properties for hydrogen generation by
decomposition of water under light irradiation.
[0110] (Example 8)
15 A hydrogen generation device was produced in the same manner as in
Example 7 except that the film 2 of Example 2 was used instead of the film 1 of
Example 1, and a photocurrent was measured. A photocurrent with a photocurrent
density of 0.1 mAcm 2 derived from NbON was obtained, although the film 2 of
Example 2 was not a single-phase film.
20
INDUSTRIAL APPLICABILITY
[0111] The NbON film of the present invention has excellent optical semiconductor
properties for hydrogen production by decomposition of water under light
irradiation. Therefore, the NbON film of the present invention is useful for various
25 photocatalyst-related techniques.

CLAIMS
1. A NbON film in which a photocurrent is generated by light irradiation, the
NbON film being a single-phase film.
5
2. The NbON film according to claim 1, wherein the NbON film is formed by
bringing, into contact with a heated substrate, vaporized R1N=Nb(NR2R3)3 (where
R1, R2, and R3 are each independently a hydrocarbon group) and at least either one
selected from oxygen and water vapor10 .
3. The NbON film according to claim2, wherein R1 is a tertiary butyl group
( C(CH3)3), and R2 and R3 are each independently a straight-chain alkyl group
(n CnH2n+1, where n is an integer of 1 or more).
15
4. A method for producing a NbON film, the method comprising the steps of:
(I) vaporizing R1N=Nb(NR2R3)3 (where R1, R2, and R3 are each
independently a hydrocarbon group); and
(II) bringing, into contact with a heated substrate, the vaporized
20 R1N=Nb(NR2R3)3 and at least either one selected from oxygen and water vapor,
wherein in the step (II), the substrate is heated to a temperature that is
equal to or higher than a boiling point of the R1N=Nb(NR2R3)3 and is equal to or
lower than a decomposition temperature of the R1N=Nb(NR2R3)3.
25
5. The method for producing a NbON film according to claim 4, wherein R1 is a
tertiary butyl group ( C(CH3)3), and R2 and R3 are each independently a
straight-chain alkyl group (n CnH2n+1, where n is an integer of 1 or more).
30 6. A hydrogen generation device comprising:
an optical semiconductor electrode including a conductor and the NbON film
according to claim 1 disposed on the conductor;
a counter electrode connected electrically to the conductor;
a water-containing electrolyte disposed in contact with a surface of the
35 NbON film and a surface of the counter electrode; and
a container containing the optical semiconductor electrode, the counter
electrode, and the electrolyte,
25
wherein hydrogen is generated by irradiating the NbON film with light.
7. An energy system comprising:
the hydrogen generation device according to claim 6;
a hydrogen storage connected to the hydrogen generation device by a firs5 t
pipe and configured to store the hydrogen generated in the hydrogen generation
device; and
a fuel cell connected to the hydrogen storage by a second pipe and
configured to convert the hydrogen stored in the hydrogen storage into electricity
10 and heat.