WO2013035291A1 - 半導体材料及びこれを用いた光水素生成デバイス並びに水素の製造方法 - Google Patents
半導体材料及びこれを用いた光水素生成デバイス並びに水素の製造方法 Download PDFInfo
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- WO2013035291A1 WO2013035291A1 PCT/JP2012/005526 JP2012005526W WO2013035291A1 WO 2013035291 A1 WO2013035291 A1 WO 2013035291A1 JP 2012005526 W JP2012005526 W JP 2012005526W WO 2013035291 A1 WO2013035291 A1 WO 2013035291A1
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Images
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
- B01J27/24—Nitrogen compounds
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J19/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
- B01J19/12—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor employing electromagnetic waves
- B01J19/122—Incoherent waves
- B01J19/127—Sunlight; Visible light
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J35/00—Catalysts, in general, characterised by their form or physical properties
- B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
- B01J35/39—Photocatalytic properties
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/34—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation
- B01J37/341—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation making use of electric or magnetic fields, wave energy or particle radiation
- B01J37/347—Ionic or cathodic spraying; Electric discharge
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
- C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
- C01B3/04—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by decomposition of inorganic compounds, e.g. ammonia
- C01B3/042—Decomposition of water
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B1/00—Electrolytic production of inorganic compounds or non-metals
- C25B1/01—Products
- C25B1/02—Hydrogen or oxygen
- C25B1/04—Hydrogen or oxygen by electrolysis of water
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B1/00—Electrolytic production of inorganic compounds or non-metals
- C25B1/50—Processes
- C25B1/55—Photoelectrolysis
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
- C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
Definitions
- the present invention relates to a semiconductor material having a photocatalytic ability suitable for water decomposition reaction by light irradiation, and a photohydrogen generation device using the same.
- the present invention also relates to a method for producing hydrogen using the semiconductor material.
- Patent Document 1 discloses a method in which an n-type semiconductor electrode and a counter electrode are arranged in an electrolytic solution, and the surface of the n-type semiconductor electrode is irradiated with light to collect hydrogen and oxygen from the surfaces of both electrodes. It is disclosed.
- the n-type semiconductor electrode it is described that a TiO 2 electrode, a ZnO electrode, a CdS electrode, or the like is used.
- Patent Document 2 discloses a gas generator having a metal electrode and a nitride semiconductor electrode connected to each other, and both electrodes are installed in a solvent.
- a nitride of a group 13 element such as indium, gallium and aluminum is used for the nitride semiconductor electrode.
- Such a conventional semiconductor electrode has a problem that the hydrogen generation efficiency in the water decomposition reaction by irradiation with sunlight is low. This is because the wavelength of light that can be absorbed by semiconductor materials such as TiO 2 and ZnO is short, and these semiconductor materials can only absorb light with a wavelength of approximately 400 nm or less, so the proportion of available light in the total sunlight is small. This is because, in the case of TiO 2 , it is very low at about 4.7%. Furthermore, the utilization efficiency of the sunlight is about 1.7% in consideration of the loss due to the fundamental heat loss in the absorbed light.
- TaON, Ta 3 N 5, Ag 3 VO 4, and the like have been reported as semiconductor materials that can absorb visible light having a longer wavelength.
- the wavelength of light that can be absorbed is at most about 500 to 600 nm.
- the proportion of available light in the total sunlight is about 19%.
- the utilization efficiency is only about 8%.
- Patent Document 3 reports that LaTaON 2 can absorb visible light up to 650 nm. This is one that can absorb light having the longest wavelength among the semiconductor materials that can be decomposed by water. In the case of LaTaON 2 that can absorb light with a wavelength of 650 nm or less, the proportion of available light in the total sunlight is about 41%. However, considering the theoretical heat loss, the utilization efficiency is only about 20%.
- compound semiconductor materials including Se and Te, and specific sulfides (CdS, ZnS, Ga 2 S 2 , In 2 S 3 , ZnIn 2 S 4 , ZnTe, ZnSe, CuAlSe 2 and CuInS 2 etc.) It is a material that can absorb light having a relatively long wavelength. However, these materials have poor water stability and are not practical in water decomposition reactions.
- Patent Document 4 discloses that carbonitride containing a Group 5 element is used as an electrode active material for an oxygen reduction electrode used as a positive electrode of a polymer electrolyte fuel cell.
- Patent Document 4 does not disclose a technical idea of using a carbonitride containing a Group 5 element as a semiconductor material (photocatalytic material) that functions as a photocatalyst.
- the carbonitride of patent document 4 is a mixture of carbonitride and an oxide etc., and the usage form differs from the photocatalyst material generally used with a single phase high crystal
- the band edge (level of valence band and conduction band) of the semiconductor material has an oxidation-reduction potential (hydrogen generation level and oxygen generation level). ). Therefore, the requirements for practically usable semiconductor materials for water splitting are that the wavelength range of light that can be absorbed is long (the band gap is small), and the band edge sandwiches the redox potential of water. And being stable in water under light irradiation. However, to date, no semiconductor material that meets all these requirements has been found.
- the hydrogen production efficiency is obtained. If the hydrogen generation efficiency is low, the installation area for generating the required amount of hydrogen will naturally increase, leading to an increase in cost as well as installing on a roof of a finite area of a detached house such as a solar cell. It becomes difficult. Since the power generation efficiency assumed to be reachable by simple (not tandem) Si solar cells is about 20%, in order to obtain an efficiency equal to or higher than that of solar cells, the absorption edge wavelength is 700 nm or more. A semiconductor material having a certain band gap is required. Furthermore, since the decomposition voltage of water is about 1.23 V at room temperature, a semiconductor material having a smaller band gap (absorption edge wavelength of 1008 nm or more) cannot theoretically decompose water. Therefore, it is desired to find a semiconductor material having a band gap in which the absorption edge wavelength is between 700 nm and 1008 nm (1.23 to 1.77 eV).
- an object of the present invention is to provide a semiconductor material that has a band gap with an absorption edge wavelength of 1008 nm or less and that makes the band gap as long as possible.
- oxynitride containing at least any one element selected from Group 4 elements and Group 5 elements at least any one part selected from oxygen and nitrogen is substituted with carbon.
- the present invention it is possible to provide a semiconductor material having a band gap with an absorption edge wavelength of 1008 nm or less, and making the band gap as long as possible.
- FIG. 1 is a conceptual diagram of energy levels of a semiconductor material and a conventional photocatalytic material in an embodiment of the present invention.
- FIG. 2A is a diagram showing a material in which oxygen sites of NbON are replaced with carbon
- FIG. 2B is a diagram showing a material in which NbON is doped with carbon.
- 3A to 3D are diagrams showing the density of electronic states of the Ta-based material by the first principle calculation.
- 4A to 4D are diagrams showing the electronic state density of the Nb-based material by the first principle calculation.
- FIGS. 5A to 5F are diagrams showing the electronic state densities of the Nb-based materials by the first principle calculation.
- 6A to 6F are diagrams showing the density of electronic states of Nb-based materials according to the first principle calculation.
- FIG. 7A to 7F are diagrams showing the electronic state densities of the Nb-based materials by the first principle calculation.
- FIG. 8 is a diagram showing a thin film X-ray diffraction measurement result of a Ta-based material.
- FIG. 9 is a diagram showing a thin film X-ray diffraction measurement result of the Ta-based material.
- FIG. 10 is a diagram showing the SIMS (Secondary / Ion / Mass / Spectrometry) measurement results of the Ta-based material.
- FIG. 11 is a diagram showing light absorption characteristics of a Ta-based material.
- FIG. 12 is a diagram showing the SIMS measurement results of the Nb-based material.
- FIG. 13 is a diagram illustrating the light absorption characteristics of the Nb-based material.
- FIG. 14 is a diagram showing a thin film X-ray diffraction measurement result of an Nb-based material.
- FIG. 15 is a schematic cross-sectional view showing an example of a photohydrogen generation device according to an embodiment of the present invention.
- FIG. 16 is a schematic sectional drawing which shows another example of the photohydrogen generating device in embodiment of this invention.
- the present inventors provide a novel semiconductor material that has a band gap with an absorption edge wavelength of 1008 nm or less, and that makes the band gap as long as possible, and is stable in water under light irradiation. It came to offer. Furthermore, the present inventors also provide a method capable of producing hydrogen with high efficiency by light irradiation using such a novel semiconductor material, and a device capable of generating hydrogen with high efficiency by light irradiation. It came to.
- the semiconductor material substituted with The semiconductor material according to the first aspect has a band gap with an absorption edge wavelength of 1008 nm or less, and the band gap is longer than that of a conventional semiconductor material.
- the semiconductor material according to the first aspect can be selected by appropriately selecting at least one element selected from Group 4 elements and Group 5 elements, an element substituted with carbon, a substitution amount with carbon, and the like.
- Its band edge sandwiches the redox potential of water, and can absorb visible light of 700 nm or more, and also has excellent stability in water (particularly neutral to acidic) during light irradiation. Materials are also feasible. Therefore, when light is decomposed by irradiating the semiconductor material of the present invention immersed in a solution containing an electrolyte and water to decompose water, hydrogen can be generated with higher efficiency than before.
- a second aspect of the present invention provides a semiconductor material having a single-phase structure in the first aspect.
- the semiconductor material according to the second aspect can realize higher charge separation efficiency.
- a third aspect of the present invention provides a semiconductor material having a monoclinic crystal structure in the first or second aspect.
- Nb is used as a Group 4 or Group 5 element
- O and / or part of NbON is replaced with C.
- O and / or NbON is maintained.
- a part of N is substituted with C.
- the semiconductor material according to the third aspect of the present invention has a monoclinic crystal structure, the crystal structure after substitution with C can maintain the crystal structure before substitution.
- the closer to a single crystal the higher the quantum efficiency can be expected, so it is desirable that the crystallinity is high.
- high quantum efficiency can be obtained although not as high as that of a single crystal.
- the semiconductor material according to any one of the first to third aspects wherein at least one element selected from the group 4 element and the group 5 element is Nb. To do.
- the semiconductor material according to the fourth aspect can absorb visible light having a higher wavelength.
- a fifth aspect of the present invention provides a semiconductor material according to any one of the first to fourth aspects, wherein the group 5 element is substantially pentavalent.
- the semiconductor material according to the fifth aspect can have a clearer band gap.
- a sixth aspect of the present invention provides a semiconductor material having a photocatalytic ability in any one of the first to fifth aspects. According to the semiconductor material which concerns on a 6th aspect, provision of the photocatalyst which can utilize sunlight effectively is attained.
- a seventh aspect of the present invention is a method for producing hydrogen, comprising the steps of immersing the semiconductor material according to the first aspect in a solution containing an electrolyte and water, and irradiating the semiconductor material with light to decompose the water I will provide a.
- hydrogen can be generated with higher efficiency than in the prior art.
- An eighth aspect of the present invention is a photohydrogen generation device including a container, an electrode including a photocatalytic material, and a counter electrode, wherein the photocatalytic material includes the semiconductor material according to the first aspect. provide. According to the hydrogen generation device according to the eighth aspect, hydrogen can be generated with higher efficiency than before.
- a material used as a photocatalyst can absorb even a relatively long wavelength visible light as shown in the band state diagram on the left of FIG.
- the semiconductor material must have a band edge (level of valence band and conduction band) between the hydrogen generation level and the oxygen generation level, and the semiconductor material is irradiated with light. Must be stable in the water below.
- the valence band of a general oxide is composed of oxygen p-orbitals
- the valence band position is usually at a deep level (high potential) (right in FIG. 1).
- the valence band of nitride and oxynitride is composed of a p-orbital of nitrogen or a hybrid state of p-orbitals of oxygen and nitrogen. Therefore, the valence band position is usually at a level (lower potential) shallower than the valence band position of the oxide (center of FIG. 1). Therefore, as disclosed in Patent Document 3, when an oxynitride is used, a photocatalytic material (semiconductor material) having a smaller band gap than when an oxide is used can be obtained.
- oxynitride is preferable to simple nitride.
- oxynitrides which have a band gap larger than the desired band gap (absorption edge wavelength 700 nm), and the band gap is about 1.91 eV (absorption edge wavelength 650 nm) at a minimum. It is.
- the present inventors have found from the results of the first principle calculation that the valence band composed of the p-orbital of carbon is a shallower level (lower potential) than the valence band positions of nitride and oxynitride. I found out. As a result of further investigations, the present inventors have determined that at least one selected from oxygen and nitrogen in an oxynitride containing at least any one element selected from Group 4 elements and Group 5 elements. It has been found that a semiconductor material partially substituted with carbon has a valence band composed of carbon p-orbitals and a smaller band gap than nitride and oxynitride. Here, many simple carbides of Group 4 or Group 5 elements have metallic conductivity, and many have no band gap. Therefore, the present invention requires a semiconductor material in which a part of oxygen and / or nitrogen of the oxynitride is substituted with carbon.
- FIGS. 2A and 2B illustrate the difference between a material in which the monoclinic NbON oxygen site is replaced with carbon and a material in which NbON is doped with carbon.
- FIG. 2A shows a state in which the oxygen site of NbON is replaced with carbon. In this state, a carbon atom is present instead of the oxygen atom at the oxygen site that was originally present.
- FIG. 2B shows a state where NbON is doped with carbon. In this state, carbon is doped in a portion that is not a site of Nb, oxygen, and nitrogen while maintaining the crystal structure of NbON.
- the energy level is described using an electrochemical energy level instead of the vacuum level often used in the semiconductor field.
- the concept is based on the vacuum level, but not necessarily the absolute level).
- the semiconductor material of the present embodiment in the oxynitride containing at least one element selected from Group 4 elements and Group 5 elements, at least one part selected from oxygen and nitrogen is carbon. Substituted semiconductor material.
- a single-phase highly crystalline semiconductor material as the photocatalytic material from the viewpoint of charge separation efficiency. This is because, generally, a highly crystalline semiconductor tends to have fewer defects. However, in the case of a single phase, there are not necessarily many defects even in an amorphous state, and in such a case, an amorphous state is acceptable.
- the semiconductor material when used as a photocatalytic material for the purpose of hydrogen generation by water splitting, in the present invention, the semiconductor material preferably has a single-phase structure. Note that the semiconductor material may contain a small amount of impurities and defects as long as the single-phase structure is maintained.
- the semiconductor material preferably has as high a crystallinity as possible.
- the amount of defects is preferably 1 mol% or less.
- the semiconductor has a thin shape as long as the single-phase structure and high crystallinity are maintained. It is desirable to be formed. That is, when a semiconductor is formed as a semiconductor layer, it is desirable that the semiconductor layer is thin. This is because the charge separation efficiency is improved when the semiconductor layer is thin.
- the thickness of the semiconductor layer is desirably 500 nm or less.
- the thickness of the semiconductor layer is desirably 10 nm or more. Therefore, the thickness of the semiconductor layer is desirably 10 nm or more and 500 nm or less.
- the semiconductor layer having a thickness of 10 nm or more and 500 nm or less has a high surface area. This is because, as described above, when the thickness of the semiconductor layer is thick, the amount of light absorption increases, but the charge separation efficiency decreases.
- the semiconductor layer has a small thickness and a high surface area. This can be achieved by devising the shape of the substrate on which the semiconductor layer is provided. This is because by making the surface area high, light transmitted through the semiconductor layer or scattered light during light irradiation is absorbed again by the semiconductor layer.
- TaON is known to be a semiconductor having a photocatalytic ability capable of absorbing light having a wavelength of 500 nm or less.
- NbON no single phase has been reported so far, but when a new synthesis process was developed in the present invention and a single phase was synthesized, a semiconductor having a photocatalytic function capable of absorbing light with a wavelength of 600 nm or less. I found out.
- both TaON and NbON are water-decomposable photocatalytic materials, and it was also confirmed that each valence band and conduction band sandwich the redox potential of water.
- the band gap of the material in which the oxygen and / or nitrogen sites of TaON were replaced with carbon was calculated by first principle calculation.
- 3A to 3D show electronic state density distributions (Density of State) according to first-principles calculations between TaON and a material in which the oxygen and / or nitrogen sites of TaON are replaced with carbon.
- the unit cell contains 4 Ta atoms, 4 oxygen atoms, and 4 nitrogen atoms, and this unit cell is infinitely continuous due to the periodic boundary condition.
- FIG. 3B shows the electronic state density distribution of the material obtained by replacing one oxygen in the unit cell with carbon. That is, FIG.
- FIG. 3B shows that the unit cell contains 4 Ta atoms, 3 oxygen atoms, 4 nitrogen atoms and 1 carbon atom, and therefore contains 8.3 at% (mol%) of carbon.
- the electronic state density distribution of the material is shown.
- FIG. 3C shows the electronic state density distribution of the material obtained by replacing one nitrogen in the unit cell with carbon. That is, FIG. 3C shows that the unit cell contains 4 Ta atoms, 4 oxygen atoms, 3 nitrogen atoms and 1 carbon atom, and therefore contains 8.3 at% (mol%) of carbon.
- FIG. 3D shows the electron density distribution of the material obtained by substituting one oxygen and one nitrogen in the unit cell with two carbons. That is, FIG. 3D shows that the unit cell contains 4 Ta atoms, 3 oxygen atoms, 3 nitrogen atoms and 2 carbon atoms, and therefore contains 16.7 at% (mol%) of carbon.
- the electronic state density distribution of the material is shown.
- FIGS. 4A to 4D show electronic state density distributions (Density of State) according to first-principles calculations between NbON and a material obtained by replacing the oxygen and / or nitrogen sites of NbON with carbon.
- the unit cell includes 4 Nb atoms, 4 oxygen atoms, and 4 nitrogen atoms, and this unit cell is infinitely continuous due to the periodic boundary condition.
- FIG. 4B shows the electronic state density distribution of the material obtained by replacing one oxygen in the unit cell with carbon. That is, FIG.
- FIG. 4B shows that the unit cell contains 4 Nb atoms, 3 oxygen atoms, 4 nitrogen atoms and 1 carbon atom, and therefore contains 8.3 at% (mol%) of carbon.
- the electronic state density distribution of the material is shown.
- FIG. 4C shows an electronic state density distribution of a material obtained by replacing one nitrogen in the unit cell with carbon. That is, FIG. 4C shows that the unit cell contains 4 Nb atoms, 4 oxygen atoms, 3 nitrogen atoms and 1 carbon atom, and therefore contains 8.3 at% (mol%) of carbon.
- FIG. 4D shows the electronic state density distribution of the material obtained by substituting one oxygen and one nitrogen in the unit cell with two carbons. That is, FIG. 4D shows that the unit cell contains 4 Nb atoms, 3 oxygen atoms, 3 nitrogen atoms, and 2 carbon atoms, and therefore contains 16.7 at% (mol%) of carbon.
- the electronic state density distribution of the material is shown.
- FIGS. 5A to 5F show electronic state density distributions (Density of State) according to first-principles calculations for NbON and a material obtained by replacing the NbON oxygen site with carbon.
- FIGS. 4A to 4D calculations were performed using a unit cell containing 4 Nb atoms.
- a unit cell containing 8 or more Nb atoms was used. Calculated as a grid. The calculation was performed assuming that the unit cell is infinitely continuous due to the periodic boundary condition. Therefore, FIG.
- FIG. 5B shows the electronic state density distribution of the material obtained by replacing one oxygen in the unit cell containing eight Nb atoms with carbon. That is, FIG. 5B shows that the unit cell contains 8 Nb atoms, 7 oxygen atoms, 8 nitrogen atoms and 1 carbon atom, and therefore contains 4.2 at% (mol%) of carbon. It is.
- FIG. 5C shows the electronic state density distribution of the material obtained by replacing three oxygen atoms in a unit cell containing 16 Nb atoms with three carbon atoms. That is, FIG. 5C shows that the unit cell contains 16 Nb atoms, 13 oxygen atoms, 16 nitrogen atoms, and 3 carbon atoms, and therefore contains 6.3 at% (mol%) of carbon. The electronic state density distribution of the material is shown.
- FIG. 5C shows the electronic state density distribution of the material obtained by replacing one oxygen in the unit cell containing eight Nb atoms with carbon. That is, FIG. 5B shows that the unit cell contains 8 Nb atoms, 7 oxygen atoms, 8
- FIG. 5D shows the electronic state density distribution of a material obtained by substituting one oxygen in a unit cell containing four Nb atoms as in FIG. 4B with carbon for reference. That is, FIG. 5D shows that the unit cell contains 4 Nb atoms, 3 oxygen atoms, 4 nitrogen atoms and 1 carbon atom, and therefore contains 8.3 at% (mol%) of carbon.
- the electronic state density distribution of the material is shown.
- FIG. 5E shows an electronic state density distribution of a material obtained by replacing one oxygen in a unit cell containing 32 Nb atoms with one carbon. That is, FIG. 5E shows that the unit cell contains 32 Nb atoms, 31 oxygen atoms, 32 nitrogen atoms, and 1 carbon atom, and therefore contains 1.0 at% (mol%) of carbon.
- FIG. 5F shows an electronic state density distribution of a material obtained by replacing one oxygen in a unit cell containing 16 Nb atoms with one carbon. That is, FIG. 5F shows that the unit cell contains 16 Nb atoms, 15 oxygen atoms, 16 nitrogen atoms, and 1 carbon atom, and therefore contains 2.1 at% (mol%) of carbon.
- the electronic state density distribution of the material is shown.
- the band gap was 1.61 eV, that is, the calculation result was 770 nm.
- the result of the band gap calculation by the first principle calculation is generally calculated to be smaller than the actual band gap. Since the actually measured band gap of NbON is 600 nm, it has been found that the band gap is calculated to be 0.78 times smaller than the actually measured as in the case of FIG. 4A in the first principle calculation.
- FIGS. 5A to 5F are calculations in which carbon is substituted for NbON having the same monoclinic crystal structure. In general, the first-principles calculation results show the same tendency for the same crystal structure. From this, the band gap was estimated by applying the ratio of the NbON band gap calculation result of FIG.
- FIGS. 5B to 5F As a result, when carbon is contained in 8.3 at% (mol%) (FIG. 5D), a band gap-shaped valley shape is observed in the electric state density, but a Fermi level exists in the valence band. In addition, since the Fermi level exists below the first peak from the top of the valence band, it can be seen that the band gap is extremely small or close to a conductor. In the case where 6.3 at% (mol%) of carbon is contained (FIG. 5C), the Fermi level (0 eV) is present in the conduction band level, so that it is clearly a conductor. However, when the carbon content is 4.2 at% (mol%) or less (FIGS.
- Fermi level (0 eV) exists in the valence band top. That is, it has been found that when carbon is substituted at the oxygen site of NbON, a more visible material can be obtained in a preferable electronic state with a carbon content of 4.2 at% (mol%) or less.
- the band gap by the quantum chemistry calculation is generally calculated smaller than the actual band gap.
- the tendency of the electronic state density distribution can be obtained with high accuracy. That is, in determining whether a semiconductor has a band gap or a conductor, it is calculated with high accuracy.
- FIGS. 6A to 6F show electronic state density distributions (Density of State) according to first-principles calculations for NbON and a material obtained by substituting NbON nitrogen sites with carbon.
- FIGS. 4A to 4D calculations were performed using a unit cell containing 4 Nb atoms in the unit cell, but in order to change the amount of carbon substitution, a unit cell containing 8 or more Nb atoms was used. As calculated. The calculation was performed assuming that the unit cell is infinitely continuous due to the periodic boundary condition. Therefore, FIG.
- FIG. 6B shows the electronic state density distribution of the material obtained by replacing one nitrogen in the unit cell containing eight Nb atoms with carbon. That is, FIG. 6B shows that the unit cell contains 8 Nb atoms, 8 oxygen atoms, 7 nitrogen atoms, and 1 carbon atom, and therefore contains 4.2 at% (mol%) of carbon.
- the electronic state density distribution of the material is shown.
- FIG. 6C shows the electronic state density distribution of the material obtained by replacing three nitrogens in a unit cell containing 16 Nb atoms with three carbons. That is, the unit cell contains 16 Nb atoms, 16 oxygen atoms, 13 nitrogen atoms, and 3 carbon atoms, and therefore contains 6.3 at% (mol%) of carbon.
- the electronic state density distribution of the material is shown.
- FIG. 6D shows the electronic state density distribution of a material obtained by replacing one nitrogen in a unit cell containing four Nb atoms as in FIG. 4C with carbon for reference. That is, FIG. 6D shows that the unit cell contains 4 Nb atoms, 4 oxygen atoms, 3 nitrogen atoms and 1 carbon atom, and therefore contains 8.3 at% (mol%) of carbon.
- the electronic state density distribution of the material is shown.
- FIG. 6E shows an electronic state density distribution of a material obtained by replacing one nitrogen in a unit cell containing 32 Nb atoms with one carbon. That is, FIG. 6E shows that the unit cell contains 32 Nb atoms, 32 oxygen atoms, 31 nitrogen atoms, and 1 carbon atom, and therefore contains 1.0 at% (mol%) of carbon.
- FIG. 6F shows an electronic state density distribution of a material obtained by replacing one nitrogen in a unit cell containing 16 Nb atoms with one carbon. That is, FIG. 6F shows that the unit cell contains 16 Nb atoms, 16 oxygen atoms, 15 nitrogen atoms and 1 carbon atom, and therefore contains 2.1 at% (mol%) of carbon.
- the electronic state density distribution of the material is shown.
- the band gap was 1.61 eV, that is, 770 nm, and the calculation result was obtained.
- the result of the band gap calculation by the first principle calculation is generally calculated to be smaller than the actual band gap. Since the actually measured band gap of NbON is 600 nm, it has been found that the band gap is calculated to be 0.78 times smaller than the actually measured as in the case of FIG. 4A in the first principle calculation.
- 6A to 6F are calculations in which carbon is substituted for NbON having the same monoclinic crystal structure. In general, the first-principles calculation results show the same tendency for the same crystal structure. Therefore, the ratio of the NbON bandgap calculation result of FIG.
- the bandgap of the semiconductor material becomes longer in any case.
- this semiconductor material is used as a photocatalytic material, the oxygen sites It has been found that a material in which is substituted with carbon is preferable.
- FIGS. 7A to 7F show electronic state density distributions (Density of State) according to first-principles calculations for NbON and a material obtained by replacing the oxygen and nitrogen sites of NbON with carbon.
- FIGS. 4A to 4D calculations were performed using a unit cell containing 4 Nb atoms in the unit cell, but in order to change the amount of carbon substitution, a unit cell containing 8 or more Nb atoms was used. As calculated. The calculation was performed assuming that the unit cell is infinitely continuous due to the periodic boundary condition. Thus, FIG.
- FIG. 7B shows the electronic state density distribution of the material obtained by replacing one oxygen and one nitrogen in a unit cell containing 16 Nb atoms with two carbons. That is, FIG. 7B shows that the unit cell contains 16 Nb atoms, 15 oxygen atoms, 15 nitrogen atoms, and 2 carbon atoms, and therefore contains 4.2 at% (mol%) of carbon.
- the electronic state density distribution of the material is shown.
- FIG. 7C shows the electronic state density distribution of the material obtained by replacing one oxygen and one nitrogen site in a unit cell containing eight Nb atoms with two carbons. That is, FIG. 7C shows that the unit cell contains 8 Nb atoms, 7 oxygen atoms, 7 nitrogen atoms and 2 carbon atoms, and therefore contains 8.3 at% (mol%) of carbon.
- FIG. 7D shows the electronic density of states of the material obtained by substituting two carbons for one oxygen and one nitrogen site in the unit cell containing the same four Nb atoms as FIG. 3D for reference. Distribution is shown. That is, FIG. 7D shows that the unit cell contains 4 Nb atoms, 3 oxygen atoms, 3 nitrogen atoms, and 2 carbon atoms, and therefore contains 16.7 at% (mol%) of carbon.
- FIG. 7E shows the electronic state density distribution of the material obtained by replacing one oxygen and two nitrogen sites in a unit cell containing 16 Nb atoms with three carbons. That is, FIG.
- FIG. 7E shows that the unit cell contains 16 Nb atoms, 15 oxygen atoms, 14 nitrogen atoms, and 3 carbon atoms, and therefore contains 6.3 at% (mol%) of carbon.
- the electronic state density distribution of the material is shown.
- FIG. 7F shows the electronic state density distribution of the material obtained by replacing two oxygen and one nitrogen sites in a unit cell containing 16 Nb atoms with three carbons. That is, FIG. 7F shows that the unit cell contains 16 Nb atoms, 14 oxygen atoms, 15 nitrogen atoms, and 3 carbon atoms, and therefore contains 6.3 at% (mol%) of carbon.
- the electronic state density distribution of the material is shown.
- FIG. 7A In the first-principles calculation of NbON in FIG. 7A, a calculation result with a band gap of 1.61 eV, that is, 770 nm was obtained.
- the result of the band gap calculation by the first principle calculation is generally calculated to be smaller than the actual band gap. Since the actually measured band gap of NbON is 600 nm, it has been found that the band gap is calculated to be 0.78 times smaller than the actually measured as in the case of FIG. 4A in the first principle calculation.
- FIGS. 7A to 7F are calculations in which carbon is substituted for NbON having the same monoclinic crystal structure. In general, the first-principles calculation results show the same tendency for the same crystal structure. Therefore, the ratio of the NbON band gap calculation result and the actual measurement value in FIG.
- FIG. 7A was applied to the band gap calculation results in FIGS. 7B to 7F to estimate the band gap.
- FIGS. 7B to 7F As a result, when 16.7 at% (mol%) of carbon is contained (FIG. 7D), it is apparent that the carbon is a conductor.
- FIG. 7C When carbon was contained in 8.3 at% (mol%) (FIG. 7C), it was found that a Fermi level (0 eV) exists at the top of the valence band. That is, it has been found that when carbon is substituted on the oxygen and nitrogen sites of NbON, a more visible material can be obtained in a preferable electronic state with a carbon content of 8.3 at% (mol%) or less. Further, even when the ratio of oxygen and nitrogen substituted with carbon is not 1: 1 (FIG. 7E), it was found that a more visible material can be obtained in a preferable electronic state. In FIG. 7F, it is a semiconductor. However, this is not preferable because there is an empty state of electrons in
- the band gap by the quantum chemistry calculation is generally calculated smaller than the actual band gap.
- the shape of the electronic state density distribution can be obtained with high accuracy. That is, it is calculated with high accuracy in determining whether or not it has a band gap as a semiconductor or a conductor.
- the conduction band is composed of the outermost d-orbital in which the metal element of Ta or Nb is empty, even if the oxygen and / or nitrogen sites are replaced with carbon, the d-orbital of Ta or Nb The level does not change. For this reason, it has been found that the effect of reducing the band gap by replacing the oxygen and / or nitrogen sites with carbon is an effect obtained by changing the valence band level. Therefore, it has been found that by controlling the carbon substitution amounts of oxygen and nitrogen, the size of the band gap can be controlled and at the same time the valence band level can be controlled.
- this semiconductor material is an n-type semiconductor, the amount of carbon substituting the sites of oxygen and nitrogen can be controlled to It is possible to freely design the oxygen generation overvoltage.
- the oxygen generation overvoltage is larger than the hydrogen generation overvoltage. Therefore, it has been found that the ability to control the oxygen generation overvoltage is effective in device design.
- the semiconductor material of the present embodiment can absorb visible light as described above, and the band edge sandwiches the redox potential of water.
- the semiconductor material of this embodiment is further excellent in stability in water during light irradiation. Therefore, if the semiconductor material of this embodiment is immersed in water containing an electrolyte and irradiated with sunlight to decompose the water, hydrogen can be generated with higher efficiency than before.
- a method for producing hydrogen including the step of decomposing water by irradiating light onto the semiconductor material of the present embodiment, which is immersed in a solution containing an electrolyte and water, can also be realized.
- the production method of the present embodiment can be carried out in the same manner as a known method (for example, see Patent Documents 1 and 2) by replacing a known photocatalytic material with the above-described photocatalytic material.
- a known method for example, see Patent Documents 1 and 2
- the following method using the photohydrogen generation device of the present embodiment may be mentioned.
- the photohydrogen generation device of the present embodiment is a photohydrogen generation device including a container, an electrode including a photocatalytic material, and a counter electrode, and the photocatalytic material includes the semiconductor material of the present embodiment.
- the structural example of the hydrogen generation device of this embodiment is shown in FIG.15 and FIG.16.
- the photocatalyst material is formed into an electrode shape, and a separate electrode that is electrically connected is provided to separate hydrogen and oxygen production sites.
- a structure may be employed in which hydrogen is generated from one surface of one electrode and oxygen is generated from the opposite surface.
- the 15 includes a container 9, a photocatalytic electrode 2, a conductive substrate 1, and a counter electrode 3.
- the container 9 has two openings 8 for collecting hydrogen and oxygen, respectively, in the upper part thereof. Moreover, it has the two opening parts 8 used as the water supply port in the lower part.
- a solution 6 containing an electrolyte and water is accommodated in the container 9.
- the container 9 has a separator 4 between the photocatalyst electrode 2 and the counter electrode 3 in order to separate hydrogen and oxygen production sites.
- the separator 4 has a function of transmitting ions and blocking a gas generated on the photocatalyst electrode 2 side and a gas generated on the counter electrode 3 side.
- positioned in the container 9 among the containers 9 is comprised with the material which permeate
- the photocatalytic electrode 2 and the counter electrode 3 are electrically connected by a conducting wire 7.
- the photocatalytic electrode 2 is a semiconductor having a band gap, it is generally less conductive than a metal or the like. In addition, it is necessary to prevent recombination of electrons and holes as much as possible. Therefore, it is preferable to reduce the thickness of the photocatalytic electrode 2. Therefore, here, the photocatalytic electrode 2 is formed on the conductive substrate 1 in a thin film (about 50 to 500 nm). Also, to increase the light absorption efficiency. It is preferable to increase the surface area of the photocatalytic electrode 2.
- the photocatalytic electrode 2 is preferably highly crystalline, and in the case of a smooth electrode, in the thickness direction of the electrode, and in the case of a non-smooth electrode, in a direction parallel to the moving direction of electrons and holes generated by photoexcitation.
- the crystal is preferably oriented.
- FIG. 16 Another photohydrogen generating device shown in FIG. 16 also includes a container 9, a photocatalytic electrode 2, a conductive substrate 1, and a counter electrode 3 (in FIG. 16, the same reference numerals as those in FIG. 15 are used for the same members).
- the container 9 has four openings 8, and a solution 6 containing an electrolyte and water is accommodated in the container 9.
- a photocatalytic electrode 2 is provided on one surface of the conductive substrate 1, and a counter electrode 3 is provided on the other surface.
- the photocatalytic electrode 2 is formed in a thin film shape (about 50 to 500 nm).
- the photocatalytic electrode 2 and the counter electrode 3 are electrically connected by the conductive substrate 1.
- the inside of the container 9 is divided into a photocatalyst electrode 2 side and a counter electrode 3 side by a separator 4 and a conductive substrate 1.
- positioned in the container 9 among the containers 9 is comprised with the material which permeate
- Hydrogen and oxygen can be generated by irradiating light (for example, sunlight) from the light incident part 5 to the photohydrogen generation device shown in FIGS.
- light for example, sunlight
- the photohydrogen generation device since the photohydrogen generation device has a long wavelength range of light that can be absorbed, hydrogen can be generated with high efficiency.
- Example 1 A TaCNO (semiconductor in which TaON oxygen or nitrogen sites are replaced with carbon) thin films and a TaON semiconductor thin film for comparison were fabricated on a quartz substrate by reactive sputtering. Table 1 shows the sputter deposition conditions.
- FIG. 8 shows a thin film X-ray diffraction pattern of a TaON thin film prepared by reactive sputtering of oxygen and nitrogen using TaN as a sputtering target (starting material). It was confirmed that a substantially single-phase TaON thin film was obtained except for the quartz halo peak of the substrate.
- FIG. 9 shows a thin film X-ray diffraction of a TaCNO thin film (thin film made of a material in which the oxygen or nitrogen sites of TaON are replaced with carbon) produced by reactive sputtering of oxygen and nitrogen using TaC as a sputtering target. It is a pattern. Similarly, it was confirmed that a substantially single-phase TaON thin film was obtained except for the quartz halo peak of the substrate.
- TaCNO As for TaCNO, TaC is used as a target, so that the crystal system of the obtained thin film is a monoclinic TaON single phase, but a small amount of carbon remains, replacing oxygen or nitrogen sites. Can be expected. Further, since the sputtering is performed at a high temperature of 800 ° C., generally, carbon should be diffused quickly and replaced with oxygen or nitrogen sites instead of defect-like dopes.
- FIG. 10 shows SIMS analysis results in the depth direction of TaON and TaCNO thin films. Since 1 ⁇ 10 23 atoms / cm 3 is about 100 at% (mol%), the carbon content of TaCNO is 1.5 to 1.0 at% (mol%), and the carbon content of TaON is 0 It was 0.5 to 0.3 at% (mol%). Thereby, it discovered that the carbon content rate of TaCNO was large by the difference of predominance over TaON.
- FIG. 11 shows the measurement results of the light absorption characteristics of the TaON thin film and the TaCNO thin film formed on the quartz substrate. Interference fringes are observed, but from the tangent line of the light absorption curve excluding the interference fringes, the TaON band gap is 500 nm, the TaCNO band gap is 580 nm, and the TaON oxygen or nitrogen sites are 1.5 to 1.0 at. It has been found that the band gap is increased by 80 nm by substitution with carbon of% (mol%).
- TaON or TaCNO was formed on the glassy carbon substrate under the same reactive sputtering conditions as the working electrode.
- the conductive glassy carbon was connected as a current collector to a platinum electrode as a counter electrode with a lead wire.
- the working electrode and counter electrode are immersed in a 0.1 M sulfuric acid aqueous solution, and a TaON or TaCNO electrode is irradiated with a xenon lamp that is split using a prism, and the wavelength dependence of photocurrent in the wavelength range of 900 nm to 300 nm. Was measured.
- the maximum photocurrent was 2 ⁇ A / cm 2 at a wavelength of 400 nm.
- Example 2 By reactive sputtering, an NbCNO (semiconductor material in which the oxygen or nitrogen sites of NbON were replaced with carbon) thin film and an NbON thin film for comparison were formed on a quartz substrate. Table 2 shows the sputter deposition conditions.
- NbCNO when the substrate temperature was increased to a temperature at which it was sufficiently crystallized, it was easy to form Nb oxide. Therefore, the substrate temperature was set to 300 ° C.
- Nb: oxygen: nitrogen 33-36 at%: 33-35 at%: 32-34 at% for both NbON and NbCNO.
- carbon since it is difficult to analyze trace amounts of carbon in Auger electron spectroscopy, carbon was quantified by another measurement.
- FIG. 12 shows SIMS analysis results in the depth direction of the NbON thin film and the NbCNO thin film. Since 1 ⁇ 10 23 atoms / cm 3 is about 100 at% (mol%), the carbon content of NbCNO is about 3.5 at% (mol%), and the carbon content of NbON is about 0.25 at% ( Mol%). Thereby, it discovered that the carbon content rate of NbCNO was large by the predominance difference over NbON.
- FIG. 13 shows the measurement results of the light absorption characteristics of the NbON thin film and the NbCNO thin film formed on the quartz substrate. Interference fringes can be seen. From the tangent line of the light absorption curve excluding the interference fringes, the NbON band gap is 600 nm, the NbCNO band gap is 720 nm, and the NbON oxygen or nitrogen site is about 3.5 at% (moles). %) was found to increase the band gap by 120 nm.
- an NbON or NbCNO film was formed on a glassy carbon substrate under the same reactive sputtering conditions to form an operating electrode.
- the conductive glassy carbon was connected as a current collector to a platinum electrode as a counter electrode with a lead wire.
- Wavelength dependence of photocurrent in the wavelength range of 900 nm to 300 nm by immersing these working electrode and counter electrode in a 0.1 M sulfuric acid aqueous solution and irradiating a NbON or NbCNO electrode with a xenon lamp that is split using a prism. was measured.
- the maximum photocurrent was 11 ⁇ A / cm 2 at a wavelength of 450 nm.
- photocurrent can be observed at a wavelength of 600 nm or less for NbON and at a wavelength of about 720 nm or less for NbCNO.
- the observation of photocurrent in an aqueous solution containing no substance other than sulfuric acid indicates that a water splitting reaction has occurred.
- continuous light irradiation was carried out for 2 weeks, but the photocurrent did not change during that time.
- Example 3 In order to confirm that NbON and NbCNO shown in Example 2 have monoclinic NbON as a parent phase, the sputter output is reduced and the deposition rate is reduced by reactive sputtering, and the NbON thin film is formed on a quartz substrate. Made above. Table 3 shows the sputter deposition conditions.
- NbON is an unknown material, and since there have been no reports of successful single-phase synthesis in the past, there is no X-ray diffraction reference data. Therefore, assuming that NbON also has the same monoclinic crystal structure as TaON, Nb atoms are arranged at the same coordinates as Ta in TaON, and the structure is optimized by first-principles calculation. Was calculated. For confirmation, the lattice constant of TaON was also calculated for TaON by using a known crystal structure and optimizing the structure by first principle calculation. The results agreed well with the reported lattice constants present in the X-ray diffraction database. In general, the crystal lattice constant according to the first principle calculation can be calculated with high accuracy. FIG.
- NbON thin film prepared by reactive sputtering of oxygen and nitrogen using NbN as a sputtering target. It was confirmed that a substantially single-phase NbON thin film was obtained except for the quartz halo peak of the substrate.
- NbON is formed on the glassy carbon substrate under the same reactive sputtering conditions as the working electrode, and the conductive glassy carbon is connected to the platinum electrode as a counter electrode and a lead wire as a current collector.
- the wavelength dependence of the photocurrent was measured in the range of 900 nm to 300 nm by irradiating the NbON electrode with a xenon lamp that was immersed in a sulfuric acid aqueous solution and spectrally separated using a prism. Although the maximum photocurrent was 20 ⁇ A / cm 2 at a wavelength of 450 nm, it was found that NbON can observe a photocurrent at a wavelength of 600 nm or less.
- TaCNO and NbCNO were produced by using a reactive sputtering method targeting TaC and NbC, respectively.
- TaCNO and NbCNO may be formed using other known thin film manufacturing methods such as sputtering, MOCVD, and plasma CVD, and well-known methods such as carbon ion implantation are applied to previously prepared TaON thin films and NbON thin films. It is also possible to employ a method of injecting carbon by the above method to obtain TaCNO and NbCNO, respectively.
- oxygen or nitrogen can be obtained by a method such as a thermal diffusion treatment in a nitrogen atmosphere or an ammonia atmosphere in which impurities such as oxygen and moisture are sufficiently removed. It is desirable to substitute carbon at the site. In the thermal diffusion treatment, if the temperature is raised to the lowest crystallization temperature of the material to be used, the shortest heat treatment time is sufficient as long as the apparatus can be set.
- the content of carbon in the semiconductor material is not particularly limited as long as the semiconductor function is not impaired by changing the crystal structure of the oxynitride. From the results of the first principle calculation, it was found that 8.3 at% (mol%) or less is preferable although it varies depending on the site where carbon is substituted. From the results of the first principle calculation, it was found that the band gap can be adjusted by controlling the amount of carbon substituted for oxygen or nitrogen within a range of 8.3 at% or less. At this time, it has been found that the electronic state of the d orbital constituting the conduction band is hardly influenced even by carbon substitution. Furthermore, it has been found that the valence band level can be controlled by controlling the amount of carbon substituting oxygen or nitrogen sites.
- the difference between the valence band level and the oxygen generation level is caused by an electrochemical reaction such as water electrolysis.
- an electrochemical reaction such as water electrolysis.
- the oxygen generation overvoltage can be controlled by controlling the carbon substitution amount and the valence band level.
- the oxygen generation overvoltage is small (the valence band level is high)
- the photocurrent per unit electrode area cannot be increased. Therefore, it is necessary to increase the electrode surface area and increase the photocurrent in device development. is there.
- there is a limit to increasing the surface area of the electrode depending on the electrode manufacturing process, there is a limit to increasing the surface area of the electrode.
- the group 5 element exhibits a semiconductor characteristic having a band gap in the case of the pentavalent maximum valence, and when the valence becomes smaller than the maximum valence, the density of electrons in the conduction band is reduced. It has been found that it has no clear band gap. Therefore, in the semiconductor material of the present invention, the Group 5 element is preferably substantially pentavalent (preferably 4.8 to pentavalent). Further, it is desirable that the Group 4 element is substantially tetravalent (preferably 3.8 to 4). This is because, for example, in the case of Nb, since the conduction band is composed of d orbitals of Nb, pentavalence in which electrons in the d orbits are empty is desirable.
- the fact that the group 5 element is substantially in a pentavalent state means that a valence in the vicinity of pentavalent is also allowed as long as it does not significantly affect the semiconductor characteristics. Is in the state of 4.8-5 valence.
- the fact that the group 4 element is substantially in a tetravalent state means that a valence in the vicinity of tetravalent is allowed as long as it does not significantly affect the semiconductor characteristics. 3.8 to 4 valence state.
- the oxygen or nitrogen sites of the group 5 element oxynitride are replaced with carbon.
- the group 4 element is composed of a tetravalent central metal element, for example, Zr 2 ON 2. It has also been found that even if the oxygen or nitrogen site of Ti 2 ON 2 is replaced with carbon, the effect of increasing the band gap wavelength can be obtained. Even when the oxygen or nitrogen site of Zr 2 ON 2 or Ti 2 ON 2 is substituted with carbon, an amorphous state is acceptable if it is a single phase, but it is preferably a cubic crystal in a crystallized state.
- hydrogen can be generated with high efficiency using sunlight.
- the obtained hydrogen can be used as a fuel for a fuel cell, for example.
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Abstract
Description
反応性スパッタにより、TaCNO(TaONの酸素又は窒素のサイトを炭素に置換した半導体)薄膜と、比較のためにTaONの半導体薄膜を、石英基板上に作製した。スパッタ成膜条件を表1に示す。
反応性スパッタにより、NbCNO(NbONの酸素または窒素のサイトが炭素で置換された半導体材料)薄膜と、比較のためのNbON薄膜とを、石英基板上に作製した。スパッタ成膜条件を表2に示す。
実施例2で示したNbONおよびNbCNOが、単斜晶系のNbONを母相としていることを確認するため、反応性スパッタにより、スパッタ出力を小さくし成膜速度を落として、NbON薄膜を石英基板上に作製した。スパッタ成膜条件を表3に示す。
Claims (8)
- 4族元素及び5族元素から選ばれる少なくとも何れか1種の元素を含有する酸窒化物において、酸素及び窒素から選ばれる少なくとも何れか1種の一部が炭素で置換された、半導体材料。
- 単相構造を有する、請求項1に記載の半導体材料。
- 単斜晶系の結晶構造を有する、請求項1に記載の半導体材料。
- 前記4族元素及び5族元素から選ばれる少なくとも何れか1種の元素がNbである、請求項1に記載の半導体材料。
- 前記5族元素が実質的に5価の状態である、請求項1に記載の半導体材料。
- 光触媒能を有する、請求項1に記載の半導体材料。
- 電解質及び水を含有する溶液に請求項1に記載の半導体材料を浸し、前記半導体材料に光を照射して前記水を分解する工程を含む、
水素の製造方法。 - 容器、光触媒材料を含む電極、及び対極を備えた光水素生成デバイスであって、
前記光触媒材料が、請求項1に記載の半導体材料を含む、光水素生成デバイス。
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CN201280043179.8A CN103889571B (zh) | 2011-09-06 | 2012-08-31 | 半导体材料及使用了它的光氢生成设备以及氢的制造方法 |
JP2013532431A JP5907973B2 (ja) | 2011-09-06 | 2012-08-31 | 水素の製造方法及び光水素生成デバイス |
US14/342,489 US9630169B2 (en) | 2011-09-06 | 2012-08-31 | Semiconductor material, optical hydrogen generating device using same, and method of producing hydrogen |
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WO2017013881A1 (ja) * | 2015-07-23 | 2017-01-26 | パナソニック株式会社 | ルチル型ニオブ酸窒化物及びその製造方法、並びに半導体構造体 |
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