JP2006224043A - PHOTOCATALYST BODY, PROCESS FOR PRODUCING THE SAME, AND ENERGY CONVERSION ELEMENT USING PHOTOCATALYST BODY - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photocatalytic body having a high photocatalytic function easily and with high productivity, and to provide a light-electric energy conversion element and a light-chemical energy conversion element with high conversion efficiency using the same.
The photocatalyst is composed of a metal oxide having a chemical bond between a metal and nitrogen, a chemical bond between the metal and oxygen, and oxygen deficiency, thereby improving electron conductivity and narrowing the energy gap. Since the width can be increased, an excellent photocatalytic effect is exhibited.
[Selection] Figure 1

Description

  The present invention relates to a photocatalyst and a method for producing the same, as well as a solar cell, an optical sensor, an optical-electric energy conversion element based on a photoelectric conversion principle, and an optical-chemical energy conversion element such as a hydrogen generator.

  In recent years, attempts to use photocatalysts have flourished, and they have a wide range of applications, from products with functions such as air purification, antifouling, antibacterial, water purification and deodorization, to components for hydrogen generators and dye-sensitized solar cells in the energy field. Development is planned.

  In the photocatalytic reaction, the photocatalyst absorbs light to be in an excited state, and molecules adsorbed thereon are activated, so that various functions are exhibited as a result. The size of this function varies depending on the photocatalyst material and irradiation light intensity. If the dependency on the irradiation light intensity is dependent on sunlight, how to design the photocatalyst material is highly functional. Is the key to

  Conventionally, a typical material that has been used as a photocatalyst is titanium oxide that has high chemical stability and is non-toxic, and is made visible light responsive by narrowing the original band gap. Many attempts have been made. One method is to coordinate a nitrogen atom in titanium oxide. In this case, due to the presence of the nitrogen atom, a valence band having a potential on the negative side of the 2p orbit of the oxygen atom or a level equivalent thereto is present. The band gap is considered to be narrowed by being formed. Specifically, first, a method of substituting a part of oxygen sites of a metal oxide such as titanium oxide with nitrogen atoms by sputtering, doping nitrogen atoms between lattices, or adding nitrogen atoms to crystal grain boundaries is mentioned. (See, for example, Patent Documents 1 to 4 below).

In addition, there is a technique obtained by firing a titanium complex in which a nitrogen-containing organic compound is coordinated to metal titanium (for example, see Patent Document 5 below). Another method is to form an ultrathin layer doped with nitrogen by exposing titanium oxide to an ion beam or alternating current plasma containing hydrogen and nitrogen (see, for example, Patent Document 6 below). There is also a method for producing titanium oxide having a Ti—O—N configuration using an emulsion combustion method (see, for example, Patent Document 7 below). Furthermore, in a method for producing titanium oxide by hydrolysis of titanium tetrachloride by burning a mixed gas of titanium tetrachloride and oxygen in the gas phase, NO, N ₂ O, or NO and N ₂ O are added to the mixed gas. There is a method of producing nitrogen-containing titanium oxide by coexistence (for example, see Patent Document 8 below). In addition, there is a method of producing visible light responsive titanium oxide containing nitrogen by lamp heating in a nitrogen-containing gas atmosphere (see, for example, Patent Document 9 below).

  Further, as a technique for obtaining visible light responsive titanium oxide, there is a method of forming an oxygen defect in a metal oxide. When oxygen defects occur, oxygen ion vacancies are generated to maintain electrical neutrality. When this occurs, tetravalent titanium ions are reduced to trivalent ions, thereby absorbing visible light. It is considered. As a method for forming such oxygen defect-containing titanium oxide, there is a method of firing titanium oxide in a reducing atmosphere containing a reducing gas (see, for example, Patent Document 10 below). In addition, there is a technique for forming an oxygen deficient type by performing any one of hydrogen plasma treatment, rare gas element plasma treatment, rare gas element ion implantation, or vacuum heating on titanium oxide (see, for example, Patent Document 11 below) ).

In addition, there is a method of shifting the light absorption edge to the long wavelength side by ion-implanting a metal element such as Cr or V into titanium oxide so as to be a visible light response type. (For example, see Patent Document 12 below).
Japanese Patent Laid-Open No. 2001-207082 JP 2001-205103 A Japanese Patent Laid-Open No. 2001-205094 JP 2003-231966 A Japanese Patent Laid-Open No. 2004-141739 JP 2003-265966 A Japanese Patent Laid-Open No. 2004-988 JP 2004-49969 A Japanese Patent Laid-Open No. 2003-40621 Japanese Patent Laid-Open No. 2002-361097 Japanese Patent Laid-Open No. 2001-212457 JP-A-9-262482

  However, each of the above-described examples has the following problems with respect to the functionality and manufacturing process of the photocatalyst.

  That is, in the photocatalysts described in Patent Documents 1 to 9, a part of oxygen sites of metal oxide such as titanium oxide is substituted with nitrogen atoms, nitrogen atoms are doped between lattices, or nitrogen atoms are added to crystal grain boundaries. Although it is a visible light responsive type by containing it, since the state density of the level formed by the inserted nitrogen impurity is not high, the excited form of carriers accompanying light absorption is the metal oxide material itself that is the base material Transition between bands is dominant, and there is a problem that visible light responsiveness is not greatly improved only by containing nitrogen.

  Further, there are various examples as described above as methods for containing nitrogen, but each method has the following problems. That is, the sputtering described in Patent Documents 1 to 4 has problems such as a low film-forming speed, damage to the substrate due to plasma, and low productivity, and the nitrogen-containing organic compound described in Patent Document 5 is disposed on titanium metal. In the method obtained by firing the positioned titanium complex, it becomes difficult to control stoichiometry due to carbon mixing, and quality degradation due to mixing of impurities in the organic compound becomes a problem. Further, in the technique of exposing titanium oxide to an ion beam or alternating current plasma containing hydrogen and nitrogen described in Patent Document 6, the ion beam has low mass productivity and difficulty in uniform formation, and exposure to alternating current plasma is based on plasma. Damage to the material, large area, and difficulty in mass processing are problems. Furthermore, the forming methods described in Patent Documents 7 to 9 are particularly high temperature processes, and have a problem that productivity is remarkably inferior.

  Further, the photocatalysts described in Patent Documents 10 and 11 are of a type having oxygen defects in the metal oxide, but the presence of oxygen defects shifts the absorption edge wavelength to a lower energy side, thereby improving the electron conductivity. On the other hand, when it is excessively contained, there is a problem that the carrier lifetime is reduced. Further, since the high temperature treatment is necessary for the formation process, there is a problem that productivity is remarkably inferior.

  The photocatalyst described in Patent Document 12 shifts the light absorption edge to the long wavelength side by ion-implanting a metal element such as Cr or V into titanium oxide, but uses ion implantation. Therefore, the manufacturing cost is high and the productivity is inferior.

  Accordingly, the present invention has been made in view of the above-mentioned problems, and the object thereof is to easily and efficiently produce a photocatalyst having a high photocatalytic function, and to use this to produce a high conversion efficiency photo-electric energy. It aims at providing a conversion element and a photochemical energy conversion element.

  The photocatalyst of the present invention is characterized by comprising a metal oxide having a chemical bond between a metal and nitrogen and a chemical bond between the metal and oxygen and having an oxygen deficiency.

  In the photocatalyst of the present invention, preferably, the metal oxide is titanium oxide or zinc oxide.

  The method for producing a photocatalyst according to the present invention comprises reducing and nitriding a metal oxide in a reducing atmosphere formed by contact of a heated catalyst with a gas having at least a nitrogen atom in the molecule. A photocatalyst is produced.

  In the method for producing a photocatalyst of the present invention, preferably, the reducing atmosphere contains ammonia.

  In the method for producing a photocatalyst of the present invention, the reducing atmosphere is preferably 200 ° C. or lower.

  The photoelectric conversion element of the present invention includes a conductive substrate serving as one electrode, a photocatalyst formed on the conductive substrate, a photoelectric converter electrically connected to the photocatalyst, and the photoelectric conversion. A hole transporter that is electrically connected to a body and transports holes, and the other electrode that is electrically connected to the hole transporter.

  The photo-chemical energy conversion element of the present invention is characterized in that the photocatalyst of the present invention is placed in water or an aqueous solution to generate hydrogen gas.

  The photovoltaic device of the present invention is characterized in that the generated electric power of the photoelectric-electrical energy conversion element of the present invention is supplied to a load.

  The photocatalyst of the present invention is composed of a metal oxide having a chemical bond between a metal and nitrogen and a metal and oxygen, and having an oxygen deficiency. Therefore, the photocatalyst is more negative than the 2p orbit of the oxygen atom due to the presence of the nitrogen atom. The band gap is considered to be narrowed by the formation of a valence band having a potential on the side (vacuum level side) or a level equivalent thereto, and the electrical neutrality is reduced when oxygen defects occur. Oxygen ion vacancies are generated to maintain this, and it is considered that metal ions are reduced thereby to absorb visible light. Accordingly, the energy gap can be narrowed and the conductivity of electrons can be improved, so that an excellent photocatalytic effect is exhibited in the visible light region. In addition, by forming the photocatalyst of the present invention at a low temperature using the active species generated by the catalytic decomposition reaction of the heated catalyst and gas, the heat history to the substrate is reduced, and light with excellent conversion efficiency. -It becomes possible to produce an electrical energy conversion element or a photo-chemical energy conversion element.

  In the photocatalyst of the present invention, since the metal oxide is preferably titanium oxide or zinc oxide, titanium and zinc are easily oxidizable metals for photocatalysts, and these oxides are chemically stable. Therefore, there is an advantage that the photocatalyst is relatively excellent in weather resistance and can be used stably for a long time.

  The method for producing a photocatalyst of the present invention comprises reducing and nitriding a metal oxide in a reducing atmosphere formed by contacting a heated catalyst with a gas having at least a nitrogen atom in the molecule, thereby producing the photocatalyst of the present invention. In the gas phase around the metal oxide, both the reduction and nitridation reactions of the metal oxide are extremely rapid due to the presence of high-density reducing radicals and radicals that contribute to nitridation. Since the process proceeds rapidly, the metal oxide can be reduced and nitrided reliably in a short time.

In the photocatalyst production method of the present invention, preferably, since the reducing atmosphere contains ammonia (NH ₃ ), ammonia is easily decomposed by the catalytic decomposition reaction between the gas and the heated catalyst body, thereby contributing to the reduction reaction. Thus, the hydrogen radical and the nitrogen-hydrogen complex radical contributing to the nitriding reaction are simultaneously generated, and the control and reproducibility of the reduction and nitriding reaction of the metal oxide can be easily performed.

  The method for producing a photocatalyst of the present invention preferably has a reducing atmosphere of 200 ° C. or lower, which is extremely low compared to the conventional method. Therefore, the influence of the thermal history on the base material of the photocatalyst and the substrate carrying the photocatalyst Can be reduced, and deterioration of the base material and the base material can be suppressed.

  The light-electric energy conversion element of the present invention includes a conductive substrate serving as one electrode, a photocatalyst formed on the conductive substrate, a photoelectric converter electrically connected to the photocatalyst, and an electric power to the photoelectric converter. In the photocatalyst that serves as an electron transporting part, a band due to the presence of nitrogen atoms is provided. Since the gap is narrowed and visible light is absorbed by a change in electron density due to oxygen ion vacancies caused by oxygen defects, it is possible to improve electron conductivity in the visible light region. Therefore, the photoelectric conversion characteristics are improved with the improvement of the light absorption characteristics and the electron transport characteristics.

  The photo-chemical energy conversion element of the present invention is such that the photocatalyst of the present invention is put into water or an aqueous solution to generate hydrogen gas. By increasing the light absorption coefficient, the efficiency of hydrogen generation is improved as the light absorption characteristics and electron transport characteristics of the photocatalyst body serving as the light absorption portion are improved.

  Since the photovoltaic device of the present invention is configured to supply the generated power of the above-mentioned photovoltaic-electric energy conversion element of the present invention to a load, the photovoltaic-electric energy of the present invention having excellent light absorption characteristics and electron transport characteristics. Since the conversion element is used, a photovoltaic device having an improved voltage value and current value after photoelectric conversion is obtained.

  Embodiments of a photocatalyst body, a photocatalyst body manufacturing method, a photo-electric energy conversion element, a photo-chemical energy conversion element, and a photovoltaic device according to the present invention will be described in detail below.

  The photocatalyst of the present invention comprises a metal oxide having a chemical bond between metal and nitrogen and a chemical bond between metal and oxygen and oxygen deficiency. The metal oxide is preferably titanium oxide, zinc oxide, tin oxide, hafnium oxide, zirconium oxide, strontium titanate, zinc titanate, tungsten oxide, barium titanate, iron titanate, bismuth oxide, iron oxide, oxide Although it consists of indium or a composite thereof, titanium oxide or zinc oxide is preferable as a material that exhibits a particularly strong photocatalytic action. Hereinafter, description will be made using titanium oxide as an example.

  FIG. 1 is a spectrum obtained by measuring the photocatalyst of the present invention by X-ray photoelectron spectroscopy (XPS). As a conventional example for comparison, titanium dioxide powder (“P25” manufactured by Nippon Aerosil Co., Ltd.) is used as ammonia. The spectrum results of the sample treated at 600 ° C. for 10 hours (hr) in the atmosphere are also shown. An X-ray photoelectron spectrometer (“Quantum 2000” manufactured by PHI) was used for XPS measurement. FIG. 1 shows the vicinity of a peak attributed to 2p electrons of titanium, and the presence or absence of a Ti—N bond, a Ti—O bond, or the like can be confirmed from the amount of chemical shift. In the conventional example, the presence of Ti—N bonds generated by the ammonia treatment is confirmed, and it can be seen that nitriding has occurred. On the other hand, in the example of the present invention, peaks derived from Ti—N bonds, Ti—O bonds and Ti atoms appear at a high level, and oxygen defects are generated due to a reduction action together with nitriding. I understand. In particular, the peak derived from the Ti atom is weak in intensity, but the anatase-type titanium oxide shows that the four bonds with the oxygen atom coordinated to titanium are substantially broken, It is thought that it received a strong reducing action locally.

  FIG. 2 is a diagram showing the light transmittance of a sample obtained by applying and baking the above conventional example and the titanium oxide of the present invention on a glass substrate on which a fluorine-doped tin oxide film is formed. The coating was performed using a paste in which titanium oxide particles were dispersed in distilled water to which a surfactant was added. From FIG. 2, the transmittance of the sample of the present invention is lower than that of the conventional example, particularly in the range of short wavelength (about 400 nm) to medium wavelength (about 800 nm), and the amount of light absorption in the titanium oxide layer is increased. You can see that

  In particular, the increase in absorption rate at short wavelengths is caused by the fact that titanium oxide is doped with nitrogen, which narrows the energy gap of titanium oxide, and as a result, the absorption edge wavelength shifts. It is considered that the increase in the absorption rate due to the presence of energy levels in the forbidden band caused by the presence of oxygen defects and free carrier absorption due to an increase in the carrier concentration in titanium oxide. From this, it can be said that a titanium oxide having a high light absorption rate was obtained from a short wavelength to a medium wavelength, unlike a simply nitrided titanium oxide or a titanium oxide having oxygen defects. Thereby, the hole generation density of titanium oxide at the time of light irradiation increases, and as a result, a high photocatalytic function is obtained.

  FIG. 3 shows an example of a production apparatus for producing the photocatalyst body of the present invention. First, the chamber 1 is a vacuum vessel made of SUS (stainless steel), quartz or the like, and has a gas introduction port 2 for introducing a gas therein, and further includes a heating catalyst body 4 connected to a power source 3. ing. The power source 3 uses a DC power source in FIG. 3, but there is no problem even if an AC power source is used. The heating catalyst body 4 is preferably made of a material having a high melting point and excellent workability, and W, Ta, C, Mo, Ti or a compound thereof is preferably used. Further, the substrate 6 having the metal oxide layer 7 formed on the heater 5 is fixed to the bottom surface of the chamber 1 to form the photocatalyst of the present invention. Hereinafter, the details of the forming method will be described.

  First, the substrate 6 only needs to have a function as a support, and a metal substrate, a glass substrate, a resin substrate, a ceramic substrate, or the like can be used. A metal oxide layer 7 such as titanium oxide or zinc oxide is formed on the substrate 6. Specifically, a slurry in which a metal oxide powder is dispersed in a solvent or a paste prepared using a sol-gel method is applied, a method of drying and firing, a method of forming by a vapor phase growth method, a surface of a metal substrate The method etc. which oxidize and make the metal oxide layer 7 are mentioned.

The substrate 6 is placed on the heater 5 and the substrate 6 temperature is adjusted to a temperature of 200 ° C. or lower. Next, a gas having hydrogen atoms and nitrogen atoms is introduced from the gas inlet 2 into the chamber 1 to adjust the pressure, and then the heating catalyst body 4 is energized and heated by the power source 3. The introduction gas, hydrogen and nitrogen, hydrogen and ammonia, the ammonia only, but nitrogen trifluoride and hydrogen, and the like, it contains at least ammonia gas, primary-hydrogen radicals and NH ₂ radicals by heating the catalyst body 4 Since they are dissociated as a reaction and each has a reducing effect and a nitriding effect on the metal oxide, there is an advantage that the treatment can be easily performed.

  Here, the temperature of the heating catalyst body 4 is preferably 700 to 1800 ° C., and if it is 700 ° C. or less, the decomposition efficiency of the gas is lowered and the progress of the reduction reaction and nitriding reaction of the metal oxide is suppressed. Further, at a temperature of 1800 ° C. or higher, there arises a problem that the components of the heating catalyst body 4 are scattered and adhered to and mixed on the substrate 6 to deteriorate the film quality of the metal oxide layer 7.

  A major feature of the formation method of the present invention is that a large amount of reducing radicals and radicals contributing to nitridation are both produced by the high gas decomposition efficiency of the heating catalyst body 4, and thus, even at a low temperature of 200 ° C. or less. Reduction and nitridation of the metal oxide are performed rapidly. When the photocatalyst of the present invention is used in a light-receiving electronic device as described below, there are many cases where it is treated together with a transparent electrode. However, considering heat resistance such as ITO, the temperature is 200 ° C. or less and for a short time. In the production method of the present invention that can be treated with the above, it is possible to form a photocatalyst having a high function without deteriorating the quality of the transparent electrode. Reduction and nitridation of the metal oxide is possible even at a substrate 6 temperature higher than 200 ° C., but this causes an increase in the resistance value and a decrease in the transmittance of the transparent electrode, resulting in a decrease in device characteristics.

  On the other hand, only the powdered metal oxide may be put in a container and the treatment may be performed using the above-described manufacturing apparatus and conditions. The container preferably has a stirring function, and a homogeneous photocatalyst can be obtained by stirring during the treatment.

  Next, an example in which the photocatalyst body of the present invention is applied to a light-electric energy conversion element will be described with reference to FIG.

  First, the substrate 8 may be any substrate as long as it has a function as a support. For example, a transparent glass substrate, a glass substrate surface having a textured structure to prevent light reflection, a translucent glass substrate, a transparent plastic plate Further, a transparent material such as a transparent plastic film or an inorganic transparent crystal, a transparent material that transmits light, a substrate of a colored material such as a metal substrate, a metal film, or a ceramic substrate can be used.

The electrode 9 formed on the upper surface of the substrate 8 is made of a low resistance material, for example, tin oxide, indium oxide, or a composite oxide thereof. More particularly, F (fluorine) or Sb _In 2 _O 3, such as _{In 2 O 3, In 4 Sn} 3 O 12 doped with _SnO 2, SnO ₂ and Mn and Mo doped with antimony () -SnO ₂ composite oxides. A tin oxide, an indium oxide, or a composite oxide thereof has a high transmittance in the visible light region among transparent conductive materials, and a low resistance material is easily obtained. ) Is particularly preferably used as an electrode material on the light receiving surface side. Further, the sheet resistance of the electrode 9 is 20Ω / □ or less, preferably 10Ω / □ or less, and in order to achieve this, an extraction electrode made of a metal layer having a mesh shape in plan view may be additionally formed. . As a material for the extraction electrode, Ag, Al, Cu, Ti, Ni, Fe, Zn, Mo, W or a compound thereof can be used.

  The electrode 9 can be easily formed by a spray pyrolysis method, a paste method, a dip coating method, or the like, in addition to a vacuum film forming technique such as a sputtering method, a vapor deposition method, an ion plating method, or a CVD method. it can.

  Further, when the substrate 8 is a sufficiently low resistance material, the electrode 9 may be omitted and the substrate 8 may have an electrode function.

SnO ₂ , ZnO, TiO ₂ or the like is used as the metal oxide that becomes the electron transport layer 10 and the base material of the photocatalyst. In addition, a band gap adjusting material or a material doped with a small amount of impurities may be used for the purpose of improving charge transport characteristics. Furthermore, the above materials may be used in combination. Among the above materials, it is particularly preferable to use titanium oxide (TiO ₂ ) or zinc oxide (ZnO). Among metal oxides used as the electron transport layer 10, this is particularly advantageous in that it has excellent carrier transport properties, a simple manufacturing process, and easy formation of a large area. Because.

  The photocatalyst may be formed by reducing and nitriding a metal oxide serving as a base material in layers on the electrode 9, or after forming the metal oxide serving as a base material in layers on the electrode 9. Reduction and nitriding may be performed. In the latter case, when the electrode 9 is a material having low reduction resistance, it is preferable to cover the exposed portion of the electrode 9 with a mask or the like during the reduction process.

Since the photocatalyst of the present invention has a high light absorption rate from the middle wavelength to the short wavelength as described above, the density of carriers excited in the photocatalyst is high. As a result, the short circuit current density increases. In addition, since the oxygen concentration (concentration of about 1 × 10 ¹⁸ / cm ³ to 1 × 10 ²² / cm ³ ) due to moderately present oxygen concentration is increased compared to the conventional one, This contributes to a decrease in internal resistance in the same layer and an increase in the internal electric field between the photoexciters, and as a result, the short-circuit current density, open-circuit voltage, and fill factor of the device are improved.

  Note that a dense layered oxide semiconductor layer may be inserted between the electrode 9 and the electron transport layer 10. Thereby, the leakage current of the element is reduced and the open circuit voltage value is improved.

  The photoexciter 11 indicates a portion where carriers are excited by light irradiation. For example, photoexciter 11 is a ruthenium complex, phthalocyanine dye, cyanine dye, merocyanine dye, porphyrin dye, perylene dye, anthraquinone dye, azo dye, quinophthalone dye, naphthoquinone dye, quinacridone dye, triphenylmethane dye, xanthene dye, berylene dye It is preferably composed of an organic dye such as an indigo dye or an inorganic dye.

In addition, considering the adsorptivity with the electron transport layer 10 and the charge transport property, the photoexciter 11 has a carboxyl group, a hydroxyl group, an alkoxy group, a sulfonic acid group, an ester group, a phosphonyl group, a hydroxyalkyl, etc. in the molecule. It is preferable to have a group. Further, as the inorganic material, a single semiconductor such as Si or Ge, a compound semiconductor such as CdSe, CdS, InP, Bi ₂ S ₃ , PbS, ZnS, CuInS ₂ , or CuInSe ₂ or those appropriately doped with impurities may be used. Good. Furthermore, organic-inorganic hybrid materials can be similarly applied.

  The counter substrate 12 only needs to have a function as a support. For example, a light-transmitting material such as a glass substrate, a plastic substrate, a plastic film, and an inorganic transparent crystal, a metal substrate, a metal film, a ceramic substrate, etc. A substrate made of a colored material can be used.

The counter electrode 13 is preferably made of a material having high conductivity, and a metal or a transparent conductive layer is suitably used. Specifically, Ag, Al, Cu, Ti, Ni, Fe, Zn, Mo, W or a compound thereof is used for metals, and SnO ₂ doped with F or Sb, SnO ₂ , Mn, or Mo is used for transparent conductive layers. Examples thereof include In ₂ O ₃ —SnO ₂ composite oxides such as In ₂ O ₃ and In ₄ Sn ₃ O ₁₂ .

  Further, when using the electrolytic solution as the hole transport layer 14, a catalyst layer of platinum, carbon, rhodium, ruthenium or the like is formed on the counter electrode 13 in order to cause the reduction reaction of redox ions in the electrolytic solution at a sufficient rate. It is preferable to form.

  Note that the sheet resistance of the counter electrode 13 is 20Ω / □ or less, preferably 10Ω / □ or less, and in order to achieve this, an extraction electrode made of a mesh metal or the like may be additionally formed. As a material for the extraction electrode, Ag, Al, Cu, Ti, Ni, Fe, Zn, Mo, W or a compound thereof can be used.

  If the counter substrate 12 is made of a sufficiently low resistance material, the counter electrode 13 may be omitted and the counter substrate 12 may have an electrode function.

  For the hole transport layer 14, as an electrolytic solution, for example, a solution containing a material containing potassium chloride or sodium hydroxide and sodium sulfide or sulfur as an aqueous solution is used. In addition, a mixture prepared by mixing tetrapropylammonium iodide, lithium iodide, iodine, or the like with acetonitrile, methoxypropionitrile, or the like can be used.

  Examples of the material for the hole transport layer 14 instead of the above include transparent conductive oxides, electrolytes such as gel electrolytes and solid electrolytes, organic hole transport agents, and ultrathin metal films.

Examples of the transparent conductive oxide include CuI, Cu ₂ O, CuS, CuInSe, CuInS, CuSCN, CoO, NiO, FeO, MoO ₂ and Cr ₂ O ₃ .

  Gel electrolytes are roughly classified into chemical gels and physical gels. The chemical gel is a gel formed by a chemical bond by a cross-linking reaction or the like, and the physical gel is gelled near room temperature by a physical interaction. As a gel electrolyte, acetonitrile, ethylene carbonate, propylene carbonate, or a mixture thereof was mixed with a host polymer such as polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polyvinyl alcohol, polyacrylic acid, polyacrylamide, and polymerized. A gel electrolyte is preferred. When using a gel electrolyte or solid electrolyte, a low-viscosity precursor is included in the oxide semiconductor layer, and a two-dimensional or three-dimensional crosslinking reaction is caused by means such as heating, ultraviolet irradiation, or electron beam irradiation. Can be gelled or solidified.

  As the ion conductive solid electrolyte, a solid electrolyte having a polymer chain such as polyethylene oxide, polyethylene oxide or polyethylene having a salt such as sulfoimidazolium salt, tetracyanoquinodimethane salt or dicyanoquinodiimine salt is preferable. As the molten salt of iodide, iodides such as imidazolium salt, quaternary ammonium salt, isoxazolidinium salt, isothiazolidinium salt, pyrazolidium salt, pyrrolidinium salt, pyridinium salt can be used.

  Examples of the molten salt of iodide include 1,1-dimethylimidazolium iodide, 1, methyl-3-ethylimidazolium iodide, 1-methyl-3-pentylimidazolium iodide, 1-methyl- 3-isopentylimidazolium iodide, 1-methyl-3-hexylimidazolium iodide, 1-methyl-3-ethylimidazolium iodide, 1,2-dimethyl-3-propylimidazole iodide, 1-ethyl- Examples thereof include 3-isopropylimidazolium iodide and pyrrolidinium iodide.

Examples of the organic hole transport agent include triphenyldiamine and OMeTAD (2,2 ′, 7,7′-tetrakis (N, N-di-p-methoxyphenyl-amine) 9,9′-spirobifluorene). Molten salt electrolytes such as imidazolium salts, triazolium salts and pyridinium salts, mixtures of LiI, NaI, KI and CaI ₂ and I ₂ , or mixtures of LiBr, NaBr, KBr and CaBr ₂ and Br ₂ with alcohols and nitrile compounds An electrolyte solution dissolved in a carbonate compound and organic polysilane are preferably used.

  The sealing material 15 is preferably one having corrosion resistance to the hole transport layer material and moisture absorption preventing function and sufficient adhesive strength, such as EVA (ethylene vinyl acetate copolymer resin), ethylene-ethyl acrylate copolymer ( EEA), fluororesin, epoxy resin, acrylic resin, saturated polyester resin, amino resin, phenol resin, polyamideimide resin, UV curable resin, silicone resin, fluororesin, urethane resin, or a composite thereof can be used.

  As described above, a photoelectric conversion element having a high photoelectric conversion efficiency can be manufactured. Further, a photovoltaic device such as a solar cell configured to supply the generated power of this element to a load may be configured. Is possible. Since this photovoltaic device uses the photoelectric energy conversion element of the present invention, it can be a photoelectric conversion device with improved voltage and current values obtained by photoelectric conversion.

Next, as an example in which the photocatalyst of the present invention is applied to an electro-chemical energy conversion element, a hydrogen generator will be described with reference to FIG. First, an aqueous solution 17 whose solution resistance is lowered by adding a supporting electrolyte or the like is filled in a container 16 having a light transmission window (not shown) at least partially. As the material of the container 16, metal, ceramics, glass, resin, or the like can be used, and it is preferable to select a material that does not cause a chemical reaction with the aqueous solution 17. Examples of the aqueous solution 17 include NaHCO ₃ aqueous solution, Na ₂ SO ₄ aqueous solution, NaOH aqueous solution, KOH aqueous solution, KCl aqueous solution, Ba (OH) ₂ aqueous solution, HNO ₃ aqueous solution, and H ₂ SO ₄ aqueous solution. These materials are preferable because the degree of dissociation of ions is high and the ions themselves have a relatively high mobility. At this time, when the ion concentration is about 3 to 4 mol / L (liter), the solution resistance becomes small.

  Next, the anode 18 and the cathode 19 are connected and immersed in the aqueous solution 17. It is preferable to use the photocatalyst of the present invention for the anode 18, and titanium oxide, strontium titanate, and barium titanate are mainly used as the base material. The photocatalyst body may be obtained by sintering a material that is a base material that has been subjected to reduction treatment and nitriding treatment, or may be subjected to reduction treatment and nitridation treatment after forming a metal oxide that serves as a base material into a plate shape. As the cathode 19, a metal such as platinum or platinum black, a p-type semiconductor, or the like can be used. Further, an oxygen collection container 20 is disposed above the anode 18, and a hydrogen collection container 21 is disposed above the cathode 19, and gas generated by each electrode is collected. Note that a bias voltage may be applied by the external power source 22 in order to adjust the potential difference between the redox potential of the aqueous solution and the work function of the electrode.

  As described above, the hydrogen generator configured as described above has a high light absorption rate from the middle wavelength to the short wavelength as described above. Therefore, the hole generation density in the photocatalyst increases, and as a result, hydrogen and oxygen The amount generated per unit time increases. This corresponds to the fact that the valence band of the nitrided metal oxide has shifted to a higher energy side as compared with the base material, and the conductivity is relatively close to the reduction potential of water like titanium oxide. A metal oxide having a band is effective because the amount of light absorption can be increased by narrowing the gap without greatly shifting the position of the conduction band. Furthermore, since the carrier concentration of the metal oxide layer is increased as compared with the conventional one due to moderately present oxygen defects, it contributes to the reduction of internal resistance in the same layer, and the unit of hydrogen and oxygen as described above The amount generated per hour increases.

  Furthermore, it is possible to construct a hybrid system having a photo-chemical-electrical energy conversion function by using hydrogen generated in the above apparatus as a hydrogen supply source of the fuel cell.

  5 g of anatase-type titanium dioxide powder (“P25” manufactured by Nippon Aerosil Co., Ltd.) is mixed with 10 ml of water, 0.1 ml of acetylacetone and 0.1 ml of polyoxyethylene octylphenyl ether, and stirred with a stirrer. A paste in which particles were dispersed was prepared. This was applied by a doctor blade method onto a glass substrate on which a fluorine-doped tin oxide film having a sheet resistance of about 10Ω / □ was formed, and then heat-treated at 450 ° C. for 30 minutes. At this time, the titanium dioxide layer after firing was a porous layer, and the film thickness was 9 μm.

  This was set in a chamber of a device in which a heating catalyst body was disposed, and reduction treatment and nitriding treatment were performed. At this time, a heated catalyst body obtained by processing a 0.5 mmφ (diameter) W wire into a coil shape was used. After introducing ammonia gas into the chamber and maintaining the pressure at 10 Pa, the heated catalyst body was heated to 1650 ° C. by electric heating. The substrate temperature was adjusted to 200 ° C. or lower. The surface of the titanium dioxide layer started to turn yellow about 30 seconds after the shutter between the substrate and the heated catalyst body was opened, and turned black when the treatment was performed for 30 minutes.

  FIG. 1 shows an XPS spectrum of a sample treated for 3 minutes. As a comparative example (conventional example), titanium dioxide powder (“P25” manufactured by Nippon Aerosil Co., Ltd.) was similarly used at 600 ° C. in an ammonia atmosphere. The spectrum results of the sample processed for 10 hours are also shown. As described above, in the titanium dioxide of the present invention, peaks derived from Ti—N bonds, Ti—O bonds, and Ti atoms appear, and oxygen defects are generated due to a reduction action as well as a nitriding action. I understand. On the other hand, in the conventional example, the presence of a slight Ti—N bond is confirmed and it can be seen that nitriding has occurred.

  The treatment time of the nitriding treatment and the reduction treatment of the present invention is overwhelmingly short compared with other methods (the other method is about 2 to 10 hours and the method of the present invention is about 5 seconds to 1 minute), The fact that ammonia was effectively decomposed into reducing radicals and radicals contributing to nitriding contributed greatly due to the high gas decomposition efficiency characteristic of the treatment method of the present invention. In addition, as shown in FIG. 2, it can be seen that in the embodiment of the present invention, the light absorption amount is increased in the region from the medium wavelength to the short wavelength as compared with the conventional example. In order to confirm the improvement of the photocatalytic function accompanying the increase in the amount of light absorption, the photocatalysts of the examples of the present invention and the conventional examples were immersed in an aqueous solution of methylene blue, and irradiated with light to evaluate the ability to decompose methylene blue. At this time, the concentration of the methylene blue aqueous solution was 5 ppm, and light irradiation was performed with an artificial solar illumination lamp (“XC-100” manufactured by Celic Co., Ltd.). As a result, the amount of change in absorbance at 660 nm was about 1.4 times that in the example of the present invention compared to the conventional example, and it was confirmed that the photocatalytic activity was greatly improved.

  5 g of zinc oxide particles (manufactured by Wako Pure Chemical Industries, Ltd., particle size 0.02 μm, purity 95.0%) are mixed with 10 ml of water, 0.2 ml of acetylacetone, and 0.1 ml of polyoxyethylene octylphenyl ether, and stirred. To obtain a paste in which zinc oxide particles are dispersed. This was applied by a doctor blade method onto a glass substrate on which fluorine-doped tin oxide having a sheet resistance of about 10Ω / □ was formed, and then heat-treated at 400 ° C. for 30 minutes. At this time, the fired zinc oxide layer was a porous layer, and the film thickness was 6 μm.

  This was set in the chamber of the same apparatus as in Example 1, and reduction treatment and nitriding treatment were performed. The heated catalyst body was heated to 1500 ° C. by electric heating, and then ammonia gas was introduced into the chamber and the pressure was maintained at 10 Pa. The substrate temperature was adjusted to 150 ° C. The surface of the zinc oxide layer started to turn yellow about 25 seconds after the shutter between the substrate and the heated catalyst body was opened, and turned black when treated for up to 20 minutes.

  In order to confirm the improvement of the photocatalytic function accompanying the increase in the light absorption amount of the zinc oxide layer formed as described above, the substrate with the zinc oxide layer of this Example 2 subjected to the treatment for 25 seconds under the above-mentioned conditions, and the treatment Substrates with a zinc oxide layer that were not used were each immersed in an aqueous solution of methylene blue, and irradiated with light to evaluate the ability to decompose methylene blue. The evaluation conditions are the same as in Example 1. As a result, the amount of change in absorbance at 660 nm was about 1.3 times that of Example 2 compared to the conventional example, and it was confirmed that the photocatalytic activity was greatly improved.

  A substrate with a titanium oxide layer formed by dissolving a ruthenium-tris transition metal complex dye in a solvent of acetonitrile and t-butanol for 3 minutes according to the method described in Example 1 is about 15 hours. A dye was formed on the titanium oxide layer by immersion. During this time, the temperature of the solution was maintained at 60 ° C to 80 ° C.

  Next, a substrate in which a fluorine-doped tin oxide film and a Pt layer serving as a counter electrode are patterned on a glass substrate serving as a counter substrate, a substrate formed up to the dye layer, and a thermoplastic epoxy resin serving as a sealing material. The periphery was sealed by local heating, leaving the electrolyte injection hole. Then, iodine 0.1M, lithium iodide 0.1M, 1,2-dimethyl-3-propylimidazolium iodide 0.7M, 4-tertbutylpyridine 8M are mixed from the injection hole provided in the counter substrate, and methoxyacetonitrile is mixed. What was prepared as a solvent was used. Finally, the electrolyte injection hole was sealed with an epoxy resin.

The device manufactured by the above method is irradiated with simulated sunlight (light of artificial solar lighting “XC-100” manufactured by Celic Co., Ltd.) whose incident light intensity is adjusted to 100 mW / cm ² to evaluate the characteristics. Was done. As a comparative example, a similar element was produced and evaluated for a titanium oxide layer that was not treated by the catalytic CVD method. As a result, the device manufactured by the method of the present invention has a short circuit current value of 1.27 times, an open circuit voltage value of 1.14 times, a fill factor of 1.01 times, and a conversion efficiency of 1.46 times that of a conventional device. Improved. This is because the photocatalyst of the present invention has a high light absorption rate, the density of carriers excited in the photocatalyst is increased, and the carrier concentration in the photocatalyst is also increased due to oxygen defects that are present appropriately. It is considered that the internal resistance in the titanium oxide layer is reduced and the internal electric field between the dye and the pigment is increased.

  As a preparation of the photocatalyst, first, 5 g of anatase-type titanium dioxide powder (“P25” manufactured by Nippon Aerosil Co., Ltd.) was placed in a SUS container, and this was set in the chamber of the same apparatus as in Example 1 for reduction treatment and nitriding. Processing was performed. At this time, the treatment was performed under the conditions described in Example 1 for 3 minutes. Next, the powder was mixed with 10 ml of water, 0.1 ml of acetylacetone, and 0.1 ml of polyoxyethylene octylphenyl ether, and stirred with a stirrer to prepare a paste in which titanium dioxide particles were dispersed.

  Next, as a preparation for the anode, a paste in which the titanium dioxide particles produced by the above method are dispersed is applied onto a platinum-plated glass substrate, and a sintering process is performed for 5 minutes in a 28 GHz microwave. It was. At this time, the sintered titanium dioxide layer was a porous layer, and its film thickness was 12 μm. Next, a part of the titanium dioxide layer was mechanically etched to expose platinum, and a platinum lead wire was fixed to the same part. A platinum plate serving as a cathode was connected to the other end of the platinum lead wire and immersed in the electrolytic solution. The platinum exposed part including the platinum wire on the anode side was coated with an epoxy resin so as not to come into contact with the electrolytic solution. Moreover, 1 mol / L sodium hydroxide aqueous solution was used for electrolyte solution. Further, a cylindrical gas collecting container made of quartz was disposed immediately above the anode and the cathode.

  In the hydrogen generator configured as described above, light irradiation was performed using a 500 W xenon lamp from the surface side of the anode on which the titanium dioxide layer was formed. As a result, gas was collected in the gas collection container. At this time, when the gas composition was analyzed by mass spectrometry, it was confirmed that oxygen was generated on the anode side and hydrogen was generated on the cathode side. Here, the photocatalyst of Example 4 in which titanium dioxide used on the anode side was produced by the above-described method, and a conventional example using titanium dioxide powder subjected to heat treatment at 600 ° C. for 10 hours in a nitrogen atmosphere as the photocatalyst. , It was confirmed that the volume of the gas collected in each gas collection container was about 1.2 times larger in Example 4 than in the conventional example. This is considered to be largely due to the fact that the photocatalyst of the present invention has a high light absorption rate and the density of carriers excited in the photocatalyst is increased.

  The present invention is not limited to the above-described embodiments and examples, and various modifications may be made without departing from the scope of the present invention.

It is a diagram which shows the XPS spectrum of the photocatalyst body of this invention. It is a diagram which shows the transmission spectrum of the photocatalyst body of this invention. It is sectional drawing which shows the outline of the manufacturing apparatus of the photocatalyst body of this invention. It is sectional drawing which shows the outline of the photoelectric conversion element of this invention. It is sectional drawing which shows the outline of the photochemical energy conversion element of this invention.

Explanation of symbols

4: Heated catalyst body 6: Substrate 7: Metal oxide layer 8: Substrate 9: Electrode
10: Electron transport layer
11: Photoexciter
12: Counter substrate
13: Counter electrode
14: Hole transport layer

Claims (8)

A photocatalyst comprising a metal oxide having a chemical bond between metal and nitrogen and a chemical bond between metal and oxygen and having an oxygen deficiency. The photocatalyst according to claim 1, wherein the metal oxide is titanium oxide or zinc oxide. The photocatalyst according to claim 1 is produced by reducing and nitriding a metal oxide in a reducing atmosphere formed by contacting the heated catalyst with a gas having at least a nitrogen atom in the molecule. A method for producing a photocatalyst body. 4. The method for producing a photocatalyst body according to claim 3, wherein the reducing atmosphere contains ammonia. The method for producing a photocatalyst according to claim 3 or 4, wherein the temperature of the reducing atmosphere is 200 ° C or lower. On the other hand, the electroconductive base | substrate used as an electrode, The photocatalyst body of Claim 1 or Claim 2 formed on this electroconductive base | substrate, The photoelectric conversion body electrically connected to this photocatalyst body, An optical-electric energy conversion element comprising: a hole transporter that is electrically connected to transport holes; and the other electrode that is electrically connected to the hole transporter. A photo-chemical energy conversion element, wherein the photocatalyst according to claim 1 or 2 is placed in water or an aqueous solution to generate hydrogen gas. 7. A photovoltaic power generation apparatus characterized in that the power generated by the photoelectric energy conversion element according to claim 6 is supplied to a load.

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