JP6156822B2 - Photocatalyst, water splitting electrode, and method for producing hydrogen and / or oxygen - Google Patents

Description

  The present invention relates to a photocatalyst capable of producing hydrogen and / or oxygen by performing a water splitting reaction utilizing sunlight.

  In recent years, attention has been focused on a technique for producing hydrogen and oxygen by decomposing water using a photocatalyst and solar energy. The photocatalyst currently being studied is usually one in which a promoter is supported on the surface of an optical semiconductor such as an oxide, oxynitride or nitride. The activity of the photocatalyst can be improved by supporting the cocatalyst.

For example, Non-Patent Document 1 discloses a technique in which Mn ₃ O ₄ nanoparticles are co-supported as an oxygen generation co-catalyst with respect to a photocatalyst formed by supporting a hydrogen generation co-catalyst on GaN: ZnO, According to this technique, the activity of the photocatalyst can be improved. However, even if the technique disclosed in Non-Patent Document 1 is applied, the photocatalytic activity is only 1.3 to 1.6 times as small as that in the case of not supporting the oxygen generation promoter. This is presumably because the hydrogen generation reaction in the water splitting reaction is rate limiting, or the photocatalytic activity is more dependent on the bulk properties of the photocatalyst itself than on the photocatalytic surface.

  On the other hand, Non-Patent Document 2 discloses that a photocatalyst in which a hydrogen generation promoter is supported on GaN: ZnO, and oxide nanoparticles of Co and Mn (Co-doped manganese oxide nanoparticles) are further used as an oxygen generation promoter. As a co-supporting technique. According to Non-Patent Document 2, although the activity of the water splitting reaction is slightly improved when the Co doping rate is 20%, a remarkable effect by doping Co cannot be obtained.

K. Maeda et al., Angew. Chem. Int. Ed. 2010, 49, 4096 Yoshinaga et al., "Rigidity of New Oxygen Generation Cocatalyst Nanoparticles for Improving Activity of Photocatalysts for Complete Water Decomposition", The 93rd Annual Meeting of the Chemical Society of Japan (2013)

  An object of the present invention is to provide a cocatalyst capable of greatly improving the photocatalytic activity, a photocatalyst having a high photocatalytic activity and applicable as a photowater splitting catalyst, and a photowater splitting electrode using the photocatalyst. .

  The present inventors have found that depending on the type of optical semiconductor, oxide particles containing Co and Mn can serve as promoters that can greatly improve the photocatalytic activity. That is, in the prior art, it has been said that the remarkable effect of doping manganese oxide with Co is not recognized, but the effect of doping with Co may become significant depending on the compatibility with the optical semiconductor. I found out.

The present invention has been made based on the above findings. That is,
The first aspect of the present invention is a photocatalyst comprising at least oxide particles containing Co and Mn as cocatalysts on a photosemiconductor containing one or more elements selected from the group consisting of Ti, V, Nb and Ta. It is.

  In the present invention, “an optical semiconductor containing one or more elements selected from the group consisting of Ti, Ta, V and Nb” means an oxide, oxynitride, nitride, (oxy) chalcogenide, etc. containing the element Means an optical semiconductor used as a photocatalyst. The form of the “photosemiconductor” may be any form that can support a cocatalyst, and various forms such as a particulate form and a massive form can be adopted. “Oxide particles containing Co and Mn” mean either a form in which manganese oxide is doped with cobalt or a form in which cobalt oxide is doped with manganese. That is, it means that Co and Mn are contained in one particle, and those obtained by simply mixing cobalt oxide particles and manganese oxide particles are not included in “oxide particles containing Co and Mn”. Shall. “At least supported” means that the co-catalyst other than the oxide particles may be supported on the optical semiconductor.

  In 1st this invention, it is preferable that the molar ratio (Co / Mn) of Co and Mn in oxide particles is 1/50 or more and 1 or less.

  In the first aspect of the present invention, the particle diameter of the oxide particles is preferably 1.0 nm or more and 25 nm or less.

  In 1st this invention, it is preferable that an oxide particle is carry | supported 0.005 mass part or more and 1.0 mass part or less with respect to 100 mass parts of optical semiconductors. In addition, the said carrying amount assumes the case where both a hydrogen production co-catalyst and an oxygen production co-catalyst are carry | supported on an optical semiconductor.

  The second aspect of the present invention is a photohydrolysis electrode using the photocatalyst according to the first aspect of the present invention.

  However, when it is set as the electrode for photo-water-splitting reaction, it is good to make it carry | support the oxide particle 0.008 mass part or more and 20.0 mass part or less with respect to 100 mass parts of optical semiconductors in a photocatalyst. Alternatively, it is preferable that 20% or more of the surface of the optical semiconductor is covered with oxide particles. The supported amount assumes a case where only the oxide particles containing Co and Mn are supported on the optical semiconductor as a promoter.

According to the second aspect of the present invention, a photocurrent density of 0.25 mA / cm ² or more at a measurement potential of 0.62 V (vs. RHE) can be achieved.

  In the third aspect of the present invention, the photocatalyst according to the first aspect of the present invention or the photocatalytic reaction electrode according to the second aspect of the present invention is immersed in water or an aqueous electrolyte solution, and the photocatalyst or the electrode for photocatalytic reaction is used. This is a method for producing hydrogen and / or oxygen, in which light water splitting is performed by irradiating light on the substrate.

  In the present invention, the oxide particles containing Co and Mn are supported on a specific optical semiconductor as a co-catalyst, so that the co-catalyst is not supported, or the oxide particles containing only Mn are supported and only Co. The photocatalytic activity can be greatly improved as compared with the case of supporting oxide particles containing. That is, according to the present invention, there are provided a cocatalyst capable of greatly improving the photocatalytic activity, a photocatalyst having a high photocatalytic activity and applicable as a photowater splitting catalyst, and a photowater splitting electrode using the photocatalyst. be able to.

It is a figure for demonstrating the apparatus used in the case of disperse | distributing photocatalyst particle | grains in water and evaluating photohydrolysis reaction activity. It is a figure which shows the evaluation result of the photohydrolysis reaction activity of each photocatalyst (Various types of promoters are changed while using SrTiO ₃ as an optical semiconductor).

1. Photocatalyst The photocatalyst according to the present invention comprises at least oxide particles containing Co and Mn as cocatalysts on an optical semiconductor containing one or more elements selected from the group consisting of Ti, V, Nb and Ta. It is characterized by.

1.1. Optical semiconductor The optical semiconductor used in the photocatalyst according to the present invention contains one or more elements selected from the group consisting of Ti, V, Nb, and Ta, and includes, for example, any of these elements. Examples thereof include oxides, oxynitrides, nitrides, (oxy) chalcogenides, and the like. Specifically, TiO ₂ , CaTiO ₃ , SrTiO ₃ , Sr ₃ Ti ₂ O ₇ , Sr ₄ Ti ₃ O ₇ , K ₂ La ₂ Ti ₃ O ₁₀ , Rb ₂ La ₂ Ti ₃ O ₁₀ , Cs ₂ La ₂ Ti ₃ O ₁₀ , CsLaTi ₂ NbO ₁₀ , La ₂ TiO ₅ , La ₂ Ti ₃ O ₉ , La ₂ Ti ₂ O ₇ , La ₂ Ti ₂ O ₇ : Ba, KaLaZr _0.3 Ti _0.7 O ₄ , La ₄ CaTi ₅ O ₇ , KTiNbO ₅ , Na ₂ Ti ₆ O ₁₃ , BaTi ₄ O ₉ , Gd ₂ Ti ₂ O ₇ , Y ₂ Ti ₂ O ₇ , (Na ₂ Ti ₃ O ₇ , K ₂ Ti ₂ O ₅ , K ₂ Ti ₄ O ₉ , Cs ₂ Ti ₂ O ₅ , H ⁺ -Cs ₂ Ti ₂ O ₅ (H ⁺ -Cs indicates that Cs is ion-exchanged with H ⁺ . The same applies hereinafter), Cs _{2 Ti 5 O 11, Cs 2 Ti} 6 O 13, H + -CsTiNbO 5, H + -CsTi 2 NbO 7, SiO 2 -pillared K 2 Ti 4 O 9, SiO 2 -pillared K 2 Ti 2.7 Mn 0. Titanium-containing oxides such as ₃ O ₇ , BaTiO ₃ , BaTi ₄ O ₉ , AgLi _1/3 Ti _2/3 O ₂ ; titanium-containing oxynitrides such as LaTiO ₂ N; La ₅ Ti ₂ CuS ₅ O ₇ , La Titanium-containing (oxy) chalcogenides such as ₅ Ti ₂ AgS ₅ O ₇ and Sm ₂ Ti ₂ O ₅ S ₂ ;
Vanadium-containing oxides such as BiVO ₄ and Ag ₃ VO ₄ ;
_{K 4 Nb 6 O 17, Rb} 4 Nb 6 O 17, Ca 2 Nb 2 O 7, Sr 2 Nb 2 O 7, Ba 5 Nb 4 O 15, NaCa 2 Nb 3 O 10, ZnNb 2 O 6, Cs 2 Nb ₄ O ₁₁ , La ₃ NbO ₇ , H ⁺ -KLaNb ₂ O ₇ , H ⁺ -RbLaNb ₂ O ₇ , H ⁺ -CsLaNb ₂ O ₇ , H ⁺ -KCa ₂ Nb ₃ O ₁₀ , SiO ₂ -pillared KCa ₂ N ₃ O ₁₀ (Chem. Mater. 1996, 8, 2534.), H ⁺ -RbCa ₂ Nb ₃ O ₁₀ , H ⁺ -CsCa ₂ Nb ₃ O ₁₀ , H ⁺ -KSr ₂ Nb ₃ O ₁₀ , H ⁺ -KCa ₂ NaNb ₄ O _13), niobium-containing oxide such _{PbBi 2 Nb 2 O 9; CaNbO} 2 N, BaNbO 2 N, SrNbO 2 , Niobium-containing oxynitride such _{LaNbON 2; Ta 2 O 5,} K 2 PrTa 5 O 15, K 3 Ta 3 Si 2 O 13, K 3 Ta 3 B 2 O 12, LiTaO 3, NaTaO 3, KTaO 3, AgTaO ₃ , KTaO ₃ : Zr, NaTaO ₃ : La, NaTaO ₃ : Sr, Na ₂ Ta ₂ O ₆ , K ₂ Ta ₂ O ₆ (pyrochlore), CaTa ₂ O ₆ , SrTa ₂ O ₆ , BaTa ₂ O ₆ , NiTa ₂ O ₆ , Rb ₄ Ta ₆ O ₁₇ , H ₂ La _2/3 Ta ₂ O ₇ , K ₂ Sr _1.5 Ta ₃ O ₁₀ , LiCa ₂ Ta ₃ O ₁₀ , KBa ₂ Ta ₃ O ₁₀ , Sr ₅ Ta ₄ O ₁₅ , Ba ₅ Ta ₄ O ₁₅ , H _1.8 Sr _0.81 Bi _0.19 Ta ₂ O ₇ , Mg-Ta oxide (C hem.Matter.2004 16, 4304-4310), LaTaO ₄ , La ₃ TaO _{7 and} other tantalum-containing oxides; Ta ₃ N _{5 and} other tantalum-containing nitrides; CaTaO ₂ N, SrTaO ₂ N, BaTaO ₂ N, LaTaO A tantalum-containing oxynitride such as ₂ N, Y ₂ Ta ₂ O ₅ N ₂ , or TaON is used.

From the viewpoint of more efficiently generating a photohydrolysis reaction using sunlight, it is preferable to use a visible light responsive optical semiconductor among the various optical semiconductors. Specifically, LaTiO ₂ N, BaNbO ₂ N, BaTaO ₂ N, TaON, BiVO ₄ , and Ta ₃ N ₅ are preferable. Among these, LaTiO ₂ N, BaNbO ₂ N, BaTaO ₂ N, TaON, and BiVO ₄ are particularly preferable. preferable. The above various optical semiconductors can be easily synthesized by a known synthesis method such as a solid phase method or a solution method.

  The form (shape) of the photo semiconductor is not particularly limited as long as it is a form capable of supporting a cocatalyst described below and functioning as a photocatalyst. A lump shape, a plate shape, or the like may be appropriately selected. In particular, when a photocatalyst for water splitting reaction is used, it is preferable to support a promoter on the surface of a particulate optical semiconductor. In this case, the lower limit of the particle diameter is preferably 50 nm or more, and the upper limit is preferably 500 μm or less. In the present application, the “particle diameter” means an average value (average particle diameter) of tangential diameters (ferret diameters) in a fixed direction and can be measured by a known means such as XRD, TEM, SEM method.

1.2. Cocatalyst The photocatalyst according to the present invention comprises at least oxide particles containing Co and Mn as cocatalysts on the above-described optical semiconductor.

The “oxide particles containing Co and Mn” may be in any form of manganese oxide doped with cobalt or cobalt oxide doped with manganese. Co _3-x Mn _x An oxide represented by O ₄ (0 <x <3) is preferable. The molar ratio of Co and Mn in the oxide particles (Co / Mn) is preferably 1/50 or more and 1 or less, the lower limit is more preferably 1/10 or more, and particularly preferably 1/9 or more, The upper limit is more preferably 4/5 or less, and particularly preferably 2/3 or less. By adjusting the molar ratio of Co and Mn to such a range, it can be set as the promoter which can improve photocatalytic activity further.

  The oxide particles may be of a size that can be supported on the surface of the optical semiconductor. In order to carry oxide particles on the surface of the optical semiconductor, it is necessary that the oxide particles are smaller than the optical semiconductor such as particles, lumps, and plates. In particular, a mode in which oxide particles having a particle diameter of 1.0 nm to 25 nm are supported on the surface of the optical semiconductor particles having a particle diameter of 50 nm to 500 μm is preferable. The lower limit of the particle diameter of the oxide particles is more preferably 1.2 nm or more, still more preferably 1.5 nm or more, and the upper limit is more preferably 20 nm or less, still more preferably 10 nm or less. By adjusting the particle diameter of the oxide particles to such a range, a promoter capable of further improving the photocatalytic activity can be obtained.

  Examples of methods for producing such nano-sized oxide particles include the following methods. That is, a manganese raw material (manganese oleate, etc.) and a cobalt raw material (cobalt stearate, etc.) are dissolved in an organic solvent (1-octadecene, etc.), degassed under reduced pressure, replaced with nitrogen, and refluxed while raising the temperature. Then, by allowing to cool, oxide nanoparticles containing Co and Mn as precipitates are obtained. Aggregation can be prevented by appropriately dispersing the obtained oxide nanoparticles in a solvent such as tetrahydrofuran. The oxide nanoparticles thus obtained become a solid solution of NaCl-type MnO and CoO.

1.3. Loading of promoter on the surface of an optical semiconductor The photocatalyst according to the present invention is formed by supporting at least the oxide particles described above as a promoter on the surface of an optical semiconductor. "At least" means that other promoters may be co-supported in addition to the oxide particles. For example, a compound containing one or more elements selected from Groups 6 to 10 of the periodic table can be co-supported as a promoter. Specifically, Pt, Pd, Rh, Ru, Ni, Au, Fe, Ru—Ir, Pt—Ir, NiO, RuO ₂ , IrO ₂ , Rh ₂ O ₃ , NiS, MoS are used as promoters for hydrogen generation. ₂ , NiMoS, Cr—Rh composite oxide, core-shell type Rh / Cr ₂ O ₃ , and Pt / Cr ₂ O ₃ , and as a catalyst for oxygen generation, Cr, Sb, Nb, Th, Mn, Fe, Co , Ni, Ru, Rh, and Ir, and oxides or composite oxides thereof (excluding oxides containing Co and Mn).

  The amount of oxide particles supported on the optical semiconductor is not particularly limited as long as it is an amount capable of improving the photocatalytic activity. For example, in the case where oxide particles having a particle diameter of 1.0 nm to 25 nm are supported on the surface of an optical semiconductor particle having a particle diameter of 50 nm or more and 500 μm or less, in addition to the oxide particles, other assistants other than the oxide particles are used. When it is desired to co-support a catalyst (such as the above-mentioned hydrogen generating co-catalyst), the oxide particles are supported by 0.005 parts by mass or more and 1.0 parts by mass or less with respect to 100 parts by mass of the optical semiconductor (photo semiconductor particles). It is preferable to do. The lower limit is more preferably 0.008 parts by mass or more, still more preferably 0.01 parts by mass or more, and the upper limit is more preferably 0.8 parts by mass or less, still more preferably 0.5 parts by mass or less. Thereby, only a part of the surface of the optical semiconductor can be covered with the oxide particles, and another promoter can be supported on the surface of the optical semiconductor not covered with the oxide particles. Such a form is suitable for the case where photohydrolysis is performed by causing both a hydrogen generation reaction and an oxygen generation reaction on the surface of one photocatalyst particle.

  Alternatively, only the oxide particles may be supported as a promoter on the surface of the optical semiconductor. For example, when only the oxide particles having a particle diameter of 1.0 nm or more and 25 nm or less are supported on the surface of the optical semiconductor particle having a particle diameter of 50 nm to 500 μm, with respect to 100 parts by mass of the optical semiconductor (photo semiconductor particle), It is preferable to support the oxide particles in an amount of 0.008 parts by mass to 20.0 parts by mass. The lower limit is more preferably 0.009 parts by mass or more, further preferably 0.010 parts by mass or more, and the upper limit is more preferably 5.0 parts by mass or less, still more preferably 3.0 parts by mass or less, particularly preferably 2 0.0 parts by mass or less. Thereby, almost the entire surface of the optical semiconductor can be uniformly covered with the oxide particles, and the photocatalytic activity is improved. Such a form is suitable when a photocatalyst is applied to an electrode for photohydrolysis reaction.

  In the case of co-supporting, if the amount of the entire cocatalyst supported is too small, there will be no effect. Otherwise, the catalytic activity is reduced. From such a viewpoint, the supported amount of the entire cocatalyst in the photocatalyst (the total of the oxide particles and other cocatalysts) is preferably 0.008 parts by mass or more and 5.0 parts by mass with respect to 100 parts by mass of the optical semiconductor. It is not more than mass parts, more preferably not less than 0.009 parts by mass and not more than 3.0 parts by mass, particularly preferably not less than 0.010 parts by mass and not more than 2.0 parts by mass.

  The method for supporting the oxide particles on the surface of the optical semiconductor is not particularly limited, but the dispersion containing the oxide particles is impregnated with the optical semiconductor, and the oxide particles are adsorbed on the surface of the optical semiconductor. In addition, a method of supporting oxide particles on the surface of the optical semiconductor by appropriately subjecting to firing is preferable. This method is suitable when it is desired to uniformly support nano-sized particles as oxide particles on the entire surface of the optical semiconductor. For example, a suitable binder for adsorbing oxide particles on the surface of the optical semiconductor particles after mixing the oxide particles and the optical semiconductor particles in an organic solvent (such as tetrahydrofuran) and optionally subjecting to ultrasonic treatment. (16-hydroxyhexadecanoic acid etc.) is added. Thereafter, the photocatalyst precursor in which the oxide particles are adsorbed on the surface of the optical semiconductor particles is obtained by appropriately stirring and then subjecting to washing treatment. By arbitrarily firing the precursor, a photocatalyst in which oxide particles are uniformly supported on the surface of the optical semiconductor can be obtained.

  Alternatively, the oxide particles can be supported on the surface of the optical semiconductor by applying the oxide particles on the optical semiconductor film by a method such as dip coating, drop casting, spray coating, electrostatic coating, or spin coating.

  As described above, according to the photocatalyst according to the present invention, the photocatalytic activity is greatly improved by supporting oxide particles containing Co and Mn on the surface of a specific optical semiconductor as a promoter. This is a remarkable and peculiar effect that cannot be conceived from the prior art, in which a conspicuous effect due to Co doping of manganese oxide is not recognized.

2. Electrode for photohydrolysis reaction There is no particular limitation on the form of the photocatalyst when the photocatalyst is actually used for water decomposition, the form in which the photocatalyst particles are dispersed in water, the photocatalyst particles are solidified and formed as a molded body A configuration in which the body is placed in water, a photocatalyst layer is provided on the base material to form a laminate, and the laminate is placed in water, a photocatalyst is immobilized on the current collector as an electrode for photohydrolysis reaction, The form etc. which are installed in are mentioned. In particular, in the case of performing the water-splitting reaction on a large scale, it is preferable to use the electrode for the water-splitting reaction from the viewpoint of applying a bias to promote the water-splitting reaction.

The electrode for photohydrolysis reaction can be produced by a known method. For example, it can be easily produced by a so-called particle transfer method (Chem. Sci., 2013, 4, 1120-1124). That is, the photocatalyst particles are placed on a first substrate such as glass to obtain a laminate of the photocatalyst layer and the first substrate layer. A conductive layer (current collector) is provided on the photocatalyst layer surface of the obtained laminate by vapor deposition or the like. Here, the photocatalyst particles in the surface layer on the conductive layer side of the photocatalyst layer are fixed to the conductive layer. Then, a 2nd base material is adhere | attached on the conductive layer surface, and a conductive layer and a photocatalyst layer are peeled from a 1st base material layer. Since some of the photocatalyst particles are immobilized on the surface of the conductive layer, the photocatalyst particles are peeled off together with the conductive layer, and as a result, a photohydrolysis reaction electrode having a photocatalyst layer, a conductive layer, and a second base material layer is obtained. be able to.
Alternatively, a slurry in which photocatalyst particles are dispersed may be applied to the surface of the current collector and dried to obtain a photohydrolysis electrode, or the photocatalyst particles and the current collector may be subjected to pressure molding or the like. May be integrated to obtain a photohydrolysis electrode. Alternatively, the current collector may be immersed in a slurry in which the photocatalyst particles are dispersed, the voltage is applied, and the photocatalyst particles may be accumulated on the current collector by electrophoresis.
Alternatively, a form in which the promoter is supported in a later step may be used. For example, in the above-described particle transfer method, a laminated body having a photo semiconductor layer, a conductive layer, and a second base material layer is obtained in the same manner using photo semiconductor particles instead of photo catalyst particles, and then the photo semiconductor An electrode for photohydrolysis reaction may be obtained by supporting oxide particles as a promoter on the surface of the layer.

  As described above, when the photocatalyst according to the present invention is applied to the electrode for photohydrolysis reaction, from the viewpoint of improving electrode performance, in the photocatalyst, the oxide particles are 0.008 parts by mass with respect to 100 parts by mass of the optical semiconductor. It is preferable that 20 parts by mass or less is supported. Alternatively, from the same viewpoint, it is preferable that 20% or more of the surface of the optical semiconductor is covered with the oxide particles. The coverage of the oxide particles on the surface of the optical semiconductor can be calculated by specifying the portion occupied by the optical semiconductor and the portion occupied by the oxide particles when the photocatalyst particles are viewed from one direction by SEM-EDS or the like. it can. For example, the area of the optical semiconductor portion and the area of the oxide particle portion in the SEM photograph are specified, and (area of the oxide particle portion) / {(area of the optical semiconductor portion) + (area of the oxide particle portion)} Thus, the coverage can be calculated.

By using the photocatalyst according to the present invention, the performance of the photocatalytic reaction electrode is improved. Specifically, the photocurrent density at a light source AM1.5G (100 mW / cm ² ) and a measurement potential of 0.62 (vs. RHE) is 0.25 mA / cm ² or more, preferably 0.29 mA / cm ² or more, more preferably 0.35 mA / cm ² or more can be achieved. When the photocurrent density is 0.25 mA / cm ² or more, water splitting with a conversion efficiency of 0.2% or more is possible, and a conversion efficiency equal to or higher than that of plants can be achieved.

3. Method for producing hydrogen and / or oxygen In the present invention, the above-mentioned photocatalyst or the above-mentioned photocatalytic reaction electrode is immersed in water or an aqueous electrolyte solution, and the photocatalyst or photocatalytic reaction electrode is irradiated with light. Then, hydrogen and / or oxygen can be produced by performing photo-water decomposition.

  For example, as described above, a photocatalyst is immobilized on a current collector made of a conductor to obtain an electrode for photohydrolysis reaction, while a conductor carrying a hydrogen generation catalyst is used as a counter electrode, and the liquid or gas The water splitting reaction proceeds by irradiating light while supplying water in the form of water. The water splitting reaction can be promoted by providing a potential difference between the electrodes as necessary. Alternatively, an optical semiconductor carrying a hydrogen generation catalyst may be used as the counter electrode. In this case, a known optical semiconductor that catalyzes a hydrogen generation reaction can be used as the optical semiconductor.

  On the other hand, the water splitting reaction may proceed by irradiating light while supplying water to a fixed product in which the photocatalyst particles are fixed on the insulating substrate or to a molded body obtained by pressure molding the photocatalyst particles. . Alternatively, the photocatalyst particles may be dispersed in water or an aqueous electrolyte solution, and light may be irradiated to proceed with the water splitting reaction. In this case, the reaction can be promoted by stirring as necessary.

The reaction conditions during the production of hydrogen and / or oxygen are not particularly limited. For example, the reaction temperature is 0 ° C. or higher and 200 ° C. or lower, and the reaction pressure is 2 MPa (G) or lower.
The irradiation light is visible light or ultraviolet light having a wavelength of 650 nm or less. Examples of the light source of irradiation light include the sun, a lamp capable of irradiating approximate sunlight, such as a xenon lamp and a metal halide lamp, a mercury lamp, and an LED.

  As described above, according to the present invention, by supporting oxide particles containing Co and Mn on a specific optical semiconductor, a photocatalyst having sufficient catalytic activity for the photo-water splitting reaction can be obtained. Hydrogen and / or oxygen can be produced on a large scale as an electrode for water splitting reaction or the like.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not restrict | limited by a following example, unless the summary is exceeded.

Example 1 SrTiO ₃
1.1. Preparation of Co _- doped MnO (Co _x Mn _1-x O solid solution) nanoparticles A method for synthesizing Co-doped MnO nanoparticles (Co-doped 40 mol%) is shown below.

Under a nitrogen atmosphere, manganese nitrate (40 mmol) and sodium oleate (80 mmol) were dissolved in a mixed solvent of ethanol (30 mL), distilled water (40 mL), and hexane (70 mL), and heated at 70 ° C. overnight. The organic phase was separated with a separatory funnel and the solvent was distilled off, followed by drying under reduced pressure for 3 days. The produced manganese oleate (0.24 mmol) and cobalt stearate (0.16 mmol) were mixed in 1-octadecene (10 mL), and heat treatment was performed in the following procedure. The mixture was heated at 120 ° C. under reduced pressure for 1 hour, and then the temperature was raised to 300 ° C. at 10 ° C. · min ⁻¹ . After stirring with a magnetic stirrer at 300 ° C. for 30 minutes, the mixture was cooled to room temperature. The product was washed with acetone and ethanol, and then dispersed in THF to obtain Co-doped MnO nanoparticles. As a result of observation with TEM (manufactured by JEOL, JEM-1011, acceleration voltage 100 kV), the average diameter of the Co-doped MnO nanoparticles was about 9 nm.

  The synthesis of Co-doped MnO nanoparticles having other Co doping ratios (Co-doping amount: 0 mol%, 10 mol%, 20 mol%, and 30 mol%) is performed by setting the above synthesis conditions and the total amount of metal precursor to 0. .4 mmol and was performed by changing the ratio of manganese oleate to cobalt stearate.

1.2. Supporting oxide nanoparticles on optical semiconductor SrCl ₃ is added to SrTiO ₃ (99.9%, Wako Pure Chemical Industries, Ltd., 99.9%), heated at 1100 ° C. for 10 hours, and washed with water to obtain SrTiO _3. Was prepared. The prepared SrTiO ₃ (150 mg) was suspended in THF in which Co-doped MnO nanoparticles (a total of 0.05% by mass of Co-doped MnO nanoparticles with respect to SrTiO ₃ ) were dispersed. After sonication, 16-hydroxyhexadecanoic acid in THF (4 mM, 4.5 mL) was added to the suspension and stirred for 3 hours. By this treatment, all Co-doped MnO nanoparticles were adsorbed on the SrTiO ₃ surface. SrTiO _{3 on} which Co-doped MnO nanoparticles were adsorbed was heated from room temperature to 400 ° C. at a rate of 5 K · min ⁻¹ in air and calcined for a total of 3 hours. After firing, the Co-doped MnO nanoparticles changed to Co _x Mn _3-x O ₄ , but no significant change in particle size was seen. It is confirmed by UV-vis spectrum that all the Co-doped MnO nanoparticles are adsorbed, and the amount of metal supported on SrTiO _{3 by} Co and Mn is 0.05% by mass, the same as the charged amount. To obtain a _{Co x Mn 3-x O 4} / SrTiO 3 as described above.

1.3. <Preparation of _{Rh / Cr 2 O 3 (core} / shell) / SrTiO 3 / Co x Mn 3-x O 4> total degradation of measurement method and measurement results
Co _x Mn _3-x O ₄ / SrTiO ₃ prepared as described above was suspended in an aqueous solution of Na ₃ RhCl ₆ (0.3% by mass Rh with respect to SrTiO ₃ ), and the apparatus shown in FIG. Rh (III) was photoreduced to metal Rh by irradiation with light (λ> 300 nm) for 4 hours in the absence of air. After precipitation of Rh, the obtained sample was suspended in a Cr (NO ₃ ) ₃ aqueous solution (0.8 mM, 0.5% by mass Cr with respect to SrTiO ₃ ), and again irradiated with light (λ> 300 nm) for 4 hours. was Cr _{(NO 3)} 3 was reduced to _Cr 2 _{O 3.} For the light irradiation, a 300 W xenon lamp equipped with a cutoff filter was used. Cooling water was used during light irradiation to keep the solution temperature at room temperature. The product was thoroughly washed with distilled water and dried thoroughly to obtain Rh / Cr ₂ O ₃ (core / shell) / SrTiO ₃ / Co _x Mn _3-x O ₄ .

<Preparation of Rh / Cr ₂ O ₃ (core / shell) / SrTiO ₃ >
Instead of Co _x Mn _3−x O ₄ / SrTiO ₃ , unsupported SrTiO ₃ was used, and Rh / Cr ₂ O ₃ (core / shell) was supported thereon as described above. Was heated to 400 ° C. at a rate of 5 K · min ⁻¹ and calcined for a total of 3 hours to prepare Rh / Cr ₂ O ₃ (core / shell) / SrTiO ₃ .

<Light water splitting reaction>
As the light irradiation device, the device shown in FIG. 1 was used. The apparatus is provided with a 300 W xenon lamp (λ> 300 nm) and a cutoff filter. The photocatalyst 0.1 g prepared above and 100 mL pure water were degassed several times in a reaction vessel connected to a closed circulation system, and it was confirmed that no air remained. Thereafter, light irradiation was started, and the amount of gas produced was measured. Gas chromatography was used for quantification of the product gas. The results are shown in FIG.

As is clear from the results shown in FIG. 2, when Co and Mn-containing oxides are co-supported as promoters in addition to Rh / Cr ₂ O ₃ , Mn oxides are co-supported as promoters. When compared with the case where only Rh / Cr ₂ O ₃ is supported, both the hydrogen gas generation amount and the oxygen gas generation amount are increased. Specifically, it can be seen that as the amount of Co-doping increases, the amount of gas generation increases and the photocatalytic activity improves.

(Examples 2-1 to 2-5) BiVO ₄
2.1. Preparation of Co-doped MnO (Co _x Mn _1-x O solid solution) nanoparticles Co-doped MnO nanoparticles (Co doping amount 10 mol%, 20 mol%, 30 mol%, 40 mol%) by the same method as described above ) Was produced.

2.2. Oxide nanoparticles supported on optical semiconductors
BiVO ₄ was synthesized by the method described in J. Am. Chem. Soc. 1999, 121, 11459-11467. Specifically _V 2 _{O 5} (manufactured by Kanto Chemical Co., Inc., 99.0%) and _{Bi (NO 3) 3 · 5H} 2 O ( Kanto Chemical Co., 99.9%) is stirred for 3 days at room temperature an aqueous solution of As a result, BiVO ₄ was obtained.
The obtained BiVO ₄ (130 mg) was suspended in THF (13 mL) in which Co-doped MnO nanoparticles (0.2% by mass or 1.0% by mass with respect to BiVO ₄ ) were dispersed. After sonication, 16-hydroxyhexadecanoic acid in THF (4 mM, 3.9 mL) was added to the suspension and stirred for 3 hours. By this treatment, all Co-doped MnO nanoparticles were adsorbed on the BiVO ₄ surface. BiVO ₄ adsorbed with Co-doped MnO was heated from room temperature to 400 ° C. at a rate of 5 K · min ⁻¹ in air and supported by firing for a total of 3 hours.

2.3. Production of Electrode for Photo-Water-Splitting Reaction BiVO ₄ (30 mg) supporting nanoparticles was suspended in 1 mL of 2-propanol, and 200 μL of this suspension was placed on the first glass substrate (soda lime glass 30 × 30 mm). The photocatalyst layer was formed by repeating dropwise addition and drying three times. Next, Ti used as a contact layer was laminated | stacked by the vacuum evaporation method. The apparatus used ULVAC VPC-260F, and laminated | stacked about 0.5 micrometer. Next, about 2 μm of Au serving as a current collecting layer was laminated by vacuum deposition. Then, the 2nd glass base material (soda lime glass) was adhere | attached on the current collection layer using the epoxy resin. Finally, the first glass substrate was removed, and ultrasonic cleaning was performed in pure water for 10 minutes to obtain a photowater decomposition reaction electrode having a photocatalyst layer / Ti contact layer / Au layer. In Comparative Example 3, an electrode was produced by the same method except that Sn was used.

2.4. Measurement Method and Measurement Result of Total Decomposition The electrolytic solution was decomposed using the photo-water decomposition reaction electrode under the following measurement conditions. The photocurrent density at a measurement potential of 0.62 V was used as an evaluation index. The results are shown in Table 1 below.

<Measurement conditions>
・ Light source AM1.5 solar simulator [AM1.5G (100 mW / cm ² )]
PH = 7.0 Electrolyte Kpi (KH ₂ PO ₄ solution / K ₂ HPO ₄ solution), 100 mL
・ Argon atmosphere ・ Reference electrode Ag / AgCl, counter electrode Pt wire ・ LSV measurement (E ₀ = −0.4 V, E ₁ = 0.8 V, T ₀ = 1 s, T ₁ = 10 ms / V)
・ Measurement potential 0.62V

(Comparative Examples 1-1 to 1-3)
2.5. Preparation of Co nanoparticles
Co nanoparticles were synthesized by the method described in Langmuir, 2010, 26, 478. Specifically, in a nitrogen atmosphere, dioctylamine (0.70 mmol) of orthodichlorobenzene (12 mL) and oleic acid (0.62 mmol) are dissolved, and 3 mL of an oleic acid solution of cobalt carbonate (0.6 mmol) is further added. And heated at 182 ° C. for 2 hours. After cooling to room temperature, the product was washed with ethanol and then dispersed in hexane to obtain Co nanoparticles. As a result of observation with TEM (manufactured by JEOL, JEM-1011, acceleration voltage 100 kV), the average diameter of the Co nanoparticles was about 8 nm.
After the obtained Co nanoparticles were supported on BiVO ₄ by the same method as in Example 2, an electrode for water photolysis reaction was produced.

  As is clear from the results shown in Table 1, when an oxide containing Co and Mn is supported as a promoter, when a promoter is not supported, when a Mn oxide is supported as a promoter, or Compared with the case where Co oxide is supported as a co-catalyst, the photocurrent density by the photohydrolysis reaction is increased.

  As described above, in an optical semiconductor containing one or more elements selected from the group consisting of Ti, V, Nb and Ta, the photocatalytic activity is improved by supporting oxide particles containing Co and Mn as promoters. It was shown that it is possible to

  The photocatalyst according to the present invention has a high water splitting activity, and is particularly preferably used for a photowater splitting reaction that produces hydrogen and / or oxygen by performing a water splitting reaction using sunlight.

Claims (9)

  A photocatalyst obtained by supporting at least oxide particles containing Co and Mn as promoters on a photo semiconductor containing one or more elements selected from the group consisting of Ti, V, Nb and Ta.   The photocatalyst according to claim 1, wherein a molar ratio (Co / Mn) of Co and Mn in the oxide particles is 1/50 or more and 1 or less.   The photocatalyst according to claim 1 or 2, wherein a particle diameter of the oxide particles is 1 nm or more and 25 nm or less.   The photocatalyst in any one of Claims 1-3 with which the said oxide particle is carry | supported 0.005 mass part or more and 1.0 mass part or less with respect to 100 mass parts of said optical semiconductors.   The electrode for photo-water-splitting reaction using the photocatalyst in any one of Claims 1-3.   The electrode for photohydrolysis reaction according to claim 5, wherein the oxide particles are supported by 0.008 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the optical semiconductor.   The electrode for photohydrolysis reaction according to claim 5 or 6, wherein 20% or more of the surface of the optical semiconductor is covered with the oxide particles. The electrode for photohydrolysis reaction according to claim 5, wherein the photocurrent density at a measurement potential of 0.62 V (vs. RHE) is 0.25 A / cm ² or more.   The photocatalyst according to any one of claims 1 to 4 or the photocatalytic reaction electrode according to any one of claims 5 to 8 is immersed in water or an aqueous electrolyte solution to be used for the photocatalyst or the photohydrolysis reaction. A method for producing hydrogen and / or oxygen, wherein light is decomposed by irradiating an electrode with light.