Photocatalyst and method for producing hydrogen and oxygen using the photocatalyst

Abstract

To provide a novel photocatalyst more excellent in photocatalytic activity, and a manufacturing method of hydrogen and oxygen using the photocatalyst.SOLUTION: A photocatalyst having a composition represented by the following general formula (I). A method for manufacturing hydrogen and oxygen in which hydrogen and oxygen are generated using a photocatalyst-immobilized product or the molded product. YaTibMcOdSe (I)(wherein M is a combination of one or more selected from an element in an electronic state of +3 or less in a solid and in a hexacoordinated state, an element whose outermost orbital is an s, p, or f orbital, or an element whose outermost orbital is a d orbital, has no unpaired electrons in its d orbital and no electron in an eg orbital, a=1.7 to 2.3, b=2, c=0.003 to 0.038, d=4.7 to 5.3, and e=1.7 to 2.3.)SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a photocatalyst and a method for producing hydrogen and oxygen using this photocatalyst.

Background Art

[0002] In recent years, the development of high-performance photoenergy conversion systems that utilize solar energy as renewable energy has become increasingly important from the perspective of suppressing global warming and moving away from dependence on depleting fossil resources. Among them, the technology of decomposing water using solar energy to produce hydrogen is not only a technology for the current raw material supply of oil refining, ammonia, and methanol, but also a technology that can be utilized as an energy carrier for fuel cells, and the social demand for its technology development is increasing.

[0003] The water decomposition reaction by photocatalysts has been widely studied for a long time. The decomposition reaction of water in an acidic aqueous solution on photocatalyst particles is presumed as follows. H 2 O + 2h + → 1 / 2O 2 + 2H + (1) 2H + + 2e - → H 2 (2)

[0004] As a photocatalyst that causes such a reaction, for example, Y 2 Ti 2 O 5 S 2 shown in Patent Document 1 is known.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The photocatalyst described in Patent Document 1 exhibits excellent photocatalytic activity, but further improvement in photocatalytic activity is desired.

[0007] An object of the present invention is to provide a novel photocatalyst having more excellent photocatalytic activity and a method for producing hydrogen and oxygen using this photocatalyst.

Means for Solving the Problems

[0008] As a result of intensive studies to solve the above problems, the inventors of the present invention found that in Y described in Patent Document 1 2 Ti 2 O 5 S 2 By adding an element in a +3 valence or lower electron state in a specific amount in the solid, preferably an element having no electrons in the eg electron orbit in the 6-coordinate (octahedral coordination) state as the additional element, particularly preferably at least one selected from Li, Mg, Al, Sc, and Rh, and adding 0.003 to 0.038 with a Ti molar ratio of 2, it was found that the photocatalytic activity is greatly improved, and the present invention was achieved.

[0009] In Patent Document 1, it is described that "Y may be substituted with Ca, Sr, Ag, In, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc. within a range not hindering the effects of the present invention. Similarly, Ti may be substituted with Al, Cr, Mn, Co, Ni, Rh, Ga, Zn, Ta, Nb, and the substitution amount is preferably 0.3 or less, more preferably 0.1 or less, in terms of the value of a or b in the above composition formula." However, this description only shows that these elements may be added within a range not hindering the implementation of the invention according to Patent Document 1, and does not suggest that when a specific element among these is added at a very limited ratio, the photocatalytic activity is greatly improved by 2 times or more, and further 3 times or more, as in the present invention. Also, the composition range is "0.3 or less", which does not suggest the limited range of the present invention.

[0010] That is, the gist of the present invention is as follows.

[0011] [1] A photocatalyst having a composition represented by the following general formula (I). Y a Ti b M c O d S e …(I) (However, M is in an electron state of +3 or lower in the solid, and in a 6 - coordinate state, it is an element whose outermost shell orbitals are s, p, f orbitals, or an element whose outermost shell orbitals are d orbitals, having no unpaired electrons in its d orbitals and having no electrons in its eg orbitals, and is a combination of one or more selected from such elements, and a = 1.7 to 2.3, b = 2, c = 0.003 to 0.038, d = 4.7 to 5.3, e = 1.7 to 2.3 are numbers.)

[0012] [2] A photocatalyst having a composition represented by the following general formula (I). Y a Ti b M c O d S e …(I) (However, M is a combination of one or more selected from Li, Na, Mg, Ca, Al, Sc, Rh, Gd, Tb, and Yb, and a = 1.7 to 2.3, b = 2, c = 0.003 to 0.038, d = 4.7 to 5.3, e = 1.7 to 2.3 are numbers.)

[0013] [3] The photocatalyst according to [1] or [2], which is a photocatalyst used for the overall water splitting.

[0014] [4] A method for producing hydrogen and oxygen, which generates hydrogen and oxygen by using a fixed product obtained by immobilizing the photocatalyst according to any one of [1] to [3], or a molded product obtained by molding.

[0015] [5] An electrode prepared by using the photocatalyst according to any one of [1] to [3].

[0016] A method for producing hydrogen and oxygen that generates hydrogen and / or oxygen using the electrode described in [5] and [6].

Advantages of the Invention

[0017] According to the present invention, a photocatalyst with remarkably excellent photocatalytic activity is provided. Using the photocatalyst of the present invention, water can be efficiently decomposed into hydrogen and oxygen.

Modes for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following description and can be arbitrarily modified and implemented without departing from the gist of the present invention. In this specification, when expressing a numerical value or physical property value before and after using "~", it shall be used as including the values before and after.

[0019] [Composition of Photocatalyst] The photocatalyst of the present invention is a photocatalyst having a composition represented by the following general formula (I). Y a Ti b M c O d S e …(I) (However, M is an element in a +3 or lower valence electron state in the solid, and in a 6-coordinate state, the outermost shell orbitals are s, p, f orbitals, or the outermost shell orbitals are d orbitals, having no unpaired electrons in the d orbitals and no electrons in the eg orbitals, and is a combination of one or more selected from such elements, and a = 1.7 to 2.3, b = 2, c = 0.003 to 0.038, d = 4.7 to 5.3, e = 1.7 to 2.3 are numbers.)

[0020] That is, when the molar number b of Ti is set to 2 as a reference, the respective molar ratios are a = 1.7 to 2.3, c = 0.003 to 0.038, d = 4.7 to 5.3, e = 1.7 to 2.3. For b = 2 moles of Ti, a, c, d, and e are preferably such that a = 1.8 to 2.2, c = 0.003 to 0.032, d = 4.8 to 5.2, and e = 1.8 to 2.2, and more preferably a = 1.85 to 2.15, c = 0.004 to 0.030, d = 4.85 to 5.15, and e = 1.85 to 2.15. In this specification, unless otherwise specified, ~ includes the upper and lower numerical values.

[0021] In formula (I), M is an element in a +3 or lower valence electron state in the solid, and in a 6 - coordinate state, an element whose outermost shell orbitals are s, p, f orbitals, or an element whose outermost shell orbitals are d orbitals, having no unpaired electrons in its d orbitals and having no electrons in its eg orbitals. However, regarding the mechanism by which the photocatalytic activity, particularly the photocatalytic activity for water splitting, is improved by incorporating such an element M in the above - specified ratio, it is considered as follows. That is, in a photocatalyst, with the deficiency of anion (oxygen, sulfur, nitrogen, etc.) elements, the Ti element that should originally exist in a stable +4 valence oxidation state exists in a reduced +3 valence state, etc., and the distortion of the electron state causes a decrease in photocatalytic activity. However, according to the present invention, by adding an element M whose stable oxidation state is +3 or lower, the generation of the +3 valence Ti element is suppressed, and good photocatalytic activity is achieved. If c, which represents the composition ratio of the element M in a +3 or lower valence electron state in this solid, is less than 0.003, the above - mentioned photocatalytic activity improvement effect by adding the element M in a +3 or lower valence electron state in the solid cannot be sufficiently obtained, so c should be 0.003 or more. On the other hand, if c exceeds 0.038, there is too much M, and an impurity phase containing M accumulates on the photocatalyst surface, which causes light absorption to be hindered, and thus the photocatalytic activity rather decreases. Therefore, c should be 0.038 or less.

[0022] Also, in a 6 - coordinate state, the element M is an element whose outermost shell orbitals are s, p, f orbitals, or an element whose outermost shell orbitals are d orbitals, having no unpaired electrons in its d orbitals and having no electrons in its eg orbitals. That is, in the electron state formed in the stable oxidation state of the added element, if there are electrons in the eg electron orbitals, originally Y 2Ti 2 O 5 S 2 In the case where electrons derived from an additive component are introduced into the eg electron orbitals having no electrons, the semiconductor properties may be impaired and the function as a photocatalyst may be reduced. For an element having no electrons in the eg electron orbitals in the 6-coordinate (i.e., octahedral coordination) state, the photocatalytic activity can be further enhanced without causing such a problem, and an excellent effect is exhibited particularly in improving the water-splitting photocatalytic activity.

[0023] As such an element M, since it has an excellent effect of improving the photocatalytic activity, Li, Na, Mg, Ca, Al, Sc, Rh, Gd, Tb, Yb are preferable, and particularly Li, Mg, Al, Sc, Rh are preferable. Note that the element M may be only one kind, or two or more kinds may be used in combination.

[0024] [Method for producing photocatalyst] The photocatalyst of the present invention can be produced by weighing raw materials serving as a Y source, a Ti source, an O source, and an S source so as to satisfy the above formula (I), sufficiently mixing them, and firing the obtained mixture. Hereinafter, the photocatalyst of the present invention may be referred to as "YTMOS".

[0025] As the Y source, one or more of Y 2 O 3 , Y 2 O 2 S, Y 2 S 3 , Y, YCl 3 etc. can be used. Here, Y 2 O 3 , Y 2 O 2 S also serves as an O source. Further, Y 2 S 3 , Y 2 O 2 S also serves as an S source.

[0026] As the Ti source, one or more of TiO 2 , TiS 2 , Ti, etc. can be used. Here, TiO2 also serves as an O source. Also, TiS 2 serves as an S source.

[0027] As the O source, as described above, it is preferable to use the Y source and the Ti source also serving as the O source.

[0028] As the S source, S, H 2 one or more of S, etc. can be used. At this time, H 2 The method of flowing H2S, etc. as a gas for reaction is one of the preferable embodiments in manufacturing the photocatalyst of the present invention. Also, as described above, Y 2 S 3 , Y 2 O 2 S, TiS 2 also serves as an S source.

[0029] As the M source, oxides, sulfides, oxysulfides, halides, etc. of the element M that satisfy the above conditions can be used. Also in this case, the oxide also serves as the O source and the sulfide also serves as the S source.

[0030] When M is any one of Li, Na, Mg, Ca, Al, Sc, Rh, Gd, Tb, Yb, as the Li source, Li 2 O, Li 2 CO 3 , Li(NO 3 ), LiCl, LiOH, LiCH 3 COO·2H 2 O, Li 2 (C 2 O 4 ), LiF, LiBr, etc. one or more of them can be used. As the Na source, Na 2 O, Na 2 CO 3 , Na(NO 3 ), NaCl, NaOH, NaCH 3 COO·2H 2 O, Na 2 (C 2 O 4 ), NaF, NaBr, etc. one or more of them can be used. As the Mg source, MgO, Mg(OH)2 , MgCO 3 , Mg(OH) 2 ·3MgCO 3 ·3H 2 O, Mg(NO 3 ) 2 ·6H 2 O, MgSO 4 , Mg(OCO) 2 ·2H 2 O, Mg(OCOCH 3 ) 2 ·4H 2 O, MgCl 2 , MgF 2 and one or more of the like can be used. As the Ca source, CaO, Ca(OH) 2 , CaCO 3 , Ca(OH) 2 ·3CaCO 3 ·3H 2 O, Ca(NO 3 ) 2 ·6H 2 O, CaSO 4 , Ca(OCO) 2 ·2H 2 O, Ca(OCOCH 3 ) 2 ·4H 2 O, CaCl 2 , CaF 2 and one or more of the like can be used. As the Al source, Al 2 O 3 , Al(OH) 3 , AlOOH, Al(NO 3 ) 3 ·9H 2 O, Al 2 (SO 4 ) 3 , AlCl 3 , AlF 3 and one or more of the like can be used. As the Sc source, Sc 2 O 3 , Sc(OH) 3 , Sc 2 (CO 3 ) 3 , Sc(NO 3 )3 , Sc 2 (SO 4 ) 3 , Sc 2 (OCO) 6 , Sc(OCOCH 3 ) 3 , ScCl 3 , ScF 3 One or more of the above can be used. As the Rh source, Rh 2 O 3 , RhO 2 , Rh(OH) 3 , Rh(OH) 4 , Rh 2 (CO 3 ) 3 , Rh(NO 3 ) 3 , Rh 2 (SO 4 ) 3 , Rh(SO 4 ) 2 , Rh 2 (OCO) 6 , Rh(OCOCH 3 ) 3 , RhCl 3 , RhCl 4 , RhF 3 One or more of the above can be used. As the Gd source, Gd 2 O 3 , GdO 2 S, GdOS 2 , Gd(OH) 3 , GdOOH, Gd 2 (CO 3 ) 3 , Gd(NO 3 ) 3 , Gd 2 (SO 4 ) 3 , Gd 2 (OCO) 6 , GdCl 3 , GdF 3 One or more of the above can be used. As the Tb source, Tb 2 O 3 , TbO 2 S, TbOS2 , Tb(OH) 3 , TbOOH, Tb 2 (CO 3 ) 3 , Tb(NO 3 ) 3 , Tb 2 (SO 4 ) 3 , Tb 2 (OCO) 6 , TbCl 3 , TbF 3 One or more of these can be used. As the Yb source, Yb 2 O 3 , YbO 2 S, YbOS 2 , Yb(OH) 3 , YbOOH, Yb 2 (CO 3 ) 3 , Yb(NO 3 ) 3 , Yb 2 (SO 4 ) 3 , Yb 2 (OCO) 6 , YbCl 3 , YbF 3 One or more of these can be used.

[0031] Note that the mixing of these raw materials is preferably carried out at -20 to 50 °C in an inert gas atmosphere such as nitrogen because air and trace amounts of moisture may be mixed in, causing the formation of impurities such as oxide phases.

[0032] The firing temperature of the mixture is not particularly limited because it also depends on the firing time, but it is preferably 450 °C or higher and less than 1000 °C. When the firing temperature is 1100 °C or higher, it is often not possible to obtain YTMOS with excellent photocatalytic activity. Also, when the firing temperature is too low, the solid-phase reaction does not proceed sufficiently, and it is often not possible to obtain high-purity YTMOS. Therefore, the firing temperature is usually 500 °C or higher, preferably 550 °C or higher, and usually less than 1100 °C, preferably 1000 °C or lower.

[0033] There is no particular limitation on the firing atmosphere, but it is preferably carried out in a vacuum from the viewpoint of preventing side reactions. The firing time varies depending on the firing temperature, but is usually 0.1 to 120 hours, preferably 1 to 48 hours.

[0034] The YTMOS obtained by firing may be heat-treated by heating in air at a temperature of 100 to 300 °C for about 0.1 to 3 hours in order to oxidize and remove excess sulfur content as necessary. After this heat treatment, it is preferable to wash with water to remove sulfur oxides and perform solid-liquid separation of YTMOS.

[0035] In addition, the obtained YTMOS may be subjected to an acid treatment in which it is brought into contact with an acid such as sulfuric acid, nitric acid, or aqua regia at about 20 to 80% by mass as necessary. By performing the acid treatment, impurities on the surface of the photocatalyst particles can be removed.

[0036] In addition, the obtained YTMOS may be subjected to size adjustment treatments such as grinding and classification as necessary. The particle size after grinding is not particularly limited, but it is preferably 1 μm or more because it becomes easier to handle. On the other hand, it is preferable to set the particle size to 20 μm or less because the surface area of the catalyst increases and the catalytic activity improves. This particle size is calculated, for example, by taking a photograph with SEM, randomly selecting about 50 particles and measuring the diameter, and calculating from the average value. When the particles after grinding deviate significantly from a spherical shape, the particle diameter may be measured and calculated as the area equivalent diameter from the photograph.

[0037] Furthermore, the obtained YTMOS may be suspended in a cocatalyst-containing solution and subjected to MW (microwave) treatment as necessary. By performing MW treatment, it may be possible to prepare the photocatalyst for evaluation described below in a short time. As the MW treatment, for example, "Microwave synthesis Reactor Monowave 300" manufactured by Anton Paar may be used, and the recommended conditions may be appropriately selected and implemented.

[0038] In the examples described later, raw materials other than the M source are mixed and calcined (first calcination) to produce a photocatalyst powder that does not contain M, and then a predetermined amount of the M source and flux are mixed with this photocatalyst powder and calcined again at the same temperature as in the first calcination for only about 1 / 10 to 1 / 2 the calcination time (second calcination) to produce the photocatalyst of the present invention. However, this is for experimental convenience to clarify the factors behind the performance improvement, since the M source can affect the particle properties in the YTOS production process. It is also possible to produce the photocatalyst of the present invention by mixing the M source together with other raw materials in a lump and calcining it once. In addition, in this second firing, KI, NaI, LiI, RbI, CsI, LiCl, NaCl, KCl, RbCl, CsCl, MgCl were added to increase the reactivity with the M source YTOS. 2 , CaCl 2 , SrCl 2 , BaCl 2 One or more of the above are used as fluxes, and 0.5 to 20 moles are mixed per mole of Ti. This is to make it easier to uniformly cover the entire YTOS particle with the M source, and the added flux is removed by washing with water after the second firing.

[0039] [Application] The photocatalyst of the present invention is effective as a photocatalyst for water splitting, exhibits particularly high photocatalytic activity, and can perform total water splitting as a photocatalyst capable of total water splitting using a single electrode, i.e., without the need for a counter electrode.

[0040] [Production methods of hydrogen and oxygen] The method for producing hydrogen and oxygen of the present invention is characterized in that hydrogen and oxygen are generated using the photocatalyst of the present invention without using a sacrificial reagent. In addition, by using the photocatalyst of the present invention, hydrogen and oxygen can be generated on the same electrode. In the present invention, a laminate having a photocatalyst layer containing the photocatalyst of the present invention provided on a substrate, or a composite containing the photocatalyst of the present invention is referred to as an electrode.

[0041] The photocatalyst of the present invention exhibits sufficient photocatalytic activity by itself, but is preferably used together with a cocatalyst.

[0042] As cocatalysts, there are an oxidation reaction cocatalyst (oxygen generation side) and a reduction reaction cocatalyst (hydrogen generation side), and it is preferable to use one or both of these supported on YTMOS. As the oxidation reaction cocatalyst, it is preferable to use any one of metals of Groups 2 to 14 of the periodic table, intermetallic compounds of the metals, alloys, or oxides, composite oxides, nitrides, oxynitrides, sulfides, oxysulfides, or mixtures thereof. Here, the "intermetallic compound" is a compound formed from two or more metal elements, and the component atomic ratio constituting the intermetallic compound is not necessarily a stoichiometric ratio and has a wide composition range. The "oxides, composite oxides, nitrides, oxynitrides, sulfides, oxysulfides thereof" refer to oxides, composite oxides, nitrides, oxynitrides, sulfides, oxysulfides of metals of Groups 2 to 14 of the periodic table, intermetallic compounds of the metals, or alloys. The "mixtures thereof" refer to mixtures of any two or more of the compounds exemplified above.

[0043] As the oxidation reaction cocatalyst, preferably, metals such as Mg, Ti, Mn, Fe, Co, Ni, Cu, Ga, Ru, Rh, Pd, Ag, Cd, In, Ce, Ta, W, Ir, Pt or Pb, oxides or composite oxides thereof, more preferably, metals such as Mn, Co, Ni, Ru, Rh, Ir, oxides or composite oxides thereof, still more preferably, Ir, MnO, MnO 2 , Mn 2 O 3 , Mn 3 O 4 , CoO, Co 3 O 4 , NiCo 2 O 4 , RuO 2 , Rh 2 O 3 , IrO 2 are used.

[0044] As the reduction reaction promoter, it is preferable to use any one of metals of Groups 3 to 13 of the periodic table, intermetallic compounds of the metals, alloys, or oxides, composite oxides, oxynitrides, sulfides, oxysulfides, carbides, nitrides, or mixtures thereof. Here, the "intermetallic compound" is the same as described above, and the "oxides, composite oxides, oxynitrides, sulfides, oxysulfides, carbides, nitrides" refer to oxides, composite oxides, oxynitrides, sulfides, oxysulfides, carbides, or nitrides of metals of Groups 3 to 13 of the periodic table, intermetallic compounds of the metals, and alloys. The "mixtures thereof" refers to mixtures of any two or more of the compounds exemplified above.

[0045] As the reduction reaction promoter, preferably, Pt, Pd, Rh, Ru, Ni, Au, Fe, NiO, RuO 2 , IrO 2 , Rh 2 O 3 , and Cr-Rh composite oxide, core-shell type Rh / Cr 2 O 3 , Pt / Cr 2 O 3 etc. can be mentioned.

[0046] Regarding the supported amount of the above-mentioned promoter, the metal supported amount of the oxidation reaction promoter is not particularly limited, but based on YTMOS (100% by mass), it is usually 0.01% by mass or more and 5% by mass or less, preferably the upper limit is 4% by mass or less, more preferably the upper limit is 3% by mass or less, and the lower limit is 0.05% by mass or more. The metal supported amount of the reduction reaction promoter is not particularly limited, but based on YTMOS (100% by mass), it is usually 0.01% by mass or more and 20% by mass or less, preferably the upper limit is 15% by mass or less, more preferably the upper limit is 10% by mass or less. The "metal supported amount" mentioned here refers to the amount occupied by the metal element in the supported promoter.

[0047] When the photocatalyst of the present invention is actually used for water decomposition, the form of the photocatalyst is not particularly limited. Examples include a form in which photocatalyst particles are dispersed in water, a form in which photocatalyst particles are solidified into a molded body and the molded body is installed in water, a form in which a photocatalyst layer is provided on a substrate to form a laminate and the laminate is installed in water, and a form in which a photocatalyst is immobilized on a current collector to form an electrode for photocatalytic water decomposition and is installed in water together with a counter electrode. In particular, when the photocatalytic water decomposition reaction is carried out on a large scale, it is preferable to use an electrode for photocatalytic water decomposition from the viewpoint of being able to promote the water decomposition reaction by applying a bias. As another aspect, taking advantage of the fact that the photocatalyst of the present invention can perform complete water decomposition alone without a catalyst, a laminate having a photocatalyst layer containing the photocatalyst of the present invention provided on a substrate without applying a bias, or a composite containing the photocatalyst of the present invention can also be installed in water. According to this aspect, it is possible to suppress the cost when used as an artificial photosynthesis device that is easy to process and handle, easy to maintain, and uses a large area, and an industrially advantageous water decomposition device, oxygen generation device, hydrogen generation device, or artificial photosynthesis system can be obtained.

[0048] The electrode for photocatalytic water decomposition can be produced by a known method. For example, it can be easily produced by the so-called particle transfer method (Chem. Sci., 2013, 4, 1120 - 1124). Here, in the particle transfer method, it is common to manufacture the electrode for photocatalytic water decomposition according to the following procedure. That is, photocatalyst particles are placed on a first substrate such as glass to obtain a laminate of a photocatalyst layer and a first substrate layer. A conductive layer (current collector) is provided on the surface of the photocatalyst layer of the obtained laminate by vapor deposition or the like. Here, the photocatalyst particles on the surface layer on the conductive layer side of the photocatalyst layer are immobilized on the conductive layer. Then, a second substrate is adhered to the surface of the conductive layer, and the first substrate layer, the conductive layer, and the photocatalyst layer are peeled off. Since a part of the photocatalyst particles is immobilized on the surface of the conductive layer, it is peeled off together with the conductive layer, and as a result, an electrode for photocatalytic water decomposition having a photocatalyst layer, a conductive layer, and a second substrate layer can be obtained. Alternatively, as another method, an electrode for photocatalytic water splitting reaction may be obtained by applying a slurry in which photocatalytic particles are dispersed onto the surface of a current collector and drying it, or by integrally forming the photocatalytic particles and the current collector through pressure molding or the like. Further, a current collector may be immersed in a slurry in which photocatalytic particles are dispersed, and a voltage may be applied to deposit the photocatalytic particles on the current collector by electrophoresis. Alternatively, it may be in a form in which the loading of the cocatalyst is carried out in a subsequent process. For example, in the above-described particle transfer method, a laminate having a photocatalyst semiconductor layer, a conductive layer, and a second base material layer is obtained in the same manner using photocatalyst semiconductor particles instead of photocatalytic particles, and then oxide particles as a cocatalyst are loaded on the surface of the photocatalyst semiconductor layer to obtain an electrode for photocatalytic water splitting reaction.

[0049] The photocatalyst of the present invention, or the above-described electrode for photocatalytic water splitting reaction, is immersed in water or an electrolyte aqueous solution, and the photocatalyst or the electrode for photocatalytic water splitting reaction is irradiated with light to perform photocatalytic water splitting, whereby hydrogen and / or oxygen can be produced.

[0050] For example, while immobilizing a photocatalyst on a current collector composed of a conductor as described above to obtain an electrode for photocatalytic water splitting reaction, a conductor carrying a hydrogen production catalyst is used as a counter electrode, and light is irradiated while supplying liquid or gaseous water to advance the water splitting reaction. By providing a potential difference between the electrodes as necessary, the water splitting reaction can be promoted. Alternatively, a photocatalyst semiconductor carrying a hydrogen production catalyst may be used as a counter electrode. In this case, a known photocatalyst semiconductor that catalyzes the hydrogen production reaction can be used as the photocatalyst semiconductor.

[0051] On the other hand, light may be irradiated while supplying water to a fixed product in which photocatalytic particles are immobilized on an insulating base material or a molded product obtained by pressure molding or the like of photocatalytic particles to advance the water splitting reaction. Alternatively, photocatalytic particles may be dispersed in water or an electrolyte aqueous solution, and light may be irradiated thereto to advance the water splitting reaction. In this case, the reaction can be promoted by stirring as necessary. Since the photocatalyst of the present invention can perform overall water splitting by itself, it is not necessary to connect an oxygen generation electrode and a hydrogen generation electrode. If the photocatalyst is placed in water and there are means for supplying water thereto and means for extracting hydrogen and / or oxygen, hydrogen and oxygen can be produced. As a result, the structure is simplified, and at the same time, it is also possible to operate with half the area compared to arranging the oxygen generation electrode and the hydrogen generation electrode in parallel. The generated hydrogen and oxygen can be separated into hydrogen and oxygen using, for example, a zeolite membrane or the like.

[0052] The reaction conditions during the production of hydrogen and / or oxygen are not particularly limited. For example, the reaction temperature is set to 0°C or higher and 200°C or lower, and the reaction pressure is set to 2 MPa(G) or lower. The irradiation light is visible light having a wavelength of 650 nm or less, or ultraviolet light. Examples of the light source of the irradiation light include the sun, lamps capable of irradiating sunlight approximation light such as xenon lamps and metal halide lamps, mercury lamps, LEDs, and the like.

[0053] As described above, according to the present invention, by using the photocatalyst of the present invention, hydrogen and / or oxygen can be efficiently produced by a photoreforming reaction.

Examples

[0054] Hereinafter, the present invention will be described more specifically based on examples, but the present invention is not limited by the following examples. Note that the values of various production conditions and evaluation results in the following examples have the meaning as the preferable values of the upper limit or the lower limit in the embodiments of the present invention, and the preferable range may be a range defined by the combination of the above-mentioned upper limit or lower limit values and the values of the following examples or the values between the examples.

[0055] [Activation treatment of photocatalyst for hydrogen generation evaluation and evaluation of photocatalytic activity] The photocatalyst powders synthesized in the following examples and comparative examples were subjected to activation treatment and evaluation of photocatalytic activity by the following method.

[0056] [Activation treatment] For each photocatalyst, as a treatment to promote the catalytic activity, air oxidation treatment and acid washing treatment were performed to obtain a photocatalyst for hydrogen generation evaluation. In the air oxidation treatment, the excess sulfur content was oxidized by heat treatment at 200 °C for 1 hour in air and then removed by water washing treatment. In the acid washing treatment, after the air oxidation treatment, 400 mg of each powder was mixed and washed in sulfuric acid with a concentration of 50 mass% for 15 minutes to remove the impurities adhering to the particle surface.

[0057] <Hydrogen Generation Evaluation Test> Using the prepared photocatalyst for hydrogen generation evaluation, the performance of the photocatalytic water splitting reaction was evaluated. The photocatalytic water splitting reaction was carried out in a closed reaction apparatus equipped with a vacuum pump for evacuation, a circulation pump, a cell containing the photocatalyst, a gas sampling valve, and a gas chromatograph analyzer (GC). As the light source, a 300 W xenon lamp (λ > 420 nm) was used, and a water filter was provided between the lamp and the cell to avoid temperature rise. Furthermore, the cell was cooled from the outside using cooling water. During the evaluation, after evacuating the reaction apparatus several times in advance, it was confirmed that no air remained. The degree of vacuum was set to about 4×10 4 Pa. Then, light irradiation was started, and the amount of gas generated was measured. The analysis conditions were column (Molecular Sieve 5A), carrier gas (argon), and temperature (50 - 70 °C). The test was carried out by enclosing 150 mL of a 0.02 M Na 2 S-Na 2 SO 3 aqueous solution in the cell.

[0058] [Synthesis and Evaluation of Photocatalyst Powder] <Example 1> Y 2 O 3 、Y 2 S 3 、TiO 2 were weighed in a molar ratio of 1:2:6, and 5 mass% of sulfur based on the whole was added. Then, N 2It was mixed in a glove box (dew point of -70°C or lower) for about 40 minutes, sealed in a quartz tube in a vacuum, and then calcined at 800°C for 96 hours to obtain photocatalyst powder A. Aluminum oxide (Al 2 O 3 ) was mixed with photocatalyst powder A obtained in Example 1 at a molar ratio of Al / Ti = 0.5 / 100, and potassium iodide (KI) flux was mixed at a molar ratio of KI / Ti = 5 / 1. After being sealed in a quartz tube in a vacuum, it was calcined at 800°C for 24 hours. Then, after removing the KI flux component by washing with water, it was filtered and dried, and the above-mentioned activation treatment was performed to obtain photocatalyst powder B. Table 1 shows the results of evaluating the hydrogen generation photocatalytic activity of the obtained photocatalyst powder B.

[0059] <Example 2> Aluminum oxide (Al 2 O 3 ) was mixed with the photocatalyst powder A described in Example 1 at a molar ratio of Al / Ti = 1.0 / 100, and potassium iodide (KI) flux was mixed at a molar ratio of KI / Ti = 5 / 1. After being sealed in a quartz tube in a vacuum, it was calcined at 800°C for 24 hours. Then, after removing the KI flux component by washing with water, it was filtered and dried, and the above-mentioned activation treatment was performed to obtain photocatalyst powder C. Table 1 shows the results of evaluating the hydrogen generation photocatalytic activity of the obtained photocatalyst powder C.

[0060] <Example 3> Aluminum oxide (Al 2 O 3 ) was mixed with the photocatalyst powder A described in Example 1 at a molar ratio of Al / Ti = 1.5 / 100, and potassium iodide (KI) flux was mixed at a molar ratio of KI / Ti = 5 / 1. After being sealed in a quartz tube in a vacuum, it was calcined at 800°C for 24 hours. Then, after removing the KI flux component by washing with water, it was filtered and dried, and the above-mentioned activation treatment was performed to obtain photocatalyst powder D. Table 1 shows the results of evaluating the hydrogen generation photocatalytic activity of the obtained photocatalyst powder D.

[0061] <Example 4> Scandium oxide (Sc2 O 3 and (O) were mixed at a molar ratio of Sc / Ti = 0.5 / 100 and potassium iodide (KI) flux at a molar ratio of KI / Ti = 5 / 1, respectively, sealed in a quartz tube in vacuo, and then calcined at 800 °C for 24 hours. Thereafter, the KI flux component was removed by washing with water, followed by filtration and drying, and the photocatalyst powder E was obtained by performing the activation treatment described above. Table 1 shows the results of evaluating the hydrogen generation photocatalytic activity of the obtained photocatalyst powder E.

[0062] <Example 5> To the photocatalyst powder A described in Example 1, scandium oxide (Sc 2 O 3 ) was mixed at a molar ratio of Sc / Ti = 0.8 / 100 and potassium iodide (KI) flux at a molar ratio of KI / Ti = 5 / 1, respectively, sealed in a quartz tube in vacuo, and then calcined at 800 °C for 24 hours. Thereafter, the KI flux component was removed by washing with water, followed by filtration and drying, and the photocatalyst powder F was obtained by performing the activation treatment described above. Table 1 shows the results of evaluating the hydrogen generation photocatalytic activity of the obtained photocatalyst powder F.

[0063] <Example 6> To the photocatalyst powder A described in Example 1, scandium oxide (Sc 2 O 3 ) was mixed at a molar ratio of Sc / Ti = 1.0 / 100 and potassium iodide (KI) flux at a molar ratio of KI / Ti = 5 / 1, respectively, sealed in a quartz tube in vacuo, and then calcined at 800 °C for 24 hours. Thereafter, the KI flux component was removed by washing with water, followed by filtration and drying, and the photocatalyst powder G was obtained by performing the activation treatment described above. Table 1 shows the results of evaluating the hydrogen generation photocatalytic activity of the obtained photocatalyst powder G.

[0064] <Example 7> To the photocatalyst powder A described in Example 1, lithium oxide (Li 2(O) was mixed with potassium iodide (KI) flux at a molar ratio of Li / Ti = 1.0 / 100 and KI / Ti = 5 / 1 respectively, sealed in a quartz tube in vacuo, and then calcined at 800 °C for 24 hours. Thereafter, the KI flux component was removed by washing with water, followed by filtration and drying, and the above-described activation treatment was performed to obtain photocatalyst powder H. Table 1 shows the results of evaluating the hydrogen generation photocatalytic activity of the obtained photocatalyst powder H.

[0065] <Example 8> Magnesium oxide (MgO) was mixed with the photocatalyst powder A described in Example 1 at a molar ratio of Mg / Ti = 1.0 / 100, and potassium iodide (KI) flux was mixed at a molar ratio of KI / Ti = 5 / 1. After sealing in a quartz tube in vacuo, it was calcined at 800 °C for 24 hours. Thereafter, the KI flux component was removed by washing with water, followed by filtration and drying, and the above-described activation treatment was performed to obtain photocatalyst powder I. Table 1 shows the results of evaluating the hydrogen generation photocatalytic activity of the obtained photocatalyst powder I.

[0066] <Example 9> Rhodium oxide (Rh 2 O 3 ) was mixed with the photocatalyst powder A described in Example 1 at a molar ratio of Rh / Ti = 1.0 / 100, and potassium iodide (KI) flux was mixed at a molar ratio of KI / Ti = 5 / 1. After sealing in a quartz tube in vacuo, it was calcined at 800 °C for 24 hours. Thereafter, the KI flux component was removed by washing with water, followed by filtration and drying, and the above-described activation treatment was performed to obtain photocatalyst powder J. Table 1 shows the results of evaluating the hydrogen generation photocatalytic activity of the obtained photocatalyst powder J.

[0067] <Example 10> Sodium oxide (Na 2(O) was mixed at a molar ratio of Na / Ti = 1.0 / 100 and potassium iodide (KI) flux at a molar ratio of KI / Ti = 5 / 1, respectively, sealed in a quartz tube in a vacuum, and then calcined at 800 °C for 24 hours. After that, the KI flux component was removed by washing with water, followed by filtration and drying, and the above-described activation treatment was performed to obtain photocatalyst powder K. Table 1 shows the results of evaluating the hydrogen generation photocatalytic activity of the obtained photocatalyst powder K.

[0068] <Example 11> Calcium oxide (CaO) was mixed with the photocatalyst powder A described in Example 1 at a molar ratio of Ca / Ti = 1.0 / 100, and potassium iodide (KI) flux at a molar ratio of KI / Ti = 5 / 1, respectively, sealed in a quartz tube in a vacuum, and then calcined at 800 °C for 24 hours. After that, the KI flux component was removed by washing with water, followed by filtration and drying, and the above-described activation treatment was performed to obtain photocatalyst powder L. Table 1 shows the results of evaluating the hydrogen generation photocatalytic activity of the obtained photocatalyst powder L.

[0069] <Example 12> Gadolinium oxide (Gd 2 O 3 ) was mixed with the photocatalyst powder A described in Example 1 at a molar ratio of Gd / Ti = 1.0 / 100, and potassium iodide (KI) flux at a molar ratio of KI / Ti = 5 / 1, respectively, sealed in a quartz tube in a vacuum, and then calcined at 800 °C for 24 hours. After that, the KI flux component was removed by washing with water, followed by filtration and drying, and the above-described activation treatment was performed to obtain photocatalyst powder M. Table 1 shows the results of evaluating the hydrogen generation photocatalytic activity of the obtained photocatalyst powder M.

[0070] <Example 13> Terbium oxide (Tb 2 O 3) was mixed with potassium iodide (KI) flux at a molar ratio of Tb / Ti = 1.0 / 100 and KI / Ti = 5 / 1 respectively, sealed in a quartz tube in vacuum, and then calcined at 800 °C for 24 hours. After that, the KI flux component was removed by washing with water, followed by filtration and drying, and the photocatalyst powder N was obtained by performing the aforementioned activation treatment. Table 1 shows the results of evaluating the hydrogen generation photocatalytic activity of the obtained photocatalyst powder N.

[0071] <Example 14> Ytterbium oxide (Yb 2 O 3 ) was mixed with potassium iodide (KI) flux at a molar ratio of Yb / Ti = 1.0 / 100 and KI / Ti = 5 / 1 respectively, sealed in a quartz tube in vacuum, and then calcined at 800 °C for 24 hours. After that, the KI flux component was removed by washing with water, followed by filtration and drying, and the photocatalyst powder O was obtained by performing the aforementioned activation treatment. Table 1 shows the results of evaluating the hydrogen generation photocatalytic activity of the obtained photocatalyst powder O.

[0072] <Comparative Example 1> Using the photocatalyst powder A described in Example 1, after performing the aforementioned activation treatment, Table 1 shows the results of evaluating the hydrogen generation photocatalytic activity.

[0073] <Comparative Example 2> Aluminum oxide (Al 2 O 3 ) was mixed with potassium iodide (KI) flux at a molar ratio of Al / Ti = 2.0 / 100 and KI / Ti = 5 / 1 respectively, sealed in a quartz tube in vacuum, and then calcined at 800 °C for 24 hours. After that, the KI flux component was removed by washing with water, followed by filtration and drying, and the photocatalyst powder P was obtained by performing the aforementioned activation treatment. Table 1 shows the results of evaluating the hydrogen generation photocatalytic activity of the obtained photocatalyst powder P.

[0074] <Comparative Example 3> Scandium oxide (Sc2 O 3 ) was mixed with potassium iodide (KI) flux at a molar ratio of Sc / Ti = 2.0 / 100 and KI / Ti = 5 / 1, respectively, sealed in a quartz tube in vacuo, and then calcined at 800 °C for 24 hours. Thereafter, the KI flux component was removed by washing with water, followed by filtration and drying, and the photocatalyst powder Q was obtained by performing the activation treatment described above. Table 1 shows the results of evaluating the hydrogen generation photocatalytic activity of the obtained photocatalyst powder Q.

[0075] <Comparative Example 4> Vanadium(V) oxide was added to the photocatalyst powder A described in Example 1 2 O 5 ) at a molar ratio of V / Ti = 1.0 / 100, and potassium iodide (KI) flux at a molar ratio of KI / Ti = 5 / 1. The mixture was sealed in a quartz tube in vacuo and then calcined at 800 °C for 24 hours. Thereafter, the KI flux component was removed by washing with water, followed by filtration and drying, and the photocatalyst powder R was obtained by performing the activation treatment described above. Table 1 shows the results of evaluating the hydrogen generation photocatalytic activity of the obtained photocatalyst powder R.

[0076] <Comparative Example 5> Chromium(III) oxide was added to the photocatalyst powder A described in Example 1 2 O 3 ) at a molar ratio of Cr / Ti = 1.0 / 100, and potassium iodide (KI) flux at a molar ratio of KI / Ti = 5 / 1. The mixture was sealed in a quartz tube in vacuo and then calcined at 800 °C for 24 hours. Thereafter, the KI flux component was removed by washing with water, followed by filtration and drying, and the photocatalyst powder S was obtained by performing the activation treatment described above. Table 1 shows the results of evaluating the hydrogen generation photocatalytic activity of the obtained photocatalyst powder S.

[0077] <Comparative Example 6> Iron(III) oxide was added to the photocatalyst powder A described in Example 1 2 O 3) was mixed with potassium iodide (KI) flux at a molar ratio of Fe / Ti = 1.0 / 100 and KI / Ti = 5 / 1, respectively, sealed in a quartz tube in vacuum, and then calcined at 800 °C for 24 hours. After that, the KI flux component was removed by washing with water, followed by filtration and drying, and the above-mentioned activation treatment was performed to obtain the photocatalyst powder T. Table 1 shows the results of evaluating the hydrogen generation photocatalytic activity of the obtained photocatalyst powder T.

[0078] <Comparative Example 7> Tin oxide (SnO 2 ) was mixed with potassium iodide (KI) flux at a molar ratio of Sn / Ti = 1.0 / 100 and KI / Ti = 5 / 1, respectively, sealed in a quartz tube in vacuum, and then calcined at 800 °C for 24 hours. After that, the KI flux component was removed by washing with water, followed by filtration and drying, and the above-mentioned activation treatment was performed to obtain the photocatalyst powder U. Table 1 shows the results of evaluating the hydrogen generation photocatalytic activity of the obtained photocatalyst powder U.

[0079] <Comparative Example 8> Tungsten oxide (WO 3 ) was mixed with potassium iodide (KI) flux at a molar ratio of W / Ti = 1.0 / 100 and KI / Ti = 5 / 1, respectively, sealed in a quartz tube in vacuum, and then calcined at 800 °C for 24 hours. After that, the KI flux component was removed by washing with water, followed by filtration and drying, and the above-mentioned activation treatment was performed to obtain the photocatalyst powder V. Table 1 shows the results of evaluating the hydrogen generation photocatalytic activity of the obtained photocatalyst powder V.

[0080] <Comparative Example 9> Zinc oxide (ZnO) was mixed with potassium iodide (KI) flux at a molar ratio of Zn / Ti = 1.0 / 100 and KI / Ti = 5 / 1, respectively, sealed in a quartz tube in vacuum, and then calcined at 800 °C for 24 hours. After that, the KI flux component was removed by washing with water, followed by filtration and drying, and the above-mentioned activation treatment was performed to obtain the photocatalyst powder W. Table 1 shows the results of evaluating the hydrogen production photocatalytic activity of the obtained photocatalytic powder W.

[0081] <Comparative Example 10> To the photocatalytic powder A described in Example 1, gallium oxide (Ga 2 O 3 ) was mixed at a molar ratio of Ga / Ti = 1.0 / 100, and potassium iodide (KI) flux was mixed at a molar ratio of KI / Ti = 5 / 1. After encapsulating in a quartz tube in vacuo, it was calcined at 800 °C for 24 hours. Then, after removing the KI flux component by washing with water, it was filtered and dried, and the photocatalytic powder X was obtained by performing the above-described activation treatment. Table 1 shows the results of evaluating the hydrogen production photocatalytic activity of the obtained photocatalytic powder X.

[0082] <Comparative Example 11> To the photocatalytic powder A described in Example 1, zirconium oxide (ZrO 2 ) was mixed at a molar ratio of Zr / Ti = 1.0 / 100, and potassium iodide (KI) flux was mixed at a molar ratio of KI / Ti = 5 / 1. After encapsulating in a quartz tube in vacuo, it was calcined at 800 °C for 24 hours. Then, after removing the KI flux component by washing with water, it was filtered and dried, and the photocatalytic powder Y was obtained by performing the above-described activation treatment. Table 1 shows the results of evaluating the hydrogen production photocatalytic activity of the obtained photocatalytic powder Y.

[0083]

Table 1

[0084] From Table 1, comparing Examples 1 to 3 to which aluminum oxide (Al 2 O 3 ) was added with Comparative Example 1, it was found that the hydrogen production activity was improved up to about 2.6 times by adding aluminum oxide. On the other hand, in Comparative Example 2, by increasing the addition amount of aluminum oxide up to a molar ratio of Al / Ti = 2.0 / 100 (0.4 mol with respect to 2 mol of Ti), results were obtained such that the hydrogen production activity significantly decreased, and excessive addition impaired the catalytic activity.

[0085] In addition, from the comparison between Examples 4 to 6 to which scandium oxide (Sc 2 O 3 ) was added and Comparative Example 1, it was found that the hydrogen generation activity was improved up to about 3.2 times by adding scandium oxide. On the other hand, in Comparative Example 3, by increasing the addition amount of scandium oxide to a molar ratio of Sc / Ti = 2.0 / 100 (0.4 mol with respect to 2 mol of Ti), the hydrogen generation activity was significantly reduced, and as a result, excessive addition impaired the catalytic activity. From the above, Y 2 Ti 2 O 5 S 2 It was confirmed that the hydrogen generation activity can be improved by adding a specific element M to the photocatalyst (photocatalyst powder A, Comparative Example 1), and it was found that the addition amount is desirably less than M / Ti = 2.0 / 100 (less than 0.4 mol with respect to 2 mol of Ti).

[0086] In addition, from the comparison between Examples 2, 6 to 14 and Comparative Examples 4 to 11, the influence on the hydrogen generation activity when various metal oxides were added could be confirmed. In particular, under the conditions of adding Sc, Al, Mg, Li, Rh, Na, Ca, Gd, Tb, Yb, a significant improvement in the hydrogen generation activity was confirmed.

[0087] In considering the influence of the added components on the hydrogen generation activity, the hydrogen generation rates of Examples 2, 6 to 14 and Comparative Examples 4 to 11 were evaluated according to the following criteria, and the oxidation states that each added element can take in the structure of Y 2 Ti 2 O 5 S 2 and the influence on the hydrogen generation activity are summarized in Table 2.

[0088] <Evaluation Criteria> ◎: Shows a hydrogen generation rate of 2 times or more with respect to the hydrogen generation rate of Comparative Example 1. ○: Shows a hydrogen generation rate of 1.1 times or more and less than 2 times with respect to the hydrogen generation rate of Comparative Example 1. △: Shows a hydrogen generation rate of 0.9 times or more and less than 1.1 times with respect to the hydrogen generation rate of Comparative Example 1. ×: The hydrogen generation rate is 0.7 times or more and less than 0.9 times that of Comparative Example 1. ××: The hydrogen generation rate is less than 0.7 times that of Comparative Example 1.

[0089]

Table 2

[0090] From Table 2, it was found that as an additive element capable of improving the hydrogen generation photocatalytic activity, satisfying the following two conditions leads to an improvement in activity. The first condition is that the stable oxidation state of the additive element is +3 or less. That is, in a Ti-based photocatalyst, with the deficiency of anion (oxygen, sulfur, nitrogen, etc.) elements, the Ti element that should originally exist in a stable +4 oxidation state is reduced to a +3 state and exists in such a state, and it is known that the photocatalytic activity is reduced due to the distortion in the electronic state. In the present invention, by adding an element with a stable oxidation state of +3 or less, the generation of the +3-valent Ti element is suppressed, and good photocatalytic activity is achieved. The second condition is that in the electronic state formed in the stable oxidation state of the additive element, that is, in the 6-coordinate (octahedral coordination) state, the outermost shell orbitals are s, p, f orbitals, or the outermost shell orbitals are d orbitals, and the element has no unpaired electrons in its d orbitals and no electrons in its eg orbitals. Although the details of the reason for this condition are not fully clear, if the outermost shell orbitals are d orbitals and there are unpaired electrons in its d orbitals or electrons in its eg orbitals, originally Y 2 Ti 2 O 5 S 2 has no electrons in it and has no electronic connection with the coordinating anion atoms, but it is presumed that the introduction of electrons derived from the additive element into the d electron orbitals impairs the semiconductor properties and reduces the function as a photocatalyst.

Claims

1. A photocatalyst having a composition represented by the following general formula (I). Y ａ Ti ｂ M ｃ O ｄ S ｅ …(I) (However, M in the general formula (I) is one or a combination of two or more selected from elements satisfying the following Condition 1 and Condition 2, and a = 1.7 to 2.3, b = 2, c = 0.003 to 0.038, d = 4.7 to 5.3, and e = 1.7 to 2.3 are numbers.) Condition 1: An element in a solid in an electron state of +3 valence or less. Condition 2: In a 6 - coordinate state, an element whose outermost shell orbitals are s, p, f orbitals, or an element whose outermost shell orbitals are d orbitals, having no unpaired electrons in its d orbitals and having no electrons in its eg orbitals.)

2. A photocatalyst having a composition represented by the following general formula (I). Y ａ Ti ｂ M ｃ O ｄ S ｅ …(I) (However, M is one or a combination of two or more selected from Li, Na, Mg, Ca, Al, Sc, Rh, Gd, Tb, and Yb, and a = 1.7 to 2.3, b = 2, c = 0.003 to 0.038, d = 4.7 to 5.3, and e = 1.7 to 2.3 are numbers.)

3. The photocatalyst according to Claim 1 or 2, which is a photocatalyst used for the overall decomposition of water.

4. A method for producing hydrogen and oxygen, which generates hydrogen and oxygen using a fixed product obtained by immobilizing the photocatalyst according to any one of Claims 1 to 3, or a molded product obtained by molding.

5. An electrode prepared using the photocatalyst according to any one of Claims 1 to 3.

6. A method for producing hydrogen and oxygen, which generates hydrogen and / or oxygen using the electrode according to Claim 5.

Images