JP2018058065A - Promoter for oxygen generating photocatalyst, and oxygen generating photocatalyst that supports the promoter, and complex and method for producing the complex - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new promoter for oxygen generating photocatalyst.SOLUTION: A promoter for oxygen generating photocatalyst has a complex containing a phosphide of a metal selected from Ni, Fe, Co, Mn, Mo and W, and an oxide of a metal selected from Ni, Fe, Co, Mn, Mo, W, Ti, Cr, Cu, Zn, In, Ir and Ru.SELECTED DRAWING: Figure 1-1

Description

  The present invention relates to a promoter for a photocatalyst for oxygen generation containing a metal phosphide and a metal oxide. The present invention also relates to a novel metal composite containing a metal phosphide and a metal oxide.

Since the fossil fuel that occupies most of the energy resources is limited, research is being conducted on the use of light energy to break down water into hydrogen and oxygen. In that case, a photocatalyst is usually used.
The photocatalyst currently being studied has a promoter supported on the surface of an optical semiconductor such as an oxide, an oxynitride, or a nitride, and the activity of the photocatalyst can be improved by supporting the promoter.

Cocatalysts for photocatalysts used for water splitting are generally roughly classified into oxygen generation promoters and hydrogen generation promoters.
As the oxygen generation co-catalyst, oxides such as Fe, Cо, Ni, and Mn are used. For example, in Patent Document 1, oxide particles containing Co and Mn are supported on a specific optical semiconductor, whereby Co A technique for making the dope effect remarkable is disclosed.

On the other hand, as a co-catalyst for hydrogen generation, for example, Non-Patent Document 1 discloses nickel compounds widely, and it is described that Ni ₂ P nanoparticles have a very high hydrogen generation capability.
Non-Patent Document 2 discloses a method for synthesizing a transition metal phosphide film used for generation of hydrogen and oxygen by electrolysis of water.

Japanese Patent Laying-Open No. 2015-112509

Eric J. Popczun, et al. Journal of the American Chemical Society, 135, 9267-9270 (2013) Carlos G. Read, et al. Applied Material & Interfaces 8, 12798-12803 (2016)

  An object of the present invention is to provide a new promoter for a photocatalyst for oxygen generation.

As a result of intensive studies to provide a new oxygen-producing photocatalyst promoter, a complex containing a specific metal phosphide and a specific metal oxide is useful as a promoter for oxygen generation. I found out. Further research on the composite has led to the completion of the present invention, conceiving that it is a new composite having a core-shell structure comprising a metal phosphide core and a metal oxide shell.
The present invention includes the following gist.

(1) From a metal phosphide selected from Ni, Fe, Co, Mn, Mo and W, and from Ni, Fe, Co, Mn, Mo, W, Ti, Cr, Cu, Zn, In, Ir and Ru A cocatalyst for photocatalyst for oxygen generation, comprising a composite comprising an oxide of a selected metal.
(2) The promoter according to (1), which has a core-shell structure in which the metal phosphide is used as a core and the metal oxide is used as a shell.
(3) A photocatalyst for oxygen generation carrying the promoter according to (1) or (2).
(4) A photocatalytic sheet having the photocatalyst described in (3).
(5) A photocatalytic electrode having the photocatalyst described in (3).
(6) A hydrogen and / or oxygen generator by water splitting, comprising the photocatalyst sheet according to (4) or the photocatalyst electrode according to (5).
(7) From a metal phosphide selected from Ni, Fe, Co, Mn, Mo and W, and from Ni, Fe, Co, Mn, Mo, W, Ti, Cr, Cu, Zn, In, Ir and Ru A composite comprising an oxide of a selected metal.
(8) The composite according to (7), which has a core-shell structure in which the metal phosphide is used as a core and the metal oxide is used as a shell.
(9) preparing a metal phosphide selected from Ni, Fe, Co, Mn, Mo and W, and the prepared phosphide and Ni, Fe, Co, Mn, Mo, W, Ti, Cr, A method for producing a composite of a metal phosphide and a metal oxide, comprising mixing a metal complex selected from Cu, Zn, In, Ir, and Ru, and firing the mixture.
(10) The method for producing a composite according to (9), wherein in the step of firing the mixture, the firing temperature is 340 ° C. or lower.
(11) An electrode for water electrolysis comprising a laminate of a catalyst layer and a conductive layer,
The catalyst layer includes a metal phosphide selected from Ni, Fe, Co, Mn, Mo and W, and Ni, Fe, Co, Mn, Mo, W, Ti, Cr, Cu, Zn, In, Ir and R
an electrode comprising a composite comprising a metal oxide selected from u.

  According to the present invention, a new promoter for a photocatalyst for oxygen generation can be provided. Further, the complex used for the oxygen-generating photocatalyst promoter is a novel complex. The composite provided by the present invention can impart high oxygen generation ability to the photocatalyst, and can efficiently generate oxygen from water.

Exhibiting a core-shell structure, showing a TEM image of a complex between the NiP _x and FeO _y according to Example 1 (drawing-substituting photograph). Exhibiting a core-shell structure, it shows a STEM-EDS images of the complex of the NiP _x and FeO _y according to Example 1 (drawing-substituting photograph). It shows TEM images of Ni ₂ P nanoparticles according to Comparative Example 1 (drawing-substituting photograph). Shows a TEM image of FeO _x nanoparticles according to Comparative Example 2 (drawing-substituting photograph). It shows TEM images of _Ni 2 P + FeO _x nanoparticles according to Comparative Example 3 (drawing-substituting photograph). It is a figure which shows the oxygen production | generation catalyst activity of the particle | grains prepared in Example 1 and Comparative Examples 1-3. It is a figure which shows the photocurrent-voltage curve of the electrode prepared in Example 2 and Comparative Examples 4-7. It is a figure which shows the photocurrent-time curve of the electrode prepared in Example 2 and Comparative Examples 4-7. Shows TEM images of _Ni x Mn _y P nanoparticles prepared in Comparative Example 8 (drawing-substituting photograph). Shows TEM images of _Ni x Zn _y P nanoparticles prepared in Comparative Example 9 (drawing-substituting photograph). It is a figure which shows the oxygen production | generation catalyst activity of the particle | grains prepared by the comparative examples 8 and 9. It is a figure which shows the photocurrent-voltage curve of the electrode prepared by the comparative examples 4, 10 and 11. It is a figure which shows the photocurrent-time curve of the electrode prepared by Comparative Examples 4, 10 and 11.

  Hereinafter, the present invention will be described in detail, but the description of the constituent elements described below is an example (representative example) of an embodiment of the present invention, and the present invention is not limited to these contents. Various modifications can be made within the scope of the gist.

One embodiment according to the present invention is a promoter for a photocatalyst for oxygen generation. The cocatalyst for photocatalyst for oxygen generation is usually carried on the photocatalyst, so that the photocatalyst has an oxygen generating function.
In this embodiment, the cocatalyst for photocatalyst for oxygen generation includes a metal phosphide selected from Ni, Fe, Co, Mn, Mo and W, and Ni, Fe, Co, Mn, Mo, W, Ti, Cr, And a complex containing a metal oxide selected from Cu, Zn, In, Ir, and Ru.
The metal phosphide forming the composite is preferably a phosphide of Ni, Fe, Co or Mn, more preferably a phosphide of nickel or iron, from the viewpoint of easy nanoparticle synthesis and catalytic activity. preferable.
The metal oxide that forms the composite is preferably an oxide of Ni, Fe, Co, or Mn, more preferably an oxide of Fe, from the viewpoint of easy shell coating and catalytic activity.

  Here, the composite refers to a composite in which some bonds are physically or chemically generated between the metal phosphide and the metal oxide. Therefore, a simple mixture of a metal phosphide and a metal oxide is not included in the composite here. In order to obtain a composite, it is necessary not only to simply mix a metal phosphide and a metal oxide but also to perform heat treatment, mechanical treatment, chemical treatment, and the like.

In the present embodiment, the composite may have any shape and is not particularly limited, but is preferably a particle or a fine particle. In the case of fine particles, the particle diameter is usually 1 nm or more, preferably 1.2 nm or more, more preferably 1.5 nm or more, from the viewpoint of easy loading on the optical semiconductor. Moreover, it is 25 nm or less normally, Preferably it is 20 nm or less.
In the present specification, 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, or SEM method. .

  As a method for producing a composite, for example, a step of preparing a phosphide of a metal selected from Ni, Fe, Co, Mn, Mo and W, and the prepared phosphide and Ni, Fe, Co, Mn, And a step of mixing a metal complex selected from Mo, W, Ti, Cr, Cu, Zn, In, Ir, and Ru, and firing the mixture.

The method for preparing the metal phosphide is not particularly limited, and a known synthesis method may be used, and when a commercially available product exists, a commercially available product may be used.
Illustrating a method for preparing NiP _x (x> 0), Ni raw materials such as Ni acetylacetonate and P raw materials such as trioctylphosphine are dissolved in an organic solvent, and preferably heated in an inert gas atmosphere. Can be obtained.
The obtained metal phosphide is preferably isolated from an organic solvent and purified using alcohol or the like.

The prepared metal phosphide is mixed with the metal complex and fired.
Metal complexes mixed with metal phosphides include metals selected from Ni, Fe, Co, Mn, Mo, W, Ti, Cr, Cu, Zn, In, Ir and Ru. Any complex may be used. Specific examples of the metal complex include Fe (CO) ₅ and (Fe (acac) ₃ ) (acac: acetylacetone), and Fe (CO) ₅ is preferable from the viewpoint of ease of shell coating.
The metal phosphide and metal complex are usually dissolved in an organic solvent and then mixed. The content ratio of the metal phosphide and the metal complex is not particularly limited, but the metal of the phosphide: metal of the complex is usually in a molar ratio of 2: 1 to 1: 4, preferably 1: 1 to 1: 2. It is. The type of the organic solvent is not particularly limited and can be appropriately set by those skilled in the art.

Calcination of the mixture of the metal phosphide and the metal complex is usually carried out at 340 ° C. or lower, preferably 310 ° C. or lower, more preferably 300 ° C. or lower. Moreover, it is 200 degreeC or more normally, Preferably it is 220 degreeC or more, More preferably, it is 240 degreeC or more. The firing time is usually 6 hours or less, preferably 4 hours or less. Moreover, it is normally 10 minutes or more, Preferably it is 30 minutes or more.
After baking, you may refine | purify as needed using alcohol.

The composite according to the present embodiment is a novel composite containing a specific metal phosphide and a specific metal oxide. As one form of the composite, a core-shell structure is formed in which a metal phosphide forms a core and a metal oxide forms a shell.
In such a structure, since the metal that forms the oxide by baking at a relatively low temperature does not form a solid solution in the metal phosphide and the particles do not agglomerate at the time of baking in the above-described composite manufacturing method, It is considered to be present because it is stably dispersed therein.
FIG. 1-1 shows a TEM image of a composite of NiP _x and FeO _y (satisfying x> 0 and y> 0). It can be understood that the Ni ₂ P nanoparticles shown in FIG. 2, the FeO _x nanoparticles shown in FIG. 3, and the Ni ₂ P + FeO _x nanoparticles shown in FIG. 4 are clearly different composites. That is, the complex according to the present embodiment is a new complex that has not existed before.
FIG. 1-2 shows a STEM-EDS image of a composite of NiP _x and FeO _y . It has been clarified that Ni and P are unevenly distributed in the central portion, and Fe and O are unevenly distributed in the peripheral portion, exhibiting a core-shell structure in which NiP _x is the core and FeO _y is the shell.

In the composite, the molar ratio of the metal forming the phosphide and the metal forming the oxide is usually 90:10 to 50:50, and preferably 85:15 to 70:30 from the viewpoint of catalytic activity. It is.
In the composite, the metal phosphide and the metal oxide may be doped with other metals. The metal to be doped is not particularly limited, but the metal used as the metal phosphide and metal oxide is doped. The amount of doping is not particularly limited.
The phosphide forming the composite is preferably a phosphide of a kind of metal selected from Ni, Fe, Co, Mn, Mo and W. On the other hand, the oxide forming the composite is a kind of metal oxide selected from Ni, Fe, Co, Mn, Mo, W, Ti, Cr, Cu, Zn, In, Ir, and Ru. preferable. Since the metal species of the metal phosphide and the metal species of the metal oxide are different metals, the catalytic activity is further improved, which is preferable.

The composite may include a phosphate of a metal selected from Ni, Fe, Co, Mn, Mo, W, Ti, Cr, Cu, Zn, In, Ir, and Ru. The concentration of the phosphate is preferably less than that of the oxide in the molar ratio between metals. The metal of the phosphate and the metal of the oxide may be the same or different.
In the case of forming the above core-shell structure, phosphate may be contained in the shell portion of the oxide.

Ni, Fe, Co, Mn, Mo, and W can be used as catalyst inks that are stably dispersed in a solvent because these phosphides can be easily synthesized as fine nanoparticles. In addition, the structure changes into a hydroxide during the oxidation reaction of water, and at that time, a solid solution can be easily formed with the other oxide phase in the composite, so various active solid solutions that are difficult to synthesize It is thought that the effect that can be formed easily is obtained.
For Ni, Fe, Co, Mn, Mo, W, Ti, Cr, Cu, Zn, In, Ir, and Ru, those oxides can be easily coated on the phosphide nanoparticles, thereby forming a composite. It can be used as a catalyst ink that is stably dispersed in a solvent. Further, it is considered that various active solid solutions that are difficult to synthesize can be easily formed by forming a solid solution with the phosphide phase in accordance with the structural change of the phosphide phase during the oxidation reaction of water.
The combination of the phosphide and the oxide is considered to suppress the recombination of oxygen and hydrogen and to obtain an effect that oxygen generation is effectively performed.

In this embodiment, the composite is used as a cocatalyst for the oxygen-producing photocatalyst, and the photocatalyst has an oxygen-generating function by being supported on the photocatalyst.
An optical semiconductor used for the photocatalyst contains one or more elements selected from the group consisting of Ti, V, Nb, and Ta, and oxides, oxynitrides, nitrides, (oxygens) containing any of these elements. ) Chalcogenide and the like.
In particular,
_{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; and titanium-containing (oxy) chalcogenides such as La ₅ Ti ₂ CuS ₅ O ₇ , La ₅ Ti ₂ AgS ₅ O ₇ , Sm ₂ Ti ₂ O ₅ S ₂ ; Containing compounds:
Vanadium-containing oxides such as BiVO ₄ and Ag ₃ VO ₄ ; vanadium-containing compounds such as:
_{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 _1
0 (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 oxides such as PbBi ₂ Nb ₂ O ₉ ; and niobium-containing oxynitrides such as CaNbO ₂ N, BaNbO ₂ N, SrNbO ₂ N, 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 T
a 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 (Chem. Mate
r. 2004 16, 4304-4310), LaTaO ₄ , La ₃ TaO _{7 and} other tantalum-containing oxides;
Tantalum-containing nitrides such as Ta ₃ N ₅ ; and tantalum-containing oxynitrides such as CaTaO ₂ N, SrTaO ₂ N, BaTaO ₂ N, LaTaO ₂ N, Y ₂ Ta ₂ O ₅ N ₂ , and TaON; Compound: etc. are 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 optical semiconductor is not particularly limited as long as it is a form that supports the complex described above as a cocatalyst and can function as a photocatalyst, according to the installation form of the photocatalyst, A particle shape, 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 specification, 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, or SEM method. .

The photocatalyst carries the above-described complex as a promoter on the surface of the optical semiconductor. In addition to the composite, another promoter may be co-supported. 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 the composite 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 a composite having a particle diameter of 1.0 nm to 25 nm is supported on the surface of an optical semiconductor particle having a particle diameter of 50 nm to 500 μm, in addition to the composite, other promoters (the above-mentioned When it is desired to co-support a hydrogen generating cocatalyst, etc., it is preferable to support 0.005 parts by mass or more and 1.0 part by mass or less of the composite with respect to 100 parts by mass of the optical semiconductor (photo semiconductor particles). 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 composite according to the present embodiment, and other promoters can be supported on the surface of the optical semiconductor not covered with the composite. 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.

Or you may carry | support only the composite_body | complex which concerns on this embodiment on the surface of an optical semiconductor as a promoter. For example, when only the composite having a particle diameter of 1.0 nm or more and 25 nm or less is supported on the surface of an optical semiconductor particle having a particle diameter of 50 nm or more and 500 μm or less, It is preferable that the body is supported by 0.008 parts by mass or more and 20.0 parts by mass or less. 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 water electrolysis.

  In the case of co-supporting, if the amount of the entire cocatalyst supported is too small, there is no effect, and if it is too large, the cocatalyst itself absorbs and scatters light, thereby preventing the photocatalyst from absorbing light or recombination centers. Otherwise, the catalytic activity is reduced. From such a viewpoint, the supported amount of the entire cocatalyst in the photocatalyst (the total of the composite according to the present embodiment and the other cocatalyst) is preferably 0.008 parts by mass or more with respect to 100 parts by mass of the optical semiconductor. 5.0 parts by mass or less, more preferably 0.009 parts by mass or more and 3.0 parts by mass or less, and particularly preferably 0.010 parts by mass or more and 2.0 parts by mass or less.

  The method of supporting the composite on the surface of the optical semiconductor is not particularly limited, but is appropriately baked after impregnating the optical semiconductor in the dispersion containing the composite and adsorbing the composite onto the surface of the optical semiconductor. It is preferable that the composite is supported on the surface of the optical semiconductor. This method is suitable when it is desired to uniformly support nano-sized composite particles on the entire surface of the optical semiconductor. For example, the composite and the optical semiconductor particles are mixed in an organic solvent (tetrahydrofuran or the like), optionally subjected to ultrasonic treatment, and then a suitable binder (16 for adsorbing the composite on the surface of the optical semiconductor particles). -Hydroxyhexadecanoic acid and the like). Thereafter, the photocatalyst precursor in which the complex is adsorbed on the surface of the photo-semiconductor particles is obtained by appropriately stirring and then subjecting to washing treatment. By arbitrarily firing the precursor, a photocatalyst in which the composite is uniformly supported on the surface of the optical semiconductor can be obtained.

  Alternatively, the composite is supported on the surface of the optical semiconductor by applying an ink in which the composite is dispersed in a solvent by a method such as dip coating, drop casting, spray coating, electrostatic coating, or spin coating on the optical semiconductor film. It can also be made. The composite according to this embodiment has good dispersibility in a solvent, and the ink containing the composite according to this embodiment is also a preferred form.

  As described above, the photocatalytic activity according to the present embodiment is greatly improved by supporting the composite according to the present embodiment as a cocatalyst on the surface of a specific optical semiconductor. That is, the composite according to the present embodiment is useful as an oxygen generation promoter.

  The form of the photocatalyst when the photocatalyst is actually used for water decomposition is not particularly limited. For example, a form in which photocatalyst particles are dispersed in water, a form in which the photocatalyst particles are solidified and a molded body is placed in water, a form in which a photocatalyst layer is provided on a base material to form a laminate, and the laminate is placed in water Examples include a mode in which a photocatalyst is immobilized on a current collector to form an electrode for water electrolysis (photocatalyst electrode) and installed in water together with a counter electrode. In particular, in the case where the photowater decomposition reaction is performed on a large scale, it is preferable to use the electrode for water electrolysis from the viewpoint of imparting a bias to promote the water decomposition reaction. In the form of the molded body and the form of the laminated body, the molded body or the laminated body may be in the form of a sheet (photocatalytic sheet).

The electrode for water electrolysis 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, an electrode for water electrolysis having a photocatalyst layer, a conductive layer, and a second substrate layer can be obtained. it can.
Alternatively, a slurry in which photocatalyst particles are dispersed may be applied to the surface of the current collector and dried to obtain an electrode for water electrolysis, or the photocatalyst particles and the current collector may be integrally formed by pressure molding or the like. You may obtain the electrode for water electrolysis by making it. 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 water electrolysis may be obtained by supporting a composite as a promoter on the surface of the layer.

  As described above, when applying a photocatalyst to an electrode for water electrolysis, from the viewpoint of improving electrode performance, in the photocatalyst, the composite is 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. It is preferable. Alternatively, from the same viewpoint, it is preferable that 20% or more of the surface of the optical semiconductor is covered with the composite. The coverage of the composite on the surface of the optical semiconductor can be calculated by specifying a portion occupied by the optical semiconductor and a portion occupied by the composite when the photocatalyst particles are viewed from one direction by SEM-EDS or the like. For example, the area of the optical semiconductor portion and the area of the composite portion in the SEM photograph are specified, and the coverage is given by (area of the composite portion) / {(area of the optical semiconductor portion) + (area of the composite portion)}. Can be calculated.

By using the photocatalyst according to the present embodiment, the performance of the water electrolysis 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.
In this embodiment, the above-described photocatalyst or the above-described electrode for water electrolysis is immersed in water or an aqueous electrolyte solution, and the photocatalyst or the electrode for water electrolysis is irradiated with light to perform photo-water decomposition, thereby producing hydrogen. And / or oxygen can be produced.

  For example, as described above, a photocatalyst is immobilized on a current collector made of a conductor to obtain an electrode for water electrolysis, while a conductor carrying a hydrogen generation catalyst is used as a counter electrode, and the liquid or gaseous state is used. Irradiate light while supplying water to promote water splitting reaction. 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.

There are no particular limitations on the reaction conditions during the production of hydrogen and / or oxygen. For example, the reaction temperature may be 0 ° C. or higher and 200 ° C. or lower, and the reaction pressure may be 2 MPa (G) or lower.
The irradiation light may be visible light having a wavelength of 650 nm or less, or ultraviolet light. 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, a photocatalyst having sufficient catalytic activity for the photo-water splitting reaction can be obtained by supporting a composite containing a specific metal phosphide and a metal oxide on a specific photo semiconductor. Hydrogen and / or oxygen can be produced on a large scale as an electrode for water electrolysis.

Hereinafter, the present invention will be described in more detail with reference to examples, but it goes without saying that the scope of the present invention is not limited to only examples.
(Measuring method)
The average particle size of the composite was measured with a transmission electron microscope (TEM).
Measuring device: JEM-1011 manufactured by JEOL
Acceleration voltage: 100 kV
Measuring method: The particle diameter of 200 particles observed by TEM was measured and averaged to obtain an average particle diameter.

Example 1
<Preparation of NiP _x / FeO _y composite particles>
Ni acetylacetonate (1 mmol), 1-octadecene (4.
5 mL), oleylamine (6.4 mL), tri-n-octylphosphine (2 mL)
) Was dissolved and heated at 230 ° C. for 30 minutes. After cooling to room temperature, ethanol (90 mL) was added and centrifuged (8000 rpm, 5 minutes), and then the supernatant solution was removed to obtain amorphous NiP _x nanoparticles. As a result of observation by TEM, the average particle diameter of the amorphous NiP _x nanoparticles was 11.5 ± 0.8 nm.
Amorphous NiP _x nanoparticles (34 mg), 1-octadecene (9 mL), oleylamine (1.9 mL), trioctylphosphine (2 mL), and pentacarbonyl iron (0.4 mmol) were mixed at 270 ° C. Heated for 1 hour. After adding ethanol (90 mL) and performing centrifugation (8000 rpm, 5 minutes), the supernatant solution was removed to remove NiP _x
/ FeO _y composite was obtained. As a result of observation by TEM, the average particle diameter of the NiP _x / FeO _y composite is 12.5 ± 0.6 nm, and the core-shell type composite particle having a core made of NiP _x and a shell made of FeO _y is obtained. there were. When the composition of the NiP _x / FeO _y composite particles was measured by X-ray fluorescence spectroscopy (XRF), it was Ni: Fe = 78: 22. Note that when elemental analysis (XRF) was performed by etching only the shell with acid, the main component of the shell was considered to be FeO because there was a tendency for only Fe to decrease.
Moreover, from the measurement result by X-ray photoelectron spectroscopy (XPS), since a peak derived from PO ₄ ³⁻ was slightly observed, it was suggested that FeO _y may contain iron phosphate. However, the main component was FeO _y .

(Comparative Example 1)
<Preparation of Ni ₂ P nanoparticles>
Ni acetylacetonate (1 mmol), 1-octadecene (4.
5 mL), oleylamine (6.4 mL), tri-n-octylphosphine (2 mL)
) Was dissolved and heated at 230 ° C. for 30 minutes. After cooling to room temperature, ethanol (90 mL) was added and centrifuged (8000 rpm, 5 minutes), and then the supernatant solution was removed to obtain amorphous NiP _x nanoparticles.
Amorphous NiP _x nanoparticles (85 mg), di-n-octyl ether (9 mL), oleylamine (1.9 mL), trioctylphosphine (2 mL) were mixed and heated at 270 ° C. for 1 hour. Ethanol (90 mL) was added and centrifuged (8000 rpm, 5 minutes), and then the supernatant solution was removed to obtain Ni ₂ P nanoparticles. As a result of observation by TEM, the average diameter of the Ni ₂ P nanoparticles was 13.0 ± 0.6 nm.

(Comparative Example 2)
<Preparation of FeO _x nanoparticles>
A mixture of pentacarbonyl iron (2 mmol) and oleylamine (2 mmol) was quickly poured into 1-octadecene (30 mL) heated to 180 ° C. in a nitrogen atmosphere, and heated at 180 ° C. for 30 minutes. After cooling to room temperature, add ethanol (70 mL) and centrifuge (8
000 rpm, 5 minutes), and then the supernatant solution was removed to obtain FeO _x nanoparticles. As a result of observation by TEM, the average particle diameter of the FeO _x nanoparticles was 6.6 ± 0.5 nm.

(Comparative Example 3)
<Preparation of Ni ₂ P + FeO _x mixed nanoparticles>
The hexane solution of Ni ₂ P nanoparticles prepared by the above technique and the hexane solution of FeO _x nanoparticles were mixed. It was prepared so that Ni: Fe = 78: 22 by XRF measurement.

<Oxygen generation catalytic activity evaluation>
The hexane solution of nanoparticles according to Example 1 and Comparative Examples 1 to 3 prepared above was mixed with a hexane dispersion of conductive carbon black XC-72 (manufactured by Cabot Corporation, hereinafter referred to as XC-72) to obtain nano particles. The particles were adsorbed on XC-72. The weight ratio of nanoparticles to XC-72 was 20:80. After centrifugation (8000 rpm, 5 minutes), the supernatant was removed, the precipitated powder was washed with acetone, and dried under reduced pressure to obtain nanoparticles / XC-72 powder. Nanoparticles / XC-72 powder (1 mg), water (396 μL), 2-propanol (94 μ
L) and a mixture of Nafion solution (10 μL) were subjected to ultrasonic irradiation for 30 minutes to obtain a catalyst slurry. A catalyst slurry (10 μL) was applied on a carbon electrode on glass having a diameter of 5 mm and dried to obtain a working electrode. For the evaluation of the oxygen-generating catalyst activity, an electrochemical analyzer (manufactured by CH Instrument, model 620C) and a triode cell were used. A 0.1 M KOH aqueous solution was used as the electrolytic solution, and the working electrode, the reference electrode (Ag / AgCl), and the counter electrode (Pt coil) were immersed, and dissolved air was removed by bubbling with Ar gas for 20 minutes. Then, cyclic voltammetry measurement was performed while rotating the working electrode at 1600 rpm, and the current value was measured.

“NiP _x / FeO _y composite particles” (Example 1), “Ni ₂ P nanoparticles” (Comparative Example 1), “FeO _x nanoparticles” (Comparative Example 2), and “Ni the _{2 P} + FeO _x mixed nanoparticle "result of comparison oxygen generating catalyst activity (Comparative example 3) shown in FIG.
As shown in FIG. 5, “NiP _x / FeO _y composite particles” (Example 1) are “Ni ₂ P nanoparticles” (Comparative Example 1), “FeO _x nanoparticles” (Comparative Example 2), “ Compared with “Ni ₂ P + FeO _x mixed nanoparticles” (Comparative Example 3), the oxygen generation overvoltage necessary to reach a current value of 10 mA / cm ² was small. From this, the effectiveness of the composite of metal phosphide and metal oxide was shown.

(Comparative Example 4)
<Preparation of BiVO ₄ electrode>
BiVO ₄ electrodes were prepared according to known literature (Science, 2014, 343, 990). In a mixed solution of bismuth nitrate, potassium iodide, parabenzoquinone, water, and ethanol, a fluorine-doped tin oxide-coated glass (hereinafter referred to as FTO), an Ag / AgCl reference electrode as a working electrode, and a Pt coil as a counter electrode were immersed. Using an electrochemical analyzer (model 620C, manufactured by CH Instrument), a voltage of −0.1 V was applied to the FTO electrode with respect to the Ag / AgCl electrode, and electrodeposition was performed for 300 seconds. A dimethyl sulfoxide solution of vanadate acetylacetonate was placed on BiOI deposited on FTO, and baked at 450 ° C. for 2 hours in the air. The produced BiVO ₄ film was immersed in sodium hydroxide (1 mol / L) for 1 hour to remove by-product divanadium pentoxide, and finally washed with water. The area of BiVO ₄ on FTO was 1.5 cm ² .

(Example 2)
<Preparation of _NiP x / FeO _y composite particles -BiVO ₄ electrode>
Hexane solution (0.25 m) of “NiP _x / FeO _y composite particles” prepared as described above.
g / mL, 50 μL) was placed on the “BiVO ₄ electrode” prepared as described above, and dried while rotating at 1000 rpm for 10 seconds with a spin coater (manufactured by Mikasa, 1H-DX2). Finally, it was washed with water.

(Comparative Example 5)
<Preparation of Ni ₂ P nanoparticles -BiVO ₄ electrode>
A hexane solution of “Ni ₂ P nanoparticles” prepared as described above (0.25 mg / mL, 5
0 μL) was placed on the “BiVO ₄ electrode” prepared as described above, and dried while rotating at 1000 rpm for 10 seconds on a spin coater (manufactured by Mikasa, 1H-DX2). Finally, it was washed with water.

(Comparative Example 6)
<Preparation of FeO _x nanoparticle-BiVO ₄ electrode>
A hexane solution of “FeO _x nanoparticles” prepared as described above (0.25 mg / mL, 5
0 μL) was placed on the “BiVO ₄ electrode” prepared as described above, and dried while rotating at 1000 rpm for 10 seconds on a spin coater (manufactured by Mikasa, 1H-DX2). Finally, it was washed with water.

(Comparative Example 7)
<Preparation of _Ni 2 P + FeO _x mixed nanoparticles -BiVO _4>
A hexane solution of “FeO _x nanoparticles” prepared as described above (0.25 mg / mL, 5
0 μL) was placed on the “BiVO ₄ electrode” prepared as described above, and dried while rotating at 1000 rpm for 10 seconds on a spin coater (manufactured by Mikasa, 1H-DX2). Finally, it was washed with water.

<Photocurrent measurement>
An electrochemical analyzer (manufactured by CH Instrument, model 620C), triode cell, 100 W xenon lamp,> 385 nm cut-off filter was used. The electrolyte used was a 0.125M potassium borate aqueous solution and the working electrode (BiVO prepared above).
₄ electrodes), a reference electrode (Ag / AgCl), and a counter electrode (Pt coil) were immersed, and dissolved air was removed by bubbling with Ar gas for 20 minutes. Thereafter, linear sweep voltammetry measurement was performed while irradiating with light, and the photocurrent value was measured.

“BiVO ₄ electrode” (Comparative Example 4), “NiP _x / FeO _y composite particle—BiVO ₄ electrode” (Example 2), “Ni ₂ P nanoparticle—BiVO ₄ electrode” (Comparative Example) prepared above. 5) and “FeO _x nanoparticle-BiVO ₄ electrode” (Comparative Example 6) and “Ni ₂ P + FeO _x mixed nanoparticle—BiVO ₄ electrode” (Comparative Example 7) are compared in terms of photocurrent-voltage curves. This is shown in FIG.
As shown in FIG. 6, “NiP _x / FeO _y composite particle—BiVO ₄ electrode” (Example 2) is “BiVO ₄ electrode” (Comparative Example 4), “Ni ₂ P nanoparticle—BiVO ₄ electrode”. Compared with (Comparative Example 5), and “FeO _x nanoparticle-BiVO ₄ electrode” (Comparative Example 6) and “Ni ₂ P + FeO _x mixed nanoparticle—BiVO ₄ electrode” (Comparative Example 7), the photocurrent value was larger. It was. From this, the effectiveness of the composite of metal phosphide and metal oxide was shown.

Prepared above, _"NiP x / FeO _y composite particles -BiVO ₄ electrode" (Example 2), "Ni ₂ P nanoparticles -BiVO ₄ electrode" (Comparative Example 5), and "FeO _x nanoparticles -Bi
FIG. 7 shows a result of comparison of photocurrent-time curves at 1.23 V vs. RHE of “VO ₄ electrode” (Comparative Example 6) and “Ni ₂ P + FeO _x mixed nanoparticles—BiVO ₄ electrode” (Comparative Example 7).
It was shown to.
As shown in FIG. 7, “NiP _x / FeO _y composite particle—BiVO ₄ electrode” (Example 2) is “Ni ₂ P nanoparticle—BiVO ₄ electrode” (Comparative Example 5), and “FeO _x Nano”. Compared to “Particle—BiVO ₄ electrode” (Comparative Example 6) and “Ni ₂ P + FeO _x mixed nanoparticle—BiVO ₄ electrode” (Comparative Example 7), the photocurrent value is large, and the photocurrent value retention rate after 10 minutes is it was high. From this, the effectiveness of the composite of metal phosphide and metal oxide was shown.

(Comparative Example 8)
<Preparation of Ni _x Mn _y P nanoparticles>
In a nitrogen atmosphere, Ni acetylacetonate (0.75 mmol), Mn acetylacetonate (0.25 mmol), n-octyl ether (5 mL), oleylamine (5 mL), tri-n-octylphosphine (2 mL) were dissolved. Heated at 270 ° C. for 30 minutes. After cooling to room temperature, ethanol (90 mL) was added and centrifuged (8000 rpm, 5 minutes), and then the supernatant solution was removed to obtain Ni _x Mn _y P nanoparticles. As a result of observation by TEM, the average diameter of the Ni _x Mn _y P nanoparticles was 16.7 ± 1.6 nm.

(Comparative Example 9)
<Preparation of Ni _x Zn _y P nanoparticles>
In a nitrogen atmosphere, Ni acetylacetonate (0.75 mmol), Zn acetylacetonate (0.25 mmol), n-octyl ether (5 mL), oleylamine (5 mL), tri-n-octylphosphine (2 mL) were dissolved, Heated at 270 ° C. for 30 minutes. After cooling to room temperature, ethanol (90 mL) was added and centrifuged (8000 rpm, 5 minutes), and then the supernatant solution was removed to obtain Ni _x Zn _y P nanoparticles. As a result of observation by TEM, the average diameter of the Ni _x Zn _y P nanoparticles was 19.7 ± 1.4 nm.

For the Ni _x Mn _y P nanoparticles and Ni _x Zn _y P nanoparticles obtained in Comparative Examples 8 and 9, the oxygen generation catalytic activity was measured in the same manner as the nanoparticles according to Example 1 and Comparative Examples 1 to 3. . The results are shown in FIG.

<Comparative Example 10>
<Preparation of Ni _x Mn _y P particle-BiVO ₄ electrode>
A hexane solution (0.25 mg / mL, 50 μL) of “Ni _x Mn _y P nanoparticles” prepared as described above is placed on the “BiVO ₄ electrode” prepared as described above, and a spin coater (Mikasa, 1H-DX2). And dried at 1000 rpm for 10 seconds. Finally, it was washed with water.

(Comparative Example 11)
<Preparation of Ni _x Zn _y P particle-BiVO ₄ electrode>
A hexane solution (0.25 mg / mL, 50 μL) of “Ni _x Zn _y P nanoparticles” prepared as described above is placed on the “BiVO ₄ electrode” prepared as described above, and a spin coater (manufactured by Mikasa, 1H-DX2 And dried at 1000 rpm for 10 seconds. Finally, it was washed with water.

  Similar to the electrodes prepared in Example 2 and Comparative Examples 4 to 7, photocurrent measurement was performed on the electrodes prepared in Comparative Examples 10 and 11. The results are shown in FIG. 11 (photocurrent-voltage curve) and FIG. 12 (photocurrent-time curve) together with the results of Comparative Example 4.

The Ni _x Mn _y P nanoparticles obtained in Comparative Example 8 are considered to have fewer reaction active points because the particle size is larger than that of Fe-based particles, and have the potential to be effective especially when supported on a photocatalyst. . Further, in cyclic voltammetry (CV), the overvoltage was about 0.07 V larger than that of Fe-based particles. This is presumably because the adsorption energy of O atoms and Mn ions is different from that of Fe. Regarding the photocurrent, the difference in CV appeared as the difference in photocurrent as it was. This is thought to be due to the difference in the pn characteristics of the promoter. In terms of durability, the activity was not as good as that of Fe-based particles, so the photocatalyst was self-corroded by the accumulation of holes.

The Ni _x Zn _y P nanoparticles obtained in Comparative Example 9 are considered to have fewer reaction active points because the particle size is larger than that of Fe-based particles, and have the potential to be effective especially when supported on a photocatalyst. . Further, in cyclic voltammetry (CV), the overvoltage was about 0.06 V larger than that of Fe-based particles. This is presumably because the adsorption energy of O atoms and Zn ions is different from that of Fe. Regarding the photocurrent, the difference in CV appeared as the difference in photocurrent as it was. This is thought to be due to the difference in the pn characteristics of the promoter. In terms of durability, the activity was not as good as that of Fe-based particles, so the photocatalyst was self-corroded by the accumulation of holes.

Claims (10)

  Metal phosphide selected from Ni, Fe, Co, Mn, Mo and W, and selected from Ni, Fe, Co, Mn, Mo, W, Ti, Cr, Cu, Zn, In, Ir and Ru A cocatalyst for photocatalyst for oxygen generation, comprising a composite containing a metal oxide.   The promoter according to claim 1, having a core-shell structure in which the metal phosphide is a core and the metal oxide is a shell.   A photocatalyst for oxygen generation carrying the promoter according to claim 1 or 2.   A photocatalyst sheet comprising the photocatalyst according to claim 3.   A photocatalytic electrode comprising the photocatalyst according to claim 3.   A hydrogen and / or oxygen generator by water splitting, comprising the photocatalyst sheet according to claim 4 or the photocatalyst electrode according to claim 5.   Metal phosphide selected from Ni, Fe, Co, Mn, Mo and W, and selected from Ni, Fe, Co, Mn, Mo, W, Ti, Cr, Cu, Zn, In, Ir and Ru A composite comprising a metal oxide.   The composite according to claim 7, having a core-shell structure in which the metal phosphide is a core and the metal oxide is a shell. Preparing a phosphide of a metal selected from Ni, Fe, Co, Mn, Mo and W, and the prepared phosphide and Ni, Fe, Co, Mn, Mo, W, Ti, Cr, Cu, Zn And a metal complex selected from In, Ir, and Ru, and firing the mixture. A method for producing a composite of a metal phosphide and a metal oxide.   The method for producing a composite according to claim 9, wherein in the step of firing the mixture, a firing temperature is 340 ° C or lower.

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