JP6049281B2 - Highly conductive titanium oxide structure - Google Patents

Description

  The present invention relates to a titanium oxide structure used for a dye-sensitized solar cell, a photocatalyst, a sensor, a resin reinforcing material, a metal ion carrier, and the like, and a method for producing the same.

  Titanium oxide is used for dye-sensitized solar cells, photocatalysts, and the like. In particular, a dye-sensitized solar cell using, for example, titanium oxide modified with a dye as an active electrode has attracted attention as a solar cell that can be easily manufactured at low cost. Among them, when used in a dye-sensitized solar cell, it has been attempted to increase the specific surface area in order to increase the active surface area, but when the specific surface area is increased by reducing the average particle diameter of titanium oxide, Interfacial resistance increases. Therefore, it is desired that the negative electrode contains a highly conductive substance.

  The same is true when using titanium oxide nanoparticles as a photocatalyst, and cracks are likely to occur when the particle size is reduced and the specific surface area is increased. Since an activity corresponding to the surface area may not be obtained, a large particle size (for example, 200 nm) having a small specific surface area may be used.

  As described above, there is a problem in using finely divided titanium oxide in any application. On the other hand, hollow titanium oxide nanotubes having a large aspect ratio are also known (Patent Documents 2 and 3).

Japanese Patent Publication No. 8-15097 Japanese Patent No. 3983533 Japanese Patent No. 3513738

  Conventional titanium oxide nanotubes tend to aggregate because of their small diameter and length, and it has been difficult to isolate them one by one. That is, the conductivity was lowered. In addition, since conventional titanium oxide nanotubes have poor dispersibility, it is difficult not only to prepare solutions and pastes for use in coating, printing, etc., but also because of poor heat resistance, the tube shape cannot be maintained by heat treatment. There were disadvantages such as.

  Accordingly, the present invention provides a titanium oxide structure having a large aspect ratio, good dispersibility in a solution, high heat resistance and high conductivity, and which can improve conversion efficiency when used in a dye-sensitized solar cell and its It aims at providing a simple manufacturing method.

As a result of intensive investigations in view of the above object, a titanium oxide structure that solves the above problems can be obtained by adding a titanium compound and a second component (metal or boron) and heating to 180 to 370 ° C. Heading and then further research to complete the present invention. That is, the present invention includes the following configurations.
Item 1. Including at least one selected from the group consisting of V, Nb, Ta and B, an average aspect ratio of 10 or more, and a powder resistance under 10 MPa of 1 × 10 ⁵ Ω · m or less, Rod-shaped titanium oxide structure.
Item 2. Item 2. The titanium oxide structure according to Item 1, which contains 0.1 to 10 mol% of at least one selected from the group consisting of V, Nb, Ta and B with respect to Ti.
Item 3. Item 3. The titanium oxide structure according to Item 1 or 2, wherein the specific surface area is 10 m ² / g or more.
Item 4. Item 4. The titanium oxide structure according to any one of Items 1 to 3, wherein the average width is 20 nm or more.
Item 5. Item 5. The titanium oxide structure according to any one of Items 1 to 4, wherein an average length in a longitudinal direction is 1 μm or more.
Item 6. Item 6. The titanium oxide structure according to any one of Items 1 to 5, wherein the alkali metal content is 2000 ppm or less.
Item 7. A method for producing a plate-like or rod-like titanium oxide structure having an average aspect ratio of 10 or more and a powder resistance under 10 MPa of 1 × 10 ⁵ Ω · m,
(1) From 160 ° C., an alkaline aqueous solution of 3 to 20 mol / L, a substance (A) containing Ti, and a substance (B) containing at least one selected from the group consisting of V, Nb, Ta and B A manufacturing method comprising a step of contacting at a high temperature, and (3) a step of heat-treating at 300 ° C. or higher.
Item 8. In the step (1), at least one content selected from the group consisting of V, Nb, Ta and B in the substance (B) is 0.1 to 10 mol% with respect to Ti in the substance (A). Item 8. The method according to Item 7, wherein
Item 9. Item 9. The method according to Item 7 or 8, wherein the substance (A) is titanium oxide and / or a precursor thereof.
Item 10. Item 10. The production method according to any one of Items 7 to 9, wherein the substance (B) is at least one selected from the group consisting of oxides, hydroxides, alkoxides and chlorides of V, Nb, Ta and B. .
Item 11. Item 11. The production method according to any one of Items 7 to 10, wherein the alkali contains at least 50% by weight of sodium hydroxide.
Item 12. The step (3)
(3-1) The manufacturing method in any one of claim | item 7 -11 which is a process heat-processed at 300 degreeC or more under the reduced pressure of 10 kPa or less.
Item 13. The step (3)
(3-2) The manufacturing method according to any one of Items 7 to 11, which is a step of heat-treating at 300 ° C. or higher in a reducing atmosphere.
Item 14. During the steps (1) and (3),
(2) The item according to any one of Items 7 to 13, comprising a step of bringing the titanium oxide-based structure obtained in the step (1) into contact with at least one selected from the group consisting of water, an acid, and an ion exchange resin. Production method.
Item 15. Item 15. The method according to Item 14, wherein the acid is at least one selected from the group consisting of hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, hydrofluoric acid, acetic acid, citric acid, formic acid, and oxalic acid.
Item 16. (1) From 160 ° C., an alkaline aqueous solution of 3 to 20 mol / L, a substance (A) containing Ti, and a substance (B) containing at least one selected from the group consisting of V, Nb, Ta and B The average aspect ratio is 10 or more, and the powder resistance under 10 MPa is 1 × 10 ⁵ Ω · m, which is produced by a method comprising a step of contacting at a high temperature and (3) a step of heat treatment at 300 ° C. or higher. The following plate-shaped or rod-shaped titanium oxide structures.
Item 17. (1) From 160 ° C., an alkaline aqueous solution of 3 to 20 mol / L, a substance (A) containing Ti, and a substance (B) containing at least one selected from the group consisting of V, Nb, Ta and B The method to suppress the shape change before and behind heat processing of a plate-shaped or rod-shaped titanium oxide structure provided with the process made to contact at high temperature.
Item 18. After the step (1),
(2) The method according to item 17, comprising a step of bringing the titanium oxide-based structure obtained in the step (1) into contact with at least one selected from the group consisting of water, an acid, and an ion exchange resin.
Item 19. Item 16. A porous titanium oxide film comprising the titanium oxide structure according to any one of Items 1 to 6 and 16, or the titanium oxide structure obtained by the production method according to any one of Items 7 to 15.
Item 20. Item 20. The porous titanium oxide film according to Item 19, further comprising titanium oxide fine particles having an average particle diameter of 1 to 500 nm.
Item 21. Item 21. An electrode in which the porous titanium oxide film according to Item 19 or 20 on which a dye is supported is formed on a conductive substrate.
Item 22. Item 22. A photoelectric conversion element comprising the electrode according to item 21.
Item 23. Item 16. A photocatalyst using the titanium oxide structure according to any one of Items 1 to 6 and 16, or the titanium oxide structure obtained by the production method according to any one of Items 7 to 15.

  According to the present invention, a titanium oxide structure having a large aspect ratio, good dispersibility in a solution, high heat resistance and high conductivity, and improved conversion efficiency when used in a dye-sensitized solar cell, and its A simple manufacturing method can be provided.

In Example 1, it is an electron microscope (TEM) photograph which shows the surface shape of the titanium oxide structure before baking (before performing a process (3)). 4 is an electron microscope (TEM) photograph showing the surface shape of the titanium oxide structure of Example 2. FIG. In the comparative example 3, it is an electron microscope (TEM) photograph which shows the surface shape of the titanium oxide structure before baking. In the comparative example 3, it is an electron microscope (SEM) photograph which shows the surface shape of the titanium oxide structure before baking.

1. Titanium oxide structure The titanium oxide structure of the present invention contains at least one selected from the group consisting of V, Nb, Ta and B, has an average aspect ratio of 10 or more, and a powder resistance of 1 × 10 ⁵ Ω. -It is a plate-shaped or rod-shaped titanium oxide structure which is m or less.

In the present invention, “titanium oxide” does not refer only to titanium dioxide (TiO ₂ ), but is composed of dititanium trioxide (Ti ₂ O ₃ ); titanium monoxide (TiO); Ti ₄ O ₇ , Ti ₅ O. _It includes those having a composition deficient in oxygen from titanium dioxide represented by ₉ etc. Further, as represented by the terminal OH group, a group other than Ti—O—Ti resulting from the synthesis of titanium oxide may be included.

  In the present invention, the “plate-like” is a structure having a length (long side) larger than a width (short side), and most of the surface is a plane. However, the surface does not necessarily have to be a complete plane, and a part of the curved surface may be included. In the present invention, the “rod shape” is a structure having a length (long side) larger than a width (short side), and most of the surface is a curved surface. However, the surface does not necessarily have to be a complete curved surface, and a part of the surface may be included. These “plate-like” and “rod-like” are not necessarily clearly distinguished, but when “plate-like” and “rod-like” are combined, the length (long side) with respect to the width (short side) It is a solid structure with a large side. The solid structure means that a hollow structure such as a nanotube is excluded. Furthermore, the surface of the titanium oxide structure of the present invention may have some unevenness.

<Shape>
The average aspect ratio (ratio of length to width, length / width) of the titanium oxide structure of the present invention is 10 or more, preferably 20 or more. When the aspect ratio is less than 10, physical properties resulting from the high aspect ratio such as high conductivity and high strength cannot be obtained. Further, in order to improve the film property when applied, the average aspect ratio of the titanium oxide structure of the present invention is preferably about 10,000 or less, more preferably about 5000 or less.

  The average width of the titanium oxide structure of the present invention is preferably 20 nm or more, and more preferably 40 nm or more from the viewpoint of excellent dispersibility because the titanium oxide structures do not entangle with each other. On the other hand, since it is preferable to increase the specific surface area, it is preferable to use the photocatalyst or the like for the purpose of carrying out the reaction on the surface, the case where the dye-sensitized solar cell has the purpose of supporting the dye on the surface, etc. The average width of the titanium oxide structure is preferably about 500 nm or less, and more preferably about 200 nm or less.

  The average length in the longitudinal direction of the titanium oxide structure is preferably 1 μm or more, and more preferably 2 μm or more from the viewpoint of excellent conductivity and improved strength when a coating film is formed or mixed with a resin. Further, in order to improve the film property when applied, the average length in the longitudinal direction of the titanium oxide structure of the present invention is preferably about 100 μm or less, and more preferably about 20 μm or less.

  The shape (average width, average aspect ratio, average length in the longitudinal direction, etc.) of the titanium oxide structure can be measured, for example, by observation with an electron microscope (SEM or TEM).

<Composition>
The titanium oxide structure of the present invention contains titanium (Ti) and oxygen (O) as main components, and further contains at least one selected from the group consisting of V, Nb, Ta and B as the third component. contains. The content of the third component is preferably 0.1 to 10 mol%, more preferably 0.3 to 8 mol%, and more preferably 0.5 to 7 mol% with respect to titanium (Ti) from the viewpoint of conductivity and photoelectric conversion efficiency. Is more preferable.

  By including these third components, a high aspect ratio can be maintained even when heat treatment (firing) is performed, and a highly conductive titanium oxide structure can be easily produced. Moreover, it can suppress that the titanium oxide structure of this invention colors more than necessary (it can be made light color). For this reason, when adding to the negative electrode of a dye-sensitized solar cell, for example, since there is no excessive light absorption, there exists an advantage that a photoelectric conversion efficiency is not reduced. That is, the photoelectric conversion efficiency can be improved according to the degree of improvement in conductivity. The effect of suppressing excessive light absorption is the same when used for a photocatalyst. On the other hand, when other components coexist, the shape of high aspect ratio cannot be maintained by heat treatment (firing), or the photoelectric conversion efficiency is lowered as a result of coloring the titanium oxide structure.

<Others>
In the titanium oxide structure of the present invention, the powder resistance under 10 MPa is 1 × 10 ⁵ Ω · m or less, preferably 5 × 10 ⁴ Ω · m or less from the viewpoint that a larger current can be obtained. When the powder resistance exceeds 1 × 10 ⁵ Ω · m, the photoelectric conversion efficiency decreases. The powder resistance is preferably as small as possible, and the lower limit is not particularly limited, but is about 0.01 Ω · m. The method for measuring the powder resistance of the titanium oxide structure is not particularly limited. For example, the current value is processed by applying a voltage of 1 V between the pellets after processing into a plate having a thickness of 0.3 mm at a pressure of 10 MPa. It can be measured by measuring.

The titanium oxide structure of the present invention supports a large amount of dye when used in a dye-sensitized solar cell, can efficiently absorb incident light, and can obtain sufficient photocatalytic ability when used in a photocatalyst. In this respect, the specific surface area is preferably 10 m ² / g or more, and more preferably 20 m ² / g or more. The larger specific surface area is preferred, and the upper limit is not particularly limited, but is about 1000 m ² / g. The specific surface area can be measured by the BET method or the like.

  When used in a dye-sensitized solar cell, the content of alkali metal (especially sodium) in the titanium oxide structure of the present invention is preferably 2000 ppm or less, more preferably 500 ppm or less, from the viewpoint of ensuring activity. In addition, in order to improve heat resistance, since it may be preferable that there is much Na, alkali metal content can be suitably set according to the objective etc. The alkali metal content can be measured by ion chromatography, ICP emission spectroscopic analysis, or the like.

  Conventional titanium oxide nanotubes (those with a low contact temperature between an aqueous alkali solution and titanium oxide) have poor heat resistance, and, for example, the shape collapses due to heat treatment (firing) at 300 ° C. or higher and becomes particulate and aggregates. Therefore, the conductivity and the aspect ratio cannot be maintained, but the titanium oxide structure of the present invention can be maintained in the conductivity and the aspect ratio because the shape does not collapse and does not aggregate even when heat treatment (baking) at 300 ° C. or higher. That is, the titanium oxide structure of the present invention can maintain conductivity, dispersibility in a solution, and high strength even at high temperatures.

2. Method for manufacturing titanium oxide structure and method for suppressing shape change before and after heat treatment The method for manufacturing a titanium oxide structure of the present invention includes:
(1) From 160 ° C., an alkaline aqueous solution of 3 to 20 mol / L, a substance (A) containing Ti, and a substance (B) containing at least one selected from the group consisting of V, Nb, Ta and B A step of contacting at a high temperature, and (3) a step of heat treatment at 300 ° C. or higher.

Moreover, the manufacturing method of the titanium oxide structure of the present invention includes the steps (1) and (3),
(2) It is preferable to include a step of bringing the titanium oxide-based structure obtained in the step (1) into contact with at least one selected from the group consisting of water, an acid, and an ion exchange resin.

<Step (1)>
In the step (1), an alkaline aqueous solution of 3 to 20 mol / L, a substance (A) containing Ti, and a substance (B) containing at least one selected from the group consisting of V, Nb, Ta and B, Contact at a temperature higher than 160 ° C.

  In the step (1), specifically, although not limited thereto, the substance (A) and the substance (B) are added to an alkaline aqueous solution of 3 to 20 mol / L, and then 160 ° C. It is preferred to heat to a higher temperature.

  As the alkaline aqueous solution, an aqueous solution of an alkali metal hydroxide is preferable from the viewpoint of dissolving the surface of the raw material titanium oxide and promoting the reaction. In addition, it is good also as an aqueous solution containing 2 or more types of alkalis as an alkali, For example, potassium hydroxide, lithium hydroxide, etc. can be used together with sodium hydroxide. In particular, as the alkali, sodium hydroxide and / or potassium hydroxide is preferable, and sodium hydroxide is particularly preferable in order to synthesize a high aspect ratio structure. When sodium hydroxide is used, a structure having a large average width tends to be generated. When potassium hydroxide is used, a structure having a small average width tends to be generated.

  In addition, as an alkali, it is preferable to contain sodium hydroxide 50weight% or more, especially 70weight% or more.

  The concentration of the aqueous alkali solution is such that the surface of the material (A) and the material (B) (particularly the material (A)) of the raw material is dissolved and the fluidity of the reaction solution is maintained, so that a plate-like titanium oxide crystal having a large aspect ratio is obtained. From the point which can produce the titanium oxide structure which consists of consisting of a long time, it is 3-20 mol / L, Preferably it is about 5-15 mol / L. In addition, when using the aqueous solution containing 2 or more types of alkalis, the density | concentration of alkaline aqueous solution is 3-30 mol / L, Preferably it is about 5-20 mol / L.

  The substance (A) containing Ti to be used is not particularly limited as long as it is a substance that becomes titanium oxide by heating. That is, the substance (A) is preferably titanium oxide and / or a titanium oxide precursor. Specifically, titanium oxide; titanium hydroxide; titanium alkoxide; titanium halide such as titanium trichloride and titanium tetrachloride; metal Examples include titanium. Moreover, only 1 type of these may be used and 2 or more types may be used together. In particular, from the viewpoint that the alkali dissolves on the surface of the raw material and the reaction proceeds, when using a solid such as titanium oxide or titanium metal, the average particle size is preferably 100 nm or less, more preferably 50 nm or less. The lower limit is not particularly set, but is usually about 3 nm. When the particle size is large, the particles may be pulverized dry or wet using a planetary ball mill, paint shaker or the like. The average particle diameter of titanium oxide can be measured, for example, by observation with an electron microscope (SEM or TEM).

  The amount of the substance (A) added to the alkaline aqueous solution is not particularly limited, but is preferably about 0.01 to 1 mol / L from the viewpoint of balancing the fluidity and productivity of the reaction solution, About 0.5 mol / L is more preferable.

The substance (B) containing at least one selected from the group consisting of V, Nb, Ta and B is not particularly limited, like the substance (A). Examples thereof include oxides, hydroxides, alkoxides and chlorides of these elements. Specifically, for example, V ₂ O ₅ , V (OH) ₂ , VCl ₄ , Nb ₂ O ₅ , Nb (OH) ₅ , Nb (OC ₂ H ₅ ) ₅ , Nb (OC ₃ H ₇ ) ₅ , _{NbCl 5, Ta 2 O 5,} Ta (OH) 5, Ta (OC 2 H 5) 5, Ta (OC 3 H 7) 5, TaCl 5, B 2 O 3, H 3 BO 3, B (OC 2 H ₅ ) ₃ , B (OC ₃ H ₇ ) ₃ , BCl _{3 and the} like. Of these, NbCl ₅ and H ₃ BO ₃ are inexpensive and preferable. As in the case of the substance (A), when a solid such as an oxide is used, the average particle size is preferably 100 nm or less, and more preferably 50 nm or less. The lower limit is not particularly set, but is usually about 3 nm. When the particle size is large, the particles may be pulverized dry or wet using a planetary ball mill, paint shaker or the like. The average particle diameter of titanium oxide can be measured, for example, by observation with an electron microscope (SEM or TEM).

  The amount of the substance (B) added to the alkaline aqueous solution is not particularly limited, but is preferably about 0.00001 to 0.1 mol / L, and preferably about 0.00025 to 0.035 mol / L from the viewpoint of enhancing conductivity. Is more preferable.

  The amount of the substance (B) added to the alkaline aqueous solution is at least one selected from the group consisting of V, Nb, Ta and B contained in the substance (B) from the viewpoint of conductivity and photoelectric conversion efficiency. The content of is preferably 0.1 to 10 mol%, more preferably 0.3 to 8 mol%, still more preferably 0.5 to 7 mol% with respect to Ti in the substance (A).

  The substance (B) may be mixed with an alkaline aqueous solution simultaneously with the substance (A), or after the substance (A) is mixed with the alkaline aqueous solution, the substance (B) may be mixed with the alkaline aqueous solution. Conversely, after the substance (B) is mixed with the alkaline aqueous solution, the substance (A) may be mixed with the alkaline aqueous solution. When the temperature is raised to a temperature higher than 160 ° C., there is no particular limitation as long as the substance (A) and the substance (B) are introduced into the alkaline aqueous solution.

  The temperature at which the alkaline aqueous solution is brought into contact with the substances (A) and (B) is higher than 160 ° C. The upper limit of the contact temperature is not particularly limited, but is usually 374 ° C., which is the critical point of water. Preferably, it is about 180-370 degreeC, More preferably, it is about 200-300 degreeC. If the contact temperature is too low, the titanium oxide structure of the present invention cannot be produced, and a massive structure in which titanium oxide is aggregated or a titanium oxide structure having a very small width is entangled to form a massive structure as a whole. Can only be manufactured. That is, a titanium oxide structure having a high aspect ratio and high dispersibility cannot be obtained. In Patent Documents 2 and 3, it is said that when the temperature is 160 ° C. or higher, it is difficult to produce a tube-shaped product ([0024] of Patent Document 2 and [0024] of Patent Document 3). Then, the titanium oxide structures are entangled with each other, so that a high aspect ratio and high dispersibility titanium oxide structure cannot be obtained. Moreover, since it aggregates, electroconductivity also deteriorates. Further, if the contact temperature is too high, it is not desirable in terms of the amount of energy used and safety.

  The time for bringing the alkaline aqueous solution into contact with the substances (A) and (B) (that is, the time for heating to a temperature higher than 160 ° C.) is not particularly limited, and is preferably about 1 to 120 hours.

  In the present invention, for example, when the substance (A) to be used is titanium oxide, there is a correlation between preferable ranges of the average particle diameter, contact temperature, and contact time, and when using titanium oxide having a larger average particle diameter. It is preferable to increase the contact temperature. For example, when the contact time is 12 hours using titanium oxide having an average particle diameter of 7 nm, the contact temperature is preferably higher than 160 ° C., but the contact time using titanium oxide having an average particle diameter of 25 nm is used. Is 12 hours, the contact temperature is preferably 185 ° C. or higher.

  By providing such a step (1), even if the obtained titanium oxide structure is subjected to a heat treatment (firing) at 300 ° C. or higher, the change in shape can be suppressed.

<Step (2)>
In step (2), specifically, when water or acid is used, for example, the titanium oxide structure obtained in step (1) is preferably added to water or an acidic aqueous solution. Moreover, when using an ion exchange resin, the liquid containing a product may be allowed to pass through a column filled with the ion exchange resin, or only mixed with the ion exchange resin and stirred.

  When an alkali metal hydroxide (NaOH or the like) is used as the alkaline aqueous solution, the titanium oxide structure obtained in the step (1) may contain an alkali metal (Na or the like). Thereby, the alkali metal contained in the titanium oxide structure can be removed.

  The acid is preferably a protonic acid capable of exchanging protons with alkali metal ions. Specific examples include general inorganic acids or organic acids such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, hydrofluoric acid, acetic acid, citric acid, formic acid, and oxalic acid. These acids may be used individually by 1 type, and may be used in combination of 2 or more type.

  Examples of the ion exchange resin include cation exchange resins such as Diaion (manufactured by Mitsubishi Chemical Corporation; registered trademark) and Amberlite (made by Rohm and Haas). These ion exchange resins may be used individually by 1 type, and may be used in combination of 2 or more type.

  Among water, acid, and ion exchange resin, it is preferable to use an acid from the viewpoint that the alkali metal contained in the titanium oxide structure obtained in the step (1) can be removed in a short time. Hydrochloric acid, nitric acid Acetic acid, oxalic acid and the like are more preferable. However, when an acid is used, it is preferable that the titanium oxide structure obtained in step (1) is brought into contact with an acid, and then the titanium oxide structure is washed with water to remove the acid.

  The time for contacting the titanium oxide structure obtained in step (1) with at least one selected from the group consisting of water, acid and ion exchange resin is preferably about 1 to 48 hours, and the alkali metal is sufficiently removed. If it is necessary to do this, 8 hours or more is more desirable.

<Step (3)>
The titanium oxide structure obtained in the above step (1) or (2) is heated (baked) to a high temperature to cause the Ti—OH group remaining in the titanium oxide structure to undergo a dehydration reaction, and to have crystallinity. Can be increased.

  The temperature at this time is 300 ° C. or higher, preferably 500 ° C. or higher, from the viewpoint of more reliably performing the dehydration reaction. The upper limit of the heating temperature is not particularly limited, but is usually 1000 ° C. or lower. If it is in this temperature range, there is no restriction in particular, but if the temperature is higher, the conductivity can be improved, and if the temperature is lower, the shape with a higher aspect ratio can be maintained. For this reason, it is preferable to set suitably according to a use.

  The firing atmosphere is not particularly limited, but low oxygen conditions, that is, reduced pressure, inert atmosphere, reducing atmosphere, and the like are preferable from the viewpoint of enhancing conductivity. In particular, a reduced pressure of 10 kPa or less or a reducing atmosphere in which hydrogen is mixed in an inert atmosphere is more preferable.

That is, step (3)
(3-1) It is preferable to set it as the process heat-processed at 300 degreeC or more under the reduced pressure of 10 kPa or less, or (3-2) the process heat-processed at 300 degreeC or more in a reducing atmosphere. Among these, the step (3-2) is preferable because the conductivity is improved, but the step (3-1) is simpler.

  In addition, when making atmosphere into pressure reduction, a pressure is 10 kPa or less, and 5 kPa or less is more preferable. The lower limit is not particularly limited, but is usually about 0.001 Pa.

  Further, when the atmosphere is a reducing atmosphere, a reducing atmosphere in which hydrogen is mixed in an inert atmosphere such as a nitrogen atmosphere or an argon atmosphere is preferable, and the amount of hydrogen gas at this time is preferably about 0.1 to 4 mol%, About 0.5-3 mol% is more preferable.

  The titanium oxide structure thus obtained has the characteristics described in the above “1. Titanium oxide structure”.

  In addition, although the example of the manufacturing method of the titanium oxide structure of the present invention has been described above, for example, by a hydrothermal synthesis method (temperature higher than 160 ° C.) using titanium oxide and / or a precursor thereof and an alkaline aqueous solution. A structure made of titanium oxide may be synthesized and then doped with a third component such as V, Nb, Ta, or B. However, when a large amount of the third component is contained, it is preferably produced by the production method of the present invention.

3. Porous titanium oxide film The porous titanium oxide film of the present invention includes the titanium oxide structure of the present invention. The porous titanium oxide film of the present invention is not necessarily composed of only the titanium oxide structure of the present invention. For example, titanium oxide fine particles having an average particle diameter of 1 to 500 nm, particularly 5 to 100 nm; A titanium oxide nanorod; a known titanium oxide nanofiber; a titanium oxide structure having a high aspect ratio, such as a tubular aggregate of titanium oxide nanoparticles, and the like may be included.

  In particular, when the titanium oxide structure of the present invention and the titanium oxide fine particles are mixed, the strength of the porous titanium oxide film of the present invention can be improved and defects such as cracks can be suppressed.

  When the titanium oxide structure of the present invention and other components are included in the porous titanium oxide film of the present invention, the porous titanium oxide film of the present invention is “the titanium oxide structure of the present invention. Or a layer containing other components ”or“ consisting of at least two layers of a layer containing other components and a layer containing the titanium oxide structure of the present invention ”. Good. Of course, you may have the structure of three or more layers.

  When the titanium oxide structure of the present invention and other components are included in the porous titanium oxide film of the present invention, it depends on the purpose of adding the content of the titanium oxide structure of the present invention and the types of other components to be combined. However, in order to improve conductivity and strength, the content of the titanium oxide structure of the present invention is preferably about 0.1 to 95% by weight, more preferably about 1 to 90% by weight. In order to increase the light diffusion effect, the ratio of the titanium oxide structure of the present invention should be increased (for example, about 5 to 95% by weight) to maintain the transparency of the film as much as possible, or the specific surface area must be increased. In addition, when the specific surface area of the other components to be combined is larger, the ratio of the titanium oxide structure of the present invention may be reduced (for example, about 1 to 20% by weight).

  The production method of the porous titanium oxide film of the present invention is not particularly limited. For example, a film-forming composition containing the titanium oxide structure of the present invention is prepared, and the film is formed on a suitable substrate. It is preferred to apply and dry the forming composition. Further, after drying, the obtained film may be subjected to a heat treatment as necessary to be baked.

  There is no restriction | limiting in particular as a board | substrate, What has a substantially smooth surface at normal temperature can be used, The surface may be either a plane or a curved surface, and may deform | transform by stress. Specific examples of the substrate that can be used include various glasses; transparent resins such as PET (polyethylene terephthalate) and PEN (polyethylene naphthalate). In addition, the porous titanium oxide film of the present invention is used as a negative electrode material for a dye-sensitized solar cell, and in the case of a structure that incorporates light from the counter electrode side, the substrate does not necessarily have to be transparent, conductive aluminum, Titanium, chromium, stainless steel, etc. may be used.

  The coating method is not particularly limited, and conventional methods such as screen printing, dip coating, spray coating, spin coating, and squeegee method can be employed.

  Moreover, there is no restriction | limiting in particular in drying conditions and baking conditions, It is preferable that drying temperature shall be about 60-250 degreeC and baking temperature shall be about 250-800 degreeC.

  In producing the porous titanium oxide film of the present invention, it is preferable to apply so that the film thickness of the obtained film is about 0.5 to 50 μm.

  When the porous titanium oxide film of the present invention has two layers, a layer containing titanium oxide fine particles and a layer containing the titanium oxide structure of the present invention, for example, a film containing titanium oxide fine particles It is preferable to apply and dry the film-forming composition containing the titanium oxide structure of the present invention on the layer containing fine titanium oxide particles after coating and drying the forming composition on the substrate. Of course, when forming a porous titanium oxide film consisting of three or more layers, it is preferable to carry out the coating and drying steps in three or more steps.

4). Electrode When forming the electrode of this invention, it is preferable to form the above-mentioned porous titanium oxide film on a conductive resin substrate or a glass substrate.

  The resin substrate is not particularly limited as long as it is a conductive resin substrate. For example, polyester such as polyethylene naphthalate resin substrate (PEN resin substrate) and polyethylene terephthalate resin substrate (PET resin substrate); polyamide; polysulfone; polyether Examples include sulfone, polyether ether ketone, polyphenylene sulfide, polycarbonate, polyimide, polymethyl methacrylate, polystyrene, cellulose triacetate, and polymethylpentene.

  There is no restriction | limiting in particular also as a glass substrate, Well-known or a commercially available thing can be used, and any of colorless or colored glass, meshed glass, a glass block etc. may be sufficient.

  As this resin substrate or glass substrate, a substrate having a thickness of about 0.05 to 10 mm can be used.

  In the present invention, the porous titanium oxide film may be directly formed on the surface of the resin substrate or the glass substrate, but may be formed via a transparent conductive film.

  Examples of the transparent conductive film include a tin-doped indium oxide film (ITO film), a fluorine-doped tin oxide film (FTO film), an antimony-doped tin oxide film (ATO film), an aluminum-doped zinc oxide film (AZO film), and a gallium-doped zinc oxide. Examples include a film (GZO film). By passing through these transparent conductive films, it becomes easy to take out the generated current to the outside. The film thickness of these transparent conductive films is preferably about 0.02 to 10 μm.

  Examples of the electrode of the present invention include the following two embodiments.

<Aspect 1>
The porous titanium oxide film of the present invention can be formed on a resin substrate or a glass substrate via a transparent conductive film to form the electrode of the present invention. The resin substrate, the glass substrate and the transparent conductive film are as described above.

  Specifically, an electrode may be formed as follows.

  First, a transparent conductive film is formed on a resin substrate or a glass substrate by a vacuum deposition method, an ion plating method, a CVD method, a sputtering method, a sol-gel method, a nanoparticle composite, or the like. The surface resistance of the substrate thus obtained is 50 Ω / sq. The following is preferable.

  And it is preferable to apply | coat and dry the above-mentioned film forming composition on it, and to heat it as needed. In the case of using a resin substrate, the drying conditions and heating conditions are preferably 150 ° C. or lower.

  At this time, it is preferable from the viewpoint of crack suppression and adhesion to the substrate that the obtained film has a thickness of about 2 to 40 μm.

<Aspect 2>
The porous titanium oxide film of the present invention may be directly formed on a resin substrate or a glass substrate, and a porous metal film may be further formed thereon to form the electrode of the present invention. The resin substrate and the glass substrate are as described above. Moreover, when forming the porous titanium oxide film of this invention on a resin substrate or a glass substrate, the method similar to the said aspect 1 is employable.

  The porous metal film that can be used in the embodiment 2 is not particularly limited as long as it is a metal that is not attacked (reacted) by ions contained in the electrolytic solution such as iodine ions and bromine ions. For example, titanium, tungsten, platinum, Gold etc. are mentioned. By forming these porous metal films, the generated current can be easily taken out to the outside. The surface low efficiency of these porous metal films is not particularly limited, but is 10 Ω / sq. The film thickness is not particularly limited, but is preferably 150 nm or more.

  In order to form the porous metal film on the porous titanium oxide film formed on the resin substrate or the glass substrate, it may be formed by a thin film forming method such as a sputtering method.

5. Photoelectric conversion element and dye-sensitized solar cell The photoelectric conversion element of the present invention forms a counter electrode (counter electrode) on the porous titanium oxide film of the electrode of the present invention, and iodine and iodide or bromine are formed between these electrodes. And an acetonitrile solution containing bromide, an ethylene carbonate solution, or a propylene carbonate solution, and a mixed solution thereof. The dye-sensitized solar cell of the present invention can be obtained by modularizing the photoelectric conversion element and providing predetermined electrical wiring.

  Thus, by using the electrode of the present invention as the negative electrode, the generated electrons can be quickly conveyed to the conductive glass on the negative electrode side. Further, compared with the case where titanium oxide fine particles are used as the negative electrode material, light can be easily diffused and the light utilization efficiency can be improved. In addition, an appropriate gap can be formed in the negative electrode to facilitate the diffusion of the electrolytic solution. Furthermore, the strength of the porous titanium oxide film of the negative electrode can be improved, and cracks that cause a leak current or the like can be prevented.

  The counter electrode may have a single layer structure made of a conductive material, or may be composed of a conductive layer and a substrate. The substrate is not particularly limited, and the material, thickness, dimensions, shape, and the like can be appropriately selected according to the purpose. For example, metal, colorless or colored glass, meshed glass, glass block, etc. are used. Resin may be used. Examples of such resins include polyesters such as polyethylene terephthalate, polyamide, polysulfone, polyether sulfone, polyether ether ketone, polyphenylene sulfide, polycarbonate, polyimide, polymethyl methacrylate, polystyrene, cellulose triacetate, and polymethylpentene. Alternatively, a counter electrode may be formed by directly applying, plating, or vapor-depositing (PVD, CVD) a conductive material on the charge transport layer.

  The electrode of the present invention can also be used as a counter electrode. If the electrode of the present invention is used as a counter electrode, effects such as expansion of the effective area of the catalyst, promotion of diffusion of the electrolyte, and improvement of the strength of the catalyst layer of the counter electrode can be expected.

  As the conductive material, metals such as platinum, gold, nickel, titanium, aluminum, copper, silver, and tungsten, and materials having a small specific resistance such as carbon materials and conductive organic substances are used.

  A metal lead may be used for the purpose of reducing the resistance of the counter electrode. The metal lead is preferably made of a metal such as platinum, gold, nickel, titanium, aluminum, copper, silver or tungsten, and particularly preferably made of aluminum or silver.

  In the present invention, before forming the counter electrode, for the purpose of improving the light absorption efficiency of the electrode of the present invention, it is preferable to support (adsorb, contain, etc.) a dye on the porous titanium oxide film.

  The dye is not particularly limited as long as it has absorption characteristics in the visible region and near infrared region, and improves (sensitizes) the light absorption efficiency of the semiconductor layer. However, metal complex dyes, organic dyes, natural dyes, semiconductors, etc. Is preferred. In addition, in order to impart adsorptivity to the porous titanium oxide film, a carboxyl group, hydroxyl group, sulfonyl group, phosphonyl group, carboxylalkyl group, hydroxyalkyl group, sulfonylalkyl group, phosphonylalkyl group in the dye molecule Those having a functional group such as are preferably used.

  As the metal complex dye, for example, a ruthenium, osmium, iron, cobalt, zinc, mercury complex (for example, mellicle chromium), metal phthalocyanine, chlorophyll, or the like can be used. Examples of organic dyes include, but are not limited to, cyanine dyes, hemicyanine dyes, merocyanine dyes, xanthene dyes, triphenylmethane dyes, metal-free phthalocyanine dyes, and the like. . As a semiconductor that can be used as a dye, an amorphous semiconductor having a large i-type light absorption coefficient, a direct transition semiconductor, or a fine particle semiconductor that exhibits a quantum size effect and efficiently absorbs visible light is preferable. Usually, one of various semiconductors, metal complex dyes and organic dyes, or two or more kinds of dyes can be mixed in order to make the wavelength range of photoelectric conversion as wide as possible and increase the conversion efficiency. Moreover, the pigment | dye to mix and its ratio can be selected so that it may match with the wavelength range and intensity distribution of the target light source.

  As a method for adsorbing the dye on the porous titanium oxide film, for example, a solution in which the dye is dissolved in a solvent is applied on the porous titanium oxide film by spray coating or spin coating and then dried. be able to. In this case, the substrate may be heated to an appropriate temperature. Alternatively, a method of immersing and adsorbing a porous titanium oxide film in a solution can be used. The immersion time is not particularly limited as long as the dye is sufficiently adsorbed, but is preferably 10 minutes to 30 hours, more preferably 1 to 20 hours. Moreover, you may heat a solvent and a board | substrate when immersing as needed. The concentration of the dye in the case of forming a solution is about 1 to 1000 mmol / L, preferably about 10 to 500 mmol / L.

  The solvent to be used is not particularly limited, but water and an organic solvent are preferably used. Examples of the organic solvent include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and t-butanol; acetonitrile, propionitrile, methoxypropionitrile, glutaronitrile, and the like. Nitriles; aromatic hydrocarbons such as benzene, toluene, o-xylene, m-xylene, p-xylene; aliphatic hydrocarbons such as pentane, hexane, heptane; alicyclic hydrocarbons such as cyclohexane; acetone, methyl ethyl ketone Ketones such as diethyl ketone and 2-butanone; ethers such as diethyl ether and tetrahydrofuran; ethylene carbonate, propylene carbonate, nitromethane, dimethylformamide, dimethyl sulfoxide, hexamethylphosphoamide, dimethoxy Ethane, γ-butyrolactone, γ-valerolactone, sulfolane, dimethoxyethane, adiponitrile, methoxyacetonitrile, dimethylacetamide, methylpyrrolidinone, dimethylsulfoxide, dioxolane, sulfolane, trimethyl phosphate, triethyl phosphate, tripropyl phosphate, ethyl phosphate Dimethyl, tributyl phosphate, tripentyl phosphate, trihexyl phosphate, triheptyl phosphate, trioctyl phosphate, trinonyl phosphate, tridecyl phosphate, tris phosphate (trifluoromethyl), tris phosphate (pentafluoroethyl), Examples thereof include triphenyl polyethylene glycol phosphate and polyethylene glycol.

  In order to reduce the interaction such as aggregation between the dyes, a colorless compound having properties as a surfactant may be added to the dye adsorbing liquid and co-adsorbed on the porous titanium oxide film. Examples of such colorless compounds include steroid compounds such as cholic acid having a carboxyl group or sulfo group, deoxycholic acid, chenodeoxycholic acid, taurodeoxycholic acid, sulfonates, and the like.

  It is preferable to remove the unadsorbed dye by washing immediately after the adsorption step. Washing is preferably performed using acetonitrile, an alcohol solvent or the like in a wet washing tank.

  After adsorbing the dye, porous using amines, quaternary ammonium salts, ureido compounds having at least one ureido group, silyl compounds having at least one silyl group, alkali metal salts, alkaline earth metal salts, etc. The surface of the quality titanium oxide film may be treated. Examples of preferred amines include pyridine, 4-t-butylpyridine, polyvinylpyridine and the like. Examples of preferred quaternary ammonium salts include tetrabutylammonium iodide, tetrahexylammonium iodide and the like. These may be used by dissolving in an organic solvent, or may be used as they are in the case of a liquid.

6). Other Applications The titanium oxide structure of the present invention can be used for a photocatalyst, a sensor, a resin reinforcing material, a metal ion carrier, etc. in addition to a dye-sensitized solar cell. At that time, the titanium oxide structure of the present invention may be used alone, or the titanium oxide structure of the present invention and titanium oxide fine particles may be mixed in the same manner as in the above “3. Porous titanium oxide film”. May be used.

  If the titanium oxide structure of the present invention and titanium oxide fine particles are mixed and used, the strength can be improved and defects such as cracks can be suppressed.

  The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

Example 1
After adding 0.8 g of titanium oxide fine particles having an average particle diameter of 7 nm and 0.066 g of niobium oxide to 100 g of distilled water and stirring, 40 g of NaOH was added and further stirred for 5 minutes (concentration of titanium oxide: 0.1 mol / L). Niobium concentration derived from niobium oxide 0.005 mol / L, concentration of aqueous alkali solution: 10 mol / L). When this mixed solution was placed in a PTFE-lined SUS316 pressure vessel and allowed to stand in a 250 ° C. heating furnace for 12 hours, a white precipitate was obtained.

  The precipitate was vigorously stirred in 500 ml of distilled water and then filtered under reduced pressure three times, followed by stirring in 500 g of pH 1 hydrochloric acid for 24 hours. Further, the operation of stirring the obtained substance in 500 ml of distilled water and then filtering under reduced pressure was repeated 5 times to obtain a white cake. The result of observing this with TEM is shown in FIG. It was found to be a plate-like substance having a large aspect ratio (average aspect ratio: 74) having an average width of 80 nm and an average length of 6 μm.

  Then, when the obtained white cake was heat-processed (baked) under reduced pressure (0.3-0.5 kPa) of 700 degreeC, 0.8 g of white substance was obtained.

  When this material was observed by SEM and TEM, it was found that it was a plate-like material having a large aspect ratio (average aspect ratio: 50) having an average width of 100 nm and an average length of 5 μm, and the shape could be substantially maintained before and after firing. . It was also found that each structure is independent and excellent in dispersibility. Furthermore, when Nb / Ti ratio of this substance was measured, it was 5 mol%.

Further, this material was processed into a flat plate having a thickness of 0.3 mm at 10 MPa, and a voltage of 1 V was applied between the pellets to measure the powder resistance. As a result, it was 1.0 × 10 ⁴ Ω · m. Moreover, it was 20 m < ² > / g when the BET specific surface area was measured. When the alkali metal (sodium) content was measured by ICP emission spectrometry, it was below the detection limit (500 ppm or less).

  In the following examples and comparative examples, the structures were evaluated in the same manner.

Example 2
The experiment was performed in the same manner as in Example 1 except that 0.8 g of titanium oxide fine particles having an average particle diameter of 25 nm were used.

As a result, 0.8 g of a white substance was obtained, the average width was 90 nm, the average length was 4.5 μm (average aspect ratio: 50), and the powder resistance was 1.1 × 10 ⁴ Ωm. In addition, the result observed with TEM is shown in FIG. It was also found that each structure is independent and excellent in dispersibility.

Moreover, it was 5 mol% when Nb / Ti ratio of this substance was measured. Furthermore, it was 22 m < ² > / g when the BET specific surface area was measured. When the alkali metal (sodium) content was measured, it was below the detection limit (500 ppm or less).

Example 3
An experiment was conducted in the same manner as in Example 1 except that 0.135 g of niobium chloride was used for 100 g of titanium oxide sol having an average particle diameter of 4 nm (including 0.8 g of titanium oxide). At this time, the concentration of titanium oxide in the alkaline aqueous solution is 0.1 mol / L, and the concentration of niobium derived from niobium chloride is 0.005 mol / L. As a result, 0.8 g of a white substance was obtained, the average width was 90 nm, the average length was 7 μm (average aspect ratio: 78), and the powder resistance was 1.3 × 10 ⁴ Ωm. It was also found that each structure is independent and excellent in dispersibility.

Moreover, it was 5 mol% when Nb / Ti ratio of this substance was measured. Furthermore, it was 26 m < ² > / g when the BET specific surface area was measured. When the alkali metal (sodium) content was measured, it was below the detection limit (500 ppm or less).

Example 4
The experiment was performed in the same manner as in Example 1 except that the reaction temperature was 200 ° C. instead of 250 ° C. As a result, 0.8 g of a white substance was obtained, the average width was 80 nm, the average length was 4.8 μm (average aspect ratio: 60), and the powder resistance was 1.2 × 10 ⁴ Ωm. It was also found that each structure is independent and excellent in dispersibility.

Moreover, it was 5 mol% when Nb / Ti ratio of this substance was measured. Furthermore, it was 30 m < ² > / g when the BET specific surface area was measured. When the alkali metal (sodium) content was measured, it was below the detection limit (500 ppm or less).

Example 5
The experiment was performed in the same manner as in Example 1 except that 60 g of NaOH was used. At this time, the concentration of titanium oxide in the alkaline aqueous solution is 0.1 mol / L, and the concentration of niobium derived from niobium chloride is 0.005 mol / L. As a result, 0.8 g of a white substance was obtained, the average width was 100 nm, the average length was 8 μm (average aspect ratio: 80), and the powder resistance was 0.9 × 10 ⁴ Ωm. It was also found that each structure is independent and excellent in dispersibility.

Moreover, it was 5 mol% when Nb / Ti ratio of this substance was measured. Furthermore, it was 21 m < ² > / g when the BET specific surface area was measured. When the alkali metal (sodium) content was measured, it was below the detection limit (500 ppm or less).

Example 6
The experiment was performed in the same manner as in Example 1 except that the reaction time was 60 hours instead of 12 hours. As a result, 0.8 g of a white substance was obtained, the average width was 100 nm, the average length was 10 μm (average aspect ratio: 100), and the powder resistance was 0.8 × 10 ⁴ Ωm. It was also found that each structure is independent and excellent in dispersibility.

Moreover, it was 5 mol% when Nb / Ti ratio of this substance was measured. Furthermore, it was 22 m < ² > / g when the BET specific surface area was measured. When the alkali metal (sodium) content was measured, it was below the detection limit (500 ppm or less).

Example 7
The experiment was performed in the same manner as in Example 1 except that the baking temperature was 800 ° C. instead of 700 ° C. As a result, 0.8 g of a white substance was obtained, the average width was 130 nm, the average length was 5 μm (average aspect ratio: 38), and the powder resistance was 0.5 × 10 ⁴ Ωm. It was also found that each structure is independent and excellent in dispersibility.

Moreover, it was 5 mol% when Nb / Ti ratio of this substance was measured. Furthermore, it was 16 m < ² > / g when the BET specific surface area was measured. When the alkali metal (sodium) content was measured, it was below the detection limit (500 ppm or less).

Example 8
The experiment was performed in the same manner as in Example 1 except that the firing atmosphere was not a reduced pressure but a nitrogen atmosphere containing 2 mol% of hydrogen. As a result, 0.8 g of a white substance was obtained, the average width was 100 nm, the average length was 5 μm (average aspect ratio: 50), and the powder resistance was 0.2 × 10 ⁴ Ωm. It was also found that each structure is independent and excellent in dispersibility.

Moreover, it was 5 mol% when Nb / Ti ratio of this substance was measured. Furthermore, it was 20 m < ² > / g when the BET specific surface area was measured. When the alkali metal (sodium) content was measured, it was below the detection limit (500 ppm or less).

Comparative Example 1
100 g of distilled water was added to only 0.8 g of titanium oxide fine particles having an average particle diameter of 7 nm and stirred, and then 40 g of NaOH was added, and an experiment was conducted in the same manner as in Example 1. That is, niobium oxide was not used.

As a result, it was a substance having a large aspect ratio (average aspect ratio: 77) having an average width of 65 nm and an average length of 5 μm before baking at 700 ° C., but 0.8 g of a white substance was obtained by baking. The width was 170 nm, the average length was 3.5 μm (average aspect ratio: 20), the powder resistance was 7 × 10 ⁵ Ωm, and the conductivity was low.

  Further, it was found that the aspect ratio was less than half compared with the case of using niobium oxide, and the shape change after firing was large.

Comparative Example 2
Instead of firing, only vacuum drying at 150 ° C. was performed, and the experiment was performed in the same manner as in Example 1.

As a result, 0.8 g of a white substance was obtained, and a substance having an average width of 65 nm and an average length of 6.5 μm (average aspect ratio: 100) was obtained, but the powder resistance was 3 × 10 ⁶ Ωm, The conductivity was low.

Comparative Example 3
The experiment was performed in the same manner as in Example 1 except that the reaction was carried out at 110 ° C. normal pressure instead of 250 ° C. under reduced pressure.

As a result, 0.8 g of a white substance was obtained before firing, but it was a mixture of a tube-like substance having a diameter of 6 nm and a sheet-like substance, agglomerated, and the length could not be observed (FIG. 3). And 4). Further, although ultrasonic dispersion was attempted in addition to water, it could not be dispersed. Therefore, heat treatment was performed as it was under reduced pressure conditions at 700 ° C., but when TEM observation was performed, the tube and sheet shapes disappeared and became particulate matter of about 2 μm. In other words, it was impossible to maintain the shape. The powder resistance was 2 × 10 ⁷ Ωm.

Experimental example: Dye-sensitized solar cell <Synthesis of titanium oxide nanoparticles (average particle size 15 nm)>
While stirring 800 g of nitric acid aqueous solution of pH 0.7, 142.1 g (0.5 mol) of titanium tetraisopropoxide and 30 g (0.5 mol) of acetic acid were added and stirred for 1 hour. The titanium oxide sol was synthesized by maintaining the time. The final weight was adjusted to 925 g. 208.1 g of this titanium oxide sol was sealed in a titanium pressure vessel and reacted at 250 ° C. for 18 hours to synthesize titanium oxide nanoparticles (average particle size 15 nm).

<Titanium oxide structure of Example 1>
Sheet resistance 8Ω / sq. 2.9 g of the synthesized titanium oxide nanoparticles (average particle size 15 nm), 0.1 g of the titanium oxide-based structure obtained in Example 1, 1.5 g of ethyl cellulose, and 10 g of α-terpineol. Then, 50 g of ethanol was mixed, ultrasonic dispersion was performed, and then a titanium oxide paste obtained by concentrating at 40 ° C. and 90 hPa for 3 h was applied to a 5 mm square × thickness of 16 μm and dried at 125 ° C.

  This coating film was baked for 1 h in air at 500 ° C. to obtain a porous titanium oxide film.

The obtained titanium oxide film was immersed in a ruthenium dye (Rutenium535-bisTBA: manufactured by SOLARONIX) / t-butanol / acetonitrile (1: 1) solution (concentration: 3.0 × 10 ⁻⁴ mol / L) for 16 hours, A dye was supported on titanium oxide.

  This conductive glass was bonded to a conductive glass (manufactured by Geomatek Co., Ltd.) subjected to Pt sputtering via an ionomer film cut out in a shape surrounding a titanium oxide layer with a thickness of 25 μm, and 0.1 mol / L of the glass was inside. An electrolytic solution in which lithium iodide, 0.03 mol / L iodine, and 0.5 mol / L 4-tert-butylpyridine was dissolved in acetonitrile was sealed.

When the cell was irradiated with pseudo sunlight (1 kW / m ² ) and the current-voltage characteristics were measured, a photoelectric conversion efficiency of 8.6% was obtained.

<Without titanium oxide structure>
The titanium oxide structure of Example 1 was used except that 0.1 g of the titanium oxide structure obtained in Example 1 was not used and 3.0 g of the synthesized titanium oxide nanoparticles (average particle size 15 nm) was used. The experiment was performed in the same manner as in the case of using.

When the cell was irradiated with pseudo sunlight (1 kW / m ² ) and the current-voltage characteristics were measured, a photoelectric conversion efficiency of 8.0% was obtained.

<Titanium oxide structure of Comparative Example 1>
The experiment was performed in the same manner as in the case of using the titanium oxide structure of Example 1 except that the titanium oxide structure was changed to that obtained in Comparative Example 1.

When the cell was irradiated with pseudo-sunlight (1 kW / m ² ) and the current-voltage characteristics were measured, a photoelectric conversion efficiency of 8.2% was obtained.

Claims (17)

It contains 0.3 to 10 mol% of Nb with respect to Ti, the average aspect ratio is 10 or more, the powder resistance under 10 MPa is 1 × 10 ⁵ Ω · m or less, and the alkali metal content is 2000 ppm or less A plate-shaped or rod-shaped titanium oxide structure for a photoelectric conversion element or a photocatalyst. The titanium oxide structure according to claim 1, wherein the specific surface area is 10 m ² / g or more. The titanium oxide structure according to claim 1 or 2, wherein the average width is 20 nm or more. The titanium oxide structure in any one of Claims 1-3 whose average length of a longitudinal direction is 1 micrometer or more. Plate shape or rod shape for photoelectric conversion elements or photocatalysts having an average aspect ratio of 10 or more, a powder resistance under 10 MPa of 1 × 10 ⁵ Ω · m or less, and an alkali metal content of 2000 ppm or less. A method for producing a titanium oxide structure of
(1) An alkaline aqueous solution of 3 to 20 mol / L, a substance (A) containing Ti, and a substance (B) containing Nb , the content of Nb in the substance (B) A manufacturing method comprising a step of contacting at a temperature higher than 160 ° C. so as to be 0.3 to 10 mol% with respect to Ti, and (3) a step of performing heat treatment at 300 ° C. or higher. The manufacturing method according to claim 5, wherein the substance (A) is titanium oxide and / or a precursor thereof. The production method according to claim 5 or 6, wherein the substance (B) is at least one selected from the group consisting of an oxide, a hydroxide, an alkoxide, and a chloride of Nb . The manufacturing method in any one of Claims 5-7 in which the said alkali contains 50 weight% or more of sodium hydroxide at least. The step (3)
(3-1) The manufacturing method in any one of Claims 5-8 which is a process heat-processed at 300 degreeC or more under the reduced pressure of 10 kPa or less. The step (3)
(3-2) The manufacturing method according to any one of claims 5 to 8, which is a step of heat-treating at 300 ° C or higher in a reducing atmosphere. During the steps (1) and (3),
(2) The method according to any one of claims 5 to 10, further comprising a step of bringing the titanium oxide-based structure obtained in the step (1) into contact with at least one selected from the group consisting of water, an acid, and an ion exchange resin. Manufacturing method. The production method according to claim 11, wherein the acid is at least one selected from the group consisting of hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, hydrofluoric acid, acetic acid, citric acid, formic acid and oxalic acid. The porous titanium oxide film for photoelectric conversion elements or photocatalysts containing the titanium oxide structure in any one of Claims 1-4. The porous titanium oxide film according to claim 13, further comprising titanium oxide fine particles having an average particle diameter of 1 to 500 nm. The electrode for photoelectric conversion elements in which the porous titanium oxide film of Claim 13 or 14 with which the pigment | dye was carry | supported is formed on the electroconductive board | substrate. A photoelectric conversion element comprising the electrode according to claim 15. The photocatalyst using the titanium oxide structure in any one of Claims 1-4.

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