JP2009274891A - Semiconductor oxide film, production method thereof, and hydrogen generation apparatus using the semiconductor oxide film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a novel film capable of being used as a photocatalytic film with a more improved photoelectric conversion efficiency than conventional, to provide a production method thereof, and to provide a hydrogen generation apparatus using such film and suited for generating hydrogen from an aqueous solution. <P>SOLUTION: In the film formed from a semiconductor oxide which produces electrons and holes upon absorption of light, the semiconductor oxide is a semiconductor oxide film being W-containing Fe<SB>2</SB>O<SB>3</SB>of a W/Fe atomic ratio of 0.02-0.08, a production method thereof, and a hydrogen generation apparatus using the film. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a semiconductor oxide film, a method for producing the same, and a hydrogen generator using the semiconductor oxide film.

  Recently, in order to prevent global warming, reduction of greenhouse gas emissions is required, and as one of the measures, introduction of clean energy such as wind power and sunlight is promoted. In addition, fuel cells, hydrogen production technologies, hydrogen storage and transport technologies, etc. are being actively researched to realize a hydrogen society where hydrogen is assumed to be a major energy source.

  Currently, hydrogen can be produced using fossil fuels such as coal, oil, and natural gas as raw materials, but in the future, hydrogen production technology using non-fossil fuels such as water and biomass and clean energy is desired. ing.

By the way, metal oxides such as titanium dioxide (TiO ₂ ) and strontium titanate (SrTiO ₃ ) are used as semiconductor photocatalysts which receive light such as sunlight and generate photovoltaic power and cause an electrochemical reaction by the photovoltaic power. Physical semiconductors are known. For example, it is known that when a platinum electrode and a titanium dioxide electrode as a semiconductor photoelectrode are placed in water and the titanium dioxide electrode is irradiated with ultraviolet rays, the water can be decomposed into hydrogen and oxygen.

  The conditions of the semiconductor photocatalyst and semiconductor photoelectrode that can electrolyze water and can fully use sunlight are as follows: (1) having a photovoltaic power of electrolysis voltage of water (theoretical value: 1.23V + overvoltage) or more; That is, the energy level of the conduction band is more negative than the hydrogen generation potential, the energy level of the valence band is more positive than the oxygen generation potential, and (2) the semiconductor photocatalyst or the semiconductor photoelectrode itself is an electrolyte. It is necessary to have chemical stability or the like that does not cause photolysis.

  Titanium dioxide, which is a typical semiconductor photocatalyst, has a large energy band gap of about 3.2 eV and satisfies the potential condition necessary for water decomposition, so that water can be decomposed and does not dissolve in the electrolyte. However, there is a problem that there is almost no sensitivity to light having a wavelength longer than about 380 nm in the sunlight spectrum, and the photoelectric conversion efficiency for sunlight is extremely low.

  In addition, since titanium dioxide satisfies the potential condition necessary for water decomposition as described above, water can be decomposed in principle, but in reality, the energy level of the conduction band of titanium dioxide is higher than the hydrogen generation potential. Since it is only slightly negative, hydrogen cannot be generated sufficiently without bias due to overvoltage or the like. Therefore, in general, water using titanium dioxide is decomposed by using a bias using an external power source or a pH difference generated by immersing titanium dioxide in an alkaline solution and a platinum electrode in an acidic solution. Chemical bias is used.

When a material having a small energy band gap (for example, about 2.5 eV for tungsten oxide (WO ₃ ) and about 2.3 eV for diiron trioxide (Fe ₂ O ₃ )) is used, light with a wavelength of about 460 nm or less is used for tungsten oxide. In addition, ferric trioxide can absorb light having a wavelength of about 540 nm or less. However, the energy level of the conduction band of these materials is more positive than the hydrogen generation potential, and hydrogen cannot be generated without a bias.

Therefore, for example, as described in JP-T-2003-504799 (Patent Document 1) and JP-T-2004-504934 (Patent Document 2), a photocatalyst and a dye-sensitized solar cell immersed in an aqueous electrolyte solution are used. A tandem cell is known in which layers are stacked and electrically connected. The outline of this tandem cell will be described with reference to FIG. The tandem cell 51 shown in FIG. 7 is composed of two photochemical systems connected in series, and the cell (first cell) shown on the left side in FIG. 7 is a water to which an electrolyte is added for the purpose of ion conduction. The aqueous electrolyte solution 53 is made of, and the aqueous electrolyte solution 53 is subjected to water photolysis. In the tandem cell 51 shown in FIG. 7, sunlight enters the cell via the glass sheet 52, passes through the aqueous electrolyte solution 53, and then is formed of an intermediate cell composed of an oxide such as WO ₃ or Fe ₂ O _3. It collides with the rear wall of the battery constituted by the semiconductor film 54 of the hole. The oxide contained in the semiconductor film 54 absorbs the blue and green portions of the solar spectrum, and yellow and red light is transmitted through the oxide. The yellow and red portions of the solar spectrum are captured by a second battery (a cell located on the right side with respect to the page of FIG. 7) mounted behind the back wall of the first cell. The second cell includes a dye-sensitized mesoporous TiO ₂ film that functions as a light-driven electrical bias. The second cell also includes a transparent conductive oxide film 55 deposited on the back surface of the glass sheet 52 constituting the rear wall of the first cell. The conductive oxide film 55 is covered with a dye-derivatized nanocrystalline titania film 56. The The dye-derivatized nanocrystalline titania film 56 is in contact with the organic redox electrolyte 57 and is also in contact with a glass counter electrode 58 that becomes conductive on the organic electrolyte side by the deposition of a transparent conductive oxide film. A water-soluble electrolytic solution 59 having the same composition as the above-described water-soluble electrolytic solution 53 is accommodated in contact with the counter electrode 58, and a cathode 60 for generating hydrogen is immersed in the water-soluble electrolytic solution 59. Yes. In the tandem cell 51 of FIG. 7, the first cell and the second cell are separated from each other by a diaphragm 61 formed of an ion conductive film or glass frit.
Special table 2003-504799 gazette Special table 2004-504934 gazette

Considering utilization of sunlight, Fe ₂ O ₃ having a smaller energy band gap is preferably used as the semiconductor photocatalyst. However, the photocatalytic action of Fe ₂ O ₃ is currently low and not practical.

  The present invention has been made in view of the circumstances as described above, and the object of the present invention is a novel film that can be used as a photocatalytic film having improved photoelectric conversion efficiency than the conventional one, a method for producing the same, and An object of the present invention is to provide a hydrogen generator suitable for generating hydrogen from an aqueous solution using such a membrane.

The present inventors tried to add various elements to Fe ₂ O _{3 in} order to improve the photogenerated current of the Fe ₂ O ₃ film. As a result, it was found that the effect was most effective when W was added to Fe ₂ O ₃ , and the present invention was completed. That is, the present invention is as follows.

The semiconductor oxide film of the present invention is a film formed of a semiconductor oxide that absorbs light and generates electrons and holes, and the semiconductor oxide has an atomic ratio of W to Fe of 0.02 to 0. 0.08 W-containing Fe ₂ O ₃ .

The present invention is also a method for producing a W-containing Fe ₂ O ₃ film having an atomic ratio of W to Fe of 0.02 to 0.08, using α-Fe ₂ O ₃ and WO ₃ as target materials. There is also provided a method for producing a semiconductor oxide film, which includes a step of forming a film by a sputtering method and a step of heat-treating the formed film at 550 to 600 ° C.

  The present invention further includes at least a semiconductor oxide film of the present invention, a transparent conductive film, a transparent substrate, and a solar cell from the light-receiving surface side, and penetrates the transparent substrate in the thickness direction, The present invention also provides a hydrogen generator characterized in that a conductive member for electrically connecting the solar cell is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the semiconductor oxide film which can be used as a photocatalyst film | membrane with the improved photoelectric conversion efficiency compared with the past can be provided. Moreover, according to the manufacturing method of the semiconductor oxide film of this invention, the semiconductor oxide film of this invention used suitably for such a photocatalyst film | membrane can be manufactured suitably. Furthermore, according to the present invention, by using the semiconductor oxide film of the present invention described above, it is possible to provide a hydrogen generator suitable for decomposing water and generating hydrogen.

The semiconductor oxide film of the present invention is a film formed of a semiconductor oxide that absorbs light and generates electrons and holes, and the semiconductor oxide has an atomic ratio of W to Fe of 0.02 to 0.02. It is characterized by being 0.08 W-containing Fe ₂ O ₃ . By using such a semiconductor oxide film of the present invention as a photocatalyst film, the photoelectric conversion efficiency can be remarkably improved as compared with the conventional case, and hydrogen is generated by decomposing water by the action mechanism described later. It can be suitably used as a material for a hydrogen generator. In the semiconductor oxide film of the present invention, the reason why photoelectric conversion efficiency is improved by adding W to Fe ₂ O ₃ is that by adding W acting as a dopant to Fe ₂ O ₃ , This is considered to be an effect of increasing the number of generated carriers or inactivating the grain boundary.

When the atomic ratio of W to Fe in the semiconductor oxide forming the semiconductor oxide film of the present invention is less than 0.02 or exceeds 0.08, there is a problem that the photoelectric conversion efficiency is low. . When the atomic ratio of W to Fe is less than 0.02, the dopant action of W is insufficient, and when the atomic ratio of W to Fe exceeds 0.08, crystals of α-Fe ₂ O ₃ This is because sex is considered to deteriorate. Fe in the semiconductor oxide that forms the semiconductor oxide film of the present invention is a balance between the effect of suppressing the recombination of generated carriers due to the dopant action of W or the inactivation of grain boundaries and the decrease in crystallinity of α-Fe ₂ O _3. It has been experimentally confirmed that the atomic ratio of W to is preferably in the range of 0.02 to 0.08, and particularly preferably 0.04 (described later). In addition, the atomic ratio of W to Fe mentioned above refers to a value measured by performing fluorescent X-ray analysis.

  The thickness of the semiconductor oxide film of the present invention is not particularly limited, but is preferably in the range of 0.1 to 0.5 μm, and more preferably in the range of 0.2 to 0.3 μm. . This is because when the thickness of the semiconductor oxide film is less than 0.1 μm, light absorption tends to be insufficient, and when the thickness of the semiconductor oxide film exceeds 0.5 μm, This is because the recombination of generated carriers tends to increase. The thickness of the semiconductor oxide film described above refers to the thickness of the semiconductor oxide film measured by, for example, observing the film cross section with a scanning electron microscope.

The method for producing the above-described semiconductor oxide film of the present invention is not particularly limited, and is formed by a sputtering method using a target material composed of α-Fe ₂ O ₃ and WO _3. The film can be particularly preferably manufactured by a method including a step of heat-treating the film at 550 to 600 ° C. The present invention also provides a method for producing such a semiconductor oxide film of the present invention.

In the method for producing a semiconductor oxide film of the present invention, first, α-Fe ₂ O ₃ and WO ₃ are used as target materials to form a film by sputtering. The apparatus for performing the sputtering method is not particularly limited, but it is preferable to employ the high-frequency magnetron sputtering method because the film thickness can be controlled with high accuracy. Also, the film forming conditions are not particularly limited, but when a high-frequency magnetron sputtering apparatus is used, the RF power source power is 100 to 200 W, the substrate temperature is 200 to 500 ° C., and the gas composition ratio is Ar: O _2. = 25: 1 to 5 (sccm), film forming pressure is 0.5 to ³ Pa, substrate-target distance is 100 to 250 mm, and the degree of vacuum in the film forming start chamber is 2 × 10 ⁻³ Pa or less. It is preferable to do. In the method for producing a semiconductor oxide film of the present invention, the atomic ratio of W to Fe in the formed film needs to be 0.02 to 0.08 (particularly preferably 0.04). As for the number ratio, for example, the RF power and substrate-target distance of one target (for example, α-Fe ₂ O ₃ ) are fixed, and the RF power and substrate-target distance of the other target (for example, WO ₃ ) are appropriately set. It can be adjusted by changing it. The above conditions are merely examples, and the film forming conditions can be changed and selected as appropriate according to the film forming apparatus to be used. The thickness of the semiconductor oxide film can be adjusted by the deposition time.

In the method for producing a semiconductor oxide film of the present invention, next, the film obtained as described above is subjected to a heat treatment at a temperature in the range of 550 to 600 ° C. This heat treatment is performed for the purpose of crystallizing a film formed by a sputtering method. When the heat treatment is not performed, the film is an amorphous film and does not exhibit photoelectric conversion characteristics. Further, when the temperature of the heat treatment is less than 550 ° C., there is a problem that crystallization is insufficient and the photoelectric conversion efficiency is low, and when the temperature of the heat treatment exceeds 600 ° C., the transparent conductive film and the semiconductor There is a problem in that a decrease in photoelectric conversion efficiency, which is considered to be caused by diffusion between the oxide film and the oxide film, occurs. By performing the heat treatment at a temperature within the range of 550 to 600 ° C., the heat treatment can be performed without breaking the α-Fe ₂ O ₃ crystal structure in the semiconductor oxide in the semiconductor oxide film. In the obtained semiconductor oxide film, whether the α-Fe ₂ O ₃ crystal structure in the semiconductor oxide is broken or not is determined by, for example, an α-ray diffraction pattern measured using an X-ray diffractometer in an α-ray diffraction pattern. This can be confirmed by the presence or absence of Fe ₂ O ₃ crystals. The heat treatment can be performed using a conventionally known appropriate apparatus such as a high temperature electric furnace. Moreover, the atmosphere in the case of heat processing is not restrict | limited in particular, For example, it can carry out in an atmospheric pressure atmosphere.

  FIG. 1 is a sectional view schematically showing a preferred example of the hydrogen generator 1 of the present invention, and FIG. 2 is a front view of the hydrogen generator 1 shown in FIG. FIG. 1 shows a cross section as viewed from the section line II in FIG. The present invention also provides a hydrogen generator using the above-described semiconductor oxide film of the present invention. As shown in FIGS. 1 and 2, the hydrogen generator 1 of the present invention includes the above-described semiconductor oxide film 2, transparent conductive film 3, transparent substrate 4, and solar cell from the light receiving surface side. And a conductive member 5a, 5b for electrically connecting the transparent conductive film 3 and the solar cell S through the transparent substrate 4 in the thickness direction.

  As the transparent substrate 4 used in the hydrogen generator 1 of the present invention, a light-transmitting substrate is used. Here, “translucency” has a property of transmitting light having a wavelength of about 350 to 1000 nm with almost no absorption, and can be confirmed by measuring a transmission spectrum with a visible ultraviolet spectrophotometer, for example. . As such a transparent substrate 4, a glass substrate, a quartz substrate, etc. can be used, for example. Among these, it is preferable to use a glass substrate because of its excellent heat resistance.

  The thickness of the transparent substrate 4 is not particularly limited, but is preferably in the range of 0.3 to 5 mm. This is because if the thickness of the transparent substrate 4 is less than 0.3 mm, it may be difficult to structurally support the hydrogen generator, and the thickness of the transparent substrate 4 may be 5 mm. This is because processing such as formation of a through hole tends to be difficult. The size and shape of the transparent substrate 4 may be any size as long as it is suitable for use in the hydrogen generator of the present invention. For example, the transparent substrate 4 having a rectangular cross section of 100 to 500 mm in length and 100 to 500 mm in width. Can be suitably used.

The transparent conductive film 3 interposed between the transparent substrate 4 and the semiconductor oxide film 2 of the present invention is not particularly limited as long as it has translucency. For example, ITO (In ₂ Preferred examples include an O ₃ —SnO ₂ ) film, an F-doped SnO ₂ film, and a ZnO film. The “translucency” in the transparent conductive film 3 is the same as the definition described above for the translucency in the transparent substrate 4 and can be confirmed by the same method.

  The thickness of the transparent conductive film 3 in the present invention is not particularly limited, but is preferably in the range of 0.1 to 0.5 μm. When the thickness of the transparent conductive film 3 is less than 0.1 μm, the series resistance tends to increase. When the thickness of the transparent conductive film 3 exceeds 0.5 μm, film peeling or cracking occurs. This is because it tends to be easier. The thickness of the transparent conductive film 3 indicates a value measured using the same method as described above for the thickness of the semiconductor oxide film of the present invention.

A solar cell S is provided on the side of the transparent substrate 4 opposite to the side where the transparent conductive film 3 is formed. The solar cell S can be used without particular limitation as long as it is a solar cell normally used in this field, but at present, it is preferable to use a crystalline silicon (Si) solar cell excellent in long-term reliability. Here, although the solar cell S may be comprised so that it may consist of one solar cell, and may be comprised so that it may consist of a several solar cell, it is high light of the semiconductor oxide film of this invention. In order to draw out a current value, it is preferable to be realized by a plurality of (three in the example shown in FIG. 1) solar cells electrically connected in series. As a characteristic required for the solar cell S, for example, when the photocurrent characteristic of the semiconductor oxide film 2 of the present invention is 4 mA / cm ² , a photocurrent of about 340 mA is generated from the transparent substrate 4. Therefore, it is preferable that the light transmitted through the semiconductor oxide film 2 has characteristics capable of generating a current of about 340 mA or more and a voltage of about 0.5 V per solar cell S.

  In the hydrogen generator 1 of the present invention, conductive members 5 a and 5 b that penetrate the transparent substrate 4 in the thickness direction and electrically connect the transparent conductive film 3 and the solar cell S are provided. The conductive members 5a and 5b are formed, for example, by embedding a conductive material in a plurality of through holes formed in advance at predetermined intervals along one side of the transparent substrate 4 having a square cross section. In the example shown in FIG. 1, a plurality of through holes are previously formed at predetermined intervals along the side of the transparent substrate 4 facing the one side and corresponding to the plurality of conductive members 5a. The conductive member 5b is formed by embedding a conductive member in the through hole. The conductive member 5b is exposed to the electrolyte aqueous solution side in the hydrogen generator 1 shown in FIG. The transparent conductive film 3 formed on the transparent substrate 4 is electrically connected to the solar cell S by such conductive members 5a and 5b. Specifically, the positive electrode Sa and the negative electrode Sb formed one by one on each of the plurality of solar cells S are electrically connected in series via the lead wires 9 between the adjacent solar cells S, The surplus positive electrode Sa is electrically connected to the conductive member 5a, and the negative electrode Sb is electrically connected to the conductive member 5b via the lead wire 9.

  The material for forming the conductive members 5a and 5b is not particularly limited as long as it is a conductive material, and examples thereof include silver and copper. Among them, since the silver paste easily becomes a low-resistance conductor by sintering, it is preferable to form the conductive members 5a and 5b by filling the through-hole and then baking the silver paste.

  Moreover, in the hydrogen generator 1 of the present invention, a plurality of conductive members 5b on the transparent substrate 4 are respectively connected to the plurality of conductive members 5b via the conductive adhesive 7 as in the example shown in FIGS. It is preferable that a wire electrode 6 is provided. The wire electrode 6 rises along the thickness direction of the transparent substrate 4 from the conductive member 5b provided with the base end portion thereof by the conductive adhesive 7, and is bent halfway so as not to contact the semiconductor oxide film 2. The semiconductor oxide film 2 is provided to extend toward the conductive member 5a while facing the semiconductor oxide film 2 with a gap. In order to prevent the tip of the wire electrode 6 from coming into contact with the semiconductor oxide film 2 even when the hydrogen generator 1 of the present invention is laid sideways or tilted, for example, the wire electrode 6 Preferably, the wire electrode 6 is formed of a material such as platinum so as to have rigidity. In addition, the wire electrode 6 may be prevented from contacting the semiconductor oxide film 2 by fixing the tip of the wire electrode 6 to the cover glass 12 of the housing 11 of the hydrogen generator 1. As described above, the wire electrode 6 is provided in close proximity to the semiconductor oxide film 2 so as not to come into contact with the semiconductor oxide film 2, thereby avoiding the structure in which the solar cell S is immersed in the electrolyte solution and is durable. In addition, the resistance can be reduced by reducing the distance between the semiconductor oxide film 2 serving as an anode and the wire electrode 6 serving as a cathode.

  In addition, as the conductive adhesive 7 used for providing the wire electrode 6 on the conductive member 5b, any conventionally known one can be appropriately used without particular limitation as long as it has conductivity and adhesiveness. . Among them, as a suitable conductive adhesive, a conductive adhesive of a type in which a metal filler such as silver, copper or nickel is kneaded with a binder such as an epoxy resin can be exemplified.

  In the hydrogen generator 1 of the present invention, as described above, the transparent substrate 4 on which the semiconductor oxide film 2 and the transparent conductive film 3 of the present invention are sequentially formed is provided with conductive members 5a and 5b penetrating in the thickness direction. This is realized by housing a structure in which the conductive film 3 and the solar cell S are electrically connected together with the aqueous electrolyte solution 8 as shown in the example shown in FIGS. 1 and 2. The housing 11 used in the hydrogen generator 1 of the present invention has an opening on one side, and is fitted into the frame 13 having a shape capable of fitting and holding the structure described above, and the opening of the frame 13. And a cover glass 12. That is, the casing 11 in the hydrogen generator 1 of the present invention has at least a light-transmitting property on the side where one side in the thickness direction of the transparent substrate 4 on which the semiconductor oxide film 2 and the transparent conductive film 3 of the present invention are formed is disposed. When generating hydrogen by water splitting, which will be described later, the side on which the cover glass 12 is provided is used as the light-receiving surface side (in the example shown in FIG. 1, the hydrogen generator 1 is indicated by a white arrow). Shows the sunlight shining on.) The housing 11 is formed to have a space for accommodating the electrolyte aqueous solution 35 between the above-described structure held by the frame 13 and the cover glass 12.

  In the example shown in FIGS. 1 and 2, on the other side in the thickness direction of the transparent substrate 4, the solar cell S is accommodated by fitting the back cover film 14 into the opening of the frame 13 of the housing 11 described above. As the back cover film 14, for example, a film such as a polyvinyl fluoride resin can be used. Further, a film 15 such as an EVA (ethylene vinyl acetate) film or an olefin resin film is interposed between the transparent substrate 4 and the solar cell S and between the solar cell S and the back cover film 14. Is preferred.

  As the aqueous electrolyte solution 8 used in the hydrogen generator 1 of the present invention, an alkaline aqueous solution such as a sodium hydroxide aqueous solution is preferably used. Note that the frame 13 in the housing 11 is preferably formed of a resin (eg, polyethylene, polypropylene, etc.) that is not altered by the electrolyte aqueous solution 8.

In addition, the hydrogen generator 1 of the present invention is characterized in that the casing 11 has outlets 18a and 19a for extracting hydrogen (H ₂ ) 16 and oxygen (O ₂ ) 17 generated by the decomposition of water. To do. In the hydrogen generator 1 of the example shown in FIGS. 1 and 2, the take-out ports 18 a and 19 a are provided in the upper part of the frame 13, respectively, for separating hydrogen 16 and oxygen 17 through the pipes 18 and 19. It is configured to be connected to a known gas separation device (not shown) provided with a hydrogen separation membrane or a polymer membrane. The take-out ports 18a and 19a are also connected to an aqueous electrolyte solution circulation device (not shown) via pipes 18 and 19 so as to circulate the electrolyte solution 8 accommodated in the housing 11 inside. Preferably it is.

The hydrogen generator 1 of the present invention can decompose water into hydrogen 16 and oxygen 17 by the following mechanism. First, sunlight (an arrow in FIG. 1) is irradiated into the hydrogen generator 1 through a cover glass 12 disposed on one side in the thickness direction of the transparent substrate 4 on which the semiconductor oxide film 2 of the present invention is formed. Let Light having a wavelength of up to about 600 nm in the spectrum of sunlight is absorbed by the semiconductor oxide film 2 of the present invention, which is a W-containing Fe ₂ O ₃ film, to generate electrons (e ⁻ ) and holes (h ⁺ ). Electrons excited in the semiconductor oxide film 2 due to the contact potential difference between the semiconductor oxide film 2 and the aqueous electrolyte solution 8 are collected by the transparent conductive film 3 on the transparent substrate 4 and pass through the conductive member 5b to the solar cell S. Flows into the positive electrode. On the other hand, holes move to the surface of the semiconductor oxide film 2. The holes on the surface of the semiconductor oxide film 2 oxidize water that is the solvent of the aqueous electrolyte solution 8 to generate oxygen 17 as follows.

4h ⁺ + 2H ₂ O → O ₂ + 4H ⁺
On the other hand, sunlight having a wavelength of about 600 nm or more transmitted through the semiconductor oxide film 2 is absorbed by the solar cell S to generate photovoltaic power. The solar cell S pushes up the energy level of electrons excited by the semiconductor oxide film 2 sufficiently more negative than the hydrogen generation potential. Therefore, in the wire electrode 6 that is a hydrogen generation electrode, water molecules are reduced and hydrogen 16 is generated as follows.

4H ^{+ +} 4e ^- → 2H ₂
Thus, water can be decomposed into oxygen and hydrogen by irradiating the hydrogen generator 1 of the present invention with sunlight.

  FIG. 3 is a diagram showing the first half of an example of the method of manufacturing the hydrogen generator 1 of the present invention of the example shown in FIGS. 1 and 2 in stages, and FIG. 4 is a diagram showing the latter half in stages. It is. Although the manufacturing method of the hydrogen generator 1 of the present invention as described above is not particularly limited, for example, it can be preferably manufactured by a procedure as shown in FIGS. 3 and 4. Hereinafter, with reference to FIG. 3 and FIG. 4, an example of the manufacturing method of the hydrogen generator 1 of this invention is demonstrated.

  First, as shown in FIG. 3A, a plurality of through holes are formed in a glass transparent substrate 4. Specifically, the case where two rows × 4 through-holes having a diameter of 0.5 mm are formed on the transparent substrate 4 having a size of 100 mm in width × 100 mm in length × 1 mm in thickness is, of course, limited to this. It is not something. The formed through holes are filled with, for example, a silver paste with a dispenser or the like and baked at about 250 ° C., thereby forming conductive members 5 a and 5 b on the transparent substrate 4.

Next, as shown in FIG. 3B, the transparent conductive film 5 is covered with, for example, ITO (In ₂ O ₃ —SnO ₂ ) so as to cover the conductive member 5a on the surface of the transparent substrate 4 on one side in the thickness direction. 3 is formed. For the formation of the transparent conductive film 3, for example, a sputtering method can be suitably used, and the transparent conductive film 3 is formed so as to have the above-described preferable thickness (for example, 0.1 μm).

Next, as shown in FIG. 3C, a W-containing Fe ₂ O ₃ film, which is the semiconductor oxide film 2 of the present invention, is formed on the transparent conductive film 3 formed on one side in the thickness direction of the transparent substrate 4. Form. As described above, the semiconductor oxide film 2 can be suitably formed using, for example, a high-frequency magnetron sputtering apparatus in which two or more types of targets can be installed, for example, under the film formation conditions described above. Specifically, an α-Fe ₂ O ₃ sintered body having a diameter of 4 inches and a thickness of 5 mm is used as the first target, and a WO ₃ sintered body having a diameter of 4 inches and a thickness of 5 mm is used as the second target. The transparent substrate 4 on which the transparent conductive film 3 is formed is placed on a sample holder, heated by a substrate heater, and two targets are simultaneously subjected to high-frequency sputtering on the transparent conductive film 3, thereby achieving a size of 95 mm × 90 mm. And although the case where the semiconductor oxide film 2 of this invention is formed with the thickness (for example, 0.3 micrometer) in the preferable range mentioned above is illustrated, of course, it is not limited to this. Next, the transparent substrate 4 after film formation is taken out of the chamber and subjected to heat treatment in an atmospheric pressure atmosphere at a temperature in the range of 550 to 600 ° C., for example, in a high temperature electric furnace.

  Next, as shown in FIG.3 (d), the solar cell S is mounted in the opposite side to the side in which the transparent conductive film 3 of the transparent substrate 4 was formed. As the solar cell S, for example, a crystalline silicon (Si) solar cell is used, and is electrically connected to the transparent conductive film 3 through a conductive member 5 formed so as to penetrate the transparent substrate 4 in the thickness direction. Specifically, for example, when using a plurality of solar cells S (three in the example shown in FIGS. 3 and 4), one positive electrode Sa and one negative electrode Sb formed on each solar cell S, Are electrically connected in series via the lead wires 9 between the adjacent solar cells S, and the surplus positive electrode Sa is electrically connected to the conductive member 5a and the negative electrode Sb is electrically connected to the conductive member 5b via the lead wire 9. To connect to.

  As described above, it is preferable to interpose a film 15 such as an EVA film between the transparent substrate 4 and the solar cell S. Further, a film 15 such as an EVA film is laminated on the side opposite to the transparent substrate 4 side of the solar cell S, and a back cover film 14 is further provided. These films are preferably laminated at about 150 ° C. after lamination.

  Next, as shown in FIG. 4 (a), the conductive member 5b exposed on one side in the thickness direction of the transparent substrate 4 was bent substantially vertically using a conductive adhesive 7. The base end portion of the wire electrode 6 is bonded and fixed so that the base end portion is substantially parallel to the thickness direction of the transparent substrate 4.

  Subsequently, as shown in FIG. 4B, the cover glass 12 side of the structure shown in FIG. 4A is arranged on one side in the thickness direction of the transparent substrate 4 on which the semiconductor oxide film 2 is formed. In this way, for example, by being fitted into the resin frame 13, the housing 11 is fixedly accommodated. Thereafter, an aqueous electrolyte solution 8 is injected between the transparent substrate 4 on which the semiconductor oxide film 2 is formed and the cover glass 12 through a take-out port 19 a formed in advance in the frame 13. As the electrolyte aqueous solution 8, for example, a 1M NaOH aqueous solution can be used. In this way, the hydrogen generator 1 of the present invention shown in FIGS. 1 and 2 can be manufactured.

  FIG. 5 is a cross-sectional view schematically showing a hydrogen generator 31 of another preferred example of the present invention. The hydrogen generator 31 of the example shown in FIG. 5 is the same as the hydrogen generator 1 of the example shown in FIG. 1 except for a part, and parts having the same configuration are denoted by the same reference numerals. Therefore, the description is omitted. In the hydrogen generator 31 of the example shown in FIG. 5, the space part which accommodates the electrolyte aqueous solution 8 between the semiconductor oxide film 2 and the cover glass 12 (specifically, between the semiconductor oxide film 2 and the wire electrode 6). In addition, an ion conductive film 32 is provided. In the hydrogen generator 31 of the example shown in FIG. 5, the upper part of the frame 34 constituting the housing 33 is between the cover glass 12 and the ion conductive film 32 and between the ion conductive film 32 and the transparent substrate 4. In between, take-out ports 35a and 36a are formed, respectively.

  When the hydrogen generator 31 of the example having the above-described configuration shown in FIG. 5 is irradiated with sunlight, oxygen 17 is generated from the surface of the semiconductor oxide film 2 by the above-described mechanism, and from the surface of the wire electrode 6. Hydrogen 16 is generated. Since the hydrogen 16 and oxygen 17 generated in this way do not permeate the ion conductive film 32, the hydrogen 16 and the electrolyte aqueous solution 8 are individually taken out together with the electrolyte aqueous solution 8 from the take-out port 35a and 36a. Can do. These take-out ports 35a and 36a are connected to, for example, an external electrolyte aqueous solution circulation device (not shown) via pipes (not shown), respectively, and are respectively connected to the pipes in front of the electrolyte aqueous solution circulation device. , Hydrogen 16 and oxygen 17 can be recovered individually. Thus, unlike the hydrogen generator 1 of the example shown in FIG. 1, the hydrogen generator 31 of the example shown in FIG. 5 does not need to be connected to the gas separation device outside the apparatus. Although not shown, openings for allowing the electrolyte aqueous solution 8 to flow into the housing 33 are also formed in the upper part of the frame 34 at positions corresponding to the extraction ports 35 a and 36 a in the thickness direction of the substrate 4. Each opening is connected to the above-described external electrolyte aqueous solution circulation device through a pipe.

  Note that the ion conductive film 32 used in the hydrogen generator 41 of the example shown in FIG. 5 is not particularly limited, and any conventionally known appropriate ion conductive film can be used. Examples of 32 include Nafion (manufactured by DuPont).

  Hereinafter, although an example of an experiment is given and the present invention is explained in detail, the present invention is not limited to these.

<Experimental example 1>
A plurality of transparent substrates having a transparent conductive film on one surface are prepared, and six types of Fe ₂ O ₃ films having different W contents are formed on the transparent conductive film of each transparent substrate at substrate temperatures of 300 ° C. and 400 ° C. Film formation was performed under the conditions, and five types of Fe ₂ O ₃ films having different W contents were formed under the conditions of the substrate temperatures of 200 ° C. and 500 ° C. to produce a total of 22 types of Fe ₂ O ₃ films.

In forming the Fe ₂ O ₃ film, a high-frequency magnetron sputtering apparatus is used, an α-Fe ₂ O ₃ sintered body having a diameter of 4 inches and a thickness of 5 mm and a WO ₃ sintered body are used as the targets, the substrate temperature is room temperature, 100 , 200 ° C., 400 ° C., 600 ° C., vacuum chamber vacuum degree 1 Pa, introduced gas Ar: O ₂ = 25: 3 (sccm), α-Fe ₂ O ₃ film sintered body and WO ₃ sintered body was carried out by cells at the same time is sputtering. The W content of each Fe ₂ O ₃ film is such that the RF power to the α-Fe ₂ O ₃ sintered body is fixed to 150 W, the substrate-target distance is fixed to 100 mm, and the RF power to the WO ₃ sintered body is fixed. Was changed by changing the distance between the substrate and the target in the range of 200 to 250 mm. The film thickness can be adjusted by changing the sputtering time, and the film thicknesses of the 22 types of photocatalysts are all about 0.2 to 0.3 μm. Each Fe ₂ O ₃ film was heat-treated at 600 ° C. for 1 hour in an air atmosphere using a high temperature electric furnace after film formation.

Table 1 shows the results of photoelectrochemical measurements on each Fe ₂ O ₃ film. For the photoelectrochemical measurement, a 0.1 W NaOH aqueous solution as an electrolyte, Pt as a counter electrode, a silver-silver chloride electrode as a reference electrode, and a 300 W xenon lamp equipped with a cutoff filter having a wavelength of 350 nm or less as a light source were used. As for the photocurrent value, the current value (unit: mA / cm ² ) at 0.7 V of the current-potential curve obtained by electrochemical measurement is shown in Table 1. In Table 1, the molar ratio of W to Fe indicates a value measured by fluorescent X-ray analysis of each Fe ₂ O ₃ film.

From the results shown in Table 1, it can be seen that the Fe ₂ O ₃ film containing W provides good photoelectric conversion characteristics. Further, among W-containing Fe ₂ O ₃ films, particularly preferable photoelectric conversion characteristics are obtained when the molar ratio of W and Fe is in the range of 0.02 to 0.08 (particularly 0.04). It was experimentally confirmed that it was obtained. Furthermore, it can be seen that the film forming conditions are preferably in the range of 300 to 400 ° C.

<Experimental example 2>
In the same manner as in Experimental Example 1, after forming a W-containing Fe ₂ O ₃ film having a molar ratio of W and Fe of 0.04 at a substrate temperature of 300 ° C., using a high temperature electric furnace, 500 ° C., 550 ° C. Heat treatment was performed at 600 ° C. and 700 ° C. for 1 hour in an air atmosphere. Table 2 shows the results of photoelectrochemical measurements performed on the obtained semiconductor oxide films in the same manner as described above.

As can be seen from Table 2, it was experimentally confirmed that the optimum temperature for the heat treatment applied to the W-containing Fe ₂ O ₃ film after film formation was 550 to 600 ° C.

FIG. 6 is a graph showing an X-ray diffraction pattern of the W-containing Fe ₂ O ₃ film after heat treatment at 600 ° C. From FIG. 6, several α-Fe ₂ O ₃ crystal peaks are observed in the formed W-containing Fe ₂ O ₃ film, and W is within a range where the structure of the α-Fe ₂ O ₃ crystal is not broken. Including it was considered preferable for obtaining good photoelectric conversion characteristics.

  The hydrogen generator of the present invention is suitable as a hydrogen generator for producing hydrogen, which is clean energy instead of non-fossil fuel, and is installed on the rooftop or roof of a building that is irradiated with sunlight to generate hydrogen. Can contribute to energy saving.

It is sectional drawing which shows typically the hydrogen generator 1 of a preferable example of this invention. It is a front view of the hydrogen generator 1 shown in FIG. It is a figure which shows the first half part of an example of the example of the manufacturing method of the hydrogen generator of this invention of the example of FIG. 1 and FIG. 2 in steps. It is a figure which shows the latter half part of an example of the manufacturing method of the hydrogen generator of this invention of the example of this invention shown in FIG. 1 and FIG. 2 in steps. It is sectional drawing which shows typically the hydrogen generator 31 of a preferable example of this invention. It is a graph showing the X-ray diffraction pattern of W-containing Fe ₂ O ₃ film after the heat treatment at 600 ° C.. It is a figure which shows typically an example of the conventional typical tandem cell.

Explanation of symbols

  1,31 Hydrogen generator, 2 semiconductor oxide film, 3 transparent conductive film, 4 transparent substrate, 5a, 5b conductive member, S solar battery, Sa solar battery positive electrode, Sb solar battery negative electrode, 6 wire electrode, 7 conductive adhesive, 8 electrolyte solution, 9 lead wire, 11, 33 housing, 12 cover glass, 13, 34 frame, 14 back cover film, 15 film, 16 hydrogen, 17 oxygen, 18, 19 pipe, 18a, 19a, 35a, 36a Extraction port, 32 ion conductive film.

Claims (3)

A film formed of a semiconductor oxide that absorbs light and generates electrons and holes, and the semiconductor oxide has a W-containing Fe ₂ O ₃ ratio of W to Fe in an atomic ratio of 0.02 to 0.08. A semiconductor oxide film. A method for producing a W-containing Fe ₂ O ₃ film having an atomic ratio of W to Fe of 0.02 to 0.08,
A method for producing a semiconductor oxide film, comprising: a step of forming a film by a sputtering method using α-Fe ₂ O ₃ and WO ₃ as a target material; and a step of heat-treating the formed film at 550 to 600 ° C. From the light receiving surface side, the semiconductor oxide film according to claim 1, a transparent conductive film, a transparent substrate, and a solar cell are provided at least,
A hydrogen generating apparatus, wherein a conductive member that penetrates the transparent substrate in a thickness direction and electrically connects the transparent conductive film and the solar cell is provided.

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