JP2006302695A - Photoelectrochemical cell and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectrochemical cell enhanced in energy conversion efficiency by preventing a reverse electron transfer reaction by eliminating IR loss on an interfacial surface between photocatalytic particles and a conductive porous film; and to provide its manufacturing method. <P>SOLUTION: This photoelectrochemical cell is characterized by having a barrier membrane 3 including: a photocatalytic electrode 5 composed by forming a coating (titanium dioxide coating 9) on one surface of a conductive porous body (titanium porous membrane 8) and by forming a photocatalyst (photocatalytic particles 10) on the other surface of the conductive porous body (titanium porous membrane 8); an electrode (platinum-supported carbon electrode 6) used as a counter electrode of the photocatalytic electrode 5; and a proton conductor (proton conducting membrane 7) sandwiched between the respective electrodes 5 and 6. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a photoelectrochemical cell applied to an energy conversion device that converts light energy into chemical energy, and a method for manufacturing the same.

  In order to effectively use solar energy, technology for converting and storing solar energy into a form that can be easily used has been actively developed. A solar cell is a typical example, but since the cost is high, it is not popularized and development of a cheaper system is desired.

Therefore, research on technology for converting light energy into chemical energy using a photocatalyst has been underway. When sunlight is irradiated onto the photocatalyst, the photocatalyst absorbs light energy to generate electrons and holes, and causes various chemical reactions. Among photocatalysts, in particular, titanium dioxide (TiO ₂ ) has a deep valence band position, and the oxidizing power due to the generated holes is stronger than chlorine or ozone.

For example, a method for decomposing water using a photocatalyst is disclosed (see Patent Document 1). The water splitting apparatus used in the water splitting method has a configuration in which photocatalyst powder is dispersed in water and the photocatalyst powder is irradiated with sunlight. When the photocatalyst is irradiated with sunlight, electrons in the valence band of the photocatalyst are excited to the conduction band, and at the same time, holes are formed in the valence band. Holes oxidatively decompose water to generate oxygen, and excited electrons reduce protons (H ⁺ ) generated by oxidative decomposition of water to generate hydrogen. However, in the above water splitting apparatus, since the outlets for hydrogen and oxygen are integrated into one, the gas obtained by splitting water becomes a mixed gas of hydrogen and oxygen, and separates hydrogen and oxygen separately. There was a need. In addition, when hydrogen and oxygen are generated at the same location, so-called reverse reaction, in which water is generated from hydrogen and oxygen, proceeds, and energy conversion efficiency (the obtained hydrogen enthalpy / incident light energy amount) is reduced. It was.

Moreover, the technique of the carbon dioxide gas reduction apparatus which reduces a carbon dioxide gas using a photocatalyst is also disclosed (refer patent document 2). In the present technology, an anode configured by forming a first photocatalyst on a flat plate on a conductive layer and a cathode configured by supporting a second photocatalyst on a conductive layer are used to provide a gap between both electrodes. A flow of electrons is generated, and carbon dioxide gas supplied to the anode side is reduced to generate fuel (methanol or the like). Furthermore, the oxygen supplied to the cathode side is oxidized to generate oxygen. This carbon dioxide reduction device can separate and recover fuel (such as methanol) and oxygen generated at the anode and cathode.
JP-A-10-218601 JP 2001-97889 A

  However, since the photocatalyst is applied to the conductive layer at the anode and cathode of the carbon dioxide gas reduction apparatus, the photocatalyst and the conductive layer are not fused, and IR loss may occur at the interface between the photocatalyst and the conductive layer. As a result, the energy conversion efficiency may be reduced.

  On the anode side, when the photocatalyst absorbs sunlight, electrons in the valence band of the photocatalyst are excited to the conduction band, and the excited electrons move to the conductive layer. However, at this time, if the conductive layer and the electrolytic solution (water) are electrically short-circuited, the excited electrons move to the electrolytic solution (water) side opposite to the conductive layer, and the reverse electron transfer reaction proceeds. However, there is a risk that water is generated from once generated oxygen and protons and the energy conversion efficiency is lowered.

  The present invention has been made to solve the above-mentioned problems. That is, the photoelectrochemical cell of the present invention has a coating film formed on the surface of the conductive porous body and one of the conductive porous bodies. A gist is provided with a diaphragm having a photocatalyst electrode having a photocatalyst formed on the surface thereof, an electrode serving as a counter electrode of the photocatalyst electrode, and a proton conductor sandwiched between the electrodes.

  The first method for producing a photoelectrochemical cell in the present invention comprises forming a film on the surface of a conductive porous body, forming a photocatalyst on one surface of the conductive porous body, and forming a photocatalytic electrode. The gist is that a proton conductor and an electrode serving as a counter electrode of the photocatalyst electrode are sequentially stacked on the side opposite to the surface on which the photocatalyst is formed, and pressure-bonded at a temperature higher than the softening temperature of the proton conductor to form a diaphragm. .

  According to the second method for producing a photoelectrochemical cell of the present invention, a film is formed on the surface of the conductive porous body, and a photocatalyst is formed by forming a photocatalyst on one surface of the conductive porous body. On the opposite side of the surface on which the photocatalyst is formed, a proton conductor and an electrode serving as a counter electrode of the photocatalyst electrode are sequentially stacked and pressed at a temperature higher than the temperature at which the proton conductor softens, and the conductive porous body is proton-conductive. The oxide film formed on the conductive porous body opposite to the surface coated with the photocatalyst particles is removed through the body, and an electrode material as a counter electrode is coated on the removed surface of the oxide film, and the proton conductor The gist is that the membrane is pressure-bonded at a temperature equal to or higher than the softening temperature.

  According to the photoelectrochemical cell of the present invention, the IR loss at the interface between the photocatalyst particles and the conductive porous membrane can be eliminated to prevent the reverse electron transfer reaction and to increase the energy conversion efficiency.

  According to the first method for producing a photoelectrochemical cell of the present invention, there is no IR loss at the interface between the photocatalyst particles and the conductive porous membrane, and a diaphragm in which reverse electron transfer reaction is prevented can be obtained.

  According to the second method for producing a photoelectrochemical cell of the present invention, the photocatalyst electrode and the counter electrode are made conductive through the conductive porous body, so that it is not necessary to join the short-circuit wire. A simplified photoelectrochemical cell can be obtained.

  Hereinafter, a photoelectrochemical cell according to an embodiment of the present invention and a method for producing the same will be described with reference to the accompanying drawings.

First Embodiment A PEM (Polymer Electrolyte Membrane) type photowater electrolysis cell will be described as a photoelectrochemical cell according to an embodiment of the present invention.

  FIG. 1 (a) is a cross-sectional view schematically showing a PEM type photowater electrolysis cell, and FIG. 1 (b) is an enlarged cross-sectional view of a diaphragm. The PEM type photowater electrolysis cell 1 has a diaphragm 3 disposed in the center of a container 2, two water storage portions 4 a and 4 b partitioned by the diaphragm 3 are formed inside the container 2, and raw materials are stored in the water storage portions 4 a and 4 b. Each water is stored.

The diaphragm 3 includes a photocatalyst electrode 5, a platinum-supporting carbon 6 that is an electrode serving as a counter electrode of the photocatalyst electrode 5, and a proton conductive membrane 7 sandwiched between the electrodes 5 and 6. The photocatalytic electrode 5 has a titanium dioxide (TiO ₂ ) film 9 as a film formed on the surface of a titanium (Ti) porous film 8 that is a conductive porous film, and one of the titanium (Ti) porous films 8. The photocatalyst particles 10 are fused to the surface. Seal portions 11a and 11b for preventing water leakage from the water storage portions 4a and 4b are formed on the upper and lower sides of the both sides of the diaphragm 3, and the diaphragm 3 is supported by the seal portions 11a and 11b. An external short-circuit line 12 is connected to the photocatalyst electrode 5 and the platinum-supporting carbon electrode 6, a bias power source is installed on the external short-circuit line 12, a bias voltage is applied, and excited electrons ( to enhance the energy of) ^- e.

  Further, the configuration of the diaphragm 3 will be described in detail.

The photocatalyst particle 10 plays a role of absorbing light having a wavelength less than a specific wavelength of sunlight and exciting electrons (e ⁻ ) existing in the valence band to the conduction band. It is preferable to use a semiconductor whose charged position is lower in energy than the oxidation-reduction potential of oxygen (1.23 V vs. NHE). Here, titanium dioxide (TiO ₂ ) was used as the photocatalyst particles 10, but in addition to titanium dioxide, iron oxide (Fe ₂ O ₃ ), niobium oxide (Nb ₂ O ₅ ), strontium titanate (SrTiO ₃ ), Barium titanate (BaTiO ₃ ), zinc oxide (ZnO), tin dioxide (SnO ₂ ), cadmium sulfide (CdS), InTaO ₄ , In _1-x Ni _x TaO _4, Rb ₂ La ₂ TiO ₁₀ , Ta ₂ O ₅ , TaON and Ta ₃ N ₅ can be selected from semiconductors that satisfy the above conditions.

The titanium (Ti) porous film 8, which is a conductive porous film, is a film that serves as a conductive portion that transmits electrons (e ⁻ ) excited by the photocatalyst particles 10 to the platinum-supporting carbon 6 side. An enlarged cross-sectional view of the titanium porous film 8 is shown in FIG. 2. In the titanium porous film 8, a titanium dioxide (TiO ₂ ) film 9 is formed on the surface of titanium metal formed by fusing titanium particles. . The titanium porous film 8 serves as a conductive portion, and the titanium dioxide film 9 prevents leakage of electrons (e ⁻ ) from the titanium porous film 8 to the electrolyte side, and prevents a short circuit between water and the titanium particles 5a. ing. The conductive porous film is not limited to the titanium porous film 8 and is preferably formed from a metal whose metal oxide is a semiconductor or an insulator. For example, a porous film formed of a material selected from titanium, aluminum, silicon, zirconium, niobium, zinc, tin, tungsten, iron, bismuth, and the like can be used. By forming a conductive porous film from the exemplified materials, an insulator coating or a semiconductor coating can be formed on the outer periphery, and a reverse electron transfer reaction at the photocatalytic electrode 5 during photowater electrolysis can be prevented. .

The proton conducting membrane 7 has a role of transporting protons (H ⁺ ) generated by the reaction of the photocatalyst particles 6 from the anode (photocatalyst electrode 5) side to the cathode (platinum-supported carbon electrode 6) side with a proton concentration gradient as a driving force. It is a film that fulfills. The proton conductive membrane 7 is not particularly limited as long as it has a function of conducting protons (H ⁺ ), and in order to have a structure in which a water storage part for storing water as a raw material is partitioned at two locations, protons are used. It is preferable to use a solid electrolyte membrane as the conductive membrane 7. As the solid electrolyte membrane, a perfluorosulfonic acid membrane represented by Nafion (registered trademark, manufactured by DuPont Co., Ltd.) can be used.

  The platinum-supporting carbon electrode 6 is used as the counter electrode of the photocatalyst electrode 5, but any electrode having a similar function such as a platinum mesh can be used. In addition to platinum, copper, ruthenium, rhodium, iridium, etc. can be used as the catalyst supported on the carbon electrode.

The structure of the diaphragm 3 is not limited, and the titanium dioxide (TiO ₂ ) coating 9 on the surface of the titanium porous film 8 that is a conductive porous film may also serve as the photocatalyst particles 10. With such a configuration, it is not necessary to apply the photocatalyst particles 10 to the titanium porous film 8, and the manufacturing method of the diaphragm 3 can be simplified.

  In addition, if the material of the coating film and the photocatalyst are different, the wavelength range of light to be absorbed is different, which may increase the energy conversion efficiency.

  Next, the operation of the PEM type photowater electrolysis cell 1 will be described with reference to FIG.

  When sunlight is irradiated onto the photocatalyst particles 10, light having a wavelength corresponding to the band gap between the valence band and the conduction band of the photocatalyst particles 10 is absorbed. Here, the relationship between the energy band gap E of the valence band and the conduction band and the light absorption wavelength λ is expressed by the following chemical formulas (1) and (2).

E = hν (h: Planck's constant) ... Chemical formula (1)
λ = c / ν (c: speed of light) (2)
That is, when light having a wavelength of λ or less is absorbed by the photocatalyst particle 10, the absorbed light is used as energy for exciting electrons from the valence band to the conduction band. The excited electrons (e ⁻ ) pass through the titanium porous film 8 and reach the external short-circuit line 12. At this time, since the titanium porous film 8 and the photocatalyst particles 10 are fused, the IR loss at the interface between the titanium porous film 8 and the photocatalyst particles 10 can be minimized.

On the other hand, holes are formed in the valence band of the photocatalyst particles 10, the reaction of the chemical formula (3) proceeds, and oxygen (O ₂ ) is generated by the oxidation of water.

^{_{2H 2 O → 4H + + O}} 2 + 4 e - ... chemical formula (3)
A titanium dioxide (TiO ₂ ) film is formed on the surface of the titanium porous film 8, and the chemical formula (4) proceeds when electrons (e ⁻ ) leak from the titanium porous film 8 to the electrolyte (water) side. ) Can be suppressed.

4H ⁺ + O ₂ + 4e ⁻ → 2H ₂ O ... Chemical formula (4)
The energy state of the excited electrons is set higher than the redox potential of hydrogen due to the bias voltage load installed on the external short-circuit line 12. When a bias voltage is applied, the electrons are energetically higher than the redox potential of hydrogen, and the excited electrons (e ⁻ ) are transported from the photocatalyst electrode 5 to the protons (H ⁺ ) And a reaction shown in the following chemical formula (5) proceeds to generate hydrogen (H ₂ ).

2H ^{+ +} 2e ^- → H ₂ ... Chemical formula (5)
Based on the above principle, water is decomposed into hydrogen and oxygen using solar energy.

  In the PEM photowater electrolysis cell 1, the conduction charge position is lower than the oxidation-reduction potential of hydrogen so that the conduction charge position is lower in energy than the oxidation-reduction potential of hydrogen or an overvoltage necessary for water electrolysis is applied. It is assumed that a photocatalyst that is not high in energy is used. For this reason, the reaction of the chemical formula (5) does not proceed only by connecting the external short-circuit wire 12 to the electrodes 5 and 6. For this reason, a bias voltage is loaded on the external short-circuit line 10 to advance the reaction of the chemical formula (5). However, when the photocatalyst particles 10 whose conduction charge position is sufficiently higher in energy than the redox potential of hydrogen are used, it is needless to say that it is not necessary to apply a bias voltage on the external short-circuit line 12.

  Furthermore, the manufacturing method of the photoelectrochemical cell which concerns on embodiment of this invention is demonstrated.

  A method for producing a photoelectrochemical cell according to an embodiment of the present invention includes forming a coating on the surface of a conductive porous membrane and forming photocatalytic particles on one surface of the conductive porous membrane to form a photocatalytic electrode. The proton conductive membrane and the counter electrode of the photocatalyst electrode are sequentially stacked on the side opposite to the surface where the photocatalyst particles of the obtained photocatalyst electrode are arranged, and pressure-bonded at a temperature higher than the softening temperature of the proton conductive membrane. A diaphragm is used. In this manner, the photocatalyst electrode and the counter electrode are overlapped with each other through the proton conducting membrane and then subjected to pressure bonding to improve the adhesion of the diaphragm, and further, protons are added to the three-phase interface, which is a reaction field for generating hydrogen and oxygen. Can be easily moved.

In the method for producing a photoelectrochemical cell, a thermal oxidation method, a chemical vapor deposition method (CVD), or an anodic oxidation method can be used as a method for forming a film on the surface of the conductive porous film. When using a thermal oxidation method or an anodic oxidation method, it is necessary to apply photocatalyst particles to the conductive porous surface in advance. In the case of using the anodizing method, the proton conductor and the photocatalyst particles may be pressure-bonded, and then the surface of the conductive porous film may be anodized to produce a diaphragm. When a semiconductor film or an insulator film is formed on a titanium porous film using the chemical vapor deposition method, in particular, a titanium (TiO ₂ ) film can be formed on the entire surface of the titanium particles in the titanium porous film. . Thus, by using a thermal oxidation method, a chemical vapor deposition method or an anodic oxidation method, a semiconductor film or an insulator film can be formed on the conductive porous film. Reverse electron transfer reaction can be prevented. In addition, when forming a film on the surface of the conductive porous film by using the anodizing method, after pressure bonding the conductive porous film to the proton conductor, the surface of the conductive porous film is anodized. A film can also be formed. Thereby, a coating film can be formed on the surface of the conductive porous membrane in the final step of the manufacturing method of the diaphragm.

  In addition, as a method for forming a film on the surface of the conductive porous film, an ozone oxidation method, a plasma oxidation method, or the like may be used.

  As a method for forming a photocatalyst on the conductive porous film, any one of a thermal oxidation method, an anodic oxidation method and a chemical vapor phase method can be used. When the thermal oxidation method or the anodic oxidation method is used, a colloid solution containing photocatalyst particles is applied on the conductive porous film in advance. When the photocatalyst particles are previously applied on the conductive porous film in this way and then a film is formed, the conductive porous film and the photocatalyst particles can be fused. When the conductive porous membrane and the photocatalyst particles are fused, IR loss at the interface between the two can be reduced, and the reverse electron reaction during photowater electrolysis can be prevented.

  Further, three methods for manufacturing the diaphragm 3 of the PEM type photowater electrolysis cell shown in FIG.

(1) First Method First, a titanium porous film is produced. A spherical Ti particle powder having a particle diameter of 45 μm to 150 μm and a binder (polyvinyl butyral) are charged into an organic solvent, and mixed and stirred to prepare a slurry. The prepared slurry is made into a thin film by the doctor blade method, and the obtained thin film is introduced into a vacuum sintering furnace. After evacuating the vacuum sintering furnace, the thin film is degreased at 500 ° C. and then sintered at 1050 ° C. to 1350 ° C. to form a porous titanium membrane.

As shown in FIG. 4 (a), a slurry 102 containing powder of photocatalyst particles 101 is applied onto the obtained titanium porous membrane 100 using a doctor blade method. Thereafter, when the titanium porous membrane 100 coated with the photocatalyst particles 101 is fired at 400 ° C. to 800 ° C., a photocatalytic electrode 104 having a TiO ₂ coating 103 formed on the surface is obtained as shown in FIG.

  Next, a paste-like mixture is prepared by uniformly mixing carbon fine particles coated with platinum catalyst and a solution mainly composed of lower alcohol in which the same kind of perfluorosulfonic acid polymer used in the proton conducting membrane is dissolved. To do. After applying the prepared paste-like mixture on the proton conducting membrane, the produced photocatalytic electrode is placed on the side opposite to the application surface of the mixture. Thereafter, hot pressing is performed under conditions of a press temperature of 120 ° C. to 150 ° C. and a press pressure of 1 MPa to 5 MPa. Then, the photocatalyst electrode is pressure-bonded to the proton conductive film, and as shown in FIG. 4C, the photocatalyst electrode 104 is formed on one surface of the proton conductive film 105, and platinum is supported on the surface opposite to the photocatalyst electrode 104. A carbon electrode 106 is formed, and the diaphragm 107 can be obtained.

  In order to prevent the proton conductive membrane 105 from being broken by the photocatalytic electrode 104, it is desirable that the proton conductive membrane 105 has a certain thickness or more. When a Nafion membrane is used as the proton conductive membrane 105, it is desirable that the thickness of the Nafion membrane be 50 μm or more.

(2) Second Method In the second method, first, the slurry 102 containing the powder of the photocatalyst particles 101 is applied onto the titanium porous film 100 by using a doctor blade method (FIG. 4A). The titanium porous film 100 coated with the photocatalyst particles 101 is baked at 400 ° C. to form a photocatalyst layer of the photocatalyst particles 101 on the surface of the titanium porous film 100. The titanium porous film 100 on which the photocatalyst layer is formed is anodized to form a TiO ₂ film 103 on the surface. More specifically, the titanium porous membrane 100 formed with the photocatalytic layer is used as a working electrode, the counter electrode is used as a carbon electrode, and an aqueous solution of H ₃ PO ₄ 0.3 mol / l and H ₂ SO ₄ 1.5 mol / l at 200 V. Perform low voltage electrolysis. By this operation, the TiO ₂ coating 103 can be formed on the surface of the titanium porous membrane 100. The subsequent manufacturing procedure is the same as that of the first method described above.

(3) Third Method In the third method, first, the slurry 102 containing the photocatalyst particles 101 is applied onto the titanium porous film 100 by using a doctor blade method (FIG. 4A). The titanium porous film 8 coated with the photocatalyst is baked at 400 ° C. to 800 ° C. At this time, the TiO ₂ film 103 can be formed on the surface of the titanium porous film (FIG. 4B). Thereby, conductivity between the photocatalyst particles 101 and the titanium porous film 100 is maintained, and at the same time, a TiO ₂ film 103 is formed between the electrolytic solution (water) and the titanium porous film 100 (FIG. 4 (c)).

  Next, a paste-like mixture is prepared by uniformly mixing carbon fine particles coated with platinum catalyst and a solution mainly composed of lower alcohol in which the same kind of perfluorosulfonic acid polymer used in the proton conducting membrane is dissolved. To do. After applying the prepared paste-like mixture on the proton conducting membrane, the produced photocatalytic electrode 104 is disposed on the side opposite to the application surface of the mixture. Thereafter, hot pressing is performed under conditions of a pressing temperature of 120 ° C. to 150 ° C. and a pressing pressure of 1 MPa to 5 MPa, and the photocatalytic electrode 104 is pressure-bonded to the proton conducting membrane 105 to form a diaphragm 107 shown in FIG.

Thereafter, the obtained diaphragm 107 was subjected to constant voltage electrolysis at 200 V in an aqueous solution of H ₃ PO ₄ 0.3 mol / l and H ₂ SO ₄ 1.5 mol / l, and a TiO ₂ coating produced during the process of manufacturing the diaphragm These defects can be selectively sealed.

  As described above, according to the present embodiment, the PEM type photowater electrolysis cell is configured by connecting the external short-circuit wire between the photocatalyst electrode in the diaphragm and the counter electrode, so that the hydrogen generation site and the oxygen generation The site can be separated. For this reason, hydrogen and oxygen produced by the decomposition of water can be separated and recovered, and the energy conversion efficiency can be increased.

  In addition, according to the present embodiment, since the bias power supply is installed on the external short-circuit line, even when the energy level of the semiconductor conduction band does not reach the redox potential of hydrogen, the bias voltage is applied to decompose water. It becomes possible.

  Furthermore, according to the present embodiment, since electrons excited by the photocatalyst particles flow to the counter electrode through the conductive porous film, the photocatalyst particles are carried on the transparent electrode, or only the photocatalyst itself flows electrons. The IR loss in the surface direction can be reduced as compared with the case of the path. As a result, the energy conversion efficiency can be increased, and the PEM photowater electrolysis cell can be easily enlarged.

Second Embodiment In this embodiment, a PEM type photowater electrolysis cell to which an improved diaphragm is applied will be described. In addition, about the structure same as the PEM type photowater electrolysis cell 1 shown in 1st Embodiment, the description is abbreviate | omitted using the same code | symbol.

  FIG. 5 (a) is a cross-sectional view of the PEM type photowater electrolysis cell according to the embodiment of the present invention, and FIG. 5 (b) is an enlarged cross-sectional view of the diaphragm. An external short-circuit line is not connected to the diaphragm 21 of the PEM type photowater electrolysis cell 20. In the diaphragm 21 shown in FIG. 5 (b), the titanium porous membrane 8 is embedded in the proton conducting membrane 7, and the titanium porous membrane 8 has a structure that penetrates the proton conducting membrane 7. Further, the titanium porous membrane 8 is electrically connected to the photocatalyst particles 10 and the platinum-supporting carbon electrode 6 respectively formed on both sides of the proton conducting membrane 7.

As the photocatalyst particles 6 in the diaphragm 21 of the PEM type photowater electrolysis cell 20, the valence charge position is energetically lower than the redox potential of oxygen (1.23 V vs. NHE), and the conduction charge position is redox of hydrogen. A material that is energetically higher than the potential (0V vs. NHE) is used. As photocatalyst particles 10, titanium strontium oxide (SrTiO ₃ ), titanium dioxide (TiO ₂ ), zirconium oxide (ZrO ₃ ), potassium tantalum oxide (KTaO ₃ ), cadmium selenide (CdSe), cadmium sulfide (CdS), InRaO ₄ , In _1-x Ni _x TaO _4, Rb ₂ La ₂ TiO ₁₀ , Ta ₂ O ₅ , TaON, Ta ₃ N ₅ and other semiconductors.

  The operation of the PEM photoelectrolysis cell 20 will be described with reference to FIG.

  First, when sunlight is irradiated onto the photocatalyst particle 10, light having a wavelength corresponding to the band gap between the valence band and the conduction band of the photocatalyst particle 10 is absorbed, as in the first embodiment. At this time, the difference from the first embodiment is that, as shown in FIG. 6, the conduction charge position of the photocatalyst particle 10 is at a position lower than the redox potential of hydrogen. When the conduction charge position of the photocatalyst particles 10 is lower than the redox potential of hydrogen, it is not necessary to apply a bias voltage, and hydrogen can be generated on the platinum-supporting carbon electrode 6 side.

  The titanium porous film 8 in the diaphragm 21 is in contact with the platinum-supporting carbon electrode 6, and electrons excited by the photocatalyst particles 10 pass through the titanium porous film 8 and directly to the platinum-supporting carbon electrode 6. Therefore, it is not necessary to connect an external short-circuit line.

  Next, a method for manufacturing the PEM type photowater electrolysis cell 20 will be described.

  First, the conductive porous membrane coated with the photocatalyst and the proton conductive membrane are overlapped and pressure-bonded at a temperature higher than the temperature at which the proton conductive membrane softens, and then the conductive porous membrane is penetrated through the proton conductive membrane. After that, after removing the oxide film on the conductive porous membrane opposite to the photocatalyst application surface and applying the electrode catalyst layer to the oxide film removal surface, the membrane is again pressure-bonded at a temperature higher than the temperature at which the proton conductive membrane softens. To do. Furthermore, it demonstrates in detail using FIG. First, a titanium porous membrane is produced. The method for producing the titanium porous membrane is the same as that in the first embodiment.

As shown in FIG. 7 (a), the slurry 102 containing the powder of the photocatalyst particles 101 is applied on the titanium porous film 100 by using a doctor blade method, and then fired at 400 ° C. to 800 ° C. to photocatalyst electrode 104. And In the photocatalyst electrode 104 obtained after firing, the photocatalyst particles 101 and the titanium porous film 100 are fused as shown in FIG. 7B, and the conductivity between the photocatalyst particles 101 and the titanium porous film 100 is fused. Is preserved. In addition, a TiO ₂ film 103 having low electron conductivity is formed on the surface of the titanium porous film 100.

  The produced photocatalytic electrode 104 is placed on the proton conductive membrane 105 and hot pressed. The proton conducting membrane 105 used here is not particularly limited as long as it is a material having a function of conducting protons. However, in order to make the titanium porous membrane 100 conductive with the platinum-supporting carbon electrode, the proton conducting membrane 105 is used. It is desirable to reduce the thickness of the. The hot pressing conditions are preferably a temperature of 120 ° C. to 150 ° C. and a pressure of 5 MPa to 10 MPa. When hot pressing is performed under these conditions, the titanium porous membrane 100 is proton-conductive as shown in FIG. It penetrates through the film 105.

Then, the surface of the titanium porous membrane 100 opposite to the surface coated with the photocatalyst particles 101,
The surface where the titanium porous membrane 100 is exposed from the proton conducting membrane 105 shown in FIG. 7C is polished to expose the metal surface 108 of the titanium porous membrane 100 as shown in FIG. 7D.

  Further, a paste-like mixture in which a finely divided carbon particle coated with a platinum catalyst and a solution mainly composed of a lower alcohol in which the same type of perfluorosulfonic acid polymer as that used in the electrolyte membrane is mixed is uniformly mixed with Ti metal. Apply to the surface and hot press again. The hot press conditions are a temperature of 120 ° C. to 150 ° C. and a pressure of 1 MPa to 5 MPa. After hot pressing, the diaphragm 109 shown in FIG. 7 (e) can be obtained.

  As described above, according to the present embodiment, since the photocatalyst electrode and the counter electrode are electrically connected only through the conductive porous film, it is not necessary to connect an external short-circuit line and install a bias power source. As a result, the PEM type photowater electrolysis cell can be simplified. Of course, in the present embodiment, the same effects as those of the first embodiment can be obtained.

In addition, although the photoelectrochemical cell and its manufacturing method of this invention were demonstrated mentioning 1st Embodiment and 2nd Embodiment mentioned above, the structure of this invention is not limited to these. For example, a conductive porous film was used as the current collector of the anode, but a conductive material with punch holes or a metal film formed on an insulating porous material to make it conductive, etc. You may apply what has the function of. Further, platinum, ruthenium oxide (RuO ₂ ), nickel oxide (NiO _x ), cerium oxide (CeO ₂ ), or the like may be dispersed and added as a co-catalyst to the semiconductor used as the photocatalyst. Moreover, although the semiconductor was used as a photocatalyst applied on the Ti porous body, a substance having a similar function such as an organic dye may be applied. Further, instead of laminating a substance having photocatalytic activity, a TiO ₂ film obtained by oxidizing titanium (Ti) may be used as a photocatalyst. In addition, as a method of forming a semiconductor or insulator coating on a portion of the support metal surface where the photocatalyst and the support metal are necked as shown in FIG. Instead of performing in an oxidizing atmosphere as described above, it may be performed in an inert gas atmosphere such as nitrogen or argon, followed by an oxidation treatment to form a semiconductor or insulator film. By using such a method, it is possible to reliably prevent an oxide film from being formed between the photocatalyst and the support metal and hindering electron injection from the photocatalyst to the support metal. In addition, as a method for applying the photocatalyst to the porous Ti material, a colloidal solution containing a photocatalyst has been taken as an example. Is obtained. Moreover, in the said embodiment, although the metal oxide was mentioned as an example as a semiconductor or an insulator which prevents the short circuit of electrolyte solution and a board | substrate metal, if it performs the same function, metal sulfide and metal carbide will be used. Also good. In the first embodiment, an external power source is used as a method of applying a bias. However, a method of applying a bias by applying a pH difference to an aqueous solution in a glass cell separated by a diaphragm may be used. Furthermore, in the present embodiment, the proton conductive membrane is used as a medium for transporting protons generated by the photocatalyst to the counter electrode. However, except for this, the electrolytic solution itself contained in the conductive porous body may be the medium. .

(A) is sectional drawing of the PEM type photowater electrolysis cell based on 1st Embodiment of this invention, (b) is an expanded sectional view of a diaphragm. It is an expanded sectional view of the titanium porous membrane shown in FIG. It is a figure explaining operation | movement of the PEM type photowater electrolysis cell 1 shown in FIG. It is a manufacturing-process figure of the diaphragm of the PEM type photowater electrolysis cell shown in FIG. (A) is sectional drawing of the PEM type photowater electrolysis cell concerning 2nd Embodiment of this invention, (b) is an expanded sectional view of a diaphragm. It is a figure explaining operation | movement of the PEM type photowater electrolysis cell shown in FIG. It is a manufacturing-process figure of the diaphragm of the PEM type photowater electrolysis cell shown in FIG.

Explanation of symbols

1 ... PEM photoelectrolysis cell,
2 ... container,
3 ... diaphragm,
4a, 4b ... water reservoir,
5 ... Photocatalytic electrode,
6 ... Platinum-supported carbon electrode,
7 ... Proton conducting membrane,
8 ... Titanium porous membrane,
9 ... Titanium dioxide coating,
10 ... photocatalyst particles,
11a, 11b ... seal part,
12 ... External short-circuit wire,

Claims (21)

A photocatalytic electrode in which a film is formed on the surface of the conductive porous body and a photocatalyst is formed on one surface of the conductive porous body;
An electrode serving as a counter electrode of the photocatalytic electrode;
A proton conductor sandwiched between the electrodes;
A photoelectrochemical cell comprising a diaphragm having the following.   2. The coating film according to claim 1, wherein the conductive porous body is made of a metal that forms a semiconductor or an insulator made of at least one of oxides, nitrides, sulfides, and carbides of the metal that forms the conductive porous body. The described photoelectrochemical cell.   The photoelectrochemical cell according to claim 1, wherein the coating is a photocatalyst formed on one surface of the conductive porous body.   The photoelectrochemical cell according to claim 1, wherein the photocatalyst is formed by fusing photocatalyst particles to a conductive porous body.   The photoelectrochemical cell according to claim 3, wherein the photocatalyst is a material different from the film.   The photoelectrochemical cell according to claim 1, wherein the conductive porous body is a sintered body of metal fine particles.   The photocatalytic electrode is different from a semiconductor or insulator made of at least one of oxide, nitride, sulfide, and carbide of a metal forming the conductive porous body on one surface of the conductive porous body. The photocatalyst is provided, and the surface of the conductive porous body is covered with a semiconductor or insulator made of at least one of metal oxide, nitride, sulfide, and carbide that forms the conductive porous body. The photoelectrochemical cell according to claim 4.   The photoelectrochemical cell according to claim 1, wherein the photocatalytic electrode and the counter electrode are electrically connected.   The photoelectrochemical cell according to claim 5, further comprising a short-circuit line connecting between the photocatalyst electrode and the electrode serving as a counter electrode.   The photoelectrochemical cell according to claim 8, wherein the photocatalyst electrode and the electrode serving as a counter electrode are electrically connected to each other through a conductive porous film.   The photoelectrochemical cell according to any one of claims 1 to 10, wherein a bias voltage is applied between the photocatalyst electrode and the electrode serving as a counter electrode.   The short circuit line which connects between the photocatalyst electrode and the electrode which serves as a counter electrode, and the bias power supply installed on the short circuit line are provided, The any one of Claims 1 thru | or 11 characterized by the above-mentioned. The described photoelectrochemical cell.   The photoelectrochemical cell according to claim 11, wherein a bias voltage is applied by providing a hydrogen ion concentration difference between compartments separated by the proton conducting membrane.   The photoelectrochemical cell according to claim 1, wherein the proton conductor is a proton conductive membrane.   The photoelectrochemical cell according to any one of claims 1 to 7, wherein the proton conductor is an electrolytic solution held inside the porous conductor.   A film is formed on the surface of the conductive porous body, and a photocatalyst is formed on one surface of the conductive porous body to form a photocatalyst electrode. Proton conduction is performed on the opposite side of the photocatalyst electrode from which the photocatalyst is formed. A method for producing a photoelectrochemical cell, comprising sequentially stacking a body and an electrode serving as a counter electrode of the photocatalytic electrode, and press-bonding at a temperature higher than a temperature at which the proton conductor softens.   A film is formed on the surface of the conductive porous body, and a photocatalyst is formed on one surface of the conductive porous body to form a photocatalyst electrode. Proton conduction is performed on the opposite side of the photocatalyst electrode from which the photocatalyst is formed. And the electrode serving as the counter electrode of the photocatalyst electrode are sequentially stacked and pressure-bonded at a temperature higher than the softening temperature of the proton conductor, and the conductive porous body is penetrated through the proton conductor to apply photocatalyst particles. The oxide film formed on the conductive porous body on the opposite side of the surface is removed, and an electrode material serving as a counter electrode is applied to the removal surface of the oxide film, and pressure bonding is performed at a temperature higher than the softening temperature of the proton conductor. A method for producing a photoelectrochemical cell, characterized in that a diaphragm is formed.   The method for producing a photoelectrochemical cell according to claim 16 or 17, wherein a film is formed on the surface of the conductive porous body using a thermal oxidation method, a chemical vapor deposition method or an anodic oxidation method.   The method for producing a photoelectrochemical cell according to claim 16 or 17, wherein the coating film is formed on a surface of the conductive porous body after applying photocatalyst particles on the conductive porous body.   18. The coating film is formed on the surface of the conductive porous body after applying photocatalyst particles on the conductive porous body and then performing a heat treatment in an inert atmosphere. Manufacturing method of photoelectrochemical cell.   18. The method for producing a photoelectrochemical cell according to claim 16, further comprising forming a film after forming the diaphragm.

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