JP6718805B2 - Semiconductor photoelectrode - Google Patents

Description

The present invention relates to a semiconductor photoelectrode having a photocatalytic function.

Conventionally, there is a semiconductor photocatalyst that exerts a catalytic function by light irradiation to cause a chemical reaction of an oxidation target substance or a reduction target substance. For example, a technique of using sunlight to generate hydrogen from water without generating carbon dioxide has been drawing attention, and has been actively studied in recent years.

However, in order to improve the quantum yield of the photocatalytic reaction, spatial separation of electron-hole pairs photoexcited in the photocatalyst and oxidation or reduction installed so as to suppress the reverse reaction of the reaction intermediate or the product. The transfer of holes or electrons to the site (oxidation reaction site or reduction reaction site) that promotes the reaction is necessary.

To solve this problem, in order to suppress the reverse reaction of the reaction intermediate or product, an electrode-type method of controlling the arrangement of the oxidation reaction site and the reduction reaction site has been proposed. For example, in Non-Patent Documents 1 to 4, in order to improve the efficiency of the carbon dioxide reduction reaction, a semiconductor photocatalyst having a photocatalytic function using a carbon dioxide reduction reaction site and a water oxidation reaction site as metal anode plates, respectively. The cathode plate is separately provided and electrically connected so that electrons flow from the cathode plate to the anode plate. In addition, by immersing the anode plate and the cathode plate in an electrolytic solution and separating each electrode with an ion exchange membrane, it is possible to suppress the reverse reaction.

S.Yotsuhashi, 6 others, “Photo-induced CO2 Reduction with GaN Electrode in Aqueous System”, Applied Physics Express 4 (2011) 117101 S.Yotsuhashi, 7 others, “Highly efficient photochemical HCOOH production from CO2 and water using an inorganic system”, AIP Advance 2, 042160 (2012) S. Yotsuhashi, 6 others, “Enhanced CO2 reduction capability in an AlGaN/GaN photoelectrode”, Applied Physics Letters 100, 243904 (2012) T. Sekimoto, 6 others, “Analysis of Products from Photoelectrochemical Reduction of CO2 by GaN-Si Based Tandem Photoelectrode”, The Journal of Physical Chemistry C in press (DOI: 10.1021/acs.jpcc.6b03840), ACS Publications

In a conventional semiconductor photoelectrode, a semiconductor thin film of gallium nitride is usually used as a semiconductor photocatalyst. This semiconductor thin film acts as a current collector, and the electrons generated by photoexcitation move from the semiconductor thin film to the counter electrode via the external circuit. However, the ohmic resistance of gallium nitride forming the semiconductor thin film is about 50 to 80 Ω, which has a resistance value higher than that of metal, so that IR loss occurs when electrons move, and electrons cannot be collected efficiently.

Further, the gallium nitride-based semiconductor thin film is self-oxidized by light irradiation and is etched, so that it is difficult to obtain a stable photocurrent. In order to solve this problem, in Non-Patent Documents 3 and 4, nickel oxide is supported on the surface of the semiconductor thin film as a co-catalyst, so that holes generated in the semiconductor thin film by light irradiation are collected in the co-catalyst to oxidize the semiconductor thin film. Is suppressed. However, it is difficult to completely suppress the self-oxidation of the semiconductor thin film because the surface of the semiconductor thin film is exposed except for the portion supporting the promoter.

The present invention has been made in view of the above circumstances, and efficiently takes out electrons or holes from a semiconductor film having a photocatalytic function to promote a chemical reaction of a target substance, thereby improving the durability of a semiconductor photoelectrode under light irradiation. The purpose is to improve sex.

In order to solve the above-mentioned problems, the semiconductor photoelectrode according to claim 1 is a semiconductor film which, when irradiated with light, exhibits a catalytic function to cause a chemical reaction of a target substance to generate electrons and holes, and A current collector layer formed in the central portion of the surface of the semiconductor film, having a structure in which a plurality of regular pentagons are arranged so as to be adjacent to each other while sharing the sides of the regular pentagon, and a current collector layer for extracting electrons or holes from the semiconductor film, It is characterized by comprising the semiconductor film and a catalyst layer formed on the entire surface of the current collector layer.

According to the present invention, a plurality of regular pentagons are arranged so as to be adjacent to each other in the central portion of the surface of the semiconductor film that exerts a catalytic function by light irradiation to cause a chemical reaction of a target substance, with the sides of the regular pentagon sharing. In order to form a current collector layer having a structure for taking out electrons or holes from the semiconductor film and forming a catalyst layer on the entire surfaces of the semiconductor film and the current collector layer, electrons or holes are removed from the semiconductor film. It can be efficiently taken out to promote the chemical reaction of the target material, and the durability of the semiconductor photoelectrode under light irradiation can be improved.

The semiconductor photoelectrode according to claim 2 is the semiconductor photoelectrode according to claim 1, wherein the semiconductor film is characterized by being composed of n-type gallium nitride.

A semiconductor photoelectrode according to a third aspect is the semiconductor photoelectrode according to the first aspect , wherein the semiconductor film is a laminated film of n-type gallium nitride and aluminum gallium nitride.

A semiconductor photoelectrode according to claim 4 is the semiconductor photoelectrode according to any one of claims 1 to 3 , wherein the catalyst layer is a metal oxide having at least one of nickel, cobalt, ruthenium, iridium, and iron. It is characterized by being a thing.

The semiconductor photoelectrode according to claim 5 is the semiconductor photoelectrode according to any one of claims 1 to 4 , wherein the current collector layer is a titanium layer, an aluminum layer, an indium layer, a nickel layer, or a stack of titanium and aluminum. , A stack of titanium and nickel, or a stack of titanium, aluminum, titanium, and platinum in that order.

A semiconductor photoelectrode according to a sixth aspect is the semiconductor photoelectrode according to any one of the first to fifth aspects, wherein the target material is an oxidation target material or a reduction target material.

According to the present invention, electrons or holes can be efficiently taken out from the semiconductor film having a photocatalytic function to promote the chemical reaction of the target substance, and the durability of the semiconductor photoelectrode under light irradiation can be improved.

It is a top view of the semiconductor photoelectrode which concerns on this Embodiment. It is sectional drawing of the side surface of the semiconductor photoelectrode which concerns on this Embodiment. It is sectional drawing of the side surface of the semiconductor photoelectrode (other structure) which concerns on this Embodiment. It is sectional drawing of the side surface of the semiconductor photoelectrode (other structure) which concerns on this Embodiment. It is a top view of the collector layer which concerns on this Embodiment. It is a figure which shows the test structure of a redox reaction. It is a figure which shows the current density in each Example and each comparative example, and the maintenance factor of a current density. It is a figure which shows the change of the current density with respect to light irradiation time.

The present invention forms a current collector layer that collects electrons or holes from the semiconductor film on a part of the surface of the semiconductor film having a photocatalytic function, and further, a semiconductor film is formed on the entire surface of the semiconductor film and the current collector layer. A catalyst layer having both a protective function and a catalytic function for preventing the membrane and the current collector layer from coming into contact with the solution is formed. As a result, electrons or holes are efficiently extracted from the semiconductor film to promote the chemical reaction of the target material, and the durability of the semiconductor photoelectrode under light irradiation is improved.

Specifically, a metal having high electron conductivity is provided on the surface of a semiconductor film of gallium nitride to form a current collecting layer, thereby reducing IR loss during electron transfer in the semiconductor film. In particular, by forming the metal current collecting layer on the plane to have the honeycomb structure surface, the electrons generated in the semiconductor film are moved to the current collecting layer at the shortest distance.

An embodiment for carrying out the present invention will be described with reference to the drawings. The present invention can be applied to both an oxidation target substance and a reduction target substance.

FIG. 1 is a top view of a semiconductor photoelectrode 100 according to this embodiment. FIG. 2 is a side sectional view of the semiconductor photoelectrode 100. The semiconductor photoelectrode 100 includes a substrate 1, a semiconductor thin film 2 stacked on the surface of the substrate 1, a semiconductor thin film 2 that exhibits a catalytic function by light irradiation to cause an oxidation reduction reaction of an oxidation target substance or a reduction target substance, and the surface of the semiconductor thin film 2. A current collector layer 3 formed on a part of the semiconductor thin film 2 for extracting electrons or holes from the semiconductor thin film 2, metal wiring 4 provided in contact with the current collector layer 3, the semiconductor thin film 2 and the current collector layer 3 And a catalyst layer 5 formed on the entire surface of.

Modifications of the semiconductor photoelectrode 100 shown in FIG. 2 are shown in FIGS. In these modifications, recesses are formed on the surface of the semiconductor thin film 2 and the current collector layer 3 is formed therein. As shown in FIG. 3, the current collector layer 3 may be formed so that the surface thereof is flush with the surface of the semiconductor thin film 2 and is flush with the surface of the semiconductor thin film 2. Alternatively, as shown in FIG. You may form so that it may become higher than the surface height of. In order to form such a current collector layer 3 on a part of the surface of the semiconductor thin film 2, the current collector layer 3 may be formed after etching the semiconductor thin film 2 using a mask. In addition to this, the current collector layer 3 may be diffused into a part of the surface of the semiconductor thin film 2 by heat treatment after forming the current collector layer 3 on the semiconductor thin film 2. Hereinafter, the semiconductor photoelectrode 100 is assumed to have the configuration and structure shown in FIG.

FIG. 5 is a top view of current collector layer 3 according to the present embodiment. The current collector layer 3 has a basic structure of a circle or a regular n-gon (n is an integer of 3 or more), and has a structure in which a plurality of the basic structures are continuously arranged. For example, it has a structure in which a plurality of circles are arranged as shown in FIG. Further, as shown in FIGS. 5B to 5E, a plurality of regular triangles, regular squares, regular pentagons, and regular hexagons may be arranged respectively. In addition, a plurality of basic structures having different n may be combined. The structure of FIG. 5 is an example, and the structure is not limited to that.

Hereinafter, the current collector layer 3 is assumed to have the regular hexagonal basic structure shown in FIG. The width of one side of the regular hexagon is 3 μm, and the length is 50 μm. Considering the light absorption characteristics and the depletion layer length of the semiconductor thin film 2 used in each example described later, the length of one side of the regular hexagon is preferably 10 μm or more and 150 μm or less. Further, the width of one side thereof is preferably 10 μm or less, which does not prevent light from entering the semiconductor thin film 2.

The substrate 1 forms a substrate for forming the semiconductor photoelectrode 100. For example, a sapphire substrate is used. Alternatively, an insulating/low-conductivity substrate such as a glass substrate, a Si substrate, or a GaN substrate may be used.

The semiconductor thin film 2 has a photocatalytic function of causing an oxidation-reduction reaction of an aqueous solution by light irradiation and generating electrons and holes. For example, a gallium nitride (GaN) single layer film or a stacked film of gallium nitride (GaN) and aluminum gallium nitride (AlGaN) is used. Alternatively, a compound semiconductor such as an aluminum gallium nitride (AlGaN) single layer film, indium gallium nitride (InGaN), indium phosphide (InP), indium gallium phosphide (InGaP), and gallium arsenide (GaAs) may be used. The semiconductor thin film 2 may be a semiconductor that causes an oxidation-reduction reaction by light irradiation to generate electrons and holes.

The current collector layer 3 is formed on a part of the surface of the semiconductor thin film 2 and has a function of extracting electrons or holes generated in the semiconductor thin film 2 by light irradiation. For example, a titanium layer and an aluminum layer are used. In addition, an indium layer, a nickel layer, a titanium/aluminum stack, a titanium/nickel stack, a titanium/aluminum/titanium/platinum stack, or the like may be used. Any metal capable of forming ohmic contact with the semiconductor thin film 2 and collecting electrons and holes from the semiconductor thin film 2 may be used. The metal before "/" is the lower layer, and the metal after "/" is the upper layer.

The catalyst layer 5 is formed on the entire surfaces of the semiconductor thin film 2 and the current collector layer 3. As a result, the catalyst layer 5 has an original catalytic function of assisting the redox reaction of the semiconductor thin film 2 and a protective function of preventing the semiconductor thin film 2 and the current collector layer 3 from coming into contact with the aqueous solution. For example, nickel oxide or cobalt oxide is used. In addition, single metal oxides such as iridium oxide, ruthenium oxide and iron oxide, and composite oxides such as nickel cobalt oxide and cobalt iron oxide may be used.

The metal wiring 4 is provided in contact with the current collector layer 3, and transmits the electrons/holes extracted by the current collector layer 3 to the counter electrode. For example, a metal wiring such as a copper wire is used.

Next, a redox reaction test method and test results of the manufactured semiconductor photoelectrode 100 will be described. When the semiconductor photoelectrode 100 described above is placed in an aqueous solution and the semiconductor thin film 2 is irradiated with light, an oxidation reaction occurs in the aqueous solution. At this time, 1 M NaOH is used as the aqueous solution. Besides, for example, an aqueous solution of KOH, H ₂ SO ₄ , HCl, Na ₂ SO ₄ , KHCO ₃ or the like may be used.

Note that in this embodiment, water is used as the oxidation and reduction target substance, and oxygen generation by water oxidation reaction and hydrogen generation by reduction of protons generated by oxidation of water are described as an example. It is not limited to. For example, the semiconductor photoelectrode 100 of the present invention can be applied to the case where hydrocarbons such as carbon monoxide, gisan, methanol, and methane are produced using carbon dioxide as a reduction target substance.

Further, the method of the redox reaction test is not limited to the method described in this embodiment. For example, the same effect can be obtained even when the semiconductor photoelectrode 100 is installed such that the longitudinal direction thereof is parallel to the water surface in an aqueous solution and sunlight is used as a light source.

<Example 1>
(Method for manufacturing semiconductor photoelectrode 100)
A method of making the semiconductor photoelectrode 100 according to the first embodiment will be described. On a 2-inch sapphire (0001) substrate 1, an n-type gallium nitride (n-GaN) thin film doped with Si is epitaxially grown by a metal organic chemical vapor deposition method. The film thickness was 2 μm. This n-GaN thin film becomes the semiconductor thin film 2.

Next, on the surface of the n-GaN thin film, a current collector layer 3 having a honeycomb-shaped structural pattern having a regular hexagon as a basic structure is formed by photolithography. At this time, it is formed in the central portion of the substrate 1 excluding the edge portion 5 mm. The current collector layer 3 is a titanium/aluminum laminated film, and is formed by a sputtering method and then heat-treated at 500° C. for 10 minutes in a muffle furnace in the air atmosphere. The thickness of the current collector layer 3 was 10 nm on the n-GaN thin film, and the width of one side of the hexagon, which is the basic structure, was 3 μm, and the length was 50 μm. In addition, it was confirmed that titanium and aluminum were diffused in the n-GaN thin film by about 130 nm.

Next, layered nickel oxide (NiO) is deposited as a catalyst layer 5 by sputtering. At this time, a film is formed using a mask so that the current collector layer 3 is partially exposed. Then, heat treatment is performed at 500° C. for 10 minutes in a muffle furnace in an oxygen atmosphere. The thickness of NiO was 5 nm.

Finally, indium is bonded with a soldering iron to a portion of the surface of the manufactured semiconductor thin film 2 where the current collector layer 3 is exposed, and a conductor wire as a metal wiring 4 is joined to the exposed portion of the epoxy resin so that the indium surface is not exposed. Cover with.

From the above, the semiconductor photoelectrode 100 having the structure shown in FIG. 4 is manufactured.

(Redox reaction test)
The redox reaction test method and test results of the manufactured semiconductor photoelectrode 100 will be described with reference to FIG. 200 mL of a 1 M NaOH aqueous solution 12 is placed as a solvent in a gas flow type light transmission cell 11 having an inner volume of 300 mL. Then, the semiconductor photoelectrode 100 manufactured by the procedure described above is dipped in the aqueous solution 12, and a Pt wire (Pt electrode made by BAS (Pt electrode (model number 002222)) is also dipped as the counter electrode 13 in the aqueous solution 12 and is passed through the ammeter 14. The metal wiring 4 of the semiconductor photoelectrode 100 is connected to the counter electrode 13. Also, after bubbling nitrogen gas at 200 mL/min for 30 minutes for defoaming and replacement, it is flown into the aqueous solution from the flow gas input pipe 15 at 5 mL/min. Then, a 300 W xenon lamp (integrated illuminance 100 mW/cm ² ) is used as the light source 16 for the redox reaction, and the surface of the semiconductor thin film of the semiconductor photoelectrode 100 is uniformly irradiated from the outside of the light transmission cell 11. The aqueous solution is stirred at a central position of the bottom of the light transmission cell 11 at a rotation speed of 250 rpm using a stirrer 17 and a stirrer (not shown).

The photoelectric flow rate after light irradiation was recorded, and the gas in the light transmission cell 11 was analyzed by directly introducing the flow gas output tube 18 of the light transmission cell 11 into the gas chromatograph. As a result, it was confirmed that hydrogen and oxygen were generated. Current density after the test after 2 hours 1.1 mA / cm ^2, gas generation amount was hydrogen 5.3nmol ^/ cm 2 · sec, oxygen 2.5nmol ^/ cm 2 · sec. In addition, the current density retention rate after light irradiation for 20 hours was 90%.

<Example 2>
On a 2-inch sapphire (0001) substrate 1, an n-type gallium nitride (n-GaN) thin film doped with Si is epitaxially grown by a metal organic chemical vapor deposition method. Next, the semiconductor thin film 2 is produced by growing AlGaN by a metal organic chemical vapor deposition method. The film thickness of AlGaN was 107 nm, and the Al composition was 9.6% (Al _0.1 Ga _0.9 N). Using this photocatalyst thin film (semiconductor thin film 2), a semiconductor photoelectrode 100 was prepared in the same manner as in Example 1, and a redox reaction test was conducted. In the case of Example 2 as well, the thickness of the current collector layer 3 made of titanium/aluminum was 10 nm on the photocatalyst thin film, and it was confirmed that titanium and aluminum were diffused to the photocatalyst thin film by about 130 nm.

In the redox reaction test using the semiconductor photoelectrode 100 of Example 2, the current density 2 hours after the start of the test was 1.44 mA/cm ² , the gas generation amount was 7.1 nmol/cm ² ·sec hydrogen, and 3.3 nmol oxygen. /Cm ² ·sec. Further, the current density maintenance ratio after light irradiation for 20 hours was 92%.

<Example 3>
In Example 3, one side of the basic structure of the current collector layer 3 had a length of 5 μm. Other than that is the same as the second embodiment. Current density after the test after 2 hours 0.38mA / cm ^2, gas generation amount was hydrogenated 1.5 nmol ^/ cm 2 · sec, oxygen 0.7nmol ^/ cm 2 · sec. Further, the current density retention rate after light irradiation for 20 hours was 85%.

<Example 4>
In Example 4, the length of one side of the basic structure of the current collector layer 3 was 500 μm. Other than that is the same as the second embodiment. Current density after the test after 2 hours 0.85 mA / cm ^2, gas generation amount was hydrogen 4.1nmol ^/ cm 2 · sec, oxygen 1.9nmol ^/ cm 2 · sec. Further, the current density retention rate after light irradiation for 20 hours was 88%.

<Comparative Example 1>
The redox reaction test results using the semiconductor photoelectrode without the collector layer 3 will be described. Example 2 is the same as Example 2 except that the current collector layer 3 is not provided. The metal wiring 4 was created by the following procedure. A part of the surface of the produced film is peeled off with a diamond scriber to expose the lower layer n-GaN. Indium is adhered to the exposed portion of n-GaN with a soldering iron to join the conductive wires. It is coated with epoxy resin so that the indium surface is not exposed. As a result, the current density 2 hours after the start of the test was 0.25 mA/cm ² , the gas generation amount was 1.4 nmol/cm ² ·sec, and oxygen was 0.6 nmol/cm ² ·sec. The current density retention rate after light irradiation for 20 hours was 94%.

<Comparative example 2>
The redox reaction test results using the semiconductor photoelectrode without the current collector layer 3 and the catalyst layer 5 will be described. The same as Comparative Example 1 except that the current collector layer 3 and the catalyst layer 5 are not provided. As a result, the current density after the test after 2 hours 0.21mA / cm ^2, gas generation amount of hydrogen 0.9nmol ^/ cm 2 · sec, was oxygen 0.2nmol ^/ cm 2 · sec. Further, the current density retention rate after light irradiation for 20 hours was 5%.

<Comparative example 3>
The results of a redox reaction test using a semiconductor photoelectrode in which island-shaped NiO is formed as the catalyst layer 5 without the current collector layer 3 will be described. Comparative Example 1 is the same as Comparative Example 1 except that the current collector layer 3 is not provided and the catalyst layer 5 is made of island-shaped NiO. The island-shaped NiO catalyst was formed by the following procedure. A MOD coating agent (SYM-NI05, manufactured by Kojundo Chemical Co., Ltd.) is used as the nickel oxide precursor formed as the catalyst layer 5. A liquid film is formed by spin-coating (5000 rpm for 30 seconds) on the semiconductor thin film using a 200-fold diluted solution of this solvent. NiO is formed by performing a heat treatment at 500° C. for 30 minutes in an atmosphere of air in a muffle furnace. From SEM observation of the surface, it was confirmed that NiO particles having a particle size of 1 to 2 μm and a thickness of 10 nm were present on the semiconductor thin film 2 at intervals of several tens of μm.

As a result, the current density after the test after 2 hours 0.28mA / cm ^2, gas generation amount of hydrogen 1.5 nmol ^/ cm 2 · sec, was oxygen 0.7nmol ^/ cm 2 · sec. The current density retention rate after light irradiation for 20 hours was 38%.

The structures of the photoelectrodes in Examples 1 to 4 and Comparative Examples 1 to 3 and the test results are shown in FIG. 7. Moreover, the time change of the photocurrent density in the oxidation-reduction reaction test of Example 2 and Comparative Example 1 is shown in FIG. All of Examples 1 to 4 showed higher current densities than the comparative example without the collector layer 3, and the current densities after the 20-hour test were maintained at 85% or more in all cases. In particular, Example 2 had the highest current density. The comparative example in which the current collector layer 3 was not formed showed a lower current density than that of the example, which suggests that the electrons generated by the light irradiation were not efficiently extracted and recombined. From this result, it was confirmed that in the present embodiment, the current collector layer 3 formed on a part of the surface of the semiconductor thin film 2 has an effect of efficiently extracting electrons.

Moreover, when Examples 2 to 4 were compared, the highest current density was shown when the length of one side of the current collector layer 3 was 50 μm. In the case of Example 3, the interval between the basic structures of the current collector layer 3 on the semiconductor thin film 2 was narrow, the coverage of the semiconductor thin film 2 with the current collector layer 3 was increased, and the light irradiation area was decreased. It suggests that the efficiency of light absorption was lower than that of Example 2. Further, in the case of Example 4, it is suggested that the interval of the basic structure of the current collector layer 3 on the semiconductor thin film 2 is wide, and the electron extraction efficiency is lower than in the case of Example 2. Furthermore, since the current density retention ratios of Comparative Examples 2 and 3 in which the layered catalyst layer was not formed were low, the catalyst layer 5 of the present invention also has the function of a protective film and is effective in improving the life. Was confirmed.

As described above, according to the present embodiment, electrons or holes are extracted from the semiconductor thin film 2 to a part of the surface of the semiconductor thin film 2 that exhibits a catalytic function by light irradiation to cause a chemical reaction of the target substance. Since the current collector layer 3 is formed and the catalyst layer 5 is formed on the entire surfaces of the semiconductor thin film 2 and the current collector layer 3, electrons or holes are efficiently taken out from the semiconductor thin film 2 and the chemistry of the target material is increased. The reaction can be promoted and the durability of the semiconductor photoelectrode 100 under light irradiation can be improved.

The present invention is a photocatalytic device that reduces carbon dioxide to carbon monoxide, formic acid, methanol, or methane by light energy, particularly sunlight energy, or a photocatalytic device that photolyzes water to produce hydrogen. It is applicable to the technical fields of solar energy conversion technology and fuel generation technology.

Further, the semiconductor photoelectrode 100 of the present invention is not limited to the configuration described in the present embodiment, and many modifications can be made by a person having ordinary skill in the art within the technical idea of the present invention. And it is clear that combinations are feasible.

100... Semiconductor photoelectrode 1... Substrate 2... Semiconductor thin film (semiconductor film)
3... Current collector layer 4... Metal wiring 5... Catalyst layer 11... Light transmission cell 12... Aqueous solution 13... Counter electrode 14... Ammeter 15... Flow gas input tube 16... Light source 17... Stirrer 18... Flow gas output tube

Claims (6)

When exposed to light, a semiconductor film that exerts a catalytic function to cause a chemical reaction of a target substance to generate electrons and holes,
A current collector layer formed in the central portion of the surface of the semiconductor film, having a structure in which a plurality of regular pentagons are arranged so as to be adjacent to each other while sharing a side of the regular pentagon, and a current collector layer for extracting electrons or holes from the semiconductor film; ,
A catalyst layer formed on the entire surface of the semiconductor film and the current collector layer;
A semiconductor photoelectrode comprising: The semiconductor film is
The semiconductor photoelectrode according to claim 1, which is composed of n-type gallium nitride. The semiconductor film is
The semiconductor photoelectrode according to claim 1, which is a laminated film of n-type gallium nitride and aluminum gallium nitride. The catalyst layer is
The semiconductor photoelectrode according to claim 1, wherein the semiconductor photoelectrode is a metal oxide containing at least one of nickel, cobalt, ruthenium, iridium, and iron. The current collector layer is
A titanium layer, an aluminum layer, an indium layer, a nickel layer, a titanium/aluminum laminate, a titanium/nickel laminate, or a titanium/aluminum/titanium/platinum laminate in that order. The semiconductor photoelectrode according to claim 1. The target material is
The semiconductor photoelectrode according to claim 1, wherein the semiconductor photoelectrode is an oxidation target material or a reduction target material.