KR20200041223A - Efficient heteroatom doping method of photoanode based metal oxide and photoanode prepared by the same - Google Patents

Abstract

The present invention relates to a method of preparing a photoanode for water splitting, comprising the following steps of: (a) preparing a mixed solution by mixing an iron source and a main dopant source which forms a tetravalent ion and is a metal with a larger ion size than Fe^3+; (b) growing FeOOH doped with main dopant on a transparent electrode substrate by immersing the transparent electrode substrate in the mixed solution and performing a heat treatment thereon; (c) preparing FeOOH doped with the main dopant and having silica (SiO_2) nanoparticles attached to the surface thereof by immersing the FeOOH doped with the main dopant in a solution where the silica nanoparticles are dispersed; and (d) preparing hematite (Fe_2O_3) co-doped with the main dopant and silicon (Si) which is object dopant by performing a heat treatment on the FeOOH doped with the main dopant and having the silica nanoparticles attached thereto, and additionally doping silicon (Si) which is the object dopant. Therefore, it is possible to specifically improve photocurrent density without using expensive process and equipment, resulting in improving performance of a water splitting apparatus.

Description

Efficient dissimilar doping method for metal oxide-based photocathodes and photocathodes for water decomposition manufactured accordingly TECHNICAL FIELD

The present invention relates to an efficient dissimilar doping method of a metal oxide-based photocathode and a photocathode for water decomposition prepared accordingly, and more specifically, the iron oxide photocatalyst is doped in a simple process without collapsing the main dopant and the object dopant in sequence. The present invention relates to a method for manufacturing a photocathode for water decomposition using an efficient different doping method of a metal oxide-based photocathode and a photocathode for water decomposition prepared accordingly.

A photoelectrochemical reaction is an electrochemical reaction that is induced by light energy. Representative photosynthesis of plants is also a type of photoelectrochemical reaction. Chloroplasts absorb light energy and oxidize water. A substance that controls the reaction rate by changing the activation energy required for such a photoreaction is called a photocatalyst. On the other hand, hydrogen is a next-generation clean energy source that does not emit contaminants during combustion, but it is mainly produced by fossil fuels, but recently, as an eco-friendly method, water decomposition reaction by light energy has been proposed as a new method for generating hydrogen.

Water decomposition is a reaction mechanism that generates hydrogen gas by solar energy in photoelectrochemical (hereinafter referred to as 'PEC') cells. The PEC cell is composed of two parts, a photoanode and a counter electrode, and the photoanode is an oxygen evolution reaction (hereinafter referred to as 'OER', 2H ₂ O + 4h + → O ₂ + 4H +). ) this takes place, and the counter electrode is the hydrogen generation reaction (hydrogen evolution reaction; less than ^{'HER', 4H + + 4e} - occurs → 2H _2). Due to the direct effect of photoexcited electrons on HER, intensive research has been conducted on HER properties in PEC systems for the past several decades.

However, recent studies have been conducted more intensively on the OER properties of photoanodes. This is because it is important to include a 4-electron transfer process of OER to improve the overall performance of the PEC system, and also has a direct interaction with light absorbers. Hematate (α-Fe ₂ O ₃ ) with a suitable visible light band gap (2.0-2.1 eV), good stability, and a theoretical solar-tohydrogen ('STH') of 15.3% It is considered a promising candidate for the PEC system.

As a photocatalyst, hematite has attracted much attention as a material suitable for photoelectrochemical water decomposition in that it is an appropriate band gap having a theoretical STH efficiency of 15.3%, excellent stability in water system, and abundant resources. Nanomaterial production is being intensively studied through innovative approaches such as morphology control and crystallinity control in order to improve hematite water decomposition performance. However, practically, hematite has a very low value than theoretical efficiency due to problems such as short hole diffusion length, low electrical conductivity, and conduction band energy level at a position lower than the water reduction potential. Although the problem of conduction band energy level can be solved by adding a heterojunction with other photocatalysts or OER catalyst, short hole diffusion length and low conductivity problems are still difficult to solve. In order to improve the efficiency of hematite, nano-structure fabrication or hetero-element (Sn, Ti, Si, Mo, Pt) doping is used to increase the concentration or mobility of charges. Sputtering, chemical vapor deposition, soft casting, pulse Laser deposition, hydrothermal action, and the like. However, some of these doping methods require complex equipment and expensive process methods, making them unsuitable for large-scale production and cost-effectiveness, the greatest advantage of hematite, which makes it difficult to commercialize the photoelectrochemical water decomposition system.

 Recently, a cheap hydrothermal method using ferric chloride has been widely used to fabricate nanostructured Ti doped hematite with the highest theoretical efficiency and good reproducibility. In order to use this method, a high temperature heat treatment of 700 ° C or higher is necessary to reduce the physical distance between the hematite and the substrate and the trapping place on the surface of the hematite. It should be noted that the second doping is performed by doping into the Ti-doped hematite lattice through thermal diffusion when the surface is treated with another material on the iron oxide surface at a high temperature heat treatment. Although this co-doping process is common in making high-performance photocatalysts, it has not been studied how Ti doping prior to doping affects the overall PEC performance of M (metal): Ti co-doped hematite.

As such, the material has shown low efficiency due to its inherent problem of low electrical conductivity and short diffusion length of holes. To overcome this, a method of doping silicon has been proposed, but an expensive manufacturing process such as atmospheric pressure chemical vapor deposition (APCVD) or ultrasonic spray pyrolysis (USP) is essential for silicon doping. However, such a high-cost manufacturing process has a problem in that it is difficult to maximize the price advantage of iron oxide.

Korean Registered Patent No. 10-1600462

Royal Society of Chemistry 2018 “On the role of metal atom doping in hematite for improved photoelectrochemical properties: a comparison study”

The object of the present invention is to solve the above problems, the phase conversion of the material and the sequential doping of the main-object dopant, doping silicon into iron oxide through a simple heat treatment method using silica (SiO ₂ ) nanoparticles. By introducing the method, the surface structure of the hematite can be stabilized by minimizing the structure collapse phenomenon of hematite by doping the main dopant first and then doping the main-object joint doping the object dopant. In addition, by controlling the main-object doping ratio of the photocathode, the photoconversion efficiency is maximized in the water decomposition reaction, and due to the material phase conversion and the main-object doping system, the photocurrent density is significantly reduced without using conventional expensive processes and equipment. It is to provide a photocathode for water decomposition that can be improved.

According to one aspect of the invention,

(a) an iron source, and a step of forming a tetravalent ion preparing a mixed solution by mixing the principal dopant ion source is greater than the Fe ^{3 +} a large metal;

(b) immersing a transparent electrode substrate in the mixed solution, followed by heat treatment to grow FeOOH doped with a main dopant on the transparent electrode substrate;

(c) immersing the main dopant-doped FeOOH in a solution in which silica (SiO ₂ ) nanoparticles are dispersed to prepare a main dopant-doped FeOOH with silica nanoparticles attached to the surface; And

(d) Main dopant doped FeOOH to which silicon dioxide nanoparticles are attached is heat-treated to further dop the object dopant silicon (Si), so that the main dopant and object dopant silicon (Si) are co-doped hematite (Fe ₂ O ₃ ) is provided; a method of manufacturing a photoanode for water decomposition comprising a.

Preferably, the main dopant of step (a) may be any one selected from titanium (Ti), tin (Sn), and manganese (Mn).

More preferably, the main dopant of step (a) may be titanium (Ti).

The titanium (Ti) source of step (a) is titanium chloride (TiCl ₃ ), titanium dioxide (TiO ₂ ), titanium hydride (TiH ₂ ), titanium tetrachloride (TiCl ₄ ), titanium nitride (TiN), and titanium isopro Foxside (C ₁₂ H ₂₈ O ₄ Ti) It may be any one selected from.

The iron source of step (a) is iron chloride (FeCl ₃ ), iron fluoride (FeF ₂ ), iron sulfide (FeSO ₄ ), iron acetate (Fe (CO ₂ CH ₃ ) ₂ ), iron nitride (Fe (NO ₃ ) ₃ ), And hydrates thereof.

The mixed solution of step (a) may contain 0.001 to 0.05 mole parts of the main dopant source with respect to 100 mole parts of the iron source.

The transparent electrode substrate of step (b) may be any one selected from FTO, ZnO, ITO, AZO, GZO, IZO, and IGZO.

The heat treatment in step (b) may be performed at a temperature of 80 to 120 ° C. for 1 to 5 hours.

The average particle diameter of the silica nanoparticles in step (c) may be 5 to 10 nm.

The immersion in step (c) may be performed for 10 to 60 minutes.

After step (c), the titanium-doped hematite to which the silica nanoparticles are attached may be further washed and then dried.

The drying may be performed using nitrogen gas.

The heat treatment of step (d) may be performed at 600 to 1000 ° C. for 5 to 30 minutes.

After step (d), (e) the main dopant and the object dopant silicon (Si) is co-doped with hematite (Fe ₂ O ₃ ) adsorbing a cocatalyst; may be further performed.

The co-catalyst may be titanium-doped FeOOH or titanium-doped FeOOH.

The cocatalyst may be titanium doped FeOOH.

Step (e) may be heat-treated by immersing the main dopant and the object dopant silicon (Si) co-doped hematite in a solution containing an iron source or a solution containing a titanium source and an iron source together.

The iron source of step (e) is iron chloride (FeCl ₃ ), iron fluoride (FeF ₂ ), iron sulfide (FeSO ₄ ), iron acetate (Fe (CO ₂ CH ₃ ) ₂ ), iron nitride (Fe (NO ₃ ) ₃ ), And hydrates thereof.

The titanium source of step (e) is titanium chloride (TiCl ₃ ), titanium dioxide (TiO ₂ ), titanium hydride (TiH ₂ ), titanium tetrachloride (TiCl ₄ ), titanium nitride (TiN), and titanium isopropoxide ( C ₁₂ H ₂₈ O ₄ Ti).

The heat treatment of step (e) may be performed at 50 to 100 ° C for 10 to 60 minutes.

According to another aspect of the invention,

A photocathode for water decomposition manufactured according to the above manufacturing method is provided.

In the photocathode for water decomposition, the main dopant content may be 1.5 to 3.0 wt% in the total weight of hematite (Fe ₂ O ₃ ) co-doped with silicon (Si), which is a main dopant and an object dopant.

According to another aspect of the invention,

There is provided a water decomposition apparatus including a photocathode for water decomposition manufactured according to the above manufacturing method.

The photoanode for water decomposition of the present invention performs a phase conversion process of a material and sequential doping of a main-object dopant, and a method of doping silicon on iron oxide through a simple heat treatment method using silica (SiO ₂ ) nanoparticles By introducing a main dopant first, and then doping the object dopant, through the main-object co-doping, the structure collapse of hematite can be minimized to stabilize the surface structure of hematite. In addition, by controlling the main-object doping ratio of the photocathode, the photoconversion efficiency is maximized in the water decomposition reaction, and due to the material phase conversion and the main-object doping system, the photocurrent density is significantly reduced without using conventional expensive processes and equipment. Can be improved, and consequently, the performance of the water decomposition device can be improved.

1 is a flowchart sequentially showing a method for manufacturing a photocathode for water decomposition of the present invention.
FIG. 2 is a JV curve comparing various hematite efficiencies with and without Ti pre-doping in Test Example 2.
3 is a SEM image comparing the characteristics of the photocathode according to Test Example 2.
4 is an XRD analysis result according to Test Example 2.
5 is a result of Raman spectrum analysis according to Test Example 2.
6 is an electrochemical impedance spectroscopy (EIS) analysis result according to Test Example 3.
7 is a Mott-Schottky measurement result according to Test Example 4.
8 is a photocurrent density measurement result of the Ti-Fe ₂ O ₃ photocathode according to the Ti dopant content according to Test Example 5.
9 is a photocurrent density measurement result of the Si: Ti-Fe ₂ O ₃ photocathode according to the Ti dopant content according to Test Example 5.
10 is a photo-current density measurement result of Ti-FeOOH / Si: Ti-Si: Ti-Fe ₂ O ₃ according to Test Example 5.
11 is a JT curve over time when using a Si: Ti-Fe ₂ O ₃ photocathode according to Test Example 5.

The present invention can be applied to various conversions and can have various embodiments, and specific embodiments will be illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all conversions, equivalents, and substitutes included in the spirit and scope of the present invention. In the description of the present invention, when it is determined that a detailed description of known technologies related to the present invention may obscure the subject matter of the present invention, the detailed description will be omitted.

The terms used in this application are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "include" or "have" are intended to indicate the presence of features, numbers, steps, actions, components, parts or combinations thereof described herein, one or more other features. It should be understood that the existence or addition possibilities of fields or numbers, steps, operations, components, parts or combinations thereof are not excluded in advance.

1 is a flow chart sequentially showing a method of manufacturing a photocatalyst for decomposition of the present invention. Hereinafter, a method of manufacturing the photocathode for water decomposition of the present invention will be described with reference to FIG. 1.

First, iron ( Fe ) Form a source, and a tetravalent ion Fe ^{3 +}  Subjects with metals with a larger ion size Dopant  The mixed solution is prepared by mixing the sources (step a).

The main dopant is preferably one selected from titanium (Ti), tin (Sn), and manganese (Mn), and more preferably titanium (Ti).

The main dopant source is titanium chloride (TiCl ₃ ), titanium dioxide (TiO ₂ ), titanium hydride (TiH ₂ ), titanium tetrachloride (TiCl ₄ ), titanium nitride (TiN), titanium isopropoxide (C ₁₂ H ₂₈ O ₄ Ti).

The mixed solution may contain 0.001 to 0.05 mole parts, and more preferably 0.003 to 0.03 mole parts, and even more preferably 0.004 to 0.02 mole parts, with respect to 100 mole parts of the iron source, and the main dopant source. have.

Next, a transparent electrode substrate in the mixed solution Immersed  After heat treatment, a main body is formed on the transparent electrode substrate. Dopant Doped FeOOH Grow (step b).

The transparent electrode substrate may be FTO, ZnO, ITO, AZO, GZO, IZO, IGZO, etc., but the scope of the present invention is not limited thereto.

The heat treatment is preferably performed at a temperature of 80 to 120 ° C for 1 to 5 hours, more preferably at 90 to 110 ° C for 2 to 4 hours.

Then, the subject Dopant Doped FeOOH Subject to heat treatment Dopant Doped  Hematite ( Fe ₂ O ₃ )of  Prepare (step c).

The heat treatment is preferably performed at 600 to 1000 ° C for 5 to 30 minutes, and more preferably at 700 to 900 ° C for 10 to 20 minutes.

Next, the subject Dopant Doped Hematite (Fe ₂ O ₃ )  Silica ( SiO ₂ ) In a solution in which nanoparticles are dispersed Immerse  Subject with silica nanoparticles attached to the surface Dopant Doped Hematite (Fe ₂ O ₃ )  Prepare (step d).

The average particle diameter of the silica nanoparticles is preferably 5 to 10 nm, and more preferably 6 to 9 nm.

The immersion is preferably performed for 10 to 60 minutes, and more preferably 20 to 40 minutes.

The titanium-doped hematite to which the silica nanoparticles are attached can be dried after washing with water. It is preferable to use nitrogen gas for the drying.

Subsequently, subject as needed With dopant  Object Dopant  silicon( Si ) This co Doped  Hematite ( Fe ₂ O ₃ ) On Co-catalyst  Adsorb (step f).

The cocatalyst is preferably one of titanium (Ti), tin (Sn) and manganese (Mn) doped FeOOH, or undoped FeOOH, and more preferably, titanium doped FeOOH.

This step may be performed by immersing the hematite co-doped with the main dopant and the object dopant silicon (Si) in a solution containing an iron source, or a solution containing a titanium source and an iron source together, followed by heat treatment.

The iron source is iron chloride (FeCl ₃ ), iron fluoride (FeF ₂ ), iron sulfide (FeSO ₄ ), iron acetate (Fe (CO ₂ CH ₃ ) ₂ ), iron nitride (Fe (NO ₃ ) ₃ ), and hydrates thereof It may be any one selected from.

The titanium source is titanium chloride (TiCl ₃ ), titanium dioxide (TiO ₂ ), titanium hydride (TiH ₂ ), titanium tetrachloride (TiCl ₄ ), titanium nitride (TiN), and titanium isopropoxide (C ₁₂ H ₂₈ O ₄ Ti).

The heat treatment is preferably performed at 50 to 100 ° C for 10 to 60 minutes, and more preferably, at 60 to 80 ° C for 20 to 40 minutes.

The present invention provides a photocathode for water decomposition prepared according to the above manufacturing method.

In the photocathode for water decomposition, the main dopant content is preferably 1.5 to 3.0 wt% in the total weight of hematite (Fe ₂ O ₃ ) co-doped with a main dopant and an object dopant (Si ₂ ), more preferably It may be 1.7 to 2.7wt%.

In addition, the present invention provides a water decomposition apparatus including a photocathode for water decomposition manufactured according to the above-described manufacturing method.

Hereinafter, a preferred embodiment is provided to help the understanding of the present invention, but the following examples are merely illustrative of the present invention, and it is apparent to those skilled in the art that various changes and modifications are possible within the scope and technical scope of the present invention. It is no wonder that such variations and modifications fall within the scope of the appended claims.

[Example]

Example  One: Si : Ti - Fe ₂ O ₃ Photo anode  Produce

(1) Preparation of mixed solution of iron source and titanium source

An aqueous solution in which ９ µl of TiCl ₃ was mixed was prepared based on 100 ml of 150 mM FeCl ₃ solution.

(2) Ti-FeOOH production

FTO in 150mM FeCl ₃ solution 100㎖ with a TiCl ₃ based 9㎕ mixed with an aqueous solution (fluorine-doped thin oxide) via a hot-water speech for 3 hours at a temperature of 100 ℃ in an oven after immersing the substrate on which a Ti-doped FeOOH (Ti -FeOOH).

(3) Preparation of Ti-FeOOH with SiO ₂ nanoparticles

The FTO substrate on which Ti-FeOOH was grown was immersed in a solution in which SiO ₂ nanoparticles having an average particle diameter of 7 nm were dispersed for 30 minutes to attach SiO ₂ nanoparticles to the Ti-FeOOH surface.

(4) Si: Ti-Fe ₂ O ₃ production

Hematite (Si: Ti-Fe ₂ O ₃ ) co-doped with silicon and titanium was prepared by further doping Si by washing the sample that had been immersed with water, drying it with nitrogen gas, and heat-treating it at 800 ° C for 20 minutes.

Example  2: Ti - FeOOH / Si : Ti - Fe ₂ O ₃ Photo anode  Produce

To adsorb Ti-FeOOH OER co-catalyst to Si: Ti-Fe ₂ O ₃ prepared according to Example 1, Si: Ti-Fe was added to a solution mixed with 7 μl of TiCl ₃ based on 100 ml of 1.5 mM FeCl ₃ solution. _{A 2} O ₃ sample was added and reacted in an oven at a temperature of 70 ° C. for 30 minutes to allow Ti-FeOOH nanoparticles to adsorb on the surface of Si: Ti-Fe ₂ O ₃ .

Comparative example  One: Si - Fe ₂ O ₃ Photo anode  Produce

To prevent Ti pre-doping, a photocathode was prepared in the same manner as in Example 1, except that a 150 mM FeCl ₃ solution was used instead of the mixed solution of FeCl ₃ and TiCl ₃ .

Comparative example  2: Ti - Fe ₂ O ₃ Photo anode  Produce

A photocathode was prepared in the same manner as in Example 1, except that an additional doping process of Si by SiO ₂ nanoparticles was not performed.

[Test Example]

Test example  One: Photoelectrochemical ( photoelectrochemical , PEC ) Characterization

To perform photoelectrochemical evaluation, Ag / AgCl electrode and Pt mesh under sunlight illumination (1 SUN) were performed using a 3-electrode system composed of a reference electrode and a counter electrode, respectively, and 1 M NaOH + 0.5 M Na as electrolyte. _{A 2} SO ₃ solution was used.

2 is a JV curve comparing various hematite efficiencies with and without Ti pre-doping. According to this, the PEC efficiency of Ti-Fe ₂ O _{3 −} is increased by about 2 times compared to the undoped Fe ₂ O _{3 −} because of increased charge density and reduced charge recombination. Similarly, doping n-type Si to hematite has been reported to improve PEC efficiency due to increased charge density and reduced charge recombination. Therefore, the efficiency of Si: Ti-Fe ₂ O ₃ of Example 1 in FIG. 2 (a) was increased by about 4 times compared to the undoped Fe ₂ O ₃ . However, in the case of Comparative Example 1 in which there is no main dopant Ti doping and only Si doping, the opposite result is obtained. It can be seen from FIG. 2 (b) that Si-Fe ₂ O ₃ shows lower PEC efficiency than undoped Fe ₂ O ₃ . This indicates that the main dopant Ti plays an important role in PEC efficiency.

On the other hand, in order to investigate the effect of Si doping with or without Ti doping, SEM images for comparing the traits of the photocathode of Example 1 and the photocathode of Comparative Example 1 are shown in FIG. 3. 3 (a) is a Si: Ti-Fe ₂ O _{3 of} Example 1, (b) is a SEM image of Si-Fe ₂ O ₃ of Comparative Example 1, it can be confirmed that SiO ₂ nanoparticles are attached to the surface. have. According to this, although Fe ₂ O ₃ with SiO ₂ nanoparticles having a similar form is formed regardless of the presence or absence of the main dopant Ti, since the PEC efficiency shows the opposite result depending on the presence or absence of the main dopant Ti, the main dopant Ti is successfully processed through heat treatment. It seems to play an important role in Si doping.

Test example  2: XRD  And Raman spectrum analysis

The results of XRD analysis to confirm the differences according to the main Ti dopant are shown in FIG. 4. According to this, the XRD pattern shows that a new material is not formed as Si is doped with Fe ₂ O ₃ with or without the main Ti dopant doping. The XRD pattern shows that 36.2 and 64.3 ° correspond to the (110) and (300) planes, respectively (other picks overlapped by the FTO). Conductivity in the (110) plane has been reported to be superior to that of other planes in the vertical direction of the plane. In addition, it can be seen that when the Si-doped to an Fe ₂ O ₃ (110) if the pick size of the Si-doped When the Ti-Fe ₂ O ₃ on the other hand to reduce 15% to 5%.

Meanwhile, the results of Raman spectrum analysis are shown in FIG. 5. According to this, the appearance of the LO mode at 660 cm ^{- 1} shows that the structural structure was collapsed due to the structural disorder, that is, the scattered LO particles. Since the structural changes that have occurred since a Si-doped peak appears at 660cm ^-1 Si- Fe ₂ O ₃ of Comparative Example 1 there is a peak be increased size and wider as compared with the first embodiment of the Si-Ti-Fe ₂ O _3, which As in the XRD results, it can be seen that the Fe ₂ O ₃ surface structure is decayed by Si doping, but when the main dopant Ti is present, the surface structure is relatively less decayed. The reason why the main dopant Ti minimizes the collapse of the surface structure is that the simultaneous injection of Ti and Si due to the sequential atomic or ionic radius of Si <Fe <Ti (or Si ^{4 +} <Fe ^{3 +} <Ti ^{4 +} ) is heterogeneous. This is because it balances the difference between each element and the ionic radius in the element structure.

Test example  3: Electrochemical impedance spectroscopy ( EIS ) analysis

In order to investigate the relationship between the presence of the subject Ti and the Si doping effect, the EIS curve was measured. FIG. 6 is a Nyquist plot measured to investigate the effect of the electrolyte / Fe ₂ O ₃ surface. The R _ct (charge transfer resistance of electrolyte / substance) of Si: Ti-Fe ₂ O ₃ prepared according to Example 1 is very small compared to other Fe ₂ O ₃ photocathodes due to co-doping of Si and Ti. Have However, R _trap is a resistance related to the proportion of holes trapped on the surface, crystalline destruction due to the object Si dopant, Ti-Fe ₂ O ₃ of Comparative Example 2 It has a slightly increased value. Although the R _trap value of Si: Ti-Fe ₂ O ₃ in Example 1 increased than the value of Ti-Fe ₂ O ₃ , it has a smaller value than that of Fe ₂ O ₃ . In the case of Si-Fe ₂ O ₃ without the main Ti dopant of Comparative Example 1, both the R _trap and R _ct values have very large values compared to other Fe ₂ O ₃ photocathodes. This Si dopants in the absence of the subject indicates that the Ti dopant doped Si ^{+ 4} is not possible as the Fe ₂ O ₃ to destroy the crystallinity.

Test example  4: Mott - Schottky  Measure

7 shows a Mott-Schottky plot. According to this, the tendency was consistent with the JV curve and EIS results. It is also possible to obtain the charge density (N _D ) inversely proportional to the slope of the curve in the Mott-Schottky plot. Representative values through Mott-Schottky plot are summarized in Table 1 below.

[Table 1]

According to this, Si: Ti-Fe ₂ O ₃ of Example 1 has the highest charge density, while Si-Fe ₂ O ₃ has the lowest value. This means that the object Si dopant in the SiO ₂ nanoparticles with the main Ti dopant is used for the doping of Fe ₂ O ₃ . However, according to the photocurrent density result, Si-Fe ₂ O ₃ is not used for doping the object Si dopant in SiO ₂ nanoparticles without the main Ti dopant. Si: Ti-Fe ₂ O ₃ of Example 1 is SiO ₂ Fe ₂ O ₃ due to Si doping and Ti in nanoparticles It has a charge carrier concentration of about 6 times higher. However, the charge concentration of Si-Fe ₂ O ₃ is reduced to 0.4 times that of Fe ₂ O ₃ . The calculated space charge layer W _sc of Si: Ti-Fe ₂ O ₃ is Fe ₂ O ₃ or Ti-Fe ₂ O ₃ Shorter. The tendency of the R _ct and Wsc values of each sample is consistent, and it can be explained that the high photocurrent is due to the strong band interference effect on the surface of the photocathode. Therefore, the reduced recombination in Si: Ti-Fe ₂ O ₃ of Example 1 improves the charge separation of the space charge layer. In contrast, in Comparative Example 1 of the W _sc Si- Fe ₂ O ₃ is low because it has a charge carrier concentration in the Fe ₂ O ₃ surface due to the object dopant Si Fe ₂ O ₃ It has a smaller value.

Test example  5: subject Ti Dopant  Effect by content

The content of Ti was changed from 0.88% to 3.38% by adjusting the amount of the main Ti dopant with a 20 wt% TiCl ₃ solution. The results of measuring the photocurrent density according to the Ti dopant content of Ti-Fe ₂ O ₃ are shown in FIG. 8. According to this, when Ti? Amount is optimized to 1.21%, Ti-Fe ₂ O ₃ at 1.23V _RHE has a photocurrent density of about 1.6mAcm ^-2 . When the Ti content increased at 1.21%, excessive Ti doping collapsed the crystal structure, resulting in a slight decrease in efficiency and a change in the starting potential toward the anode.

On the other hand, the object Si dopant in Ti-Fe ₂ O ₃ is SiO ₂ The results of photocurrent density measurement according to the Ti dopant content of Si: Ti-Fe ₂ O ₃ doped in nanoparticles are shown in FIG. 9. According to this, the optimized Ti content of the Si: Ti-Fe ₂ O ₃ photocathode increased to 2.51% and the photocurrent density at 1.23V _RHE increased to 4.6mAcm ^-2 . These results are due to the increase in charge density without collapsing the structure due to the stable structure change due to the harmonious doping of Ti and Si in Si: Ti-Fe ₂ O ₃ .

To further improve PEC efficiency. Si: Ti-Si: Ti-Fe ₂ O ₃ optimized for Ti-FeOOH oxygen generating catalyst (OEC) The photocurrent density of Ti-FeOOH / Si: Ti-Si: Ti-Fe ₂ O ₃ attached on the top was measured and shown in 10. Referring to this, the photocurrent density at 1.23V _RHE was 5.4mAcm ^{-2, which} was 1.2 and 4 times higher than Si: Ti-Fe ₂ O ₃ and Fe ₂ O ₃ , respectively.

In addition, in order to test the feasibility of Si: Ti-Fe ₂ O ₃ as an actual photocathode in the water decomposition reaction, the JT curve was measured at 1.23V _RHE for a long time and the results are shown in FIG. 11. According to this, Si: Ti-Fe ₂ O ₃ of Example 1 of the present invention It was confirmed that the photocathode remained constant without a significant decrease in photocurrent density until 100 hours.

The embodiments of the present invention have been described above, but those skilled in the art can add, change, delete, or add components within the scope of the present invention as set forth in the claims. The present invention may be variously modified and changed by the like, and it will be said that this is also included within the scope of the present invention.

Claims (23)

(a) an iron source, and a step of forming a tetravalent ion preparing a mixed solution by mixing the principal dopant ion source is greater than the Fe ^{3 +} a large metal;
(b) immersing a transparent electrode substrate in the mixed solution, followed by heat treatment to grow FeOOH doped with a main dopant on the transparent electrode substrate;
(c) immersing the main dopant-doped FeOOH in a solution in which silica (SiO ₂ ) nanoparticles are dispersed to prepare a main dopant-doped FeOOH with silica nanoparticles attached to the surface; And
(d) Main dopant doped FeOOH to which silicon dioxide nanoparticles are attached is heat-treated to further dop the object dopant silicon (Si), so that the main dopant and object dopant silicon (Si) are co-doped hematite (Fe ₂ O ₃ ) to prepare; a method for producing a photocathode for photolysis (photoanode). According to claim 2,
The main dopant of step (a) is titanium (Ti), tin (Sn), and manganese (Mn) is selected from any one of the method for producing a photocathode (photoanode) for decomposition. According to claim 2,
The main dopant of step (a) is titanium (Ti), characterized in that the method for producing a photocatalyst (photoanode) for water decomposition. According to claim 3,
The titanium (Ti) source of step (a) is titanium chloride (TiCl ₃ ), titanium dioxide (TiO ₂ ), titanium hydride (TiH ₂ ), titanium tetrachloride (TiCl ₄ ), titanium nitride (TiN), and titanium isopro Method for producing a photoanode for water decomposition, characterized in that any one selected from the Foxside (C ₁₂ H ₂₈ O ₄ Ti). According to claim 1,
The iron source of step (a) is iron chloride (FeCl ₃ ), iron fluoride (FeF ₂ ), iron sulfide (FeSO ₄ ), iron acetate (Fe (CO ₂ CH ₃ ) ₂ ), iron nitride (Fe (NO ₃ ) ₃ ), And any one selected from hydrates thereof. According to claim 1,
The mixed solution of step (a) is a method for manufacturing a photoanode for water decomposition, characterized in that it comprises 0.001 to 0.05 mol by weight of the main dopant source relative to 100 mol by weight of the iron source. According to claim 1,
The transparent electrode substrate of step (b) is FTO, ZnO, ITO, AZO, GZO, IZO, and IGZO method for producing a photocathode for photolysis, characterized in that any one selected from the. The method of claim 7,
Heat treatment of step (b) is a method for producing a photocatalyst (photoanode) for water decomposition, characterized in that is carried out for 1 to 5 hours at a temperature of 80 to 120 ℃. According to claim 1,
The method of manufacturing a photoanode for water decomposition, characterized in that the average particle diameter of the silica nanoparticles in step (c) is 5 to 10nm. According to claim 1,
Method of producing a photocathode for water decomposition, characterized in that the immersion in step (c) is performed for 10 to 60 minutes. According to claim 1,
After step (c), the method for producing a photocathode for water decomposition, characterized in that the silica-doped titanium doped hematite is further washed and then dried with water. The method of claim 11,
The drying is a method for producing a photocathode for water decomposition, characterized in that is performed using nitrogen gas. According to claim 1,
The heat treatment of step (d) is a method for producing a photocathode for water decomposition, characterized in that is performed for 5 minutes to 30 minutes at 600 to 1000 ℃. According to claim 1,
After step (d),
(e) adsorbing a cocatalyst on hematite (Fe ₂ O ₃ ) co-doped with a main dopant and an object dopant (Si); a method for producing a photocathode for water decomposition, further comprising: . The method of claim 14,
The cocatalyst is a method for producing a photocathode for water decomposition, characterized in that the titanium doped FeOOH or titanium doped FeOOH. The method of claim 15,
The cocatalyst is a method for producing a photocathode for water decomposition, characterized in that the titanium doped FeOOH. The method of claim 14,
Step (e) is characterized in that the main dopant and the object dopant silicon (Si) co-doped hematite is immersed in a solution containing an iron source or a solution containing a titanium source and an iron source together and heat-treated. Method for manufacturing photocathode for water decomposition. The method of claim 17,
The iron source of step (e) is iron chloride (FeCl ₃ ), iron fluoride (FeF ₂ ), iron sulfide (FeSO ₄ ), iron acetate (Fe (CO ₂ CH ₃ ) ₂ ), iron nitride (Fe (NO ₃ ) ₃ ), And any one selected from hydrates thereof. The method of claim 17,
The titanium source of step (e) is titanium chloride (TiCl ₃ ), titanium dioxide (TiO ₂ ), titanium hydride (TiH ₂ ), titanium tetrachloride (TiCl ₄ ), titanium nitride (TiN), and titanium isopropoxide ( C ₁₂ H ₂₈ O ₄ Ti) method for producing a photoanode for water decomposition, characterized in that any one selected from. The method of claim 17,
The method of manufacturing the photocathode for water decomposition, characterized in that the heat treatment of step (e) is performed at 50 to 100 ° C for 10 to 60 minutes. A photocathode for water decomposition manufactured according to the method of any one of claims 1 to 20. The method of claim 21,
In the photocathode for water decomposition, the main dopant and object dopant silicon (Si) co-doped hematite (Fe ₂ O ₃ ) in the total weight of the main dopant content is characterized in that the photocatalyst for water decomposition is 1.5 to 3.0wt% . A water decomposition apparatus comprising a photocathode for water decomposition manufactured according to the method of any one of claims 1 to 20.

Images