KR102387153B1 - Photoelectrode comprising bismuth vanadate/indium oxide heterogeneous nanorods and manufacturing method thereof - Google Patents

Abstract

The present invention provides an indium oxide thin film and an indium oxide nanorod formed on the thin film; and a bismuth vanadate/indium oxide heterojunction nanorod comprising bismuth vanadate electrodeposited on the nanorod, and a method for manufacturing the same. In the photoelectrode of the present invention, the nanostructure of the upper electrode is possible by introducing a lower electrode having a nanorod structure, and the separation of photocharges is improved, thereby increasing the solar water decomposition efficiency.

Description

Photoelectrode comprising bismuth vanadate/indium oxide heterojunction nanorods and manufacturing method thereof

The present invention relates to a photoelectrode comprising a bismuth vanadate/indium oxide heterojunction nanorod and a method for manufacturing the same.

Fossil fuels, which have been used for about 300 years since the Industrial Revolution, have caused numerous energy and environmental problems, such as global warming and air pollution. To solve this problem, a number of studies are underway to develop eco-friendly new and renewable energy that does not emit carbon. energy being received.

However, the conventional form of solar cells, which converts solar energy into electric energy, has several limitations in terms of energy storage and transport, and thus conversion to solar fuel form is attracting attention. Among them, hydrogen energy is attracting attention as a clean energy without pollution because it does not generate by-products other than water during combustion.

To solve this problem, solar water splitting hydrogen production technology is being actively researched. The solar water decomposition hydrogen production technology produces hydrogen by decomposing water at the interface between the photoelectrode and the electrolyte using electrons and holes generated when sunlight is incident on the photoelectrode. The voltage to cause this water decomposition reaction is 1.23 V thermodynamically, but an overvoltage is required due to the interfacial reaction rate. However, in the conventional water decomposition hydrogen production method, since the photovoltage produced by the photoelectrode is less than 1.23 V + overvoltage required for water decomposition, hydrogen production is performed as an involuntary reaction requiring an external bias. In particular, since the overvoltage of the photoanode, where oxygen generation reaction occurs during the water decomposition reaction, is a reaction rate determining step that is higher than the overvoltage of the photocathode, it is necessary to develop a photoanode material that can produce a high photovoltage and maximize the interfacial reaction rate. Do.

Bismuth vanadate (BiVO ₄ ), which is widely used as a conventional photoanode material, is a non-precious metal-based material that is inexpensive and has the advantage of having a band gap (2.5 eV) suitable for water decomposition and a band position suitable for oxygen evolution reaction. The slow interfacial reaction rate caused various problems such as charge recombination and photocorrosion.

To solve this problem, change the internal properties of BiVO ₄ through doping of external elements or control the concentration of oxygen voids, or by bonding other photoelectrode materials to BiVO ₄ to form a heterojunction to improve the physical properties of the entire photoelectrode. It is necessary to increase the efficiency of the water decomposition reaction.

Republic of Korea Patent Publication No. 2010-0073864

An object of the present invention is to provide a photoanode comprising a heterojunction nanorod having an upper electrode formed by electrodeposition of bismuth vanadate on a lower electrode having an indium oxide thin film and an indium oxide nanorod, and a method for manufacturing the same.

However, the technical problem to be achieved by the present invention is not limited to the above-mentioned problems, and other problems not mentioned will be clearly understood by those skilled in the art from the following description.

As a technical means for achieving the above technical problem, the first aspect of the present application, a conductive substrate;

an indium oxide thin film formed on the conductive substrate and an indium oxide nanorod formed on the thin film; and

Provided is a photoelectrode comprising a bismuth vanadate/indium oxide heterojunction nanorod comprising bismuth vanadate electrodeposited on the nanorod.

According to one embodiment of the present application, the photoelectrode is characterized in that for solar water decomposition.

The second aspect of the present invention, the present invention comprises the steps of depositing an indium oxide thin film on the conductive substrate (S1);

manufacturing a lower electrode by depositing an indium oxide nanorod on the thin film by a glancing angle deposition method (S2); and

Provided is a method of manufacturing a photoelectrode including bismuth vanadate/indium oxide heterojunction nanorods, comprising the step (S3) of electrodepositing bismuth vanadate on the lower electrode prepared in step S2 to form an upper electrode.

According to one embodiment of the present invention, the deposition in step S2 is characterized in that it is performed while rotating the conductive substrate on which the indium oxide thin film is deposited at an oblique angle of 70° to 90° at 50 to 100 rpm.

According to one embodiment of the present invention, the deposition rate of the step S2 is characterized in that 0.1 Å / s to 1 Å / s.

According to one embodiment of the present invention, when the deposition of step S2 is completed, it characterized in that it further comprises a step (S2') of heat treatment at a temperature of 400 to 600 ℃ for 60 minutes to 240 minutes.

According to an embodiment of the present invention, the step S3,

Preparing a counter electrode, a reference electrode, and the lower electrode supported in the electrodeposition solution (S3-1); and

and applying a pulse current to the lower electrode to electrodeposit bismuth vanadate on the surface of the lower electrode (S3-2).

According to one embodiment of the present application, the electrodeposition solution is characterized in that it contains vanadyl sulfate and bismuth (III) nitrate, the pH is 4 to 6, and the temperature is 60 to 100 ℃.

According to the exemplary embodiment of the present application, the counter electrode is a platinum electrode, and the reference electrode is an Ag/AgCl electrode.

According to an embodiment of the present application, the pulse current is

It is applied repeatedly with a predetermined period composed of an on time and an off time, the on time is 10 seconds, and the off time of the pulse current is 30 seconds.

According to one embodiment of the present application, the pulse current is characterized in that it is repeatedly applied in 1 to 60 cycles.

According to an exemplary embodiment of the present application, the pulse current is repeatedly applied in 3 cycles.

The photoelectrode of the present invention uses a lower electrode having a nanorod structure, and may be formed by nanostructured BiVO ₄ upper electrode. As a result, light reflection can be reduced and light absorption can be increased, the distance to the photoelectrode/electrolyte interface is reduced, which increases the transfer and separation efficiency of charges, and the overall surface reaction sites increase due to an increase in specific surface area, resulting in improved water decomposition efficiency. Since it can increase, it can be used as a photoelectrode that can be used for water decomposition by efficient sunlight. In addition, by introducing In ₂ O ₃ as a lower electrode material to form a Type II band structure with BiVO ₄ , separation of photocharges is improved and excellent photoelectrochemical properties can be obtained.

1 is a view showing a cross-section of a BiVO ₄ /In2O ₃ heterojunction photoelectrode of the present invention.
2 is a diagram schematically illustrating a method for manufacturing a heterojunction photoelectrode.
3 is a view showing an X-ray diffraction (XRD) analysis result, a linear scanning potential (LSV) measurement result and a scanning electron microscope analysis result according to the heat treatment temperature of indium oxide in the manufacturing method of the present invention.
4 is a view showing the results of X-ray diffraction (XRD) analysis of the photoelectrode manufactured by the manufacturing method of the present invention.
5 is a view showing a scanning electron microscope analysis result of the photoelectrode according to the pulse cycle in the manufacturing method of the present invention.
6 is a view showing the results of linear scanning potential (LSV) analysis of the photoelectrode according to the pulse cycle in the manufacturing method of the present invention (back incident, front incident, 1.23 V).
7 is a view showing the analysis result of the band structure of the photoelectrode of the present invention (UV-vis, UPS, band structure).

Since the present invention can apply various transformations and can have various embodiments, specific embodiments are illustrated and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention.

Terms used in the present invention are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present invention, terms such as include or have are intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, but one or more other features, number, step , it should be understood that it does not preclude in advance the possibility of the presence or addition of an operation, component, part, or combination thereof.

In order to efficiently generate hydrogen through water decomposition by sunlight, it is necessary to increase the efficiency of the three steps of water decomposition: light absorption, photocharge separation, and surface charge transfer. For this, nano-structuring of the photoelectrode material is required. When the photoelectrode has a nanostructure, light absorption increases as the light reflectance decreases compared to the flat structure, the distance from the inside of the material to the interface with the electrolyte decreases, so the movement of photocharge increases, and the specific surface area increases to transfer surface charge Efficiency can be increased in all three aspects by increasing the surface reaction rate by increasing the available area.

Accordingly, the present inventors paid attention to a photoelectrode based on bismuth vanadate, and introduced an oxide photoelectrode having a nanorod structure as a lower electrode of BiVO ₄ for the nanostructure of the BiVO ₄ -based photoelectrode. In addition, it was confirmed that when BiVO _{4 was synthesized on the nanorod structure by the pulse-based electrodeposition method, the effect of increasing the efficiency by the nanostructure could be obtained compared to BiVO 4 synthesized} on the thin film structure by uniformly coated on the rod.

Therefore, the present invention is a conductive substrate; an indium oxide thin film formed on the conductive substrate and an indium oxide nanorod formed on the thin film; and a bismuth vanadate/indium oxide heterojunction nanorod comprising bismuth vanadate electrodeposited on the nanorod. it was

Referring to FIG. 1 , the photoelectrode of the present invention includes an In ₂ O ₃ thin film structure lower electrode 100 , an In ₂ O ₃ nanorod structure lower electrode 200 , and a BiVO ₄ upper electrode 300 . .

In addition, the present invention comprises the steps of depositing an indium oxide thin film on the conductive substrate (S1); manufacturing a lower electrode by depositing an indium oxide nanorod on the thin film by a glancing angle deposition method (S2); and forming an upper electrode by electrodepositing bismuth vanadate on the lower electrode prepared in step S2 (S3). The manufacturing method is schematically shown in FIG. 2 .

The photoelectrode of the present invention is used as an electrode for solar water decomposition. The photoelectrode of the present invention can be used as a photoelectrode having excellent photoelectrochemical efficiency by forming a heterojunction structure.

Step S1 of the present invention is a step of depositing an indium oxide thin film on the conductive substrate. The conductive substrate may be used without limitation as long as it has conductivity, for example, ITO, FTO, etc. may be used, but is not limited thereto. The deposition may be performed using an E-beam evaporator. The deposition may be performed without rotating the substrate at an angle of 0°. The thin film may be deposited to a thickness of 1 to 100 nm, but is not limited thereto.

Step S2 of the present invention is a step of manufacturing a lower electrode by depositing indium oxide nanorods on the thin film formed in step S1 in a glancing angle deposition method. Step S2 is also performed using electron beam deposition equipment and may be performed while rotating the conductive substrate on which the indium oxide thin film is deposited at an oblique angle of 70° to 90° at 50 to 100 rpm. More preferably, it may be performed at an angle of 80 to 85°. The deposition rate of step S2 may be 0.1 Å/s to 1 Å/s. If it exceeds 1 Å/s, it may affect the degree of vacuum of the electron beam deposition equipment. The nanorods may be formed to have a length of 1 to 5 μm.

When the deposition of step S2 is completed, the step (S2') of heat treatment at a temperature of 400 to 600° C. for 60 minutes to 240 minutes may be further performed. More preferably, it may be carried out at a temperature of 500 ° C. to 600 ° C. for 90 minutes to 150 minutes.

Step S3 of the present invention is a step of forming an upper electrode by electrodepositing bismuth vanadate on the lower electrode prepared in step S2. The electrodeposition is performed through a pulse-based electrodeposition method, and more specifically, the steps of preparing a counter electrode, a reference electrode, and the lower electrode supported in an electrodeposition solution (S3-1); and electrodepositing bismuth vanadate on the surface of the lower electrode by applying a pulse current to the lower electrode (S3-2). The electrodeposition solution may include vanadyl sulfate and bismuth (III) nitrate, and may have a pH of 4 to 6, and a temperature of 60 to 100°C.

In step S3-2, the current is applied by configuring a pulse cycle to be repeated with a predetermined period composed of an on time and an off time. The on time may be 10 seconds, and the off time of the pulse current may be 30 seconds. As in the embodiment of the present invention, 0V: 1.5 ~ 2.0 V = 30 s: A pulse cycle can be configured to be 10 s.

The pulse current may be repeatedly applied in 1 to 60 cycles. Preferably, repeated application in 3 cycles causes indium oxide and bismuth vanadate to form a Type II band structure, thereby improving separation of photocharges and having excellent photoelectrochemical properties.

The counter electrode may be a platinum electrode, and the reference electrode may be an Ag/AgCl electrode, but is not limited thereto.

In the present invention, the In ₂ O ₃ nanorod photoelectrode was introduced to realize the nanostructure of BiVO ₄ as well as to form a Type II heterojunction band structure. In the Type II heterojunction band structure, the band positions of the valence and conduction bands of two or more semiconductors form a stepped structure to maximize the separation and movement of photocharges (electrons, holes). There were WO ₃ , SnO ₂ and the like as materials for forming the conventional BiVO ₄ and Type II heterojunction band structure, but in the present invention, it was confirmed for the first time that In ₂ O ₃ has a Type II band structure with BiVO ₄ , remarkably Improved photoelectrochemical properties have been confirmed.

In an embodiment of the present invention, BiVO ₄ was nanostructured by introducing In ₂ O ₃ nanorods to improve the photoelectrochemical efficiency of BiVO ₄ , and as a result, BiVO ₄ and Type II band structure were formed to maximize photocharge separation. Confirmed.

Hereinafter, preferred embodiments of the present invention will be described so that those of ordinary skill in the art can easily implement them with reference to the accompanying drawings. In addition, in the description of the present invention, when it is determined that a detailed description of a related known function or a known configuration may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. In addition, certain features presented in the drawings are enlarged, reduced, or simplified for ease of explanation, and the drawings and components thereof are not necessarily drawn to scale. However, those skilled in the art will readily understand these details.

Example 1. In through glancing angle deposition method based on E-beam evaporator ₂ O ₃ Nanorod Synthesis

In Example 1, In ₂ O ₃ nanorods were synthesized on the FTO substrate through the glancing angle deposition method using an E-beam evaporator. After putting the In ₂ O ₃ source in the equipment and loading the FTO, the glancing angle was set to 0° to increase the adhesion of the nanorods, and a 20 nm In ₂ O ₃ thin film was deposited without rotating the substrate.

When the deposition was completed, the lower electrode was manufactured by depositing the nanorods while rotating the substrate at about 82 to 84 rpm with the glancing angle set to 82.5° again. The deposition rate was 1 Å/s or less, and deposition was performed until the length of the nanorods was about 3 μm.

After deposition, heat treatment was performed at 400° C., 500° C., and 600° C. for 2 hours, respectively. At this time, the temperature increase rate was 2°C/min. When the heat treatment was completed, X-ray diffraction analysis (Bruker, D8-advance), linear scanning potential (LSV) measurement, and scanning electron microscope analysis (MERLIN Compact, FE-SEM) were performed, and are shown in FIG. 3 .

As shown in FIG. 3 , as a result of XRD analysis, it was confirmed that cubic structure In ₂ O ₃ was well formed at all heat treatment temperatures, and LSV measurement results in 0.5 M KP _i + 1.05 M Na ₂ SO ₃ electrolyte, heat treatment at 600° C. It was confirmed that In ₂ O ₃ showed the best photoelectrochemical properties.

Example 2. BiVO via pulse-based electrodeposition ₄ /In ₂ O ₃ synthesis

In this Example 2, BiVO ₄ was electrodeposited on the In ₂ O ₃ nanorods synthesized in Example 1 by a pulse-based electrodeposition method. The procedure for making the electrodeposition solution is as follows. After dissolving 30 mM VOSO ₄ in 130 ml DI water, the pH was lowered to 0.5 or less using HNO ₃ . Then, after dissolving Bi(NO ₃ ) ₃ 30 mM, 2 M CH ₃ COONa was added to raise the pH to 5.1, and finally to pH 4.7 using HNO ₃ , an electrodeposition solution was prepared.

For the electrodeposition, a Pt mesh was used as the counter electrode, a 3M Ag/AgCl electrode was used as the reference electrode, and the In ₂ O ₃ electrode prepared in Example 1 was used as the working electrode. The three electrodes were immersed in the electrodeposition solution temperature adjusted to 80 ° C., and the pulse cycle was configured so that 0V: 1.95 V = 30 s: 10 s. carried out. After the synthesis, heat treatment was performed at 500° C. for 6 hours, and the temperature increase rate was 2° C./min.

An XRD analysis was performed on the electrode on which the electrodeposition was completed, and is shown in FIG. 4 . As can be seen in FIG. 4 , it was confirmed that In ₂ O ₃ of all cubic structures and BiVO ₄ of monoclinic structures were well formed.

Example 3. Confirmation of characteristics of photoelectrodes according to pulse cycle

The photoanode manufactured in Example 2 was confirmed through a scanning electron microscope, and is shown in FIG. 5 . As a result of SEM analysis in FIG. 5 , it can be seen that the In ₂ O ₃ nanorods are thickly covered as the pulse cycle of BiVO ₄ synthesized by the pulse electrodeposition method increases.

FIG. 6 shows the linear scanning potential (LSV) measurement results of the BiVO ₄ /In ₂ O ₃ heterojunction photoanode according to the pulse cycle. As a result of measuring the back incident and front incident light in 0.5 M K-Pi + 1.0 M Na ₂ SO ₃ electrolyte, respectively, the BiVO ₄ /In ₂ O ₃ heterojunction photoelectrode sample subjected to 3 cycles of pulse electrodeposition was It was confirmed that the highest photocurrent density was shown at 1.23 V based on RHE, and more excellent photoelectrochemical properties were observed at the back incident.

Example 4. BiVO ₄ /In ₂ O ₃ Band structure analysis of heterojunction photoanode

The band structure of the photoelectrode subjected to the 3 cycle pulse electrodeposition method in Example 2 with the heat treatment at 600° C. in Example 1 was analyzed and shown in FIG. 7 .

The work function (the energy difference from the vacuum level to the Fermi energy level) and the energy difference from the Fermi energy to the valence band were obtained through UPS measurement, and In ₂ O ₃ and BiVO ₄ light through absorbance analysis through UV-vis spectroscopy measurement The band gap of the electrode was derived. Through the derived results, it was possible to understand the band structure of the BiVO ₄ /In ₂ O ₃ heterojunction photoelectrode, and the BiVO ₄ /In ₂ O ₃ photoelectrode had a Type II band structure (the position of the valence band and the conduction band had a stepped structure). formation) was confirmed.

The present invention was carried out with the support of the "Heterojunction nanostructured photoelectrode material development for solar water splitting" project with the financial resources of Korea Hydro & Nuclear Power Co., Ltd. (0543-20190019).

As a specific part of the present invention has been described in detail above, for those of ordinary skill in the art, it is clear that this specific description is only a preferred embodiment, and the scope of the present invention is not limited thereby. will be. Accordingly, it is intended that the substantial scope of the present invention be defined by the appended claims and their equivalents.

Claims (12)

conductive substrate; and
an indium oxide thin film formed on the conductive substrate and an indium oxide nanorod formed on the thin film; and
A photoelectrode comprising a bismuth vanadate/indium oxide heterojunction nanorod comprising bismuth vanadate electrodeposited on the nanorod,
The indium oxide nanorods and the bismuth vanadate have a Type II heterojunction band structure in which the band positions of the valence band and the conduction band form a stepped structure.
2. The method of claim 1
The photoelectrode is a photoelectrode comprising a bismuth vanadate/indium oxide heterojunction nanorod for solar water decomposition.
depositing an indium oxide thin film on the conductive substrate (S1);
manufacturing a lower electrode by depositing an indium oxide nanorod on the thin film by a glancing angle deposition method (S2); and
and forming an upper electrode by electrodepositing bismuth vanadate on the lower electrode prepared in step S2 (S3),
The method of manufacturing a photoelectrode, characterized in that the indium oxide nanorods and the bismuth vanadate have a Type II heterojunction band structure in which the band positions of the valence band and the conduction band form a stepped structure.

4. The method of claim 3,
The deposition in step S2 is performed while rotating the conductive substrate on which the indium oxide thin film is deposited at an oblique angle of 70° to 90° at 50 to 100 rpm, light containing bismuth vanadate/indium oxide heterojunction nanorods A method for manufacturing an electrode.
4. The method of claim 3,
The deposition rate of the step S2 is 0.1 Å/s to 1 Å/s.
4. The method of claim 3,
When the deposition of the step S2 is completed, the light comprising a bismuth vanadate / indium oxide heterojunction nanorod further comprising the step (S2') of heat treatment at a temperature of 400 to 600 ° C. for 60 minutes to 240 minutes A method for manufacturing an electrode.
4. The method of claim 3,
In step S3,
Preparing a counter electrode, a reference electrode, and the lower electrode supported in the electrodeposition solution (S3-1); and
A method of manufacturing a photoelectrode including a bismuth vanadate/indium oxide heterojunction nanorod comprising the step of electrodepositing bismuth vanadate on the surface of the lower electrode by applying a pulse current to the lower electrode (S3-2).
8. The method of claim 7,
The electrodeposition solution includes vanadyl sulfate and bismuth (III) nitrate, a pH of 4 to 6, and a temperature of 60 to 100° C. A photoelectrode including bismuth vanadate/indium oxide heterojunction nanorods manufacturing method.
8. The method of claim 7,
The counter electrode is a platinum electrode, and the reference electrode is an Ag/AgCl electrode.
8. The method of claim 7,
The pulse current is
Light containing bismuth vanadate/indium oxide heterojunction nanorods, which is applied to be repeated with a predetermined period consisting of an on time and an off time, the on time is 10 seconds, and the off time of the pulse current is 30 seconds A method for manufacturing an electrode.
11. The method of claim 10,
The method for manufacturing a photoelectrode comprising a bismuth vanadate/indium oxide heterojunction nanorod, wherein the pulse current is applied repeatedly in cycles of 1 to 60.
12. The method of claim 11,
The method of manufacturing a photoelectrode comprising a bismuth vanadate/indium oxide heterojunction nanorod, wherein the pulse current is repeatedly applied in three cycles.

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