KR102620261B1 - Photocatalyst, manufacturing method thereof, and photoelectrochemical device including the same - Google Patents

Abstract

The present invention can provide a photocatalyst capable of improving photoelectrochemical performance, a method for manufacturing the same, and a photoelectrochemical device including the same.

Description

Photocatalyst, manufacturing method thereof, and photoelectrochemical device including the same}

The present invention relates to a photocatalyst, a method for producing the same, and a photoelectrochemical device comprising the same.

Sustainable energy has recently been intensively researched and developed as a way to solve fossil fuel depletion and environmental problems. Among sustainable energies, solar energy can be used as an infinite resource as the amount of solar energy reaching the earth's surface is much more than the amount of energy consumed by mankind, and it is eco-friendly as it does not cause greenhouse gases or air pollution. Because of this, it is attracting attention as one of the promising alternatives.

As ongoing research into sustainable energy, there is a method of producing hydrogen through photoelectrochemical water splitting technology using solar energy. In particular, in the case of photoelectrochemical water splitting technology, finding a suitable photocatalyst is a major technological challenge, and technology using oxide semiconductors is being intensively researched as a photocatalyst due to its low manufacturing cost and high stability.

However, in the case of oxide semiconductors, which are widely used as photocatalysts, due to their relatively high energy band gap, they exhibit high activity in the ultraviolet region, which accounts for approximately 4% of sunlight, and thus exhibit low efficiency, acting as an obstacle to the commercialization of oxide semiconductors. I'm doing it. Therefore, there is a need to develop a photocatalyst that is advantageous for absorbing visible light.

Therefore, the problem to be solved by the present invention is to provide a photocatalyst that is advantageous for absorbing visible light in order to improve the water decomposition efficiency of a photocatalyst using solar energy. The technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the description below.

Since the present invention can make various changes and have various embodiments, specific embodiments will be illustrated in the drawings and described in detail. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all changes, equivalents, and substitutes included in the spirit and technical scope of the present invention.

The terms used in this application are only used to describe specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

In this specification, terms such as “comprise” or “have” are intended to designate the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, but are not intended to indicate the presence of one or more other features. It should be understood that this does not exclude in advance the possibility of the existence or addition of elements, numbers, steps, operations, components, parts, or combinations thereof.

In this specification, “visible light” refers to light having a shorter wavelength than infrared light and longer wavelength than ultraviolet light, which falls within the wavelength range of about 300 to 800 nm, for example, 330 to 440 nm, and belongs to sunlight. It accounts for the highest proportion of light (e.g., ultraviolet rays, visible rays, infrared rays, etc.).

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related technology, and unless explicitly defined in the present application, should not be interpreted in an idealized or excessively formal sense. No.

Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the attached drawings. In order to facilitate overall understanding when describing the present invention, the same reference numerals are used for the same components in the drawings, and duplicate descriptions for the same components are omitted.

<Photocatalyst>

In one embodiment, the present invention provides a photocatalyst. Figures 1 and 2 show a schematic diagram of a photocatalyst according to an embodiment, and will be described below with reference to the drawings. In the present invention, a photocatalyst refers to a catalyst that accelerates a photoreaction. By not directly participating in the reaction, it is not consumed even when the reaction is performed, and accelerates the reaction rate by providing a mechanism path different from that of existing photoreactions. It can mean ordering. A photochemical reaction using a photocatalyst may include a series of processes in which light with energy exceeding the bandgap energy is absorbed to generate electrons and holes, and their charge pairs generate active species, causing oxidation and reduction.

In particular, the photocatalyst of the present invention can exhibit catalytic activity to generate hydrogen gas by decomposing water as shown in the following formula (1), especially under visible light irradiation, and the water decomposition reaction is a standard Giabbs free energy change (△). It has a G°) value of 237 KJ/mol and a band gap energy of 1.23 eV.

[Formula 1]

H ₂ O (l) → 0.5 O ₂ (g) + H ₂ (g)

In one example, the photocatalyst of the present invention may include a substrate 200 and a catalyst layer 100 formed on the substrate including monoclinic bismuth vanadate (BiVO ₄ ), which is an n-type metal oxide semiconductor. .

The substrate 200 can be used without limitation as long as it is a conductive or transparent material. According to one example, the substrate 200 may include one or more of FTO, ITO, IZO, silver nanowire, and carbon nanotube.

Bismuth vanadate (BiVO ₄ ) included in the catalyst layer 100 has high stability in an aqueous environment, exhibits a fast charge transfer rate due to its relatively small effective mass of electrons and charges, and has a band gap energy of the level required for water decomposition. You can be satisfied. In particular, the bandgap energy of pure monoclinic bismuth vanadate (BiVO ₄ ) is 2.4 eV, and it absorbs visible wavelengths of sunlight to create holes and electrons, making it a photocatalyst that uses the ultraviolet wavelength range. The efficiency can be very high. Here, pure bismuth vanadate (BiVO ₄ ) means bismuth vanadate (BiVO ₄ ) that has not been doped or further processed.

However, pure bismuth vanadate (BiVO ₄ ) has a problem in that it has limitations in improving energy conversion efficiency due to low charge mobility and fast recombination rate of electron-hole pairs. Therefore, in order to solve this problem, the present application suppresses recombination of electrons and holes and reacts with water by ensuring that electrons and holes generated by irradiation of solar energy have fast mobility and are efficiently separated. A photocatalyst with increased probability can be provided. In addition, the present application can provide a catalyst that can efficiently absorb photons by lowering the bandgap energy to absorb visible light with less energy. Details will be explained below.

According to one embodiment of the present invention, bismuth vanadate (BiVO ₄ ) may be doped with at least one metal from the group consisting of Ag, Fe, Mo, Ru, Cu, Fe, T, and W. That is, bismuth vanadate (BiVO ₄ ) of the present invention can be doped with the above metal in its crystal structure. In this way, bismuth vanadate (BiVO ₄ ) doped with metal has improved electron concentration and mobility, thereby effectively reducing the bulk recombination rate and improving photocurrent density.

In one example, bismuth vanadate (BiVO ₄ ) is doped with Mo, wherein Mo is 1.3 to 2.7 atomic percent, 1.5 to 2.5 atomic percent, or 1.7 to 2.3 atomic percent relative to the number of atoms of bismuth vanadate (BiVO ₄ ). It can be included in atomic percent. By doping with the above content, the initiation potential is lowered without increasing the number of defects that act as traps for electrons and holes, thereby improving the photocurrent density, thereby enabling excellent electrochemical performance.

According to one embodiment of the present invention, the catalyst layer 100 may include a passivation layer 120 on one side having an electron concentration in the range of 3.6×10 ²⁴ to 9.7×10 ²⁸ m ^-3 . As an example, the electron concentration may be measured using the Mott-Schottky method, and the electron concentration of the passivation layer 120 is 1.5 × 10 ²⁵ m ^-3 or more, 5 × 10 ²⁷ m ^-3 or more, 7×10 ²⁷ m ^-3 or more, 8×10 ²⁷ m ^-3 or more, 9×10 ²⁷ m ^-3 or more, 1×10 ²⁹ m ^-3 or less, 1×10 ²⁸ m ^-3 or less. . The electron concentration of the passivation layer 120 may be more than 2,000 times that of pure monoclinic bismuth vanadate (BiVO ₄ ).

In the present invention, the electron concentration may be calculated according to the following equation through the Mott-Schottky graph according to FIG. 8, assuming ideal semiconductor characteristics.

[Equation]

In the above equation, V is the conduction band potential (V), V _fb is the flat band potential (V), K _B is the Boltzmann constant, T is the temperature (K), e is the charge of the electron (C), and ε is The relative dielectric constant, ε may represent the dielectric constant, _ND may represent the electron concentration per unit volume (cm ³ ), C may represent the surface charge capacitance (F/cm ² ), and A may represent the surface area of the electrode (cm ² ).

More specifically, the catalyst layer 100 according to the present application may have different electron concentration or oxygen vacancy concentration in the thickness direction. In detail, the passivation layer 120 may have a relatively low electron concentration and a higher concentration of oxygen vacancies compared to the base layer 110 located on the substrate 200. In other words, the photocatalyst layer according to the present application has a surface electron density of the doped bismuth vanadate (BiVO ₄ ) catalyst layer that is higher than that of the base layer without separately depositing a separate layer of a different material, so the surface defect state is deactivated. It can exhibit excellent surface electronic properties and, in addition, can exhibit improved photocurrent density through a cathodic shift in the onset potential.

The thickness of the catalyst layer 100 may be 400 to 800 nm, 500 to 700 nm, or 550 to 650 nm. As an example, the thickness of the passivation layer 120 may be thinner than the thickness of the base layer 110. That is, the catalyst layer 100 may include a passivation layer 120 having a high electron concentration that is formed to a depth of 50%, 40%, 30%, or 20% from the surface (top surface) compared to the thickness of the catalyst layer. Additionally, the passivation layer 120 may be a surface that contacts the electrolyte within the electrochemical device.

Meanwhile, in a semiconductor, recombination of electrons and holes can occur on the surface and in the bulk. Recombination loss in the bulk and recombination loss on the surface can occur independently, and in order to absorb sunlight and perform a chemical reaction, Suppressing recombination loss at the surface can be very important. The photocatalyst according to the present application includes a passivation layer with a very high electron concentration as described above, so that not only recombination loss in the bulk but also recombination loss on the surface can be improved, and the life-time of the carrier can be increased. there is.

As an example, it may include vanadium in the form of tetravalent vanadium ions (V ₄₊ ) and pentavalent vanadium ions (V ₅₊ ), and according to X-ray photoelectron spectroscopy (XPS), pentavalent vanadium (V ⁵⁺ ) The ratio of tetravalent vanadium (V ⁴⁺ ) peak area to peak area may satisfy General Formula 1 below.

[General Formula 1]

0.3〈 Peak Area (V ₄₊ )/ Peak Area (V ₅₊ ) 〈 0.6

The lower limit according to General Formula 1 may be 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, or 0.47, and the upper limit may be 0.58, 0.56, 0. 54, It may be 0.52, 0.5, or 0.49.

Additionally, as an example, it may include oxygen in the form of -divalent oxygen ions (O ^2- ) and hydroxide ions (OH ^- ), and the hydroxide ion (OH ^- ) peak according to X-ray photoelectron spectroscopy (XPS). The -divalent oxygen ion (O ^2- ) peak area ratio to area may satisfy General Formula 2 below.

[General Formula 2]

0.5〈 Peak area (O ^2- )/ Peak area (OH ^- ) 〈 5

The lower limit according to General Formula 2 may be 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3, or 3.1, and the upper limit may be 4.8, 4.6, 4.4, 4.2, It may be 4, 3.8, 3.6, 3.4, or 3.2.

That is, according to the present application, the ratio of the tetravalent vanadium (V ⁴⁺ ) peak area to the pentavalent vanadium (V ⁵⁺ ) peak area is controlled to the above specific range, and the ratio of the peak area to the hydroxide ion (OH ^- ) peak area is -2. By controlling the oxygen ion (O ^2- ) peak area ratio to the above specific range, the repulsive electrostatic interaction between positive holes and positive defect sites is reduced due to the reduction of the positive charge of surface defects, resulting in hole movement to the photocatalyst surface. can promote and improve PEC performance.

As an example, the photocatalyst may have a band gap energy of 2 eV or more and 2.3 eV or less, for example, 2.1 eV or more and less than 2.3 eV. A photoreaction using a photocatalyst excites electrons in the valence band, forming electrons in the conduction band and forming holes in the valence band. Here, the formed electrons and holes can diffuse to the surface of the photocatalyst and participate in photochemical reactions. The photocatalyst of the present invention uses the bandgap energy, which is the gap between the valence band and the conduction band, to pure monoclinic bismuth vanadate (BiVO ₄ ). By lowering the band gap energy to less than 2.4 eV, photoreaction can be performed with high efficiency in the visible light region.

Accordingly, the photoelectrochemical device using the photocatalyst of the present application can have a photocurrent density of more than 2 mA/cm ² and less than 5 mA/cm ² , which is 33 times higher than that of pure monoclinic bismuth vanadate (BiVO ₄ ). This is a higher value. In addition, the photoelectrochemical device using the photocatalyst of the present application can exhibit a photocatalytic efficiency (IPCE, Incident-Photon-to-electron conversion efficiency) of 35% or more, for example, 37% or more, 40% or more, or 43% or more. , or it may exhibit a photocatalytic efficiency of 45% or more, but 80% or less, 70% or less, or 60% or less. A photoelectrochemical device using a photocatalyst according to the present application can exhibit excellent conversion efficiency. In this specification, photocurrent density, electron concentration, and electron efficiency can be measured through Mott-schottky analysis results.

<Photocatalyst manufacturing method>

Additionally, in another embodiment, the present invention provides a method for producing a photocatalyst.

First, the method for producing the photocatalyst of the present invention may include preparing the composite (A).

The step of preparing the complex (A) is to mix 0.5 to 5 moles of ammonium vanadate or its hydrate with a dilute aqueous acid solution for 1 mole of bismuth nitrate or its hydrate to produce clear blue first bismuth vanadate (BiVO ₄ ). forming a complex solution (a1); It may include adding an inorganic compound containing a metal to be doped or a hydrate thereof to the obtained first bismuth vanadate complex solution (a1) to form a second bismuth vanadate complex solution (a2). For example, but not limited to this, ammonium heptamolybdate, etc. may be used as a metal compound containing the metal to be doped. Additionally, the step of preparing the composite (A) may include forming the composite (A) by dip coating a substrate on the second bismuth vanadate composite solution (a2) obtained above.

In one example, the dip coating step may include dipping the substrate into a second bismuth vanadate complex solution (a2). Dipping may be carried out repeatedly or continuously several times, for example 2 to 8 times, with calcining at 300 to 400 °C or 330 to 370 °C for 1 to 10 minutes between each dipping step. . In this way, the present application includes the step of performing an intermediate heat treatment process between dipping performed several times, thereby forming a monoclinic crystal structure without generating a secondary phase such as metal oxide due to metal doping. It can be maintained. Additionally, after the final dipping step, it can be calcined at 350 to 550 °C for 7 to 13 hours. The calcination temperature may specifically be 370 to 530 °C, 400 to 500 °C, or 420 to 480 °C, and the time may be 8 to 12 hours or 9 to 11 hours.

That is, the present application can obtain doped bismuth vanadate through a dip coating step, and by the method according to the present application, the crystal structure of the existing monoclinic bismuth vanadate can still be maintained even after doping.

Here, the composite (A) includes a catalyst layer containing bismuth vanadate (BiVO ₄ ) doped with at least one metal from the group consisting of Ag, Fe, Mo, Ru, Cu, Fe, T, and W, , the product of the step prior to performing the step of exposure under a light source (i.e., the step of exposure under a light source was not performed), having an electron concentration in the range of (3.6Х10 ²⁴ to 9.7Х10 ²⁸ m ^-3) on one side of the catalyst layer. ) It may refer to a photocatalyst that does not include a passivation layer.

Next, the method for producing the photocatalyst of the present invention involves exposing a photoelectrochemical device including the prepared composite (A) as one electrode to a light source in an open-circuit (OC) configuration for 5 to 15 hours or 7 to 13 hours. It may include the step of asking. The step of exposing under a light source may be performed until the potential appears stably at the equilibrium potential when continuously exposed to the light source. As an example, light source irradiation may be performed from the front or back, and preferably may be performed from the front. Front irradiation may mean that light is irradiated from the photocatalyst layer (passivation layer/base layer)/substrate in the direction from the passivation layer to the catalyst, and back irradiation means that light is irradiated in the direction from the substrate to the catalyst. It can mean becoming. As an example, a two-electrode system or a three-electrode system can be used as a photoelectrochemical device, for example, in the case of a three-electrode system, composite (A) as the working electrode, platinum as the counter electrode, and Ag/AgCl as the reference electrode. can be used. Additionally, an aqueous salt solution having a pH of 6 to 8 may be used as the electrolyte, and the light source may be a Xe lamp that is 100 to 200 W and satisfies 50 to 200 mW/cm ² .

According to the above method, the monoclinic crystal structure of composite (A) can be maintained even if the exposure step is performed under a light source. In addition, the present application may include a passivation layer 120 with a lower concentration of oxygen vacancies while increasing the electron concentration in the catalyst layer 100 by including the step of exposing in an open circuit configuration under a light source, and a large cathode at the onset potential. By inducing cathodic shift, a photoelectrochemical device with excellent photoelectric efficiency can be provided.

<Photoelectrochemical device>

Additionally, in another embodiment, the present invention provides a photoelectrochemical device. The photoelectrochemical cell includes, but is not limited to, a photoelectrode containing the photocatalyst described above; and an electrolyte, and may further include at least one from the group consisting of a counter electrode or a reference electrode in addition to the photoelectrode.

Although not limited thereto, a material selected from Pt, Au, Ni, Cu, Ag, In, Ru, Pd, Rh, Ir, Os, C, conductive polymer, and a combination of two or more of the foregoing may be used as the counter electrode. It can be included. The conductive polymer may be selected from polymers including, for example, polyaniline, polypyrrole, polythiophene, polybenzene, and acetylene. In addition, although not limited thereto, Ag/AgCl, etc. can be used as a reference electrode, and a dilute aqueous solution of pH 6 to 8 can be used as an electrolyte.

As described above, the photocatalyst according to the embodiments of the present invention can efficiently absorb photons by having a low bandgap energy, and at the same time can efficiently separate electrons and holes, showing excellent water decomposition and hydrogen conversion efficiency. . However, the effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description below.

Figure 1 shows a schematic diagram of a photocatalyst according to one embodiment.
Figure 2 shows a schematic diagram of a photocatalyst according to another example.
Figure 3 relates to scanning electron microscopy images of the example composite (A) and the example photocatalyst.
Figure 4 is a graph showing the XPS analysis of the complex of the example (doped bismuth vanadate (2% Mo-BiVO ₄ )).
Figure 5 shows photocurrent density in Examples and Comparative Examples.
Figure 6 shows the photocurrent density for the example composite and the example photocatalyst.
Figure 7 shows the chronoamperometric measurement results for the example composite and the example photocatalyst.
Figure 8 shows the results according to the Mott-Schottky measurement method for the composite of the example and the photocatalyst of the example.
Figure 9 shows the results of photoelectron spectroscopy (XPS) for the composite of the example and the photocatalyst of the example.
Figure 10 shows photostability-related results for the example complex and the example photocatalyst.

Below, a preferred experimental example (example) is presented to aid understanding of the present invention. However, the following experimental examples are only intended to aid understanding of the present invention, and the present invention is not limited by the following experimental examples.

Example

6 mmol bismuth nitrate (Bi(NO ₃ ) ₃ 5H ₂ O), 6 mmol ammonium vanadate (NH ₄ VO ₃ ), and 2.52 g citric acid were mixed with 15 mL nitric acid, 30 mL distilled water, 5 mL acetic acid, and 3 g poly. By slowly adding and mixing to a solution of vinyl alcohol (weight average molecular weight 89,000 to 98,000), a clear blue first bismuth vanadate (BiVO ₄ ) complex solution was obtained. The obtained first complex solution was stirred at room temperature of 25 °C for 4 hours. Then, using ammonium heptamolybdate ((NH ₄ ) ₆ Mo ₇ O ₂₄ 4H ₂ O), an agent that can be doped with 2 atomic percent based on the number of bismuth vanadate (BiVO ₄ ) atoms is prepared. 2 A solution of bismuth vanadate (2% Mo-BiVO ₄ ) complex was obtained.

The washed FTO glass was dipped into the second composite solution four times, and calcination was performed at 350 °C for 5 minutes immediately after 1 to 3 dipping, and immediately after the last dipping, at 450 °C for 10 minutes. By performing calcination for a period of time, bismuth vanadate (2% Mo-BiVO ₄ ) doped at 2 atomic percent based on the number of bismuth vanadate (BiVO ₄ ) atoms was obtained as composite (A). .

Next, the composite obtained above (bismuth vanadate (2% Mo-BiVO ₄ ) doped with 2 atomic percent) as the working electrode, platinum as the counter electrode, and Ag/AgCl as the reference electrode, and pH as the electrolyte. A three-electrode photoelectrochemical device consisting of a 0.5 M Na ₂ SO ₄ aqueous solution with a value of 7 was exposed under front illumination of a 150 W Xe lamp (100 mW/cm ² ) in an open circuit configuration for 10 hours to ensure a stable equilibrium potential. When it appeared, the photocatalyst was finally obtained.

Comparative Example 1

Bismuth vanadate (BiVO ₄ ) is produced as a photocatalyst using a second bismuth vanadate (1% Mo-BiVO ₄ ) complex solution that can be doped at 1 atomic percent based on the number of bismuth vanadate (BiVO ₄ ) atoms. ) A photocatalyst was obtained using the same manufacturing method as in the example, except that bismuth vanadate (1% Mo-BiVO ₄ ) doped at 1 atomic percent relative to the number of atoms was used.

Comparative Example 2

Using a second bismuth vanadate (3% Mo-BiVO ₄ ) complex solution that can be doped at 3 atomic percent based on the number of bismuth vanadate (BiVO ₄ ) atoms, bismuth vanadate (BiVO ₄ ) was produced as a photocatalyst. ) A photocatalyst was obtained using the same manufacturing method as in the example, except that bismuth vanadate (3% Mo-BiVO ₄ ) doped at 3 atomic percent with respect to the number of atoms was used.

Comparative Example 3

Using a second bismuth vanadate (5% Mo-BiVO ₄ ) complex solution that can be doped at 5 atomic percent based on the number of bismuth vanadate (BiVO ₄ ) atoms, bismuth vanadate (BiVO ₄ ) atoms are used as a photocatalyst. A photocatalyst was obtained using the same manufacturing method as in the example, except that bismuth vanadate (5% Mo-BiVO ₄ ) doped at 5 atomic percent was used.

Comparative Example 4

6 mmol bismuth nitrate (Bi(NO ₃ ) ₃ 5H ₂ O), 6 mmol ammonium vanadate (NH ₄ VO ₃ ), and 2.52 g citric acid were mixed with 15 mL nitric acid, 30 mL distilled water, 5 mL acetic acid, and 3 g poly. By slowly adding and mixing a solution of vinyl alcohol (weight average molecular weight 89,000 to 98,000), a clear blue bismuth vanadate (BiVO ₄ ) complex solution was obtained. The obtained composite solution was stirred at room temperature of 25 °C for 4 hours, the washed FTO glass was dipped into the composite solution four times, and immediately after 1 to 3 dipping, it was calcined at 350 °C for 5 minutes. ) was performed, and immediately after the final dipping, calcination was performed at 450 °C for 10 hours to obtain pure bismuth vanadate (BiVO ₄ ) as a photocatalyst.

Figure 3 relates to scanning electron microscopy images of the example composite (A) and the example photocatalyst. In particular, (a) and (c) are scans taken at different magnifications of the composite (A) before exposure under a light source, and (b) and (d) are scans of the photocatalyst obtained by exposing the composite (A) under a light source. This is an electron microscope (SEM) image. According to Figure 3, it can be confirmed that there is no change in morphology and crystal structure before and after exposure to a light source.

Figure 4 is a graph showing the XPS analysis of the complex of the example (doped bismuth vanadate (2% Mo-BiVO ₄ )).

Referring to FIG. 4, the doped bismuth vanadate (2% Mo-BiVO ₄ ) of _the example is molybdenum ( It can be seen that the mixed oxide BiV _0.98 Mo _0.02 O ₄ is formed by replacing the Mo) atom with a vanadium (V) atom. Looking at the Mo 3d core level peak, the Mo 3d peak appears in the composite of the example (doped bismuth vanadate (2% Mo-BiVO ₄ )), while the pure bismuth vanadate (BiVO ₄ ) according to Comparative Example 4 It can be confirmed that does not show the corresponding peak.

Figure 5 shows the photocurrent density in the Examples and Comparative Examples, and Figure 6 shows the photocurrent density for the composite of the Example and the photocatalyst of the Example, and the photocatalyst and counter electrode according to the Examples and Comparative Examples as the photoelectrode, respectively. It was measured by photoelectrochemical measurement using platinum as the reference electrode, Ag/AgCl as the reference electrode, and 0.5 M Na ₂ SO ₄ aqueous solution with a pH of 7 as the electrolyte.

Referring to FIG. 5, it can be seen that the photocurrent density is further improved by performing a step of exposing the photoelectrochemical device under a light source in an open circuit (OC) configuration for a certain period of time, that is, performing an optical charging step. Referring to FIG. 6, it can be seen that exposing the photoelectrochemical device in an open circuit (OC) configuration under a light source for a long time is much more effective at low bias voltage.

Figure 7 shows the chronoamperometric measurement results for the example composite and the example photocatalyst, measured over 4 cycles at a voltage of 1.23 V (vs. RHE), and the photocurrent shows an immediate jump after the light is turned on, showing an immediate jump in the photocatalyst. Indicates rapid charge collection.

Figure 8 shows the results according to the Mott-Schottky measurement method for the composite of the example and the photocatalyst of the example.

In the present invention, all PEC measurements are performed using a three-electrode system consisting of a photocatalyst according to Examples or Comparative Examples as a working electrode, platinum as a counter electrode, Ag/AgCl as a reference electrode, and a 0.5 M Na ₂ SO ₄ aqueous solution with a pH of 7 as an electrolyte. It may have been performed with a photoelectrochemical device, and the IPCE results may have been calculated from time-to-current measurements at 0.6 V (vs. Ag/AgCl) (1.23 V vs. RHE).

The electron density and flat band potential can be obtained from the slope and intercept of the Mott-Schottky spectrum as shown in Table 1 below, and the Mott-Schottky ) Through analysis, the effect on electrochemical performance can be understood by performing the step of exposing the photoelectrochemical device under a light source for a certain period of time in an open circuit (OC) configuration.

Table 1 below summarizes the electron density, flat band potential, photocurrent density (at 1.23V), and photoelectric efficiency (IPCE at 0.6V) of Example and Comparative Example 4.

electron density
(m ^-3 ) flat band potential
(V) photocurrent density
(at 1.23V)
(mA/ ^cm2 ) IPCE
(at 0.6V)
(%) Example 9.77 × 10 ²⁷ -0.36 0.088 4 Comparative Example 4 3.68 × 10 ²⁴ -0.6 3 49.2

Figure 9 shows the results of photoelectron spectroscopy (XPS) for the example complex and the example photocatalyst.

Referring to Figures 9(a) and (b), a clear cathodic shift can be confirmed with respect to the V2P _3/2 orbital of the photocatalyst. Additionally, referring to Figures 9(c) and 9(d), it can be seen that the peak intensity of O1s of the photocatalyst decreased and the full width at half maximum (FWMH) also increased.

V ⁵⁺ and V ⁴⁺ peaks can appear at approximately 517 eV and 516 eV, respectively, O ^2- and OH ^- peaks can appear at approximately 530 eV and 531.5 eV, respectively, and the peaks of hydroxyl groups are more pronounced in the photocatalyst compared to the composite. may appear prominently.

Figure 10 shows photostability-related results for the example complex and the example photocatalyst.

Although the description has been made with reference to the above examples, those skilled in the art will understand that various modifications and changes can be made to the present invention without departing from the spirit and scope of the present invention as set forth in the claims below. You will be able to.

Claims (12)

A catalyst layer containing bismuth vanadate (BiVO ₄ ) doped with Mo, wherein Mo is contained in an amount of 1.3 to 2.7 atomic percent based on the number of atoms of bismuth vanadate (BiVO ₄ ),
The catalyst layer includes a passivation layer on one side having an electron concentration in the range of 7×10 ²⁷ to 9.7×10 ²⁸ m ^-3 ,
-Contains oxygen in the form of divalent oxygen ions (O ^2- ) and hydroxide ions (OH ^- ), and -divalent oxygen ions ⁽ O ^2- ) Photocatalyst whose peak area ratio satisfies the following general formula 2:
[General Formula 2]
0.5〈 Peak area (O ^2- )/ Peak area (OH ^- )〈 5. delete According to claim 1,
It contains vanadium in the form of tetravalent vanadium ion (V ⁴⁺ ) and pentavalent vanadium ion (V ⁵⁺ ), and tetravalent vanadium (V ⁵⁺ ) peak area according to X-ray photoelectron spectroscopy (XPS). A photocatalyst whose vanadium (V ⁴⁺ ) peak area ratio satisfies the following general formula 1:
[General Formula 1]
0.3〈 Peak Area (V ⁴⁺ )/ Peak Area (V ⁵⁺ ) 〈 0.6 delete According to claim 1,
A photocatalyst with a band gap energy of 2 eV or more and 2.3 eV or less. According to claim 1,
A photocatalyst that exhibits catalytic activity to generate hydrogen by decomposing water under visible light irradiation. Preparing complex (A); and
A method for producing a photocatalyst according to claim 1, comprising the step of producing a photocatalyst by exposing a photoelectrochemical device including the composite (A) as one electrode under a light source in an open circuit (OC) configuration for 5 to 15 hours. . According to claim 7,
The step of preparing complex (A) is,
mixing bismuth nitrate or its hydrate and ammonium vanadate or its hydrate to form a bismuth first vanadate complex solution (a1);
Forming a second bismuth vanadate complex solution (a2) by adding a metal compound containing a metal to be doped; and
A method for producing a photocatalyst comprising forming a composite (A) by dip coating a substrate in a second bismuth vanadate composite solution (a2). According to claim 8,
The dip coating step is,
Dipping the substrate into a second bismuth vanadate complex solution (a2); and
A method for producing a photocatalyst comprising calcining at 350 to 550 °C for 7 to 13 hours. According to claim 8,
The dipping step is repeated 2 to 8 times,
A method for producing a photocatalyst comprising calcining at 300 to 400 °C for 1 to 10 minutes between each dipping step. A photoelectrode comprising the photocatalyst according to claim 1; and a photoelectrochemical device comprising an electrolyte. According to claim 11,
A photoelectrochemical device using an aqueous solution with a pH of 6 to 8 as the electrolyte.