KR102027768B1 - Seawater splitting electrode, Method for manufacturing the same, and seawater splitting apparatus - Google Patents

Abstract

A seawater decomposition electrode, a manufacturing method thereof, and a seawater decomposition apparatus are provided. The seawater decomposition apparatus includes a counter electrode connected to the cathode of the power supply unit, the electrode being immersed in seawater to generate oxygen, and a working electrode connected to the anode of the power supply unit, immersed in the seawater, and light is incident to generate hydrogen. The working electrode includes a transparent conductor and a cobalt oxide film coupled to the transparent conductor and including a Kirkendall void.

Description

Seawater splitting electrode, Method for manufacturing the same, and seawater splitting apparatus

The present invention relates to a seawater decomposition electrode, a manufacturing method thereof and a seawater decomposition apparatus.

Hydrogen generation by seawater decomposition using sunlight is a very promising approach to hydrogen economy to satisfy energy generation and storage. Sunlight can generate highly pure hydrogen and generate electricity without contaminants. Unlike fresh water, sea water has inherently a conductivity of 33.9 mS / cm at 25 ° C and a neutral nature of pH 6.44. Therefore, hydrogen production from seawater based on photoelectrochemical cells (PECC) has been spotlighted as a way to realize a green economy.

In order to realize practical solar-based hydrogen production, sea water PECC (SW-PECC) utilizes abundant materials on earth, and has high photoactivity, low cost, non-toxicity, narrow band gap and strong chemical stability. Have. This approach has been carried out by using metal oxides such as BiVO ₄ , Fe ₂ O ₃ , TiO ₂ and WO ₃ as photoanodes of SW-PECC. These metal oxides are protected by oxygen evolution reaction (OER) catalysts such as Co-Pi, C ₃ N ₄ and RhO ₂ to generate chlorine gas at the working electrode and hydrogen at the Pt counter electrode. Generate. However, a more effective design is to achieve hydrogen evolution at the photoactive working electrode.

Among many metal oxides, Co ₃ O ₄ is abundant on the earth and has a high absorption coefficient. Furthermore, the intrinsic p-type conductive Co ₃ O ₄ has direct double band gaps of 1.5 eV and 2.2 eV.

Like the advantages of the photoelectric properties described above, Co ₃ O ₄ also has excellent electrochemical catalytic properties for water decomposition reactions of oxygen evolution reactions (OER) and hydrogen evolution reactions (HER). These two properties (OER and HER) were demonstrated by Co ₃ O ₄ / graphene, Co ₃ O ₄ / carbon fiber and NiCo / NiCoO _x heterostructures.

Patent Publication No. 10-2017-0107642

The problem to be solved by the present invention is to provide a seawater decomposition apparatus with improved operating performance.

Another object of the present invention is to provide a seawater decomposition electrode included in a seawater decomposition apparatus with improved operating performance.

Another object of the present invention is to provide a method for producing a seawater decomposition electrode included in a seawater decomposition apparatus with improved operating performance.

Problems to be solved by the present invention are 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.

Seawater decomposition apparatus according to an embodiment of the present invention for solving the above problems is connected to the negative electrode of the power supply unit, the counter electrode is immersed in seawater to generate oxygen and connected to the positive electrode of the power supply unit, is immersed in the sea water, A walking electrode includes a working electrode through which light is incident to generate hydrogen, wherein the working electrode includes a transparent conductor and a cobalt oxide film coupled to the transparent conductor and including a Kirkendall void.

The seawater decomposition electrode according to an embodiment of the present invention for solving the above other problems includes a transparent conductor and a photocatalyst layer in contact with the transparent conductor and including Co 3 O 4, wherein the photocatalytic layer includes a kekendal void.

The seawater decomposition electrode manufacturing method according to an embodiment of the present invention for solving the above another problem is to provide a transparent substrate, to deposit a cobalt film on the transparent substrate, rapid thermal treatment of the cobalt film to use the Kirkendal diffusion To form a cobalt oxide film comprising Co 3 O 4.

Specific details of other embodiments are included in the detailed description and the drawings.

According to one embodiment of the present invention, there are at least the following effects.

That is, the seawater decomposition apparatus according to some embodiments of the present invention may generate hydrogen and obtain resources with high efficiency.

In addition, the seawater decomposition electrode manufacturing method according to some embodiments of the present invention can ensure high crystallinity and permeability.

The effects according to the present invention are not limited by the contents exemplified above, and more various effects are included in the present specification.

1 is a conceptual diagram illustrating a seawater decomposition apparatus according to some embodiments of the present invention.
FIG. 2 is a conceptual diagram for describing the Co 3 O 4 film of FIG. 1 in detail.
3 is a conceptual diagram illustrating a seawater decomposition apparatus according to some embodiments of the present invention.
4 to 6 are intermediate step views for explaining a method of manufacturing a seawater decomposition electrode in accordance with some embodiments of the present invention.
7 is an X-ray diffraction (XRD) spectrum in a Co state and a Co ₃ O ₄ state of Example 1 of the present invention.
8 is a graph showing transmittance according to the wavelength of incident light of Example 1 and Comparative Example 1 of the present invention.
9 is a graph showing absorption coefficients according to photon energy of Example 1 and Comparative Example 1 of the present invention.
10 is a graph showing the tau graph and the derivative of ln (αhν) according to the photon energy of Example 1 and Comparative Example 1 of the present invention.
11 is a conceptual diagram for explaining the configuration of the second embodiment of the present invention.
FIG. 12 is a graph illustrating linear sweep voltammetry (LSV) measurement results of Example 2, Comparative Example 2, and Comparative Example 3 of the present invention.
FIG. 13 is a graph illustrating results of measuring Tafel slopes of Example 2, Comparative Example 2, and Comparative Example 3 of the present invention. FIG.
14 is a graph illustrating the results of linear scanning potential measurement in the range of 0.4 to -0.3 (V vs. RHE (reversible hydrogen electrode)) under pulsed light conditions of Example 2 of the present invention.
15A is a graph showing the results of linear scanning potential measurement in the range of 0 to -0.8 (V vs. RHE) in the pulsed light condition of Example 2 of the present invention.
FIG. 15B is an enlarged graph of -0.5 to -0.6 (V vs. RHE) of FIG. 15A.
FIG. 16A is a graph showing current time characteristics when an overpotential of −0.34 (V vs. RHE) is applied under the white light condition of Example 2 of the present invention. FIG.
FIG. 16B is an enlarged graph of part A of FIG. 16A.
FIG. 17 is a graph showing current time characteristics when an overpotential of 0.58 and 0.83 (V vs. RHE) is applied under the white light condition of Example 2 of the present invention.
18 is a conceptual diagram illustrating a by-product of Embodiment 2 of the present invention.
19 is a graph showing the current time characteristic according to the wavelength of various incident light of Example 2 of the present invention.
FIG. 20 is a graph illustrating incident photon to charge carrier efficiency (IPCE) according to wavelength at −0.33 (V vs. RHE) of Example 2 of the present invention. FIG.
21 is a graph of 1 / C ² and V in dark and light conditions of Example 2 of the present invention.
FIG. 22 is a graph showing the current-voltage characteristics of the steady-state of Example 2 of the present invention. FIG.
FIG. 23 is a diagram illustrating an estimated energy band edge of a double bandgap of Co ₃ O ₄ .
24 is an energy band diagram of a normal depletion situation of Embodiment 2 of the present invention.
FIG. 25 is an energy band diagram of an inversion situation of Embodiment 2 of the present invention. FIG.
FIG. 26 is an energy band diagram of a deep inversion situation of Embodiment 2 of the present invention. FIG.
27 shows Nyquist plots when the overvoltage of Example 2 of the present invention is applied.
FIG. 28 is a table showing measurement and estimation parameters at −0.44 to −0.53 (V vs. RHE) in Example 2 of the present invention. FIG.
FIG. 29 is an energy dispersive spectra (EDS) of the byproduct obtained in Example 2 of the present invention. FIG.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various forms, and only the present embodiments are intended to complete the disclosure of the present invention, and the general knowledge in the art to which the present invention pertains. It is provided to fully convey the scope of the invention to those skilled in the art, and the present invention is defined only by the scope of the claims. Like reference numerals refer to like elements throughout.

Although the first, second, etc. are used to describe various elements, components and / or sections, these elements, components and / or sections are of course not limited by these terms. These terms are only used to distinguish one element, component or section from another element, component or section. Therefore, the first device, the first component, or the first section mentioned below may be a second device, a second component, or a second section within the technical spirit of the present invention.

When elements or layers are referred to as "on" or "on" of another element or layer, intervening other elements or layers as well as intervening another layer or element in between. It includes everything. On the other hand, when a device is referred to as "directly on" or "directly on" indicates that no device or layer is intervened in the middle.

The spatially relative terms " below ", " beneath ", " lower ", " above ", " upper " It may be used to easily describe the correlation of a device or components with other devices or components. Spatially relative terms are to be understood as including terms in different directions of the device in use or operation in addition to the directions shown in the figures. For example, when flipping a device shown in the figure, a device described as "below or beneath" of another device may be placed "above" of another device. Thus, the exemplary term "below" can encompass both an orientation of above and below. The device may be oriented in other directions as well, in which case spatially relative terms may be interpreted according to orientation.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. In this specification, the singular also includes the plural unless specifically stated otherwise in the phrase. As used herein, “comprises” and / or “comprising” refers to the presence of one or more other components, steps, operations and / or elements. Or does not exclude additions.

Unless otherwise defined, all terms (including technical and scientific terms) used in the present specification may be used in a sense that can be commonly understood by those skilled in the art. In addition, the terms defined in the commonly used dictionaries are not ideally or excessively interpreted unless they are specifically defined clearly.

Hereinafter, a seawater decomposition apparatus according to some embodiments of the present invention will be described with reference to FIGS. 1 and 2.

1 is a conceptual diagram illustrating a seawater decomposition apparatus according to some embodiments of the present invention, Figure 2 is a conceptual diagram for explaining in detail the Co3O4 film of FIG.

Referring to FIG. 1, a seawater decomposition apparatus according to some embodiments of the present disclosure includes a power supply unit 100, a counter electrode 200, and a working electrode 300.

The power supply unit 100 may include a positive electrode 110 and a negative electrode 120. The anode 110 of the power supply unit 100 may be a terminal that supplies current and receives electrons. The cathode 120 of the power supply unit 100 may be a terminal that supplies electrons and receives current. The anode 110 may be connected to the working electrode 300, and the cathode 120 may be connected to the counter electrode 200.

Sea water 400 can be obtained directly from the sea. Thus, seawater 400 may be the most abundant and readily available material on earth. Therefore, due to these characteristics, the method of obtaining hydrogen or the like by decomposing the sea water 400 is spotlighted as a future energy source.

The counter electrode 200 may be immersed in the sea water 400. That is, at least a part of the counter electrode 200 may be in direct contact with the seawater 400 in the seawater 400. The counter electrode 200 may generate oxygen (O ₂ ) gas at a surface in contact with the sea water 400. The counter electrode 200 may receive electrons from the power supply unit 100.

The working electrode 300 may also be immersed in the sea water 400. That is, at least a part of the working electrode 300 may be in direct contact with the seawater 400 in the seawater 400. The working electrode 300 may generate hydrogen (H ₂ ) gas at a surface in contact with the sea water 400. The working electrode 300 may receive a current from the power supply unit 100.

The incident light 500 may reach the working electrode 300 from the outside. The working electrode 300 may generate hydrogen (H ₂ ) gas through a photocatalytic reaction. The working electrode 300 may be a multi-structure in which various layers are formed.

In detail, the working electrode 300 may include a transparent conductor 310 and a cobalt oxide film 320.

The transparent conductor 310 may include at least one of fluorine doped tin oxide (FTO), indium tin oxide (ITO), and metal nanowires. However, the present embodiment is not limited thereto. The transparent conductor 310 may be transparent to allow the incident light 500 to transmit therethrough. Therefore, the incident light 500 may pass through the transparent conductor 310 to reach the cobalt oxide film 320.

The cobalt oxide film 320 may include Co ₃ O ₄ . The cobalt oxide film 320 may be translucent. The cobalt oxide film 320 may perform photoreaction by incident light as a photocatalyst. Through this, hydrogen (H ₂ ) gas may be generated using the current supplied from the anode 110 of the power supply unit 100.

Referring to FIG. 2, the cobalt oxide film 320 may include a void 325 therein. That is, the cobalt oxide film 320 may be a porous film. The void 325 may be a Kirkendal void 325. This may be due to using Kirkendall-diffusion when manufacturing the cobalt oxide film 320.

The cobalt oxide film 320 may be translucent. That is, although all components of incident light are not transmitted optically, a part of incident light corresponding to a part of wavelength range can be transmitted.

The cobalt oxide film 320 may have very good performance as a hydrogen generation reaction catalyst. In addition, the cobalt oxide film 320 may have high sustainability for seawater decomposition performance. Through the various experimental examples introduced later, the characteristics of the seawater decomposition apparatus according to some embodiments of the present invention will be described in detail.

Hereinafter, a seawater decomposition apparatus according to some embodiments of the present invention will be described with reference to FIG. 3.

3 is a conceptual diagram illustrating a seawater decomposition apparatus according to some embodiments of the present invention.

Referring to FIG. 3, the working electrode 300 of the seawater decomposition apparatus according to some embodiments of the present disclosure may include a transparent substrate 330.

The transparent substrate 330 may be a glass substrate or a silicon substrate. The transparent substrate 330 may be transparent to transmit the incident light 500. The transparent substrate 330 may be disposed on one surface of the transparent conductor 310, and the cobalt oxide film 320 may be disposed on the other surface of the transparent conductor 310.

The incident light 500 may pass through the transparent substrate 330 and the transparent conductor 310 to reach the cobalt oxide film 320.

In this embodiment, the cobalt oxide film 320 is stably formed through the transparent substrate 330, and the cobalt oxide film 320 may be used as the working electrode 300 as it is. Hereinafter, a method of forming the working electrode 300 will be described.

4 to 6 are intermediate step views for explaining a method of manufacturing a seawater decomposition electrode in accordance with some embodiments of the present invention.

First, referring to FIG. 4, a transparent conductor 310 is formed on the transparent substrate 330. In this case, the substrate coated with the transparent conductor 310 on the transparent substrate 330 may also be used as a laminated structure.

The transparent substrate 330 and the transparent conductor 310 may be cleaned by ultrasonication with isopropyl alcohol, acetone and distilled water. However, the present embodiment is not limited thereto.

Subsequently, a thin cobalt film 320P may be deposited on the transparent conductor 310 through sputtering. The cobalt film 320P may include pure Co. In this case, the cobalt film may be formed by the first height H1 on average.

The first height H1 may be, for example, 10 to 300 nm. However, it is not limited thereto. If the first height H1 is too small, it is difficult to form the cobalt oxide film 320 later. If the first height H1 is too high, the characteristics of the permeability and porosity of the cobalt oxide film 320 will not be well expressed later. You may not.

Subsequently, referring to FIG. 5, the cobalt film 320P may be rapidly thermally treated 600 (Rapid Thermal Process, RTP) in the air.

The rapid heat treatment 600 may be divided into two sequential sections of the first and second sections. First, the rapid heat treatment 600 may be performed while increasing the temperature in the first section, and then the rapid heat treatment 600 may be performed while the temperature is increased higher in the second section.

For example, the temperature of the first section may be increased to 300 ° C at room temperature, and the temperature of the second section may be increased to 300 ° C from 500 ° C. However, the present embodiment is not limited thereto. For example, the first interval and the second interval may be performed for 5 minutes each.

Referring to FIG. 6, a cobalt oxide film 320 may be formed.

Cobalt oxide film 320 may include voids 325 by Kerkendal diffusion. Kerkendal diffusion may mean that voids are formed in the metal that diffuses faster as the diffusion rates on both sides differ between the boundaries of the two alloys.

That is, as the diffusion of cobalt atoms occurs in the direction of the transparent conductor 310 by rapid heat treatment 600 at the boundary between the cobalt film 320P and the transparent conductor 310 of FIG. 5, the cobalt film 320P as shown in FIG. 6. A void 325 may be formed therein.

At this time, the cobalt film 320P of FIG. 5 may grow into the cobalt oxide film 320 by oxidation. The cobalt oxide film 320 may have a second height H2 on average. The second height H2 may naturally be greater than the first height H1. The second height H2 may be, for example, 10 nm to 500 nm. However, the present embodiment is not limited thereto.

Example 1-Porous Samples

A glass substrate coated with FTO was used as a laminated structure of the transparent substrate 330 and the transparent conductor 310. At this time, the sheet resistance of the laminated structure may be 7 Ω / □. The laminated structure was cleaned by sonication with isopropyl alcohol, acetone and distilled water.

Subsequently, a Co target having a pure diameter of 4 inches was sputter deposited on the laminated structure with a DC power of up to 10 W / cm ² . At this time, the pressure is 5 X 10 ^- is ⁶ Torr, sputtering gas Ar was supplied to 5sccm. At this time, the Co film may have a height of up to 65.5 nm.

The Co was rapidly heat treated at 550 ° C. for 10 minutes to form a Co ₃ O ₄ film. At this time, the rapid heat treatment was first performed at room temperature (25 ° C.) for 5 minutes to 300 ° C., and then heat treatment was performed at 300 ° C. to 550 ° C. for 5 minutes.

After the rapid heat treatment, a natural structure formed a laminated structure of glass substrate, FTO and Co ₃ O ₄ film. At this time, the height of the Co ₃ O ₄ film may be up to 151nm.

7 is an X-ray diffraction (XRD) spectrum in a Co state and a Co 3 O 4 state of Example 1 of the present invention.

Referring to FIG. 7, the Co film deposited in Example 1 is cubic crystal symmetry. This Co film can be completely converted to Co ₃ O ₄ through rapid heat treatment in the atmospheric phase. The cobalt oxide film is an equiaxial crystal system having a = 8.079 GPa. The enhanced diffraction peak strongly indicates that the cobalt oxide film is a high crystalline structure, which may be due to the rapid heat treatment to improve the quality of the film.

The strong diffraction peak at 2θ = 36.91 ° shows higher growth rate of Co ₃ O ₄ in the [311] direction and d-spacing of 2.432 kPa. Diffraction peaks at 19.06 °, 31.34 °, 44.88 °, 55.73 °, 59.43 ° and 65.31 ° are determined by (111), (220), (400), (422), (511) and (404) crystal planes, respectively. Corresponds well. According to the Debye-Scherrer theory, a crystalline size of 189 μs is estimated at the extended (311) diffraction peak.

Comparative Example 1 dense dense sample

It was prepared in the same manner as in Example 1 except that the rapid heat treatment was longer. As the rapid heat treatment is longer, the height of the cobalt oxide film is higher to 160 nm, and the shape of the surface may be more dense.

Experimental Example 1

In order to confirm the optical characteristics of Example 1 and Comparative Example 1, the transmittance according to the wavelength of the incident light was measured.

8 is a graph showing transmittance according to the wavelength of incident light of Example 1 and Comparative Example 1 of the present invention. In FIG. 8, Example 1 may be labeled "porous", and Comparative Example 1 may be labeled "dense".

Referring to FIG. 8, two optical transitions corresponding to two optical band gaps are shown. Example 1 and Comparative Example 1 may be translucent.

Cobalt oxide films exhibit high absorption in the visible region. The absorption coefficient α of Example 1 and Comparative Example 1 can be calculated by the relation of α = (1 / d) ln ((1-R) ² / T). Where d and R are the thickness and the reflectivity, respectively.

9 is a graph showing absorption coefficients according to photon energy of Example 1 and Comparative Example 1 of the present invention.

With reference to FIG. 9, the calculated α is shown as a function of photon energy hv. Where h and v are Planck's constant and photon frequency, respectively. It can be seen that the cobalt oxide film has an α value greater than ⁵ × 10 ⁴ cm ⁻¹ when hν is greater than 1.5 eV, so that 200 nm is sufficient to absorb the visible light spectrum of sunlight.

FIG. 10 is a graph showing derivatives of a Tauc plot and ln (αhν) according to photon energy of Example 1 and Comparative Example 1 of the present invention. The band gap E _g of the cobalt oxide film can be measured according to the tau graph or the derivative. Referring to FIG. 10, both methods can provide similar E _g values.

Example 1 and Comparative Example 1 show two direct band gaps (E _g 1 = 1.5 eV and E _g 2 = 2.3 eV), which are the same as previously reported values.

In Example 1 and Comparative Example 1, both E _g 1 is about 1.5 eV, while the E _g 2 value of Example 1 is about 2.3 eV, which may be slightly higher than about 2.2 eV of Comparative Example 1.

Example 2

11 is a conceptual diagram for explaining the configuration of the second embodiment of the present invention.

Referring to FIG. 11, the working electrode 300 has a structure in which 150 nm of Co ₃ O ₄ is formed on a laminated structure of FTO / glass, and the reference electrode 700 for voltage measurement is a silver-silver chloride electrode (Ag / AgCl electrode). The reference electrode 700 may be connected to the anode 110 of the power supply unit 100 and immersed in the sea water 400. The counter electrode 200 was made of platinum gauze (Pt).

The measured voltage (V vs. Ag / AgCl) is scaled to a reversible hydrogen electrode (RHE) scale by the Nernst relation (E _RHE = E _{Ag / AgCl} + 0.059 pH + E ° _{Ag / AgCl} ). Was converted. In the Nernst relation, E _RHE is the voltage converted to (vs. RHE), E ° _{Ag / AgCl} is 0.210V at 25 ° C., and E _{Ag / AgCl} is the measured voltage relative to the Ag / AgCl reference.

Comparative Example 2

The working electrode of Example 2 was the same as in Example 2 except that a working electrode containing only FTO was used without a Co ₃ O ₄ film.

Comparative Example 3

Except for employing a working electrode containing only commercial Pt gauze in the working electrode of Example 2 was the same as in Example 2.

Experimental Example 2

Linear sweep voltammetry (LSV) measurements were performed to determine the hydrogen production reaction (HER) activity of Example 2, Comparative Example 2 and Comparative Example 3.

12 is a graph showing the measurement results of the linear scanning potential method of Example 2, Comparative Example 2 and Comparative Example 3 of the present invention. 12 shows a polarization curve (iR correction) in the negative direction.

Referring to Figure 12, Example 2 shows a very high activity of the starting potential of 850 mV. In order to obtain a HER current density of 20 mA / cm 2, Example 2 has a slight overpotential of 960 mV for seawater decomposition. This value is an enhanced value, and very, RuCoMo of catalyst based (overpotential ~ 700 mV @ 20 mA / cm 2) and close than the performance of the commercially available Ti foil (1400 mV @ 20 mA / cm 2).

The HER activity of Example 2 thus achieved can be very advantageous for hydrogen production from seawater or for electrolysis of brine, which requires high voltage values (2.1V-4.5V) to produce hydrogen.

FIG. 13 is a graph illustrating results of measuring Tafel slopes of Example 2, Comparative Example 2, and Comparative Example 3 of the present invention. FIG. 13 is shown by the Tafel equation, η = blog (J) + c. Where b is the Tafel slope.

Referring to FIG. 13, the calculated Tafel slopes of Comparative Example 3, Comparative Example 2 and Example 2 are 85, 183, and 20 mV / dec, respectively. This may mean the high HER activity of Example 2. According to rate determining, the Tafel slope of 120, 40 or 30 mV / dec is estimated in Volmer, Heyrovsky or Tafel phases, respectively.

The measured 20 mV / dec Tafel slope of Example 2 is of a very good scale, meaning forward recombination of the two protons producing hydrogen. In the Volmer-Tafel mechanism, a limiting value of 30 mV / dec at 25 ° C. indicates a strong catalytic effect of Co ₃ O ₄ of Example 2. HER catalytic seawater decomposition using such porous Co ₃ O ₄ electrode is expected to further reduce the overvoltage in the form of heterojunction of Co / Co ₃ O ₄ .

Experimental Example 3

In order to confirm the photoactivity of Example 2 which is electrochemically active in natural seawater, the linear scanning potential method under pulsed light (100 mW / cm ² ) was measured. The scan rate of the measurement is 25 mV / s.

14 is a graph showing the results of linear scanning potential measurement in the range of 0.4 to -0.3 (V vs. RHE) in the pulsed light condition of Example 2 of the present invention.

Referring to FIG. 14, the photocurrent density (J _Photo ) of 120 μA / cm ² at -0.32 V vs RHE obtained is related to the high absorption coefficient of Co ₃ O ₄ material, suitable band gap and possible separation of photogenerated charges. Can be obtained by

In FIG. 14, the catalytic action or the electrical characteristics of the porous Co 3 O 4 film may be confirmed.

FIG. 15A is a graph showing the results of linear scanning potential measurement in the range of 0 to -0.8 (V vs. RHE) in the pulsed light condition of Example 2 of the present invention, and FIG. 15B is -0.5 to -0.6 of FIG. 15A. (V vs. RHE) This is an enlarged graph of the range part.

15A and 15B, the photo-induced HER activity of the working electrode of Example 2 is due to the combination of the catalyst and the light absorbing ability. As a result, an obtained current density of about 10 mA / cm ² is obtained at overvoltage of 0.6 V under light conditions. This means the voltage of photoelectrochemical activity in seawater decomposition of Example 2.

Experimental Example 4

For continuous hydrogen production, the photochemical stability of PEC cells is an important issue. Chronoamperometry (current time characteristic) analysis was performed to confirm the seawater decomposition performance of PEC cells.

FIG. 16A is a graph showing current time characteristics when an overvoltage of −0.34 (V vs. RHE) is applied under the white light condition of Example 2 of the present invention, and FIG. 16B is an enlarged graph of part A of FIG. 16A. .

16A and 16B, hydrogen generation stability through seawater decomposition of a photoelectrochemical cell (PECC) of a porous Co ₃ O ₄ film may be confirmed. In the test for 3600 seconds, a stable current value (initial current density: 2.7 mA / cm ² , current density after 1000 seconds: 1.6 mA / cm ² ) was confirmed. In addition, the stability to photocurrent was also confirmed.

FIG. 17 is a graph showing current time characteristics when overvoltages of 0.58 and 0.83 (V vs. RHE) are applied under the white light condition of Example 2 of the present invention, and FIG. 18 is a by-product of Example 2 of the present invention. It is a conceptual diagram for illustration.

Referring to FIGS. 17 and 18, a continuous ejection of hydrogen bubbles with white byproduct 800 was observed at a current density of 25 mA / cm ² . In steady conditions of seawater decomposition, the by-products were below the PEC cell. An argon (Ar) purge of the PEC cell was performed to prevent accumulation of the white byproduct on the surface of the Co ₃ O ₄ electrode.

The obtained current density as seen with the light off shows a net gain of 2.1 mA / cm ² . The photocurrent is very stable for 1800 seconds and has a current density of 25 mA / cm ² . Current density is proportional to the input bias (-0.58 vs RHE and -0.83 V vs RHE). At conditions of 0.83 V vs RHE, a very improved 25 mA / cm ² current density is obtained and measured very stably for 1800 seconds.

Experimental Example 5

In order to measure the incident photon to charge carrier efficiency (IPCE) of the working electrode of Example 2, a monochromatic light source having various wavelengths (λ) of λ = 365, 460, 520, and 620 nm was used. IPCE means the ratio of the photo-induced photocurrent and the incident photon as a function of the wavelength, it can be calculated by IPCE = (1240 XJ _Photo X 100) / (λ XI _Light ). Where J _Photo is the light current density and I _Light is the intensity of light according to the wavelength.

19 is a graph showing the current time characteristic according to the wavelength of various incident light of Example 2 of the present invention.

Referring to Fig. 19, a good photoreaction is obtained via wide wavelength light, and large current enhancement appears at short wavelengths. Co ₃ O ₄ electrodes have little trapping effect on instantaneous current changes, unlike the capacitive effects seen in current transients in current BiVO ₄ / Co ₃ O ₄ systems.

FIG. 20 is a graph illustrating incident photon to charge carrier efficiency (IPCE) according to wavelength at −0.33 (V vs. RHE) of Example 2 of the present invention. FIG.

Referring to FIG. 20, the relationship of IPCE to wavelength corresponds well to the transmission and absorption spectra shown in FIGS. 8 and 9. The 150 nm thick porous and translucent Co ₃ O ₄ photocathode shows an IPCE as high as about 9% when λ = 365 nm. The IPCE results show that Co ₃ O ₄ photocathodes are effective at enhancing hydrogen evolution because of high optical absorption, excessive charge generation and separation.

Porous Co ₃ O ₄ at long wavelengths of photons The high optical transmission of the film, i.e. the IPCE, remains low compared to short wavelength photons. Because of the advantage of high permeability, Co ₃ O ₄ Photoanodes can be integrated with existing solar energy materials such as Si, InP and GaAs for solar hydrogen generation from seawater with photoactive HER catalysts.

Experimental Example 6

Mott-Schottky measurements were performed to analyze the flat band potential (V _FB ), carrier concentration and conductivity of the multiple carriers of the working electrode of Example 2.

21 is a graph of 1 / C ² and V in dark and light conditions of Example 2 of the present invention.

Referring to FIG. 21, two distinct slopes appear, which correspond to two energy bandgaps. The negative linear slope is Co ₃ O ₄ with acceptor carrier concentration (N _A ) and V _FB The p-type conductivity of the photoanode is shown.

The measurement of the Mort Schottky characteristic is performed under dark and light conditions to induce a change in N _A value depending on the photogenerated transient carriers. V _FB And Co ₃ O ₄ to find the value of N _A. It can be used with two energy bandgaps (E _g1 = 1.5 eV and E _g2 = 2.3 eV) where the energy bandgap estimate of the electrode is present.

In FIG. 21, a large change of the acceptor carrier N _A1 with respect to E _g1 in the light condition is shown. Under dark conditions, the N _A1 value is 7 × 10 ¹⁹ cm ⁻³ . On the other hand, under light conditions, a very enhanced transient carrier appears N _A1 = 7 × ^{10 20} cm ⁻³ . In the case of E _g2 , there are relatively relaxed changes in N _A2 = 3.7 × 10 ¹⁹ cm ⁻³ under dark conditions and N _A2 = 6.4 × 10 ¹⁹ cm ⁻³ under light conditions.

The V _FB1 and V _FB2 values are assigned to Fermi levels (E _F ) where 0.78 and 0.18 V vs RHE respectively correspond to E _g1 = 1.5 eV and E _g2 = 2.3 eV.

FIG. 22 is a graph showing the current-voltage characteristics of the steady-state of Example 2 of the present invention. FIG.

Referring to FIG. 22, the current voltage curve clearly shows two onset voltages of 0.72 and 0.12 V vs RHE, which correspond to the V _FB values of 0.78 and 0.18 V vs RHE, respectively. Because of the presence of a double band gap, a high photocurrent of 0.2 mA / cm ² appears at -0.35 V vs RHE and rapidly decreases at a second onset voltage of 0.12 V vs RHE.

FIG. 23 is a diagram illustrating an estimated energy band edge of a double bandgap of Co ₃ O ₄ . In Figure 23, E _C and E _V are the conduction and balance bands, respectively. Furthermore, FIG. 24 is an energy band diagram of a general depletion situation of Embodiment 2 of the present invention, and FIG. 25 is an energy band diagram of an inversion situation of Embodiment 2 of the present invention. FIG. 26 is an energy band diagram of a deep inversion situation of Embodiment 2 of the present invention. FIG.

Experimental Example 7

Electrochemical impedance spectroscopy (EIS) analysis was performed to investigate the HER kinetic on the surface of Co3O4.

FIG. 27 shows Nyquist plots when the overvoltage of Example 2 of the present invention is applied, and FIG. 28 is measured at -0.44 to -0.53 (V vs. RHE) in Example 2 of the present invention. And a table showing estimation parameters.

FIG. 27 is one semicircle trajectory showing one-time constant behaviors for charge-transfer resistance (Rct) at various overvoltage values of (0.44-0.53 V). The curve can be represented by the equivalent circuit diagram shown in FIG. 27. Where R _S and Q are the series resistance and constant phase element, respectively. One half circle of the Nyquist plot suggests that kinetic impedance is the major axis controlling HER activity.

The parameters applied to FIG. 27 are summarized in the table of FIG. 28. 27 and 28, the relationship between the HER current J and Rct is well defined and shows an inverse relationship. By having a small magnitude of Rct, an improved HER current value can be obtained. As shown in FIG. 28, the calculated Rct of 3.4 Ω / cm ² enables a HER current density of 15.2 mA / cm ² at a voltage of −0.53 V vs RHE.

This means that the Co ₃ O ₄ / FTO electrode has excellent HER performance of seawater decomposition. Clearly, the porous Co ₃ O ₄ structure facilitates the Tafel process (chemical desorption: H _ads + H _ads → H ₂ ), which is advantageous over the Volmer-Heyrovsky process.

Furthermore, the value of Rs can be almost constant (about 24.8 Ω / cm ² ) regardless of the change in overvoltage. Further reduction of Rs may also be possible by replacing the FTO with Ni foam or by decorating the surface of Co 3 O 4 to enhance seawater decomposition performance.

Experimental Example 8

Again, Referring to Figure 18, photocathodes Co ₃ O ₄ is tapel reaction ^{(i.e., 2H + + 2e - → H} 2) to follow, the platinum electrode is a counter ^reaction may follow _{^{(2Cl + 2h + → Cl 2}} ) have. Because of the much higher solubility of Cl ₂ in seawater, no bubbles were found at the platinum electrode. By-product 800 of FIG. 18 was collected, placed on a silicon wafer, and dried using N ₂ gas. The energy dispersive spectra (EDS) of the byproduct 800 were measured.

FIG. 29 is an energy dispersive spectra (EDS) of the byproduct obtained in Example 2 of the present invention. FIG.

Referring to FIG. 29, the byproduct 800 may be Mg (OH) ₂ and Ca (OH) ₂ after sea cucumber decomposition. The EDS analysis showed Mg and Ca of 17.7 and 0.23 at%, respectively. It may be a high proportion of Mg (OH) ₂ . Due to the low component ratio (0.23%), the composition of Ca (OH) ₂ can be ignored. In addition, the same ratio of about 11% of Na and Cl is due to NaCl via Cl ₂ dissolved in PEC cells.

Although the embodiments of the present invention have been described with reference to the experimental examples and the accompanying drawings, those skilled in the art may implement the present invention in other specific forms without changing the technical spirit or essential features of the present invention. I can understand that it can be. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

100: power supply unit 200: counter electrode
300: working electrode 400: seawater

Claims (14)

A counter electrode connected to the cathode of the power supply unit to receive electrons and immersed in seawater to generate oxygen; And
A working electrode connected to the anode of the power supply unit to receive a current, immersed in the sea water as the counter electrode, and injecting light to generate hydrogen;
The working electrode is a transparent conductor,
A seawater decomposition device coupled to the transparent conductor and comprising a cobalt oxide film comprising Kirkendall void. The method of claim 1,
The cobalt oxide film is a seawater decomposition apparatus comprising Co ₃ O ₄ . The method of claim 1,
The counter electrode comprises Pt seawater decomposition apparatus. The method of claim 1,
The cobalt oxide film is a translucent seawater decomposition device. The method of claim 1,
The thickness of the cobalt oxide film is 10 to 500nm seawater decomposition apparatus. The method of claim 1,
The transparent conductor is a seawater decomposition apparatus including at least one of a fluorine-doped tin oxide (FTO), indium tin oxide (ITO) and metal nanowires. The method of claim 1,
The working electrode is a seawater decomposition device to produce by-products on the surface. The method of claim 7, wherein
The by-product is at least one of Mg (OH) ₂ and Ca (OH) ₂ seawater decomposition apparatus. Transparent conductors; And
Including a photocatalyst layer in contact with the transparent conductor, Co ₃ O ₄ ,
The photocatalyst layer is a seawater decomposition electrode comprising a Kirkendal void. The method of claim 9,
A seawater decomposition electrode further comprising a transparent substrate in contact with the transparent conductor. Providing a transparent substrate,
Depositing a cobalt film on the transparent substrate,
Method of manufacturing a seawater decomposition electrode comprising the step of rapid heat treatment of the cobalt film to form a cobalt oxide film containing Co3O4 using a Kirkendal diffusion. The method of claim 11, wherein
The cobalt film is of a first thickness,
The cobalt oxide film is a second thickness larger than the first thickness of the seawater decomposition electrode manufacturing method. The method of claim 11, wherein
The rapid heat treatment includes first and second sections,
The first section is performed at a first temperature,
The second section is a seawater decomposition electrode manufacturing method performed at a second temperature higher than the first temperature. The method of claim 13,
The rapid heat treatment includes first and second sections,
The first section raises the temperature from room temperature to an intermediate temperature,
The second section is a seawater decomposition electrode manufacturing method for raising the temperature from the intermediate temperature to the maximum temperature.

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