Photoanode for flexible photoelectrolysis device, and manufacturing method therefor

Abstract

The present invention provide a photoanode for a photoelectrolysis device, and a manufacturing method therefor. The photoanode for a photoelectrolysis device comprises: a polyimide (PI) layer; a laser-induced graphene (LIG) substrate formed by irradiating the PI layer with a laser; and a monoclinic tungsten oxide (m-WO3) nanostructure layer formed on the LIG substrate, wherein the PI layer is a flexible substrate and the photoanode is flexible.

Description

Photoanode of a flexible photovoltaic device and method for manufacturing the same

[0001] The present invention relates to a photoanode of a photoelectric water electrolysis device.

[0002] Photoelectrolysis technology is attracting attention as an important clean energy technology that utilizes sunlight to decompose water and produce hydrogen and oxygen. Among these components, the photoanode is a key element that enables efficient photoelectrolysis by promoting the Oxygen Evolution Reaction (OER).

[0003] WO₃ (tungsten oxide) is widely studied as a constituent material for photoanodes due to its excellent photoreactivity and electrochemical properties. However, for WO₃ to efficiently perform photoreactions, it must have a monoclinic structure; to achieve this, heat treatment at 500°C or higher is generally required after synthesis, such as through hydrothermal synthesis. However, since such high-temperature heat treatment is difficult to apply to flexible substrates, previously only rigid and inflexible substrates such as FTO (FTO-glass, fluorine-doped tin oxide) could be used. This is the technology disclosed in the present inventor's Korean Patent 10-2024-0120971. This has resulted in limitations in application fields requiring flexibility.

[0004] To solve this problem, the inventors intended to manufacture a WO₃ photoanode based on a heat-resistant flexible substrate. Initially, electrode materials such as ITO (Indium Tin Oxide) were used, but ITO had poor chemical durability, leading to a problem where performance deteriorated significantly upon repeated use.

[0005] In this process, the inventors confirmed that laser-induced graphene (LIG) possesses flexibility while exhibiting excellent heat resistance and chemical resistance. In particular, they discovered that by hydrothermally synthesizing WO3 based on LIG and then converting it into a monoclinic structure through heat treatment using a femtosecond laser, a photoanode with high photoresponsiveness and stability can be manufactured without thermal damage to both the LIG and the supporting polyimide (PI) substrate.

[0006] Accordingly, in the present invention, a flexible yet high-performance photoanode is realized by forming LIG on a PI layer, hydrothermally synthesizing WO₃ thereon, crystallizing it into a monoclinic structure using a femtosecond laser, and finally adding a catalyst layer. This invention overcomes the limitations of existing non-flexible photoanodes and provides a technological advancement that can significantly expand the efficiency and application possibilities of photowater electrolysis devices.

[0007] In order for WO₃ photoanodes to react efficiently, a monoclinic structure is required, but high-temperature heat treatment of over 500°C, which is necessary to achieve this, is impossible on flexible substrates. Consequently, only rigid and inflexible substrates such as FTO could be used in the past, which limited applications requiring flexibility. Furthermore, conventionally used ITO (Indium Tin Oxide) electrodes had the problem of poor chemical durability, leading to significant performance degradation upon repeated use. To solve these problems, the present invention aims to provide a technology that can crystallize WO₃ into a monoclinic structure while preventing damage to the flexible substrate due to high-temperature heat treatment.

[0008] In one aspect, the present invention claims a photoanode of a photowater electrolysis device comprising: a polyimide (PI) layer; a laser-induced graphene (LIG) substrate formed by irradiating the PI layer with a laser; and a monoclinic tungsten oxide (m-WO3) nanostructure layer formed on the LIG substrate.

[0009] A photoelectrolyte is a device that utilizes both electrical and light energy to decompose water into hydrogen and oxygen. This device fundamentally includes two electrodes, namely an anode and a cathode; the anode is responsible for producing oxygen through a water oxidation reaction, while the cathode is responsible for producing hydrogen through a water reduction reaction.

[0010] In particular, by using a photoreactive material in the photoanode of a photowater electrolysis device such as the present invention, the efficiency of the electrochemical reaction is maximized by utilizing electrons and holes generated by the absorption of light. The photoanode plays a role in promoting the oxidation reaction of water by utilizing light energy in the photowater electrolysis device.

[0011] In the present invention, the nanostructure layer may additionally include a nickel-iron layered double hydroxide (NiFe LDH). The nickel-iron layered double hydroxide plays a role in improving the hydrogen production performance of photowater electrolysis by effectively transferring photogenerated holes to the electrolyte.

[0012] In the present invention, the PI layer is characterized as being a flexible substrate, and the photoanode is a photoanode having flexible properties.

[0013] In the present invention, the LIG substrate is formed by irradiating the surface of the PI layer with a laser to break the chemical bonds (C-N or C-O) of the PI layer and re-bond carbon atoms to form a graphene structure layer. Laser irradiation (DLWC process) generates a locally very high temperature in the PI layer, which breaks the chemical bonds (C-N or C-O) and rearranges the aromatic rings to form a graphene structure, and these surface functional groups contribute to promoting the hydrothermal synthesis of WO₃ nanorods.

[0014] In the present invention, the nanostructure layer comprises forming WO₃ nanostructures on the LIG substrate through a hydrothermal synthesis process and crystallizing the WO₃ nanostructures into a monoclinic structure by irradiating them with a femtosecond laser.

[0015] In the present invention, the WO₃ nanostructure is formed through a hydrothermal synthesis process using a precursor solution containing ammonium tungstate, hydrochloric acid, and hydrogen peroxide, and is crystallized from a tetragonal structure to a monoclinic structure by treatment with a femtosecond laser through a two-photon absorption mechanism. The ultrafast pulses of the femtosecond laser can minimize thermal damage to the substrate.

[0016] In another aspect, the present invention claims a photoanode of a photowater electrolysis device in which the WO₃ nanostructure is treated with a femtosecond laser through a two-photon absorption mechanism to crystallize from a tetragonal structure to a monoclinic structure.

[0017] The present invention is characterized by including the step of forming a laser-induced graphene (LIG) layer by irradiating a laser onto the surface of a PI layer to break the chemical bonds (C-N or C-O) of the PI layer and re-bond carbon atoms.

[0018] In the present invention, a sample after the fs-LIPT process using a laser output of p is defined as "p-fs-LIPT".

[0019] In the present invention, the nanostructure layer forms WO3 nanostructures on the LIG substrate through a hydrothermal synthesis process, and crystallizes the WO₃ nanostructures into a monoclinic structure by irradiating them with a femtosecond laser.

[0020] The WO3 nanostructure of the present invention is formed through a hydrothermal synthesis process using a precursor solution containing ammonium tungstate, hydrochloric acid, and hydrogen peroxide.

[0021] The WO3 nanostructure of the present invention is characterized by being treated with a femtosecond laser through a two-photon absorption mechanism, thereby crystallizing from a tetragonal structure to a monoclinic structure.

[0022] The present invention realizes a photoanode that can be used in various applications requiring flexibility by utilizing a flexible PI substrate instead of a conventional rigid and inflexible substrate. By using laser-induced graphene as an electrode, the durability issues of conventional ITO electrodes are resolved, and excellent chemical durability and thermal stability are provided.

[0023] In addition, by introducing femtosecond laser heat treatment technology to convert WO₃ into a monoclinic structure, high crystallinity was secured without high-temperature heat treatment. This prevented physical damage to the flexible substrate and enabled the development of a photowater electrolysis device that possesses both flexibility and high efficiency. The present invention expands the potential for application in various fields, such as wearable devices, secondary batteries, and next-generation energy devices, and provides a technological advancement that overcomes the application limitations of existing photoanodes.

[0024] Figure 1 is an SEM image of WO₃ nanorods before and after the fs-LIPT process with different laser powers.

[0025] Figure 2 is an image showing the change in the crystal structure of WO₃ nanorods before and after the fs-LIPT process by XRD analysis.

[0026] Figure 3 is a TEM image of WO₃ nanorods before the fs-LIPT process and after the fs-LIPT process with a laser power of 60 mW.

[0027] Figures 4 (a) to (c) are graphs measured to compare the performance of the fs-LIPT process according to laser power. (d) to (f) are graphs measured to evaluate the photoanode performance after NiFe-LDH catalyst electrodeposition.

[0028] Figure 5 is a graph showing the results of testing the mechanical durability of a flexible photoanode.

[0029] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. Since the present invention is susceptible to various modifications and may take various forms, specific embodiments are illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to the specific disclosed forms, and it should be understood that it includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the present invention. Similar reference numerals have been used for similar components in the description of each drawing. In the attached drawings, the dimensions of the structures are shown enlarged compared to the actual dimensions for the clarity of the present invention.

[0030] The terms used in this application are used merely to describe specific embodiments and are not intended to limit the invention. Furthermore, the description of one aspect of the invention may be applied identically or similarly to identical or similar configurations or terms in the description of other aspects.

[0031] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this application.

[0032] The embodiments of the present invention are described below. However, the embodiments described below are merely partial embodiments of the present invention, and the scope of the present invention is not limited to the following embodiments.

[0033] Examples

[0034] After washing the PI film with acetone, ethanol, and deionized water, an LIG substrate is prepared by irradiating the PI film with an Nd:YAG CW laser (Lighthouse Photonics, wavelength: 532 nm) combined with a 2D laser scanning system (hurrySCAN II 14, SCANLAB) and an F-theta telecentric lens (4401-461-000-21, LINOS).

[0035] 0.8g of ammonium tungstate is dissolved in 93mL of deionized water and mixed by vigorous stirring at 90℃ for 1 hour, and 1.6mL of 37% hydrochloric acid and 2mL of 30% hydrogen peroxide are added to prepare a precursor solution.

[0036] The above LIG substrate is placed in a Teflon-lined stainless steel container in a 100 mL autoclave, 60 mL of the prepared precursor solution is filled, and WO₃ nanorods are hydrothermally synthesized on the LIG substrate by heating in a convection oven at 160°C for 4 hours.

[0037] The LIG substrate on which WO₃ nanorods were synthesized is washed with deionized water after cooling to remove remaining impurities.

[0038] A LIG substrate on which WO₃ nanorods are synthesized is placed on a 2D motorized linear stage (V-408 PIMag, PI), and an fs-LIPT process is performed using a femtosecond laser (fs laser, FFultra780, Toptica) at a wavelength of 780 nm, a pulse duration of 130 fs, and a repetition rate of 80 MHz. The laser beam is focused through a 10× object lens (PAL-10-NIR, Optosigma). After optimizing the laser output, the stage movement speed (10 mm / s) and the spacing between laser beam paths (0.002 mm) are fixed.

[0039] Preparation Example 1

[0040] In Preparation Example 1, to investigate the effect of laser output in the fs-LIPT process, the laser output in the above-described examples was varied to 30, 40, 50, 60, and 70 mW, respectively, to prepare a photoanode of a photoelectrolyte device.

[0041] Figure 1 shows SEM images of WO₃ nanorods before and after the fs-LIPT process with different laser powers. Referring to Figures 1 (b) to (f), changes in the shape of the nanorods according to laser powers of 30, 40, 50, 60, and 70 mW, respectively, can be observed. At a power of 30 mW, the rectangular shape of the nanorods is maintained, but at powers of 40 mW or higher, the shape of the nanorods is not maintained and is damaged, and at a power of 70 mW, it can be confirmed that they are completely damaged.

[0042] In Figure 2, changes in the crystal structure of WO₃ nanorods before and after the fs-LIPT process were investigated by XRD analysis. Before fs-LIPT, diffraction peaks were observed at 22.9°, 24.1°, 26.9°, and 27.9°. These peaks correspond to the (002), (200), (022), and (220) crystal planes of o-WO₃ and represent the typical crystal structure of tetragonal WO₃ (o-WO₃). After the fs-LIPT process, new diffraction peaks appeared at 23.6° and 34.2°, which correspond to the (020) and (220) crystal planes of m-WO₃. As the laser power increased, the m-WO₃ peaks became more distinct, and at a power of 60 mW, the o-WO₃ peaks completely disappeared, leaving only the m-WO₃ peaks. Through this, o-WO₃ is converted to m-WO₃ via the fs-LIPT process, and in this process, laser power acts as a key factor in the crystal structure transformation, and it can be seen that 60 mW is a desirable laser power.

[0043] Figure 3 is a TEM image of WO₃ nanorods before the fs-LIPT process and after the fs-LIPT process with a laser power of 60 mW. In Figure 3, before the process (a), it can be seen that it is o-WO₃ with (022) crystal planes spaced 0.39 nm apart, and after the process (b), it can be seen that it is m-WO₃ with (002) crystal planes spaced 0.38 nm apart and (022) crystal planes spaced 0.27 nm apart.

[0044] Furthermore, we intend to evaluate the performance of the fabricated photoanodes according to laser power. Figure 4 (a) is a graph of the linear sweep voltammetry (LSV) curves according to laser power. Except for 70 mW, as the laser power increases, the sample fully converted to m-WO₃ shows a high photocurrent density.

[0045] Figure 4 (b) shows the 1.23 V of the fabricated photoanode according to laser output. RHE This shows the photocurrent measured at 60-fs-LIPT. It shows the highest photocurrent at 60-fs-LIPT, and it can be seen that the photocurrent decreases rapidly at 70-fs-LIPT.

[0046] Figure 4 (c) shows the resistance measured at the fabricated photoanode according to laser power. The lowest resistance is observed at a laser power of 60 mW, which indicates that the performance of the photoanode is improved by facilitating the transfer of charge to the electrolyte.

[0047] Preparation Example 2

[0048] In Preparation Example 2, a photoanode of a photowater electrolysis device was prepared by additionally electrodepositing a NiFe-LDH catalyst in the preparation example described above.

[0049] The NiFe-LDH catalyst was electrodeposited onto m-WO₃ nanorods. The electrodeposition was performed in a three-electrode system using an m-WO₃-based flexible photoanode as the working electrode, an Ag / AgCl electrode immersed in 3 M KCl as the reference electrode, and a platinum plate as the counter electrode. The precursor solution was prepared by dissolving 0.15 M nickel(II) sulfate hexahydrate (Ni(SO₄)·6H₂O, ≥98%, Sigma-Aldrich) and 0.15 M iron(II) sulfate heptahydrate (Fe(SO₄)·7H₂O, ≥97.0%, Sigma-Aldrich) in 80 mL of deionized water. The electrodeposition was performed at -1.0 V relative to Ag / AgCl for 20 seconds, followed by washing with deionized water and drying at room temperature.

[0050] In order to determine the performance after NiFe-LDH catalyst electrodeposition in Figures 4 (d) to (f), the performance of 60-fs-LIPT before and after NiFe-LDH catalyst electrodeposition was compared.

[0051] Figure 4 (d) shows an LSV curve graph to evaluate the effect on the photoelectrochemical performance of the photoanode. 1.23 V RHE The current density of 60-fs-LIPT without NiFe-LDH catalyst is 1.12 mA / cm², and the current density of 60-fs-LIPT with electrodeposited NiFe-LDH catalyst is 1.46 mA / cm². This indicates that the NiFe-LDH catalyst improves electron transfer efficiency at the interface between m-WO₃ and the electrolyte, and enhances PEC performance.

[0052] Figure 4 (e) shows the Nyquist curve, and the 60-fs-LIPT with the NiFe-LDH catalyst electrodeposited exhibits lower resistance than the 60-fs-LIPT without the NiFe-LDH catalyst electrodeposited. This indicates that the NiFe-LDH catalyst improves the charge transfer rate in the PEC reaction and increases the efficiency of the interfacial reaction.

[0053] Figure 4 (f) shows the current density curve over time. It can be observed that the 60-fs-LIPT without the NiFe-LDH catalyst electrodeposited retains only about 30% of the initial photocurrent after 2 hours of operation, whereas the 60-fs-LIPT with the NiFe-LDH catalyst electrodeposited retains about 86%. This indicates that the NiFe-LDH catalyst also improves the long-term stability of the photoanode.

[0054] Preparation Example 3

[0055] In Manufacturing Example 3, to evaluate the mechanical durability of the flexible photoanode, the photoanode from the above-described example was attached to a substrate of a different curvature and the following measurements were performed.

[0056] Figure 5 (a) shows the photocurrent density according to the number of repetitions of concave and convex bending conditions with a radius of 5 mm. It demonstrates excellent mechanical stability by maintaining approximately 90% of the initial photocurrent density even after 3,000 repeated bending experiments.

[0057] Figure 5 (b) shows the photocurrent density over time under bending conditions. This confirms that the photocurrent density is maintained stably even under a long-term bending state.

[0058] Figures 5 (c) and (d) show the photocurrent density under various radius conditions. It can be observed that the photocurrent density is similar to that when not bent, even under various radius conditions.

[0059] Figures 5 (e) and (f) show the photocurrent density measured by attaching a flexible photoanode to various structures. This demonstrates that the flexible photoanode can operate stably while maintaining mechanical durability even in various forms such as Figure 5 (e).

[0060] Although the present invention has been described above with reference to preferred embodiments, those skilled in the art will understand that various modifications and changes can be made to the invention without departing from the spirit and scope of the invention as set forth in the following claims.

Claims

1. Polyimide (PI) layer; A laser-induced graphene (LIG) substrate formed by irradiating a laser onto the above PI layer; and A monoclinic tungsten oxide (m-WO3) nanostructure layer formed on the above LIG substrate, Photoanode of a photoelectrolyte.

2. In Paragraph 1, The above nanostructure layer further comprises nickel-iron layered double hydroxide (NiFe LDH), Photoanode of a photoelectrolyte.

3. In Paragraph 1, The above PI layer is characterized as being a flexible substrate, and The above photoanode is a photoanode having flexible characteristics, Photoanode of a photoelectrolyte.

4. In Paragraph 3, The above LIG substrate is formed by a method of irradiating the surface of the above PI layer with a laser to break the chemical bonds (C-N or C-O) of the PI layer and recombine carbon atoms to form a graphene structure layer. Photoanode of a photoelectrolyte.

5. In Paragraph 1, The above nanostructure layer forms WO₃ nanostructures on the LIG substrate through a hydrothermal synthesis process, and Comprising crystallizing the above WO₃ nanostructure into a monoclinic structure by irradiating it with a femtosecond laser, Photoanode of a photoelectrolyte.

6. In Paragraph 5, The above WO₃ nanostructures are formed through a hydrothermal synthesis process using a precursor solution containing ammonium tungstate, hydrochloric acid, and hydrogen peroxide, Photoanode of a photoelectrolyte.

7. In Paragraph 5, The above WO₃ nanostructures are treated with a femtosecond laser through a two-photon absorption mechanism, Crystallized from a tetragonal structure to a monoclinic structure, Photoanode of a photoelectrolyte.

8. As a method for manufacturing a photoanode according to claim 1, The above LIG layer comprises the step of irradiating the surface of the PI layer with a laser to break the chemical bonds (C-N or C-O) of the PI layer and recombine carbon atoms to form a laser-induced graphene (LIG) layer. Method for manufacturing a photoanode of a photoelectrolyte device.

9. In Paragraph 8, The above nanostructure layer forms WO3 nanostructures on the LIG substrate through a hydrothermal synthesis process, and Comprising crystallizing the above WO₃ nanostructure into a monoclinic structure by irradiating it with a femtosecond laser, Method for manufacturing a photoanode of a photoelectrolyte device.

10. In Paragraph 9, The above WO3 nanostructure is formed through a hydrothermal synthesis process using a precursor solution containing ammonium tungstate, hydrochloric acid, and hydrogen peroxide, Method for manufacturing a photoanode of a photoelectrolyte device.

11. In Paragraph 10, The above WO3 nanostructure is treated with a femtosecond laser through a two-photon absorption mechanism, Crystallized from a tetragonal structure to a monoclinic structure, Method for manufacturing a photoanode of a photoelectrolyte device.

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