Hierarchical porous transport layer, manufacturing method for hierarchical porous transport layer, and water electrolysis apparatus comprising hierarchical porous transport layer

Abstract

According to one embodiment of the present invention, a hierarchical porous transport layer comprises: a first porous layer which has first pores and which is formed of first particles or fibers; a second porous layer which includes second pores having an average size smaller than that of the first pores and which is formed of second particles or fibers on the first porous layer; and an intermediate layer which is formed between the first porous layer and the second porous layer, and in which the first particles or fibers and the second particles or fibers are mixed and thermally bonded to each other.

Description

Hierarchical diffuser, method for manufacturing hierarchical diffuser, and electrolysis device including hierarchical diffuser

[0001] The present invention relates to a hierarchical diffuser, a method for manufacturing a hierarchical diffuser, and a water electrolysis device including a hierarchical diffuser.

[0002] We are currently on the verge of entering a hydrogen society. A hydrogen society is one in which hydrogen is centrally used as an energy source, making hydrogen available and readily available to all regions. To achieve this, the establishment of a stable hydrogen industry value chain is essential. In particular, for this value chain to function smoothly, it is crucial to produce the hydrogen needed in the hydrogen society in a way that meets demand.

[0003] Hydrogen production methods include byproduct hydrogen, which utilizes hydrogen as a byproduct of other industries, and extractive hydrogen, which actively produces hydrogen by reforming and decomposing fossil fuels or water. Because byproduct hydrogen production alone cannot meet the growing demand for hydrogen, extractive hydrogen methods are increasingly important. From an environmental perspective, the development of water electrolysis, which uses renewable energy sources like solar and wind power to decompose water, is crucial, rather than fossil fuel reforming for hydrogen production.

[0004] A representative example of a water electrolysis device is a proton exchange membrane (PEM) water electrolysis device. A PEM water electrolysis device is composed of a bipolar plate, a diffusion layer (PTL: porous transport layer), an oxygen electrode, a cation exchange membrane, a hydrogen electrode, a diffusion layer, and a bipolar plate sequentially stacked. Water flowing into a PEM water electrolysis device passes through the diffusion layer to the oxygen electrode, where it is separated into oxygen and hydrogen cations. The hydrogen cations then pass through the cation exchange membrane and receive electrons from the hydrogen electrode, producing hydrogen. At this time, the diffusion layer serves the role of supplying water to the electrodes and removing the generated gases, and also serves the role of passing current to each electrode.

[0005] However, as oxygen is generated at the oxygen electrode, it accumulates on the electrode surface, forming a bubble blockage, which acts as a mass transfer resistance. The formation of a mass transfer resistance means that the water supply, which is the raw material for the PEM electrolyzer, is not smooth, which naturally reduces the performance of the PEM electrolyzer.

[0006] Furthermore, each element of a PEM electrolyzer is pressurized and stacked on top of each other. Since the diffusion layer has pores, the area in contact with the Membrane Electrode Assembly (MEA) is inevitably smaller than the actual area. In other words, the contact area between the diffusion layer and the MEA is proportional to the utilization of the electrode's catalyst layer.

[0007] To solve these problems, several methods have been proposed to control the pores of the diffusion layer, and a representative method is the introduction of a micro porous layer (MPL).

[0008] Forming a microporous layer on one side of the diffusion layer, particularly on the electrode side, enhances mass transfer through capillary action, thereby preventing bubble obstruction caused by gas accumulation on the electrode surface. Furthermore, because the particle size of the microporous layer is smaller than that of the diffusion layer, the contact area with the electrode's catalyst layer increases, thereby enhancing the electrode's catalyst utilization. In other words, introducing a microporous layer enhances mass transfer performance and thus the utilization of the electrode catalyst layer.

[0009] However, the introduction of a microporous layer inevitably creates an interface between the diffusion layer and the microporous layer. This interface acts as a resistive element that reduces electrical conductivity. Furthermore, during prolonged operation of the PEM electrolyzer, the interface delaminates, reducing its durability.

[0010] In addition, conventionally, a microporous layer was formed on a titanium substrate (diffusion layer) through vacuum spraying plasma, but the process is very complex and there is a problem in that it is difficult to uniformly form a microporous layer over a large area.

[0011] There is a need for new solutions to solve these problems.

[0012]

[0013] [Prior Art Literature]

[0014] [Patent Document]

[0015] Japanese Patent Publication No. 2023-003697

[0016] [Non-patent literature]

[0017] Lettenmeier, P., Kolb, S., Burggraf, F., Gago, A. S., & Friedrich, K. A. (2016). Towards developing a backing layer for proton exchange membrane electrolyzers. Journal of Power Sources, 311, 153-158. https: / / doi.org / 10.1016 / j.jpowsour.2016.01.100

[0018] Schuler, T., et al. (2020). Hierarchically Structured Porous Transport Layers for Polymer Electrolyte Water Electrolysis. Advanced Energy Materials, 10(19), 1903216. https: / doi.org / 10.1002 / aenm.201903216

[0019] Stieber, S., et al. (2022). A high-performance, durable and low-cost proton exchange membrane electrolyser with stainless steel components. Energy & Environmental Science, 15, 109. https: / doi.org / 10.1039 / D1EE02694F

[0020] One object of the present invention is to provide a hierarchical diffuser having low interfacial resistance between a diffusion layer and a microporous layer and improved interfacial adhesion between the diffusion layer and the microporous layer.

[0021] In addition, another object of the present invention is to provide a method for manufacturing a hierarchical diffuser, which can manufacture a hierarchical diffuser more easily and simply than in the past, and further, can uniformly form a microporous layer over a large area on the diffusion layer.

[0022] Meanwhile, other unspecified purposes of the present invention will be additionally considered within a range that can be easily inferred from the detailed description and effects thereof below.

[0023] To solve the problem described above, the following solutions are proposed.

[0024] A hierarchical diffuser according to one embodiment of the present invention comprises: a first porous layer formed with first pores and formed of first particles or fibers; a second porous layer formed with second particles or fibers on the first porous layer and including second pores having an average size smaller than the first pores; and an intermediate layer formed between the first porous layer and the second porous layer, the first particles or fibers and the second particles or fibers being mixed and thermally bonded to each other.

[0025] In one embodiment, the first particle or fiber may be a titanium fiber, and the second particle or fiber may be a titanium metal particle.

[0026] In one embodiment, the thickness (T) of the second porous layer M ) and the intermediate layer (T I ) thickness ratio (T M / T I ) can be 0.5 to 2.3.

[0027] In one embodiment, the thickness of the intermediate layer may be 20 to 30 μm.

[0028] In one embodiment, the pore size of the first porous layer may be 40 to 60 μm, and the pore size of the second porous layer may be 6 to 10 μm.

[0029] In one embodiment, the porosity of the first porous layer may be 40 to 80%, and the porosity of the second porous layer may be 20 to 30%.

[0030] In one embodiment, the content of the second particles or fibers in the intermediate layer may gradually increase in the direction from the first porous layer to the second porous layer.

[0031] A PEM electrolysis device according to another embodiment of the present invention comprises a bipolar plate, a diffusion layer for an oxygen electrode, an oxygen electrode, a cation exchange membrane, a hydrogen electrode, a diffusion layer for a hydrogen electrode, and a bipolar plate sequentially stacked, wherein the diffusion layer for the oxygen electrode is the hierarchical diffuser described above.

[0032] A method for manufacturing a hierarchical diffuser according to another embodiment of the present invention comprises the steps of: (a) forming a first sheet composed of first particles or fibers coated with a binder; (b) forming a second sheet by applying a slurry containing second particles or fibers having a smaller particle size or a thinner fiber diameter than the first particles or fibers on a transfer film; (c) positioning the first sheet on the second sheet and thermally compressing the first sheet; and (d) removing the transfer sheet and performing a heat treatment to sinter it.

[0033] In another embodiment, in step (c), the second particles or fibers may penetrate between the first particles or fibers by pressure, so that the first particles or fibers and the second particles or fibers are mixed and thermally bonded to each other to form an intermediate layer.

[0034] In another embodiment, the step (d) may further include a step of coating at least one catalyst selected from the group consisting of platinum and iridium.

[0035] A hierarchical diffuser according to one embodiment of the present invention has a diffusion layer and a microporous layer formed on the diffusion layer, and has an intermediate layer between the diffusion layer and the microporous layer in which the material (particles or fibers) forming the diffusion layer and the material (particles or fibers) forming the microporous layer are thermally bonded to each other. That is, unlike conventional devices, the diffusion layer and the microporous layer do not form only an interface, but are in contact with each other within a certain volume and are further thermally bonded, so that the interfacial resistance is very low, and at the same time, the adhesive strength between the diffusion layer and the microporous layer is very high.

[0036] Meanwhile, the method for manufacturing a hierarchical diffuser according to another embodiment of the present invention utilizes transfer to manufacture the hierarchical diffuser, making it easier and more convenient to manufacture the hierarchical diffuser than in the past. Furthermore, the method for manufacturing a hierarchical diffuser according to another embodiment of the present invention utilizes transfer to uniformly form a microporous layer over a large area.

[0037] Meanwhile, even if the effect is not explicitly mentioned herein, it is added that the effect and its provisional effect described in the following specification expected by the technical features of the present invention are treated as described in the specification of the present invention.

[0038] FIG. 1 is a schematic cross-sectional view of a hierarchical diffuser according to one embodiment of the present invention.

[0039] Figure 2 is a schematic flow chart of a method for manufacturing a hierarchical diffuser according to another embodiment of the present invention.

[0040] Figure 3 is a schematic diagram illustrating each step of a method for manufacturing a hierarchical diffuser according to another embodiment of the present invention.

[0041] Fig. 4 is a 3D rendering modeling of an image stack of a 3D image of a diffuser (titanium fiber) of a comparative example taken by X-ray computed tomography (CT), and Fig. 5 is a 3D rendering modeling of an image stack of a 3D image of a hierarchical diffuser of an embodiment taken by X-ray computed tomography (CT).

[0042] Fig. 6 is a photograph of the front side (the side on the MEA side inside the electrolysis device) of the hierarchical diffuser (Ti fiber MPL) of the embodiment and the diffuser (Ti fiber) of the comparative example, and Fig. 7 is a photograph of the back side of the hierarchical diffuser (Ti fiber MPL) of the embodiment and the diffuser (Ti fiber) of the comparative example.

[0043] Fig. 8 is a SEM (Scanning Electron Microscope) image of the front surface of the hierarchical diffuser of the embodiment, Fig. 9 is a SEM image of a cross-section of the hierarchical diffuser of the embodiment, and Fig. 10 is a SEM image of the surface of the MEA (Membrane Electrode Assembly) that was in contact with the hierarchical diffuser of the embodiment.

[0044] Fig. 11 is an SEM image of the front surface of the diffuser of the comparative example, Fig. 12 is an SEM image of the cross-section of the diffuser of the comparative example, and Fig. 13 is an SEM image of the surface of the MEA that was in contact with the diffuser of the comparative example.

[0045] Figure 14 shows the results of an imbibition experiment of a diffuser of a comparative example, and Figure 15 shows the results of an imbibition experiment of a hierarchical diffuser of an example.

[0046] Fig. 16 is a tape test image for confirming the interface adhesion of an example, and Fig. 17 is a tape test image for confirming the interface adhesion of a comparative example.

[0047] Fig. 18 shows the results of measuring cell voltage according to current density for evaluating the electrochemical performance of a cell introducing a hierarchical diffuser of an example and a diffuser of a comparative example, Fig. 19 shows the results of comparing the voltage with the electrolyte membrane and conductor resistance (IR) removed and the current density displayed on a logarithmic scale, and Fig. 20 shows the results of measuring mass transfer overvoltage according to current density.

[0048] Figures 21 to 23 are Nyquist plots showing the results measured using electrochemical impedance spectroscopy (EIS), and are intended to compare the Rct (reaction resistance) and Rmass (mass transfer resistance) of cells using the hierarchical diffuser of the example and the diffuser of the comparative example.

[0049] It is to be understood that the attached drawings are provided for reference only to help understand the technical concept of the present invention, and the scope of the present invention is not limited thereby.

[0050] Hereinafter, with reference to the drawings, the configuration of the present invention, guided by various embodiments thereof, and the effects resulting from such configurations will be examined. In describing the present invention, detailed descriptions of related, well-known functions that are obvious to those skilled in the art and that may unnecessarily obscure the gist of the present invention will be omitted.

[0051] The hierarchical diffuser of the present invention can be applied to electrochemical energy storage or generation technologies that utilize hydrogen and oxygen evolution reactions as their reaction mechanisms. However, for clarity, the present invention will be described below based on a PEM water electrolysis device.

[0052] FIG. 1 is a schematic cross-sectional view of a hierarchical diffuser according to one embodiment of the present invention.

[0053] A hierarchical diffuser (100) according to one embodiment of the present invention is composed of a first porous layer (10), a second porous layer (20), and an intermediate layer (30).

[0054] The first porous layer (10) has first pores and is formed of first particles or fibers. For example, the first porous layer (10) may be formed of at least one selected from the group consisting of titanium metal particles, titanium fibers, stainless steel, titanium mesh, and carbon fibers. The thickness of the first porous layer (10) may be 200 to 1000 μm, the size of the first pores may be 40 to 60 μm, and the porosity may be 40 to 80%. The first porous layer (10) may be located on the bipolar plate side in a PEM water electrolysis device.

[0055] The second porous layer (20) has second pores and is formed of second particles or fibers. For example, the second porous layer (20) may be formed of at least one selected from the group consisting of titanium metal particles, titanium fibers, stainless steel, and carbon fibers. In addition, the second particles or fibers have a smaller particle size or a thinner fiber diameter than the first particles or fibers. Accordingly, the second pores are smaller than the first pores. Since the size of the second pores is very small, such as 5 to 20 ㎛, the capillary force becomes stronger, thereby increasing the material transfer capability, and thus, bubbles generated in the catalyst layer of the electrode can be quickly discharged. Meanwhile, the porosity of the second pores may be 20 to 50%.

[0056] An intermediate layer (30) is positioned between the first porous layer (10) and the second porous layer (20). The intermediate layer (30) is a mixture of first particles or fibers and second particles or fibers, and in particular, the first particles or fibers and the second particles or fibers are thermally bonded to each other. As described below, a hierarchical diffuser according to an embodiment of the present invention can uniformly form a second porous layer (microporous layer) over a large area on the first porous layer (diffusion layer) by a transfer process. However, when the second porous layer (20) is simply formed by transfer on the first porous layer (10), the interfacial adhesive strength is very low, which causes a problem of low durability when used in a water electrolysis device, and also causes a problem of high resistance between the interfaces. Therefore, the hierarchical diffuser according to an embodiment of the present invention forms the intermediate layer through thermal compression. Since the first particle or fiber and the second particle or fiber are in wide contact with each other within a certain volume of the formed intermediate layer, and furthermore, the first particle or fiber and the second particle or fiber are thermally bonded, there is an advantage in that the interfacial resistance between the first porous layer and the second porous layer is very low, and at the same time, the adhesive force between the first porous layer and the second porous layer is very high.

[0057] At this time, the thickness of the second porous layer (T M ) and the middle layer (T I ) thickness ratio (T M / T I ) can be 0.5 to 2.3. Preferably, the thickness of the two porous layers (T M ) and the middle layer (T I ) thickness ratio (T M / T I ) can be 0.5 to 2.0. T M / T I If this exceeds 2.3, there is a problem that the interfacial adhesive strength between the first porous layer and the second porous layer becomes too low, and T M / T I If it is less than 0.5, the intermediate layer may actually hinder material transfer, and the uniformity of the second porous layer may become too low.

[0058] Meanwhile, when examining the change in the content of the second particles or fibers in the intermediate layer, the content of the second particles or fibers gradually increases from the first porous layer toward the second porous layer because the intermediate layer was formed by thermal compression.

[0059] The hierarchical diffuser described above can be used as a diffusion layer for an oxygen electrode in a PEM water electrolysis device in which a bipolar plate, a diffusion layer for an oxygen electrode, an oxygen electrode, a cation exchange membrane, a hydrogen electrode, a diffusion layer for a hydrogen electrode, and a bipolar plate are sequentially stacked.

[0060] FIG. 2 is a schematic flow chart of a method for manufacturing a hierarchical diffuser according to another embodiment of the present invention, and FIG. 3 is a schematic diagram illustrating each step of a method for manufacturing a hierarchical diffuser according to another embodiment of the present invention.

[0061] Referring to FIGS. 2 and 3, a method for manufacturing a hierarchical diffuser according to another embodiment of the present invention will be described.

[0062] A method for manufacturing a hierarchical diffuser according to another embodiment of the present invention comprises the steps of forming a first sheet, forming a second sheet, thermally compressing the first sheet and the second sheet, and heat-treating the thermally compressible laminate.

[0063] The step of forming the first sheet is performed by coating a binder on the surface of the first particle or fiber. The first particle or fiber may be a titanium metal particle or a titanium fiber. Coating the binder on the surface of the first particle or fiber may be performed by dipping the first particle or fiber into a binder solution. The first particle or fiber is dipped in a binder dispersion solution dispersed in a solvent such as water or ethanol at 5 to 20 wt. % for about 5 to 30 minutes, then taken out and the solvent is dried. The binder may be at least one selected from the group consisting of PVB (Polyvinyl butyral), PEG (Polyethylene glycol), CMC (Carboxymethyl cellulose), PVA (Polyvinyl alcohol), PMMA (Polymethyl Methacrylate), PVAc (Polyvinyl Acetate), EVA (Ethylene-Vinyl Acetate), paraffin wax, and acrylic resins.

[0064] The step of forming the second sheet is first performed from the step of preparing a slurry for forming the second sheet. The slurry for forming the second sheet can be performed by mixing second particles or fibers, a binder, a solvent, and a plasticizer. The slurry for forming the second sheet can include 60 to 80 wt% of the second particles or fibers, 1 to 10 wt% of the binder, 20 to 30 wt% of the solvent, and 0.5 to 2 wt% of the plasticizer. Titanium metal particles or titanium fibers can be used as the second particles or fibers. As a binder, at least one selected from the group consisting of PVB (Polyvinyl butyral), PEG (Polyethylene glycol), CMC (Carboxymethyl cellulose), PVA (Polyvinyl alcohol), PMMA (Polymethyl Methacrylate), PVAc (Polyvinyl Acetate), EVA (Ethylene-Vinyl Acetate), Paraffin wax, and Acrylic Resins can be used. As a solvent, ethanol or water can be used. As a plasticizer, PEG (Polyethylen glycol), Glycerine, or Ethylene glycol can be used. Then, the manufactured slurry for forming the second sheet is cast on a transfer film to form the second sheet. As the transfer film, PI (Polyimide), PTFE (Polytetraflouroethylene), PET (Polyethylene terephthalate), or FEP (Fluorinated ethylene propylene) film can be used.

[0065] Next, the first sheet is placed on the second sheet and thermocompression is performed. The intermediate layer is formed by the thermocompression process. If the intermediate layer is not formed because the thermocompression process is not performed, there is a problem that the interfacial electronic conductivity and bonding strength between the diffusion layer and the microporous layer are reduced. During the thermocompression process, the pressure is applied to the thickness (T) of the second porous layer.M ) and the middle layer (T I ) thickness ratio (T M / T I ) can be adjusted to be 0.5 to 2.3, and the temperature can be higher than the glass transition temperature of the binder and lower than the melting point. For example, the thermal decomposition temperature can be 50 to 200 ℃. The pressure and time of the thermocompression process are 1 to 5 kg each. f / cm 2 It takes 2 to 10 minutes. Through the thermocompression process, the first particles or fibers and the second particles or fibers are mixed with the binder within the intermediate layer. Meanwhile, during the thermocompression process, it is preferable that the second layer be positioned below and the first layer above it. Since the second layer is the surface that comes into contact with the MEA, by positioning the second layer below and performing the thermocompression, the surface of the second layer can be made more uniform.

[0066] Next, the transfer film is removed and a heat treatment step is performed to manufacture a hierarchical diffuser. The heat treatment is performed in two steps. The first step is a step for thermal decomposition of the binder. The first heat treatment can be performed at 400-600°C in an inert gas atmosphere (such as Ar) for 4-8 hours. The second step is a step for sintering the first particles or fibers and the second particles or fibers. The second heat treatment can be performed at 900-1200°C in a vacuum atmosphere for 4-8 hours.

[0067] Through this process, a hierarchical diffuser according to one embodiment of the present invention can be manufactured.

[0068]

[0069] Example 1

[0070] To be used as a diffusion layer, a first sheet having a thickness of 230 μm was manufactured by coating a PVB binder on a Ti fiber. The second sheet was manufactured by mixing 73.5 wt% of Ti metal particles having an average particle size of 25 μm, 2.2 wt% of PVB binder, 23.2 wt% of ethanol solvent, and 1.1 wt% of PEG400 plasticizer to manufacture a slurry, which was then cast on a PI film and dried to manufacture a thickness of 40 μm. The first sheet was laminated on the second sheet, and thermocompression was performed in a press at a temperature of 80 °C for 2 minutes. The thermocompression was performed so that the total thickness of the first sheet, the intermediate layer, and the second sheet was 250 μm (the thickness of the intermediate layer was 20 μm). The PI film was removed from the laminate formed by thermocompression, and heat treatment was performed. Heat treatment was performed at 500°C in an Ar atmosphere for 5 hours, followed by 1000°C in a vacuum atmosphere for 5 hours. The sintered diffusion layer was coated with 100 nm of platinum using a sputtering device on the surface to increase electronic conductivity.

[0071]

[0072] Example 2

[0073] A hierarchical diffuser was manufactured using the same method as Example 1, but the thickness of the microporous layer was controlled to be 50 μm.

[0074]

[0075] Example 3

[0076] A hierarchical diffuser was manufactured using the same method as Example 1, but the thickness of the microporous layer was controlled to be 70 μm.

[0077]

[0078] Comparative Example 1

[0079] A diffuser was manufactured with the same Ti fiber as the first sheet of Example 1 to have a thickness of 250 μm.

[0080]

[0081] Comparative Example 2

[0082] A hierarchical diffuser was manufactured in the same manner as Example 1, but no thermal compression was performed, so no intermediate layer was formed.

[0083]

[0084] Comparative Example 3

[0085] A hierarchical diffuser was manufactured in the same manner as Example 1, but the thickness of the microporous layer was controlled to be 160 μm.

[0086]

[0087] Experimental Example 1

[0088] The three-dimensional shape, surface and cross-section shape, etc. of the diffuser of Comparative Example 1 and the hierarchical diffuser of Example 1 were investigated.

[0089] Fig. 4 is a 3D rendering modeling of an image stack of a 3D image of a diffuser (titanium fiber) of a comparative example taken by X-ray computed tomography (CT), and Fig. 5 is a 3D rendering modeling of an image stack of a 3D image of a hierarchical diffuser of an embodiment taken by X-ray computed tomography (CT).

[0090] As shown in Fig. 4, in the case of the diffuser of Comparative Example 1, the Ti fibers are entangled with each other to form a single layer. In contrast, in the case of Example 1 of the present invention, as shown in Fig. 5, it can be seen that it has a first porous layer (10) made of Ti fibers, a second porous layer (30) made of Ti metal particles, and an intermediate layer (30) in which Ti fibers and Ti metal particles are mixed and exist between the first porous layer (10) and the second porous layer (20).

[0091] Fig. 6 is a photograph of the front side (the side on the MEA side inside the electrolysis device) of the hierarchical diffuser (Ti fiber MPL) of the embodiment and the diffuser (Ti fiber) of comparative example 1, and Fig. 7 is a photograph of the back side of the hierarchical diffuser (Ti fiber MPL) of the embodiment and the diffuser (Ti fiber) of comparative example 1.

[0092] Looking at FIGS. 6 and 7 together, it can be seen that in the case of the diffuser of Comparative Example 1, one side and the other side are in the same state. This is natural because Comparative Example 1 is formed only of Ti fibers. In contrast, it can be seen that the front side of the hierarchical diffuser of Example 1 has a side formed only of Ti metal particles with a somewhat dark feel, and the back side has a side formed only of Ti fibers, similar to the diffuser of Comparative Example 1. For reference, the Ti fibers are not exposed on the front side of the hierarchical diffuser of Example 1.

[0093] Fig. 8 is a SEM (Scanning Electron Microscope) image of the front surface of the hierarchical diffuser of the embodiment, Fig. 9 is a SEM image of a cross-section of the hierarchical diffuser of the embodiment, and Fig. 10 is a SEM image of the surface of an MEA (Membrane Electrode Assembly) that was in contact with the hierarchical diffuser of the embodiment. In addition, Fig. 11 is a SEM image of the front surface of the diffuser of the comparative example, Fig. 12 is a SEM image of a cross-section of the diffuser of the comparative example, and Fig. 13 is a SEM image of the surface of the MEA that was in contact with the diffuser of the comparative example.

[0094] As shown in Fig. 8, the hierarchical diffuser of Example 1 has only Ti metal particles exposed on the surface, and accordingly, it can be confirmed that it made uniform contact with the surface of the MEA, as shown in Fig. 10. Meanwhile, as shown in Fig. 9, it can be seen that the hierarchical diffuser of Example 1 was sintered so that the Ti metal particles (corresponding to the second particles or fibers) partially surrounded the uppermost exposed portion of the Ti fibers (corresponding to the first particles or fibers). That is, the Ti metal particles are sintered in a form that holds at least one fiber, thereby improving the bonding strength between the diffusion layer and the microporous layer.

[0095] Meanwhile, the diffuser of Comparative Example 1 shows only Ti fibers on both the surface (Fig. 11) and the cross-section (Fig. 12), and the contact area on the MEA surface (Fig. 13) is also found to be small and not uniform.

[0096]

[0097] Experimental Example 2

[0098] To confirm the mass transfer capability of the hierarchical diffuser of Example 1, a wetting experiment was performed.

[0099] Figure 14 shows the results of an imbibition experiment of the diffuser of Comparative Example 1, and Figure 15 shows the results of an imbibition experiment of the hierarchical diffuser of Example 1.

[0100] Comparing Figures 14 and 15, it can be confirmed that the small pores of the microporous layer in the hierarchical diffuser increase the capillary force of water, allowing water to flow smoothly into the diffuser even at high pressure.

[0101]

[0102] Experimental Example 3

[0103] For the hierarchical diffusers of Examples 1, 2, and 3 and the diffusers of Comparative Examples 2 and 3, a tape test was performed to confirm the interfacial adhesiveness and the mass transfer capability was evaluated. The tape test was performed 10 times, and if the microporous layer was separated even once, an X was marked, otherwise an O was marked. If the mass transfer capability was equivalent to that of Example 1, an O was marked, and if it was inferior, an X was marked. The results are shown in Table 1 below.

[0104]

[0105] Thickness of the sample middle layer (㎛) Thickness of the microporous layer (㎛) T M / T I Tape Test Material Transfer Ability Comparison Example 2040-XO Example 120201OO Example 225502OO Example 330702.3O△Comparative Example 3401604OX

[0106]

[0107] As shown in Table 1 and Fig. 17, when thermal compression is not performed and there is no intermediate layer, there is a problem in that some or all of the microporous layer falls off in the tape test due to insufficient interfacial adhesive strength. On the other hand, when the thickness of the microporous layer exceeds 160 ㎛, the first particles or fibers and the second particles or fibers are mixed with each other, forming a layer with significantly smaller pores, which causes a problem in that the material transfer capability is reduced. Therefore, the presence of the intermediate layer has the effect of strengthening the bonding strength of the two layers, and the thickness of the microporous layer is preferably 70 ㎛ or less.

[0108] Experimental Example 4

[0109] Fig. 18 shows the results of measuring cell voltage according to current density for evaluating the electrochemical performance of a cell introducing the hierarchical diffuser of Example 1 and the diffuser of Comparative Example 1, Fig. 19 shows the results of comparing the voltage with the electrolyte membrane and conductor resistance (IR) removed and the current density displayed on a logarithmic scale, and Fig. 18 shows the results of measuring mass transfer overvoltage according to current density.

[0110] Looking at Figure 18, in the case of Experimental Example 1, a high current density can be achieved at a lower voltage compared to Comparative Example 1, which means that the electrochemical performance of the water electrolysis device is improved when the hierarchical diffuser of Experimental Example 1 is introduced.

[0111] Figure 19 shows the relationship between the voltage with the electrolyte membrane and wire resistance (IR) removed and the current density expressed on a logarithmic scale. Since the IR-free voltage is a value that removes the voltage loss due to components other than the electrode, it more closely represents the voltage required for the actual electrode reaction and shows how the voltage loss at the electrode changes as the current density increases. As shown in Figure 19, it can be confirmed that the hierarchical diffusion layer of Example 1 has a more uniform and larger contact area with the MEA, thereby exhibiting superior electrochemical performance. In particular, the high performance of Example 1 at low current densities indicates that the catalyst utilization is higher than that of Comparative Example 1. Meanwhile, the high electrochemical performance over the entire current density range also indicates that the microporous layer of the hierarchical diffusion layer of Experimental Example 1 did not negatively affect the electrochemical performance.

[0112] Figure 20 shows the mass transfer overvoltage according to current density. The overvoltage is the difference between the theoretical voltage expected under ideal conditions and the actually measured voltage. The mass transfer overvoltage represents the voltage loss that occurs during the process of reactants moving to the electrode surface. In other words, a higher overvoltage indicates greater mass transfer limitation. As shown in Figure 18, the hierarchical diffuser of Example 1 has a lower overvoltage, which means that the hierarchical diffuser of Example 1 has higher mass transfer characteristics due to effects such as increased capillary force in Experimental Example 2.

[0113]

[0114] Experimental Example 5

[0115] Figures 21 to 23 are Nyquist plots showing the results measured using electrochemical impedance spectroscopy (EIS), and are for comparing the Rct (reaction resistance, front semicircle) and Rmass (mass transfer resistance, rear semicircle) of cells using the hierarchical diffuser of the example and the diffuser of the comparative example.

[0116] As can be seen in FIGS. 21 to 23, the difference in resistance between the two diffusers increases as the current increases. As the current increases, the amount of oxygen bubbles generated on the electrode surface increases, but the diffuser of Comparative Example 1 cannot properly remove the generated oxygen bubbles, so the increase in Rmass is noticeable as the current increases. In contrast, the hierarchical diffuser of Example 1 does not show the phenomenon of Rmass increasing as the current increases, which can be seen to be efficient in removing oxygen bubbles that increase in proportion to the increase in current, unlike the diffuser of Comparative Example 1.

[0117] The hierarchical diffuser described above can be applied not only to PEM electrolysis devices, but also to other electrochemical energy storage or generation technologies that use hydrogen and oxygen gas evolution reactions as reaction mechanisms (e.g., anion exchange membrane electrolysis, chloro-alkali processes, fuel cells, metal-oxygen batteries, etc.).

[0118] Meanwhile, in the above examples and experimental examples, titanium metal fibers and titanium metal particles were used, but it was confirmed that the same effect was achieved when stainless steel, titanium mesh, and carbon fiber were also used.

[0119] The scope of protection of the present invention is not limited to the description and expression of the embodiments explicitly described above. Furthermore, it should be noted that the scope of protection of the present invention may not be limited by obvious modifications or substitutions within the technical field to which the present invention pertains.

Claims

1. A first porous layer in which first pores are formed and first particles or fibers are formed; A second porous layer formed on the first porous layer, which includes second pores having an average size smaller than that of the first pores and is formed of second particles or fibers; and A hierarchical diffuser comprising an intermediate layer formed between the first porous layer and the second porous layer, the first particles or fibers and the second particles or fibers being mixed and thermally bonded to each other.

2. In paragraph 1, A hierarchical diffuser wherein the first particle or fiber is at least one selected from the group consisting of titanium metal, stainless steel, and carbon fiber, and the second particle or fiber is at least one selected from the group consisting of titanium metal, titanium metal, stainless steel, and carbon fiber.

3. In paragraph 1, The thickness of the second porous layer (T) M ) and the intermediate layer (T I ) thickness ratio (T M / T I ) is a hierarchical diffuser with a coefficient of variation of 0.5 to 2.

3.

4. In paragraph 1, A hierarchical diffuser having a thickness of 20 to 40 ㎛ in the above intermediate layer.

5. In paragraph 1, A hierarchical diffuser wherein the pore size of the first porous layer is 40 to 100 μm, and the pore size of the second porous layer is 5 to 15 μm.

6. In paragraph 1, A hierarchical diffuser wherein the porosity of the first porous layer is 40 to 80% and the porosity of the second porous layer is 20 to 40%.

7. In paragraph 1, A hierarchical diffuser in which the content of the second particles or fibers gradually increases in the direction from the first porous layer to the second porous layer in the intermediate layer.

8. A PEM water electrolysis device in which a bipolar plate, a diffusion layer for an oxygen electrode, an oxygen electrode, a cation exchange membrane, a hydrogen electrode, a diffusion layer for a hydrogen electrode, and a bipolar plate are sequentially laminated, A PEM water electrolysis device in which the oxygen electrode diffusion layer is a hierarchical diffuser according to any one of claims 1 to 7. 9.(a) a step of forming a first sheet made of first particles or fibers coated with a binder; (b) a step of forming a second sheet by applying a slurry including second particles or fibers having a smaller particle size or thinner fiber diameter than the first particles or fibers on the transfer film; (c) a step of positioning the first sheet on the second sheet and thermally pressing it; (d) a method for manufacturing a hierarchical diffuser, comprising the step of removing the above-mentioned transfer sheet, performing heat treatment, and sintering.

10. In paragraph 9, A method for manufacturing a hierarchical diffuser, wherein in step (c), the second particles or fibers penetrate between the first particles or fibers by pressure, thereby forming an intermediate layer in which the first particles or fibers and the second particles or fibers are mixed and thermally bonded to each other.

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