Electrolytic cell and anion exchange conductive hollow fiber tube matrix thereof

Abstract

To provide an electrolytic cell and its anion exchange conductive hollow fiber tube matrix.SOLUTION: The anion exchange conductive hollow fiber tube matrix 10 of the electrolytic cell is provided with a plurality of conductive hollow fiber tubes 1 exhibiting an adjacent matrix array, having a diffusion surface 11 and respectively having an inlet 12 and an outlet 13 at the opposite ends. The anode 20 and the cathode 30 of the electrolytic cell are installed adjacent to the diffusion surface 11, and the electrolytic bath 40 of the electrolytic cell is communicated with the inlet 12 and the outlet 13. When the power is turned on, the water in the electrolytic cell 40 enters the conductive hollow fiber tube 1 from the inlet 12, and the water molecules enter the cathode 30 from the diffusion surface 11 and are decomposed to generate hydrogen and hydroxide ions. The hydrogen is discharged from the cathode 30, and the hydroxide ions return to the conductive hollow fiber tube 1 from the diffusion surface 11 and enter the anode 20 from the diffusion surface 11 to generate oxygen. Oxygen is discharged from the surface of the anode 20, and water is returned to the electrolytic cell 40 through the outlet 13.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an electrolytic cell and an anion exchange conductive hollow fiber tube matrix thereof. More specifically, the present invention relates to an electrolytic cell and an anion exchange conductive hollow fiber tube matrix thereof, which have a matrix film composed of conductive hollow fiber tubes as an ion exchange interface between the anode and cathode of the electrolytic cell, and in which water or an electrolyte is directly injected into the conductive hollow fiber tubes, thereby achieving lower mass transfer resistance and energy-saving hydrogen generation compared to conventional AEM electrolytic cells. [Background technology]

[0002] Hydrogen is an important green energy source because it produces water after combustion and does not emit greenhouse gases such as carbon dioxide. Hydrogen produced by electrolyzing water is an effective hydrogen source, and in the future, this will become an important hydrogen production method, along with solar energy and wind power generation, for obtaining clean, green hydrogen.

[0003] The principle of producing hydrogen by electrolyzing water is that an electrolytic cell is formed by a circuit consisting of an anode, a cathode, and water or electrolyte in an electrolytic cell. After passing an electric current through it, the water undergoes an oxidation-reduction reaction, producing hydrogen at the cathode and oxygen at the anode.

[0004] As shown in Figure 10, anion exchange membrane electrolysis (AEM) can electrolyze water or a low-concentration electrolyte to produce hydrogen. The AEM electrolysis cell includes the steps of placing an anion exchange membrane A between an anode B and a cathode C and connecting an electrolytic cell D to the anode B. After turning on the power, water in the electrolytic cell D is injected into the anode B. The water molecules diffuse, pass through the anion exchange membrane A, and enter the cathode C. The water molecules are decomposed to generate hydrogen and hydroxide ions. The hydroxide ions then diffuse, pass through the anion exchange membrane A, and return to the anode B, generating oxygen. The oxygen is then recycled to the electrolytic cell D and discharged through the exhaust valve. The water molecules and hydroxide ions diffuse isotropically through the anion exchange membrane A, and only the membrane surface of the anion exchange membrane A serves as the mass transfer area. Summary of the Invention [Problem to be solved by the invention]

[0005] However, test results showed that the AEM electrolysis cell requires an energy consumption of approximately 50 kWh to 55 kWh to produce 1 kg of hydrogen. The main reason for this high energy consumption is the small mass transfer area, which causes oxygen bubbles to obstruct contact between the anode and the electrolyte or water when oxygen is generated, resulting in high mass transfer resistance.

[0006] Furthermore, oxygen in the AEM electrolysis cell bubbles at the anode / electrolyte interface before being discharged back into the electrolytic cell, where it mixes with the partial water or electrolyte, increasing the alkalinity of the discharged oxygen and its water content.

[0007] Therefore, the present inventors believed that the above drawbacks could be improved, and as a result of extensive research, they came up with the proposal of the present invention, which effectively improves the above problems through rational design.

[0008] The present invention was made in view of the above problems and is the result of extensive research by the present inventors. An object of the present invention is to provide an electrolytic cell and an anion-exchange conductive hollow fiber tube matrix thereof. [Means for solving the problem]

[0009] To achieve the above object, one embodiment of the present invention provides an anion exchange conductive hollow fiber tube matrix comprising a plurality of conductive hollow fiber tubes arranged in an adjacent matrix, each of the conductive hollow fiber tubes having a diffusion surface and an inlet and an outlet at opposite ends thereof.

[0010] The electrolytic cell includes the anion exchange conductive hollow fiber tube matrix, an anode and a cathode disposed adjacent to the diffusion surface, an electrolytic cell communicating with the inlet and the outlet, and a power source connected to the anode and the cathode.

[0011] In operation, when the power supply is turned on and water in the electrolytic cell is allowed to enter the conductive hollow fiber tube from the inlet, water molecules enter the cathode through the diffusion surface and are decomposed to generate hydrogen and hydroxide ions. The hydrogen is discharged from the cathode, the hydroxide ions return from the diffusion surface to the conductive hollow fiber tube and then enter the anode through the diffusion surface to generate oxygen. The oxygen is discharged from the surface of the anode, and water returns to the electrolytic cell through the outlet.

[0012] In a preferred embodiment of the present invention, the conductive hollow fiber tube has been subjected to an ammoniating treatment.

[0013] In a preferred embodiment of the present invention, a catalyst is disposed between the anion exchange conductive hollow fiber tube matrix and the anode, and between the anion exchange conductive hollow fiber tube matrix and the cathode. Specifically, the catalyst may be a nickel / iron alloy oxide. Furthermore, the catalyst may be coated on the diffusion surface of the conductive hollow fiber tube.

[0014] In a preferred embodiment of the present invention, a conductive carbon fiber diffusion layer is disposed between the anion exchange conductive hollow fiber tube matrix and the anode, and between the anion exchange conductive hollow fiber tube matrix and the cathode.

[0015] In a preferred embodiment of the present invention, a non-electrical photocatalytic hydrogen generation mechanism is provided, the non-electrical photocatalytic hydrogen generation mechanism comprising a water supply tank having a first photocatalyst installed in the water supply tank and connected to the anode, and a second photocatalyst installed in the water supply tank and connected to the cathode, the first photocatalyst and the second photocatalyst generating hydrogen at the adjacent cathode and generating oxygen at the adjacent anode through photoreaction.

[0016] In a preferred embodiment of the present invention, a non-electrical chemical energy hydrogen generation mechanism is provided, the non-electrical chemical energy hydrogen generation mechanism comprising a reaction tank in which chemical agents are input and reacted to generate hydrogen at the adjacent cathode and oxygen at the adjacent anode.

[0017] In a preferred embodiment of the present invention, the conductive hollow fiber tube is produced by forming regular or irregular holes in a conductive film. [Effects of the Invention]

[0018] The present invention is configured as described above and therefore provides the following effects. 1. In the electrolysis cell of the present invention, water or electrolyte is directly introduced into the anion exchange conductive hollow fiber tube matrix, and oxygen is generated and discharged directly on the surface of the wet anode, eliminating the generation of oxygen bubbles that would interfere with the contact between the anode and the electrolyte or water. This reduces mass transfer resistance and preserves the effective electrode area. Tests have shown that the electrolysis cell of the present invention consumes approximately 40 kWh to 45 kWh of energy to produce 1 kg of hydrogen, compared to the approximately 50 kWh to 55 kWh required by an AEM electrolysis cell to produce 1 kg of hydrogen. This allows for more energy-efficient hydrogen production. 2. In the electrolysis cell of the present invention, water molecules and hydroxide ions diffuse anisotropically in the anion-exchange conductive hollow fiber tube matrix, which has a large mass transfer area (the entire wall of each conductive hollow fiber tube is a mass transfer surface), resulting in high efficiency and low power consumption. 3. When water is electrolyzed to produce hydrogen using the electrolytic cell of the present invention, oxygen generated on the surface of the anode is directly emitted from the surface of the anode without being mixed into the water or the electrolyte, thereby achieving suitable alkalinity, low water content, and high-pressure oxygen collection. 4. The electrolysis cell of the present invention is equipped with a non-electrical photocatalytic hydrogen generation mechanism or a non-electrical chemical energy hydrogen generation mechanism, and can generate hydrogen continuously and stably even in situations where there is no power supply.

[0019] At least the following points will become clear from the description and drawings to be described later. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a perspective view showing an external appearance of an electrolysis cell and its anion exchange conductive hollow fiber tube matrix according to one embodiment of the present invention. [Figure 2] 1 is a schematic diagram illustrating an electrolysis cell according to one embodiment of the present invention. [Figure 3] FIG. 1 is a schematic diagram illustrating how water or an electrolyte flows into and diffuses into an anion-exchange conductive hollow fiber tube matrix when an electrolysis cell according to an embodiment of the present invention electrolyzes water to produce hydrogen. [Figure 4] 1 shows electrolysis voltage curves at the same current density when an electrolysis cell according to the present invention and a conventional AEM electrolysis cell electrolyze water. [Figure 5] 1 shows electrolysis voltage curves when the electrolysis cell of the present invention and the conventional AEM electrolysis cell electrolyze water under the same hydrogen production rate, number of battery stacks, and current conditions. [Figure 6] 1 is a schematic diagram of an electrolysis cell according to the present invention, in which a catalyst and a conductive carbon fiber diffusion layer are disposed between an anion-exchange conductive hollow fiber tube matrix and an anode / cathode. [Figure 7A] 1 is a schematic diagram (1) of the anion exchange conductive hollow fiber tube matrix of the present invention, in which a catalyst is coated on the conductive hollow fiber tube. [Figure 7B] 1 is a schematic diagram (II) of the anion exchange conductive hollow fiber tube matrix of the present invention, in which a catalyst is coated on the conductive hollow fiber tube. [Figure 7C] 1 is a schematic diagram (3) of the anion exchange conductive hollow fiber tube matrix of the present invention, in which a catalyst is coated on the conductive hollow fiber tube. [Figure 8] FIG. 1 is a schematic diagram of an electrolysis cell according to the present invention that adds a non-electric photocatalytic hydrogen generation mechanism. [Figure 9] FIG. 1 is a schematic diagram of an electrolysis cell according to the present invention that adds a non-electrical photocatalytic hydrogen generation mechanism. [Figure 10] FIG. 1 is a schematic diagram illustrating a conventional AEM electrolysis cell. [Figure 11] FIG. 1 is a schematic diagram showing a conductive hollow fiber tube formed by forming a plurality of linearly and regularly arranged continuous holes on a conductive film in an embodiment of the present invention. [Figure 12] FIG. 1 is a schematic diagram showing a conductive hollow fiber tube formed by forming a plurality of spirally and regularly arranged continuous holes on a conductive film in an embodiment of the present invention. [Figure 13] FIG. 1 is a schematic diagram showing a conductive hollow fiber tube formed by forming a plurality of alternating straight lines and irregularly arranged continuous holes on a conductive film in an embodiment of the present invention. [Figure 14] FIG. 1 is a schematic diagram showing a conductive hollow fiber tube formed by forming a plurality of irregularly arranged holes of different sizes on a conductive film in an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] The following describes in detail the embodiments of the present invention, but the present invention is not limited to these, and various modifications are possible within the scope of the description. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0022] FIG. 1 is a perspective view showing an anion-exchange conductive hollow fiber tube matrix 10 according to one embodiment of the present invention. The anion exchange conductive hollow fiber tube matrix 10 comprises a plurality of conductive hollow fiber tubes 1 arranged in an adjacent matrix. Each conductive hollow fiber tube 1 has a diffusion surface 11 and an inlet 12 and an outlet 13 at opposite ends, respectively. The conductive hollow fiber tubes 1 are made of conductive carbon fiber. The anion exchange conductive hollow fiber tube matrix 10 of this embodiment has a plurality of conductive hollow fiber tubes 1 arranged as a 10 cm x 10 cm film, has a thickness of approximately 20 μm, and the diameter of the flow path of the conductive hollow fiber tubes 1 is in the range of approximately 5 μm to 15 μm. The conductive hollow fiber tube 1 is subjected to an ammoniating treatment, and the ammoniating treatment converts the polymeric conductive hollow fiber tube 1 into (NH4 + ) ammonium ion functional group is formed. The ammonium ion functional group is an important medium for electrolysis of water (OH - ) hydroxide ions, giving it anion conducting properties.

[0023] Referring again to FIGS. 11 to 14 , in addition to arranging a plurality of individual conductive hollow fiber tubes 1 as the anion exchange conductive hollow fiber tube matrix 10, the conductive hollow fiber tubes 1 may be manufactured by regularly or irregularly perforating a conductive film, and then arranged as the anion exchange conductive hollow fiber tube matrix 10. For example, Fig. 11 is a schematic diagram of forming a conductive hollow fiber tube 1 by forming a plurality of linear, regularly arranged continuous holes 14 on a conductive film. Fig. 12 is a schematic diagram of forming a plurality of spiral, regularly arranged continuous holes 14 on a conductive film to form a conductive hollow fiber tube 1. Fig. 13 is a schematic diagram of forming a plurality of alternating linear, irregularly arranged continuous holes 14 on a conductive film to form a conductive hollow fiber tube 1. Fig. 14 is a schematic diagram of forming a plurality of irregularly arranged holes 14 of different sizes on a conductive film to form a conductive hollow fiber tube 1.

[0024] As shown in FIG. 2 , the electrolytic cell of this embodiment includes an anion exchange conductive hollow fiber tube matrix 10, an anode 20 and a cathode 30, which are disposed adjacent to the anion exchange conductive hollow fiber tube matrix 10 and adjacent to the diffusion surface 11, preferably disposed on opposite sides of the anion exchange conductive hollow fiber tube matrix 10, and which in this embodiment use foam nickel electrodes; an electrolytic cell 40 connected to an inlet 12 and an outlet 13; and a power supply connected to the anode 20 and the cathode 30 (the power supply is not shown in the figure because the connection between the power supply and the anode 20 and the cathode 30 is conventional).

[0025] As shown in Figures 2 and 3, in operation, when the power is turned on and water in the electrolytic cell 40 is allowed to enter the conductive hollow fiber tube 1 through the inlet 12, the water molecules enter the cathode 30 through the diffusion surface 11 and are decomposed to generate hydrogen and hydroxide ions. The hydrogen is discharged from the cathode 30, and the hydroxide ions return from the diffusion surface 11 to the conductive hollow fiber tube 1 and then enter the anode 20 through the diffusion surface 11 to generate oxygen. The oxygen is discharged directly from the surface of the anode 20, and the water returns to the electrolytic cell 40 through the outlet 13. The water molecules and hydroxide ions diffuse anisotropically in the anion exchange conductive hollow fiber tube matrix 10, which has a large mass transfer area (the entire wall of each conductive hollow fiber tube 1 is a mass transfer surface), resulting in high efficiency and low power consumption. Furthermore, in the electrolysis cell of the present invention, water or electrolyte is directly introduced into the anion exchange conductive hollow fiber tube matrix 10, and oxygen is directly generated and discharged from the surface of the wet anode 20, eliminating the generation of oxygen bubbles that would interfere with contact between the anode 20 and the electrolyte or water. This reduces mass transfer resistance, maintains the effective electrode area, and improves hydrogen production efficiency.

[0026] As shown in Figure 4, the large mass transfer area reduces the mass transfer resistance while maintaining the effective area of ​​the electrode. At the same current density, the electrolytic cell of the present invention has a lower electrolysis voltage than the conventional AEM electrolytic cell.

[0027] As shown in FIG. 5 , when the electrolytic cell of the present invention and the conventional AEM electrolytic cell are continuously operated for 400 minutes at the same hydrogen production rate, with the same number of cell stacks and under the same current conditions, the electrolytic cell of the present invention has a lower electrolysis voltage than the conventional AEM electrolytic cell.

[0028] Based on the above description and tests, the electrolytic cell of the present invention requires only about 40 kWh to 45 kWh of energy consumption per kg of hydrogen produced, compared to the AEM electrolytic cell, which requires about 50 kWh to 55 kWh of energy consumption per kg of hydrogen produced, allowing the electrolytic cell of the present invention to produce hydrogen with less energy consumption.

[0029] Furthermore, when the electrolytic cell according to the present invention electrolyzes water to produce hydrogen, oxygen generated on the surface of the anode 20 is not mixed into the water or the electrolyte but is discharged directly from the surface of the anode 20, making it possible to achieve low alkalinity, low water content, and high-pressure oxygen collection.

[0030] As shown in FIG. 6, in order to improve the ion diffusion efficiency, the electrolysis cell includes a catalyst 50 and a conductive carbon fiber diffusion layer 60 disposed between the anion exchange conductive hollow fiber tube matrix 10 and the anode 20, and between the anion exchange conductive hollow fiber tube matrix 10 and the cathode 30. Specifically, the catalyst 50 is made of nickel / iron alloy oxide, and the catalyst 50 is disposed as a slurry and applied to the conductive carbon fiber diffusion layer 60. The conductive carbon fiber diffusion layer 60 has pores filled with carbon fibers, and the catalyst 50 is adsorbed onto the surface of the conductive carbon fiber diffusion layer 60, and then dried, so that the catalyst 50 and the conductive carbon fiber diffusion layer 60 assume a film form. The catalyst 50 reduces the activation energy for electrolyzing water in an alkaline environment, allowing water to be more easily decomposed (dissociated) into hydrogen ions and hydroxide ions. Furthermore, because hydroxide ions are easily oxidized to oxygen, installing the catalyst 50 reduces the energy consumption for electrolyzing water and increases the efficiency of hydrogen production.

[0031] 7A to 7C, the catalyst 50 may be applied to the diffusion surface 11 of the conductive hollow fiber tube 1. For example, in FIG. 7A, the catalyst 50 is applied to the inner and outer surfaces of the diffusion surface 11 of the conductive hollow fiber tube 1, in FIG. 7B, the catalyst 50 is applied to the outer surface of the diffusion surface 11 of the conductive hollow fiber tube 1, and in FIG. 7C, the catalyst 50 is applied to the inner surface of the diffusion surface 11 of the conductive hollow fiber tube 1. In this way, the specific surface area on which the catalyst 50 reacts is increased, thereby improving the reaction efficiency.

[0032] As shown in FIG. 8 , a non-electrical photocatalytic hydrogen generation mechanism 70 may be added to the electrolysis cell, and the non-electrical photocatalytic hydrogen generation mechanism 70 includes a water supply tank 701 having a first photocatalyst 702 disposed in the water supply tank 701 and connected to the anode 20, and a second photocatalyst 703 disposed in the water supply tank 701 and connected to the cathode 30. A voltmeter 704 is connected between the anode 20 and the cathode 30, and the first photocatalyst 702 and the second photocatalyst 703 generate hydrogen at the adjacent cathode 30 and oxygen at the adjacent anode 20 through photoreaction, and the voltage value can be read by the voltmeter 704. In this way, hydrogen can be generated stably and continuously by the non-electric photocatalytic hydrogen generation mechanism 70 even when power is not supplied.

[0033] As shown in Fig. 9, a non-electrical chemical energy hydrogen generation mechanism 80 may be added to the electrolysis cell, and the non-electrical chemical energy hydrogen generation mechanism 80 includes a reaction vessel 801. By inputting a chemical agent into the reaction vessel 801 and causing it to react with an alkali metal or alkaline earth metal, for example, an acidic or alkaline solution is used, thereby generating hydrogen at the adjacent cathode 30 and oxygen at the adjacent anode 20. In this way, the non-electrical chemical energy hydrogen generation mechanism 80 can stably and continuously generate hydrogen even without the supply of power.

[0034] Although the embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and design changes and the like are also included within the scope that does not deviate from the gist of the present invention. [Explanation of symbols]

[0035] 10 Anion-exchange conductive hollow fiber tube matrix 1. Conductive hollow fiber tube 11 Diffusion Surface 12 Entrance 13 Exit 14 holes 20 Anode 30 cathode 40 Electrolytic cell 50 Catalyst 60 Conductive carbon fiber diffusion layer 70 Non-electrical photocatalytic hydrogen generation mechanism 701 Water Tank 702 1st photocatalyst 703 Second photocatalyst 704 Voltmeter 80 Non-electrical chemical energy hydrogen generation mechanism 801 Reactor A Anion Exchange Membrane B Anode C cathode D Electrolytic cell

Claims

1. a plurality of conductive hollow fiber tubes arranged in an adjacent matrix, each having a diffusion surface and an inlet and an outlet at opposite ends; an anode and a cathode of an electrolytic cell are disposed adjacent to the diffusion surface, an electrolytic cell of the electrolytic cell is connected to the inlet and the outlet, and a power source is connected to the anode and the cathode; an anion exchange conductive hollow fiber tube matrix for an electrolytic cell, wherein when the power supply is turned on and water in the electrolytic cell is allowed to enter the conductive hollow fiber tube from the inlet, water molecules enter the cathode through the diffusion surface and are decomposed to generate hydrogen and hydroxide ions, the hydrogen is discharged from the cathode, the hydroxide ions return from the diffusion surface to the conductive hollow fiber tube and then enter the anode through the diffusion surface to generate oxygen, the oxygen is discharged from the surface of the anode, and water returns to the electrolytic cell through the outlet.

2. 2. The anion exchange conductive hollow fiber tube matrix for an electrolytic cell according to claim 1, wherein the conductive hollow fiber tube is further subjected to an ammonification treatment.

3. 2. The anion exchange conductive hollow fiber tube matrix for an electrolytic cell according to claim 1, wherein a catalyst is coated on the diffusion surface of the conductive hollow fiber tube.

4. 4. The anion exchange conductive hollow fiber tube matrix of claim 3, wherein the catalyst is a nickel / iron alloy oxide.

5. 2. The anion exchange conductive hollow fiber tube matrix for an electrolytic cell according to claim 1, wherein the conductive hollow fiber tube has a conductive film with regularly or irregularly perforated holes.

6. an anion exchange conductive hollow fiber tube matrix including a plurality of conductive hollow fiber tubes arranged in an adjacent matrix, each of the conductive hollow fiber tubes having a diffusion surface, and each of the conductive hollow fiber tubes having an inlet and an outlet at opposite ends thereof; an anode and a cathode disposed adjacent to the diffusion surface; an electrolytic cell connected to the inlet and the outlet; a power source connected to the anode and the cathode; an electrolytic cell characterized in that, when the power supply is turned on and water in the electrolytic cell is allowed to enter the conductive hollow fiber tube from the inlet, water molecules enter the cathode from the diffusion surface and are decomposed to generate hydrogen and hydroxide ions, the hydrogen is discharged from the cathode, the hydroxide ions return from the diffusion surface to the conductive hollow fiber tube and then enter the anode from the diffusion surface to generate oxygen, the oxygen is discharged from the surface of the anode, and water returns to the electrolytic cell from the outlet.

7. 7. The electrolytic cell according to claim 6, wherein the conductive hollow fiber tube has been subjected to an ammoniating treatment.

8. 7. The electrolytic cell according to claim 6, further comprising a catalyst disposed between the anion exchange conductive hollow fiber tube matrix and the anode, and between the anion exchange conductive hollow fiber tube matrix and the cathode.

9. 9. The electrolysis cell according to claim 8, wherein the catalyst is applied to the diffusion surface of the conductive hollow fiber tube.

10. 9. The electrolysis cell of claim 8, wherein the catalyst is a nickel / iron alloy oxide.

11. 7. The electrolytic cell according to claim 6, further comprising a conductive carbon fiber diffusion layer disposed between the anion exchange conductive hollow fiber tube matrix and the anode, and between the anion exchange conductive hollow fiber tube matrix and the cathode.

12. 7. The electrolysis cell according to claim 6, further comprising a water supply tank having a first photocatalyst installed in the water supply tank and connected to the anode, and a second photocatalyst installed in the water supply tank and connected to the cathode, wherein the first photocatalyst and the second photocatalyst are provided with a non-electrical photocatalytic hydrogen generation mechanism that generates hydrogen at the adjacent cathode and generates oxygen at the adjacent anode through a photoreaction.

13. 7. The electrolytic cell according to claim 6, further comprising a non-electrical chemical energy hydrogen generation mechanism having a reaction vessel in which chemical agents are introduced and reacted to generate hydrogen at the adjacent cathode and generate oxygen at the adjacent anode.

14. 7. The electrolysis cell according to claim 6, wherein the conductive hollow fiber tube has a conductive film with regularly or irregularly perforated holes.

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