Gas diffusion layer for anion exchange membrane water electrolysis and method for producing the same

Abstract

The present invention provides a gas diffusion layer for anion exchange membrane water electrolysis that is hydrophilic and exhibits excellent gas permeability, and a method for producing the same.

Description

[Technical Field]

[0001] Mutual citation with related applications This application claims priority based on Korean Patent Application No. 10-2021-0169324 dated November 30, 2021, and all content disclosed in the said Korean Patent Application is incorporated herein as part of this specification. This invention relates to a gas diffusion layer for anion exchange membrane water electrolysis and a method for producing the same. Specifically, this invention relates to a gas diffusion layer containing a network of carbon nanofiber films and a method for producing the same. [Background technology]

[0002] The gas diffusion layer (GDL) is a core component in fuel cells (FCs) and water electrolysis (ECs), serving as a passage for transferring reactants to electrodes while simultaneously discharging products. It also plays a role in heat dissipation and electrode support.

[0003] Most commercially available gas diffusion layers (GDLs) are used in polymer electrolyte membrane fuel cells (PEMFCs), and have a structure in which a microporous layer (MPL) containing a hydrophobic polymer is coated onto porous carbon paper. In fuel cells, water flooding can occur, where water generated from the oxygen electrode clogs the pores of the gas diffusion layer, so the gas diffusion layer must be hydrophobic. Therefore, PTFE and a binder are used as the polymer to impart hydrophobicity to the gas diffusion layer of fuel cells.

[0004] The gas diffusion layer for water electrolysis is an interface where electrical conduction occurs while gases such as hydrogen (H2), oxygen (O2), and water (H2O), which are reactants and products of the electrochemical reaction, move freely between the catalyst layer and the electrodes. Therefore, porous carbon materials such as carbon fibers, which have porosity and electrical conductivity and do not undergo side reactions with the salt for the electrochemical reaction, are used.

[0005] However, conventionally used carbon fiber paper had a problem where surface roughness caused interfacial contact resistance between the electrode layer and the catalyst layer. Therefore, to solve this problem, a microporous layer was formed by applying polymer materials such as powdered carbon paste or binders. However, microporous layers containing polymer materials such as carbon paste or binders have the problem that the hydrophilicity and electrical conductivity are reduced by the polymer components, resulting in inferior properties for the gas diffusion layer used for water electrolysis. Therefore, a method was devised to impart hydrophilicity by controlling the binder polymer contained in the microporous layer, but there was still the problem of reduced electrical conductivity and, additionally, the problem of hindering gas transfer.

[0006] Therefore, there is a need to develop a hydrophilic gas diffusion layer with excellent electrical conductivity that can be used in anion exchange membrane water electrolysis, as well as a method for manufacturing the same. [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention aims to provide a gas diffusion layer for anion exchange membrane water electrolysis and a method for producing the same. Specifically, the present invention aims to provide a gas diffusion layer for anion exchange membrane water electrolysis containing a hydrophilic, mesh-like carbon nanofiber film with excellent gas permeability, and a method for producing these. [Means for solving the problem]

[0008] The gas diffusion layer for water electrolysis in an anion exchange membrane according to one embodiment of the present invention includes a film in which carbon nanofibers are arranged in a network, and the carbon nanofibers may have a diameter of 500 nm or less. Furthermore, the method for producing a gas diffusion layer for anion exchange membrane water electrolysis according to one embodiment of the present invention may include the steps of: spinning a carbon precursor material to form a mesh-shaped product (step 1); and heat-treating the mesh-shaped product to obtain a mesh-like carbon nanofiber film (step 2). [Effects of the Invention]

[0009] The gas diffusion layer containing a mesh-like carbon nanofiber film according to the present invention has higher porosity than powdered carbon materials or polymers such as binders, which is very advantageous for the movement of hydrogen and oxygen gases generated in the catalyst layer, and facilitates gas transfer from the electrolyte to the outside. This provides a gas diffusion layer for an anion exchange membrane water electrolysis that can improve the efficiency of the water electrolysis cell.

[0010] Furthermore, the mesh-like carbon nanofiber film according to the present invention has high hydrophilicity, which can improve the wettability of the electrolyte in the gas diffusion layer. Furthermore, the present invention provides a method for producing a gas diffusion layer in an anion exchange membrane water electrolysis using a spinning method.

[0011] Furthermore, the present invention provides a method for using and manufacturing a network-like carbon nanofiber film as a gas diffusion layer itself. Furthermore, the present invention provides a method for applying a conventionally used gas diffusion layer in addition to a network-like carbon nanofiber film. [Brief explanation of the drawing]

[0012] [Figure 1] This image shows the surface structure of the gas diffusion layer in one embodiment of the present invention, as observed by SEM. [Figure 2] This image shows the side structure of the gas diffusion layer in one embodiment of the present invention, as observed by SEM. [Figure 3] This document shows experimental photographs comparing the contact angle of a gas diffusion layer according to one embodiment of the present invention with the contact angle of an existing gas diffusion layer. [Figure 4]This is a graph showing the measurement and comparison of the gas permeability of the gas diffusion layer of one embodiment of the present invention and the gas permeability of an existing gas diffusion layer.

Embodiments for Carrying Out the Invention

[0013] In the present invention, terms such as first, second, etc. are used to describe various components, and the terms are used only for the purpose of distinguishing one component from another.

[0014] Also, the terms used in this specification are used only for the purpose of explaining exemplary embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as "including", "comprising", or "having" are intended to specify the presence of implemented features, numbers, steps, components, or combinations thereof, and should not be construed as precluding the presence or addition possibility of one or more other features, numbers, steps, components, or combinations thereof.

[0015] Also, in the present invention, when each layer or element is referred to as being "formed on" or "above" each layer or element, it means that each layer or element is formed directly on each layer or element, or that other layers or elements can be additionally formed between each layer, on the object, or on the substrate.

[0016] The present invention can be modified in various ways and can have various forms. Specific embodiments will be exemplified and described in detail below. However, this is not intended to limit the present invention to a specific disclosed form, and it should be understood to include all modifications, equivalents, and alternatives included in the spirit and technical scope of the present invention.

[0017] In anion exchange membrane water electrolysis, the efficiency of the cell can be increased because the wettability and permeability of the electrolyte increase as the hydrophilicity of the gas diffusion layer increases. Therefore, existing gas diffusion layers for fuel cells that have a hydrophobic fine porous layer reduce the wettability of the electrolyte, and at the same time, the thickness of the fine porous layer, which can reach tens of micrometers (μm), can cause a decrease in the porosity of the porous support of the gas diffusion layer.

[0018] Therefore, the inventors have devised a method to use a network of carbon nanofiber films as a gas diffusion layer without using polymer materials such as binders that conventionally impart hydrophobicity (binder-free).

[0019] According to the present invention, by eliminating the use of polymers to form a paste as a network carbon nanofiber film material, it is expected that the roughness and interfacial resistance of the interface between the electrode and the catalyst will be reduced. Furthermore, since carbon nanofibers have higher porosity than powdered carbon materials or polymers such as binders, they are very advantageous for the movement of hydrogen and oxygen gases generated in the catalyst layer, and gas transfer from the electrolyte to the outside is easy, which is expected to improve the efficiency of the water electrolysis cell. In addition, the carbon nanofiber film according to the present invention is expected to have high hydrophilicity, which will also improve the wettability of the electrolyte.

[0020] Below, we will examine in detail the gas diffusion layer for water electrolysis of the anion exchange membrane according to the present invention.

[0021] The gas diffusion layer for anion exchange membrane water electrolysis of the present invention may be a network of carbon nanofibers itself. Furthermore, the gas diffusion layer for anion exchange membrane water electrolysis of the present invention may include a porous support and a network of carbon nanofibers.

[0022] The gas diffusion layer in one embodiment of the present invention includes a film in which carbon nanofibers are arranged in a network, and the carbon nanofibers may have a diameter of 500 nm or less. Specifically, the gas diffusion layer may be a network-like carbon nanofiber film.

[0023] Specifically, the carbon nanofibers have a diameter of 50 nm or more, 100 nm or more, or 150 nm or more, and may also be 500 nm or less, 400 nm or less, 300 nm or less, or 200 nm or less.

[0024] The gas diffusion layer may have a thickness of 50 to 500 μm. Specifically, the gas diffusion layer may have a thickness of 50 μm or more, 100 μm or more, 150 μm or more, or 200 μm or more, and may be 500 μm or less, 450 μm or less, 400 μm or less, 350 μm or less, 300 μm or less, or 250 μm or less.

[0025] The anion exchange membrane gas diffusion layer for water electrolysis may have a contact angle with water of 20° or less. Since the gas diffusion layer of the present invention exhibits hydrophilicity due to carbon nanofibers, it is preferable not to limit the lower limit of the contact angle (water contact angle), and specifically the contact angle may be 0°. By exhibiting superhydrophilicity with a contact angle of 20° or less, the wettability of the electrolyte can be ensured when used as a gas diffusion layer for water electrolysis. This has the advantage of favoring electrolyte movement and internal circulation compared to a gas diffusion layer using a hydrophobic microporous layer, and facilitating the electrolysis reaction of water.

[0026] In this invention, the term "water contact angle" refers to the angle formed when a liquid and a gas are in thermodynamic equilibrium on a surface. The contact angle in this invention can be measured by placing a film-like sample on a flat surface, dropping 5-10 μl of distilled water onto it, and then observing its shape from the side using DSA to calculate the angle. As shown in Figure 4, when compared with existing gas diffusion layers, the gas diffusion layer of this invention has a contact angle of 0° and exhibits superhydrophilicity.

[0027] Furthermore, the anion exchange membrane gas diffusion layer for water electrolysis has a gas permeability of 1 × 10⁻⁶ -12 m 2 The gas diffusion layer for water electrolysis of the anion exchange membrane of the present invention is of higher quality the higher the gas permeability, so it is preferable not to limit the upper limit. Specifically, the gas permeability is 1 × 10⁻⁶. -12 m2 Above, 1.25×10 -12 m 2 Above, 1.5×10 -12 m 2 Above, 1.75×10 -12 m 2 Above, or 2×10 -12 m 2 Above, and 4×10 -12 m 2 Below, 3×10 -12 m 2 Below, or 2.5×10 -12 m 2 It may be below.

[0028] If the gas permeability is low, there may be a problem that the overall efficiency decreases when used in water electrolysis or the like, because the mobility of oxygen and hydrogen that must be discharged to the outside through the gas diffusion layer decreases. [[ID=3&]]

[0029] The gas permeability of the present invention can be determined by using a GDL basic physical property evaluation apparatus (CPRT 10, a self - standard of the Korea Institute of Energy Technology), randomly contacting the surface of the gas diffusion layer a total of three times, and using the following paper and Equation 1.

[0030] The gas permeability is determined by the Trough plane permeability method of the paper "In - plane and through - plane gas permeability of carbon ber electrode backing layers (Jeff T. Gostick, et al., Sep 1 2006)", and the gas permeability (K, unit m 2 ) can be calculated by the following [Equation 1].

[0031]

Equation

[0032] In equation 1 above, K is the gas permeability, μ is the dynamic viscosity of the gas used, A is the area of ​​the cross-section through which the gas permeates, t is the thickness of the gas diffusion layer through which the gas permeates, m is the flow rate (mass) of the gas flowing per unit area, P1 is the pressure before gas permeation, P2 is the pressure after gas permeation, R is the gas constant, T is the temperature, M is the weight of the gas used, and P avg This represents the average value of P1 and P2.

[0033] Furthermore, the anion exchange membrane water electrolysis gas diffusion layer may further include a porous support on one surface of a network of carbon nanofiber films. Specifically, the gas diffusion layer may be in a form in which the carbon nanofiber film is provided on one surface of the porous support.

[0034] The porous support is not limited to any porous material, but may be, for example, porous carbon paper, carbon fiber film, carbon nanofiber film, and carbon nanotube film. The porous support may also have a thickness of 50 to 500 μm, or a thickness of 100 to 500 μm.

[0035] Furthermore, the present invention can provide a method for producing a gas diffusion layer for anion exchange membrane water electrolysis, comprising the steps of: spinning a carbon precursor material to form a mesh-shaped product (Step 1); and heat-treating the mesh-shaped product to obtain a mesh-like carbon nanofiber film (Step 2).

[0036] The carbon precursor material in step 1 may be one or more selected from the group consisting of polyacrylonitrile, polyvinyl alcohol, polyvinylpyrrolidone, and their precursors, cellulose, lignin, and pitch.

[0037] The spinning described in (Step 1) may be one or more selected from the group consisting of electrospinning, centrifugal jet spinning, meltblown spinning, and jet spinning. Specifically, the spinning may be electrospinning.

[0038] When spinning is performed via the electrospinning method described above, the carbon precursor material in solution can be spun through a nozzle with a diameter of 1 to 5 mm. A voltage of 5 to 30 kV may be applied to the nozzle, and the distance between the nozzle and ground may be 5 to 30 cm. In this case, the carbon precursor material in solution can be spun through the nozzle at a constant rate of 1 to 10 ml / hour. One or more nozzles can be used, and the number of nozzles or the spinning time can be increased to obtain the desired thickness.

[0039] Through the heat treatment described above (Step 2), the net-shaped product formed in the spinning stage is carbonized into a net-like carbon nano fiber A film is formed. The heat treatment step involves first stabilizing the mesh-formed product in an air atmosphere or a gas atmosphere mixed with oxygen at a temperature range of 200 to 400°C for more than one hour, and then carbonizing it at a temperature of 700 to 1500°C using an inactive gas for more than one hour. After that, it is cooled to room temperature in an inactive gas atmosphere to form a mesh-like carbon nano fiber The film is obtained. At this time, the carbonization cooling process, which is the stabilization step, is carried out while maintaining an inactive gas atmosphere.

[0040] Furthermore, the spinning of the carbon precursor material in step 1 may be carried out on a porous support.

[0041] Alternatively, the method for producing the gas diffusion layer for anion exchange membrane water electrolysis is to produce the network of carbon nano obtained in (step 2). fiber The process may further include a step of attaching the film to a porous support. Specifically, the method for attaching the porous support to a mesh-like carbon nanofiber film may be a method of applying an adhesive to one surface of the porous support and then attaching it. In this case, the adhesive used may contain a substance with high electrical conductivity, a substance with high viscosity, or both.

[0042] The porous support is not limited to any porous material, but may be, for example, porous carbon paper, carbon fiber film, carbon nanofiber film, and carbon nanotube film. The porous support may also have a thickness of 50 to 500 μm, or a thickness of 100 to 500 μm.

[0043] The following are preferred embodiments to aid in understanding the invention. However, these embodiments are merely illustrative and do not limit the invention to them. [Examples]

[0044] Examples In this example, a network of carbon nanoparticles was formed using the electrospinning method. fiber A gas diffusion layer in the form of a film was fabricated. First, polyacrylonitrile, a carbon precursor material in solution, was spun through a 3 mm diameter nozzle at a constant rate of 5 ml per hour for 3 hours. At this time, aluminum foil was placed on the grounded collector to facilitate sample removal, and the polyacrylonitrile was electrospun on top of the foil. A voltage of 15 kV was applied to the nozzle. The distance between the nozzle and the ground was maintained at 15 cm. Although more than one nozzle can be used, in this example, one nozzle was used to spin polyacrylonitrile to a thickness of 500 μm to form a mesh-shaped product.

[0045] Next, the mesh-formed product was stabilized in an air atmosphere (containing oxygen) at a temperature of 270-300°C for 1 hour. After that, it was carbonized in an inactive gas N2 atmosphere at a temperature of 1000°C for 1 hour. After the heat treatment process, the sample was cooled to room temperature to obtain a mesh-like carbon nanofiber film. The formed mesh-like carbon nanofiber film had a thickness of 200 μm.

[0046] Comparative Example As a comparative example, we used JTN20-A6H, a conventional commercially available gas diffusion layer product for PEMFCs from JTG Corporation.

[0047] Experimental Example 1 - Surface Observation The surface and side surfaces of the fabricated network of carbon nanofiber films were observed using a scanning electron microscope (SEM) and are shown in Figures 1 and 2, respectively. As can be seen from the drawings, we were able to confirm that the carbon nanofiber film, which is the gas diffusion layer of the present invention, is formed in a mesh-like film shape and maintains its porosity.

[0048] Experimental Example 2 - Measurement of Contact Angle The contact angle of the mesh-like carbon nanofiber film of the example with respect to distilled water droplets was measured and is shown in Figure 3. The contact angle was measured by placing the film-like sample on a flat surface, dropping 5-10 μl of distilled water onto it, and then observing its shape from the side using DSA to calculate the angle. As can be seen from the drawings, the mesh-like carbon nanofiber film of the example exhibits superhydrophilicity with a contact angle of 0° compared to the gas diffusion layer of the comparative example.

[0049] Experimental Example 3 - Observation of Gas Permeability Gas permeability was measured using a GDL basic physical property evaluation device (CPRT 10, Korea Advanced Institute of Energy standard) by randomly contacting the surface of the gas diffusion layer and taking a total of three measurements. The gas permeability was then determined using the following paper and Equation 1.

[0050] The gas permeability was calculated using the through-plane permeability method described in the paper "In-plane and through-plane gas permeability of carbon ber electrode backing layers (Jeff T. Gostick, et al., Sep 1 2006)," and the gas permeability (K, unit m) was calculated using the following [Equation 1]. 2 The calculation is shown in Figure 4.

[0051]

number

[0052] By comparing the gas permeability of the mesh-like carbon nanofiber film in the example with that of the gas diffusion layer in the comparative example, it was confirmed that the example exhibited even superior gas permeability.

Claims

1. An anion exchange membrane gas diffusion layer for water electrolysis comprising a film in which carbon nanofibers are arranged in a network, wherein the carbon nanofibers have a diameter of 500 nm or less, and the gas diffusion layer for water electrolysis has a contact angle with water of 20° or less.

2. The anion exchange membrane gas diffusion layer for water electrolysis has a gas permeability of 1 × 10⁻⁶ －１２ I understand ２ The gas diffusion layer for anion exchange membrane water electrolysis according to claim 1.

3. The anion exchange membrane gas diffusion layer for water electrolysis according to claim 1, further comprising a porous support on one surface of a network of carbon nanofiber films.

4. The anion exchange membrane gas diffusion layer for water electrolysis according to claim 3, wherein the porous support is one or more selected from the group consisting of porous carbon paper, carbon fiber film, carbon nanofiber film, and carbon nanotube film.

5. Step 1: Spinning a carbon precursor material to form a mesh-shaped product; and Step 2: Heat-treating the aforementioned mesh-molded product to obtain a mesh-like carbon nanofiber film; A method for manufacturing an anion exchange membrane water electrolysis gas diffusion layer, wherein the gas diffusion layer for anion exchange membrane water electrolysis has a contact angle with water of 20° or less.

6. The method for producing a gas diffusion layer for an anion exchange membrane water electrolysis according to claim 5, wherein in step 1, the carbon precursor material is one or more selected from the group consisting of polyacrylonitrile, polyvinyl alcohol, polyvinylpyrrolidone, and their precursors, cellulose, lignin, and pitch.

7. The method for producing a gas diffusion layer for an anion exchange membrane water electrolysis according to claim 5, wherein the spinning in step 1 is one or more selected from the group consisting of electrospinning, centrifugal jet spinning, meltblown, and jet spinning.

8. The method for producing a gas diffusion layer for an anion exchange membrane water electrolysis according to claim 7, wherein the electrospinning is performed by spinning a carbon precursor material in a solution state through a nozzle with a diameter of 1 to 5 mm, and a voltage of 5 to 30 kV is applied to the nozzle.

9. The method for producing a gas diffusion layer for anion exchange membrane water electrolysis according to claim 5, wherein the heat treatment step of step 2 is performed at a temperature of 700 to 1500°C for 1 hour or more.

10. The method for producing a gas diffusion layer for an anion exchange membrane water electrolysis according to claim 5, wherein the spinning of the carbon precursor material in step 1 is performed on a porous support.

11. The method for producing a gas diffusion layer for an anion exchange membrane water electrolysis according to claim 5, further comprising the step of attaching the network-like carbon nanofiber film obtained in step 2 to a porous support.

12. The method for producing a gas diffusion layer for an anion exchange membrane water electrolysis according to claim 10 or claim 11, wherein the porous support is one or more selected from the group consisting of porous carbon paper, carbon fiber film, carbon nanofiber film, and carbon nanotube film.

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