Flexible gas diffusion electrode, its preparation method and application

Abstract

This invention discloses a flexible gas diffusion electrode, its preparation method, and its applications. The flexible gas diffusion electrode includes a flexible electrode substrate and a metal layer disposed on a portion of the surface of the flexible electrode substrate. The flexible electrode substrate is formed at least by interwoven linear carbon nanomaterials, and the metal layer has multiple through-hole structures extending along its thickness direction, exposing a portion of the surface of the flexible electrode substrate through these through-hole structures. The highly conductive flexible gas diffusion electrode provided by this invention is suitable for electrochemical energy conversion devices requiring gas participation, reducing the device's mass / volume, increasing its power density, and improving its specific power. Furthermore, the preparation method is simple to operate and achieves selective deposition, uniform deposition, and high bonding strength between the deposited metal layer and the substrate, improving the electrode's electrochemical performance while ensuring flexibility and uniformity.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy technology, and in particular to a flexible gas diffusion electrode, its preparation method and application. Background Technology

[0002] Smaller size / weight and higher output power have always been the goals pursued by electrochemical energy conversion devices. In particular, flexible electrochemical energy conversion devices (such as supercapacitors, lithium-ion batteries, metal-air batteries, and fuel cells) need to provide higher energy / power in a smaller size / weight to significantly extend the battery life and driving range of electrical appliances.

[0003] Meanwhile, lightweight, high power density energy devices have a wide range of applications, such as unmanned aerial vehicles, individual soldier power supplies, and emergency power supplies. Some of the electrochemical energy conversion devices mentioned above require gas to participate in the reaction and further convert the chemical energy of the reacting gas into electrical energy, such as metal-air batteries and fuel cells. Therefore, gas diffusion electrodes are an important component of electrochemical energy conversion devices that require gas to participate in the reaction.

[0004] Gas diffusion electrodes typically include carbon fiber paper, porous carbon black paper, carbon nanotubes, or carbon nanofiber membranes. These electrodes possess tunable gas diffusion capabilities, providing abundant transport channels for reactants, which is beneficial for reaction occurrence and energy conversion. However, gas diffusion electrodes have low conductivity, making them unsuitable for current collection. Directly using gas diffusion electrodes for current collection results in a significant voltage drop due to their low conductivity, further reducing the output power density. Therefore, porous, highly conductive materials are necessary as current collectors to reduce voltage drops during discharge and further improve power density. Currently, highly conductive porous graphite plates, metal plates, and metal foams are commonly used for current collection.

[0005] Specifically, in the existing technology, as described in the technical literature (Small 2021, 17, 2007579), researchers achieved improved conductivity and a sheet resistance of less than 0.1 Ω·sq by uniformly depositing metal on various non-conductive substrates through a layer-by-layer self-assembly induced metal electrodeposition method. -1 This highly conductive porous material was used as a current harvesting device to improve the performance of supercapacitors.

[0006] In a technical paper published in Advanced Materials, 2016, 28, 6421–6428, researchers used highly conductive stainless steel mesh as current collector and electrode material, and further loaded it with catalysts, to improve the performance of zinc-air batteries.

[0007] Currently, gas diffusion electrodes in flexible electrochemical energy conversion devices are typically composed of carbon-based gas diffusion electrodes used in combination with metal current collectors or metal foams. The gas diffusion electrode provides a channel for gas reactions, while the porous metal mesh or highly conductive metal foam collects the current. Due to the high conductivity of the metal current collector (metal foam), its use does indeed lead to increased current density and power density. However, the use of metal current collectors (metal foams) has several serious drawbacks:

[0008] First, the heavy metal current collector and metal foam will greatly increase the overall weight of the electrochemical energy conversion device, which is not conducive to the lightweighting and miniaturization of the electrochemical energy conversion device.

[0009] Secondly, the contact between the gas diffusion electrode and the metal current collector (metal current collector foam) is poor, resulting in a large contact resistance, which is not conducive to improving the current density and power density of electrochemical energy reaction devices.

[0010] Third, the opening parameters of the metal current collector (metal foam) affect gas transport, which is not conducive to the transport of reactant gas and further reduces the current density of electrochemical energy devices.

[0011] Fourth, the rigidity of the metal current collector (metal foam) itself, and the poor contact between it and the gas diffusion electrode, are not conducive to the flexibility of electrochemical energy devices.

[0012] In summary, current technologies struggle to achieve a gas diffusion electrode that combines flexibility, high conductivity, and high gas diffusion capability. The gas diffusion electrode proposed in this invention, possessing both high conductivity and high gas diffusion capability, enables a reduction in the volume / mass of electrochemical energy conversion devices, an increase in power density, and a higher power-to-weight ratio. Summary of the Invention

[0013] To address the shortcomings of existing technologies, the present invention aims to provide a flexible gas diffusion electrode, its preparation method, and its application.

[0014] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0015] In a first aspect, the present invention provides a flexible gas diffusion electrode, comprising a flexible electrode substrate and a metal layer disposed on a portion of the surface of the flexible electrode substrate;

[0016] The flexible electrode substrate is formed by interlacing linear carbon nanomaterials, and the metal layer has a plurality of through-hole structures extending along the thickness direction of the metal layer, so that a portion of the surface of the flexible electrode substrate is exposed through the through-hole structures.

[0017] Secondly, the present invention also provides a method for preparing a flexible gas diffusion electrode, comprising:

[0018] A flexible electrode substrate is provided, wherein the flexible electrode substrate is formed by at least interlacing linear carbon nanomaterials;

[0019] A metal layer is formed on a portion of the surface of the flexible electrode substrate;

[0020] During or after the formation of the metal layer, a plurality of pore structures are formed in the metal layer, the pore structures extending along the thickness direction of the metal layer, so that a portion of the surface of the flexible electrode substrate is exposed through the pore structures.

[0021] Thirdly, the present invention also provides the application of the above-mentioned flexible gas diffusion electrode in the fabrication of fuel cells and metal-air batteries.

[0022] Fourthly, the present invention also provides a self-breathing fuel cell, wherein the cathode adopts the above-mentioned flexible gas diffusion electrode.

[0023] Based on the above technical solution, compared with the prior art, the beneficial effects of the present invention include at least the following:

[0024] The highly conductive flexible gas diffusion electrode provided by this invention is suitable for electrochemical energy conversion devices that require gas participation. It can reduce the mass / volume of the device, increase the power density of the device, and improve the specific power.

[0025] The preparation method provided by this invention is simple to operate and can achieve selective deposition, uniform deposition, and high bonding strength between the deposited metal layer and the substrate, thereby improving the electrochemical performance of the electrode while ensuring flexibility and uniformity.

[0026] The above description is merely an overview of the technical solution of the present invention. In order to enable those skilled in the art to better understand the technical means of this application and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described below in conjunction with detailed drawings. Attached Figure Description

[0027] Figure 1 This is a schematic flowchart of a method for preparing a flexible gas diffusion electrode provided in some typical embodiments of the present invention;

[0028] Figure 2 This is an SEM image of the fabrication process of the flexible gas diffusion electrode provided in a typical embodiment of the present invention;

[0029] Figure 3 This is a gas permeation performance test diagram of the fabrication process of the flexible gas diffusion electrode provided in a typical embodiment of the present invention.

[0030] Figure 4 These are comparative test diagrams of the conductivity of flexible gas diffusion electrodes provided in some typical embodiments of the present invention.

[0031] Figure 5 These are comparative test charts of the volt-ampere characteristics of self-breathing fuel cells provided in some typical embodiments of the present invention;

[0032] Figure 6 These are peak power density comparison test charts of self-breathing fuel cells provided in some typical embodiments of the present invention. Detailed Implementation

[0033] In view of the shortcomings of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The purpose of this invention is to achieve the fabrication of a gas diffusion electrode that balances high conductivity and high gas flux. This gas diffusion electrode simultaneously functions as a diffusion layer and a current collector, which can significantly reduce the mass / volume of electrochemical energy conversion devices that require gas participation in the reaction, increase power density, improve stability, and achieve a significant increase in specific power.

[0034] The following will provide a further explanation of the technical solution, its implementation process, and its principles.

[0035] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0036] Moreover, relational terms such as “first” and “second” are used merely to distinguish one component or method step from another that has the same name, and do not necessarily require or imply any such actual relationship or order between these components or method steps.

[0037] See Figure 2 The first aspect of the present invention provides a flexible gas diffusion electrode, comprising a flexible electrode substrate and a metal layer disposed on a portion of the surface of the flexible electrode substrate; the flexible electrode substrate is formed by interlacing linear carbon nanomaterials, and the metal layer is provided with a plurality of pore structures extending along the thickness direction of the metal layer, so that a portion of the surface of the flexible electrode substrate is exposed by the pore structures.

[0038] In some implementation schemes, such as Figure 2 As shown in Figure f, a portion of the linear carbon nanomaterial located at the interface between the flexible electrode substrate and the metal layer is partially encapsulated by the metal in the metal layer.

[0039] In some implementations, the interface is further provided with multiple metal seed particles.

[0040] In some implementations, the metal seed particles are made of the same material as the metal layer.

[0041] In some embodiments, the flexible electrode substrate includes any one or a combination of two or more of carbon fiber paper, porous carbon black paper, carbon nanotube film, and carbon nanofiber film.

[0042] In some embodiments, the flexible electrode substrate comprises a blended film formed by interweaving carbon fibers and carbon nanotube fibers.

[0043] In practice, the inventors discovered that a preferred flexible electrode substrate can be prepared, for example, by filtration of a mixture of carbon fibers and carbon nanotubes. In this substrate, carbon fibers act as the framework, enhancing the strength of the flexible electrode. The entangled carbon nanotubes fill the framework formed by the carbon fibers, improving the conductivity of the flexible electrode substrate. Furthermore, compared to carbon fiber paper and carbon nanotube films, this flexible electrode substrate also exhibits a uniform pore size distribution and excellent porosity. Compared to other types of flexible electrode substrates, it has better compatibility with metal layers, achieving a relatively optimal balance between permeability and conductivity.

[0044] In some embodiments, the mass ratio of carbon fiber to carbon nanotube in the blended film is 5-1:1; the length of the carbon fiber is 10-100 μm and the diameter is 3-10 μm; the length of the carbon nanotube is 1-10 μm and the diameter is 5-20 nm.

[0045] Through long-term practice, the inventors of this invention have discovered that, compared to carbon fiber paper composed solely of carbon fibers or carbon nanotube films composed of carbon nanotubes, a flexible electrode substrate composed of a mixture of carbon fibers and carbon nanotubes with two different physical properties is more suitable for the structure of the gas diffusion electrode of this invention. The reason is that relatively thick, long, and high-flexural-modulus carbon fibers form the main network, and carbon nanotube fibers are dispersed in the main network to form a highly flexible capillary branch network. The air permeability of the air-permeable interface formed by the main network and the branch network is excellent, and the interface structure formed in this way has multi-branched ends. While maintaining flexibility, it can tightly bond with the metal layer. This allows for high air permeability while further reducing contact resistance, thereby achieving a more superior combination of gas permeability, conductivity, and flexibility.

[0046] In some embodiments, the areal density of the metal layer is 0.5-6 mg·cm³. -2 .

[0047] In some implementations, the pore size of the hole structure is 0.1-3 μm.

[0048] In some implementations, the total area of ​​the plurality of said hole structures accounts for 20-70% of the surface area of ​​the metal layer.

[0049] In some embodiments, the material of the metal layer is selected from any one or a combination of two or more of Au, Ag, and Cu.

[0050] In some embodiments, the metal layer is formed using an electrochemical deposition method.

[0051] In some embodiments, the sheet resistance of the flexible gas diffusion electrode is as low as 0.01 Ω·cm. -2 .

[0052] In some embodiments, the gas flux of the flexible gas diffusion electrode is 30-150 mL·min. -1 ·KPa·cm -2 The preferred concentration is 20-150 mL / min. -1 ·KPa·cm -2 .

[0053] See Figures 1-4 The second aspect of this invention provides a method for preparing a flexible gas diffusion electrode, comprising the following steps:

[0054] A flexible electrode substrate is provided, the flexible electrode substrate being formed by at least interwoven linear carbon nanomaterials.

[0055] A metal layer is formed on a portion of the surface of the flexible electrode substrate.

[0056] During or after the formation of the metal layer, a plurality of pore structures are formed in the metal layer, the pore structures extending along the thickness direction of the metal layer, so that a portion of the surface of the flexible electrode substrate is exposed through the pore structures.

[0057] Figure 1 This is a flowchart of the technical solution of the present invention. The conductivity of the gas diffusion electrode is improved by electroplating a highly conductive metal on the gas diffusion electrode. The gas transport capability of the highly conductive gas diffusion electrode is further improved by adjusting the electroplating scheme or by subsequent patterning processing, and finally a gas diffusion electrode with high conductivity and high gas transport capability is obtained.

[0058] The flowchart here illustrates two implementation schemes. The first one is... Figure 1 The first type, shown in AD, is a gas diffusion electrode with high conductivity and high gas transport capability, obtained through magnetron sputtering, electroplating, and laser patterning. The second type is... Figure 1 As shown in section ae, this is a gas diffusion electrode with high conductivity and high gas transport capability obtained through direct electroplating. Embodiments of this invention are not limited to the two schemes listed here. Furthermore, the scheme "magnetron sputtering-electroplating-laser patterning" is the preferred scheme, and each part will be described in detail below.

[0059] Specifically, embodiments of the present invention provide a general solution for a gas diffusion electrode with high conductivity and high gas transport capability achieved through electroplating, such as... Figure 1 As shown, one fabrication step (a)-(d) involves a "sputtering-electroplating-laser patterning" method to prepare a gas diffusion electrode with high conductivity and high gas transport capability. (a) represents carbon paper; (b) represents magnetron sputtering a layer of metal seed particles onto the carbon paper, which is the same metal as the metal layer to be electroplated later; (c) represents electroplating a metal coating uniformly onto one side of the sputtered metal; and (d) represents patterning the electroplated metal layer using laser etching to ultimately obtain a gas diffusion electrode with high conductivity and high gas transport capability. Another fabrication step (a)-(e) involves a direct electroplating method to prepare a gas diffusion electrode with high conductivity and high gas transport capability. (e) represents a gas diffusion electrode with high conductivity and high gas transport capability obtained through direct electroplating. During the direct electroplating process, it is necessary to control the condition parameters to achieve a porous metal layer with both current conduction and gas permeability in a one-step process.

[0060] Therefore, in some embodiments, the preparation method may specifically include the following steps:

[0061] Multiple metal islands are formed on a portion of the surface of the flexible electrode substrate by a first electrochemical deposition. The multiple metal islands are interconnected and surround each other to form the porous structure.

[0062] In some embodiments, the conditions for the first electrochemical deposition are a current density of less than 20 mA cm⁻¹. -2 The electrolyte is mechanically stirred (at a speed of 100-300 rpm), and the entire electroplating process is carried out at room temperature (e.g., 15-30℃).

[0063] The advantage of the above preparation method is that it can directly form a metal layer with excellent conductivity and gas permeability in one step. This method has the advantages of simple process and low cost. The key lies in the control of electrochemical deposition conditions. By controlling the above conditions, the deposited metal tends to aggregate in an island-like manner rather than being uniformly distributed, thus forming a number of dispersed island growth states. As the islands gradually expand, multiple islands connect to form a conductive network. Furthermore, by controlling the degree of growth, sufficient pore structure is still left between the islands to achieve the best balance between conductivity and gas permeability.

[0064] In some embodiments, the preparation method may specifically include the following steps:

[0065] Metal seed particles are deposited on a portion of the surface of the flexible electrode substrate using a physical sputtering method.

[0066] In practice, a flexible electrode substrate for gas diffusion can be fixed to a flat glass plate using insulating tape, and then placed inside the magnetron sputtering cavity. The magnetron sputtering load can be changed by adjusting the current and time, and the type of metal sputtered can be changed by replacing the target. The preferred metals for sputtering are the three metals with the best conductivity: Au, Ag, and Cu. The magnetron sputtering current can be set to, for example, 2.0 mA, and the sputtering time is preferably set to 10-120 s.

[0067] A conductive layer precursor is deposited on the surface of the portion loaded with the metal seed particles by a second electrochemical deposition.

[0068] In practice, the second electrochemical deposition can be carried out, for example, by the following steps 1-2:

[0069] (1) Preparation of electroplating solution:

[0070] For electroplating, the three metals with the highest conductivity are Au, Ag, and Cu. For Au electroplating, the plating solution composition is, for example, 20 g / L. -1 Chloroauric acid (HAuCl4), 10 g·L -1 Hydrochloric acid (HCl) and deionized water. For Ag electroplating, the composition of the plating solution could be, for example, 34 g / L. -1 Silver nitrate (AgNO3), 6 g·L -1 Nitric acid (HNO3), 3 g·L -1 Citric acid (C6H8O7) and deionized water. For Cu electroplating, the electrolyte composition could be, for example, 1000 g·L⁻¹. -1 Copper(II) sulfate pentahydrate (CuSO4·5H2O), 50 g·L -1Sulfuric acid (H2SO4) and deionized water.

[0071] (2) Electroplating

[0072] The self-made gas diffusion electrode, already magnetron sputtered, was cut to a size of 5cm × 10cm. It was then fixed to a plastic plate with insulating tape. Simultaneously, a stainless steel sheet was fixed to the top layer of the gas diffusion electrode using insulating tape. The stainless steel sheet connects the gas diffusion electrode to the power supply. The gas diffusion electrode serves as the negative electrode, and the corresponding electroplated metal sheet acts as the positive electrode for electroplating. The voltages for electroplating Cu, Ag, and Au can be 2V, 1.5V, and 1V, respectively. The electroplating metal loading was adjusted by changing the electroplating time to 0.5, 1, 2, 3, 4, 5, and 6 mg / cm². -2 The relationship between the loading of electroplated metal and time can be calculated using Faraday's formula. Finally, the electroplated gas diffusion electrode is cleaned with ethanol and water, and then dried at 60°C.

[0073] The conductive layer precursor is patterned to form a plurality of patterned hole structures.

[0074] In some implementations, the patterning process is selected from laser etching.

[0075] In addition to laser etching, other methods for forming the above-mentioned patterned hole structure distribution include patterned chemical etching, patterned physical etching, etc. Specifically, a patterned mask can be formed by coating photoresist and then exposing and developing it. Then, the underlying metal layer can be chemically etched or physically etched by plasma bombardment based on the mask. It is not limited to the laser etching method in the preferred example above.

[0076] However, the preferred embodiment is to perform laser etching, at least the metal layer closest to the flexible electrode substrate (the last part to be etched) is laser etched, for example, patterned chemical etching is performed first, and then laser etching is performed to expose the flexible electrode substrate. This is because, compared with other etching methods, laser etching, while heating and vaporizing the metal layer to form a cavity structure, will inevitably irradiate the surface of the flexible electrode substrate exposed from the cavity structure, making it loose, expanding the gas passage, and at the same time, causing the nearby metal layer to partially melt, enhancing the bonding degree, thereby improving the air permeability and current conduction capacity at the cavity structure, resulting in better overall performance.

[0077] In practice, the above patterning process can be implemented using, for example, the following steps:

[0078] The dried electroplated metal diffusion layer is placed on the worktable of the UV laser marking machine, ensuring the flatness of the electroplated metal layer as much as possible. The drilling size, spacing, and drilling area are set using the laser marking software. Different drilling sizes and spacings may affect the conductivity and gas transport capacity of the metal layer. The laser current and the number of marking passes are adjusted to ensure that the laser etching depth only etches the surface metal plating without etching the gas diffusion electrode. Here, the drilling size is set to 50 μm, the hole spacing to 50 μm, and the drilling area to be less than 10 cm × 10 cm. For a loading of 5 mg / cm²... -2 For Au plating, the marking current was set to 4A, and the marking frequency was set to 1 time. For a loading of 5mg / cm³... -2 For Ag plating, the marking current was set to 4.5A, and the marking frequency was set to 2 times. For a loading of 5mg / cm³... -2 The Cu coating was applied, with a marking current of 6.5A and two marking cycles. The laser-marked gas diffusion electrode was then cleaned with ethanol and water and dried at 60°C to obtain the highly conductive and highly gas-permeable flexible gas diffusion electrode proposed in this invention.

[0079] The third aspect of the present invention also provides the application of a flexible gas diffusion electrode in the fabrication of fuel cells and metal-air batteries.

[0080] See Figures 5-6 As one specific implementation of the above application, a fourth aspect of the present invention also provides a self-breathing fuel cell, wherein the cathode of the self-breathing fuel cell adopts the flexible gas diffusion electrode provided in any of the above embodiments.

[0081] In some implementations, the peak power density of the self-breathing fuel cell can reach a maximum of 355 mW / cm³. 2 .

[0082] The technical solution of the present invention will be further described in detail below through several embodiments and in conjunction with the accompanying drawings. However, the selected embodiments are only for illustrating the present invention and do not limit the scope of the present invention.

[0083] Example 1

[0084] Example 1 of this embodiment describes the fabrication process of a flexible gas diffusion electrode with high conductivity and high gas diffusion performance using a direct electroplating method, as detailed below:

[0085] The flexible electrode substrate, using a blended film of carbon fiber filaments and carbon nanotubes, is prepared as follows: First, carbon fibers and carbon nanotubes are uniformly dispersed in a solution using a cell disruptor. Second, the solutions of carbon fibers and carbon nanotubes are mixed in different mass ratios. Finally, the flexible carbon-based substrate is obtained by vacuum filtration. The average diameter of the carbon fiber filaments is 5 μm, and the average length is 100 μm. The average diameter of the carbon nanotubes is 5 nm, and the average length is 20 nm. The mass ratio of carbon fibers to carbon nanotubes is 1:1.

[0086] A gold-plating electroplating method was used to directly deposit a metal layer on one side of the flexible electrode substrate, controlling the metal loading to be 0.5 mg·cm³. -2 The composition of the gold plating solution is: 20 g·L -1 Chloroauric acid (HAuCl4), 10 g·L -1 Hydrochloric acid (HCl) and deionized water.

[0087] The final result is a metal layer composed of multiple interconnected islands of gold, with pores between these islands. The pore size is primarily 0.1-3 μm. The porosity varies from 10⁻¹⁰ to 10⁻¹⁰ in different regions. 3 / cm 2 Between the metal layer and the flexible electrode substrate, a flexible gas diffusion electrode is formed.

[0088] Then control the electroplating time to achieve a metal loading of 6 mg·cm³. -2 It is possible to obtain flexible gas diffusion electrodes with the same level of microstructure, permeability, and conductivity.

[0089] Example 2

[0090] Example 1 of this embodiment describes the fabrication process of a flexible gas diffusion electrode with high conductivity and high gas diffusion performance using a "sputtering-electroplating-laser patterning" method, as detailed below:

[0091] Using the same flexible electrode substrate as in Example 1, magnetron sputtering was first employed to sputter gold. The magnetron sputtering current was 20 mA, and the sputtering time was 30 s, resulting in the formation of multiple gold particles.

[0092] Electroplating was then carried out on the sputtered substrate using the same plating solution as in Example 1, with a metal loading of 5 mg / cm³. -2 .

[0093] Finally, a laser marking machine was used, with the marking current set to 4A, the marking frequency set to 1, the hole size to 50μm, the hole spacing to 50μm, and the machine power set to 2.6W, to form a shape like... Figure 2 The diagram in Figure g shows a structure with multiple through holes.

[0094] Examples 3-8

[0095] The fabrication process of the flexible gas diffusion electrode with high conductivity and high gas diffusion performance using the "sputtering-electroplating-laser patterning" method in Example 1 of this embodiment is largely the same as that in Example 2, with the main difference being:

[0096] The electroplating time was adjusted to achieve metal loadings of 0.5, 1, 2, 3, 4, and 6 mg·cm³, respectively. -2 These correspond to Examples 3-8, respectively.

[0097] Example 9

[0098] This embodiment is largely the same as Embodiment 2, with the main difference being:

[0099] The flexible electrode substrate was replaced with carbon fiber paper of the same size and thickness by replacing the carbon fiber and carbon nanotube hybrid film. All other steps and implementation parameters remained unchanged.

[0100] Example 10

[0101] This embodiment is largely the same as Embodiment 2, with the main difference being:

[0102] The flexible electrode substrate was replaced by a carbon nanotube film of the same size and thickness, while all other steps and implementation parameters remained unchanged.

[0103] Example 11

[0104] This embodiment is largely the same as Embodiment 2, with the main difference being:

[0105] The flexible electrode substrate was replaced by a carbon nanotube film of the same size and thickness, while all other steps and implementation parameters remained unchanged.

[0106] Example 12

[0107] This embodiment is largely the same as Embodiment 2, with the main difference being:

[0108] The magnetron sputtering metal target was replaced with Ag, and the electroplated metal was also replaced with Ag. Specifically, the composition of the electroplating solution was 34 g / L. -1 Silver nitrate (AgNO3), 6 g·L -1 Nitric acid (HNO3), 3 g·L -1 Citric acid (C6H8O7) and deionized water were used, while all other steps and implementation parameters remained unchanged.

[0109] Example 13

[0110] This embodiment is largely the same as Embodiment 2, with the main difference being:

[0111] The magnetron sputtering metal target was replaced with Cu, and the electroplated metal was also replaced with Cu. Specifically, the electrolyte composition was: 1000 g·L⁻¹ -1 Copper(II) sulfate pentahydrate (CuSO4·5H2O), 50 g·L -1 Sulfuric acid (H2SO4) and deionized water.

[0112] All other steps and implementation parameters remain unchanged.

[0113] Example 14

[0114] This embodiment is largely the same as Embodiment 2, with the main difference being:

[0115] Instead of laser etching, a plasma etching method using a photoresist mask is employed to etch the gold layer, forming a porous structure of the same size and density.

[0116] All other steps and implementation parameters remain unchanged.

[0117] Blank example 1

[0118] The same flexible electrode substrate used in Example 1 was directly used as the flexible gas diffusion electrode.

[0119] Comparative Example 1

[0120] A metal current collector is attached to one side of commercial carbon fiber paper to further fabricate a fuel cell. During battery testing and use, the outer side of the metal current collector is secured with a non-conductive, porous plastic plate. The porous plastic plate is secured with screws.

[0121] The porous plastic plate applies a certain pressure to the metal current collector, further reducing the contact resistance between the metal current collector and the carbon fiber paper, thereby improving battery performance.

[0122] Comparative Example 2

[0123] Metal foam is attached to one side of commercial carbon fiber paper to further fabricate a fuel cell. During battery testing and use, the outer side of the metal foam is secured with a non-conductive, porous plastic plate. The porous plastic plate is secured with screws. The porous plastic plate applies pressure to the metal foam, further reducing the contact resistance between the metal foam and the carbon fiber paper, thereby improving battery performance.

[0124] Application Example 1

[0125] This application example illustrates some application instances of fabricating self-breathing fuel cells using the flexible gas diffusion electrodes provided in the above embodiments and blank examples, as detailed below:

[0126] 1) First, prepare the microporous layer slurry. Mix Vulcan-X-72 with 20% polytetrafluoroethylene (PTFE) and disperse evenly in a solution of water and isopropanol. Further, ultrasonically homogenize the slurry and spray it onto one side of the aforementioned gas diffusion electrode without a metal coating. The loading amount of Vulcan-X-72 is 0.5 mg / cm³. -2 And dry at 350℃.

[0127] 2) Next, the catalyst slurry was prepared by dispersing 70% Pt / C and Nafion in a solution of water and isopropanol at a certain ratio, and then ultrasonically dispersing it into a uniform slurry. Further, the uniformly dispersed catalyst slurry was loaded onto a microporous layer by spraying, with a catalyst loading of 0.5 mg Pt·cm³. -2 The catalyst-loaded gas diffusion electrode was placed in an oven at 105°C and left to stand for 2 hours.

[0128] 3) Next, the membrane electrode was prepared by placing the proton exchange membrane (DuPont XL) between the anode and cathode, and incubating at 130℃ and 40 kgf·cm⁻¹. -2 Press down with hot pressure for two minutes.

[0129] 4) The membrane electrode is encapsulated. A polyoxymethylene silane (PDMS) membrane is used to encapsulate the anode side, with a small hole on each side at opposite corners for hydrogen inlet / outlet channels. The space between the PDMS membrane and the membrane electrode forms the flow field at the anode. The cathode side is directly exposed to air and is not encapsulated.

[0130] 5) Battery Testing: The encapsulated membrane electrode assembly (MEA) was tested using a 0.5mm thick, 50mm wide silver sheet connected to the anode and cathode of the MEA and the external circuit. The MEA performance was tested using an electrochemical workstation. The battery polarization curve was measured using a linear voltammetry method at room temperature and pressure, and the battery power curve was calculated. The hydrogen flow rate was 15 mL / min. -1 The scan rate of the linear scanning voltammeter is 10 mV·s. -1 The cutoff voltage is 0.2V.

[0131] Electrode performance testing items and methods

[0132] 1. Morphology (SEM) of the highly conductive metal layer:

[0133] The structure and morphology of the highly conductive metal layer were obtained by observing its front and cross-section using a scanning electron microscope. The uniformity, continuity, and flatness of the electroplated metal were observed (SEM image of the front side); the location of the electroplated metal deposition was also observed (SEM image of the cross-section).

[0134] 2. Gas transmission capacity

[0135] Gas transport capability is one of the important evaluation indicators for gas diffusion electrodes. Here, we evaluate the gas transport capability of gas diffusion electrodes using the parameter of gas flux. The unit of gas flux is mL. -1 ·min -1 ·kPa -1 ·cm -2 It refers to the gas flow rate per unit cross-sectional area of ​​an object under different pressures. Here, a self-made gas flow meter is used for testing. (1) Fix a metal layer with a size of 2cm×2cm in the fixture and connect the device. (2) Turn on the air pump to let the gas flow in from the air pump, pass through the fixture, and flow out from the air flow meter. (3) Adjust the flow valve on the device to make the air flow rate increase from slow to fast, and record the pressure reading (unit: kPa) and the flow rate (unit: mL·min) through the pressure gauge. -1 ·cm -2 (4) Repeat each set of data 2-3 times and record at least 7 sets of data to obtain the final result.

[0136] 3. Electrical conductivity:

[0137] The conductivity of the gas diffusion electrode is a key characteristic of the gas diffusion electrode that this invention emphasizes. This is achieved by measuring the sheet resistance (R□, unit: Ω·sq) of the metal layer. -1 This is used to evaluate the conductivity of the gas diffusion electrode. Sheet resistance, also known as film resistance, is independent of sample size. The smaller the sheet resistance, the faster electrons move within the diffusion layer.

[0138] The sheet resistance of the gas diffusion electrode, with a size of at least 4cm × 4cm, was measured using a four-probe resistance meter. Measurements were taken at 50 points at different locations. Gaussian fitting was then applied to these 50 measurements to obtain the average sheet resistance of the gas diffusion electrode. The full width at half maximum (FWHM) of the Gaussian fitting was used to evaluate the uniformity of the metal layer's conductivity.

[0139] Analysis of Electrode Performance and Battery Performance Test Results

[0140] 1. Scanning electron microscope (SEM) of highly conductive metal layers

[0141] like Figure 2The smaller images a and b in the figure show SEM images of the front and cross-section of the self-made gas diffusion electrode. From... Figure 2 Figure a shows that the self-made gas diffusion electrode is mainly composed of carbon fibers and carbon nanotubes. The carbon fibers and carbon nanotubes are intertwined and randomly stacked to form the self-made gas diffusion electrode. Figure b shows that the thickness of the self-made gas diffusion electrode is 45 μm. After magnetron sputtering Au, the morphology of the self-made gas diffusion electrode (Figure c) did not change significantly. This is mainly because the sputtered Au particles are relatively small and difficult to observe in SEM. However, the elemental scan inset in Figure c clearly shows the characteristic peaks of Au. Therefore, Au nanoparticles sputtered by magnetron sputtering can be loaded onto the self-made gas diffusion electrode. From a cross-sectional SEM at a higher magnification (Figure d), the presence of sputtered Au nanoparticles can be seen, wrapped around the gas diffusion electrode like cotton wool.

[0142] Electroplating yielded a gas diffusion electrode with a metal coating, as shown in Figure e. Figure e clearly shows that the electroplated layer exhibits a continuous, uniform, and flat distribution. Figure f shows that the electroplated layer is confined to one side of the sputtered metal gas diffusion electrode, with no obvious metal deposition inside or on the back side of the electrode. This confined deposition is crucial for ensuring the gas transport capability of the gas diffusion electrode. Metal confined to the surface of the gas diffusion electrode is easily etched away by laser, while metal inside and on the back side is difficult to etch away, significantly reducing the gas transport capability. Simultaneously, this uniform and continuous metal coating also endows the gas diffusion electrode with excellent conductivity. The inset of Figure f shows the electroplated metal tightly wrapped around the carbon fiber, much like human skin. This morphology-adaptive and uniform metal electrodeposition behavior is essential for forming a uniform electroplated layer on the uneven surface of the gas diffusion electrode, further ensuring the uniformity of its conductivity.

[0143] To achieve superior gas transport capabilities, the electroplated gas diffusion electrode is patterned. Figure g shows the patterned gas diffusion electrode after laser marking. Through laser etching, the metal plating on the surface of the gas diffusion electrode is removed. The etched metal plating provides a transport channel for gas diffusion, improving the gas transport capability of the electroplated gas diffusion electrode. Simultaneously, the remaining metal plating layers are interconnected, thus the patterned gas diffusion electrode also possesses high conductivity. Figure h shows that this laser etching is selective, etching only the surface metal plating of the gas diffusion electrode without etching the internal gas diffusion electrode itself, thus preserving its structure and properties. Therefore, through sputtering, electroplating, and laser patterning, a gas diffusion electrode with both high conductivity and high gas transport capability is obtained.

[0144] in, Figure 2 In the figures, (a)-(b) are SEM images of the front and cross-section of the carbon-based flexible electrode substrate prepared in the examples. (c)-(d) are SEM images of the front and cross-section after magnetron sputtering. The magnetron sputtering metal is gold, the magnetron sputtering current is 20 mA, and the sputtering time is 30 s. (e)-(f) are SEM images of the front and cross-section of the gas-diffused metal layer after electroplating. The electroplated metal is gold, and the electroplating loading is 5 mg / cm³. -2 (g)-(h) are SEM images of the front and cross-section of the patterned highly conductive metal layer.

[0145] 2. Gas transmission capacity

[0146] like Figure 3 As shown, the gas flux of the self-made gas diffusion electrode is 124 mL. -1 ·min -1 ·kPa -1 ·cm -2 After metal sputtering, the gas flux of the gas diffusion electrode was 128 mL. -1 ·min -1 ·kPa -1 ·cm -2 The change was not significant compared to before sputtering. After metal plating, the gas flux of the gas diffusion electrode decreased significantly, dropping to 22 mL. -1 ·min -1 ·kPa -1 ·cm -2This is mainly because the electroplated metal is deposited uniformly and continuously on one side of the sputtered metal on the gas diffusion electrode, forming a continuous metal coating. This continuous metal coating significantly reduces the gas transport capacity of the gas diffusion electrode. After patterning the electroplated gas diffusion electrode using laser etching, the gas flux of the gas diffusion electrode was increased to 92 mL. -1 ·min -1 ·kPa -1 ·cm -2 This is mainly because some of the electroplated metal is etched away by the laser. The etched metal opens up gas transport channels, improving the gas transport capability of the gas diffusion electrode. Compared to an untreated gas diffusion electrode, the gas transport capability of the patterned gas diffusion electrode is still somewhat reduced. This is mainly because the unetched metal plating reduces the gas transport area to some extent, thus lowering the gas transport capability. However, this reduction in gas transport capability is acceptable.

[0147] 3. Electrical conductivity

[0148] Figure 4 The sheet resistance of the gas diffusion electrode is shown for different Au loadings. First, it can be seen that the sheet resistance of the gas diffusion electrode continuously decreases with increasing Au loading. This decreasing trend of sheet resistance with increasing Au loading can be clearly divided into two stages. When the Au loading is less than 2 mg·cm⁻¹... -2 At this time, the sheet resistance of the gas diffusion electrode decreases rapidly with increasing Au plating loading. When the Au plating loading exceeds 2 mg·cm⁻¹, the sheet resistance decreases evenly. -2 At this time, the sheet resistance of the gas diffusion electrode slowly decreases with increasing Au plating loading. Meanwhile, the error bars for different Au plating loadings show that the uniformity of conductivity of the gas diffusion electrode continuously increases with increasing Au plating loading. When the Au plating loading is 5 mg·cm⁻¹... -2 At that time, the sheet resistance of the gas diffusion electrode was only 0.023 Ω·sq. -1 Its full width at half maximum (FWHM) is only 0.027. The sheet resistance of the untreated gas diffusion electrode is as high as 1.49 Ω·sq. -1 Its full width at half maximum (FWHM) is only 0.37. Therefore, the gas diffusion electrode obtained by this invention has better conductivity and uniformity.

[0149] in, Figure 4 The figure shows the sheet resistance of gas diffusion electrodes with different Au loadings. The error bar is the full width at half maximum (FWHM) of the sheet resistance obtained by Gaussian fitting after 50 measurements.

[0150] 4. Battery performance test

[0151] like Figure 5The figure shows the polarization curves of a self-breathing fuel cell using gas diffusion electrodes with different Au loadings. It can be seen that the Au loading affects the cell's performance. Figure 6 As can be seen, with the increase of Au plating loading, the peak power density of the battery first increases and then decreases. When the Au plating loading is less than 5 mg·cm³, the peak power density of the battery decreases. -2 At this time, the battery performance continues to improve. When the Au loading in the electroplated layer is less than 5 mg·cm³, the battery performance continues to improve. -2 At that time, the battery performance deteriorated. The Au loading in the electroplated layer was 5 mg·cm³. -2 At this time, the battery performance is optimal, with a peak power density of 355 mW·cm³. -2 Compared to the performance of a fuel cell fabricated with an untreated gas diffusion electrode (40 mW·cm⁻¹), -2 The performance of batteries prepared with highly conductive gas diffusion electrodes is significantly improved, with an improvement of up to 8.9 times.

[0152] Since Example 2 uses a more preferred substrate structure, the electrode performance of Examples 9-10 has decreased compared to Example 2. Specifically, the conductivity has decreased by about 30% and the gas permeability has decreased by about 20% compared to Example 2. Correspondingly, the peak power of the batteries with the same structure has decreased by about 40%.

[0153] Meanwhile, since laser etching is superior to other physical / chemical etching methods, the conductivity of Example 14, which uses mask etching, is reduced by about 10% compared to Example 2, and the air permeability is also reduced by about 15%.

[0154] Furthermore, Comparative Examples 1 and 2 used existing metal conductive meshes or metal foams to form gas diffusion electrodes, and their overall performance was also weaker than that of Example 2. Specifically, the conductivity was reduced by about 10% compared to Example 2, the gas permeability was reduced by about 20%, and the peak power of the batteries with the same structure was reduced by about 30%.

[0155] More importantly, Comparative Examples 1 and 2 not only show a decrease in peak power density (area density), but also a decrease in peak specific power (power / weight). This is due to the excessive specific gravity of the electrodes. Specifically, after conversion, the specific power of Example 2 is 1150 W / kg, while that of Comparative Examples 1 and 2 is around 100 W / kg. Furthermore, the flexibility of Comparative Examples 1 and 2 is worse than that of Example 2, which is also due to the relatively greater rigidity of the metal foam or metal conductive mesh.

[0156] Based on the above embodiments, as well as the blank examples and comparative examples, it can be clearly understood that:

[0157] (1) The flexible gas diffusion electrode and its preparation method provided in the embodiments of the present invention, especially the proposed metal electroplating method, can achieve selective metal deposition. The sputtering process can change the hydrophilicity or hydrophobicity of the sample, while the sputtered metal provides uniform nucleation sites. Therefore, these two aspects are beneficial to the selective deposition of metal during the electroplating process. During the electroplating process, the metal can preferentially bind to the nucleation sites, further producing selectivity for metal deposition. As in this scheme, the electroplated metal is only deposited on the side of the gas diffusion electrode where the sputtered metal is deposited, and no obvious metal deposition is generated on the interior and back of the gas diffusion electrode where no sputtered metal is deposited.

[0158] (2) The flexible gas diffusion electrode and its preparation method provided in the embodiments of the present invention, especially the proposed metal electroplating method, can achieve uniform metal deposition. For samples with large surface undulations, the uniformity of electroplating is relatively low. The method of first magnetron sputtering and then electroplating in the present invention has the characteristic of "adaptive" to the morphology of the sample during the electroplating process, and can form a uniform electroplated metal layer on samples with large surface undulations. As in this scheme, for self-made gas diffusion electrodes with large surface roughness and unevenness, the electroplated metal can uniformly cover every part of the gas diffusion electrode.

[0159] (3) The flexible gas diffusion electrode and its preparation method provided in the embodiments of the present invention, especially the proposed metal electroplating method, are universal and applicable to the uniform electroplating and deposition of other metals. For example, in this scheme, the method can achieve uniform electroplating of Au, Ag, and Cu metals.

[0160] (4) The flexible gas diffusion electrode and its preparation method provided in the embodiments of the present invention, especially the proposed metal electroplating method, have strong stability, and the electroplated metal can be tightly bonded to the sample. For example, in this scheme, the electroplated Au can be tightly attached to the sample and has good stability.

[0161] (5) The flexible gas diffusion electrode and its preparation method provided in this embodiment of the invention employ a "magnetron sputtering-electroplating-patterning" process to achieve the preparation of a gas diffusion electrode with high conductivity and high gas transport capability. This gas diffusion electrode with high conductivity and high gas transport capability can simultaneously serve as a diffusion electrode and a current collector, which can significantly reduce the mass and volume of the electrochemical energy conversion device, while increasing the output power density of the electrochemical energy conversion device, ultimately achieving a reduction in the mass / volume of the electrochemical energy conversion device, an increase in power density, and an improvement in specific power.

[0162] (6) The flexible gas diffusion electrode provided in the embodiments of the present invention is not only applicable to fuel cells, but also to electrochemical energy conversion devices that require gas participation, such as metal-air batteries.

[0163] Therefore, the highly conductive flexible gas diffusion electrode provided in this embodiment of the invention is suitable for electrochemical energy conversion devices that require gas participation, and can reduce the mass / volume of the device, increase the power density of the device, and achieve an improvement in specific power.

[0164] The preparation method provided in this invention is simple to operate and can achieve selective deposition, uniform deposition, and high bonding strength between the deposited metal layer and the substrate, thereby improving the electrochemical performance of the electrode while ensuring flexibility and uniformity.

[0165] It should be understood that the above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A flexible gas diffusion electrode, characterized by, The flexible electrode substrate is formed by interlacing linear carbon nanomaterials, and a metal layer is arranged on a part of the surface of the flexible electrode substrate. The metal layer has a plurality of hole structures penetrating through the thickness direction of the metal layer, so that a part of the surface of the flexible electrode substrate is exposed by the hole structures, and a part of the linear carbon nanomaterials at the interface between the flexible electrode substrate and the metal layer are wrapped by the metal in the part of the metal layer. The metal layer has a surface density of 0.5-6 mg·cm -2 The pore size of the pore structure is 0.1-3 μm, the total area of the plurality of pore structures accounts for 20-70 % of the surface area of the metal layer, the material of the metal layer is selected from any one or a combination of two or more of Au, Ag, and Cu, and the metal layer is formed by electrochemical deposition.

2. The flexible gas diffusion electrode according to claim 1, characterized in that, A plurality of metal seed particles are arranged at the interface, and the material of the metal seed particles is the same as that of the metal layer.

3. The flexible gas diffusion electrode according to claim 1, wherein, The flexible electrode substrate includes any one of carbon fiber paper, porous carbon black paper, carbon nanotube film, and nanometer carbon fiber film, or a combination of two or more thereof.

4. The flexible gas diffusion electrode according to claim 3, characterized in that, The flexible electrode substrate includes a blended film formed by interlacing carbon fibers and carbon nanotube fibers.

5. The flexible gas diffusion electrode according to claim 4, characterized in that, In the blended film, the mass ratio of the carbon fibers to the carbon nanotubes is 5-1:1, the length of the carbon fibers is 10-100 μm, and the diameter of the carbon fibers is 3-10 μm; the length of the carbon nanotubes is 1-10 μm, and the diameter of the carbon nanotubes is 5-20 nm.

6. The flexible gas diffusion electrode of claim 1, wherein, The flexible gas diffusion electrode has a sheet resistance of 0.01 Ω·cm -2 Below.

7. The flexible gas diffusion electrode of claim 1, wherein, The gas flux of the flexible gas diffusion electrode is 20-150 mL·min -1 · KPa·cm -2 .

8. The method for producing a flexible gas diffusion electrode according to any one of claims 1 to 7, characterized in that, The method comprises the following steps: providing a flexible electrode substrate formed by interlacing linear carbon nanomaterials; forming a metal layer on a part of the surface of the flexible electrode substrate; forming a plurality of hole structures in the metal layer at the same time as forming the metal layer or after forming the metal layer, the hole structures penetrating through the thickness direction of the metal layer, so that a part of the surface of the flexible electrode substrate is exposed by the hole structures.

9. The production method according to claim 8, characterized by, The method specifically comprises the following steps: forming a plurality of metal islands on a part of the surface of the flexible electrode substrate by first electrochemical deposition, the plurality of metal islands being connected to each other and surrounding the hole structures.

10. The method of claim 9, wherein, The first electrochemical deposition has a current density less than 20 mA cm -2 ; and the electrolyte is mechanically stirred at a stirring speed of 100-300 rpm and a plating solution temperature of 15-30°C.

11. The preparation method according to claim 8, characterized in that, The method specifically comprises the following steps: depositing metal seed particles on a part of the surface of the flexible electrode substrate by physical sputtering; depositing a conductive layer precursor on the part of the surface loaded with the metal seed particles by second electrochemical deposition; performing a patterning process on the conductive layer precursor to form a plurality of patterned hole structures.

12. The method of claim 11, wherein, The patterning process is selected from laser etching.

13. Use of the flexible gas diffusion electrode according to any one of claims 1-7 in the manufacture of a fuel cell or a metal-air battery.

14. A self-breathing fuel cell, characterized by: The cathode of the self-breathing fuel cell uses the flexible gas diffusion electrode according to any one of claims 1-7.

15. A self-breathing fuel cell according to claim 14, wherein The peak power density of the self-breathing fuel cell can reach 355 mW / cm 2 .

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