Gradient metal diffusion structure and preparation method thereof

Abstract

The invention discloses a gradient metal diffusion structure and a preparation method thereof, the diffusion structure comprises a powder sintered metal green body, a multi-layer metal wire mesh and a binder layer located in the middle, the powder sintered metal green body is laid on the surface of the metal wire mesh, and the binder layer is used for compounding the powder sintered metal green body and the metal wire mesh; the multiple layers of metal wire meshes are formed by sequentially overlapping at least three layers of metal wire meshes with different mesh numbers in a crossed manner; the metal wire meshes are arranged in a gradient manner from large mesh number to small mesh number in the direction far away from the powder sintered metal green body; and two adjacent layers of the metal wire mesh rotate by a target angle and are fixed by spot welding. The gradient metal diffusion structure has good air permeability and drainage performance and good electronic conductivity, the gradient structure is beneficial for optimizing the migration path of ions in the battery, improving the charging and discharging performance of the battery and prolonging the cycle life of the battery, it can be ensured that stress distribution is uniform in the cold and hot environment, and good mechanical support is provided for the proton exchange membrane.

Description

Technical Field

[0001] This solution relates to the field of composite material technology, and in particular to a gradient metal diffusion structure and its preparation method. Background Technology

[0002] With increasing energy demand and growing environmental awareness, new energy batteries have experienced rapid development due to their significant advantages. Proton exchange membrane (PEM) electrolyzers and anion exchange membrane (AEM) electrolyzers produce hydrogen from water through acidic / alkaline membranes, respectively. Hydrogen fuel cells (including PEMFCs and AEMFCs) use hydrogen as fuel through the reverse reaction of water electrolysis, reacting it with oxygen to convert chemical energy into electrical energy. The reverse reaction characteristics of both are the theoretical basis for the closed-loop design of hydrogen energy systems.

[0003] In proton exchange membrane fuel cells and anion exchange membrane fuel cells, the gas diffusion structure serves as the transport path for hydrogen, oxygen, and the reaction product water. Therefore, the diffusion structure is required to have good permeability and drainage performance, good electronic conductivity, good contact with the catalyst surface, and the ability to provide a certain mechanical support strength for the proton exchange membrane.

[0004] Traditional battery structures typically employ serpentine flow channels (S-FC) to transport and distribute reactants and products, resulting in highly uneven stress distribution. Consequently, the anode catalyst layer (ACL) in high-stress regions is severely deformed, while low-stress regions remain inactive due to poor electrical contact. Summary of the Invention

[0005] This solution aims to at least solve the technical problems existing in the prior art. To this end, the first aspect of the present invention proposes a gradient metal diffusion structure, the diffusion structure comprising a powder sintered metal green body, a multilayer metal mesh, and an adhesive layer located between the powder sintered metal green body and the metal mesh. The powder sintered metal green body is laid flat on the surface of the metal mesh, and the adhesive layer is used to bond the powder sintered metal green body and the metal mesh. The size of the powder sintered metal green body is the same as that of the metal mesh. The multilayer metal wire mesh consists of at least three layers of metal wire mesh with different mesh counts stacked in a cross-over pattern; the metal wire meshes are arranged in a gradient order of decreasing mesh count in the direction away from the powder sintered metal green body; the metal wire meshes are rotated at a target angle and spot-welded to each other between adjacent layers.

[0006] A second aspect of this invention provides a method for preparing a gradient metal diffusion structure, the method comprising: Multiple pre-treated metal wire meshes are stacked in a cross-over pattern according to their mesh count from largest to smallest. The adjacent layers are rotated at the target angle and then spot-welded to fix them, thus obtaining a well-proportioned metal wire mesh. An organic adhesive is coated on the fine mesh side of the prepared metal wire mesh to obtain a multilayer metal wire mesh covered with adhesive. Select metal powder with a target particle size to make a metal powder green blank, and cut the metal powder green blank to the same size as the metal wire mesh to obtain the metal green blank; The metal green blank is laid flat on the multilayer metal wire mesh with the adhesive side to obtain a composite metal green blank; After constraining the composite metal green blank in a specific tooling, it is degreased and sintered to obtain a gradient metal diffusion structure.

[0007] Optionally, the adhesive is one or more of methylcellulose, ethylcellulose, polyvinyl butyral, polyvinylpyrrolidone, polymethyl methacrylate, and polyethyl methacrylate. The adhesive is used in conjunction with a solvent, wherein the solvent is one or two of methanol, ethanol, ethylene glycol, isopropanol, and butanol; The ratio of the adhesive to the solvent is 10%:90%~3%:97%.

[0008] Optionally, the number of layers of the metal wire mesh is 3 to 8; the four corners of the metal wire mesh are spot welded, and the remaining edge positions of the metal wire mesh are increased by 1 to 2 welds according to the edge size.

[0009] Optionally, before stacking the pretreated wire mesh in a staggered manner according to the order of coarse, thick, and thin mesh, the method further includes: Obtain a metal wire mesh that is undamaged, has uniform mesh size, and is flat, and cut the wire mesh to the target size; The cut wire mesh is degreased, then rinsed clean and air-dried or oven-dried to obtain pre-treated wire mesh.

[0010] Optionally, cutting the wire mesh to the target size includes: The wire mesh is cut to the target size using a shearing machine or laser cutting. The degreasing treatment of the cut wire mesh includes: Use one of the following: acetone, alcohol, or detergent powder, to degrease the cut wire mesh.

[0011] Optionally, coating the fine mesh side of the prepared wire mesh with an organic adhesive includes: An organic adhesive is applied to the fine mesh side of the prepared metal wire mesh by brushing or spraying, and the thickness of the organic adhesive is such that it immerses one layer of the metal wire mesh.

[0012] Optionally, the material of the metal powder preform includes titanium alloy, nickel-based alloy or stainless steel; the forming method of the metal powder preform includes rolling, molding, isostatic pressing, slurry coating.

[0013] Optionally, the specific tooling has good flatness, and the surface roughness of the specific tooling in contact with the composite metal billet is less than 10 μm.

[0014] Optionally, the degreasing temperature is 200-500℃, the heating rate is 2-10℃ / min, and the holding time is 1-2h; the sintering temperature is 950-1100℃, the heating rate is 2-10℃ / min, and the holding time is 1-3h.

[0015] The embodiments of the present invention have the following beneficial effects: The gradient metal diffusion structure provided in this invention includes a powder-sintered metal green body, a multilayer metal mesh, and a binder layer located between the powder-sintered metal green body and the metal mesh. The powder-sintered metal green body is laid flat on the surface of the metal mesh. The binder layer is used to bond the powder-sintered metal green body and the metal mesh. The size of the powder-sintered metal green body is the same as that of the metal mesh. The multilayer metal mesh consists of at least three layers of metal mesh with different mesh counts stacked alternately. The metal meshes are arranged in a gradient order of decreasing mesh count in the direction away from the powder-sintered metal green body. Adjacent layers of the metal mesh are rotated by a target angle and spot-welded together. This gradient metal diffusion structure has good air permeability and drainage performance, good electronic conductivity, and the gradient structure helps optimize the migration path of ions in the battery, improving the charge-discharge performance and cycle life of the battery. It can ensure uniform stress distribution under hot and cold environments, good contact with the catalyst surface, and provide good mechanical support for the proton exchange membrane. Attached Figure Description

[0016] Figure 1 This is a mechanical structure diagram of a gradient metal diffusion structure provided in an embodiment of the present invention; Figure 2 This is a flowchart illustrating the steps of a method for preparing a gradient metal diffusion structure according to an embodiment of the present invention; Figure 3 A scanning electron microscope (SEM) image of sample 1 provided in an embodiment of the present invention; Figure 4 The image shows a scanning electron microscope (SEM) image of sample 3 provided in an embodiment of the present invention. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present solution, and not all embodiments. Based on the embodiments of the present solution, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present solution.

[0018] Hereinafter, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of this disclosure, unless otherwise stated, "a plurality of" means two or more. Furthermore, the use of "based on" or "according to" implies openness and inclusiveness, because processes, steps, calculations, or other actions "based on" or "according to" one or more of the stated conditions or values ​​may in practice be based on additional conditions or beyond the stated values.

[0019] Figure 1 This is a mechanical structure diagram of a gradient metal diffusion structure provided in an embodiment of the present invention.

[0020] like Figure 1 As shown, the diffusion structure includes a powder sintered metal green body 1, a multilayer metal mesh 3, and an adhesive layer 2 located between the powder sintered metal green body and the metal mesh. The powder sintered metal green body 1 is laid flat on the surface of the metal mesh 3. The adhesive layer 2 is used to bond the powder sintered metal green body 1 and the metal mesh 3. The size of the powder sintered metal green body 1 is the same as that of the metal mesh 3. The multilayer metal wire mesh 3 consists of at least three layers of metal wire mesh with different mesh counts stacked in a cross-over pattern; the metal wire meshes are arranged in a gradient order of decreasing mesh count in the direction away from the powder sintered metal green body; the metal wire meshes are rotated at a target angle and spot-welded to each other between adjacent layers.

[0021] In this embodiment of the invention, the powder-sintered metal green body 1 is a flat, porous metal sheet. It is typically made of the same or compatible metal as the wire mesh. The powder-sintered metal green body 1 has the same dimensions as the metal wire mesh 3, ensuring the integrity of the structure and the integrity of the edges, facilitating overall installation and sealing. The powder-sintered metal green body 1 itself does not have high mechanical strength; however, when combined with the metal wire mesh 3, the combined structure provides a certain mechanical support for the proton exchange membrane.

[0022] The metal wire mesh 3 is arranged in descending order of mesh size, away from the powder sintered metal green blank 1. That is, the layer closest to the powder sintered metal green blank 1 is the finest mesh with the largest mesh size, the middle layer is the medium / coarse mesh with a medium mesh size, and the layer furthest from the powder sintered metal green blank is the coarsest mesh with the smallest mesh size.

[0023] The diffusion structure primarily serves as the transport path for hydrogen, oxygen, and the reaction product water. A gradient-arranged metal diffusion structure is used to fulfill this function. The fine mesh, with its smallest pores, disperses the fluid or gas into numerous tiny, uniform turbulent or laminar flows. The medium / coarse meshes act as a transition and secondary distribution layer, while also reinforcing the structure. The coarse mesh, located on the top layer, withstands the main frontal impact of the fluid or gas, protects the inner fine mesh, and facilitates macroscopic initial diffusion. Furthermore, the powder-sintered metal green body, with even smaller pores than the fine mesh, is located on one side. This gradient diffusion structure provides excellent permeability and drainage, helping to optimize the migration path of ions within the battery and improve its charge-discharge performance and cycle life.

[0024] The warp and weft threads of adjacent mesh layers are not aligned, but rotated relative to each other by a target angle (usually 30°, 45°, or 90°). This forces the fluid or gas to repeatedly turn and mix in three-dimensional space, achieving optimal diffusion and mixing effects.

[0025] After the layers are cross-stacked, the contact points of adjacent wire meshes are locally fused together using methods such as multi-point resistance welding. This prevents relative slippage between the wire mesh layers during use and maintains the designed cross angle.

[0026] The binder layer 2 is made of organic material. Its function is to optimize the interfacial bonding between the powder-sintered metal green body 1 and the metal mesh 3, prevent the powder-sintered metal green body from sinking, and maintain good flatness.

[0027] The gradient metal diffusion layer provided by this invention has adjustable pore size combinations and thicknesses, and can be combined with green bodies and wire meshes of different materials, powder particle sizes, pore sizes and channel distributions according to the application scenario.

[0028] The gradient metal diffusion layer provided by this invention prevents metal powder from sinking into the mesh pores, has good surface flatness, and has many contact points with the catalyst layer of the battery, resulting in a large contact area, which is more conducive to improving the catalytic utilization rate.

[0029] The gradient metal diffusion layer provided by this invention is formed by sintering the metal powder green body with the metal mesh 3 in a single process. The process is simple and the prepared gradient metal diffusion layer has a good bonding effect.

[0030] In summary, the gradient metal diffusion structure provided by the embodiments of the present invention includes a powder-sintered metal green body, a multilayer metal mesh, and an adhesive layer located between the powder-sintered metal green body and the metal mesh. The powder-sintered metal green body is laid flat on the surface of the metal mesh, and the adhesive layer is used to bond the powder-sintered metal green body and the metal mesh. The size of the powder-sintered metal green body is the same as that of the metal mesh. The multilayer metal mesh consists of at least three layers of metal mesh with different mesh counts stacked in a cross-over pattern. The metal meshes are arranged in a gradient order of decreasing mesh count in the direction away from the powder-sintered metal green body. The adjacent layers of the metal mesh are rotated by a target angle and spot-welded to fix them.

[0031] This gradient metal diffusion structure has good air permeability and drainage performance, good electronic conductivity, and the gradient structure helps to optimize the migration path of ions in the battery, improve the charge and discharge performance and cycle life of the battery, ensure uniform stress distribution under hot and cold environments, have good contact with the catalyst surface, and provide good mechanical support for the proton exchange membrane.

[0032] Figure 2 This is a flowchart illustrating the steps of a method for preparing a gradient metal diffusion structure according to an embodiment of the present invention. Figure 2 As shown, the method includes: Step 101: Stack the pre-treated wire meshes in a cross-over pattern according to the mesh count from largest to smallest, rotate the adjacent layers by the target angle and spot weld them in place to obtain the properly proportioned wire mesh.

[0033] Pre-treatment mainly includes the selection, cutting, degreasing, and drying of the wire mesh to ensure the quality of subsequent processes.

[0034] The metal wire mesh consists of at least three layers, arranged in descending order of mesh count away from the metal green blank. That is, the bottom layer, which is closest to the metal green blank, is the finest mesh with the largest mesh count; the middle layer is a medium / coarse mesh with a medium mesh count; and the top layer is an extra-coarse mesh with the smallest mesh count.

[0035] Adjacent layers of wire mesh are rotated by a target angle (usually 30°, 45° or 90°) and then cross-stacked. Through multi-point resistance welding and other methods, local welding is carried out at multiple contact points between the layers to form a stable and integrated structure of multiple layers of wire mesh, thereby obtaining a well-proportioned wire mesh.

[0036] Step 102: Coat the fine mesh side of the prepared metal wire mesh with an organic adhesive to obtain a multi-layer metal wire mesh covered with adhesive.

[0037] Applying the binder to the fine mesh side means that the binder is applied to the side that is in contact with the powder-sintered metal green body.

[0038] Step 103: Select metal powder with the target particle size to make metal powder green blank, and cut the metal powder green blank to the same size as the metal wire mesh to obtain the metal green blank.

[0039] Selecting the target particle size of the metal powder directly determines the porosity and mechanical strength of the final sintered metal green body. Through powder metallurgy forming techniques such as molding, rolling, or tape casting, the metal powder is mixed with an appropriate amount of forming agent and pressed into a thin sheet-like metal green body with a certain strength and shape.

[0040] The metal blanks are cut to the exact same size as the metal mesh to ensure edge alignment during subsequent lamination.

[0041] Step 104: The metal green blank is laid flat on the multilayer metal wire mesh on the side with the adhesive to obtain a composite metal green blank.

[0042] The metal blank is laid flat on the fine mesh side of a multi-layer metal wire mesh coated with adhesive. The two are bonded together by the adhesive properties of the organic adhesive to form a composite metal blank.

[0043] Step 105: After constraining the composite metal green billet vertically in a specific tooling, degrease and sinter it to obtain a gradient metal diffusion structure.

[0044] The composite metal blank is placed in a specially designed high-temperature resistant fixture, such as a graphite mold or an alumina plate, and moderate constraints are applied from above and below, such as lightly pressing a flat plate.

[0045] In a protective atmosphere or vacuum environment, the components are heated to a certain temperature at a slow and controlled heating rate to remove the grease. The main purpose of degreasing is to completely volatilize or decompose the organic binder and allow it to be expelled through gas.

[0046] Continue to raise the temperature to 70%-90% of the metal's melting point, reaching the sintering temperature, and hold at that temperature for a period of time. At high temperatures, metal atoms begin to diffuse violently. Metal atoms at the spot welds between metal powders, between powders and wire mesh, and between wire mesh layers diffuse into adjacent areas, achieving mutual fusion and ultimately forming a robust gradient metal diffusion structure.

[0047] As an optional embodiment, the adhesive is one or more of methylcellulose, ethylcellulose, polyvinyl butyral, polyvinylpyrrolidone, polymethyl methacrylate, and polyethyl methacrylate. The adhesive is used in conjunction with a solvent, wherein the solvent is one or two of methanol, ethanol, ethylene glycol, isopropanol, and butanol; The ratio of the adhesive to the solvent is 10%:90%~3%:97%.

[0048] In this embodiment of the invention, the adhesive serves to temporarily bond and fix loose or delaminated components together during the processing stage before sintering. Methylcellulose, ethylcellulose, polyvinyl butyral, polyvinylpyrrolidone, polymethyl methacrylate, and polyethyl methacrylate are all high molecular weight polymers, making them very suitable as process adhesives.

[0049] The role of the solvent is to dissolve or disperse the polymer binder to form a uniform, easy-to-coat solution.

[0050] The ratio of binder solids to total solvent mass can be 10%:90% to 3%:97%. At a ratio of 10%:90%, the viscosity is higher, allowing for more binder solids to be carried in a single coat. This is suitable for applications requiring strong temporary bond strength, fewer coats, or where the metal mesh surface is rough, porous, and highly absorbent of the solution. At a ratio of 3%:97%, the viscosity is lower, resulting in better flowability, easier wetting and spreading, and the formation of a very uniform, thin binder film. This is suitable for applications requiring fine and uniform coating.

[0051] As an optional embodiment, the number of layers of the metal wire mesh is 3 to 8; the four corners of the metal wire mesh are spot welded, and the remaining edge positions of the metal wire mesh have 1 to 2 additional weld points depending on the edge size.

[0052] Specifically, three layers of metal mesh are the minimum requirement to form a complete gradient. This typically corresponds to a "fine-medium-coarse" three-layer structure, which enables basic anti-clogging, rectification, and diffusion functions. It is suitable for scenarios where diffusion uniformity requirements are not extremely stringent.

[0053] Eight layers of metal mesh can achieve a smoother and finer pore gradient, with up to eight layers transitioning from "ultra-fine to fine to medium-fine to medium to medium-coarse to coarse to ultra-coarse." Its pore size change is more continuous, which can significantly reduce the pressure drop when the fluid passes through, and the fluid segmentation and mixing process is more gradual and smooth.

[0054] Four-corner spot welding is the most effective and basic method of positioning and fixing. To prevent the long side from bulging, separating or deforming in the middle, add 1 to 2 more welds depending on the size of the side to improve welding reliability.

[0055] As an optional embodiment, before stacking the pretreated wire mesh in a staggered manner according to the order of coarse mesh, thick mesh, and thin mesh, the method further includes: Step 201: Obtain a metal wire mesh that is undamaged, has uniform mesh size, and is flat, and cut the wire mesh to the target size; Step 202: Degrease the cut wire mesh, rinse it clean, and air dry or bake it to obtain the pretreated wire mesh.

[0056] Specifically, the selected wire mesh raw materials must be undamaged, with uniform and flat mesh openings, ensuring cleanliness, regularity, and consistent surface activity. They are then cut to specified sizes to achieve dimensional standardization and ensure edge alignment during subsequent stacking.

[0057] The cut wire mesh is degreased to remove rolling oil, rust-preventive oil, lubricating oil, and organic contaminants picked up during handling. It is then rinsed clean and air-dried or oven-dried to remove any residual chemical reagents and emulsified oil.

[0058] As an optional embodiment, step 201, cutting the wire mesh to the target size, includes: The wire mesh is cut to the target size using a shearing machine or laser cutting. Step 201 involves degreasing the cut wire mesh, including: Use one of the following: acetone, alcohol, or detergent powder, to degrease the cut wire mesh.

[0059] In this embodiment of the invention, the shearing principle utilizes mechanical pressure to cut the material using upper and lower blades. Flat-blade shears or precision shearing machines are typically used for screen cutting.

[0060] The principle of laser cutting is to use a high-energy-density laser beam to irradiate the workpiece, causing the material to melt and vaporize locally and instantly, and then complete the cutting by moving the laser spot.

[0061] The most suitable process can be selected based on one's own equipment conditions, cost budget, wire mesh specifications, and requirements for edge quality.

[0062] Acetone is a powerful organic solvent that can quickly dissolve most non-polar organic substances such as mineral oils, greases, and synthetic oils. Alcohol is a moderately polar organic solvent that can dissolve many polar organic substances and removes oil stains through the physical action of wiping. Scouring powder is an alkaline chemical cleaning agent that works through saponification and emulsification, followed by physical scrubbing to remove dirt.

[0063] The degreaser selected must be compatible with the wire mesh material, and its residues must not affect the subsequent spot welding quality and the coating effect of the adhesive.

[0064] As an optional embodiment, step 102 involves coating the fine mesh side of the prepared wire mesh with an organic adhesive, including: An organic adhesive is applied to the fine mesh side of the prepared metal wire mesh by brushing or spraying, and the thickness of the organic adhesive is such that it immerses one layer of the metal wire mesh.

[0065] Flat brushing refers to using a soft brush to apply an appropriate amount of adhesive solution to the screen surface in a smooth, unidirectional or cross-directional manner. The equipment is simple, the cost is low, and it has good adaptability to viscosity, making it suitable for small batches.

[0066] Spray coating refers to the process of using a spray gun to evenly spray atomized adhesive solution onto the surface of a wire mesh. Spray coating offers good coating uniformity, high production efficiency, and good coverage on complex or uneven surfaces, but it also incurs high equipment investment and maintenance costs.

[0067] The choice between flat brushing and spraying depends on the production scale, equipment conditions, adhesive solution characteristics, and the requirements for coating uniformity.

[0068] The fine mesh side of the wire mesh refers to the side with the smallest mesh openings in the entire multi-layered wire mesh. This side will directly contact and bond with the metal powder green body. The smallest mesh openings provide the largest and densest contact area, which is beneficial for forming stronger adhesion and a more uniform stress distribution. The binder solution has a certain fluidity. If applied to the coarse mesh side, the solution easily penetrates downwards under gravity, accumulating excessively in the internal fine mesh layer and even clogging the tiny mesh openings, severely damaging the gradient pore structure. Applying it to the fine mesh side effectively limits the depth and range of the binder's upward penetration.

[0069] In addition, the amount of adhesive applied should be sufficient to completely saturate and cover the entire surface of the bottom layer of fine mesh, and slightly fill its mesh openings, but not so much as to overflow and significantly penetrate into the structure of the upper layer.

[0070] As an optional embodiment, the material of the metal powder preform includes titanium alloy, nickel-based alloy or stainless steel; the forming method of the metal powder preform includes rolling, molding, isostatic pressing, slurry coating.

[0071] The choice of which material to use for the metal powder preform is determined by the product's final usage environment (temperature, medium, stress, regulations) and cost budget. Based on the powder characteristics of the material, the required shape and size of the metal preform, and performance requirements (density, uniformity, thickness), the most suitable one or combination of four forming methods is selected.

[0072] As an optional embodiment, the specific tooling has good flatness, and the surface roughness of the specific tooling in contact with the composite metal billet is less than 10 μm.

[0073] During the debinding and sintering process in step 105, the composite metal green billet is in a state of lowest strength and most easily deformable. The role of the specific tooling is to provide stable physical constraints and support for the metal green billet throughout the high-temperature process, preventing it from deforming due to its own weight and internal stress. Flatness and roughness are fundamental to achieving this function.

[0074] A roughness of less than 10 μm means that this is a fairly smooth surface with very small microscopic bumps and undulations.

[0075] As an optional embodiment, the degreasing temperature is 200-500℃, the heating rate is 2-10℃ / min, and the holding time is 1-2h; the sintering temperature is 950-1100℃, the heating rate is 2-10℃ / min, and the holding time is 1-3h.

[0076] The purpose of debinding is to completely decompose and remove all organic matter before sintering begins. The specific debinding temperature depends on the decomposition characteristics of the specific binder system used. The heating rate can control the rate at which gases are generated from the decomposition of organic matter. For complex composite metal green blanks, due to the tortuous gas discharge path, a slower heating rate (such as 2-5℃ / min) is usually preferred to ensure safety.

[0077] Holding the metal blank at the set degreasing temperature for 1-2 hours ensures that the organic matter inside the entire green metal blank, especially in the thicker parts, has enough time to completely decompose and be discharged.

[0078] The purpose of sintering is to drive mass migration at the atomic scale and achieve metallurgical bonding between particles. The sintering temperature is 950-1100℃, which is approximately 70%-85% of the melting point of the metals involved. At this temperature, metal atoms gain sufficient kinetic energy to undergo bulk diffusion.

[0079] The heating rate from the degreasing temperature to the sintering temperature still needs to be controlled at 2-10℃ / min. The main purpose is to reduce thermal stress and avoid deformation or cracking caused by uneven heating of different parts of the metal blank. The holding time is 1-3 hours to achieve sufficient diffusion and homogenization.

[0080] Example 1 Titanium exhibits minimal corrosivity under acidic conditions and high anodic potential, boasts mature processing capabilities, and possesses excellent electrical conductivity, making it the mainstream choice for the anode diffusion layer of PEM electrolytic cells. It withstands strong acid environments and efficiently removes oxygen. To achieve efficient mass transfer, electrical conductivity, and a robust mechanical support structure, this embodiment selects metallic titanium as the raw material and employs a composite structure design with two different types, totaling seven layers of wire mesh. The specific steps are as follows: Five layers of titanium stretched wire mesh with aperture sizes of 2×2.5mm, 0.9×1.5mm, and 0.5×1mm were selected to enhance the supporting strength. Two layers of 200-mesh titanium square mesh were used to optimize the gas diffusion path. After passing inspection, the mesh was laser-cut to a size of 400×600mm. The cut mesh was cleaned with alcohol, rinsed thoroughly, and dried in an oven at 80℃ for 24 hours. The two different types of mesh were then stacked alternately in order of coarseness, coarseness, and fineness, with each layer rotated 90° to enhance structural stability. The four corners were fixed by spot welding between the layers to ensure bonding strength, thus preparing the metal mesh.

[0081] Select 160-250 mesh titanium powder. The raw material powder is pretreated to remove iron impurities. Select appropriate parameters to roll titanium metal green billet to a thickness of 0.25 mm. After cutting, form a green billet of the same size as the wire mesh.

[0082] The binder, methylcellulose, and the solvent, ethylene glycol, were mixed evenly at a ratio of 5 wt%: 95 wt%. Using a specialized brush applicator, the mixed binder was evenly applied to one side of the fine mesh of the metal wire mesh and dried at 50°C for 24 hours. The prepared titanium metal green blank was then laid flat on the side of the metal wire mesh coated with the binder, ensuring no misalignment. The composite metal green blank was then transferred into a specific constraint fixture with a constraint force of 150 N.

[0083] The constrained composite metal green billet was degreased and sintered. First, it was held at 200℃ for 1 hour in an argon atmosphere, then the temperature was increased to 500℃ at a rate of 3℃ / min and held for 1 hour to fully degrease. Then, a vacuum was drawn, and the furnace temperature was increased to 1000℃ at a rate of 3℃ / min and held for 2 hours for composite sintering to obtain sample 1.

[0084] Figure 3 The image shows a scanning electron microscope (SEM) image of sample 1 provided in an embodiment of the present invention.

[0085] like Figure 3 As shown, scanning electron microscopy (SEM) tests were performed on the surface and reverse side of sample 1, respectively. The results showed that sample 1 had a porosity of 25%, an average pore size of 10 μm, and an air permeability of 252 μm. 3 / (kpa·h·m 2 The roughness of the titanium sintered metal billet in the diffusion layer is 5 μm.

[0086] Example 2 Porosity is a key structural parameter of the gas diffusion layer in PEM, which directly affects its conductivity, mass transfer efficiency and thermal management capability. To obtain a larger porosity, coarser raw material powder can be preferred, as described in this example.

[0087] The difference from Example 1 lies in the preparation of the titanium green billet. A green billet with a thickness of 0.4 mm was rolled from 100-160 mesh titanium powder, resulting in Sample 2. Testing showed that Sample 2 had a porosity of 35%, an average pore size of 12 μm, and an air permeability of 289 μm. 3 / (kpa·h·m 2 The roughness of the titanium sintered metal billet in the diffusion layer is 7 μm.

[0088] Example 3 Nickel-based materials exhibit high activity and selectivity in the hydrogen evolution reaction, which can reduce overpotential and improve hydrogen production efficiency. Moreover, as a non-precious metal catalyst, nickel has certain cost advantages and can be selected in scenarios that require a more catalytically active diffusion layer.

[0089] In hydrogen production via water electrolysis, under high current density conditions or high-voltage electrolysis systems, the rates of gas and liquid water generated by the reaction increase significantly. The gas diffusion layer needs to withstand a greater pressure difference. In such cases, the casting method for preparing the green sheet is more flexible and has a significantly higher porosity compared to rolling, making it more suitable for this scenario. The diffusion layer selected under the above conditions can still be prepared using the method described in this patent, as detailed below.

[0090] In this embodiment, a powder-sintered nickel metal green body was prepared using a tape casting method. The raw material had a particle size of -325 mesh. After mixing, coating, and drying, a nickel metal green body with a certain strength and a thickness of 0.2 mm was formed. After cutting, a green body of the same size as the wire mesh was formed. The green body was bound together with the wire mesh coated with binder and then degreased and sintered in a hydrogen atmosphere to obtain sample 3.

[0091] Figure 4 The image shows a scanning electron microscope (SEM) image of sample 3 provided in an embodiment of the present invention.

[0092] like Figure 4 As shown, the Ni metal diffusion layer was tested for air permeability and roughness, revealing a porosity of 49%, an average pore size of 10 μm, and an air permeability of 540 μm. 3 / (kpa·h·m 2 The roughness of the nickel sintered metal billet in the diffusion layer is 2.8 μm.

[0093] This invention relates to a gradient metal diffusion layer and its preparation method. The process is simple, easy to operate, and capable of mass production. This invention uses a high-concentration binder solution to coat and dry on the surface of a wire mesh. The surface of the fine mesh is sealed by an organic layer, effectively preventing deformation and collapse of the green body during composite sintering, ensuring the surface smoothness of the gradient diffusion layer, and facilitating increased bonding area and sites with the catalyst layer. The gradient metal diffusion layer provided by this invention can be designed with porous properties according to the needs of different application scenarios, selecting appropriate metal green bodies and wire mesh raw materials and preparation processes to achieve optimal customized production.

[0094] In summary, the method for preparing a gradient metal diffusion structure provided in this embodiment of the invention includes: Multiple pre-treated metal wire meshes are stacked in a staggered manner according to their mesh count from largest to smallest. Adjacent layers are rotated at a target angle and spot-welded to fix them, resulting in a pre-mixed metal wire mesh. An organic binder is coated onto the fine mesh side of the pre-mixed metal wire mesh, resulting in a multi-layered metal wire mesh covered with binder. Metal powder of a target particle size is selected to form a metal powder green body, which is then cut to the same size as the metal wire mesh, resulting in a metal green body. The metal green body is laid flat on the multi-layered metal wire mesh with the binder on one side, resulting in a composite metal green body. The composite metal green body is constrained vertically in a specific fixture, then degreased and sintered to obtain a gradient metal diffusion structure. This preparation method has a simple process flow, produces a gradient metal diffusion layer that is easy to demold, has a non-sagging surface film, and good flatness. It does not restrict the forming method, powder particle size, or green body thickness of the metal powder green body, and allows for free selection of the green body and wire mesh combination for different working conditions, enabling customized preparation of the gradient metal diffusion layer.

[0095] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0096] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions of the method embodiments.

[0097] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A gradient metal diffusion structure, characterized in that, The diffusion structure includes a powder sintered metal green body, a multilayer metal mesh, and an adhesive layer located between the powder sintered metal green body and the metal mesh. The powder sintered metal green body is laid flat on the surface of the metal mesh. The adhesive layer is used to bond the powder sintered metal green body and the metal mesh. The powder sintered metal green body has the same size as the metal mesh. The multilayer metal wire mesh consists of at least three layers of metal wire mesh with different mesh counts stacked in a cross-over pattern; the metal wire meshes are arranged in a gradient order of decreasing mesh count in the direction away from the powder sintered metal green body; the metal wire meshes are rotated at a target angle and spot-welded to each other between adjacent layers.

2. A method for preparing a gradient metal diffusion structure, characterized in that, The method includes: Multiple pre-treated metal wire meshes are stacked in a cross-over pattern according to their mesh count from largest to smallest. The adjacent layers are rotated at the target angle and then spot-welded to fix them, thus obtaining a well-proportioned metal wire mesh. An organic adhesive is coated on the fine mesh side of the prepared metal wire mesh to obtain a multilayer metal wire mesh covered with adhesive. Select metal powder with a target particle size to make a metal powder green blank, and cut the metal powder green blank to the same size as the metal wire mesh to obtain the metal green blank; The metal green blank is laid flat on the multilayer metal wire mesh with the adhesive side to obtain a composite metal green blank; After constraining the composite metal green blank in a specific tooling, it is degreased and sintered to obtain a gradient metal diffusion structure.

3. The method according to claim 2, characterized in that, The adhesive is one or more of the following: methylcellulose, ethylcellulose, polyvinyl butyral, polyvinylpyrrolidone, polymethyl methacrylate, and polyethyl methacrylate. The adhesive is used in conjunction with a solvent, wherein the solvent is one or two of methanol, ethanol, ethylene glycol, isopropanol, and butanol; The ratio of the adhesive to the solvent is 10%:90%~3%:97%.

4. The method according to claim 2, characterized in that, The metal wire mesh has 3 to 8 layers; the four corners of the metal wire mesh are spot welded, and the remaining edges of the metal wire mesh have 1 to 2 additional welds depending on the edge size.

5. The method according to claim 2, characterized in that, Before the pretreated wire mesh is stacked in a staggered pattern of extra-coarse, coarse, and fine mesh, the process also includes: Obtain a metal wire mesh that is undamaged, has uniform mesh size, and is flat, and cut the wire mesh to the target size; The cut wire mesh is degreased, then rinsed clean and air-dried or oven-dried to obtain pre-treated wire mesh.

6. The method according to claim 5, characterized in that, The step of cutting the wire mesh to the target size includes: The wire mesh is cut to the target size using a shearing machine or laser cutting. The degreasing treatment of the cut wire mesh includes: Use one of the following: acetone, alcohol, or detergent powder, to degrease the cut wire mesh.

7. The method according to claim 2, characterized in that, The step of coating the fine mesh side of the prepared metal wire mesh with an organic adhesive includes: An organic adhesive is applied to the fine mesh side of the prepared metal wire mesh by brushing or spraying, and the thickness of the organic adhesive is such that it immerses one layer of the metal wire mesh.

8. The method according to claim 2, characterized in that, The material of the metal powder preform includes titanium alloy, nickel-based alloy or stainless steel; the forming method of the metal powder preform includes rolling, molding, isostatic pressing, slurry coating.

9. The method according to claim 2, characterized in that, The specific tooling has good flatness, and the surface roughness of the specific tooling in contact with the composite metal billet is less than 10 μm.

10. The method according to claim 2, characterized in that, The degreasing temperature is 200-500℃, the heating rate is 2-10℃ / min, and the holding time is 1-2h; the sintering temperature is 950-1100℃, the heating rate is 2-10℃ / min, and the holding time is 1-3h.

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