A method of making an anisotropic carbon paper having a z-axis oriented conductive network

Abstract

The present disclosure relates to a preparation method of anisotropic carbon paper with Z-axis oriented conductive network, comprising: preparing a mixed pulp; the mixed pulp comprises short-cut carbon fibers and a sacrificial magnetic guide template, the sacrificial magnetic guide template comprises a nickel-plated carbon material; placing the mixed pulp in a dewatering forming area of a wet papermaking device, and applying an external steady magnetic field perpendicular to the paper surface in the dewatering forming area to induce the nickel-plated carbon material to be oriented and bridged with each other along the Z-axis direction to form a Z-axis oriented structure, thereby obtaining a nascent composite paper base; using a thermosetting resin to impregnate the nascent composite paper base, and performing hot-pressing and curing treatment on the impregnated nascent composite paper base, thereby obtaining a cured paper base; and performing pre-carbonization treatment, nickel removal treatment and high-temperature graphitization treatment on the cured paper base, thereby obtaining anisotropic carbon paper with carbon Z-axis oriented conductive network. The present disclosure can reduce the through-plane resistance of the carbon paper, and also take into account the pore structure, air permeability and low metal residue.

Description

Technical Field

[0001] This disclosure relates to the field of preparation of key materials for proton exchange membrane fuel cells, and in particular to a method for preparing anisotropic carbon paper with a Z-axis oriented conductive network. Background Technology

[0002] In proton exchange membrane fuel cells, the gas diffusion layer is typically used to achieve functions such as electron conduction, gas diffusion, water generation and discharge, heat transfer, and structural support. As an important substrate material for the gas diffusion layer, carbon paper's conductivity, pore structure, and mechanical properties directly affect the operating efficiency and stability of the fuel cell. Existing carbon paper is usually produced by wet forming of short-cut carbon fibers combined with resin impregnation, curing, carbonization, and graphitization processes. However, because short-cut carbon fibers tend to spread along the paper surface during the forming process, it is difficult to effectively form conductive channels in the thickness direction of the carbon paper, resulting in its Z-axis conductivity still needing improvement.

[0003] In related technologies, the conductivity of carbon paper is typically improved by increasing the compaction degree of the carbon paper, increasing the amount of resin, or introducing conductive fillers. However, these methods are difficult to construct a directional conductive network that runs through the thickness direction of the carbon paper, and they can easily have adverse effects on the porosity, air permeability, and drainage performance of the carbon paper. Furthermore, some external field-induced orientation schemes may suffer from insufficient stability of the orientation structure or metal residues that affect the long-term operational reliability of fuel cells. Therefore, there is an urgent need for a method to prepare anisotropic carbon paper with a Z-axis directional conductive network, so as to improve the conductivity of the carbon paper in the thickness direction while taking into account the pore structure, mass transfer performance, and long-term operational reliability. Summary of the Invention

[0004] This disclosure provides a method for preparing anisotropic carbon paper with a Z-axis oriented conductive network, including: A mixed slurry is prepared; wherein the mixed slurry includes chopped carbon fibers and a sacrificial magnetic template, and the sacrificial magnetic template includes nickel-plated carbon material; The mixed slurry is placed in the dewatering and forming zone of the wet papermaking equipment, and an external steady magnetic field perpendicular to the paper surface is applied in the dewatering and forming zone to induce the nickel-plated carbon material to align and bridge each other along the Z-axis to form a Z-axis orientation structure, thus obtaining the primary composite paper base. The nascent composite paper base is impregnated with thermosetting resin and then hot-pressed to lock the Z-axis orientation structure in the nascent composite paper base, thus obtaining a cured paper base. By pre-carbonizing, denickelizing, and high-temperature graphitizing the cured paper base, anisotropic carbon paper with a carbonaceous Z-axis oriented conductive network is obtained.

[0005] Furthermore, the nickel-plated carbon material is prepared through the following steps: The carbon core is subjected to acidification, cleaning and activation treatments to obtain the treated carbon core; A nickel-plated carbon material is obtained by coating the surface of the treated carbon core with a nickel layer using a chemical plating method.

[0006] Furthermore, the carbon core includes one or more of the following: carbon nanofibers, single-walled carbon nanotubes, multi-walled carbon nanotubes, vapor-grown carbon fibers, and chopped carbon fiber powder.

[0007] Furthermore, the electroless nickel plating solution used in the electroless plating method includes nickel salts, reducing agents, and complexing agents; wherein, the nickel salts include one or more of nickel sulfate hexahydrate and nickel chloride hexahydrate, the reducing agent includes sodium hypophosphite monohydrate, and the complexing agent includes one or more of sodium citrate, lactic acid, and sodium acetate.

[0008] Furthermore, the mixed slurry also includes a temporary binder and a dispersant; wherein the temporary binder includes one or more of polyvinyl alcohol, acrylic emulsion and phenolic emulsion, and the dispersant includes one or more of anionic polyacrylamide, polyethylene oxide and sodium carboxymethyl cellulose.

[0009] Furthermore, an external steady magnetic field is used to overcome the gravitational and flow field shearing effects of the mixed slurry during the dewatering process, so that the nickel-plated carbon material is transformed from a random distribution in the XY plane to an ordered arrangement along the Z-axis.

[0010] Furthermore, an external steady magnetic field perpendicular to the paper surface is applied to the dehydration and forming zone, including: An external steady magnetic field is applied during the dewatering process of the mixed slurry, and the external steady magnetic field is maintained after the dewatering is completed; wherein, the magnetic field strength of the external steady magnetic field is 0.45T to 0.70T, and the external steady magnetic field is maintained for 60s to 180s after the dewatering is completed.

[0011] Furthermore, the nickel-plated carbon material includes a carbon core and a nickel layer covering the surface of the carbon core; based on the mass of solid components in the mixed slurry, the chopped carbon fibers are 80 to 98 parts by mass, the carbon core is 0.5 to 8 parts by mass, the temporary binder is 1 to 8 parts by mass, and the dispersant is 0.02 to 0.8 parts by mass.

[0012] Furthermore, the thermosetting resin includes one or more of alcohol-soluble phenolic resin, furan resin, and epoxy-modified phenolic resin; the solid content of the impregnation liquid corresponding to the thermosetting resin is from 10 wt% to 45 wt%.

[0013] Furthermore, the impregnation liquid corresponding to the thermosetting resin also includes a resin modifier; the resin modifier includes polyvinylidene fluoride and propylene carbonate; or, the resin modifier includes polyvinylidene fluoride, propylene carbonate, and at least one selected from ethylene carbonate and dimethyl carbonate; wherein the mass of the resin modifier is 5 wt% to 30 wt% of the solids mass of the thermosetting resin.

[0014] Furthermore, the nickel removal process includes a mixed acid immersion process; the mixed acid immersion process includes: placing the pre-carbonized paper base, formed after pre-carbonization treatment of the cured paper base, into a nickel removal acid solution, so that the nickel layer on the surface of the nickel-plated carbon material is converted into a soluble salt and washed off; wherein, the nickel removal acid solution includes hydrochloric acid and nitric acid.

[0015] Furthermore, the nickel removal process also includes: after the pre-carbonized paper base is subjected to a mixed acid immersion process, a complexing cleaning solution is used to clean the pre-carbonized paper base after the mixed acid immersion process; wherein, the complexing cleaning solution includes an ethylenediaminetetraacetic acid solution.

[0016] Furthermore, the nickel removal process includes a high-temperature vapor phase halogenation process; the high-temperature vapor phase halogenation process includes: placing the pre-carbonized paper base formed after pre-carbonization treatment in an inert gas mixed atmosphere containing chlorine, so that the nickel layer on the surface of the nickel-plated carbon material is converted into nickel chloride and removed.

[0017] Furthermore, the pre-carbonization treatment is carried out in a protective gas atmosphere to convert the thermosetting resin into resin carbon and fix the Z-axis orientation structure; the high-temperature graphitization treatment is carried out in a protective gas atmosphere to form a carbonaceous Z-axis oriented conductive network; wherein the protective gas includes one of nitrogen, argon and nitrogen-argon mixture.

[0018] This disclosure provides a method for preparing anisotropic carbon paper with a Z-axis oriented conductive network. First, a mixed slurry is prepared, comprising chopped carbon fibers and a sacrificial magnetic template, the sacrificial magnetic template comprising nickel-plated carbon material. Then, the mixed slurry is placed in the dehydration forming zone of a wet papermaking apparatus, and an external stable magnetic field perpendicular to the paper surface is applied in the dehydration forming zone to induce the nickel-plated carbon material to oriented and bridge itself along the Z-axis, forming a Z-axis oriented structure to obtain a nascent composite paper base. Next, the nascent composite paper base is impregnated with a thermosetting resin, and then hot-pressed and cured to lock the Z-axis oriented structure in the nascent composite paper base, obtaining a cured paper base. Finally, the cured paper base undergoes pre-carbonization, nickel removal, and high-temperature graphitization treatment to obtain anisotropic carbon paper with a carbonaceous Z-axis oriented conductive network.

[0019] As described above, the embodiments of this disclosure first prepare a mixed slurry comprising chopped carbon fibers and a sacrificial magnetic template, so that the sacrificial magnetic template, including nickel-plated carbon material, can be uniformly dispersed in the chopped carbon fiber system, providing a basis for the subsequent formation of conductive channels in the thickness direction. Then, by placing the mixed slurry in the dehydration forming zone of a wet papermaking apparatus and applying an external stable magnetic field perpendicular to the paper surface in the dehydration forming zone, the nickel-plated carbon material can be oriented and bridged along the Z-axis, thereby forming a Z-axis oriented structure in the nascent composite paper base, improving the problem of insufficient conductive channels in the thickness direction of traditional carbon paper. Subsequently, the nascent composite paper base is impregnated with a thermosetting resin, and the impregnated nascent composite paper base is hot-pressed and cured, which can lock the Z-axis oriented structure in the nascent composite paper base and reduce the risk of the Z-axis oriented structure rebounding, collapsing or deflecting during subsequent processing. Finally, by pre-carbonizing, denicking and high-temperature graphitizing the cured paper base, the nickel in the nickel-plated carbon material can be removed, and a carbonaceous Z-axis oriented conductive network can be formed. Therefore, the embodiments of this disclosure can form a stable carbon Z-axis oriented conductive network in the thickness direction of the carbon paper, which reduces the area resistance in the penetration direction, reduces the impact of magnetic metal residue on the long-term operational reliability of the fuel cell, and takes into account the pore structure and air permeability of the carbon paper. Attached Figure Description

[0020] The above and other objects, features, and advantages of this disclosure will become more apparent from the more detailed description of the embodiments thereof in conjunction with the accompanying drawings. The drawings are provided to further illustrate the embodiments of this disclosure and form part of the specification. They are used together with the embodiments of this disclosure to explain the disclosure and do not constitute a limitation thereof. In the drawings, the same reference numerals generally represent the same components or steps.

[0021] Figure 1 A flowchart illustrating a method for preparing anisotropic carbon paper with a Z-axis oriented conductive network, provided as an exemplary embodiment of this disclosure; Figure 2 A flowchart illustrating a method for preparing a nickel-plated carbon material as provided in an exemplary embodiment of this disclosure. Detailed Implementation

[0022] Embodiments of this disclosure will now be described in more detail with reference to the accompanying drawings. While some embodiments of this disclosure are shown in the drawings, it should be understood that this disclosure can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of this disclosure. It should be understood that the accompanying drawings and embodiments of this disclosure are for illustrative purposes only and are not intended to limit the scope of protection of this disclosure.

[0023] It should be understood that the steps described in the method embodiments of this disclosure may be performed in different orders and / or in parallel. Furthermore, the method embodiments may include additional steps and / or omit the steps shown. The scope of this disclosure is not limited in this respect.

[0024] The term "comprising" and its variations as used herein are open-ended, meaning "including but not limited to". The term "based on" means "at least partially based on". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments". Definitions of other terms will be given in the description below. It should be noted that the concepts of "first", "second", etc., used in this disclosure are only used to distinguish different devices, modules, or units, and are not intended to limit the order of functions performed by these devices, modules, or units or their interdependencies.

[0025] It should be noted that the terms "a" and "a plurality of" used in this disclosure are illustrative rather than restrictive, and those skilled in the art should understand that, unless otherwise expressly indicated in the context, they should be understood as "one or more". In proton exchange membrane fuel cells, the gas diffusion layer is typically located between the bipolar plates and the catalyst layer. It needs to simultaneously perform functions such as electron conduction, reactant gas diffusion, water generation and discharge, heat transfer, and mechanical support for the membrane electrode assembly. As an important substrate material for the gas diffusion layer, the carbon paper's conductivity, pore structure, permeability, drainage performance, and mechanical properties directly affect the fuel cell's output efficiency and operational stability. Existing carbon paper is generally made from short-cut carbon fibers through wet papermaking, followed by resin impregnation or hot-pressing composite, hot-pressing curing, carbonization, and graphitization processes. However, during wet papermaking and dehydration forming, short-cut carbon fibers tend to preferentially spread along the paper surface, making it easier for the carbon paper to form a conductive network in the XY plane. Electron transport in the thickness direction mainly relies on random point contacts between fibers and local resin carbon connections, resulting in insufficient number of through-channel conductive channels in the Z-axis direction of the carbon paper, and the resistance in the penetration direction is usually higher than ideal.

[0026] In existing technologies, to improve the conductivity of carbon paper, methods such as increasing resin impregnation, increasing hot-pressing pressure, or increasing carbon paper compaction density are commonly used to enhance the contact between fibers and the overall conductivity. Other approaches involve adding conductive fillers such as carbon black, graphite, carbon nanotubes, or carbon fiber powder to the resin impregnation solution, the carbon paper base, or the functional coating to supplement the conductive pathways. Still other approaches utilize modified phenolic resins or carbon fiber powder modification processes to improve the mechanical properties, conductivity, and air permeability of the carbon paper. For example, some existing methods prepare high-strength, thin carbon paper through processes such as carbon fiber powder preparation, resin / carbon fiber powder impregnation, foam coating of carbon fiber powder layers, hot-pressing curing, and carbonization / graphitization. Other methods modify phenolic resins with PVDF and carbonates, then laminate them with the carbon paper base after film formation through hot pressing to improve the carbon paper's toughness. While these methods can improve the overall performance of carbon paper to some extent, they primarily rely on disordered conductive filler filling, resin modification, or fiber contact compaction, making it difficult to specifically construct a directional conductive network that runs through the thickness direction of the carbon paper.

[0027] Furthermore, while simply increasing the amount of disordered conductive powder or improving the hot-pressing density can help reduce the resistivity of carbon paper, it can easily clog the pores or reduce the porosity, thereby affecting gas diffusion and water drainage capabilities, and even increasing the risk of flooding. It is difficult to balance conductivity and mass transfer performance. A few approaches attempt to induce orientation in the carbon paper through magnetic materials or metal-coated carbon materials using an external field. However, if magnetic metals such as nickel, iron, and cobalt or their coatings are directly retained in the carbon paper, metal ion dissolution may occur in the acidic operating environment of the fuel cell, increasing the risk of proton exchange membrane contamination, catalyst poisoning, and membrane degradation, thus affecting the long-term operational reliability of the fuel cell. At the same time, the temporary orientation structure formed by external field induction is prone to rebound, collapse, or deflection during transport, drying, impregnation, and high-temperature treatment, making it difficult to maintain the established thickness-oriented conductive structure stably. Therefore, it is necessary to provide a method for preparing anisotropic carbon paper with a Z-axis oriented conductive network to improve the thickness-oriented conductivity of the carbon paper while taking into account the pore structure, gas permeability and drainage performance, and the long-term operational reliability of the fuel cell.

[0028] To facilitate understanding of the embodiments of this disclosure, the preparation method of anisotropic carbon paper with a Z-axis oriented conductive network provided in the embodiments of this disclosure is described below. The embodiments of this disclosure mainly form a carbonaceous Z-axis oriented conductive network in anisotropic carbon paper through sacrificial magnetic permeability template, external steady magnetic field induction, thermosetting resin locking, nickel removal treatment and high temperature graphitization treatment.

[0029] In one embodiment, such as Figure 1 As shown, a method for preparing anisotropic carbon paper with a Z-axis oriented conductive network is provided, comprising the following steps: Step 101: Prepare the mixed slurry.

[0030] Here, before preparing anisotropic carbon paper with a Z-axis oriented conductive network, a mixed slurry needs to be prepared. The mixed slurry includes chopped carbon fibers and a sacrificial magnetic template. The sacrificial magnetic template includes nickel-plated carbon material. The chopped carbon fibers form the main skeleton of the anisotropic carbon paper and provide planar conductivity and mechanical support. The sacrificial magnetic template is used to orient itself under the subsequent application of a constant magnetic field to form a conductive bridging base in the thickness direction of the anisotropic carbon paper. The nickel-plated carbon material can be understood as a material formed by coating a nickel layer on the surface of the carbon core. The carbon core serves as the carbon basis for the subsequent carbon-based Z-axis oriented conductive network, and the nickel layer enables the carbon core to have magnetic permeability characteristics in response to the applied constant magnetic field. Thus, the nickel-plated carbon material can participate in wet forming as a sacrificial magnetic template in the mixed slurry, and the nickel layer is removed during the subsequent denicking process, resulting in a carbon-based Z-axis oriented conductive network in the final anisotropic carbon paper.

[0031] In one possible embodiment, such as Figure 2 As shown, nickel-plated carbon material is prepared through the following steps: Step 201: The carbon core is subjected to acidification, cleaning and activation treatment to obtain the treated carbon core; Step 202: A nickel layer is coated onto the surface of the treated carbon core using a chemical plating method to obtain a nickel-plated carbon material.

[0032] Specifically, in this embodiment, the carbon core can be selected according to the construction requirements of the subsequent Z-axis orientation structure. For example, the carbon core may include one or more of carbon nanofibers, single-walled carbon nanotubes, multi-walled carbon nanotubes, vapor-grown carbon fibers, and chopped carbon fiber powder. By acidifying, cleaning, and activating the carbon core, the reactivity of the carbon core surface can be improved, and the adhesion stability of the subsequent nickel layer on the carbon core surface can be improved. Furthermore, by chemically plating the surface of the treated carbon core with a nickel layer, a nickel-plated carbon material with magnetic permeability can be obtained, enabling the nickel-plated carbon material to be oriented and bridged with each other along the Z-axis direction under the action of a subsequent external steady magnetic field.

[0033] In one possible embodiment, in order to prepare anisotropic carbon paper with a Z-axis oriented conductive network, the corresponding raw materials, auxiliary materials and processing media can be selected according to different process stages. For example, the specific types, recommended ranges, preferred ranges and functions of each component can be shown in Table 1: Table 1. Specific types, ranges, and functions of each component

[0034] It should be noted that the main carbon fiber, sacrificial magnetic template carbon core, chemically plated nickel salt, reducing agent, complexing agent, dispersant, and temporary binder listed in Table 1 can be used for the preparation of the mixed slurry in step 101. The thermosetting resin and resin modifier listed in Table 1 can be used for subsequent impregnation and hot-press curing of the nascent composite paper base. The nickel removal acid listed in Table 1 can be used for subsequent nickel removal treatment. The protective gas listed in Table 1 can be used for subsequent pre-carbonization and high-temperature graphitization treatment. The types, recommended ranges, and preferred ranges of the above components are illustrative examples. While ensuring the desired functionality, adjustments can be made based on the thickness, basis weight, porosity, air permeability, electrical conductivity, and process conditions of the wet papermaking equipment.

[0035] In one possible embodiment, the electroless nickel plating solution used in the electroless plating method includes a nickel salt, a reducing agent, and a complexing agent. The nickel salt includes one or more of nickel sulfate hexahydrate and nickel chloride hexahydrate, the reducing agent includes sodium hypophosphite monohydrate, and the complexing agent includes one or more of sodium citrate, lactic acid, and sodium acetate. The nickel salt is used to provide Ni2+, the reducing agent is used to reduce and deposit nickel ions onto the surface of the carbon core, and the complexing agent is used to stabilize the electroless nickel plating solution and control the nickel layer deposition rate.

[0036] In one possible embodiment, the mixed slurry further includes a temporary binder and a dispersant, wherein the temporary binder includes one or more of polyvinyl alcohol, acrylic emulsion and phenolic emulsion, and the dispersant includes one or more of anionic polyacrylamide, polyethylene oxide and sodium carboxymethyl cellulose. The temporary binder is used to improve the strength of the wet paper sheet and can be removed or converted during subsequent carbonization. The dispersant is used to improve the dispersion uniformity of chopped carbon fibers and sacrificial magnetic template in the aqueous system.

[0037] In one possible embodiment, the nickel-plated carbon material comprises a carbon core and a nickel layer covering the surface of the carbon core. Based on the mass of solid components in the mixed slurry, the chopped carbon fibers are 80 to 98 parts by mass, the carbon core is 0.5 to 8 parts by mass, the temporary binder is 1 to 8 parts by mass, and the dispersant is 0.02 to 0.8 parts by mass. Preferably, the chopped carbon fibers are 90 to 96 parts by mass, the carbon core is 1.5 to 4 parts by mass, the temporary binder is 2 to 5 parts by mass, and the dispersant is 0.05 to 0.3 parts by mass. By controlling the amount of carbon core, it is beneficial to form a conductive bridge in the Z-axis direction during the subsequent magnetic field induction process, while avoiding excessive addition of sacrificial magnetic permeability template, which could lead to pore blockage or decreased air permeability.

[0038] Step 102: The mixed slurry is placed in the dewatering and forming zone of the wet papermaking equipment, and an external stable magnetic field perpendicular to the paper surface is applied in the dewatering and forming zone to induce the nickel-plated carbon material to align and bridge each other along the Z-axis to form a Z-axis orientation structure, thereby obtaining the nascent composite paper base.

[0039] Here, after the mixed pulp is prepared, it can be placed in the dewatering and forming zone of the wet papermaking equipment, and an external steady magnetic field perpendicular to the paper surface is applied in the dewatering and forming zone. The dewatering and forming zone can be understood as the area in the wet papermaking equipment used to dewater the mixed pulp and form the paper base. The external steady magnetic field can be understood as a magnetic field that maintains a relatively stable direction and intensity in the dewatering and forming zone. Since the nickel-plated carbon material includes a carbon core and a nickel layer covering the surface of the carbon core, the nickel layer enables the nickel-plated carbon material to have magnetic permeability. Therefore, under the action of the external steady magnetic field, the nickel-plated carbon material can be transformed from a random distribution state to a Z-axis oriented arrangement state, and bridge each other in the thickness direction of the anisotropic carbon paper, thereby forming a Z-axis oriented structure in the nascent composite paper base.

[0040] In one possible embodiment, the applied steady magnetic field is perpendicular to the paper surface. This field overcomes the gravitational and flow shear effects of the mixed slurry during dehydration, transforming the random distribution of the nickel-plated carbon material in the XY plane into an ordered arrangement along the Z-axis. Specifically, without an applied steady magnetic field, the chopped carbon fibers and nickel-plated carbon material in the mixed slurry tend to distribute along the paper surface due to the flow field during wet dehydration, making it difficult to form conductive channels in the thickness direction. By applying an applied steady magnetic field perpendicular to the paper surface in the dehydration forming zone, the nickel-plated carbon material can be induced to oriented along the carbon paper thickness direction, causing multiple nickel-plated carbon materials to contact or overlap each other in the thickness direction, thereby forming a Z-axis orientation structure for subsequent construction of a carbon-based Z-axis oriented conductive network.

[0041] In one possible embodiment, an external steady magnetic field perpendicular to the paper surface is applied to the dewatering and forming zone, including: applying the external steady magnetic field during the dewatering process of the mixed slurry, and continuing to maintain the external steady magnetic field after dewatering is completed, wherein the magnetic field strength of the external steady magnetic field is 0.45T to 0.70T, and the external steady magnetic field is maintained for 60s to 180s after dewatering is completed.

[0042] By applying an external steady magnetic field during the dewatering process of the mixed slurry, the nickel-plated carbon material can be oriented in the Z-axis direction simultaneously as the paper base gradually forms. By continuing to maintain the external steady magnetic field after dewatering, the possibility of the nickel-plated carbon material deflecting, falling back, or becoming disordered due to gravity, flow field disturbance, or fiber rebound after dewatering can be further reduced, thereby improving the stability of the Z-axis orientation structure in the nascent composite paper base.

[0043] In one specific embodiment, the mixed slurry obtained in step 101 can be poured into a wet forming apparatus with a diameter of 200 mm. Electromagnets are arranged above and below the mesh section of the wet forming apparatus so that the magnetic lines of force are perpendicular to the paper surface. Before dewatering, a constant magnetic field of 0.60 T can be applied for 30 s; during dewatering, the constant magnetic field of 0.60 T can be maintained for 60 s; after dewatering, the constant magnetic field can be maintained for another 120 s, thereby obtaining a nascent composite paper base. Through the above treatment, nickel-plated multi-walled carbon nanotubes can be oriented and bridged together along the Z-axis under the action of an external constant magnetic field to form a Z-axis oriented structure in the nascent composite paper base. Optionally, the basis weight of the target base paper can be 45 g / m².

[0044] In another specific embodiment, when the sacrificial magnetic permeability template uses nickel-plated vapor-grown carbon fibers, the magnetic field strength of the applied steady magnetic field can be set to 0.70T, and the applied steady magnetic field can be maintained for 150s after dehydration. In this way, the nickel-plated vapor-grown carbon fibers can be oriented and bridged with each other along the Z-axis during the dehydration and forming process, thereby forming a Z-axis oriented structure in the nascent composite paper matrix.

[0045] In another specific embodiment, when the sacrificial magnetic permeability template is composed of nickel-plated multi-walled carbon nanotubes and nickel-plated chopped carbon fiber powder, the magnetic field strength of the external steady magnetic field in the wet dehydration zone can be set to 0.45T, and the external steady magnetic field can be maintained for 120s after dehydration. By using a composite magnetic permeability template and a lower magnetic field strength, nickel-plated carbon materials of different sizes can also be oriented and bridged together along the Z-axis in the nascent composite paper matrix to construct a Z-axis oriented structure.

[0046] It should be noted that the dimensions of the wet forming apparatus, the magnetic field strength of the applied constant magnetic field, the application time before dehydration, the holding time during dehydration, the continued holding time after dehydration, and the basis weight of the target base paper are all exemplary conditions for illustrating the embodiments of this disclosure and are not intended to limit the scope of protection of this disclosure. Under the premise that the nickel-plated carbon materials can be oriented and bridged with each other along the Z-axis to form a Z-axis oriented structure, those skilled in the art can make adaptive adjustments to the above conditions according to the solid content of the mixed slurry, the specifications of the wet papermaking equipment, the paper base thickness, the basis weight of the target base paper, and the type and amount of the sacrificial magnetic permeable template.

[0047] Step 103: Impregnate the nascent composite paper base with thermosetting resin, and then perform hot pressing curing on the impregnated nascent composite paper base to lock the Z-axis orientation structure in the nascent composite paper base, thereby obtaining a cured paper base.

[0048] Here, after obtaining the nascent composite paper base, a thermosetting resin can be used to impregnate the nascent composite paper base, and then a hot-press curing treatment can be performed on the impregnated nascent composite paper base to lock the Z-axis orientation structure in the nascent composite paper base, resulting in a cured paper base. Specifically, the thermosetting resin can undergo a cross-linking reaction after being heated, and form a cured connection structure inside the nascent composite paper base, thereby locking the Z-axis orientation structure formed in step 102 in situ. Through the above impregnation treatment and hot-press curing treatment, the risk of springback, collapse or deflection of the Z-axis orientation structure during transportation, drying, pre-carbonization treatment, nickel removal treatment and high-temperature graphitization treatment can be reduced, and the morphological stability of the Z-axis orientation structure can be improved.

[0049] In one possible embodiment, the thermosetting resin includes one or more of alcohol-soluble phenolic resin, furan resin, and epoxy-modified phenolic resin. The solid content of the impregnation liquid corresponding to the thermosetting resin is 10wt% to 45wt%, preferably 20wt% to 35wt%. By controlling the solid content of the impregnation liquid, the thermosetting resin can fully penetrate the pore structure of the nascent composite paper base and lock the Z-axis orientation structure during the hot-pressing curing process, while avoiding excessive filling of the pores due to excessively high solid content of the impregnation liquid.

[0050] In one possible embodiment, the impregnation liquid corresponding to the thermosetting resin further includes a resin modifier. The resin modifier includes polyvinylidene fluoride and propylene carbonate, or the resin modifier includes polyvinylidene fluoride, propylene carbonate, and at least one selected from ethylene carbonate and dimethyl carbonate. The mass of the resin modifier is 5 wt% to 30 wt% of the solid resin mass in the thermosetting resin, preferably 10 wt% to 22 wt% of the solid resin mass in the thermosetting resin. The resin modifier is used to improve the toughness and melt penetration stability of the thermosetting resin, giving the impregnation liquid better penetration ability and curing stability in the nascent composite paper base.

[0051] In one specific embodiment, a modified phenolic resin impregnation solution can be prepared. Specifically, the modified phenolic resin impregnation solution may include 100 parts of alcohol-soluble phenolic resin, 6 parts of polyvinylidene fluoride, 12 parts of propylene carbonate, 120 parts of ethanol, 5 parts of carbon fiber powder, and 0.5 parts of FC-16 fluorocarbon surfactant, wherein the solid content of the alcohol-soluble phenolic resin can be 60 wt%. Stirring the above components at 70°C for 1 hour yields a modified phenolic resin impregnation solution with a solid content of approximately 33 wt%.

[0052] After obtaining the modified phenolic resin impregnation solution, the nascent composite paper base obtained in step 102 can be impregnated in the modified phenolic resin impregnation solution for 3 minutes. After removal, the solution can be squeezed out using a pressure roller to control the resin coating amount to approximately 28 wt% of the dry paper mass. Then, it can be pre-dried at 80°C for 10 minutes to bring the nascent composite paper base to a semi-dry state. Subsequently, the pre-dried nascent composite paper base can be placed in a flatbed hot press and hot-pressed at 165°C and 4 MPa for 6 minutes to obtain a cured paper base. Through the above impregnation and hot-pressing curing processes, the modified phenolic resin can be cured in the nascent composite paper base to form a cross-linked structure, thereby locking the Z-axis orientation structure.

[0053] In another specific embodiment, the impregnation solution corresponding to the thermosetting resin can be a common alcohol-soluble phenolic resin / ethanol system, the solid content of the impregnation solution can be 30 wt%, and polyvinylidene fluoride and propylene carbonate can be omitted. In this embodiment, the resin coating amount can be approximately 26 wt% of the dry paper weight, and the hot-pressing conditions can be 170°C, 5 MPa, and 5 min. By using a common alcohol-soluble phenolic resin / ethanol system, the Z-axis orientation structure in the nascent composite paper base can also be locked to obtain a cured paper base.

[0054] It should be noted that the types of thermosetting resins, the solid content of the impregnation liquid, the types and amounts of resin modifiers, the impregnation time, the amount of resin applied, the pre-drying temperature and time, the hot-pressing temperature, the hot-pressing pressure, and the hot-pressing time mentioned above are all exemplary conditions for illustrating the embodiments of this disclosure and are not intended to limit the scope of protection of this disclosure. Under the premise that the thermosetting resin can lock the Z-axis orientation structure in the nascent composite paper base and obtain a cured paper base, those skilled in the art can make adaptive adjustments to the above conditions according to the thickness, porosity, target resin content, subsequent pre-carbonization treatment conditions, and the target performance of anisotropic carbon paper.

[0055] Step 104 involves pre-carbonizing, denicking, and high-temperature graphitizing the cured paper substrate to obtain anisotropic carbon paper with a carbon Z-axis oriented conductive network.

[0056] Here, after obtaining the cured paper base, it can be subjected to pre-carbonization, nickel removal, and high-temperature graphitization to obtain anisotropic carbon paper with a carbon-based Z-axis oriented conductive network. The pre-carbonization process converts the thermosetting resin in the cured paper base into resin carbon, further fixing the Z-axis orientation structure locked in step 103. The nickel removal process removes the nickel layer from the nickel-plated carbon material, ensuring that nickel only serves as a sacrificial magnetic template in the forming stage, participating in the construction of the Z-axis orientation structure, rather than being retained as a functional metal in the final anisotropic carbon paper. The high-temperature graphitization process increases the graphitization degree of the carbon material and allows the nickel-removed carbon material to form a carbon-based Z-axis oriented conductive network. Therefore, by combining the pre-carbonization, nickel removal, and high-temperature graphitization processes, the stability of the Z-axis orientation structure can be maintained while reducing magnetic metal residue, resulting in anisotropic carbon paper with a carbon-based Z-axis oriented conductive network.

[0057] It should be noted that the carbon Z-axis oriented conductive network in this embodiment can be understood as a conductive network formed in the thickness direction of the carbon paper by the carbon core, resin carbon, or carbon structure retained after nickel removal treatment, or after high-temperature graphitization treatment. The nickel layer is mainly used as a sacrificial magnetic template in response to the applied constant magnetic field during the forming stage, and is not retained as a functional metal conductive phase in the final anisotropic carbon paper for a long period of time. The above-mentioned carbon Z-axis oriented conductive network does not exclude the unavoidable trace metal residues during the preparation process.

[0058] In one possible embodiment, the pre-carbonization treatment is carried out in a protective gas atmosphere to convert the thermosetting resin into resin carbon and fix the Z-axis orientation structure. The high-temperature graphitization treatment is carried out in a protective gas atmosphere to form a carbonaceous Z-axis oriented conductive network. The protective gas may include one of nitrogen, argon, and a nitrogen-argon mixture. Optionally, the purity of the protective gas may be not less than 99.9%. By carrying out the pre-carbonization treatment and high-temperature graphitization treatment in a protective gas atmosphere, the risk of oxidation damage to the paper base during high-temperature processing can be reduced, and it is beneficial to maintain the Z-axis orientation structure.

[0059] In one possible embodiment, the nickel removal treatment includes a mixed acid immersion process, which includes placing a pre-carbonized paper substrate, formed after pre-carbonization treatment, into a nickel removal acid solution to convert the nickel layer on the surface of the nickel-plated carbon material into a soluble salt and wash it off. The nickel removal acid solution may include hydrochloric acid and nitric acid. Optionally, the concentration of hydrochloric acid may be 1 mol / L to 4 mol / L, and the concentration of nitric acid may be 0.1 mol / L to 1 mol / L. Preferably, the concentration of hydrochloric acid may be 2 mol / L, and the concentration of nitric acid may be 0.5 mol / L. Through the mixed acid immersion process, the nickel layer on the surface of the nickel-plated carbon material can be converted into a soluble salt and washed off from the pre-carbonized paper substrate, thereby reducing the nickel residue in the anisotropic carbon paper.

[0060] In one possible embodiment, the nickel removal process further includes: after the pre-carbonized paper base is subjected to a mixed acid immersion process, cleaning the pre-carbonized paper base treated by the mixed acid immersion process with a complexing cleaning solution, wherein the complexing cleaning solution includes an ethylenediaminetetraacetic acid solution. By using the ethylenediaminetetraacetic acid solution for cleaning, residual nickel ions or nickel salts in the pre-carbonized paper base can be further complexed and removed, thereby further reducing magnetic metal residue.

[0061] In one specific embodiment, the cured paper base obtained in step 103 can be placed in a tube furnace, heated to 900°C at 2°C / min under nitrogen protection, and held for 1 hour to obtain a pre-carbonized paper base. Subsequently, the pre-carbonized paper base can be immersed in a mixed acid consisting of 2 mol / L hydrochloric acid and 0.5 mol / L nitric acid, and soaked at 70°C for 6 hours. After removal, it can be washed with deionized water and the acid washing can be repeated once. Then, it can be washed again with 0.05 mol / L ethylenediaminetetraacetic acid solution at 60°C for 1 hour, washed with deionized water until neutral, and then dried at 100°C. The dried sample is then subjected to high-temperature graphitization treatment at 2500°C for 1 hour under argon protection to obtain anisotropic carbon paper with a carbon Z-axis oriented conductive network.

[0062] In another possible embodiment, the nickel removal process includes a high-temperature vapor-phase halogenation process. This process involves placing a pre-carbonized paper substrate (formed after pre-carbonization) in an inert gas mixture containing chlorine, causing the nickel layer on the surface of the nickel-plated carbon material to be converted into nickel chloride and removed. Through this high-temperature vapor-phase halogenation process, the nickel layer can be converted into migratable or removable nickel halides, thereby achieving the removal of the nickel layer.

[0063] In one specific embodiment, the paper base pre-carbonized at 900℃ can be placed in a corrosion-resistant high-temperature furnace, and a mixture of argon gas containing 2 vol% chlorine is introduced. The furnace is then held at 850℃ for 1 hour to convert the nickel layer into nickel chloride, which migrates and is removed under the influence of the gas flow. Subsequently, the furnace can be purged with pure argon gas for 1 hour and cooled to room temperature. To reduce residual chloride salts, the sample can also be soaked in 0.5 mol / L hydrochloric acid at room temperature for 1 hour, washed with deionized water until neutral, dried at 100℃, and then subjected to high-temperature graphitization treatment at 2500℃ for 1 hour to obtain anisotropic carbon paper with a carbonaceous Z-axis oriented conductive network. This high-temperature gas-phase halogenation process is suitable for continuous high-temperature processing equipment. When using this process, a tail gas absorption device and a safety interlock device can be installed to improve process safety.

[0064] It should be noted that the heating rate, pre-carbonization temperature, holding time, composition and concentration of the nickel removal acid solution, mixed acid immersion temperature and time, complexing cleaning solution concentration, cleaning temperature and time, high-temperature vapor-phase halogenation treatment temperature and time, chlorine gas integral, purging time, high-temperature graphitization temperature and time, and type of protective gas described above are all exemplary conditions for illustrating the embodiments of this disclosure and are not intended to limit the scope of protection of this disclosure. Provided that the thermosetting resin can be converted into resin carbon, the nickel layer in the nickel-plated carbon material can be removed, and a carbonaceous Z-axis oriented conductive network can be formed, those skilled in the art can adaptively adjust the above process parameters according to the thickness of the cured paper base, the amount of nickel-plated carbon material, the nickel layer thickness, the target residual nickel content, and the conditions of the high-temperature treatment equipment.

[0065] This disclosure provides a method for preparing anisotropic carbon paper with a Z-axis oriented conductive network. First, a mixed slurry is prepared, comprising chopped carbon fibers and a sacrificial magnetic template, the sacrificial magnetic template comprising nickel-plated carbon material. Then, the mixed slurry is placed in the dehydration forming zone of a wet papermaking apparatus, and an external stable magnetic field perpendicular to the paper surface is applied in the dehydration forming zone to induce the nickel-plated carbon material to oriented and bridge itself along the Z-axis, forming a Z-axis oriented structure to obtain a nascent composite paper base. Next, the nascent composite paper base is impregnated with a thermosetting resin, and then hot-pressed and cured to lock the Z-axis oriented structure in the nascent composite paper base, obtaining a cured paper base. Finally, the cured paper base undergoes pre-carbonization, nickel removal, and high-temperature graphitization treatment to obtain anisotropic carbon paper with a carbonaceous Z-axis oriented conductive network.

[0066] As described above, the embodiments of this disclosure first prepare a mixed slurry comprising chopped carbon fibers and a sacrificial magnetic template, so that the sacrificial magnetic template, including nickel-plated carbon material, can be uniformly dispersed in the chopped carbon fiber system, providing a basis for the subsequent formation of conductive channels in the thickness direction. Then, by placing the mixed slurry in the dehydration forming zone of a wet papermaking apparatus and applying an external stable magnetic field perpendicular to the paper surface in the dehydration forming zone, the nickel-plated carbon material can be oriented and bridged along the Z-axis, thereby forming a Z-axis oriented structure in the nascent composite paper base, improving the problem of insufficient conductive channels in the thickness direction of traditional carbon paper. Subsequently, the nascent composite paper base is impregnated with a thermosetting resin, and the impregnated nascent composite paper base is hot-pressed and cured, which can lock the Z-axis oriented structure in the nascent composite paper base and reduce the risk of the Z-axis oriented structure rebounding, collapsing or deflecting during subsequent processing. Finally, by pre-carbonizing, denicking and high-temperature graphitizing the cured paper base, the nickel in the nickel-plated carbon material can be removed, and a carbonaceous Z-axis oriented conductive network can be formed. Therefore, the embodiments of this disclosure can form a stable carbon Z-axis oriented conductive network in the thickness direction of the carbon paper, which reduces the area resistance in the penetration direction, reduces the impact of magnetic metal residue on the long-term operational reliability of the fuel cell, and takes into account the pore structure and air permeability of the carbon paper.

[0067] As can be seen from steps 101 to 104 above, the core of this disclosure does not lie in simply changing a certain raw material or a certain heat treatment parameter, but in the continuous coordination of the magnetic field-induced orientation of the sacrificial magnetic permeable template, the structural locking effect of the thermosetting resin, and the subsequent nickel removal and high-temperature graphitization treatments. This allows the nickel-plated carbon material to first construct a Z-axis oriented structure in the wet forming stage, and then remove the nickel layer and transform it into a carbonaceous Z-axis oriented conductive network in the subsequent processing. To further illustrate that different types of sacrificial magnetic permeable templates, different magnetic field induction conditions, different resin impregnation systems, and different nickel removal routes can all be used to achieve the above technical concept, the following description, in conjunction with Examples 1 to 4 and comparative examples, further illustrates this disclosure. It should be noted that the following examples are only used to illustrate the specific implementation of this disclosure and are not intended to limit the scope of protection of this disclosure.

[0068] Example 1: Preparation of anisotropic carbon paper using nickel-plated templates of multi-walled carbon nanotubes.

[0069] Example 1 is a typical implementation of this disclosure. It uses multi-walled carbon nanotubes as the carbon core corresponding to the sacrificial magnetic permeability template. Nickel-plated multi-walled carbon nanotubes are prepared by chemical plating. The nickel-plated multi-walled carbon nanotubes are then mixed with PAN-based short-cut carbon fibers, temporary binders and dispersants to form a mixed slurry. The slurry is then subjected to vertical magnetic field-induced forming, resin impregnation and hot pressing locking, pre-carbonization, mixed acid denicking and high-temperature graphitization treatment to obtain anisotropic carbon paper with a carbon Z-axis oriented conductive network.

[0070] Specifically, 10.0 g of multi-walled carbon nanotubes (MWCNTs) were taken, wherein the outer diameter of the MCCNTs was 30 nm to 50 nm, the length was 10 μm to 20 μm, and the purity was not less than 95%. The MCCNTs were added to 300 mL of a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid (volume ratio of concentrated sulfuric acid to concentrated nitric acid was 3:1), and stirred in a 60 °C water bath for 2 h. After cooling, the solution was washed with deionized water until the pH of the filtrate was approximately 6.5, and then vacuum dried at 80 °C for 12 h to obtain acidified MCCNTs. Then, the… The acidified multi-walled carbon nanotubes were dispersed in 1.5L of electroless plating solution, which consisted of 25g / L nickel sulfate hexahydrate, 22g / L sodium hypophosphite monohydrate, 35g / L sodium citrate, and 20g / L ammonium chloride. The pH was adjusted to 8.8 with ammonia. The reaction was carried out at 80℃ for 45min. After filtration, washing, and drying at 80℃, nickel-plated multi-walled carbon nanotubes were obtained. The nickel content in the obtained nickel-plated multi-walled carbon nanotubes was approximately 28wt%, and the equivalent thickness of the nickel layer was approximately 20nm to 35nm.

[0071] Subsequently, on a dry basis, 95.0 parts of PAN-based chopped carbon fibers, 2.5 parts of nickel-plated multi-walled carbon nanotubes, 2.0 parts of polyvinyl alcohol (PVA) fibers, 0.2 parts of anionic polyacrylamide (APAM), and 0.3 parts of sodium carboxymethyl cellulose (CMC) were added to deionized water to prepare a slurry with a solid content of 0.10 wt%. The PAN-based chopped carbon fibers had a diameter of 7 μm and a length of 6 mm. The slurry was first stirred at 1200 rpm for 15 min, and then ultrasonically dispersed for 10 min to obtain a mixed slurry. The mixed slurry was then poured into a wet forming apparatus with a diameter of 200 mm. Electromagnets were arranged above and below the mesh of the wet forming apparatus so that the magnetic lines of force were perpendicular to the paper surface. A constant magnetic field of 0.60 T was applied for 30 s before dewatering, and the constant magnetic field of 0.60 T was maintained for 60 s during dewatering. After dewatering, the constant magnetic field was maintained for another 120 s to obtain the nascent composite paper base with a target basis weight of 45 g / m².

[0072] Next, a modified phenolic resin impregnation solution was prepared, comprising 100 parts of alcohol-soluble phenolic resin, 6 parts of polyvinylidene fluoride (PVDF), 12 parts of propylene carbonate, 120 parts of ethanol, 5 parts of carbon fiber powder, and 0.5 parts of FC-16 fluorocarbon surfactant. The alcohol-soluble phenolic resin had a solid content of 60 wt%. The above components were stirred at 70°C for 1 hour to obtain an impregnation solution with a solid content of approximately 33 wt%. The nascent composite paper base was impregnated in the impregnation solution for 3 minutes, removed, and squeezed with a pressure roller to control the resin coating amount to approximately 28 wt% of the dry paper mass. It was then pre-dried at 80°C for 10 minutes to a semi-dry state. Subsequently, the pre-dried nascent composite paper base was placed in a flatbed hot press and hot-pressed at 165°C and 4 MPa for 6 minutes to obtain a cured paper base.

[0073] Finally, the cured paper base was placed in a tube furnace and heated to 900°C at a rate of 2°C / min under nitrogen protection, and held at that temperature for 1 hour to obtain a pre-carbonized paper base. Subsequently, the pre-carbonized paper base was immersed in a mixed acid solution consisting of 2 mol / L hydrochloric acid and 0.5 mol / L nitric acid, and soaked at 70°C for 6 hours. After removal, it was washed with deionized water and the acid washing was repeated once. Then, it was washed with 0.05 mol / L EDTA solution at 60°C for 1 hour, washed with deionized water until neutral, and dried at 100°C. The dried sample was graphitized at 2500°C for 1 hour under argon protection to obtain the anisotropic carbon paper of Example 1.

[0074] Example 2: Preparation of anisotropic carbon paper using a nickel-plated carbon fiber template grown in the vapor phase.

[0075] The preparation process of Example 2 is basically the same as that of Example 1. The difference is that in Example 2, vapor-grown carbon fibers are used instead of multi-walled carbon nanotubes as the carbon core corresponding to the sacrificial magnetic permeability template to verify that the carbon core of the sacrificial magnetic permeability template can be replaced. The diameter of the vapor-grown carbon fibers is 120nm to 180nm and the length is 30μm to 60μm. The chemical nickel plating reaction time is 60min. The nickel content in the obtained nickel-plated vapor-grown carbon fibers is about 24wt%.

[0076] In Example 2, the dry-based formulation of the mixed slurry was: 94.0 parts of PAN-based chopped carbon fiber, 3.5 parts of nickel-plated vapor-grown carbon fiber, 2.0 parts of polyvinyl alcohol (PVA), 0.2 parts of anionic polyacrylamide (APAM), and 0.3 parts of sodium carboxymethyl cellulose (CMC). During the wet forming process, the applied constant magnetic field strength was 0.70T, and the magnetic field was maintained for 150s after dehydration. The remaining resin impregnation, hot-press curing, pre-carbonization, mixed acid denickelization, and high-temperature graphitization processes in Example 2 were the same as in Example 1. Example 2 demonstrates that the sacrificial magnetic template is not limited to nickel-plated multi-walled carbon nanotubes; nickel-plated vapor-grown carbon fibers can also be used to construct Z-axis oriented structures.

[0077] Example 3: Preparation of anisotropic carbon paper using composite magnetic permeability templates and lower magnetic field strength.

[0078] The preparation process of Example 3 is basically the same as that of Example 1. The difference is that Example 3 uses a composite magnetic permeable template and a lower magnetic field strength and a common alcohol-soluble phenolic resin system to verify that the sacrificial magnetic permeable template can be formed by compounding a variety of nickel-plated carbon materials, and the resin system and magnetic field conditions can be adjusted according to process requirements.

[0079] Specifically, in Example 3, the sacrificial magnetic template is composed of 1.5 parts of nickel-plated multi-walled carbon nanotubes and 1.0 part of nickel-plated chopped carbon fiber powder. The main body consists of 95.0 parts of chopped carbon fiber, 2.0 parts of polyvinyl alcohol (PVA), 0.2 parts of anionic polyacrylamide (APAM), and 0.3 parts of sodium carboxymethyl cellulose (CMC). The carbon core length of the nickel-plated chopped carbon fiber powder is 50 μm to 120 μm, the diameter is about 7 μm, and the nickel content is about 18 wt%. The magnetic field strength in the wet dehydration zone is set to 0.45 T, and the magnetic field is maintained for 120 s after dehydration. The resin impregnation solution uses a common alcohol-soluble phenolic resin / ethanol system with a solid content of 30 wt%, and no PVDF or propylene carbonate is added. The resin coating amount is 26 wt% of the dry paper mass. The hot pressing conditions are 170°C, 5 MPa, and 5 min. The pre-carbonization, denickelization, and high-temperature graphitization conditions in Example 3 are the same as in Example 1. Example 3 demonstrates that nickel-plated carbon materials of different sizes can be used in combination and can form a Z-axis oriented structure under a lower magnetic field strength.

[0080] Example 4: High-temperature vapor-phase halogenation denickelization route.

[0081] The preparation process of Example 4 is basically the same as that of Example 1. The difference is that the nickel removal process in Example 4 adopts a high-temperature gas phase halogenation process to verify that the nickel removal process is not limited to the mixed acid immersion process, and the nickel layer can also be removed by gas phase chlorination.

[0082] Specifically, the paper base pre-carbonized at 900℃ was placed in a corrosion-resistant high-temperature furnace, and a mixture of argon gas containing 2 vol% chlorine was introduced. The furnace was then kept at 850℃ for 1 hour to convert the nickel layer into nickel chloride, which migrated and was removed under the influence of the gas flow. Subsequently, the furnace was purged with pure argon gas for 1 hour and cooled to room temperature. To reduce residual chloride salts, the sample was soaked in 0.5 mol / L hydrochloric acid at room temperature for 1 hour and washed with deionized water until neutral. After drying at 100℃, the sample was subjected to a high-temperature graphitization treatment at 2500℃ for 1 hour to obtain the anisotropic carbon paper of Example 4. This route is suitable for continuous high-temperature processing equipment. When using this route, a tail gas absorption device and a safety interlock device can be set up to improve process safety.

[0083] To verify the technical effects of the embodiments of this disclosure, the samples obtained from Examples 1 to 4 and Comparative Examples 1 to 4 were tested. The test results are shown in Table 2. Among them, Comparative Example 1 is ordinary carbon paper without a Z-axis oriented conductive network, Comparative Example 2 is carbon paper with added nickel-plated multi-walled carbon nanotubes but without an applied external stable magnetic field, Comparative Example 3 is carbon paper without nickel removal treatment, and Comparative Example 4 is carbon paper with an excessive amount of sacrificial magnetic permeability template. The specific contents of Table 2 are as follows: Table 2 Test data for both examples and comparative examples sample Thickness (μm) Quantitative (g / m²) Porosity (%) Gurley (s / 100cc) In-plane resistivity (mΩ·cm) Area resistivity in the penetration direction (mΩ·cm²) Tensile strength (N / cm) Bending strength (MPa) Ni residue (ppm) Example 1 165 46.2 79.4 8.6 5.8 6.1 39.5 30.2 3.8 Example 2 172 47.8 77.6 9.4 6.2 5.8 42.1 32.8 4.6 Example 3 158 45.5 80.6 7.9 6.8 7.2 34.6 26.7 3.2 Example 4 168 46.9 78.2 8.9 5.9 6.4 38.8 29.5 2.8 Comparative Example 1 160 45.1 81.2 7.5 8.7 14.8 35.2 25.4 <1.0 Comparative Example 2 163 46.0 79.8 8.0 7.5 11.9 36.1 27.0 4.1 Comparative Example 3 166 46.4 78.9 8.7 5.6 5.9 39.0 29.8 4250 Comparative Example 4 181 51.3 68.5 18.6 5.1 5.3 37.4 28.2 5.5 The test results from Examples 1 to 4 and Comparative Example 1 show that, while maintaining a porosity of 77.6% to 80.6%, the area resistivity in the penetration direction of Examples 1 to 4 is 5.8 mΩ·cm² to 7.2 mΩ·cm², while that of Comparative Example 1 is 14.8 mΩ·cm². This demonstrates that by inducing the nickel-plated carbon materials to align and bridge each other along the Z-axis using an external steady magnetic field, an effective Z-axis oriented conductive network can be formed in the thickness direction of the carbon paper, thereby significantly improving the electron transport capability in the thickness direction.

[0084] The test results of Example 1 and Comparative Example 2 show that both Example 1 and Comparative Example 2 added nickel-plated multi-walled carbon nanotubes, but Comparative Example 2 did not apply an external steady magnetic field, and its area resistivity in the penetration direction was 11.9 mΩ·cm², which is significantly higher than that of Example 1 (6.1 mΩ·cm²). This indicates that the key to reducing the resistance in the Z-axis direction in this embodiment is not simply adding conductive fillers, but rather in inducing the nickel-plated carbon material to align along the Z-axis direction and form conductive bridges by applying an external steady magnetic field.

[0085] The test results of Example 1 and Comparative Example 3 show that Comparative Example 3, without nickel removal treatment, had a resistivity of 5.9 mΩ·cm² in the penetration direction, but the residual Ni was as high as 4250 ppm. Example 1, after nickel removal treatment, had a Ni residue reduced to 3.8 ppm while still maintaining a low resistivity in the penetration direction. This indicates that the nickel layer is suitable as a sacrificial magnetic template in the forming stage to participate in magnetic field-induced orientation, but it is not suitable as a functional metal to be retained long-term in the final carbon paper. Subsequent nickel removal treatment can maintain the conductivity in the Z-axis direction while reducing the impact of magnetic metal residue on the long-term operational reliability of the fuel cell.

[0086] The test results of Example 1 and Comparative Example 4 show that, in Comparative Example 4, due to the excessive addition of sacrificial magnetic template, although the resistivity in the penetration direction decreased to 5.3 mΩ·cm², the porosity decreased to 68.5%, and the Gurley permeability increased to 18.6 S / 100 cc. This indicates that excessive sacrificial magnetic template can easily cause pore blockage and reduce air permeability. Therefore, the amount of sacrificial magnetic template needs to be controlled within a reasonable range, preferably between 1.5 and 4 parts by mass, to improve the conductivity in the thickness direction while also considering the pore structure and mass transfer performance of the carbon paper.

[0087] In summary, Examples 1 to 4 demonstrate that the embodiments of this disclosure, through a continuous process of "sacrificial magnetic permeable template - external steady magnetic field induction - thermosetting resin locking - pre-carbonization, denickelization and high-temperature graphitization", can form a carbonaceous Z-axis oriented conductive network in anisotropic carbon paper, significantly reducing the area resistivity in the penetration direction. While maintaining high porosity and good air permeability, it effectively reduces magnetic metal residue, thereby improving the overall performance and long-term operational reliability of anisotropic carbon paper as a substrate material for fuel cell gas diffusion layers.

[0088] As described above, the technical solution disclosed herein utilizes a combined process of magnetic field-induced orientation, resin cross-linking and locking, and deep removal of sacrificial templates. During the wet forming stage, the magnetic response characteristics of nickel-plated carbon materials are used to orient the sacrificial magnetic templates along the thickness direction of the carbon paper and allow them to bridge each other, thereby constructing a conductive channel penetrating the Z-axis. This effectively improves the problems of insufficient conductive channels in the thickness direction and high resistance in the penetration direction of traditional carbon paper. Furthermore, this technical solution does not rely on the accumulation of a large amount of disordered conductive filler or excessive compaction of the carbon paper to reduce resistance. Instead, it uses a small number of oriented sacrificial magnetic templates to form effective conductive bridges. This helps to improve the conductivity in the Z-axis direction while maintaining the porosity, air permeability, and drainage performance of the carbon paper, thus alleviating the tension between improving conductivity and maintaining mass transfer performance. The present invention addresses the contradiction of the Z-axis orientation structure by impregnating it with thermosetting resin and hot-pressing it to reduce the risk of rebound, collapse or deflection of the orientation structure during subsequent processing such as transport, drying, carbonization and graphitization, thereby improving the structural stability of the directional conductive network. Furthermore, the present invention addresses the issue of nickel denicking and high-temperature graphitization, where nickel is used only as a sacrificial magnetic template in the forming stage to participate in the orientation construction. Ultimately, the carbon material after nickel denicking forms a carbon Z-axis directional conductive network, thereby reducing the risk of metal ion dissolution, proton membrane contamination, catalyst poisoning or membrane degradation caused by magnetic metal residues. This improves the overall performance and long-term operational reliability of the resulting anisotropic carbon paper as a substrate material for the gas diffusion layer of a proton exchange membrane fuel cell.

[0089] The above description is merely an embodiment of this disclosure and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of this disclosure is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the above-described concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features disclosed in this disclosure that have similar functions.

[0090] While specific embodiments of this disclosure have been described in detail by way of example, those skilled in the art should understand that the examples are for illustrative purposes only and not intended to limit the scope of this disclosure. Those skilled in the art should understand that modifications can be made to the above embodiments without departing from the scope and spirit of this disclosure. The scope of this disclosure is defined by the appended claims.

Claims

1. A method for preparing anisotropic carbon paper with a Z-axis oriented conductive network, characterized in that, The method includes: A mixed slurry is prepared; wherein the mixed slurry comprises chopped carbon fibers and a sacrificial magnetic permeable template, the sacrificial magnetic permeable template comprising a nickel-plated carbon material; The mixed slurry is placed in the dewatering and forming zone of a wet papermaking equipment, and an external steady magnetic field perpendicular to the paper surface is applied in the dewatering and forming zone to induce the nickel-plated carbon material to align and bridge each other along the Z-axis to form a Z-axis orientation structure, thereby obtaining a nascent composite paper base. The nascent composite paper base is impregnated with a thermosetting resin, and then the impregnated nascent composite paper base is hot-pressed and cured to lock the Z-axis orientation structure in the nascent composite paper base, thereby obtaining a cured paper base. The cured paper substrate is subjected to pre-carbonization treatment, nickel removal treatment and high-temperature graphitization treatment to obtain anisotropic carbon paper with a carbon Z-axis oriented conductive network.

2. The method according to claim 1, characterized in that, The nickel-plated carbon material is prepared by the following steps: The carbon core is subjected to acidification, cleaning and activation treatments to obtain the treated carbon core; A nickel-plated carbon material is obtained by coating the surface of the treated carbon core with a nickel layer using a chemical plating method.

3. The method according to claim 2, characterized in that, The carbon core includes one or more of the following: carbon nanofibers, single-walled carbon nanotubes, multi-walled carbon nanotubes, vapor-grown carbon fibers, and chopped carbon fiber powder.

4. The method according to claim 2, characterized in that, The electroless plating method uses an electroless nickel plating solution comprising nickel salts, a reducing agent, and a complexing agent; wherein the nickel salts comprise one or more of nickel sulfate hexahydrate and nickel chloride hexahydrate, the reducing agent comprises sodium hypophosphite monohydrate, and the complexing agent comprises one or more of sodium citrate, lactic acid, and sodium acetate.

5. The method according to claim 1, characterized in that, The mixed slurry further includes a temporary binder and a dispersant; wherein the temporary binder includes one or more of polyvinyl alcohol, acrylic emulsion and phenolic emulsion, and the dispersant includes one or more of anionic polyacrylamide, polyethylene oxide and sodium carboxymethyl cellulose.

6. The method according to claim 1, characterized in that, The external steady magnetic field is used to overcome the effects of gravity and flow field shearing on the mixed slurry during the dehydration process, so that the nickel-plated carbon material is transformed from a random distribution in the XY plane to an ordered arrangement along the Z-axis.

7. The method according to claim 6, characterized in that, The application of an external, stable magnetic field perpendicular to the paper surface in the dehydration and forming zone includes: An external steady magnetic field is applied during the dewatering process of the mixed slurry, and the external steady magnetic field is maintained after dewatering is completed; wherein the magnetic field strength of the external steady magnetic field is 0.45T to 0.70T, and the external steady magnetic field is maintained for 60s to 180s after dewatering is completed.

8. The method according to claim 5, characterized in that, The nickel-plated carbon material includes a carbon core and a nickel layer covering the surface of the carbon core; based on the mass of solid components in the mixed slurry, the chopped carbon fibers are 80 to 98 parts by mass, the carbon core is 0.5 to 8 parts by mass, the temporary binder is 1 to 8 parts by mass, and the dispersant is 0.02 to 0.8 parts by mass.

9. The method according to claim 1, characterized in that, The thermosetting resin includes one or more of alcohol-soluble phenolic resin, furan resin, and epoxy-modified phenolic resin; the solid content of the impregnation liquid corresponding to the thermosetting resin is 10wt% to 45wt%.

10. The method according to claim 9, characterized in that, The impregnation liquid corresponding to the thermosetting resin further includes a resin modifier; the resin modifier includes polyvinylidene fluoride and propylene carbonate; or, the resin modifier includes polyvinylidene fluoride, propylene carbonate, and at least one selected from ethylene carbonate and dimethyl carbonate; wherein the mass of the resin modifier is 5 wt% to 30 wt% of the solid mass of the resin in the thermosetting resin.

11. The method according to claim 1, characterized in that, The nickel removal process includes a mixed acid immersion process; the mixed acid immersion process includes: placing the pre-carbonized paper base formed after the pre-carbonization treatment into a nickel removal acid solution, so that the nickel layer on the surface of the nickel-plated carbon material is converted into a soluble salt and washed off; wherein, the nickel removal acid solution includes hydrochloric acid and nitric acid.

12. The method according to claim 11, characterized in that, The nickel removal process further includes: after the pre-carbonized paper base is subjected to the mixed acid soaking process, the pre-carbonized paper base treated by the mixed acid soaking process is cleaned with a complexing cleaning solution; wherein the complexing cleaning solution includes an ethylenediaminetetraacetic acid solution.

13. The method according to claim 1, characterized in that, The nickel removal process includes a high-temperature vapor phase halogenation process; the high-temperature vapor phase halogenation process includes: placing the pre-carbonized paper base formed after the pre-carbonization treatment in an inert gas mixed atmosphere containing chlorine, so that the nickel layer on the surface of the nickel-plated carbon material is converted into nickel chloride and removed.

14. The method according to claim 1, characterized in that, The pre-carbonization treatment is carried out in a protective gas atmosphere to convert the thermosetting resin into resin carbon and fix the Z-axis orientation structure; the high-temperature graphitization treatment is carried out in a protective gas atmosphere to form the carbonaceous Z-axis oriented conductive network; wherein the protective gas includes one of nitrogen, argon and nitrogen-argon mixture.

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