N-doped porous flexible carbon paper and its preparation method and application

Abstract

The present invention provides an N-doped porous flexible carbon paper and its preparation method and application. The N-doped porous flexible carbon paper of the present invention is prepared from poly (p-phenylene benzobisoxazole) fibers, the carbon paper has a layered structure, the nitrogen content in the carbon paper is ≥5.4wt%, and the specific surface area of ​​the carbon paper is ≥450m 2 / g, an average pore size of 1μm to 3μm, and a tensile strength of ≥0.12MPa. The N-doped porous flexible carbon paper of the present invention has excellent flexibility, a high nitrogen content, a suitable specific surface area, and a layered fiber structure. It can be used as a cathode material for flexible zinc-air batteries, capable of fixing active catalysts and preventing charge and discharge termination in flexible zinc-air batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-performance fibers and products and composite materials, and particularly relates to an N-doped porous flexible carbon paper and a preparation method and application thereof. Background Art

[0002] As traditional fossil fuels fail to meet human needs, energy storage and conversion technologies, such as metal-air batteries and fuel cells, are gaining increasing attention. Electrocatalytic oxygen reduction (ORR) is a crucial reaction in energy conversion technology, but its complex multi-step electron transfer pathways result in slow kinetics and significant energy losses.

[0003] The air cathode is a key component in zinc-air batteries, where the oxygen reduction reaction (ORR) reaction occurs. Consequently, much research has focused on the preparation of this electrode, including cathode structural design, the creation of a highly stable interface, and the development of catalysts. Functionally, the cathode of a flexible zinc-air battery consists of a current collector, an air diffusion layer, and a catalyst. These three components serve, respectively, as charge transport, oxygen transfer, and lowering the reaction energy barrier. Appropriate hydrophilicity and hydrophobicity on different sides of the cathode are also crucial for battery stability. A qualified flexible cathode should possess the following characteristics: 1. Excellent conductivity to facilitate charge transfer; 2. Appropriate porosity to ensure optimal O2 diffusion; 3. Good bifunctional catalysis to enhance ORR efficiency; and 4. Appropriate hydrophilicity and hydrophobicity to form a stable three-phase interface. Given these requirements, it is essential to design an air cathode material that exhibits good conductivity, high chemical and electrochemical stability, high gas permeability, and a certain degree of flexibility.

[0004] Carbon-based materials are widely available, have strong design capabilities, are lightweight, have strong hydrophobicity, and have adjustable surface affinity, which can well meet the requirements of flexible zinc-air batteries. With a wide range of structural design possibilities, carbon-based materials have advantages in flexible battery design.

[0005] At present, the carbon-based cathode materials of flexible zinc-air batteries still face many problems. The most important problem is their stability in use. Under charging conditions, deformation conditions and stress introduction conditions, the active catalyst will separate from the carbon-based material. Designing materials rich in micro-mesoporous materials can well fix the active catalyst. The natural high porosity and surface area of ​​carbon paper are not always suitable for three-phase reactions. Although the high surface area ensures the active sites for ORR, the bubble oxygen may accumulate in the pores with a relatively small volume and size, resulting in charge and discharge termination due to blockage.

[0006] Prior art discloses a method for preparing aramid-based carbon fibers. This method involves carbonizing aramid fibers in an atmosphere containing ammonia to produce nitrogen-doped aramid-based porous carbon fibers with a hierarchical pore structure. These fibers exhibit stable tensile strength and high mechanical strength. However, the resulting aramid paper samples are not suitable for bending and other experiments and exhibit poor flexibility. Summary of the Invention

[0007] The purpose of the present invention is to solve the defects and shortcomings of poor flexibility of existing aramid-based carbon fibers and to provide an N-doped porous flexible carbon paper with good flexibility.

[0008] Another object of the present invention is to provide a method for preparing N-doped porous flexible carbon paper.

[0009] Another object of the present invention is to provide an application of N-doped porous flexible carbon paper in the preparation of zinc-air battery cathode materials.

[0010] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0011] A N-doped porous flexible carbon paper is prepared from poly(p-phenylene benzobisoxazole) fibers, wherein the carbon paper has a layered structure, wherein the nitrogen content in the carbon paper is ≥5.4 wt%, and the specific surface area of ​​the carbon paper is ≥450 m 2 / g, average pore size is 1μm~3μm, and tensile strength is ≥0.12MPa.

[0012] The N-doped porous flexible carbon paper of the present invention is prepared from poly(p-phenylene benzobisoxazole) fibers, can be bent, and has good flexibility and suitable tensile strength.

[0013] The N-doped porous flexible carbon paper of the present invention can be used as a carbon-based cathode material for flexible zinc-air batteries, solving the problem that the specific surface area and porosity of existing carbon-based cathode materials for flexible zinc-air batteries are not suitable and active catalysts cannot be fixed. The N-doped porous flexible carbon paper of the present invention can solve the phenomenon of catalyst agglomeration and has good dispersibility for Pt, thereby increasing the reaction active area, and is an excellent catalyst carrier.

[0014] The N-doped porous flexible carbon paper of the present invention can be used as the cathode material of the zinc-air battery. Constructing a gas diffusion channel in the cathode material can properly solve the technical problem of fixing the active catalyst and preventing the termination of charge and discharge of the flexible zinc-air battery.

[0015] The N-doped porous flexible carbon paper of the present invention has a high nitrogen content, a suitable specific surface area, and a layered fiber structure, capable of immobilizing active catalysts and preventing charge and discharge termination in flexible zinc-air batteries. This is because the electronic structure and electronegativity of the carbon paper undergo a certain degree of change after N-doping, resulting in a significant improvement in catalytic activity. Furthermore, the N-doped carbon paper of the present invention forms further chemical bonds with the catalyst, thereby inhibiting catalyst aggregation, improving catalyst dispersion, and increasing the catalyst's reactive surface area.

[0016] The carbon paper of the present invention has a porous structure, which can improve the dispersion effect of the catalyst and prevent the catalyst from aggregating on the carbon paper to cause a reduction in the reaction active area of ​​the catalyst.

[0017] When the carbon paper of the present invention is used as the cathode material for zinc-air batteries, if the specific surface area of ​​the carbon paper is too large, it may lead to excessive micropores on the carbon paper. After loading the catalyst and performing high-temperature thermal reduction, the micropores may close, thereby encapsulating the catalyst within the carbon paper, preventing the catalyst from contacting the reactants and forming an ineffective catalyst. If the specific surface area of ​​the carbon paper is too small, the carbon paper will have too little catalyst loaded on it and easily cause the catalyst to aggregate, resulting in reduced catalytic efficiency.

[0018] A higher tensile strength is beneficial to the stability of the carbon paper. A lower tensile strength will reduce the stability of the carbon paper and make it less durable.

[0019] Preferably, the carbon paper has a nitrogen content of 6 to 8 wt %, and a specific surface area of ​​480 to 700 m 2 / g, and the average pore size is 1.0μm~2μm.

[0020] More preferably, the carbon paper has a nitrogen content of 6.5 to 8 wt %, and a specific surface area of ​​480 to 500 m 2 / g, and the average pore size is 1.5μm to 1.8μm.

[0021] Preferably, the carbon paper includes micropores and mesopores, the pore diameter of the micropores is less than 2 nm; and the pore diameter of the mesopores is 2 to 50 nm.

[0022] The present invention also protects a method for preparing N-doped porous flexible carbon paper, comprising the following steps:

[0023] S1. Preparation of poly(p-phenylene benzobisoxazole) fiber pulp paper: poly(p-phenylene benzobisoxazole) fiber raw materials were sequentially beaten, papermaking and dried to obtain poly(p-phenylene benzobisoxazole) fiber pulp paper;

[0024] S2. Preparation of poly(p-phenylene benzobisoxazole) fiber carbon paper: The poly(p-phenylene benzobisoxazole) fiber pulp paper obtained in step S1 was physically activated in CO2 and high-temperature activated at 850 to 950 ° C for 1 to 2 h to obtain poly(p-phenylene benzobisoxazole) fiber carbon paper;

[0025] Preparation of S3.N-doped porous flexible carbon paper

[0026] S31. The flexible carbon paper prepared in S2 was immersed in a dicyandiamide solution for 4 to 8 hours and then dried;

[0027] S32. The paper obtained in S31 was physically activated in CO2 and high-temperature activated at 850-950°C for 1-2h to obtain N-doped porous flexible carbon paper;

[0028] In step S1 , the beating degree of the poly(p-phenylene benzobisoxazole) fiber raw material is 29-40° SR.

[0029] The poly(p-phenylene benzobisoxazole) fiber pulp paper has a three-dimensional pore structure formed by non-directional accumulation of poly(p-phenylene benzobisoxazole) fiber pulp.

[0030] In step S32 of the present invention, carbon dioxide reacts with carbon under high temperature conditions to generate carbon monoxide, thereby etching the carbon paper. The activation effect of the carbon dioxide is utilized to form a pore structure.

[0031] The invention uses poly (p-phenylene benzobisoxazole) fiber as a carbon source, dicyandiamide as a nitrogen source, and carbonizes, activates and nitrogen-dopes poly (p-phenylene benzobisoxazole) fiber pulp paper to prepare N-doped porous flexible carbon paper.

[0032] The present invention utilizes the good conductivity of carbon paper, a large number of mesopores provided by physical activation, and high active sites provided by N doping to obtain a flexible zinc-air battery cathode material with superior performance.

[0033] Preferably, the beating degree in step S1 is 25-35° SR. The purpose of beating is to fibrillate the poly(p-phenylene benzobisoxazole) fibers. Within the beating degree range of the present invention, the poly(p-phenylene benzobisoxazole) fibers in the prepared N-doped porous flexible carbon paper can be ensured to have a diameter of 100 nm to 5 μm.

[0034] Preferably, the papermaking in step S1. is oblique mesh papermaking.

[0035] Preferably, the flow rate of the papermaking channel in step S1 is 120 to 180 m 3 / h; more preferably 150 to 180m 3 / h.

[0036] Preferably, the drying in step S1. is performed at 100-150° C. until the moisture content of the poly(p-phenylene benzobisoxazole) fiber pulp paper is 1-5 wt %.

[0037] Preferably, the physical activation in step S2. is a high-temperature activation at 700-900°C for 1-2 hours at a CO2 flow rate of 100-200 mL / min, and more preferably a high-temperature activation time of 1-1.5 hours at a CO2 flow rate of 120-150 mL / min.

[0038] More preferably, in step S2., the CO2 flow rate is 120 to 200 mL / min.

[0039] Preferably, the physical activation in step S2 is carried out in two stages: first, the temperature is raised to 300-600°C at a rate of 2-8°C / min and maintained for 1-2 hours; then, the temperature is raised to 700-900°C at a rate of 5-10°C / min and maintained for 1-2 hours.

[0040] Preferably, in step S1, the basis weight of the poly(p-phenylene benzobisoxazole) fiber pulp paper is 50 to 80 g / m 2 .

[0041] Preferably, the concentration of the dicyandiamide solution in step S31 is 3 wt % to a saturated solution.

[0042] The present invention mainly controls the nitrogen doping amount by adjusting the concentration of the dicyandiamide solution.

[0043] Preferably, the drying temperature in step S31 is 105-120°C.

[0044] Preferably, the physical activation in step S32 is performed at a high temperature of 700-900°C for 1-2 hours at a CO2 flow rate of 100-200 mL / min, and more preferably at a CO2 flow rate of 120-150 mL / min and a high temperature activation time of 1-1.5 hours.

[0045] More preferably, in step S32, the carbon dioxide flow rate is 120-200 mL / min.

[0046] Preferably, the physical activation in step S32 is carried out in two stages. First, the temperature is raised to 300-600°C at a rate of 2-8°C / min and maintained for 1-2 hours; then the temperature is raised to 700-900°C at a rate of 5-10°C / min and maintained for 1-2 hours.

[0047] The application of the above-mentioned N-doped porous flexible carbon paper in flexible zinc-air batteries is also within the protection scope of the present invention.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] The present invention discloses an N-doped porous flexible carbon paper, which is prepared from poly(p-phenylene benzobisoxazole) fibers. The carbon paper has a layered structure, a nitrogen content of ≥5.4wt%, and a specific surface area of ​​≥450m 2 / g, an average pore size of 1μm to 3μm, and a tensile strength of ≥0.12MPa. The N-doped porous flexible carbon paper of the present invention has excellent flexibility, a high nitrogen content, a suitable specific surface area, and a layered fiber structure. It can be used as a cathode material for flexible zinc-air batteries, capable of fixing active catalysts and preventing charge and discharge termination in flexible zinc-air batteries.

[0050] The present invention designs the chemical composition and morphological structure of the flexible zinc-air battery electrode to prepare a porous N-doped carbon paper using poly(p-phenylene benzobisoxazole) fiber as a precursor. The precursor contains both a carbon source and a nitrogen source. After physical activation and impregnation with dicyandiamide as a nitrogen source, the obtained material has a three-dimensional pore structure and has the advantages of a high specific surface area, a high nitrogen content, and a layered structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is a schematic structural diagram of the N-doped porous flexible carbon paper prepared in Example 1 of the present invention.

[0052] Figure 2 This is a cross-sectional view of the N-doped porous flexible carbon paper in Example 1.

[0053] Figure 3 This is an electron microscope image of the N-doped porous flexible carbon paper in Example 1.

[0054] Figure 4 This is a physical picture of the flexible carbon paper prepared in Example 3.

[0055] Figure 5 TEM image of Pt loaded on flexible carbon paper prepared in Example 3.

[0056] Figure 6 This is a pore size distribution diagram of the N-doped porous flexible carbon paper prepared in Example 1 of the present invention.

[0057] Figure 7 These are the test results of the specific surface area of ​​the N-doped porous flexible carbon paper prepared by Examples 1 and 2 of the present invention. DETAILED DESCRIPTION

[0058] The present invention will be further described below with reference to specific examples and accompanying drawings, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0059] Unless otherwise specified, all reagents and materials used in the present invention are commercially available.

[0060] Example 1

[0061] In this embodiment, an N-doped porous flexible carbon paper is prepared according to a method comprising the following steps:

[0062] S1. Preparation of poly(p-phenylene benzobisoxazole) fiber pulp paper

[0063] 80g of poly(p-phenylene benzobisoxazole) fiber was added with water in a fiber deflaking machine to a fiber concentration of 0.4wt%, and after uniform dispersion, it was diluted with a slurry pump to a fiber concentration of 0.04wt%, and beaten to obtain a poly(p-phenylene benzobisoxazole) fiber slurry with a beating degree of 29°SR; the obtained poly(p-phenylene benzobisoxazole) fiber slurry was placed on an inclined wire papermaking machine at 150m 3 / h flow rate after sheeting forming and dehydration to obtain wet paper sheet, dried at 130 ° C to obtain dry paper sheet (water content of 10wt%), the dry paper sheet is dried at 120 ° C for 3 hours to a water content of 1-5wt%, and the poly (p-phenylene benzobisoxazole) fiber pulp paper is obtained, wherein the basis weight of the poly (p-phenylene benzobisoxazole) fiber pulp paper is 80g / m 2 ;

[0064] S2. Preparation of Flexible Carbon Paper

[0065] The poly(p-phenylene benzobisoxazole) fiber pulp paper obtained in S1. was kept at 600°C for 1 h under N2 gas conditions with a flow rate of 120 ml / min and a heating rate of 5°C / min; then it was subjected to high-temperature physical activation at 900°C for 1 h under CO2 gas conditions with a flow rate of 120 ml / min and a heating rate of 5°C / min. After the cooling was completed, flexible carbon paper was obtained.

[0066] Preparation of S3.N-doped porous flexible carbon paper

[0067] S31. Immerse the flexible carbon paper obtained in S2. in a 4 wt% dicyandiamide solution for 6 h, and then dry it at 120° C. for 4 h to obtain dicyandiamide-impregnated carbon paper.

[0068] S32. The carbon paper dried in S31. was kept at 600°C for 1 h under N2 gas conditions with a flow rate of 120 ml / min and a heating rate of 5°C / min; then, it was subjected to high-temperature physical activation at 900°C for 1 h under CO2 gas conditions with a flow rate of 120 ml / min and a heating rate of 5°C / min. After the cooling was completed, N-doped porous flexible carbon paper was obtained.

[0069] Example 2

[0070] This embodiment prepares an N-doped porous flexible carbon paper, which differs from the embodiment 1 in that:

[0071] S1. Preparation of poly(p-phenylene benzobisoxazole) fiber pulp paper

[0072] 50g of poly(p-phenylene benzobisoxazole) fiber was added with water in a fiber deflaking machine to a fiber concentration of 0.4wt%, wherein the basis weight of the poly(p-phenylene benzobisoxazole) fiber pulp paper was 50g / m 2 .

[0073] The rest is the same as in Example 1 and will not be described again here.

[0074] Example 3

[0075] This embodiment provides an N-doped porous flexible carbon paper, which is different from Embodiment 1 in that, in step S31 , the flexible carbon paper is immersed in a saturated dicyandiamide solution.

[0076] The rest is the same as in Example 1 and will not be described again here.

[0077] Example 4

[0078] This embodiment provides an N-doped porous flexible carbon paper, which is different from Embodiment 1 in that in steps S2 and S32, the carbon dioxide flow rate is 200 mL / min.

[0079] The rest is the same as in Example 1 and will not be described again here.

[0080] Example 5

[0081] This embodiment provides an N-doped porous flexible carbon paper, which is different from Example 2 in that in steps S2 and S32, the carbon dioxide flow rate is 200 mL / min.

[0082] The rest is the same as in Example 1 and will not be described again here.

[0083] Comparative Example 1

[0084] This embodiment prepares an N-doped porous flexible carbon paper, which differs from Example 1 in that:

[0085] S32. The carbon paper dried in S31 is carbonized at 900°C for 1 h under N2 gas conditions with a flow rate of 120 ml / min and a heating rate of 5°C / min. After cooling, N-doped porous flexible carbon paper can be obtained.

[0086] The rest is the same as in Example 1 and will not be described again here.

[0087] Comparative Example 2

[0088] In this embodiment, an N-doped porous flexible carbon paper is prepared according to a method comprising the following steps:

[0089] The difference from Example 3 is:

[0090] S32. The carbon paper dried in S31 is carbonized at 900°C for 1 h under N2 gas conditions with a flow rate of 120 ml / min and a heating rate of 5°C / min. After cooling, N-doped porous flexible carbon paper can be obtained.

[0091] The rest is the same as in Example 3 and will not be described again here.

[0092] Comparative Example 3

[0093] This comparative example provides a porous flexible carbon paper, which is different from Example 1 in that no dicyandiamide impregnation is performed.

[0094] Comparative Example 4

[0095] This comparative example provides an N-doped porous flexible carbon paper, which is different from Example 1 in that, in step S1, the beating degree of the poly(p-phenylene benzobisoxazole) fiber pulp is 45° SR.

[0096] Comparative Example 5

[0097] This comparative example provides an N-doped porous flexible carbon paper, which is different from Example 2 in that, in step S1, the beating degree of the poly(p-phenylene benzobisoxazole) fiber pulp is 45° SR.

[0098] Comparative Example 6

[0099] This comparative example provides an N-doped porous carbon paper, which is different from Example 1 in that, in step S2, the poly(p-phenylene benzobisoxazole) fiber pulp is replaced with para-aramid pulp.

[0100] Comparative Example 7

[0101] This comparative example provides an N-doped porous flexible carbon paper, which is different from Example 1 in that in steps S2 and S32, the activation temperature is 800°C.

[0102] Comparative Example 8

[0103] This comparative example provides an N-doped porous flexible carbon paper, which is different from Example 1 in that it is immersed in ammonia water.

[0104] Performance Testing

[0105] The structure and performance of the carbon paper prepared in the above examples and comparative examples were tested. The specific test contents and results are as follows:

[0106] 1. Maximum pore size of flexible carbon paper: The pore size of N-doped porous flexible carbon paper was measured using a PMI pore size analyzer. The test results are detailed in Tables 1, 2, and Figure 5 ;

[0107] 2. Flexible Carbon Paper Tensile Strength The tensile strength of the N-doped porous flexible carbon paper prepared in the Examples and Comparative Examples was tested in accordance with GB / T 3690-2017.

[0108] 3. Specific surface area of ​​flexible carbon paper: The specific surface area of ​​the N-doped porous flexible carbon paper prepared in the examples and comparative examples was tested using a Micromeritics ASAP 2460 instrument. The test results are detailed in Table 1 and Figure 6 ;

[0109] 4. Appearance morphology and pore structure of flexible carbon paper: Scanning electron microscopy (SEM) was used to test and analyze the appearance morphology and pore structure of N-doped porous flexible carbon paper. The test results are detailed in Figure 3 and Figure 4 ;

[0110] 5. Nitrogen content of flexible carbon paper: The nitrogen content in the nitrogen-doped porous flexible carbon paper was determined using an elemental analyzer.

[0111] 6. Electrochemical performance test:

[0112] Table 1 is the test results of carbon paper in various embodiments

[0113] Performance Testing Example 1 Example 2 Example 3 Example 4 Example 5 N content (wt%) 6.56 7.68 7.67 6.21 7.67 <![CDATA[Specific surface area (m 2 / g)]]> 521.6 518.4 548.6 612.2 497.8 Average pore size of carbon paper (μm) 1.7 1.46 1.73 1.82 1.73 Tensile strength (MPa) 0.2 0.27 0.18 0.19 0.24 Maximum pore size of carbon paper (μm) 10.65 8.35 10.24 11.25 10.24

[0114] Table 2 is the test results of carbon paper of each comparative example

[0115]

[0116]

[0117] From the results in Table 1 and Table 2, we can see that:

[0118] As can be seen from the examples and comparative examples 1 and 2, in step S32, the use of nitrogen and carbon dioxide for physical activation is too infrequent, resulting in a low specific surface area for the resulting carbon paper. This is because nitrogen cannot activate carbon paper; in a nitrogen atmosphere, it only carbonizes the paper without increasing its specific surface area. In contrast, the carbon dioxide used in the examples has an activating effect. Under high temperature conditions, carbon dioxide reacts with carbon to form carbon monoxide, which etches the carbon paper and forms a porous structure.

[0119] It can be seen from Comparative Example 3 that without dicyandiamide impregnation, the N content in the obtained carbon paper is too low, making it difficult to form further chemical bonds with the catalyst, unable to inhibit the aggregation of the catalyst, and the catalyst dispersion effect is poor, which will significantly reduce the reaction active area of ​​the catalyst.

[0120] It can be seen from Comparative Examples 4 and 5 that the beating degree of the poly(p-phenylene benzobisoxazole) fiber pulp is 45°SR, which results in an excessively small specific surface area.

[0121] Comparative Example 6 shows that the tensile strength cannot be measured when the poly(p-phenylene benzobisoxazole) fiber pulp is replaced with para-aramid pulp, indicating that the tensile strength is too low. In addition, the carbon paper prepared with para-aramid pulp has poor flexibility and flatness.

[0122] As can be seen from Comparative Example 7, in steps S2 and S32, if the activation temperature is too low, the specific surface area of ​​the carbon paper will be too low, which will easily lead to too little catalyst loaded on the carbon paper and catalyst aggregation, resulting in reduced catalytic efficiency.

[0123] It can be seen from Comparative Example 8 that the use of ammonia water for impregnation results in a lower N content.

[0124] Figure 1 This is a schematic diagram of the structure of the N-doped porous flexible carbon paper prepared in Example 1 of the present invention. Figure 1 It can be seen that N is doped into the carbon skeleton.

[0125] Figure 2 : is a cross-sectional view of the N-doped porous flexible carbon paper in Example 1. Figure 2 It can be seen that the N-doped porous flexible carbon paper in Example 1 has a layered structure.

[0126] Figure 3 This is an electron microscope image of the N-doped porous flexible carbon paper in Example 1. It can be seen that the porous flexible carbon paper prepared by the present invention is a three-dimensional disordered structure composed of many randomly arranged fibers of different thicknesses, and has a complex pore structure.

[0127] Figure 4 This is a physical picture of the flexible carbon paper prepared in Example 3, which shows that the prepared carbon paper has good flexibility and can be used for experiments such as bending.

[0128] Figure 5 This is a TEM image of the flexible carbon paper loaded with Pt prepared in Example 3. It can be seen that Pt is evenly distributed on the flexible carbon paper and does not agglomerate.

[0129] Figure 6 This is the pore size distribution diagram of the N-doped porous flexible carbon paper prepared in Example 1 of the present invention. Figure 6 It can be seen that the pore sizes of N-doped porous flexible carbon paper are mostly distributed around 1-3 μm, and the pore size distribution range is wide, which is conducive to gas diffusion.

[0130] Figure 7 The test results of the specific surface area of ​​N-doped porous flexible carbon paper prepared by Example 1 and Example 2 of the present invention are as follows. Figure 7It can be seen that the prepared carbon paper isotherms show an obvious combination of type I and type IV isotherms, that is, at the relative pressure p / p o When the relative pressure is between 0 and 0.1, the adsorption curve of the tip increases sharply, indicating the presence of a microporous structure. o The type IV isotherm with a visible hysteresis cycle in the range of 0.4 to 1 indicates that the carbon paper contains mesopores. Therefore, the prepared material contains a rich micro-mesoporous structure, which can effectively promote the rapid diffusion of ions and the rapid transfer of substances.

[0131] In the embodiment of the present invention, the tensile stress of the N-doped porous flexible carbon paper is greater than or equal to 0.12 MPa, which is more conducive to the durability of the carbon paper and the structure of the carbon paper is more stable.

[0132] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method 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 should be included in the scope of protection of the present invention.

Claims

1. An N-doped porous flexible carbon paper for zinc-air battery cathode material, characterized in that: The carbon paper is made of poly (p-phenylene benzobisoxazole) fiber, and has a layered structure. The nitrogen content of the carbon paper is ≥5.4wt%, and the specific surface area of ​​the carbon paper is ≥450m 2 / g, average pore size of 1μm to 3μm, tensile strength ≥0.12MPa; The preparation method of the N-doped porous flexible carbon paper comprises the following steps: S1. Preparation of poly(p-phenylene benzobisoxazole) fiber pulp paper: poly(p-phenylene benzobisoxazole) fiber raw materials were sequentially beaten, papermaking and dried to obtain poly(p-phenylene benzobisoxazole) fiber pulp paper; S2. Preparation of poly(p-phenylene benzobisoxazole) fiber carbon paper: The poly(p-phenylene benzobisoxazole) fiber pulp paper obtained in step S1 was physically activated in CO2 and high-temperature activated at 850 to 950 ° C for 1 to 2 h; obtaining poly(p-phenylene benzobisoxazole) fiber carbon paper; Preparation of S3.N-doped porous flexible carbon paper: S31. The carbon paper obtained in S2 was soaked in a dicyandiamide solution for 4 to 8 hours and dried; S32. The paper obtained in S31 was physically activated in CO2 and high-temperature activated at 850-950°C for 1-2h to obtain N-doped porous flexible carbon paper; In step S1 , the beating degree of the poly(p-phenylene benzobisoxazole) fiber raw material is 25-35° SR.

2. The N-doped porous flexible carbon paper according to claim 1, characterized in that: The carbon paper has a nitrogen content of 6 to 8 wt %, and a specific surface area of ​​480 to 700 m 2 / g, and the average pore size is 1.0μm~2μm.

3. The N-doped porous flexible carbon paper according to claim 1, characterized in that: The carbon paper has a nitrogen content of 6.5 to 8 wt %, and a specific surface area of ​​480 to 550 m 2 / g, and the average pore size is 1.5μm to 1.8μm.

4. The N-doped porous flexible carbon paper according to claim 1, characterized in that: The carbon paper comprises micropores and mesopores, wherein the pore diameter of the micropores is less than 2 nm, and the pore diameter of the mesopores is 2 to 50 nm.

5. The N-doped porous flexible carbon paper according to claim 1, characterized in that: In step S1, the basis weight of the poly(p-phenylene benzobisoxazole) fiber pulp paper is 50 to 80 g / m 2 .

6. The N-doped porous flexible carbon paper according to claim 1, characterized in that: In step S31, the mass concentration of the dicyandiamide solution is 3 wt % to a saturated solution.

7. The N-doped porous flexible carbon paper according to claim 1, characterized in that: In step S2, the flow rate of carbon dioxide is 120-200 mL / min.

8. The N-doped porous flexible carbon paper according to claim 1, characterized in that: In step S32, the flow rate of carbon dioxide is 120-200 mL / min.

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