Method for preparing forest processing residue-based nitrogen and phosphorus co-doped carbon aerogel ORR catalyst based on joule heating flash evaporation technology

Abstract

The present application relates to a method for preparing a forest processing residue-based nitrogen and phosphorus co-doped carbon aerogel ORR catalyst based on a Joule heat flash evaporation technique, which comprises the following steps in sequence: forest processing residue pretreatment, ternary eutectic solvent preparation, forest processing residue-based cellulose extraction, cellulose-phosphoric acid sol preparation, nitrogen and phosphorus co-doped carbon aerogel precursor preparation, Joule heat rapid carbonization and post-treatment, so as to obtain a forest processing residue-based nitrogen and phosphorus co-doped carbon aerogel ORR catalyst. The present application effectively realizes high-value utilization of agricultural and forestry solid waste, and can prepare a special ORR electrocatalyst which is free of noble metals, has high activity, long service life, low energy consumption and strong adaptability.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalysis technology, and specifically relates to a method for preparing nitrogen-phosphorus co-doped carbon aerogel ORR catalyst based on forestry processing residues using Joule thermal flash evaporation technology, which is particularly suitable for proton exchange membrane fuel cells and alkaline fuel cell cathode oxygen reduction reaction scenarios. Background Technology

[0002] The oxygen reduction reaction (ORR) is the core reaction at the cathode of a fuel cell. Its kinetic rate is slow, requiring a highly active electrocatalyst to accelerate the reaction. Existing ORR catalysts heavily rely on 20wt% Pt / C noble metal catalysts. However, these noble metal catalysts suffer from key drawbacks such as high cost, scarcity of reserves, poor stability, and susceptibility to methanol permeation poisoning, which severely restrict the large-scale commercialization of fuel cells.

[0003] Biomass carbon materials, due to their renewable raw materials, abundant porous structure, tunable electronic conductivity, and environmental friendliness, have become ideal ORR catalytic supports to replace precious metals. The current research and development bottlenecks of biomass-based oxygen reduction reaction (ORR) catalysts mainly involve five core problems: limited raw material sources, low activity, poor stability, high energy consumption in preparation, and insufficient morphological adaptability. Specifically: Single source of raw materials and low utilization rate of solid waste: Existing research is mostly limited to specific single biomass raw materials such as cotton stalks and eucalyptus wood. However, a large amount of residues generated from forestry processing (such as sawdust, branches and bark) have not yet been efficiently converted and utilized for high value, resulting in serious waste of resources.

[0004] 2. Poor stability: Traditional acid-base cooking and binary eutectic solvent (DES) pretreatment methods are difficult to completely remove lignin and hemicellulose, resulting in low cellulose extraction rate. As a result, carbon materials prepared in this way generally have many skeletal defects and insufficient exposure of heteroatom active sites, leading to poor long-term stability of the materials.

[0005] 3. Low activity: Currently, most are dominated by single nitrogen doping, which makes it difficult to form efficient and synergistic ORR active sites, thus limiting the further improvement of catalytic activity.

[0006] 4. High energy consumption in preparation: It relies on traditional tube furnaces for long-term pyrolysis, which is slow to heat up and takes several hours. This can easily lead to the collapse of carbon channels, a significant decrease in specific surface area, and poor ORR mass transfer and charge transport efficiency.

[0007] 5. Insufficient morphological adaptability: Traditional products are mostly in the form of powder or ordinary nanosheet structure, lacking a self-supporting structure with three-dimensional through-pores. This insufficient morphological adaptability leads to a long oxygen diffusion path and poor electrolyte wettability, ultimately resulting in a low ORR limiting current density and failure to meet long-term cycling stability. Summary of the Invention

[0008] The technical problem to be solved by this invention is to overcome the above-mentioned defects of the prior art and provide a method for preparing nitrogen-phosphorus co-doped carbon aerogel ORR catalysts based on forestry processing residues using Joule thermal flash evaporation technology. This method effectively realizes the high-value utilization of agricultural and forestry solid waste and can prepare specialized ORR electrocatalysts that are free of precious metals, highly active, long-lived, low-energy, and highly adaptable.

[0009] This invention is achieved through the following technical solution: A method for preparing nitrogen-phosphorus co-doped carbon aerogel ORR catalyst based on forest processing residues using Joule thermal flash evaporation technology includes the following steps: S1: Pretreatment of forest processing residues: Take forest processing residues, crush them through a 120-300 mesh sieve, and dry them to obtain pretreated raw materials for forest processing residues; S2: Preparation of ternary eutectic solvent: Weigh choline chloride, ferric chloride and polyethylene glycol 400, mix them and stir at 60~80℃ until completely melted to obtain a transparent and uniform ternary eutectic solvent. S3: Cellulose extraction: The pretreated raw material of forest processing residue from step S1 is added to the ternary eutectic solvent obtained in step S2, and stirred at a constant temperature of 70~120℃ for 2~4h. Then, 5~10 times the volume of deionized water is added, and the mixture is stirred for 30min. After filtration, the precipitate is collected, washed with deionized water until neutral, and dried at 60~80℃ for 8~12h to obtain forest processing residue-based cellulose. S4: Preparation of cellulose-phosphate sol: At room temperature, the forest processing residue-based cellulose prepared in step S3 is added to a phosphoric acid solution with a mass fraction of 80%~85%, and stirred for 1~2 hours until the forest processing residue-based cellulose is completely dissolved to obtain a transparent cellulose-phosphate solution; then, polyethyleneimine with a molecular weight of 8000-10000 g / mol is added at 30%~50% of the cellulose mass, and stirred continuously at room temperature for 1~3 hours to form a stable and homogeneous cellulose-phosphate sol; S5: Sol-gel and freeze-drying. The cellulose-phosphate sol obtained in step S4 is poured into a mold and aged at room temperature for 8-12 h to complete the sol-gel conversion. Then the gel is pre-frozen at -40℃ to -60℃ for 2-4 h and transferred to a freeze dryer for freeze-drying to remove the solvent and obtain the nitrogen-phosphorus co-doped carbon aerogel precursor. S6: Joule thermal rapid carbonization. Take 0.1~0.3g of the nitrogen-phosphorus co-doped carbon aerogel precursor from step S5 and place it in a graphite tube. Seal both ends with graphite blocks and place it in a Joule thermal carbonization apparatus. Introduce argon gas into the reaction tube at a flow rate of 20~50mL / min and purge for 5~20min to remove air. Perform second-level thermal shock carbonization at a carbonization temperature of 1200~2000℃ and a treatment time of 3~20s. After carbonization, allow it to cool naturally to room temperature to obtain primary carbon aerogel. S7: Post-treatment: The primary carbon aerogel obtained in step S6 is added to a 1 mol / L hydrochloric acid solution, ultrasonically washed for 30-60 min, then washed with deionized water until neutral, and dried at 60-80℃ for 6-12 h to obtain a forest processing residue-based nitrogen and phosphorus co-doped carbon aerogel ORR catalyst.

[0010] As an optimization, the wood processing residue in step S1 is one or more of sawdust, branches, or bark.

[0011] As an optimization, the drying temperature in step S1 is 80~105℃ and the drying time is 6~12h.

[0012] As an optimization, the molar ratio of choline chloride, ferric chloride and polyethylene glycol 400 in step S2 is 2:8:1 to 1:6:2.

[0013] As an optimization, the solid-liquid ratio of the pretreated raw material of forest processing residue and the ternary eutectic solvent in step S3 is 1:15~1:25 g / mL.

[0014] As an optimization, the solid-liquid ratio of forest processing residue cellulose to phosphoric acid solution in step S4 is 1:8~1:12 g / mL.

[0015] As an optimization, the freeze-drying conditions in step S5 are a temperature of -50℃, a vacuum degree of ≤10Pa, and a time of 12~24 h.

[0016] As an optimization, in step S6, argon gas is introduced into the reaction tube at a flow rate of 30 mL / min, and the tube is purged for 10 min to remove air.

[0017] As an optimization, the carbonization temperature in step S6 is 1500℃ and the processing time is 10 s.

[0018] As an optimization, the concentration of the hydrochloric acid solution in step S7 is 0.5~1 mol / L.

[0019] The beneficial effects of this invention are: This invention uses green and low-cost raw materials: for the first time, high-performance ORR carbon aerogels are prepared using forestry processing residues as a carbon source, turning waste into treasure, reducing raw material costs by more than 70%, and realizing the high-value utilization of agricultural and forestry solid waste.

[0020] This invention offers high efficiency and good stability in fiber extraction: it uses a ternary eutectic solvent to directionally remove lignin / hemicellulose, achieving a cellulose extraction rate of ≥90% and significantly improving the integrity of the carbon skeleton.

[0021] This invention features in-situ high-efficiency doping with high activity: phosphoric acid provides phosphorus and polyethyleneimine provides nitrogen, resulting in in-situ uniform co-doping and the formation of high-density N / P synergistic ORR active sites.

[0022] This invention features ultra-fast, low-energy carbonization: Joule thermal carbonization at 1200~2000℃ for 3~20 seconds, reducing time by 99% and energy consumption by 85%, perfectly preserving the three-dimensional aerogel interconnected channels, ultra-high temperature rapid molding, and more precise control over the degree of graphitization and pore structure.

[0023] This invention has strong morphological adaptability: the self-supporting structure of the three-dimensional through-hole significantly improves oxygen diffusion and electrolyte transport efficiency, eliminates the risk of methanol poisoning, and can be stably adapted to the operating conditions of fuel cell cathodes.

[0024] The ORR catalyst of this invention exhibits excellent performance: it requires no noble metal loading, achieves an ORR half-wave potential of 0.88 V, and a limiting current density of 6.8 mA / cm². 2 After 30,000 seconds of continuous operation, the current retention rate is ≥92%, and the overall performance is better than that of commercial 20wt% Pt / C. Attached Figure Description

[0025] The method for preparing nitrogen-phosphorus co-doped carbon aerogel ORR catalysts based on forest processing residues using Joule thermal flash evaporation technology is further explained below with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the preparation process of the ORR catalyst of the present invention; Figure 2 is a SEM image (three-dimensional porous carbon aerogel morphology) of the ORR catalyst in Example 1 of the present invention. Figure 3 is the XPS total spectrum (characteristic peaks of C, N, O, and P elements) of the ORR catalyst in Example 1 of the present invention. Figure 4 shows the ORR linear sweep voltammetric curves of the ORR catalyst of Example 1 and the comparative catalyst Pt / C of the present invention. Figure 5 shows the ORR stability test curve of the ORR catalyst in Example 1 of the present invention. Detailed Implementation

[0026] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be noted that the following embodiments are for illustrative purposes only and do not limit the scope of the application. Similarly, the following embodiments are only some, not all, embodiments of the present application, and all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application. Example

[0027] Please see Figure 1 , Figure 1 This is a schematic diagram of the preparation process of the ORR catalyst of the present invention; the method for preparing a nitrogen-phosphorus co-doped carbon aerogel ORR catalyst based on forest processing residues using Joule thermal flash evaporation technology includes the following steps: Pretreatment of forest processing residues: Eucalyptus bark is crushed and passed through a 200-mesh sieve, and dried at 95℃ for 9 hours to obtain raw materials for pretreatment of forest processing residues. Other tree barks can also be used. Preparation of ternary eutectic solvent: Weigh choline chloride, ferric chloride and polyethylene glycol 400, with a molar ratio of choline chloride:ferric chloride:PEG400 of 1:6:2. Mix and stir at 70°C until completely melted to obtain a transparent and homogeneous ternary eutectic solvent. Cellulose extraction: The pretreated raw material of forest processing residue from step 1 was added to the ternary eutectic solvent obtained in step 2. The solid-liquid ratio of the pretreated raw material of forest processing residue to the ternary eutectic solvent was 1:20 g / mL. The mixture was stirred at 90℃ for 3 hours. Then, 5 to 10 times the volume of deionized water was added, and the mixture was stirred for 30 minutes. The mixture was then filtered, the precipitate was collected, washed with deionized water until neutral, and dried at 70℃ for 10 hours to obtain forest processing residue-based cellulose. Preparation of cellulose-phosphate sol: At room temperature, the forest processing residue-based cellulose prepared in step 3 was added to a phosphoric acid solution with a mass fraction of 82%, and the solid-liquid ratio of forest processing residue-based cellulose to phosphoric acid solution was 1:10 g / mL. The mixture was stirred for 1.5 h until the forest processing residue-based cellulose was completely dissolved to obtain a transparent cellulose-phosphate solution. Subsequently, polyethyleneimine with a molecular weight of 9000 g / mol was added at 40% of the cellulose mass, and the mixture was stirred continuously at room temperature for 2 h to form a stable and homogeneous cellulose-phosphate sol. 5. Sol-gel and freeze-drying: The cellulose-phosphate sol obtained in step 4 was poured into a mold and allowed to stand at room temperature for 9 hours to complete the sol-gel conversion. The gel was then pre-frozen at -50°C for 3 hours and transferred to a freeze dryer for freeze-drying. The freeze-drying conditions were -50°C, vacuum degree 8 Pa, and time 18 hours to remove the solvent and obtain the nitrogen-phosphorus co-doped carbon aerogel precursor. 6. Joule heating rapid carbonization: Take 0.2 g of the nitrogen-phosphorus co-doped carbon aerogel precursor from step 5 and place it in a graphite tube. Seal both ends with graphite blocks and place it in a Joule heating carbonization apparatus. Introduce argon gas into the reaction tube at a flow rate of 30 mL / min and purge for 10 min to remove air. Perform second-level thermal shock carbonization at a carbonization temperature of 1500℃ and a treatment time of 10 s. After carbonization, allow it to cool naturally to room temperature to obtain the primary carbon aerogel. 7. Post-treatment: The primary carbon aerogel obtained in step 6 was added to a 1 mol / L hydrochloric acid solution, ultrasonically washed for 45 min, then washed with deionized water until neutral, and dried at 70 °C for 9 h to obtain the forest processing residue-based nitrogen and phosphorus co-doped carbon aerogel ORR catalyst NP-CA-1. Example

[0028] The difference from Example 1 is that in the preparation of the ternary eutectic solvent, the molar ratio of choline chloride:ferric chloride:PEG400 is 2:8:1, the Joule temperature is 1800℃, and the treatment time is 15 s, to obtain the ORR catalyst NP-CA-2. Example

[0029] The difference from Example 1 is that the amount of polyethyleneimine added is 35% of the cellulose mass, the Joule heating temperature is 1300℃, and the treatment time is 8s, resulting in ORR catalyst NP-CA-3.

[0030] Comparative Example 1 (Traditional binary eutectic solvent) Choline chloride, ferric chloride, and polyethylene glycol 400 ternary eutectic solvent were replaced with a traditional choline chloride-urea binary eutectic solvent at a molar ratio of 1:2, with the rest remaining the same as in Example 1, to obtain the ORR catalyst DP-CA.

[0031] Comparative Example 2 (Traditional single nitrogen doping) Phosphoric acid was used to supply phosphorus, and polyethyleneimine was used to supply nitrogen. In-situ uniform co-doping was replaced with single nitrogen doping, and the rest was the same as in Example 1, to obtain the ORR catalyst N-CA.

[0032] Comparative Example 3 (Carbonization in a conventional tubular furnace) Joule heating was replaced by conventional tubular furnace carbonization at 900°C for 2 hours, with the rest being the same as in Example 1, to obtain the ORR catalyst TP-CA.

[0033] Comparative Example 4 (Commercial 20wt% Pt / C) A commercially available 20wt% Pt / C catalyst was used directly as a comparison.

[0034] ORR performance tests were conducted using the catalysts of Examples 1-3 and Comparative Examples 1-4 (0.1M KOH electrolyte, three-electrode system, reference electrode is graphite rod, counter electrode is Hg / HgO electrode), and the test results are summarized in Table 1.

[0035] Table 1 Test results show that the dedicated ORR catalyst prepared by the method of preparing forest processing residue-based nitrogen-phosphorus co-doped carbon aerogel ORR catalyst based on Joule thermal flash evaporation technology of this invention has significantly better half-wave potential, limiting current density, cycle stability and kinetic performance than samples prepared by traditional methods and commercial Pt / C.

[0036] Comparative Example 1 uses a traditional choline chloride-urea binary eutectic solvent, which struggles to completely remove lignin and hemicellulose, resulting in a low cellulose extraction rate. The carbon materials prepared in this way generally suffer from numerous skeletal defects and insufficient exposure of heteroatom active sites, leading to poor long-term stability. The ORR half-wave potential is only 0.81 V, the limiting current density is only 4.2 mA / cm², and the current retention rate is only 76.5% after 30,000 s of continuous operation. Comparative Example 2 uses traditional single nitrogen doping, which fails to form highly efficient and synergistic ORR active sites, limiting catalytic activity. The ORR half-wave potential is only 0.75 V, the limiting current density is only 4.1 mA / cm², and the current retention rate is only 70.4% after 30,000 s of continuous operation. Comparative Example 3 uses a traditional tubular furnace for carbonization, which requires a long pyrolysis time, resulting in slow heating and several hours of operation. This easily leads to carbon channel collapse and a significant decrease in specific surface area, resulting in poor ORR mass transfer and charge transport efficiency. The ORR half-wave potential is only 0.74 V, the limiting current density is only 3.9 mA / cm², and the current retention rate is only 68.5% after 30,000 s of continuous operation. Comparative Example 4 directly uses a commercial 20 wt% Pt / C catalyst. Although its ORR performance test results are slightly better than Comparative Examples 1-3 (ORR half-wave potential is 0.85 V, limiting current density is 5.2 mA / cm², and current retention rate is 78.6% after 30,000 s of continuous operation), its overall performance is still significantly inferior to the ORR catalyst prepared by the method of this invention. In addition, its high cost, scarcity of reserves, poor stability, and susceptibility to methanol permeation poisoning are key drawbacks that severely restrict the large-scale commercialization of fuel cells. Please refer to [link / reference]. Figures 2-5Figure 2 is a SEM image of the ORR catalyst of Example 1 of the present invention (three-dimensional porous carbon aerogel morphology); Figure 3 is the XPS total spectrum of the ORR catalyst of Example 1 of the present invention (characteristic peaks of C, N, O, and P elements); Figure 4 is the ORR linear sweep voltammetric curve of the ORR catalyst of Example 1 of the present invention and the comparative catalyst Pt / C; Figure 5 is the ORR stability test curve of the ORR catalyst of Example 1 of the present invention. It can be seen that the special ORR catalyst prepared by the method of preparing forest processing residue-based nitrogen-phosphorus co-doped carbon aerogel ORR catalyst based on Joule thermal flash evaporation technology of the present invention has high fiber extraction efficiency and good stability: lignin / hemicellulose is directionally removed using a ternary eutectic solvent, with a cellulose extraction rate ≥90% and significantly improved carbon skeleton integrity. In-situ high-efficiency doping and high activity: phosphoric acid provides phosphorus and polyethyleneimine provides nitrogen, with in-situ uniform co-doping forming high-density N / P synergistic ORR active sites. Ultrafast, low-energy carbonization: Joule-thermal carbonization at 1200~2000℃ for 3~20 seconds reduces time by 99% and energy consumption by 85%, perfectly preserving the three-dimensional aerogel's interconnected channels. Ultra-high temperature rapid molding allows for more precise control of graphitization degree and pore structure. Strong morphology adaptability: The self-supporting structure of the three-dimensional interconnected channels significantly improves oxygen diffusion and electrolyte transport efficiency, eliminating the risk of methanol poisoning and ensuring stable adaptation to fuel cell cathode conditions. Excellent ORR catalyst performance: No precious metal loading; ORR half-wave potential reaches 0.88V; limiting current density reaches 6.8 mA / cm². 2 After continuous operation for 30,000 seconds, the current retention rate can reach over 92%.

[0037] Unlike existing technologies, the method for preparing nitrogen-phosphorus co-doped carbon aerogel ORR catalyst based on forest processing residues using Joule thermal flash evaporation technology provided in this application includes the following steps: pretreatment of forest processing residues, taking forest processing residues, crushing, sieving, and drying; preparation of a ternary eutectic solvent, weighing choline chloride, ferric chloride, and polyethylene glycol 400, mixing, and stirring until completely melted; cellulose extraction, adding the pretreated forest processing residue raw material to the ternary eutectic solvent, stirring at a constant temperature, adding deionized water, stirring, filtering, collecting the precipitate, washing with deionized water until neutral, and drying to obtain forest processing residue-based cellulose; and preparation of cellulose-phosphate sol, adding forest processing residue-based cellulose to a phosphoric acid solution at room temperature, stirring until the forest processing residue-based cellulose is completely dissolved to obtain a transparent cellulose-phosphate solution. Polyethyleneimine was then added, and the mixture was continuously stirred at room temperature to form a stable and homogeneous cellulose-phosphate sol. Sol-gel and freeze-drying were then performed: the cellulose-phosphate sol was poured into a mold and allowed to age at room temperature to complete the sol-gel conversion; the gel was then pre-frozen and transferred to a freeze dryer for freeze-drying to remove the solvent, yielding a nitrogen-phosphorus co-doped carbon aerogel precursor; Joule heating rapid carbonization was then performed: the nitrogen-phosphorus co-doped carbon aerogel precursor was placed in a graphite tube, sealed at both ends with graphite blocks, and placed in a Joule heating carbonization apparatus; argon gas was introduced into the reaction tube for second-level thermal shock carbonization; after carbonization, the mixture was naturally cooled to room temperature to obtain a primary carbon aerogel; post-treatment involved adding the primary carbon aerogel to a hydrochloric acid solution, ultrasonically washing, then washing with deionized water until neutral, and drying to obtain a forestry processing residue-based nitrogen-phosphorus co-doped carbon aerogel ORR catalyst. This invention effectively realizes the high-value utilization of agricultural and forestry solid waste and can prepare a dedicated ORR electrocatalyst that is free of precious metals, highly active, long-lived, low-energy, and highly adaptable. This application utilizes green and low-cost raw materials: For the first time, high-performance ORR carbon aerogels are prepared using forestry processing residues as a carbon source, turning waste into treasure and reducing raw material costs by over 70%, achieving high-value utilization of agricultural and forestry solid waste. Highly efficient fiber extraction: A ternary eutectic solvent is used for directional removal of lignin / hemicellulose, achieving a cellulose extraction rate of ≥90% and significantly improving the integrity of the carbon skeleton. In-situ efficient doping: Phosphoric acid provides phosphorus, and polyethyleneimine provides nitrogen, enabling in-situ uniform co-doping to form high-density N / P synergistic ORR active sites. Ultrafast and low-energy carbonization: Joule thermal carbonization at 1200~2000℃ for 3~20 seconds reduces time by 99% and energy consumption by 85%, perfectly preserving the three-dimensional aerogel's interconnected pores. Ultra-high temperature rapid molding allows for more precise control of graphitization and pore structure. Strong adaptability: The three-dimensional porous structure significantly improves oxygen diffusion and electrolyte transport efficiency, eliminates the risk of methanol poisoning, and can stably adapt to fuel cell cathode conditions. ORR catalyst exhibits excellent performance: without precious metal loading, the ORR half-wave potential reaches 0.88V, and the limiting current density reaches 6.8 mA / cm². 2After 30,000 seconds of continuous operation, the current retention rate is ≥92%, and the overall performance is better than that of commercial 20wt% Pt / C.

[0038] The foregoing description illustrates the main features, basic principles, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments or examples described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the above embodiments or examples should be considered exemplary and not restrictive. The scope of the present invention is defined by the appended claims rather than the foregoing description, and therefore all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims. Any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the technical principles of the present invention should fall within the patent protection scope of the present invention.

Claims

1. A method for preparing nitrogen-phosphorus co-doped carbon aerogel ORR catalyst based on forestry processing residues using Joule thermal flash evaporation technology, characterized in that, Includes the following steps: S1: Pretreatment of forest processing residues: Take forest processing residues, crush them through a 120-300 mesh sieve, and dry them to obtain pretreated raw materials for forest processing residues; S2: Preparation of ternary eutectic solvent: Weigh choline chloride, ferric chloride and polyethylene glycol 400, mix them and stir at 60~80℃ until completely melted to obtain a transparent and uniform ternary eutectic solvent. S3: Cellulose extraction: The pretreated raw material of forest processing residue from step S1 is added to the ternary eutectic solvent obtained in step S2, and stirred at a constant temperature of 70~120℃ for 2~4h. Then, 5~10 times the volume of deionized water is added, and the mixture is stirred for 30min. After filtration, the precipitate is collected, washed with deionized water until neutral, and dried at 60~80℃ for 8~12h to obtain forest processing residue-based cellulose. S4: Preparation of cellulose-phosphate sol: At room temperature, the forest processing residue-based cellulose prepared in step S3 is added to a phosphoric acid solution with a mass fraction of 80%~85%, and stirred for 1~2 hours until the forest processing residue-based cellulose is completely dissolved to obtain a transparent cellulose-phosphate solution; then, polyethyleneimine with a molecular weight of 8000-10000 g / mol is added at 30%~50% of the cellulose mass, and stirred continuously at room temperature for 1~3 hours to form a stable and homogeneous cellulose-phosphate sol; S5: Sol-gel and freeze-drying. The cellulose-phosphate sol obtained in step S4 is poured into a mold and aged at room temperature for 8-12 h to complete the sol-gel conversion. Then the gel is pre-frozen at -40℃ to -60℃ for 2-4 h and transferred to a freeze dryer for freeze-drying to remove the solvent and obtain the nitrogen-phosphorus co-doped carbon aerogel precursor. S6: Joule thermal rapid carbonization. Take 0.1~0.3g of the nitrogen-phosphorus co-doped carbon aerogel precursor from step S5 and place it in a graphite tube. Seal both ends with graphite blocks and place it in a Joule thermal carbonization apparatus. Introduce argon gas into the reaction tube at a flow rate of 20~50mL / min and purge for 5~20min to remove air. Perform second-level thermal shock carbonization at a carbonization temperature of 1200~2000℃ and a treatment time of 3~20s. After carbonization, allow it to cool naturally to room temperature to obtain primary carbon aerogel. S7: Post-treatment: The primary carbon aerogel obtained in step S6 is added to a 1 mol / L hydrochloric acid solution, ultrasonically washed for 30-60 min, then washed with deionized water until neutral, and dried at 60-80℃ for 6-12 h to obtain a forest processing residue-based nitrogen and phosphorus co-doped carbon aerogel ORR catalyst.

2. The method for preparing forestry processing residue-based nitrogen-phosphorus co-doped carbon aerogel ORR catalyst based on Joule thermal flash evaporation technology as described in claim 1, characterized in that: The wood processing residue in step S1 is one or more of sawdust, branches, or bark.

3. The method for preparing forestry processing residue-based nitrogen-phosphorus co-doped carbon aerogel ORR catalyst based on Joule thermal flash evaporation technology as described in claim 2, characterized in that: In step S1, the drying temperature is 80~105℃ and the drying time is 6~12h.

4. The method for preparing forestry processing residue-based nitrogen-phosphorus co-doped carbon aerogel ORR catalyst based on Joule thermal flash evaporation technology as described in claim 1, characterized in that: In step S2, the molar ratio of choline chloride, ferric chloride and polyethylene glycol 400 is 2:8:1 to 1:6:

2.

5. The method for preparing forestry processing residue-based nitrogen-phosphorus co-doped carbon aerogel ORR catalyst based on Joule thermal flash evaporation technology as described in claim 1, characterized in that: In step S3, the solid-liquid ratio of the pretreated raw material of forestry processing residue and the ternary eutectic solvent is 1:15~1:25 g / mL.

6. The method for preparing forestry processing residue-based nitrogen-phosphorus co-doped carbon aerogel ORR catalyst based on Joule thermal flash evaporation technology as described in claim 1, characterized in that: In step S4, the solid-liquid ratio of the forest processing residue cellulose to the phosphoric acid solution is 1:8~1:12 g / mL.

7. The method for preparing forestry processing residue-based nitrogen-phosphorus co-doped carbon aerogel ORR catalyst based on Joule thermal flash evaporation technology as described in claim 1, characterized in that: The freeze-drying conditions in step S5 are a temperature of -50℃, a vacuum degree of ≤10Pa, and a time of 12~24 h.

8. The method for preparing forestry processing residue-based nitrogen-phosphorus co-doped carbon aerogel ORR catalyst based on Joule thermal flash evaporation technology as described in claim 1, characterized in that: In step S6, argon gas is introduced into the reaction tube at a flow rate of 30 mL / min, and the tube is purged for 10 min to remove air.

9. The method for preparing forestry processing residue-based nitrogen-phosphorus co-doped carbon aerogel ORR catalyst based on Joule thermal flash evaporation technology as described in claim 1, characterized in that: In step S6, the carbonization temperature is 1500℃ and the processing time is 10 s.

10. The method for preparing forestry processing residue-based nitrogen-phosphorus co-doped carbon aerogel ORR catalyst based on Joule thermal flash evaporation technology as described in claim 1, characterized in that: The concentration of the hydrochloric acid solution in step S7 is 0.5~1 mol / L.

Images