Modified substrate nitrogen-doped carbon thin film, preparation method and application thereof

Abstract

This invention relates to the field of thin film preparation technology, specifically to a modified substrate nitrogen-doped carbon thin film, its preparation method, and its application, comprising the following preparation steps: S1. Substrate etching modification; S2. Substrate impregnation modification; S3. Nitrogen-doped carbon thin film deposition; S4. High-temperature annealing treatment. This invention achieves precise control over the composition, structure, and interfacial properties of the thin film through the synergistic effect of a multi-step process of "etching modification – impregnation modification – magnetron sputtering deposition – high-temperature annealing," resulting in a modified substrate nitrogen-doped carbon thin film exhibiting excellent oxygen reduction catalytic activity and good stability in fuel cells, significantly reducing catalyst costs and facilitating industrial production.

Description

Technical Field

[0001] This invention relates to the field of thin film preparation technology, specifically to a modified substrate nitrogen-doped carbon thin film, its preparation method, and its application. Background Technology

[0002] Fuel cells, as efficient and clean energy conversion devices, have shown broad application prospects in portable power sources, electric vehicles, and stationary power stations due to their advantages such as high energy density, environmental friendliness, and low operating temperature. Among these, the cathode oxygen reduction reaction (ORR) is a key electrochemical process in fuel cells. Its reaction kinetics are slow, typically requiring the use of precious metal platinum (Pt)-based catalysts to increase the reaction rate. However, the scarcity and high cost of platinum, along with its susceptibility to methanol poisoning and CO deactivation, severely restrict the large-scale commercial application of fuel cells. Therefore, the development of efficient, stable, and low-cost non-precious metal catalysts has become a current research hotspot.

[0003] Nitrogen-doped carbon materials are considered among the most promising non-platinum catalysts due to their excellent electrical conductivity, structural tunability, and superior electrocatalytic activity. Studies have shown that nitrogen doping can introduce active sites into the carbon framework, promoting oxygen adsorption and reduction processes. Nitrogen-doped carbon thin films, in particular, have significant application value in micro fuel cells and MEMS devices due to their dense structure, ease of integration, and good substrate adhesion.

[0004] However, existing nitrogen-doped carbon films still have the following technical defects: (1) Poor adhesion between the film and the substrate: The interfacial adhesion between nitrogen-doped carbon films prepared by traditional methods and the substrate is weak, and they are prone to peeling during long-term operation or thermal cycling, affecting the stability of the device. (2) Low density of active sites: Conventional nitrogen doping methods are difficult to form high-density, high-activity catalytic sites in the film, which limits its electrocatalytic performance. (3) Insufficient catalytic activity: The intrinsic catalytic activity of single nitrogen-doped carbon materials is still far lower than that of platinum-based catalysts, especially the ORR activity in alkaline or acidic electrolytes needs to be improved. (4) Difficulty in controlling the uniformity of the substrate surface: The surface energy of unmodified substrates varies greatly, resulting in uneven deposition of subsequent films, affecting the consistency and repeatability of the films. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a modified substrate nitrogen-doped carbon thin film, its preparation method and its application.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a modified substrate nitrogen-doped carbon thin film includes the following preparation steps: S1. Substrate etching modification: The substrate material is cleaned and etched with an etching modifier for 3-5 minutes, followed by ultrasonic cleaning with ultrapure water for 20-30 minutes to obtain the etch-modified substrate. S2. Substrate impregnation modification: The etch-modified substrate is impregnated in the impregnation modification solution for 5-10 minutes, and then dried by gradient heating to obtain the impregnated modified substrate; S3. Nitrogen-doped carbon thin film deposition: The impregnated modified substrate is placed in a vacuum chamber at a pressure of 5 × 10⁻⁶. -4 After Pa, gas is introduced into it, and a nitrogen-doped carbon thin film is deposited on the impregnated modified substrate using a magnetron sputtering process to obtain a substrate with a deposited nitrogen-doped carbon thin film. S4. High-temperature annealing treatment: The substrate with the deposited nitrogen-doped carbon thin film obtained in step S3 is placed in a high-temperature vacuum annealing furnace, where the pressure in the vacuum chamber reaches 5 × 10⁻⁶. -4 After Pa, a protective gas Ar is introduced, and annealing is carried out at a segmented heating rate to obtain a modified substrate nitrogen-doped carbon thin film. The preparation of the etching modifier includes the following steps: S11. By mass, add 70-80 parts of deionized water to a polytetrafluoroethylene container, slowly add 10-15 parts of hydrofluoric acid with a mass concentration of 35-40% and 5-8 parts of nitric acid with a mass concentration of 60-65%, and stir until homogeneous to obtain a preliminary mixture. S12. Add 2-4 parts of glacial acetic acid and 1-2 parts of hydrogen peroxide with a mass concentration of 25-30% to the preliminary mixture obtained in step S11, stir evenly to obtain the secondary mixture; S13. Add 0.05-0.1 parts of polyethylene glycol octylphenyl ether and 0.2-0.5 parts of ethylenediaminetetraacetic acid to the mixture obtained in step S12, stir at a speed of 200-300 r / min for 10-15 min, and after standing to defoam, obtain the etching modifier.

[0007] Preferably, the preparation of the impregnation modification solution includes the following steps: S21. By mass, mix 95-98 parts of deionized water with 0.5-1.5 parts of dopamine hydrochloride and 1-2 parts of urea, and stir at 200-300 r / min for 10-15 min to obtain a preliminary modified solution; S22. Add 8-12 parts of electrocatalytic active modifier to the preliminary modified solution obtained in step S21, and continue stirring at a speed of 200-300 r / min for 10-15 min to obtain the secondary modified solution; S23. Add 0.1-0.3 parts of tromethamine to the modified solution obtained in step S22, adjust the pH to 8-8.5, and stir evenly to obtain the impregnation modified solution.

[0008] Preferably, the preparation of the electrocatalytically active modifier includes the following steps: S221. By weight, dissolve 10-13 parts of acrylic acid and 8-11 parts of acrylamide in 60-80 parts of deionized water, stir at 400-500 r / min until completely dissolved and control the pH to 6.5-7 to obtain a transparent solution; S222. Add 0.2-0.5 parts of cobalt nitrate, 0.05-0.1 parts of methylenebisacrylamide and 0.1-0.2 parts of ammonium persulfate to the transparent solution obtained in step S221. Stir the mixture at 300-400 r / min at 65-75℃ for 2-3 hours. After freeze-drying, grind the mixture into powder to obtain the electrocatalytically active modifier.

[0009] Preferably, the substrate material is either monocrystalline silicon or polycrystalline titanium.

[0010] Preferably, when the substrate material is monocrystalline silicon, the cleaning method is as follows: ultrasonically clean it with acetone, ethanol and ultrapure water for 20-30 minutes in sequence to remove the stains on its surface. When polycrystalline titanium is selected as the substrate material, the cleaning method is as follows: boil it in a hydrochloric acid solution with a volume ratio of hydrogen chloride to water of 1:3 for 30-40 minutes to remove the oxides on its surface, and then ultrasonically clean it with ultrapure water for 20-30 minutes.

[0011] Preferably, the gas in step S3 includes: ionized gas Ar, reactant gases N2 and CH4, and auxiliary gas He; the flow rates of ionized gas Ar, reactant gases N2 and CH4, and auxiliary gas He are 25-35 sccm, 20-25 sccm, 5-10 sccm, and 3-5 sccm, respectively.

[0012] Preferably, the magnetron sputtering process parameters in step S3 are: RF power of 160-170W; substrate bias of -12.3V to -200V; sputtering time of 40-50min; sputtering pressure of 0.5-1Pa; and the sputtering target used in the magnetron sputtering process is a high-purity carbon target with a diameter of 6cm and a thickness of 1mm and a purity of 99.95%.

[0013] Preferably, in step S4, the initial stage heating rate of the segmented heating rate for annealing is 4-5℃ / min to 550-600℃, the second stage heating rate is 8-10℃ / min to 800-1000℃, and after holding at that temperature for 10-15 minutes, the furnace is slowly cooled to room temperature.

[0014] A modified substrate nitrogen-doped carbon thin film is prepared by the above preparation method.

[0015] Application of a modified substrate nitrogen-doped carbon thin film in fuel cells.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention utilizes the synergistic effect of an electrocatalytic active modifier, an etching modifier, and an impregnation modifier to create a uniform nanoscale rough structure on the substrate material, forming a uniform and dense polydopamine layer on the substrate surface. This polydopamine layer is rich in catechol and amino functional groups. On one hand, it acts as an adhesion layer, forming strong chemical bonds with the etched substrate. On the other hand, it serves as a nucleation promoting layer for subsequent nitrogen-doped carbon films, effectively improving the bonding strength between the film and the substrate and preventing peeling during long-term use or thermal cycling. Simultaneously, the synergistic effect of these three agents effectively avoids the problem of metal particle agglomeration in traditional methods, significantly improving the density and utilization rate of active sites.

[0017] 2. This invention achieves precise control over the composition, structure and interface properties of thin films through the synergistic effect of a multi-step process of "etching modification - impregnation modification - magnetron sputtering deposition - high temperature annealing". This results in the modified substrate nitrogen-doped carbon thin film exhibiting excellent oxygen reduction catalytic activity and good stability in fuel cells, significantly reducing catalyst costs and facilitating industrial production. Attached Figure Description

[0018] Figure 1 This is a process flow diagram for preparing the modified substrate nitrogen-doped carbon thin film of the present invention; Figure 2 This is a flow chart of the preparation process of the etching modifier of the present invention; Figure 3 This is a flow chart of the preparation process of the impregnation modification liquid of the present invention; Figure 4 This is a process flow diagram for preparing the electrocatalytically active modifier of the present invention; Figure 5 The bar chart shows the content of pyridine N and pyrrole N on the surface of the modified substrate nitrogen-doped carbon thin films obtained in Examples 1-3 and Comparative Examples 1-2 of this invention. Figure 6 The LSV diagrams of ORR for the modified substrate nitrogen-doped carbon films obtained in Examples 1-3 and Comparative Examples 1-3 are shown. Figure 7 The graphs show the performance test curves of anion exchange membrane fuel cells using the modified substrate nitrogen-doped carbon thin film obtained in Example 3 and Comparative Example 3 of the present invention as the cathode catalyst. Figure 8 The chronoamperometry (COP) plots for ORR are shown for the modified substrate nitrogen-doped carbon thin films obtained in Example 3 and Comparative Example 3 of this invention. Detailed Implementation

[0019] The present invention will now be clearly and completely described in conjunction with embodiments thereof. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] Please see Figures 1-8 The present invention provides a technical solution: Example 1 A method for preparing nitrogen-doped carbon thin films on modified substrates: Before preparing the modified substrate nitrogen-doped carbon thin film, the electrocatalytically active modifier, etching modifier, and impregnation modification solution are prepared first: The preparation of electrocatalytically active modifiers includes the following steps: S221. Dissolve 10g of acrylic acid and 8g of acrylamide in 60g of deionized water, stir at 400r / min until completely dissolved and control the pH to 6.5 to obtain a transparent solution; S222. Add 0.2g cobalt nitrate, 0.05g methylenebisacrylamide and 0.1g ammonium persulfate to the transparent solution obtained in step S221. Stir the mixture at 300r / min at 65℃ for 2h. After freeze-drying, grind it into powder to finally obtain the electrocatalytic active modifier.

[0021] The preparation of the etching modifier includes the following steps: S11. Add 70g of deionized water to a polytetrafluoroethylene container, slowly add 10g of hydrofluoric acid with a mass concentration of 35% and 5g of nitric acid with a mass concentration of 60%, and stir until homogeneous to obtain a preliminary mixture. S12. Add 2g of glacial acetic acid and 1g of hydrogen peroxide with a mass concentration of 25% to the preliminary mixture obtained in step S11, stir evenly to obtain the secondary mixture; S13. Add 0.05g polyethylene glycol octylphenyl ether and 0.2g ethylenediaminetetraacetic acid to the secondary mixture obtained in step S12, stir at 200r / min for 10min, and let stand to defoam before obtaining the etching modifier.

[0022] The preparation of the impregnation modification solution includes the following steps: S21. Mix 95g of deionized water with 0.5g of dopamine hydrochloride and 1g of urea, and stir at 200r / min for 10min to obtain a preliminary modified solution; S22. Add 8g of electrocatalytic active modifier to the preliminary modified solution obtained in step S21, and continue stirring at 200r / min for 10min to obtain the secondary modified solution; S23. Add 0.1g of tromethamine to the modified solution obtained in step S22, adjust the pH to 8, and stir evenly to obtain the impregnation modified solution.

[0023] S1. Substrate etching modification: The substrate material is cleaned (the substrate material is monocrystalline silicon, and the cleaning method is as follows: it is ultrasonically cleaned with acetone, ethanol and ultrapure water for 20 minutes in sequence to remove the stains on its surface) and etched with etching modifier for 3 minutes. Then, it is ultrasonically cleaned with ultrapure water for 20 minutes to obtain the etch-modified substrate. S2. Substrate impregnation modification: The etch-modified substrate is impregnated in the impregnation modification solution for 5 minutes, and then dried by gradient heating to obtain the impregnated modified substrate; S3. Nitrogen-doped carbon thin film deposition: The impregnated modified substrate is placed in a vacuum chamber at a pressure of 5 × 10⁻⁶. -4 After Pa, a gas (including ionized gas Ar, reactive gases N2 and CH4, and auxiliary gas He; the flow rates of ionized gas Ar, reactive gases N2 and CH4, and auxiliary gas He are 25 sccm, 20 sccm, 5 sccm, and 3 sccm, respectively) is introduced into the substrate. A nitrogen-doped carbon thin film is deposited on the impregnated modified substrate using a magnetron sputtering process (RF power of 160W; substrate bias of -12.3V; sputtering time of 40min; sputtering pressure of 0.5Pa; the sputtering target used is a high-purity carbon target with a diameter of 6cm and a thickness of 1mm and a purity of 99.95%). S4. High-temperature annealing treatment: The substrate with the deposited nitrogen-doped carbon thin film obtained in step S3 is placed in a high-temperature vacuum annealing furnace, where the pressure in the vacuum chamber reaches 5 × 10⁻⁶. -4 After Pa, a protective gas Ar is introduced, and annealing is carried out at a segmented heating rate (the initial heating rate is 4℃ / min to 550℃, the second heating rate is 8℃ / min to 800℃, and after holding at this temperature for 10 min, the furnace is slowly cooled to room temperature to obtain a modified substrate nitrogen-doped carbon film.

[0024] Example 2 A method for preparing nitrogen-doped carbon thin films on modified substrates: Before preparing the modified substrate nitrogen-doped carbon thin film, the electrocatalytically active modifier, etching modifier, and impregnation modification solution are prepared first: The preparation of electrocatalytically active modifiers includes the following steps: S221. Dissolve 13g of acrylic acid and 11g of acrylamide in 80g of deionized water, stir at 500r / min until completely dissolved and control the pH to 7 to obtain a transparent solution; S222. Add 0.5g cobalt nitrate, 0.1g methylenebisacrylamide and 0.2g ammonium persulfate to the transparent solution obtained in step S221. Stir the mixture at 75°C and 400r / min for 3h. After freeze-drying, grind it into powder to finally obtain the electrocatalytic active modifier.

[0025] The preparation of the etching modifier includes the following steps: S11. Add 80g of deionized water to a polytetrafluoroethylene container, slowly add 15g of hydrofluoric acid with a mass concentration of 40% and 8g of nitric acid with a mass concentration of 65%, and stir until homogeneous to obtain a preliminary mixture. S12. Add 4g of glacial acetic acid and 2g of hydrogen peroxide with a mass concentration of 30% to the preliminary mixture obtained in step S11, stir evenly to obtain the secondary mixture; S13. Add 0.1g polyethylene glycol octylphenyl ether and 0.5g ethylenediaminetetraacetic acid to the mixture obtained in step S12, stir at 300r / min for 15min, and let stand to defoam before obtaining the etching modifier.

[0026] The preparation of the impregnation modification solution includes the following steps: S21. Mix 98g of deionized water with 1.5g of dopamine hydrochloride and 2g of urea, and stir at 300r / min for 15min to obtain a preliminary modified solution; S22. Add 12g of electrocatalytic active modifier to the preliminary modified solution obtained in step S21, and continue stirring at 300r / min for 15min to obtain the secondary modified solution; S23. Add 0.3g of tromethamine to the modified solution obtained in step S22, adjust the pH to 8.5, and stir evenly to obtain the impregnation modified solution.

[0027] S1. Substrate Etching Modification: The substrate material is cleaned (the substrate material is polycrystalline titanium, and the cleaning method is as follows: it is boiled in a hydrochloric acid solution with a volume ratio of hydrogen chloride to water of 1:3 for 40 minutes to remove the oxides on its surface, and then ultrasonically cleaned with ultrapure water for 30 minutes). The substrate is then etched with an etching modifier for 5 minutes, followed by ultrasonic cleaning with ultrapure water for 30 minutes to obtain the etch-modified substrate. S2. Substrate impregnation modification: The etch-modified substrate is impregnated in the impregnation modification solution for 10 minutes, and then dried by gradient heating to obtain the impregnated modified substrate; S3. Nitrogen-doped carbon thin film deposition: The impregnated modified substrate is placed in a vacuum chamber at a pressure of 5 × 10⁻⁶. -4After Pa, a gas (including ionized gas Ar, reactive gases N2 and CH4, and auxiliary gas He; the flow rates of ionized gas Ar, reactive gases N2 and CH4, and auxiliary gas He are 35 sccm, 25 sccm, 10 sccm, and 5 sccm, respectively) is introduced into the substrate. A nitrogen-doped carbon thin film is deposited on the impregnated modified substrate using a magnetron sputtering process (RF power of 170W; substrate bias of -200V; sputtering time of 50min; sputtering pressure of 1Pa; the sputtering target used is a high-purity carbon target with a diameter of 6cm and a thickness of 1mm and a purity of 99.95%). S4. High-temperature annealing treatment: The substrate with the deposited nitrogen-doped carbon thin film obtained in step S3 is placed in a high-temperature vacuum annealing furnace, where the pressure in the vacuum chamber reaches 5 × 10⁻⁶. -4 After Pa, a protective gas Ar is introduced, and annealing is carried out at a segmented heating rate (the initial heating rate is 5℃ / min to 600℃, the second heating rate is 10℃ / min to 1000℃, and after holding at this temperature for 15 min, the furnace is slowly cooled to room temperature) to obtain a modified substrate nitrogen-doped carbon film.

[0028] Example 3 A method for preparing nitrogen-doped carbon thin films on modified substrates: Before preparing the modified substrate nitrogen-doped carbon thin film, the electrocatalytically active modifier, etching modifier, and impregnation modification solution are prepared first: The preparation of electrocatalytically active modifiers includes the following steps: S221. Dissolve 11g of acrylic acid and 10g of acrylamide in 70g of deionized water, stir at 450r / min until completely dissolved and control the pH to 6.7 to obtain a transparent solution; S222. Add 0.3g cobalt nitrate, 0.08g methylenebisacrylamide and 0.15g ammonium persulfate to the transparent solution obtained in step S221. Stir the mixture at 350r / min at 70℃ for 2.5h. After freeze-drying, grind it into powder to finally obtain the electrocatalytic active modifier.

[0029] The preparation of the etching modifier includes the following steps: S11. Add 75g of deionized water to a polytetrafluoroethylene container, slowly add 12g of hydrofluoric acid with a mass concentration of 38% and 7g of nitric acid with a mass concentration of 63%, stir evenly to obtain a preliminary mixture. S12. Add 3g of glacial acetic acid and 1.5g of hydrogen peroxide with a mass concentration of 28% to the preliminary mixture obtained in step S11, stir evenly to obtain the secondary mixture; S13. Add 0.08g polyethylene glycol octylphenyl ether and 0.4g ethylenediaminetetraacetic acid to the secondary mixture obtained in step S12, stir at 250r / min for 12min, and let stand to defoam before obtaining the etching modifier.

[0030] The preparation of the impregnation modification solution includes the following steps: S21. Mix 97g of deionized water with 1g of dopamine hydrochloride and 1.5g of urea, and stir at 240r / min for 12min to obtain a preliminary modified solution; S22. Add 10g of electrocatalytic active modifier to the preliminary modified solution obtained in step S21, and continue stirring at 240r / min for 12min to obtain the secondary modified solution; S23. Add 0.2g of tromethamine to the modified solution obtained in step S22, adjust the pH to 8.3, and stir evenly to obtain the impregnation modified solution.

[0031] S1. Substrate etching modification: The substrate material is cleaned (the substrate material is monocrystalline silicon, and the cleaning method is as follows: it is ultrasonically cleaned with acetone, ethanol and ultrapure water for 25 minutes in sequence to remove the stains on its surface) and etched with etching modifier for 4 minutes. Then, it is ultrasonically cleaned with ultrapure water for 25 minutes to obtain the etch-modified substrate. S2. Substrate impregnation modification: The etch-modified substrate is impregnated in the impregnation modification solution for 8 minutes, and then dried by gradient heating to obtain the impregnated modified substrate; S3. Nitrogen-doped carbon thin film deposition: The impregnated modified substrate is placed in a vacuum chamber at a pressure of 5 × 10⁻⁶. -4 After Pa, a gas (including ionized gas Ar, reactive gases N2 and CH4, and auxiliary gas He) is introduced into the substrate. The flow rates of ionized gas Ar, reactive gases N2 and CH4, and auxiliary gas He are 30 sccm, 23 sccm, 8 sccm, and 4 sccm, respectively. A nitrogen-doped carbon thin film is deposited on the impregnated modified substrate using a magnetron sputtering process (RF power of 165W; substrate bias of -100V; sputtering time of 45min; sputtering pressure of 0.8Pa; the sputtering target used is a high-purity carbon target with a diameter of 6cm and a thickness of 1mm and a purity of 99.95%). S4. High-temperature annealing treatment: The substrate with the deposited nitrogen-doped carbon thin film obtained in step S3 is placed in a high-temperature vacuum annealing furnace, where the pressure in the vacuum chamber reaches 5 × 10⁻⁶. -4After Pa, a protective gas Ar is introduced, and annealing is carried out at a segmented heating rate (the initial heating rate is 4.5℃ / min to 580℃, the second heating rate is 9℃ / min to 900℃, and after holding at this temperature for 12 min, the furnace is slowly cooled to room temperature) to obtain a modified substrate nitrogen-doped carbon film.

[0032] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that no electrocatalytic modifier was added in this comparative example; the other steps are exactly the same in Comparative Example 1 and Example 1.

[0033] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that the etching modifier in this comparative example is replaced with a mixture of hydrofluoric acid and nitric acid. The remaining steps are exactly the same in Comparative Example 2 and Example 1.

[0034] Comparative Example 3 Commercially available Pt / C catalyst was used as Comparative Example 3. The Pt / C catalyst was purchased from Hunan Minsizhuang Technology Co., Ltd.

[0035] Performance testing: The ORR electrocatalytic activity of the thin-film catalyst was characterized using a PARSTAT 2273 electrochemical workstation in a three-electrode electrochemical electrolysis cell. The modified nitrogen-doped carbon films obtained in Examples 1-3 and Comparative Examples 1-3 were used as cathode catalysts in anion exchange membrane fuel cells. Single cells were fabricated, and the discharge performance of the cells was tested to characterize the catalytic activity of the catalyst in the actual working environment of the fuel cell. The total N, pyridine N, and pyrrole N were finally obtained. (Pyridine N and pyrrole N are the most common types of N doped in carbon matrices. Because pyridine N has a lone pair of electrons, it can increase electron donation ability, which is beneficial for the adsorption of O2 molecules and O2.) The breaking of the O bond, which is considered to promote a 4-electron transfer ORR and thus has high ORR catalytic activity, is shown in Table 1 below: Table 1. Total N, pyridine N, and pyrrole N content on the surface of different nitrogen-doped carbon films and their impact on ORR electrocatalytic performance parameters, compared with Pt / C catalysts. As shown in Table 1, the single cells prepared from the modified substrate nitrogen-doped carbon films obtained in the examples all outperformed the comparative examples in terms of electrocatalytic performance. This demonstrates that the present invention successfully improved ORR activity through the synergistic effect of electrocatalytic activity modifiers, etching modifiers, and impregnation modification liquids, achieving precise control of film composition, structure, and interface properties. The invention successfully prepared modified substrate nitrogen-doped carbon films with high catalytic activity, high stability, and strong interfacial bonding, which have broad application prospects in the field of fuel cells.

[0036] Appendix Figure 5 The figures show bar charts illustrating the pyridine N and pyrrole N content on the surface of the modified nitrogen-doped carbon films obtained in Examples 1-3 and Comparative Examples 1-2 of this invention. As can be seen from the figures, compared to the comparative examples, the nitrogen content in the modified nitrogen-doped carbon films obtained in the examples is significantly increased, indicating that the synergistic effect of the electrocatalytically active modifier, etching modifier, and impregnation modifier can facilitate the adsorption of nitrogen atoms in the film. Furthermore, the pyridine nitrogen content is the highest in Example 3. Generally, pyridine nitrogen and pyrrole nitrogen are the most common types of N doped in carbon matrices. Since pyridine nitrogen has a lone pair of electrons, it can increase electron-donating ability, which is beneficial for the adsorption of O2 molecules and the breaking of OO bonds. Therefore, it is considered to promote a 4-electron transfer ORR and has high ORR catalytic activity.

[0037] Appendix Figure 6 The figures show the LSV diagrams of ORR for the modified nitrogen-doped carbon films obtained in Examples 1-3 and Comparative Examples 1-3 of this invention. The Pt / C catalyst corresponds to Comparative Example 3. The figures show that in O2-saturated 0.1M KOH solution, the catalytic activity of the modified nitrogen-doped carbon films obtained in the examples is significantly better than that of the comparative examples. Furthermore, the nitrogen-doped carbon film in Example 3 exhibits the highest catalytic activity, with an on-potential of -0.02V, the same as that of the Pt / C catalyst, and a limiting current density of 6.45 mA cm⁻¹. -2 .

[0038] Appendix Figure 7 The graphs show the performance test curves of anion exchange membrane fuel cells using the modified nitrogen-doped carbon thin film obtained in Example 3 and Comparative Example 3 as the cathode catalyst. The Pt / C catalyst in the graph corresponds to Comparative Example 3. Using the optimized nitrogen-doped carbon thin film of Example 3 and Pt / C as the cathode catalysts of the present invention, the performance of the anion exchange membrane fuel cell was tested to evaluate the catalyst's catalytic activity for ORR under actual fuel cell operating conditions. Figure 7 As shown, when nitrogen-doped carbon thin film Example 3 and Pt / C are used as catalysts, the results show that the catalytic activity of the nitrogen-doped carbon thin film catalyst is comparable to that of the commercial Pt / C catalyst under actual fuel cell operating conditions.

[0039] Appendix Figure 8The figures show the chronoamperometry (CMT) curves of the modified nitrogen-doped carbon films obtained in Example 3 and Comparative Example 3 of this invention for ORR. Test conditions: electrode potential -0.26V, electrode rotation speed 1600rpm; electrolyte: O2-saturated 0.1M KOH solution. The figures show the CMT curves in O2-saturated 0.1M KOH solution at a fixed electrode potential (-0.26V). It can be seen that during the 18000 s CMT test, the nitrogen-doped carbon film catalyst exhibits excellent stability, while the catalytic activity of the commercial Pt / C catalyst begins to decrease at 11000 s, and by 18000 s, the catalytic activity has decreased by 76%.

[0040] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a modified substrate nitrogen-doped carbon thin film, characterized in that, The preparation steps include the following: S1. Substrate etching modification: The substrate material is cleaned and etched with an etching modifier for 3-5 minutes, followed by ultrasonic cleaning with ultrapure water for 20-30 minutes to obtain the etch-modified substrate. S2. Substrate impregnation modification: The etch-modified substrate is impregnated in the impregnation modification solution for 5-10 minutes, and then dried by gradient heating to obtain the impregnated modified substrate; S3. Nitrogen-doped carbon thin film deposition: The impregnated modified substrate is placed in a vacuum chamber at a pressure of 5 × 10⁻⁶. -4 After Pa, gas is introduced into it, and a nitrogen-doped carbon thin film is deposited on the impregnated modified substrate using a magnetron sputtering process to obtain a substrate with a deposited nitrogen-doped carbon thin film. S4. High-temperature annealing treatment: The substrate with the deposited nitrogen-doped carbon thin film obtained in step S3 is placed in a high-temperature vacuum annealing furnace, where the pressure in the vacuum chamber reaches 5 × 10⁻⁶. -4 After Pa, a protective gas Ar is introduced, and annealing is carried out at a segmented heating rate to obtain a modified substrate nitrogen-doped carbon thin film. The preparation of the etching modifier includes the following steps: S11. By mass, add 70-80 parts of deionized water to a polytetrafluoroethylene container, slowly add 10-15 parts of hydrofluoric acid with a mass concentration of 35-40% and 5-8 parts of nitric acid with a mass concentration of 60-65%, and stir until homogeneous to obtain a preliminary mixture. S12. Add 2-4 parts of glacial acetic acid and 1-2 parts of hydrogen peroxide with a mass concentration of 25-30% to the preliminary mixture obtained in step S11, stir evenly to obtain the secondary mixture; S13. Add 0.05-0.1 parts of polyethylene glycol octylphenyl ether and 0.2-0.5 parts of ethylenediaminetetraacetic acid to the mixture obtained in step S12, stir at a speed of 200-300 r / min for 10-15 min, and after standing to defoam, obtain the etching modifier.

2. The method for preparing a modified substrate nitrogen-doped carbon thin film according to claim 1, characterized in that, The preparation of the impregnation modification solution includes the following steps: S21. By mass, mix 95-98 parts of deionized water with 0.5-1.5 parts of dopamine hydrochloride and 1-2 parts of urea, and stir at 200-300 r / min for 10-15 min to obtain a preliminary modified solution; S22. Add 8-12 parts of electrocatalytic active modifier to the preliminary modified solution obtained in step S21, and continue stirring at a speed of 200-300 r / min for 10-15 min to obtain the secondary modified solution; S23. Add 0.1-0.3 parts of tromethamine to the modified solution obtained in step S22, adjust the pH to 8-8.5, and stir evenly to obtain the impregnation modified solution.

3. The method for preparing a modified substrate nitrogen-doped carbon thin film according to claim 2, characterized in that, The preparation of the electrocatalytically active modifier includes the following steps: S221. By weight, dissolve 10-13 parts of acrylic acid and 8-11 parts of acrylamide in 60-80 parts of deionized water, stir at 400-500 r / min until completely dissolved and control the pH to 6.5-7 to obtain a transparent solution; S222. Add 0.2-0.5 parts of cobalt nitrate, 0.05-0.1 parts of methylenebisacrylamide and 0.1-0.2 parts of ammonium persulfate to the transparent solution obtained in step S221. Stir the mixture at 300-400 r / min at 65-75℃ for 2-3 hours. After freeze-drying, grind the mixture into powder to obtain the electrocatalytically active modifier.

4. The method for preparing a modified substrate nitrogen-doped carbon thin film according to claim 1, characterized in that, The substrate material is either monocrystalline silicon or polycrystalline titanium.

5. The method for preparing a modified substrate nitrogen-doped carbon thin film according to claim 1, characterized in that, When the substrate material is selected as monocrystalline silicon, the cleaning method is as follows: ultrasonically clean it with acetone, ethanol and ultrapure water for 20-30 minutes in sequence to remove the stains on its surface. When the substrate material is polycrystalline titanium, the cleaning method is as follows: boil it in a hydrochloric acid solution with a volume ratio of hydrogen chloride to water of 1:3 for 30-40 minutes to remove the oxides on its surface, and then ultrasonically clean it with ultrapure water for 20-30 minutes.

6. The method for preparing a modified substrate nitrogen-doped carbon thin film according to claim 1, characterized in that, The gases mentioned in step S3 include: ionized gas Ar, reactant gases N2 and CH4, and auxiliary gas He; the flow rates of ionized gas Ar, reactant gases N2 and CH4, and auxiliary gas He are 25-35 sccm, 20-25 sccm, 5-10 sccm, and 3-5 sccm, respectively.

7. The method for preparing a modified substrate nitrogen-doped carbon thin film according to claim 1, characterized in that, In step S3, the magnetron sputtering process parameters are: RF power of 160-170W; substrate bias of -12.3V to -200V; sputtering time of 40-50min; sputtering pressure of 0.5-1Pa; and the sputtering target used in the magnetron sputtering process is a high-purity carbon target with a diameter of 6cm and a thickness of 1mm and a purity of 99.95%.

8. The method for preparing a modified substrate nitrogen-doped carbon thin film according to claim 1, characterized in that, In step S4, the initial stage of annealing is heated at a rate of 4-5℃ / min to 550-600℃, and the second stage is heated at a rate of 8-10℃ / min to 800-1000℃. After holding at this temperature for 10-15 minutes, the furnace is slowly cooled to room temperature.

9. A modified substrate nitrogen-doped carbon thin film, characterized in that, It is prepared by the preparation method described in any one of claims 1-8.

10. The application of a modified substrate nitrogen-doped carbon thin film according to claim 9 in a fuel cell.

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