Platinum-loaded porous carbon fiber catalyst used as proton exchange membrane cathode material as well as preparation method and application of platinum-loaded porous carbon fiber catalyst

Abstract

The invention discloses a platinum-loaded porous carbon fiber catalyst used as a proton exchange membrane cathode material and a preparation method and application of the platinum-loaded porous carbon fiber catalyst, and particularly relates to and belongs to the technical field of acidic water electrolysis. The preparation method comprises the following steps that one-dimensional porous carbon fibers (NPCNFs) are prepared through electrostatic spinning; and then loading Pt on the NPCNFs by using an ethylene glycol reduction method to obtain the Pt / NPCNFs catalyst. The Pt loading capacity of the prepared Pt / NPCNFs is 0.21 mg cm <-2 >, the loading capacity of a commercial Pt / C catalyst is 0.3 mg cm <-2 >, the Pt loading capacity of the commercial Pt / C catalyst is 30% lower than that of the commercial Pt / C catalyst, and the overall performance of the commercial Pt / C catalyst is better than that of the commercial Pt / C catalyst. The preparation method of the catalyst is easy to operate, the catalytic activity is improved, the dosage of precious metal is reduced, and more design space and possibility are provided for development of novel catalysts.

Description

Technical Field

[0001] This invention belongs to the field of acidic water electrolysis technology, specifically relating to a platinum-supported porous carbon fiber catalyst used as a proton exchange membrane cathode material, its preparation method, and its application. Background Technology

[0002] Driven by ever-increasing global energy demands and environmental concerns, clean hydrogen energy is receiving increasing attention. Water electrolysis for hydrogen production, as a green and flexible technology, has become a research hotspot for the commercialization of hydrogen energy. Among these technologies, proton exchange membrane (PEM) water electrolysis, with its high operating current density and overall efficiency, is a promising candidate. In PEMWE systems, platinum (Pt) is a highly efficient but expensive catalyst, and its scarcity limits its large-scale commercial application. Therefore, finding alternatives to Pt or reducing its usage to lower costs while maintaining good catalytic performance is an urgent need for commercialization.

[0003] Carbon nanofibers are considered an excellent catalyst matrix due to their high specific surface area and conductivity. Loading a small amount of Pt onto them can ensure excellent catalytic performance while reducing the amount of Pt required, providing a feasible approach for subsequent commercialization.

[0004] Chinese patent application CN114221002A discloses a high-performance membrane electrode assembly (MEA) for proton exchange membrane fuel cells and its fabrication method. The MEA includes a proton exchange membrane, a cathode material consisting of a first catalyst layer and a first gas diffusion layer disposed on the upper and lower surfaces of the MEA, and an anode material consisting of a second catalyst layer and a second gas diffusion layer. Both the first and second gas diffusion layers include a conductive support layer and a microporous layer. The first and second catalyst layers are platinum / nickel material layers supported on molybdenum disulfide / graphene hybrid nanosheets. The conductive support layer is carbon paper. The microporous layer is a porous carbon fiber and carbon nanotube composite material layer. The proton exchange membrane is a sulfonated silicon fiber hybrid polyvinylidene fluoride-trifluoroethylene film. However, the fabrication method in this patent is complex and does not mention optimizations for reducing the amount of Pt used; therefore, further improvements are needed. Summary of the Invention

[0005] The technical problem to be solved by this invention is how to provide a method for preparing a proton exchange membrane water electrolysis cathode material with low platinum loading, reducing the amount of Pt used, while having excellent stability and outstanding electrochemical performance.

[0006] The present invention solves the above-mentioned technical problems through the following technical means: This invention proposes a method for preparing a platinum-supported porous carbon fiber catalyst for use as a proton exchange membrane cathode material, comprising the following steps: (1) Dissolve zinc salt and 2-methylimidazole separately in methanol solvent; mix and stir; after centrifugation, wash and dissolve the precipitate with N,N-dimethylformamide (DMF) to obtain ZIF-8 / DMF solution; (2) Add polyacrylonitrile (PAN) to the ZIF-8 / DMF obtained in step (1), stir to obtain spinning solution, and obtain one-dimensional material ZIF-8@PAN by electrospinning. After heating and calcining and cooling, one-dimensional porous nitrogen-doped carbon nanofibers are obtained. (3) Mix H2PtCl6, sodium citrate and ethylene glycol, adjust the pH, add one-dimensional porous nitrogen-doped carbon nanofibers, heat, wash and dry to obtain the product.

[0007] Preferably, in step (1), the zinc salt is Zn(NO3)2.

[0008] Preferably, in step (1), the mass ratio of zinc salt to 2-methylimidazole is 1:2.13-2.28.

[0009] Preferably, in step (1), the mixing and stirring method is to mix and stir at room temperature for 4-8 hours.

[0010] Preferably, in step (1), the centrifugation speed is 10000-14000 rpm and the time is 5-10 min.

[0011] Preferably, in step (1), the amount of DMF used is 5-10 mL.

[0012] Preferably, in step (2), the mass ratio of PAN to ZIF-8 / DMF is 1:14.75-16.29.

[0013] Preferably, in step (2), the electrospinning method involves using a 10 mL syringe to fill the spinning solution, with a DC voltage of 10~11 kV and a flow rate of 0.18-0.3 mL / h. -1 The distance between the needle and the collector is 10-13 cm.

[0014] Preferably, in step (2), the heating and calcination method is to use a high-temperature tube furnace under an inert atmosphere at 5°C. o C min -1 Heat to 180-250 o Hold at C for 1-3 hours, then heat to 980-1200 at the same rate. o Keep warm at room temperature for 3.5-5 hours.

[0015] Preferably, in step (3), the mass ratio of H2PtCl6 to sodium citrate is 1:0.39-0.56.

[0016] Preferably, in step (3), the amount of ethylene glycol used is 55-61g.

[0017] Preferably, in step (3), the pH is adjusted to 8.5-9.0 using a 4 mg / mL NaOH / ethylene glycol solution.

[0018] Preferably, in step (3), the amount of one-dimensional porous nitrogen-doped carbon nanofibers added is 5-15 mg.

[0019] Preferably, in step (3), the heating method is through a condensation reflux device at 100-150°C. o Heat at C for 3-5 hours.

[0020] Preferably, in step (3), the drying temperature is 60-80°C. o C.

[0021] The present invention also proposes a platinum-supported porous carbon fiber catalyst prepared by the above preparation method, which can be used as a proton exchange membrane cathode material.

[0022] The present invention also proposes the application of the platinum-supported porous carbon fiber catalyst prepared by the above preparation method as a proton exchange membrane cathode material in PEM water electrolysis cathode material.

[0023] The beneficial effects of this invention are as follows: 1. This invention synthesizes platinum-supported one-dimensional porous nitrogen-doped carbon nanofibers (Pt / NPCNFs) catalytic materials by electrospinning and ethylene glycol reduction, and prepares a water electrolysis cathode material with low Pt loading and high activity.

[0024] 2. The product obtained by this invention has excellent stability and outstanding activity, and can be used as a catalyst material in the hydrogen evolution reaction, effectively solving the problems of high cost and poor stability of platinum-based catalysts in the hydrogen evolution reaction.

[0025] 3. The preparation method of Pt / NPCNFs material provided by the present invention has the advantages of simple and rapid operation, good repeatability, and uniform product structure.

[0026] 4. The Pt loading of the Pt / NPCNFs prepared in this invention is 0.21 mg / cm³. -2 The loading of commercial Pt / C catalyst is 0.3 mg cm⁻¹. -2 Compared to commercial catalysts, the Pt loading is 30% lower, but the overall performance is better than that of commercial Pt / C catalysts.

[0027] Of course, implementing any product or method of the present invention does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0028] Figure 1 The images shown are transmission and scanning images of the ZIF-8 nanoparticles obtained in step 1 of Example 1 of the present invention, where image a is a scanning image and image b is a transmission image. Figure 2 The X-ray diffraction pattern of the ZIF-8 nanoparticles obtained in step 1 of Example 1 of this invention; Figure 3 The images shown are transmission and scanning images of the ZIF-8@PAN fiber obtained in step 2 of Embodiment 1 of the present invention, where a and b are scanning images of ZIF-8@PAN at different magnifications, and c and d are transmission images of ZIF-8@PAN at different magnifications. Figure 4 The scan images are of NPCNFs and Pt / NPCNFs obtained in steps 3 and 4 of Embodiment 1 of the present invention, where a is the scan image of NPCNFs and b is the scan image of Pt / NPCNFs. Figure 5 The transmission maps of NPCNFs and Pt / NPCNFs obtained in step 4 of Embodiment 1 of the present invention are shown, where a is the transmission map of NPCNFs and b is the transmission map of Pt / NPCNFs. Figure 6 The X-ray diffraction pattern of Pt / NPCNFs obtained in step 4 of Embodiment 1 of the present invention; Figure 7 The following are the EDX diagrams and elemental content distributions of Pt / NPCNFs obtained in step 4 of Embodiment 1 of the present invention, where diagram a is the EDX diagram of Pt / NPCNFs and diagram b is the content of different elements in the EDX energy spectrum of Pt / NPCNFs. Figure 8 The above is the XPS spectrum of Pt / NPCNFs obtained in step 4 of embodiment 1 of the present invention, where a is the total XPS spectrum of Pt / NPCNFs, b is C 1s, c is N 1s, and d is Pt 2p. Figure 9 This is a comparison chart of the electrochemical performance of the Pt / NPCNFs catalyst obtained in Example 1 of this invention and commercial platinum-carbon (Pt / C); Figure 10 This is a comparison chart of the PEM performance of the Pt / NPCNFs catalyst obtained in Example 1 of this invention and commercial platinum carbon (Pt / C). Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical terms used below have the same meaning as understood by those skilled in the art.

[0030] Unless otherwise specified, the test materials and reagents used in the following examples are commercially available or prepared by known methods.

[0031] Unless otherwise specified, all techniques or conditions described in the embodiments can be performed in accordance with the techniques or conditions described in the literature in this field or in the product manual. Unless otherwise specified, the quantitative experiments in the following embodiments are all repeated three times or more, and the results are averaged.

[0032] Example 1 In this embodiment, the Pt / NPCNFs catalyst was prepared according to the following steps: Step 1: Add 100 mL of methanol to each of 250 mL beakers A and B. Weigh 1.462 g of Zn(NO3)2·6H2O into beaker A and stir until dissolved. Weigh 3.275 g of 2-methylimidazole into beaker B and stir until dissolved. Quickly pour solution A into solution B, then stir on a magnetic stirrer at room temperature for 6 h (400 rpm). Centrifuge at 12000 rpm (5 min) to remove the supernatant and retain the precipitate. Wash once with N,N-dimethylformamide (DMF), centrifuge (12000 rpm, 5 min) to remove the supernatant, and dissolve the precipitate in 5 mL of DMF using sonication to obtain ZIF-8 / DMF solution.

[0033] Step 2: Add 0.372 g of PAN to 5 mL of ZIF-8 / DMF solution and stir overnight at room temperature to completely dissolve the polymer and form a homogeneous solution as the spinning solution. Then, load the spinning solution into a 10 mL syringe. During electrospinning, the DC voltage is 10.5 kV, the flow rate of the electrospinning solution is 0.3 mL / h, and the distance between the needle and the collector is 10 cm, resulting in the one-dimensional material ZIF-8@PAN.

[0034] Step 3: The one-dimensional material ZIF-8@PAN is placed in a high-temperature tube furnace under a nitrogen (N2) atmosphere at 5°C. o Heat to 200 °C / min oHold at C for 2 hours, then heat to 1000 at the same rate. o The mixture was kept at C for 4 h. Then it was cooled to room temperature to obtain one-dimensional porous nitrogen-doped carbon nanofibers (NPCNFs).

[0035] Step 4: Add 25 mg of H₂PtCl₆ and 54 mg of sodium citrate to a three-necked flask, add 50 mL of fresh ethylene glycol, and then stir magnetically for 30 min (300 rpm). Adjust the pH to 8.5-9.0 with 4 mg / mL NaOH / ethylene glycol solution, and stir magnetically for 30 min (300 rpm). Add 9.8 mg of NPCNFs material, and continue stirring magnetically for 30 min (300 rpm). Set up a reflux condenser and heat to 130°C. o Reflux at C for 4 h to ensure all Pt is reduced; wash once with deionized water (10000 rpm, 8 min), and finally reflux at 60°C. o The platinum-supported one-dimensional porous nitrogen-doped carbon nanofibers (Pt / NPCNFs) were dried in a vacuum drying oven.

[0036] like Figure 1 As shown, the ZIF-8 synthesized in Example 1 is uniform in size and no excess impurities were found, indicating that the particles synthesized using methanol as a solvent have good uniformity and crystallinity.

[0037] like Figure 2 The image shown is an X-ray diffraction pattern of the ZIF-8 nanoparticles obtained in step 1 of Example 1.

[0038] like Figure 3 The figures show the transmission and scanning electron microscope (SEM) images of the ZIF-8@PAN fibers obtained in step 2 of Example 1. a and b are SEM images of ZIF-8@PAN at different magnifications, and c and d are transmission images of ZIF-8@PAN at different magnifications. The figures show that the ZIF-8@PAN fibers have a uniform one-dimensional structure and obvious surface particles, indicating that ZIF-8 was successfully assembled into the PAN electrospun fibers.

[0039] like Figure 4 The image shows scans of NPCNFs and Pt / NPCNFs obtained in steps 3 and 4 of Example 1. It can be seen from the image that the loading of Pt nanoparticles did not change the original morphology of the NPCNFs fibers.

[0040] like Figure 5 The image shown is a transmission spectrum of Pt / NPCNFs obtained in step 4 of Example 1. The image further confirms that Pt nanoparticles are uniformly loaded on NPCNFs fibers.

[0041] like Figure 6The image shows the X-ray diffraction pattern of Pt / NPCNFs obtained in step 4 of Example 1. Compared with the XRD standard card of pure Pt, the diffraction peak positions of the Pt / NPCNFs catalyst match those of the standard card, further proving that Pt was successfully loaded onto porous fibers.

[0042] like Figure 7 The figure shows the EDX diagram and elemental distribution of Pt / NPCNFs obtained in step 4 of Example 1, where figure a is the EDX diagram of Pt / NPCNFs and figure b is the content of different elements in the EDX spectrum of Pt / NPCNFs. The EDX diagram shows that C, N, Pt, and O elements are present and uniformly distributed in Pt / NPCNFs, further confirming the successful loading of Pt into NPCNFs.

[0043] like Figure 8 The image shows the XPS spectrum of Pt / NPCNFs obtained in step 4 of Example 1, where a is the overall XPS spectrum of Pt / NPCNFs, b is C 1s, c is N 1s, and d is Pt 4f. The overall XPS spectrum and high-resolution fine spectra of each element confirm the presence of C, N, O, and Pt elements in Pt / NPCNFs, consistent with the EDX elemental mapping results. This also reflects the various bonds corresponding to C in Pt / NPCNFs and the three forms of nitrogen (graphitic nitrogen, pyrrole nitrogen, and pyridine nitrogen). Furthermore, it further confirms the presence of Pt.

[0044] Application Example 1 Application of the Pt / NPCNFs material prepared in Example 1 as a cathode material for PEM water electrolysis: 2 mg of Pt / NPCNFs material was weighed and added to 400 μL of isopropanol and 15 μL of Nafion. The mixture was sonicated for at least 30 min to ensure uniform catalyst dispersion. Then, 20 μL of the dispersion was dropped onto a glassy carbon electrode. After drying, the electrode was used as the working electrode for hydrogen evolution reaction testing. The reference electrode was Ag / AgCl, and the counter electrode was a carbon rod electrode. Electrochemical tests were performed in a 0.5 M H2SO4 electrolyte saturated with H2. The same tests were performed using commercial platinum-carbon (Pt / C) as a control.

[0045] like Figure 9 The figure shows a comparison of the electrochemical performance of the Pt / NPCNFs catalyst obtained in Example 1 and commercial platinum-carbon (Pt / C). The electrochemical performance was compared at a current density of 10 mA cm⁻¹. -2 When the overpotential is only 17 mV, it is significantly better than commercial platinum-carbon (Pt / C) catalysts.

[0046] Application Example 2 Application of the Pt / NPCNFs material prepared in Example 1 as a cathode material for PEM water electrolysis: Weigh 3.5 mg of Pt / NPCNFs material, add 0.5 mL of water, 1.5 mL of isopropanol, and 20 μL of Nafion, and sonicate for at least 30 min to ensure uniform catalyst dispersion. Simultaneously weigh 7.14 mg of commercial IrO2 material, add 2 mL of isopropanol and 15 μL of Nafion, and sonicate for at least 30 min to ensure uniform catalyst dispersion. Then, incubate both catalysts at 60 °C. o C was sprayed onto both sides of the 212 film on the heating plate. Then, at 80°C... o Hot-pressed for 3 min at 0.5 MPa (C). Tested in a PEM fixture. The same test was performed using commercial platinum-carbon (Pt / C) as a control.

[0047] like Figure 10 The figure shows a comparison of the PEM performance of the Pt / NPCNFs catalyst obtained in Example 1 and commercial platinum-carbon (Pt / C). The cathode loadings of 60% Pt / C and Pt / NPCNFs catalysts were 0.3 mg / cm³, respectively. -2 and 0.21 mg cm -2 The loading of the anolyte IrO2 catalyst is approximately 0.5 mg cm⁻¹. -2 .from Figure 10 The results show that Pt / NPCNFs outperform commercial platinum-carbon (Pt / C) catalysts in overall performance at a current density of 1 A cm⁻¹. -2 At that time, the voltage was only 1.5688 V, which is better than commercial platinum-carbon (Pt / C) catalysts.

[0048] Example 2 The difference between this embodiment and Embodiment 1 is that in step 1, the centrifugation speed is 10,000 rpm and the time is 10 min; the amount of DMF used is 10 mL.

[0049] Example 3 The difference between this embodiment and Embodiment 1 is that in step 3, the hot calcination method is carried out in an inert atmosphere in a high-temperature tube furnace at 5°C. o C min -1 Heat to 250 o Hold at C for 1.5 h, then heat to 1200 at the same rate. o Keep warm at C for 3.5 hours.

[0050] Example 4 The difference between this embodiment and Embodiment 1 is that in step 4, the heating method is through a condensation reflux device at 100°C. o Heat at C for 5 hours.

[0051] Comparative Example 1 The difference between this comparative example and Example 1 is that in step 1, the amount of DMF used is 20 mL; and in step 2, the amount of PAN used is 0.2 g.

[0052] As a backbone material for nanofibers, PAN (poly(acetal nanofiber)) in insufficient amounts can lead to uneven diameter and low mechanical strength in the resulting electrospun fibers, making them prone to breakage during subsequent pre-oxidation and carbonization processes, thus affecting the material morphology. Conversely, both excessively low PAN and excessively high DMF (dimethylaminomethyl ether) amounts can result in uneven nanofiber diameter and easy breakage during spinning.

[0053] Comparative Example 2 The difference between this comparative example and Example 1 is that in step 4, the amount of H2PtCl6 used is 10mg, the amount of sodium citrate used is 30mg, and the amount of ethylene glycol used is 40g.

[0054] Insufficient H2PtCl6 content will result in low Pt loading on Pt / NPCNFs, affecting the electrocatalytic performance of the material.

[0055] Comparative Example 3 The difference between this comparative example and Example 1 is that in step 4, the heating method is through a condensation reflux device at 80°C. o Heat at C for 1 hour.

[0056] When the heating temperature is too low, the kinetics of the reduction reaction are insufficient, the reducing power of ethylene glycol is weak, resulting in a slow reduction rate of chloroplatinic acid, uneven size and distribution of the obtained platinum nanoparticles, and poor electrocatalytic performance of the material.

[0057] Insufficient heating time can lead to incomplete reaction, with Pt not being fully loaded onto NPCNFs. In addition, insufficient heating time can also result in insufficient growth time for nanoparticles, leading to severe agglomeration and small size of nanoparticles, resulting in poor electrocatalytic performance.

[0058] Comparative Example 4 The difference between this comparative example and Example 1 is that in step 3, the carbonization temperature during calcination is 700°C. o C, keep warm for 1 hour.

[0059] When the carbonization temperature and time are too low, PAN carbonization is uneven and its interior is not completely carbonized. The resulting NPCNFs have poor electrical conductivity, low mechanical strength, and are easily broken. At the same time, too low carbonization temperature and time will also lead to incomplete volatilization of ZIF-8, poor pore structure of NPCNFs, low catalyst specific surface area, affecting the loading of Pt nanoparticles and resulting in poor catalytic performance of the material.

[0060] Comparative Example 5 The difference between this comparative example and Example 1 is that in step 4, the pH of the solution is adjusted to 10-11. When the pH is too high, the reducing power of ethylene glycol is greatly enhanced, the reaction is violent, resulting in small Pt nanoparticle size and severe agglomeration, and poor electrocatalytic performance of the material.

[0061] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a platinum-supported porous carbon fiber catalyst for use as a proton exchange membrane cathode material, characterized in that: (1) Dissolve zinc salt and 2-methylimidazole separately in methanol solvent; mix and stir; after centrifugation, wash and dissolve the precipitate with DMF to obtain ZIF-8 / DMF solution; (2) Add polyacrylonitrile to the ZIF-8 / DMF obtained in step (1), stir to obtain spinning solution, obtain one-dimensional material by electrospinning, and obtain one-dimensional porous nitrogen-doped carbon nanofibers after heating and calcining and cooling. (3) Mix H2PtCl6, sodium citrate and ethylene glycol, adjust the pH, add one-dimensional porous nitrogen-doped carbon nanofibers, heat, wash and dry to obtain the product.

2. The preparation method according to claim 1, characterized in that, In step (1), the zinc salt is Zn(NO3)2; the mass ratio of zinc salt to 2-methylimidazole is 1:2.14-2.

17.

3. The preparation method according to claim 1, characterized in that, In step (1), the mixing and stirring method is to mix and stir at room temperature for 4-8 hours; the centrifugation speed is 10000-14000 rpm, the centrifugation time is 5-10 min; and the amount of DMF used is 5-10 mL.

4. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of polyacrylonitrile to ZIF-8 / DMF is 1:14.75-16.

29.

5. The preparation method according to claim 1, characterized in that, In step (2), the electrospinning method involves using a 10 mL syringe to fill the spinning solution, with a DC voltage of 10~11 kV and a flow rate of 0.18-0.3 mL / h. -1 The distance between the needle and the collector is 10-13 cm.

6. The preparation method according to claim 1, characterized in that, In step (2), the heating and calcination method is to use a high-temperature tube furnace under an inert atmosphere at 5°C. o C min -1 Heat to 180-250 o Hold at C for 1-3 hours, then heat to 980-1200 at the same rate. o Keep warm at room temperature for 3.5-5 hours.

7. The preparation method according to claim 1, characterized in that, In step (3), the mass ratio of H2PtCl6 to sodium citrate is 1:0.39-0.56; the amount of ethylene glycol used is 55-61g; the pH is adjusted to 8.5-9.0 by using 4 mg / mL NaOH / ethylene glycol solution.

8. The preparation method according to claim 1, characterized in that, In step (3), the amount of one-dimensional porous nitrogen-doped carbon nanofibers added is 5-15 mg; the heating method is through a condenser reflux device at 100-150 °C. o Heat at C for 3-5 hours; drying temperature is 60-80°C. o C.

9. A platinum-supported porous carbon fiber catalyst prepared by the method according to any one of claims 1-8 and used as a proton exchange membrane cathode material.

10. The application of the platinum-supported porous carbon fiber catalyst as described in claim 9, used as a proton exchange membrane cathode material, in PEM water electrolysis cathode materials.

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