A non-precious metal nitrogen-carbon supported platinum alloy electrocatalyst for fuel cells and its preparation method and application

Abstract

The present invention discloses a non-precious metal nitrogen-carbon-loaded platinum alloy electrocatalyst for fuel cells, as well as a preparation method and application, and belongs to the field of fuel cells. The method uses metal nitrogen-carbon obtained by high-temperature carbonization of an imidazole metal organic framework as a carrier, ultrasonically disperses the platinum precursor and the metal nitrogen-carbon, dries, heat-treats in a reducing atmosphere, and combines an acid pickling and etching process to obtain a catalyst. The nitrogen-doped carbon carrier can inhibit the agglomeration of nanoparticles during high-temperature roasting, which is conducive to obtaining a catalyst with small and uniformly dispersed metal nanoparticles. In addition, the transition metal in the catalyst is introduced from the carrier without the need to add additional metal salts. Electrochemical studies have shown that the catalyst prepared by the present invention has excellent electrochemical activity and stability. The preparation method of the present invention is simple and easy to mass produce.

Description

Technical Field

[0001] The present invention belongs to the field of fuel cells, and in particular relates to a non-noble metal nitrogen-carbon loaded platinum alloy electrocatalyst for fuel cells, a preparation method and an application thereof. Background Art

[0002] Fuel cells convert chemical energy into electrical energy through electrochemical methods. They are efficient and clean energy conversion devices with advantages such as high energy conversion efficiency, fast startup at low temperatures, and environmental friendliness. They are widely used in aerospace, portable power supplies, public transportation, and other fields. Automotive fuel cells are in the early stages of commercialization, but their cost and lifespan limit their large-scale adoption.

[0003] Electrocatalysts are key materials that restrict the cost and lifespan of fuel cells. It is well known that Pt / C catalysts, dispersed in the form of nanoparticles on a carbon support, are currently the most widely used oxygen reduction catalysts. However, Pt, as a rare and precious metal, has limited reserves and a high price, resulting in high fuel cell costs and a significant impediment to their commercialization. Alloying Pt with transition metals (such as Fe, Co, Ni, and Mn) can significantly enhance the oxygen reduction activity of the catalyst through electronic and geometric effects. However, transition metals are susceptible to dissolution and loss in the highly acidic, oxidizing, and high-potential operating environments of fuel cells, thereby reducing catalyst activity and stability. Furthermore, lost transition metal particles can migrate to the proton exchange membrane through concentration differences, causing irreversible degradation of the membrane and ultimately shortening the fuel cell's lifespan. High-temperature heat treatment of Pt and transition metals followed by acid removal can effectively alleviate this transition metal loss problem. However, high-temperature heat treatment of conventional carbon supports (such as XC-72 and BP2000) can easily lead to sintering and agglomeration of nanoparticles, reducing catalyst utilization. In recent years, non-precious metal nitrogen-carbon-oxygen reduction catalysts (such as Fe-NC, Co-NC, and Mn-NC) have made significant progress under harsh acidic conditions. Their large surface area allows for uniform dispersion of nanoparticles, and the synergistic effect of non-precious metal nitrogen-carbon supports and Pt nanoparticles further enhances catalytic activity.

[0004] Chinese patents (109616671A and 110649273A) use graphene oxide as a carrier. A noble metal precursor and a non-noble gold salt are mixed in an aqueous solution, freeze-dried to form a highly dispersible precursor, and then heat-treated at high temperature to form an alloy, thereby avoiding sintering and agglomeration of the nanoparticles. However, this process requires the addition of an additional transition metal salt solution. Summary of the Invention

[0005] The present invention provides a non-precious metal nitrogen-carbon-supported platinum alloy electrocatalyst for fuel cells, as well as its preparation method and application. The present invention utilizes catalytically active non-precious metal nitrogen-carbon as a support, and employs ultrasonic impregnation reduction and high-temperature calcination to prepare a fuel cell electrocatalyst. This electrocatalyst exhibits high catalytic activity and stability, and its large electrochemically active area facilitates improved catalyst utilization, thereby reducing fuel cell costs and extending their lifespan. Furthermore, the preparation method is simple, the process is controllable, and it is readily adaptable to mass production.

[0006] The technical solution adopted in the present invention is as follows:

[0007] The present invention provides a method for preparing a non-noble metal nitrogen-carbon supported platinum alloy electrocatalyst for a fuel cell, comprising the following steps:

[0008] (1) carbonizing a zinc-based imidazole metal organic framework at high temperature in an inert gas atmosphere to obtain a metal nitrogen-carbon support;

[0009] (2) uniformly dispersing the platinum precursor and the metal nitrogen-carbon carrier in water or an organic solvent to obtain a mixed solution;

[0010] (3) evaporating the solvent from the mixed solution to obtain a solid product;

[0011] (4) reducing the solid product obtained in step (3) at a low temperature of 200-300° C. in a reducing atmosphere, and then calcining it at a high temperature of 700-950° C. to obtain a platinum alloy catalyst;

[0012] (5) The platinum alloy catalyst obtained in step (4) is acid-washed and dried to obtain the platinum alloy electrocatalyst.

[0013] Based on the above technical solution, the zinc-based imidazole metal organic framework includes: Zn / Fe-ZIF, Zn / Co-ZIF, Zn / Ni-ZIF, Zn / Mn-ZIF, Zn / Cu-ZIF, the molar ratio of transition metal to total metal is 5%-80%, the high-temperature carbonization temperature is 900-1100°C, the high-temperature carbonization time is 1-6h, and the inert gas range is N2 or Ar.

[0014] Based on the above technical solution, the platinum precursor in step (2) includes sodium chloroplatinate, chloroplatinic acid or platinum acetylacetonate; the organic solvent includes: one of ethylene glycol, acetone or n-hexane; the uniform dispersion is achieved by ultrasonic dispersion, and the ultrasonic dispersion time is 1-12 hours.

[0015] Based on the above technical solution, the mass ratio of the metal nitrogen-carbon carrier to the platinum precursor in step (2) is 1:0.1-1:5.

[0016] Based on the above technical solution, when water is used to disperse the platinum precursor in step (2), freeze drying is used to volatilize the solvent in step (3), the freeze drying temperature is -30 to -50°C, and the freeze drying time is 12 to 48 hours; when an organic solvent is used to disperse the platinum precursor in step (2), rotary evaporation is used to volatilize the solvent, the rotary evaporation temperature is 60 to 180°C, and the rotary evaporation time is 6 to 24 hours.

[0017] Based on the above technical solution, the reduction time at 200-300° C. in step (4) is 2-12 h, and the high-temperature calcination time at 700-950° C. is 1-12 h.

[0018] Based on the above technical solution, the reducing atmosphere in step (4) is a H2 / Ar or H2 / N2 mixed gas, wherein the volume ratio of H2 to Ar or N2 gas is 5-20%.

[0019] Based on the above technical solution, the acid used for pickling in step (5) is 0.1-1 mol L -1 The pickling temperature is 50-80°C, the pickling time is 12-48h, and the catalyst after pickling is freeze-dried at -30-50°C or dried in a vacuum oven at 60-80°C for 12-24h;

[0020] The present invention also provides a non-noble metal nitrogen-carbon supported platinum alloy electrocatalyst for a fuel cell prepared according to the above preparation method. The nanoparticles of the catalyst have a particle size of 2-10 nm and are evenly distributed.

[0021] The present invention also provides an application of the catalyst, which is applied to a proton exchange membrane fuel cell.

[0022] Beneficial effects

[0023] (1) The present invention uses high specific surface area Zn-M-ZIF as a precursor, and during the high-temperature carbonization process, the volatilization of Zn produces a non-noble metal nitrogen-carbon carrier with oxygen reduction activity;

[0024] (2) The present invention introduces non-precious metals from the carrier under a reducing atmosphere to form a platinum alloy. The synergistic effect of the carrier and the alloying effect are beneficial to improving the intrinsic activity of the catalyst;

[0025] (3) The nitrogen in the non-noble metal nitrogen-carbon carrier of the present invention can inhibit the sintering and agglomeration of nanoparticles during high-temperature calcination, which is conducive to obtaining nanoparticles with small particle size and uniform dispersion, thereby obtaining a larger electrochemical active area and improving the utilization rate of the catalyst;

[0026] (4) The alloy electrocatalyst prepared by the present invention is heat treated at high temperature and pickled to remove excess non-precious metals, which is beneficial to enhancing the stability of the catalyst;

[0027] (5) The composition of the electrocatalyst prepared by the present invention is adjustable, and the preparation method is simple and easy to scale up. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 (a) is the X-ray diffraction pattern of the Pt3Co / Co-NC catalyst prepared in Example 1; Figure 1 (b) Transmission electron microscopy image of Pt3Co / Co-NC prepared in Example 1.

[0029] Figure 2 (a) shows the oxygen reduction polarization curve of the Co-NC support prepared in Example 1. The test was carried out in an O2-saturated 0.1 M HClO4 electrolyte with a scan rate of 5 mV / s in the positive direction and an RDE speed of 1600 rpm / min. Figure 2 (b) Cyclic voltammetry (CV) curve of Pt3Co / Co-NC prepared in Example 1, tested in N2-saturated 0.1 M HClO4 electrolyte at a scan rate of 50 mV / s; Figure 2 (c) is the ORR polarization curve of Pt3Co / Co-NC prepared in Example 1.

[0030] Figure 3 Figure 2 shows the oxygen reduction polarization curves before and after accelerated decay for Pt3Co / Co-NC and commercial Pt / C(TKK) prepared in Example 1. Accelerated decay tests were conducted in a nitrogen-saturated 0.1 M HClO4 electrolyte, with a scan potential range of 0.6-1.0 V vs. RHE, 20,000 cycles at room temperature, and a scan rate of 50 mV / s.

[0031] Figure 4 (a) is the X-ray diffraction pattern of the catalyst prepared in Comparative Example 1; Figure 4 (b) is the oxygen reduction polarization curve of the catalyst prepared in Comparative Example 1.

[0032] Figure 5 (a) is the X-ray diffraction pattern of the catalyst prepared in Comparative Example 2; Figure 5 (b) is the oxygen reduction polarization curve of the catalyst prepared in Comparative Example 2.

[0033] Figure 6 This is the oxygen reduction polarization curve of the catalyst prepared in Comparative Example 3.

[0034] Figure 7 This is the oxygen reduction polarization curve of Pt3Mn / Mn-NC prepared in Example 2.

[0035] Figure 8 This is the oxygen reduction polarization curve of Pt3Fe / Fe-NC prepared in Example 3.

[0036] Figure 9 This is the oxygen reduction polarization curve of PtFe / Fe-NC prepared in Example 4. DETAILED DESCRIPTION

[0037] The following examples are further illustrations of the present invention, which also protects obvious variations and equivalent substitutions.

[0038] Example 1

[0039] (1) Synthesis of 40% Zn-Co-ZIF: According to the conventional synthesis method of ZIF, Co(NO3)2·6H2O and Zn(NO3)2·6H2O were dissolved in anhydrous methanol, and dimethylimidazole was used as a ligand. The 40% value indicates that the molar ratio of Co to the total metal content is 40%, the molar ratio of dimethylimidazole to Zn(NO3)2·6H2O is 4, and the concentration of Zn(NO3)2·6H2O dissolved in anhydrous methanol is 20 mmol L -1 The mixed solution was allowed to stand at 60°C for 24 hours, and the product was collected by centrifugation and washed three times with ethanol. Finally, it was dried in a vacuum oven at 60°C. The prepared 40% Zn-Co-ZIF was carbonized at 1100°C for 2 hours under a nitrogen atmosphere. Since the boiling point of Zn is 902°C, a Co-NC support was obtained after carbonization.

[0040] (2) Ultrasonic dispersion of Co-NC carrier in 10 mg mL -1 In the aqueous chloroplatinic acid solution, the mass ratio of the carrier to chloroplatinic acid is 1:1, and the ultrasonic time is 2 h.

[0041] (3) The mixed solution in step (2) was frozen with liquid nitrogen and then dried in a freeze dryer at -50°C for 24 h.

[0042] (4) The Co-NC adsorbed with chloroplatinic acid was calcined in a 5% H2 / Ar mixed gas at 200°C for 6 h, and then heated to 700°C for 3 h.

[0043] (5) The sample after high temperature calcination was -1 The catalyst was washed in perchloric acid at 70°C for 24 h and dried in a vacuum oven at 60°C for 12 h to obtain the catalyst.

[0044] Figure 1 (a) is the XRD pattern of the catalyst prepared in this example, and its results correspond to the standard card 29-0499 of Pt3Co, indicating that Pt3Co alloy was obtained after high-temperature calcination and acid washing using Co-NC as the carrier.

[0045] Figure 1(b) is a TEM image of the Pt3Co alloy prepared in this example, which shows that the average particle size of the Pt3Co nanoparticles is about 3 nm and is evenly distributed on the Co-NC support.

[0046] Figure 2 (a) The Co-NC support prepared in this example was heated in 0.1 mol L -1 Oxygen reduction polarization curve in HClO4. The test shows that the Co-NC support has oxygen reduction activity, with a half-wave potential of 0.78V vs. RHE (reversible hydrogen electrode).

[0047] Figure 2 (b) and Figure 2 (c) CV curve and polarization curve of Pt3Co / Co-NC prepared in this example. The electrochemical active area (ECSA) calculated from the CV curve is 79m 2 g -1 , the ORR polarization curve shows that its half-wave potential is 0.910 V vs. RHE.

[0048] Figure 3 Performance comparison of the Pt3Co / Co-NC catalyst prepared in this example and the commercial Pt / C catalyst before and after accelerated decay. As can be seen from the figure, the performance and stability of the Pt3Co / Co-NC catalyst are superior to those of the commercial Pt / C.

[0049] In order to illustrate the effects of high-temperature calcination and calcination temperature on the catalyst activity in step (4) of Example 1 of the present invention, the following comparative experiment was conducted.

[0050] Comparative Example 1

[0051] Comparative Example 1 The high temperature calcination step (4) in Example 1 was deleted, that is, (4) the Co-NC adsorbed with chloroplatinic acid was calcined at 200 ° C for 6 h in a 5% H2 / Ar mixed gas. (5) The obtained sample was heated to 0.5 mol L -1 The catalyst was washed in perchloric acid at 70°C for 24 hours and dried in a vacuum oven at 60°C for 12 hours. The remaining steps were the same as those in Example 1. The catalyst of Comparative Example 1 was obtained.

[0052] Figure 4 (a) is the XRD pattern of the catalyst prepared in Comparative Example 1, which corresponds to the Pt standard card 04-0802, indicating that after calcination at 200°C for 6h, Pt can only be reduced on the Co-NC support and no PtCo alloy can be formed.

[0053] Figure 4 (b) is the ORR polarization curve of the catalyst prepared in Comparative Example 1, and its half-wave potential is only 0.830 V vs. RHE.

[0054] Comparative Example 2

[0055] Comparative Example 2: The high-temperature calcination temperature in Example 1 was reduced from 700°C to 600°C, i.e. (4) Co-NC adsorbed with chloroplatinic acid was calcined at 200°C for 6 h in a 5% H2 / Ar mixed gas, and then the temperature was raised to 600°C and calcined for 3 h. (5) The obtained sample was heated to 0.5 mol L -1 The catalyst was washed with perchloric acid at 70°C for 24 hours and dried in a vacuum oven at 60°C for 12 hours. The remaining steps were the same as those in Example 1. The catalyst of Comparative Example 2 was obtained.

[0056] Figure 5 (a) is the XRD pattern of the catalyst prepared in Comparative Example 2, the results of which correspond to the Pt standard card 04-0802, indicating that after calcination at 600°C for 3h, Pt cannot form an alloy with Co in the Co-NC support.

[0057] Figure 5 (b) ORR polarization curves of the catalyst prepared in Comparative Example 2 and the commercial Pt / C catalyst. The half-wave potential of the catalyst in Comparative Example 2 is 0.858 V vs. RHE, and the half-wave potential of the commercial Pt / C catalyst is 0.880 V vs. RHE.

[0058] The above experimental results show that when Pt and non-precious metal supports are not calcined at high temperature or the calcination temperature is not enough to form an alloy (less than 700°C), the catalytic activity of the prepared Pt / Co-NC is lower than that of commercial Pt / C.

[0059] In addition, to illustrate the effect of reducing atmosphere on the catalyst activity during the calcination process in step (4) of Example 1, the following comparative experiment was conducted.

[0060] Comparative Example 3

[0061] Comparative Example 3: The atmosphere during the high-temperature calcination stage in step (4) of Example 1 was changed to Ar. Specifically, in step (4), the Co-NC adsorbed with chloroplatinic acid was calcined at 200°C in a 5% H2 / Ar mixture for 6 h, and then the temperature was raised to 700°C under Ar for 3 h. The remaining steps were the same as in Example 1, yielding the catalyst of Comparative Example 3.

[0062] Figure 6 The ORR polarization curve for the catalyst prepared in Comparative Example 3 showed a half-wave potential of 0.885 V vs. RHE, slightly higher than that of commercial Pt / C (half-wave potential 0.880 V vs. RHE) but lower than that of the catalyst calcined in a reducing atmosphere in Example 1 (half-wave potential 0.910 V vs. RHE). These experimental results demonstrate that high-temperature calcination of Pt and a non-precious metal support in a reducing atmosphere is beneficial for producing a highly active catalyst.

[0063] Example 2

[0064] (1) Synthesis of 20% Zn-Mn-ZIF: Following the conventional ZIF synthesis method, MnCl2 and Zn(NO3)2·6H2O were dissolved in anhydrous methanol with dimethylimidazole as the ligand, where 20% represents a 20% molar ratio of Mn to the total metal content. The mixture was carbonized at 900°C for 3 h under an Ar atmosphere and ground to obtain the Mn-NC support.

[0065] (2) Ultrasonic dispersion of Mn-NC carrier in 10 mg mL -1 In the sodium chloroplatinate aqueous solution, the mass ratio of the carrier to chloroplatinic acid is 1:2, and the ultrasonic time is 2h.

[0066] (3) Freeze the mixture in step (2) with liquid nitrogen, and then transfer it to a freeze dryer and dry it at -45°C for 24 hours.

[0067] (4) The Mn-NC adsorbed with sodium chloroplatinic acid salt was calcined in a 10% H2 / Ar mixed gas at 300°C for 2 h, and then heated to 950°C for 2 h.

[0068] (5) The sample after high temperature calcination was -1 The catalyst was washed in hydrochloric acid at 80°C for 24 h and dried in a vacuum oven at 60°C for 12 h to obtain the catalyst.

[0069] Figure 7 This is the polarization curve of Pt3Mn / Mn-NC prepared in this example, and its half-wave potential is 0.905 V vs. RHE.

[0070] Example 3

[0071] (1) Synthesis of 10% Zn-Fe-ZIF: Following conventional ZIF synthesis methods, 10% Fe-Zn-ZIF was synthesized by dissolving Fe(NO₃)₂·6H₂O and Zn(NO₃)₂·6H₂O in anhydrous methanol with dimethylimidazole as a ligand, where 10% represents the molar ratio of Fe to the total metal content. The Fe-NC support was carbonized at 1100°C for 1 h under a nitrogen atmosphere and ground.

[0072] (2) Ultrasonic dispersion of Fe-NC carrier in 10 mg mL -1 In the aqueous chloroplatinic acid solution, the mass ratio of the carrier to chloroplatinic acid is 1:0.5, and the ultrasonic time is 2 h.

[0073] (3) Freeze the mixture in step (2) with liquid nitrogen, and then transfer it to a freeze dryer and dry it at -35°C for 24 hours.

[0074] (4) The Fe-NC adsorbed with chloroplatinic acid was calcined in a 15% H2 / Ar mixed gas at 220°C for 3 h, and then heated to 850°C for 6 h.

[0075] (5) The sample after high temperature calcination was -1 The catalyst was acid washed in nitric acid at 50°C for 12 h and dried in a freeze dryer at -40°C for 12 h to obtain the catalyst.

[0076] Figure 8 This is the polarization curve of Pt3Fe / Fe-NC prepared in this example, and its half-wave potential is 0.912 V vs. RHE.

[0077] Example 4

[0078] (1) Synthesis of 30% Zn-Fe-ZIF: Following conventional ZIF synthesis methods, 30% Fe-Zn-ZIF was synthesized by dissolving Fe(NO₃)₂·6H₂O and Zn(NO₃)₂·6H₂O in anhydrous methanol with dimethylimidazole as a ligand. 30% represents the molar ratio of Fe to the total metal content. The Fe-NC support was carbonized at 1000°C for 2 h under a nitrogen atmosphere and ground.

[0079] (2) Ultrasonic dispersion of Fe-NC carrier in 15 mg mL -1 In the acetone solution of platinum acetylacetonate, the mass ratio of the carrier to platinum acetylacetonate is 1:1, and the ultrasonic time is 1 h.

[0080] (3) The solvent of the mixed solution in the above step (2) is evaporated to dryness by rotary evaporation.

[0081] (4) The Fe-NC adsorbed with platinum acetylacetonate was calcined in a 10% H2 / Ar mixed gas at 250°C for 6 h, and then heated to 900°C for 2 h.

[0082] (5) The sample after high temperature calcination was 1 mol L -1 The catalyst was washed with perchloric acid at 60°C for 12 h and dried in a vacuum oven at 60°C for 12 h to obtain the catalyst.

[0083] Figure 9 This is the polarization curve of the PtFe / Fe-NC catalyst prepared in this example, and its half-wave potential is 0.902 V vs. RHE.

Claims

1. A method for preparing a non-noble metal nitrogen-carbon supported platinum alloy electrocatalyst for a fuel cell, characterized in that: The steps include: (1) carbonizing a zinc-based imidazole metal organic framework at high temperature in an inert gas atmosphere to obtain a metal nitrogen-carbon support; (2) uniformly dispersing the platinum precursor and the metal nitrogen-carbon carrier in water or an organic solvent to obtain a mixed solution; (3) evaporating the solvent from the mixed solution to obtain a solid product; (4) reducing the solid product obtained in step (3) at a low temperature of 200-300° C. in a reducing atmosphere, and then calcining it at a high temperature of 700-950° C. to obtain a platinum alloy catalyst; (5) The platinum alloy catalyst obtained in step (4) is acid-washed and dried to obtain the platinum alloy electrocatalyst.

2. The preparation method according to claim 1, characterized in that The zinc-based imidazole metal organic framework includes Zn / Fe-ZIF, Zn / Co-ZIF, Zn / Ni-ZIF, Zn / Mn-ZIF or Zn / Cu-ZIF, the molar ratio of transition metal to total metal is 5%-80%, the high-temperature carbonization temperature is 900-1100°C, the high-temperature carbonization time is 1-6h, and the inert gas atmosphere is N2 or Ar.

3. The preparation method according to claim 1, characterized in that In step (2), the platinum precursor includes sodium chloroplatinate, chloroplatinic acid or platinum acetylacetonate; and the organic solvent includes one of ethylene glycol, acetone or n-hexane.

4. The preparation method according to claim 1, characterized in that In step (2), the mass ratio of the metal nitrogen-carbon carrier to the platinum precursor is 1:0.1-1:

5.

5. The preparation method according to claim 1, characterized in that When water is used to disperse the platinum precursor in step (2), freeze drying is used to volatilize the solvent in step (3), the freeze drying temperature is -30 to -50°C, and the freeze drying time is 12 to 48 hours; when an organic solvent is used to disperse the platinum precursor in step (2), rotary evaporation is used to volatilize the solvent, the rotary evaporation temperature is 60 to 180°C, and the rotary evaporation time is 6 to 24 hours.

6. The preparation method according to claim 1, characterized in that In step (4), the reduction time at 200-300° C. is 2-12 h, and the high-temperature calcination time at 700-950° C. is 1-12 h.

7. The preparation method according to claim 1, characterized in that The reducing atmosphere in step (4) is a H2 / Ar or H2 / N2 mixed gas, wherein the volume ratio of H2 to Ar or N2 gas is 5-20%.

8. The preparation method according to claim 1, characterized in that: The acid used for pickling in step (5) is 0.1-1 mol L -1 The pickling temperature is 50-80℃, the pickling time is 12-48h, and the catalyst after pickling is freeze-dried at -30-50℃ or vacuum-dried at 60-80℃.

9. The fuel cell non-noble metal nitrogen-carbon supported platinum alloy electrocatalyst prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The nanoparticles of the catalyst have a particle size of 2-10 nm and are evenly distributed.

10. Use of the electrocatalyst according to claim 9, characterized in that: Applied to proton exchange membrane fuel cells.

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