A non-precious metal catalyst for fuel cells, its preparation method and application

Abstract

This invention belongs to the field of new energy materials and applications, and relates to a non-precious metal catalyst for fuel cells, its preparation method, and its application. This invention utilizes a metal framework compound ZIF-8 as a self-template and employs a one-step pyrolysis method to obtain a highly active non-precious metal catalyst with a Co-N-C component. The cobalt nanoparticles within the material are uniformly dispersed in nitrogen-containing porous carbon, exhibiting good reactivity and excellent catalytic oxygen reduction performance in a three-electrode system. It shows promising application prospects in fuel cells and other new energy devices.

Description

Technical Field

[0001] This invention relates to a non-precious metal catalyst for oxygen reduction catalysis in fuel cells, and a method for preparing such a catalyst, belonging to the field of new energy materials and applications, and specifically to a non-precious metal catalyst for fuel cells, its preparation method, and its application. Background Technology

[0002] Hydrogen fuel cells, capable of operating at low temperatures (0-200℃), have long been favored as a future-oriented sustainable energy conversion device. However, commercial Pt / C catalysts utilize large amounts of the precious metal platinum. For example, patent 202410453556.X discloses platinum-based intermetallic compound catalysts, preparation methods, membrane electrode assemblies, and fuel cells, using thiol-containing organic compounds as complexing agents to prepare highly ordered platinum-based intermetallic compound catalysts. Patent 202410328792.9 discloses a binary Pt-based ordered alloy fuel cell catalyst and its preparation method; these patents use platinum-based materials to prepare fuel cell catalysts, which are expensive and have unsatisfactory lifespans, hindering their commercialization. Therefore, developing high-quality, low-cost fuel cell catalysts, especially oxygen reduction reaction (ORR) catalysts based on the cell cathode, has been a persistent pursuit.

[0003] Among numerous non-noble metal oxygen reduction catalysts, although Fe-NC exhibits higher catalytic activity, it can catalyze the Fenton reaction, generating free radicals that attack the proton exchange membrane, causing membrane thinning, surface roughness, cracks, and pinholes, thus affecting proton conductivity, gas diffusion and permeation, and proton membrane stability. Therefore, Co-NC is considered the most promising material system. In Co-NC catalysts, the ORR reaction activity depends on the amount of CoNx. However, in existing technologies, Co-NC catalysts are prepared by simply increasing the cobalt content, leading to Co agglomeration and resulting in poor catalytic performance. Furthermore, the preparation process is complex and the raw materials are expensive. Therefore, there is an urgent need for a high-performance Co-NC catalyst and synthesis method that can be obtained through a one-step pyrolysis. Summary of the Invention

[0004] The purpose of this invention is to provide a non-precious metal catalyst for fuel cells, its preparation method and application. Using the metal framework compound ZIF-8 as a self-template, a high-performance Co-NC catalyst is obtained by one-step pyrolysis. The obtained non-precious metal catalyst for fuel cells exhibits excellent catalytic oxygen reduction performance in both alkaline and acidic electrolytes, and has good application prospects in fuel cells and other energy devices.

[0005] The technical solution provided by this invention is as follows:

[0006] A method for preparing a non-precious metal catalyst for fuel cells includes the following steps:

[0007] Zinc and cobalt salts were dissolved in deionized water to form the first solution;

[0008] 2-Methylimidazole and triethylamine were dissolved in deionized water to form a second solution;

[0009] The first solution was added dropwise to the second solution, and after stirring and reacting, the solid was separated by centrifugation.

[0010] The solid was washed, vacuum dried, ground, and then pyrolyzed to obtain a non-precious metal catalyst (Co-NC catalyst) for fuel cells.

[0011] The above method uses ZIF-8 as a self-template to obtain highly dispersed cobalt nanoparticles, thereby effectively avoiding the aggregation of cobalt nanoparticles. A high-performance Co-NC catalyst can be obtained through one-step pyrolysis.

[0012] Furthermore, the zinc salt is one or more of zinc nitrate, zinc sulfate, and zinc chloride, and the cobalt salt is one or more of cobalt nitrate, cobalt chloride, cobalt oxalate, cobalt sulfate, and cobalt acetate; preferably, the zinc nitrate is zinc nitrate hexahydrate, and the cobalt nitrate is cobalt nitrate hexahydrate. The types of zinc and cobalt salts may affect the composition, structure, and performance of the final catalyst. By selecting different zinc and cobalt salts, key performance indicators such as the activity, selectivity, and stability of the catalyst can be controlled to meet the needs of fuel cells in different application scenarios.

[0013] Furthermore, the molar ratio of zinc salt to cobalt salt is (1-50):1. Different zinc-cobalt ratios can result in different particle sizes for the Co-NC catalyst. By controlling the ratio of zinc nitrate to cobalt nitrate within a suitable range, the Co-NC catalyst can achieve a better particle size.

[0014] Furthermore, the molar ratio of 2-methylimidazole to triethylamine is (0.1–1):1. Controlling the ratio of 2-methylimidazole to triethylamine within a suitable range can improve the carbonization effect of ZIF-8.

[0015] Furthermore, the total molar ratio of metal ions in the first solution to the molar ratio of 2-methylimidazole in the second solution is 1:(1-10). By controlling the metal ions and 2-methylimidazole within appropriate ranges, the first and second solutions can also be controlled within appropriate ranges, which can improve the ORR activity of the catalyst.

[0016] Furthermore, the first solution is added dropwise to the second solution, and the mixture is stirred to allow for a reaction. The stirring time is 20–50 minutes, and the stirring speed is 300–800 rpm. Controlling the stirring time and speed of the first and second solutions can improve their reaction efficiency and allow the cobalt atoms to exert a better synergistic effect with the nitrogen-doped carbon substrate.

[0017] Furthermore, the centrifugation speed is 500–3000 rpm. Controlling the centrifugation speed of the mixture of the first and second solutions allows for better separation of the solid product.

[0018] In one embodiment, the pyrolysis temperature is 500–1000°C, and the pyrolysis time is 1–10 h. By controlling the pyrolysis temperature and time of the reaction products of the first and second solution mixture, the obtained catalyst can have better sintering effect and stability, exhibiting ORR activity comparable to Pt / C in both alkaline and acidic systems.

[0019] Furthermore, the solid obtained after centrifugation is pyrolyzed at high temperature under an inert atmosphere, namely nitrogen or argon. High-temperature pyrolysis under an inert gas atmosphere can improve the stability of the product.

[0020] Furthermore, after adding the first solution dropwise to the second solution, the reaction is stirred for 20–50 minutes at a speed of 300–800 rpm. Appropriate stirring time and speed help form catalyst particles with uniform structure and narrow particle size distribution. This helps increase the specific surface area and the number of active sites of the catalyst, thereby improving its catalytic performance.

[0021] The present invention also provides a non-precious metal catalyst for fuel cells, which is prepared by the above method.

[0022] The present invention also provides the application of the above-mentioned non-precious metal catalyst for fuel cells in the preparation of methanol poisoning resistant fuel cells.

[0023] Beneficial effects

[0024] This invention utilizes deionized water as a solvent to synthesize cobalt-doped ZIF-8 simply and efficiently in the presence of triethylamine. A high-performance Co-NC catalyst can then be obtained through one-step pyrolysis. This method uses ZIF-8 as a self-template to obtain highly dispersed cobalt nanoparticles, effectively preventing their aggregation. Furthermore, thanks to the synergistic effect of cobalt atoms and the nitrogen-doped carbon substrate, the catalyst exhibits ORR activity comparable to Pt / C in both alkaline and acidic systems. A 10-hour stability test shows that the Co-NC catalyst exhibits a degradation of 92.9%, a 16.8% improvement compared to Pt / C. It also demonstrates excellent methanol resistance, thus showing promising application prospects in fuel cells and other energy devices. Attached Figure Description

[0025] Figure 1 Zn obtained using ZIF 8 as a self-template in Examples 1-3 and Comparative Example 1 1-x Co x XRD pattern of (MeIM)2 (x = 0, 0.05, 0.075, 0.1);

[0026] Figure 2 The XRD patterns of Co-NCx obtained using ZIF 8 as a self-template in Examples 1-3 and Comparative Example 1 are shown (x = 0, 0.05, 0.075, 0.1).

[0027] Figure 3 The graph shows a comparison of the ORR performance of Co-NCx and Pt / C with different cobalt contents obtained using ZIF 8 as a template in Examples 1-3 and Comparative Example 1 in alkaline solutions.

[0028] Figure 4 The graph shows the stability and methanol resistance of Co-NC-0.05 with different cobalt contents obtained by using ZIF 8 as a template in Example 1 in alkaline solution. Detailed Implementation

[0029] Example 1

[0030] 1) Dissolve 0.6952 g of zinc nitrate hexahydrate and 0.0358 g of cobalt nitrate heptahydrate in 50 mL of deionized water, and denote this as solution A. The molar ratio of zinc nitrate hexahydrate to cobalt nitrate heptahydrate is 95:5.

[0031] 2) Dissolve 1.642 g of 2-methylimidazole and 3 mL of triethylamine in 50 mL of deionized water, denoted as solution B. The molar ratio of 2-methylimidazole to triethylamine is 1:1. The total molar ratio of metal ions in step 1) to the molar ratio of 2-methylimidazole in step 2) is 1:8.

[0032] 3) Slowly add solution A to solution B, stir for 30 min at 500 rpm, and centrifuge to obtain a purple solid.

[0033] 4) The solid obtained in step 2) is redispersed in deionized water for 24 h, then centrifuged and washed, and vacuum dried at 100°C for 24 h. The obtained solid is then ground into powder with a vacuum degree of -0.08~-0.1MPa.

[0034] 5) The powder obtained in step 3) was pyrolyzed at 1000 °C for 3 hours under an inert atmosphere to prepare the Co-NC-0.05 catalyst.

[0035] Example 2

[0036] 1) Dissolve 0.6769 g of zinc nitrate hexahydrate and 0.0537 g of cobalt nitrate heptahydrate in 50 mL of deionized water, and denote this as solution A. The molar ratio of zinc nitrate hexahydrate to cobalt nitrate heptahydrate is 92.5 : 7.5.

[0037] 2) Dissolve 1.642 g of 2-methylimidazole and 3 mL of triethylamine in 50 mL of deionized water, denoted as solution B. The molar ratio of 2-methylimidazole to triethylamine is 1:1. The total molar ratio of metal ions in step 1) to the molar ratio of 2-methylimidazole in step 2) is 1:8.

[0038] 3) Slowly add solution A to solution B, stir for 30 min at 500 rpm, and centrifuge to obtain a purple solid.

[0039] 4) The solid obtained in step 2) is redispersed in deionized water for 24 h, then centrifuged and washed, and vacuum dried at 100 °C for 24 h. The obtained solid is then ground into powder with a vacuum degree of -0.08~-0.1 MPa.

[0040] 5) The powder obtained in step 3) was pyrolyzed at 1000 °C for 3 hours under an inert atmosphere to prepare the Co-NC-0.075 catalyst.

[0041] Example 3

[0042] 1) Dissolve 0.6586 g of zinc nitrate hexahydrate and 0.07160 g of cobalt nitrate heptahydrate in 50 mL of deionized water, and denote this as solution A. The molar ratio of zinc nitrate hexahydrate to cobalt nitrate heptahydrate is 90:10.

[0043] 2) Dissolve 1.642 g of 2-methylimidazole and 3 mL of triethylamine in 50 mL of deionized water, denoted as solution B. The molar ratio of 2-methylimidazole to triethylamine is 1:1. The total molar ratio of metal ions in step 1) to the molar ratio of 2-methylimidazole in step 2) is 1:8.

[0044] 3) Slowly add solution A to solution B, stir for 30 min at 500 rpm, and centrifuge to obtain a purple solid.

[0045] 4) The solid obtained in step 2) is redispersed in deionized water for 24 h, then centrifuged and washed, and vacuum dried at 100 °C for 24 h. The obtained solid is then ground into powder with a vacuum degree of -0.08~-0.1 MPa.

[0046] 5) The powder obtained in step 3) was pyrolyzed at 1000 °C for 3 hours under an inert atmosphere to prepare the Co-NC-0.1 catalyst.

[0047] Comparative Example 1

[0048] 1) Dissolve 0.732g of zinc nitrate hexahydrate in 50 mL of deionized water, and denote this solution as solution A.

[0049] 2) Dissolve 1.642 g of 2-methylimidazole and 3 mL of triethylamine in 50 mL of deionized water, denoted as solution B. The molar ratio of 2-methylimidazole to triethylamine is 1:1. The total molar ratio of metal ions in step 1) to the molar ratio of 2-methylimidazole in step 2) is 1:8.

[0050] 3) Slowly add solution A to solution B, stir for 30 min at 500 rpm, and centrifuge to obtain a grayish-white solid.

[0051] 4) The solid obtained in step 2) is redispersed in deionized water for 24 h, then centrifuged and washed, and vacuum dried at 100 °C for 24 h. The obtained solid is then ground into powder with a vacuum degree of -0.08~-0.1 MPa.

[0052] 5) The powder obtained in step 3) was pyrolyzed at 1000 °C for 3 hours under an inert atmosphere to prepare the Co-NC-0 catalyst.

[0053] X-ray diffraction (XRD) can be used to characterize the phase structure of the prepared sample. For example... Figure 1 As shown, Zn 1-x Co xAll peaks of the (MeIM)2 precursor showed excellent agreement with the simulated ZIF-8, demonstrating the precursor's high crystallinity and similar zeolite structure. Through further high-temperature pyrolysis, we directly obtained Co-NC catalysts with different Co doping levels. Figure 2 It can be seen that the peak at approximately 22.8° corresponds to the C(002) crystal plane, and the other peaks at approximately 44.3° are attributed to metallic β-Co (PDF: 15-0806). Furthermore, with increasing Co doping concentration, the Scherrer equation indicates that the Co metal particle size in the Co-NC catalyst gradually increases, suggesting that high Co content leads to Co sintering in the catalyst. Meanwhile, in the XRD patterns, no obvious Co metal particles were found in the ZIF-8 carbonized NC and Co-NC-0.05. This indicates that the increased Zn content leads to spatial isolation of Co, thereby inhibiting Co sintering.

[0054] To evaluate the electrocatalytic performance of Co-NC, we used linear sweep voltammetry to test its performance at different rotational speeds in 0.1 M KOH solution. Figure 3 As shown, by comparing the half-wave potentials (E1 / 2) of the RDE polarization curves, Co-NC-0.05 exhibits the best ORR activity, while the undoped NC (carbonized ZIF-8) performs the worst. More importantly, the half-wave potential of Co-NC-0.05 (0.84 V vs RHE) is comparable to that of 20 wt% Pt / C (0.84 V vs RHE), which is higher than the performance of some other reported non-noble metal electrocatalysts. This indicates that the Co-NC synthesized in this experiment possesses high electrocatalytic ORR activity.

[0055] The stability and resistance to methanol poisoning of a catalyst are also important indicators for evaluating its quality. Figure 4 It can be seen that Co-NC-0.05 exhibits superior resistance to methanol poisoning and stability. Chronoamperometry (ChRM) curves tested at 1600 rpm show that after 10 hours, the performance of Co-NC-0.05 decreased to 92.9%, while that of Pt / C decreased to 76.1%. Furthermore, after adding 3 M methanol to the electrolyte, the CV curve and the original cathode ORR current of Co-NC-0.05 remained almost unchanged, while the corresponding current on Pt / C instantly changed from the cathode ORR current to the reverse anodic current. This indicates that methanol underwent an oxidation reaction on Pt / C, and Co-NC-0.050 possesses excellent resistance to methanol poisoning.

[0056] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0057] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. The application of non-precious metal catalysts for fuel cells in the preparation of methanol-resistant fuel cells, characterized in that, The preparation method of the non-precious metal catalyst for fuel cells includes the following steps: Zinc nitrate hexahydrate and cobalt nitrate heptahydrate are dissolved in deionized water and denoted as solution A; the molar ratio of zinc nitrate hexahydrate to cobalt nitrate heptahydrate is 95:5; 2-Methylimidazole and triethylamine are dissolved in deionized water and denoted as solution B; the molar ratio of 2-methylimidazole to triethylamine is 1:1; the total molar number of metal ions in solution A is in the molar ratio of 2-methylimidazole to 1:8; Solution A was slowly added to solution B, stirred for 30 min at 500 rpm, and centrifuged to obtain a purple solid. The obtained solid was redispersed in deionized water and then centrifuged and washed. It was then vacuum dried at 100°C for 24 h. The obtained solid was then ground into powder under a vacuum of -0.08 to -0.1 MPa. The obtained powder was pyrolyzed at 1000 °C for 3 hours under an inert atmosphere to prepare the Co-NC-0.05 catalyst.

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