Fe-based bimetallic-nitrogen-carbon catalyst of alkaline earth metal coordination site as well as preparation method and application of Fe-based bimetallic-nitrogen-carbon catalyst
By constructing Fe/M-Nx active centers and utilizing catalysts formed by heavier alkaline earth metals and Fe, the problems of easy dissolution of active sites and low proton supply efficiency of Fe-NC catalysts in acidic environments were solved, achieving high activity and high stability in oxygen reduction reactions.
Patent Information
- Application Number
- CN202511198203.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-26
- Publication Date
- 2025-11-11
AI Technical Summary
Existing Fe-NC catalysts have active sites that are easily dissolved in acidic environments, leading to decreased catalytic stability and low proton supply efficiency, which affects the oxygen reduction reaction rate. Existing diatomic catalysts have failed to effectively solve this problem.
Heavier alkaline earth metals (Ca, Sr, Ba) are used to form Fe/M-Nx active centers with Fe. These centers are constructed using the soft acid-soft base theory to enhance the Fe-N bond strength and build proton transfer channels, thereby achieving proton-electron transfer rate matching and enhancing the activity and stability of the catalyst.
This improved the oxygen reduction reaction activity and stability of the Fe-NC catalyst under acidic conditions, broke through the proton transfer bottleneck, and enhanced the overall performance of the catalyst.
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Figure CN120933388A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of oxygen reduction catalyst technology for fuel cell cathodes, and in particular to an Fe-based bimetallic nitrogen-carbon catalyst with alkaline earth metal synergistic sites, its preparation method, and its application. Background Technology
[0002] Proton exchange membrane fuel cells (PEMFCs), as a highly efficient and clean energy conversion device, have broad application prospects in fields such as new energy vehicles. The oxygen reduction (ORR) reaction at the cathode has a high activation energy barrier and a complex reaction process, resulting in an extremely slow reaction rate, requiring highly efficient catalysts to accelerate the reaction. Currently, widely used platinum-based catalysts are expensive and scarce, severely restricting the large-scale commercial application of fuel cells. Fe-NC catalysts exhibit unique metal-ligand interactions and ultra-high atom utilization, and are considered one of the most promising alternatives to platinum-based catalysts due to their excellent activity. However, the strong adsorption characteristics of Fe-N4 active sites for hydroxyl radicals (*OH) severely hinder their desorption process, leading to an increased energy barrier. This makes the reduction reaction of *OH to water a decisive step, and the dissolution of iron ions from the active sites in acidic electrolytes causes a rapid decrease in catalytic stability.
[0003] Diatomic catalysts, combining the high atom utilization of single-atom catalysts with the synergistic effects of multi-atom catalysts, have become a research hotspot in recent years. However, optimized active sites are often more susceptible to the influence of complex electrochemical environments. In acidic environments, the typical four-electron oxygen reduction reaction (ORR) involves two proton-coupled electron transfer (PCET) steps in a radical reaction (O2*→OOH* and O*→OH*). For Fe-NC catalysts with Fe-N4 active sites, the continuous ORR process at the metal center depends on a rapid proton supply mechanism. On the other hand, the decrease in Fe-NC activity is mainly attributed to the demetallization of Fe-N4 sites due to electrochemical dissolution. Existing diatomic catalysts have not yet solved the constraints of proton supply efficiency and reaction steps, and have not overcome the demetallization problem caused by electrochemical dissolution of active sites, resulting in significant room for improvement in their activity and stability. Furthermore, they face significant challenges in the precise construction of catalysts and the control of active sites. Summary of the Invention
[0004] In view of this, this application provides a Fe-based bimetallic-nitrogen-carbon catalyst with synergistic alkaline earth metal sites, its preparation method, and its application. This application selects heavier alkaline earth metals (Ca, Sr, Ba, i.e., M) and constructs Fe / MN using the soft acid-soft base theory. xBy using an active center to break down proton transport barriers and simultaneously enhance the Fe-N bond strength, Fe-based bimetallic-nitrogen-carbon catalysts with high intrinsic activity and high stability can be prepared, effectively overcoming the shortcomings of the aforementioned existing technologies.
[0005] The first aspect of this application provides a method for preparing an Fe-based bimetallic-nitrogen-carbon catalyst with alkaline earth metal synergistic sites, comprising the following steps:
[0006] S1. Dissolve zinc nitrate hexahydrate, anhydrous ferric chloride and alkaline earth metal salt in methanol, stir and sonicate to obtain a red mixed solution;
[0007] S2. Dissolve 2-methylimidazole in methanol and stir until completely dissolved to obtain a transparent mixed solution;
[0008] S3. Slowly add the transparent mixed solution to the red mixed solution to carry out the reaction. After the reaction is completed, centrifuge to collect the yellow solid, dry and grind it to obtain the precursor powder.
[0009] S4. The precursor powder is pyrolyzed to obtain an Fe-based bimetallic nitrogen-carbon catalyst with alkaline earth metal synergistic sites.
[0010] Based on Pearson's soft acid-soft base theory, the softness parameter (σ) of heavier alkaline earth metals (Ca, Sr, Ba, denoted as M) in the periodic table is significantly higher than that of transition metals. They exhibit greater orbital overlap with protons (soft acids) and lower interaction energies (ΔE). Theoretical calculations show that alkaline earth metal complexes (such as MN)... x Fe / MN has a proton binding energy 0.3-0.5 eV lower than that of transition metal complexes, which is more conducive to proton capture and transport. Based on this, this application innovatively proposes the construction of atomically precise Fe / MN complexes. x Interface: By utilizing the strong interaction between M and protons to construct a "proton transfer channel," the proton supply bottleneck of Fe-N4 sites in the ORR process is broken, achieving matching of proton-electron transfer rates; at the same time, the bond energy of Fe-N bonds is enhanced through the electronic synergistic effect between Fe and M (such as charge transfer from M to Fe), thus inhibiting the electrochemical dissolution of Fe. This strategy achieves performance breakthroughs through the following mechanisms: (1) MN x The unit acts as a proton "relay station," accelerating proton transfer in the PCET step and lowering the energy barrier from O to OH; (2) Fe / MN x The redistribution of electrons at the interface regulates the d-band center of Fe, weakening the adsorption energy of OH*; (3) the synergistic coordination of Fe and M enhances the electron-donating ability of N atoms, improving the stability of Fe-N bonds. This design provides a new approach to solving the problem of synergistic optimization of catalyst activity and stability in acidic ORR, and has important application prospects in the field of fuel cell cathode catalysis.
[0011] Preferably, in step S1, the alkaline earth metal salt is selected from one of anhydrous calcium chloride, anhydrous strontium chloride, and anhydrous barium chloride.
[0012] Preferably, in step S1, the ratio of zinc nitrate hexahydrate, anhydrous ferric chloride, anhydrous calcium chloride, and methanol is (0.1-1g):(0.01-0.1g):(0.01-0.15g):50mL.
[0013] Preferably, in step S2, the ratio of 2-methylimidazole to methanol is (1.0-5.0g):
[0014] Preferably, in step S3, the reaction temperature is 25°C and the reaction time is 3 hours.
[0015] Preferably, in step S4, the pyrolysis temperature is 1100℃ and the reaction time is 8h.
[0016] The second aspect of this application also provides an Fe-based bimetallic nitrogen-carbon catalyst with alkaline earth metal synergistic sites, which is prepared by the above method.
[0017] The third aspect of this application also provides the application of the aforementioned Fe-based bimetallic nitrogen-carbon catalyst with alkaline earth metal synergistic sites in the oxygen reduction reaction at the cathode of a fuel cell.
[0018] Compared with the prior art, this application has the following advantages:
[0019] This application selects heavier alkaline earth metals (Ca, Sr, Ba, i.e., M) and constructs Fe / MN using the soft acid-soft base theory. x By utilizing the active center to overcome proton transport barriers and simultaneously enhance the Fe-N bond strength, a Fe-based bimetallic-nitrogen-carbon catalyst with high intrinsic activity and stability can be prepared. This application achieves precise bimetallic doping by simultaneously introducing an iron source and a heavier alkaline earth metal M source (Ca, Sr, Ba), and by leveraging the strong adsorption between metal ions and specific ligand functional groups. This synthetic strategy combines simplicity and feasibility of proportional quantification, laying a more solid foundation for the preparation of highly efficient heteronuclear bimetallic fuel cell oxygen reduction catalysts with precise Fe / M bimetallic atomic sites. Attached Figure Description
[0020] To more clearly illustrate the technical solutions in this application or the prior art, the drawings used in the description of this application or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.
[0021] Figure 1 SEM image of the Fe / Ca-NC catalyst;
[0022] Figure 2 SEM image of the Fe / Sr-NC catalyst;
[0023] Figure 3 Comparison of SCV values for Fe / Ca-NC, Fe / Sr-NC, Fe / Ba-NC, and Fe-NC catalysts;
[0024] Figure 4 The images show the XRD patterns of Fe / Ca-NC, Fe / Sr-NC, Fe / Ba-NC, and Fe-NC catalysts. Detailed Implementation
[0025] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0026] Unless otherwise specified, the experimental methods used in the embodiments of this application are all conventional methods.
[0027] In the following examples and comparative examples, unless otherwise specified, all raw materials can be prepared by commercial purchase or conventional methods.
[0028] Example 1
[0029] The preparation method of the Fe-based bimetallic-nitrogen-carbon catalyst with alkaline earth metal synergistic sites in this embodiment includes the following steps:
[0030] 0.5 g of zinc nitrate hexahydrate, 0.09 g of anhydrous ferric chloride (FeCl3), and 0.08 g of anhydrous calcium chloride (CaCl2) were dissolved in 50 mL of methanol and stirred and sonicated for 20 min to obtain a red mixed solution. 1.1 g of 2-methylimidazole was weighed and dissolved in 50 mL of methanol and stirred until completely dissolved to obtain a transparent mixed solution. The transparent mixed solution was then slowly added to the red mixed solution and reacted at room temperature (25 °C) for 3 h. After centrifugation (9000 rpm, 3 min), the yellow solid was collected and dried in a 60 °C forced-air drying oven. The dried sample was then ground to obtain Fe / Ca-NC precursor powder. The Fe / Ca-NC precursor powder was pyrolyzed in a tube furnace at 1100 °C for 8 h to obtain the final Fe / Ca-NC catalyst for testing.
[0031] Example 2
[0032] The preparation method of the Fe-based bimetallic-nitrogen-carbon catalyst with alkaline earth metal synergistic sites in this embodiment includes the following steps:
[0033] 0.5 g of zinc nitrate hexahydrate, 0.09 g of anhydrous ferric chloride (FeCl3), and 0.07 g of anhydrous strontium chloride (SrCl2) were dissolved in 50 mL of methanol and stirred and sonicated for 20 min to obtain a red mixed solution. 1.1 g of 2-methylimidazole was weighed and dissolved in 50 mL of methanol and stirred until completely dissolved to obtain a transparent mixed solution. The transparent mixed solution was then slowly added to the red mixed solution and reacted at room temperature (25 °C) for 3 h. After centrifugation (9000 rpm, 3 min), the yellow solid was collected and dried in a 60 °C forced-air drying oven. The dried sample was then ground to obtain Fe / Sr-NC precursor powder. The Fe / Sr-NC precursor powder was pyrolyzed in a tube furnace at 1100 °C for 8 h to obtain the final Fe / Sr-NC catalyst for testing.
[0034] Example 3
[0035] The preparation method of the Fe-based bimetallic-nitrogen-carbon catalyst with alkaline earth metal synergistic sites in this embodiment includes the following steps:
[0036] 0.5 g of zinc nitrate hexahydrate, 0.09 g of anhydrous ferric chloride (FeCl3), and 0.11 g of anhydrous barium chloride (BaCl2) were dissolved in 50 mL of methanol and stirred and sonicated for 20 min to obtain a red mixed solution. 1.1 g of 2-methylimidazole was weighed and dissolved in 50 mL of methanol and stirred until completely dissolved to obtain a transparent mixed solution. The transparent mixed solution was then slowly added to the red mixed solution and reacted at room temperature (25 °C) for 3 h. After centrifugation (9000 rpm, 3 min), the yellow solid was collected and dried in a 60 °C forced-air drying oven. The dried sample was then ground to obtain Fe / Ba-NC precursor powder. The Fe / Ba-NC precursor powder was pyrolyzed in a tube furnace at 1100 °C for 8 h to obtain the final Fe / Ba-NC catalyst for testing.
[0037] Comparative Example 1
[0038] The preparation method of the Fe-NC catalyst in this comparative example includes the following steps:
[0039] 0.1-1 g of zinc nitrate hexahydrate and 0.01-0.1 g of anhydrous ferric chloride (FeCl3) were dissolved in methanol and stirred with sonication to obtain a red mixed solution. 1.0-5.0 g of 2-methylimidazole was weighed and dissolved in methanol, stirred until completely dissolved to obtain a transparent mixed solution. The transparent mixed solution was then slowly added to the red mixed solution for reaction. After centrifugation, the yellow solid was collected and dried in a forced-air drying oven. The dried sample was then ground to obtain Fe-NC precursor powder. The Fe-NC precursor powder was pyrolyzed in a tube furnace to obtain the final Fe-NC catalyst for testing.
[0040] Test case
[0041] Depend on Figure 1 It can be seen that the SEM image of the Fe / Ca-NC catalyst shows a clear dodecahedral morphology, but the ZIF-8 particles are observed to be of uneven size and have some collapse.
[0042] Depend on Figure 2 It can be seen that the SEM image of the Fe / Sr-NC catalyst also shows a clear dodecahedral morphology, but the ZIF-8 particles are observed to be relatively uniform in size and without obvious collapse.
[0043] Depend on Figure 3 It can be seen that the Fe / Sr-NC catalyst exhibits the highest half-wave potential E. 1 / 2 =0.82V vs. RHE, followed by Fe / Ca-NC, Fe-NC, and Fe / Ba-NC, with half-wave potentials of 0.81V vs. RHE, 0.80V vs. RHE, and 0.79V vs. RHE, respectively.
[0044] Depend on Figure 4 It can be seen that the two broad diffraction peaks at 24.1° and 43.3° correspond to partially graphitized carbon. Apart from the diffraction peaks of carbon, no other material-related peaks were observed. This indicates that Fe in Fe / Ca-NC, Fe / Sr-NC, Fe / Ba-NC, and Fe-NC is distributed in the carbon support in the form of single atoms.
[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application 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 or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.
Claims
1. A method for preparing an alkaline earth metal synergistic site Fe-based bimetallic-nitrogen-carbon catalyst, characterized in that, Includes the following steps: S1. Dissolve zinc nitrate hexahydrate, anhydrous ferric chloride and alkaline earth metal salt in methanol, stir and sonicate to obtain a red mixed solution; S2. Dissolve 2-methylimidazole in methanol and stir until completely dissolved to obtain a transparent mixed solution; S3. Slowly add the transparent mixed solution to the red mixed solution to carry out the reaction. After the reaction is completed, centrifuge to collect the yellow solid, dry and grind it to obtain the precursor powder. S4. The precursor powder is pyrolyzed to obtain an Fe-based bimetallic nitrogen-carbon catalyst with alkaline earth metal synergistic sites.
2. The method for preparing the Fe-based bimetallic-nitrogen-carbon catalyst with alkaline earth metal synergistic sites according to claim 1, characterized in that, In step S1, the alkaline earth metal salt is selected from one of anhydrous calcium chloride, anhydrous strontium chloride, and anhydrous barium chloride.
3. The method for preparing the Fe-based bimetallic-nitrogen-carbon catalyst with alkaline earth metal synergistic sites according to claim 1, characterized in that, In step S1, the ratio of zinc nitrate hexahydrate, anhydrous ferric chloride, anhydrous calcium chloride and methanol is (0.1-1g):(0.01-0.1g):(0.01-0.15g):50mL.
4. The method for preparing the Fe-based bimetallic-nitrogen-carbon catalyst with alkaline earth metal synergistic sites according to claim 1, characterized in that, In step S2, the ratio of 2-methylimidazole to methanol is (1.0-5.0g):50mL.
5. The method for preparing the Fe-based bimetallic-nitrogen-carbon catalyst with alkaline earth metal synergistic sites according to claim 1, characterized in that, In step S3, the reaction temperature is 25°C and the reaction time is 3 hours.
6. The method for preparing the Fe-based bimetallic-nitrogen-carbon catalyst with alkaline earth metal synergistic sites according to claim 1, characterized in that, In step S4, the pyrolysis temperature is 1100℃ and the reaction time is 8h.
7. A Fe-based bimetallic-nitrogen-carbon catalyst with alkaline earth metal synergistic sites, characterized in that, Fe-based bimetallic nitrogen-carbon catalyst with alkaline earth metal synergistic sites prepared by the method according to any one of claims 1-6.
8. The application of the Fe-based bimetallic nitrogen-carbon catalyst with alkaline earth metal synergistic sites as described in claim 7 in the oxygen reduction reaction at the cathode of a fuel cell.