A method for preparing a Pt-based oxygen reduction catalyst based on a metalloporphyrin polymer
Nitrogen-doped porous carbon-supported Pt-based alloy nanoparticle catalysts were prepared by one-pot synthesis and segmented high-temperature calcination, solving the problems of high cost and easy agglomeration of Pt-based catalysts. This resulted in a Pt-based oxygen reduction catalyst with low platinum loading, high activity, and high dispersion, which is suitable for proton exchange membrane fuel cells.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHAANXI NORMAL UNIV
- Filing Date
- 2026-03-23
- Publication Date
- 2026-06-19
AI Technical Summary
Existing Pt-based catalysts suffer from high platinum consumption, high cost, easy agglomeration and poor dispersibility of active metal components, and complex synthesis processes, making them difficult to apply on a large scale.
A one-pot method was used to synthesize metal porphyrin-based polymer precursors, and nitrogen-doped porous carbon-supported Pt-based alloy nanoparticle catalysts were obtained by segmented high-temperature calcination. The strong coordination ability of porphyrin macrocycles was utilized to anchor multiple metals such as Pt, Fe, and Zn during the polymer synthesis stage. Combined with Zn as a pore-forming agent and alloy component, metal migration and agglomeration were inhibited, forming uniformly distributed active centers.
The theoretical loading of Pt is significantly reduced to 8 wt%–12 wt%, improving the activity and stability of the catalyst. The ORR half-wave potential reaches 0.88 V, which is superior to commercial Pt/C. The reaction process is mainly via a four-electron pathway, with low hydrogen peroxide yield, showing good prospects for large-scale application.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of fuel cell catalyst technology, specifically relating to a method for preparing Pt-based oxygen reduction catalysts based on metalloporphyrin polymers. The method involves synthesizing a metalloporphyrin-based polymer precursor via a one-pot process, followed by high-temperature calcination to obtain a nitrogen-doped porous carbon-supported Pt-based alloy nanoparticle catalyst. Background Technology
[0002] Fuel cells, as power generation devices that efficiently convert chemical energy into electrical energy, are one of the key technologies for the development of electric vehicles. Among them, proton exchange membrane fuel cells (PEMFCs) use hydrogen and oxygen as fuel, and the slow oxygen reduction reaction (ORR) kinetics at the cathode are crucial to the cell's performance. Commercial Pt / C catalysts are widely used due to their excellent ORR activity, but their high cost and limited platinum resources severely hinder the large-scale commercialization of fuel cells. Furthermore, during catalyst preparation and use, active nanoparticles are prone to migration and aggregation, leading to a decrease in electrochemical active surface area and deterioration in stability. This is also one of the core problems that urgently need to be solved in current Pt-based catalyst research.
[0003] To reduce platinum usage and improve catalytic performance, researchers have focused on developing Pt-based transition metal alloy (Pt-M, where M = Fe, Co, Ni, Zn, etc.) catalysts. For example, Ni is abundant and widely distributed. Reported PtNi nano-octahedrons (50 wt% Pt content) (Science, 2016, 354, 1414-1419) and shape-controllable PtNi nanoparticles (15 wt% Pt content) (J. Am. Chem. Soc, 2017, 139, 16536-16547) have shown good ORR performance, with half-wave potentials of 950 mV and 920 mV, respectively. However, the diffusion coefficient of Ni in Pt is lower than that of Fe and Co, making the alloy's ordered transformation more difficult. Furthermore, the Pt content in the aforementioned catalysts is all above 15 wt%, indicating that further improvements in economic efficiency are needed.
[0004] Researchers have conducted extensive explorations into Pt-based alloy systems. For example, a highly dispersed, small-sized PtCo intermetallic compound (CN119725582A) has been synthesized with a half-wave potential of 910 mV. However, this method, using a commercially available support, results in low metal dispersion and weak support-metal interaction. Another example is a mixed PtFe / Fe-NC catalyst (J. Am. Chem. Soc, 2024, 146, 22650-22660) reported in the literature (J. Am. Chem. Soc, 2024, 146, 22650-22660) containing a carbon support with dispersed atomic Fe sites and PtFe nanoparticles, which effectively reduces the negative impact of the Fenton reaction, achieving a half-wave potential of 930 mV. However, the synthesis process is complex and cannot be applied on a large scale. Patent (CN116885220A) reports a PtNP-FeSAC@MCHS with a half-wave potential of 0.86 V, but it relies on a complex template method, making large-scale production difficult.
[0005] Regarding the PtZn system, previous studies have synthesized a series of PtZn catalysts under Ce regulation (Yan Liang. Preparation and Performance Study of Binary Platinum-Based Catalysts for Fuel Cells. Shanxi University, 2024), with half-wave potentials of PtZn and PtZn respectively. 0.51 Zn 0.49 (904mV), Pt 0.47 Zn 0.53 (885 mV), Pt 0.54 Zn 0.46 (890 mV) exhibited good catalytic activity. However, the preparation process of the above catalyst requires the introduction of Ce as a regulator, and the Pt content is still 12 wt% to 15 wt%; in addition, the dispersion of its active components is highly dependent on the precise control of the synthesis conditions, which increases the complexity of large-scale production to some extent.
[0006] Metal macrocyclic complexes, due to their well-defined M-N4 coordination environment and unique electronic structure, are often used as ORR model catalysts. However, these molecular catalysts suffer from drawbacks such as low intrinsic conductivity, easy aggregation, and difficulty in functionalization, which limit their practical applications. Integrating them into conjugated polymers can leverage the polymer's high carrier mobility, tunable interactions, and porous structure advantages, providing an ideal platform for ORR catalysis. For example, the literature (Angew. Chem. Int. Ed, 2024, 63,e202405594) achieved regulation of metal conjugated polymers by changing the organic linkers, thereby optimizing ORR catalytic performance. The half-wave potentials were CNTs@bTDA-CoPc-CPs (868 mV), CNTs@TDA-CoPc-CPs (838 mV), and CNTs@TA-CoPc-CPs (820 mV), corresponding to thiophene-3-dicarboxaldehyde, 2,5-thiophene-3-dicarboxaldehyde, and terephthalaldehyde, respectively. The literature (J. Mater. Chem. A, 2018, 6, 22851-22857) synthesized a series of acetylene-linked phthalocyanine-porphyrin-based conjugated microporous polymer catalysts via a Sonogashira-Hagihara coupling reaction, with half-wave potentials of FePcZnPor-CMP (866 mV), FePcFePor-CMP (863 mV), and ZnPcFePor-CMP (724 mV). Among them, the Zn-containing FePcZnPor-CMP exhibited superior catalytic activity compared to the Zn-free ZnPcFePor-CMP, suggesting that Zn may play a positive role in the construction of active sites in porphyrin-based catalysts.
[0007] In summary, although porphyrin-based polymers have been widely developed as oxygen reduction reaction (ORR) catalysts, and linker engineering as a core strategy for regulating their electronic structure, active site dispersion, and catalytic performance has been validated, there is currently no systematic research exploring the regulatory mechanism of linker structural characteristics on ORR catalytic performance for Pt-based (especially multi-element alloy metal) porphyrin-based polymer catalysts. Existing Pt-based catalyst preparation methods generally suffer from the following technical problems: (1) high platinum loading, resulting in high costs; (2) easy aggregation and poor dispersibility of the metal active components; (3) complex synthesis processes, making large-scale application difficult; and (4) insufficient research on the synergistic effect between multi-element Pt-based alloys and porphyrin polymer supports. Therefore, developing a simple, efficient, low-platinum-loading, highly active, and highly dispersed active site Pt-based oxygen reduction catalyst preparation method is of great significance for promoting the commercial development of fuel cells. Summary of the Invention
[0008] The purpose of this invention is to solve the problems existing in the preparation of Pt-based catalysts, such as high platinum loading, high cost, easy agglomeration and poor dispersibility of active metal components, as well as complex synthesis processes and difficulty in large-scale production. The invention provides a method for preparing Pt-based oxygen reduction catalysts based on metalloporphyrin polymers. This method is simple and efficient, and the resulting catalyst has low platinum loading, high activity, and highly dispersed active sites.
[0009] To achieve the above objectives, the present invention employs a method for preparing Pt-based oxygen reduction catalysts based on metalloporphyrin polymers, comprising the following steps:
[0010] Step 1: Add the aldehyde linker, pyrrole, nitrobenzene, metal acetate, and chloroplatinic acid to acetic acid, mix thoroughly, then add trifluoroacetic acid, and carry out the polymerization reaction under reflux conditions. After the reaction is completed, the mixture is separated into solid and liquid phases, washed, and dried to obtain the metalloporphyrin-based polymer precursor. The aldehyde linker is 4,4-biphenyldicarboxaldehyde or terephthalaldehyde; the metal acetate is zinc acetate or a mixture of zinc acetate and iron acetate.
[0011] Step 2: The metalloporphyrin-based polymer precursor obtained in Step 1 is subjected to segmented high-temperature calcination under an inert atmosphere to obtain nitrogen-doped porous carbon-supported Pt-based alloy nanoparticles, i.e., Pt-based oxygen reduction catalysts; the segmented high-temperature calcination procedure is as follows: the first stage is calcined at 450-550°C for 0.5-2 h; the second stage is calcined at 900-1100°C for 1-3 h.
[0012] Furthermore, in step 1, the metal acetate is a mixture of zinc acetate and iron acetate, wherein the molar ratio of Zn to Fe is 1:1 to 3:1.
[0013] Furthermore, in step 1, the polymerization reaction is carried out at a temperature of 90–110°C for a time of 1–3 hours.
[0014] Furthermore, in step 2, the first stage heats to 450-550°C at a heating rate of 4-8°C / min, and the second stage heats to 900-1100°C at a heating rate of 2-5°C / min.
[0015] Furthermore, in step 2, the theoretical total loading of metal in the Pt-based oxygen reduction catalyst is 15 wt% to 25 wt%, of which the theoretical loading of Pt is 8 wt% to 12 wt%.
[0016] Compared with the prior art, the present invention has the following beneficial effects:
[0017] 1. This invention is the first to propose using porphyrin-based polymers as precursors, leveraging the strong coordination ability of porphyrin macrocycles to simultaneously anchor multiple metals such as Pt, Fe, and Zn during the polymer synthesis stage, forming multiple uniformly distributed active centers. This "molecular-level pre-assembly" strategy fundamentally inhibits the migration and aggregation of metal ions during subsequent processing, achieving uniform dispersion of active components inside and outside the catalyst particles.
[0018] 2. This invention creatively introduces Zn as a pore-forming agent and alloying component. On the one hand, Zn volatilizes during high-temperature calcination, generating abundant mesoporous structures and significantly increasing the specific surface area of the catalyst; on the other hand, the residual Zn forms alloys with Pt and Fe, while MN... x The coordination structure anchors the metal nanoparticles, effectively inhibiting the migration and aggregation of Pt during high-temperature processing. This synergistic "pore-forming-anchoring" mechanism solves the key problem of easy aggregation of active particles in traditional high-temperature calcination processes.
[0019] 3. This invention employs a one-pot method to synthesize metalloporphyrin-based polymer precursors. The method is simple to operate, highly reproducible, and avoids the introduction of complex templates or expensive reagents, demonstrating promising prospects for large-scale application. Furthermore, the calcination process is carried out under an argon atmosphere, eliminating the need for reducing gases such as hydrogen, significantly improving experimental safety. The segmented heating program facilitates the gradual carbonization of the polymer precursor and the ordered transformation of the metal alloy, further optimizing the catalyst's microstructure.
[0020] 4. In the Pt-based oxygen reduction catalyst prepared by this invention, the theoretical Pt loading can be reduced to 8 wt%–12 wt%, far lower than the 15 wt%–50 wt% commonly reported in existing literature. While significantly reducing the amount of precious metal, the catalyst still achieves an oxygen reduction half-wave potential of 0.88 V (vs. RHE) in acidic media, which is superior to commercial Pt / C (0.83 V). Furthermore, its Tafel slope is lower than that of commercial Pt / C, the reaction process is dominated by a four-electron pathway (electron transfer number n is close to 4), and the hydrogen peroxide yield is less than 2.5%, exhibiting excellent electrocatalytic activity and kinetic performance, and showing broad application prospects in the field of proton exchange membrane fuel cells.
[0021] 5. This invention achieves the regulation of the electronic structure and pore properties of porphyrin-based polymers by selecting aldehyde linkers with different structures (4,4-biphenyldicarboxaldehyde and terephthalaldehyde), thereby affecting the ORR performance of the final catalyst. This provides new ideas and experimental basis for the design and development of low-platinum-load Pt-based catalysts, and expands the application of linker engineering in the field of multi-element alloy catalysts. Attached Figure Description
[0022] Figure 1This is a SEM image of the PtZn-based porphyrin-based polymer precursor prepared in Example 1.
[0023] Figure 2 This is a SEM image of the PtZn-based oxygen reduction catalyst prepared in Example 1.
[0024] Figure 3 This is a SEM image of the PtZnFe-based porphyrin-based polymer precursor prepared in Example 2.
[0025] Figure 4 This is a SEM image of the PtZnFe-based oxygen reduction catalyst prepared in Example 2.
[0026] Figure 5 This is a TEM image of the PtZnFe-based oxygen reduction catalyst prepared in Example 2.
[0027] Figure 6 This is a SEM image of the PtZnFe-based oxygen reduction catalyst prepared in Example 3.
[0028] Figure 7 This is a SEM image of the PtFe-based porphyrin-based polymer precursor prepared in Comparative Example 1.
[0029] Figure 8 This is a SEM image of the PtFe-based oxygen reduction catalyst prepared in Comparative Example 1.
[0030] Figure 9 This is a SEM image of the PtZnFe-based oxygen reduction catalyst prepared in Comparative Example 2.
[0031] Figure 10 The above are XRD patterns of the oxygen reduction catalysts prepared in Comparative Example 1 and Examples 1-2.
[0032] Figure 11 The images show the XRD patterns of PtZnFe-based oxygen reduction catalysts prepared by different aldehyde linkers in Examples 2-3 and Comparative Example 2.
[0033] Figure 12 This is an LSV test diagram of the oxygen reduction catalysts prepared in Comparative Example 1 and Examples 1-2.
[0034] Figure 13 These are LSV test results for PtZnFe-based oxygen reduction catalysts prepared with different aldehyde linkers in Examples 2-3 and Comparative Example 2.
[0035] Figure 14 This is a diagram showing the number of transferred electrons in the oxygen reduction catalysts prepared in Comparative Example 1 and Examples 1-2.
[0036] Figure 15The diagram shows the number of transferred electrons for PtZnFe-based oxygen reduction catalysts prepared by different aldehyde linkers in Examples 2-3 and Comparative Example 2.
[0037] Figure 16 This is a graph showing the hydrogen peroxide yield of the oxygen reduction catalysts prepared in Comparative Example 1 and Examples 1-2.
[0038] Figure 17 The graph shows the hydrogen peroxide yield of PtZnFe-based oxygen reduction catalysts prepared with different aldehyde linkers in Examples 2-3 and Comparative Example 2. Detailed Implementation
[0039] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited to these embodiments.
[0040] Example 1
[0041] Step 1: Dissolve 31 mg of 4,4-biphenyldicarboxaldehyde, 22 μL of pyrrole, 1.2 mL of nitrobenzene, 42 mg of zinc acetate dihydrate, and 2.7 mL of 10 mg / mL H2PtCl6·6H2O aqueous solution in 50 mL of acetic acid. Stir for 10 minutes, then add 25 μL of trifluoroacetic acid dropwise while stirring. Reflux at 100°C for 2 h, filter, wash with plenty of water and ethanol, and dry in an oven at 60°C for 2 h to obtain a black solid powder, which is the PtZn-based porphyrin-based polymer precursor.
[0042] Step 2: The PtZn-based porphyrin-based polymer precursor was calcined in stages at high temperature in a tube furnace under an argon atmosphere. In the first stage, the temperature was increased to 500°C at a heating rate of 6°C / min and calcined at a constant temperature for 1 h. In the second stage, the temperature was increased to 1000°C at a heating rate of 3°C / min and calcined at a constant temperature for 2 h to obtain the PtZn-based oxygen reduction catalyst (named PtZn-NC). The theoretical total loading of Pt and Zn in the PtZn-based oxygen reduction catalyst was 20 wt%, of which the theoretical loading of Pt was 10 wt%.
[0043] Example 2
[0044] Step 1: Dissolve 31 mg of 4,4-biphenyldicarboxaldehyde, 22 μL of pyrrole, 1.2 mL of nitrobenzene, 19 mg of ferric acetate, 24 mg of zinc acetate dihydrate, and 1.5 mL of 10 mg / mL H2PtCl6·6H2O aqueous solution in 50 mL of acetic acid. Stir for 10 minutes, then add 25 μL of trifluoroacetic acid dropwise while stirring. Reflux at 100°C for 2 h, filter, wash with plenty of water and ethanol, and dry in an oven at 60°C for 2 h to obtain a black solid powder, which is the precursor of PtZnFe-based porphyrin-based polymer.
[0045] Step 2: The PtZnFe-based porphyrin-based polymer precursor was calcined in stages at high temperature in a tube furnace under an argon atmosphere. In the first stage, the temperature was increased to 500°C at a heating rate of 6°C / min and calcined at a constant temperature for 1 h. In the second stage, the temperature was increased to 1000°C at a heating rate of 3°C / min and calcined at a constant temperature for 2 h to obtain the PtZnFe-based oxygen reduction catalyst (named PtZnFe-NC-2). The theoretical total loading of Pt, Zn, and Fe in the PtZnFe-based oxygen reduction catalyst was 20 wt%, of which the theoretical loading of Pt was 10 wt%, and the molar ratio of Zn to Fe was 1:1.
[0046] Example 3
[0047] In step 1 of this embodiment, 20 mg of terephthalaldehyde was used to replace 4,4-biphenyldialdehyde in step 1 of Example 2. The other steps were the same as in Example 2, yielding a PtZnFe-based oxygen reduction catalyst (named PtZnFe-NC-1). The theoretical total loading of Pt, Zn, and Fe in the PtZnFe-based oxygen reduction catalyst was 20 wt%, with a theoretical Pt loading of 10 wt% and a Zn to Fe molar ratio of 1:1.
[0048] Comparative Example 1
[0049] In this comparative example, 33 mg of ferric acetate replaced zinc acetate dihydrate in Example 1, and the other steps were the same as in Example 1, to obtain a PtFe-based oxygen reduction catalyst (named PtFe-NC). The theoretical total loading of PtFe in the PtFe-based oxygen reduction catalyst was 20 wt%, of which the theoretical loading of Pt was 10 wt%.
[0050] Comparative Example 2
[0051] In this comparative example, 4,4-biphenyldicarboxaldehyde in Example 2 was replaced with 42 mg of 4,4-m-triphenyldicarboxaldehyde, and the other steps were the same as in Example 2, to obtain a PtZnFe-based oxygen reduction catalyst (named PtZnFe-NC-3).
[0052] The polymer precursors and oxygen reduction catalysts prepared in Examples 1-3 and Comparative Examples 1-2 were characterized in morphology and analyzed in structure, and the results are shown in the figure. Figures 1-9 .
[0053] From the morphology of the polymer precursor, the PtZn-based porphyrin-based polymer precursor of Example 1 exhibits an irregular blocky morphology with a relatively smooth surface. Figure 1 In Example 2, after the introduction of Fe, the morphology of the precursor did not change significantly. Figure 3In Comparative Example 1, without the addition of Zn, the morphology of the precursor was basically the same as that of Examples 1 and 2. Figure 7 This indicates that the one-pot synthesis system has good universality for different metal components. After high-temperature calcination, the morphology of each catalyst changed significantly. The PtZn-NC catalyst in Example 1 transformed into more uniformly sized particles with a rougher surface. Figure 2 This can be attributed to the pore-forming effect resulting from the carbonization of the polymer precursor and the volatilization of the Zn component. The PtZnFe-NC-2 catalyst in Example 2 maintained its particulate morphology and exhibited a more abundant surface pore structure. Figure 4 This indicates that the introduction of Fe further promoted the development of the pore structure. From Figure 5 TEM images provide a clearer view of the uniform dispersion of numerous nanoparticles in the PtZnFe-NC-2 catalyst, exhibiting a narrow particle size distribution and no obvious agglomeration. This indicates that the coordination anchoring effect of the porphyrin polymer and the Zn volatilization pore-forming strategy effectively inhibit the migration and agglomeration of metal particles at high temperatures. Comparison of catalyst morphologies with different metal compositions verifies the pore-forming effect of Zn. (Comparison with Zn-containing catalysts...) Figure 2 , Figure 4 Compared to Comparative Example 1, the surface pore structure of the PtFe-NC catalyst was significantly reduced. Figure 8 This confirms the crucial role of Zn as a pore-forming agent during high-temperature calcination. Comparing the effects of different aldehyde linkers on catalyst morphology, it is evident that in Example 3, after replacing 4,4-biphenyldicarboxaldehyde with terephthalaldehyde, the PtZnFe-NC-1 catalyst still maintained a particulate morphology, but the particle packing was more dense. Figure 6 This indicates that the linker structure has a certain influence on the catalyst's microstructure. Comparative Example 2, using 4,4-m-triphenyldicarboxaldehyde as the linker, resulted in a PtZnFe-NC-3 catalyst with larger particle size and slightly poorer uniformity of distribution. Figure 9 This is speculated to be related to the differences in polymer network crosslinking density and pore structure caused by the molecular configuration of the linker.
[0054] Depend on Figure 10 As can be seen, the Pt-based oxygen reduction catalysts prepared in Examples 1, 2, and Comparative Example 1 all exhibit characteristic diffraction peaks near 2θ ≈ 40°, 47°, 68°, and 82°, corresponding to the (111), (200), (220), and (311) crystal planes of the face-centered cubic (fcc) Pt structure, respectively. Compared with the standard diffraction peaks of pure Pt, the diffraction peaks of the alloy catalysts are all shifted to higher angles to varying degrees, indicating that the transition metals Fe or Zn have successfully entered the Pt lattice, forming a Pt-based alloy structure, leading to lattice shrinkage. Among them, the PtZnFe-NC-2 diffraction peak shift in Example 2 is the most significant, indicating a higher degree of alloying. Figure 11As can be seen, the diffraction peak positions of the PtZnFe-based oxygen reduction catalysts prepared by different aldehyde linkers in Examples 2, 3, and Comparative Example 2 are basically consistent, all showing alloying characteristics, indicating that the change of linker did not affect the phase structure of PtZnFe alloy. However, there are differences in the full width at half maximum (FWHM) of the diffraction peaks: the PtZnFe-NC-2 diffraction peak in Example 2 is the widest, suggesting its smaller grain size; while the PtZnFe-NC-3 diffraction peak in Comparative Example 2 is sharper, indicating its relatively larger grain size, which is consistent with the SEM observation results.
[0055] To demonstrate the beneficial effects of the present invention, the oxygen reduction catalysts prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to ORR performance tests in an O2-saturated 0.1 M HClO4 aqueous solution at a scan rate of 5 mV / s. -1 The rotational speed was 1600 rpm, and the results were compared with commercial Pt / C (20 wt%). See the results below. Figures 12-17 .
[0056] Depend on Figure 12 It can be seen that the half-wave potential (E) of each catalyst 1 / 2 The order of the catalysts was: Example 2 (PtZnFe-NC-2, 880 mV) > Example 1 (PtZn-NC, 863 mV) > Commercial Pt / C (20 wt%, 830 mV) > Comparative Example 1 (PtFe-NC, 812 mV). The results showed that the PtZnFe ternary alloy catalyst exhibited the best ORR activity, significantly superior to commercial Pt / C; the PtZn binary alloy also showed better activity than commercial Pt / C; while the PtFe binary alloy had relatively low activity, which may be related to the fact that Fe readily initiates the Fenton reaction, leading to a decrease in the stability of the active sites.
[0057] Depend on Figure 13 As can be seen, the half-wave potentials of the PtZnFe-based oxygen reduction catalysts prepared with different aldehyde linkers are ranked as follows: Example 2 (PtZnFe-NC-2, 880 mV) > Example 3 (PtZnFe-NC-1, 872 mV) > Comparative Example 2 (PtZnFe-NC-3, 819 mV). This result indicates that the structure of the aldehyde linker has a significant impact on the ORR performance of the catalyst. PtZnFe-NC-2, prepared with 4,4-biphenyldicarboxaldehyde as the linker, exhibits the best catalytic activity, which may be attributed to the polymer network constructed by its suitable molecular configuration being more conducive to the exposure of active sites and mass transfer processes. In contrast, the use of 4,4-m-triphenyldicarboxaldehyde as the linker in Comparative Example 2, with its larger molecular size and rigid structure, may lead to an overly dense or disordered polymer network, which is not conducive to the uniform dispersion of active sites and the mass transfer of reactants, thus significantly reducing the ORR performance.
[0058] Depend on Figures 14-15 The calculated number of transferred electrons (n) for each catalyst at different potentials shows that the n values for Examples 1, 2, 3, and Comparative Example 1 are all close to 4.0, indicating that the oxygen reduction reaction mainly follows a highly efficient four-electron pathway, directly reducing O2 to H2O. The n value of PtZnFe-NC-3 in Comparative Example 2 is slightly lower than 4.0, indicating that its four-electron selectivity is slightly worse.
[0059] Depend on Figures 16-17 The hydrogen peroxide yield (H2O2%) curves for each catalyst show that the H2O2 yield of all catalysts is below 2.5%, further confirming that the reaction is dominated by the four-electron pathway. Among them, PtZnFe-NC-2 in Example 2 has the lowest H2O2 yield (<1.5%), indicating that it has the best reaction selectivity; PtZnFe-NC-3 in Comparative Example 2 has a relatively high H2O2 yield (close to 2.5%), which is consistent with its slightly lower number of transferred electrons.
Claims
1. A method for preparing Pt-based oxygen reduction catalysts based on metalloporphyrin polymers, characterized in that: Includes the following steps: Step 1: Add the aldehyde linker, pyrrole, nitrobenzene, metal acetate, and chloroplatinic acid to acetic acid, mix thoroughly, then add trifluoroacetic acid, and carry out the polymerization reaction under reflux conditions. After the reaction is completed, the mixture is separated into solid and liquid phases, washed, and dried to obtain the metalloporphyrin-based polymer precursor. The aldehyde linker is 4,4-biphenyldicarboxaldehyde or terephthalaldehyde. The metal acetate is zinc acetate or a mixture of zinc acetate and iron acetate. Step 2: The metalloporphyrin-based polymer precursor obtained in Step 1 is subjected to segmented high-temperature calcination under an inert atmosphere to obtain nitrogen-doped porous carbon-supported Pt-based alloy nanoparticles, i.e., Pt-based oxygen reduction catalysts; the segmented high-temperature calcination procedure is as follows: the first stage is calcined at 450-550°C for 0.5-2 h; the second stage is calcined at 900-1100°C for 1-3 h.
2. The method for preparing Pt-based oxygen reduction catalysts based on metalloporphyrin polymers according to claim 1, characterized in that: In step 1, the metal acetate is a mixture of zinc acetate and iron acetate, wherein the molar ratio of Zn to Fe is 1:1 to 3:
1.
3. The method for preparing Pt-based oxygen reduction catalysts based on metalloporphyrin polymers according to claim 1, characterized in that: In step 1, the polymerization reaction is carried out at a temperature of 90–110°C for 1–3 hours.
4. The method for preparing Pt-based oxygen reduction catalysts based on metalloporphyrin polymers according to claim 1, characterized in that: In step 2, the first stage heats to 450-550°C at a heating rate of 4-8°C / min, and the second stage heats to 900-1100°C at a heating rate of 2-5°C / min.
5. The method for preparing Pt-based oxygen reduction catalysts based on metalloporphyrin polymers according to claim 1, characterized in that: In step 2, the theoretical total loading of metals in the Pt-based oxygen reduction catalyst is 15 wt% to 25 wt%, of which the theoretical loading of Pt is 8 wt% to 12 wt%.
6. A Pt-based oxygen reduction catalyst obtained by the preparation method according to any one of claims 1 to 5.