A porous Fe-NC oxygen reduction catalyst, its preparation method and application

Abstract

This invention relates to a porous Fe-N-C oxygen reduction catalyst, its preparation method, and its applications. It pertains to the field of oxygen reduction catalyst materials technology. The invention uses appropriate amounts of m-phenylenediamine as carbon and nitrogen sources, iron acetylacetone as an iron source, melamine as an etchant and nitrogen dopant, and ammonium persulfate as an initiator. First, the components are ground and mixed uniformly. Then, a precursor is obtained using a solid-state synthesis method. The precursor is then subjected to high-temperature carbonization under a protective atmosphere to obtain the porous Fe-N-C oxygen reduction catalyst. Compared with existing technologies, the process for preparing the porous Fe-N-C oxygen reduction catalyst is simple, requires no template agent, uses relatively inexpensive raw materials, generates no waste liquid, is more environmentally friendly, and is easy to mass-produce. The porous oxygen reduction catalyst prepared by the above method has a large specific surface area and a large number of active sites. The catalyst exhibits a higher half-wave potential in alkaline electrolyte than commercial 20wt% Pt / C catalysts, demonstrating excellent ORR performance and broad prospects for industrial application.

Description

Technical Field

[0001] This invention relates to the field of oxygen reduction catalyst materials technology, and in particular to a porous Fe-NC oxygen reduction catalyst, its preparation method, and its application. Background Technology

[0002] Proton exchange membrane fuel cell (PEMFC) technology is considered one of the most promising clean energy technologies due to its high energy conversion efficiency and zero emissions. However, the slow oxygen reduction reaction on the cathode side often requires large amounts of precious metal platinum-based catalysts, resulting in high stack costs and hindering the large-scale commercial application of fuel cell technology. Therefore, developing inexpensive, highly active, and stable non-precious metal catalysts is of great significance for accelerating the commercialization of fuel cells.

[0003] In existing research, Peng et al. used aniline, melamine, and FeCl3 as precursors and 0.75M HCl solution as solvent to obtain a series of graphene-like Fe-NC catalysts through polymerization, evaporation, high-temperature decomposition, and acid washing. These catalysts exhibited ORR activity similar to that of 20wt% commercial Pt / C catalysts in acidic media. Scientific reports , 2013, 3(1): 1-7.). Li et al. used glucose and aniline as precursors, SiO2 as template agent, ferric chloride as iron source, and dilute hydrochloric acid aqueous solution as solvent. After low-temperature polymerization, drying at 100 degrees Celsius, high-temperature pyrolysis, and removal of SiO2 template by 2M NaOH, they obtained a Fe / FeC x @NC-800 -0.5 A carbon-based catalyst that exhibits superior ORR performance in alkaline media compared to commercial Pt / C catalysts. International Journal of Hydrogen Energy , 2018, 43(3): 1386-1395.). In addition, Chinese patent document CN112582628A discloses a method using ethanol as a solvent to ultrasonically disperse a nitrogen-containing carbon substrate, nitrogen source, ligand, pore-forming agent, ferric salt and divalent manganese salt in ethanol to obtain a dispersion. The dispersion is then dried by heating in an oil bath and ground into powder. NaCl is added to the powder as a template agent and calcined. After two calcinations, the NaCl is washed off to obtain a FeMn bimetallic single-atom oxygen reduction catalyst. Although these catalysts exhibit relatively excellent ORR performance, the monomer polymerization process often requires a large amount of solvent, causing environmental pollution and a sharp increase in production costs, thus making it difficult to mass-produce. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides a green preparation method for high-performance porous Fe-NC oxygen reduction catalysts. This method is simple to prepare, generates no wastewater, is environmentally friendly, and is low in cost.

[0005] Specifically, the present invention uses m-phenylenediamine as a carbon and nitrogen source, iron acetylacetone as an iron source, melamine as an etchant and nitrogen dopant, and ammonium persulfate as an initiator. The components are first ground and mixed evenly, and then a precursor is obtained by solid-phase synthesis. The precursor is then carbonized at high temperature under a protective atmosphere to obtain a porous Fe-NC oxygen reduction catalyst.

[0006] The reaction temperature of the solid-phase synthesis method is 45℃~55℃, and the reaction time is 2.5h~4h.

[0007] In one embodiment of the present invention, during the high-temperature carbonization treatment, the temperature is increased to 850°C to 950°C at a rate of 3°C to 8°C / min, and then held at that temperature for 1.5h to 3h. Further, after the high-temperature carbonization treatment, the temperature is decreased to about 500°C at a rate of 5°C / min, and then allowed to cool naturally.

[0008] The mass ratio of m-phenylenediamine, melamine, ferric acetylacetone and ammonium persulfate is (0.25-0.35):(1.6-2.8):(0.28-0.38):(0.28-0.38).

[0009] Preferably, the mass ratio of m-phenylenediamine, melamine, ferric acetylacetone and ammonium persulfate is 0.3:1.8:0.3:0.3.

[0010] In one embodiment of the present invention, the precursor is pretreated at 45°C to 55°C for 3 to 4 hours before high-temperature carbonization.

[0011] In one embodiment of the present invention, the process for preparing a porous Fe-NC oxygen reduction catalyst specifically includes the following steps:

[0012] 1. Grind and mix an appropriate amount of m-phenylenediamine and melamine evenly;

[0013] 2. Dissolve an appropriate amount of acetylacetone iron in a trace amount of ethanol, and then add it to the mixture obtained in step 1 and grind and mix evenly.

[0014] 3. Dissolve an appropriate amount of ammonium persulfate in a trace amount of water, and then add it to the mixture obtained in step 2 and grind and mix evenly;

[0015] 4. The mixture obtained in step 3 is reacted at a constant temperature of 45℃~55℃ for 2.5h~4h to obtain the precursor;

[0016] V. Pre-treat the precursor at 75℃~85℃ for 6h~12h.

[0017] 6. The pretreated precursor is heated to 850℃~950℃ at a rate of 5℃~8℃ / min under a protective atmosphere, held at that temperature for 90min~180min, and then cooled to about 500℃ at a rate of 5℃ / min and allowed to cool naturally to obtain the porous Fe-NC oxygen reduction catalyst.

[0018] In addition, the present invention also relates to a porous Fe-NC oxygen reduction catalyst prepared by the above preparation method, and a fuel cell electrode slurry, fuel cell electrode sheet or fuel cell containing the porous Fe-NC oxygen reduction catalyst.

[0019] The process for preparing the porous Fe-NC oxygen reduction catalyst of this invention is simple, requires no template agent, uses relatively inexpensive raw materials, generates no waste liquid, is more environmentally friendly, and is easy to mass-produce. Furthermore, the porous oxygen reduction catalyst prepared by the above method has a large specific surface area and a large number of active sites. This catalyst exhibits a higher half-wave potential in alkaline electrolytes than commercial 20wt% Pt / C catalysts, demonstrating excellent ORR performance and broad prospects for industrial application. Attached Figure Description

[0020] Figure 1 The images show the XRD patterns of the Fe-NC catalysts prepared in Example 1 and Comparative Examples 1-2.

[0021] Figure 2 The graphs show the electrochemical performance of the Fe-NC catalysts prepared in Example 1 and Comparative Examples 1-2. Detailed Implementation

[0022] To help those skilled in the art better understand the differences between the present invention and the prior art, the present invention will be further described below with reference to specific embodiments. The content described in the embodiments should not be construed as a limitation of the present invention.

[0023] Example 1:

[0024] I. Preparation of the target product.

[0025] Weigh out 0.3g of m-phenylenediamine and 1.8g of melamine, and grind and mix them evenly using an agate mortar.

[0026] Weigh 0.3g of acetylacetone iron and dissolve it in 1ml of ethanol. Then add it to the agate mortar and grind it again until well mixed.

[0027] Dissolve 0.3g of ammonium persulfate in 1ml of water, and add it to the agate mortar. Grind and mix thoroughly again.

[0028] The well-mixed sample was placed in a drying oven and reacted at a constant temperature of 50°C for about 3 hours. After the reaction was completed, the precursor was obtained.

[0029] The precursor was placed in a vacuum drying oven and pretreated at a constant temperature of 80°C for 8 hours.

[0030] The pretreated precursor was taken out and ground in an agate mortar. Then, it was placed in a tube furnace and carbonized at 900°C for 2 hours under an argon atmosphere at a rate of 5°C / min. After that, it was cooled down to 500°C at a rate of 5°C / min and allowed to cool naturally. After cooling, it was ground in an agate mortar to obtain the target product.

[0031] II. Product morphology analysis and performance testing.

[0032] The product exhibits a loose and porous structure, combined with Figure 1 The X-ray diffraction pattern of the product shown confirms that the obtained product is a porous Fe-NC product.

[0033] Preparation of working electrode: Weigh 5 mg of the target product and disperse it in 1 ml of 0.2 wt% Nafion isopropanol solution. Disperse it evenly by ultrasonication to obtain a slurry. Take 20 μL of catalyst slurry and drop it onto a glassy carbon electrode. After drying, the working electrode is obtained.

[0034] Electrochemical testing method: An appropriate amount of 0.1M KOH solution was added to the electrolytic cell. Before testing, N2 or O2 was continuously passed through the electrolyte for approximately one hour, followed by CV or LSV testing. The test potential range was -0.8V to 0.2V (vs. Hg / HgO), and the scan rate was 10 mV / s. During LSV testing, the rotating electrode was rotated at 1600 rpm. LSV test results are shown below. Figure 2 As shown (corresponding to Fe-NC-0.3 in the figure), its half-wave potential in alkaline electrolyte is about 16mV positive compared to commercial 20wt% Pt / C.

[0035] Example 2:

[0036] I. Preparation of the target product.

[0037] Weigh out 0.25g of m-phenylenediamine and 1.6g of melamine, and grind and mix them evenly using an agate mortar.

[0038] Weigh 0.28g of acetylacetone iron and dissolve it in 1ml of ethanol. Then add it to the agate mortar and grind it again until well mixed.

[0039] Dissolve 0.28g of ammonium persulfate in 1ml of water, and add it to the agate mortar. Grind and mix thoroughly again.

[0040] The well-mixed sample was placed in a drying oven and reacted at a constant temperature of 55°C for about 2.5 hours. After the reaction was completed, the precursor was obtained.

[0041] The precursor was placed in a vacuum drying oven and pretreated at a constant temperature of 75°C for approximately 12 hours.

[0042] The pretreated precursor was taken out and ground in an agate mortar. Then, it was placed in a tube furnace and heated to 850°C at 3°C / min for 3 hours under an argon atmosphere. After that, it was cooled to 500°C at 5°C / min and allowed to cool naturally. After cooling, it was ground in an agate mortar to obtain the target product.

[0043] The morphology of the product obtained in this embodiment is basically the same as that in Example 1, and it is a porous Fe-NC product. The electrochemical performance test method of the product in this embodiment is the same as that in Example 1. The electrochemical performance of the product prepared in this embodiment is similar to that in Example 1, and its half-wave potential in alkaline electrolyte is about 4 mV positive compared with commercial 20 wt% Pt / C.

[0044] Example 3:

[0045] I. Preparation of the target product.

[0046] Weigh out 0.35g of m-phenylenediamine and 2.8g of melamine, and grind and mix them evenly using an agate mortar.

[0047] Weigh 0.38g of acetylacetone iron and dissolve it in 1ml of ethanol. Then add it to the agate mortar and grind it again until well mixed.

[0048] Dissolve 0.38g of ammonium persulfate in 1ml of water, and add it to the agate mortar. Grind and mix thoroughly again.

[0049] The well-mixed sample was placed in a drying oven and reacted at a constant temperature of 45°C for about 4 hours. After the reaction was completed, the precursor was obtained.

[0050] The precursor was placed in a vacuum drying oven and pretreated at a constant temperature of 85°C for approximately 6 hours.

[0051] After pretreatment, the precursor was taken out and ground in an agate mortar. Then, it was placed in a tube furnace and carbonized at 950°C for 1.5 hours under an argon atmosphere by heating at 8°C / min. After that, it was cooled to 500°C by 5°C / min and allowed to cool naturally. After cooling, it was ground in an agate mortar to obtain the target product.

[0052] The product obtained in this embodiment is a porous Fe-NC product. Its electrochemical performance was tested using the same method as in Example 1, and its half-wave potential in alkaline electrolyte is approximately 11 mV positive compared to commercial 20 wt% Pt / C.

[0053] Comparative Example 1:

[0054] I. Preparation of the target product.

[0055] Weigh out 0.3g of m-phenylenediamine and 1.8g of melamine, and grind and mix them evenly using an agate mortar.

[0056] Weigh 0.03g of acetylacetone iron and dissolve it in 1ml of ethanol. Then add it to the agate mortar and grind it again until well mixed.

[0057] Dissolve 0.3g of ammonium persulfate in 1ml of water, and add it to the agate mortar. Grind and mix thoroughly again.

[0058] The well-mixed sample was placed in a drying oven and reacted at a constant temperature of 50°C for about 3 hours. After the reaction was completed, the precursor was obtained.

[0059] The precursor was placed in a vacuum drying oven and pretreated at a constant temperature of 80°C for 8 hours.

[0060] The pretreated precursor was taken out and ground in an agate mortar. Then, it was placed in a tube furnace and carbonized at 900°C for 2 hours under an argon atmosphere at a rate of 5°C / min. After that, it was cooled down to 500°C at a rate of 5°C / min and allowed to cool naturally. After cooling, it was ground in an agate mortar to obtain the target product.

[0061] II. Product morphology analysis and performance testing.

[0062] The product exhibits a loose and porous structure, combined with Figure 1 The X-ray diffraction results of the product shown (corresponding to Fe-NC-0.03 in the figure) indicate that the product is a porous Fe-NC product. The electrochemical performance testing method for the product is the same as in Example 1, and will not be repeated here. The corresponding LSV test results are shown in [Figure Number]. Figure 2 As shown (corresponding to Fe-NC-0.03 in the figure), its half-wave potential in alkaline electrolyte is 5mV negative than that of commercial 20wt% Pt / C.

[0063] Comparative Example 2:

[0064] I. Preparation of the target product.

[0065] Weigh out 0.3g of m-phenylenediamine and 1.8g of melamine, and grind and mix them evenly using an agate mortar.

[0066] Weigh 0.9g of acetylacetone iron and dissolve it in 1ml of ethanol. Then add it to the agate mortar and grind it again until well mixed.

[0067] Dissolve 0.3g of ammonium persulfate in 1ml of water, and add it to the agate mortar. Grind and mix thoroughly again.

[0068] The well-mixed sample was placed in a drying oven and reacted at a constant temperature of 50°C for about 3 hours. After the reaction was completed, the precursor was obtained.

[0069] The precursor was placed in a vacuum drying oven and pretreated at a constant temperature of 80°C for 8 hours.

[0070] The pretreated precursor was taken out and ground in an agate mortar. Then, it was placed in a tube furnace and carbonized at 900°C for 2 hours under an argon atmosphere at a rate of 5°C / min. After that, it was cooled down to 500°C at a rate of 5°C / min and allowed to cool naturally. After cooling, it was ground in an agate mortar to obtain the target product.

[0071] II. Product morphology analysis and performance testing.

[0072] The product obtained in this comparative example exhibits a loose and porous structure. Figure 1 The X-ray diffraction results of the product shown (corresponding to Fe-NC-0.9 in the figure) indicate that the product is a porous Fe-NC product. The electrochemical performance testing method for the product is the same as in Example 1; the corresponding LSV test results are shown below. Figure 2 As shown (corresponding to Fe-NC-0.9 in the figure), its half-wave potential in alkaline electrolyte is 23mV negative compared to commercial 20wt% Pt / C.

[0073] It should be noted that the purpose of using trace amounts of ethanol and water to dissolve the components in Examples 1-5 above is to help to uniformly mix the corresponding components into the sample. Ethanol and water will evaporate upon heating during the reaction. In industrial production, methods different from those in the above examples can also be used, such as ball milling to achieve uniform grinding and mixing of the components. As can be seen from the process of preparing porous Fe-NC oxygen reduction catalysts in the above examples, the preparation method used in this invention is simple and easy to operate, requires no template agent, uses relatively inexpensive raw materials, generates no waste liquid, is more environmentally friendly, and is easy to mass-produce. Particularly noteworthy is that the oxygen reduction catalysts prepared in each example have a higher half-wave potential in alkaline electrolyte than commercial 20wt% Pt / C (the catalyst in Example 1 is 18 mV higher than commercial Pt / C), exhibiting excellent ORR performance and showing promise for industrial application in fuel cells. In addition, although the comparative example used a similar preparation method as the example, the performance of the oxygen reduction catalyst prepared in the comparative example differed from that in the example due to the different ratio of the core components. This is because the porous oxygen reduction catalyst prepared in the example has a larger specific surface area and more active sites than the oxygen reduction catalyst prepared in the comparative example.

[0074] Those skilled in the art should understand that the above embodiments are merely preferred implementations of the present invention. In addition, the present invention can be implemented in other ways, and any obvious substitutions without departing from the concept of the present technical solution are within the protection scope of the present invention.

[0075] To facilitate understanding by those skilled in the art of the improvements of this invention over the prior art, some of the accompanying drawings and descriptions have been simplified, and for clarity, some other elements have been omitted from this application. Those skilled in the art should realize that these omitted elements may also constitute the content of this invention.

Claims

1. A method for preparing a porous Fe-NC oxygen reduction catalyst, characterized in that, Includes the following steps: I. Using appropriate amounts of m-phenylenediamine as a carbon and nitrogen source, ferric acetylacetone as an iron source, melamine as an etching agent and nitrogen dopant, and ammonium persulfate as an initiator, the components are first ground and mixed evenly. The mass ratio of m-phenylenediamine, melamine, ferric acetylacetone, and ammonium persulfate is (0.25–0.35):(1.6–2.8):(0.28–0.38):(0.28–0.38).

2. The precursor is obtained by solid-phase synthesis, wherein the reaction temperature of the solid-phase synthesis method is 45℃~55℃ and the reaction time is 2.5h~4h; Third, the obtained precursor is pretreated at 75℃~85℃ for 6h~12h. Fourth, the porous Fe-NC oxygen reduction catalyst is obtained by high-temperature carbonization under a protective atmosphere. During the high-temperature carbonization process, the temperature is increased to 850℃~950℃ at a rate of 3℃~8℃ / min, and then held for 1.5h~3h. After cooling, the porous Fe-NC oxygen reduction catalyst is obtained.

2. The preparation method of the porous Fe-NC oxygen reduction catalyst as described in claim 1, characterized in that: In step four, after high-temperature carbonization, the temperature is reduced to about 500°C at a rate of 5°C / min, and then allowed to cool naturally.

3. The method for preparing the porous Fe-NC oxygen reduction catalyst as described in claim 1 or 2, characterized in that, Step one includes: 1.1 Grind and mix an appropriate amount of m-phenylenediamine and melamine evenly; 1.2 Dissolve an appropriate amount of acetylacetone iron in a trace amount of ethanol, and then add it to the mixture obtained in step 1.1 and grind and mix evenly; 1.3 Dissolve an appropriate amount of ammonium persulfate in a trace amount of water, and then add it to the mixture obtained in step 1.2 and grind and mix evenly.

4. A porous Fe-NC oxygen reduction catalyst, characterized in that: It is prepared by any one of the preparation methods described in claims 1-3.

5. A fuel cell electrode slurry comprising the porous Fe-NC oxygen reduction catalyst of claim 4.

6. A fuel cell electrode sheet comprising the porous Fe-NC oxygen reduction catalyst of claim 4.

7. A fuel cell comprising the porous Fe-NC oxygen reduction catalyst of claim 4.

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