A non-noble metal fuel cell oxygen reduction catalyst based on self-assembled semi-interpenetrating polymer network and its preparation method and application

Abstract

The present application relates to a non-precious metal fuel cell oxygen reduction catalyst based on a self-assembled semi-interpenetrating polymer network, its preparation method and application, and belongs to the technical field of fuel cell oxygen reduction catalysts. The preparation method of the catalyst of the present application comprises the following steps: S1, dissolving the polysaccharide in ultrapure water, heating and stirring, then adding the polymer monomer, polymerization initiator, salt template and non-precious metal source solution, heating and stirring until a uniform orange-red hydrogel is obtained, then adding a nitrogen source, continuing heating and stirring and evaporating the solvent, and freeze-drying to obtain an orange powder sample; S2, pyrolyzing the orange powder sample to obtain a black powder sample, and obtaining a precursor product after acid washing, filtration and drying; S3, pyrolyzing the precursor product again to obtain a catalyst. The semi-interpenetrating polymer network hydrogel is synthesized by self-assembly, and a high-load and atomically dispersed catalyst is formed by pyrolysis.

Description

Technical Field

[0001] The present application relates to the technical field of fuel cell oxygen reduction catalysts, and in particular to a non-precious metal fuel cell oxygen reduction catalyst based on a self-assembled semi-interpenetrating polymer network, and a preparation method and application thereof. Background Art

[0002] At present, under the background of global energy transformation and my country's clean and low-carbon energy transformation, hydrogen energy development and utilization technology represented by fuel cells has made significant breakthroughs. However, the slow rate of oxygen reduction reaction (ORR) at the cathode of fuel cells has seriously hindered its development. To date, platinum (Pt)-based catalysts are still the most commonly used and efficient catalysts for ORR, but their high cost and easy poisoning characteristics have largely hindered their large-scale application. Therefore, the development of various inexpensive, highly active and stable transition metal-based and metal-free catalysts as alternatives to Pt-based catalysts has received widespread attention.

[0003] The co-pyrolysis of metal-organic frameworks (MOFs) and transition metal sources at high temperatures is a common method for synthesizing transition metal-nitrogen-carbon (MNC) catalysts, but several challenges remain, preventing them from fully meeting industrial needs. One challenge is the incomplete sublimation of the coordinated metals in the MOF during pyrolysis, resulting in insufficient defects in the MOF matrix and a low active site density. Furthermore, MOF-based MNC catalysts typically confine the metal within the MOF cavity, which easily leads to sintering and agglomeration of the metal into micro- / nanoparticles during pyrolysis. These aggregated particles not only reduce the utilization of metal atoms but also easily dissolve in acidic environments, thereby affecting the activity and stability of the catalyst. Therefore, methods for precisely anchoring and dispersing metal ions are needed to overcome the drawbacks of these synthetic methods. Currently, some studies have utilized the numerous functional groups in monomeric hydrogels to anchor metal ions in an "egg-box" structure, and subsequently pyrolyze to form atomically dispersed MNC catalysts. However, due to the single pore structure of this type of monomer hydrogel and the insufficient chelating strength between it and metal ions, the catalyst after thermal decomposition still has problems such as uneven metal-nitrogen coordination structure (such as some unstable Fe-N2 / N3 sites) and limited mass transfer and diffusion. Summary of the Invention

[0004] In view of this, the present application provides a non-precious metal fuel cell oxygen reduction catalyst based on a self-assembled semi-interpenetrating polymer network, as well as its preparation method and application. After polymerization of cheap polysaccharides (such as carboxymethyl chitosan (CMCS), sodium carboxymethyl starch (CMS), and hydroxypropyl cellulose (HPC)), and polymer monomers (acrylamide (AM), acrylonitrile (AN), and fumaric acid (FA), such as AM), iron ions are anchored, and a semi-interpenetrating polymer network hydrogel is synthesized by self-assembly, which is then thermally decomposed to form a high-load and atomically dispersed catalyst. The entire synthesis process does not require the assistance of any high-temperature or high-pressure equipment, and the new synthetic route has high atomic utilization and simple process. It can provide a new idea for the commercial large-scale production of high-efficiency oxygen reduction catalysts. The catalyst prepared in the present application has the advantages of high stability and high activity, and can effectively overcome the defects of the above-mentioned prior art.

[0005] In a first aspect, the present application provides a method for preparing a non-noble metal fuel cell oxygen reduction catalyst based on a self-assembled semi-interpenetrating polymer network, comprising the following steps:

[0006] S1. Dissolve the polysaccharide in ultrapure water, heat and stir, then add the polymer monomer, polymerization initiator, salt template and non-precious metal source solution, heat and stir until a uniform orange-red hydrogel is obtained, then add a nitrogen source, continue heating and stirring, evaporate the solvent, and freeze-dry to obtain an orange powder sample;

[0007] S2. Pyrolysis the orange powder sample to obtain a black powder sample, which is then acid-washed, filtered, and dried to obtain a precursor product;

[0008] S3. The precursor product is pyrolyzed again to obtain a non-precious metal fuel cell oxygen reduction catalyst based on a self-assembled semi-interpenetrating polymer network.

[0009] Specifically, the method includes the following steps:

[0010] S1. Dissolve the polysaccharide in ultrapure water, heat and stir, then add the polymer monomer, azobisisobutylamidine hydrochloride, sodium chloride and ferric nitrate solution, heat and stir until a uniform orange-red hydrogel is obtained, then add urea, continue heating and stirring, evaporate the solvent, and freeze-dry to obtain an orange powder sample;

[0011] S2. Pyrolysis the orange powder sample to obtain a black powder sample, which is then acid-washed, filtered, and dried to obtain a precursor product;

[0012] S3. The precursor product is pyrolyzed again to obtain a non-precious metal fuel cell oxygen reduction catalyst based on a self-assembled semi-interpenetrating polymer network.

[0013] This application introduces an additional non-crosslinked linear polymer on the basis of a single polymer hydrogel to construct a hydrogel with a semi-interpenetrating polymer network. Compared with the single polymer hydrogel, the semi-interpenetrating polymer network hydrogel has both chemical and physical double crosslinking. The chemical crosslinking can form a relatively stable network, and the presence of physical crosslinking increases the flexibility and dynamics of the network. This semi-interpenetrating polymer network allows for a large number of crosslinking points within the hydrogel, which can achieve more effective anchoring of metal ions, resulting in a more stable Fe-N4 / C active site and a richer three-dimensional microporous / mesoporous / macroporous structure in the catalyst after pyrolysis, further improving the stability of the catalyst and the mass transfer of reactants / products.

[0014] Preferably, in step S2, the specific conditions of the pyrolysis are: placing the orange powder sample in a tube furnace, heating it to 700-1000°C at a heating rate of 10°C / min under an argon atmosphere, and pyrolyzing it at this temperature for 3 hours; or

[0015] In step S3, the specific conditions of the pyrolysis are: heating to 700-1000°C at a heating rate of 10°C / min under an argon atmosphere, and pyrolyzing at this temperature for 3 hours.

[0016] Preferably, in step S2, the specific conditions of the pickling are: pickling at 120° C. in 500 mL of 1 M H 2 SO 4 solution.

[0017] Preferably, in step S1, the polysaccharide is selected from one of carboxymethyl chitosan, sodium carboxymethyl starch, and hydroxypropyl cellulose; or

[0018] In step S1, the polymer monomer is selected from one of acrylamide, acrylonitrile, and fumaric acid; or

[0019] In step S1, the heating and stirring temperature is 50-80°C.

[0020] Preferably, the usage ratio of the polysaccharide, ultrapure water, polymer monomer, azobisisobutylamidine hydrochloride, sodium chloride, ferric nitrate and urea is (1.0-4.0g):500mL:(0.5-2.0mL):(0.05-0.2g):3.0g:(0.5-1.0g):(0.5-2.0g).

[0021] Preferably, in step S1, the polymerization initiator is selected from one of azobisisobutylamidine hydrochloride, azobisisobutylimidazoline hydrochloride, and azobisisopropylimidazoline; or

[0022] The salt template is selected from one of sodium chloride, sodium carbonate, sodium sulfate, potassium chloride and potassium sulfate; or

[0023] The non-noble metal source is an iron salt, and the iron salt is selected from one of ferric nitrate, ferric chloride, and ferric sulfate; or

[0024] The nitrogen source is selected from one of urea, aniline, melamine and dicyandiamide.

[0025] The second aspect of the present application also provides a non-precious metal fuel cell oxygen reduction catalyst based on a self-assembled semi-interpenetrating polymer network, which is prepared by the above method.

[0026] The third aspect of the present application also provides the use of the above-mentioned non-noble metal fuel cell oxygen reduction catalyst based on the self-assembled semi-interpenetrating polymer network in the battery cathode material.

[0027] The fourth aspect of the present application further provides a working electrode, comprising the above-mentioned non-noble metal fuel cell oxygen reduction catalyst based on the self-assembled semi-interpenetrating polymer network.

[0028] A fifth aspect of the present application further provides a method for preparing the above-mentioned working electrode, comprising the following steps:

[0029] The non-noble metal fuel cell oxygen reduction catalyst based on the self-assembled semi-interpenetrating polymer network, membrane solution and solvent are mixed in a certain proportion, ultrasonically applied to form a uniformly dispersed slurry, and the slurry is drop-coated on the disk / ring disk electrode to obtain a working electrode.

[0030] Compared with the prior art, this application has the following beneficial effects:

[0031] In this application, cheap polysaccharides (taking carboxymethyl chitosan (CMCS), sodium carboxymethyl starch (CMS), and hydroxypropyl cellulose (HPC) as examples) and polymer monomers (acrylamide (AM), acrylonitrile (AN), and fumaric acid (FA), taking AM as an example) are polymerized to anchor iron ions, and a semi-interpenetrating polymer network hydrogel is synthesized by self-assembly, which is then thermally decomposed to form a high-load and atomically dispersed catalyst. The entire synthesis process does not require the assistance of any high-temperature or high-pressure equipment, and the new synthetic route has high atomic utilization and simple process, which can provide a new idea for the commercial large-scale production of high-efficiency oxygen reduction catalysts. The catalyst prepared in this application has the advantages of high stability and high activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the present application or the prior art, the following briefly introduces the drawings required for use in the description of the present application or the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0033] Figure 1 TEM image of CMS-PAM-Fe-N catalyst;

[0034] Figure 2 XRD comparison diagrams of CMCS-PAM-Fe-N catalyst, CMS-PAM-Fe-N catalyst, HPC-PAM-Fe-N catalyst, and PAM-Fe-N catalyst;

[0035] Figure 3 This is the SCV comparison diagram of CMCS-PAM-Fe-N catalyst, CMS-PAM-Fe-N catalyst, HPC-PAM-Fe-N catalyst, and PAM-Fe-N catalyst;

[0036] Figure 4 This is a comparison chart of the hydrogen peroxide yield and the number of transferred electrons of CMCS-PAM-Fe-N catalyst, CMS-PAM-Fe-N catalyst, HPC-PAM-Fe-N catalyst, and PAM-Fe-N catalyst. DETAILED DESCRIPTION

[0037] To make the objectives, technical solutions, and advantages of this application more clear, the technical solutions of this application will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of this application, not all of them. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this application.

[0038] Unless otherwise specified, the experimental methods used in the examples of this application are all conventional methods.

[0039] In the following examples and comparative examples, unless otherwise specified, all raw materials can be purchased commercially or prepared by conventional methods.

[0040] Example 1

[0041] First, weigh 0.8 g of ferric nitrate nonahydrate and add 10 mL of ultrapure water. Stir at room temperature until completely dissolved and set aside. Add 2.4 g of carboxymethyl chitosan to 500 mL of ultrapure water and stir at 70°C until completely dissolved. Then, add 1.1 mL of acrylamide, followed by 0.1 g of azobisisobutylamidine hydrochloride, and stir for 15 minutes. Then, add 3.0 g of sodium chloride to the solution. Then, slowly add 10 mL of ferric nitrate solution using a rubber-tipped pipette and stir until a uniform orange-red hydrogel is obtained. Then, add 1.0 g of urea and continue stirring. The solvent is evaporated until only approximately 80 mL remains. Heating is stopped and the sample is freeze-dried to obtain an orange-yellow powder. The powder sample is then placed in a tube furnace and pyrolyzed at 800°C for 3 hours under an argon atmosphere at a heating rate of 10°C / min. Upon completion of pyrolysis, a black powder is obtained. The black powder is then acid-washed in 500 mL of 1 M H₂SO₄ solution at 120°C. The product was then filtered with 3 L of water, dried, and then pyrolyzed for the second time. The temperature was raised to 800 °C at a heating rate of 10 °C / min under an argon atmosphere and pyrolyzed at this temperature for 3 h to obtain the CMCS-PAM-Fe-N catalyst, which was used for subsequent characterization and electrochemical testing.

[0042] Example 2

[0043] Except for the following steps which are different from those in Example 1, other preparation and testing methods are exactly the same as those in Example 1.

[0044] Take 2.0g of sodium carboxymethyl starch and add it to 500mL of ultrapure water. Stir at 70℃ until it is completely dissolved. Then add 1.1mL of acrylamide, followed by 0.05-0.2g of azobisisobutylamidine hydrochloride and stir for 15min. Then add 3.0g of sodium chloride to the above solution, and then slowly add 10mL of ferric nitrate solution with a rubber-tipped dropper and stir until a uniform orange-red hydrogel is obtained. Then add 1.0g of urea and continue stirring. Then evaporate the solvent until only about 80mL is left. Then stop heating and freeze-dry to obtain an orange-yellow powder sample. Then place the powder sample in a tube furnace and pyrolyze it at 800℃ for 3h under an argon atmosphere at a heating rate of 10℃ / min. After the pyrolysis is completed, a black powder sample is obtained. The black powder sample is then acid-washed in 500mL of 1M H2SO4 solution at 120℃. The product was then filtered with 3 L of water, dried, and then pyrolyzed for the second time. The temperature was raised to 800 °C at a heating rate of 10 °C / min under an argon atmosphere and pyrolyzed at this temperature for 3 h to obtain the CMS-PAM-Fe-N catalyst, which was used for subsequent characterization and electrochemical testing.

[0045] Example 3

[0046] Except for the following steps which are different from those in Example 1, other preparation and testing methods are exactly the same as those in Example 1.

[0047] 2.5 g of hydroxypropyl cellulose was added to 500 mL of ultrapure water and stirred at 70°C until completely dissolved. Then, 1.1 mL of acrylamide was added, followed by 0.1 g of azobisisobutylamidine hydrochloride, and stirred for 15 minutes. 3.0 g of sodium chloride was then added to the solution, followed by a slow dripping of 10 mL of ferric nitrate solution using a rubber-tipped pipette, and stirred until a uniform orange-red hydrogel was obtained. 1.0 g of urea was then added and stirring continued. The solvent was then evaporated until only about 80 mL remained. Heating was stopped, and the sample was freeze-dried to obtain an orange-yellow powder. The powder sample was then placed in a tube furnace and pyrolyzed at 800°C for 3 hours under an argon atmosphere at a heating rate of 10°C / min. Upon completion of the pyrolysis, a black powder sample was obtained. The black powder sample was then acid-washed in 500 mL of 1 M H2SO4 solution at 120°C. The product was then filtered with 3 L of water, dried, and then pyrolyzed for the second time. The temperature was raised to 800 °C at a heating rate of 10 °C / min under an argon atmosphere and pyrolyzed at this temperature for 3 h to obtain the HPC-PAM-Fe-N catalyst, which was used for subsequent characterization and electrochemical testing.

[0048] Example 4

[0049] This embodiment can refer to Example 1, except that the polymer monomer is acrylonitrile.

[0050] Example 5

[0051] This embodiment can refer to Example 1, except that the polymer monomer is fumaric acid.

[0052] Comparative Example 1

[0053] 1.0 mL of acrylamide solution was added to 500 mL of ultrapure water and stirred at 70°C. Subsequently, 0.8 g of ferric nitrate nonahydrate and 0.1 g of azobisisobutylamidine hydrochloride were added sequentially to the solution and stirred at 70°C until a uniform, dark yellow gel-like suspension was obtained. 1.0 g of urea was then added, and the solvent was evaporated with continued stirring to obtain an orange powder sample. The sample was then pyrolyzed at 800°C for 3 h in a tube furnace under an argon atmosphere at a heating rate of 10°C / min. Upon completion of the pyrolysis, a black powder sample was obtained. The black powder sample was then acid-washed in 500 mL of 1M H₂SO₄ solution at 120°C. The PAM-Fe-N catalyst was then filtered through 3 L of water, dried, and subjected to secondary pyrolysis, which was used for subsequent characterization and electrochemical testing.

[0054] Test Case

[0055] The electrocatalyst materials in Examples 1-3 and Comparative Example 1 were mixed with a membrane solution (nafion solution) and a solvent (isopropanol / water (1:1)) at a ratio of catalyst:nafion solution:solvent = 10 mg:40 μL:1 mL, and the mixture was ultrasonicated for 30 min to form a uniformly dispersed slurry. 10 μL of the slurry was drop-coated on a disk / ring-disk electrode to obtain a working electrode.

[0056] Depend on Figure 1 It can be seen that the CMS-PAM-Fe-N catalyst has an obvious porous sheet structure, and no Fe-related nanoparticles are observed.

[0057] Depend on Figure 2 It can be seen that the two broad diffraction peaks at 24.1° and 43.3° correspond to partially graphitized carbon. In addition to the diffraction peak of carbon, no peaks related to any other substances are observed, which indicates that Fe is distributed in the carbon support in the form of single atoms.

[0058] Depend on Figure 3 It can be seen that CMS-PAM-Fe-N exhibits the highest half-wave potential E 1 / 2 =0.80V vs.RHE.

[0059] Depend on Figure 4 It can be seen that Figure 4 The results show that the average H2O2 yield of all catalysts is less than 2% (in the potential range of 0.2-0.8 V vs. RHE); the electron transfer number (n) of all catalysts is greater than 3.95, indicating that all catalysts mainly reduce O2 to H2O through a four-electron transfer process.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a non-noble metal fuel cell oxygen reduction catalyst based on a self-assembled semi-interpenetrating polymer network, characterized in that: The following steps are involved: S1. Dissolve the polysaccharide in ultrapure water, heat and stir, then add the polymer monomer, polymerization initiator, salt template and non-precious metal source solution, heat and stir until a uniform orange-red hydrogel is obtained, then add a nitrogen source, continue heating and stirring, evaporate the solvent, and freeze-dry to obtain an orange powder sample; S2. Pyrolysis the orange powder sample to obtain a black powder sample, which is then acid-washed, filtered, and dried to obtain a precursor product; S3, pyrolyzing the precursor product again to obtain a non-noble metal fuel cell oxygen reduction catalyst based on a self-assembled semi-interpenetrating polymer network; In step S1, the polymerization initiator is azobisisobutylamidine hydrochloride, the salt template is sodium chloride, the non-precious metal source is ferric nitrate, and the nitrogen source is urea; The usage ratio of the polysaccharide, ultrapure water, polymer monomer, azobisisobutylamidine hydrochloride, sodium chloride, ferric nitrate and urea is (1.0-4.0 g):500 mL:(0.5-2.0 mL):(0.05-0.2 g):3.0 g:(0.5-1.0 g):(0.5-2.0 g).

2. The method for preparing a non-noble metal fuel cell oxygen reduction catalyst based on a self-assembled semi-interpenetrating polymer network according to claim 1, characterized in that: In step S2, the specific conditions of the pyrolysis are: placing the orange powder sample in a tube furnace, heating it to 700-1000°C at a heating rate of 10°C / min under an argon atmosphere, and pyrolyzing it at this temperature for 3 hours; or In step S3, the specific conditions of the pyrolysis are: heating to 700-1000°C at a heating rate of 10°C / min under an argon atmosphere, and pyrolyzing at this temperature for 3 hours.

3. The method for preparing a non-noble metal fuel cell oxygen reduction catalyst based on a self-assembled semi-interpenetrating polymer network according to claim 1, characterized in that: In step S2, the specific conditions of the pickling are: pickling is performed at 120° C. in 500 mL of 1 MH 2 SO 4 solution.

4. The method for preparing a non-noble metal fuel cell oxygen reduction catalyst based on a self-assembled semi-interpenetrating polymer network according to claim 1, characterized in that: In step S1, the polysaccharide is selected from one of carboxymethyl chitosan, sodium carboxymethyl starch, and hydroxypropyl cellulose; or In step S1, the polymer monomer is selected from one of acrylamide, acrylonitrile, and fumaric acid; or In step S1, the temperature of the heating and stirring is 50-80°C.

5. A non-precious metal fuel cell oxygen reduction catalyst based on a self-assembled semi-interpenetrating polymer network, characterized in that: A non-noble metal fuel cell oxygen reduction catalyst based on a self-assembled semi-interpenetrating polymer network, prepared by the method according to any one of claims 1 to 4.

6. Use of the non-noble metal fuel cell oxygen reduction catalyst based on the self-assembled semi-interpenetrating polymer network according to claim 5 in battery cathode materials.

7. A working electrode, characterized in that The method comprises the non-noble metal fuel cell oxygen reduction catalyst based on the self-assembled semi-interpenetrating polymer network as claimed in claim 5.

8. A method for preparing the working electrode according to claim 7, characterized in that: The following steps are involved: The non-noble metal fuel cell oxygen reduction catalyst based on the self-assembled semi-interpenetrating polymer network, membrane solution and solvent are mixed in a certain proportion, ultrasonically applied to form a uniformly dispersed slurry, and the slurry is drop-coated on the disk / ring disk electrode to obtain a working electrode.

Images