A non-noble metal oxygen reduction electrocatalyst based on strong chelation and a preparation method and application thereof

Abstract

The application relates to a non-noble metal oxygen reduction electrocatalyst based on strong chelation and a preparation method and application thereof, and belongs to the technical field of electrochemical energy sources. The preparation method of the electrocatalyst comprises the following steps: S1, adding an organic complex into ultrapure water, heating and stirring until complete dissolution, then sequentially adding a salt template and an iron source, and heating and stirring until a deep yellow gel-like suspension is obtained; S2, adding an ammonium source into the gel-like suspension, continuing to stir until complete dissolution, stopping heating after evaporating part of the solvent by heating, and performing freeze-drying to obtain an orange powder; S3, then pyrolyzing the orange powder to obtain a black powder; S4, performing acid pickling, suction filtration and drying on the black powder to obtain a precursor product; and S5, pyrolyzing the precursor product again to obtain an NH4Cl-organic complex-Fe catalyst, namely the electrocatalyst. The electrocatalyst with high graphitization degree can be prepared.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of electrochemical energy sources, in particular to a non-noble metal oxygen reduction electrocatalyst based on strong chelation and a preparation method and application thereof. BACKGROUND

[0002] As a conversion device of hydrogen energy, a proton exchange membrane fuel cell (PEMFC) has the advantages of high conversion efficiency, large power density and environmental protection, and is considered as one of the important ways to realize the transformation to clean energy. However, the cathode oxygen reduction reaction (ORR) of the PEMFC is slow, and a platinum-based catalyst which is expensive is used as a high-efficiency ORR catalyst, but the high cost and easy poisoning of the platinum-based catalyst seriously hinder the commercial development of the PEMFC. Therefore, developing a non-noble metal catalyst with low cost, high activity and high stability to replace the platinum-based catalyst has become an important measure to promote the development of the PEMFC.

[0003] A transition metal atom-nitrogen-carbon (M-N-C) catalyst has become the most promising substitute for the platinum-based catalyst, and most of the catalysts are prepared by pyrolyzing a metal organic framework (MOF) loaded with a transition metal. However, this synthesis method has certain limitations. First, the metal center ions of the MOF sublimate to generate defects in the pyrolysis process, thereby inducing Fe 3+ filling, so that the combination between the transition metal atom and the nitrogen atom is weak, the degree of graphitization is reduced, a large amount of metal is dissolved in the acid ORR process, and the intrinsic activity and stability of the ORR are greatly limited; second, the carbon support of the catalyst prepared by the synthesis method has a low degree of graphitization, so that the carbon support is oxidized and corroded in the long-term operation process, and the active sites of the entire catalyst layer are peeled off or even the structure is collapsed. SUMMARY

[0004] Therefore, the application provides a non-noble metal oxygen reduction electrocatalyst based on strong chelation and a preparation method and application thereof. The strong chelation and high order between iron ions (Fe 3+ ) and functional groups such as -COOH and -NH2 in organic complexes (such as 2-amino terephthalic acid (H2atpt), nicotinamide (VPP) and acetylsalicylic acid (Aspirin)) are used to prepare a high-stability non-noble metal oxygen reduction electrocatalyst with a high degree of graphitization. The entire synthesis process is simple to operate, no hazardous solvent is used, a single batch production can reach more than kilograms, high atomic utilization rate is achieved while high stability is maintained, a new idea is provided for preparing a high-activity and high-stability fuel cell cathode oxygen reduction non-noble metal catalyst and realizing commercial large-scale production, and the defects in the prior art can be effectively overcome.

[0005] The first aspect of the present application provides a method for preparing a non-noble metal oxygen reduction electrocatalyst based on strong chelation, comprising the following steps:

[0006] S1. Add the organic complex to ultrapure water, heat and stir until completely dissolved, then add the salt template and iron source in sequence, and heat and stir until a dark yellow gel suspension is obtained;

[0007] S2. Add an ammonium source to the gel suspension, continue stirring until completely dissolved, then heat to evaporate part of the solvent, stop heating, and freeze-dry to obtain an orange powder;

[0008] S3, then pyrolyzing the orange powder to obtain a black powder;

[0009] S4, washing the black powder with acid, filtering, and drying to obtain a precursor product;

[0010] S5. The precursor product is pyrolyzed again to obtain an NH4Cl-organic complex-Fe catalyst, i.e., a non-precious metal oxygen reduction electrocatalyst based on strong chelation.

[0011] Specifically, the method includes the following steps:

[0012] S1. Add the organic complex to ultrapure water, heat and stir until completely dissolved, then add potassium chloride and anhydrous ferric chloride, and heat and stir until a dark yellow gel suspension is obtained;

[0013] S2. Add ammonium chloride to the gel suspension, continue stirring until completely dissolved, then heat to evaporate part of the solvent, stop heating, and freeze-dry to obtain an orange powder;

[0014] S3, then pyrolyzing the orange powder to obtain a black powder;

[0015] S4. The black powder is acid-washed, filtered, and dried to obtain a precursor product:

[0016] S5. The precursor product is pyrolyzed again to obtain an NH4Cl-organic complex-Fe catalyst, i.e., a non-precious metal oxygen reduction electrocatalyst based on strong chelation.

[0017] This application utilizes the advantages of functional groups (such as -COOH, -NH2, etc.) in nitrogen-containing carboxylic acid organic complexes, such as strong chelation of metal ions, extremely high coordination order, and avoidance of a large number of defect formation, to prepare MNC catalysts. This method can achieve high graphitization of the catalyst while maintaining high activity, thereby solving the above problems. The advantages of this preparation method are as follows: First, the oxygen atom (O) in the carboxyl group can act as a coordinating atom to form a monodentate coordination with the metal ion. In certain circumstances, the oxygen atom can also be connected to two different metal sites, thereby forming a bidentate coordination. This coordination mode has high directionality and strong stability. It can restrict the movement of carbon atoms while avoiding defects caused by the sublimation of the metal center ion in the MOF, promoting a more orderly rearrangement of carbon atoms and ultimately forming a regular graphite structure. Second, the carboxyl group can also form a bridging structure with the carboxyl groups of other acids, thereby further improving the chelation stability of the metal ion. Third, the carboxyl group and the amino group can participate in the coordination reaction together, combining with the metal ion through the O, N-chelation mode, and can also form more complex structures, such as tridentate coordination configurations, through the bridging effect. This preparation method not only significantly improves metal atom utilization and enhances the binding energy of the M-N bond in the MNC catalyst, but also achieves a high degree of graphitization, effectively reducing the amount of metal ion dissolution during the acidic ORR process and achieving high catalyst stability. Therefore, the preparation of highly graphitized non-precious metal catalysts for fuel cell cathode ORR through the strong chelation between metal ions and nitrogen-containing carboxylic acid organic complexes is a new approach to replace traditional methods for preparing MNC catalysts.

[0018] Preferably, in step S1, the organic complex is selected from one of 2-aminoterephthalic acid, nicotinamide, and acetylsalicylic acid; or

[0019] In step S1, the salt template is selected from one of potassium chloride, zinc chloride, and sodium chloride; or

[0020] In step S1, the iron source is selected from one of anhydrous ferric chloride, ferric sulfate, and ferric nitrate; or

[0021] In step S2, the ammonium source is selected from one of ammonium chloride, ammonium sulfate and ammonium nitrate.

[0022] Preferably, in step S3, the specific conditions of the pyrolysis are: first pyrolysis at 500°C for 1 hour, then heating to 1000°C and pyrolysis at this temperature for 1 hour; or

[0023] In step S5, the pyrolysis temperature is 1000° C. and the pyrolysis time is 1 hour.

[0024] Preferably, in step S4, the specific conditions for pickling are: pickling in H2SO4 solution for 10-15 hours.

[0025] Preferably, the usage ratio of the organic complex, ultrapure water, potassium chloride, anhydrous ferric chloride and ammonium chloride is (1-9 g):200 mL:(1-5 g):(0.1-1 g):(1-8 g).

[0026] The second aspect of the present application further provides a non-precious metal oxygen reduction electrocatalyst based on strong chelation, which is prepared by the above method.

[0027] The third aspect of the present application also provides the use of the above-mentioned non-noble metal oxygen reduction electrocatalyst based on strong chelation in battery cathode materials.

[0028] The fourth aspect of the present application further provides a working electrode, which includes the above-mentioned non-noble metal oxygen reduction electrocatalyst based on strong chelation.

[0029] A fifth aspect of the present application further provides a method for preparing the above-mentioned working electrode, comprising the following steps:

[0030] 10 mg of the non-precious metal oxygen reduction electrocatalyst material based on strong chelation was weighed, and 1 mL of isopropyl alcohol was added sequentially and ultrasonicated until uniform. After uniformity, the mixture was dropped onto the disk electrode to obtain a working electrode. Finally, the oxygen reduction electrochemical performance was tested.

[0031] Compared with the prior art, this application has the following beneficial effects:

[0032] This application utilizes iron ions (Fe 3+ ) and organic complexes (such as 2-aminoterephthalic acid (H2atpt), nicotinamide (VPP), acetylsalicylic acid (Aspirin) and other functional groups such as -COOH, -NH2) and high order to prepare non-precious metal oxygen reduction electrocatalysts with high graphitization degree; the entire synthesis process is simple to operate and does not use hazardous solvents. Single batch production can reach above gram level, achieving high atomic utilization while maintaining high stability. It can provide a new idea for the preparation of highly active and highly stable non-precious metal catalysts for fuel cell cathode oxygen reduction and realize commercial large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] 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.

[0034] Figure 1This is a SEM image of the NH4Cl-H2atpt-Fe catalyst of Example 1 of the present application;

[0035] Figure 2 This is a SEM image of the NH4Cl-VPP-Fe catalyst of Example 2 of the present application;

[0036] Figure 3 The Raman comparison chart of NH4Cl-H2atpt-Fe catalyst, NH4Cl-VPP-Fe catalyst and NH4Cl-Aspirin-Fe catalyst of Examples 1-3 of the present application (I D Indicates the degree of defect, I G Indicates the degree of graphitization);

[0037] Figure 4 This is a SCV comparison chart of the NH4Cl-H2atpt-Fe catalyst, NH4Cl-VPP-Fe catalyst and NH4Cl-Aspirin-Fe catalyst of Examples 1-3 of the present application. DETAILED DESCRIPTION

[0038] 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.

[0039] Unless otherwise specified, the experimental methods used in the examples of this application are all conventional methods.

[0040] In the following examples, unless otherwise specified, all raw materials can be purchased commercially or prepared by conventional methods.

[0041] Example 1

[0042] Into 200 ml of ultrapure water, 3 g of H2atpt was added and heated with stirring until completely dissolved. Subsequently, 3 g of potassium chloride and 0.55 g of anhydrous ferric chloride were added to the above solution in turn, and heated with stirring until a deep yellow gel-like suspension was obtained. 5 g of ammonium chloride was added, and stirring was continued until completely dissolved. When the solvent was evaporated to 50 mL with heating, heating was stopped, and the sample was placed in a freeze dryer to dry, obtaining an orange powder. Subsequently, the sample was placed in a tube furnace for pyrolysis, first at 500°C for 1 h, and then at 1000°C for 1 h, obtaining a black powder. The black powder was acid washed in an H2SO4 solution for 12 h. After suction filtration and drying, secondary pyrolysis was performed at a pyrolysis temperature of 1000°C for 1 h, obtaining an NH4Cl-H2atpt-Fe catalyst, which was used for subsequent characterization and electrochemical testing.

[0043] Example 2

[0044] Into 200 ml of ultrapure water, 5 g of VPP was added and heated with stirring until completely dissolved. Subsequently, 5 g of potassium chloride and 0.55 g of anhydrous ferric chloride were added to the above solution in turn, and heated with stirring until a deep yellow gel-like suspension was obtained. 5 g of ammonium chloride was added, and stirring was continued until completely dissolved. When the solvent was evaporated to 50 mL with heating, heating was stopped, and the sample was placed in a freeze dryer to dry, obtaining an orange powder. Subsequently, the sample was placed in a tube furnace for pyrolysis, first at 500°C for 1 h, and then at 1000°C for 1 h, obtaining a black powder. The black powder was acid washed in an H2SO4 solution for 12 h. After suction filtration and drying, secondary pyrolysis was performed at a pyrolysis temperature of 1000°C for 1 h, obtaining an NH4Cl-VPP-Fe catalyst, which was used for subsequent characterization and electrochemical testing.

[0045] Example 3

[0046] Into 200 ml of ultrapure water, 4 g of Aspirin was added and heated with stirring until completely dissolved. Subsequently, 4 g of potassium chloride and 0.55 g of anhydrous ferric chloride were added to the above solution in turn, and heated with stirring until a deep yellow gel-like suspension was obtained. 5 g of ammonium chloride was added, and stirring was continued until completely dissolved. When the solvent was evaporated to 50 mL with heating, heating was stopped, and the sample was placed in a freeze dryer to dry, obtaining an orange powder. Subsequently, the sample was placed in a tube furnace for pyrolysis, first at 500°C for 1 h, and then at 1000°C for 1 h, obtaining a black powder. The black powder was acid washed in an H2SO4 solution for 12 h. After suction filtration and drying, secondary pyrolysis was performed at a pyrolysis temperature of 1000°C for 1 h, obtaining an NH4Cl-Aspirin-Fe catalyst, which was used for subsequent characterization and electrochemical testing.

[0047] Comparative Example 1

[0048] Into 200 ml of ultrapure water, 3 g of XC-72 carbon powder was added and heated and stirred until completely dissolved. Subsequently, 3 g of potassium chloride and 0.55 g of anhydrous ferric chloride were added to the above solution in turn, and heated and stirred until a deep yellow gel-like suspension was obtained. 5 g of ammonium chloride was added, and stirring was continued until completely dissolved. While heating and evaporating the solvent to 50 ml, heating was stopped, and the sample was placed in a freeze dryer to dry, obtaining an orange powder. The sample was then placed in a tube furnace for pyrolysis, first at 500°C for 1 h, and then at 1000°C for 1 h, obtaining a black powder. The black powder was acid washed in an H2SO4 solution for 12 h. After suction filtration and drying, a second pyrolysis was performed, at a pyrolysis temperature of 1000°C and a pyrolysis time of 1 h, obtaining the NH4Cl-XC-Fe catalyst, which was used for subsequent characterization and electrochemical tests.

[0049] The experimental scheme provided in the present comparative example can refer to Example 1, except that XC-72 carbon powder without chelation was used instead of 2-amino terephthalic acid (H2atpt).

[0050] Test Example

[0051] 10 mg of each of the non-noble metal oxygen reduction electrocatalyst materials based on strong chelation in Examples 1-3 were taken and added to 1 mL of isopropyl alcohol in turn and ultrasonically stirred until uniform. After uniformity, the mixture was dropped onto a disc electrode for oxygen reduction electrochemical performance testing.

[0052] Figure 1 In the present example, the prepared NH4Cl-H2atpt-Fe catalyst was in the form of strips, and no obvious iron nanoparticles were observed.

[0053] Figure 2 In the present example, the prepared NH4Cl-VPP-Fe catalyst was in the form of sheets, and no obvious iron nanoparticles were observed.

[0054] Figure 3 In the present example, it can be seen from the comparison of the Raman test results that the graphitization degrees of the non-noble metal oxygen reduction electrocatalysts prepared based on strong chelation of different organic complexes are different, I D represents the degree of defects, I G represents the degree of graphitization, I D / I G The larger the numerical value, the higher the degree of defects, and vice versa, the higher the degree of graphitization. It can be seen from the comparison that the prepared NH4Cl-H2atpt-Fe catalyst has the highest degree of graphitization, followed by the NH4Cl-VPP-Fe catalyst, and finally the NH4Cl-Aspirin-Fe catalyst.

[0055] Figure 4The oxygen reduction performance of three catalysts was tested. The test results showed that the oxygen reduction performance of NH4Cl-H2atpt-Fe catalyst was the best. In the acidic electrolyte test, the half-wave potential (E 1 / 2 ) can reach 0.82V, followed by NH4Cl-Aspirin-Fe catalyst, E 1 / 2 is 0.80V, and finally the NH4Cl-VPP-Fe catalyst, E 1 / 2 is 0.78V.

[0056] 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 oxygen reduction electrocatalyst based on strong chelation, characterized in that: The following steps are involved: S1. Add the organic complex to ultrapure water, heat and stir until completely dissolved, then add the salt template and iron source in sequence, and heat and stir until a dark yellow gel suspension is obtained; S2. Add an ammonium source to the gel suspension, continue stirring until completely dissolved, then heat to evaporate part of the solvent, stop heating, and freeze-dry to obtain an orange powder; S3, then pyrolyzing the orange powder to obtain a black powder; S4, washing the black powder with acid, filtering, and drying to obtain a precursor product; S5, pyrolyzing the precursor product again to obtain an NH4Cl-organic complex-Fe catalyst, i.e., a non-noble metal oxygen reduction electrocatalyst based on strong chelation; In step S1, the organic complex is selected from one of 2-aminoterephthalic acid, nicotinamide, and acetylsalicylic acid; in step S1, the salt template is selected from one of potassium chloride, zinc chloride, and sodium chloride; in step S3, the specific pyrolysis conditions are: first pyrolysis at a temperature of 500°C for 1 hour, then heating to 1000°C, and pyrolysis at this temperature for 1 hour; in step S5, the pyrolysis temperature is 1000°C and the pyrolysis time is 1 hour.

2. The method for preparing a non-noble metal oxygen reduction electrocatalyst based on strong chelation according to claim 1, characterized in that: In step S1, the iron source is selected from one of anhydrous ferric chloride, ferric sulfate, and ferric nitrate; in step S2, the ammonium source is selected from one of ammonium chloride, ammonium sulfate, and ammonium nitrate.

3. The method for preparing a non-noble metal oxygen reduction electrocatalyst based on strong chelation according to claim 1, characterized in that: In step S4, the specific conditions for pickling are: pickling in H2SO4 solution for 10-15 hours.

4. The method for preparing a non-noble metal oxygen reduction electrocatalyst based on strong chelation according to claim 2, characterized in that: The usage ratio of the organic complex, ultrapure water, potassium chloride, anhydrous ferric chloride and ammonium chloride is (1-9 g):200 mL:(1-5 g):(0.1-1 g):(1-8 g).

5. A non-noble metal oxygen reduction electrocatalyst based on strong chelation, characterized in that A non-noble metal oxygen reduction electrocatalyst based on strong chelation prepared by the method according to any one of claims 1 to 4.

6. Use of the non-noble metal oxygen reduction electrocatalyst based on strong chelation as claimed in claim 5 in battery cathode materials.

7. A working electrode, characterized in that It comprises the non-noble metal oxygen reduction electrocatalyst based on strong chelation 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: 10 mg of the non-noble metal oxygen reduction electrocatalyst material based on strong chelation was weighed, and 1 mL of isopropanol was added successively and ultrasonicated until uniform. After uniformity, the mixture was dropped onto the disk electrode to obtain a working electrode.

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