Fe-n-c cathode oxygen reduction catalyst based on fe supramolecule and preparation method thereof

Abstract

The disclosure provides a preparation method of an Fe-N-C cathode oxygen reduction catalyst based on Fe supermolecule, comprising: performing first pyrolysis on ZIF-8 in a protective atmosphere to obtain a carbon-nitrogen base, wherein the carbon-nitrogen base has a positive dodecahedron framework structure; under the condition of stirring, adding a mixed solution to a melamine solution to obtain an iron supermolecule precursor, the mixed solution comprising cyanuric acid, iron ions and oxalate ions; ultrasonic dispersing the iron supermolecule precursor and the carbon-nitrogen base in water to obtain a catalyst precursor, and performing second pyrolysis on the catalyst precursor to obtain the Fe-N-C cathode oxygen reduction catalyst. The disclosure further provides the Fe-N-C cathode oxygen reduction catalyst obtained based on the foregoing preparation method and application thereof.

Description

TECHNICAL FIELD

[0001] The present disclosure belongs to the field of catalysts and their preparation technology, and particularly relates to an Fe-N-C cathode oxygen reduction catalyst based on Fe supramolecule and a preparation method thereof. BACKGROUND

[0002] Fuel cells are a clean and efficient way of energy utilization, which is of great significance for improving the environment and sustainable development. Developing high-activity, stable and economical cathode oxygen reduction reaction catalysts has important practical significance for promoting the application of fuel cells.

[0003] Due to the high cost and low reserves of platinum, Fe-N-C catalysts without platinum group metals are considered as a very promising oxygen reduction catalyst due to their low cost and high efficiency. In the synthesis of Fe single atoms, a high-temperature pyrolysis step is usually included to form Fe-N4 active sites with oxygen reduction catalytic activity. However, the pyrolysis step usually also leads to the agglomeration of Fe atoms, limiting the improvement of Fe single atom site density. At the same time, under the working conditions of fuel cells, the cathode Fe-N-C catalysts usually also face the problem of performance degradation caused by the dissolution of active sites. How to synthesize single-atom Fe-N-C catalysts with high loading, high activity and high stability has attracted widespread attention.

[0004] In the related art, single-atom iron catalysts can be prepared by strategies such as cage-like encapsulation of precursors and pyrolysis. For example, zeolitic imidazolate framework (ZIF-8) is used as a molecular cage to separate and encapsulate metal precursor iron acetate (molecular diameter about 9.7 Å), and after high-temperature pyrolysis, the obtained catalyst has monodisperse Fe-N4 active sites; adding H2 in an inert argon atmosphere adjusts the local coordination structure and site density of FeN4, which has excellent activity and stability in fuel cells; on the basis of ZIF-8 material, Fe-N-C catalysts with high Fe single atom loading (about 2.0 wt%) and utilization (90 %) are synthesized by chemical vapor deposition method.

[0005] Although the above prepared catalysts have certain single atom site density and oxygen reduction catalytic activity, compared with noble metal catalysts, the active site density is still low, and the stability is not satisfactory.

[0006] Therefore, under the premise of ensuring the oxygen reduction catalytic activity, it has far-reaching practical significance to find a method to improve the single atom site density of Fe-N-C catalysts and avoid the agglomeration of iron atoms. SUMMARY

[0007] In view of this, to solve at least one of the technical problems in the related art and other aspects, the present disclosure provides a preparation method of an Fe-N-C cathode oxygen reduction catalyst based on Fe supermolecules, comprising:

[0008] In a protective atmosphere, the ZIF-8 is subjected to a first pyrolysis to obtain a carbon-nitrogen base, wherein the carbon-nitrogen base has a framework structure of a regular dodecahedron.

[0009] Under stirring, the melamine solution is added with a mixed solution to obtain an iron supermolecule precursor, the mixed solution comprising cyanuric acid, iron ions and oxalate ions.

[0010] The iron supermolecule precursor is ultrasonically dispersed with the carbon-nitrogen base in water to obtain a catalyst precursor, and the catalyst precursor is subjected to a second pyrolysis to obtain the Fe-N-C cathode oxygen reduction catalyst.

[0011] According to an embodiment of the present disclosure, the preparation method of the ZIF-8 comprises:

[0012] The methanol solution of zinc nitrate and the methanol solution of dimethyl imidazole are mixed uniformly to obtain a suspension, and the ZIF-8 is obtained after centrifugation.

[0013] The molar ratio of zinc nitrate to dimethyl imidazole is 6:13.

[0014] According to an embodiment of the present disclosure, in the first pyrolysis, the pyrolysis temperature is 900-1100℃, and the heating rate is 3-10℃ / min.

[0015] According to an embodiment of the present disclosure, the preparation process of the mixed solution comprises:

[0016] The oxalic acid solution and the iron salt are dispersed into water, and then the cyanuric acid solution is added and stirred uniformly, wherein the molar ratio of the oxalate ions to the iron ions is 1:1-1:3.

[0017] According to an embodiment of the present disclosure, the mass ratio of the iron supermolecule precursor to the carbon-nitrogen base is greater than 5.

[0018] According to an embodiment of the present disclosure, in the second pyrolysis, the temperature is first increased to 500-600℃ at a heating rate of 3-10℃ / min, and then maintained for 1-3h, and then the temperature is increased to 900-1100℃ at a heating rate of 3-10℃ / min, and then maintained for 1-2h.

[0019] In another aspect of the present disclosure, an Fe-N-C cathode oxygen reduction catalyst obtained by the aforementioned preparation method is also provided, comprising: a carbon-nitrogen base having a framework structure of a regular dodecahedron and an active center; and the active center is Fe-N4 loaded in the framework structure, and the FeN4 exists in the form of supermolecules.

[0020] According to an embodiment of the present disclosure, the mass fraction of the active center relative to the Fe-N-C cathode oxygen reduction catalyst is 4 wt%-6 wt%.

[0021] In another aspect of the present disclosure, the use of the aforementioned Fe-N-C cathode oxygen reduction catalyst in a fuel cell is also provided.

[0022] According to an embodiment of the present disclosure, the fuel cell includes a hydrogen-oxygen fuel cell and a hydrogen-air fuel cell, the peak power density of the hydrogen-oxygen fuel cell is 1.3-1.6 W / cm 2 , and the peak power density of the hydrogen-air fuel cell is 0.6-0.8 W / cm 2 .

[0023] According to an embodiment of the present disclosure, cyanuric acid and melamine interact through non-covalent bonds to form ordered structural modules. These modules further guide and construct the basic framework of the supramolecular form of iron. Oxalate ions can form stable coordination compounds with iron ions (such as Fe 3+ ), and the coordination action not only helps the stable existence of iron ions, but also provides an important structural basis for the formation of iron supramolecules. In the single-atom Fe-N-C cathode oxygen reduction catalyst based on the Fe supramolecular form, Fe single atoms act as active centers and are dispersed in the carbon-nitrogen matrix. The active center sites have good dispersity, high degree, excellent oxygen reduction catalytic activity and stability. At the same time, the method provided by the present disclosure is simple and easy to operate, and is suitable for large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 A scanning electron microscope (SEM) image of the Fe-N-C cathode oxygen reduction catalyst prepared in Example 1 of the present disclosure;

[0025] Figure 2 A linear sweep voltammetry curve of the Fe-N-C cathode oxygen reduction catalyst prepared in Example 1 of the present disclosure in a 0.1 M perchloric acid solution;

[0026] Figure 3 A three-electrode oxygen reduction performance change graph of the Fe-N-C cathode oxygen reduction catalyst prepared in Example 1 of the present disclosure after accelerated stability testing (ADT) in a 0.1 M perchloric acid solution;

[0027] Figure 4 A polarization curve of the Fe-N-C cathode oxygen reduction catalyst prepared in Example 1 of the present disclosure in a hydrogen-oxygen and hydrogen-air proton exchange membrane fuel cell;

[0028] Figure 5 An N 1s X-ray photoelectron spectroscopy graph of the Fe-N-C cathode oxygen reduction catalyst prepared in Example 1 of the present disclosure;

[0029] Figure 6 The above are comparative linear sweep voltammetric curves of the Fe-NC cathode oxygen reduction catalysts prepared in Examples 2 to 10 of this disclosure in 0.1 M perchloric acid solution. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0031] The endpoints and any values ​​of the ranges disclosed in this disclosure are not limited to the precise ranges or values, and such ranges or values ​​should be understood to include values ​​close to such ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this disclosure.

[0032] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0033] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0034] It should be noted that, unless otherwise defined, the technical or scientific terms used in this disclosure should have the ordinary meaning understood by a person with ordinary skill in the art to which this disclosure pertains. Where the terms "first," "second," etc., are used throughout, they are used only to distinguish similar objects and should not be construed as indicating or implying their relative importance, order of precedence, or implicitly specifying the number of technical features indicated. It should be understood that the data described by "first," "second," etc., can be interchanged where appropriate.

[0035] Similarly, to simplify this disclosure and aid in understanding one or more of the various aspects of the disclosure, in the above description of exemplary embodiments of the present disclosure, various features of the present disclosure are sometimes grouped together in a single embodiment, figure, or description thereof. The use of terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refers to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the present disclosure. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0036] Furthermore, the technical solutions of the various embodiments can be combined with each other, but only if they are based on the ability of a person skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed in this disclosure.

[0037] In the process of realizing this disclosure, it was discovered that in fuel cells, non-noble metal Fe-NC catalysts still require a high catalyst loading to compensate for insufficient active site density. Traditional methods for preparing Fe-NC catalysts often lead to Fe atom aggregation. Therefore, to develop stable single-atom Fe-NC catalysts with high active site density, appropriate strategies must be adopted to suppress Fe atom aggregation during pyrolysis, promote Fe atom dispersion, and improve the stability of active sites, in order to obtain Fe-NC catalysts with excellent acid oxygen reduction activity and stability.

[0038] The method for preparing the Fe-NC cathode oxygen reduction catalyst based on Fe supramoleculars proposed in this disclosure involves high-temperature pyrolysis of Fe supramolecular precursors and ZIF-8-NC precursors in a tube furnace under argon atmosphere. This method avoids the aggregation of Fe atoms during pyrolysis to a certain extent, promotes the dispersion of Fe single-atom sites, and greatly improves the catalytic activity of the catalyst under ORR conditions.

[0039] This disclosure proposes a method for preparing an Fe-NC cathode oxygen reduction catalyst based on Fe supramolecular structure, comprising the following steps S101 to S103:

[0040] Step S101: In a protective atmosphere, ZIF-8 is subjected to a first pyrolysis to obtain a carbon-nitrogen substrate, wherein the carbon-nitrogen substrate has a dodecahedral framework structure.

[0041] In some specific embodiments, the obtained ZIF-8 is placed in a tube furnace and pyrolyzed at high temperature under argon protection, and then naturally cooled to room temperature to obtain a carbon-nitrogen substrate (which can be simply referred to as ZIF-8-NC).

[0042] Step S102: Under stirring conditions, a mixed solution is added to the melamine solution to obtain an iron supramolecular precursor. The mixed solution includes cyanuric acid, iron ions, and oxalate ions.

[0043] In some specific embodiments, melamine and cyanuric acid were dispersed in water at 80 °C and labeled as solutions A and B, respectively. Oxalic acid dihydrate and ferric nitrate nonahydrate were also dispersed in water and labeled as solution C. Solution C and solution B were mixed and stirred for 10 min. Then, under stirring, the mixture of C and B was slowly added dropwise to solution A over 4 h to obtain the Fe supramolecular precursor.

[0044] Step S103: The iron supramolecular precursor and the carbon-nitrogen substrate are ultrasonically dispersed in water to obtain the catalyst precursor. The catalyst precursor is then subjected to a second pyrolysis to obtain the Fe-NC cathode oxygen reduction catalyst.

[0045] In some specific embodiments, the obtained Fe supramolecular precursor was centrifuged, pyrolyzed ZIF-8-NC and water were added, ultrasonically dispersed for 5 min, and stirred at room temperature for 12 h. The solution was centrifuged again and dried overnight in a vacuum drying oven at 60 °C. The resulting composite solid was then pyrolyzed at high temperature in a tube furnace to obtain the Fe-NC cathodic oxygen reduction catalyst based on Fe supramolecular structure.

[0046] According to embodiments of this disclosure, cyanuric acid and melamine interact non-covalently to form ordered structural modules. These modules further guide and construct the basic framework of supramolecular iron, where oxalate ions can interact with iron ions (such as Fe). 3+ This process forms stable coordination compounds, and coordination not only contributes to the stable existence of iron ions but also provides an important structural basis for the formation of iron supramolecular structures. In the single-atom Fe-NC cathode oxygen reduction catalyst based on the Fe supramolecular form, the Fe single atom serves as the active center dispersed in the carbon-nitrogen substrate. The active center sites exhibit good dispersion and high degree of dispersion, resulting in excellent oxygen reduction catalytic activity and stability. Furthermore, the method provided in this disclosure is simple and easy to implement, making it suitable for large-scale production.

[0047] According to embodiments of this disclosure, the preparation method of ZIF-8 includes:

[0048] A methanol solution of zinc nitrate and a methanol solution of dimethylimidazole were mixed evenly to obtain a suspension, which was then centrifuged to obtain ZIF-8.

[0049] According to embodiments of this disclosure, the methanol solution of zinc nitrate and the methanol solution of dimethylimidazole ensure that the prepared ZIF-8 is a metal-organic framework material with a dodecahedral structure. This structure is conducive to the distribution of the active center FeN4 in the form of single atoms, thereby improving the catalytic mass transfer efficiency.

[0050] In some specific embodiments, at room temperature, 6 g of zinc nitrate hexahydrate is dissolved in 80 mL of methanol beforehand, and 13 g of dimethylimidazole is dissolved in 160 mL of methanol beforehand. The two solutions are stirred until dissolved and then mixed, and stirring continues for 24 h to obtain a suspension. The suspension is centrifuged, and the resulting solid is washed three times with methanol by centrifugation to obtain pure ZIF-8, which is then dried overnight in a vacuum drying oven at 60°C. Specifically, the separation method can be centrifugation at 10,000 rpm for 3 min; the washing method can be centrifugation at 10,000 rpm for 3 min, requiring a total of three washes.

[0051] According to embodiments of this disclosure, in the first pyrolysis, the pyrolysis temperature is 900℃-1100℃, for example, 900℃, 950℃, 1000℃, 1050℃, 1100℃, etc., and the heating rate is 3-10℃ / min, for example, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, etc.

[0052] According to embodiments of this disclosure, the preparation process of the mixed solution includes:

[0053] Disperse oxalic acid solution and iron salt in water, then add cyanuric acid solution and stir until homogeneous. The molar ratio of oxalate ions to iron ions is 1:1 to 1:3, for example, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, etc.

[0054] According to embodiments of this disclosure, the mass ratio of the iron supramolecular precursor to the carbon-nitrogen substrate is greater than 5.

[0055] According to embodiments of this disclosure, in the second pyrolysis, the temperature is first raised to 500℃-600℃ at a heating rate of 3-10℃ / min and held for 1-3 hours. The heating rate can be 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, etc. The initial heating temperature can be 500℃, 520℃, 540℃, 560℃, 580℃, 600℃, etc., and the initial holding time can be 1 hour. 2h, 3h, etc.; then raise the temperature to 900℃-1100℃ at a heating rate of 3-10℃ / min and hold for 1-2h. The heating rate can be 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, etc. The temperature of the second heating can be 900℃, 950℃, 1000℃, 1050℃, 1100℃, etc., and the first holding time can be 1h, 1.5h, 2h, etc.

[0056] In another aspect of this disclosure, a Fe-NC cathode oxygen reduction catalyst obtained by the aforementioned preparation method is also proposed, comprising: a carbon-nitrogen substrate having a dodecahedral framework structure and an active center; the active center is Fe-N4 supported within the framework structure, wherein FeN4 exists in the form of supramolecular molecules.

[0057] According to embodiments of this disclosure, compared with existing non-precious metal MNC catalysts, this disclosure adds Fe supramolecular molecules to the ZIF-8-NC base to promote the formation of Fe single-atom sites and avoid Fe atom aggregation, resulting in better activity and stability of the Fe-NC cathode oxygen reduction catalyst and higher site density.

[0058] According to embodiments of this disclosure, the active center has a mass fraction of 4 wt% to 6 wt% relative to the Fe-NC cathode oxygen reduction catalyst.

[0059] According to embodiments of this disclosure, the density of Fe-N4 active sites in the catalyst is significantly increased thanks to the precise introduction and distribution control of Fe supramolecular molecules. This not only means that more reactions can occur simultaneously on the catalyst surface, but also accelerates the reaction rate and further improves catalytic efficiency.

[0060] In another aspect of this disclosure, the application of the aforementioned Fe-NC cathode oxygen reduction catalyst in a fuel cell is also proposed.

[0061] According to embodiments of this disclosure, the Fe-NC cathode oxygen reduction catalyst exhibits higher catalytic activity under ORR conditions due to the high-density distribution of Fe single-atom sites and the avoidance of agglomeration effects. Simultaneously, the stable single-atom structure enhances the long-term stability of the catalyst, enabling it to maintain excellent performance during continuous reactions.

[0062] According to embodiments of this disclosure, the fuel cell includes a hydrogen-oxygen fuel cell and a hydrogen-air fuel cell, wherein the peak power density of the hydrogen-oxygen fuel cell is 1.3-1.6 W / cm³. 2 The peak power density of hydrogen-air fuel cells is 0.6-0.8 W / cm³. 2 It should be noted that the described embodiments are merely some, not all, of the embodiments disclosed herein. Other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without inventive effort are all within the scope of protection of this disclosure.

[0063] Example 1

[0064] At room temperature, 6 g of zinc nitrate hexahydrate and 13 g of dimethylimidazole were dispersed in 80 mL and 160 mL of methanol, respectively. After stirring and dissolving, they were mixed and stirred for 24 h. The suspension was centrifuged and the resulting solid was washed three times with methanol by centrifugation to obtain pure ZIF-8, which was then dried overnight in a vacuum drying oven at 60 °C.

[0065] The obtained ZIF-8 was heated to 950 °C in a tube furnace under argon protection at a heating rate of 5 °C / min and held for 1 h, and then allowed to cool naturally to room temperature to obtain carbon-nitrogen substrate ZIF-8-NC.

[0066] 378 mg of melamine and 309 mg of cyanuric acid were dispersed in 80 mL and 64 mL of water, respectively, at 80 °C, and labeled as solutions A and B, respectively. Separately, 226.9 mg of oxalic acid dihydrate and 241.8 mg of ferric nitrate nonahydrate were dispersed in 56 mL of water and labeled as solution C. Solution C was mixed with solution B and stirred for 10 min. The mixture of C and B was then slowly added dropwise to solution A while it was still being stirred over 4 h to obtain the Fe supramolecular precursor.

[0067] The obtained Fe supramolecular precursor was centrifuged, and 120 mg of pyrolyzed ZIF-8-NC and 50 mL of water were added. The mixture was ultrasonically dispersed for 5 min and stirred at room temperature for 12 h. The solution was centrifuged again and dried overnight in a vacuum drying oven at 60 °C.

[0068] The dried composite solid was heated to 550 °C in a tube furnace at a heating rate of 5 °C / min and held for 2 h. Then, the temperature was increased to 950 °C at a heating rate of 5 °C / min and held for 1 h. The solid was then allowed to cool naturally to room temperature to obtain the Fe-NC cathode oxygen reduction catalyst based on Fe supramolecular structure.

[0069] The Fe-NC cathode oxygen reduction catalyst based on Fe supramoleculars in Example 1 was imaged using scanning electron microscopy.

[0070] Figure 1 This is a scanning electron microscope (SEM) image of the Fe-NC cathode oxygen reduction catalyst prepared in Example 1 of this disclosure.

[0071] like Figure 1 As shown, the catalyst obtained in Example 1 has a relatively complete ZIF-8 morphology, with no obvious metal particles appearing, and iron self-assembled to form a supramolecular form.

[0072] The Fe-NC cathode oxygen reduction catalyst based on Fe supramoleculars from Example 1 was subjected to linear sweep voltammetry in 0.1 M perchloric acid solution. The linear sweep voltammetry test potential range was 1.03 V to 0.05 V (VS RHE), the scan rate was 20 mV / s, and the rotating disk electrode used was rotated at 900 rpm.

[0073] Figure 2 The linear sweep voltammetry curve of the Fe-NC cathode oxygen reduction catalyst prepared in Example 1 of this disclosure in 0.1 M perchloric acid solution is shown.

[0074] like Figure 2 As shown, the catalyst obtained in Example 1 exhibits excellent acidic oxygen reduction activity, with a half-wave potential of 0.87 V, which is close to that of commercial platinum-carbon catalysts. This demonstrates that the oxygen-etched Fe-NC cathode oxygen reduction catalyst obtained in Example 1 has high electrode reaction activity in electrochemical reactions and can more effectively promote the electrochemical reaction.

[0075] The Fe-NC cathode oxygen reduction catalyst based on Fe supramoleculars in Example 1 was subjected to accelerated stability testing in 0.1 M perchloric acid solution.

[0076] Figure 3 The graph shows the changes in the three-electrode oxygen reduction performance of the Fe-NC cathode oxygen reduction catalyst prepared in Example 1 of this disclosure after accelerated stability testing (ADT) in 0.1 M perchloric acid solution.

[0077] like Figure 3As shown, after 30,000 cycles of accelerated stability testing at 0.6 V-0.95 V in a three-electrode system, the obtained catalyst exhibits excellent acidic oxygen reduction stability, with a half-wave potential decay of only 20 mV, and excellent corrosion resistance.

[0078] The membrane electrode assembly using the Fe-NC cathode oxygen reduction catalyst based on Fe supramoleculars from Example 1 as the cathode catalyst was subjected to polarization curve testing in hydrogen-oxygen and hydrogen-air proton exchange membrane fuel cells.

[0079] Figure 4 The polarization curves of the Fe-NC cathode oxygen reduction catalyst prepared in Example 1 of this disclosure in hydrogen-oxygen and hydrogen-air proton exchange membrane fuel cells are shown.

[0080] like Figure 4 As shown, the membrane electrode prepared by the obtained catalyst as a cathode oxygen reduction catalyst exhibits excellent fuel cell performance.

[0081] Figure 5 The image shows the N 1s X-ray photoelectron spectrum of the Fe-NC cathode oxygen reduction catalyst prepared in Example 1 of this disclosure.

[0082] like Figure 5 As shown, the catalyst prepared in Example 1 has a higher pyrrole nitrogen content, which helps to improve the activity of single atomic sites.

[0083] Example 2

[0084] At room temperature, 6 g of zinc nitrate hexahydrate and 13 g of dimethylimidazole were dispersed in 80 mL and 160 mL of methanol, respectively. After stirring and dissolving, they were mixed and stirred for 24 h. The suspension was centrifuged and the resulting solid was washed three times with methanol by centrifugation to obtain pure ZIF-8, which was then dried overnight in a vacuum drying oven at 60 °C.

[0085] The obtained ZIF-8 was heated to 950 °C in a tube furnace under argon protection at a heating rate of 5 °C / min and held for 1 h, and then allowed to cool naturally to room temperature to obtain carbon-nitrogen substrate ZIF-8-NC.

[0086] 378 mg of melamine and 309 mg of cyanuric acid were dispersed in 80 mL and 64 mL of water, respectively, at 80 °C, and labeled as solutions A and B, respectively. Separately, 226.9 mg of oxalic acid dihydrate and 241.8 mg of ferric nitrate nonahydrate were dispersed in 56 mL of water and labeled as solution C. Solution C was mixed with solution B and stirred for 10 min. The mixture of C and B was then slowly added dropwise to solution A while it was still being stirred over 4 h to obtain the Fe supramolecular precursor.

[0087] The obtained Fe supramolecular precursor was centrifuged, and 100 mg of pyrolyzed ZIF-8-NC and 50 mL of water were added. The mixture was ultrasonically dispersed for 5 min and stirred at room temperature for 12 h. The solution was centrifuged again and dried overnight in a vacuum drying oven at 60 °C.

[0088] The dried composite solid was heated to 550 °C in a tube furnace at a heating rate of 5 °C / min and held for 2 h. Then, the temperature was increased to 950 °C at a heating rate of 5 °C / min and held for 1 h. The solid was then allowed to cool naturally to room temperature to obtain the Fe-NC cathode oxygen reduction catalyst based on Fe supramolecular structure.

[0089] The Fe-NC cathode oxygen reduction catalyst based on Fe supramoleculars in Example 2 was analyzed by scanning electron microscopy, linear scanning voltammetry, accelerated stability, and proton exchange membrane fuel cells for hydrogen-oxygen and hydrogen-air. The results were similar to those in Example 1.

[0090] Example 3

[0091] At room temperature, 6 g of zinc nitrate hexahydrate and 13 g of dimethylimidazole were dispersed in 80 mL and 160 mL of methanol, respectively. After stirring and dissolving, they were mixed and stirred for 24 h. The suspension was centrifuged and the resulting solid was washed three times with methanol by centrifugation to obtain pure ZIF-8, which was then dried overnight in a vacuum drying oven at 60 °C.

[0092] The obtained ZIF-8 was heated to 950 °C in a tube furnace under argon protection at a heating rate of 5 °C / min and held for 1 h, and then allowed to cool naturally to room temperature to obtain carbon-nitrogen substrate ZIF-8-NC.

[0093] 378 mg of melamine and 309 mg of cyanuric acid were dispersed in 80 mL and 64 mL of water, respectively, at 80 °C, and labeled as solutions A and B, respectively. Separately, 226.9 mg of oxalic acid dihydrate and 241.8 mg of ferric nitrate nonahydrate were dispersed in 56 mL of water and labeled as solution C. Solution C was mixed with solution B and stirred for 10 min. The mixture of C and B was then slowly added dropwise to solution A while it was still being stirred over 4 h to obtain the Fe supramolecular precursor.

[0094] The obtained Fe supramolecular precursor was centrifuged, and 150 mg of pyrolyzed ZIF-8-NC and 50 mL of water were added. The mixture was ultrasonically dispersed for 5 min and stirred at room temperature for 12 h. The solution was centrifuged again and dried overnight in a vacuum drying oven at 60 °C.

[0095] The dried composite solid was heated to 550 °C in a tube furnace at a heating rate of 5 °C / min and held for 2 h. Then, the temperature was increased to 950 °C at a heating rate of 5 °C / min and held for 1 h. The solid was then allowed to cool naturally to room temperature to obtain the Fe-NC cathode oxygen reduction catalyst based on Fe supramolecular structure.

[0096] The Fe-NC cathode oxygen reduction catalyst based on Fe supramoleculars in Example 3 was analyzed by scanning electron microscopy, linear scanning voltammetry, accelerated stability, and proton exchange membrane fuel cells for hydrogen-oxygen and hydrogen-air. The results were similar to those in Example 1.

[0097] Example 4

[0098] At room temperature, 6 g of zinc nitrate hexahydrate and 13 g of dimethylimidazole were dispersed in 80 mL and 160 mL of methanol, respectively. After stirring and dissolving, they were mixed and stirred for 24 h. The suspension was centrifuged and the resulting solid was washed three times with methanol by centrifugation to obtain pure ZIF-8, which was then dried overnight in a vacuum drying oven at 60 °C.

[0099] The obtained ZIF-8 was heated to 950 °C in a tube furnace under argon protection at a heating rate of 5 °C / min and held for 1 h, and then allowed to cool naturally to room temperature to obtain carbon-nitrogen substrate ZIF-8-NC.

[0100] 378 mg of melamine and 309 mg of cyanuric acid were dispersed in 80 mL and 64 mL of water, respectively, at 80 °C, and labeled as solutions A and B, respectively. Separately, 151.3 mg of oxalic acid dihydrate and 161.2 mg of ferric nitrate nonahydrate were dispersed in 56 mL of water and labeled as solution C. Solution C was mixed with solution B and stirred for 10 min. The mixture of C and B was then slowly added dropwise to solution A while it was still being stirred over 4 h to obtain the Fe supramolecular precursor.

[0101] The obtained Fe supramolecular precursor was centrifuged, and 120 mg of pyrolyzed ZIF-8-NC and 50 mL of water were added. The mixture was ultrasonically dispersed for 5 min and stirred at room temperature for 12 h. The solution was centrifuged again and dried overnight in a vacuum drying oven at 60 °C.

[0102] The dried composite solid was heated to 550 °C in a tube furnace at a heating rate of 5 °C / min and held for 2 h. Then, the temperature was increased to 950 °C at a heating rate of 5 °C / min and held for 1 h. The solid was then allowed to cool naturally to room temperature to obtain the Fe-NC cathode oxygen reduction catalyst based on Fe supramolecular structure.

[0103] The Fe-NC cathode oxygen reduction catalyst based on Fe supramoleculars in Example 4 was analyzed by scanning electron microscopy, linear scanning voltammetry, accelerated stability, and proton exchange membrane fuel cells for hydrogen-oxygen and hydrogen-air. The results were similar to those in Example 1.

[0104] Example 5

[0105] At room temperature, 6 g of zinc nitrate hexahydrate and 13 g of dimethylimidazole were dispersed in 80 mL and 160 mL of methanol, respectively. After stirring and dissolving, they were mixed and stirred for 24 h. The suspension was centrifuged and the resulting solid was washed three times with methanol by centrifugation to obtain pure ZIF-8, which was then dried overnight in a vacuum drying oven at 60 °C.

[0106] The obtained ZIF-8 was heated to 950 °C in a tube furnace under argon protection at a heating rate of 5 °C / min and held for 1 h, and then allowed to cool naturally to room temperature to obtain carbon-nitrogen substrate ZIF-8-NC.

[0107] 378 mg of melamine and 309 mg of cyanuric acid were dispersed in 80 mL and 64 mL of water, respectively, at 80 °C, and labeled as solutions A and B, respectively. Separately, 151.3 mg of oxalic acid dihydrate and 161.2 mg of ferric nitrate nonahydrate were dispersed in 56 mL of water and labeled as solution C. Solution C was mixed with solution B and stirred for 10 min. The mixture of C and B was then slowly added dropwise to solution A while it was still being stirred over 4 h to obtain the Fe supramolecular precursor.

[0108] The obtained Fe supramolecular precursor was centrifuged, and 100 mg of pyrolyzed ZIF-8-NC and 50 mL of water were added. The mixture was ultrasonically dispersed for 5 min and stirred at room temperature for 12 h. The solution was centrifuged again and dried overnight in a vacuum drying oven at 60 °C.

[0109] The dried composite solid was heated to 550 °C in a tube furnace at a heating rate of 5 °C / min and held for 2 h. Then, the temperature was increased to 950 °C at a heating rate of 5 °C / min and held for 1 h. The solid was then allowed to cool naturally to room temperature to obtain the Fe-NC cathode oxygen reduction catalyst based on Fe supramolecular structure.

[0110] The Fe-NC cathode oxygen reduction catalyst based on Fe supramoleculars in Example 5 was analyzed by scanning electron microscopy, linear scanning voltammetry, accelerated stability, and proton exchange membrane fuel cells for hydrogen-oxygen and hydrogen-air. The results were similar to those in Example 1.

[0111] Example 6

[0112] At room temperature, 6 g of zinc nitrate hexahydrate and 13 g of dimethylimidazole were dispersed in 80 mL and 160 mL of methanol, respectively. After stirring and dissolving, they were mixed and stirred for 24 h. The suspension was centrifuged and the resulting solid was washed three times with methanol by centrifugation to obtain pure ZIF-8, which was then dried overnight in a vacuum drying oven at 60 °C.

[0113] The obtained ZIF-8 was heated to 950 °C in a tube furnace under argon protection at a heating rate of 5 °C / min and held for 1 h, and then allowed to cool naturally to room temperature to obtain carbon-nitrogen substrate ZIF-8-NC.

[0114] 378 mg of melamine and 309 mg of cyanuric acid were dispersed in 80 mL and 64 mL of water, respectively, at 80 °C, and labeled as solutions A and B, respectively. Separately, 151.3 mg of oxalic acid dihydrate and 161.2 mg of ferric nitrate nonahydrate were dispersed in 56 mL of water and labeled as solution C. Solution C was mixed with solution B and stirred for 10 min. The mixture of C and B was then slowly added dropwise to solution A while it was still being stirred over 4 h to obtain the Fe supramolecular precursor.

[0115] The obtained Fe supramolecular precursor was centrifuged, and 150 mg of pyrolyzed ZIF-8-NC and 50 mL of water were added. The mixture was ultrasonically dispersed for 5 min and stirred at room temperature for 12 h. The solution was centrifuged again and dried overnight in a vacuum drying oven at 60 °C.

[0116] The dried composite solid was heated to 550 °C in a tube furnace at a heating rate of 5 °C / min and held for 2 h. Then, the temperature was increased to 950 °C at a heating rate of 5 °C / min and held for 1 h. The solid was then allowed to cool naturally to room temperature to obtain the Fe-NC cathode oxygen reduction catalyst based on Fe supramolecular structure.

[0117] The Fe-NC cathode oxygen reduction catalyst based on Fe supramoleculars in Example 6 was analyzed by scanning electron microscopy, linear scanning voltammetry, accelerated stability, and proton exchange membrane fuel cells for hydrogen-oxygen and hydrogen-air. The results were similar to those in Example 1.

[0118] Example 7

[0119] At room temperature, 6 g of zinc nitrate hexahydrate and 13 g of dimethylimidazole were dispersed in 80 mL and 160 mL of methanol, respectively. After stirring and dissolving, they were mixed and stirred for 24 h. The suspension was centrifuged and the resulting solid was washed three times with methanol by centrifugation to obtain pure ZIF-8, which was then dried overnight in a vacuum drying oven at 60 °C.

[0120] The obtained ZIF-8 was heated to 950 °C in a tube furnace under argon protection at a heating rate of 5 °C / min and held for 1 h, and then allowed to cool naturally to room temperature to obtain carbon-nitrogen substrate ZIF-8-NC.

[0121] 378 mg of melamine and 309 mg of cyanuric acid were dispersed in 80 mL and 64 mL of water, respectively, at 80 °C, and labeled as solutions A and B, respectively. Separately, 226.9 mg of oxalic acid dihydrate and 241.8 mg of ferric nitrate nonahydrate were dispersed in 56 mL of water and labeled as solution C. Solution C was mixed with solution B and stirred for 10 min. The mixture of C and B was then slowly added dropwise to solution A while it was still being stirred over 4 h to obtain the Fe supramolecular precursor.

[0122] The obtained Fe supramolecular precursor was centrifuged, and 120 mg of pyrolyzed ZIF-8-NC and 50 mL of water were added. The mixture was ultrasonically dispersed for 5 min and stirred at room temperature for 12 h. The solution was centrifuged again and dried overnight in a vacuum drying oven at 60 °C.

[0123] The dried composite solid was heated to 600 °C in a tube furnace at a heating rate of 5 °C / min and held for 2 h. Then, the temperature was increased to 950 °C at a heating rate of 5 °C / min and held for 1 h. The solid was then allowed to cool naturally to room temperature to obtain the Fe-NC cathode oxygen reduction catalyst based on Fe supramolecular structure.

[0124] The Fe-NC cathode oxygen reduction catalyst based on Fe supramoleculars in Example 7 was analyzed by scanning electron microscopy, linear scanning voltammetry, accelerated stability, and proton exchange membrane fuel cells for hydrogen-oxygen and hydrogen-air. The results were similar to those in Example 1.

[0125] Example 8

[0126] At room temperature, 6 g of zinc nitrate hexahydrate and 13 g of dimethylimidazole were dispersed in 80 mL and 160 mL of methanol, respectively. After stirring and dissolving, they were mixed and stirred for 24 h. The suspension was centrifuged and the resulting solid was washed three times with methanol by centrifugation to obtain pure ZIF-8, which was then dried overnight in a vacuum drying oven at 60 °C.

[0127] The obtained ZIF-8 was heated to 950 °C in a tube furnace under argon protection at a heating rate of 5 °C / min and held for 1 h, and then allowed to cool naturally to room temperature to obtain carbon-nitrogen substrate ZIF-8-NC.

[0128] 378 mg of melamine and 309 mg of cyanuric acid were dispersed in 80 mL and 64 mL of water, respectively, at 80 °C, and labeled as solutions A and B, respectively. Separately, 226.9 mg of oxalic acid dihydrate and 241.8 mg of ferric nitrate nonahydrate were dispersed in 56 mL of water and labeled as solution C. Solution C was mixed with solution B and stirred for 10 min. The mixture of C and B was then slowly added dropwise to solution A while it was still being stirred over 4 h to obtain the Fe supramolecular precursor.

[0129] The obtained Fe supramolecular precursor was centrifuged, and 120 mg of pyrolyzed ZIF-8-NC and 50 mL of water were added. The mixture was ultrasonically dispersed for 5 min and stirred at room temperature for 12 h. The solution was centrifuged again and dried overnight in a vacuum drying oven at 60 °C.

[0130] The dried composite solid was heated to 550 °C in a tube furnace at a heating rate of 5 °C / min and held for 4 h. Then, the temperature was increased to 950 °C at a heating rate of 5 °C / min and held for 1 h. The solid was then allowed to cool naturally to room temperature to obtain the Fe-NC cathode oxygen reduction catalyst based on Fe supramolecular structure.

[0131] The Fe-NC cathode oxygen reduction catalyst based on Fe supramoleculars in Example 8 was analyzed by scanning electron microscopy, linear scanning voltammetry, accelerated stability, and proton exchange membrane fuel cells for hydrogen-oxygen and hydrogen-air. The results were similar to those in Example 1.

[0132] Example 9

[0133] At room temperature, 6 g of zinc nitrate hexahydrate and 13 g of dimethylimidazole were dispersed in 80 mL and 160 mL of methanol, respectively. After stirring and dissolving, they were mixed and stirred for 24 h. The suspension was centrifuged and the resulting solid was washed three times with methanol by centrifugation to obtain pure ZIF-8, which was then dried overnight in a vacuum drying oven at 60 °C.

[0134] The obtained ZIF-8 was heated to 950 °C in a tube furnace under argon protection at a heating rate of 5 °C / min and held for 1 h, and then allowed to cool naturally to room temperature to obtain carbon-nitrogen substrate ZIF-8-NC.

[0135] 378 mg of melamine and 309 mg of cyanuric acid were dispersed in 80 mL and 64 mL of water, respectively, at 80 °C, and labeled as solutions A and B, respectively. Separately, 226.9 mg of oxalic acid dihydrate and 241.8 mg of ferric nitrate nonahydrate were dispersed in 56 mL of water and labeled as solution C. Solution C was mixed with solution B and stirred for 10 min. The mixture of C and B was then slowly added dropwise to solution A while it was still being stirred over 4 h to obtain the Fe supramolecular precursor.

[0136] The obtained Fe supramolecular precursor was centrifuged, and 120 mg of pyrolyzed ZIF-8-NC and 50 mL of water were added. The mixture was ultrasonically dispersed for 5 min and stirred at room temperature for 12 h. The solution was centrifuged again and dried overnight in a vacuum drying oven at 60 °C.

[0137] The dried composite solid was heated to 600 °C in a tube furnace at a heating rate of 5 °C / min and held for 4 h. Then, the temperature was increased to 950 °C at a heating rate of 5 °C / min and held for 1 h. The solid was then allowed to cool naturally to room temperature to obtain the Fe-NC cathode oxygen reduction catalyst based on Fe supramolecular structure.

[0138] The Fe-NC cathode oxygen reduction catalyst based on Fe supramoleculars in Example 9 was analyzed by scanning electron microscopy, linear scanning voltammetry, accelerated stability, and proton exchange membrane fuel cells for hydrogen-oxygen and hydrogen-air. The results were similar to those in Example 1.

[0139] Example 10

[0140] At room temperature, 6 g of zinc nitrate hexahydrate and 13 g of dimethylimidazole were dispersed in 80 mL and 160 mL of methanol, respectively. After stirring and dissolving, they were mixed and stirred for 24 h. The suspension was centrifuged and the resulting solid was washed three times with methanol by centrifugation to obtain pure ZIF-8, which was then dried overnight in a vacuum drying oven at 60 °C.

[0141] The obtained ZIF-8 was heated to 950 °C in a tube furnace under argon protection at a heating rate of 5 °C / min and held for 1 h, and then allowed to cool naturally to room temperature to obtain carbon-nitrogen substrate ZIF-8-NC.

[0142] 378 mg of melamine and 309 mg of cyanuric acid were dispersed in 80 mL and 64 mL of water, respectively, at 80 °C, and labeled as solutions A and B, respectively. Separately, 189.1 mg of oxalic acid dihydrate and 201.5 mg of ferric nitrate nonahydrate were dispersed in 56 mL of water and labeled as solution C. Solution C was mixed with solution B and stirred for 10 min. The mixture of C and B was then slowly added dropwise to solution A while it was still being stirred over 4 h to obtain the Fe supramolecular precursor.

[0143] The obtained Fe supramolecular precursor was centrifuged, and 120 mg of pyrolyzed ZIF-8-NC and 50 mL of water were added. The mixture was ultrasonically dispersed for 5 min and stirred at room temperature for 12 h. The solution was centrifuged again and dried overnight in a vacuum drying oven at 60 °C.

[0144] The dried composite solid was heated to 550 °C in a tube furnace at a heating rate of 5 °C / min and held for 2 h. Then, the temperature was increased to 950 °C at a heating rate of 5 °C / min and held for 1 h. The solid was then allowed to cool naturally to room temperature to obtain the Fe-NC cathode oxygen reduction catalyst based on Fe supramolecular structure.

[0145] The Fe-NC cathode oxygen reduction catalyst based on Fe supramoleculars in Example 11 was analyzed by scanning electron microscopy, linear scanning voltammetry, accelerated stability, and proton exchange membrane fuel cells for hydrogen-oxygen and hydrogen-air. The results were similar to those in Example 1.

[0146] Figure 6 The above are comparative linear sweep voltammetric curves of the Fe-NC cathode oxygen reduction catalysts prepared in Examples 2 to 10 of this disclosure in 0.1 M perchloric acid solution.

[0147] like Figure 6 As shown, the catalysts obtained in different embodiments have similar three-electrode half-wave potentials, verifying that the Fe-NC cathode oxygen reduction catalyst based on Fe supramolecular proposed in this disclosure has good stability.

[0148] The specific embodiments described above further illustrate the purpose, technical solutions, and beneficial effects of this disclosure. It should be understood that the above descriptions are merely specific embodiments of this disclosure and are not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. A method for preparing an Fe-NC cathode oxygen reduction catalyst based on Fe supramolecular structure, comprising: In a protective atmosphere, ZIF-8 is subjected to a first pyrolysis to obtain a carbon-nitrogen substrate, wherein the carbon-nitrogen substrate has a dodecahedral framework structure; Under stirring conditions, a mixed solution is added to a melamine solution to obtain an iron supramolecular precursor. The mixed solution includes cyanuric acid, iron ions, and oxalate ions. The preparation process of the mixed solution includes: dispersing oxalic acid solution and iron salt in water, then adding cyanuric acid solution and stirring until homogeneous. The molar ratio of oxalate ions to iron ions is 1:1 to 1:

3. The iron supramolecular precursor and the carbon-nitrogen substrate are ultrasonically dispersed in water to obtain a catalyst precursor, wherein the mass ratio of the iron supramolecular precursor to the carbon-nitrogen substrate is greater than 5. The catalyst precursor is subjected to a second pyrolysis to obtain the Fe-NC cathode oxygen reduction catalyst. In the second pyrolysis, the temperature is first raised to 500℃-600℃ at a heating rate of 3-10℃ / min and held for 1-3 hours. Then, the temperature is raised to 900℃-1100℃ at a heating rate of 3-10℃ / min and held for 1-2 hours.

2. The preparation method according to claim 1, wherein, The preparation method of ZIF-8 includes: A methanol solution of zinc nitrate and a methanol solution of dimethylimidazole were mixed thoroughly to obtain a suspension, which was then centrifuged to obtain ZIF-8.

3. The preparation method according to claim 1, wherein, In the first pyrolysis, the pyrolysis temperature is 900℃-1100℃, and the heating rate is 3-10℃ / min.

4. A Fe-NC cathode oxygen reduction catalyst obtained by the preparation method according to any one of claims 1 to 3, comprising: A carbon-nitrogen substrate having a dodecahedral framework structure; The active center is Fe-N4 loaded within the framework structure, and the FeN4 exists in the form of a supramolecular structure.

5. The Fe-NC cathode oxygen reduction catalyst according to claim 4, wherein, The active center has a mass fraction of 4 wt%-6 wt% relative to the Fe-NC cathode oxygen reduction catalyst.

6. The application of the Fe-NC cathode oxygen reduction catalyst as described in any one of claims 4 or 5 in a fuel cell.

7. The application according to claim 6, wherein, The fuel cells include hydrogen-oxygen fuel cells and hydrogen-air fuel cells, wherein the peak power density of the hydrogen-oxygen fuel cells is 1.3-1.6 W / cm³. 2 The peak power density of the hydrogen-air fuel cell is 0.6-0.8 W / cm³. 2 .

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