High-stability Fe-N-C catalyst based on supramolecular modification as well as preparation method and application of high-stability Fe-N-C catalyst

Abstract

The invention relates to a supramolecular modification-based high-stability Fe-N-C catalyst as well as a preparation method and application thereof, and belongs to the technical field of fuel cells. The preparation method of the high-stability Fe-N-C catalyst based on supramolecular modification comprises the following steps: S1, dissolving a supramolecular modifier in methanol, uniformly mixing, and adding Fe-N-C under a stirring condition to obtain a mixture; s2, the mixture is subjected to self-assembly, a precipitate is obtained through centrifugal separation after self-assembly is finished, and p-SC4-coated Fe-N-C powder is obtained after washing and drying; and S3, performing pyrolysis curing on the p-SC4-coated Fe-N-C powder, and after the pyrolysis curing is finished, naturally cooling to room temperature to obtain the supramolecular modification-based high-stability Fe-N-C fuel cell oxygen reduction catalyst. According to the supramolecular modified high-stability Fe-N-C catalyst provided by the invention, the multi-site synergistic effect of the supramolecular assembly can form stable coordination with Fe through a plurality of functional groups (such as amino, carboxyl and pyridine ring), so that the dispersity and anchoring strength of Fe are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fuel cells, in particular to a high-stability Fe-N-C catalyst based on supramolecular modification and a preparation method and application thereof. BACKGROUND

[0002] Fuel cells have broad application prospects as a high-efficiency and clean energy conversion device. The oxygen reduction reaction (ORR) kinetics of the cathode is slow, and needs efficient catalysts to accelerate. At present, the high cost of commercial platinum (Pt) based catalysts limits large-scale application, and it is crucial to develop low-cost and high-activity non-noble metal catalysts (such as M-N-C). Non-noble metal Fe-N-C catalysts are of great concern because their activity is close to that of Pt-based catalysts and their cost is low. However, in practical applications, on the one hand, in the acidic environment of fuel cells, Fe active sites are prone to dissolution and oxidation, Fe 2+ is oxidized to Fe 3+ , resulting in loss of active sites. On the other hand, hydrogen peroxide (H2O2) is produced during the ORR process, and H2O2 can generate highly active hydroxyl radicals (·OH) through an electrochemical Fenton reaction (Fe 2+ + H2O2→ Fe 3+ + ·OH + OH - ). These radicals have strong oxidizing properties and can accelerate the loss of Fe sites and cause corrosion of the carbon support, thereby leading to catalyst deactivation. In addition, the adsorption of reaction intermediates can also occupy the active sites on the catalyst surface, affecting the continuation of the reaction, and their accumulation can have a toxic effect on the catalyst.

[0003] To weaken the catalyst Fe active site shedding and inhibit activity attenuation, current some researches adopt interface modification strategies such as metal oxide (SiO2, TiO2, Al2O3, etc.) coating modification, polymer (polytetrafluoroethylene, polyaniline, etc.) coating modification, carbon-based material (carbon nanotube, graphene, carbon quantum dot, etc.) composite modification, metal / metal ion (non-active metal, such as Zr, Ce, W, etc.) interface anchoring modification. These strategies can inhibit active site loss, carbon carrier corrosion and other problems by regulating the surface chemical environment of the catalyst (such as electronic structure, hydrophilic / hydrophobic property), constructing a physical barrier (isolating corrosive medium) or strengthening the binding force of active sites, but these modification methods may cause active site coverage or mass transfer obstruction while forming a physical barrier, and it is difficult to balance stability and activity; the combination of the modified layer and Fe-N-C mainly depends on weak interaction (hydrogen bond, van der Waals force), which may fail after long-term circulation; at the same time, in the complex environment of fuel cell "acidity + high potential + free radicals", a single modification strategy is difficult to resist the synergistic effect of multiple corrosion mechanisms (such as Fe dissolution, carbon corrosion, intermediate product corrosion). Therefore, the interface modification strategy that can achieve precise modification (avoiding active site coverage) and has self-repairing function to cope with local damage has more potential in "protection-activity" balance and long-term stability, and provides some new ideas for long-life non-noble metal fuel cell catalysts. SUMMARY

[0004] Therefore, the application provides a high-stability Fe-N-C catalyst based on supramolecular modification, a preparation method and application thereof. Based on the shortcoming of the stability of the existing Fe-N-C catalyst in an acidic environment, the application proposes a supramolecular interface modification strategy, which can effectively overcome the defects of the prior art.

[0005] The first aspect of the application provides a preparation method of a high-stability Fe-N-C catalyst based on supramolecular modification, comprising the following steps:

[0006] S1, dissolving a supramolecular modifier in methanol, mixing uniformly, and adding Fe-N-C under stirring to obtain a mixture;

[0007] S2, self-assembling the mixture, obtaining a precipitate by centrifugal separation after the self-assembly is completed, and obtaining p-SC4@Fe-N-C powder after washing and drying;

[0008] S3, pyrolyzing and solidifying the p-SC4@Fe-N-C powder, and obtaining a high-stability Fe-N-C fuel cell oxygen reduction catalyst based on supramolecular modification after natural cooling to room temperature.

[0009] Preferably, in step S1, the supramolecular modifier is selected from one of sulfonated calix[4]arene, cucurbit[5]uril and 15-crown-5.

[0010] Preferably, in step S1, the ratio of the supermolecular modifier to methanol is (0.2-0.5 g):50 ml.

[0011] Preferably, in step S1, the preparation process of the Fe-N-C is as follows:

[0012] Dissolve anhydrous zinc chloride and ferric nitrate in methanol to obtain solution A; dissolve 2-methylimidazole in methanol to obtain solution B; slowly add the solution B to the solution A under stirring to obtain a mixture; stir the mixture at room temperature for 3 h, separate the precipitate by centrifugation, and obtain Fe / ZIF-8 precursor powder after washing and drying; place the Fe / ZIF-8 precursor powder in a quartz boat and transfer it to a tube furnace, pyrolyze the sample at 1100℃ for 3 h under a flowing argon atmosphere at a heating rate of 5℃ / min, and then naturally cool to room temperature to obtain Fe-N-C.

[0013] Preferably, in step S2, the self-assembly is performed under stirring at 60℃ for 3 h.

[0014] Preferably, in step S2, the washing is performed once with methanol.

[0015] Preferably, in step S2, the drying is performed in a vacuum oven at 60℃ overnight.

[0016] Preferably, in step S3, the pyrolysis and curing is performed at 300℃ for 1 h under a flowing argon atmosphere at a heating rate of 2℃ / min.

[0017] The second aspect of the present application also provides a high-stability Fe-N-C catalyst based on supermolecular modification, which is prepared by the above method.

[0018] The third aspect of the present application also provides the use of the above high-stability Fe-N-C catalyst based on supermolecular modification in fuel cell oxygen reduction reaction.

[0019] Compared with the prior art, the present application has the following beneficial effects:

[0020] Based on the short board of the stability of the existing Fe-N-C catalyst in the acidic environment, a supramolecular interface modification strategy is proposed. The supramolecular modification relies on the formation of dynamic reversible molecular assembly structure by non-covalent interaction. Compared with traditional covalent bond modification, the “multi-site synergistic effect” of the supramolecular assembly can form stable coordination with Fe through multiple functional groups (such as amino, carboxyl, pyridine ring), which can significantly improve the dispersion and anchoring strength of Fe; at the same time, the supramolecular skeleton can induce the formation of more defect sites during pyrolysis, promote the generation and stability of Fe-N x active sites, and thus construct Fe-N-C catalysts with high electrochemical stability and excellent oxygen reduction activity. Specifically, the strategy anchors the carbon defect region around the Fe-N x site through the π-π stacking of the supramolecular modifier (sulfonated calix[4]arene, cucurbit[5]uril, 15-crown-5), and the cavity structure of the supramolecular modifier forms a molecular level barrier on the surface of the catalyst, which can selectively block the contact of H2O2, ·OH and anions (such as Cl - , SO4 2- ) in the electrolyte with the active site; at the same time, the supramolecular-iron phthalocyanine complex in the modification layer can undergo reversible coordination bond reorganization in the acidic environment, and realize micro-zone self-repair when the local structure is damaged. The present application provides a new technical idea for the commercial large-scale production of high-efficiency oxygen reduction catalysts. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the present application or prior art, the following will briefly introduce the drawings needed to be used in the description of the present application or prior art. Obviously, the drawings described below are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0022] Figure 1 SEM electron micrograph of Fe-N-C p-SC4 ;

[0023] Figure 2 Raman comparison chart of Fe-N-C, Fe-N-C p-SC4 , Fe-N-C Q[5] , Fe-N-C 15-C-5 ;

[0024] Figure 3 SCV comparison chart of Fe-N-C, Fe-N-C p-SC4 , Fe-N-C Q[5] , Fe-N-C 15-C-5 ;

[0025] Figure 4 Fe-N-C p-SC4Long time galvanostatic stability test. DETAILED DESCRIPTION

[0026] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be described clearly and completely below in conjunction with the accompanying drawings in the present application. Obviously, the described embodiments are only some, but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0027] The experimental methods used in the embodiments of the present application are all conventional methods unless otherwise specified.

[0028] In the following examples and comparative examples, all raw materials can be obtained by commercial purchase or conventional methods unless otherwise specified.

[0029] Example 1

[0030] First, anhydrous zinc chloride (ZnCl2, 0.50 g), iron nitrate (Fe(NO3)3, 0.3 g) were dissolved in 50 ml of methanol (labeled as solution A). In addition, 2-methylimidazole (2-MeIm, 1.5 g) was dissolved in 50 ml of methanol (labeled as solution B). Solution B was slowly added to solution A under stirring, and the mixture was stirred at room temperature for 3 h. The precipitate was separated by centrifugation, washed with methanol for several times, and then dried in an oven at 60°C overnight. Subsequently, the Fe / ZIF-8 precursor powder was placed in a quartz boat and transferred to a tube furnace. The sample was pyrolyzed at 1100°C for 3 h under a flowing argon atmosphere with a heating rate of 5°C / min, and then naturally cooled to room temperature to obtain Fe-N-C.

[0031] Sulfonated calix[4]arene (p-SC4, 0.3 g) was dissolved in 50 ml of methanol (labeled as solution C). Fe-N-C was added to solution C under stirring, and the mixture was stirred at 60°C for 3 h for self-assembly. The precipitate was separated by centrifugation, washed with methanol once, and then dried in a vacuum oven at 60°C overnight. Subsequently, the p-SC4@Fe-N-C powder was placed in a quartz boat and transferred to a tube furnace. The sample was pyrolyzed and cured at 300°C for 1 h under a flowing argon atmosphere with a heating rate of 2°C / min, and then naturally cooled to room temperature to obtain Fe-N-C p-SC4 .

[0032] Example 2

[0033] First, anhydrous zinc chloride (ZnCl2, 0.50 g), iron nitrate (Fe(N03)3, 0.3 g) were dissolved in 50 ml of methanol (labeled as solution A). Separately, 2-methylimidazole (2-MeIm, 1.5 g) was dissolved in 50 ml of methanol (labeled as solution B). Solution B was slowly added to solution A under stirring conditions and the mixture was stirred at room temperature for 3 h. The precipitate was obtained by centrifugation, washed thoroughly with methanol several times, and then dried in an oven at 60 °C overnight. Subsequently, the Fe / ZIF-8 precursor powder was placed in a quartz boat and transferred to a tube furnace. The sample was pyrolyzed at 1100 °C for 3 h under flowing argon atmosphere with a ramping rate of 5 °C / min, and then naturally cooled to room temperature to obtain Fe-N-C.

[0034] Cucurbit[5]uril (Q[5], 0.2 g) was dissolved in 50 ml of methanol (labeled as solution C). Fe-N-C was added to solution C under stirring conditions and the mixture was stirred at 60 °C for 3 h for self-assembly. The precipitate was obtained by centrifugation, washed once with methanol, and then dried in a vacuum oven at 60 °C overnight. Subsequently, the p-SC4@Fe-N-C powder was placed in a quartz boat and transferred to a tube furnace. The sample was pyrolyzed at 300 °C for 1 h under flowing argon atmosphere with a ramping rate of 2 °C / min, and then naturally cooled to room temperature to obtain Fe-N-C Q[5] .

[0035] Example 3

[0036] First, anhydrous zinc chloride (ZnCl2, 0.50 g), iron nitrate (Fe(N03)3, 0.3 g) were dissolved in 50 ml of methanol (labeled as solution A). Separately, 2-methylimidazole (2-MeIm, 1.5 g) was dissolved in 50 ml of methanol (labeled as solution B). Solution B was slowly added to solution A under stirring conditions and the mixture was stirred at room temperature for 3 h. The precipitate was obtained by centrifugation, washed thoroughly with methanol several times, and then dried in an oven at 60 °C overnight. Subsequently, the Fe / ZIF-8 precursor powder was placed in a quartz boat and transferred to a tube furnace. The sample was pyrolyzed at 1100 °C for 3 h under flowing argon atmosphere with a ramping rate of 5 °C / min, and then naturally cooled to room temperature to obtain Fe-N-C.

[0037] 15-crown ether-5 (15-C-5, 0.5 g) was dissolved in 50 mL of methanol (labeled as solution C). Fe-NC was added to solution C under stirring, and the mixture was stirred at 60 °C for 3 h to allow self-assembly. The precipitate was obtained by centrifugation, washed once with methanol, and then dried overnight in a vacuum oven at 60 °C. Subsequently, p-SC4@Fe-NC powder was placed in a quartz boat and transferred to a tube furnace. The sample was pyrolyzed and solidified at 300 °C for 1 h under a flowing argon atmosphere at a heating rate of 2 °C / min, and then naturally cooled to room temperature to obtain Fe-NC. 15-C-5 .

[0038] Comparative Example 1

[0039] First, anhydrous zinc chloride (ZnCl2, 0.50 g) and ferric nitrate (Fe(NO3)3, 0.3 g) were dissolved in 50 ml of methanol (labeled as solution A). Separately, 2-methylimidazole (2-MeIm, 1.5 g) was dissolved in 50 ml of methanol (labeled as solution B). Solution B was slowly added to solution A under stirring, and the mixture was stirred at room temperature for 3 h. The precipitate was obtained by centrifugation, washed thoroughly several times with methanol, and then dried overnight in an oven at 60 °C. Subsequently, the Fe / ZIF-8 precursor powder was placed in a quartz boat and transferred to a tube furnace. The sample was pyrolyzed at 1100 °C for 3 h under a flowing argon atmosphere at a heating rate of 5 °C / min, and then naturally cooled to room temperature to obtain Fe-NC.

[0040] Test case

[0041] Figure 1 It is Fe-NC p-SC4 The scanning electron microscope (SEM) image shows that Fe-NC p-SC4 It does not have the typical dodecahedral structure of ZIF-8, but instead exhibits a wrinkled dodecahedral structure with a particle size range of 100-200nm.

[0042] Depend on Figure 2 It can be seen that Fe-NC p-SC4 Fe-NC Q[5] Fe-NC 15-C-5 I D / I G The smaller size compared to Fe-NC indicates that Fe-NC carbon matrix contains more defects. Specifically, Fe-NC... p-SC4 I D / I G The smallest value indicates the highest degree of graphitization, which may result in better stability.

[0043] Depend on Figure 3 It can be seen that Fe-NCp-SC4 Fe-N-C Q[5] Fe-N-C 15-C-5 Fe-N-C p-SC4 Fe-N-C 1 / 2 Fe-N-C

[0044] As can be seen from Figure 4 Fe-N-C p-SC4 at a current density of 200 mA cm -2 -2, the catalyst can be continuously and stably operated for more than 100 h without substantial voltage loss, indicating that Fe-N-C p-SC4 has good stability under the fuel cell test system.

[0045] Finally, it should be noted that: the above examples are only to illustrate the technical solutions of the present application, rather than limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a highly stable Fe-NC catalyst based on supramolecular modification, characterized in that, Includes the following steps: S1. Dissolve the supramolecular modifier in methanol, mix thoroughly, and add Fe-NC under stirring conditions to obtain a mixture; S2. The mixture is self-assembled, and the precipitate is obtained by centrifugation after completion. After washing and drying, p-SC4@Fe-NC powder is obtained. S3. The p-SC4@Fe-NC powder is pyrolyzed and solidified, and then naturally cooled to room temperature to obtain a highly stable Fe-NC fuel cell oxygen reduction catalyst based on supramolecular modification.

2. The method for preparing a highly stable Fe-NC catalyst based on supramolecular modification according to claim 1, characterized in that, In step S1, the supramolecular modifier is selected from one of sulfonated calix[4]arene, cucurbit[5]urea, and 15-crown ether-5.

3. The method for preparing a highly stable Fe-NC catalyst based on supramolecular modification according to claim 1, characterized in that, In step S1, the ratio of supramolecular modifier to methanol is (0.2-0.5g):50ml.

4. The method for preparing a highly stable Fe-NC catalyst based on supramolecular modification according to claim 1, characterized in that, In step S1, the preparation process of Fe-NC is as follows: Anhydrous zinc chloride and ferric nitrate were dissolved in methanol to obtain solution A; 2-methylimidazole was dissolved in methanol to obtain solution B; solution B was slowly added to solution A under stirring to obtain a mixture; the mixture was stirred at room temperature for 3 hours, and the precipitate was obtained by centrifugation, washed, and dried to obtain Fe / ZIF-8 precursor powder; the Fe / ZIF-8 precursor powder was placed in a quartz boat and transferred to a tube furnace, and the sample was pyrolyzed at 1100℃ for 3 hours at a heating rate of 5℃ / min under a flowing argon atmosphere, and then naturally cooled to room temperature to obtain Fe-NC.

5. The method for preparing a highly stable Fe-NC catalyst based on supramolecular modification according to claim 1, characterized in that, In step S2, the self-assembly conditions are: stirring at 60°C for 3 hours to carry out self-assembly.

6. The method for preparing a highly stable Fe-NC catalyst based on supramolecular modification according to claim 1, characterized in that, In step S2, the specific conditions for washing are: washing once with methanol.

7. The method for preparing a highly stable Fe-NC catalyst based on supramolecular modification according to claim 1, characterized in that, In step S2, the specific drying conditions are: drying overnight in a vacuum oven at 60°C.

8. The method for preparing a highly stable Fe-NC catalyst based on supramolecular modification according to claim 1, characterized in that, In step S3, the pyrolysis curing conditions are as follows: under a flowing argon atmosphere, pyrolysis curing is performed at 300°C for 1 hour at a heating rate of 2°C / min.

9. A highly stable Fe-NC catalyst based on supramolecular modification, characterized in that, A highly stable Fe-NC catalyst based on supramolecular modification prepared by the method described in any one of claims 1-8.

10. The application of the highly stable Fe-NC catalyst based on supramolecular modification as described in claim 9 in the oxygen reduction reaction of fuel cells.

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