A FeAl diatomic catalyst with axial chlorine modification and its preparation method and application

Abstract

An FeAl dual-atom catalyst with axial chlorine modification, its preparation method and application, which relate to atomically dispersed catalysts, their preparation methods and applications. The FeAl dual-atom catalyst with axial chlorine modification provided by the present invention has nitrogen-doped carbon as the main body, and FeAlClN6 active sites are distributed in the main body; the structure of FeAlClN6 is: both Fe and Al are coordinated with four N atoms, and two of the N atoms are bridging N atoms that are coordinated with both Fe and Al at the same time; the eight atoms of FeAlN6 are in the same plane, and Al is also coordinated with Cl in the vertical direction. Preparation method: Dispersing a carbon matrix, an iron source, an aluminum source, and a nitrogen source in a solvent and stirring, then evaporating to dryness, and heat-treating the solid under an inert atmosphere to obtain the catalyst. The maximum power density of a fuel cell assembled with this catalyst reaches 1339 mW / cm 2 , and the half-wave potential retention rate remains 98% after 30,000 cycles of cyclic aging, and it can be applied to electrocatalytic fields such as pollutant degradation, chemical nitrogen fixation and carbon fixation, and catalytic energy conversion.

Description

Technical Field

[0001] The invention relates to an atomic-level dispersed catalyst, a preparation method thereof and an electrocatalytic application thereof. Background Art

[0002] With the rapid growth of the global population and the upgrading of social consumption, people's demand for industrial products has reached an unprecedented height. Most of the production processes of industrial products require catalytic steps. However, due to the low activity and poor selectivity of traditional catalysts, the industrial production process consumes a lot of energy and emits by-products into the environment. Atomic-level dispersed catalysts, such as single-atom catalysts, diatomic catalysts, and multi-atom catalysts, as new materials that have emerged in recent years, combine the properties of high catalytic activity, stability, selectivity, and reusability, and show great potential in various heterogeneous (electro) catalytic reactions such as oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, nitrogen reduction reaction, carbon dioxide reduction reaction, and hydrogenation reaction.

[0003] The performance of atomically dispersed catalysts is closely related to the coordination structure of the metal in its active center. By adjusting the surrounding coordination environment of the active center, the activity and stability of the catalyst can be directional controlled. However, the current control directions of the catalyst are, first, doping a second metal or other non-metal in the adjacent position in the carbon plane, and second, adjusting the non-metal in the axial direction of the active site. There is no report on the method of jointly regulating the adjacent positions in the plane and the adjacent axial direction. Summary of the invention

[0004] The present invention aims to provide a FeAl diatomic catalyst with axial chlorine modification and a preparation method and application thereof. The novel Fe, Al diatomic catalyst of the present invention has higher catalytic activity and stability than the existing catalyst.

[0005] The FeAl diatomic catalyst with axial chlorine modification of the present invention is composed of nitrogen-doped carbon as the main body, and the FeAlClN6 active sites are distributed in the main body; the structure of FeAlClN6 is: the Fe atom and the Al atom are coordinated with four N atoms, two of which are bridging N atoms coordinated with the Fe atom and the Al atom at the same time; the eight atoms of FeAlN6 are in the same plane, and the Al atom is also coordinated with a Cl atom in the direction perpendicular to the plane.

[0006] Furthermore, the eight atoms of FeAlN6 are in the same plane, which is approximately the same plane.

[0007] Furthermore, in the FeAlClN6 active site, the Fe-N coordination bond length is The Al-N coordination bond length is The Al-Cl coordination bond length is

[0008] Furthermore, in the FeAl diatomic catalyst with axial chlorine modification (FeAl-DAC), the mass fraction of N is 1% to 20%, the mass fraction of metal is 1% to 5%, and the molar ratio of Fe to Al is (0.6 to 1.5):1.

[0009] The preparation method of the above-mentioned FeAl diatomic catalyst with axial chlorine modification is carried out according to the following steps:

[0010] 1. Dispersing the carbon matrix, iron source, aluminum source and nitrogen source in a solvent, ultrasonicating and stirring to make them dispersed evenly, to obtain a mixed solution; then using a rotary evaporator to evaporate the solvent in the mixed solution to obtain a solid mixture;

[0011] 2. The solid mixture is placed in a high-temperature furnace, heated to 800°C to 1100°C under an inert atmosphere and maintained for 1 to 5 hours for heat treatment, and then cooled to room temperature to obtain an FeAl diatomic catalyst with axial chlorine modification, denoted as FeAl-DAC.

[0012] Furthermore, the carbon matrix described in step 1 is carbon black or nitrogen-doped carbon.

[0013] Furthermore, the iron source in step 1 is ferric nitrate or ferrous sulfate.

[0014] Furthermore, the aluminum source in step 1 is phthalocyanine aluminum chloride, tetraphenylporphyrin aluminum chloride or 2,3-naphthocyanine aluminum chloride. These aluminum sources are organic metal aluminum compounds containing axial chlorine coordination.

[0015] Furthermore, the nitrogen source in step 1 is one or a combination of bipyridine, o-phenanthroline, melamine and urea.

[0016] Furthermore, the solvent in step 1 is one or a combination of water, methanol, ethanol, and isopropanol.

[0017] Furthermore, the total mass of the carbon matrix, iron source, aluminum source and nitrogen source in the mixed solution in step 1 accounts for 0.1% to 1% of the mass of the solvent.

[0018] Furthermore, in step one, the total mass of the carbon matrix, iron source, aluminum source and nitrogen source is recorded as M, the mass of Fe in the iron source is (0.5%~3%)M; the mass of nitrogen in the nitrogen source is (2%~40%)M; the molar ratio of Al in the aluminum source to Fe in the iron source is (0.6~1.5):1.

[0019] Furthermore, the ultrasonic dispersion time in step 1 is 4 to 24 hours.

[0020] Furthermore, the temperature of the rotary evaporation in step 1 is 50-70°C.

[0021] The application of the above-mentioned FeAl diatomic catalyst with axial chlorine modification is to use the catalyst as an electrocatalyst for electrochemical degradation of pollutants in water; or for electrochemical fixation of nitrogen or carbon dioxide; or for electrochemical energy conversion reactions such as oxygen reduction and water electrolysis.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The present invention provides a novel Fe, Al diatomic catalyst having a brand new FeAlClN6 active site. Based on the currently reported FeN4 site, the active site is modified by incorporating Al elements at the adjacent position of Fe in the plane, and also modifies it by providing Cl atoms in the vertical direction of the adjacent Al atoms.

[0024] (2) The preparation method of the present invention is simple and feasible. This method does not use the conventional method of first synthesizing an in-plane structure and then performing axial coordination post-processing. Instead, it directly uses an Al source (such as aluminum phthalocyanine chloride) containing planar N coordination and axial Cl coordination as a precursor. This ensures that the coordination of Cl occurs only on Al atoms and ensures that the Fe atom at the reaction center is fully exposed, which is conducive to the occurrence of the catalytic reaction.

[0025] (3) The FeAl diatomic catalyst with axial chlorine modification of the present invention has better activity and stability than the traditional Fe-SAC catalyst. The maximum power density of the fuel cell prepared by the FeAl diatomic catalyst with axial chlorine modification of the present invention reaches 1339 mW / cm 2 After 30,000 cycles of aging, the half-wave potential only decays by 17mV (0.856V to 0.839V), with a retention rate of 98%. It can be applied to various electrocatalytic fields such as pollutant degradation, chemical nitrogen and carbon fixation, and catalytic energy conversion. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the structure of the active site of FeAlClN6;

[0027] Figure 2 It is a schematic diagram of the structure of aluminum phthalocyanine chloride;

[0028] Figure 3 is a scanning electron microscope image of the FeAl-DAC of Example 1;

[0029] Figure 4 is a scanning electron microscope image of the FeAl-DAC of Example 2;

[0030] Figure 5It is the X-ray diffraction spectrum of FeAl-DAC of Example 1 and Example 2;

[0031] Figure 6 The synchrotron radiation XANES spectrum of FeAl-DAC of Example 1 is

[0032] Figure 7 The R spatial spectrum and its fitting image of the synchrotron radiation EXAFS of the FeAl-DAC of Example 1

[0033] Figure 8 Spherical aberration corrected electron microscope image of FeAl-DAC of Example 1

[0034] Fig. 9 It is a fuel cell performance test curve diagram of FeAl-DAC of Example 1 and Example 2 and Fe-SAC of Comparative Example 1 and Comparative Example 2;

[0035] Fig.10 It is a comparison diagram of polarization curves before and after aging of FeAl-DAC of Example 1 and Fe-SAC of Comparative Example 1;

[0036] Fig.11 It is a comparison diagram of the CV curves of FeAl-DAC of Example 1 and Fe-SAC of Comparative Example 1 before and after aging. DETAILED DESCRIPTION

[0037] The technical scheme and application of the present invention will be described in detail below with reference to the drawings in the embodiments of the present invention through specific examples. The scope of protection of the present invention is not limited thereto. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] Example 1: The preparation method of the FeAl diatomic catalyst with axial chlorine modification in this example is carried out according to the following steps:

[0039] 1. Dissolve 150 mg of nitrogen-doped carbon (NC), 20 mg of ferric nitrate nonahydrate, 20 mg of aluminum phthalocyanine chloride, 30 mg of bipyridine, and 30 mg of melamine in 100 mL of a mixed solvent; wherein the mixed solvent is prepared in a volume ratio of water to ethanol of 1:1; ultrasonicate and stir for 12 h to make it evenly dispersed to obtain a mixed solution; then use a rotary evaporator to evaporate the solvent in the mixed solution at 60° C. to obtain a solid mixture;

[0040] The preparation method of nitrogen-doped carbon (NC) is as follows: 15.42 g of zinc nitrate hexahydrate is dissolved in 400 mL of methanol to obtain a zinc nitrate solution; 19.2 g of 2-methylimidazole is dissolved in 400 mL of methanol to obtain a 2-methylimidazole solution; then the zinc nitrate solution is added to the 2-methylimidazole solution, stirred at a stirring speed of 500 rpm for 10 minutes, and then allowed to stand at room temperature for 24 hours to generate a white suspension in the solution; the white suspension is centrifuged and dried and ground to obtain a white powder; the white powder is then placed in a high-temperature furnace, heated to 1000° C. in an argon atmosphere and maintained for 2 hours for heat treatment, and then cooled to room temperature to obtain nitrogen-doped carbon;

[0041] The structural diagram of aluminum phthalocyanine chloride is as follows Figure 2 As shown;

[0042] 2. The solid mixture obtained in step 1 is placed in a high-temperature furnace, heated to 1000°C in an argon atmosphere and maintained for 1 hour for heat treatment, and then cooled to room temperature to obtain an FeAl diatomic catalyst with axial chlorine modification, denoted as FeAl-DAC.

[0043] Example 2: The preparation method of the FeAl diatomic catalyst with axial chlorine modification in this example is carried out according to the following steps:

[0044] 1. Dissolve 150 mg of carbon black ECP-600JD, 20 mg of ferric nitrate nonahydrate, 20 mg of phthalocyanine aluminum chloride, 30 mg of bipyridine, and 300 mg of melamine in 100 mL of water; ultrasonicate and stir for 12 h to disperse them evenly to obtain a mixed solution; then use a rotary evaporator to evaporate the solvent in the mixed solution at 60° C. to obtain a solid mixture; the structural schematic diagram of phthalocyanine aluminum chloride is as follows Figure 2 As shown; in this step, since carbon black ECP-600JD does not contain nitrogen, it is necessary to increase the amount of nitrogen source;

[0045] 2. The solid mixture obtained in step 1 is placed in a high-temperature furnace, heated to 1000°C in an argon atmosphere and maintained for 1 hour for heat treatment, and then cooled to room temperature to obtain an FeAl diatomic catalyst with axial chlorine modification, denoted as FeAl-DAC.

[0046] Comparative Example 1: This comparative example is to prepare Fe single atom catalyst (Fe-SAC), and the specific steps are as follows:

[0047] 1. Dissolve 150 mg of nitrogen-doped carbon (NC), 20 mg of ferric nitrate nonahydrate, 30 mg of bipyridine, and 30 mg of melamine in 100 mL of a mixed solvent; wherein the mixed solvent is prepared in a volume ratio of water to ethanol of 1:1; ultrasonicate and stir for 12 h to make it evenly dispersed to obtain a mixed solution; then use a rotary evaporator to evaporate the solvent in the mixed solution at 60° C. to obtain a solid mixture;

[0048] The preparation method of nitrogen-doped carbon (NC) is as follows: 15.42 g of zinc nitrate hexahydrate is dissolved in 400 mL of methanol to obtain a zinc nitrate solution; 19.2 g of 2-methylimidazole is dissolved in 400 mL of methanol to obtain a 2-methylimidazole solution; then the zinc nitrate solution is added to the 2-methylimidazole solution, stirred at a stirring speed of 500 rpm for 10 minutes, and then allowed to stand at room temperature for 24 hours to generate a white suspension in the solution; the white suspension is centrifuged and dried and ground to obtain a white powder; the white powder is then placed in a high-temperature furnace, heated to 1000° C. in an argon atmosphere and maintained for 2 hours for heat treatment, and then cooled to room temperature to obtain nitrogen-doped carbon;

[0049] 2. The solid mixture obtained in step 1 is placed in a high-temperature furnace, heated to 1000°C in an argon atmosphere and maintained for 1 hour for heat treatment, then cooled to room temperature to obtain a Fe single-atom catalyst, recorded as Fe-SAC.

[0050] Comparative Example 2: In this comparative example, Fe-SAC was prepared using carbon black (ECP-600JD) as a carbon source. The specific steps are as follows:

[0051] 1. Dissolve 150 mg of carbon black ECP-600JD, 20 mg of ferric nitrate nonahydrate, 30 mg of bipyridine and 300 mg of melamine in 100 mL of water; ultrasonicate and stir for 12 h to make them dispersed evenly to obtain a mixed solution; then use a rotary evaporator to evaporate the solvent in the mixed solution at 60° C. to obtain a solid mixture; in this step, since carbon black ECP-600JD does not contain nitrogen, it is necessary to increase the amount of nitrogen source;

[0052] 2. The solid mixture obtained in step 1 is placed in a high-temperature furnace, heated to 1000°C in an argon atmosphere and maintained for 1 hour for heat treatment, then cooled to room temperature to obtain a Fe single-atom catalyst, recorded as Fe-SAC.

[0053] Figure 3 is a scanning electron microscope image of the FeAl-DAC prepared in Example 1, Figure 4 is a scanning electron microscope image of the FeAl-DAC prepared in Example 2. Figure 3 and Figure 4 It can be seen that both samples are nanomaterials and retain the basic morphology of their carbon sources.

[0054] Figure 5 1 is the XRD spectrum of FeAl-DAC prepared in Example 1 and Example 2. Figure 5 The spectrum shows only the (002) and (101) peaks of the carbon matrix, and does not contain diffraction peaks of metal particles, indicating that the metal doped therein is dispersed at the atomic level.

[0055] Figure 6 This is the synchrotron radiation XANES spectrum of Example 1. Figure 6 It shows that the absorption edge of the metal elements in the FeAl-DAC catalyst is significantly different from that of the corresponding metal elements and oxides, which also proves that it is atomic-level dispersion.

[0056] Figure 7 The synchrotron radiation X-ray extended edge absorption structure R space spectrum and its fitting spectrum of Example 1. The fitting parameters are shown in Table 1. The results show that Fe and Al in the FeAl-DAC catalyst of Example 1 are dispersed in the form of FeAlClN6 sites. Among them, the iron-nitrogen 4-coordinate, the average distance Aluminum-nitrogen 4-coordination, average distance Al-Cl 1 coordination, average distance

[0057] Table 1 EXAFS fitting results of FeAl-DAC catalyst of Example 1

[0058]

[0059] Figure 8 This is an atomic resolution transmission microscope high-angle annular dark field image of the FeAl-DAC catalyst in Example 1. Figure 8 It can be seen that there are a large number of metal atom pairs on the substrate, one bright and one dark, respectively representing Fe and Al.

[0060] Fig. 9 The fuel cell polarization curves and power density curves of Example 1, Example 2 and Comparative Example 1, Comparative Example 2 are shown in FIG. Fig. 9 It can be found that under the regulation of Al and Cl, the highest power density of the FeAl-DAC catalyst in Example 1 is 1339 mW / cm 2 Compared with the comparative example 1, the maximum power density is increased by 31%. The maximum power density of the FeAl-DAC catalyst in Example 2 is 1035 mW / cm 2 , the maximum power density of the Fe-SAC in comparative example 2 is increased by 34%.

[0061] Fig.10 Comparison of polarization curves of the FeAl-DAC catalyst of Example 1 and the Fe-SAC of Comparative Example 1 before and after 30,000 cycles of aging. Fig.10 It is shown in the figure that the half-wave potential of the FeAl-DAC catalyst of Example 1 before and after aging is 0.856V and 0.839V, respectively, which only decreases by 17mV, and the retention rate is 98%. The half-wave potential of the Fe-SAC of Comparative Example 1 before and after aging is 0.815V and 0.782V, and the attenuation degree is nearly twice, that is, 33mV.

[0062] Fig.11 The cyclic voltammetry curves of the FeAl-DAC catalyst of Example 1 and the Fe-SAC of Comparative Example 1 before and after 30,000 cycles of aging are compared. The results show that after aging, the electrochemical properties of the Fe-SAC of Comparative Example 1 changed significantly, including a 15.4% increase in double-layer capacitance, oxidation of the carbon support, the appearance of quinone-hydroquinone redox point pairs, the release of active Fe atoms, and a decrease in the redox peak of Fe. In contrast, the FeAl-DAC catalyst of Example 1 hardly changed, showing enhanced stability.

[0063] The present invention is not limited to the above embodiments, and a number of changes and improvements made without departing from the core of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A FeAl diatomic catalyst with axial chlorine modification, characterized in that The catalyst is composed of nitrogen-doped carbon as the main body, and the active sites of FeAlClN6 are distributed in the main body; the structure of FeAlClN6 is: the Fe atom and the Al atom are coordinated with four N atoms, two of which are bridge N atoms coordinated with the Fe atom and the Al atom at the same time; the eight atoms of FeAlN6 are in the same plane, and the Al atom is also coordinated with a Cl atom in the direction perpendicular to the plane.

2. The FeAl diatomic catalyst with axial chlorine modification according to claim 1, characterized in that: In the FeAlClN6 active site, the Fe-N coordination bond length is The Al-N coordination bond length is The Al-Cl coordination bond length is 3. The FeAl diatomic catalyst with axial chlorine modification according to claim 1 or 2, characterized in that: The mass fraction of N in the FeAl diatomic catalyst with axial chlorine modification is 1% to 20%, the mass fraction of metal is 1% to 5%, and the molar ratio of Fe to Al is (0.6 to 1.5):

1.

4. A method for preparing the FeAl diatomic catalyst with axial chlorine modification according to claim 1, characterized in that: The method proceeds as follows:

1. Dispersing a carbon matrix, an iron source, an aluminum source, and a nitrogen source in a solvent, ultrasonicating and stirring to make them evenly dispersed, to obtain a mixed solution; then using a rotary evaporator to evaporate the solvent in the mixed solution to obtain a solid mixture; wherein the aluminum source is phthalocyanine aluminum chloride, tetraphenylporphyrin aluminum chloride, or 2,3-naphthocyanine aluminum chloride.

2. The solid mixture is placed in a high-temperature furnace, heated to 800°C to 1100°C under an inert atmosphere and maintained for 1 to 5 hours for heat treatment, and then cooled to room temperature to obtain an FeAl diatomic catalyst with axial chlorine modification, denoted as FeAl-DAC.

5. The method for preparing the FeAl diatomic catalyst with axial chlorine modification according to claim 4, characterized in that: The carbon matrix described in step 1 is carbon black or nitrogen-doped carbon.

6. The method for preparing the FeAl diatomic catalyst with axial chlorine modification according to claim 4 or 5, characterized in that: The iron source described in step 1 is ferric nitrate or ferrous sulfate.

7. The method for preparing the FeAl diatomic catalyst with axial chlorine modification according to claim 4 or 5, characterized in that: The nitrogen source described in step 1 is one or a combination of bipyridine, o-phenanthroline, melamine and urea.

8. The method for preparing the FeAl diatomic catalyst with axial chlorine modification according to claim 4 or 5, characterized in that: The solvent described in step 1 is one or a combination of water, methanol, ethanol, and isopropanol.

9. The method for preparing the FeAl diatomic catalyst with axial chlorine modification according to claim 4 or 5, characterized in that: In step 1, the total mass of the carbon matrix, iron source, aluminum source and nitrogen source is recorded as M, the mass of Fe in the iron source is (0.5%~3%)M; the mass of nitrogen in the nitrogen source is (2%~40%)M; the molar ratio of Al in the aluminum source to Fe in the iron source is (0.6~1.5):

1.

10. Use of the FeAl diatomic catalyst with axial chlorine modification according to claim 1, characterized in that The application is to use the FeAl diatomic catalyst with axial chlorine modification as an electrocatalyst for electrochemical degradation of pollutants in water; or for electrochemical fixation of nitrogen or carbon dioxide; or for electrochemical energy conversion reactions such as oxygen reduction and water electrolysis.

Images