A semi-metal doped Fe-based single-atom catalyst and its preparation method and application

Abstract

A semi-metal doped Fe-based single-atom catalyst, its preparation method and application. It relates to Fe-based single-atom catalysts, their preparation methods and applications, and aims to solve the problem of insufficient activity and stability of iron-based non-precious metal single-atom catalysts in the oxygen reduction reaction. The catalyst of the present invention is formed by atoms of two metals, Fe and Sb, forming an atomic pair and being embedded in a carbon support, showing a Fe=2N=Sb coordination structure, and there is a hydroxyl group axially on the Sb atom. Preparation method: ZIF-8 is heat-treated to obtain an N-doped porous carbon material, which is mixed with Fe salt and Sb salt solutions, evaporated to dryness and then thermally activated to obtain the catalyst. The half-wave potential of the fabricated electrode only decreases by 18 mV after aging for 30,000 cycles in a 0.1 M HClO4 solution. The assembled proton exchange membrane fuel cell has power densities of 1098.3 and 613.41 mW / cm2 under hydrogen-oxygen and hydrogen-air conditions respectively, and can be used in the field of fuel cells.

Description

Technical Field

[0001] The present invention relates to an Fe-based single-atom catalyst and a preparation method thereof, belonging to the field of preparation of electrocatalysts. Background Art

[0002] Proton exchange membrane fuel cells have attracted much attention as a clean energy conversion device. However, the oxygen reduction reaction at the cathode is slow. Currently, the Pt-based noble metal catalyst with the most ideal performance has low reserves, high cost, is easily poisoned, and has poor stability, which limits its large-scale commercialization. Developing non-noble metal ORR catalysts with high activity and low cost is crucial. In recent years, the research on non-noble metal catalysts has entered the atomic level. Fe-based single-atom catalysts have high oxygen reduction activity, but the adsorption energy of Fe-based single-atom catalysts to OH* is relatively large, which limits the further improvement of their performance. Summary of the Invention

[0003] The present invention aims to solve the technical problem of the insufficient catalytic activity and stability of existing Fe-based catalysts, and provides a preparation method for a semi-metal doped Fe-based single-atom catalyst.

[0004] The semi-metal doped Fe-based single-atom catalyst of the present invention is formed by atoms of two metals, Fe and Sb, forming atomic pairs and embedding in a carbon support. Among them, Fe and Sb are respectively coordinated with 4 N atoms, and Fe and Sb share two N atoms, showing a N-bridged Fe=2N=Sb coordination structure. At the same time, there is a hydroxyl group axially on the Sb atom. This catalyst is denoted as FeSbNC.

[0005] The preparation method of the semi-metal doped Fe-based single-atom catalyst of the present invention is carried out according to the following steps:

[0006] I. Preparation of ZIF-8 precursor: First, 2-methylimidazole is uniformly dissolved in a methanol solution to obtain solution A; then zinc nitrate is dissolved in a methanol solution to obtain solution B; solution B is added to solution A, stirred at room temperature for 20 - 24 h, and then centrifuged, washed, and dried to obtain the ZIF-8 precursor;

[0007] II. Preparation of N-doped porous carbon material: After grinding the ZIF-8 precursor, it is placed in a tubular furnace, heated to 800 - 1100 °C in an inert atmosphere and kept for 1 - 2 h for heat treatment. After cooling, the N-doped porous carbon material, denoted as NC, is obtained;

[0008] 3. Preparation of FeSbNC single-atom catalyst: Fe salt, Sb salt and methanol are thoroughly mixed to obtain solution C; then, the N-doped porous carbon material and solution C are evenly mixed, heated and stirred in a water bath until the methanol is completely volatilized, and dried to obtain a precursor; the precursor is then placed in a tube furnace and heated to 900-1100°C under an inert atmosphere for 0.5-2.5 hours for thermal activation. After cooling, the semi-metal-doped Fe-based single-atom catalyst is obtained.

[0009] Furthermore, the molar ratio of 2-methylimidazole to zinc nitrate in step 1 is (2-4):1.

[0010] Furthermore, the stirring speed in step 1 is 90 to 120 r / min.

[0011] Furthermore, the heating rate of the tube furnace in step 2 is 2-10° C. / min.

[0012] Furthermore, the iron salt in step three is ferric chloride, ferric nitrate or ferric acetylacetonate.

[0013] Furthermore, the antimony salt in step three is antimony chloride or antimony nitrate.

[0014] Furthermore, the mass ratio of the antimony salt to the iron salt in step three is (0.5-2):1.

[0015] Furthermore, the mass ratio of the antimony salt to the N-doped porous carbon material in step three is (0.05-0.4):1.

[0016] Furthermore, the water bath heating temperature in step 3 is 50-70°C.

[0017] Furthermore, the heating rate of the tubular furnace in step three is 2-10° C. / min.

[0018] Furthermore, the drying temperature in steps 1 and 3 is 50-70° C., and the drying time is 5-8 hours.

[0019] Furthermore, the inert atmosphere in steps 2 and 3 is Ar or N2.

[0020] The application of the above-mentioned semi-metal-doped Fe-based single-atom catalyst is to use it for the cathode oxygen reduction reaction of a proton exchange membrane fuel cell.

[0021] The present invention uses ZIF-8 as a carrier, adopts rotary evaporation to prepare the precursor, and obtains the single-atom catalyst FeSbNC by high-temperature heat treatment. The activity and stability of the obtained catalyst are significantly higher than those of the FeNC single-atom catalyst. Figure 1 shown.

[0022] The beneficial effects of the present invention compared with the prior art are as follows:

[0023] (1) The present invention can dope the semi-metal element Sb on the basis of the original FeNC single-atom catalyst, reduce the adsorption of the OH* intermediate by the Fe active site during the oxygen reduction process, and thereby improve the intrinsic activity of the FeNC single-atom catalyst;

[0024] (2) Compared with the FeNC single-atom catalyst, the present invention has a higher half-wave potential and a limiting current density in an acidic electrolyte. The lower hydrogen peroxide yield and the more direct four-electron process make the carbon matrix more corrosion-resistant. In the fuel cell test, its peak power density exceeds 1 W / cm 2 , and it can be used in the field of proton exchange membrane fuel cells.

[0025] (3) Through a two-step heat treatment process, the present invention improves the graphitization degree of the carbon matrix, improves the stability of the catalyst. At the same time, the high specific surface area of the carbon matrix enables the oxygen reduction reaction to have more active sites and improves the reaction kinetics of the catalyst. The electrode prepared from the semi-metal-doped Fe-based single-atom catalyst of the present invention has a half-wave potential drop of only 18 mV after aging for 30,000 cycles in a 0.1 M HClO4 solution. The assembled proton exchange membrane fuel cell has a peak power density of 1098.3 mW / cm 2 under hydrogen-oxygen test conditions, and a peak power density of 613.41 mW / cm 2 under hydrogen-air test conditions, and it can be used in the field of fuel cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is the preparation flow chart of the semi-metal-doped Fe-based single-atom catalyst of the present invention;

[0027] Figure 2 is the SEM image of the FeSbNC single-atom catalyst prepared in Example 1;

[0028] Figure 3 is the TEM image of the FeSbNC single-atom catalyst prepared in Example 1;

[0029] Figure 4 is the aberration-corrected electron microscopy image of the FeSbNC single-atom catalyst prepared in Example 1;

[0030] Figure 5 is the EDS surface scanning image of the FeSbNC single-atom catalyst prepared in Example 1;

[0031] Figure 6 is the structural schematic diagram of the FeSbNC single-atom catalyst prepared in Example 1;

[0032] Figure 7XRD patterns of the FeSbNC single-atom catalyst prepared in Example 1, the FeNC single-atom catalyst prepared in Comparative Example 1, and the SbNC single-atom catalyst prepared in Comparative Example 2;

[0033] Figure 8 Raman graphs of the FeSbNC single-atom catalyst prepared in Example 1, the FeNC single-atom catalyst prepared in Comparative Example 1, and the SbNC single-atom catalyst prepared in Comparative Example 2;

[0034] Figure 9 ORR polarization graphs of the FeSbNC single-atom catalyst prepared in Example 1, the FeNC single-atom catalyst prepared in Comparative Example 1, and the SbNC single-atom catalyst prepared in Comparative Example 2;

[0035] Figure 10 ORR polarization graphs of the FeSbNC single-atom catalyst prepared in Example 1 before and after aging;

[0036] Figure 11 ORR polarization graphs of the FeNC single-atom catalyst prepared in Comparative Example 1 before and after aging;

[0037] Figure 12 Performance comparison graph of the FeSbNC single-atom catalyst prepared in Example 1 in fuel cell tests. Detailed implementation mode

[0038] The technical solutions of the present invention will be further described below in conjunction with the drawings and embodiments, but are not limited thereto. Any modification or equivalent replacement of the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention shall be covered within the protection scope of the present invention.

[0039] Example 1: The preparation method of the semi-metal doped Fe-based single-atom catalyst in this example is carried out according to the following steps:

[0040] I. Preparation of the ZIF-8 precursor: First, 19.275 g of 2-methylimidazole is uniformly dissolved in 500 ml of methanol solution to obtain solution A; then, 24 g of zinc nitrate is dissolved in 500 ml of methanol solution to obtain solution B; solution B is poured into solution A, and stirred vigorously at 100 r / min at room temperature of 24 °C for 24 h, then centrifuged, washed, and dried in an oven at a temperature of 60 °C for 7 h to obtain the ZIF-8 precursor;

[0041] II. Preparation of the N-doped porous carbon material: After grinding the ZIF-8 precursor, it is placed in a tubular furnace, heated to 1000 °C at a rate of 5 °C / min under an Ar atmosphere and held for 1.5 h for heat treatment. After cooling to room temperature, the N-doped porous carbon material is obtained, denoted as NC;

[0042] III. Preparation of FeSbNC single-atom catalyst: 20 mg of iron nitrate, 20 mg of antimony chloride and 60 ml of methanol were fully mixed to obtain solution C; subsequently, 120 mg of N-doped porous carbon material was fully mixed with solution C, heated and stirred in a water bath at 60 °C until the methanol was completely volatilized, and then dried in an oven at 60 °C for 7 h to obtain a precursor; then the precursor was placed in a tubular furnace, and under an Ar atmosphere, it was heated to 1000 °C at a rate of 5 °C / min and held for 1 h. After cooling, a semi-metal-doped Fe-based single-atom catalyst, denoted as FeSbNC, was obtained.

[0043] The SEM photograph of the FeSbNC single-atom catalyst prepared in Example 1 is as Figure 2 shown, and the TEM photograph is as Figure 3 shown; from Figure 2 and Figure 3 it can be seen that the FeSbNC single-atom catalyst particles are dodecahedrons, with a uniform morphology and a particle size of 100 - 200 nm.

[0044] The aberration-corrected electron microscopy image of the FeSbNC single-atom catalyst prepared in Example 1 is as Figure 4 shown, and the EDS surface scanning image is as shown in Figure 5; from Figure 4 and Figure 5 it can be seen that there are no metal particles or clusters in the FeSbNC single-atom catalyst, and the two atoms of Fe and Sb are atomically dispersed.

[0045] The structural schematic diagram of the FeSbNC single-atom catalyst prepared in Example 1 is as Figure 6 shown; the brown small balls are C, the gray small balls are N, the yellow small balls are Fe, the brown small balls are Sb, the red small balls are O, the pink small balls are H. The atoms of the two metals Fe and Sb form atomic pairs and are embedded in the carbon support. Among them, Fe and Sb are respectively coordinated with 4 N atoms, and Fe and Sb share two N atoms, showing an N-bridged Fe=2N=Sb coordination structure. At the same time, there is a -OH group axially on the Sb atom, and Sb plays a role in regulating the Fe active site.

[0046] Comparative Example 1: In this comparative example, an FeNC single-atom catalyst was prepared, and the specific method is as follows:

[0047] I. Preparation of ZIF-8: First, 19.275 g of 2-methylimidazole was uniformly dissolved in 500 ml of methanol solution to obtain solution A; then 24 g of zinc nitrate was dissolved in 500 ml of methanol solution to obtain solution B; solution B was poured into solution A, and it was vigorously stirred at 100 r / min at room temperature of 23 °C for 24 h, then centrifuged, washed, and then dried in an oven at 60 °C for 7 h to obtain a ZIF-8 precursor;

[0048] II. Preparation of NC: After grinding the ZIF-8 precursor, it was placed in a tube furnace. Under an Ar atmosphere, it was heated to 1000 °C at a rate of 5 °C / min and held for 1.5 h. After cooling, a nitrogen-doped porous carbon material was obtained;

[0049] III. Preparation of FeNC single-atom catalyst: 20 mg of iron nitrate was fully mixed with 60 ml of methanol to obtain solution C; subsequently, 120 mg of the nitrogen-doped porous carbon material was fully mixed with solution C, heated and stirred in a 60 °C water bath until the methanol completely evaporated, and then dried in an oven at 60 °C for 7 h to obtain an Fe precursor; the Fe precursor was placed in a tube furnace. Under an Ar atmosphere, it was heated to 1000 °C at a rate of 5 °C / min and held for 1 h. After cooling, an FeNC single-atom catalyst was obtained.

[0050] Comparative Example 2: In this comparative example, an SbNC single-atom catalyst was prepared. The specific method was carried out according to the following steps:

[0051] I. Preparation of ZIF-8: 19.275 g of 2-methylimidazole was uniformly dissolved in 500 ml of methanol solution to obtain solution A; then, 24 g of zinc nitrate was dissolved in 500 ml of methanol solution to obtain solution B; solution B was poured into solution A, and it was vigorously stirred at a speed of 100 r / min at a room temperature of 23 °C for 24 h, then centrifuged, washed, and dried in an oven at 60 °C for 7 h to obtain a ZIF-8 precursor;

[0052] II. Preparation of NC: After grinding the ZIF-8 precursor, it was placed in a tube furnace. Under an Ar atmosphere, it was heated to 1000 °C at a rate of 5 °C / min and held for 1.5 h. After cooling, a nitrogen-doped porous carbon material was obtained;

[0053] III. Preparation of SbNC single-atom catalyst: 20 mg of antimony chloride was fully mixed with 60 ml of methanol to obtain solution C; subsequently, 120 mg of the nitrogen-doped porous carbon material was fully mixed with solution C, heated and stirred in a water bath at 60 °C until the methanol completely evaporated, and dried in an oven at 60 °C for 7 h to obtain an Sb precursor; then, the Sb precursor was placed in a tube furnace. Under an Ar atmosphere, it was heated to 1000 °C at a rate of 5 °C / min and held for 1 h. After cooling, an SbNC single-atom catalyst was obtained.

[0054] The XRD patterns of the FeSbNC single-atom catalyst prepared in Example 1, the FeNC single-atom catalyst prepared in Comparative Example 1, and the SbNC single-atom catalyst prepared in Comparative Example 2 are as Figure 7 shown, from Figure 7It can be seen that the diffraction peaks of graphite carbon only appear at 26.8° and 42°, and no sharp metal peaks appear, which proves that there are no metal particles or clusters in the FeSbNC single-atom catalyst prepared in Example 1, the FeNC single-atom catalyst prepared in Comparative Example 1, and the SbNC single-atom catalyst prepared in Comparative Example 2, verifying its atomic-level dispersion.

[0055] The Raman spectra of the FeSbNC single-atom catalyst prepared in Example 1, the FeNC single-atom catalyst prepared in Comparative Example 1, and the SbNC single-atom catalyst prepared in Comparative Example 2 are as Figure 8 shown. Compared with the FeNC single-atom catalyst prepared in Comparative Example 1, the FeSbNC single-atom catalyst prepared in Example 1 has a decrease in I D / I G , indicating that the addition of Sb element increases the graphitization degree of the catalyst, thereby improving the stability of the catalyst.

[0056] The ORR activities of the FeSbNC single-atom catalyst prepared in Example 1, the FeNC single-atom catalyst prepared in Comparative Example 1, and the SbNC single-atom catalyst prepared in Comparative Example 2 were tested. Using the staircase voltammetry (SCV), in an oxygen-saturated 0.1 M HClO4 solution, the potential range was 1.0 - 0.1 V, stepped every 0.05 V, and the step time interval was 30 seconds. The rotation speed of the RRDE rotating disk electrode was 900 rpm. The obtained ORR polarization curves are as Figure 9 shown. From Figure 9 it can be seen that in a 0.1 M HClO4 solution, compared with the FeNC single-atom catalyst, the FeSbNC single-atom catalyst has a higher half-wave potential and a larger limiting current density.

[0057] The FeSbNC single-atom catalyst prepared in Example 1 was subjected to an accelerated aging test. In an oxygen-saturated electrolyte solution, cyclic voltammetry tests were carried out, and the scanning potential range was 0.6 - 1.0 V (vs. RHE), and the scanning rate was 200 mV / s. The ORR polarization curves of the FeSbNC single-atom catalyst prepared in Example 1 before and after aging are as Figure 10 shown. From Figure 10 it can be seen that after aging for 30,000 cycles in a 0.1 M HClO4 solution, the half-wave potential of the FeSbNC single-atom catalyst only decreased by 18 mV. Under the same conditions, the FeNC single-atom catalyst prepared in Comparative Example 1 was subjected to an accelerated aging test. The ORR polarization curves of the FeNC single-atom catalyst prepared in Comparative Example 1 before and after aging are as Figure 11 shown. From Figure 11It can be seen that after aging for 30,000 cycles in 0.1 M HClO4 solution, the half-wave potential of the FeSbNC single-atom catalyst decreases by 33 mV. This shows that the FeSbNC single-atom catalyst prepared in Example 1 has better stability than the FeNC single-atom catalyst.

[0058] The FeSbNC single-atom catalyst prepared in Example 1 was brushed to form a cathode with a loading of 2 mg / cm 2 The anode was a Pt catalyst with a loading of 0.1 mg / cm 2 and a fuel cell was assembled. The anode test gases were air and oxygen (flow rate 2 ml / min), and the cathode test gas was hydrogen (flow rate 0.5 ml / min). The polarization curve and power density performance of the cell were tested. The performance comparison chart in the fuel cell test is shown in Figure 12 As shown, in the proton exchange membrane fuel cell, the peak power density of the FeSbNC single-atom catalyst under hydrogen-oxygen test conditions reached 1098.3 mW / cm 2 , and the peak power density under hydrogen-air test conditions reached 613.41 mW / cm 2 . It has high practical value.

Claims

1. A semi-metal-doped Fe-based single-atom catalyst, characterized in that The catalyst is composed of two metal atoms, Fe and Sb, forming atomic pairs and embedded in a carbon support. Fe and Sb are each coordinated with four nitrogen atoms, and they share two nitrogen atoms, forming an N-bridged Fe=2N=Sb coordination structure. Furthermore, there is a hydroxyl group on the axial direction of the Sb atom. The catalyst is designated as FeSbNC. The preparation method of the catalyst is carried out according to the following steps:

1. Preparation of ZIF-8 precursor: First, 2-methylimidazole is uniformly dissolved in methanol solution to obtain solution A; then, zinc nitrate is dissolved in methanol solution to obtain solution B; solution B is added to solution A, stirred at room temperature for 20-24 hours, and then centrifuged, washed, and dried to obtain ZIF-8 precursor; 2. Preparation of N-doped porous carbon materials: After grinding the ZIF-8 precursor, place it in a tube furnace and heat it to 800-1100°C under an inert atmosphere for 1-2 hours. After cooling, the N-doped porous carbon material is obtained, which is denoted as NC.

3. Preparation of FeSbNC single-atom catalyst: Fe salt, Sb salt and methanol are thoroughly mixed to obtain solution C; then, the N-doped porous carbon material and solution C are evenly mixed, heated and stirred in a water bath until the methanol is completely volatilized, and dried to obtain a precursor; the precursor is then placed in a tube furnace and heated to 900-1100°C under an inert atmosphere for 0.5-2.5 hours for thermal activation. After cooling, the semi-metal-doped Fe-based single-atom catalyst is obtained.

2. The method for preparing a semi-metal-doped Fe-based single-atom catalyst according to claim 1, characterized in that The method proceeds as follows:

1. Preparation of ZIF-8 precursor: First, 2-methylimidazole is uniformly dissolved in methanol solution to obtain solution A; then, zinc nitrate is dissolved in methanol solution to obtain solution B; solution B is added to solution A, stirred at room temperature for 20-24 hours, and then centrifuged, washed, and dried to obtain ZIF-8 precursor; 2. Preparation of N-doped porous carbon materials: After grinding the ZIF-8 precursor, place it in a tube furnace and heat it to 800-1100°C under an inert atmosphere for 1-2 hours. After cooling, the N-doped porous carbon material is obtained, which is denoted as NC.

3. Preparation of FeSbNC single-atom catalyst: Fe salt, Sb salt and methanol are thoroughly mixed to obtain solution C; then, the N-doped porous carbon material and solution C are evenly mixed, heated and stirred in a water bath until the methanol is completely volatilized, and dried to obtain a precursor; the precursor is then placed in a tube furnace and heated to 900-1100°C under an inert atmosphere for 0.5-2.5 hours for thermal activation. After cooling, the semi-metal-doped Fe-based single-atom catalyst is obtained.

3. The method for preparing a semi-metal-doped Fe-based single-atom catalyst according to claim 2, characterized in that: The molar ratio of 2-methylimidazole to zinc nitrate in step 1 is (2-4):

1.

4. The method for preparing a semi-metal-doped Fe-based single-atom catalyst according to claim 2 or 3, characterized in that: The heating rate of the tube furnace described in step 2 is 2-10°C / min.

5. The method for preparing a semi-metal-doped Fe-based single-atom catalyst according to claim 2 or 3, characterized in that: The iron salt described in step 3 is ferric chloride, ferric nitrate or ferric acetylacetonate.

6. The method for preparing a semi-metal-doped Fe-based single-atom catalyst according to claim 2 or 3, characterized in that: The antimony salt described in step 3 is antimony chloride or antimony nitrate.

7. The method for preparing a semi-metal-doped Fe-based single-atom catalyst according to claim 2 or 3, characterized in that: The mass ratio of the antimony salt to the iron salt described in step 3 is (0.5~2):

1.

8. The method for preparing a semi-metal-doped Fe-based single-atom catalyst according to claim 2 or 3, characterized in that: The mass ratio of the antimony salt to the N-doped porous carbon material in step 3 is (0.05-0.4):

1.

9. The method for preparing a semi-metal-doped Fe-based single-atom catalyst according to claim 2 or 3, characterized in that: The water bath heating temperature described in step 3 is 50~70℃.

10. The use of a semi-metal-doped Fe-based single-atom catalyst according to claim 1, characterized in that: This application is to use semi-metal-doped Fe-based single-atom catalysts for the cathode oxygen reduction reaction in proton exchange membrane fuel cells.

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