Preparation method and application of tin-based nitrogen-doped carbon electrocatalyst

Abstract

The application provides a preparation method and application of a tin-based nitrogen-doped carbon electrocatalyst. A ZIF-8 precursor is added into a methanol solution of tetrachloride tin pentahydrate and phenanthroline, soaked and stirred, then centrifugally washed with methanol, and vacuum dried to obtain a powder which is uniformly ground and then placed into a first corundum boat, then the powder is placed into a second corundum boat and filled with activated carbon, and finally placed in the center of a tube furnace, and high-temperature pyrolysis in an inert atmosphere obtains a Sn / NC electrocatalyst. The catalyst has simple preparation process, good repeatability, excellent oxygen reduction electrocatalytic activity and stability.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method and ORR performance research of a tin-based nitrogen-doped carbon electrocatalyst and belongs to the field of oxygen reduction applications. BACKGROUND

[0002] With the increasing consumption of fossil fuels, energy crisis and environmental pollution problems are becoming increasingly serious, and research and development of sustainable new energy to meet the growing energy demand of people is the trend of the times. At present, electrochemical energy storage and conversion is an important part of the sustainable development chain, such as fuel cells, metal-air batteries and supercapacitors. Among them, the cathode reaction kinetics process of metal-air batteries and fuel cells is slow, which limits the energy conversion efficiency and large-scale application. Therefore, the development of low-cost and high-performance oxygen reduction electrocatalysts has great significance for electrochemical energy storage and conversion. Research has found that noble metal Pt-based materials have high oxygen reduction catalytic performance, but their price is high, the stability is poor and they are easy to be poisoned, which hinders their large-scale development, so the research and development of non-noble metal catalysts are promoted. Among the research of many types of non-noble metal catalysts, nitrogen-doped carbon material loaded with transition metals (Fe, Co, Ni, etc.) is considered to be one of the most promising oxygen reduction catalysts to replace noble metals.

[0003] When a single metal is loaded on nitrogen-doped carbon, the size and dispersity of metal particles can be adjusted through the interaction between the carrier and the metal to improve the oxygen reduction performance. When the metal is reduced to the atomic level, the metal is usually coordinated with nitrogen, which uniformly anchors the isolated metal atoms on the carrier, realizes the maximum atomic utilization rate, and is beneficial to improve the ORR performance of the catalyst. Metal-organic framework (MOF) material is assembled by strong coordination between metal ions, clusters and organic ligands, has the characteristics of high specific surface area, rich pore structure and controllable nitrogen-containing ligand, and is an ideal precursor material. Based on the above background, the patent takes ZIF-8 as a precursor and introduces main group metal element Sn to invent a tin-based nitrogen-doped carbon electrocatalyst. The ORR performance of the electrocatalyst is excellent, the stability is good, the repeatability is good and the synthesis process is simple, and the electrocatalyst has potential application in the field of oxygen reduction. SUMMARY

[0004] The purpose of the application is to provide a tin-based nitrogen-doped carbon electrocatalyst with excellent ORR catalytic performance. The preparation method comprises the following specific steps:

[0005] Step 1: 2-methylimidazole is dissolved in methanol to obtain solution A; then zinc nitrate hexahydrate (Zn(NO3)2·6H2O) is dissolved in methanol to obtain solution B. Then, solution A and B are mixed and stirred uniformly, the product is centrifuged and washed with methanol, and finally vacuum drying is carried out to obtain ZIF-8 precursor;

[0006] Step 2: SnCl4·5H2O and phenanthroline are dispersed in methanol in turn, and then the ZIF-8 precursor is added for soaking and stirring, followed by centrifugal washing with methanol, and finally vacuum drying in a vacuum drying box.

[0007] Step 3: The powder obtained in step 2 is uniformly ground and placed in a first corundum boat, then the first corundum boat is placed in a second corundum boat, and activated carbon is filled in the second corundum boat, and finally placed in the center of a tube furnace for high-temperature pyrolysis in an inert atmosphere to obtain the Sn / NC electrocatalyst.

[0008] The mass ratio of the 2-methylimidazole to zinc nitrate hexahydrate is 1:0.8-1.5.

[0009] The mass ratio of the SnCl4·5H2O to phenanthroline is 1:0.3-1.8.

[0010] In step 3, the obtained powder is uniformly ground and then placed in a first corundum boat, then placed in a second corundum boat and filled with activated carbon, and the raw materials in the first corundum boat are not in contact with the activated carbon filled in the second corundum boat, and finally placed in the center of a tube furnace, and the activated carbon is used to provide a reducing atmosphere during annealing.

[0011] The tin-based nitrogen-doped carbon electrocatalyst and the preparation method thereof have the following remarkable features:

[0012] (1) The Sn / NC electrocatalyst is prepared by the method of high-temperature pyrolysis after stirring adsorption, with ZIF-8 as the precursor,

[0013] The preparation process is simple and low in cost, and the electrocatalyst has good repeatability.

[0014] (2) The Sn / NC electrocatalyst has excellent ORR performance and good stability, and has certain application prospect in the field of oxygen reduction. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 XRD patterns of the samples prepared in Examples 1, 2, 3 and 4.

[0016] Figure 2 SEM image of the sample prepared in Example 2.

[0017] Figure 3 LSV curves of the samples prepared in Examples 1, 2, 3 and 4 and Pt / C.

[0018] Figure 4 n and H2O2 yield curves of the samples prepared in Examples 1, 2, 3 and 4.

[0019] Figure 5ORR stability curves of the samples prepared in Example 2.

[0020] Figure 6 LSV curves of Sn / NC-1, Sn / NC-2, Sn / NC-3, and Sn / NC-4 samples. DETAILED DESCRIPTION

[0021] Example 1

[0022] First, 8 g of 2-methylimidazole was dissolved in 200 mL of methanol to obtain solution A; then, 7 g of Zn(NO3)2·6H2O was dissolved in 200 mL of methanol to obtain solution B. Solution A and B were mixed, stirred at room temperature for 30 min, and then placed at 60 o C for 24 h. The obtained product was washed and centrifuged with methanol, and finally dried in a vacuum drying box for 12 h to obtain a ZIF-8 precursor. Subsequently, 0.24 g of SnCl4·5H2O and 0.20 g of phenanthroline were dispersed in 100 mL of methanol, and then 1.5 g of the ZIF-8 precursor was added and stirred for 4 h. The product was washed and centrifuged with methanol, and then vacuum dried for 12 h. Finally, the obtained powder was uniformly ground and placed in a corundum boat (1#), which was then placed in a corundum boat (2#) and filled with activated carbon. Finally, it was placed in the center of a tube furnace, heated to 900 o C at a heating rate of 5 o C / min in a high-purity Ar atmosphere, and pyrolyzed at high temperature for 3 h to obtain a Sn / NC electrocatalyst, labeled as Sn / NC-1.

[0023] Figure 1 The Sn / NC-1 in a is the XRD pattern of the catalyst prepared in this example, and from the figure it can be seen that the sample in this example only has diffraction peaks at 26° and 42°, corresponding to the (002) and (100) crystal planes of graphitized carbon (PDF #41-1487), which is derived from the high-temperature carbonization of the ZIF-8 precursor. In addition, no diffraction peaks of Sn metal or its compounds were found in the XRD pattern, which may be because the particles are too small or the crystallinity is too poor. The sample in this example was prepared into a slurry and ultrasonicated for 4 h, then drop-coated on a rotating disc electrode and naturally dried into a film. The ORR performance was tested in an O2-saturated 0.1 M KOH solution at a rotation speed of 1600 rpm. The LSV curve of Sn / NC-1 is shown in Figure 3 From the figure, the half-wave potential of Sn / NC-1 is 0.85 V vs. RHE, the limiting current density is 5.1 mA cm -2 , and the onset potential is 0.93 V vs. RHE, showing excellent ORR performance. Figure 4The Sn / NC-1 in the figure represents the ring disk test results of the catalyst prepared in this example. As can be seen from the figure, in the potential range of 0.4–0.8 V vs. RHE, the yield of the byproduct H₂O₂ is 0.24–15.44%, and the number of transferred electrons is 3.70–3.99, close to the theoretical value of 4, indicating that it satisfies the ORR requirement of 4e⁻¹. - Transfer routes.

[0024] Example 2

[0025] First, dissolve 8 g of 2-methylimidazole in 200 mL of methanol to obtain solution A; then dissolve 7 g of Zn(NO3)2∙6H2O in 200 mL of methanol to obtain solution B. Mix solutions A and B, stir at room temperature for 30 min, and then heat at 60 °C. o The product was allowed to stand at C for 24 h, then washed with methanol and centrifuged. Finally, it was dried in a vacuum drying oven for 12 h to obtain the ZIF-8 precursor. Subsequently, 0.24 g of SnCl4∙5H2O and 0.30 g of phenanthroline were dispersed in 100 mL of methanol, and 1.5 g of ZIF-8 precursor was added. After soaking and stirring for 4 h, the product was washed with methanol by centrifugation and vacuum dried for 12 h. Finally, the obtained powder was ground evenly and placed in a corundum boat (1#), then placed in a corundum boat (2#) and filled with activated carbon. Finally, it was placed in the center of a tube furnace and heated at a rate of 5°C in a high-purity Ar atmosphere. o Heat to 900 C / min o C, high-temperature pyrolysis for 3 h yielded Sn / NC electrocatalyst, labeled as Sn / NC-2.

[0026] The XRD pattern of the catalyst prepared in this example is as follows: Figure 1 As shown in Sn / NC-2 in Example 1, this example sample also has only two graphitized carbon peaks generated by the high-temperature carbonization of the ZIF-8 precursor, located at 26° and 42°, corresponding to the (002) and (100) crystal planes of graphitized carbon (PDF#41-1487). SEM analysis of this example sample revealed its morphology as follows: Figure 2 As shown, the sample mainly consists of irregular spindle-shaped polyhedra and nitrogen-carbon particles, with a disordered morphological distribution. A slurry of this example sample was prepared, ultrasonically dispersed, and drop-coated onto a rotating disk electrode. After uniform film formation, the ORR performance was tested in an O2-saturated 0.1 M KOH solution at a rotation speed of 1600 rpm. Figure 3 Sn / NC-2 in the figure represents the LSV curve of this example sample, as shown in the figure. Its half-wave potential is 0.88 V vs. RHE, and its limiting current density is 4.8 mA cm⁻². -2The onset potential was 0.96 V vs. RHE, and its ORR performance was significantly better than that of Example 1. The LSV curve of commercial Pt / C is shown below. Figure 3 As shown, the half-wave potential is 0.86 V vs. RHE, and the limiting current density is 5.0 mA cm⁻¹. -2 The onset potential was 0.96 V vs. RHE, and its ORR performance was inferior to Sn / NC-2. Subsequently, the sample prepared in this example was subjected to ring-disc testing, such as... Figure 4 As shown, in the oxygen reduction reaction, the electrocatalyst exhibits a H₂O₂ yield of 0.14-7.76% and a transferred electron number of 3.84-3.99 in the 0.4-0.8 V vs. RHE potential range, confirming the efficient 4e⁻ reaction pathway of Sn / NC⁻. The ORR stability of this example sample was tested using chronoamperometry, as shown... Figure 5 As shown, under the conditions of a potential of 0.5 V vs. RHE and a rotation speed of 1600 rpm, after continuous constant voltage operation for 7200 s, the current of this example sample only decreased by 5%, while that of commercial Pt / C decreased by 23%, indicating that the ORR stability of the sample obtained under this example is excellent.

[0027] Example 3

[0028] First, dissolve 8 g of 2-methylimidazole in 200 mL of methanol to obtain solution A; then dissolve 7 g of Zn(NO3)2∙6H2O in 200 mL of methanol to obtain solution B. Mix solutions A and B, stir at room temperature for 30 min, and then heat at 60 °C. o The product was allowed to stand at C for 24 h, then washed with methanol and centrifuged. Finally, it was dried in a vacuum drying oven for 12 h to obtain the ZIF-8 precursor. Subsequently, 0.24 g of SnCl4∙5H2O and 0.40 g of phenanthroline were dispersed in 100 mL of methanol, and 1.5 g of ZIF-8 precursor was added. After soaking and stirring for 4 h, the product was washed with methanol by centrifugation and vacuum dried for 12 h. Finally, the obtained powder was ground evenly and placed in a corundum boat (1#), then placed in a corundum boat (2#) and filled with activated carbon. Finally, it was placed in the center of a tube furnace and heated at a rate of 5°C in a high-purity Ar atmosphere. o Heat to 900 C / min o C, high-temperature pyrolysis for 3 h yielded Sn / NC electrocatalyst, labeled as Sn / NC-3.

[0029] Figure 1The Sn / NC-3 in a is the XRD pattern of the catalyst prepared in this example, from the figure, it can be seen that the phase of the sample in this example is the same as that in examples 1 and 2, and only two diffraction peaks at 26° and 42° are observed, corresponding to the (002) and (100) crystal planes of graphitized carbon (PDF #41-1487), and no diffraction peaks corresponding to Sn metal or its compounds are found. In order to study the ORR activity of the sample in this example, it was prepared into a slurry and then ultrasonically dispersed uniformly, dropped onto a rotating disc electrode and naturally air-dried into a film, and then, the ORR activity was tested in a 0.1 M KOH solution saturated with oxygen at a rotation speed of 1600 rpm. Figure 3 The Sn / NC-3 in a is the LSV curve of the sample in this example, as shown in the figure, the half-wave potential thereof is 0.87 V vs. RHE, and the limiting current density is 4.7 mA cm -2 , and the onset potential is 0.95 V vs. RHE, and the ORR activity thereof is better than that in example 1, but slightly worse than that in example 2. The sample in this example was tested by a rotating ring disc electrode (RRDE), and from Figure 4 , it can be seen that in the potential range of 0.4-0.8 V vs. RHE, the by-product H2O2 yield thereof is 0.28-13.05%, and the number of transferred electrons is 3.75-3.98, indicating that the sample obtained in this example satisfies the 4e - transfer pathway of ORR.

[0030] Example 4

[0031] First, 8 g of 2-methylimidazole was dissolved in 200 mL of methanol to obtain solution A; then, 7 g of Zn(NO3)2·6H2O was dissolved in 200 mL of methanol to obtain solution B. Solution A and B were mixed, stirred at room temperature for 30 min, and then placed at 60 o C for 24 h, and then the obtained product was washed and centrifuged with methanol, and finally dried in a vacuum drying box for 12 h to obtain a ZIF-8 precursor. Subsequently, 0.24 g of (CH3COO)2Sn and 0.30 g of phenanthroline were dispersed in 100 mL of methanol, and then 1.5 g of the ZIF-8 precursor was added and soaked and stirred for 4 h, and then centrifuged and washed with methanol, and vacuum dried for 12 h. Finally, the obtained powder was uniformly ground and placed in a corundum boat (1#), and then placed in a corundum boat (2#) and filled with activated carbon, and finally placed in the center of a tube furnace, heated to 900 o C at a heating rate of 5 o C / min in a high-purity Ar atmosphere, and pyrolyzed at a high temperature for 3 h to obtain a Sn / NC electrocatalyst, which is marked as Sn / NC-4.

[0032] The XRD pattern of the catalyst prepared in this example is as follows:Figure 1 As shown in b, unlike Examples 1, 2, and 3, Sn / NC-4, in addition to a broad diffraction peak at 26°, corresponding to the (002) crystal plane of graphitized carbon (PDF#41-1487), also exhibits diffraction peaks at 30.6°, 32.1°, 43.9°, and 45.1°, corresponding to the (200), (101), (220), and (211) crystal planes of metallic Sn (PDF#04-0673), respectively. This is because SnCl4∙5H2O in Examples 1, 2, and 3 was replaced with (CH3COO)2Sn. After preparing the slurry of this example sample, it was ultrasonically dispersed evenly, and then the ORR performance of the sample in 0.1 M KOH solution at a rotation speed of 1600 rpm was tested using a rotating disk electrode (RDE). The LSV curve of the catalyst prepared in this example is shown below. Figure 3 As shown in Sn / NC-4, its half-wave potential is 0.84 V vs. RHE, and its limiting current density is 4.7 mA cm⁻¹. -2 The initial potential is 0.92 V vs. RHE, and its ORR performance is worse than that of Example 1. Figure 4 Sn / NC-4 in the figure represents the ring disk test results of the catalyst prepared in this example. As can be seen from the figure, in the potential range of 0.4-0.8 V vs. RHE, the yield of byproduct H2O2 is 0.69-21.36%, and the number of transferred electrons is 3.58-3.97, which is close to the theoretical value of 4, proving that it has excellent oxygen reduction electrocatalytic activity.

[0033] Compared to Example 2, if the experimental steps, other reagents, and dosages remain unchanged, but the amount of SnCl4∙5H2O is reduced to 0.12 g, the resulting sample is labeled Sn / NC-5. The oxygen reduction LSV curve of this sample is as follows. Figure 6 As shown in the figure, at 1600 rpm, its half-wave potential decreases to 0.83 V vs. RHE, and its limiting current density decreases to 3.9 mAcm⁻¹. -2 The initial potential is 0.93 V vs. RHE, and its ORR performance is significantly worse.

[0034] Compared to Example 2, if the experimental steps, other reagents, and dosages remain unchanged, but the amount of SnCl4∙5H2O is increased to 0.36 g, the resulting sample is labeled Sn / NC-6. The oxygen reduction LSV curve of this sample is as follows. Figure 6 As shown in the figure, at 1600 rpm, its half-wave potential is only 0.84 V vs. RHE, and the limiting current density drops to 4.3 mAcm. -2 With an initial potential of only 0.94 V vs. RHE, its ORR performance is significantly reduced.

[0035] Compared to Example 2, if the experimental steps, other reagents, and amounts remain unchanged, but the solvents for SnCl4∙5H2O and phenanthroline are replaced with ethanol, the resulting sample is labeled Sn / NC-7. The oxygen reduction LSV curve of this sample is shown below. Figure 6 As shown in the figure, at 1600 rpm, its half-wave potential decreases to 0.81 V vs. RHE, and its limiting current density decreases to 3.7 mA cm⁻¹. -2 With an initial potential of only 0.93 V vs. RHE, its ORR performance is significantly poor.

[0036] Compared to Example 2, if the experimental steps, reagents, and dosages remain unchanged, the powder obtained during pyrolysis is ground uniformly, placed in a corundum boat (1#), and then directly placed in the center of a tube furnace for high-temperature pyrolysis in an inert atmosphere. The resulting sample is labeled Sn / NC-8. The oxygen reduction LSV curve of this sample is as follows: Figure 6 As shown in the figure, at 1600 rpm, its half-wave potential drops sharply to 0.73 V vs. RHE, and the limiting current density drops to 3.0 mA cm⁻¹. -2 When the initial potential drops to 0.88V vs. RHE, its ORR performance degrades significantly.

Claims

1. A method for preparing a tin-based nitrogen-doped carbon electrocatalyst, characterized in that, Includes the following steps: Step 1: Mix 2-methylimidazole in methanol and zinc nitrate hexahydrate in methanol until homogeneous, then wash the product with methanol by centrifugation and vacuum dry to obtain the ZIF-8 precursor. Step 2: Sequentially disperse tin tetrachloride pentahydrate and phenanthroline in methanol, then add ZIF-8 precursor, soak and stir, wash with methanol by centrifugation, and vacuum dry. The mass of tin tetrachloride pentahydrate and phenanthroline is 0.24 g and 0.20 g, respectively; or the mass of tin tetrachloride pentahydrate and phenanthroline is 0.24 g and 0.30 g, respectively; or the mass of tin tetrachloride pentahydrate and phenanthroline is 0.24 g and 0.40 g, respectively. Step 3: After grinding the powder obtained in Step 2 evenly, put it into the first corundum boat, then put the first corundum boat into the second corundum boat, and fill the second corundum boat with activated carbon. Finally, place it in the center of the tube furnace and pyrolyze it at high temperature in an inert atmosphere to obtain the Sn / NC electrocatalyst.

2. The method for preparing a tin-based nitrogen-doped carbon electrocatalyst according to claim 1, characterized in that, The mass ratio of 2-methylimidazole to zinc nitrate hexahydrate is 1:0.8-1.

5.

3. The application of the Sn / NC electrocatalyst prepared by the preparation method according to any one of claims 1-2 in the catalytic oxygen reduction reaction.

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