Preparation method and application of MnO / Sn-NC electrocatalyst

Abstract

The application provides a preparation method and application of an MnO / Sn-NC electrocatalyst. A manganese chloride tetrahydrate ethanol solution and a tin acetate ethanol solution are prepared, then NC is first added into the manganese chloride tetrahydrate ethanol solution for soaking and ultrasonic stirring, and then added into the tin acetate ethanol solution for soaking and ultrasonic stirring, and after soaking, centrifugal washing and drying are carried out; the obtained powder is annealed in a tube furnace to obtain the MnO / Sn-NC electrocatalyst. The application takes the NC obtained by high-temperature pyrolysis of ZIF-8 as a precursor, and then MnCl2.4H2O and C4H6O4Sn are sequentially adsorbed on the surface of the NC, and then a novel MnO / Sn-NC electrocatalyst is obtained by high-temperature pyrolysis again, and the material components are MnO, Sn and NC. The MnO / Sn-NC electrocatalyst has excellent ORR performance and good stability, and has a significant application prospect in the field of oxygen reduction.

Description

Technical Field

[0001] This invention relates to a class of efficient and inexpensive ORR electrocatalysts, and particularly to a method for preparing a MnO / Sn-NC electrocatalyst and its oxygen reduction performance, belonging to the field of oxygen reduction applications. Background Technology

[0002] The increasing demand for energy and the continued deterioration of the ecological environment have intensified the societal need for renewable energy storage technologies. Rechargeable zinc-air batteries have attracted widespread attention due to their high energy density, abundant zinc reserves, low cost, and high safety. However, the slow kinetics of the oxygen reduction and evolution reactions (ORR) at the air cathode lead to unsatisfactory energy efficiency in zinc-air batteries, significantly hindering their practical application. Therefore, highly efficient electrocatalysts are needed to accelerate oxygen electrocatalytic kinetics. Noble metal electrocatalysts dominated by Pt, RuO2, and IrO2 exhibit high activity; however, their high cost, resource scarcity, and low durability severely impede their large-scale commercial application. Therefore, developing novel, efficient, and low-cost ORR electrocatalysts to replace noble metal Pt-based catalysts is imperative.

[0003] Among numerous candidate electrocatalysts, inexpensive nitrogen-doped carbon (NC) supported transition metal (Fe, Co, Ni, etc.) systems have shown great potential in the field of electrocatalysis. In such electrocatalysts, transition metals and their compounds, including oxides, sulfides, and phosphides, can transfer electrons to the NC interface, thereby significantly improving electrocatalytic performance. Compared to transition metals, main group elements with incomplete p orbitals (Bi, Sb, Sn, etc.) are less commonly used in electrocatalysis. Studies have shown that introducing both transition metals and main group elements simultaneously not only does not affect the electrocatalytic activity of transition metals but can also modulate the electronic structure of transition metals, thereby controlling electrocatalytic performance. Against this background, this invention uses ZIF-8 annealed nitrogen-doped carbon as a support, introduces the transition metal element Mn and the non-transition metal element Sn, and invents a novel MnO / Sn-NC electrocatalyst. This electrocatalyst exhibits excellent electrocatalytic performance and good stability, and has potential application value in the field of oxygen reduction. Summary of the Invention

[0004] The purpose of this invention is to provide a novel MnO / Sn-NC electrocatalyst with excellent oxygen reduction performance. The specific preparation steps of the MnO / Sn-NC electrocatalyst are as follows:

[0005] Step 1: Prepare methanol solutions of 2-methylimidazole and zinc nitrate hexahydrate separately, then mix them, stir evenly, and let stand at a certain temperature. Centrifuge, wash and dry the precipitate to obtain ZIF-8 powder.

[0006] Step 2: Place ZIF-8 powder in a tube furnace for annealing to obtain nitrogen-doped carbon (NC).

[0007] Step 3: Prepare ethanol solutions of manganese chloride tetrahydrate and tin acetate respectively. Then, first soak NC in the ethanol solution of manganese chloride tetrahydrate and stir ultrasonically, then soak it in the ethanol solution of tin acetate and stir ultrasonically. After soaking, centrifuge, wash and dry. Anneal the obtained powder in a tube furnace to obtain MnO / Sn-NC electrocatalyst.

[0008] The mass concentration of the ethanol solution of manganese chloride tetrahydrate is 0.5-1.5 mg / ml; it is soaked in an ultrasonic frequency of 2500-4000 Hz for 20-60 min.

[0009] The ethanol solution of tin acetate has a mass concentration of 0.1-0.2 mg / ml; it is soaked in an ultrasonic frequency of 2500-4000 Hz for 20-60 min.

[0010] The obtained powder is heated to 1000-1200℃ in a tube furnace at a heating rate of 5-10℃ / min and annealed for 2-3 hours.

[0011] The temperature was increased to 1000℃ in a tube furnace at a heating rate of 10℃ / min, and annealed for 2 hours.

[0012] Another technical solution of the present invention is to use the prepared MnO / Sn-NC electrocatalyst as a catalyst for oxygen reduction reaction.

[0013] The MnO / Sn-NC electrocatalyst and its preparation method involved in this invention have the following significant characteristics:

[0014] (1) Using NC obtained by high-temperature pyrolysis of ZIF-8 as a precursor, MnCl2∙4H2O and C4H6O4Sn are sequentially adsorbed on its surface, and then pyrolyzed again at high temperature to obtain a new MnO / Sn-NC electrocatalyst. The material composition is MnO, Sn and NC.

[0015] (2) MnO / Sn-NC electrocatalysts have excellent ORR performance and good stability, and have significant application prospects in the field of oxygen reduction. Attached Figure Description

[0016] Figure 1 XRD patterns of the samples prepared in Examples 1, 2, 3, and 4.

[0017] Figure 2 SEM image of the sample prepared in Example 1.

[0018] Figure 3LSV curves of the samples prepared in Examples 1, 2, 3, and 4 and Pt / C.

[0019] Figure 4 Oxygen reduction electron transfer number (n) and H2O2 yield curves of the samples prepared in Examples 1, 2, 3, and 4 and Pt / C.

[0020] Figure 5 ORR stability curve of the sample prepared in Example 1.

[0021] Figure 6 The LSV curves are for samples MnO / Sn-NC-5, MnO / Sn-NC-6, and MnO / Sn-NC-7. Detailed Implementation

[0022] Example 1

[0023] 6.78 g of zinc nitrate hexahydrate (Zn(NO3)2∙6H2O) and 7.88 g of dimethylimidazole (C4H6N2) were dissolved separately in 150 mL of methanol and stirred for 5 min each. The two solutions were then mixed and stirred for 30 min. The mixture was then allowed to stand at 60 °C for 24 h, centrifuged, washed, and dried at 60 °C to obtain ZIF-8 powder. ZIF-8 was then pyrolyzed in a tube furnace under an argon atmosphere at a rate of 10 °C / min to 900 °C for 2 h to obtain NC powder. 59 mg of manganese chloride tetrahydrate (MnCl2∙4H2O) and 7.1 mg of tin acetate (C4H6O4Sn) were dissolved in 60 mL of ethanol to obtain ethanol solutions of manganese chloride tetrahydrate and tin acetate. 300 mg of NC was first added to the ethanol solution of manganese chloride tetrahydrate and soaked at an ultrasonic frequency of 3000 Hz for 30 min. Then it was added to the ethanol solution of tin acetate and soaked at an ultrasonic frequency of 3000 Hz for 30 min. After stirring continuously for 2 h, the mixture was centrifuged, washed, and dried at 60 ℃. The resulting powder was then pyrolyzed in an argon atmosphere in a tube furnace at a temperature of 10 ℃ / min to 1000 ℃ for 2 h to obtain a novel MnO / Sn-NC electrocatalyst, denoted as MnO / Sn-NC-1.

[0024] Figure 1 The image shows the XRD pattern of the catalyst in this example, MnO / Sn-NC-1. In the figure, the catalyst located at 26... oThe relatively broad diffraction peaks on the left and right are the (002) peaks of graphitized carbon, which originate from the high-temperature carbonization of the ZIF-8 precursor. The sharp diffraction peaks at 30.6 °, 32.0 ° and 44.9 ° correspond to the (200), (101) and (211) crystal planes of metallic Sn (PDF#04-0673), respectively, while the sharp diffraction peaks at 34.9 °, 40.5 ° and 58.7 ° correspond to the (111), (200) and (220) crystal planes of MnO (PDF#07-0230), respectively, indicating that the sample prepared in this example is a composite material of MnO, Sn and NC. Figure 2 The image shows the SEM image of the sample. It can be seen that the sample basically retains the morphology of the ZIF-8 rhombic dodecahedron, with a size of approximately 0.4–1 µm. The ORR performance of the example sample was tested using a rotating disk electrode in an O2-saturated 0.1 M KOH solution at 1600 rpm. The LSV curve of MnO / Sn-NC-1 is shown below. Figure 3 As shown in the figure, at a rotational speed of 1600 rpm, its half-wave potential is 0.88 V vs. RHE, and its limiting current density is 5.1 mA cm⁻¹. -2 The onset potential was 0.99 V vs. RHE, demonstrating excellent ORR performance. Figure 4 The rotating ring disk test for the example sample shows that, as can be seen from the figure, in the oxygen reduction reaction within the potential range of 0.4–0.8 V vs. RHE, the yield of the byproduct H₂O₂ is 1.63%–10.8%, and the number of transferred electrons is 3.78–3.97, which is close to 4 and meets the theoretical requirement of 4 electrons. - Transfer routes. Figure 5 For the stability test of the example sample, after a constant voltage test for 7200 s, the current decay was only 5.7%, further proving that the sample obtained under this example has excellent ORR stability.

[0025] Compared to Example 1, keeping the synthesis steps and other sample contents unchanged, the synthesized ZIF-8 was directly immersed in an ethanol solution of MnCl2∙4H2O and C4H6O4Sn without high-temperature annealing to obtain NC. The resulting sample could not maintain its three-dimensional structure, and the polyhedral morphology was destroyed.

[0026] Compared to Example 1, keeping the synthesis steps and other sample contents unchanged, the amount of tin acetate (C4H6O4Sn) was increased to 23.7 mg. The LSV curve of the resulting sample MnO / Sn-NC-5 is shown below. Figure 6 As shown in the figure, at 1600 rpm, its half-wave potential is only 0.81 V vs. RHE, and the limiting current density drops to 4.4 mA cm⁻¹. -2The initial potential is 0.92 V vs. RHE, and its ORR performance is poor.

[0027] Compared to Example 1, keeping the synthesis steps and other sample contents unchanged, the amount of tin acetate (C4H6O4Sn) was reduced to 4.7 mg. The LSV curve of the resulting sample MnO / Sn-NC-6 is shown below. Figure 6 As shown in the figure, at 1600 rpm, its half-wave potential is only 0.79 V vs. RHE, and the limiting current density drops to 4.3 mA cm⁻¹. -2 With an initial potential of 0.94 V vs. RHE, its ORR performance decreased significantly.

[0028] Compared with Example 1, keeping other steps and sample contents unchanged, 59 mg of manganese chloride tetrahydrate (MnCl2∙4H2O) and 7.1 mg of tin acetate (C4H6O4Sn) were dissolved in 120 mL of ethanol to obtain an ethanol solution containing manganese chloride tetrahydrate and tin acetate. Then, 300 mg of NC containing the ethanol solution of manganese chloride tetrahydrate and tin acetate was immersed in an ultrasonically controlled solution at 3000 Hz for 60 min. The LSV curve of the resulting sample MnO / Sn-NC-7 is shown below. Figure 6 As shown in the figure, at 1600 rpm, its half-wave potential decreases to 0.79 V vs. RHE, and the limiting current density decreases to 3.3 mA cm⁻¹. -2 With an initial potential of 0.89 V vs. RHE, its ORR performance drops sharply.

[0029] Example 2

[0030] 6.78 g of zinc nitrate hexahydrate (Zn(NO3)2∙6H2O) and 7.88 g of dimethylimidazole (C4H6N2) were dissolved in 150 mL of methanol, respectively, and stirred for 5 min each. The two solutions were then mixed and stirred for 30 min. The mixture was then allowed to stand at 60 °C for 24 h, centrifuged, washed, and dried at 60 °C to obtain ZIF-8 powder. ZIF-8 was then pyrolyzed in a tube furnace under an argon atmosphere at a rate of 10 °C / min to 900 °C for 2 h to obtain NC powder.

[0031] 68.8 mg of manganese chloride tetrahydrate (MnCl2∙4H2O) and 8.4 mg of tin acetate (C4H6O4Sn) were dissolved in 60 mL of ethanol, respectively, to obtain ethanol solutions of manganese chloride tetrahydrate and tin acetate. 300 mg of NC was first added to the ethanol solution of manganese chloride tetrahydrate and soaked under ultrasonication at 3000 Hz for 30 min. Then, it was added to the ethanol solution of tin acetate and soaked under ultrasonication at 3000 Hz for another 30 min, followed by continuous stirring for 2 h. Finally, the mixture was centrifuged, washed, and dried at 60 °C. The solution was then pyrolyzed at 1000 °C at a rate of 10 °C / min for 2 h to obtain a novel MnO / Sn-NC electrocatalyst, denoted as MnO / Sn-NC-2.

[0032] Figure 1 The XRD pattern of the catalyst in this example is shown in the figure, with the peak at 26°C. o The broader diffraction peaks on the left and right are the (002) peaks of graphitized carbon, originating from the high-temperature carbonization of the ZIF-8 precursor. The sharp diffraction peaks at other angles correspond one-to-one with the MnO standard card (PDF#07-0230) and the Sn standard card (PDF#04-0673), proving that the experimentally prepared sample is also a composite material of MnO, Sn, and NC. The ORR performance of the example sample was tested at 1600 rpm in an O2-saturated 0.1 M KOH solution. The LSV curve of MnO / Sn-NC-2 is shown below. Figure 3 As shown in the figure, at a rotational speed of 1600 rpm, its half-wave potential is 0.87 V vs. RHE, and its limiting current density is 5.0 mA·cm⁻¹. -2 The onset potential was 0.97 V vs. RHE, demonstrating excellent ORR performance. Figure 4 The rotating ring disk test for the example sample shows that, as can be seen from the figure, in the oxygen reduction reaction within the potential range of 0.4-0.8 V vs. RHE, the yield of the byproduct H2O2 is 6.37%-12%, and the number of transferred electrons is 3.76-3.87, which is close to 4, and meets the theoretical requirement of 4e. - The transfer pathway further demonstrates that the sample obtained in this example exhibits excellent ORR performance.

[0033] Example 3

[0034] 6.78 g of zinc nitrate hexahydrate (Zn(NO3)2∙6H2O) and 7.88 g of dimethylimidazole (C4H6N2) were dissolved separately in 150 mL of methanol and stirred for 5 min each. The two solutions were then mixed and stirred for 30 min. The mixture was then allowed to stand at 60 °C for 24 h, centrifuged, washed, and dried at 60 °C to obtain ZIF-8 powder. ZIF-8 was then pyrolyzed in a tube furnace under an argon atmosphere at a rate of 10 °C / min to 900 °C for 2 h to obtain NC powder.

[0035] 59 mg of manganese chloride tetrahydrate (MnCl2∙4H2O) and 7.8 mg of tin acetate (C4H6O4Sn) were dissolved in 60 mL of ethanol, respectively, to obtain ethanol solutions of manganese chloride tetrahydrate and tin acetate. 300 mg of NC was first added to the ethanol solution of manganese chloride tetrahydrate and soaked under ultrasonication at 3000 Hz for 30 min. Then, it was added to the ethanol solution of tin acetate and soaked under ultrasonication at 3000 Hz for another 30 min, followed by continuous stirring for 2 h. Finally, the mixture was centrifuged, washed, and dried at 60 ℃. The temperature was then increased to 1000 ℃ at a rate of 10 ℃ / min, and pyrolyzed for 2 h to obtain a novel MnO / Sn-NC electrocatalyst, denoted as MnO / Sn-NC-3.

[0036] Figure 1 The XRD pattern of the catalyst in this example is shown in the figure for MnO / Sn-NC-3. The position at 26 is... o The broader diffraction peaks on the left and right are the (002) peaks of graphitized carbon, originating from the high-temperature carbonization of the ZIF-8 precursor. The sharp diffraction peaks at other angles correspond one-to-one with the MnO standard card (PDF#07-0230), proving that the experimentally prepared sample is a composite material of MnO alloy and NC. The difference is that the diffraction peaks of metallic tin disappear after increasing the concentration of tin acetate; compared to Example 2, the intensity change of the MnO diffraction peaks is smaller. The ORR performance of the example sample was tested at 1600 rpm in an O2-saturated 0.1 M KOH solution. The LSV curve of MnO / Sn-NC-3 is shown below. Figure 3 As shown in the figure, at a rotational speed of 1600 rpm, its half-wave potential is 0.88 V vs. RHE, and its limiting current density is 4.9 mA·cm⁻¹. -2 The onset potential was 0.98 V vs. RHE, demonstrating excellent ORR performance. Figure 4 The rotating ring disk test for the example sample shows that, as can be seen from the figure, in the oxygen reduction reaction within the potential range of 0.4–0.8 V vs. RHE, the yield of the byproduct H₂O₂ is 0.59%–6.08%, and the number of transferred electrons is 3.88–3.99, which is very close to 4, satisfying the theoretical 4e⁻¹. -The transfer pathway further demonstrates that the sample obtained in this example exhibits excellent ORR performance.

[0037] Example 4

[0038] 6.78 g of zinc nitrate hexahydrate (Zn(NO3)2∙6H2O) and 7.88 g of dimethylimidazole (C4H6N2) were dissolved separately in 150 mL of methanol and stirred for 5 min each. The two solutions were then mixed and stirred for 30 min. The mixture was then allowed to stand at 60 °C for 24 h, centrifuged, washed, and dried at 60 °C to obtain ZIF-8 powder. ZIF-8 was then pyrolyzed in a tube furnace under an argon atmosphere at a rate of 10 °C / min to 900 °C for 2 h to obtain NC powder.

[0039] 59 mg of manganese chloride tetrahydrate (MnCl2∙4H2O) and 8.8 mg of tin acetate (C4H6O4Sn) were dissolved in 60 mL of ethanol, respectively, to obtain ethanol solutions of manganese chloride tetrahydrate and tin acetate. 300 mg of NC was first added to the ethanol solution of manganese chloride tetrahydrate and soaked under ultrasonication at 3000 Hz for 30 min. Then, it was added to the ethanol solution of tin acetate and soaked under ultrasonication at 3000 Hz for another 30 min, followed by continuous stirring for 2 h. Finally, the mixture was centrifuged, washed, and dried at 60 °C. The solution was then pyrolyzed at 1000 °C at a rate of 10 °C / min for 2 h to obtain a novel MnO / Sn-NC electrocatalyst, designated MnO / Sn-NC-4.

[0040] Figure 1 The image 8-1 shows the XRD pattern of the catalyst in this example, located at 26. o The broader diffraction peaks on the left and right are the (002) peaks of graphitized carbon, originating from the high-temperature carbonization of the ZIF-8 precursor. The sharp diffraction peaks at other angles correspond one-to-one with the MnO standard card (PDF#07-0230) and the Sn standard card (PDF#04-0673), proving that the experimentally prepared sample is a composite material of MnO alloy and NC. With further increases in tin acetate concentration, the diffraction peak intensity of metallic Sn also increases significantly. The ORR performance of the example sample was tested at 1600 rpm in an O2-saturated 0.1 M KOH solution. The LSV curve of MnSn / NC 8-1 is shown below. Figure 3 As shown in the figure, at a rotational speed of 1600 rpm, its half-wave potential is 0.88 V vs. RHE, and its limiting current density is 5.17 mA·cm⁻¹. -2 The onset potential was 0.98 V vs. RHE, demonstrating excellent ORR performance. Figure 4The rotating ring disk test for the example sample shows that, as can be seen from the figure, in the oxygen reduction reaction within the potential range of 0.4–0.8 V vs. RHE, the yield of the byproduct H₂O₂ is 2.34%–10.9%, and the number of transferred electrons is 3.78–3.95, which is close to 4, satisfying the theoretical 4e⁻¹⁴ ... - The transfer pathway demonstrates that the sample obtained in this example exhibits excellent ORR performance.

Claims

1. A method for preparing a MnO / Sn-NC electrocatalyst, characterized in that, Includes the following steps: Step 1: Prepare methanol solutions of 2-methylimidazole and zinc nitrate hexahydrate separately, then mix them, stir evenly, and let stand at a certain temperature. Centrifuge, wash and dry the precipitate to obtain ZIF-8 powder. Step 2: Anneal the ZIF-8 powder in a tube furnace to obtain nitrogen-doped carbon; Step 3: Prepare ethanol solutions of manganese chloride tetrahydrate and tin acetate separately. First, soak the nitrogen-doped carbon in the ethanol solution of manganese chloride tetrahydrate and then sonicate it. Next, soak the carbon in the ethanol solution of tin acetate and sonicate it again. After soaking, centrifuge, wash, and dry the carbon. Anneal the resulting powder in a tube furnace to obtain the MnO / Sn-NC electrocatalyst. The mass concentration of the manganese chloride tetrahydrate ethanol solution is 0.5-1.5 mg / ml; soak the carbon in the ethanol solution at an ultrasonic frequency of 2500-4000 Hz for 20-60 min. The mass concentration of the tin acetate ethanol solution is 0.1-0.2 mg / ml; soak the carbon in the ethanol solution at an ultrasonic frequency of 2500-4000 Hz for 20-60 min.

2. The method for preparing the MnO / Sn-NC electrocatalyst according to claim 1, characterized in that, The obtained powder is heated to 1000-1200℃ in a tube furnace at a heating rate of 5-10℃ / min and annealed for 2-3 hours.

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