FeMn oxygen reduction electrocatalyst, preparation method and application thereof

Abstract

The application relates to an FeMn oxygen reduction electrocatalyst and a preparation method and application thereof, the preparation method comprises the following steps: S1, dissolving fumaric acid, an iron source and a manganese source in an organic solvent to obtain a first solution; S2, dissolving hexamethylenetetramine in an organic solvent to obtain a second solution; S3, dissolving zinc nitrate hexahydrate in an organic solvent to obtain a third solution; S4, mixing the first solution and the second solution, and adding the third solution dropwise to react, centrifuging, washing and drying, and then annealing under an inert atmosphere to obtain N-doped porous carbon nanosheets dispersing FeO and FeMn single atoms, which are recorded as SA-FeMn / FeO-NC catalysts. Compared with the prior art, the SA-FeMn / FeO-NC catalyst prepared by the application has a hierarchical porous two-dimensional sheet structure, and shows oxygen reduction electrocatalytic activity and stability superior to commercial Pt / C.

Description

Technical Field

[0001] This invention relates to the field of fuel cells, and in particular to a FeMn oxygen reduction electrocatalyst, its preparation method, and its application. Background Technology

[0002] Proton exchange membrane fuel cells and metal-air batteries, among other novel power technologies, possess significant advantages such as high energy conversion efficiency, cleanliness, and sustainability, and are expected to be widely applied in important fields such as new energy vehicles, distributed stationary power stations, and portable electronic devices. The oxygen reduction reaction (ORR) is one of the key steps in clean energy-related technologies (such as metal-air batteries and fuel cells). This reaction requires multiple electron transfer processes, has a complex reaction mechanism, slow kinetics, and high overpotential. Therefore, efforts have been made to develop highly efficient ORR electrocatalysts to overcome these challenges. It is well known that platinum-based materials remain the best catalysts for this reaction; however, the scarcity and high price of platinum resources, as well as its stability issues (e.g., microcrystal dissolution and nanoparticle agglomeration), have become significant obstacles to the industrialization of fuel cells. Therefore, developing non-precious metal catalysts with high activity, stability, and low cost is crucial.

[0003] Patent CN110504458A discloses a method for preparing bimetallic-nitrogen-doped carbon nanotube electrocatalytic materials, comprising the following steps: (a) dissolving a trivalent iron source compound in a polyvinyl alcohol solution, stirring and adding a nitrogen-containing polymer monomer to obtain a mixed solution A; after polymerization at room temperature for a certain time, polymer nanomaterials are obtained through flocculation, separation, and washing; (b) adding Fe-M bimetallic chloride and low-melting-point chloride salt to the polymer nanomaterials in step a in a certain mass ratio, mixing and drying to obtain a molten salt-coated polymer precursor; wherein, M = Ni, Co, or Mn; (c) placing the molten salt-coated polymer precursor obtained in step b into a tube furnace and annealing it at high temperature under inert gas protection to obtain a carbonized product; (d) pulverizing, acid washing, water washing, and drying the carbonized product obtained in step c to obtain bimetallic-nitrogen-doped carbon nanotube electrocatalytic materials. The catalyst has the morphology of nanoparticles. The preparation method is relatively complex and uses strong acid to wash the catalyst, which is very harmful to the environment. In addition, molten salt is used in the preparation method, and the carbonized material needs to be washed with water in subsequent steps, making the experimental steps cumbersome. Summary of the Invention

[0004] The purpose of this invention is to overcome the defects of the prior art by providing a FeMn oxygen reduction electrocatalyst, its preparation method, and its application.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] One of the technical solutions of the present invention is to provide a method for preparing a FeMn oxygen reduction electrocatalyst, comprising the following steps:

[0007] S1. Dissolve fumaric acid, iron source and manganese source in an organic solvent to obtain the first solution;

[0008] S2. Dissolve hexamethylenetetramine in an organic solvent to obtain a second solution;

[0009] S3. Dissolve zinc nitrate hexahydrate in an organic solvent to obtain a third solution;

[0010] S4. Mix the first solution with the second solution and add the third solution dropwise to react. After centrifugation, washing and drying, anneal under an inert atmosphere to obtain N-doped porous carbon nanosheets dispersed with FeO and FeMn single atoms, which is the FeMn oxygen reduction electrocatalyst, denoted as SA-FeMn / FeO-NC catalyst.

[0011] Furthermore, in step S1, the ratio of organic solvent, fumaric acid, iron source, and manganese source is 10–20 mL: 20–40 mg: 20–50 mg: 10–25 mg.

[0012] Furthermore, in step S1, the iron source is Fe(NO3)3·9H2O, and the manganese source is Mn(CH3COO)2·H2O.

[0013] Furthermore, in steps S1-S3, the organic solvent is ethanol.

[0014] Furthermore, in step S2, the ratio of hexamethylenetetramine to organic solvent is 1 mol: 50–60 mL.

[0015] Furthermore, in step S3, the ratio of zinc nitrate hexahydrate to organic solvent is 1–1.5 mol: 15–20 mL.

[0016] Furthermore, in step S4, the reaction time is 1–3 hours; the drying conditions are: vacuum drying, and the drying temperature is 50–70°C.

[0017] Furthermore, in step S4, the inert atmosphere is argon, and the annealing conditions are: annealing temperature of 700–900℃, annealing time of 1–3 h, and heating rate of 2–5℃ / min.

[0018] The second technical solution of the present invention is to provide a FeMn oxygen reduction electrocatalyst, which is based on the preparation method described in one of the above technical solutions.

[0019] The FeMn oxygen reduction electrocatalyst possesses a hierarchical porous two-dimensional sheet structure. This two-dimensional sheet structure provides more active sites during the reaction, thereby improving catalytic performance. It exhibits superior oxygen reduction electrocatalytic activity and stability compared to commercial Pt / C catalysts.

[0020] The third technical solution of the present invention is to provide an application of the SA-FeMn / FeO-NC catalyst as described in the second technical solution above, wherein the SA-FeMn / FeO-NC catalyst is used as the cathode catalyst of a proton exchange membrane fuel cell.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) This invention provides a simple template-free method for synthesizing N-doped porous carbon nanosheets of FeMn oxygen reduction electrocatalyst, which exhibits high catalytic activity and good stability, demonstrating excellent catalytic activity for ORR. In this catalyst, FeMn exists in atomic form, forming Fe-N or Mn-N bonds with N, serving as the active center of the catalyst. In addition, FeO is also an important active substance in the oxygen reduction reaction, synergistically promoting the oxygen reduction reaction with Fe-N and Mn-N bonds, thus giving SA-FeMn / FeO-NC high catalytic activity and stability. It can be used as a cathode catalyst in proton exchange membrane fuel cells and is a promising ORR material that can replace Pt-based catalysts in fuel cells.

[0023] (2) The FeMn oxygen reduction electrocatalyst of this invention avoids the disadvantage of Pt-based catalysts being limited in application due to their scarcity. At the same time, compared with Fe, Mn hardly reacts with hydrogen peroxide, exhibiting Fenton inactivity. Therefore, the addition of Mn can overcome the drawback of the decrease in catalytic activity caused by the Fenton reaction faced by Fe-based catalysts.

[0024] (3) Experimental results show that, compared with commercial Pt-based catalysts, the FeMn oxygen reduction electrocatalyst of the present invention has higher ORR performance in alkaline media than that of commercial 20% Pt / C catalysts, and has higher stability.

[0025] (4) The raw materials used in this invention are inexpensive and abundant, the preparation process is simple, and the two-dimensional nanosheet materials are synthesized by a template-free method without the need for acid washing and water washing, which is conducive to large-scale production and has high practical value. Attached Figure Description

[0026] Figure 1 This is a transmission electron microscope (TEM) image of the SA-FeMn / FeO-NC catalyst prepared in Example 1.

[0027] Figure 2 The image shows the XRD pattern of the SA-FeMn / FeO-NC catalyst prepared in Example 1.

[0028] Figure 3 The image shows the linear sweep voltammetry results of the catalysts in Example 1 and Comparative Example 1 in 0.1 M KOH solution. Detailed Implementation

[0029] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0030] Unless otherwise specified, the raw materials or processing techniques used in the following embodiments and comparative examples are all conventional commercially available raw materials or conventional processing techniques in the art.

[0031] Example 1:

[0032] A nitrogen-doped porous carbon nanosheet FeMn oxygen reduction electrocatalyst for fuel cells is prepared using the following steps:

[0033] (1) Take 20 mg of fumaric acid, 40 mg of Fe(NO3)3·9H2O and 20 mg of Mn(CH3COO)2·H2O respectively and dissolve them in 10 mL of ethanol solution, and sonicate to dissolve (referred to as solution 1).

[0034] (2) Dissolve 1.4019 g of hexamethylenetetramine in 50 mL of ethanol solution (referred to as solution 2).

[0035] (3) Dissolve 2.9749 g of zinc nitrate hexahydrate in 20 mL of ethanol solution (referred to as solution 3);

[0036] (4) Pour solution 1 into solution 2, and then add solution 3 dropwise to the above mixed solution. React at room temperature for 1 h. Centrifuge the above reaction product, wash it, and place the product in a vacuum at 60 °C. Place the obtained dried product in a porcelain boat and anneal it at 800 °C for 2 h under an argon atmosphere with a heating rate of 2 °C / min. Then cool it to room temperature to obtain N-doped porous carbon nanosheets with FeO and FeMn single atoms dispersed, which is the FeMn oxygen reduction electrocatalyst, denoted as SA-FeMn / FeO-NC catalyst.

[0037] The prepared SA-FeMn / FeO-NC catalyst was analyzed, and its TEM image is shown below. Figure 1 As shown, the overall outline of the SA-FeMn / FeO-NC catalyst is a sheet-like structure. At a magnification of 100 nm, the black dots can be seen to be FeO dispersed on the sheet-like support.

[0038] Its XRD pattern is as follows Figure 2 As shown, the peaks at 36.073°, 41.896°, 60.744°, 72.724°, and 76.522° correspond to PDF#77-2355 of FeO, further confirming the presence of FeO in the SA-FeMn / FeO-NC catalyst. The peaks at 40.932°, 47.615°, and 69.626° correspond to PDF#87-1524 of C3N4, further confirming the presence of C3N4 in the SA-FeMn / FeO-NC catalyst.

[0039] Comparative Example 1:

[0040] Commercially available Pt / C catalyst, purchased from Johnson-Matthery.

[0041] The SA-FeMn / FeO-NC catalyst prepared in Example 1 and the commercial Pt / C catalyst of Comparative Example 1 were tested by rotating disk electrode voltammetry in O2-saturated KOH solution (0.1M) using a linear sweep voltammetry method. The rotation speed was 1600 rpm and the scan rate was 5 mV / s. -1 The result is as follows Figure 3 As shown. From Figure 3 As can be seen, the SA-FeMn / FeO-NC catalyst has a high onset potential (E). onset =1.03V) and a more positive half-wave potential (E 1 / 2 =0.893V), exceeding that of commercial Pt / C catalysts (E onset =0.99V, E 1 / 2 =0.86V), indicating a small overpotential during the ORR process and low energy consumption required to generate ORR intermediates.

[0042] In addition, a linear sweep voltammetry method was used (test conditions: rotation speed 1600 rpm, sweep speed 5 mV / s). -1 The limiting current density (J) of the SA-FeMn / FeO-NC catalyst was measured. L ) reached 5.46 mA cm -2 It is far superior to commercial Pt / C catalysts (J L =5.31mA cm -2 ).

[0043] In summary, this invention employs a simple method to synthesize an N-doped porous carbon nanosheet SA-FeMn / FeO-NC catalyst for ORR electrocatalysis. The SA-FeMn / FeO-NC catalyst with a hierarchical porous structure exhibits excellent oxygen reduction electrocatalytic activity.

[0044] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a FeMn oxygen reduction electrocatalyst, characterized in that, Includes the following steps: S1. Dissolve fumaric acid, Fe(NO3)3·9H2O and Mn(CH3COO)2·H2O in an organic solvent to obtain the first solution; S2. Dissolve hexamethylenetetramine in an organic solvent to obtain a second solution; S3. Dissolve zinc nitrate hexahydrate in an organic solvent to obtain a third solution; S4. Mix the first solution with the second solution and add the third solution dropwise to react. After centrifugation, washing and drying, anneal under an inert atmosphere to obtain N-doped porous carbon nanosheets dispersed with FeO and FeMn single atoms, which is the FeMn oxygen reduction electrocatalyst, denoted as SA-FeMn / FeO-NC catalyst. in, In step S1, the ratio of organic solvent, fumaric acid, Fe(NO3)3·9H2O, and Mn(CH3COO)2·H2O is 10~20 mL: 20~40 mg: 20~50 mg: 10~25 mg; In step S4, the reaction time is 1-3 hours; the drying conditions are: vacuum drying, and the drying temperature is 50-70℃. The inert atmosphere is argon, and the annealing conditions are: annealing temperature of 700~900℃, annealing time of 1~3 h, and heating rate of 2~5 ℃ / min.

2. The preparation method of the FeMn oxygen reduction electrocatalyst according to claim 1, characterized in that, In steps S1-S3, the organic solvent is ethanol.

3. The preparation method of the FeMn oxygen reduction electrocatalyst according to claim 1, characterized in that, In step S2, the ratio of hexamethylenetetramine to organic solvent is 1 mol: 50~60 mL.

4. The preparation method of the FeMn oxygen reduction electrocatalyst according to claim 1, characterized in that, In step S3, the ratio of zinc nitrate hexahydrate to organic solvent is 1~1.5 mol: 15~20 mL.

5. A FeMn oxygen reduction electrocatalyst, characterized in that, The preparation method of the FeMn oxygen reduction electrocatalyst according to any one of claims 1-4.

6. The application of the FeMn oxygen reduction electrocatalyst as described in claim 5, characterized in that, The FeMn oxygen reduction electrocatalyst is used as the cathode catalyst in a proton exchange membrane fuel cell.

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