N, P, S / Fe co-doped carbon catalyst and preparation method and application thereof

Abstract

The invention belongs to the field of electrochemistry, and particularly relates to an N, P and S / Fe co-doped carbon catalyst and a preparation method and application thereof.The preparation method comprises the following steps that S1, silkworm excrement is soaked in a ferric salt solution and mixed to be uniform; s2, drying the mixed solution obtained in the step S1; and S3, performing pyrolysis carbonization on the solid product obtained by drying in the step S2, performing acid treatment, washing, and drying to obtain the N, P, S / Fe co-doped carbon catalyst. Compared with the prior art, the problems that in the prior art, a preparation method is complex, the cost is high, more chemical reagents are used, and the environment is not friendly are solved; according to the scheme, the multi-heteroatom co-doped catalyst material which is simple in preparation method, low in cost, environment-friendly and good in catalytic performance is realized.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemistry, and particularly relates to an N, P, S / Fe co-doped carbon catalyst, a preparation method thereof and an application thereof. Background Art

[0002] A fuel cell is a device that can directly convert the chemical energy of a fuel into electrical energy. Different from ordinary batteries, fuel cells have no capacity limit. In theory, as long as fuel is continuously supplied to the fuel cell, it can continuously output electrical energy. Since there is no heat engine process in the whole energy conversion process, fuel cells are not restricted by the Carnot cycle, so fuel cells generally have a relatively high energy conversion rate. However, so far, fuel cells have not been mass-produced and applied on a large scale, and an important restricting factor is its cathode catalyst. Currently, such catalysts mainly use precious metals, especially platinum-based materials. Due to their scarcity, high cost, poor long-term durability and carbon monoxide poisoning, it is of great significance to replace the precious platinum catalyst with a cheap and commercially available ORR material.

[0003] Porous carbon materials have been widely used in catalysts, catalyst carriers, supercapacitors and lithium-ion batteries due to their good conductivity and high specific surface area. Carbon containing doped elements, such as nitrogen (N), sulfur (S), phosphorus (P), boron (B) and fluorine (F), as well as transition metal elements, such as Fe, Co, Ni and their metal carbides, nitrides, oxides, have been proven to be promising candidate materials for ORR electrocatalysts. When heteroatoms are doped into porous carbon materials, the charge density of the porous carbon materials increases, forming an n-type semiconductor, thereby increasing the conductivity of the porous carbon materials. The introduction of heteroatoms into the structure of porous carbon materials will also increase the defect sites of the porous carbon materials and improve the catalytic activity of the catalyst.

[0004] As disclosed in "Salt assisted fabrication of lignin-derived Fe,N,P,S codoped porous carbon as trifunctional catalyst for Zn-air batteries and water-splitting devices", a trifunctional catalyst (Fe-N-C / FeP) in which FeN x and FeP x are coupled with an N / P / S doped carbon skeleton x / NPSC); for another example, "Modulating Coordination of Iron Atom Clusters on N,P,S Triply-Doped Hollow Carbon Support towards Enhanced Electrocatalytic Oxygen Reduction" discloses the construction of metal ACs in a triply-doped hollow carbon matrix of N, P, and S (MACs / NPS-HC, M = Mn, Fe, Co, Ni, Cu). However, the preparation methods disclosed in the prior art all use the template method to construct the precursor and then obtain the catalyst material co-doped with multiple heteroatoms through calcination and carbonization. The process is complex and requires strict control of the preparation parameters, resulting in still relatively high production costs; and a large amount of chemical reagents need to be used, and post-treatment is required to avoid environmental pollution, further increasing the process cost.

[0005] Therefore, there is a need to propose a preparation method for a catalyst material co-doped with multiple heteroatoms that is simple, low-cost, environmentally friendly, and has good catalytic performance. Summary of the Invention

[0006] The purpose of the present invention is to provide an N, P, S / Fe co-doped carbon catalyst, its preparation method and application to solve at least one of the above problems, so as to solve the problems of complex preparation methods, high costs, large amounts of chemical reagents used, and environmental unfriendliness in the prior art; this solution realizes a catalyst material co-doped with multiple heteroatoms that has a simple preparation method, low cost, is environmentally friendly, and has good catalytic performance.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] The first aspect of the present invention discloses a preparation method for an N, P, S / Fe co-doped carbon catalyst, including the following steps:

[0009] S1: Immerse silkworm excrement in an iron salt solution and mix evenly;

[0010] S2: Dry the mixture obtained in step S1;

[0011] S3: Pyrolyze and carbonize the solid product obtained by drying in step S2, wash and dry after acid treatment to obtain the N, P, S / Fe co-doped carbon catalyst.

[0012] Preferably, in step S1, the iron salt solution is obtained by dissolving ferric nitrate hexahydrate in deionized water.

[0013] Preferably, the mass ratio of silkworm excrement to ferric nitrate hexahydrate is 2-5:1-5.

[0014] Preferably, in step S2, the drying is vacuum drying, the temperature is 60 - 80 °C, and the time is 12 - 24 h.

[0015] Preferably, in step S3, for the pyrolytic carbonization: under an inert atmosphere, the heating rate is 5 °C / min, the carbonization temperature is 600 - 800 °C, and the carbonization time is 1 - 4 h.

[0016] Preferably, in step S3, the acid treatment is: impregnating the carbonized product in a sulfuric acid solution to remove soluble impurities.

[0017] Preferably, the concentration of the sulfuric acid solution is 0.5 - 5 mol·L -1 ; the impregnation time is 4 - 12 h.

[0018] Preferably, in step S3, the washing is: washing with deionized water until the pH of the residual water is neutral; the drying is vacuum drying.

[0019] The second aspect of the present invention discloses an N, P, S / Fe co-doped carbon catalyst prepared by any of the above methods.

[0020] The third aspect of the present invention discloses an application of the above-mentioned N, P, S / Fe co-doped carbon catalyst in a fuel cell.

[0021] The working principle of the present invention is:

[0022] As a biomass material rich in heteroatoms, silkworm excrement has the advantages of being cheap, easily available, and environmentally friendly. The abundant heteroatoms nitrogen, phosphorus, and sulfur therein can coordinate with transition metals to form active sites effective for ORR. Demetallization and carbon corrosion are the main reasons affecting the stability of non-precious metal catalysts. Introducing the transition metal Fe into the catalyst can also catalyze the graphitization of the carbon matrix and form a graphitized encapsulation around the metal Fe particles, thereby ensuring the stability of the activity of the prepared catalyst. The pore structure generated during the pyrolysis process and the pickling process enables the catalyst to have a large specific surface area, thereby exposing more active sites. Cooperating with the partially graphitized carbon matrix, the N, P, S / Fe-co-doped carbon material can thus have excellent oxygen reduction catalytic activity and stability.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The preparation method is simple: directly impregnating, drying, calcining, and then acid treating can obtain a heteroatom co-doped carbon material.

[0025] (2) The silkworm excrement used is a biomass material, that is, the excrement of silkworms, which is rich in resources, cheap and easily available, and has abundant and uniformly distributed natural heteroatoms and a porous hierarchical system structure.

[0026] (3) The catalyst used has a hierarchical porous structure and a high specific surface area, which can expose more pyridine N, Fe-N x , Fe-P x and Fe-S x and other active sites beneficial to ORR, thus improving the catalytic activity. The Fe nanoparticles encapsulated by graphite layers are embedded in partially graphitized porous carbon, ensuring the stability of the catalyst. The coexistence of graphitized carbon and amorphous carbon can synergistically balance the conductivity and defect sites beneficial to the ORR process, so that the prepared catalyst has excellent oxygen reduction activity under alkaline conditions, certain activity in acid, and better stability than commercial Pt / C catalysts. Description of the Drawings

[0027] Figure 1 SEM image (50000x) of the N, P, S / Fe co-doped carbon catalyst prepared in Example 1;

[0028] Figure 2 TEM image of the metal particles of the N, P, S / Fe co-doped carbon catalyst prepared in Example 1;

[0029] Figure 3 Nitrogen adsorption-desorption isotherm of the N, P, S / Fe co-doped carbon catalyst prepared in Example 1;

[0030] Figure 4 X-ray photoelectron spectroscopy analysis chart of the N, P, S / Fe co-doped carbon catalyst prepared in Example 1;

[0031] Figure 5 Chronoamperometry curves of the N, P, S / Fe co-doped carbon catalyst prepared in Example 1 and commercial platinum-carbon catalyst;

[0032] Figure 6 Cyclic voltammetry curves of the N, P, S / Fe co-doped carbon catalysts prepared in Examples 1-3 in an alkaline environment;

[0033] Figure 7 Cyclic voltammetry curve of the N, P, S / Fe co-doped carbon catalyst prepared in Example 1 in an alkaline environment. Detailed Embodiments

[0034] The present invention will be described in detail below with reference to the drawings and specific embodiments.

[0035] In the following description, if not otherwise specified, the reagents used are conventional commercially available products, and the methods used are well-known means in the art.

[0036] In the present invention, biomass feces of silkworms (abbreviated as FB), which is rich in resources, environmentally friendly, inexpensive and easy to obtain, and contains heterogeneous elements (nitrogen, phosphorus and sulfur), is used as a carbon source. The silkworm feces is impregnated in a prepared iron nitrate solution, and then dried to obtain a catalyst precursor. The precursor is then pyrolyzed and carbonized in an inert atmosphere, and finally impurities are removed by acid etching to obtain an N, P, S / Fe co-doped carbon material oxygen reduction catalyst (FBC-Fe). As follows, FB is the abbreviation of silkworm feces, and FBC is the abbreviation after carbonization of silkworm feces. Because iron (Fe) is compounded in it, for the convenience of labeling, it is abbreviated as FBC-Fe.

[0037] A preparation method of a silkworm feces-derived N, P, S / Fe-co-doped carbon as an effective electrocatalyst for the oxygen reduction reaction is as follows:

[0038] 1) Immerse the silkworm feces in an aqueous solution dissolving iron nitrate, and stir and mix evenly at room temperature;

[0039] 2) Dry the mixed system in step 1) in a vacuum oven;

[0040] 3) Put the dried product obtained in step 2) into a tubular furnace, under an inert atmosphere, heat up to 600-800 °C at a rate of 5 °C / min and carbonize for 1-4 hours. Finally, immerse the carbonized sample in a sulfuric acid solution, stir to remove soluble impurities, then wash with deionized water until the pH of the residual water is neutral, and then dry in vacuum to obtain an N, P, S / Fe-co-doped carbon oxygen reduction catalyst.

[0041] In the above step 1), the mass ratio of the silkworm feces to iron nitrate hexahydrate is (2-5):(1-5).

[0042] In the above step 2), the drying conditions are a temperature of 60-80 °C and a time of 12-24 h.

[0043] In the above step 3), the concentration of the sulfuric acid solution is 0.5-5 mol·L -1 , and the impregnation and stirring time is 4-12 hours.

[0044] The present invention also provides an N, P, S / Fe-co-doped carbon oxygen reduction catalyst prepared by the above preparation method.

[0045] The present invention further provides an application of the above N, P, S / Fe-co-doped carbon oxygen reduction catalyst.

[0046] The described N, P, S / Fe-co-doped carbon material is applied to a fuel cell cathode oxygen reduction catalyst.

[0047] The information on the models and manufacturers of the instruments or equipment used in the examples of the present invention is as follows:

[0048] Blast drying oven, model DHG-9920A, manufacturer: Shanghai Yiheng Scientific Instrument Co., Ltd.;

[0049] Scanning electron microscope (SEM), model Phenom Pro X, manufacturer: Phenom-World B.V. (Netherlands);

[0050] Transmission electron microscope (TEM), model: JEM-2010HT, manufacturer: JEOL Ltd. (Japan);

[0051] X-ray photoelectron spectrometer, model: AXIS UltraDLD, manufacturer: Shimadzu Corporation (Japan);

[0052] Electrochemical workstation, model: Autolab PGSTAT302N, manufacturer: Metrohm AG (Switzerland).

[0053] In the examples of the present invention, the cyclic voltammogram of the sample was measured on an Autolab PGSTAT302N electrochemical workstation. The specific test conditions were as follows: under a three-electrode system, with Ag / AgCl as the reference electrode, a platinum wire as the counter electrode, and a glassy carbon electrode loaded with the catalyst as the working electrode, the scanning rate was 10 mV / s; the preparation process of the working electrode was as follows: 5 mg of the catalyst was dissolved in a mixed solution of 1 mL of ethanol and 50 μL of Nafion (5% solution, purchased from DuPont Company, USA), and after ultrasonic dispersion, 10 μL was taken and dropped onto the glassy carbon electrode. After drying at room temperature, it was the working electrode. When performing the cyclic voltammogram test, nitrogen and oxygen were respectively introduced into a 0.1 M KOH electrolyte solution to create a nitrogen / oxygen atmosphere. Before the test, the electrode was cycled 10 times in the electrolyte solution to activate the electrode, and then the test was carried out.

[0054] In the embodiments of the present invention, the cyclic voltammetry curve of the sample was measured on an Autolab PGSTAT302N electrochemical workstation. The test conditions were as follows: under a three-electrode system, with Ag / AgCl as the reference electrode, a platinum sheet as the counter electrode, and a rotating disk electrode loaded with the catalyst as the working electrode, 0.1 M KOH as the electrolyte solution, and a scanning rate of 10 mV / s; in the acidic environment test, the electrolyte solution was 0.5 M H2SO4 aqueous solution, and the test method was the same as that in the alkaline medium. The preparation process of the working electrode was as follows: 5 mg of the catalyst was dissolved in a mixed solution of 1 mL of ethanol and 50 μL of Nafion (5% solution, purchased from DuPont, USA), ultrasonically dispersed, and then 10 μL was taken and dropped onto the rotating disk electrode. After drying at room temperature, it became the working electrode. When performing the cyclic voltammetry curve test, nitrogen and oxygen were respectively introduced into the 0.1 M KOH electrolyte solution to create a nitrogen / oxygen atmosphere. Before the test, the electrode was cycled 10 times in the electrolyte solution to activate the electrode. When testing in an oxygen atmosphere, the cyclic voltammetry curves of the test electrode were measured under different rotation speeds (400 - 2000 rpm).

[0055] In the embodiments of the present invention, the chronoamperometry curve of the sample was measured on an Autolab PGSTAT302N electrochemical workstation. The test conditions were as follows: under a three-electrode system, with Ag / AgCl as the reference electrode, a platinum sheet as the counter electrode, and a rotating disk electrode loaded with the catalyst as the working electrode, 0.1 M KOH as the electrolyte solution, and a scanning rate of 10 mV / s; the preparation process of the working electrode was as follows: 5 mg of the catalyst was dissolved in a mixed solution of 1 mL of ethanol and 50 μL of Nafion (5% solution, purchased from DuPont, USA), ultrasonically dispersed, and then 10 μL was taken and dropped onto the rotating disk electrode. After drying at room temperature, it became the working electrode. The test conditions for the chronoamperometry curve were as follows: at a constant potential of -0.35 V and a rotation speed of 1600 rpm, the change in current over time within 10000 s was measured.

[0056] Example 1

[0057] 2.5 g of silkworm excrement was impregnated in an aqueous solution containing 1.0 g of ferric nitrate hexahydrate and stirred at room temperature for 12 h until the silkworm excrement was completely impregnated. The mixed system was dried in a vacuum oven; then the obtained dried product was placed in a tubular furnace and carbonized at 800 °C for 2 h under an inert atmosphere at a heating rate of 5 °C / min. Finally, the carbonized sample was impregnated and stirred in a sulfuric acid solution to remove soluble impurities, then washed with deionized water until the pH of the residual water was neutral, and then vacuum dried to obtain the N, P, S / Fe-codoped carbon oxygen reduction catalyst.

[0058] From Figure 1 、 2The distribution of carbon, oxygen, nitrogen, phosphorus, sulfur, and iron elements in the material is known, and the material has a good porous structure.

[0059] Figure 3 The typical type-IV mesoporous curve also proves that the synthesized N, P, S / Fe-codoped carbon has a good mesoporous structure.

[0060] From Figure 4 it can be seen that there are only three elements in the nitrogen-doped carbon spheres, and the contents of carbon, oxygen, nitrogen, phosphorus, sulfur, and iron elements are 90.16%, 6.42%, 1.53%, 0.37%, 1.31%, and 0.12% respectively.

[0061] From Figure 5 it can be seen that after 10,000 s, the current density of this catalyst remains at 97.5%, while that of the commercial platinum-carbon catalyst (20%, brand: Johnmn Matthey) is 87%, indicating that the catalyst prepared in Example 1 has significantly better durability than the commercial platinum-carbon catalyst.

[0062] From Figure 6 it can be seen that at a voltage of 0.8 V vs. RHE, the N, P, S / Fe-codoped porous carbon has obvious oxygen reduction performance.

[0063] Figure 7 This is the CV curve diagram of the catalyst in an acidic environment. The peak value of the FBC-Fe curve is 0.55 V (RHE). Although the catalytic activity is not as high as that in the alkaline environment, it still indicates that the catalyst has good potential for application in an acidic environment.

[0064] Example 2

[0065] 2.5 g of silkworm excrement was impregnated in an aqueous solution containing 1.0 g of ferric nitrate hexahydrate, stirred at room temperature for 12 h until the silkworm excrement was completely impregnated, and the mixed system was dried in a vacuum oven; then the obtained dried product was placed in a tubular furnace, and under an inert atmosphere, it was heated to 600 °C at a rate of 5 °C / min and carbonized for 2 h. Finally, the carbonized sample was impregnated and stirred in a sulfuric acid solution to remove soluble impurities, then washed with deionized water until the pH of the remaining water was neutral, and then dried in vacuum to obtain the N, P, S / Fe-codoped carbon oxygen reduction catalyst.

[0066] From Figure 6 it can be seen that at a voltage of 0.77 V vs. RHE, the N, P, S / Fe-codoped porous carbon has an obvious oxygen peak, indicating that the catalyst has certain oxygen reduction performance.

[0067] Example 3

[0068] 2.5 g of silkworm excrement was impregnated in an aqueous solution containing 1.0 g of ferric nitrate hexahydrate and stirred at room temperature for 12 h until the silkworm excrement was completely impregnated. The mixed system was dried in a vacuum oven. Then, the obtained dried product was placed in a tube furnace and carbonized at 700 °C for 2 h at a heating rate of 5 °C / min under an inert atmosphere. Finally, the carbonized sample was impregnated and stirred in a sulfuric acid solution to remove soluble impurities, washed with deionized water until the pH of the residual water was neutral, and then dried in vacuo to obtain the N, P, S / Fe-codoped carbon oxygen reduction catalyst.

[0069] It can be seen from Figure 6 that at a voltage of 0.64 V vs. RHE, the N, P, S / Fe-codoped porous carbon has an obvious oxygen peak, indicating that the catalyst has certain oxygen reduction performance.

[0070] Example 4

[0071] 1.5 g of silkworm excrement was impregnated in an aqueous solution containing 1.0 g of ferric nitrate hexahydrate and stirred at room temperature for 12 h until the silkworm excrement was completely impregnated. The mixed system was dried in a vacuum oven. Then, the obtained dried product was placed in a tube furnace and carbonized at 800 °C for 2 h at a heating rate of 5 °C / min under an inert atmosphere. Finally, the carbonized sample was impregnated and stirred in a sulfuric acid solution to remove soluble impurities, washed with deionized water until the pH of the residual water was neutral, and then dried in vacuo to obtain the N, P, S / Fe-codoped carbon oxygen reduction catalyst.

[0072] The materials used in the present invention are inexpensive and easily available, and the preparation method is simple and easy for large-scale production. The prepared catalyst has obvious oxygen reduction characteristic peaks. Compared with the commercial Pt / C catalyst, the catalyst has low cost and good stability.

[0073] The above description of the embodiments is provided to enable those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A preparation method of an N, P, S / Fe co-doped carbon catalyst, characterized in that, It includes the following steps: S1: Immerse silkworm excrement in an iron salt solution and mix evenly; S2: Dry the mixture obtained in step S1; S3: Pyrolyze and carbonize the solid product obtained by drying in step S2, wash and dry it after acid treatment to obtain an N, P, S / Fe co-doped carbon catalyst.

2. The preparation method of an N, P, S / Fe co-doped carbon catalyst according to claim 1, characterized in that, In step S1, the iron salt solution is obtained by dissolving ferric nitrate hexahydrate in deionized water.

3. The preparation method of an N, P, S / Fe co-doped carbon catalyst according to claim 2, wherein, The mass ratio of silkworm excrement to ferric nitrate hexahydrate is 2 - 5:1 - 5.

4. The preparation method of an N, P, S / Fe co-doped carbon catalyst according to claim 1, characterized in that, In step S2, the drying is vacuum drying, the temperature is 60 - 80 °C, and the time is 12 - 24 h.

5. The preparation method of an N, P, S / Fe co-doped carbon catalyst according to claim 1, characterized in that, In step S3, for the pyrolysis and carbonization: under an inert atmosphere, the heating rate is 5 °C / min, the carbonization temperature is 600 - 800 °C, and the carbonization time is 1 - 4 h.

6. The preparation method of an N, P, S / Fe co-doped carbon catalyst according to claim 1, characterized in that, In step S3, the acid treatment is: Immerse the carbonized product in a sulfuric acid solution to remove soluble impurities.

7. The preparation method of an N, P, S / Fe co-doped carbon catalyst according to claim 6, characterized in that, The concentration of the sulfuric acid solution is 0.5 to 5 mol·L -1 ; the impregnation time is 4 to 12 h.

8. The preparation method of an N, P, S / Fe co-doped carbon catalyst according to claim 1, characterized in that, In step S3, the washing is: Wash with deionized water until the pH of the remaining water is neutral; the drying is vacuum drying.

9. A N, P, S / Fe co-doped carbon catalyst, characterized in that, It is prepared by using the method described in any one of claims 1 - 8.

10. Application of an N, P, S / Fe co-doped carbon catalyst as described in claim 9 in a fuel cell.

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