CN110492114A - A kind of N doping porous carbon oxygen reduction catalyst and its preparation method and application - Google Patents

Abstract

The invention relates to a nitrogen-doped porous carbon-oxygen reduction catalyst and its preparation method and application, belonging to the field of fuel cell catalyst materials. A preparation method of a nitrogen-doped porous carbon-oxygen reduction catalyst, which is obtained by hydrothermal reaction after mixing polyvinylpyrrolidone and polyethylene oxide-polypropylene oxide-polyethylene oxide tri-block copolymer (F127) The intermediate product is obtained by drying the intermediate product to obtain a transparent film-like substance; then carbonizing the transparent film-like substance under nitrogen, washing, drying and grinding the obtained product. The method for preparing the nitrogen-doped nanometer hollow capsule-like porous carbon material is simple in operation, less in flow process, less in equipment investment, good in repeatability, and convenient to solve the problem of difficulty in large-scale production.

Description

A nitrogen-doped porous carbon-oxygen reduction catalyst and its preparation method and application

technical field

The invention relates to a nitrogen-doped porous carbon-oxygen reduction catalyst and its preparation method and application, belonging to the field of fuel cell catalyst materials.

Background technique

In recent years, energy shortage and environmental pollution are two major problems faced by human beings. It is urgent to find an alternative new energy source. As an energy conversion device, fuel cells have the advantages of high energy conversion rate and environmental friendliness. The oxygen reduction reaction at the fuel cell cathode plays a key role in the fuel cell due to its slow kinetic-controlled step that limits the reaction rate of the fuel cell. Although conventional Pt-based materials are the most practical and efficient electrocatalysts for oxygen reduction reactions, they are hindered by high cost and susceptibility to poisoning in the industrialization of fuel cells. Therefore, it is imperative to develop cheap, efficient, high-tolerance and stable electrocatalysts.

Doping with heteroatoms will destroy the electrical neutrality of carbon materials and increase the adsorption sites and oxygen reduction sites of oxygen molecules. Therefore, heteroatom-doped carbon materials have received extensive attention. The radius of N is larger than that of carbon, the electronegativity is slightly smaller than that of carbon, and it is easier to combine with carbon than other heteroatoms such as phosphorus and sulfur. There are 5 electrons in the outer electrons so that nitrogen has a better electron contribution. This nitrogen source comes from pyrrole nitrogen, which can significantly improve the catalytic performance, which is more significant than that of phosphorus, sulfur and other heteroatoms. When N-doped carbon, the interaction between nitrogen atoms and surrounding C atoms leads to the redistribution of charge density and spin density, and then generates some active sites with abundant electrons or lacking electrons on the surface of carbon materials. Therefore, nitrogen doping can improve the electronic binding properties of carbon materials and enhance the catalytic activity. However, the current nitrogen-doped porous carbon-oxygen reduction catalyst experiment mainly uses MgO hard template, the preparation process is cumbersome, and the hard template needs to be removed.

Contents of the invention

In order to find an alternative catalyst and solve the problems of high preparation cost and cumbersome preparation process of the existing catalyst, the present invention provides a preparation method of a nitrogen-doped nano hollow capsule porous carbon-oxygen reduction catalyst with simple preparation process.

In order to realize the above-mentioned purpose of the invention, the present invention adopts the following technical solutions:

One aspect of the present invention provides a method for preparing a nitrogen-doped porous carbon-oxygen reduction catalyst, mixing polyvinylpyrrolidone (PVP) and polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer Afterwards, the intermediate product is obtained through hydrothermal self-assembly, the intermediate product is dried and then carbonized, and the obtained product is washed, dried and ground to obtain the obtained product.

The amount of polyvinylpyrrolidone used in the above preparation method is 10% to 30% of the mass of the polyethylene oxide-polypropylene oxide-polyethylene oxide tri-block copolymer.

Preferably, the polyvinylpyrrolidone is used in an amount of 10% of the mass of the polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer.

The conditions for the hydrothermal self-assembly reaction in the above preparation method are: 25-100° C., heat preservation for 2-24 hours.

In the above preparation method, Zn(OH) ₂ is added before the hydrothermal self-assembly reaction, and the mass ratio of Zn(OH) ₂ to polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer is 1 ~2:4.

In the above preparation method, the carbonization condition is: under nitrogen atmosphere, the temperature is raised to 500-1000°C at a heating rate of 2°C/min-5°C/min, kept for 2-6 hours and then cooled to room temperature with the furnace.

In the above preparation method, the washing is: soaking in 1-8mol/L HCl solution, centrifuging with deionized water at 2500r/min-4000r/min for 5-10min, repeated centrifugation until neutral, and then centrifuging with absolute ethanol for washing.

Preferably, the HCl solution used is a 2mol/L HCl solution.

Another aspect of the present invention provides a nitrogen-doped porous carbon-oxygen reduction catalyst, the catalyst is prepared by the above preparation method, the catalyst is a material with a nano-hollow capsule structure, and its specific surface area is 100-2000 g/m ² .

The third aspect of the present invention provides the application of the nitrogen-doped porous carbon-oxygen reduction catalyst as a fuel cell cathode catalyst material and catalyst carrier material.

Beneficial effects of the present invention: the method of the present invention selects mature commercial raw materials in terms of cost. The triblock copolymer material only contains C, H, and O, and the functional groups are only hydroxyl groups. It is a carbon source that is relatively friendly to the environment, and porous carbon shows The hollow nanocapsule structure, due to its large specific surface area, is more likely to provide electrical transfer paths and oxygen absorption sites. After the introduction of N heteroatoms, the active sites are increased and the catalytic performance is greatly improved.

The catalyst material prepared by using the method of the invention is a three-dimensional porous material with a high specific surface area, has good electrocatalytic performance, and significantly reduces the cost of the catalyst.

The method for preparing the nitrogen-doped porous carbon material of the invention is simple in operation, less in flow process, less in equipment investment, good in repeatability, and convenient to solve the problem of large-scale production.

Description of drawings

Fig. 1 is the characterization figure of embodiment 1 of the present invention; (a) is the SEM image (scale is 200nm) of the nitrogen-doped porous carbon-oxygen reduction catalyst material prepared in embodiment 1; Fig. 1 (b), (c) is The TEM image of the nitrogen-doped porous carbon-oxygen reduction catalyst material prepared in Example 1; Figure 1(d) is an electron diffraction pattern of the nitrogen-doped porous carbon-oxygen reduction catalyst material prepared in Example 1;

Fig. 2 is the XRD spectrogram of the nitrogen-doped porous carbon-oxygen reduction catalyst material prepared in Comparative Examples of the present invention and Examples 1-3;

Fig. 3 is the Raman spectrogram of the nitrogen-doped porous carbon-oxygen reduction catalyst material prepared in Comparative Example 1 and Examples 1-3 of the present invention;

Fig. 4 is the full spectrum and C1s and N1s spectrogram of the nitrogen-doped porous carbon-oxygen reduction catalyst material prepared in embodiment 1; Fig. 4 (a) XPS general spectrogram, Fig. 4 (b) C1s spectrogram, Fig. 4 (c ) N1s spectrogram;

Fig. 5 is a test result figure; Fig. 5 (a) is the 1600rpm polarization curve of the nitrogen-doped porous carbon-oxygen reduction catalyst material prepared by comparative examples and Examples 1 to 3 of the present invention, and Fig. 5 (b) is an embodiment Figure 5(c) is the K-L curve of Example 1, and Figure 5(d) is the cycle life curve of Example 2.

Detailed ways

The following non-limiting examples can enable those skilled in the art to understand the present invention more fully, but do not limit the present invention in any way.

The test methods described in the following examples, unless otherwise specified, are conventional methods; the reagents and materials, unless otherwise specified, can be obtained from commercial sources.

comparative example

1) Take 4g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (abbreviation: F127), add 100ml of deionized water, stir evenly, and obtain a clear and transparent solution.

2) Add 1.6g of zinc hydroxide to the solution, move it into the reaction kettle, set the hydrothermal temperature to 80°C, keep it warm for 12h, then take it out, and dry it at 60°C for 24h to a transparent film-like substance.

3) Carbonize the transparent film-like substance in a tube furnace with nitrogen gas. The carbonization procedure is as follows: from room temperature to 700°C at a heating rate of 2°C/min, keep it warm for 3 hours, then cool to room temperature with the furnace, and take it out; First soak in 2mol/L HCl solution, centrifuge with deionized water at 4000r/min for 5min, repeat centrifugation until neutral, then centrifuge with absolute ethanol, dry and grind.

Example 1

1) Take 4g of F127, add 100ml of deionized water, stir well, and get a clear and transparent solution.

2) Add 10% polyvinylpyrrolidone (PVP) based on the mass of F127, that is, 0.4 g of PVP, and stir evenly to obtain a clear and transparent solution.

3) Add 1.6g of zinc hydroxide to the solution, move it into the reaction kettle, set the hydrothermal temperature at 80°C, keep it warm for 12h, then take it out, and dry it at 60°C for 24h to a transparent film-like substance.

4) Carbonize the transparent film-like substance in a tube furnace with nitrogen gas. The carbonization procedure is as follows: from room temperature to 700°C at a heating rate of 2°C/min, keep it warm for 3 hours, then cool to room temperature with the furnace, and take it out; First soak in 2mol/L HCl solution, centrifuge with deionized water at 4000r/min for 5min, repeat centrifugation until neutral, then centrifuge with absolute ethanol, dry and grind.

Example 2

1) Take 4g of F127, add 100ml of deionized water, stir well, and get a clear and transparent solution.

2) Add 20% polyvinylpyrrolidone (PVP) based on the mass of F127, that is, 0.8 g of PVP, and stir evenly to obtain a clear and transparent solution.

3) Add 1.6g of zinc hydroxide to the solution, move it into the reaction kettle, set the hydrothermal temperature at 80°C, keep it warm for 12h, then take it out, and dry it at 60°C for 24h to a transparent film-like substance.

4) Carbonize the transparent film-like substance in a tube furnace with nitrogen gas. The carbonization procedure is as follows: from room temperature to 700°C at a heating rate of 2°C/min, keep it warm for 3 hours, then cool to room temperature with the furnace, and take it out; First soak in 2mol/L HCl solution, centrifuge with deionized water at 4000r/min for 5min, repeat centrifugation until neutral, then centrifuge with absolute ethanol, dry and grind.

Example 3

1) Take 4g of F127, add 100ml of deionized water, stir well, and get a clear and transparent solution.

2) Add 30% polyvinylpyrrolidone (PVP) by mass of F127, namely 1.2 g of PVP, and stir evenly to obtain a clear and transparent solution.

3) Add 1.6g of zinc hydroxide to the solution, move it into the reaction kettle, set the hydrothermal temperature at 80°C, keep it warm for 12h, then take it out, and dry it at 60°C for 24h to a transparent film-like substance.

4) Carbonize the transparent film-like substance in a tube furnace with nitrogen gas. The carbonization procedure is as follows: from room temperature to 700°C at a heating rate of 2°C/min, keep it warm for 3 hours, then cool to room temperature with the furnace, and take it out; First soak in 2mol/L HCl solution, centrifuge with deionized water at 4000r/min for 5min, repeat centrifugation until neutral, then centrifuge with absolute ethanol, dry and grind.

Effect example: In order to explore the morphology characteristics and electrochemical performance of the prepared nitrogen-doped carbon catalyst, SEM, XRD, XPS, Raman and other means were used to physically characterize the prepared product and prepare the product into an electrode to test the corresponding electrochemical performance.

Fig. 1 (a) is the SEM photo (scale is 200nm) of the nitrogen-doped carbon catalyst prepared in embodiment 1, it can be seen from Fig. 1 (a) SEM photo that under 50000 times magnification, it is nanocapsule-like porous carbon; From the TEM photos of Figure 1(b)(c), it can be seen that the interior is a hollow structure with a wall thickness of about 5nm, and Figure 1(d) is its electron diffraction ring, indicating a high degree of graphitization.

Fig. 2 (a) shows the XRD spectrograms of the nitrogen-doped carbon catalysts prepared in Comparative Examples and Examples 1 to 3, corresponding to the (002) crystal plane at 2θ=29°, which is graphitized carbon, polyvinylpyrrolidone doped The size of the peak varies with the amount of impurity, and the peak is the largest when the addition ratio is 10%. It shows that C-N-10% has a high degree of graphitization and good electrical conductivity. The Raman spectrum is shown in Figure 3. D peak appears at 1350cm-1, G peak appears at 1580cm-1. It can be seen from the D peak and G peak that there is a good defect degree and graphitization degree.

The full spectrum and C1s and N1s spectra of the material obtained in Example 1 are shown in Figure 4(a)-(c). From Figure 4(a), it can be clearly found that there are C and N elements, and the presence of sp3-C, sp2-C, and C-N can be analyzed in the spectrum of C1s. In the N1s spectrum, pyrrole nitrogen, pyridine nitrogen, and graphitic nitrogen can be analyzed, and the proportion of pyrrole nitrogen is relatively large, indicating that N has been doped into carbon.

The prepared catalyst was coated on the glassy carbon electrode, and the cyclic voltammetry, polarization curve and stability tests were carried out in 0.1M KOH solution. The test results are shown in Figure 5.

It can be seen from Fig. 5(a) that F127 is a carbon material with a molecular weight of Mn=12600g/mol, without adding Zn(OH) ₂ , and without adding PVP. In the polarization curve of 1600rpm of the catalyst material of different ratios, when the PVP ratio of adding is 10%, embodies optimal performance: very good starting potential, very good limiting current density (embodiment 1), from Fig. 5(b) It can be seen that the limiting current density of the catalyst in Example 1 increases with the increase of the number of revolutions of the rotating disk, indicating that the diffusion layer is very thin, indicating that there are many active sites. Figure 5(c) shows the number of transferred electrons at each potential, and the number of transferred electrons calculated according to the KL formula is 3.98, which is conducive to four-electron transfer and is suitable for oxygen reduction catalysts. It can be seen from Figure 5(d) that the measured polarization curve decays little after 2000 and 5000 cycles, indicating that the stability is very good.

For any person skilled in the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or be modified to be equivalent to equivalent changes. Example. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention should still fall within the protection scope of the technical solution of the present invention.

Claims (9)

1. a kind of preparation method of N doping porous carbon oxygen reduction catalyst, it is characterised in that: by polyvinylpyrrolidone and gather Obtain intermediate product through hydro-thermal self assembly after the mixing of oxide-polypropylene oxide-polyethylene oxide triblock copolymer, will in Between product it is dry after be carbonized, products therefrom washing, dry, grinding, both.

2. a kind of preparation method of N doping porous carbon oxygen reduction catalyst according to claim 1, it is characterised in that: institute The dosage for stating polyvinylpyrrolidone is polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer amount of substance 10%~30%.

3. a kind of preparation method of N doping porous carbon oxygen reduction catalyst according to claim 2, it is characterised in that: institute The dosage for stating polyvinylpyrrolidone is polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer amount of substance 10%.

4. a kind of preparation method of N doping porous carbon oxygen reduction catalyst according to claim 1, it is characterised in that: institute State hydro-thermal self-assembling reaction condition are as follows: 25~100 DEG C, heat preservation 2~for 24 hours.

5. a kind of preparation method of N doping porous carbon oxygen reduction catalyst according to claim 1, which is characterized in that water Zn (OH) is added before hot self-assembling reaction₂, Zn (OH)₂With polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer The mass ratio of object is 1~2:4.

6. a kind of preparation method of N doping porous carbon oxygen reduction catalyst according to claim 1, which is characterized in that institute State Carbonization Conditions are as follows: under nitrogen atmosphere, 500~1000 DEG C are warming up to 2 DEG C/min~5 DEG C/min heating rate, heat preservation 2~ Cool to room temperature after 6h with the furnace.

7. a kind of preparation method of N doping porous carbon oxygen reduction catalyst according to claim 1, which is characterized in that institute State washing are as follows: impregnated using 1~8mol/LHCl solution, under 2500r/min~4000r/min with deionized water centrifugation 5~ Then 10min, repeated centrifugation to neutrality use dehydrated alcohol eccentric cleaning.

8. a kind of N doping porous carbon oxygen reduction catalyst, which is characterized in that the catalyst is by any one of claim 1~7 The method is prepared.

9. N doping porous carbon oxygen reduction catalyst is as fuel battery cathod catalyst material and catalyst described in claim 8 The application of carrier material.