阅读说明：本技术 磷、氮共掺杂多孔碳阴极氧还原铁基催化剂、制备及应用 (Phosphorus and nitrogen co-doped porous carbon cathode oxygen reduction iron-based catalyst, preparation and application ) 是由 江畔 金具涛 施志聪 于 2020-03-20 设计创作，主要内容包括：本发明属于催化技术领域,涉及一种磷、氮共掺杂多孔碳铁基催化剂；所述催化剂具有三维多孔结构、比表面积为每克1000-2000平方米,孔隙率为每克1-2立方厘米；磷和铁原子结合,负载在掺杂氮的石墨碳上,构成新型催化剂。该催化剂用湿化学的方法制备前躯体,随后用热解法制得。与现有技术相比,该方法简单易行,制备过程无需任何模板,其低成本有望成为代替铂基催化剂的候选材料。此外,本实验用氢氧化钾二次活化催化剂,增加其石墨化程度,提高催化剂的稳定性和疏水性,是一种良好的阴极氧还原催化剂；不仅可以用在质子交换膜燃料电池中,还也可以扩展到其他应用,比如析氢、析氧,也可用到锂电池和金属-空气电池中。(The invention belongs to the technical field of catalysis, and relates to a phosphorus and nitrogen co-doped porous carbon iron-based catalyst; the catalyst has a three-dimensional porous structure, the specific surface area is 1000 and 2000 square meters per gram, and the porosity is 1-2 cubic centimeters per gram; phosphorus and iron atoms are combined and loaded on the graphite carbon doped with nitrogen to form the novel catalyst. The catalyst is prepared by a precursor prepared by a wet chemical method and then a pyrolysis method. Compared with the prior art, the method is simple and easy to implement, does not need any template in the preparation process, and is expected to become a candidate material for replacing a platinum-based catalyst at low cost. In addition, the potassium hydroxide secondary activation catalyst for the experiment increases the graphitization degree of the catalyst, improves the stability and hydrophobicity of the catalyst, and is a good cathode oxygen reduction catalyst; it can be used not only in proton exchange membrane fuel cells, but also in other applications, such as hydrogen evolution, oxygen evolution, lithium batteries and metal-air batteries.)

1. A phosphorus and nitrogen co-doped porous carbon cathode oxygen reduction iron-based catalyst is characterized in that: the catalyst has a three-dimensional porous structure, a specific surface area of 1000 and 2000 square meters per gram and a porosity of 1-2 cubic centimeters per gram.

2. The preparation method of the phosphorus and nitrogen co-doped porous carbon cathode oxygen reduction iron-based catalyst according to claim 1, characterized by comprising the following steps: the preparation method of the iron-based catalyst comprises the following steps:

step 1, respectively adding phosphoric acid and pentaerythritol into a round-bottom flask according to certain mass, stirring and reacting for certain time at certain temperature to obtain a product solution of the phosphoric acid and the pentaerythritol;

step 2, adding a certain amount of nitrogen precursor, carbon precursor and iron precursor into a certain amount of absolute ethyl alcohol, and stirring for a certain time at room temperature;

step 3, cooling the mixture in the step 1, adding the solution in the step 2 into the mixture in the step 1, reacting for a certain time at a certain temperature, and then performing rotary evaporation and drying to obtain white powder;

step 4, pyrolyzing the white powder obtained in the step 3 in a tube furnace to obtain a powdery intermediate product;

step 5, mixing the powder obtained in the step 4 with potassium hydroxide according to a certain weight ratio, and simultaneously carrying out secondary carbonization in a tubular furnace to obtain a catalyst;

and 6, carrying out acid washing on the obtained catalyst, then washing with deionized water, and carrying out vacuum drying to prepare the iron-based catalyst.

3. The preparation method of the phosphorus and nitrogen co-doped porous carbon cathode oxygen reduction iron-based catalyst according to claim 2, characterized in that: 29.6 g of phosphoric acid in the step 1; pentaerythritol 6.8 g; the volume of the round-bottom flask is 250 ml; the reaction was carried out in a rotary evaporator at 120 ℃ for 2 hours.

4. The preparation method of the phosphorus and nitrogen co-doped porous carbon cathode oxygen reduction iron-based catalyst according to claim 2, characterized in that: in the step 2, the nitrogen precursor is melamine, and the dosage of the nitrogen precursor is 13.6 g; the carbon precursor is glucose, and the dosage is 0.5 g; the iron precursor is ferric trichloride, and the dosage is 2.6 g; the absolute ethyl alcohol is 120 ml, and the stirring temperature is room temperature; the stirring time was 2 hours.

5. The preparation method of the phosphorus and nitrogen co-doped porous carbon cathode oxygen reduction iron-based catalyst according to claim 2, characterized in that: the reaction temperature in the step 3 is 80 ℃; the reaction time was 6 hours.

6. The preparation method of the phosphorus and nitrogen co-doped porous carbon cathode oxygen reduction iron-based catalyst according to claim 2, characterized in that: in the step 4, the pyrolysis temperature in the tubular furnace is 450 ℃, and the heating rate is 5 ℃ per minute; the carbonization time was 1 hour.

7. The preparation method of the phosphorus and nitrogen co-doped porous carbon cathode oxygen reduction iron-based catalyst according to claim 2, characterized in that: in the step 5, the powder obtained in the step 4 is mixed with potassium hydroxide according to the weight ratio of 5:1, the secondary carbonization temperature is 800 ℃, and the heating rate is 5 ℃ per minute; the carbonization time was 2 hours.

8. The preparation method of the phosphorus and nitrogen co-doped porous carbon cathode oxygen reduction iron-based catalyst according to claim 2, wherein in the step 6, the sulfuric acid concentration is 0.5 mol/L, the pickling temperature is 80 ℃, the pickling time is 12 hours, and all water is deionized water.

9. The application of the phosphorus and nitrogen co-doped porous carbon cathode oxygen reduction iron-based catalyst in claim 1, wherein: the phosphorus and nitrogen co-doped porous carbon cathode oxygen reduction iron-based catalyst is used in an alkaline environment.

10. The use of the phosphorus and nitrogen co-doped porous carbon cathode oxygen reduction iron-based catalyst according to claim 9, wherein: the phosphorus and nitrogen co-doped porous carbon cathode oxygen reduction iron-based catalyst is used in a lithium metal or metal-air fuel cell.

Technical Field

The invention belongs to the field of energy materials and electrochemistry, and particularly relates to a phosphorus and nitrogen co-doped porous carbon iron-based catalyst.

Background

The development of modern new energy technology is as follows: the development of fuel cells and the commercial application of metal-air cells depends largely on the electrocatalyst of the slow cathode Oxygen Reduction Reaction (ORR). The most widely used at present are a series of platinum-based catalysts. However, high cost, resource shortage, and insufficient stability of Pt have greatly hindered their continued development. Recently, Fe/nitrogen doped carbon (Fe/NC) catalysts have become promising candidates for replacing noble metal catalysts, and it has been reported that the activity in alkaline electrolytes has surpassed that of platinum-based catalysts. However, the stability of the catalyst is still to be improved due to the easy oxidation of the matrix carbon of the iron-based catalyst at a high potential and the unstable mosaic of central atomic iron atoms at a low potential. Therefore, the precise regulation and control of the structural parameters of the active center of the iron-based catalyst and the deep research on the ORR mechanism are expected to optimize the catalytic efficiency and improve the stability of the iron-based catalyst. Here we prepared a novel iron-based catalyst using wet chemistry. The catalyst is supported on N, P doped porous carbon by Fe atoms, and the degree of graphitization of the catalyst is enhanced by secondary activation of potassium hydroxide. The catalyst has the advantages that P is doped, the P has a relatively large radius compared with N and is easier to cause defects, and the larger electronegativity can adjust the electronic structure of an active center atom. The combination of P and O creates a stable structure, making its oxygen more likely to form a single electron to bind to the Fe atom, and iron more likely to form a +2 or +3 valence to form a high performance ORR catalyst. The porous carbon with high specific surface area and high porosity becomes a stable matrix of the catalyst, forms the lowest activation energy and hydrophobicity, and thus improves the durability of the ORR catalyst.

Disclosure of Invention

Aiming at the technical problems in the prior art, the invention provides a phosphorus and nitrogen co-doped porous carbon catalyst with high specific surface area and high porosity, and preparation and application thereof.

In order to achieve the purpose, the invention is realized by adopting the following specific modes:

a phosphorus and nitrogen co-doped porous carbon cathode oxygen reduction iron-based catalyst is characterized in that: has three-dimensional porous structure, specific surface area of 1000 and 2000 square meters per gram and porosity of 1-2 cubic centimeters per gram. The preparation method of the iron-based catalyst comprises the following steps:

step 1, respectively adding phosphoric acid and pentaerythritol into a round-bottom flask according to certain mass, stirring and reacting for certain time at certain temperature to obtain a product solution of the phosphoric acid and the pentaerythritol;

step 2, adding a certain amount of nitrogen precursor, carbon precursor and iron precursor into a certain amount of absolute ethyl alcohol, and stirring for a certain time at room temperature;

step 3, cooling the mixture in the step 1, adding the solution in the step 2 into the mixture in the step 1, reacting for a certain time at a certain temperature, and then performing rotary evaporation and drying to obtain white powder;

step 4, pyrolyzing the white powder obtained in the step 3 in a tube furnace to obtain a powdery intermediate product;

step 5, mixing the powder obtained in the step 4 with potassium hydroxide according to a certain weight ratio, and simultaneously carrying out secondary carbonization in a tubular furnace to obtain a catalyst;

and 6, carrying out acid washing on the obtained catalyst, then washing with deionized water, and carrying out vacuum drying to prepare the iron-based catalyst.

Further, the phosphoric acid in the step 1 is 29.6 g; pentaerythritol 6.8 g; the volume of the round-bottom flask is 250 ml; the reaction was carried out in a rotary evaporator at 120 ℃ for 2 hours.

Further, the nitrogen precursor in the step 2 is melamine, and the dosage of the nitrogen precursor is 13.6 g; the carbon precursor is glucose, and the dosage is 0.5 g; the iron precursor is ferric trichloride, and the dosage is 2.6 g; the absolute ethyl alcohol is 120 ml, and the stirring temperature is room temperature; the stirring time was 2 hours.

Further, the reaction temperature in the step 3 is 80 ℃; the reaction time was 6 hours.

Further, in the step 4, the pyrolysis temperature in the tubular furnace is 450 ℃, and the heating rate is 5 ℃ per minute; the carbonization time was 1 hour.

Further, in the step 5, the powder obtained in the step 4 is mixed with potassium hydroxide according to the weight ratio of 5:1, the secondary carbonization temperature is 800 ℃, and the heating rate is 5 ℃ per minute; the carbonization time was 2 hours.

Furthermore, in the step 6, the concentration of sulfuric acid is 0.5 mol/L, the pickling temperature is 80 ℃, the pickling time is 12 hours, and all the water is deionized water.

The invention also provides an application of the phosphorus and nitrogen co-doped porous carbon cathode oxygen reduction iron-based catalyst, and the phosphorus and nitrogen co-doped porous carbon cathode oxygen reduction iron-based catalyst is used in an alkaline environment.

Further, the phosphorus and nitrogen co-doped porous carbon cathode oxygen reduction iron-based catalyst is used in lithium metal or metal-air fuel cells

Compared with the prior art, the invention has the advantages that:

(1) the structure of the doping element in the porous carbon can be regulated, and the obtained iron and nitrogen doped matrix carbon in a separated state can keep the doping nature of phosphorus and nitrogen, and is a good electro-catalytic material. The catalyst in a state of combining phosphorus and iron is obtained, and the prepared graphitized carbon has a porous structure and can be prevented from agglomerating;

(2) the phosphorus and nitrogen co-doped porous carbon cathode oxygen reduction iron-based catalyst is prepared by preparing a precursor by a wet chemical method and then preparing a final iron-based catalyst by a pyrolysis method.

Drawings

FIGS. 1A-1B are SEM images of the iron-oxide-reduced catalyst of the present invention.

FIG. 2 shows the polarization curves of the iron-based catalyst at 400/s, 900/s, 1225/s, 1600/s, 2025/s.

FIG. 3 is a plot of I-V polarization for an iron-based catalyst and a commercial PTC catalyst at 1600/s.

FIG. 4 is an I-V polarization curve of an iron-based catalyst at different temperatures and at 1600/s rotation speed.

Detailed Description

The invention is explained in more detail below with reference to examples 1 to 5 and FIGS. 1 to 4