Lignin-based fe, cu, mo-n, br co-doped porous carbon and preparation method thereof

Abstract

The present application relates to the technical field of electrocatalysis, in particular to a lignin-based Fe, Cu, Mo-N, Br co-doped porous carbon and a preparation method thereof. The ORR electrocatalytic activity of conventional lignin-based porous carbon materials is poor. In view of the above problem, the present application provides a lignin-based Fe, Cu, Mo-N, Br co-doped porous carbon. The physical structure and chemical properties of the lignin-based carbon material are changed by adopting the mode of non-metallic element and metal element multi-heteroatom co-doping, the active sites of the lignin-based carbon material are obviously increased, the electronic conductivity thereof is significantly improved, and the ORR electrocatalytic property is greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrocatalysis, and particularly relates to a lignin-based Fe, Cu, Mo-N, Br co-doped porous carbon and a preparation method thereof. BACKGROUND

[0002] Whether it is a fuel cell, a metal-air battery or a water electrolysis hydrogen production technology, an efficient and economical electrocatalyst is needed as the kinetic support for the electrochemical reaction. Materials based on platinum group metals (PGM) have been proven to be the most effective catalysts for the oxygen reduction reaction (ORR) to date. However, the scarcity, high cost and low stability of noble metals hinder their application in practice, in which case, some carbon-based composite materials complexed by nitrogen, phosphorus, chlorine and other heteroatoms have become the most promising substitutes for PGM catalysts due to their low cost, high activity and stability.

[0003] In recent years, porous carbon materials have shown wide application prospects in the fields of adsorption, catalysis, biology, electronics and other fields due to their developed pore structure, high specific surface area, excellent heat resistance, acid and alkali resistance and unique electronic conductivity. Heteroatom-doped carbon materials have shown great application potential in the field of electrocatalytic oxygen reduction due to their unique structure and performance. By introducing heteroatoms (such as nitrogen, phosphorus, sulfur, etc.) into the skeleton of carbon materials, their electronic structure and surface properties can be effectively changed, thereby improving their electrocatalytic activity. These heteroatoms not only can provide additional active sites, but also can promote the transfer of electric charge and the adsorption of reactants, thereby significantly improving the efficiency of electrocatalytic oxygen reduction.

[0004] Lignin is a waste produced in the bio-refining process, and has the advantages of low price, high carbon content, good thermal stability and good biodegradability, and is a potential precursor of carbon materials. However, conventional lignin-based porous carbon materials often lack sufficient heteroatom content, and have poor ORR electrocatalytic activity. SUMMARY

[0005] The existing problem in the prior art is that the ORR electrocatalytic activity of conventional lignin-based porous carbon materials is poor. In view of the above problem, the present application provides a lignin-based Fe, Cu, Mo-N, Br co-doped porous carbon, and a preparation method thereof, which comprises the following steps:

[0006] (1) the lignin is dispersed into an organic solvent and uniformly dispersed by ultrasonic dispersion, then triethylamine and 4-dimethylaminopyridine are added into the reaction system, the mixture is stirred and uniformly mixed, then 2-bromoisobutyryl bromide is added dropwise into the reaction system, the reaction is stirred at room temperature, the ester bond between the lignin and 2-bromoisobutyryl bromide is generated, then methanol is added into the reaction system to remove the unreacted 2-bromoisobutyryl bromide, then water is added into the reaction system, the mixture is stirred and uniformly mixed, then solid-liquid separation is performed, then the obtained product is washed by DMF and 95% ethanol and dried, thereby obtaining the bromine-substituted lignin;

[0007] (2) the bromine-substituted lignin is dispersed into water, then a nitrogen source, an iron source, a copper source and a molybdenum source are added into the reaction system, the mixture is stirred and uniformly mixed, then the mixture is dried to remove the water in the mixture, thereby obtaining the porous carbon precursor;

[0008] (3) the porous carbon precursor obtained in step (1) is subjected to high-temperature carbonization reaction in a nitrogen environment, then the obtained product is subjected to acid washing and water washing until neutral, and finally dried, thereby obtaining the porous carbon.

[0009] Preferably, the organic solvent comprises at least one of DMF, DMSO and dioxane.

[0010] Preferably, the mass ratio of the lignin, triethylamine, 4-dimethylaminopyridine and 2-bromoisobutyryl bromide is 5-10g:10-15g:10-15g:15-20g.

[0011] Preferably, in step (2), the mass ratio of the bromine-substituted lignin, the nitrogen source, the iron source, the copper source and the molybdenum source is 1:1-3:1:1:1.

[0012] Preferably, in step (3), the temperature of the high-temperature carbonization is 900±50℃, and the time of the high-temperature carbonization is at least 2h.

[0013] Preferably, the nitrogen source comprises one or more than two combinations of melamine, dicyandiamide, dimethylimidazole, carbon nitride, urea and cyanamide.

[0014] Preferably, the copper source comprises one or more than two combinations of copper chloride, copper nitrate trihydrate and copper nitrate hexahydrate.

[0015] Preferably, the molybdenum source comprises one or more than two combinations of sodium molybdate, ammonium molybdate and molybdenum chloride.

[0016] Preferably, the iron source comprises one or more than two combinations of iron chloride, iron nitrate and iron sulfate.

[0017] Preferably, the porous carbon precursor needs to be ground to 100 mesh before high-temperature carbonization.

[0018] The present application has the following beneficial effects:

[0019] The lignin-based Fe, Mo, Cu-N, Br co-doped porous carbon material obtained by the method has more electrocatalytic active sites, the metal elements and non-metal elements co-doped with multiple heteroatoms change the physical structure and chemical properties of the lignin-based carbon material, significantly improve the electronic conductivity thereof, and the ORR electrocatalytic property is significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 TEM image of ELC-3N obtained in Example 1. DETAILED DESCRIPTION

[0021] The application will be described in detail below in combination with examples. It should be understood that the following examples are only illustrative of the embodiments of the application, but not a limitation on the scope of the application.

[0022] The enzymatic lignin in the following examples and comparative examples of the application is from Hailun Bioenergy Co., Ltd.

[0023] The acid washing solution used in the following examples of the application is a hydrochloric acid solution with a concentration of 2 mol / L.

[0024] Example 1

[0025] 5 g of enzymatic lignin was added to 50 mL of DMF and ultrasonically dispersed for 4 h, then 10 g of triethylamine and 10 g of 4-dimethylaminopyridine were added to the reaction system, and after stirring uniformly, 15 g of 2-bromoisobutyryl bromide was added dropwise to the reaction system, then the reaction was stirred at room temperature for 6 h, after the reaction was completed, 10 mL of methanol was added to the reaction system, and the reaction was stirred for 1 h, after the reaction was completed, 200 mL of deionized water was added to the reaction system, the reaction liquid was separated by centrifugation, and the solid product was collected, the obtained solid product was washed once with DMF and four times with an ethanol aqueous solution, to obtain a bromine-substituted lignin;

[0026] (2) 5 g of the bromine-substituted lignin was dispersed in 100 mL of water and stirred at 80℃ until dispersion, then 15 g of melamine, 5 g of iron nitrate hexahydrate, 5 g of copper nitrate hexahydrate, and 5 g of ammonium molybdate were sequentially added to the reaction system, and the mixture was continuously stirred at constant temperature for 2 h, then the mixture was placed in a blast drying oven and dried at 105℃ to obtain a porous carbon precursor;

[0027] (3) The prepared precursor material was ground to 100 mesh, placed in a porcelain boat and placed in a tube furnace, dried at 5℃ / min under N2 atmosphere to 800℃, held for 2 h, then cooled to room temperature, and the obtained porous carbon material was taken out. -1at a heating rate of 5 ℃ / min to a set temperature of 900 ℃, and kept for 2 h. After carbonization, the obtained product was washed with acid, washed with water until neutral, and dried to obtain a lignin-based Fe, Mo, Cu-N, Br co-doped porous carbon material, denoted as ELC-3N. A TEM image of the obtained ELC-3N is shown in FIG. 6. Figure 1

[0028] Example 2

[0029] 5 g of enzyme lignin was added to 50 mL of DMF and ultrasonically dispersed for 4 h. Then, 10 g of triethylamine and 10 g of 4-dimethylaminopyridine were added to the reaction system, and stirred uniformly. Then, 15 g of 2-bromoisobutyryl bromide was added dropwise to the reaction system, and then stirred at room temperature for 6 h. After the reaction was completed, 10 mL of methanol was added to the reaction system, and stirred for 1 h. After the reaction was completed, 200 mL of deionized water was added to the reaction system, and the reaction liquid was centrifuged to collect the solid product. The obtained solid product was washed once with DMF and four times with an ethanol aqueous solution to obtain a bromine-substituted lignin.

[0030] (2) 5 g of the bromine-substituted lignin was dispersed in 100 mL of water and stirred at 80 ℃ until dispersion. Then, 10 g of melamine, 5 g of iron nitrate hexahydrate, 5 g of copper nitrate hexahydrate, and 5 g of ammonium molybdate were sequentially added to the reaction system, and continued to be stirred at constant temperature for 2 h. Then, the mixed liquid was placed in a blast drying oven and dried at 105 ℃ to obtain a porous carbon precursor.

[0031] (3) The obtained precursor material was ground to 100 mesh, placed in a porcelain boat, and placed in a tube furnace. Under N2 atmosphere, the temperature was raised to a set temperature of 900 ℃ at a heating rate of 5 ℃ / min, and kept for 2 h. After carbonization, the obtained product was washed with acid, washed with water until neutral, and dried to obtain a lignin-based Fe, Mo, Cu-N, Br co-doped porous carbon material, denoted as ELC-2N. -1

[0032] Example 3

[0033] 5 g of enzyme lignin was added to 50 mL of DMF and ultrasonically dispersed for 4 h. Then, 10 g of triethylamine and 10 g of 4-dimethylaminopyridine were added to the reaction system, and stirred uniformly. Then, 15 g of 2-bromoisobutyryl bromide was added dropwise to the reaction system, and then stirred at room temperature for 6 h. After the reaction was completed, 10 mL of methanol was added to the reaction system, and stirred for 1 h. After the reaction was completed, 200 mL of deionized water was added to the reaction system, and the reaction liquid was centrifuged to collect the solid product. The obtained solid product was washed once with DMF and four times with an ethanol aqueous solution to obtain a bromine-substituted lignin.

[0034] ​​(2) Disperse 5g of bromine-substituted lignin in 100mL of water and stir at 80℃ until dispersed. Then add 5g of melamine, 5g of ferric nitrate hexahydrate, 5g of copper nitrate hexahydrate and 5g of ammonium molybdate to the reaction system in sequence. Continue stirring at a constant temperature for 2h. Place the mixture in a forced-air drying oven and dry at 105℃ to obtain a porous carbon precursor.

[0035] (3) The obtained precursor material is ground to 100 mesh, placed in a porcelain boat and then placed in a tube furnace. Under a N2 atmosphere, it is heated at 5℃ for 1 minute. -1 The heating rate was increased to the set temperature of 900℃, and the temperature was held for 2 hours. After carbonization, the obtained product was acid washed, water washed until neutral, and dried to obtain lignin-based Fe,Mo,Cu-N,Br co-doped porous carbon material, denoted as ELC-1N.

[0036] Example 4 is the same as Example 1, except that in Example 4, sodium molybdate is added in the same amount to replace ammonium molybdate in Example 1.

[0037] Comparative Example 1 is the same as Example 1, except that melamine was not added in step (1) of Comparative Example 1.

[0038] Comparative Example 2 is the same as Example 1, except that melamine was added in excess in Comparative Example 2, specifically in an amount of 20g.

[0039] Comparative Example 3

[0040] (1) Mix 5g of enzymatically hydrolyzed lignin and 5g of NaOH in 100mL of water until they are completely dissolved. Stir at 80℃ until the lignin is completely dissolved. Then slowly add 15g of 3-bromopropionic acid to the above reaction system and stir at a constant temperature for 90min. During the stirring reaction, 3-bromopropionic acid and enzymatically hydrolyzed lignin undergo esterification to generate modified lignin. After the reaction is completed, add 15g of melamine, 5g of ferric nitrate hexahydrate, 5g of copper nitrate hexahydrate and 5g of ammonium molybdate to the reaction system in sequence. Continue to stir at a constant temperature for 2h. Then place the mixture in a forced-air drying oven and dry at 105℃ to obtain a porous carbon precursor.

[0041] (2) The obtained precursor material was ground to 100 mesh and placed in a porcelain boat in a tube furnace. Under a N2 atmosphere, it was heated at 5°C for 1 minute. -1 The heating rate was increased to the set temperature of 900℃, and the temperature was held for 2 hours. After carbonization, the obtained product was acid washed, water washed until neutral, and dried to obtain lignin-based Fe,Mo,Cu-N,Br co-doped porous carbon material.

[0042] Comparative Example 4 is the same as Example 1, except that the amount of ammonium molybdate added in Comparative Example 4 is 10g.

[0043] Comparative Example 5 is the same as Example 1, except that no ammonium molybdate is added in Comparative Example 5.

[0044] Comparative Example 6 is the same as Example 1, except that the amount of iron nitrate hexahydrate added in Comparative Example 6 is 10 g.

[0045] Comparative Example 7 is the same as Example 1, except that no iron nitrate hexahydrate is added in Comparative Example 7.

[0046] Comparative Example 8 is the same as Example 1, except that the amount of copper nitrate hexahydrate added in Comparative Example 8 is 10 g.

[0047] Comparative Example 9 is the same as Example 1, except that no copper nitrate hexahydrate is added in Comparative Example 9.

[0048] Electrocatalytic performance test

[0049] The carbon materials obtained in Examples 1-4 and Comparative Examples 1-9 are respectively ground to 1000 mesh, 2 mg of carbon material is selected and dispersed in a solvent composed of 300 μL of pure water, 200 μL of ethanol, and 14 μL of Nafion with a mass fraction of 5% to form a catalyst solution with a mass concentration of 3.89 g / L, and then 20 μL of the catalyst solution is added dropwise on the surface of a clean glassy carbon electrode with a diameter of 5 mm, and the effective coating area of the glassy carbon electrode surface is 0.396 mg / cm 2 After the dropwise addition is completed, the glassy carbon electrode is placed under infrared light for drying to obtain a working electrode.

[0050] A Shanghai Chenhua CHI760D electrochemical workstation is used for the test, and a three-electrode system is used for the experiment: a working electrode, a saturated calomel electrode as a reference electrode, and a platinum sheet electrode as a counter electrode.

[0051] The test solution is a 0.1 M KOH aqueous solution, and the initial potential, half-wave potential, and limiting current density of the working electrode are tested by linear sweep voltammetry, and the voltage scanning range is -1.011 V to 0.189 V, and the scanning rate is 0.005 V / s.

[0052] The specific test results are shown in Table 1.

[0053] Table 1

[0054]

[0055] From Table 1, it can be seen that the lignin-based Fe, Cu, Mo-N, Br co-doped porous carbon material obtained in Example 1 has the best ORR electrocatalytic performance, which may be due to the following reasons: first, the process of acyl bromide substitution of lignin introduces a large amount of bromine, which increases the content of heteroatom doping in the structure of the carbon material, thereby increasing the number of electrocatalytic active sites; second, the introduction of an appropriate amount of nitrogen source uses the negative adsorption of the amino group on the surface of the nitrogen source to adsorb a specific amount of metal ions such as Fe 3+ , Cu 2+ , etc., thereby avoiding the agglomeration of metal particles; third, through the combination of multiple elements of metal and non-metal, the obtained carbon material contains a large amount of pyridine-N, M-N / Br and M-C, etc. electrocatalytic active sites, which synergistically act with the carbon matrix to significantly improve the ORR catalytic performance of the Fe, Cu, Mo-N, Br co-doped porous carbon catalyst.

[0056] Based on the above ideal embodiments according to the present application, through the above description, relevant personnel can make various changes and modifications without deviating from the technical idea of the present application. The technical scope of the present application is not limited to the contents of the specification, and must be determined according to the scope of the claims.

Claims

1. A lignin-based Fe, Cu, Mo-N, Br co-doped porous carbon, characterized in that, The preparation method comprises the following steps: (1) uniformly dispersing lignin into an organic solvent by ultrasonic dispersion, then adding triethylamine and 4-dimethylaminopyridine into the reaction system, stirring and mixing uniformly, then adding 2-bromoisobutyryl bromide drop by drop into the reaction system, stirring and reacting at room temperature, forming an ester bond between lignin and 2-bromoisobutyryl bromide, then adding methanol into the reaction system to remove unreacted 2-bromoisobutyryl bromide, then adding water into the reaction system, stirring uniformly, then performing solid-liquid separation, then performing DMF washing, 95% ethanol washing and drying, thereby obtaining bromine-substituted lignin; (2) dispersing the bromine-substituted lignin into water, then adding a nitrogen source, an iron source, a copper source and a molybdenum source into the reaction system, stirring and mixing uniformly, then drying the obtained mixture to remove water in the mixture, thereby obtaining a porous carbon precursor; (3) placing the porous carbon precursor obtained in step (1) into a nitrogen environment to perform a high-temperature carbonization reaction, then performing acid washing and water washing to neutralization on the obtained product, and finally performing drying, thereby obtaining the porous carbon.

2. The lignin-based Fe, Cu, Mo-N, Br co-doped porous carbon according to claim 1, characterized in that, The organic solvent comprises at least one of DMF, DMSO and dioxane.

3. The lignin-based Fe, Cu, Mo-N, Br co-doped porous carbon according to claim 1, characterized in that, The lignin, triethylamine, 4-dimethylaminopyridine and 2-bromoisobutyryl bromide are used in a ratio of 5-10 g: 10-15 g: 10-15 g: 15-20 g.

4. The lignin-based Fe, Cu, Mo-N, Br co-doped porous carbon of claim 1, characterized in that, In step (2), the mass ratio of the bromine-substituted lignin, the nitrogen source, the iron source, the copper source and the molybdenum source is 1: 1-3: 1: 1:

1.

5. The lignin-based Fe, Cu, Mo-N, Br co-doped porous carbon of claim 1, wherein, In step (3), the high-temperature carbonization temperature is 900±50℃, and the high-temperature carbonization time is at least 2 h.

6. The lignin-based Fe, Cu, Mo-N, Br co-doped porous carbon of claim 1, wherein, The nitrogen source comprises one or more than two combinations of melamine, dicyandiamide, dimethylimidazole, carbon nitride, urea and cyanamide.

7. The lignin-based Fe, Cu, Mo-N, Br co-doped porous carbon of claim 1, wherein, The copper source comprises one or more than two combinations of copper chloride, copper nitrate trihydrate and copper nitrate hexahydrate.

8. The lignin-based Fe, Cu, Mo-N, Br co-doped porous carbon of claim 1, wherein, The molybdenum source comprises one or more than two combinations of sodium molybdate, ammonium molybdate and molybdenum chloride.

9. The lignin-based Fe, Cu, Mo-N, Br co-doped porous carbon of claim 1, wherein, The iron source comprises one or more than two combinations of iron chloride, iron nitrate and iron sulfate.

10. The lignin-based Fe, Cu, Mo-N, Br co-doped porous carbon of claim 1, wherein, The porous carbon precursor needs to be ground to 100 mesh before high-temperature carbonization.

Images