CN113292061A - Carbon aerogel catalyst synthesized under microwave action and synthesis method and application thereof - Google Patents

Carbon aerogel catalyst synthesized under microwave action and synthesis method and application thereof Download PDF

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CN113292061A
CN113292061A CN202110591160.8A CN202110591160A CN113292061A CN 113292061 A CN113292061 A CN 113292061A CN 202110591160 A CN202110591160 A CN 202110591160A CN 113292061 A CN113292061 A CN 113292061A
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reaction
carbon aerogel
microwave
aerogel catalyst
catalyst
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王建国
彭小革
张世杰
包志康
季文凯
丁磊
王国梁
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Zhejiang University of Technology ZJUT
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Abstract

The invention discloses a carbon aerogel catalyst synthesized under the action of microwaves, a synthesis method and application thereof, wherein the preparation method of the catalyst comprises the following steps: and (2) taking resorcinol and formaldehyde as reaction raw materials, taking water as a solvent, adding the reaction raw materials into the water, adjusting the pH value to be 5-7, then placing the reaction liquid system in a microwave radiation environment for reaction, drying after the reaction is finished, and transferring the obtained solid to a tubular furnace for roasting in a nitrogen atmosphere to obtain the carbon aerogel catalyst product. The method for preparing the carbon aerogel catalyst by using the microwave synthesis method instead of the normal-temperature stirring method has the advantages of simple operation and rapid synthesis, and researches the influence of the selectivity of the carbon aerogel catalyst in preparing hydrogen peroxide by electrocatalytic oxidation reduction by controlling the time for synthesizing the carbon aerogel catalyst by using microwaves.

Description

Carbon aerogel catalyst synthesized under microwave action and synthesis method and application thereof
Technical Field
The invention belongs to the technical field of material preparation, and particularly relates to a carbon aerogel catalyst synthesized under the action of microwaves, and a synthesis method and application thereof.
Background
Hydrogen peroxide is an important chemical substance and has wide application in the fields of industry, medicine, environmental protection, war industry, food, environment and the like. He has both oxidizing and reducing properties and no secondary pollution after use, and is defined as a green chemical product. At present, the most mature method for industrially producing hydrogen peroxide on a large scale is the anthraquinone method, but the anthraquinone method not only has complicated steps, but also uses some organic solvents to cause secondary pollution to the environment, so that the green and efficient method for producing hydrogen peroxide is urgently found.
In the electrochemical Oxygen Reduction Reaction (ORR), there are two reaction pathways:
O2+2H++2e-→H2O2 (1)
O2+4H++4e-→2H2O (2)
i.e. reaction transfer of the 4 e-pathway to H2O (formula 1) and reaction transfer of the 2 e-pathway to H2O2(formula 2), and the selectivity of the catalyst is one of the key factors determining the reaction pathway. Thus, selection of a suitable catalyst promotes the 2 e-pathway of the oxygen reduction reaction, producing and accumulating large quantities of H2O2And the aim of efficiently and environmentally producing hydrogen peroxide on a small scale is fulfilled.
Most of the existing high-efficiency catalysts for electrocatalytic oxidation-reduction reaction select a 4 e-way; only noble metals and alloys thereof, monatomic catalysts, carbon-based materials, metal complexes and the like can catalyze and select the 2 e-path, but the price is high, the structure of the catalyst needs to be accurately controlled, and the preparation conditions are harsh.
As a novel carbon material, the carbon aerogel has the properties of low density, light weight, large specific surface area, large porosity, hydrophobic surface, good conductivity and the like, and has wide application in the fields of adsorption, energy conversion and storage, capacitors, catalysts and the like.
The conventional methods for preparing the carbon aerogel are a normal-temperature normal-pressure drying method, a supercritical drying method and the like, the supercritical drying method can theoretically eliminate the surface tension in the drying process, but the operation of the supercritical drying method under a high-temperature high-pressure environment has certain danger, the period of a solvent replacement process is long, water in wet gel needs to be replaced by a supercritical drying medium (such as carbon dioxide, petroleum ether or ethanol and the like), and then the drying medium is discharged, so that the process needs to be extremely slow to avoid the supercritical state of the medium from being damaged. In recent years, the atmospheric drying method for studying comparative heat is to repeatedly soak wet gel in a solvent with a low surface tension coefficient, replace water in the wet gel with the solvent with the low surface tension coefficient, not only is the time consumed in the process, but also the solvent with dozens of times to hundreds of times of gel volume is needed, and the organic solvents such as ethanol, acetone and other various organic solvents are volatile, toxic, difficult to recover and cause great pollution to the environment.
Disclosure of Invention
Aiming at the problems in the prior art, the invention aims to provide a carbon aerogel catalyst synthesized under the action of microwaves, and a synthesis method and application thereof.
The method for synthesizing the carbon aerogel catalyst based on the microwave action is characterized by comprising the following steps of: and (2) taking resorcinol and formaldehyde as reaction raw materials, taking water as a solvent, adding the reaction raw materials into the water, adjusting the pH value to be 5-7, then placing the reaction liquid system in a microwave radiation environment for reaction, drying after the reaction is finished, and transferring the obtained solid to a tubular furnace for roasting in a nitrogen atmosphere to obtain the carbon aerogel catalyst product.
The method for synthesizing the carbon aerogel catalyst based on the microwave action is characterized by comprising the following steps of:
1) adding resorcinol and a deionized water solvent into a beaker, stirring, adding a formaldehyde solution, uniformly stirring, and then adjusting the pH to be between 5 and 7 by using a sodium hydroxide solution with the concentration of 0.5 to 2 mol/L;
2) transferring the reaction liquid system obtained in the step 1) into a reaction tube, placing the reaction tube into a microwave synthesizer, starting the microwave synthesizer to perform microwave radiation heating, heating the reaction liquid system to 70-90 ℃ for reaction, and controlling the microwave radiation time to be 10-30 min to enable the reaction liquid system to react in the reaction tube to form wet gel;
3) and 2) after the reaction is finished, transferring the synthesized wet gel into a culture dish from the reaction tube, then putting the culture dish into an oven for drying, transferring the dried solid into a porcelain boat, then putting the porcelain boat into a tube furnace for roasting in nitrogen atmosphere, cooling to room temperature after the roasting is finished, and fully grinding by using a mortar to obtain the final carbon aerogel catalyst.
The method for synthesizing the carbon aerogel catalyst based on the microwave effect is characterized in that in the step 1), the mass concentration of a formaldehyde solution is 30-40%, and preferably 35-37%; the molar ratio of the resorcinol to the formaldehyde is 0.33-0.7: 1, preferably 0.5: 1; the ratio of the mass of the resorcinol to the volume of the deionized water solvent is 1: 3-8, preferably 1:5, the unit of the mass is g, and the unit of the volume is mL.
The method for synthesizing the carbon aerogel catalyst based on the microwave effect is characterized in that in the step 1), the concentration of a sodium hydroxide solution is 1mol/L, and the pH value is adjusted to 5.8-6.2 by using the sodium hydroxide solution.
The method for synthesizing the carbon aerogel catalyst based on the microwave effect is characterized in that in the step 2), the operating power of a microwave synthesizer is controlled to be 100-300W, preferably 200W; the reaction temperature is controlled at 85 ℃, and the microwave radiation time is controlled at 15 min.
The method for synthesizing the carbon aerogel catalyst based on the microwave effect is characterized in that in the step 3), the drying temperature in an oven is 50-80 ℃, and preferably 60 ℃; the drying time is 8-18 h, preferably 12 h.
The method for synthesizing the carbon aerogel catalyst based on the microwave action is characterized in that in the step 3), the roasting process in the tubular furnace is as follows: heating to 500-900 ℃ from room temperature at a heating rate of 3-10 ℃/min, preferably 600 ℃, then roasting at constant temperature for 1-5 h, preferably 3h, and finally naturally cooling to room temperature to obtain a catalyst product; wherein the heating rate of the tube furnace is preferably 5 ℃/min.
The carbon aerogel catalyst synthesized according to the method.
The carbon aerogel catalyst is applied to preparing hydrogen peroxide by electrocatalytic oxygen reduction.
Compared with the existing catalyst, the catalyst prepared by the technology has the following beneficial effects:
the invention adopts the process of preparing the carbon aerogel catalyst by a microwave method, microwave radiation is used as a heating source in organic xerogel synthesis, so that all stages (gelation, aging and drying) are simple to operate in a simple and quick device, the time consumption is short, and the prepared catalyst has better selectivity, excellent cycle stability and good electrochemical activity.
Drawings
FIG. 1 is an SEM photograph of 10-CXGs-600 prepared by microwave synthesis for 10min in example 1 of the present invention;
FIG. 2 is an SEM image of 15-CXGs-600 prepared by microwave synthesis for 15min in example 2 of the present invention;
FIG. 3 is an SEM image of 20-CXGs-600 prepared by microwave synthesis for 20min in example 3 of the present invention;
FIG. 4 is an SEM photograph of 25-CXGs-500 prepared by microwave synthesis for 25min in example 4 of the present invention;
FIG. 5 is an SEM photograph of 25-CXGs-600 prepared by microwave synthesis for 25min in example 5 of the present invention;
FIG. 6 is an SEM photograph of 30-CXGs-500 prepared by microwave synthesis for 30min in example 6 of the present invention;
FIG. 7 is an SEM photograph of 30-CXGs-800 prepared by microwave synthesis for 30min in example 7 of the present invention;
FIG. 8 is an SEM photograph of 30-CXGs-600 prepared by microwave synthesis for 30min in example 8 of the present invention;
FIG. 9 is an SEM image of CXGs-600 prepared by stirring at normal temperature in comparative example 1 of the present invention;
FIG. 10 is an SEM image of CXGs-800 prepared by stirring at normal temperature in comparative example 2 of the present invention;
FIG. 11 is an SEM image of CXGs-500 prepared by stirring at normal temperature in comparative example 3 of the present invention;
FIG. 12 is a graph comparing the selectivity of hydrogen peroxide versus voltage for electrocatalytic reactions using the catalysts of examples 1-8, respectively;
FIG. 13 is a graph comparing the electron transfer number of the reaction with the voltage when electrocatalytic reactions are performed using the catalysts of examples 1-8, respectively;
FIG. 14 is a graph comparing the relationship between the hydrogen peroxide selectivity and the voltage in the electrocatalytic reaction with the catalysts of comparative examples 1-3, respectively;
FIG. 15 is a graph comparing the electron transfer number of the reaction with the voltage when electrocatalytic reactions are performed using the catalysts of comparative examples 1 to 3, respectively;
FIG. 16 is a graph of the hydrophobicity of catalyst 25-CXGs-600;
FIG. 17 is a graph of the stability of catalyst 25-CXGs-600.
Detailed Description
The present invention is further illustrated by the following examples, which should not be construed as limiting the scope of the invention.
Example 1
Microwave synthesis for 10min to prepare 10-CXGs-600, comprising the following steps:
weighing resorcinol with the mass of 2.20g, placing the resorcinol in a 50mL beaker, adding 10.8mL water, stirring at the rotating speed of 700rpm for 10min at room temperature, taking 4mL formaldehyde solution (with the mass concentration of 37%) by a pipette, adding the formaldehyde solution into the solution, stirring at the rotating speed of 700rpm for 10min, and dropwise adding 1mol/L sodium hydroxide solution to adjust the pH value to be about 6. Then the obtained reaction liquid system is transferred to a reaction tube, the reaction tube is placed in a microwave synthesizer, the microwave synthesizer is started to carry out microwave radiation heating (the running power of the microwave synthesizer is controlled at 200W, and the microwave power of the following embodiment is the same as that of the embodiment 1), so that the reaction liquid system is heated to 85 ℃ and the microwave radiation time is 10 min. The resultant wet gel was then transferred from the reaction tube to a petri dish and placed in an oven for drying at 60 ℃ for 12 h. Then transferring the mixture to a porcelain boat, putting the porcelain boat in a tube furnace, heating the mixture to 600 ℃ from room temperature at the heating rate of 5 ℃/min by using nitrogen as protective gas, then calcining the mixture at the constant temperature of 600 ℃ for 3h, and then cooling the mixture to room temperature. Grinding the calcined block into powder to obtain 10-CXGs-600.
Example 2
Microwave synthesis for 15min to prepare 15-CXGs-600, comprising the following steps;
weighing resorcinol with the mass of 2.20g, placing the resorcinol in a 50mL beaker, adding 10.8mL water, stirring at the rotating speed of 700rpm for 10min at room temperature, taking 4mL formaldehyde solution (with the mass concentration of 37%) by a pipette, adding the formaldehyde solution into the solution, stirring at the rotating speed of 700rpm for 2min, and dropwise adding 1mol/L sodium hydroxide solution to adjust the pH value to be about 6. And transferring the obtained reaction liquid system into a reaction tube, placing the reaction tube in a microwave synthesizer, starting the microwave synthesizer to perform microwave radiation heating, and heating the reaction liquid system to 85 ℃ for 15min through microwave radiation. The resultant wet gel was then transferred from the reaction tube to a petri dish and placed in an oven for drying at 60 ℃ for 12 h. Then transferring the mixture to a porcelain boat, putting the porcelain boat in a tube furnace, heating the mixture to 600 ℃ from room temperature at the heating rate of 5 ℃/min by using nitrogen as protective gas, then calcining the mixture at the constant temperature of 600 ℃ for 3h, and then cooling the mixture to room temperature. And grinding the calcined blocks into powder to obtain 15-CXGs-600.
Example 3
Microwave synthesis for 20min to prepare 20-CXGs-600, comprising the following steps:
weighing resorcinol with the mass of 2.20g, placing the resorcinol in a 50mL beaker, adding 10.8mL water, stirring at the rotating speed of 700rpm for 10min at room temperature, taking 4mL formaldehyde solution (with the mass concentration of 37%) by a pipette, adding the formaldehyde solution into the solution, stirring at the rotating speed of 700rpm for 10min, and dropwise adding 1mol/L sodium hydroxide solution to adjust the pH value to be about 6. And transferring the obtained reaction liquid system into a reaction tube, placing the reaction tube in a microwave synthesizer, starting the microwave synthesizer to perform microwave radiation heating, and heating the reaction liquid system to 85 ℃ for 20min through microwave radiation. The resultant wet gel was then transferred from the reaction tube to a petri dish and placed in an oven for drying at 60 ℃ for 12 h. Then transferring the mixture to a porcelain boat, putting the porcelain boat in a tube furnace, heating the mixture to 600 ℃ from room temperature at the heating rate of 5 ℃/min by using nitrogen as protective gas, then calcining the mixture at the constant temperature of 600 ℃ for 3h, and then cooling the mixture to room temperature. And grinding the calcined blocks into powder to obtain the 20-CXGs-600.
Example 4
Microwave synthesis for 25min to prepare 25-CXGs-500, comprising the following steps:
weighing resorcinol with the mass of 2.20g, placing the resorcinol in a 50mL beaker, adding 10.8mL water, stirring at the rotating speed of 700rpm for 10min at room temperature, taking 4mL formaldehyde solution (with the mass concentration of 37%) by a pipette, adding the formaldehyde solution into the solution, stirring at the rotating speed of 700rpm for 10min, and dropwise adding 1mol/L sodium hydroxide solution to adjust the pH value to be about 6. And transferring the obtained reaction liquid system into a reaction tube, placing the reaction tube in a microwave synthesizer, starting the microwave synthesizer to perform microwave radiation heating, and heating the reaction liquid system to 85 ℃ for 25min through microwave radiation. The resultant wet gel was then transferred from the reaction tube to a petri dish and placed in an oven for drying at 60 ℃ for 12 h. Then transferring the mixture to a porcelain boat, putting the porcelain boat in a tube furnace, heating the porcelain boat to 500 ℃ from room temperature at a heating rate of 5 ℃/min by using nitrogen as protective gas, then calcining the porcelain boat at the constant temperature of 500 ℃ for 3h, and then cooling the porcelain boat to room temperature. Grinding the calcined block into powder to obtain 25-CXGs-500.
Example 5
Microwave synthesis for 25min to prepare 25-CXGs-600 comprises the following steps:
weighing resorcinol with the mass of 2.20g, placing the resorcinol in a 50mL beaker, adding 10.8mL water, stirring at the rotating speed of 700rpm for 10min at room temperature, taking 4mL formaldehyde solution (with the mass concentration of 37%) by a pipette, adding the formaldehyde solution into the solution, stirring at the rotating speed of 700rpm for 10min, and dropwise adding 1mol/L sodium hydroxide solution to adjust the pH value to be about 6. And transferring the obtained reaction liquid system into a reaction tube, placing the reaction tube in a microwave synthesizer, starting the microwave synthesizer to perform microwave radiation heating, and heating the reaction liquid system to 85 ℃ for 25min through microwave radiation. The resultant wet gel was then transferred from the reaction tube to a petri dish and placed in an oven for drying at 60 ℃ for 12 h. Then transferring the mixture to a porcelain boat, putting the porcelain boat in a tube furnace, heating the mixture to 600 ℃ from room temperature at the heating rate of 5 ℃/min by using nitrogen as protective gas, then calcining the mixture at the constant temperature of 600 ℃ for 3h, and then cooling the mixture to room temperature. And grinding the calcined blocks into powder to obtain 25-CXGs-600.
Example 6
Microwave synthesis for 30min to prepare 30-CXGs-500, comprising the following steps:
weighing resorcinol with the mass of 2.20g, placing the resorcinol in a 50mL beaker, adding 10.8mL water, stirring at the rotating speed of 700rpm for 10min at room temperature, taking 4mL formaldehyde solution (with the mass concentration of 37%) by a pipette, adding the formaldehyde solution into the solution, stirring at the rotating speed of 700rpm for 10min, and dropwise adding 1mol/L sodium hydroxide solution to adjust the pH value to be about 6. And transferring the obtained reaction liquid system into a reaction tube, placing the reaction tube in a microwave synthesizer, starting the microwave synthesizer to perform microwave radiation heating, and heating the reaction liquid system to 85 ℃ for 30min through microwave radiation. The resultant wet gel was then transferred from the reaction tube to a petri dish and placed in an oven for drying at 60 ℃ for 10 h. Then transferring the mixture to a porcelain boat, putting the porcelain boat in a tube furnace, heating the mixture to 500 ℃ from room temperature at a heating rate of 3 ℃/min by using nitrogen as protective gas, then calcining the mixture at the constant temperature of 500 ℃ for 4h, and then cooling the mixture to room temperature. Grinding the calcined block into powder to obtain 30-CXGs-500.
Example 7
Microwave synthesis for 30min to prepare 30-CXGs-800, comprising the following steps:
weighing resorcinol with the mass of 2.20g, placing the resorcinol in a 50mL beaker, adding 10.8mL water, stirring at the rotating speed of 700rpm for 10min at room temperature, taking 4mL formaldehyde solution (with the mass concentration of 37%) by a pipette, adding the formaldehyde solution into the solution, stirring at the rotating speed of 700rpm for 10min, and dropwise adding 1mol/L sodium hydroxide solution to adjust the pH value to be about 6. And transferring the obtained reaction liquid system into a reaction tube, placing the reaction tube in a microwave synthesizer, starting the microwave synthesizer to perform microwave radiation heating, and heating the reaction liquid system to 85 ℃ for 30min through microwave radiation. The resultant wet gel was then transferred from the reaction tube to a petri dish and placed in an oven for drying at 60 ℃ for 8 h. Then transferring the ceramic boat to a porcelain boat, putting the ceramic boat in a tube furnace, heating the ceramic boat to 800 ℃ from room temperature at a heating rate of 5 ℃/min by using nitrogen as protective gas, then calcining the ceramic boat at the constant temperature of 800 ℃ for 5h, and then cooling the ceramic boat to room temperature. And grinding the calcined block into powder to obtain 30-CXGs-800.
Example 8
The microwave synthesis for 30min to prepare 30-CXGs-600 comprises the following steps:
weighing resorcinol with the mass of 2.02g, placing the resorcinol in a 50mL beaker, adding 10.8mL water, stirring at the rotating speed of 700rpm for 10min at room temperature, taking 4mL formaldehyde solution (with the mass concentration of 37%) by a pipette, adding the formaldehyde solution into the solution, stirring at the rotating speed of 700rpm for 10min, and dropwise adding 1mol/L sodium hydroxide solution to adjust the pH value to be about 6. And transferring the obtained reaction liquid system into a reaction tube, placing the reaction tube in a microwave synthesizer, starting the microwave synthesizer to perform microwave radiation heating, and heating the reaction liquid system to 85 ℃ for 30min through microwave radiation. The resultant wet gel was then transferred from the reaction tube to a petri dish and placed in an oven for drying at 60 ℃ for 8 h. Then transferring the mixture to a porcelain boat, putting the porcelain boat in a tube furnace, heating the mixture to 600 ℃ from room temperature at the heating rate of 5 ℃/min by using nitrogen as protective gas, then calcining the mixture at the constant temperature of 600 ℃ for 5h, and then cooling the mixture to room temperature. And grinding the calcined blocks into powder to obtain the 30-CXGs-600.
Comparative example 1
Stirring at normal temperature to prepare CXGs-600, comprising the following steps:
weighing resorcinol with the mass of 2.20g, placing the resorcinol in a 50mL beaker, adding 10.8mL water, stirring at the rotating speed of 700rpm for 10min at room temperature, taking 4mL formaldehyde solution (with the mass concentration of 37%) by a pipette, adding the formaldehyde solution into the solution, stirring at the rotating speed of 700rpm for 10min, and dropwise adding 1mol/L sodium hydroxide solution to adjust the pH value to be about 6. Stirring at normal temperature for 24h, transferring the synthesized wet gel from the beaker into a culture dish, and drying in an oven at 60 ℃ for 8 h. Then transferring the mixture to a porcelain boat, putting the porcelain boat in a tube furnace, heating the mixture to 600 ℃ from room temperature at the heating rate of 5 ℃/min by using nitrogen as protective gas, then calcining the mixture at the constant temperature of 600 ℃ for 5h, and then cooling the mixture to room temperature. Grinding the calcined block into powder to obtain CXGs-600.
Comparative example 2
Stirring at normal temperature to prepare CXGs-800, comprising the following steps:
weighing resorcinol with the mass of 2.20g, placing the resorcinol in a 50mL beaker, adding 10.8mL water, stirring at the rotating speed of 700rpm for 10min at room temperature, taking 4mL formaldehyde solution (with the mass concentration of 37%) by a pipette, adding the formaldehyde solution into the solution, stirring at the rotating speed of 700rpm for 10min, and dropwise adding 1mol/L sodium hydroxide solution to adjust the pH value to be about 6. Stirring at normal temperature for 24h, transferring the synthesized wet gel from the beaker into a culture dish, and drying in an oven at 60 ℃ for 8 h. Then transferring the ceramic boat to a porcelain boat, putting the ceramic boat in a tube furnace, heating the ceramic boat to 800 ℃ from room temperature at a heating rate of 5 ℃/min by using nitrogen as protective gas, then calcining the ceramic boat at the constant temperature of 800 ℃ for 5h, and then cooling the ceramic boat to room temperature. Grinding the calcined block into powder to obtain CXGs-800.
Comparative example 3
Stirring at normal temperature to prepare CXGs-500, comprising the following steps:
weighing resorcinol with the mass of 2.02g, placing the resorcinol in a 50mL beaker, adding 10.8mL water, stirring at the rotating speed of 700rpm for 10min at room temperature, taking 4mL formaldehyde solution (with the mass concentration of 37%) by a pipette, adding the formaldehyde solution into the solution, stirring at the rotating speed of 700rpm for 10min, and dropwise adding 1mol/L sodium hydroxide solution to adjust the pH value to be about 6. Stirring at normal temperature for 24h, transferring the synthesized wet gel from the beaker into a culture dish, and drying in an oven at 60 ℃ for 8 h. Then transferring the mixture to a porcelain boat, putting the porcelain boat in a tube furnace, heating the mixture to 500 ℃ from room temperature at a heating rate of 5 ℃/min by using nitrogen as protective gas, then calcining the mixture at the constant temperature of 500 ℃ for 5h, and then cooling the mixture to the room temperature. Grinding the calcined block into powder to obtain CXGs-500.
From the experimental procedures of examples 1-8 and comparative examples 1-3, the synthesis time of the microwave-synthesized carbon aerogel catalyst was greatly shortened as compared to the conventional normal-temperature synthesis of carbon aerogel.
SEM images of the catalysts prepared in examples 1-8 are shown in fig. 1-8, respectively. Fig. 1 to 8 show the SEM image morphology of the catalysts prepared under different microwave synthesis conditions, and it can be seen that: the prepared catalyst is spherical when the microwave time is 10-30 min and the carbonization temperature is 500-800 ℃, the size of the sphere is uniform, and the appearance of the catalyst is not obviously damaged when the carbonization temperature is increased by 3-5 nm.
SEM images of the catalysts prepared in comparative examples 1 to 3 are shown in fig. 9 to 11, respectively. FIGS. 9-11 show SEM image morphology of catalysts prepared under normal temperature stirring conditions, and it can be seen that: the catalyst prepared by stirring at normal temperature is in a porous nano block shape, and the edge of the block shape has a plurality of defects.
Comparing the characterization results of FIGS. 1-8 and FIGS. 9-11, it can be seen that the catalysts synthesized by the two methods have distinct morphologies. The catalysts obtained in examples 1 to 8 by the microwave synthesis method have better morphology than the preparation methods of comparative examples 1 to 3, from which it is concluded that: compared with the conventional normal-temperature synthesis of carbon aerogel, the carbon aerogel catalyst synthesized by microwave has the advantages that the synthesis time is greatly shortened, and the carbon aerogel catalyst has better electrocatalysis performance. The reason for the great differences in morphology of the catalysts obtained due to the differences in the two synthetic methods is presumed to be: the reaction liquid system is heated and reacted under microwave radiation, formaldehyde and resorcinol are used as heating media, the conductivity and the polarizability are good, in addition, the formaldehyde molecules are small, the polarity is relatively large, so that the formaldehyde molecules can absorb microwaves more easily to be heated, and in the synthesis process, spheres are directly synthesized from a precursor without a blocky process.
Application example 1:
electrocatalytic performance of the catalysts of examples 1-8 and comparative examples 1-3 were verified separately:
catalyst slurries were prepared with the catalysts of examples 1-8 and comparative examples 1-3, respectively: the catalyst was dispersed uniformly by sonication for 30min using 4.0mg of catalyst, 100. mu.L of Dupont 5% nafion solution and 900. mu.L of absolute ethanol to obtain corresponding catalyst slurries prepared using the catalysts of examples 1-8 and comparative examples 1-3, respectively. 5 mul of catalyst slurry was coated onto a circular glassy carbon area of a rotating disk electrode and dried to form a working electrode.
An electrochemical workstation is adopted as an electrochemical generating device, a rotating ring disk electrode coated with a catalyst is used as a working electrode, a platinum wire is used as a counter electrode, saturated calomel is used as a reference electrode, and the voltage E of the platinum ring endring=1.3VRHE(voltage E at platinum Ring terminalringIs a parameter which must be set when a rotating ring disk electrode is used for testing, and the voltage set by a platinum ring is set according to the principle that the oxidation reaction can generate H2O2But is unable to oxidize H present in solution2O, thereby enabling H to be tested2O2Current of oxidation, reaction of production H2O2Selectivity of (ii). Using 0.1M KOH aqueous solution as electrolyte, and continuously introducing oxygen (oxygen flow 60mL/min) into the electrolyte, wherein the selective oxygen reduction test voltage range is 0.0-0.5VRHEThe sweep rate was 10 mV/s. During the electrochemical test, the disk current and the ring current in the rotating ring disk electrode are detected.
The electron number of cathode oxygen reduction and the selectivity of hydrogen peroxide are researched by utilizing a Koutecky-Levich (K-L) equation, and calculation formulas are respectively shown as a formula (3) and a formula (4):
Figure BDA0003089347410000131
Figure BDA0003089347410000132
in the formula (3), n represents the number of transferred electrons for cathodic oxygen reduction; i isDAnd IRThe current collection coefficient of the platinum ring on the ring disc electrode in the experiment is defined as 0.41;
and (4)% H2O2Hydrogen peroxide selectivity representing cathode oxygen reduction; i isDAnd IRRespectively the disk current and the ring current in the rotating ring disk electrode, NThe current collection coefficient of the platinum ring at the ring disk electrode for the experiment was defined as 0.41.
In the test process, when electrocatalytic reactions were performed with the catalysts of examples 1 to 8, the results of selectivity to hydrogen peroxide under different voltage conditions are shown in fig. 12, and the results of the number of transferred electrons under different voltage conditions are shown in fig. 13. The results of the selectivity to hydrogen peroxide under different voltage conditions and the results of the number of transferred electrons under different voltage conditions when electrocatalytic reactions were carried out with the catalysts of comparative examples 1 to 3, respectively, are shown in fig. 14 and fig. 15.
FIGS. 12-15 summarize the results of the electro-catalytic chemical performance tests of the catalysts, and it can be seen that: the catalyst of example 5 has the best selectivity to the di-electron hydrogen peroxide, and the highest selectivity can reach 90%, namely the catalyst prepared under the conditions that the microwave synthesis time is 25min and the carbonization temperature is 600 ℃ has the best effect. In the preparation process of the catalyst, the microwave synthesis time needs to be selected within a reasonable range, because when the microwave synthesis time is long and the carbonization temperature is high, the formed hydrogel has a large number of cross-linked structures, and the structures collapse and active sites are damaged during high-temperature carbonization, so that the oxygen reduction reaction is not facilitated; and the microwave time is short, the gel is not completely formed at a low carbonization temperature, the formaldehyde and the resorcinol do not reach the gel point, so that the synthesized structure is weakly branched, the gel is not completely formed, the mechanical strength is weak, the active site is influenced, and the electrocatalytic effect of the prepared hydrogel is poor.
FIG. 16 is a hydrophobicity plot of 25-CXGs-600, where 0.5g of the catalyst of example 5 is placed on a table, and when 5 drops of water are dropped on the catalyst, the small beads will fuse into large beads, and if the catalyst is hydrophilic, it will also dissolve in water, and as can be seen in FIG. 16, the catalyst is coated on the surface of the beads rather than being soluble in water.
Application example 2 (test of catalyst life):
a catalyst slurry was prepared using the 25-CXGs-600 material of example 5 as the catalyst: taking 4.0mg of catalyst, 100 mu L of 5 percent nafion solution of DuPont and 900 mu L of absolute ethyl alcohol, and carrying out ultrasonic treatment for 30min to uniformly disperse the catalyst to obtain catalyst slurry.
Hydrogen peroxide solutionLife test (current i-time t): 5 mul of catalyst slurry was coated onto a circular glassy carbon area of a rotating disk electrode and dried to form a working electrode. An electrochemical workstation is adopted as an electrochemical generating device, a rotating ring disk electrode coated with a catalyst is used as a working electrode, a platinum wire is used as a counter electrode, saturated calomel is used as a reference electrode, and the voltage E of the platinum ring endring=1.3VRHE. A0.1M KOH aqueous solution was used as an electrolyte, and oxygen gas was continuously introduced into the electrolyte (oxygen flow rate: 60 mL/min). The voltage is kept at 0.2V during the testRHEAnd (4) detecting the change of the disk current i with the time t by using the electrochemical workstation. The decrease in the disc current i may reflect its instability and easy deactivation during the long time t reaction. The results of the lifetime test (current i-time t) in the application of electrocatalytic hydrogen peroxide production are shown in fig. 17.
FIG. 17 reflects the stability of the electrocatalytic reaction of 25-CXGs-600, with the current density remaining unchanged after 60 hours of reaction. Therefore, the conclusion can be drawn that the gelation of resorcinol and formaldehyde can be promoted by regulating and controlling the microwave synthesis time and the carbonization temperature, so that the prepared carbon aerogel has better stability, the morphology is easier to expose active sites in the reaction, the electrocatalytic oxygen reduction process is promoted, and a good catalytic effect is achieved.
The statements in this specification merely set forth a list of implementations of the inventive concept and the scope of the present invention should not be construed as limited to the particular forms set forth in the examples.

Claims (10)

1. A method for synthesizing a carbon aerogel catalyst based on the action of microwaves is characterized by comprising the following steps: and (2) taking resorcinol and formaldehyde as reaction raw materials, taking water as a solvent, adding the reaction raw materials into the water, adjusting the pH value to be 5-7, then placing the reaction liquid system in a microwave radiation environment for reaction, drying after the reaction is finished, and transferring the obtained solid to a tubular furnace for roasting in a nitrogen atmosphere to obtain the carbon aerogel catalyst product.
2. The method for synthesizing carbon aerogel catalyst based on microwave action according to claim 1, comprising the following steps:
1) adding resorcinol and a deionized water solvent into a beaker, stirring, adding a formaldehyde solution, uniformly stirring, and then adjusting the pH to be between 5 and 7 by using a sodium hydroxide solution with the concentration of 0.5 to 2 mol/L;
2) transferring the reaction liquid system obtained in the step 1) into a reaction tube, placing the reaction tube into a microwave synthesizer, starting the microwave synthesizer to perform microwave radiation heating, heating the reaction liquid system to 70-90 ℃ for reaction, and controlling the microwave radiation time to be 10-30 min to enable the reaction liquid system to react in the reaction tube to form wet gel;
3) and 2) after the reaction is finished, transferring the synthesized wet gel into a culture dish from the reaction tube, then putting the culture dish into an oven for drying, transferring the dried solid into a porcelain boat, then putting the porcelain boat into a tube furnace for roasting in nitrogen atmosphere, cooling to room temperature after the roasting is finished, and fully grinding by using a mortar to obtain the final carbon aerogel catalyst.
3. The method for synthesizing the carbon aerogel catalyst based on the microwave action according to claim 2, wherein in the step 1), the mass concentration of the formaldehyde solution is 30-40%, preferably 35-37%; the molar ratio of the resorcinol to the formaldehyde is 0.33-0.7: 1, preferably 0.5: 1; the ratio of the mass of the resorcinol to the volume of the deionized water solvent is 1: 3-8, preferably 1:5, the unit of the mass is g, and the unit of the volume is mL.
4. The method for synthesizing carbon aerogel catalyst based on microwave as claimed in claim 2, wherein in step 1), the concentration of the sodium hydroxide solution is 1mol/L, and the pH is adjusted to 5.8-6.2 by the sodium hydroxide solution.
5. The method for synthesizing carbon aerogel catalyst based on microwave as claimed in claim 2, wherein in step 2), the operating power of the microwave synthesizer is controlled to be between 100W and 300W, preferably 200W; the reaction temperature is controlled at 85 ℃, and the microwave radiation time is controlled at 15 min.
6. The microwave-based method for synthesizing the carbon aerogel catalyst according to claim 2, wherein in the step 3), the drying temperature in the oven is 50-80 ℃, preferably 60 ℃; the drying time is 8-18 h, preferably 12 h.
7. The method for synthesizing carbon aerogel catalyst based on microwave as claimed in claim 2, wherein the calcination process in the tube furnace in step 3) is: heating to 500-900 ℃ from room temperature at a heating rate of 3-10 ℃/min, preferably 600 ℃, then roasting at constant temperature for 1-5 h, preferably 3h, and finally naturally cooling to room temperature to obtain a catalyst product; wherein the heating rate of the tube furnace is preferably 5 ℃/min.
8. A carbon aerogel catalyst synthesized by the method of any of claims 1 to 7.
9. The carbon aerogel catalyst of claim 8, in the preparation of hydrogen peroxide by electrocatalytic oxygen reduction.
10. The application of claim 9, wherein an electrochemical workstation is used as an electrochemical generating device, a three-electrode measuring system is adopted, the carbon aerogel catalyst is coated on a rotating ring disk electrode to be used as a working electrode, a platinum wire is used as a counter electrode, saturated calomel is used as a reference electrode, KOH aqueous solution is used as electrolyte, and electrochemical oxygen reduction reaction is carried out to produce hydrogen peroxide product; wherein, the concentration of the KOH aqueous solution is 0.05-0.2mol/L, preferably 0.1 mol/L.
CN202110591160.8A 2021-05-28 2021-05-28 Carbon aerogel catalyst synthesized under microwave action and synthesis method and application thereof Pending CN113292061A (en)

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Application publication date: 20210824