Preparation method of carbon catalyst for electrocatalytic preparation of hydrogen peroxide and the catalyst

Abstract

The present invention discloses a preparation method of a carbon catalyst for electrocatalytic preparation of hydrogen peroxide and the prepared catalyst. First, phthalamide or phthalonitrile is mixed with phosphorus pentoxide and a conductive carbon additive in a mass ratio of 1:8-14:0.8-1.2 to obtain a reaction mixture; then the reaction mixture is loaded into a container and evacuated, and then reacted at 350-750 °C; after the reaction is completed, the product is washed with water to remove phosphorus pentoxide, and then dried to obtain a carbon catalyst for electrocatalytic preparation of hydrogen peroxide. The catalyst prepared by this method ensures high conductivity of the material while introducing high-content oxygen heteroatom active sites, realizing high activity and high selectivity of the material for electrocatalytic production of hydrogen peroxide.

Description

Technical Field

[0001] The present invention relates to the preparation of a catalyst, and particularly to a method for preparing a carbon catalyst for electrocatalytic production of hydrogen peroxide and the prepared catalyst. Background Art

[0002] As a green and pollution-free catalyst, hydrogen peroxide has important and extensive applications in fields such as chemical engineering and medicine. Currently, hydrogen peroxide is mainly synthesized industrially by the anthraquinone method, but this method requires the consumption of the precious metal catalyst Pd and produces a large amount of by-products, polluting the environment. Moreover, there is a risk of explosion when hydrogen and oxygen are directly mixed to prepare hydrogen peroxide. Electro-catalytic preparation of hydrogen peroxide, as a green method, has begun to receive wide attention. This method is to generate hydrogen peroxide from oxygen molecules and water through a two-electron pathway under electrolysis conditions with the help of a catalyst. However, if the selectivity of the catalyst is not high, oxygen molecules are prone to generate water through a four-electron pathway, thereby reducing the yield of hydrogen peroxide. Existing electro-catalysts include precious metal catalysts, non-precious metal catalysts, carbon material catalysts, and covalent organic framework materials (COFs), etc. Among them, precious metal catalysts exhibit high activity and high selectivity. For example, Pt(111) crystal planes are prepared by mixing polypeptides with H2PtCl6 and then loaded onto carbon black to form a Pt(111) / C structure. However, this method has high costs and poor stability. Introducing non-precious metals into the nitrogen-doped carbon material framework can form non-precious metal-nitrogen-carbon (M-N-C) active sites with catalytic activity for oxygen reduction reactions. By regulating the composition of non-precious metals and the atomic complexation state around them, selective control of the electro-catalytic reaction process can be achieved. For example, it has been found that pyrrolic Co-N4 can increase the selectivity of the two-electron process of the electro-catalytic oxygen reduction reaction to 94%, while pyridinic Co-N4 exhibits a four-electron process of the electro-catalytic oxygen reduction reaction. Although non-precious metal electro-catalysts have significant advantages over precious metal catalysts in terms of preparation cost and catalytic stability, it is extremely challenging to precisely regulate the complexation state of metal active centers, which also greatly increases the difficulty of their large-scale industrial production. Among carbon material catalysts, carbon materials doped with N elements can effectively weaken the O-O bond and reduce the overpotential of the oxygen reduction reaction. Using the larger atomic size and lower electronegativity of P elements can induce the formation of defects and provide active sites for adsorbed oxygen. In addition, O elements can also serve as active sites for electro-catalytic oxygen reduction. Therefore, co-doping with N, P, and O elements simultaneously can increase the active sites for the electro-catalytic oxygen reduction reaction, maximize the synergistic mechanism of heteroatom doping, and contribute to improving the electro-catalytic performance of the catalyst. Covalent organic framework materials have adjustable structures and can introduce electro-catalytic active sites by reasonably selecting reaction monomers and catalysts, etc. For example, naphthalene diimide-based COF synthesized by hydrothermal synthesis of 1,4,5,8-naphthalenetetracarboxylic dianhydride and triamine compounds can introduce abundant reaction active sites. However, the COF materials synthesized in this way have low conductivity, resulting in difficult material migration during the reaction process and being unfavorable for the improvement of catalytic activity. Although the current methods for synthesizing such materials can controllably introduce active sites, how to improve their conductivity still needs to be further solved. Summary of the Invention

[0003] The object of the present invention is to provide a preparation method of a carbon catalyst for electrocatalytic preparation of hydrogen peroxide. The catalyst prepared by this method ensures high conductivity of the material while introducing high-content oxygen heteroatom active sites, achieving high activity and high selectivity for electrocatalytic production of hydrogen peroxide by the material.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A preparation method of a carbon catalyst for electrocatalytic preparation of hydrogen peroxide, comprising the following steps:

[0006] Step S1: Mix phthalamide or phthalonitrile with phosphorus pentoxide and a conductive carbon additive in a mass ratio of 1:8-14:0.8-1.2 to obtain a reaction mixture, wherein the phthalamide is terephthalamide or phthalamide, and the phthalonitrile is terephthalonitrile, phththalonitrile or isophthalonitrile;

[0007] Step S2: Load the reaction mixture into a container and evacuate it, and then carry out the reaction at 350-750 °C;

[0008] Step S3: After the reaction is completed, wash the product with water to remove phosphorus pentoxide, and then dry to obtain a carbon catalyst for electrocatalytic preparation of hydrogen peroxide.

[0009] Preferably, in the step S1, the conductive carbon additive is Ketjen black, carbon nanotubes or graphene.

[0010] Preferably, in the step S3, the drying is carried out at 70-100 °C.

[0011] Preferably, in the step S1, mix terephthalamide with phosphorus pentoxide and Ketjen black in a mass ratio of 1:12.5:1; in the step S2, load the reaction mixture into a container and evacuate it, and then carry out the reaction at 400 °C for 6 h.

[0012] The method of the present invention uses phosphorus pentoxide as a catalyst to polymerize phthalamide or phthalonitrile into a triazine-based polymer, and at the same time in-situ composes a conductive carbon additive. Through heat treatment, a carbon material co-doped with N, P and O elements is obtained. In this reaction process, phosphorus pentoxide not only catalyzes the polymerization of the amide group [C(=O)-NH2] in phthalamide into a triazine-based polymer, but also the excessive phosphorus pentoxide can endow the prepared carbon catalyst with rich oxygen heteroatom active sites. At the same time, conductive additives such as Ketjen black or carbon nanotubes are in-situ composited with the polymer, which helps to improve conductivity and prevent polymer stacking, ensuring that the catalyst has a conductive network for rapid ion / electron transport. Tests show that the catalyst prepared by the present invention exhibits high activity and high selectivity in the process of electrocatalytic production of hydrogen peroxide and has good stability. Brief Description of the Drawings

[0013] Figure 1 Scanning electron microscope image of the carbon catalyst prepared in Example 1;

[0014] Figure 2 Transmission electron microscope image of the carbon catalyst prepared in Example 1;

[0015] Figure 3 Infrared spectrum of the carbon catalyst prepared in Example 1;

[0016] Figure 4 XPS spectrum of the carbon catalyst prepared in Example 1;

[0017] Figure 5 XPS peak fitting results of oxygen element in the carbon catalyst prepared in Example 1;

[0018] Figure 6 Cyclic voltammetry curve of the carbon catalyst prepared in Example 1 under test conditions;

[0019] Figure 7 Linear sweep voltammetry curve of the carbon catalyst prepared in Example 1 under test conditions;

[0020] Figure 8 For Figure 7 Electron transfer number and hydrogen peroxide selectivity in the catalytic reaction process calculated;

[0021] Figure 9 Stability test results of the carbon catalyst prepared in Example 1;

[0022] Figure 10 Actual electrocatalytic hydrogen peroxide production rate test and corresponding Faraday efficiency of the carbon catalyst prepared in Example 1 in an H-type electrolytic cell;

[0023] Figure 11 Organic pollutant degradation curve of the carbon catalyst prepared in Example 1 for on-line hydrogen peroxide generation;

[0024] Figure 12 Transmission electron microscope image of the carbon catalyst prepared in Example 2;

[0025] Figure 13 Transmission electron microscope image of the carbon catalyst prepared in Example 3;

[0026] Figure 14 Schematic diagram of the synthesis reaction of Example 1. Detailed Description of the Invention

[0027] The present invention will be described in detail below through specific examples:

[0028] I. Preparation Examples

[0029] Example 1 Preparation Example 1 of Carbon Catalyst for Electro-Catalytic Preparation of Hydrogen Peroxide

[0030] Step S1: In a glove box, 0.32 g of terephthalamide monomer, 4 g of phosphorus pentoxide, and 0.32 g of Ketjen black are mixed evenly in a mortar to obtain a reaction mixture.

[0031] Step S2: The reaction mixture is placed in an ampoule. After three cycles of vacuum pumping / nitrogen filling, it is finally evacuated and sealed. Then the ampoule is placed in a muffle furnace and heated to 400 °C at a heating rate of 5 °C / min and maintained for 6 h. -1 and maintained for 6 h.

[0032] Step S3: After the reaction is completed, the product is washed several times with deionized water to remove phosphorus pentoxide, and finally placed in a drying oven and dried at 80 °C to obtain a carbon catalyst for electro-catalytic preparation of hydrogen peroxide.

[0033] The reaction schematic diagram of the above preparation process is as Figure 14 shown.

[0034] The prepared product is characterized. The scanning electron microscope image is as Figure 1 shown, the transmission electron microscope image is as Figure 2 shown, the infrared spectrum is as Figure 3 shown, the XPS spectrum is as Figure 4 shown, and the XPS peak deconvolution result of oxygen element is as Figure 5 shown. From Figure 1 and Figure 2 it can be seen that through the in-situ catalytic reaction preparation process, terephthalamide can achieve uniform coating on the surface of Ketjen black, and this composite effect can ensure the efficient utilization of active sites. From Figure 3 it can be seen that there are carbon-oxygen double bonds and carbon-oxygen single bonds in the product. From Figure 4 it can be seen that there is a 1s peak of O in the product. From Figure 5 it can be seen that the oxygen element is mainly in the form of ether bonds, and existing literature also proves that this form of oxygen element is the most electro-catalytically active for synthesizing hydrogen peroxide. The above can prove that oxygen active sites have been successfully generated in the product.

[0035] Example 2 Preparation Example 2 of Carbon Catalyst for Electro-Catalytic Preparation of Hydrogen Peroxide

[0036] Step S1: In a glove box, 0.32 g of phthalamide monomer, 2.56 g of phosphorus pentoxide, and 0.27 g of carbon nanotubes are mixed evenly in a mortar to obtain a reaction mixture.

[0037] Step S2: Place the reaction mixture in an ampoule, perform three vacuum / argon gas filling cycles, and finally vacuum and seal it. Then place the ampoule in a muffle furnace and heat it to 350 °C at a heating rate of 5 °C / min and maintain for 10 h. -1 and hold at this temperature for 10 h.

[0038] Step S3: After the reaction is completed, wash the product several times with deionized water to remove phosphorus pentoxide, and finally place it in a drying oven to dry at 100 °C to obtain a carbon catalyst for electrocatalytic preparation of hydrogen peroxide.

[0039] The transmission electron microscope image of the product is as Figure 12 shown.

[0040] Example 3 Preparation Example 3 of Carbon Catalyst for Electrocatalytic Preparation of Hydrogen Peroxide

[0041] Step S1: In a glove box, mix 0.26 g of terephthalonitrile monomer, 3.64 g of phosphorus pentoxide, and 0.31 g of graphene powder evenly in a mortar to obtain a reaction mixture.

[0042] Step S2: Place the reaction mixture in an ampoule, perform three vacuum / argon gas filling cycles, and finally vacuum and seal it. Then place the ampoule in a muffle furnace and heat it to 750 °C at a heating rate of 5 °C / min -1 and hold at this temperature for 12 h.

[0043] Step S3: After the reaction is completed, wash the product several times with deionized water to remove phosphorus pentoxide, and finally place it in a drying oven to dry at 70 °C to obtain a carbon catalyst for electrocatalytic preparation of hydrogen peroxide.

[0044] The transmission electron microscope image of the product is as Figure 13 shown.

[0045] II. Electrocatalytic Performance Test

[0046] Using the carbon catalyst prepared in Example 1 as the test sample for electrocatalytic performance test, the test method: Add the sample material to a mixed solution of deionized water, absolute ethanol, and Nafion (mass fraction 5%) with a volume ratio of 2:3:0.2 (the volumes of deionized water, absolute ethanol, and Nafion are 200 μL, 300 μL, and 20 μL respectively), and add to obtain a uniform slurry with a concentration of 5 mg / mL, and drop-coat it onto a glassy carbon electrode as the working electrode. Select 0.1 M potassium hydroxide solution as the electrolyte, and a metal platinum sheet (or platinum wire, graphite rod) as the counter electrode for electrocatalytic reaction test. The test methods include cyclic voltammetry, linear sweep voltammetry, and stability test. The potential range applied to the working electrode is between 0 and 0.9 V (relative to the standard hydrogen electrode).

[0047] The carbon catalyst prepared in Example 1 was configured into a slurry in the same manner and drop-coated onto the gas diffusion electrode as the cathode; a metal platinum sheet (or platinum wire, graphite rod) was used as the anode, and the electrocatalytic synthesis of hydrogen peroxide reaction was carried out in 0.1 M potassium hydroxide solution. The potential range applied to the working electrode was between 0 and 0.9 V (versus standard hydrogen electrode).

[0048] The test results are as Figures 6 to 10 shown, Figure 6 is the cyclic voltammogram of the carbon catalyst under the test conditions, where the oxygen reduction peak is 0.712 V, indicating strong oxygen reduction reaction activity. Figure 7 is the linear sweep voltammogram of the carbon catalyst under the test conditions, from which the number of electron transfers and the hydrogen peroxide selectivity in the corresponding electrocatalytic reaction process can be calculated. Figure 8 is from Figure 7 the number of electron transfers and the hydrogen peroxide selectivity in the catalytic reaction process calculated from the linear sweep voltammogram. The obtained number of electron transfers is between 2.1 - 2.3, and the hydrogen peroxide selectivity is as high as over 85%, indicating a very high selectivity. Figure 9 is the stability test of the carbon catalyst, including the first linear sweep voltammogram and the linear sweep voltammogram after 5000 cycles. It can be seen that the two basically coincide, indicating that the stability is still very high after 5000 cycles. Figure 10 is the actual electrocatalytic hydrogen peroxide production performance test and the corresponding Faraday efficiency of the carbon catalyst in the H-type electrolytic cell. It can be seen that in a wide potential range, this catalyst can maintain a very high hydrogen peroxide production rate, and the Faraday efficiency always remains above 90%. Especially when the cathode potential is 0.3 V, its production rate can reach nearly 317 ppm / h, indicating that this catalyst has very high activity in the electrocatalytic hydrogen peroxide production reaction.

[0049] III. Actual organic pollutant degradation test

[0050] The carbon catalyst prepared in Example 1 was configured into a slurry in the same manner and drop-coated onto the gas diffusion electrode as the cathode; a metal platinum sheet (or platinum wire, graphite rod) was used as the anode, and the organic pollutant degradation test of on-line electrocatalytic synthesis of hydrogen peroxide was carried out in 0.1 M potassium hydroxide solution and 50 mg / L rhodamine B solution. The potential applied to the working electrode was 0.3 V (versus standard hydrogen electrode).

[0051] Figure 11 is the curve of the concentration change of the oxidation degradation of organic pollutants (rhodamine B) using on-line produced hydrogen peroxide over time. The results show that after 60 min of degradation, the degradation efficiency of organic pollutants can be as high as 97.75%, indicating that this oxygen-doped carbon catalyst material has potential commercial value in actual electrocatalytic hydrogen peroxide production.

[0052] Similar experiments were carried out on the products of Examples 2 and 3, and the experimental results were similar to the electrocatalytic performance of the products of Example 1, all having good high selectivity and stability, and also having high activity in the electrocatalytic hydrogen peroxide production reaction.

[0053] The above embodiments are only several illustrations of the concept and implementation of the present invention, and are not intended to limit it. Under the concept of the present invention, technical solutions without substantial transformation are still within the protection scope.

Claims

1. A preparation method of a carbon catalyst for electrocatalytic preparation of hydrogen peroxide, characterized in that It includes the following steps: Step S1: Mix phthalamide or phthalonitrile with phosphorus pentoxide and a conductive carbon additive in a mass ratio of 1:8 - 14:0.8 - 1.2 to obtain a reaction mixture. The phthalamide is terephthalamide or phthalamide, and the phthalonitrile is terephthalonitrile, phththalonitrile or isophthalonitrile; Step S2: Load the reaction mixture into a container and evacuate it, and then carry out the reaction at 350 - 750 °C; Step S3: After the reaction is completed, wash the product with water to remove phosphorus pentoxide, and then dry it to obtain a carbon catalyst for electrocatalytic preparation of hydrogen peroxide.

2. The preparation method of the carbon catalyst for electrocatalytic preparation of hydrogen peroxide according to claim 1, characterized in that: In the step S1, the conductive carbon additive is Ketjen black, carbon nanotubes or graphene.

3. The preparation method of the carbon catalyst for electrocatalytic preparation of hydrogen peroxide according to claim 1, characterized in that: In the step S3, the drying is carried out at 70 - 100 °C.

4. The preparation method of the carbon catalyst for electrocatalytic preparation of hydrogen peroxide according to claim 2, characterized in that: In the step S1, mix terephthalamide with phosphorus pentoxide and Ketjen black in a mass ratio of 1:12.5:1; In the step S2, load the reaction mixture into a container and evacuate it, and then carry out the reaction at 400 °C for 6 h.

5. A carbon catalyst for electrocatalytic preparation of hydrogen peroxide, characterized in that It is prepared by the preparation method described in any one of claims 1 - 4.

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