Preparation method and application of Zn-NC electrocatalyst for synthesizing H2O2

Abstract

The invention discloses a preparation method and application of a Zn-N-C electrocatalyst for synthesizing H2O2. A Zn-N-C electrocatalyst with high selectivity for synthesizing H2O2 is synthesized by using polypyrrole nanowires as a carbon and nitrogen source and ZIF-8 of a zeolite structure as a metal zinc source, wherein metal Zn is loaded on a nitrogen-doped carbon material in the form of a single atom, and the loading amount of metal Zn is 5wt%-25wt%. The selectivity of the Zn-N-C electrocatalyst for catalytic synthesis of H2O2 is close to 100%. The present invention uses polypyrrole as a carbon and nitrogen source, which is easier to anchor metal zinc ions. The catalyst is formed by one-step pyrolysis of a composite material of polypyrrole and ZIF-8, has a simple preparation process, and the electrocatalyst raw materials are widely available and low in cost.

Description

Technical Field

[0001] The invention belongs to the technical field of synthesis of metal-supported electrocatalysts, and specifically relates to a preparation method of a Zn-NC electrocatalyst for synthesizing H2O2 and an application thereof. Background Art

[0002] As a high-value oxidant, H2O2 is widely used in industries such as wastewater treatment, papermaking, and chemical synthesis. In 2020, the global H2O2 production was about 4.5 million tons, and it is expected that the global annual production will reach 6 million tons by 2027. However, currently about 99% of H2O2 is synthesized through the high-energy anthraquinone process, and this process can only be carried out in centralized factories, which will produce a large amount of waste chemicals. Therefore, in the context of carbon neutrality, it is particularly important to find energy-saving, efficient and green H2O2 preparation processes. Electrochemical two-electron oxygen reduction method (2e − Electrochemical oxygen reduction (ORR) reduces O2 to H2O2. The synthesized H2O2 solution is free of impurities and has high purity, and can be directly used in sewage treatment and other aspects. Electrochemical oxygen reduction has the advantages of simple reaction conditions, clean production process and low time consumption. It is a safe, energy-saving, green and sustainable way to produce H2O2.

[0003] At present, the catalysts used for electrocatalytic synthesis of H2O2 mainly include precious metals and their alloys, single atom catalysts (SACs) and carbon-based materials. Single atom catalysts are favored by researchers because of their high atomic utilization and fully exposed active sites. Unlike traditional nanoparticle catalysts, SACs have the following characteristics: First, the isolated atomic sites in single atom catalysts can promote the terminal adsorption of O2 and reaction intermediates, thereby hindering the cleavage of the OO bond and completely reducing it to water; second, the electronic structure of the catalyst surface can be regulated by the coordination of the metal-substrate, thereby regulating the adsorption of reaction intermediates and optimizing the electrocatalytic activity and selectivity. In many studies, SACs have shown more stable physical and chemical properties and longer cycle life than conventional nanoparticles. However, the synthesis of high-performance single atom catalysts is still a key bottleneck restricting the electrocatalytic synthesis of H2O2. Therefore, designing efficient and selective single atom catalysts is a top priority for achieving green production of H2O2. Summary of the invention

[0004] The technical problem solved by the present invention is to provide a preparation method of a Zn-NC electrocatalyst for synthesizing H2O2 and its application. The method uses polypyrrole nanowires as carbon and nitrogen sources and zeolite-structured ZIF-8 as a metal zinc source to synthesize a Zn-NC electrocatalyst with high selectivity for synthesizing H2O2.

[0005] The present invention adopts the following technical solution to solve the above technical problems: a method for preparing a Zn-NC electrocatalyst for synthesizing H2O2, characterized in that: in the Zn-NC electrocatalyst, metal Zn is loaded on a nitrogen-doped carbon material in the form of a single atom, and the loading amount of metal Zn is 5wt%-25wt%;

[0006] The specific preparation process of the Zn-NC electrocatalyst is as follows:

[0007] Step S1: using CTAB as a template agent and ammonium persulfate as an oxidant, stirring pyrrole at 0-5°C to react to obtain polypyrrole nanowires;

[0008] Step S2: ultrasonically dispersing the polypyrrole nanowires obtained in step S1 in methanol, adding zinc nitrate and stirring, then adding 2-methylimidazole, standing, performing solid-liquid separation, and drying;

[0009] Step S3: placing the material obtained in step S2 in a tube furnace, heating it to 600° C. at a heating rate of 1-10° C. / min under an inert gas atmosphere and keeping the temperature constant for 2-4 hours, and then naturally cooling it to room temperature;

[0010] Step S4: soaking the material obtained in step S3 with an acid solution, then filtering it, washing it with water until it is neutral, and drying it to obtain a Zn-NC electrocatalyst.

[0011] It is further defined that the inert gas in step S3 is one or more of nitrogen, argon or helium.

[0012] It is further defined that the acid solution in step S4 is one or more of hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid or acetic acid, the concentration of the acid solution is 0.5-4 mol / L, the acid treatment temperature is 25-100° C., and the acid treatment time is 2-24 h.

[0013] The method for preparing the Zn-NC electrocatalyst for synthesizing H2O2 of the present invention is characterized by the following specific steps:

[0014] Step S1: using 0.22 g CTAB as a template and 2.0 g ammonium persulfate as an oxidant, 600 μL pyrrole was stirred and reacted at 0-5 °C for 12 h to obtain polypyrrole nanowires;

[0015] Step S2: ultrasonically disperse 0.1 g of the polypyrrole nanowires obtained in step S1 in 120 mL of methanol, add 2.38 g of zinc nitrate and stir for 12 h, then add 1.64 g of 2-methylimidazole, let stand for 12 h, perform solid-liquid separation, and dry at 80° C.

[0016] Step S3: placing the material obtained in step S2 in a tube furnace, heating it to 600° C. at a heating rate of 3° C. / min under a nitrogen atmosphere and keeping the temperature constant for 3 h, and then naturally cooling it to room temperature;

[0017] Step S4: Soak the material obtained in step S3 in 2 mol / L hydrochloric acid at room temperature for 24 h, then filter it, wash it with water until it is neutral, and dry it at 80° C. to obtain a Zn-NC electrocatalyst.

[0018] The application of the Zn-NC electrocatalyst for catalytic synthesis of H2O2 described in the present invention is characterized by the specific process of: dispersing 1 mg of the prepared Zn-NC electrocatalyst in a mixed solution of water, ethanol and Nafion, and after ultrasonic dispersion, taking an appropriate amount of the solution and dropping it on a ring disk electrode, drying it in the air, and using a three-electrode system for testing, wherein a Hg / HgO electrode and a platinum sheet are used as a reference electrode and a counter electrode, respectively, and the electrolyte is an O2-saturated 0.1 mol / L KOH aqueous solution. The selectivity of the Zn-NC electrocatalyst for catalytic synthesis of H2O2 is close to 100%.

[0019] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0020] 1. Compared with the traditional anthraquinone method, the method for preparing H2O2 of the present invention is green and environmentally friendly, and can be directly used in the fields of sewage treatment.

[0021] 2. The present invention uses polypyrrole as a carbon and nitrogen source, which is easier to anchor metal zinc ions. The catalyst is prepared by one-step pyrolysis of a composite material of polypyrrole and ZIF-8, and the preparation process is simple. The electrocatalyst raw material source is wide and the cost is low.

[0022] The catalyst provided by the present invention can be evaluated by the following method:

[0023] The catalytic performance of the catalyst was tested using a rotating ring disk electrode and an electrochemical workstation. The catalyst was ultrasonically dispersed in a mixed solution of water, ethanol and Nafion. After uniform dispersion, an appropriate amount was added to the rotating ring disk electrode and dried naturally. The electrolyte was 0.1M KOH. Linear sweep voltammetry (LSV) and cyclic voltammetry (CV) tests were carried out in an oxygen-saturated electrolyte. The results showed that the selectivity of the catalyst for the synthesis of H2O2 was almost 100%. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a SEM image of the Zn-NC electrocatalyst prepared in Example 1;

[0025] Figure 2 is the XRD pattern of the Zn-NC electrocatalyst prepared in Example 1;

[0026] Figure 3 is a HADDF-STEM image of the Zn-NC electrocatalyst prepared in Example 1;

[0027] Figure 4 is the H2O2 selectivity curve of the Zn-NC electrocatalyst prepared in Example 1;

[0028] Figure 5 is the number of electrons transferred by the Zn-NC electrocatalyst prepared in Example 1 in the oxygen reduction reaction. DETAILED DESCRIPTION

[0029] The above contents of the present invention are further described in detail below through examples, but this should not be understood as the scope of the above subject matter of the present invention being limited to the following examples, and all technologies implemented based on the above contents of the present invention belong to the scope of the present invention. Example 1

[0030] Step S1: using 0.22 g CTAB as a template and 2.0 g ammonium persulfate as an oxidant, 600 μL pyrrole was stirred and reacted at 0-5 °C for 12 h to obtain polypyrrole nanowires;

[0031] Step S2: ultrasonically disperse 0.1 g of the polypyrrole nanowires obtained in step S1 in 120 mL of methanol, add 2.38 g of zinc nitrate and stir for 12 h, then add 1.64 g of 2-methylimidazole, let stand for 12 h, perform solid-liquid separation, and dry at 80° C.

[0032] Step S3: placing the material obtained in step S2 in a tube furnace, heating it to 600° C. at a heating rate of 3° C. / min under a nitrogen atmosphere and keeping the temperature constant for 3 h, and then naturally cooling it to room temperature;

[0033] Step S4: Soak the material obtained in step S3 in 2 mol / L hydrochloric acid at room temperature for 24 h, then filter it, wash it with water until it is neutral, and dry it at 80° C. to obtain a Zn-NC electrocatalyst.

[0034] 1 mg of the above-prepared Zn-NC electrocatalyst was dispersed in a mixed solution of water, ethanol and Nafion. After uniform ultrasonic dispersion, an appropriate amount of the solution was dripped onto the ring-disk electrode and dried in the air. The three-electrode system was used for testing, with Hg / HgO electrode and platinum sheet as reference electrode and counter electrode respectively, and the electrolyte was an O2-saturated 0.1 mol / L KOH aqueous solution. The scan speed during the test was 10 mV / s, and the scan range was 0V~1.2V (vs. RHE). Example 2

[0035] Step S1: using 0.22 g CTAB as a template and 2.0 g ammonium persulfate as an oxidant, 600 μL pyrrole was stirred and reacted at 0-5 °C for 12 h to obtain polypyrrole nanowires;

[0036] Step S2: ultrasonically disperse 0.2 g of the polypyrrole nanowires obtained in step S1 in 480 mL of methanol, add 9.52 g of zinc nitrate and stir for 12 h, then add 9.84 g of 2-methylimidazole, let stand for 12 h, perform solid-liquid separation, and dry at 80° C.

[0037] Step S3: placing the material obtained in step S2 in a tube furnace, heating it to 600° C. at a heating rate of 5° C. / min under a nitrogen atmosphere and keeping the temperature constant for 4 hours, and then naturally cooling it to room temperature;

[0038] Step S4: Soak the material obtained in step S3 in 2 mol / L hydrochloric acid at room temperature for 24 h, then filter it, wash it with water until it is neutral, and dry it at 80° C. to obtain a Zn-NC electrocatalyst. Example 3

[0039] Step S1: using 0.22 g CTAB as a template and 2.0 g ammonium persulfate as an oxidant, 600 μL pyrrole was stirred and reacted at 0-5 °C for 12 h to obtain polypyrrole nanowires;

[0040] Step S2: ultrasonically disperse 0.2 g of the polypyrrole nanowires obtained in step S1 in 240 mL of methanol, add 2.38 g of zinc nitrate and stir for 12 h, then add 13.14 g of 2-methylimidazole, let stand for 10 h, perform solid-liquid separation, and dry at 80° C.

[0041] Step S3: placing the material obtained in step S2 in a tube furnace, heating it to 600° C. at a heating rate of 5° C. / min under a nitrogen atmosphere and keeping the temperature constant for 2 h, and then naturally cooling it to room temperature;

[0042] Step S4: Soak the material obtained in step S3 in 1 mol / L hydrochloric acid at room temperature for 12 h, then filter it, wash it with water until it is neutral, and dry it at 80° C. to obtain a Zn-NC electrocatalyst. Example

[0043] Step S1: using 0.22 g CTAB as a template and 2.0 g ammonium persulfate as an oxidant, 600 μL pyrrole was stirred and reacted at 0-5 °C for 12 h to obtain polypyrrole nanowires;

[0044] Step S2: ultrasonically disperse 0.1 g of the polypyrrole nanowires obtained in step S1 in 120 mL of methanol, add 2.38 g of zinc nitrate and stir for 5 h, then add 1.64 g of 2-methylimidazole, let stand for 10 h, perform solid-liquid separation, and dry at 80° C.;

[0045] Step S3: placing the material obtained in step S2 in a tube furnace, heating it to 600° C. at a heating rate of 5° C. / min under a nitrogen atmosphere and keeping the temperature constant for 2 h, and then naturally cooling it to room temperature;

[0046] Step S4: Soak the material obtained in step S3 in 2 mol / L hydrochloric acid at room temperature for 24 h, then filter it, wash it with water until it is neutral, and dry it at 80° C. to obtain a Zn-NC electrocatalyst.

[0047] The above embodiments describe the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for illustrating the principles of the present invention. Without departing from the scope of the principles of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a Zn-NC electrocatalyst for synthesizing H2O2, characterized in that: In the Zn-NC electrocatalyst, metal Zn is loaded on the nitrogen-doped carbon material in the form of single atoms, and the loading amount of metal Zn is 5wt%-25wt%; The specific preparation process of the Zn-NC electrocatalyst is as follows: Step S1: using CTAB as a template agent and ammonium persulfate as an oxidant, stirring pyrrole at 0-5°C to react to obtain polypyrrole nanowires; Step S2: ultrasonically dispersing the polypyrrole nanowires obtained in step S1 in methanol, adding zinc nitrate and stirring, then adding 2-methylimidazole, standing, performing solid-liquid separation, and drying; Step S3: placing the material obtained in step S2 in a tube furnace, heating it to 600° C. at a heating rate of 1-10° C. / min under an inert gas atmosphere and keeping the temperature constant for 2-4 hours, and then naturally cooling it to room temperature; Step S4: soaking the material obtained in step S3 with an acid solution, then filtering it, washing it with water until it is neutral, and drying it to obtain a Zn-NC electrocatalyst.

2. The method for preparing the Zn-NC electrocatalyst for synthesizing H2O2 according to claim 1, characterized in that: The inert gas in step S3 is one or more of nitrogen, argon or helium.

3. The method for preparing the Zn-NC electrocatalyst for synthesizing H2O2 according to claim 1, characterized in that: The acid solution in step S4 is one or more of hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid or acetic acid, the concentration of the acid solution is 0.5-4 mol / L, the acid treatment temperature is 25-100° C., and the acid treatment time is 2-24 h.

4. The method for preparing the Zn-NC electrocatalyst for synthesizing H2O2 according to claim 1, characterized in that The specific steps are: Step S1: using 0.22 g CTAB as a template and 2.0 g ammonium persulfate as an oxidant, 600 μL pyrrole was stirred and reacted at 0-5 °C for 12 h to obtain polypyrrole nanowires; Step S2: ultrasonically disperse 0.1 g of the polypyrrole nanowires obtained in step S1 in 120 mL of methanol, add 2.38 g of zinc nitrate and stir for 12 h, then add 1.64 g of 2-methylimidazole, let stand for 12 h, perform solid-liquid separation, and dry at 80° C. Step S3: placing the material obtained in step S2 in a tube furnace, heating it to 600° C. at a heating rate of 3° C. / min under a nitrogen atmosphere and keeping the temperature constant for 3 h, and then naturally cooling it to room temperature; Step S4: Soak the material obtained in step S3 in 2 mol / L hydrochloric acid at room temperature for 24 h, then filter it, wash it with water until it is neutral, and dry it at 80° C. to obtain a Zn-NC electrocatalyst.

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