A nitrogen-doped biomass carbon-based bifunctional catalyst and its preparation method and application

Abstract

The present invention discloses a nitrogen-doped biomass carbon-based bifunctional catalyst, its preparation method, and application. The method pretreats biomass feedstock with a deep eutectic solvent to dissolve some biomass components, obtaining a pretreated biomass material. The resulting material is then mixed with a nitrogen-containing compound and carbonized to form a nitrogen-doped porous catalyst material. The prepared catalyst exhibits excellent bifunctional catalytic activity for oxygen reduction and oxygen evolution. Furthermore, the catalyst has a simple preparation process, low cost, and is amenable to large-scale production and application.

Description

Technical Field

[0001] The present invention belongs to the field of electrocatalysis technology, and specifically relates to a nitrogen-doped biomass carbon-based bifunctional catalyst, its preparation method, and application. Specifically, it relates to a method for preparing a nitrogen-doped biomass carbon-based bifunctional catalyst by pretreating biomass feedstock using a deep eutectic solvent, and its application. Background Art

[0002] Energy is an important foundation for national economic and social development. Fossil energy has always made important contributions to the development of human society. However, as a non-renewable resource, overreliance on fossil energy has led to a sharp rise in its price, resulting in an energy crisis. At the same time, the widespread use of fossil fuels has also brought about a series of natural environmental problems, such as the emission of waste gases and dust such as carbon dioxide, nitrogen oxides, and sulfur oxides. The greenhouse effect and environmental pollution caused by these problems will seriously threaten human survival. Therefore, we urgently need to develop clean, efficient, and sustainable green energy to replace traditional fossil energy in order to achieve the long-term sustainable development of human society. As a green and clean energy device, zinc-air batteries have attracted widespread attention due to their high energy density, good stability, and ease of use.

[0003] At present, the oxygen reduction and oxygen evolution reactions occurring at the cathode of zinc-air batteries have slow kinetics in actual operation, which reduces the energy conversion efficiency and limits their large-scale commercial application. Therefore, catalysts must be used to reduce the energy barrier of the reaction and accelerate the oxygen reduction and oxygen evolution reactions at the cathode. Precious metals such as Pt, Ru and Ir and their oxides are commonly used battery cathode catalysts, but they are expensive, have poor stability and scarce reserves, and cannot meet the requirements of large-scale commercial application. Recent studies have shown that carbon materials, especially carbon materials prepared from biomass as raw materials, have good catalytic activity. However, the biomass materials with good electrochemical properties currently require relatively complex processes and high energy consumption in the preparation process. At the same time, the catalysts often only have single catalytic activity, and there are few catalysts with oxygen reduction and oxygen evolution catalytic activity. Therefore, there is an urgent need to develop a low-cost, green and simple process technology to prepare biomass carbon-based bifunctional catalysts with good catalytic activity. Summary of the Invention

[0004] In order to address the shortcomings and deficiencies of the prior art, the primary purpose of the present invention is to provide a method for preparing a nitrogen-doped biomass carbon-based bifunctional catalyst, which uses a low eutectic solvent to pretreat the biomass raw material, dissolve some biomass components, obtain a pretreated biomass material, and then mix it with a nitrogen-containing compound and carbonize it to form a nitrogen-doped porous catalyst material; so as to solve the problems of complex process and high cost in the existing preparation of carbon-based catalysts using biomass as raw material, while improving the catalytic activity of the catalyst (for oxygen reduction reaction and oxygen evolution reaction).

[0005] Another object of the present invention is to provide a nitrogen-doped biomass carbon-based bifunctional catalyst prepared by the above preparation method.

[0006] Another object of the present invention is to provide an application of the above-mentioned nitrogen-doped biomass carbon-based bifunctional catalyst.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A method for preparing a nitrogen-doped biomass carbon-based bifunctional catalyst comprises the following steps:

[0009] (1) heating and mixing the hydrogen bond donor and the hydrogen bond acceptor to obtain a DES solvent;

[0010] (2) adding the biomass raw material to a DES solvent, heating, washing, and drying to obtain an EDS-treated biomass raw material;

[0011] (3) The biomass raw material treated with EDS is mixed with nitrogen-containing compounds and carbonized to obtain a nitrogen-doped porous biomass carbon-based bifunctional catalyst.

[0012] Preferably, the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor in step (1) is 1:0.2-10.

[0013] Preferably, the hydrogen bond acceptor in step (1) is at least one of choline chloride and betaine; and the hydrogen bond donor is at least one of formic acid, acetic acid, oxalic acid, ethylene glycol, glycerol, urea and imidazole.

[0014] Preferably, the heating in step (1) is at 70-90° C. for 0.25-1 h.

[0015] Preferably, the heating in step (1) is performed while stirring, and the stirring speed is 100 to 300 rpm.

[0016] Preferably, the biomass raw material in step (2) is at least one of eucalyptus, poplar and birch; and the particle size of the biomass raw material is 40 to 120 meshes.

[0017] Preferably, the mass ratio of the biomass raw material to the DES solvent in step (2) is 1:10-50.

[0018] Preferably, the temperature of the heating treatment in step (2) is 70-110° C., and the time is 0.5-48 h.

[0019] Preferably, the stirring speed of the heating treatment in step (2) is 100 to 300 rpm.

[0020] Preferably, the washing in step (2) refers to washing with water and ethanol and filtering; the water is ultrapure water, deionized water or tap water, and the ethanol is 95% ethanol.

[0021] Preferably, the drying in step (2) is freeze drying, wherein the sample is first frozen with liquid nitrogen and then placed in a freeze dryer for conventional freeze drying, and the drying time is 6 to 24 hours.

[0022] Preferably, the nitrogen-containing compound in step (3) is at least one of ammonium chloride, urea, dicyandiamide and thiourea.

[0023] Preferably, the mass ratio of the biomass raw material after EDS treatment to the nitrogen-containing compound in step (3) is 1:1 to 50.

[0024] Preferably, the carbonization temperature in step (3) is 800-1000° C., and the time is 0.5-3 h.

[0025] Preferably, the heating rate of the carbonization in step (3) is 1 to 10°C / min.

[0026] A nitrogen-doped biomass carbon-based bifunctional catalyst is prepared by the above method.

[0027] The application of the above-mentioned nitrogen-doped biomass carbon-based bifunctional catalyst in zinc-air batteries.

[0028] Preferably, the nitrogen-doped biomass carbon-based bifunctional catalyst is used as a cathode electrode material for zinc-air batteries.

[0029] The present invention utilizes a deep eutectic solvent to pretreat the biomass raw material. The deep eutectic solvent is a low eutectic mixture formed by mixing hydrogen bond donors and hydrogen bond acceptors in a certain proportion. The strong hydrogen bond network formed can dissolve part of the lignin and hemicellulose, destroy the original structure of the lignocellulose, and form pores and defects on the biomass material. Further by freeze drying, its structure can be kept intact. The pretreated biomass material is mixed with a nitrogen-containing compound, and after high-temperature carbonization, a high specific surface area and abundant active sites can be formed, ultimately forming a biomass carbon-based catalyst with good catalytic activity.

[0030] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0031] (1) Eucalyptus and birch are biomass raw materials with low prices and abundant reserves. The use of these biomass raw materials to prepare catalysts can not only achieve high-value utilization of biomass materials, but also their good catalytic performance can alleviate the energy crisis to a certain extent.

[0032] (2) The low eutectic solvent used in the pretreatment has the advantages of simple preparation, recyclability, and low price, which is conducive to the large-scale preparation and utilization of the catalyst. The pretreatment conditions are mild, the process is simple, and it is easy to operate.

[0033] (3) The biomass-based catalyst prepared by this preparation method has good catalytic effect. The oxygen reduction catalytic effect is comparable to that of 20% Pt / C, and the oxygen evolution catalytic effect is equivalent to that of RuO2. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The oxygen reduction catalytic performance of the prepared nitrogen-doped biomass carbon-based catalyst is shown in the figure. As can be seen from the figure, the half-wave potential of the comparative example 1 is 0.65V, and the catalytic activity of oxygen reduction is poor. The half-wave potential of the catalyst materials prepared in Examples 1-3 is between 0.85 and 0.86V, which is better than the commercial Pt / C material. At the same time, the limiting current density is about 5.5mA / cm 2 , with good conductivity.

[0035] Figure 2 The oxygen evolution catalytic performance of the prepared nitrogen-doped biomass carbon-based catalyst is shown in the figure. As can be seen from the figure, the oxygen evolution catalytic performance of Comparative Example 1 is poor, while the catalytic oxygen evolution reaction of the catalyst materials prepared in Examples 1-3 is good and can be compared with RuO2. 2 At a current density of 1.5 GHz, the overpotential is only 330-390 mV.

[0036] Figure 3 The N2 isothermal adsorption-desorption curve of the prepared nitrogen-doped biomass carbon-based catalyst is shown in the figure. It can be seen from the figure that the specific surface area of ​​comparative example 1 is only 123.04 m 2 / g, the specific surface areas of the catalyst materials prepared in Examples 1 to 3 were 1183.144 m 2 / g、1128.213m 2 / g and 1136.985m 2 / g, the specific surface area of ​​the treated sample is greatly increased. A larger specific surface area is conducive to the formation of more active sites, thereby enhancing the catalytic effect of the catalyst.

[0037] Figure 4 The pore size distribution of the prepared nitrogen-doped biomass carbon-based catalyst can be seen from the figure. The catalysts prepared after pretreatment (Examples 1-3) have formed abundant micro-mesopores with pore sizes between 1 and 3 nanometers. DETAILED DESCRIPTION

[0038] The present invention will be described in further detail below with reference to examples and drawings, but the embodiments of the present invention are not limited thereto.

[0039] In the examples of the present invention, if the specific conditions are not specified, the experiments were carried out according to conventional conditions or the conditions recommended by the manufacturer. All raw materials and reagents used without specifying the manufacturer are conventional products that can be purchased from the market.

[0040] Example 1

[0041] (1) A hydrogen bond donor, acetic acid, and a hydrogen bond acceptor, choline chloride, were mixed in a molar ratio of 2:1, and stirred at 75°C with magnetic stirring at a speed of 200 rpm for 0.5 h until a transparent solution was formed, thereby preparing a deep eutectic solvent.

[0042] (2) Adding dried eucalyptus to the DES solvent described in step (1), heating to 80 degrees Celsius, magnetic stirring at a stirring speed of 200 rpm, and holding for 6 hours, the eucalyptus particle size is 60 mesh, and the mass ratio of eucalyptus to DES is 1:20. After the treatment is completed, the product is repeatedly washed with deionized water and 95% ethanol and filtered, and the filtered product is freeze-dried for 12 hours to obtain a biomass material pretreated with the DES solvent.

[0043] (3) The pretreated biomass material obtained in step (2) was mixed with ammonium chloride in a mass ratio of 1:10, and the mixture was placed in a tubular furnace. Under the protection of N2 gas, the mixture was carbonized at 900 degrees Celsius for 2 hours. The carbonization heating rate was 5°C / min to obtain a nitrogen-doped biomass carbon-based bifunctional catalyst.

[0044] Electrochemical tests were performed using a rotating disk and an electrochemical workstation. After fully grinding the catalyst material obtained in step (3), 5 mg of the catalyst was added to 1 mL of a 0.25% Nafion / ethanol solution and ultrasonicated for 30 minutes to form a uniform black suspension. 10 μL of the suspension was then added dropwise to the surface of a glassy carbon electrode (5 mm in diameter). The reference electrode was an Ag / AgCl electrode, the counter electrode was a platinum sheet electrode, and a 0.1 mol / L potassium hydroxide solution was used as the electrolyte. The rotating rod rotated at 1600 rpm and the scanning speed was 10 mV / s. The performance of oxygen reduction and oxygen precipitation was tested respectively.

[0045] Example 2

[0046] (1) The hydrogen bond donor glycerol and the hydrogen bond acceptor choline chloride were mixed in a molar ratio of 1:1, and magnetically stirred at a temperature of 80 degrees Celsius at a stirring speed of 200 rpm for 0.5 h until a transparent solution was formed to prepare a deep eutectic solvent.

[0047] (2) Adding dried eucalyptus to the DES solvent described in step (1), heating to 90 degrees Celsius, magnetic stirring at a stirring speed of 200 rpm, and holding for 12 hours, the eucalyptus particle size is 60 mesh, and the mass ratio of eucalyptus to DES is 1:20. After the treatment is completed, the product is repeatedly washed with deionized water and 95% ethanol and filtered, and the filtered product is freeze-dried for 12 hours to obtain a biomass material pretreated with the DES solvent.

[0048] (3) The pretreated biomass material obtained in step (2) was mixed with ammonium chloride in a mass ratio of 1:10, and the mixture was placed in a tubular furnace. Under the protection of N2 gas, the mixture was carbonized at 900 degrees Celsius for 2 hours. The carbonization heating rate was 5°C / min to obtain a nitrogen-doped biomass carbon-based bifunctional catalyst.

[0049] Electrochemical tests were performed using a rotating disk and an electrochemical workstation. After fully grinding the catalyst material obtained in step (3), 5 mg of the catalyst was added to 1 mL of a 0.25% Nafion / ethanol solution and ultrasonicated for 30 minutes to form a uniform black suspension. 10 μL of the suspension was then added dropwise to the surface of a glassy carbon electrode (5 mm in diameter). The reference electrode was an Ag / AgCl electrode, the counter electrode was a platinum sheet electrode, and a 0.1 mol / L potassium hydroxide solution was used as the electrolyte. The rotating rod rotated at 1600 rpm and the scanning speed was 10 mV / s. The performance of oxygen reduction and oxygen precipitation was tested respectively.

[0050] Example 3

[0051] (1) The hydrogen bond donor oxalic acid and the hydrogen bond acceptor choline chloride were mixed in a molar ratio of 1:2, and the mixture was stirred at 80 degrees Celsius with a magnetic stirring speed of 200 rpm for 0.5 h until a transparent solution was formed to prepare a deep eutectic solvent.

[0052] (2) Adding dried eucalyptus to the DES solvent described in step (1), heating to 80 degrees Celsius, magnetic stirring at a stirring speed of 200 rpm, and holding for 6 hours, the eucalyptus particle size is 60 mesh, and the mass ratio of eucalyptus to DES is 1:20. After the treatment is completed, the product is repeatedly washed with deionized water and 95% ethanol and filtered, and the filtered product is freeze-dried for 12 hours to obtain a biomass material pretreated with the DES solvent.

[0053] (3) The pretreated biomass material obtained in step (2) was mixed with ammonium chloride in a mass ratio of 1:10, and the mixture was placed in a tubular furnace. Under the protection of N2 gas, the mixture was carbonized at 900 degrees Celsius for 2 hours. The carbonization heating rate was 5°C / min to obtain a nitrogen-doped biomass carbon-based bifunctional catalyst.

[0054] Electrochemical tests were performed using a rotating disk and an electrochemical workstation. After fully grinding the catalyst material obtained in step (3), 5 mg of the catalyst was added to 1 mL of a 0.25% Nafion / ethanol solution and ultrasonicated for 30 minutes to form a uniform black suspension. 10 μL of the suspension was then added dropwise to the surface of a glassy carbon electrode (5 mm in diameter). The reference electrode was an Ag / AgCl electrode, the counter electrode was a platinum sheet electrode, and a 0.1 mol / L potassium hydroxide solution was used as the electrolyte. The rotating rod rotated at 1600 rpm and the scanning speed was 10 mV / s. The performance of oxygen reduction and oxygen precipitation was tested respectively.

[0055] Comparative Example 1

[0056] Eucalyptus powder and ammonium chloride were mixed in a mass ratio of 1:10, placed in a tube furnace, and carbonized at 900 degrees Celsius for 2 hours under the protection of N2 gas. The carbonization heating rate was 5°C / min to obtain a comparative biomass carbon material.

[0057] Electrochemical tests were performed using a rotating disk and an electrochemical workstation. After fully grinding the catalyst material obtained in step (3), 5 mg of the catalyst was added to 1 mL of a 0.25% Nafion / ethanol solution and ultrasonicated for 30 minutes to form a uniform black suspension. 10 μL of the suspension was then added dropwise to the surface of a glassy carbon electrode (5 mm in diameter). The reference electrode was an Ag / AgCl electrode, the counter electrode was a platinum sheet electrode, and a 0.1 mol / L potassium hydroxide solution was used as the electrolyte. The rotating rod rotated at 1600 rpm and the scanning speed was 10 mV / s. The performance of oxygen reduction and oxygen precipitation was tested respectively.

[0058] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing a nitrogen-doped biomass carbon-based bifunctional catalyst, characterized in that: The following steps are involved: (1) heating and mixing the hydrogen bond donor and the hydrogen bond acceptor to obtain a DES solvent; (2) adding the biomass raw material to a DES solvent, heating, washing, and drying to obtain an EDS-treated biomass raw material; (3) mixing the EDS-treated biomass raw material with a nitrogen-containing compound and carbonizing the mixture to obtain a nitrogen-doped porous biomass carbon-based bifunctional catalyst; The molar ratio of the hydrogen bond donor to the hydrogen bond acceptor in step (1) is 1:0.2-10; The hydrogen bond acceptor in step (1) is at least one of choline chloride and betaine; the hydrogen bond donor is at least one of formic acid, acetic acid, oxalic acid, ethylene glycol, glycerol, urea and imidazole; The mass ratio of the biomass raw material to the DES solvent in step (2) is 1:10-50; The drying in step (2) is freeze drying, wherein the sample is first frozen with liquid nitrogen and then placed in a freeze dryer for drying for 6 to 24 hours; The heating temperature of step (2) is 70-110° C. and the heating time is 0.5-48 h; The biomass raw material in step (2) is at least one of eucalyptus, poplar and birch.

2. The method for preparing a nitrogen-doped biomass carbon-based bifunctional catalyst according to claim 1, characterized in that: The nitrogen-containing compound in step (3) is at least one of ammonium chloride, urea, dicyandiamide and thiourea; The mass ratio of the biomass raw material after EDS treatment to the nitrogen-containing compound in step (3) is 1:1 to 50.

3. The method for preparing a nitrogen-doped biomass carbon-based bifunctional catalyst according to claim 1, characterized in that: The carbonization temperature in step (3) is 800-1000° C., and the time is 0.5-3 h.

4. The method for preparing a nitrogen-doped biomass carbon-based bifunctional catalyst according to claim 1, characterized in that: The particle size of the biomass raw material is 40 to 120 meshes.

5. The method for preparing a nitrogen-doped biomass carbon-based bifunctional catalyst according to claim 1, characterized in that: The heating temperature in step (1) is 70-90° C. and the heating time is 0.25-1 h; The washing in step (2) refers to washing with water and ethanol and filtering; The heating rate of the carbonization in step (3) is 1 to 10°C / min.

6. A nitrogen-doped biomass carbon-based bifunctional catalyst prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the nitrogen-doped biomass carbon-based bifunctional catalyst according to claim 6.

Images