Oxygen reduction catalyst, method for preparing the same, and use thereof

Abstract

The application discloses an oxygen reduction catalyst and a preparation method and application thereof. The preparation method of the oxygen reduction catalyst comprises the following steps: S1: mixing mycelia of filamentous fungi, ferrocene and a nitrogen source, and performing first calcination to obtain a mixture A; and S2: mixing the mixture A and a ZnCl2 solution, and performing activation and carbonization reaction to obtain the oxygen reduction catalyst. The preparation method can realize environmental management through waste recycling, and has the advantages of easy preparation of raw materials, low cost, simple preparation method, and suitability for large-scale preparation and application. Meanwhile, the oxygen reduction catalyst has the advantages of obvious three-dimensional porous structure, large specific surface area, rich active sites, good catalytic activity and stability.

Description

Technical Field

[0001] This invention relates to the technical field of resource recycling and regeneration, specifically to an oxygen reduction catalyst, its preparation method, and its application. Background Technology

[0002] The oxygen reduction reaction (ORR) is an electrode reaction in fuel cells, and its catalyst plays a crucial role in improving electrode reaction performance and battery performance. Due to the advantages of carbon, such as porous structure, chemical stability, and high conductivity, Pt exhibits high catalytic activity, and Pt / C is currently a commonly used catalyst on the market.

[0003] In pursuit of higher catalytic activity, existing technologies often employ the design of different forms of Pt catalysts to reduce both cost and performance. However, due to the finite nature of resources, different forms of Pt catalysts still suffer from problems such as high cost, poor stability, complex preparation processes, and difficulty in large-scale preparation and application.

[0004] Meanwhile, biomass materials have diverse structures, and biochar of a certain shape can be directly obtained through high-temperature carbonization, and the resulting biochar has certain oxygen reduction catalytic activity. CN 105633424 A discloses a porous activated carbon fiber material based on spider silk and its application. By activating and carbonizing spider silk at high temperature, an activated carbon fiber with a microporous structure can be obtained. However, this solution has the problems of difficulty in obtaining spider silk and difficulty in fully utilizing biomass materials.

[0005] Therefore, there is an urgent need to develop a catalyst that has readily available raw materials, low cost, simple preparation, large specific surface area, and good oxygen reduction performance under alkaline conditions. Summary of the Invention

[0006] In order to overcome the problems existing in the prior art, the purpose of this invention is to provide an oxygen reduction catalyst, its preparation method and application.

[0007] The inventive concept of this invention is as follows: First, by rapidly and massively culturing filamentous bacteria using chicken manure, a relatively stable filamentous bacterial cell with a multi-layered three-dimensional structure composed of numerous interconnected filamentous structures is obtained. Then, by designing the addition of appropriate amounts of ferrocene and a nitrogen source (e.g., melamine) to the bacterial cell, followed by calcination, a biomass carbon material is formed by encapsulating hematite particles with carbon nitride. Finally, this intermediate product is activated with ZnCl2, so that when the temperature reaches the melting point of ZnCl2, the solid ZnCl2 begins to melt into a liquid state, penetrating into the carbonized filamentous bacteria to form a framework. When the temperature rises to the boiling point of ZnCl2, Zn ions crystallize and evaporate, thereby creating cavities on the surface of the carbon material. Ultimately, an oxygen reduction catalyst with a microporous tubular structure, large specific surface area, and high oxygen reduction catalytic efficiency is obtained.

[0008] The oxygen reduction catalyst of the present invention is based on a three-dimensional layered structure composed of relatively long "carbon nanotubes". The surface of the "carbon nanotubes" has a porous structure with many holes and is doped with nanoparticles. These nanoparticles are spherical particles of hematite encapsulated by nitrogen carbide (the overall particle size of the spherical particles of hematite encapsulated by nitrogen carbide is 20-60 nm).

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] In a first aspect, the present invention provides a method for preparing an oxygen reduction catalyst, comprising the following steps:

[0011] S1: Filamentous fungal cells, ferrocene and nitrogen source are mixed and calcined to obtain mixture A;

[0012] S2: Mix mixture A and ZnCl2 solution, and then perform activation and carbonization reactions to obtain an oxygen reduction catalyst.

[0013] Preferably, the method for preparing the precipitate of the filamentous fungi includes the following steps:

[0014] 1) Mix chicken manure and a leavening agent, then control the moisture content of the raw materials to 50% to 60%, and carry out aerobic composting for 15 to 20 days to obtain fermented raw materials;

[0015] 2) Control the moisture content of the fermented raw material to 45%–55%, and culture it at a constant temperature of 35℃–40℃ and an oxygen concentration greater than 10% for 10–15 days to obtain the raw material after constant temperature culture.

[0016] 3) Add the raw material after constant temperature incubation to water, stir and let stand, take the upper liquid, and centrifuge at 8000-12000 rpm, freeze dry to obtain filamentous mycelium.

[0017] Preferably, the settling time in step 3) is 0.5 to 1.5 hours. More preferably, it is 1 hour.

[0018] Preferably, if the temperature of the aerobic composting in step 1) is above 65°C for more than 5 days, the aerobic composting time is set to 15 days; if the temperature of the aerobic composting in step 1) is between 55°C and 65°C for more than 7 days, the aerobic composting time is set to 20 days; if the temperature conditions exceed 7 days, then the conditions for obtaining the fermented raw materials need not be met.

[0019] Preferably, the leavening agent in step 1) is one or more of rice husks, sawdust, wood chips, and straw.

[0020] Preferably, the mass ratio of chicken manure to leavening agent in step 1) is (2-6):1.

[0021] Preferably, the mass ratio of chicken manure to leavening agent in step 1) is (3-5):1.

[0022] Preferably, step 2) further includes the step of washing the precipitate with water.

[0023] Preferably, in step S1, the filamentous fungi are mainly actinomycetes.

[0024] Preferably, in step S1, the mass ratio of the filamentous fungal cells, ferrocene, and nitrogen source is 1:(0.2-0.5):(0.2-0.5).

[0025] Preferably, in step S1, the nitrogen source is one or more of melamine, cyanamide, dicyandiamide, and urea.

[0026] Preferably, in step S1, the calcination conditions are: heating to 500℃~550℃ at a heating rate of 5℃ / min~10℃ / min, and holding at that temperature for 4h~5h.

[0027] Preferably, step S1 further includes naturally cooling to 20°C to 35°C after roasting.

[0028] Preferably, in step S2, the mass ratio of the mixture A to the volume ratio of the ZnCl2 solution is 0.2-0.5 g / mL.

[0029] Preferably, in step S2, the concentration of the ZnCl2 solution is 160-200 g / L.

[0030] Preferably, in step S2, the activation reaction temperature is 55°C to 85°C.

[0031] Preferably, in step S2, the activation reaction takes 4 to 8 hours.

[0032] More preferably, in step S2, the activation reaction takes 6 hours.

[0033] Preferably, in step S2, the carbonization reaction conditions are as follows: first, the temperature is increased to 400℃ to 500℃ at a heating rate of 5 to 10℃ / min, and held for 0.5 to 1.5 hours, then the temperature is increased to 800℃ to 900℃ at a heating rate of 2 to 6℃ / min, and held for 0.5 to 2 hours.

[0034] More preferably, in step S2, the carbonization reaction conditions are as follows: first, the temperature is increased to 430℃~450℃ at a heating rate of 5~10℃ / min, and held for 1 hour, then the temperature is increased to 800℃~900℃ at a heating rate of 5℃ / min, and held for 1 hour.

[0035] Specifically, during the carbonization reaction, the melting and penetration of ZnCl2 into the skeleton in the sample are controlled by regulating the heating rate, temperature, and holding time of the heat treatment, thereby inhibiting tar formation. When the temperature is raised to a higher level, the ZnCl2 melts and penetrates the skeleton. 2+ It undergoes a strong chemical reaction with C atoms, which leads to the continuous aromatization and expansion of the carbon layer, eventually forming a large number of microporous structures.

[0036] Preferably, both the roasting and the carbonization reactions are carried out under a protective atmosphere.

[0037] Preferably, the protective gas is one or more of nitrogen and argon.

[0038] In a second aspect, the present invention provides an oxygen reduction catalyst prepared by the preparation method described in the first aspect.

[0039] Preferably, the oxygen reduction catalyst comprises a three-dimensional framework structure formed by overlapping carbon nanotubes, wherein spherical particles of hematite encapsulated by nitrogen carbide are loaded on the carbon nanotubes.

[0040] Preferably, the oxygen reduction catalyst has a three-dimensional porous structure, and the three-dimensional porous structure is composed of microbial carbon filaments with a diameter of approximately 50 nm.

[0041] Specifically, the oxygen reduction catalyst has a three-dimensional porous structure (with obvious pore structure) composed of the tubular structure of the filamentous bacteria themselves; the oxygen reduction catalyst also has a microporous structure.

[0042] Preferably, the oxygen reduction catalyst has a specific surface area of ​​1100–1300 m². 2 / g.

[0043] More preferably, the oxygen reduction catalyst has a specific surface area of ​​1180–1240 m². 2 / g.

[0044] Preferably, the oxygen reduction catalyst comprises a microporous structure of ≤10 nm.

[0045] More preferably, the oxygen reduction catalyst comprises a microporous structure of ≤6 nm.

[0046] Specifically, the pore size of the microporous structure is 0.1–6 nm.

[0047] Preferably, the particle size of the spherical particles of hematite encapsulated by nitrogen carbide is 20–60 nm.

[0048] Thirdly, the present invention provides the oxygen reduction catalyst and its application in catalytic reactions.

[0049] Preferably, the electrolyte for the electrocatalytic oxygen reduction reaction is an alkaline electrolyte.

[0050] Preferably, the pH of the alkaline electrolyte is greater than 7.0.

[0051] More preferably, the alkaline electrolyte is a 0.1M KOH solution.

[0052] The beneficial effects of this invention are: the method for preparing the iron-nitrogen-doped oxygen reduction catalyst provided by this invention not only enables environmental remediation through waste recycling, but also utilizes readily available and low-cost raw materials, and is simple to prepare, making it particularly suitable for large-scale preparation and application. Furthermore, the iron-nitrogen-doped oxygen reduction catalyst prepared by this method also possesses a significant three-dimensional porous structure, with advantages such as large specific surface area, abundant active sites, good catalytic activity, and good stability. Specifically:

[0053] (1) This invention can not only make full use of chicken manure after aerobic composting to produce filamentous bacteria in batches, but also use filamentous bacteria to make iron-nitrogen doped oxygen reduction catalyst simply and at low cost by adding dopant source and activator step by step and calcining and carbonizing.

[0054] (2) The method for preparing the iron-nitrogen-doped oxygen reduction catalyst of the present invention does not require the introduction of noble metals and multiple transition metals as active sites, thus it has the advantage of relatively low preparation cost and is suitable for practical large-scale preparation and application.

[0055] (3) The iron-nitrogen-doped oxygen reduction catalyst of the present invention has the advantages of microporous structure, tubular structure of filamentous bacteria, abundant active sites, large specific surface area and high oxygen reduction catalytic efficiency.

[0056] (4) This invention uses chicken manure as raw material to obtain filamentous bacteria through recycling, aerobic composting, fermentation, cultivation, and purification. These bacteria are then mixed with ferrocene and melamine, pre-carbonized, and activated using zinc chloride solution. The resulting oxygen reduction catalyst is obtained through programmed temperature carbonization. This invention uses abundant, readily available, and low-cost chicken manure as biomass raw material to prepare a carbon substrate with a three-dimensional tubular structure. Furthermore, it activates spherical particles of hematite encapsulated in nitrogen carbide loaded on the carbon substrate, improving the specific surface area, active sites, and conductivity of the material. This achieves electrochemical performance comparable to Pt / C for a non-precious metal-carbon composite catalyst. It also solves the technical problem of oxygen reduction catalysts with large surface areas, numerous active sites, and high activity being prone to structural collapse and poor electrochemical stability. Attached Figure Description

[0057] Figure 1 This is a SEM image of the oxygen reduction catalyst in Example 1.

[0058] Figure 2 This is a SEM image of the surface particles of the oxygen reduction catalyst in Example 1.

[0059] Figure 3 The image shows the XRD pattern of the surface particles of the oxygen reduction catalyst in Example 1.

[0060] Figure 4 This is the energy dispersive spectroscopy (EDS) analysis diagram of the oxygen reduction catalyst in Example 1.

[0061] Figure 5 This is a TEM image of the surface particles of the oxygen reduction catalyst in Example 1.

[0062] Figure 6 The image shows the energy spectrum of the surface particles of the oxygen reduction catalyst in Example 1.

[0063] Figure 7 This is a pore distribution diagram of the oxygen reduction catalyst in Example 1.

[0064] Figure 8 The graph shows the linear voltammetric test results of the oxygen reduction catalysts in Example 1 and Comparative Examples 1-5.

[0065] Figure 9 This is a graph showing the stable operation curve of the oxygen reduction catalyst in Example 1.

[0066] Figure 10 The graph shows the resistance of the oxygen reduction catalyst to methanol interference in Example 1. Detailed Implementation

[0067] The present invention will be further described in detail below through specific embodiments.

[0068] Unless otherwise specified, the culture, enrichment, separation and purification of bacteria used in the embodiments of the present invention are all conventional technical means, and the raw materials used are all commercially available.

[0069] Example 1

[0070] This embodiment provides a method for preparing an oxygen reduction catalyst, including the following steps:

[0071] (1) Culture of filamentous fungi:

[0072] Take 120 kg of fresh chicken manure and 40 kg of rice husks, mix them evenly, and control the moisture content of the raw materials to 60%. Carry out aerobic composting fermentation for 15 days (the maximum composting temperature is 72℃, and the high-temperature period with a temperature greater than 60℃ is 6 days) to obtain the raw materials after aerobic fermentation.

[0073] Take the above-mentioned aerobic fermented raw materials, control the moisture content to 50%, and culture at a constant temperature (temperature: 35-40℃, oxygen volume concentration: 20%). Set the time to loosen the raw materials slightly every 3 days to maintain the porosity of the raw material particles. The total culture time is 15 days, during which filamentous fungi (such as actinomycetes) multiply in large quantities.

[0074] (2) Collection of filamentous fungi:

[0075] First, immerse all the cultured material in water, use a magnetic stirrer (speed: 200 rpm / min), let stand for 30 minutes, discard the precipitate, and obtain the upper layer of bacteria;

[0076] Then, the upper liquid was filtered through 0.45 μm filter paper, the supernatant was discarded, deionized water was added and washed twice, and then freeze-dried to obtain filamentous mycelium.

[0077] Electron microscopy revealed that the microbial cells were mainly filamentous, classifying them as filamentous fungal cells.

[0078] (3) Preparation of oxygen reduction catalyst:

[0079] S1: Add 1g of ferrocene and 1g of melamine to 2g of bacterial cells from step (2), stir and mix evenly to obtain a mixture;

[0080] S2: Place the S1 mixture into a high-temperature furnace, introduce nitrogen gas, heat to 500℃~550℃ at a heating rate of 5℃ / min~10℃ / min, hold for 4h~5h, and then cool to room temperature;

[0081] S3: Add 1g of composite material to 5mL of 180g / L ZnCl2 solution and activate it at 60℃ for 6h. Then evaporate and dry the solution in a 60℃ drying oven to obtain the activated composite material.

[0082] S4: Transfer the activated composite material from S3 to a high-temperature furnace, introduce nitrogen gas, first heat it to 450℃ at a heating rate of 5℃ / min, hold it for 1 hour, then continue heating it to 800℃ at a heating rate of 5℃ / min, hold it for 1 hour, and then cool it to room temperature (25~30℃).

[0083] Finally, the catalyst was washed with deionized water and evaporated at 60°C to obtain the oxygen reduction catalyst.

[0084] The scanning electron microscope (SEM) image of the oxygen reduction catalyst in Example 1 is shown below. Figure 1 As shown in the figure, the bacterial cells exhibit a three-dimensional structure, crisscrossed and composed of tubular or ribbon-like structures of varying sizes, with lengths reaching the micrometer (µm) and tube diameters between 100-200 nm. This indicates a large specific surface area, numerous catalytic sites, and high catalytic activity.

[0085] Figure 2This is a SEM image of the doped particles on the surface of the tubular bacterial cells in Example 1. The image shows that the particles are uniform in size (particle size: 20–60 nm), on the order of nanometers.

[0086] Further utilizing X-ray diffraction (XRD) spectroscopy Figure 3 ) and transmission electron microscopy (TEM) Figure 5 The composition of the particle was analyzed. Figure 3 It can be seen that the iron crystal structure on the particle surface is mainly hematite. From Figure 4 As can be seen from the infrared spectroscopy analysis, the particles have a nitrogen carbide structure. From the TEM image (… Figure 5 As can be seen, the particle has a core in the center, which, according to diffraction pattern analysis, is mainly composed of iron; the outer layer is mainly composed of carbon, thus indicating that the particle belongs to an iron structure with carbon and other elements encapsulating its surface. Further energy dispersive spectroscopy analysis shows that the particle is mainly composed of C, O, Fe, N, and other elements. Figure 6 ).

[0087] After being treated with ZnCl2, the oxygen reduction catalyst of Example 1 developed a large number of porous structures on its surface, further enhancing the pore distribution and increasing the surface area to 1230.3 m². 2 / g( Figure 7 ).

[0088] Example 2

[0089] This embodiment provides a method for preparing an oxygen reduction catalyst, including the following steps:

[0090] (1) Culture of filamentous fungi:

[0091] Take 150 kg of fresh chicken manure and 30 kg of sawdust, mix them evenly, and control the moisture content of the raw materials to 60%. Carry out aerobic composting fermentation for 15 days (the maximum composting temperature is 72℃, and the high-temperature period with a temperature greater than 60℃ is 6 days) to obtain the raw materials after aerobic fermentation.

[0092] Take the above-mentioned aerobic fermented raw materials, control the moisture content to 50%, and culture at a constant temperature (temperature: 35-40℃, oxygen volume concentration: 20%). Set the time to loosen the raw materials slightly every 3 days to maintain the porosity of the raw material particles. The total culture time is 15 days, during which filamentous fungi (such as actinomycetes) multiply in large quantities.

[0093] (2) Collection of filamentous fungi:

[0094] First, immerse all the cultured material in water, use a magnetic stirrer (speed: 200 rpm / min), let stand for 30 minutes, discard the precipitate, and obtain the upper layer of bacteria;

[0095] Then, the upper liquid was filtered through 0.45 μm filter paper, the supernatant was discarded, deionized water was added and washed twice, and then freeze-dried to obtain filamentous bacterial cells.

[0096] (3) Preparation of oxygen reduction catalyst:

[0097] S1: Add 0.8g of ferrocene and 0.5g of melamine to 2g of the precipitate from step (2), stir and mix evenly to obtain a mixture;

[0098] S2: Place the S1 mixture into a high-temperature furnace, introduce nitrogen gas, heat to 500℃~550℃ at a heating rate of 5℃ / min~10℃ / min, hold for 4h~5h, and then cool to room temperature;

[0099] S3: Add 1g of composite material to 5mL of 160g / L ZnCl2 solution and activate it at 60℃ for 6h. Then dry the solution at 60℃ to obtain the activated composite material.

[0100] S4: Transfer the activated composite material from S3 to a high-temperature furnace, introduce nitrogen gas, first heat to 430℃ at a heating rate of 10℃ / min, hold for 1 hour, then continue heating to 900℃ at a heating rate of 5℃ / min, hold for 1 hour, and cool to room temperature (25~30℃).

[0101] Finally, the catalyst was washed with deionized water and evaporated at 60°C to obtain the oxygen reduction catalyst.

[0102] Example 3

[0103] This embodiment provides a method for preparing an oxygen reduction catalyst, including the following steps:

[0104] (1) Culture of filamentous fungi:

[0105] Take 150 kg of fresh chicken manure and 30 kg of sawdust, mix them evenly, and control the moisture content of the raw materials to 60%. Carry out aerobic composting fermentation for 15 days (the maximum composting temperature is 72℃, and the high-temperature period with a temperature greater than 60℃ is 6 days) to obtain the raw materials after aerobic fermentation.

[0106] Take the above-mentioned aerobic fermented raw materials, control the moisture content to 50%, and culture at a constant temperature (temperature: 35-40℃, oxygen volume concentration: 20%). Set the time to loosen the raw materials slightly every 3 days to maintain the porosity of the raw material particles. The total culture time is 15 days, during which filamentous fungi (such as actinomycetes) multiply in large quantities.

[0107] (2) Collection of filamentous fungi:

[0108] First, immerse all the cultured material in water, use a magnetic stirrer (speed: 200 rpm / min), let stand for 30 minutes, discard the precipitate, and obtain the upper layer of bacteria;

[0109] Then, the upper liquid was filtered through 0.45 μm filter paper, the supernatant was discarded, deionized water was added and washed twice, and then freeze-dried to obtain filamentous bacterial cells.

[0110] (3) Preparation of oxygen reduction catalyst:

[0111] S1: Add 1.2g of ferrocene and 1.2g of melamine to 2g of the precipitate from step (2), stir and mix evenly to obtain a mixture;

[0112] S2: Place the above mixture in a high-temperature furnace, introduce nitrogen gas, heat to 500℃~550℃ at a heating rate of 5℃ / min~10℃ / min, hold for 4h~5h, and then cool to room temperature;

[0113] S3: Add 1g of the composite material prepared in the previous step to 5mL of 200g / L ZnCl2 solution and activate it at 60℃ for 6h. Then dry the solution at 60℃ to obtain the activated composite material.

[0114] S4: Transfer the activated composite material from S3 to a high-temperature furnace, introduce nitrogen gas, first heat to 450℃ at a heating rate of 8℃ / min, hold for 1 hour, then continue heating at a heating rate of 5℃ / min to 800℃, hold for 1 hour, and cool to room temperature (25~30℃).

[0115] Finally, the catalyst was washed with deionized water and evaporated at 60°C to obtain the oxygen reduction catalyst.

[0116] Comparative Example 1

[0117] The difference between this comparative example and Example 1 is that this comparative example uses filamentous bacteria as raw material, only modifies the surface of the biochar material with elements such as iron and nitrogen, and does not use ZnCl2 solution activation treatment, and includes the following steps:

[0118] (1) Cultivation of filamentous fungi: Same as in Example 1;

[0119] (2) Isolation and purification of filamentous bacteria: Same as in Example 1;

[0120] (3) Preparation of oxygen reduction catalyst:

[0121] S1: Place the filamentous bacteria from step (2) in a high-temperature furnace, introduce nitrogen gas, raise the temperature to 450°C at a rate of 5°C / min, hold for 1 hour, then raise the temperature to 800°C at a rate of 5°C / min, hold for 1 hour, and cool to room temperature (25-30°C). Finally, wash with deionized water and evaporate and dry at 60°C to obtain the biomass carbon-based oxygen reduction catalyst.

[0122] Comparative Example 2

[0123] The difference between this comparative example and Example 2 is that this comparative example uses filamentous bacteria as raw material, does not modify the surface of the material or dope it with other elements, and only performs ZnCl2 solution activation treatment on the material, including the following steps:

[0124] (1) Cultivation of filamentous fungi: Same as in Example 2;

[0125] (2) Isolation and purification of filamentous bacteria: Same as in Example 2;

[0126] (3) Preparation of oxygen reduction catalyst:

[0127] S1: Add 1g of filamentous bacteria from step (2) to 5mL of 160g / L ZnCl2 solution and activate at 60℃ for 6h. Then dry the solution at 60℃ to obtain the activated composite material.

[0128] Finally, the catalyst was washed with deionized water and evaporated at 60°C to obtain a biomass carbon-based oxygen reduction catalyst.

[0129] Comparative Example 3

[0130] The difference between this comparative example and Example 3 is that the doping process in this comparative example does not use ferrocene, but only melamine raw material for doping, and is activated with ZnCl2, including:

[0131] (1) Cultivation of filamentous fungi: Same as in Example 3;

[0132] (2) Isolation and purification of filamentous bacteria: Same as in Example 3;

[0133] (3) Preparation of oxygen reduction catalyst:

[0134] S1: Add 1.2g of melamine to 2g of the precipitate from step (2), stir and mix evenly to obtain a mixture;

[0135] S2: Place the above mixture in a high-temperature furnace, introduce nitrogen gas, heat to 500℃~550℃ at a heating rate of 5℃ / min~10℃ / min, hold for 4h~5h, and then cool to room temperature;

[0136] S3: Add 1g of the composite material prepared in the previous step to 5mL of 200g / L ZnCl2 solution and activate it at 60℃ for 6h. Then dry the solution at 60℃ to obtain the activated composite material.

[0137] S4: Transfer the activated composite material from S3 to a high-temperature furnace, introduce nitrogen gas, first heat to 450℃ at a heating rate of 8℃ / min, hold for 1 hour, then continue heating at a heating rate of 5℃ / min to 800℃, hold for 1 hour, and cool to room temperature (25~30℃).

[0138] Finally, the catalyst was washed with deionized water and evaporated at 60°C to obtain the oxygen reduction catalyst.

[0139] Comparative Example 4

[0140] The difference between this comparative example and Example 1 is that the doping process in this comparative example does not use melamine, but only a single ferrocene raw material for doping, and is activated with ZnCl2, including:

[0141] (1) Cultivation of filamentous fungi: Same as in Example 1;

[0142] (2) Isolation and purification of filamentous bacteria: Same as in Example 1;

[0143] (3) Preparation of oxygen reduction catalyst:

[0144] S1: Add 1g of ferrocene to 2g of the bacterial cells from step (2), stir and mix evenly to obtain a mixture;

[0145] S2: Place the S1 mixture into a high-temperature furnace, introduce nitrogen gas, heat to 500℃~550℃ at a heating rate of 5℃ / min~10℃ / min, hold for 4h~5h, and then cool to room temperature;

[0146] S3: Add 1g of composite material to 5mL of 180g / L ZnCl2 solution and activate it at 60℃ for 6h. Then evaporate and dry the solution in a 60℃ drying oven to obtain the activated composite material.

[0147] S4: Transfer the activated composite material from S3 to a high-temperature furnace, introduce nitrogen gas, first heat it to 450℃ at a heating rate of 5℃ / min, hold it for 1 hour, then continue heating it to 800℃ at a heating rate of 5℃ / min, hold it for 1 hour, and then cool it to room temperature (25~30℃).

[0148] Finally, the catalyst was washed with deionized water and evaporated at 60°C to obtain the oxygen reduction catalyst.

[0149] Comparative Example 5

[0150] The oxygen reduction catalyst used in this comparative example is a commercially available Pt / C catalyst.

[0151] Performance testing

[0152] 1. Morphological observation and testing: The specific surface area of ​​the oxygen reduction catalysts in Examples 1-3 and Comparative Examples 1-6 was tested using the nitrogen adsorption method (Kunta Instruments, model: ASIQMO002-2). The test results are shown in Table 1.

[0153] The instrument used for SEM characterization was a Japanese-made SEM (S-4800FE-SEM) with an operating voltage of 10–30 kV. The instrument used for TEM was a Japanese-made JEM-2100F high-resolution transmission electron microscope with an accelerating voltage of 200 kV.

[0154] Infrared spectroscopy was performed using a Thermo Fisher Scientific Fourier transform infrared spectrometer (Nicolet Is 50) to analyze the function bonds of the samples. Sample preparation employed the KBr pellet method: KBr and a small amount of solid sample were placed in a mortar, ground evenly, and then dried in an infrared lamp oven. Finally, a pellet was formed using a pellet mold and placed in the sample chamber of the infrared spectrometer to measure the absorption spectrum of the sample. The scanning range was 400–4000 cm⁻¹. -1 The result is as follows Figure 4 As shown in the figure. It can be seen from the figure that the tensile vibrations of N(-C)3 and C-NH-C occur at 800 cm⁻¹. -1 There are distinct peaks at 3000–3500 cm⁻¹. -NH₂ and -NH₃ show peaks at 3000–3500 cm⁻¹. -1 The peaks almost disappeared; 3202 was the -OH vibration peak; 1639 and 1563 were double bond peaks such as -C=O and C=N; and 1242 was the vibration peak of bonds such as -CO and -CN. These results indicate the presence of nitrogen carbide.

[0155] 2. Samples to be tested: Oxygen reduction catalysts of Examples 1-3 and Comparative Examples 1-6

[0156] Electrochemical performance testing method: Weigh 2 mg of the catalyst or Pt / C prepared above and pour it into a 1.5 mL centrifuge tube; then, add 1 mL of anhydrous ethanol and 10 μL of Nafion (5%), and sonicate in an ultrasonic cleaner for 20 min to obtain a uniform suspension. Use a pipette to drop 20 μL of the above suspension onto the cleaned glassy carbon electrode surface, and allow it to air dry at room temperature before testing.

[0157] Using the electrode containing the test sample as the working electrode, the Ag / AgCl electrode as the reference electrode, and 0.1 mol / L KOH as the electrolyte, the test voltage was set to -0.8 to 0.2 V (vs. Ag / AgCl). The electrochemical performance of different oxygen reduction catalysts was tested using linear voltammetry with a rotating disk electrode. The test results are as follows: Figure 8 As shown in Table 1.

[0158] Table 1: Performance test results of catalysts in Examples 1-3, Comparative Examples 1-3, and Comparative Example 6

[0159] Group <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Half-wave potential E 1 / 2 (V Ag / AgCl )]]> Example 1 1230.3 -0.12V Example 2 1147.4 -0.12V Example 3 1184.8 -0.13V Comparative Example 1 506.7 -0.31V Comparative Example 2 652.4 -0.29V Comparative Example 3 672.3 -0.20V Comparative Example 4 793.5 -0.17V Comparative Example 5 (Pt / C) 857.2 -0.11V

[0160] Note: The half-wave potentials in Table 1 were measured in 0.1 mol / L KOH solution.

[0161] Depend on Figure 8 As shown in Table 1, under alkaline conditions (i.e., 0.1 mol / L KOH solution), the half-wave potential (E) of the working electrodes prepared by oxygen reduction in Examples 1, 2, and 3 is... 1 / 2 The oxygen reduction properties of the catalysts in Examples 1-3 are close to those of commercial Pt / C catalysts, ranging from -0.12 to -0.13 V (reference electrode: Ag / AgCl). This indicates that the oxygen reduction properties of these catalysts are similar to those of commercial Pt / C catalysts. Furthermore, from... Figure 8 Based on the current density, the oxygen reduction catalyst of Example 1...

[0162] Combined with the specific surface area test results, it is shown that the oxygen reduction catalysts prepared in Examples 1-3 have a high specific surface area and a large number of highly active sites.

[0163] 3. Stability Test

[0164] The catalyst stability was tested by rotating the electrode at 1600 rpm in an O2-saturated 0.1 mol / L KOH solution and using a chronoamperometry method to measure the current-time curve. The initial current was set as 1, and the "relative percentage" represents the ratio of the decrease in current to the initial current. The results are as follows: Figure 9 As shown in the figure, the catalyst prepared by the method of the present invention showed a relative current decrease of about 12% after a 10,000s stability test, while the relative current of commercial Pt / C decreased by about 30%. The prepared catalyst is significantly better than commercial Pt / C.

[0165] Test of the oxygen reduction catalyst's resistance to methanol interference: A chronoamperometry method was used. 100 μL of 3 mol / L methanol was added to an O2-saturated 0.1 mol / L KOH solution, and the change in catalytic current before and after methanol addition was measured. The test results are as follows: Figure 10As shown in the figure, with the initial current as 1, the "relative percentage" represents the ratio of the decreased current to the initial current. The figure shows that the performance of the prepared catalyst is essentially unaffected by the addition of methanol. In contrast, the commercial Pt / C catalyst experienced a decrease in output current of approximately 15% after the addition of methanol, indicating that the prepared catalyst exhibits better anti-interference performance than the commercial Pt / C catalyst.

[0166] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing an oxygen reduction catalyst, characterized in that, Includes the following steps: S1: Filamentous fungal cells, ferrocene, and a nitrogen source are mixed and calcined to obtain mixture A; S2: Mix mixture A and ZnCl2 solution, and then perform activation and carbonization reactions to obtain an oxygen reduction catalyst.

2. The preparation method according to claim 1, characterized in that: The method for preparing the filamentous fungal cells includes the following steps: 1) Mix chicken manure and a leavening agent, control the moisture content of the raw materials to 50%~60%, and carry out aerobic composting for 15~20 days to obtain fermented raw materials; 2) Control the moisture content of the fermented raw material to 45%~55%, and culture it at a constant temperature of 35℃~40℃ and an oxygen volume concentration greater than 10% for 10~15 days to obtain the raw material after constant temperature culture. 3) Add the raw material after constant temperature incubation to water, stir and let stand, take the upper liquid, filter and separate it, freeze dry to obtain filamentous mycelium.

3. The preparation method according to claim 1, characterized in that: In step S1, the mass ratio of the filamentous fungal cells, ferrocene, and nitrogen source is 1:(0.2~0.5):(0.2~0.5).

4. The preparation method according to claim 1, characterized in that: In step S1, the calcination conditions are as follows: heating to 500℃~550℃ at a heating rate of 5℃ / min~10℃ / min, and holding at that temperature for 4 h~5 h.

5. The preparation method according to claim 1, characterized in that: In step S2, the carbonization reaction conditions are as follows: first, the temperature is increased to 400℃~500℃ at a heating rate of 5~10℃ / min, and held for 0.5~1.5h, then the temperature is increased to 800℃~900℃ at a heating rate of 2~6℃ / min, and held for 0.5~2h.

6. The preparation method according to claim 1, characterized in that: In step S2, the activation reaction temperature is 55℃~85℃; the activation reaction time is 4h~8h.

7. An oxygen reduction catalyst prepared by the method according to any one of claims 1 to 6, characterized in that: The oxygen reduction catalyst comprises a three-dimensional framework structure formed by overlapping carbon nanotubes, on which spherical particles of hematite encapsulated by nitrogen carbide are loaded.

8. The oxygen reduction catalyst according to claim 7, characterized in that: The oxygen reduction catalyst has a specific surface area of ​​1100~1300 m². 2 / g; the particle size of the spherical particles of hematite encapsulated by nitrogen carbide is 20~60nm.

9. An electrode, characterized in that, Includes the oxygen reduction catalyst as described in claim 7 or 8.

10. The application of the electrode according to claim 9 in the electrocatalytic oxygen reduction reaction.

Images