CN109301266B - Oxygen reduction catalyst, preparation method and application thereof - Google Patents

Oxygen reduction catalyst, preparation method and application thereof Download PDF

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CN109301266B
CN109301266B CN201811132388.5A CN201811132388A CN109301266B CN 109301266 B CN109301266 B CN 109301266B CN 201811132388 A CN201811132388 A CN 201811132388A CN 109301266 B CN109301266 B CN 109301266B
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metal
catalyst
compound
oxygen reduction
carbon
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CN109301266A (en
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戚玉欣
董祥国
苗建朋
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Dezhou Xindongneng Iron Tower Power Generation Co ltd
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Dezhou Xindongneng Iron Tower Power Generation Co ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • H01M4/9075—Catalytic material supported on carriers, e.g. powder carriers
    • H01M4/9083—Catalytic material supported on carriers, e.g. powder carriers on carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • H01M4/9008—Organic or organo-metallic compounds
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M2008/1095—Fuel cells with polymeric electrolytes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

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  • Engineering & Computer Science (AREA)
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  • General Chemical & Material Sciences (AREA)
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Abstract

The invention discloses an oxygen reduction catalyst, a preparation method and application thereof. The oxygen reduction catalyst is prepared by reacting an organic chelate with a salt of a first metal in a molar ratio of 1:1 to 1:3Reacting at a certain ratio to obtain N4-an M compound; will N4-M compound is supported on a carbon support containing a second metal to obtain a supported N4-an M compound; under inert gas to load type N4-heat treatment of the compound M to obtain a catalyst precursor; the catalyst precursor is milled to obtain the oxygen reduction catalyst of the present invention. The method simplifies the preparation process, and the obtained catalyst has high activity and strong stability.

Description

Oxygen reduction catalyst, preparation method and application thereof
Technical Field
The invention relates to the field of fuel cell catalysts, in particular to an oxygen reduction catalyst with improved stability for a fuel cell, and a preparation method and application thereof.
Background
The fuel cell is a power generation device which directly changes the chemical energy of fuel into electric energy in an electrochemical reaction mode without combustion, is a new technology for energy utilization, and has the characteristics of cleanness and high efficiency. The low-temperature fuel cell is an ideal substitute power supply for field power stations, electric automobiles and portable power supplies due to the characteristics of low working temperature, quick start, high energy conversion rate and the like, receives wide attention, and is a fuel cell which works by using a proton exchange membrane at low temperature, including H fuel cells2/O2Proton Exchange Membrane Fuel Cells (PEMFCs), Direct Formic Acid Fuel Cells (DFAFCs), and Direct Methanol Fuel Cells (DMFCs), among others.
PEMFCs are one of the most widely applicable types of fuel cells, and mainly include two types, a stationary power source and a mobile power source. The fixed power PEMFC can be used as a power generation device with any scale and is suitable for being used as a distributed power station. The mobile power PEMFC has the characteristics of low working temperature, high starting speed, high power density, small size and the like, and can be used as a vehicle power source and a plurality of portable small mobile power sources. Among them, mobile PEMFC electric vehicles are recognized as a future development direction of electric vehicles.
So far, the catalyst of PEMFC mainly uses Pt as an electrocatalyst, and although it can operate for a long time under high-purity hydrogen conditions, the cost of PEMFC is high due to the expensive price of platinum. In order to replace Pt, the development of non-noble metal catalysts is of great importance. Macrocyclic molecular structure compounds have electrocatalytic activity on oxygen and are valued for their high chemical stability due to their conjugated structure. However, because the catalytic activity of the compound cannot be compared with that of the traditional Pt catalyst, the best result reported in the prior publication is 65% of the Pt activity under the same condition, and the catalyst has poor stability and complex preparation process, thereby restricting the further development of the catalyst.
Disclosure of Invention
In order to solve at least part of the problems, the invention provides a preparation method of an oxygen reduction catalyst, which overcomes the problems of complex preparation process, low activity and low stability of the obtained catalyst. Specifically, the present invention includes the following.
In a first aspect of the present invention, there is provided a method for preparing an oxygen-reducing catalyst, comprising the steps of:
(1) reacting the organic chelate with a salt of a first metal in a molar ratio of 1:1 to 1:3 to obtain N4-an M compound;
(2) the N is4the-M compound is loaded on a carbon carrier to obtain a loaded N4-an M compound, wherein the carbon support is doped with a second metal;
(3) subjecting the supported N to inert gas4-heat treatment of the compound M to obtain a catalyst precursor;
(4) milling the catalyst precursor to obtain the oxygen reduction catalyst.
In certain embodiments, the organic chelate is at least one selected from the group consisting of tetracarboxylic phthalocyanine, tetramethylporphyrine, and tetramethyloxyporphyrin.
In certain embodiments, the first metal and the second metal are each selected from the group consisting of iron and cobalt, and the first metal is different from the second metal.
In certain embodiments, said step (1) and said step (2) are performed simultaneously.
In certain embodiments, the preparation method of the present invention comprises dispersing the organic chelate compound, the salt of the first metal and the carbon support in a reaction solvent, acetic acid, by ultrasonic treatment, and reacting for 60 to 120 minutes with a microwave generator heated to 65 to 95 ℃.
In certain embodiments, the carbon support in step (2) is obtained by: treating the carbon powder doped with the second metal with 20-35% of hydrogen peroxide at room temperature for 5-10 hours, and then drying to obtain the carbon powder; or treating the second metal-doped carbon powder with nitric acid with the concentration of 2M-5M at 50-60 ℃ for 30-60 minutes, and then washing and drying to obtain the second metal-doped carbon powder.
In certain embodiments, the organic chelate is tetramethylporphyrine, the first metal is cobalt, and the second metal is iron.
In some embodiments, the heat treatment temperature in the step (3) is 600-900 ℃ and the heat treatment time is 4-7 hours.
In a second aspect of the invention, there is provided an oxygen reduction catalyst prepared by the process of the first aspect of the invention.
In a third aspect of the invention, there is provided the use of an oxygen reduction catalyst in the manufacture of a proton exchange membrane fuel cell, wherein the proton exchange membrane fuel cell comprises a catalytic layer, a diffusion layer and an exchange membrane, the catalytic layer comprising the catalyst of the second aspect of the invention; the diffusion layer is used for supporting the catalytic layer and comprises a porous composition made of a conductive material; and the exchange membrane is a composite membrane of a perfluorinated sulfonic acid material and polytetrafluoroethylene, and the thickness of the exchange membrane is 50-180 mu m.
The preparation method of the invention promotes the combination of the organic chelate and carbon through the synergistic action of iron and cobalt, and further strengthens the combination through the treatment step of hydrogen peroxide or nitric acid, thereby improving the activity and stability of the prepared catalyst. Preferably, the preparation method of the present invention simplifies the preparation process and improves efficiency by allowing the synthesis of the metal chelate and the loading with the carbon support to be completed in the same step.
Detailed Description
Reference will now be made in detail to various exemplary embodiments of the invention, the detailed description should not be construed as limiting the invention but as a more detailed description of certain aspects, features and embodiments of the invention.
It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Further, for numerical ranges in this disclosure, it is understood that the upper and lower limits of the range, and each intervening value therebetween, is specifically disclosed. Every smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in a stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. Unless otherwise indicated, "%" refers to percent by weight.
The "oxygen reduction catalyst" of the present invention, sometimes referred to simply as "catalyst of the present invention", refers to catalysts based on organic chelates, in particular catalysts based on transition metal chelates, which are useful in place of noble metal catalysts for catalyzing fuel reactions in fuel cells, in particular Proton Exchange Membrane Fuel Cells (PEMFCs). Preferably, the catalyst of the present invention is used to catalyze the reaction of hydrogen and oxygen to convert chemical energy directly into electrical energy. The catalyst of the present invention is preferably used as a cathode catalyst for a fuel cell.
In a first aspect of the present invention, there is provided a method for preparing an oxygen-reducing catalyst, comprising the steps of:
(1) reacting the organic chelate with a salt of a first metal in a molar ratio of 1:1 to 1:3 to obtain N4-an M compound; (2) the N is4the-M compound is loaded on a carbon carrier to obtain a loaded N4-an M compound, wherein the carbon support comprises a second metal thereon; (3) subjecting the supported N to inert gas4-heat treatment of the compound M to obtain a catalyst precursor; (4) before grinding the catalystThe oxygen reduction catalyst is obtained. The respective steps are explained in detail below.
Step (1)
Step (1) of the present invention is a step of obtaining a metal chelate compound, and specifically comprises reacting an organic chelate compound with a salt of a first metal at a molar ratio of 1:0.6 to 1:1.5, preferably 1:0.6 to 1:1, to obtain N4-an M compound. The organic chelate compound of the present invention is preferably a tetracarboxylic phthalocyanine or tetraphenylporphyrin compound. More preferred are tetramethylporphyrins and tetramethoxyporphyrins. The first metal of the present invention is a transition metal, preferably iron and/or cobalt. The metal chelate compound obtained in the step (1) has N4-M catalytically active centres, wherein M is iron and/or cobalt. In certain embodiments, the metal chelate is cobalt tetramethylphenylporphyrin, which has 4 Co — N active sites. In the present invention, the salt of the first metal may be an inorganic salt such as nitrate, sulfate, chloride, phosphate, hydrogen phosphate, carbonate, etc.; organic salts such as acetates, formates, propionates, and the like are also possible. Organic salts, such as cobalt acetate or iron acetate, are preferred.
Step (2)
The step (2) of the invention is to load the metal chelate on a carbon carrier to obtain the loaded N4-a step of compound M. Wherein the carbon support is doped with a second metal, the second metal being a transition metal, preferably iron and/or cobalt. It should be noted that, the first metal and the second metal of the present invention may be the same metal, or the first metal and the second metal may be different, that is, when the first metal is iron, the second metal is cobalt; when the first metal is cobalt, the second metal is iron. The invention finds that when a small amount of second metal is doped on the carbon carrier, the prepared catalyst has higher activity and durability. The applicant believes that it may be that the presence of the second metal promotes the conductivity of the carbon support on the one hand, and on the other hand the second metal may also participate in binding to the N atom in the chelate complex, thereby promoting binding of the chelate complex to the carbon support. Preferably, the second metal is present in the carbon support in an amount of 1% to 2%, preferably 1% to 1.5%, based on the total weight. The conductivity of the carbon support is rather decreased due to the excessively high content of the second metal, probably becauseIf the content is too high, the particles of the second metal tend to melt and aggregate with each other upon subsequent heat treatment.
In the present invention, the second metal-doped carbon support can be obtained by a known method. For example, processes for preparing ultra-fine iron particles on carbon by impregnating carbon with liquid iron pentacarbonyl and then heating the impregnated support material to decompose the iron pentacarbonyl to metallic iron, see, j.van Wonterghem and s.morup, j.phys.chem.1988, 92, 1013-. As another example, by vapor deposition of iron pentacarbonyl onto carbon. After the deposition of iron pentacarbonyl, the catalyst precursor thus obtained is reduced with hydrogen. Or by applying an aqueous solution of iron (III) nitrate to a carbon support and reducing the iron cations to elemental iron with hydrogen. See, J.Schwar et al, J.Vac.Sci.Technol.A 9(2), 1991, 238-. The particle size of the carbon in the carbon support can be controlled to a specified size by conventional means. For example, it is generally controlled to 10-40nm, preferably 20-40nm, and the specific surface area is 200-1500m2Per g, preferably 400-1000 m2/g。
In certain embodiments, to further enhance catalytic activity, the second metal doped carbon support is further subjected to the following pretreatment. A: treating the carbon powder doped with the second metal by 20-35% of hydrogen peroxide at room temperature for 5-10 hours, and then drying; b: treating the second metal-doped carbon powder with nitric acid at the concentration of 2-5M at 50-60 ℃ for 30-60 minutes, and then washing and drying.
And C, increasing oxygen-containing groups such as hydroxyl (-OH) on the surface of the carrier after the treatment in the step A, improving the adsorption and distribution of metals and oxides on the surface of the carrier, increasing the surface concentration of N and C atoms of the catalyst, and facilitating the formation of a Co-N4-C catalytic active site.
Wherein, the activity and the stability of the catalyst can be improved after the treatment of the step B. The specific reason is not clear, and the reason may be presumed to be: (1) the adsorption strength (or called bonding strength) between different particles of the second metal and carbon is different, and the acting force between the second metal with weak adsorption strength and carbon is weak, so that the conductivity between the second metal and carbon is weak, and further the conductivity and mass transfer of the catalyst are influenced, namely the catalytic activity is influenced. The treatment in step B can remove the metal having a weak adsorption strength from the carbon, and retain the metal having a high adsorption strength on the carbon particles as much as possible, thereby improving the activity of the catalyst. (2) The particles of the second metal particles are also made smaller under the action of nitric acid. It is known that the smaller the particle diameter of the metal particles, the higher the catalytic activity. (3) The nitric acid treatment can also remove impurities generated on the carbon surface, improve the purity of the carrier and simultaneously increase the concentration of nitrogen-containing genes on the carbon surface.
Since nitric acid has an effect on the second metal, the reaction conditions in step B are very important. In order to control the appropriate rate of dissolution, the nitric acid concentration is generally in the range of 2M to 5M, preferably 2M to 4M, more preferably 2.5 to 3.5M. An excessively high concentration is advantageous for removing the second metal particles having a low adsorption strength, but also affects the metal particles having a high adsorption strength, so that the amount of the metal supported is excessively low, thereby reducing the catalyst activity. On the other hand, if the concentration is too low, the removal of the metal having a low adsorption strength is insufficient, and it is not favorable to obtain a high-activity catalyst. In order to obtain a carbon support having a suitable amount of the second metal content. It is necessary to use a carbon support having a relatively high doping amount of the second metal before the treatment using the B step. For example, the second metal content prior to the treatment in step B is 2% to 5%, preferably 2% to 3%, based on the total weight. The time of the nitric acid treatment of step B is also important for the achievement of the object of the invention. The nitric acid treatment time is generally from 30 minutes to 60 minutes, preferably from 10 minutes to 40 minutes. For example 30 minutes. If the treatment time is too long, the amount of the metal carried is too low, and the catalyst activity is lowered. If the treatment time is too short, the treatment effect is insufficient and the degree of improvement in the catalytic activity is insufficient. The temperature of the nitric acid treatment of step B is also important for the achievement of the object of the invention. The acid treatment temperature of the present invention is 50 to 60 ℃, preferably 50 to 55 ℃. On the one hand, the treatment temperature is too low, the reaction between the metal and the acid is insufficient, even the metal does not react, and the purpose of treatment cannot be achieved. On the other hand, when the treatment temperature is too high, the reaction between the metal and the acid is too violent, which affects the amount of the metal supported, and thus lowers the catalytic activity. And the step B also comprises a water washing process after the acid treatment, so that redundant acid is removed, and the possible adverse effect of the acid on a subsequent catalyst is avoided.
In certain embodiments, step (1) and step (2) are performed simultaneously. The invention can greatly shorten the reaction time by simultaneously carrying out the step (1) and the step (2), and has simple operation. Preferably, the step (1) and the step (2) are performed by a microwave method, which not only shortens the reaction time but also improves the catalytic activity. Specifically, the microwave method comprises dispersing an organic chelate, a salt of a first metal and a carbon support in a reaction solvent, acetic acid, heating to 65-95 ℃ using a microwave reactor, and reacting at this temperature for 60-120 minutes. It is necessary to sufficiently mix the above-mentioned substances in the reaction solvent. Physical dispersion means may be employed for dispersion, and examples thereof include stirring, ultrasonic treatment. For example, treatment under sonication conditions is for 1 to 3 hours. The ultrasonic treatment is preferably performed while strongly stirring. In the microwave method, the weight ratio of the organic chelate compound to the carbon carrier is preferably 1:1 to 1:2, preferably 1:1 to 1: 5. The weight of the salt of the first metal is generally 3% to 10%, preferably 3% to 5%, more preferably 3% to 4% of the total weight of the organic chelate, the salt of the first metal and the carbon support. The ratio of the weight (g) of the organic chelate compound to the volume (ml) of the reaction solvent is 1:120 to 1:240, preferably 1:150 to 1: 200. The microwave reactor preferably has a reflux condenser. In certain embodiments, the microwave reactor has a power of 65-200W. Preferably, the reaction is cooled after microwave reaction, then precipitates are separated out by ethanol, and then the precipitates are stood, filtered and dried.
It is essential in the present invention that the first metal and the second metal are present on the carbon support at the same time. The existence of the first metal and the second metal is beneficial to forming a specific space structure between Fe and/or Co and N of the organic chelate, so that the bonding strength of the organic chelate and carbon is improved.
Step (3)
Step (3) of the present invention is to obtain a supported N4-a step of subjecting the M compound to a heat treatment, thereby obtaining a catalyst precursor. The heat treatment is generally carried out under an inert gas (e.g., argon) at a temperature of 600-. The above heat treatment conditions are favorableGenerating M-N4-C oxygen reduction catalytic active sites. If the temperature is too high, the organic chelate compound tends to decompose, so that the above-mentioned catalytically active site cannot be obtained.
Step (4)
Step (4) of the present invention is to grind the catalyst precursor to obtain the oxygen reduction catalyst. The grinding of the present invention can be carried out by any technique such as ball milling or the like.
In a second aspect of the present invention, there is provided an oxygen reduction catalyst (sometimes simply referred to as "the catalyst of the present invention") which is prepared by the process of the present invention. The bonding strength of the organic chelate and the carbon carrier in the catalyst is greatly improved, so that the stability of the catalyst is enhanced, and the activity of the catalyst is improved by the synergistic effect of the first metal and the second metal.
In a third aspect of the invention, there is provided the use of the oxygen reduction catalyst of the invention in the manufacture of a fuel cell. The catalyst of the present invention can be used as a cathode catalyst for a fuel cell. Preferably, the catalyst of the invention is used for the preparation of proton exchange membrane fuel cell PEMFCs. Examples thereof include a stationary power supply and a mobile power supply. The fixed power supply can be made into a power generation device with any scale and is suitable for being used as a distributed power station. The mobile power supply has the characteristics of low working temperature, high starting speed, high power density, small size and the like, and can be used as a vehicle power source and a plurality of portable small mobile power supplies. More preferably, the catalyst of the invention is used for the preparation of mobile power sources.
Preferably, the proton exchange membrane fuel cell of the present invention comprises a catalytic layer, a diffusion layer and an exchange membrane. Wherein the catalytic layer comprises the catalyst of the present invention. The catalyst layer can be a hydrophobic catalyst layer, the thickness of the catalyst layer is more than 50 μm, and the catalyst layer is mainly prepared by mixing platinum black or carbon-supported platinum catalyst and PTFE particles, coating the mixture on a diffusion layer by screen printing, coating, spraying and other methods, and carrying out heat treatment. The PTFE in the catalytic layer provides gas diffusion channels, while the catalyst provides channels for the transfer of electrons and water. The catalytic layers of the present invention can also be hydrophilic catalytic layers and ultra-thin catalytic layers having improved proton conductivity and increasing the area of the three-phase interface of the catalyst, reaction gas and proton exchange membrane. The diffusion layer of the present invention comprises a porous composite made of a conductive material, functions to support the catalytic layer, collect current, and provide an electron channel, a gas channel, and a water discharge channel for electrochemical reactions. The diffusion layer is generally formed by using porous carbon paper or carbon cloth as a substrate and treating the porous carbon paper or carbon cloth with Polytetrafluoroethylene (PTFE) and carbon black, and the thickness of the diffusion layer is about 0.2-0.3 mm. In the diffusion layer, the large pores covered with PTFE are hydrophobic pores, and the small pores not covered with PTFE are hydrophilic pores. The reactant gases are transported through the hydrophobic pores, while the product water is discharged through the hydrophilic pores. The exchange membrane is a composite membrane of perfluorosulfonic acid material and polytetrafluoroethylene, and the thickness of the exchange membrane is 50-180 μm, preferably 60-100 μm.
Example 1
(1) Iron-doped carbon powder (Vulcan X-72, iron content 1.2% based on the total weight after doping) was treated with 20% hydrogen peroxide at room temperature for 5 hours and then vacuum dried at constant temperature of 100 ℃ to obtain a dried carbon support.
(2) Adding 2.5 g of tetramethylphenyl porphyrin, 1.5 g of cobalt acetate and 5 g of carbon carrier into 250ml of acetic acid, ultrasonically dispersing for 25 minutes, then placing the mixture into a microwave oven with a reflux condenser tube, controlling the microwave oven to be stable at about 90 ℃, carrying out reaction reflux for 60 minutes, then cooling, adding 350ml of methanol for separation, standing, filtering, washing with methanol until the filtrate is colorless, and drying the precipitate in vacuum to obtain the supported N4-Co compound.
(3) Under the protection of argon, the obtained supported N4-Co compound is subjected to heat treatment at 900 ℃ for 3 hours, naturally cooled and ground to the required particle size, and the oxygen reduction catalyst 1 is obtained.
Example 2
(1) Iron-doped carbon powder (Vulcan X-72, iron content 2.3% based on the total weight after doping) was treated with 100ml of 4M nitric acid at 45 ℃ for 40 minutes, then washed with water to pH 7.0, and vacuum-dried at constant temperature of 100 ℃ to obtain a dried carbon support.
(2) Adding 2.5 g of tetramethylphenyl porphyrin, 1.5 g of cobalt acetate and 5 g of carbon carrier into 250ml of acetic acid, ultrasonically dispersing for 25 minutes, then placing the mixture into a microwave oven with a reflux condenser tube, controlling the microwave oven to be stable at about 90 ℃, carrying out reaction reflux for 60 minutes, then cooling, adding 350ml of methanol for separation, standing, filtering, washing with methanol until the filtrate is colorless, and drying the precipitate in vacuum to obtain the supported N4-Co compound.
(3) And under the protection of argon, carrying out heat treatment on the obtained supported N4-Co compound at 850 ℃ for 4 hours, naturally cooling, and grinding to obtain the oxygen reduction catalyst 2.
Example 3
(1) Iron-doped carbon powder (Vulcan X-72, iron content 2.3% based on the total weight after doping) was treated with 100ml of 4M nitric acid at 48 ℃ for 30 minutes, and then vacuum-dried at constant temperature of 100 ℃ to obtain a dried carbon support.
(2) Adding 2.3 g of tetramethoxyphenyl porphyrin, 1.5 g of cobalt acetate and 5 g of carbon carrier into 250ml of acetic acid, ultrasonically dispersing for 25 minutes, then placing the mixture into a microwave oven with a reflux condenser tube, controlling the microwave oven to be stable at about 90 ℃, carrying out reaction reflux for 60 minutes, then cooling, adding 350ml of methanol for precipitation, standing, filtering, washing with methanol until the filtrate is colorless, and drying the precipitate in vacuum to obtain the supported N4-Co compound.
(3) Under the protection of argon, the obtained supported N4-Co compound is subjected to heat treatment at 900 ℃ for 4.7 hours, naturally cooled and ground to the required particle size, and the oxygen reduction catalyst 3 is obtained.
Example 4
(1) Cobalt-doped carbon powder (Vulcan X-72, cobalt content 2.5% based on the total weight after doping) was treated with 100ml of 3M nitric acid at 48 ℃ for 30 minutes, and then vacuum-dried at constant temperature of 100 ℃ to obtain a dried carbon support.
(2) Adding 2.3 g of tetramethylphenyl porphyrin, 1.8 g of iron acetate and 5 g of carbon carrier into 250ml of acetic acid, ultrasonically dispersing for 25 minutes, then placing the mixture into a microwave oven with a reflux condenser tube, controlling the microwave oven to be stable at about 90 ℃, carrying out reaction reflux for 60 minutes, then cooling, adding 350ml of methanol for separation, standing, filtering, washing with methanol until the filtrate is colorless, and drying the precipitate in vacuum to obtain the supported N4-Fe compound.
(3) And under the protection of argon, carrying out heat treatment on the obtained supported N4-Fe compound at 900 ℃ for 4 hours, naturally cooling, and grinding to obtain the oxygen reduction catalyst 4.
Comparative example 1
(1) Adding 2.5 g of tetramethylphenyl porphyrin, 1.5 g of cobalt acetate and 5 g of carbon powder (Vulcan X-72, not doped with iron) into 250ml of acetic acid, ultrasonically dispersing for 25 minutes, then placing the mixture into a microwave oven with a reflux condenser, controlling the microwave oven to be stable at about 90 ℃, carrying out reaction reflux for 60 minutes, then cooling, adding 350ml of methanol for precipitation, standing, filtering, washing with methanol until filtrate is colorless, and drying the precipitate in vacuum to obtain the supported N4-Co compound.
(2) The obtained supported N4-Co compound was heat-treated at 850 ℃ for 4 hours under the protection of argon, naturally cooled, and ground to the desired particle size to obtain comparative oxygen reduction catalyst 1.
Comparative example 2
(1) Adding 2.3 g of tetramethylphenyl porphyrin, 1.8 g of iron acetate and 5 g of carbon powder (Vulcan X-72, not doped with iron) into 250ml of acetic acid, ultrasonically dispersing for 25 minutes, then placing the mixture into a microwave oven with a reflux condenser, controlling the microwave oven to be stable at about 90 ℃, carrying out reaction reflux for 60 minutes, then cooling, adding 350ml of methanol for precipitation, standing, filtering, washing with methanol until filtrate is colorless, and drying the precipitate in vacuum to obtain the supported N4-Fe compound.
(2) The obtained supported N4-Fe compound was heat-treated at 850 ℃ for 4 hours under the protection of argon, naturally cooled, and ground to the desired particle size to obtain comparative oxygen reduction catalyst 2.
Test example
1. The maximum output power of a single cell of each catalyst was tested under the following conditions
Each catalyst is taken as H2-O2Cathode catalyst for proton exchange membrane fuel cell. The experimental conditions are as follows: the temperature of the battery is 50 ℃ and H2、O2The pressure is 0.2MPa, the gas is completely humidified, and the anode catalyst is Pt/C (0.35mg Pt/cm)2) The loading amount of the cathode catalyst is 10-12mg/cm2。
2. The lifetime of each catalyst was tested under the following conditions
Each catalyst is taken as H2-O2Cathode catalyst for proton exchange membrane fuel cell. The experimental conditions are as follows: the polarization current density was 0.2A cm-2The battery temperature is 50 ℃ and H2、O2The pressure is 0.2MPa, and the gases are completely humidified. The test current density is 200mA/cm2The battery output voltage was maintained at 0.5V without a significant drop in time.
TABLE 1
Figure GDA0002683794840000111
Figure GDA0002683794840000121
It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the present disclosure without departing from the scope or spirit of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification. The specification and examples are exemplary only.

Claims (8)

1. A method of preparing an oxygen reduction catalyst comprising the steps of:
(1) reacting the organic chelate with a salt of a first metal in a molar ratio of 1:1 to 1:3 to obtain N4-an M compound;
(2) the N is4the-M compound is loaded on a carbon carrier to obtain a loaded N4-an M compound, wherein the carbon support is doped with a second metal and is obtained by: treating the carbon powder doped with the second metal with 20-35 wt% of hydrogen peroxide at room temperature for 5-10 hours, and then drying to obtain the carbon powder; or treating the carbon powder doped with the second metal by nitric acid with the concentration of 2M-5M at 50-60 ℃ for 30-60 minutes, and then washing and drying to obtain the carbon powder;
(3) subjecting the supported N to an inert gas at 600-900 DEG C4-heat treatment of the compound M to obtain a catalyst precursor;
(4) milling the catalyst precursor to obtain the oxygen reduction catalyst;
wherein the first metal and the second metal are respectively selected from the group consisting of iron and cobalt, and the first metal is different from the second metal.
2. The production method according to claim 1, wherein the organic chelate compound is at least one selected from the group consisting of tetracarboxylic phthalocyanine, tetramethylporphyrine and tetramethyloxyporphyrin.
3. The production method according to claim 1, wherein the step (1) and the step (2) are performed simultaneously.
4. The preparation method according to claim 3, which comprises dispersing the organic chelate, the salt of the first metal and the carbon carrier in a reaction solvent, acetic acid, by ultrasonic treatment, and reacting for 60 to 120 minutes with a microwave generator heated to 65 to 95 ℃.
5. The preparation method according to claim 1, wherein the organic chelate is tetramethylporphyrine, the first metal is cobalt, and the second metal is iron.
6. The preparation method according to claim 1, wherein the heat treatment temperature in the step (3) is 600 ℃ to 900 ℃ and the heat treatment time is 4 to 7 hours.
7. An oxygen reduction catalyst prepared by the method according to any one of claims 1 to 6.
8. Use of an oxygen reduction catalyst in the preparation of a proton exchange membrane fuel cell, wherein the proton exchange membrane fuel cell comprises a catalytic layer comprising the catalyst of claim 7, a diffusion layer, and an exchange membrane; the diffusion layer is used for supporting the catalytic layer and comprises a porous composition made of a conductive material; and the exchange membrane is a composite membrane of a perfluorinated sulfonic acid material and polytetrafluoroethylene, and the thickness of the exchange membrane is 50-180 mu m.
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CN104525185A (en) * 2014-12-26 2015-04-22 清华大学 Carbon-based composite fuel cell cathode oxygen reduction catalyst and preparation method thereof

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