A platinum-cobalt alloy graded pore doped carbon catalyst for fuel cells and a method of preparing the same

Abstract

The application belongs to the technical field of heterojunction electrocatalytic fuel cells, and specifically discloses a platinum-cobalt alloy graded-pore doped carbon catalyst for a fuel cell and a preparation method thereof. The application forms a platinum-cobalt alloy by calcining porous carbon material, nitrogen-containing organic molecules and a cobalt source and further reducing a platinum source in a wet method. The method modifies the structure of the porous carbon material by introducing nitrogen-containing organic small molecules to form micropore-mesopore-macropore graded pores, and uniformly pre-embeds cobalt nanoparticles in the porous carbon material, thereby improving the interaction between the carrier and the metal particles. The wet immersion reduction makes the platinum source and the cobalt nanoparticles form alloy nanoparticles, realizes the uniform distribution of the ultrafine alloy nanoparticles, and prolongs the stability and service life of the catalyst. The platinum-cobalt alloy catalyst as a new type of catalyst has broad application potential in oxygen reduction reactions, and has the advantages of simple manufacturing process, safety, greenness, low cost and the ability to meet the needs of large-scale production.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of heterojunction electrocatalytic fuel cells, and relates to a platinum-cobalt alloy heterojunction structure oxygen reduction reaction catalyst, in particular to a platinum-cobalt alloy graded pore doped carbon catalyst for a fuel cell and a preparation method thereof. BACKGROUND

[0002] The energy shortage caused by the accelerated consumption of traditional fossil energy and the resulting climate problems have made it urgent to develop green and sustainable energy and energy conversion devices. Green and inexpensive hydrogen energy and its device, hydrogen fuel cell, have naturally received extensive attention. Proton exchange membrane fuel cell (PEMFC) has the advantages of high power density, high energy conversion efficiency, low working temperature, fast start-up, good stability, environmental friendliness and the like, and has great potential in solving energy and climate problems.

[0003] Catalysts are one of the core materials of PEMFC, and have a significant impact on fuel cell production cost, energy conversion efficiency and cell life. However, the slow kinetics is a major limitation for the further development of PEMFC, so it is crucial to develop ORR catalysts with high catalytic activity and high stability. Platinum and platinum-based materials are still the best electrocatalysts for oxygen reduction reaction. Although widely used, the low tolerance of platinum-based catalysts to small molecules such as methanol, carbon monoxide and phosphoric acid, poor stability and high cost limit their further development and application in proton exchange membrane fuel cells. Alloying platinum with non-noble metals to form alloys or core / shell structures is a mainstream means to reduce the cost of platinum-based catalysts and improve the catalytic performance of oxygen reduction reaction. Alloying not only improves the utilization efficiency of platinum, but also optimizes the adsorption strength of oxygen-containing intermediates through potential ligand / strain effects. In addition to alloying, the combination of several typical strategies such as increasing the exposure of surface active atoms, defect engineering and local coordination optimization can also effectively improve the utilization of platinum.

[0004] Although efficient utilization of platinum and reduction of platinum consumption have been achieved, the good results of these platinum catalysts often cannot be reproduced in industrial practice. And these complex and precise surface modification strategies often cannot provide large-scale industrial synthesis of kilograms of catalysts, which is still a very challenging problem in actual production.

[0005] Based on the above points, the present application focuses on platinum-cobalt alloy catalysts, aiming to mass-produce platinum-cobalt alloy catalysts that amplify the catalytic activity of platinum with transition metals. SUMMARY

[0006] In view of the deficiencies of the prior art, the present application provides a platinum-cobalt alloy catalyst for oxygen reduction reaction, which is prepared by generating fine platinum-cobalt alloy nanoparticles on the surface of cobalt-nitrogen co-doped carbon material through high-temperature calcination and wet reduction, and has the advantages of simple synthesis method, mature industrial preparation conditions, and good electrochemical performance.

[0007] The specific technical solutions adopted by the present application are as follows:

[0008] In a first aspect, the present application provides a preparation method of a platinum-cobalt alloy hierarchical pore doped carbon catalyst for fuel cells, comprising the following steps:

[0009] (1) mixing porous carbon material, cobalt source and nitrogen-containing organic small molecules uniformly, and then obtaining cobalt-nitrogen co-doped carbon material with micro-mesopore-macropore hierarchical pore structure through calcination; performing acid washing, suction filtration and drying on the material powder;

[0010] (2) dispersing the cobalt-nitrogen co-doped carbon material into water through ultrasonic and stirring, adding platinum source solution into the solution containing the cobalt-nitrogen co-doped carbon material, adjusting pH value, and reducing with a reducing agent by using a wet impregnation reduction method; washing and drying the product, and the obtained sample is a platinum-cobalt alloy catalyst.

[0011] Further, in step (1), the porous carbon material includes but is not limited to one of activated carbon, XC-72, XC-72R, BP2000 and Super P Li, and is preferably XC-72R.

[0012] Further, in step (1), the cobalt source includes but is not limited to one of cobalt nitrate hexahydrate, cobalt chloride hexahydrate and cobalt sulfate, and is preferably cobalt chloride hexahydrate.

[0013] Further, in step (1), the nitrogen-containing organic small molecule includes but is not limited to one or more of dicyanediamine, triethylenediamine, 1,10-phenanthroline, cucurbit[7]uril, 1,4,7,10-tetraazacyclododecane, azacrown-18-ether-6 and tetraphenylporphyrin, and is preferably azacrown-18-ether-6 and cucurbituril.

[0014] Further, in step (1), the molar ratio of the cobalt source to the nitrogen-containing organic small molecule satisfies the coordination number of cobalt, and is preferably 1:2 (the above-mentioned ratio can ensure complete coordination under the selection of the type of the cobalt source and the nitrogen-containing organic small molecule).

[0015] Further, in step (1), the calcination temperature is 800-1200℃, and is preferably 900℃; the calcination is carried out in a protective atmosphere, and the protective atmosphere is an inert gas, including but not limited to one of argon, nitrogen and helium, and is preferably nitrogen.

[0016] Further, in step (1), the cobalt-nitrogen co-doped carbon material is subjected to acid pickling using one of, but not limited to, sulfuric acid, nitric acid, and perchloric acid solution, preferably perchloric acid solution; the concentration of the acid is controlled at 1-2 mol / L, preferably 1 mol / L; the acid pickling time is 12-24 h, preferably 12 h.

[0017] Further, in step (2), the platinum source includes, but is not limited to, one of platinum nitrate, tetraammine platinum nitrate, platinum chloride, chloroplatinic acid hexahydrate, potassium chloroplatinate, sodium chloroplatinate, and platinum acetylacetonate, preferably platinum nitrate.

[0018] Further, in step (2), the pH adjustment is performed by an alkaline solution, which includes, but is not limited to, one of sodium hydroxide and potassium hydroxide, preferably sodium hydroxide; the pH value of the solution is in the range of 12-14, preferably 13.

[0019] Further, in step (2), the reducing agent includes, but is not limited to, one of sodium borohydride, ethylene glycol, and polyvinylpyrrolidone, preferably sodium borohydride.

[0020] In a second aspect, the present application provides a platinum-cobalt alloy graded pore doped carbon catalyst for fuel cells prepared by the above preparation method.

[0021] Further, in the platinum-cobalt alloy catalyst, the mass percentage of platinum is 0.0001-70 wt%, the mass percentage of cobalt is 0.0001-50 wt% (preferably 2-50 wt%), and the ratio of platinum to cobalt can be arbitrarily controlled by the ratio of metal sources.

[0022] Further, in the platinum-cobalt alloy catalyst, the particle size of the metal nanoparticles is in the range of 1.2-4.2 nm.

[0023] The present application has the following beneficial effects:

[0024] 1. The platinum-cobalt alloy catalyst of the present application can be prepared into an electrode, which has high catalytic activity in a fuel cell and maintains stable catalytic performance for a long time.

[0025] 2. The platinum-cobalt alloy heterojunction structure is prepared by high-temperature calcination and wet reduction method, which has the characteristics of simple process, green and safe, easy to control, good stability of the prepared catalyst activity, and can realize large-scale production and preparation.

[0026] 3. The platinum-cobalt alloy catalyst electrochemical catalyst developed in the present application not only has important applications in the fields of chemical industry and energy, but also provides a new perspective for the research of electrocatalytic materials. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 TEM image of platinum-cobalt alloy catalyst prepared for Example 13 of the present invention.

[0028] Figure 2 Particle size distribution histogram of platinum-cobalt alloy catalyst prepared for Example 13 of the present invention.

[0029] Figure 3 PXRD image of platinum-cobalt alloy catalyst prepared for Example 13 of the present invention.

[0030] Figure 4 LSV image of platinum-cobalt alloy catalyst prepared for Example 13 and Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0031] In view of the problems of the prior art platinum-cobalt alloy catalyst preparation method being complex, difficult to reproduce in industrial practice, and not capable of large-scale synthesis, the present invention provides a method for preparing a platinum-cobalt alloy catalyst in two steps of high-temperature calcination and wet reduction. The method introduces a nitrogen-containing organic small molecule to modify the structure of the porous carbon material to form microporous-mesoporous-macroporous hierarchical pores in the calcination step, and uniformly pre-embeds cobalt nanoparticles in the porous carbon material to improve the interaction between the carrier and the metal particles. The wet impregnation reduction allows the platinum source and the cobalt nanoparticles to further form alloy nanoparticles with a proportion that can be arbitrarily adjusted, and the strong interaction between platinum and cobalt and the anchoring effect of cobalt on the carrier form a structure in which the concentration of cobalt increases from the alloy to the carrier, thereby achieving uniform distribution of ultra-fine alloy nanoparticles and prolonging the stability and life of the catalyst. Thus, while simplifying the process steps, the quality of the platinum-cobalt alloy catalyst is ensured, and large-scale production can be realized. The preparation method specifically includes the following steps:

[0032] (1) uniformly mix the porous carbon material, the cobalt source, and the nitrogen-containing organic small molecule: the porous carbon material includes but is not limited to one of activated carbon, XC-72, XC-72R, BP2000, and Super P Li, the cobalt source includes but is not limited to one of cobalt nitrate hexahydrate, cobalt chloride hexahydrate, and cobalt sulfate, and the nitrogen-containing organic small molecule includes but is not limited to one or more of dicyanediamine, triethylenediamine, 1,10-phenanthroline, cucurbit[7]uril, 1,4,7,10-tetraazacyclododecane, azo-18-crown-6, and tetraphenylporphyrin; the molar ratio of the cobalt source to the nitrogen-containing organic small molecule satisfies the coordination number of cobalt;

[0033] The cobalt-nitrogen co-doped carbon material with micro-mesopore-macropore hierarchical pore structure is obtained by calcination: the calcination temperature is 800-1200℃; the calcination is carried out in a protective atmosphere, which is an inert gas, including but not limited to one of argon, nitrogen and helium; the main factors affecting the formation of the micro-mesopore-macropore hierarchical pore structure are the calcination temperature, the type of organic small molecule and the type of carbon material, and the use of different porous carbon materials, organic small molecules and calcination temperatures can effectively adjust the surface area of the carrier and the cobalt content;

[0034] Then the cobalt-nitrogen co-doped carbon material powder is subjected to acid washing, suction filtration and drying: the acid washing solution includes but is not limited to one of sulfuric acid, nitric acid and perchloric acid solution, the concentration is controlled at 1-2 mol / L, and the acid washing time is 12-24 h;

[0035] (2) The cobalt-nitrogen co-doped carbon material is dispersed into water by ultrasonic and stirring, and a platinum source solution is added into the solution containing the cobalt-nitrogen co-doped carbon material: the platinum source includes but is not limited to one of platinum nitrate, tetraammine platinum nitrate, platinum chloride, chloroplatinic acid hexahydrate, potassium chloroplatinate, sodium chloroplatinate and platinum acetylacetone;

[0036] Then the pH value is adjusted, and a reducing agent is used to reduce by a wet impregnation reduction method: the pH adjustment is carried out by an alkaline solution, which includes but is not limited to one of sodium hydroxide and potassium hydroxide, and the solution pH value ranges from 12 to 14; the reducing agent includes but is not limited to one of sodium borohydride, ethylene glycol and polyvinylpyrrolidone;

[0037] Finally, the product is washed and dried, and the obtained sample is a platinum-cobalt alloy catalyst. The factors affecting the quality of the catalyst product mainly lie in the ratio of the cobalt source, the organic small molecule and the carbon carrier, and the calcination temperature, wherein: the molar ratio of the cobalt source to the nitrogen-containing organic small molecule should meet the coordination number of cobalt, the coordination ability and the ratio of the organic molecule affect the pore structure in the carrier and the particle size of the cobalt particles; too high cobalt content is not easy to form an alloy, and too low content affects the adsorption capacity of platinum particles, and it is appropriate to control the cobalt content in the product to be 2-50wt%; the calcination temperature affects the pore structure, the cobalt content and the particle size distribution, and too low temperature causes incomplete decomposition of the organic molecule, and too high temperature causes collapse of the pore structure.

[0038] The following are specific examples of catalyst preparation according to the above method, which are used to further illustrate the present application.

[0039] Example 1

[0040] A mixture of 1 g, 2.08 g, 1.84 g, 8.14 g of XC-72R, cobalt chloride hexahydrate, azido-18-crown-6, calix[7]urea, 240 ml of deionized water and 180 ml of acetonitrile was placed in a beaker and heated at 70 °C until the water was completely evaporated. The resulting solid powder was calcined under nitrogen at 800 °C. The resulting cobalt-nitrogen co-doped carbon material was acid washed, suction filtered, and oven dried. A solution containing 5850 mg of platinum tetrachloride was added to 1 g of the cobalt-nitrogen co-doped carbon material and reduced with stirring at room temperature. The product was washed, dried, and then reduced with sodium borohydride at room temperature. A platinum-cobalt alloy catalyst was obtained.

[0041] Example 2

[0042] A mixture of 1 g, 2.08 g, 1.84 g, 8.14 g of XC-72R, cobalt chloride hexahydrate, azido-18-crown-6, calix[7]urea, 240 ml of deionized water and 180 ml of acetonitrile was placed in a beaker and heated at 70 °C until the water was completely evaporated. The resulting solid powder was calcined under nitrogen at 800 °C. The resulting cobalt-nitrogen co-doped carbon material was acid washed, suction filtered, and oven dried. A solution containing 5850 mg of platinum tetrachloride was added to 1 g of the cobalt-nitrogen co-doped carbon material and reduced with stirring at room temperature. The product was washed, dried, and then reduced with sodium borohydride at room temperature. A platinum-cobalt alloy catalyst was obtained.

[0043] Example 3

[0044] A mixture of 1 g, 2.08 g, 1.84 g, 8.14 g of XC-72R, cobalt chloride hexahydrate, azido-18-crown-6, calix[7]urea, 240 ml of deionized water and 180 ml of acetonitrile was placed in a beaker and heated at 70 °C until the water was completely evaporated. The resulting solid powder was calcined under nitrogen at 800 °C. The resulting cobalt-nitrogen co-doped carbon material was acid washed, suction filtered, and oven dried. A solution containing 5850 mg of platinum tetrachloride was added to 1 g of the cobalt-nitrogen co-doped carbon material and reduced with stirring at room temperature. The product was washed, dried, and then reduced with sodium borohydride at room temperature. A platinum-cobalt alloy catalyst was obtained.

[0045] Example 4

[0046] Place 1 g, 0.26 g, 0.23 g, 1.02 g of XC-72R, cobalt chloride hexahydrate, azido-18-crown-6, calix[7]urea, 240 ml of deionized water and 180 ml of acetonitrile mixture in a beaker and heat to dryness at 70 °C. The resulting solid powder is calcined under nitrogen at 800 °C. The resulting cobalt-nitrogen co-doped carbon material is acid washed, vacuum filtered, and oven dried. A solution containing 5850 mg of platinum tetrachloride is added to 1 g of the cobalt-nitrogen co-doped carbon material and reduced with stirring at room temperature. The product is washed, dried, and then reduced with sodium borohydride at room temperature. A platinum-cobalt alloy catalyst is obtained.

[0047] Example 5

[0048] Place 1 g, 0.29 g, 0.26 g, 1.16 g of Super P, cobalt chloride hexahydrate, azido-18-crown-6, calix[7]urea, 240 ml of deionized water and 180 ml of acetonitrile mixture in a beaker and heat to dryness at 70 °C. The resulting solid powder is calcined under nitrogen at 800 °C. The resulting cobalt-nitrogen co-doped carbon material is acid washed, vacuum filtered, and oven dried. A solution containing 5850 mg of platinum tetrachloride is added to 1 g of the cobalt-nitrogen co-doped carbon material and reduced with stirring at room temperature. The product is washed, dried, and then reduced with sodium borohydride at room temperature. A platinum-cobalt alloy catalyst is obtained.

[0049] Example 6

[0050] Place 1 g, 0.73 g, 0.66 g, 2.91 g of BP2000, cobalt chloride hexahydrate, azido-18-crown-6, calix[7]urea, 240 ml of deionized water and 180 ml of acetonitrile mixture in a beaker and heat to dryness at 70 °C. The resulting solid powder is calcined under nitrogen at 800 °C. The resulting cobalt-nitrogen co-doped carbon material is acid washed, vacuum filtered, and oven dried. A solution containing 5850 mg of platinum tetrachloride is added to 1 g of the cobalt-nitrogen co-doped carbon material and reduced with stirring at room temperature. The product is washed, dried, and then reduced with sodium borohydride at room temperature. A platinum-cobalt alloy catalyst is obtained.

[0051] Example 7

[0052] A mixture of 1 g, 0.40 g, 0.46 g, 2.03 g of XC-72R, cobalt nitrate hexahydrate, azido-18-crown-6, calix[7]urea, 240 ml of deionized water and 180 ml of acetonitrile was placed in a beaker and heated at 70 °C until the water was completely evaporated. The resulting solid powder was calcined under nitrogen at 800 °C. The resulting cobalt-nitrogen co-doped carbon material was acid washed, suction filtered, and oven dried. A solution containing 5850 mg of platinum tetrachloride was added to 1 g of the cobalt-nitrogen co-doped carbon material and reduced with stirring at room temperature. The product was washed, dried, and then reduced with sodium borohydride at room temperature. A platinum-cobalt alloy catalyst was obtained.

[0053] Example 8

[0054] A mixture of 1 g, 0.61 g, 0.46 g, 2.03 g of XC-72R, cobalt sulfate, azido-18-crown-6, calix[7]urea, 240 ml of deionized water and 180 ml of acetonitrile was placed in a beaker and heated at 70 °C until the water was completely evaporated. The resulting solid powder was calcined under nitrogen at 800 °C. The resulting cobalt-nitrogen co-doped carbon material was acid washed, suction filtered, and oven dried. A solution containing 5850 mg of platinum tetrachloride was added to 1 g of the cobalt-nitrogen co-doped carbon material and reduced with stirring at room temperature. The product was washed, dried, and then reduced with sodium borohydride at room temperature. A platinum-cobalt alloy catalyst was obtained.

[0055] Example 9

[0056] A mixture of 1 g, 0.52 g, 0.24 g, 0.20 g of XC-72R, cobalt chloride hexahydrate, dicyanediamine, triethylenediamine, 240 ml of deionized water and 180 ml of acetonitrile was placed in a beaker and heated at 70 °C until the water was completely evaporated. The resulting solid powder was calcined under nitrogen at 800 °C. The resulting cobalt-nitrogen co-doped carbon material was acid washed, suction filtered, and oven dried. A solution containing 5850 mg of platinum tetrachloride was added to 1 g of the cobalt-nitrogen co-doped carbon material and reduced with stirring at room temperature. The product was washed, dried, and then reduced with sodium borohydride at room temperature. A platinum-cobalt alloy catalyst was obtained.

[0057] Example 10

[0058] A mixture of 1 g, 0.52 g, 0.24 g, 0.31 g of XC-72R, cobalt chloride hexahydrate, dicyano diamine, 1,10-phenanthroline, 240 ml of deionized water and 180 ml of acetonitrile was placed in a beaker and heated at 70 °C until the water was completely evaporated. The resulting solid powder was calcined under nitrogen at 800 °C. The resulting cobalt-nitrogen co-doped carbon material was acid washed, suction filtered, and oven dried. A solution containing 5850 mg of platinum tetrachloride was added to 1 g of the cobalt-nitrogen co-doped carbon material and reduced by stirring at room temperature. The product was washed, dried, and then reduced by heating with ethylene glycol at 120 °C. A platinum-cobalt alloy catalyst was obtained.

[0059] Example 11

[0060] A mixture of 1 g, 0.52 g, 0.71 g of XC-72R, cobalt chloride hexahydrate, 1,4,7,10-tetraazacyclododecane, 240 ml of deionized water and 180 ml of acetonitrile was placed in a beaker and heated at 70 °C until the water was completely evaporated. The resulting solid powder was calcined under nitrogen at 800 °C. The resulting cobalt-nitrogen co-doped carbon material was acid washed, suction filtered, and oven dried. A solution containing 5850 mg of platinum tetrachloride was added to 1 g of the cobalt-nitrogen co-doped carbon material and reduced by stirring at room temperature. The product was washed, dried, and then reduced by heating with ethylene glycol at 120 °C. A platinum-cobalt alloy catalyst was obtained.

[0061] Example 12

[0062] A mixture of 1 g, 0.52 g, 1.08 g of XC-72R, cobalt chloride hexahydrate, tetraphenylporphyrin, 240 ml of deionized water and 180 ml of acetonitrile was placed in a beaker and heated at 70 °C until the water was completely evaporated. The resulting solid powder was calcined under nitrogen at 800 °C. The resulting cobalt-nitrogen co-doped carbon material was acid washed, suction filtered, and oven dried. A solution containing 5850 mg of platinum tetrachloride was added to 1 g of the cobalt-nitrogen co-doped carbon material and reduced by stirring at room temperature. The product was washed, dried, and then reduced by heating with ethylene glycol at 120 °C. A platinum-cobalt alloy catalyst was obtained.

[0063] Example 13

[0064] XC-72R, cobalt chloride hexahydrate, azido-18-crown-6, cucurbit[7]uril, 240 mL of deionized water and 180 mL of acetonitrile were placed in a beaker and heated at 70 °C until the water was completely evaporated. The resulting solid powder was calcined under nitrogen at 900 °C. The resulting cobalt-nitrogen co-doped carbon material was acid washed, suction filtered, and oven dried. A solution containing 5850 mg of platinum tetrachloride was added to 1 g of the cobalt-nitrogen co-doped carbon material and reduced at room temperature with stirring. The product was washed and dried, and then reduced with polyvinylpyrrolidone at 80 °C. A platinum-cobalt alloy catalyst was obtained.

[0065] Comparative Example 1: Preparation of a commercial platinum-carbon electrode

[0066] This comparative example is to prepare an electrode using a commercial noble metal platinum which is widely used in current research, and to compare the performance with Example 13. The specific operation is as follows: 2 mg of commercial platinum-carbon with a mass fraction of 40% purchased from a chemical platform was ground and treated, and then added to a glass bottle. 0.40 mL of ultrapure water, 0.50 mL of isopropyl alcohol, and 0.1 mL of a 5% nafion solution were added, and an ink was formed by ultrasonic treatment. 0.005 mL of the ink was dropped on a rotating disc electrode and naturally air-dried. The platinum-cobalt alloy catalyst prepared in Example 13 was also used to prepare an electrode according to this operation.

[0067] The platinum-cobalt alloy catalysts prepared in Examples 1-13 have uniform alloy particle sizes and are uniformly distributed on the carrier, respectively, with a cobalt content in the range of 5-40 wt%, and have good catalytic activity and electrochemical stability. The following are the results of observation and evaluation of the platinum-cobalt alloy catalyst obtained in Example 13.

[0068] Figure 1 The TEM image of the platinum-cobalt alloy catalyst prepared in Example 13 can be seen to show that the carrier still retains the basic morphology of the porous carbon material before calcination and that the alloy nanoparticles are uniformly distributed on the carrier.

[0069] Figure 2 The particle size distribution histogram of the platinum-cobalt alloy catalyst prepared in Example 13 can be seen to show that the size of the nanoparticles is uniform and is concentrated at 2.7 nm.

[0070] Figure 3 The PXRD pattern of the platinum-cobalt alloy catalyst prepared in Example 13 can be seen to show that the diffraction peaks of the synthesized catalyst are consistent with the diffraction peaks of a standard platinum-cobalt alloy, proving that the nanoparticles loaded are indeed platinum-cobalt alloy. And the half-peak width of the main diffraction peak indicates that the grain size is small.

[0071] Figure 4The LSV plots of the electrodes made from the catalysts of Example 13 and Comparative Example 1 show that the half-wave potential, active mass and limiting current of Example 13 are all superior to those of the commercial platinum carbon, proving that the ORR performance of Example 13 is superior to that of the commercial platinum carbon. Specifically, the limiting current density of Example 13 is 5.9 mA / cm 2 , the half-wave potential is 0.89 V; the limiting current density of Comparative Example 1 is 5.6 mA / cm 2 , the half-wave potential is 0.88 V; the active mass is a normalized comparable value obtained by dividing the exchange current density at 0.9 V by the platinum content in the catalyst, and Example 13 is 0.5 A / mg Pt , Comparative Example 1 is 0.2 A / mg Pt .

[0072] The specific embodiments are only illustrative of the present application, and are not intended to limit the present application. Any changes made by those skilled in the art after reading the specification of the present application, as long as they are within the scope of the claims of the present application, will be protected by the patent law.

Claims

1. A method for the preparation of a platinum cobalt alloy graded pore doped carbon catalyst for fuel cells, characterized by, The method comprises the following steps: (1) mixing a porous carbon material, a cobalt source and a nitrogen-containing organic small molecule uniformly, wherein the porous carbon material is one of activated carbon, XC-72, XC-72R, BP2000 and Super P Li; the cobalt source is one of cobalt nitrate hexahydrate, cobalt chloride hexahydrate and cobalt sulfate; the nitrogen-containing organic small molecule is one or more of dicyanediamine, triethylenediamine, 1,10-phenanthroline, cucurbit[7]uril, 1,4,7,10-tetraazacyclododecane, azido-18-crown-6 ether and tetraphenylporphyrin; and the molar ratio of the cobalt source to the nitrogen-containing organic small molecule satisfies the coordination number of cobalt; The cobalt-nitrogen co-doped carbon material with a hierarchical pore structure of micropore-mesopore-macropore is obtained by calcination at a temperature of 800-1200 ℃; The material powder is subjected to acid pickling, suction filtration and drying; (2) dispersing the cobalt-nitrogen co-doped carbon material into water by ultrasonic and stirring, adding a platinum source solution into the solution containing the cobalt-nitrogen co-doped carbon material, adjusting the pH value, and reducing the material by a wet impregnation reduction method using a reducing agent; The product is washed and dried, and the obtained sample is a platinum-cobalt alloy catalyst.

2. The method for preparing a platinum-cobalt alloy graded pore doped carbon catalyst for a fuel cell according to claim 1, characterized by, In step (1), the calcination is performed in a protective atmosphere, and the protective atmosphere is an inert gas.

3. The method for preparing a platinum cobalt alloy graded pore doped carbon catalyst for a fuel cell according to claim 1, characterized in that, In step (1), the cobalt-nitrogen co-doped carbon material is subjected to acid pickling using one of sulfuric acid, nitric acid and perchloric acid solution, the concentration of the acid is controlled to be 1-2 mol / L, and the acid pickling time is 12-24 h.

4. The method for preparing a platinum cobalt alloy graded pore doped carbon catalyst for a fuel cell according to claim 1, characterized in that, In step (2), the platinum source is one of platinum nitrate, tetraammine platinum nitrate, platinum chloride, chloroplatinic acid hexahydrate, potassium chloroplatinate, sodium chloroplatinate and platinum acetylacetonate.

5. The method for preparing a platinum cobalt alloy graded pore doped carbon catalyst for a fuel cell according to claim 1, characterized in that, In step (2), in the wet impregnation reduction method, the pH value of the solution is adjusted to be 12-14, and the reducing agent is one of sodium borohydride, ethylene glycol and polyvinylpyrrolidone.

6. The platinum-cobalt alloy hierarchical pore doped carbon catalyst for fuel cells prepared by the preparation method in any one of claims 1-5.

7. The platinum cobalt alloy graded pore doped carbon catalyst for fuel cells of claim 6, wherein, In the platinum-cobalt alloy catalyst, the mass percentage of platinum is 0.0001-70 wt%, the mass percentage of cobalt is 0.0001-50 wt%, and the ratio of platinum to cobalt can be arbitrarily controlled by the ratio of metal sources.

8. The platinum cobalt alloy graded pore doped carbon catalyst for fuel cells of claim 6, wherein, In the catalyst, the particle size of the platinum-cobalt alloy nanoparticles on the carbon carrier is 1.2 nm-4.2 nm.

Images