Preparation method of microwave calcined high-dispersity platinum-cobalt alloy catalyst

Abstract

The invention provides a preparation method of a microwave-calcined high-dispersity platinum-cobalt alloy catalyst, which is mainly applied to the field of hydrogen fuel cells, and comprises the following key steps: (1) adding platinum salt, cobalt salt and a reducing agent into a binary / trihydric alcohol solution containing a conductive carbon carrier, adjusting the pH value, and carrying out heating reaction to obtain precursor slurry; (2) after freeze-drying the catalyst precursor, raising the temperature to 250-300 DEG C at a speed of 1.5-2.5 DEG C / min in a reducing atmosphere, preserving heat for 4 hours, carrying out low-temperature microwave calcination once, and carrying out acid pickling, filtering, water washing and freeze-drying to obtain a catalyst intermediate; and (3) heating the catalyst intermediate to 450-500 DEG C at a heating rate of 1.5-2.5 DEG C / min, carrying out heat preservation for 4 hours, and carrying out secondary high-temperature microwave calcination to obtain the platinum-cobalt catalyst. The catalyst prepared by the method has relatively low noble metal content and relatively good catalyst activity, the platinum-cobalt atomic ratio is controllable, the platinum-cobalt particle size is small, the particle size distribution range is narrow, and no obvious agglomerated particles appear.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method of a hydrogen fuel cell catalyst, in particular to a preparation method of a microwave calcined high-dispersity platinum-cobalt alloy catalyst. BACKGROUND

[0002] With the increase of global energy demand and the emphasis on environmental protection, the traditional energy has been unable to meet the growing energy demand of human beings. It is of great significance to develop and utilize green, sustainable and efficient renewable new energy to replace traditional fossil energy. Hydrogen energy has the characteristics of high calorific value, non-toxicity and non-pollution, and is a recognized green energy. The hydrogen energy industry has extremely broad development prospects. Proton exchange membrane fuel cell (PEMFC) capable of utilizing hydrogen for chemical energy-electric energy conversion is a core component of a hydrogen energy vehicle, and its development technology is one of the new energy conversion technologies with the greatest development potential at present. The catalyst is a core part of the PEMFC, however, the fuel cell catalyst is mainly platinum at present, and the cost is high. In order to reduce the cost of the catalyst, the addition of other metals to the catalyst to replace part of the noble metal has become a research hotspot at present. Through the synergistic effect and stress effect of the binary metal, the stability and activity of the catalyst can be improved while the noble metal loading in the catalyst is reduced.

[0003] At present, the common binary metal catalyst is a platinum-cobalt alloy catalyst, that is, a uniform nanoparticle internally occupied by cobalt atoms and composed of platinum and cobalt on the surface. Most of the prepared platinum-cobalt catalysts are only subjected to one high-temperature calcination at present, which can increase the alloy strength and improve the performance of the catalyst, but the prepared catalyst has the problems of poor stability, large agglomerated particles and poor dispersity; meanwhile, the platinum-cobalt atomic ratio of the catalyst after high-temperature calcination is uncontrollable, so that the performance of the catalyst is unstable, and the batch stability is poor. SUMMARY

[0004] In order to solve the problems existing in the preparation of the platinum-cobalt catalyst, the application provides a preparation method of a microwave calcined high-dispersity platinum-cobalt alloy catalyst, which comprises the following steps:

[0005] (1) platinum salt, cobalt salt, carbon black carrier and reducing agent are added into a solvent, the pH value of the solution is adjusted to 9-11, and the solution is heated at 50-60 DEG C for 3-5 h to obtain a precursor slurry;

[0006] (2) the precursor slurry obtained in the step (1) is filtered and washed, and the obtained solid precursor is freeze-dried;

[0007] (3) Put the freeze-dried precursor obtained in step (2) into a fluidized reactor, and perform a first microwave calcination under a reducing atmosphere; the microwave calcination is heated at a rate of 1.5-2.5 ℃ / min from room temperature to 250-300 ℃, and kept at the peak temperature for 4 h, and then naturally cooled to room temperature;

[0008] (4) Put the first microwave calcination catalyst obtained in step (3) into a reaction kettle, and add an acid solution for pickling;

[0009] (5) Filter and wash the pickled catalyst obtained in step (4), and freeze-dry the obtained solid catalyst;

[0010] (6) Put the freeze-dried catalyst obtained in step (5) into a fluidized reactor, and perform a second microwave calcination under a reducing atmosphere; the microwave calcination is heated at a rate of 1.5-2.5 ℃ / min from room temperature to 450-500 ℃, and kept at the peak temperature for 4 h, and then naturally cooled to room temperature, to obtain a platinum-cobalt alloy catalyst.

[0011] Further, the power of the first microwave calcination and the second microwave calcination is 1.8-2.5 kW, and the microwave frequency is 2.45 GHz.

[0012] Further, in step (1), the platinum salt is one of ammonium chloroplatinate, chloroplatinic acid or platinum nitrate.

[0013] Further, in step (1), the cobalt salt is one of cobalt nitrate, cobalt carbonate, cobalt chloride or cobalt sulfate.

[0014] Further, in step (1), the reducing agent is one of ethyl borane, dimethylamine borane or sodium borohydride.

[0015] Further, in step (1), the carbon black carrier is one of Ketjen black, Cabot black or acetylene black.

[0016] Further, in step (1), the solvent is one of water, ethanol or ethylene glycol.

[0017] Further, in step (3) and step (6), the reducing atmosphere is a mixed gas of hydrogen and argon, wherein the volume percentage of hydrogen is 3%-4.5%.

[0018] Further, in step (4), the acid solution is one of sulfuric acid, perchloric acid, nitric acid or acetic acid, with a concentration of 0.1-4 mol / L, and the pickling time is 2-8 h.

[0019] The beneficial effects of the technical scheme of the present application are as follows:

[0020] (1) The method of two microwave calcination is adopted. The first low-temperature microwave can effectively improve the alloying degree of platinum and cobalt atoms, enhance the synergistic effect between platinum and cobalt atoms, and reduce the agglomeration and adhesion of catalyst particles during calcination. The second high-temperature microwave can further alloy the catalyst particles, strengthen the grain structure, increase the dispersibility of catalyst particles, and increase the reactive surface area, thereby improving the activity and durability of the catalyst.

[0021] (2) The prepared platinum-cobalt catalyst has an adjustable platinum-cobalt atomic ratio, small platinum-cobalt nanoparticles with a narrow particle size distribution range, no obvious agglomeration particles, and high catalytic activity.

[0022] (3) The prepared catalyst has a platinum content of less than 45 wt.% and a cobalt content of less than 10 wt.%, with a platinum-cobalt atomic ratio between 7:1 and 9:1, and a peak power density of up to 1840.1 mW / cm³. 2 The mass activity at 0.9V decays by less than 10% after 10,000 cycles, demonstrating superior performance while reducing the amount of precious metals required.

[0023] (4) All raw materials used are non-toxic and harmless, no harmful substances are generated during the production process, and the process adopted can minimize the generation of waste. Attached Figure Description

[0024] Figure 1 This is a flow chart of the platinum-cobalt alloy catalyst preparation process of the present invention;

[0025] Figure 2 The image shows the microstructure of the platinum-cobalt alloy catalyst prepared in Example 1.

[0026] Figure 3 Comparison of fuel cell performance curves for the platinum-cobalt alloy catalysts prepared in Examples 2 and 3;

[0027] Figure 4 A comparison graph showing the fuel cell performance curves of the platinum-cobalt alloy catalysts prepared in Comparative Example 1 and Example 1. Detailed Implementation

[0028] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0029] Example 1

[0030] In this embodiment, the preparation of the platinum-cobalt alloy catalyst includes the following steps:

[0031] (1) Add 302 mg chloroplatinic acid, 30 mg cobalt chloride hexahydrate, 153 mg carbon black and 400 mg dimethylaminoborane to 100 mL of ethylene glycol, adjust the pH of the mixture to 9 with sodium hydroxide solution, heat in an oil bath to 55 °C and react for 4 h to obtain the precursor slurry.

[0032] (2) Filter the precursor slurry, wash it with deionized water 2-3 times, and freeze-dry the precursor obtained after filtration for 12 hours.

[0033] (3) Microwave calcination was carried out once in a hydrogen-argon mixed atmosphere with a hydrogen volume percentage of 3%. The microwave power was 1.8kW, the microwave frequency was 2.45GHz, the heating rate was 1.5℃ / min, the temperature was raised to 300℃ and held for 4h, and then cooled to room temperature.

[0034] (4) The obtained catalyst was placed in a reaction vessel and 1M perchloric acid was added and stirred for 6 hours.

[0035] (5) The acid-washed catalyst was subjected to secondary microwave calcination in a hydrogen-argon mixed atmosphere with a hydrogen volume percentage of 4%. The microwave power was 2.0 kW, the microwave frequency was 2.45 GHz, the heating rate was 2 °C / min, the temperature was raised to 450 °C and held for 4 h, and then cooled to room temperature and the sample was collected.

[0036] The catalyst sample prepared in this embodiment achieved a peak power density of 1769.7 mW / cm³. 2 The mass activity at 0.9V reached 0.39A / mg. Pt .

[0037] Example 2

[0038] In this embodiment, the preparation of the platinum-cobalt alloy catalyst includes the following steps:

[0039] (1) Add 302 mg chloroplatinic acid, 32 mg cobalt chloride hexahydrate, 153 mg carbon black and 400 mg dimethylaminoborane to 100 mL of ethylene glycol, adjust the pH of the mixture to 10 with sodium hydroxide solution, heat in an oil bath to 55 °C for 3 h to obtain the precursor slurry.

[0040] (2) Filter the precursor slurry, wash it with deionized water 2-3 times, and freeze-dry the precursor obtained after filtration for 12 hours.

[0041] (3) Microwave calcination was carried out once in a hydrogen-argon mixed atmosphere with a hydrogen volume percentage of 4%. The microwave power was 1.8kW, the microwave frequency was 2.45GHz, the heating rate was 2℃ / min, the temperature was raised to 250℃ and held for 4h, and then cooled to room temperature.

[0042] (4) The obtained catalyst was placed in a reaction vessel and 1M perchloric acid was added and stirred for 6 hours.

[0043] (5) The acid-washed catalyst was subjected to secondary microwave calcination in a hydrogen-argon mixed atmosphere (hydrogen: 5%; argon: 95%) with a hydrogen volume percentage of 4.5%. The microwave power was 2.0 kW, the microwave frequency was 2.45 GHz, the heating rate was 2 °C / min, the temperature was raised to 450 °C and held for 4 h, and then cooled to room temperature and the sample was collected.

[0044] The catalyst sample prepared in this embodiment achieved a peak power density of 1840.1 mW / cm³. 2 The mass activity at 0.9V reached 0.55A / mg. Pt .

[0045] Example 3

[0046] In this embodiment, the preparation of the platinum-cobalt alloy catalyst includes the following steps:

[0047] (1) Add 302 mg chloroplatinic acid, 32 mg cobalt chloride hexahydrate, 153 mg carbon black and 400 mg dimethylaminoborane to 100 mL of ethylene glycol, adjust the pH of the mixture to 10 with sodium hydroxide solution, heat in an oil bath to 55 °C and react for 5 h to obtain the precursor slurry.

[0048] (2) Filter the precursor slurry, wash it with deionized water 2-3 times, and freeze-dry the precursor obtained after filtration for 12 hours.

[0049] (3) Microwave calcination was carried out once in a hydrogen-argon mixed atmosphere with a hydrogen volume percentage of 4%. The microwave power was 1.8kW, the microwave frequency was 2.45GHz, the heating rate was 2℃ / min, the temperature was raised to 250℃ and held for 4h, and then cooled to room temperature.

[0050] (4) The obtained catalyst was placed in a reaction vessel and 1M perchloric acid was added and stirred for 6 hours.

[0051] (5) The acid-washed catalyst was subjected to secondary microwave calcination in a hydrogen-argon mixed atmosphere with a hydrogen volume percentage of 4.5%. The microwave power was 2.5kW, the microwave frequency was 2.45GHz, the heating rate was 2.5℃ / min, the temperature was raised to 500℃ and held for 4h, and then cooled to room temperature and the sample was collected.

[0052] The catalyst sample prepared in this embodiment achieved a peak power density of 1743.1 mW / cm³. 2 The mass activity at 0.9V reached 0.41A / mg. Pt .

[0053] Table 1. Platinum and cobalt content and atomic ratio in the platinum-cobalt alloy catalysts prepared in each example.

[0054] Group Platinum content (wt. %) Cobalt content (wt. %) Platinum cobalt atomic ratio Example 1 41.969 1.641 8.12:1 Example 2 41.278 1.714 7.27:1 Example 3 41.742 1.728 7.30:1

[0055] Comparative Example

[0056] The preparation method of the platinum-cobalt alloy catalyst differs from that of Example 1 in that only one microwave calcination treatment is used; the remaining process conditions are the same as in Example 1. Testing showed that the peak power density of Comparative Example 1 was only 541 W / cm³. 2 The mass activity at 0.9V is only 0.01A / mg. Pt .

[0057] The above description is a preferred embodiment of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a microwave-calcined highly dispersed platinum-cobalt alloy catalyst, characterized in that, Includes the following steps: (1) Platinum salt, cobalt salt, carbon black carrier and reducing agent are added to solvent, the pH value of the solution is adjusted to 9-11, and the reaction is heated at 50-60℃ for 3-5 hours to obtain precursor slurry; (2) The precursor slurry obtained in step (1) is filtered and washed, and the resulting solid catalyst is freeze-dried. (3) The freeze-dried precursor obtained in step (2) is placed in a fluidized reactor and subjected to microwave calcination in a reducing atmosphere. The microwave calcination starts from room temperature and heats up to 250-300°C at a rate of 1.5-2.5°C / min, holds at the peak temperature for 4 hours, and then cools down naturally to room temperature. (4) The catalyst obtained in step (3) after microwave calcination is placed in the reaction vessel and acid solution is added for acid washing; (5) The acid-washed catalyst obtained in step (4) is filtered and washed, and the resulting solid catalyst is freeze-dried. (6) The freeze-dried catalyst obtained in step (5) is placed in a fluidized reactor and subjected to secondary microwave calcination under a reducing atmosphere; The microwave calcination process begins at room temperature and is heated to 450–500°C at a rate of 1.5–2.5°C / min, held at the peak temperature for 4 hours, and then allowed to cool naturally to room temperature to obtain a platinum-cobalt alloy catalyst.

2. The preparation method according to claim 1, characterized in that: The power of the primary and secondary microwave calcination is 1.8–2.5 kW, and the microwave frequency is 2.45 GHz.

3. The preparation method according to claim 1, characterized in that: In step (1), the platinum salt is one of ammonium chloroplatinate, chloroplatinic acid, or platinum nitrate.

4. The preparation method according to claim 1, characterized in that: In step (1), the cobalt salt is one of cobalt nitrate, cobalt carbonate, cobalt chloride, or cobalt sulfate.

5. The preparation method according to claim 1, characterized in that: In step (1), the reducing agent is one of diborane, dimethylamineborane, or sodium borohydride.

6. The preparation method according to claim 1, characterized in that: In step (1), the carbon black carrier is one of Ketjen black, Cabot black or acetylene black.

7. The preparation method according to claim 1, characterized in that: In step (1), the solvent is one of water, ethanol or ethylene glycol.

8. The preparation method according to claim 1, characterized in that: In steps (3) and (6), the reducing atmosphere is a mixture of hydrogen and argon, wherein the volume percentage of hydrogen is 3 to 4.5%.

9. The preparation method according to claim 1, characterized in that: In step (4), the acid solution is one of sulfuric acid, perchloric acid, nitric acid or acetic acid, with a concentration of 0.1 to 4 mol / L and an acid washing time of 2 to 8 h.

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