Fuel cell cathode catalyst and preparation method thereof

Abstract

The invention discloses a fuel cell cathode catalyst and a preparation method thereof, and belongs to the technical field of fuel cells. The preparation method of the fuel cell cathode catalyst comprises the following steps: adding a modified multi-walled carbon nanotube into a chloroplatinic acid aqueous solution with the mass concentration of 5g / L, carrying out ultrasonic treatment at 30-50 DEG C for 1-2 hours, and then carrying out freeze drying; and putting the dry powder into a horizontal tube furnace, introducing inert gas as protective gas, heating to 450-500 DEG C, preserving heat for 1 hour, cooling to room temperature along with the furnace, and taking out to obtain the fuel cell cathode catalyst. The modified multi-walled carbon nanotube is MWCNT / PEI / 5-formyl-2-thiopheneboronic acid, and the 5-formyl-2-thiopheneboronic acid is grafted after the PEI is grafted on the surface of the MWCNT, so that the dispersity of the MWCNT can be obviously improved, the agglomeration phenomenon of the MWCNT is reduced, the dispersion is more uniform, the loading capacity of platinum is high, the electrocatalytic activity of the catalyst is obviously enhanced, and the dosage of platinum is reduced.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and in particular to a fuel cell cathode catalyst and its preparation method. Background Technology

[0002] Fuel cells, as power generation devices that directly convert the chemical energy of fuel into electrical energy through electrochemical reactions, are a promising clean energy source for the 21st century, expected to replace current traditional energy sources and rechargeable lithium-ion batteries. As alkaline fuel cells can operate smoothly at low temperatures, their development is receiving increasing attention. However, key performance characteristics of fuel cells, such as efficiency and lifespan, are limited by electrode catalysts, especially the cathode electrocatalyst.

[0003] The oxygen reduction reaction (ORR) occurs at the cathode of a fuel cell. Its reaction kinetics are slow, and platinum-carbon (Pt / C) electrocatalysts are typically used to accelerate the ORR reaction rate. However, several problems remain: (1) Pt metal particles are prone to dissolution, growth, aggregation, and migration during fuel cell operation, leading to the separation of PtNPs from the carbon support; (2) The carbon support material is susceptible to oxidation and corrosion in harsh electrolyte environments. Fuel cells operate under high pressure and strong acid conditions. When a fuel cell starts or stops, the potential fluctuates drastically, easily oxidizing and corroding the carbon support material, thus shortening the fuel cell's lifespan. The support material forms the supporting framework for the active components of the catalyst and can effectively reduce the aggregation of metal particles. The support material directly affects the distribution, electrochemical activity, specific surface area, stability, and utilization rate of the catalyst.

[0004] Patent CN105489907B provides a method for preparing carbon nanotube-supported platinum-iron superlattice alloy nanoparticles. This patent uses chloroplatinic acid and ferrous nitrate as precursors and prepares carbon nanotube-supported platinum-iron alloy nanoparticles in ethylene glycol solution via sodium borohydride reduction. Then, it transforms them into carbon nanotube-supported platinum-iron superlattice alloy nanoparticles through thermal annealing in an inert gas atmosphere, thereby improving the catalytic activity of the catalyst. However, the support in this invention is prone to agglomeration, which will affect the catalyst loading and the improvement of electrocatalytic activity. Summary of the Invention

[0005] This invention provides a fuel cell cathode catalyst and its preparation method, which can solve the problem that the prior art is prone to agglomeration, which affects the catalyst loading and the improvement of electrocatalytic activity.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing a fuel cell cathode catalyst, comprising the following steps:

[0008] Modified multi-walled carbon nanotubes were added to a chloroplatinic acid aqueous solution with a mass concentration of 5 g / L, and sonicated at 30-50℃ for 1-2 h, followed by freeze drying. The dried powder was placed in a horizontal tube furnace, and an inert gas was introduced as a protective gas. The temperature was raised to 450-500℃, held for 1 h, and then cooled to room temperature with the furnace to obtain the fuel cell cathode catalyst.

[0009] As a preferred embodiment of the present invention, the ratio of the modified multi-walled carbon nanotubes to the chloroplatinic acid aqueous solution is 5-10g:100-200mL.

[0010] This invention uses a pyrolysis method to prepare the catalyst, which reduces washing and filtration steps compared to the liquid phase method, and makes experimental conditions easier to control.

[0011] As a preferred embodiment of the present invention, the heating rate of the heat treatment in the tubular furnace is 3-5℃ / min.

[0012] As a preferred embodiment of the present invention, the inert gas is any one of nitrogen, argon, and helium.

[0013] As a preferred embodiment of the present invention, the heat preservation process involves evacuation and ventilation every 20 minutes.

[0014] As a preferred embodiment of the present invention, the method for preparing the modified multi-walled carbon nanotubes is as follows:

[0015] S1: Carboxylated multi-walled carbon nanotubes were dispersed in deionized water, then EDC·HCl and NHS were added, and the mixture was stirred at room temperature for 2-3 hours. Polyethyleneimine was then added, and the mixture was stirred at room temperature for 8-10 hours. The mixture was washed by centrifugation with distilled water several times and then freeze-dried to obtain MWCNT / PEI.

[0016] The ratio of carboxylated multi-walled carbon nanotubes, deionized water, EDC·HCl, NHS, and polyethyleneimine used is 0.4g:10-20mL:0.2g:0.2g:1.2-2g.

[0017] In the above reaction steps, the carboxyl groups in the carboxylated multi-walled carbon nanotubes and the amino groups in polyethyleneimine undergo an amide reaction under the action of condensing agents EDC·HCl and NHS, causing PEI to be grafted onto the surface of the carbon nanotubes, thus obtaining MWCNT / PEI. The long-chain structure of PEI forms a steric hindrance layer, which can prevent the carbon nanotubes from entanglement and aggregation caused by π-π stacking or van der Waals forces, significantly improving their dispersion stability in solvents, thus making them more favorable for loading Pt. Furthermore, the amino groups in PEI can coordinate with Pt, further improving the dispersion of palladium. The PEI molecule is rich in amino groups, which, after grafting onto carbon nanotubes, provide a large number of nucleophilic reaction sites for the material, which is conducive to the occurrence of subsequent reactions.

[0018] S2: Dissolve MWCNT / PEI in DMF and stir for 20-30 min to obtain solution A; dissolve 5-aldehyde-2-thiopheneboronic acid in DMF to obtain solution B; add solution B to solution A and stir for 12-14 h, then filter, wash, freeze dry for 24 h, and grind to obtain MWCNT / PEI / 5-aldehyde-2-thiopheneboronic acid.

[0019] In solution A, the ratio of MWCNT / PEI to DMF is 5g:50mL; in solution B, the ratio of 5-aldehyde-2-thiopheneboronic acid to DMF is 0.8-1.2g:10mL; and the volume ratio of solution B to solution A is 1:5.

[0020] In the above steps, the remaining amino group in MWCNT / PEI can continue to react with the aldehyde group of 5-aldehyde-2-thiopheneboronic acid to undergo a Schiff base reaction, ultimately yielding MWCNT / PEI / 5-aldehyde-2-thiopheneboronic acid.

[0021] As a preferred embodiment of the present invention, the molecular weight of the polyethyleneimine is 600-2000.

[0022] Secondly, the present invention provides a fuel cell cathode catalyst, which is prepared by the method for preparing fuel cell cathode catalyst described in any one of the above contents.

[0023] The beneficial effects of this invention are:

[0024] 1. This invention uses MWCNT / PEI / 5-aldehyde-2-thiopheneboronic acid as the support for a platinum catalyst. 5-aldehyde-2-thiopheneboronic acid and the amino group of PEI form a cross-linked network through a Schiff base reaction. This three-dimensional cross-linked structure restricts the migration of Pt nanoparticles through steric hindrance, thus improving the dispersion of Pt. Pt can coordinate with the N and S groups of the support, further increasing the dispersion of Pt and reducing Pt aggregation. Higher Pt dispersion results in a greater number of active sites, which can improve the catalytic activity of the catalyst.

[0025] 2. Modified multi-walled carbon nanotubes are doped with three elements: B, N, and S. The incorporation of B, N, and S disrupts the spline structure of the carbon nanotubes. 2 The structure generates a large number of edge defects and topological defects, which participate in the catalytic reaction as additional active sites, improving its electrocatalytic activity and thus enhancing the catalytic activity of the fuel cell cathode catalyst.

[0026] 3. Grafting PEI onto the surface of MWCNT followed by grafting 5-aldehyde-2-thiopheneboronic acid can significantly improve the dispersion of MWCNT, reduce the aggregation of MWCNT, make the dispersion more uniform, increase the platinum loading, significantly enhance the electrocatalytic activity of the catalyst, and reduce the amount of platinum used. Detailed Implementation

[0027] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0028] The carboxylated multi-walled carbon nanotubes in this application have a diameter of 4 nm, a length of 10 μm, and an oxygen content of 6.60 wt%, and were purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd.

[0029] Preparation Example 1

[0030] The preparation method of modified multi-walled carbon nanotubes is as follows:

[0031] S1: 0.4 g of carboxylated multi-walled carbon nanotubes were dispersed in 20 mL of deionized water, followed by the addition of 0.2 g of EDC·HCl and 0.2 g of NHS. The mixture was stirred at room temperature for 2 h, and then 1.2 g of polyethyleneimine (molecular weight 2000) was added. The mixture was stirred at room temperature for 8 h, washed by centrifugation with distilled water multiple times, and freeze-dried to obtain MWCNT / PEI.

[0032] S2: Dissolve 5g of MWCNT / PEI in 50mL of DMF and stir for 20min to obtain solution A; dissolve 0.8g of 5-aldehyde-2-thiopheneboronic acid in 10mL of DMF to obtain solution B; add 10mL of solution B to 50mL of solution A and stir for 12h, then filter, wash, freeze dry for 24h, and grind to obtain MWCNT / PEI / 5-aldehyde-2-thiopheneboronic acid.

[0033] Preparation Example 2

[0034] The preparation method of modified multi-walled carbon nanotubes is as follows:

[0035] S1: 0.4 g of carboxylated multi-walled carbon nanotubes were dispersed in 20 mL of deionized water, followed by the addition of 0.2 g of EDC·HCl and 0.2 g of NHS. The mixture was stirred at room temperature for 3 h, and then 1.6 g of polyethyleneimine (molecular weight 2000) was added. The mixture was stirred at room temperature for 10 h, washed by centrifugation with distilled water multiple times, and freeze-dried to obtain MWCNT / PEI.

[0036] S2: Dissolve 5g of MWCNT / PEI in 50mL of DMF and stir for 30min to obtain solution A; dissolve 1g of 5-aldehyde-2-thiopheneboronic acid in 10mL of DMF to obtain solution B; add 10mL of solution B to 50mL of solution A and stir for 13h, then filter, wash, freeze dry for 24h, and grind to obtain MWCNT / PEI / 5-aldehyde-2-thiopheneboronic acid.

[0037] Preparation Example 3

[0038] The preparation method of modified multi-walled carbon nanotubes is as follows:

[0039] S1: 0.4 g of carboxylated multi-walled carbon nanotubes were dispersed in 20 mL of deionized water, followed by the addition of 0.2 g of EDC·HCl and 0.2 g of NHS. The mixture was stirred at room temperature for 3 h, and then 2 g of polyethyleneimine (molecular weight 2000) was added. The mixture was stirred at room temperature for 10 h, washed by centrifugation with distilled water multiple times, and freeze-dried to obtain MWCNT / PEI.

[0040] S2: Dissolve 5g of MWCNT / PEI in 50mL of DMF and stir for 30min to obtain solution A; dissolve 1.2g of 5-aldehyde-2-thiopheneboronic acid in 10mL of DMF to obtain solution B; add 10mL of solution B to 50mL of solution A and stir for 14h. Then filter, wash, freeze dry for 24h, and grind to obtain MWCNT / PEI / 5-aldehyde-2-thiopheneboronic acid.

[0041] Compare with Example 1

[0042] Compared with Preparation Example 1, the only difference is that 5-aldehyde-2-thiopheneboronic acid is replaced with 2-thiophenecarboxaldehyde. The specific steps are as follows:

[0043] S1: 0.4 g of carboxylated multi-walled carbon nanotubes were dispersed in 20 mL of deionized water, followed by the addition of 0.2 g of EDC·HCl and 0.2 g of NHS. The mixture was stirred at room temperature for 2 h, and then 1.2 g of polyethyleneimine (molecular weight 2000) was added. The mixture was stirred at room temperature for 8 h, washed by centrifugation with distilled water multiple times, and freeze-dried to obtain MWCNT / PEI.

[0044] S2: Dissolve 5g of MWCNT / PEI in 50mL of DMF and stir for 20min to obtain solution A; dissolve 0.8g of 2-thiophenecarboxaldehyde in 10mL of DMF to obtain solution B; add 10mL of solution B to 50mL of solution A and stir for 12h. Then filter, wash, freeze dry for 24h, and grind to obtain MWCNT / PEI / 5-aldehyde-2-thiopheneboronic acid.

[0045] Compare with Example 2

[0046] Compared with Preparation Example 1, the only difference is the omission of 5-aldehyde-2-thiopheneboronic acid. The specific steps are as follows:

[0047] 0.4 g of carboxylated multi-walled carbon nanotubes were dispersed in 20 mL of deionized water, followed by the addition of 0.2 g of EDC·HCl and 0.2 g of NHS. The mixture was stirred at room temperature for 2 h, and then 1.2 g of polyethyleneimine (molecular weight 2000) was added. The mixture was stirred at room temperature for 8 h, washed repeatedly by centrifugation with distilled water, and freeze-dried to obtain MWCNT / PEI.

[0048] Compare with Example 3

[0049] In this comparative example, the modified multi-walled carbon nanotubes were replaced with carboxylated multi-walled carbon nanotubes.

[0050] Example 1

[0051] A method for preparing a fuel cell cathode catalyst includes the following steps:

[0052] 5g of the modified multi-walled carbon nanotubes prepared in Preparation Example 1 were added to 100mL of chloroplatinic acid aqueous solution with a mass concentration of 5g / L, and sonicated at 30℃ for 1h, followed by freeze drying. The dried powder was placed in a horizontal tube furnace, nitrogen was introduced as a protective gas, the temperature was raised to 450℃ at a heating rate of 5℃ / min, and held at this temperature for 1h. The gas was evacuated and ventilated every 20min. After cooling to room temperature with the furnace, the fuel cell cathode catalyst was obtained.

[0053] Example 2

[0054] A method for preparing a fuel cell cathode catalyst includes the following steps:

[0055] 6.25 g of the modified multi-walled carbon nanotubes prepared in Preparation Example 1 were added to 125 mL of chloroplatinic acid aqueous solution with a mass concentration of 5 g / L, and sonicated at 30 °C for 1 h, followed by freeze drying. The dried powder was placed in a horizontal tube furnace, nitrogen was introduced as a protective gas, the temperature was raised to 450 °C at a heating rate of 5 °C / min, and held at that temperature for 1 h. The gas was evacuated and ventilated every 20 min. After cooling to room temperature with the furnace, the fuel cell cathode catalyst was obtained.

[0056] Example 3

[0057] A method for preparing a fuel cell cathode catalyst includes the following steps:

[0058] 7.5 g of the modified multi-walled carbon nanotubes prepared in Preparation Example 2 were added to 150 mL of chloroplatinic acid aqueous solution with a mass concentration of 5 g / L, and sonicated at 50 °C for 2 h, followed by freeze drying. The dried powder was placed in a horizontal tube furnace, nitrogen was introduced as a protective gas, the temperature was raised to 500 °C at a heating rate of 3 °C / min, and held at that temperature for 1 h. The gas was evacuated and ventilated every 20 min. After cooling to room temperature with the furnace, the fuel cell cathode catalyst was obtained.

[0059] Example 4

[0060] A method for preparing a fuel cell cathode catalyst includes the following steps:

[0061] 8.75 g of the modified multi-walled carbon nanotubes prepared in Preparation Example 3 were added to 175 mL of chloroplatinic acid aqueous solution with a mass concentration of 5 g / L, and sonicated at 50 °C for 2 h, followed by freeze drying. The dried powder was placed in a horizontal tube furnace, nitrogen was introduced as a protective gas, the temperature was raised to 500 °C at a rate of 5 °C / min, and held at that temperature for 1 h. The gas was evacuated and vented every 20 min. After cooling to room temperature with the furnace, the fuel cell cathode catalyst was obtained.

[0062] Example 5

[0063] A method for preparing a fuel cell cathode catalyst includes the following steps:

[0064] 10g of the modified multi-walled carbon nanotubes prepared in Preparation Example 3 were added to 200mL of chloroplatinic acid aqueous solution with a mass concentration of 5g / L, and sonicated at 50℃ for 2h, followed by freeze drying. The dried powder was placed in a horizontal tube furnace, nitrogen was introduced as a protective gas, the temperature was raised to 500℃ at a heating rate of 5℃ / min, and held at that temperature for 1h. The gas was evacuated and ventilated every 20min. After cooling to room temperature with the furnace, the fuel cell cathode catalyst was obtained.

[0065] Comparative Example 1

[0066] The only difference between this comparative example and Example 1 is that the modified multi-walled carbon nanotubes obtained in Example 1 are replaced with the product in Control Example 1.

[0067] Comparative Example 2

[0068] The only difference between this comparative example and Example 1 is that the modified multi-walled carbon nanotubes obtained in Example 1 were replaced with the product in Control Example 2.

[0069] Comparative Example 3

[0070] The only difference between this comparative example and Example 1 is that the modified multi-walled carbon nanotubes obtained in Example 1 were replaced with the product in Control Example 3.

[0071] The catalysts prepared in Examples 1-5 and Comparative Examples 1-3 were subjected to performance tests. The test items are as follows, and the results are shown in Table 1:

[0072] 1. Dispersion: The dispersion of Pt in the catalysts prepared in Examples 1-5 and Comparative Examples 1-3 was measured using the CO gas pulse method.

[0073] 2. Electrocatalytic activity test: The catalysts prepared in Examples 1-5 and Comparative Examples 1-3 were coated onto glassy carbon electrodes for catalytic testing. A saturated calomel electrode was used as the reference electrode, a platinum wire electrode as the counter electrode, and the glassy carbon electrode coated with the catalyst sample was used as the working electrode. The working electrode was prepared as follows: the catalyst was prepared into a mixed solution of 5 mg / ml deionized water and anhydrous ethanol (1:1), sonicated for 10 minutes, and then 8 μL (4 μL in two separate drops) was transferred using a micropipette onto a polished rotating disk electrode. The electrode was allowed to air dry naturally. Then, 8 μL of a 0.05% anhydrous ethanol solution was dropped onto the electrode surface and allowed to air dry naturally. The initial potential and half-wave potential after 3000 cycles were measured using cyclic voltammetry.

[0074] Table 1

[0075]

[0076] Table 1 shows that the catalysts prepared in the examples have better overall performance than those prepared in the comparative examples. Comparative Example 1 does not contain boric acid groups, and the electrocatalytic activity of Pt is lower than that in Example 1, indicating that the incorporation of B disrupts the sp(s) structure of carbon nanotubes. 2 The structure generates a large number of edge defects and topological defects, which participate in the catalytic reaction as additional active sites, improving its electrocatalytic activity and thus enhancing the catalytic activity of the fuel cell cathode catalyst.

[0077] Comparative Example 2, which does not contain 5-aldehyde-2-thiopheneboronic acid, exhibited lower dispersibility and electrocatalytic activity than Example 1. This indicates that grafting PEI onto the MWCNT surface followed by grafting 5-aldehyde-2-thiopheneboronic acid significantly improves the dispersion of MWCNTs, reduces their aggregation, results in more uniform dispersion, higher platinum loading, and significantly enhances the catalyst's electrocatalytic activity. Furthermore, the incorporation of B and S disrupts the sp[s] of carbon nanotubes. 2 The structure generates a large number of edge defects and topological defects, which participate in the catalytic reaction as additional active sites, improving its electrocatalytic activity and thus enhancing the catalytic activity of the fuel cell cathode catalyst.

[0078] In Comparative Example 3, replacing the modified multi-walled carbon nanotubes with carboxylated multi-walled carbon nanotubes resulted in the worst dispersibility and electrocatalytic activity. This indicates that 5-aldehyde-2-thiopheneboronic acid and the amino group of PEI form a cross-linked network through a Schiff base reaction. The three-dimensional cross-linked structure restricts the migration of Pt nanoparticles through steric hindrance, thereby improving the dispersibility of Pt. Pt can coordinate with the N and S atoms of the support, further improving the dispersibility of Pt and reducing Pt aggregation. Higher Pt dispersibility means a greater number of active sites, which can improve the catalytic activity of the catalyst.

[0079] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A method for preparing a fuel cell cathode catalyst, characterized in that, Includes the following steps: Modified multi-walled carbon nanotubes were added to a chloroplatinic acid aqueous solution with a mass concentration of 5 g / L, and sonicated at 30-50℃ for 1-2 h, followed by freeze drying. The dried powder was placed in a tube furnace, inert gas was introduced, the temperature was raised to 450-500℃, and the temperature was held for 1 h. After cooling to room temperature with the furnace, the powder was removed to obtain the fuel cell cathode catalyst.

2. The method for preparing a fuel cell cathode catalyst according to claim 1, characterized in that, The ratio of the modified multi-walled carbon nanotubes to the chloroplatinic acid aqueous solution is 5-10g:100-200mL.

3. The method for preparing a fuel cell cathode catalyst according to claim 1, characterized in that, The heating rate in the tubular furnace heat treatment is 3-5℃ / min.

4. The method for preparing a fuel cell cathode catalyst according to claim 1, characterized in that, The inert gas is any one of nitrogen, argon, or helium.

5. The method for preparing a fuel cell cathode catalyst according to claim 1, characterized in that, During the heat preservation process, air extraction and ventilation are performed every 20 minutes.

6. The method for preparing a fuel cell cathode catalyst according to claim 1, characterized in that, The method for preparing the modified multi-walled carbon nanotubes is as follows: S1: Carboxylated multi-walled carbon nanotubes were dispersed in deionized water, then EDC·HCl and NHS were added, and the mixture was stirred at room temperature for 2-3 hours. Polyethyleneimine was then added, and the mixture was stirred at room temperature for 8-10 hours. The mixture was washed by centrifugation with distilled water several times and then freeze-dried to obtain MWCNT / PEI. S2: Dissolve MWCNT / PEI in DMF and stir for 20-30 min to obtain solution A; 5-Aldehyde-2-thiopheneboronic acid was dissolved in DMF to obtain solution B; Solution B was added to solution A, and the mixture was stirred for 12-14 hours. After that, the mixture was filtered, washed, freeze-dried for 24 hours, and ground to obtain MWCNT / PEI / 5-aldehyde-2-thiopheneboronic acid.

7. The method for preparing a fuel cell cathode catalyst according to claim 6, characterized in that, In step S1, the ratio of carboxylated multi-walled carbon nanotubes, deionized water, EDC·HCl, NHS, and polyethyleneimine is 0.4g:10-20mL:0.2g:0.2g:1.2-2g.

8. The method for preparing a fuel cell cathode catalyst according to claim 6, characterized in that, In step S2, the ratio of MWCNT / PEI to DMF in solution A is 5g:50mL; the ratio of 5-aldehyde-2-thiopheneboronic acid to DMF in solution B is 0.8-1.2g:10mL; and the volume ratio of solution B to solution A is 1:

5.

9. The method for preparing a fuel cell cathode catalyst according to claim 6, characterized in that, The molecular weight of the polyethyleneimine is 600-2000.

10. A cathode catalyst for a fuel cell, characterized in that, It is prepared by the method for preparing the fuel cell cathode catalyst according to any one of claims 1-9.

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