Cerium-doped carbon quantum dot as well as preparation method and application thereof

Abstract

The invention relates to the technical field of fuel cells, in particular to a cerium-doped carbon quantum dot and a preparation method and application thereof. The cerium-doped carbon quantum dots are synthesized by adopting a hydrothermal method, and the cerium-doped carbon quantum dots can be used as a free radical scavenger, so that the technical problems that the proton exchange membrane fuel cell is attacked by free radicals in the operation process and the chemical stability is reduced can be solved. Specifically, cerium can be firmly fixed by the cerium-doped carbon quantum dots, and migration of independent cerium ions is avoided; meanwhile, the cerium and the carbon quantum dots can synergistically exert the free radical scavenging effect.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and particularly relates to a cerium-doped carbon quantum dot, a preparation method thereof, and an application thereof. Background Art

[0002] Disclosing the information of this background art section is only intended to enhance the understanding of the overall background of the present invention, and is not necessarily to be regarded as an admission or an implication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] A proton exchange membrane fuel cell (PEMFC) is a device that uses hydrogen as fuel to convert chemical energy into electrical energy. Among them, the proton exchange membrane is the core unit of the proton exchange membrane fuel cell, which conducts protons to form a battery circuit and can separate the anode and cathode of the fuel cell at the same time. Therefore, the electrical conductivity and stability of the proton exchange membrane are of great significance.

[0004] During the operation of the fuel cell, incomplete reaction of oxygen and protons on the cathode side generates hydrogen peroxide. Further reaction of hydrogen peroxide will generate hydroxyl radicals and hydrogen peroxide radicals. On the anode side, hydrogen radicals will be formed on the surface of the catalyst layer by hydrogen, and the hydrogen radicals react with oxygen permeating from the cathode side to generate hydrogen peroxide radicals. Among them, part of the hydrogen peroxide radicals will react with hydrogen ions to generate hydrogen peroxide, and further undergo the same reaction as on the anode side to generate hydroxyl radicals and hydrogen peroxide radicals.

[0005] Conventional proton exchange membranes are prone to attack by free radicals due to the presence of ether bonds, carbon-sulfur bonds, benzene rings, etc. in their structures, resulting in the degradation of polymer chains and reducing the stability of the proton exchange membrane. Therefore, the performance of the fuel cell is unstable.

[0006] Ce-based substances such as CeO2 are currently the most effective free radical scavengers. However, due to the migration of cerium ions, on the one hand, it will produce a poisoning effect on the catalyst loaded on the proton exchange membrane and affect proton conduction in the proton membrane. On the other hand, the large loss of cerium caused by migration hinders its long-term application. Summary of the Invention

[0007] In order to overcome the above problems, the present invention provides a cerium-doped carbon quantum dot, a preparation method thereof, and an application thereof.

[0008] To achieve the above technical objectives, the present invention adopts the following technical solutions:

[0009] In the first aspect of the present invention, there is provided a cerium-doped carbon quantum dot composition, comprising the following components:

[0010] Citric acid, urea, and a soluble cerium salt;

[0011] The molar ratio of the citric acid, urea and cerium salt is (40 - 50):(115 - 130):(2 - 4);

[0012] In the second aspect of the present invention, there is provided a cerium-doped carbon quantum dot, which is synthesized by a hydrothermal method from the cerium-doped carbon quantum dot composition described in the first aspect.

[0013] In the third aspect of the present invention, there is provided a preparation method of the cerium-doped carbon quantum dot described in the second aspect, comprising the following steps:

[0014] (1) Disperse citric acid, urea and a soluble cerium salt in water, mix evenly and then carry out a hydrothermal reaction, and naturally cool to room temperature after the reaction ends;

[0015] (2) Centrifuge the product obtained in step (1), take the supernatant, and obtain the cerium-doped carbon quantum dot after dialysis and drying.

[0016] In the fourth aspect of the present invention, there is provided an application of the cerium-doped carbon quantum dot described in the second aspect in the preparation of a proton exchange membrane or a battery.

[0017] In the fifth aspect of the present invention, there is provided a radical scavenger, which comprises the cerium-doped carbon quantum dot described in the second aspect.

[0018] In the sixth aspect of the present invention, there is provided a proton exchange membrane, which comprises the cerium-doped carbon quantum dot described in the second aspect or the radical scavenger described in the fifth aspect.

[0019] In the seventh aspect of the present invention, there is provided a proton exchange membrane fuel cell, which comprises the cerium-doped carbon quantum dot described in the second aspect or the radical scavenger described in the fifth aspect.

[0020] The beneficial effects of the present invention are as follows:

[0021] (1) The present invention relates to the technical field of fuel cells, and particularly relates to a cerium-doped carbon quantum dot and its preparation method and application. In the present invention, a cerium-doped carbon quantum dot is synthesized by a hydrothermal method. The cerium-doped carbon quantum dot can be used as a radical scavenger, and can solve the technical problem that the proton exchange membrane fuel cell is attacked by radicals during operation and its chemical stability decreases. Specifically, the cerium-doped carbon quantum dot can firmly fix cerium, avoiding the migration of individual cerium ions; at the same time, cerium and the carbon quantum dot can synergistically play the effect of radical scavenging.

[0022] (2) The preparation method of the cerium-doped carbon quantum dot provided by the present invention is simple and low-cost, which is beneficial to industrial production. Description of the Drawings

[0023] The accompanying drawings of the specification, which form a part of the present invention, are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0024] Figure 1 It is the transmission electron microscope picture of the cerium-doped carbon quantum dots prepared in Example 1;

[0025] Figure 2 It is the test result of the durability performance of the membrane electrode. Detailed Description of the Invention

[0026] It should be noted that the following detailed descriptions are all exemplary and are intended to provide further explanations of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0027] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0028] The first typical embodiment of the present invention provides a cerium-doped carbon quantum dot composition, which includes the following components:

[0029] Citric acid, urea, and soluble cerium salt;

[0030] The molar ratio of the citric acid, urea, and cerium salt is (40 - 50):(115 - 130):(2 - 4).

[0031] In one or more embodiments, the molar ratio of the citric acid, urea, and cerium salt is 44:120:2.4.

[0032] In one or more embodiments, the cerium salt is selected from one or more of cerium chloride, cerium nitrate, cerium acetate, ammonium cerium nitrate, and preferably cerium nitrate.

[0033] The second typical embodiment of the present invention provides a cerium-doped carbon quantum dot, which is synthesized by a hydrothermal method from the cerium-doped carbon quantum dot composition described in the first aspect.

[0034] The third typical embodiment of the present invention provides a preparation method of the cerium-doped carbon quantum dot described in the second aspect, which includes the following steps:

[0035] (1)Disperse citric acid, urea, and soluble cerium salt in water, mix them evenly, and then carry out a hydrothermal reaction. After the reaction is completed, naturally cool it to room temperature;

[0036] (2)Centrifuge the product obtained in step (1), take the supernatant, and obtain cerium-doped carbon quantum dots after dialysis and drying.

[0037] In one or more embodiments, the concentration of citric acid in the aqueous solution is 0.5 - 0.6 mol / L, preferably 0.54 mol / L.

[0038] In one or more embodiments, the temperature of the hydrothermal reaction is 130 - 180 °C, preferably 160 °C; the time of the hydrothermal reaction is 3.5 - 5 h, preferably 4 h.

[0039] In one or more embodiments, in step (2), the molecular weight of the dialysis bag used for dialysis is 1000 - 3500 Da, and the dialysis time is 48 - 72 h.

[0040] The fourth typical embodiment of the present invention provides the application of the cerium-doped carbon quantum dots described in the second aspect in the preparation of a proton exchange membrane or a battery.

[0041] The fifth typical embodiment of the present invention provides a radical scavenger, which includes the cerium-doped carbon quantum dots described in the second aspect.

[0042] The sixth typical embodiment of the present invention provides a proton exchange membrane, which includes the cerium-doped carbon quantum dots described in the second aspect or the radical scavenger described in the fifth aspect.

[0043] The seventh typical embodiment of the present invention provides a proton exchange membrane fuel cell, which includes the cerium-doped carbon quantum dots described in the second aspect or the radical scavenger described in the fifth aspect.

[0044] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in combination with specific embodiments.

[0045] Example 1

[0046] Disperse 43.7 mmol of citric acid, 120 mmol of urea, and 9.6 mmol of Ce(NO3)3·6H2O in 80 mL of ultrapure water, and ultrasonically mix (200 w) for 10 min to make the mixture uniform. Transfer the mixture to a high-pressure reaction kettle with a polytetrafluoroethylene inner liner, react at 160 °C for 4 h. After the reactor cools to room temperature, centrifuge (8000 r / min, 10 min), remove the solid, collect the supernatant. Dialyze the collected supernatant with a 3000 Da dialysis bag for 72 h, and finally freeze-dry the obtained liquid to obtain cerium-doped carbon quantum dots.

[0047] The transmission electron microscope image of the cerium-doped carbon quantum dots obtained in this example is as Figure 1 shown. It can be seen from Figure 1 that the particle size of the cerium-doped carbon quantum dots is about 5 nm, and there is an obvious carbon lattice structure.

[0048] Example 2

[0049] Disperse 40 mmol of citric acid, 115 mmol of urea, and 2 mmol of Ce(NO3)3·6H2O in 80 mL of ultrapure water, and ultrasonically mix (200 w) for 10 min to make the mixture uniform. Transfer the mixture to a high-pressure reaction kettle with a polytetrafluoroethylene inner liner, react at 150 °C for 5 h. After the reactor cools to room temperature, centrifuge (8000 r / min, 10 min), remove the solid, collect the supernatant. Dialyze the collected supernatant with a 3000 Da dialysis bag for 72 h, and finally freeze-dry the obtained liquid to obtain cerium-doped carbon quantum dots.

[0050] Example 3

[0051] Disperse 50 mmol of citric acid, 125 mmol of urea, and 3 mmol of Ce(NO3)3·6H2O in 80 mL of ultrapure water, and ultrasonically mix (200 w) for 10 min to make the mixture uniform. Transfer the mixture to a high-pressure reaction kettle with a polytetrafluoroethylene inner liner, react at 160 °C for 4 h. After the reactor cools to room temperature, centrifuge (8000 r / min, 10 min), remove the solid, collect the supernatant. Dialyze the collected supernatant with a 3000 Da dialysis bag for 72 h, and finally freeze-dry the obtained liquid to obtain cerium-doped carbon quantum dots.

[0052] Example 4

[0053] Disperse 43.7 mmol of citric acid, 120 mmol of urea, and 2.4 mmol of cerium chloride heptahydrate in 80 mL of ultrapure water, and ultrasonicate (200 w) for 10 min to mix evenly. Transfer the mixture to a high-pressure reaction kettle with a polytetrafluoroethylene liner, react at 160 °C for 4 h. After the reactor is cooled to room temperature, centrifuge (8000 r / min, 10 min) to remove solids, collect the supernatant. Dialyze the collected supernatant with a 3000 Da dialysis bag for 72 h, and finally freeze-dry the obtained liquid to obtain cerium-doped carbon quantum dots.

[0054] Example 5

[0055] Specific preparation process of the proton exchange membrane:

[0056] Cut out proton exchange membranes coated with the cerium-doped carbon quantum dots prepared in Example 1, proton exchange membranes coated with CeO2, and proton exchange membranes without adding radical scavengers into 5×5 cm sizes respectively, and immerse them in the same Fenton's reagent (specific concentrations of each substance), soak at 95 °C for 24 h. Take out the proton exchange membrane and detect the F - concentration in the Fenton's reagent after soaking. The results are shown in Table 1. It can be seen from Table 1 that the cerium-doped carbon quantum dots have good radical scavenging ability and can reduce the damage of radicals to the proton exchange membrane.

[0057] Table 1 Precipitation amount of F - in the proton exchange membrane

[0058]

[0059] Example 6

[0060] Spray the cerium-doped carbon quantum dots or cerium dioxide prepared in Example 1 on the cathode-side carbon paper and test the single-cell durability for 20 h. The specific operation is as follows: Take 5 mg of the cerium-doped carbon quantum dots or cerium dioxide prepared in Example 1, 50 mL of isopropanol, and 0.5 mL of membrane solution (5% mass fraction of Nafion solution), mix them evenly, and spray them on the microporous layer of the cathode-side carbon paper twice at a rate of 2 mL / min. The durability conditions are open-circuit voltage, temperature 90 °C, relative humidity 50%. Run a polarization curve before and after durability, and the polarization temperature is 70 °C. By comparing the two polarization curves before and after durability, the attenuation situation can be obtained. And compare with the membrane electrode without spraying radical scavengers and the membrane electrode sprayed with cerium oxide. The results Figure 2 are shown in Table 2. It can be seen from Figure 2 it that the introduction of cerium-doped carbon quantum dots can effectively improve the durability of the membrane electrode, and cerium dioxide fails to effectively play its radical scavenging effect in the membrane electrode.

[0061] Table 2 Membrane electrode durability data

[0062]

[0063]

[0064] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A cerium-doped carbon quantum dot composition, characterized in that: Includes the following components: Citric acid, urea and soluble cerium salts; The molar ratio of the citric acid, urea and cerium salt is (40-50):(115-130):(2-4).

2. The cerium-doped carbon quantum dot composition according to claim 1, characterized in that The cerium salt is selected from one or more of cerium chloride, cerium nitrate, cerium acetate, and ammonium cerium nitrate, preferably cerium nitrate.

3. A cerium-doped carbon quantum dot, characterized in that: The cerium-doped carbon quantum dot composition according to claim 1 or 2 is synthesized by a hydrothermal method.

4. The method for preparing cerium-doped carbon quantum dots according to claim 3, characterized in that: The steps include: (1) dispersing citric acid, urea and a soluble cerium salt in water, mixing them evenly and then performing a hydrothermal reaction, and naturally cooling the mixture to room temperature after the reaction is completed; (2) The product obtained in step (1) is centrifuged, and the supernatant is taken, dialyzed, and dried to obtain cerium-doped carbon quantum dots.

5. The preparation method according to claim 4, characterized in that: The concentration of citric acid in the aqueous solution is 0.5-0.6 mol / L, preferably 0.54 mol / L; Alternatively, the temperature of the hydrothermal reaction is 150-170° C., preferably 160° C.; the time of the hydrothermal reaction is 3.5-5 h, preferably 4 h.

6. The preparation method according to claim 4, characterized in that: The molecular weight of the dialysis bag used for dialysis in step (2) is 1000-3500Da, and the dialysis time is 48-72h.

7. Use of the cerium-doped carbon quantum dots according to claim 3 in the preparation of proton exchange membranes or batteries.

8. A free radical scavenger, characterized in that Includes the cerium-doped carbon quantum dots as described in claim 3.

9. A proton exchange membrane, characterized in that: It includes the cerium-doped carbon quantum dots as described in claim 3 or the free radical scavenger as described in claim 8.

10. A proton exchange membrane fuel cell, characterized in that: It includes the cerium-doped carbon quantum dots as described in claim 3 or the free radical scavenger as described in claim 8.

Images