Cu, Se diatomic catalysts and preparation methods and applications thereof

Abstract

The invention discloses a Cu, Se diatomic catalyst and a preparation method and application thereof, wherein the preparation method comprises: (1) dissolving 2-methylimidazole and a zinc precursor in methanol at a certain molar ratio, and self-assembling into 2-methylimidazole zinc salt ZIF-8 under stirring; (2) then dissolving the dried ZIF-8 and a copper precursor in ethanol at a certain molar ratio, stirring and adsorbing to obtain Cu-ZIF; (3) grinding the reaction product Cu-ZIF of step (2) with diphenyl selenide at a certain ratio, annealing at 950° C., and post-processing to obtain a Cu, Se diatomic catalyst. The present invention introduces Se atoms as the second reaction site, adjusts the local chemical environment of Cu atoms and synergistically completes the catalytic reaction, so that the obtained Cu, Se diatomic catalyst has efficient alkaline ORR catalytic activity, which is beneficial to improving the energy conversion efficiency of electrochemical oxygen reduction reaction.

Description

Technical Field

[0001] The invention belongs to the technical field of electrocatalysis, and specifically relates to a Cu, Se diatomic catalyst and a preparation method and application thereof. Background Art

[0002] As an ideal, clean and efficient energy conversion device, fuel cells are the most promising power generation technology from the perspective of energy conservation and ecological environment protection. Fuel cells are an electrochemical power generation device that can directly convert chemical energy into electrical energy. They are not restricted by the Carnot cycle, so they have high energy conversion efficiency and are pollution-free. They are an ideal energy conversion method. However, the electrochemical cathode oxygen reduction reaction (ORR) is kinetically slow, which limits the energy conversion efficiency of the entire reaction. Therefore, the development of efficient ORR electrocatalysts is of great significance to accelerate the reaction and improve the energy conversion efficiency.

[0003] Currently, precious metal platinum-based catalysts PtC are considered to be the most active ORR electrocatalysts; however, their large-scale application is limited due to their relative scarcity and high cost. Summary of the invention

[0004] The present invention aims to solve one of the technical problems in the related art to at least a certain extent. To this end, the purpose of the present invention is to propose a Cu, Se diatomic catalyst and its preparation method and application. The present invention introduces Se atoms as the second reaction site, adjusts the local chemical environment of Cu atoms and synergistically completes the catalytic reaction, so that the obtained Cu, Se diatomic catalyst has efficient alkaline ORR catalytic activity, which is beneficial to improve the energy conversion efficiency of electrochemical oxygen reduction reaction.

[0005] To achieve the above object, in one aspect of the present invention, the present invention provides a method for preparing a Cu, Se diatomic catalyst. The method comprises:

[0006] (1) 2-methylimidazole and zinc precursor were dissolved in methanol at a certain molar ratio and self-assembled into ZIF-8 under stirring conditions;

[0007] (2) Dissolving the dried ZIF-8 and copper precursor in ethanol at a certain molar ratio, stirring and adsorbing to obtain Cu-ZIF;

[0008] (3) Grinding the reaction product Cu-ZIF and diphenyl diselenide in a certain ratio and co-annealing at 950° C. for post-treatment to obtain a Cu, Se diatomic catalyst.

[0009] In addition, the method for preparing Cu and Se diatomic catalysts according to the present invention may also have the following additional technical features:

[0010] Preferably, the zinc precursor is selected from Zn(NO3)2.6H2O, and the copper precursor is selected from at least one of Cu(NO3)2.3H2O and Cu(NO3)2.6H2O.

[0011] Preferably, in step (1), the molar ratio of 2-methylimidazole to zinc precursor is 6-8:0.5-1.5, and the molar concentration of zinc after the zinc precursor is dissolved in methanol is 0.10-0.15 mol / L.

[0012] Preferably, in step (1), 2-methylimidazole and the zinc precursor are reacted with stirring for 18-30 hours.

[0013] Preferably, in step (2), the molar ratio of ZIF-8 to copper precursor is 15.2-16:0.5-1.5.

[0014] Preferably, in step (3), the reaction product Cu-ZIF of step (2) and diphenyl diselenide are ground in a ratio of 18-22:1 and then annealed at 940-960° C. in an argon atmosphere for 1-3 h.

[0015] Preferably, in step (3), the specific process of the post-treatment is: cooling, washing, centrifuging, drying and grinding the sample after the reaction is completed.

[0016] In another aspect of the present invention, the present invention provides a Cu, Se diatomic catalyst. The Cu, Se diatomic catalyst is prepared by the method described above.

[0017] In the third aspect of the present invention, the present invention proposes the use of the above-mentioned Cu, Se diatomic catalyst in ORR electrocatalyst. Therefore, the Cu, Se diatomic catalyst has efficient alkaline ORR catalytic activity, which is beneficial to improve the energy conversion efficiency of electrochemical oxygen reduction reaction.

[0018] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention.

[0019] Beneficial effects of the present invention:

[0020] The present invention introduces Se atoms as the second reaction site, adjusts the local chemical environment of Cu atoms and synergistically completes the catalytic reaction, so that the obtained Cu, Se diatomic catalyst has efficient alkaline ORR catalytic activity, which is beneficial to improve the energy conversion efficiency of the electrochemical oxygen reduction reaction. Compared with the common single-atom Cu-based catalyst, the Cu, Se diatomic catalyst prepared by the present invention increases the specific surface area of ​​the catalyst, thereby exposing more catalytic active sites, increasing the adsorption and activation efficiency of the reactants, and thus improving the catalytic activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0022] Figure 1 It is a comparison chart of the X-ray diffraction patterns (XRD) of the products prepared in Example 1 and Comparative Examples 1 and 2;

[0023] Figure 2 is a transmission electron microscopy (TEM) image of the Cu and Se diatomic catalyst prepared in Example 1;

[0024] Figure 3 This is the energy spectrum analysis (EDS-mapping) of the Cu and Se diatomic catalyst prepared in Example 1;

[0025] Figure 4 It is a comparison diagram of the linear scanning voltammetric curves of the products prepared in Example 1 and Comparative Examples 1 and 2 in an O2-saturated 0.1M KOH solution at a rotation speed of 1600 rpm, a scanning speed of 10 mV / s and 90% IR compensation. DETAILED DESCRIPTION

[0026] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0027] In one aspect of the present invention, the present invention provides a method for preparing a Cu, Se diatomic catalyst. According to an embodiment of the present invention, the method comprises:

[0028] S100: Mix zinc precursor, 2-methylimidazole and methanol

[0029] In this step, zinc precursor, 2-methylimidazole and methanol are mixed to obtain a clear white precursor mixture solution.

[0030] In the embodiment of the present invention, the specific type of the nickel precursor is not particularly limited, and those skilled in the art can select it at will according to actual conditions. As a preferred solution, the zinc precursor is selected from Zn(NO3)2·6H2O.

[0031] In an embodiment of the present invention, the methanol is preferably anhydrous methanol.

[0032] According to a specific embodiment of the present invention, the ratio of 2-methylimidazole to zinc precursor is (6-8):(0.5-1.5), for example 6:0.5, 6:1, 6:1.5, 7:0.5, 7:1, 7:1.5, 8:0.5, 8:1, 8:1.5, etc. The inventors found that if the content of 2-methylimidazole is too low, the carbon-nitrogen substrate will be too small, the adsorption of subsequent Cu sites will be insufficient, and the performance improvement will not be obvious enough; if the content of 2-methylimidazole is too high, the ZIF-8 particles will be too large, reducing the catalytic activity.

[0033] According to another specific embodiment of the present invention, in the mixed solution, the molar concentration of the zinc precursor is (0.10-0.15) mol / L, such as 0.10 / 0.125 / 0.15 mol / L, etc., thereby, the morphology and structure of the generated Cu, Se diatomic catalyst are relatively uniform and controllable.

[0034] According to another specific embodiment of the present invention, the copper precursor, ZIF-8 and ethanol are mixed and stirred for 24 hours to accelerate the dissolution while ensuring sufficient mixing of the copper precursor and ZIF-8 to obtain a clear blue precursor solution.

[0035] S200: Under stirring conditions, slowly drip the copper precursor into the mixed solution to react

[0036] In this step, the copper precursor is slowly dropped into the mixed solution under stirring conditions to react so as to obtain Cu-ZIF.

[0037] In the embodiment of the present invention, slowly dripping while stirring is to control ZIF-8 to fully adsorb the copper precursor, Cu-ZIF, to prevent excessive adsorption resulting in too low a copper content, and to facilitate the subsequent formation of Cu-ZIF with sufficient copper active sites.

[0038] According to another specific embodiment of the present invention, the molar ratio of ZIF-8 to the copper precursor in the ethanol solution is (15.2-16):(0.5-1.5), for example, 15.2:0.5, 15.2:1, 15.2:1.5, 16:0.5, 16:1, 16:1.5, etc. The inventors found that if the copper content is too high, copper will agglomerate to generate copper particles rather than single copper atoms; if the copper content is too low, too few copper sites will result, thereby reducing the activity of the catalyst.

[0039] In the embodiments of the present invention, the specific type of the ethanol solution is not particularly limited, and those skilled in the art can select it at will according to actual conditions. As a preferred solution, the ethanol is selected from anhydrous ethanol.

[0040] S300: grinding the reaction product of step S200 and diphenyl selenide in a certain ratio and then annealing at 900-1000°C.

[0041] In this step, the reaction product of step S200 is placed at 900-1000°C (e.g., 900°C, 950°C, 1000°C, etc.) for annealing reaction and post-treatment to obtain a Cu, Se diatomic catalyst, introduce Se atoms as the second reaction site and adjust the local chemical environment of the active site Cu atom, Se atoms cooperate with Cu atoms to improve the catalytic performance, so that the obtained Cu, Se diatomic catalyst has efficient alkaline ORR catalytic activity, which is beneficial to improve the energy conversion efficiency of the electrochemical oxygen reduction reaction. The inventors found that if the reaction temperature is lower than 900°C, it will cause the Se atoms to agglomerate and make them unevenly dispersed; if the reaction temperature is higher than 1000°C, it will cause the reaction to be too violent and a large amount of Se atoms will volatilize.

[0042] According to another specific embodiment of the present invention, the reaction product of step S200 is placed at 900-1000°C for hydrothermal aging reaction for 1-3h (for example, 1h, 2h, 3h, etc.). The inventors found that if the reaction time is less than 1h, the reaction will be incomplete and the content of the generated Cu and Se double sites will be less; if the reaction time is more than 3h, it will cause excessive reaction and Se will aggregate to form Se particles.

[0043] According to another specific embodiment of the present invention, the specific process of the post-treatment is: cooling, washing, centrifuging, drying, grinding, and grinding the sample after the reaction to a finer powder. As a specific example, after the sample after the reaction is naturally cooled to room temperature, it is washed three to five times with a hydrochloric acid solution to remove excess free ions. After washing, the product is collected by centrifugation at a speed of (3000-5000) r / min, and the obtained product is placed in a vacuum drying oven at 50-70°C and dried overnight. The dried product is fully ground in a mortar, and the obtained black powder is the Cu, Se diatomic catalyst.

[0044] According to the method for preparing a Cu, Se diatomic catalyst according to an embodiment of the present invention, the present invention introduces Se atoms as the second reaction site, adjusts the local chemical environment of the Cu atoms and synergistically completes the catalytic reaction, so that the obtained Cu, Se diatomic catalyst has efficient alkaline ORR catalytic activity, which is beneficial to improving the energy conversion efficiency of the electrochemical oxygen reduction reaction. Compared with the common single-atom Cu-based catalyst, the Cu, Se diatomic catalyst prepared by the present invention increases the specific surface area of ​​the catalyst, thereby exposing more catalytic active sites, increasing the adsorption and activation efficiency of the reactants, and thus improving the catalytic activity.

[0045] In another aspect of the present invention, the present invention proposes a Cu, Se diatomic catalyst. According to an embodiment of the present invention, the Cu, Se diatomic catalyst is prepared by the method described in the above embodiment. Therefore, the present invention introduces Se atoms as the second reaction site, adjusts the local chemical environment of the Cu atoms and synergistically completes the catalytic reaction, so that the obtained Cu, Se diatomic catalyst has efficient alkaline ORR catalytic activity, which is beneficial to improve the energy conversion efficiency of the electrochemical oxygen reduction reaction. Compared with the common single-atom Cu-based catalyst, the Cu, Se diatomic catalyst prepared by the present invention increases the specific surface area of ​​the catalyst, thereby exposing more catalytic active sites, increasing the adsorption and activation efficiency of the reactants, and thus improving the catalytic activity.

[0046] In the third aspect of the present invention, the present invention proposes the use of the Cu and Se diatomic catalysts described in the above embodiments in ORR electrocatalysts. Thus, the Cu and Se diatomic catalysts have efficient alkaline ORR catalytic activity, which is beneficial to improving the energy conversion efficiency of the electrochemical oxygen reduction reaction.

[0047] The embodiments of the present invention are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and cannot be interpreted as limiting the present invention. In addition, if not explicitly stated, all reagents used in the following embodiments are commercially available, or can be synthesized according to this article or known methods, and the reaction conditions not listed are also easily available to those skilled in the art.

[0048] Example 1

[0049] 0.07mol2-methylimidazole and 0.01molZn(NO3)2·6H2O were dissolved in 80mL methanol, stirred for 24h, and then centrifuged to dry. Then the obtained ZIF-8 was transferred to 50mL ethanol, and 0.08mmolCu(NO3)2·3H2O was slowly added. After stirring for 24h, Cu-ZIF was obtained by centrifugation. Cu-ZIF and diphenylselenide were ground in a ratio of 20:1, annealed at 950℃ and argon atmosphere for 2h, and then naturally cooled to room temperature. After the sample after the reaction was completed was naturally cooled to room temperature, it was washed three to five times with hydrochloric acid solution to remove excess free ions and metal particles. After washing, the product was collected by centrifugation at a speed of 4000r / min, and the obtained product was placed in a vacuum drying oven at 60℃ and dried overnight. The dried product was fully ground in a mortar, and the obtained black powder was the Cu, Se diatomic catalyst.

[0050] Example 2

[0051] 0.16mol2-methylimidazole and 0.01molZn(NO3)2·6H2O were dissolved in 150mL methanol, stirred for 30h, and then centrifuged to dry. Then the obtained ZIF-8 was transferred to 100mL ethanol, and 0.005mmolCu(NO3)2·3H2O was slowly added. After stirring for 24h, Cu-ZIF was obtained by centrifugation. Cu-ZIF and diphenylselenide were ground in a ratio of 18:1, annealed at 940℃ and argon atmosphere for 3h, and then naturally cooled to room temperature. After the sample after the reaction was completed was naturally cooled to room temperature, it was washed three to five times with hydrochloric acid solution to remove excess free ions and metal particles. After washing, the product was collected by centrifugation at a speed of 4000r / min, and the obtained product was placed in a vacuum drying oven at 60℃ for overnight. The dried product was fully ground in a mortar, and the obtained black powder was the Cu, Se diatomic catalyst.

[0052] Example 3

[0053] 0.04mol2-methylimidazole and 0.01molZn(NO3)2·6H2O were dissolved in 70mL methanol, stirred for 18h, and then centrifuged to dry. Then the obtained ZIF-8 was transferred to 50mL ethanol, and 0.08mmolCu(NO3)2·3H2O was slowly added. After stirring for 24h, it was centrifuged to dry to obtain Cu-ZIF. Cu-ZIF and diphenylselenide were ground in a ratio of 22:1, annealed at 960℃ and argon atmosphere for 1h, and then naturally cooled to room temperature. After the sample after the reaction was completed was naturally cooled to room temperature, it was washed three to five times with hydrochloric acid solution to remove excess free ions and metal particles. After washing, the product was collected by centrifugation at a speed of 4000r / min, and the obtained product was placed in a vacuum drying oven at 60℃ for overnight. The dried product was fully ground in a mortar, and the obtained black powder was the Cu, Se diatomic catalyst.

[0054] Comparative Example 1

[0055] 0.07mol2-methylimidazole and 0.01molZn(NO3)2·6H2O were dissolved in 80mL methanol, stirred for 24h, and then centrifuged to dry. The obtained ZIF-8 was then transferred to 50mL ethanol, and 0.08mmolCu(NO3)2·3H2O was slowly added. After stirring for 24h, Cu-ZIF was naturally cooled to room temperature after annealing at 950℃ and argon atmosphere for 2h. After the sample after the reaction was completed was naturally cooled to room temperature, it was washed three to five times with hydrochloric acid solution to remove excess free ions. After washing, the product was collected by centrifugation at a speed of (3000-5000)r / min, and the obtained product was placed in a vacuum drying oven at 50-70℃ and dried overnight. The dried product was fully ground in a mortar, and the obtained black powder was the Cu single atom catalyst.

[0056] Comparative Example 2

[0057] 0.07 mol 2-methylimidazole and 0.01 mol Zn(NO3)2·6H2O (are dissolved in 80 mL methanol, stirred for 24 h, and then centrifuged to dry. The obtained ZIF-8 is then annealed at 950 ° C in an argon atmosphere for 2 h and then naturally cooled to room temperature. After the sample is cooled to room temperature after the reaction is completed, it is washed three to five times with a hydrochloric acid solution to remove excess free ions. After washing, the product is collected by centrifugation at a speed of (3000-5000) r / min. The obtained product is placed in a vacuum drying oven at 50-70 ° C and dried overnight. The dried product is fully ground in a mortar, and the obtained black powder is a carbon-nitrogen catalyst without loaded metal single atoms.

[0058] Figure 1is the X-ray diffraction pattern (XRD) of the products prepared in Example 1, Comparative Example 1 and Comparative Example 2, by Figure 1 From the XRD results, it can be seen that the diffraction peaks of the Cu and Se diatomic catalysts prepared in Example 1 correspond to the Cu single atoms in Comparative Examples 1 and 2, and the CN catalysts are all (002) and (010) crystal planes of graphene, and no metal / metal oxide / alloy crystal phase is formed. This indicates that the original phase structure of the CN substrate is not changed after the loading of Cu and Se / Cu in Example 1, indicating that Cu and Se may exist in the form of single atoms on the CN substrate.

[0059] Figure 2 2a is a TEM image of the Cu and Se diatomic catalyst prepared in Example 1, wherein 2b is a high-resolution TEM image of the Cu and Se diatomic catalyst. Figure 2 As can be seen in a, the sample has a rough polygonal structure and the particle size is about 400nm. Figure 2 A clear graphite carbon layer can be observed in the high-resolution image (HRTEM) of the sample in b, which corresponds to the XRD results and can effectively improve the conductivity.

[0060] The energy spectrum analysis of Cu and Se diatomic atoms prepared in Example 1 ( Figure 3 ) It can be seen that the Cu and Se elements are evenly distributed on the CN substrate. Figure 3 a is the distribution diagram of the C element, 3b is the distribution diagram of the N element, 3c is the distribution diagram of the Cu element, and 3d is the distribution diagram of the Se element.

[0061] In order to evaluate the ORR activity of the catalysts in Example 1 and Comparative Examples 1-2 under alkaline conditions, an ORR electrocatalytic performance test was performed. The specific test steps and results are as follows:

[0062] (1) 5 mg of the catalysts in Example 1 and Comparative Examples 1-2 were respectively ultrasonically dispersed in 1 mL of a mixed solution of water and anhydrous ethanol in a volume ratio of 1:3. In addition, 20 μL of perfluorosulfonic acid (5 wt%) was added as a binder, and the ultrasonic treatment was continued for more than 6 h to obtain a uniformly mixed suspension. 10 μL of the suspension was accurately pipetted with a pipette and evenly dropped on the surface of a clean disk electrode with a diameter of 5 mm. The catalyst loading on the disk electrode was 0.26 mg cm -2 , and then test after natural drying.

[0063] (2) In 0.1M KOH solution, a graphite rod was used as the counter electrode and a silver / silver chloride electrode was used as the reference electrode. The three-electrode mode was used for testing and all potentials were converted to reversible hydrogen electrode potentials (RHE). High-purity O2 was continuously introduced into the electrolyte solution for 30 minutes before the test. The anode linear voltammetry scan rate was controlled at 10mVs-1, the IR compensation was 90%, and the disk electrode speed was 1600rpm. The test results are shown in Figure 4 As shown, Figure 4 The linear sweep voltammetric curves of Example 1 and Comparative Examples 1 and 2 in an O2-saturated 0.1M KOH solution at a scan rate of 10mV / s and a disk electrode rotation speed of 1600rpm under 90% IR compensation conditions are shown in FIG. As can be seen from the figure, compared with Comparative Examples 1-2, the Cu, Se diatomic catalyst prepared in Example 1 has the best alkaline ORR activity, with a half-wave potential of 0.906Vvs.RHE, which is much higher than the Cu single atom catalyst in Comparative Example 1 (0.804vs.RHE) and the CN catalyst in Comparative Example 2 (0.674vs.RHE).

[0064] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0065] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a Cu, Se diatomic catalyst, characterized in that: The following steps are involved: (1) 2-Methylimidazole and zinc precursor were dissolved in methanol at a certain molar ratio and self-assembled into ZIF-8 under stirring conditions; (2) Dissolving the dried ZIF-8 and copper precursor in ethanol at a certain molar ratio, stirring and adsorbing to obtain Cu-ZIF; (3) grinding the reaction product of step (2), Cu-ZIF, and diphenyl diselenide, in a certain ratio, and then co-annealing at a certain temperature, and post-treating the mixture to obtain a Cu, Se diatomic catalyst; In step (1), the molar ratio of 2-methylimidazole to zinc precursor is 6-8: 0.5-1.5, the molar concentration of zinc after the zinc precursor is dissolved in methanol is 0.10-0.15 mol / L; In step (2), the molar ratio of ZIF-8 to copper precursor is 15.2-16:0.5-1.5; In step (3), Cu-ZIF and diphenyl diselenide are annealed together at 940-960° C. for 1-3 h, and the mass ratio of Cu-ZIF to diphenyl diselenide is 18-22:

1.

2. The method for preparing the Cu, Se diatomic catalyst according to claim 1, characterized in that: In step (1), the zinc precursor is selected from Zn(NO3)2·6H2O, and the copper precursor is selected from at least one of Cu(NO3)2·3H2O and Cu(NO3)2·6H2O.

3. The method for preparing the Cu, Se diatomic catalyst according to claim 1, characterized in that: In step (1), 2-methylimidazole and zinc precursor are reacted with stirring for 18-30 hours.

4. The method for preparing the Cu, Se diatomic catalyst according to claim 1, characterized in that: In step (3), the specific process of the post-treatment is: cooling, washing, centrifuging, drying and grinding the sample after the reaction is completed.

5. A Cu, Se diatomic catalyst, characterized in that: The Cu, Se diatomic catalyst is prepared by the method according to any one of claims 1 to 4.

6. The use of the Cu and Se diatomic catalysts in ORR electrocatalysts as claimed in claim 5, characterized in that: The Cu and Se diatomic catalysts have efficient alkaline ORR catalytic activity, which is beneficial to improving the energy conversion efficiency of the electrochemical oxygen reduction reaction.

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