ZIF-8-derived ruthenium elementary substance-ruthenium oxide-loaded catalyst as well as preparation method and application of ZIF-8-derived ruthenium elementary substance-ruthenium oxide-loaded catalyst

Abstract

The invention relates to a noble metal catalyst derived from a metal organic framework, in particular to a ZIF-8-derived ruthenium elementary substance-ruthenium oxide-loaded catalyst as well as a preparation method and application thereof, and belongs to the technical field of advanced nonferrous metal materials, in particular to the field of noble metal nano catalytic materials. According to the invention, the zinc-based metal organic framework compound ZIF-8 is used as a precursor, the ruthenium-loaded elemental ruthenium-ruthenium oxide catalyst is controllably synthesized, and the catalytic activity and stability of the ruthenium oxide catalyst are effectively improved, so that the ruthenium oxide catalyst can be used as a high-activity and good-stability PEM electrolyzed water cathode / anode catalyst.

Description

Technical Field

[0001] The present invention relates to a metal organic framework (MOF)-derived noble metal catalyst, and specifically to a ZIF-8-derived ruthenium-loaded elemental ruthenium-oxide catalyst, and a preparation method and application thereof. The invention belongs to the technical field of advanced non-ferrous metal materials, in particular to the field of noble metal nanocatalytic materials. Background Art

[0002] The extensive use of fossil fuels has led to energy depletion and environmental pollution, and the search for sustainable and clean energy has become a consensus. Hydrogen has a high calorific value, and the only combustion product is water. Currently, the most promising way to produce hydrogen is to couple renewable energy with water electrolysis technology to ultimately achieve the production of green hydrogen. Compared with IrO2, RuO2 is a lower cost and relatively more active anode catalyst commonly used in commercial proton exchange membrane (PEM) electrolyzers, making it a promising alternative catalyst. However, the acidic conditions and high oxidation potential of PEM electrolyzers cause severe degradation of RuO2. Therefore, how to break through the bottleneck of RuO2's activity and stability is a prerequisite for the commercialization of RuO2. Summary of the Invention

[0003] In order to solve the above problems, the present invention uses a zinc-based metal organic framework compound as a precursor to controllably synthesize a catalyst loaded with ruthenium element - ruthenium oxide, which effectively improves the catalytic activity and stability of the ruthenium oxide catalyst, so that it can be used as a highly active and stable PEM water electrolysis cathode / anode catalyst.

[0004] The first object of the present invention is to provide a method for preparing a ZIF-8-derived ruthenium-supported ruthenium oxide catalyst, which comprises the following steps:

[0005] (1) dissolving a ruthenium salt in a solvent and adding ZIF-8 under stirring to obtain ruthenium-loaded ZIF-8;

[0006] (2) carbonizing the ruthenium-loaded ZIF-8 at elevated temperature in an inert atmosphere to obtain a nitrogen-doped carbon material loaded with ruthenium derived from ZIF-8;

[0007] (3) The nitrogen-doped carbon material loaded with ruthenium derived from ZIF-8 is heated and oxidized to obtain a ZIF-8-derived ruthenium loaded with ruthenium element-ruthenium oxide catalyst.

[0008] Furthermore, the ruthenium salt includes but is not limited to ruthenium chloride hydrate, ruthenium acetylacetonate, and potassium pentachlororuthenate hydrate.

[0009] Furthermore, the concentration of the ruthenium salt in the solvent is 4-8 g / L.

[0010] Furthermore, the solvent includes tetrahydrofuran, methanol, ethanol, water or a mixed solvent thereof.

[0011] Furthermore, in step (1), the mass ratio of ruthenium salt to ZIF-8 is 1:1 to 1:4.

[0012] Furthermore, in step (1), stirring is continued for 12 to 36 hours after the addition of ZIF-8, so that Ru ions are adsorbed into ZIF-8.

[0013] Furthermore, the stirring is carried out under light-proof conditions.

[0014] Furthermore, the stirring speed is 200-500 r / min.

[0015] Furthermore, the ZIF-8 can be prepared by conventional methods well known in the art. One such preparation method comprises: dissolving a zinc salt and dimethylimidazole in an organic solvent, mixing the two and then allowing them to react, collecting the precipitate by centrifugation, washing, and drying to obtain ZIF-8.

[0016] Furthermore, the zinc salt includes zinc nitrate or zinc acetate.

[0017] Furthermore, the organic solvent includes methanol.

[0018] Furthermore, the heating rate of the carbonization in step (2) is 2-5°C / min, the temperature is 600-1000°C, and the holding time is 1-6h.

[0019] Preferably, the temperature of the carbonization is 900°C.

[0020] Furthermore, the heating oxidation in step (3) has a heating rate of 2 to 5°C / min, a temperature of 300 to 400°C, and a holding time of 1 to 6 hours.

[0021] Preferably, the temperature of the heating oxidation is 350°C.

[0022] The second object of the present invention is to provide a ZIF-8-derived ruthenium-loaded ruthenium oxide catalyst obtained by the preparation method described herein.

[0023] Furthermore, the ruthenium loading amount in the ZIF-8-derived ruthenium-loaded ruthenium oxide catalyst is 0.30-0.45 wt.%, and the zinc loading amount is 0.005-0.025 wt.%.

[0024] As used herein, the ruthenium loading refers to the mass percentage of the total amount of ruthenium and ruthenium oxide supported on the catalyst; the zinc loading refers to the mass percentage of the total amount of zinc supported on the catalyst.

[0025] Furthermore, the ZIF-8-derived catalyst loaded with elemental ruthenium and ruthenium oxide has a ruthenium-ruthenium oxide heterojunction interface structure, and the molar ratio of metallic ruthenium to oxidized ruthenium components is 1.4 to 2.0.

[0026] The third object of the present invention is to provide a use of the ZIF-8-derived catalyst loaded with elemental ruthenium - ruthenium oxide as described herein in the electrolysis of water.

[0027] Furthermore, the ZIF-8-derived ruthenium-supported ruthenium oxide catalyst described herein can be used as an anode and / or cathode catalyst in water electrolysis.

[0028] Furthermore, the ZIF-8-derived ruthenium-supported ruthenium oxide catalyst described herein can be used as a catalyst for acidic oxygen evolution reaction and / or acidic hydrogen evolution reaction in water electrolysis.

[0029] Advantageous Effects of the Invention

[0030] 1. The present invention can realize the synthesis of a ZIF-8-derived catalyst of ruthenium-loaded elemental ruthenium - ruthenium oxide, and the sample is in a dark black powder state; it has the characteristics of simple preparation and high repeatability.

[0031] 2. The ZIF-8-derived ruthenium-loaded ruthenium oxide catalyst prepared by the present invention has a heterojunction structure, which improves the intrinsic activity and stability of the catalyst. The single-atom zinc doping improves the electronic structure of the ruthenium component, realizing the dual functions of efficient hydrogen evolution reaction and oxygen evolution reaction.

[0032] 3. The ZIF-8-derived ruthenium-supported ruthenium oxide catalyst provided by the present invention has a current density of 10 mA / cm in the acidic oxygen evolution reaction. 2 When the overpotential is 168mV, it is stable for more than 100h.

[0033] 4. The ZIF-8-derived ruthenium-supported ruthenium oxide catalyst provided by the present invention has a current density of 10 mA / cm in the acidic hydrogen evolution reaction. 2 When the overpotential is 57mV, it is stable for more than 100h. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The present invention provides a schematic flow chart of the preparation of a ZIF-8-derived catalyst containing ruthenium element and ruthenium oxide.

[0035] Figure 2 The X-ray diffraction (XRD) pattern of the ZIF-8-derived ruthenium-supported ruthenium oxide catalyst prepared in Example 1;

[0036] Figure 3A scanning electron microscope (SEM) image of the ZIF-8-derived ruthenium-supported ruthenium oxide catalyst prepared in Example 1;

[0037] Figure 4 Synchrotron radiation data of the ZIF-8-derived ruthenium-supported ruthenium oxide catalyst prepared in Example 1;

[0038] Figure 5 This is a transmission electron microscope (TEM) image of the ZIF-8-derived ruthenium-supported ruthenium oxide catalyst prepared in Example 1;

[0039] Figure 6 a is the acidic oxygen evolution reaction polarization curve of the ZIF-8-derived ruthenium-supported ruthenium oxide catalyst prepared in Example 1 measured in a three-electrode test system;

[0040] Figure 6 b is the acidic oxygen evolution reaction stability curve of the ZIF-8-derived ruthenium-supported ruthenium oxide catalyst prepared in Example 1 measured in a three-electrode test system;

[0041] Figure 7 a is the acidic hydrogen evolution reaction polarization curve of the ZIF-8-derived ruthenium-supported ruthenium oxide catalyst prepared in Example 1 measured in a three-electrode test system;

[0042] Figure 7 b is the acidic hydrogen evolution reaction stability curve of the ZIF-8-derived ruthenium-supported ruthenium oxide catalyst prepared in Example 1 measured in a three-electrode test system;

[0043] Figure 8 XRD pattern of the ZIF-8-derived ruthenium oxide-loaded catalyst prepared in Comparative Example 1;

[0044] Figure 9 This is the XRD pattern of the ZIF-8-derived ruthenium-loaded catalyst prepared in Comparative Example 2. DETAILED DESCRIPTION

[0045] The present invention is further described below with reference to specific examples, which, however, are not intended to limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the art.

[0046] Example 1: Preparation and performance characterization of ZIF-8-derived ruthenium-supported ruthenium oxide catalyst

[0047] like Figure 1 As shown, a method for preparing a ZIF-8-derived ruthenium-supported ruthenium oxide catalyst is provided, which comprises

[0048] (1) 1.75 g of Zn(CH3COO)2 and 2.63 g of 2-methylimidazole were dissolved in 200 mL of methanol to obtain solutions A and B, respectively. Solution A was quickly poured into solution B and magnetically stirred at 400-800 rpm for 20 min. The mixture was then allowed to stand at room temperature for 24 h to obtain a white precipitate. After centrifugation, the precipitate was washed six times with a large amount of methanol and finally dried in a forced air drying oven for 12 h to obtain the zinc-based metal organic framework compound ZIF-8.

[0049] (2) 0.2 g of RuCl3-xH2O was weighed and dissolved in 30 mL of tetrahydrofuran. The mixture was stirred for 10 min to completely dissolve the RuCl3 solution, and then 0.2 g of ZIF-8 was slowly added to the RuCl3 solution while stirring continuously at 300 r / min. The mixture was stirred in the dark for 24 h to allow for sufficient impregnation and adsorption. After centrifugation, the mixture was washed six times with tetrahydrofuran and finally dried in a forced air drying oven for 12 h to obtain a composite material of ruthenium and a zinc-based metal organic framework compound, namely, ruthenium-loaded ZIF-8 (also known as ZIF-8-Ru).

[0050] (3) ZIF-8-Ru was annealed in an argon atmosphere (Ar: 100 sccm) in a tube furnace with a heating rate of 2°C / min, an annealing temperature of 900°C, and a holding time of 2 h. The sample was naturally cooled to room temperature to obtain a ZIF-8-derived nitrogen-doped carbon material loaded with ruthenium.

[0051] (4) The nitrogen-doped carbon material loaded with ruthenium derived from ZIF-8 was placed in a muffle furnace for heating and oxidation at a heating rate of 2°C / min, an annealing temperature of 350°C, a holding time of 2 h, and naturally cooled to room temperature to obtain a ZIF-8-derived ruthenium-loaded ruthenium oxide catalyst.

[0052] Structural characterization of ZIF-8-derived ruthenium-supported ruthenium oxide catalyst:

[0053] Figure 2 The XRD pattern of the sample prepared in Example 1 has characteristic peaks of ruthenium and ruthenium oxide, indicating that the catalyst contains two ruthenium components at the same time; Figure 3 The SEM of the sample prepared in Example 1 shows that the sample is in the form of loose particles; Figure 4 Synchrotron radiation data for the sample prepared in Example 1 show that the ruthenium spectrum of the sample contains Ru-O and Ru-Ru bonds, while the zinc spectrum contains Zn-O but no Zn-Zn bonds, proving that the sample contains metallic and oxidized ruthenium, and that zinc exists in a single atomic form. Figure 5 From the TEM of the sample prepared in Example 1, it can be observed that the sample contains two lattices, Ru(101) and RuO2(110), with obvious grain boundaries and heterogeneous interfaces.

[0054] Characterization of the electrocatalytic performance of ZIF-8-derived ruthenium-supported ruthenium oxide catalyst:

[0055] The electrocatalytic performance of the prepared ZIF-8-derived ruthenium-loaded elemental ruthenium oxide catalyst was evaluated in a 0.5M H2SO4 electrolyte under a three-electrode system. All electrochemical experiments were performed on a Chenhua electrochemical workstation (CHI 660E). A glassy carbon electrode, KCl-saturated Hg / HgO, and a carbon rod were used as the working electrode, reference electrode, and counter electrode, respectively. Before using the glassy carbon electrode, the electrode surface was carefully polished with 50nm Al2O3 powder to obtain a mirror-like surface, and then washed multiple times with deionized water and ethanol. Preparation of the working electrode: 5mg of the catalyst was dispersed in a mixed solution of 500μL deionized water and 500μL ethanol, sonicated for 30min, and then 20μL Nafion (5wt%) was added and sonicated for 30min to obtain a uniformly dispersed catalyst slurry. 10μL of the slurry was dropped on the surface of the glassy carbon electrode and dried at room temperature to obtain the final working electrode. Figure 6 a is the polarization curve of the oxygen evolution reaction of the ZIF-8-derived ruthenium-supported ruthenium oxide catalyst, with a current density of 10 mA / cm 2 5b shows that the voltage of the catalyst did not drop significantly after 100 h of oxygen evolution reaction stability test. Figure 7 a is the polarization curve of hydrogen evolution reaction of ZIF-8-derived ruthenium-supported ruthenium oxide catalyst, with a current density of 10 mA / cm 2 When , the overpotential is 57mV. Figure 7 b shows that after the catalyst underwent 100h of hydrogen evolution reaction stability test, the voltage did not drop significantly.

[0056] Example 2

[0057] Compared with Example 1, the zinc-based metal organic framework compound in step (1) is prepared as follows, and the rest is the same as Example 1.

[0058] 4.05g Zn(NO3)2 and 2.63g 2-methylimidazole were dissolved in 200mL methanol to obtain solutions A and B, respectively. Solution A was quickly poured into solution B, magnetically stirred for 20min, and then allowed to stand at room temperature for 24h to obtain a white precipitate. After centrifugation, it was washed with a large amount of methanol 6 times and finally dried in a forced air drying oven for 12h to obtain ZIF-8. A ZIF-8-derived ruthenium-loaded ruthenium oxide catalyst was still obtained, and its oxygen evolution overpotential was 202mV@10mA / cm 2 , its hydrogen evolution overpotential is 105mV@10mA / cm 2 .

[0059] Example 3

[0060] Compared with Example 1, the zinc-based metal organic framework compound in step (1) is prepared as follows, and the rest is the same as Example 1.

[0061] Pour 1.75g Zn(CH3COO)2 and 2.63g 2-methylimidazole into the same beaker and stir magnetically for 30-60min to ensure that the two powdered reagents are fully mixed. Add 200mL of methanol to the above beaker, stir again for 20min, and then let it stand at room temperature for 24h to obtain a white precipitate. After centrifugation, wash it with a large amount of methanol 6 times and finally dry it in a forced air drying oven for 12h to obtain ZIF-8. A ZIF-8-derived ruthenium-loaded ruthenium oxide catalyst can still be obtained, and its oxygen evolution overpotential is 176mV@10mA / cm 2 , its hydrogen evolution overpotential is 132mV@10mA / cm 2 .

[0062] Example 4

[0063] Compared with Example 1, the oxidation temperature in step (4) of this embodiment is adjusted to 300°C, and the rest are the same as Example 1. A ZIF-8-derived ruthenium-supported ruthenium oxide catalyst is still obtained, and its oxygen evolution overpotential is 220mV@10mA / cm 2 , its hydrogen evolution overpotential is 180mV@10mA / cm 2 .

[0064] Example 5

[0065] Compared with Example 1, the oxidation temperature in step (4) of this embodiment is adjusted to 400°C, and the rest are the same as Example 1. A ZIF-8-derived ruthenium-supported ruthenium oxide catalyst is still obtained, and its oxygen evolution overpotential is 201mV@10mA / cm 2 , its hydrogen evolution overpotential is 193mV@10mA / cm 2 .

[0066] Comparative Example 1

[0067] Compared with Example 1, this example deletes step (3), and the rest is the same as Example 1, and a ZIF-8-derived ruthenium oxide-loaded catalyst can be obtained. Figure 8 The XRD pattern of the sample in control example 1 proves that the sample contains only ruthenium oxide, and its oxygen evolution overpotential is 330mV@10mA / cm 2 , its hydrogen evolution overpotential is 221mV@10mA / cm 2 .

[0068] Comparative Example 2

[0069] Compared with Example 1, this example deletes step (4), and the rest is the same as Example 1, and a ZIF-8-derived catalyst loaded with ruthenium can be obtained. Figure 9 The XRD pattern of the sample in control example 2 proves that the sample contains only elemental ruthenium, and its oxygen evolution overpotential is 412mV@10mA / cm 2 , its hydrogen evolution overpotential is 121mV@10mA / cm 2 .

[0070] Based on characterization and test data, it was demonstrated that metallic ruthenium and oxidized ruthenium heterojunction catalysts can be obtained through carbonization and oxidation steps. Compared with single-phase (metallic ruthenium or oxidized ruthenium) catalysts, the former has improved oxygen and hydrogen evolution activities.

[0071] It should be noted that the preferred embodiments of the present invention are given in the specification and drawings of the present invention. However, the present invention can be implemented in many different forms and is not limited to the embodiments described in this specification. These embodiments are not intended to be additional limitations on the content of the present invention. The purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive. In addition, the above-mentioned technical features can be combined with each other to form various embodiments not listed above, which are all considered to be within the scope of the description of the present invention. Furthermore, it is obvious to those skilled in the art that improvements or changes can be made based on the above description, and all such improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for preparing a ZIF-8-derived ruthenium-supported ruthenium oxide catalyst, characterized in that: The following steps are involved: (1) dissolving a ruthenium salt in a solvent and adding ZIF-8 under stirring to obtain ruthenium-loaded ZIF-8; (2) carbonizing the ruthenium-loaded ZIF-8 at elevated temperature in an inert atmosphere to obtain a nitrogen-doped carbon material loaded with ruthenium derived from ZIF-8; (3) The nitrogen-doped carbon material loaded with ruthenium derived from ZIF-8 is heated and oxidized to obtain a ZIF-8-derived ruthenium loaded ruthenium oxide catalyst.

2. The preparation method according to claim 1, characterized in that The ruthenium salt includes ruthenium chloride hydrate, ruthenium acetylacetonate, and hydrated potassium pentachlororuthenate; Preferably, the concentration of the ruthenium salt in the solvent is 4-8 g / L.

3. The preparation method according to claim 1, characterized in that The solvent includes tetrahydrofuran, methanol, ethanol, water or a mixed solvent thereof.

4. The preparation method according to claim 1, characterized in that In step (1), the mass ratio of ruthenium salt to ZIF-8 is 1:1 to 1:4; Preferably, in step (1), stirring is continued for 12 to 36 hours after adding ZIF-8; Preferably, the stirring is carried out under light-proof conditions; Preferably, the stirring speed is 200-500 r / min.

5. The preparation method according to claim 1, characterized in that The preparation method of ZIF-8 comprises: dissolving zinc salt and dimethylimidazole in an organic solvent respectively, mixing the two uniformly and then standing for reaction, collecting the precipitate by centrifugation, washing and drying to obtain ZIF-8.

6. The preparation method according to claim 5, characterized in that The zinc salt includes zinc nitrate or zinc acetate; The organic solvent includes methanol.

7. The preparation method according to claim 1, characterized in that The heating rate of the carbonization in step (2) is 2-5°C / min, the temperature is 600-1000°C, and the holding time is 1-6h. Preferably, the temperature of the carbonization is 900°C; The heating rate of the heating oxidation in step (3) is 2-5°C / min, the temperature is 300-400°C, and the holding time is 1-6h. Preferably, the temperature of the heating oxidation is 350°C.

8. The preparation method according to claim 1, characterized in that The ZIF-8-derived catalyst containing ruthenium-containing elemental substance (ruthenium oxide) has a ruthenium loading of 0.30-0.45 wt.%, and a zinc loading of 0.005-0.025 wt.%. Preferably, the ZIF-8-derived catalyst loaded with elemental ruthenium and ruthenium oxide has a ruthenium-ruthenium oxide heterojunction interface structure, wherein the molar ratio of metallic ruthenium to oxidized ruthenium components is 1.4 to 2.

0.

9. A ZIF-8-derived catalyst containing ruthenium element and ruthenium oxide prepared by the method according to any one of claims 1 to 8.

10. Use of the ZIF-8-derived ruthenium-supported ruthenium oxide catalyst as claimed in claim 9 in electrolysis of water; Furthermore, the ZIF-8-derived catalyst of loaded ruthenium element - ruthenium oxide is used as a catalyst for acidic oxygen evolution reaction and / or acidic hydrogen evolution reaction in electrolyzed water.

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