Noble metal or oxidizer-Co3O4 heterojunction nanoflower thereof and preparation method and application of noble metal or oxidizer-Co3O4 heterojunction nanoflower

Abstract

The invention discloses a noble metal or an oxide-Co3O4 heterojunction nanoflower thereof as well as a preparation method and application thereof, and belongs to the field of electrocatalysis. The preparation method of the heterojunction nanoflower comprises the following steps: (1) dissolving cobalt salt, precious metal salt and cobalt salt ligand tetracyanoethylene in a solvent to obtain a mixed solution; (2) carrying out solvent heat treatment on the mixed solution, washing and drying to obtain a cobalt ion / noble metal ion-containing nano flower-shaped complex; and (3) carrying out pyrolysis oxidation treatment on the cobalt ion / noble metal ion-containing nano flower-shaped complex. The heterojunction nanoflower is used as an electrocatalyst, and by virtue of a three-dimensional porous flower-shaped structure, a large specific surface area and abundant heterojunction interface active sites, the activity and stability of oxygen evolution reaction (OER) are remarkably improved, so that the efficiency of hydrogen production by electrolysis of water is improved, and a technical guarantee is provided for commercial application of the heterojunction nanoflower; and the preparation method with low cost and high efficiency has strong economic competitiveness and wide market application prospect.

Description

Technical Field

[0001] The present invention relates to the field of electrocatalysis, and in particular to a noble metal or its oxide-Co3O4 heterojunction nanoflower and a preparation method and application thereof. Background Art

[0002] Electrocatalytic water splitting to produce hydrogen and other energy conversion technologies are gaining increasing attention. Among them, the oxygen evolution reaction (OER), as a key reaction in the process of water electrolysis to produce hydrogen, affects the overall energy conversion efficiency. Therefore, the development of highly active and stable OER catalysts has become a hot topic in current research. At present, traditional OER catalysts mainly include precious metal oxides such as RuO2 and IrO2, which exhibit excellent catalytic performance. However, the high cost and limited resources of precious metal materials limit their popularity in large-scale applications. Therefore, researchers are constantly exploring new low-cost and efficient catalysts.

[0003] Cobalt-based materials (such as Co3O4) have become important candidate materials for replacing precious metal catalysts due to their good electrocatalytic performance, abundant resources and low cost. In order to further improve the catalytic performance, researchers have also proposed to improve the performance of catalysts by constructing heterojunction catalysts. Among them, RuO2-Co3O4 heterojunction catalysts have become an ideal choice for improving OER performance due to their good electronic interactions, synergistic effects and porous structures. In addition, the preparation of nanomaterials with good morphology control is also an effective way to improve catalyst performance. Porous nanoflower structures can provide a larger specific surface area and more active sites, further improving the catalytic efficiency. However, the current preparation methods of most RuO2-Co3O4 heterojunction catalysts are relatively complicated, and often involve high-temperature treatment and cumbersome synthesis steps.

[0004] For example, the patent with publication number CN117926323A discloses a heterojunction catalyst for electrocatalytic oxygen evolution reaction under high current density, the catalyst includes a conductive substrate and a RuO2-Co3O4 heterojunction, the RuO2-Co3O4 heterojunction is loaded on a conductive substrate in the form of a nano flower array, and nickel foam or carbon cloth is used as a supporting material in the patent, and Co3O4 is synthesized by a hydrothermal method, and then reacted with RuCl3, and finally a composite is formed by an ion exchange method. Although the method can prepare a composite material, the substrate material (nickel foam or carbon cloth) may limit the specific surface area and porosity of the catalyst. Although nickel foam and carbon cloth provide support, their pore structure and surface properties may not be as conducive to the increase of catalytic active sites as porous nano flower structures. In addition, in the process of forming a composite by an ion exchange method, the structure of the composite material may be uniform enough, affecting catalytic performance. And the patent adopts steps such as hydrothermal method, ion exchange method and annealing, the process is more complicated, the drugs used are more, and the ion exchange method may cause uneven metal distribution, affecting the performance of the catalyst. In addition, the annealing process may cause the catalyst particles to agglomerate, reducing the catalytic activity. Moreover, the pyrolysis temperature in the patent is an ultra-high temperature of 1100-1300°C, which consumes a lot of energy.

[0005] For example, the patent with publication number CN114592210A discloses a preparation method and application of Co3O4-RuO2 composite materials. The patent uses ZIF-67 as a precursor material to react with RuCl3, performs solvent thermal synthesis, and finally performs calcination. Although ZIF-67 has good porosity and specific surface area as a metal organic framework (MOF) precursor material, its structure may lose a certain porosity and order after calcination, resulting in a decrease in the specific surface area and porosity of the catalyst. In addition, as a metal organic framework material, ZIF-67 may have its framework structure destroyed during high-temperature calcination, resulting in reduced porosity or partial loss of metal ions, thereby affecting the specific surface area and structural stability of the catalyst. By mixing the RuCl3 solution with the ZIF-67 suspension, the Ru 3+ Ions and Co in ZIF-67 2+ Ions undergo ion exchange reactions. Co 2+ With Ru 3+ During ion exchange, the reaction may be incomplete or uneven, resulting in uneven distribution of Ru elements in the composite material. This will cause local differences in the catalytic performance of the resulting composite material, affecting the overall catalytic activity.

[0006] Therefore, developing a simple, controllable and efficient preparation method is of great significance for improving OER catalytic performance and reducing production costs. Summary of the invention

[0007] Purpose of the invention: The first purpose of the present invention is to provide a precious metal or its oxide-Co3O4 heterojunction nanoflower with excellent catalytic activity and stability. The second purpose of the present invention is to provide a method for preparing the above-mentioned precious metal or its oxide-Co3O4 heterojunction nanoflower. The third purpose of the present invention is to provide the application of the above-mentioned precious metal or its oxide-Co3O4 heterojunction nanoflower.

[0008] Technical solution: The method for preparing the noble metal or its oxide-Co3O4 heterojunction nanoflowers of the present invention comprises the following steps:

[0009] (1) dissolving a cobalt salt, a noble metal salt and a cobalt salt ligand tetracyanoethylene in a solvent to obtain a mixed solution;

[0010] (2) subjecting the mixed solution to solvent thermal treatment, washing and drying to obtain a nano-flower-like complex containing cobalt ions / noble metal ions;

[0011] (3) The cobalt ion / noble metal ion nanoflower-like complex is subjected to a pyrolysis and oxidation treatment to obtain a noble metal or its oxide-Co3O4 heterojunction nanoflower.

[0012] Furthermore, in step (1), the cobalt salt is cobalt acetylacetonate, and the solvent is N,N-dimethylformamide; the noble metal salt is ruthenium acetylacetonate or platinum acetylacetonate; the molar ratio of the cobalt salt to the noble metal salt is 5-20:1, preferably 8:1. When the molar ratio of the cobalt salt to the noble metal salt is less than 5:1, a uniform three-dimensional nanoflower structure cannot be formed. When the molar ratio is greater than 20:1, there is no effect on the nanoflower structure. However, if the noble metal content is too low, a heterojunction phase cannot be formed, and the application performance will also be affected. The molar ratio of the cobalt salt to the cobalt salt ligand tetracyanoethylene is 1:1-10, preferably 1:1-4. By reasonably regulating the ratio of the cobalt salt to the ligand, a high yield of the catalyst is ensured, and a three-dimensional porous flower structure is formed.

[0013] Furthermore, in step (2), the solvent thermal treatment is carried out under the conditions of: heating at 120-200° C. for 2-12 h.

[0014] Furthermore, in step (3), the conditions for the pyrolysis oxidation are: the oxidizing atmosphere is air, the temperature is increased to 300-500°C at a heating rate of 1-5°C / min for pyrolysis treatment, and maintained for 1-5h.

[0015] The present invention provides a noble metal or its oxide-Co3O4 heterojunction nanoflower prepared by the preparation method.

[0016] Furthermore, the microstructure of the noble metal or its oxide-Co3O4 heterojunction nanoflower is: a three-dimensional nanoflower structure composed of numerous nanosheets, and numerous holes are distributed on the nanosheets. This structure helps to increase the specific surface area and expose more active sites, thereby effectively enhancing its electrocatalytic performance.

[0017] The present invention provides the use of the above-mentioned noble metal or its oxide-Co3O4 heterojunction nanoflower as a catalyst in the field of electrocatalysis.

[0018] Principle of the invention: The present invention uses cobalt salt and noble metal salt as metal precursors, tetracyanoethylene as ligand and morphology directing agent, N,N-dimethylformamide as solvent, and uses solvothermal method to prepare Co-containing 2+ / Ru 3+ The nanoflower-like complex is then subjected to pyrolysis and oxidation treatment to obtain a porous noble metal or its oxide-Co3O4 heterojunction nanoflower, which has a rich heterojunction interface and a good three-dimensional nanoflower-like structure, and contains many holes on the surface. The present invention significantly improves the activity of the catalyst in the electrocatalytic oxygen evolution reaction by finely regulating the heterojunction interface and structural design of the noble metal or its oxide and Co3O4. The unique three-dimensional porous flower-like structure not only increases the reaction interface, but also promotes the effective transmission of electrons, thereby improving the overall OER performance of the catalyst.

[0019] Compared with the prior art, the present invention only uses tetracyanoethylene as a morphology regulator and utilizes the heat of dissolution and pyrolysis oxidation method to synthesize heterojunction nanoflowers. The advantage is that it does not rely on the substrate material, but directly prepares a catalyst with a porous three-dimensional nanoflower structure, which has a larger specific surface area and more reaction active sites.

[0020] In the present invention, the effect of Co ions and tetracyanoethylene determines the morphology of the catalyst, and the nanoflower precursor composed of nanosheets is first formed by solvent thermal reaction, and the formation of the nanoflower structure mainly comes from the coordination of Co ions and tetracyanoethylene. If the noble metal salt is removed in the preparation step, the nanoflower complex can still be obtained after solvent thermal reaction, and the porous Co3O4 nanoflower is obtained after pyrolysis, while the cobalt salt is removed and only the noble metal salt is retained. After solvent thermal reaction, no obvious complex can be collected or only small noble metal nanoparticles can be obtained. It can be seen that the innovation of the present invention is to find that the coordination of Co ions and tetracyanoethylene is conducive to the formation of nanoflowers composed of sheets, and one-step air pyrolysis is used to generate a noble metal or its oxide-Co3O4 heterojunction nanoflower with a porous structure and a three-dimensional nanosheet structure.

[0021] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0022] 1. Social Effects:

[0023] 1. Improve energy efficiency: The excellent performance of the noble metal or its oxide-Co3O4 heterojunction nanoflowers prepared by the present invention as catalysts in alkaline oxygen evolution reaction (OER) provides a more efficient catalytic material for water electrolysis hydrogen production technology, which can significantly improve the yield of hydrogen. This technology can provide efficient, long-term stable and reliable electrocatalysts for future renewable energy applications (such as hydrogen economy), thereby promoting the development of green energy and reducing dependence on traditional fossil fuels.

[0024] 2. Promote the development of the clean energy industry: The application of this catalyst can effectively reduce the cost of hydrogen production by water electrolysis, promote the rapid development of the clean energy industry, and provide technical support for achieving a low-carbon society and mitigating climate change.

[0025] 2. Economic Effects:

[0026] 1. Low-cost and efficient preparation method: The template-free solvothermal method and pyrolysis oxidation treatment method used in the present invention have lower production costs and simplified operation steps compared to the traditional template method or solution chemical method. This makes the production of the catalyst more economical and can be widely used in fields such as large-scale hydrogen production. The use of a template-free synthesis method avoids the waste of template materials and reduces the consumption and cost of raw materials in the production process. In addition, it also avoids the large-scale use of precious metal materials and is suitable for large-scale production.

[0027] 2. Promote industrial application: Due to the high performance and low cost of the catalyst of the present invention, it is widely used in the fields of water electrolysis, batteries, supercapacitors, etc., and has significant commercial prospects. According to research, the industrialization of hydrogen energy technology is an important direction in the future energy field, and the high-efficiency catalyst provided by the present invention will become a key technology to reduce costs and promote the industrialization process.

[0028] 3. Technical Effects:

[0029] 1. Improve electrocatalytic performance: Higher electrocatalytic activity: The noble metal or its oxide-Co3O4 heterojunction nanoflowers of the present invention show excellent catalytic performance as catalysts in the electrocatalytic oxygen evolution reaction (OER). Experimental results show that the catalyst of the present invention has a lower overpotential and a higher current density. For example, when the catalyst of the present invention is used for OER testing, its overpotential is significantly lower than that of commercial catalysts such as RuO2, indicating that it has a higher catalytic efficiency. Experimental data show that the OER current density of the RuO2-Co3O4 heterojunction catalyst is 10mA·cm -2 The overpotential is only 275 mV (vs. RHE), which is much lower than the value of the single material (341 mV).

[0030] 2. Excellent stability: Long-term stability test: The stability of the catalyst is also a key indicator for evaluating its application potential. In the experiment, the catalyst of the present invention was able to maintain a stable current density after a long OER reaction, and there was no significant attenuation of catalytic performance. For example, after 100,000 seconds of continuous reaction, the current density decay rate of the catalyst of the present invention was less than 19%, which is much lower than the decay rate of commercial RuO2 catalyst (38%). This stability performance is due to its good porous structure and heterojunction interface, which effectively avoids catalyst corrosion and material shedding.

[0031] 3. High specific surface area and active site density: The catalyst of the present invention presents a three-dimensional porous nanoflower structure, which greatly increases the specific surface area, which is crucial for improving electrocatalytic activity. Experimental results show that the surface of the prepared RuO2-Co3O4 heterojunction nanoflower has rich heterogeneous interfaces and porous structures. This advantage enables the catalyst to provide more active sites, thereby improving the catalytic efficiency.

[0032] 4. Enhanced heterojunction interface effect: The heterojunction interface of the catalyst of the present invention can promote the rapid transmission of electrons, reduce the resistance generated during the reaction, and thus increase the catalytic reaction rate. Studies have shown that the electron transmission capacity of the RuO2-Co3O4 heterojunction is stronger than that of a single material, and can effectively carry out oxygen evolution reaction at a lower voltage, further enhancing the catalytic performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 TEM image of the RuO2-Co3O4 heterojunction nanoflower prepared in Example 1 before pyrolysis;

[0034] Figure 2 The XRD pattern of the RuO2-Co3O4 heterojunction nanoflower prepared in Example 1;

[0035] Figure 3 This is the SEM image of the RuO2-Co3O4 heterojunction nanoflower prepared in Example 1;

[0036] Figure 4 TEM image of the RuO2-Co3O4 heterojunction nanoflower prepared in Example 1;

[0037] Figure 5 HRTEM image of RuO2-Co3O4 heterojunction nanoflowers prepared in Example 1 and lattice fringe images of RuO2 and Co3O4;

[0038] Figure 6 TEM image (a) of the RuO2-Co3O4 heterojunction nanoflower prepared in Example 2 before pyrolysis and TEM image (b) after pyrolysis;

[0039] Figure 7 TEM image (a) of the RuO2-Co3O4 heterojunction nanoflower prepared in Example 3 before pyrolysis and TEM image (b) after pyrolysis;

[0040] Figure 8 TEM image (a) before pyrolysis, TEM image (b) and XRD image (c) after pyrolysis of Co3O4 nanoflowers prepared in Comparative Example 1;

[0041] Fig. 9 TEM image (a) before pyrolysis, TEM image (b) and XRD image (c) after pyrolysis of the Pt-Co3O4 heterojunction nanoflower prepared in Example 4;

[0042] Fig.10 TEM image of Pt nanoparticles prepared in Comparative Example 2;

[0043] Fig.11 A comparison diagram of the oxygen evolution (OER) performance polarization curves of the RuO2-Co3O4 heterojunction nanoflowers prepared in Example 1, the porous Co3O4 heterojunction nanoflowers prepared in Comparative Example 1, and the commercial RuO2 catalyst in 1M KOH solution;

[0044] Fig.12 A comparison diagram of the oxygen evolution (OER) performance polarization curves of RuO2-Co3O4 heterojunction nanoflowers prepared in Example 1, Example 2, and Example 3, respectively, in 1M KOH solution;

[0045] Fig.13 This is a comparison chart of the chronoamperometric curves of the RuO2-Co3O4 heterojunction nanoflowers prepared in Example 1 and commercial RuO2 in 1M KOH solution. DETAILED DESCRIPTION

[0046] The present invention is further described below in conjunction with specific embodiments and drawings.

[0047] Embodiment 1: The preparation method of the RuO2-Co3O4 heterojunction nanoflower provided in this embodiment comprises the following steps:

[0048] (1) Containing Co 2+ / Ru 3+ Preparation of nanoflower-like complex: 50 mg of cobalt acetylacetonate, 10 mg of ruthenium acetylacetonate and 50 mg of tetracyanoethylene (the molar ratio of cobalt acetylacetonate / ruthenium acetylacetonate / tetracyanoethylene is 8:1:16) are weighed and added to a reactor containing 30 mL of N,N-dimethylformamide; mechanical stirring and ultrasound are performed at room temperature to completely dissolve the solid and mix it evenly; then the reactor containing the dissolved solution is placed in an oven for reaction at 160°C for 6 hours, and after cooling to room temperature, the obtained product is washed several times with ethanol and dried to obtain a nanoflower-like complex containing Co.2+ / Ru 3+ Nanoflower-like complexes;

[0049] (2) Preparation of RuO2-Co3O4 heterojunction nanoflowers: The Co-containing 2+ / Ru 3+ The nanoflower-like complex was pyrolyzed in air at a heating rate of 5°C / min to 450°C, maintained at 450°C for 3h, and then cooled to room temperature to obtain RuO2-Co3O4 heterojunction nanoflowers.

[0050] Embodiment 2: The preparation method of the RuO2-Co3O4 heterojunction nanoflower provided in this embodiment comprises the following steps:

[0051] (1) Containing Co 2+ / Ru 3+ Preparation of nanoflower-like complex: 50 mg of cobalt acetylacetonate, 10 mg of ruthenium acetylacetonate and 25 mg of tetracyanoethylene (the molar ratio of cobalt acetylacetonate / ruthenium acetylacetonate / tetracyanoethylene is 8:1:8) are weighed and added to a reactor containing 30 mL of N,N-dimethylformamide; mechanical stirring and ultrasound are performed at room temperature to completely dissolve the solid and mix it evenly; then the reactor containing the dissolved solution is placed in an oven for reaction at 160°C for 6 hours, and after cooling to room temperature, the obtained product is washed several times with ethanol and dried to obtain a nanoflower-like complex containing Co. 2+ / Ru 3+ Nanoflower-like complexes;

[0052] (2) Preparation of RuO2-Co3O4 heterojunction nanoflowers: The Co-containing 2+ / Ru 3+ The nanoflower-like complex is pyrolyzed in air at a heating rate of 5°C / min to 450°C, maintained at 450°C for 3h, and then cooled to room temperature to obtain RuO2-Co3O4 heterojunction nanoflowers.

[0053] Embodiment 3: The preparation method of RuO2-Co3O4 heterojunction nanoflowers provided in this embodiment comprises the following steps:

[0054] (1) Containing Co 2+ / Ru 3+Preparation of nanoflower-like complex: 50 mg of cobalt acetylacetonate, 10 mg of ruthenium acetylacetonate and 100 mg of tetracyanoethylene (the molar ratio of cobalt acetylacetonate / ruthenium acetylacetonate / tetracyanoethylene is 8:1:32) are weighed and added to a reactor containing 30 mL of N,N-dimethylformamide; mechanical stirring and ultrasound are performed at room temperature to completely dissolve the solid and mix it evenly; then the reactor containing the dissolved solution is placed in an oven for reaction at 160°C for 6 hours, and after cooling to room temperature, the obtained product is washed several times with ethanol and dried to obtain a nanoflower-like complex containing Co. 2+ / Ru 3+ Nanoflower-like complexes;

[0055] (2) Preparation of RuO2-Co3O4 heterojunction nanoflowers: The Co-containing 2+ / Ru 3+ The nanoflower-like complex is pyrolyzed in air at a heating rate of 5°C / min to 450°C, maintained at 450°C for 3h, and then cooled to room temperature to obtain RuO2-Co3O4 heterojunction nanoflowers.

[0056] Embodiment 4: The preparation method of Pt-Co3O4 heterojunction nanoflowers provided in this embodiment comprises the following steps:

[0057] (1) Containing Co 2+ / Pt 2+ Preparation of nanoflower-like complex: 50 mg of cobalt acetylacetonate, 10 mg of platinum acetylacetonate and 50 mg of tetracyanoethylene (the molar ratio of cobalt acetylacetonate / platinum acetylacetonate / tetracyanoethylene is 8:1:16) are weighed and added to a reactor containing 30 mL of N,N-dimethylformamide; mechanical stirring and ultrasound are performed at room temperature to completely dissolve the solid and mix it evenly; then the reactor containing the dissolved solution is placed in an oven for reaction at 160°C for 6 hours, and after cooling to room temperature, the obtained product is washed several times with ethanol and dried to obtain a nanoflower-like complex containing Co. 2+ / Pt 2+ Nanoflower-like complexes;

[0058] (2) Preparation of Pt-Co3O4 heterojunction nanoflowers: The Co-containing 2+ / Pt 2+ The nanoflower-like complex is pyrolyzed in air at a heating rate of 5°C / min to 450°C, maintained at 450°C for 3h, and then cooled to room temperature to obtain Pt-Co3O4 heterojunction nanoflowers.

[0059] Comparative Example 1: The preparation method of Co3O4 nanoflowers provided in this comparative example comprises the following steps:

[0060] (1) Containing Co2+ Preparation of nanoflower-like complex: 50 mg of cobalt acetylacetonate and 50 mg of tetracyanoethylene (the molar ratio of cobalt acetylacetonate / tetracyanoethylene is 8:16) are weighed and added to a reactor containing 30 mL of N,N-dimethylformamide; the solid is completely dissolved and mixed evenly by mechanical stirring and ultrasound at room temperature; the reactor containing the dissolved solution is then placed in an oven for reaction at 160°C for 6 hours, and after cooling to room temperature, the obtained product is washed several times with ethanol and dried to obtain a nanoflower-like complex containing Co. 2+ Nanoflower-like complexes;

[0061] (2) Preparation of Co3O4 nanoflowers: The Co-containing 2+ The nanoflower-like complex is pyrolyzed in air at a heating rate of 5°C / min to 450°C, maintained at 450°C for 3h, and then cooled to room temperature to obtain Co3O4 nanoflowers.

[0062] Comparative Example 2: The preparation method of Pt nanoparticles provided in this comparative example comprises the following steps:

[0063] 10 mg of acetylacetonate platinum and 100 mg of tetracyanoethylene (the molar ratio of acetylacetonate platinum / tetracyanoethylene is 1:16) are weighed and added to a reactor containing 30 mL of N,N-dimethylformamide; the solid is completely dissolved and mixed evenly by mechanical stirring and ultrasound at room temperature; then the reactor containing the dissolved solution is placed in an oven for reaction at 160°C for 6 hours. After cooling to room temperature, the obtained product is washed several times with ethanol and dried to obtain Pt-containing nanoparticles.

[0064] The RuO2-Co3O4 heterojunction nanoflowers prepared in the above Example 1 were physically characterized by TEM, SEM, XRD and HRTEM.

[0065] Figure 1 The RuO2-Co3O4 heterojunction nanoflower prepared in Example 1 of the present invention before pyrolysis (i.e., containing Co 2+ / Ru 3+ TEM image of the nanoflower-like complex) shows that it has a good three-dimensional flower-like morphology before pyrolysis. Figure 2 The XRD diagram of the RuO2-Co3O4 heterojunction nanoflower prepared in Example 1 of the present invention. Figure 2 It can be seen that: near 28° and 35° are the 110 and 101 crystal planes of RuO2, and near 31° and 36° are the 220 and 311 crystal planes of Co3O4, indicating that the catalyst prepared under this condition has obvious Co3O4 and RuO2 phases.

[0066] Figure 3 , Figure 4The SEM and TEM images are respectively of the RuO2-Co3O4 heterojunction nanoflowers prepared in Example 1 of the present invention. Figure 3 and Figure 4 It can be seen that the morphology of the prepared catalyst is uniform, and it is a three-dimensional nanoflower structure composed of numerous porous nanosheets, and there are numerous holes distributed on the nanosheets. This structure helps to increase the specific surface area and expose more active sites.

[0067] Figure 5 This is a HRTEM image of the RuO2-Co3O4 heterojunction nanoflower prepared in Example 1 of the present invention. Figure 5 It can be seen that the lattice fringes of Co3O4 and RuO2 are 0.238nm and 0.301nm, respectively, corresponding to the 311 crystal plane of Co3O4 and the 110 crystal plane of RuO2, which are consistent with the results of XRD. In addition, the heterojunction interface of Co3O4 and RuO2 can be clearly seen from the HRTEM image. This unique heterojunction structure is beneficial for the material to resist strong oxidation under high current, so that the catalyst prepared by the present invention still has good performance under high current density.

[0068] Figure 6 , Figure 7 The TEM images obtained by changing the amount of tetracyanoethylene under the conditions of Example 1 for Example 2 and Example 3 show that the amount of tetracyanoethylene affects the morphology of the catalyst before and after pyrolysis. When the amount of tetracyanoethylene is reduced to 25 mg, there are relatively few two-dimensional sheets in the nanoflowers. When the amount of tetracyanoethylene is increased to 100 mg, the nanoflowers undergo cross-linking and poor dispersibility. The results show that the amount of tetracyanoethylene affects the morphology of the catalyst.

[0069] Figure 8 The product obtained by removing ruthenium acetylacetonate under the conditions of Example 1 is shown in Comparative Example 1. The results show that in the absence of ruthenium acetylacetonate, three-dimensional nanoflowers can still be well synthesized, and after air pyrolysis, the product is a porous Co3O4 nanoflower catalyst. The results show that the formation of the nanoflower structure mainly comes from the coordination of Co ions and tetracyanoethylene.

[0070] Fig. 9 This is the product obtained by replacing ruthenium acetylacetonate with platinum acetylacetonate under the conditions of Example 1 in Example 4. The results show that nanoflower-like complexes can still be obtained after solvothermal treatment, and porous Pt-Co3O4 heterojunction nanoflowers are obtained after pyrolysis.

[0071] Fig.10 For comparative example 2, under the conditions of example 1, both ruthenium acetylacetonate and cobalt acetylacetonate were removed and replaced with platinum acetylacetonate, and only Pt nanoparticles were obtained after solvothermal treatment. Fig. 9 and Fig.10The results further indicate that the formation of nanoflower-like structures depends on the coordination of Co ions with tetracyanoethylene.

[0072] In an environment of 25-30°C, the electrocatalytic oxygen evolution performance of the porous RuO2-Co3O4 heterojunction nanoflowers prepared in Example 1 above was tested using a three-electrode system. The three-electrode system is divided into a working electrode, a reference electrode and a counter electrode, wherein the working electrode is the catalyst of Example 1 of the present invention, the catalyst of Comparative Example 1 and the commercial catalyst RuO2, respectively, the saturated calomel electrode is the reference electrode, the carbon rod electrode is the counter electrode, and the electrolyte used is 1 mol·L -1 The linear scan rate was 5 mv·s -1 , the scanning voltage is 0.0V to 0.9V.

[0073] Fig.11 This is a comparison chart of the oxygen evolution (OER) performance polarization curves of the porous RuO2-Co3O4 heterojunction nanoflowers prepared in Example 1 of the present invention, the porous Co3O4 heterojunction nanoflowers prepared in Comparative Example 1, and commercial RuO2 in 1M KOH solution. Fig.11 It can be seen that the prepared porous RuO2-Co3O4 heterojunction nanoflowers have a high conductivity at 10 mA·cm -2 The overpotential at is 275 mV, which is much smaller than the 395 mV overpotential of the porous Co3O4 heterojunction nanoflower in Comparative Example 1 and the 341 mV overpotential of the commercial RuO2 catalyst, indicating that the porous RuO2-Co3O4 heterojunction nanoflower catalyst prepared in Example 1 has better OER performance.

[0074] Fig.12 The comparison diagram of the oxygen evolution (OER) performance polarization curves of RuO2-Co3O4 heterojunction nanoflowers prepared in Example 1, Example 2, and Example 3 in 1M KOH solution. The results show that the amount of tetracyanoethylene has an effect on the morphology of the catalyst. Fig.12 It can be seen that the porous RuO2-Co3O4 heterojunction nanoflowers prepared in Example 2 and Example 3 both exhibit OER performance at 10 mA cm -2 The overpotentials at are 330 and 360 mV, respectively, which are much smaller than 275 mV of the Co3O4 heterojunction nanoflower in Example 1, indicating that the morphology of the catalyst has an impact on the catalyst performance, and the uniform and complete porous nanoflower structure exhibits better OER performance.

[0075] Fig.13 This is a comparison of the chronoamperometric curves of the porous RuO2-Co3O4 heterojunction nanoflowers prepared in Example 1 and commercial RuO2 in 1M KOH solution. Fig.13It can be seen that after 100,000 s of OER chronoamperometric test, compared with the commercial RuO2 catalyst (decayed to 62%), the prepared porous RuO2-Co3O4 heterojunction nanoflower catalyst can still maintain 81% of the initial current, indicating that it has excellent OER stability.

[0076] Combining the above embodiments and comparative examples, it can be seen that: 1. Under the above standard synthesis conditions, ruthenium acetylacetonate is removed, and nano-flower-like complexes can still be obtained after solvent thermal treatment, and porous Co3O4 nano-flowers are obtained after pyrolysis. 2. Under the above standard synthesis conditions, cobalt acetylacetonate is removed, and no obvious complex can be collected after solvent thermal treatment. 3. Under the above standard synthesis conditions, ruthenium acetylacetonate is replaced with platinum acetylacetonate, and nano-flower-like complexes can still be obtained after solvent thermal treatment, and porous Pt-Co3O4 nano-flowers are obtained after pyrolysis. 4. Under the above standard synthesis conditions, both ruthenium acetylacetonate and cobalt acetylacetonate are removed and replaced with platinum acetylacetonate, and only nano-particles can be obtained after solvent thermal treatment. These comparative experiments show that the innovation of the present invention lies in the discovery that the coordination effect of Co ions and tetracyanoethylene is conducive to the formation of nano-flowers with a sheet-like composition, and one-step pyrolysis generates a porous structure of precious metal or its oxide-Co3O4 heterojunction nano-flower materials. The above results all indicate that the noble metal or its oxide-Co3O4 material prepared by the present invention has a good application prospect as an oxygen evolution (OER) electrocatalyst material.

Claims

1. A method for preparing a noble metal or its oxide-Co3O4 heterojunction nanoflower, characterized in that: The following steps are involved: (1) dissolving a cobalt salt, a noble metal salt and a cobalt salt ligand tetracyanoethylene in a solvent to obtain a mixed solution; (2) subjecting the mixed solution to solvent thermal treatment, washing and drying to obtain a nano-flower-like complex containing cobalt ions / noble metal ions; (3) The cobalt ion / noble metal ion nanoflower-like complex is subjected to a pyrolysis and oxidation treatment to obtain a noble metal or its oxide-Co3O4 heterojunction nanoflower.

2. The preparation method according to claim 1, characterized in that: In step (1), the cobalt salt is cobalt acetylacetonate and the solvent is N,N-dimethylformamide.

3. The preparation method according to claim 1, characterized in that: In step (1), the noble metal salt is ruthenium acetylacetonate or platinum acetylacetonate.

4. The preparation method according to claim 1, characterized in that: In step (1), the molar ratio of the cobalt salt to the noble metal salt is 5-20:

1.

5. The preparation method according to claim 1, characterized in that: In step (1), the molar ratio of the cobalt salt to the cobalt salt ligand tetracyanoethylene is 1:1-10.

6. The preparation method according to claim 1, characterized in that: In step (2), the solvent thermal treatment is carried out under the conditions of: heating at 120-200° C. for 2-12 hours.

7. The preparation method according to claim 1, characterized in that: In step (3), the conditions for pyrolysis oxidation are: the oxidizing atmosphere is air, the temperature is increased to 300-500°C at a heating rate of 1-5°C / min for pyrolysis treatment, and maintained for 1-5h.

8. A noble metal or its oxide-Co3O4 heterojunction nanoflower prepared by the preparation method according to any one of claims 1 to 7.

9. The noble metal or its oxide-Co3O4 heterojunction nanoflower according to claim 8, characterized in that: The microstructure of the noble metal or its oxide-Co3O4 heterojunction nanoflower is a three-dimensional nanoflower structure composed of numerous nanosheets, and numerous holes are distributed on the nanosheets.

10. Use of the noble metal or its oxide-Co3O4 heterojunction nanoflower as claimed in any one of claims 8 to 9 as a catalyst in the field of electrocatalysis.

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