A method for preparing a composite oxygen reduction electrocatalyst

Abstract

This invention belongs to the field of oxygen reduction electrocatalyst technology, specifically disclosing a method for preparing a composite oxygen reduction electrocatalyst. This invention uses two non-noble metals, Cu and Ni, as raw materials, and adds the polymer PVP to form a MOF-type material, PVP@Ni-Cu-MOF, with a stable structure and tunable pore size. The PVP@Ni-Cu-MOF composite oxygen reduction electrocatalyst provided by this invention is low in cost, simple to prepare, and has stable performance, especially exhibiting excellent oxygen reduction performance under strongly alkaline conditions. It is expected to replace the noble metal platinum as an oxygen reduction electrocatalyst for commercial fuel cells and other applications.

Description

Technical Field

[0001] This invention relates to the field of oxygen reduction electrocatalyst technology, and in particular to a method for preparing a composite oxygen reduction electrocatalyst. Background Technology

[0002] The electroreduction of oxygen is one of the most important electrocatalytic reactions, with wide applications in fuel cells and metal-air batteries. Platinum and platinum-based catalysts are commonly used in fuel cells, but their high cost, limited resources, and significant performance degradation over long periods hinder the development of fuel cells and related fields.

[0003] The aforementioned shortcomings of platinum-based catalysts have spurred the development of new catalytic materials with high catalytic activity. In recent years, MOF (Metal-Organic Facility) materials, characterized by infinitely variable structures formed by coordination bonds between metal ions and organic ligands, have attracted widespread attention. These materials possess advantages such as tunable pore size, large specific surface area, diverse framework structures, and modifiable surfaces, and are widely used in adsorption and separation, heterogeneous catalysis, as supports and templates for metal nanoparticles, and in microreactors.

[0004] The present invention aims to provide a low-cost, simple-to-prepare MOF-based composite oxygen reduction electrocatalyst and its preparation method. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a composite oxygen reduction electrocatalyst. The method of this invention has low preparation cost, is simple to prepare, and the obtained composite oxygen reduction electrocatalyst has excellent catalytic performance.

[0006] To address the above problems, the present invention adopts the following technical solution: Firstly, the present invention provides a method for preparing a composite oxygen reduction electrocatalyst, wherein the composite oxygen reduction electrocatalyst is PVP@Ni-Cu-MOF, and the preparation method includes the following steps:

[0007] (1) Ni-MOF was prepared by heating a nickel source, pyromellitic acid, base and mixed solvent at 100℃~200℃;

[0008] (2) Mix the copper source solution with the pyromellitic acid solution to obtain a mixed reaction solution. Soak the Ni-MOF in the mixed reaction solution for 20 to 30 hours to prepare Ni-Cu-MOF, wherein the molar ratio of the copper source to the nickel source is (2 to 4): 1.

[0009] (3) The Ni-Cu-MOF is added to the PVP solution and reacted for 20 to 30 hours. The solid is then separated, washed, dried and annealed to obtain the PVP@Ni-Cu-MOF product.

[0010] In one embodiment of the present invention, the nickel source is nickel chloride hexahydrate.

[0011] In one embodiment of the present invention, the alkali is NaOH or KOH, preferably NaOH.

[0012] In one embodiment of the present invention, the mixed solvent is a mixed solution of DMF, deionized water and ethanol, preferably the volume ratio of DMF, deionized water and ethanol in the mixed solvent is 1:1:1.

[0013] In one embodiment of the present invention, the molar ratio of the nickel source, pyromellitic acid, and base is 1:2:(2-3).

[0014] In one embodiment of the present invention, step (1) is carried out in a high-pressure reactor. The pressure range of the high-pressure reactor during the reaction is 3-6 MPa, and the reaction time is 10-12 hours. After the reaction is completed, the solid is filtered out and separated. After washing and drying, Ni-MOF is obtained.

[0015] In one embodiment of the present invention, the copper source is copper nitrate trihydrate.

[0016] In one embodiment of the present invention, the molar ratio of the copper source to the nickel source is 3:1.

[0017] In one embodiment of the present invention, the concentration of the copper source in the mixed reaction solution is 0.02-0.04 mol / L, and the concentration of pyromellitic acid is 0.01-0.02 mol / L.

[0018] Preferably, the concentration of the copper source in the mixed reaction solution is 0.03 mol / L, and the concentration of pyromellitic acid is 0.015 mol / L.

[0019] As one embodiment of the present invention, the method for preparing the mixed reaction solution includes: slowly adding a pyromellitic acid methanol solution to a copper nitrate trihydrate methanol solution and stirring to obtain the mixed reaction solution.

[0020] More preferably, the concentration of the pyromellitic acid methanol solution is 0.03 mol / L; and the concentration of the copper nitrate trihydrate methanol solution is 0.06 mol / L.

[0021] In one embodiment of the present invention, the PVP solution is an ethanol solution of PVP, preferably with a PVP concentration of 0.03 to 0.06 g / ml, and more preferably with a PVP concentration of 0.05 g / ml.

[0022] In one embodiment of the present invention, the mass ratio of the Ni-Cu-MOF to the PVP contained in the PVP solution is 1:(20-150), preferably 1:(25-125), and more preferably 1:75.

[0023] In one embodiment of the present invention, the annealing temperature is 600–900°C, for example, 600°C, 700°C, 800°C, or 900°C, preferably 700°C. The annealing time is preferably 1–3 hours.

[0024] In one embodiment of the present invention, in step (3), the drying process after separating the solids is carried out at 60°C for 8 to 12 hours.

[0025] Secondly, the present invention provides a composite oxygen reduction electrocatalyst, which is prepared by the preparation method described in the present invention, and the composite oxygen reduction electrocatalyst is PVP@Ni-Cu-MOF.

[0026] Thirdly, the present invention provides the application of a composite oxygen reduction electrocatalyst, namely, the application of the PVP@Ni-Cu-MOF as an oxygen reduction electrocatalyst in a fuel cell.

[0027] This invention uses two non-precious metals, Cu and Ni, as raw materials. By adding the polymer polyvinylpyrrolidone (PVP), a MOF-type material with a stable structure and tunable pore size is formed. Tristyric acid is used, whose carboxyl (-COOH) organic ligands have strong coordination ability. After the removal of small molecule ligands, the holes in the formed MOF framework can remain stable, overcoming the instability of neutral organic ligand structures and enabling the formation of high-dimensional structures.

[0028] Specifically, this invention first prepares Ni-Cu dual non-noble metal MOF material Ni-Cu-MOF under liquid-phase conditions using a low-cost and simple process. Then, it is mixed with the polymer polyvinylpyrrolidone (PVP). The introduction of the polymer supports the MOF framework and prevents drying agglomeration. More importantly, it was found that reacting Ni-Cu-MOF with PVP in a specific ratio significantly improves the oxygen reduction performance of the resulting product, exhibiting oxygen reduction performance comparable to that of a traditional Pt / C electrode under alkaline conditions.

[0029] The PVP@Ni-Cu-MOF composite oxygen reduction electrocatalyst provided by this invention is low in cost, simple to prepare, and has stable performance. In particular, it has excellent oxygen reduction performance in a strongly alkaline environment and is expected to replace the precious metal platinum as an oxygen reduction electrocatalyst for commercial fuel cells. Attached Figure Description

[0030] Figure 1This is a cyclic voltammetry curve of the PVP@Ni-Cu-MOF product obtained in Example 1 of this invention;

[0031] Figure 2 This is the LSV curve in Experiment Example 2 of the present invention;

[0032] Figure 3 This is the LSV curve in Experiment Example 3 of the present invention;

[0033] Figure 4 This is the comparative LSV curve in 0.1M KOH solution in Experiment Example 4 of the present invention;

[0034] Figure 5 This is the comparative LSV curve in 0.1M phosphate buffer solution in Experiment Example 4 of the present invention;

[0035] Figure 6 This is the comparative LSV curve in 0.5M H2SO4 solution in Experiment Example 4 of the present invention;

[0036] Figure 7 This is a scanning electron microscope (SEM) image of the PVP@Ni-Cu-MOF product prepared in Example 1 of this invention. Detailed Implementation

[0037] The specific embodiments of the present invention will be further described in detail below with reference to examples. These embodiments are used to illustrate the present invention, but are not intended to limit the scope of the invention.

[0038] Example 1

[0039] This embodiment provides a method for preparing a composite oxygen reduction electrocatalyst, wherein the composite oxygen reduction electrocatalyst is PVP@Ni-Cu-MOF, and the preparation method includes the following steps:

[0040] (1) Add nickel chloride hexahydrate (1 mmol), pyromellitic acid (2 mmol), and 6 mL of NaOH aqueous solution (0.4 mol / L) to 60 mL of mixed solvent. The mixed solvent is a mixture of DMF, deionized water, and ethanol, with a volume ratio of DMF, deionized water, and ethanol of 1:1:1. Stir for 30 minutes, then transfer to a high-pressure reactor, seal the high-pressure reactor, and heat the reaction at 150 °C. The reaction pressure range is 3-6 MPa, and the reaction is carried out for 10 hours. After the reaction is completed, filter to separate the solid. The obtained solid is washed with ethanol and then dried to obtain Ni-MOF.

[0041] (2) Dissolve 1.5 mmol of pyromellitic acid in 50 mL of methanol, and label the solution as solution A; dissolve 3 mmol of copper nitrate trihydrate in 50 mL of methanol, and label the solution as solution B; slowly add solution A to solution B and stir for 10 minutes to obtain a mixed reaction solution. Then, place the Ni-MOF obtained in step (1) into the mixed reaction solution and soak it at room temperature for 24 hours; then filter and collect the solid. Wash the obtained solid with ethanol to obtain Ni-Cu-MOF.

[0042] (3) Dissolve 15g of PVP (polyvinylpyrrolidone) in 300ml of ethanol to prepare a PVP solution. Add 0.2g of Ni-Cu-MOF (mass ratio of Ni-Cu-MOF to PVP is 1:75) to the prepared PVP solution and stir at room temperature for 24 hours. Then separate the solid, wash the obtained solid with ethanol, dry it at 60℃ for 12 hours, and then anneal it at 700℃ to obtain the PVP@Ni-Cu-MOF product. The scanning electron microscope (SEM) image of the product is shown below. Figure 7 As shown.

[0043] Examples 2-4

[0044] Examples 2-4 differ from Example 1 only in that different annealing temperatures were used in the experiments, resulting in corresponding PVP@Ni-Cu-MOF products. The annealing temperatures used in Examples 2-4 are shown in Table 1.

[0045] Table 1

[0046] Example 2 3 4 Annealing temperature (°C) 600 800 900

[0047] Examples 5-8

[0048] Examples 5-8 differ from Example 1 only in that different amounts of Ni-Cu-MOF were added to the prepared PVP solution in step (3) for the reaction. The amounts of Ni-Cu-MOF and their mass ratios to PVP in Examples 5-8 are shown in Table 2.

[0049] Table 2

[0050] Example 5 6 7 8 Ni-Cu-MOF(g) 0.6g 0.3g 0.15g 0.12g Ni-Cu-MOF / PVP (g / g) 1:25 1:50 1:100 1:125

[0051] Comparative Example 1

[0052] This comparative example provides a PVP@Cu-MOF preparation method including the following steps:

[0053] (1) Dissolve 1.5 mmol of pyromellitic acid in 50 mL of methanol and label the solution as solution A; dissolve 3 mmol of copper nitrate trihydrate in 50 mL of methanol and label the solution as solution B; slowly add solution A to solution B, stir for 10 minutes, and let stand at room temperature for 24 hours; then filter and collect the solid, wash the obtained solid with ethanol to obtain Cu-MOF;

[0054] (2) Dissolve 15g of PVP (polyvinylpyrrolidone) in 300ml of ethanol solution to prepare PVP solution. Add 0.2g of Cu-MOF (the mass ratio of Cu-MOF to PVP is 1:75) to the prepared PVP solution and stir at room temperature for 24 hours. Then separate the solid. Wash the obtained solid with ethanol, dry it at 60℃ for 12 hours, and then anneal it at 700℃ to obtain PVP@Cu-MOF product.

[0055] Comparative Example 2

[0056] This comparative example provides a PVP@Ni-MOF, and the preparation method includes the following steps:

[0057] (1) Add nickel chloride hexahydrate (1 mmol), pyromellitic acid (2 mmol), and 6 mL of NaOH aqueous solution (0.4 mol / L) to 60 mL of mixed solvent. The mixed solvent is a mixture of DMF, deionized water, and ethanol, with a volume ratio of DMF, deionized water, and ethanol of 1:1:1. Stir for 30 minutes, then transfer to a high-pressure reactor, seal the high-pressure reactor, and heat the reaction at 150 °C. The pressure range during the reaction is 3-6 MPa. The reaction is carried out for 10 hours. After the reaction is completed, filter to separate the solid. The obtained solid is washed with ethanol and then dried to obtain Ni-MOF.

[0058] (2) Dissolve 15g of PVP (polyvinylpyrrolidone) in 300ml of ethanol solution to prepare PVP solution. Add 0.2g of Ni-MOF (mass ratio of Ni-MOF to PVP is 1:75) to the prepared PVP solution and stir at room temperature for 24 hours. Then separate the solid, wash the obtained solid with ethanol, dry at 60℃ for 12 hours, and then anneal at 700℃ to obtain PVP@Ni-MOF product.

[0059] Effect Experiment Example 1

[0060] The cyclic performance of the PVP@Ni-Cu-MOF catalyst product prepared in Example 1 was tested, and the cyclic voltammetry curves are shown below. Figure 1 As shown in the figure, the catalyst material does not exhibit a cathodic reduction peak under an Ar atmosphere, but only shows a significant cathodic reduction peak under an O2 atmosphere.

[0061] Effect Experiment Example 2

[0062] The performance of the PVP@Ni-Cu-MOF catalyst products prepared in Examples 1 and 5-8 were tested, and the LSV curves obtained are shown in the figure. Figure 2 As shown in the figure, Ni-Cu-MOF is the product obtained in step (2) of Example 1. It can be seen from the figure that the mixing ratio of PVP and Ni-Cu-MOF will significantly affect the oxygen reduction performance of the final product. The effect of Example 1 is the best, that is, when the mass ratio of Ni-Cu-MOF to PVP is 1:75, the best performance is achieved.

[0063] Effect Experiment Example 3

[0064] The performance of the PVP@Ni-Cu-MOF catalyst products prepared in Examples 1 and 2-4 were tested, and the LSV curves obtained are shown in the figure. Figure 3 As shown in the figure, the PVP@Ni-Cu-MOF products obtained at different annealing temperatures exhibit different properties, with the most suitable annealing temperature being 700℃.

[0065] Effect Experiment Example 4

[0066] Performance tests were conducted on Example 1, Comparative Example 1, Comparative Example 2, and existing Pt / C catalysts in different solution systems.

[0067] in, Figure 4 The LSV curves are compared between the PVP@Ni-Cu-MOF catalyst obtained in Example 1, the PVP@Cu-MOF obtained in Comparative Example 1, the PVP@Ni-MOF obtained in Comparative Example 2, and the Pt / C electrode in 0.1M KOH solution.

[0068] Figure 5 The LSV curves are compared between the PVP@Ni-Cu-MOF catalyst obtained in Example 1, the PVP@Cu-MOF obtained in Comparative Example 1, the PVP@Ni-MOF obtained in Comparative Example 2, and the Pt / C electrode in 0.1M phosphate buffer solution.

[0069] Figure 6 The LSV curves are compared between the PVP@Ni-Cu-MOF catalyst obtained in Example 1, the PVP@Cu-MOF obtained in Comparative Example 1, the PVP@Ni-MOF obtained in Comparative Example 2, and the Pt / C electrode in 0.5M H2SO4 solution.

[0070] Figures 4-6The PVP@Ni-Cu-MOF catalyst consists of three parts: a kinetic control region with extremely low current (>0.9V), a kinetic and diffusion combined control region with rapidly increasing current (0.6-0.9V), and a constant current diffusion control region (<0.6V). Through comparison of samples under three different pH electrolyte conditions, it was found that the PVP@Ni-Cu-MOF catalyst exhibits oxygen reduction performance equivalent to that of a Pt / C electrode under alkaline conditions, with a half-wave potential E(…). 1 / 2 The voltage is 0.825V, which is very close to the 0.835V of the Pt / C electrode. The performance decreases slowly with increasing solution acidity, but it still shows a high degree of similarity under pH (7-8) conditions.

[0071] The experimental data above demonstrate that the Ni-Cu-MOF electrocatalyst generated under liquid-phase conditions can be used to obtain an oxygen reduction catalyst with performance comparable to that of the Pt / C electrode under alkaline to neutral conditions by introducing the macromolecular polymer PVP and controlling the ratio between reactants and the annealing temperature. This composite catalyst has a simple preparation method and low preparation cost, and is expected to become a substitute for the precious metal Pt as an oxygen reducing agent in commercial fuel cells.

[0072] The above embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Although the invention has been described in detail with reference to the embodiments, those skilled in the art should understand that various combinations, modifications, or equivalent substitutions of the technical solutions of the invention do not depart from the spirit and scope of the invention and should be covered within the scope of the claims of the invention.

Claims

1. A method for preparing a composite oxygen reduction electrocatalyst, characterized by, The composite oxygen reduction electrocatalyst is PVP@Ni-Cu-MOF, and the preparation method comprises the following steps: (1) heating a nickel source, a trimesic acid, an alkali and a mixed solvent at 100-200°C to prepare Ni-MOF; (2) mixing a copper source solution and a trimesic acid solution to obtain a mixed reaction solution, immersing the Ni-MOF in the mixed reaction solution for 20-30 hours to prepare Ni-Cu-MOF, wherein the molar ratio of the copper source to the nickel source is (2-4):1; (3) adding the Ni-Cu-MOF into a PVP solution to react for 20-30 hours, then separating the solid, washing and drying the solid, and then annealing to obtain the PVP@Ni-Cu-MOF product.

2. The production method according to claim 1, characterized by, The nickel source is nickel chloride hexahydrate; and / or the alkali is NaOH or KOH; and / or the mixed solvent is a mixed solution of DMF, deionized water and ethanol, and the volume ratio of DMF, deionized water and ethanol in the mixed solvent is 1:1:

1.

3. The production method according to claim 1 or 2, characterized by, The molar ratio of the amount of the nickel source, the trimesic acid and the alkali is 1:2:(2-3).

4. The method of claim 1, wherein, The copper source is copper nitrate trihydrate; and / or the concentration of the copper source in the mixed reaction solution is 0.02-0.04 mol / L, and the concentration of the trimesic acid is 0.01-0.02 mol / L.

5. The preparation method according to claim 4, characterized in that, The preparation method of the mixed reaction solution comprises: adding a trimesic acid methanol solution into a copper nitrate trihydrate methanol solution, and stirring to obtain the mixed reaction solution. The concentration of the trimesic acid methanol solution is 0.03 mol / L, and the concentration of the copper nitrate trihydrate methanol solution is 0.06 mol / L.

6. The method of claim 1, wherein, The PVP solution is a PVP ethanol solution, and the concentration of PVP is 0.03-0.06 g / ml.

7. The preparation method according to claim 1, characterized in that, The mass ratio of the Ni-Cu-MOF to PVP contained in the PVP solution is 1:(20-150).

8. The preparation method according to claim 7, characterized in that, The temperature of the annealing treatment is 600-900°C.

9. The composite oxygen reduction electrocatalyst PVP@Ni-Cu-MOF prepared by the preparation method in any one of claims 1-8.

10. The use of the PVP@Ni-Cu-MOF in claim 9 as an oxygen reduction electrocatalyst in a fuel cell.

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