Preparation method and application of porous composite electrocatalyst

Abstract

The invention relates to the technical field of preparation of electrocatalytic materials, and discloses a preparation method and application of a porous composite electrocatalyst. The preparation method comprises the following steps: firstly, respectively dissolving nickel salt and hexacyanocobaltate in a mixed solution, and dropwise adding a nickel salt solution into a K3Co (CN) 6 solution for reaction to prepare a precursor; then calcining the precursor in an inert atmosphere to prepare a porous composite electrocatalyst; the preparation method is rapid and simple, the process is green, and the prepared electrocatalyst has a rich pore structure and good hydrophilicity. According to the invention, the porous non-noble metal composite electrocatalyst is developed, the effective area of electrochemical reaction is effectively increased, the water electrolysis hydrogen production efficiency is improved, and the water electrolysis hydrogen production cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of electrocatalytic materials, and particularly relates to a preparation method and application of a porous composite electrocatalyst. Background Art

[0003] Currently, the most studied non-noble metal catalysts include some typical transition metals and their carbides, nitrides, sulfides, oxides, alloys and phosphides. Although transition metal-based catalysts (such as Ni, Co) have low costs, they have problems such as small specific surface area, insufficient active sites, and poor stability under acidic conditions. In the prior art, although the carbon-coated materials derived from metal-organic frameworks (MOFs) can improve the specific surface area, the pore distribution of the materials synthesized by the traditional hydrothermal method is uneven, and the structure is prone to collapse during the calcination process, resulting in limited catalytic performance. In addition, it is difficult to achieve efficient combination of active components and carbon matrix by conventional methods, which restricts the conductivity and stability of the materials.

[0004] Therefore, it is of great significance to develop a preparation method of non-noble metal electrocatalytic materials with low cost, high activity and corrosion resistance. In view of this situation, the present invention aims to provide a preparation method of a porous composite electrocatalyst. Summary of the Invention

[0005] The present invention proposes a preparation method based on the "nano micro-region" effect of an ionic liquid mixed system to optimize the porous structure and electrocatalytic performance of the catalyst material, so as to improve the problems of low specific surface area, poor pore structure and insufficient active sites of non-noble metal catalysts in the prior art.

[0006] The technical solution adopted by the present invention is: a porous composite electrocatalyst, and the preparation method includes the following steps:

[0007] 1) Preparation of the precursor: Dissolve 0.3-0.4 parts of nickel salt and 0.3-0.4 parts of cobalt hexacyanoate in 20-40 parts of a mixed solution composed of an ionic liquid, water and an inorganic salt respectively. Drop the nickel salt solution into the cobalt hexacyanoate solution, carry out stirring reaction, centrifuge after standing for 24-72 h, wash, and vacuum dry to obtain a nickel-cobalt Prussian blue analogue NiCo-PBA precursor.

[0008] 2) Preparation of the porous composite electrocatalyst: Calcinate the precursor in an inert atmosphere to obtain a porous composite electrocatalyst NiCo@NC.

[0009] Further, in the above-mentioned porous composite electrocatalyst, in step 1), the nickel salt is one or a mixture of two or more of nickel chloride hexahydrate NiCl2·6H2O, nickel nitrate hexahydrate Ni(NO3)2·6H2O or nickel sulfate hexahydrate NiSO4·6H2O.

[0010] Further, in the above-mentioned porous composite electrocatalyst, in step 1), the hexacyanocobaltate is one or a mixture of two of potassium hexacyanocobaltate K3Co(CN)6 or sodium hexacyanocobaltate Na3Co(CN)6.

[0011] Further, in the above-mentioned porous composite electrocatalyst, in step 1), in the mixed solution, the proportion of the ionic liquid is 60 - 80 wt%, the proportion of water is 20 - 40 wt%, and the concentration of the inorganic salt is 0.05 - 0.2 mol / L.

[0012] Further, in the above-mentioned porous composite electrocatalyst, in step 1), the ionic liquid is 1-ethyl-3-methylimidazolium tetrafluoroborate [C n mim][BF4] (n = 2 - 8), 1-ethyl-3-methylimidazolium hexafluorophosphate [C n mim][PF6] (n = 2 - 8) or a mixture of one or more of them.

[0013] Further, in the above-mentioned porous composite electrocatalyst, in step 1), the inorganic salt is one or a mixture of two or more of magnesium chloride MgCl2, calcium chloride CaCl2 or zinc chloride ZnCl2.

[0014] Further, in the above-mentioned porous composite electrocatalyst, in step 1), the stirring reaction is carried out at 20 - 30 °C for 12 - 36 h.

[0015] Further, in the above-mentioned porous composite electrocatalyst, in step 2), the calcination is carried out by heating to 400 - 700 °C at a heating rate of 3 - 10 °C / min and calcining for 2 - 6 h.

[0016] Further, in the above-mentioned porous composite electrocatalyst, in step 2), the inert atmosphere is one or a mixture of two or more of nitrogen, argon or helium.

[0017] Further, the application of the above porous composite electrocatalyst in electrocatalytic water hydrogen evolution.

[0018] The beneficial effects of the present invention are as follows:

[0019] 1. Aiming at the problems of low specific surface area, poor pore structure and insufficient stability in acidic electrolytes of existing non-noble metal catalysts, the present invention proposes a preparation method based on the "nano-microzone" effect of an ionic liquid mixed system, realizing a significant improvement in the structure, performance and preparation process of non-noble metal electrocatalytic materials.

[0020] 2. The process flow of the present invention is simple and easy to produce. Compared with traditional non-noble metal catalysts, it has the advantages of high activity and efficient catalytic performance. The hierarchical porous structure improves mass transfer and exposes active sites, and it also has excellent chemical stability and durability. Moreover, it has low cost, simple process, no harmful by-products, is environmentally friendly, and has obvious social and economic benefits. Description of the Drawings

[0021] Figure 1 It is a scanning electron microscope image of the porous composite electrocatalyst (NiCo@NC) in Example 1.

[0022] Figure 2 It is a transmission electron microscope image of the porous composite electrocatalyst (NiCo@NC) in Example 1.

[0023] Figure 3 It is an X-ray diffraction analysis spectrum of the precursors in Examples 1 and 2.

[0024] Figure 4 It is an X-ray diffraction analysis spectrum of the porous composite electrocatalysts (NiCo@NC) in Examples 1, 2, and 3.

[0025] Figure 5 It is an N2 adsorption-desorption curve of the porous composite electrocatalysts (NiCo@NC) in Examples 1, 2, and 3.

[0026] Figure 6 It is a pore size distribution curve of the porous composite electrocatalysts (NiCo@NC) in Examples 1, 2, and 3. Detailed Embodiments

[0027] The following further illustrates the content of the present invention with specific examples, but it should not be construed as a limitation to the present invention. Without departing from the spirit and essence of the present invention, any modifications or substitutions made to the methods, steps or conditions of the present invention should be covered within the scope of the claims of the present invention.

[0028] Example 1

[0029] (1) Preparation of the precursor

[0030] According to the mass fraction, 0.3 parts of NiCl2·6H2O and 0.3 parts of K3Co(CN)6 are respectively dissolved in 20 parts and 40 parts of the [C2mim][BF4] / H2O / MgCl2 mixed solution; wherein, the mixed solution contains 60 wt% ionic liquid and 40 wt% water, and the concentration of MgCl2 is 0.08 mol / L; then, the solution containing NiCl2·6H2O is slowly dropped into the solution containing K3Co(CN)6 with a syringe, and the reaction temperature is controlled at 30 °C; after the dropping is completed, the reaction solution is stirred at 30 °C for 18 h, and after stopping stirring, the solution is allowed to stand for 24 h; then the mixture is centrifuged, and the precipitate is washed 3 times with water and ethanol and then placed in a vacuum drying oven at 55 °C for drying for 24 h to obtain the precursor NiCo-PBA.

[0031] The X-ray diffraction analysis spectrum is as Figure 3 shown (corresponding to Figure 3 precursor 1 therein), from which it can be seen that the peaks on the XRD spectrum are not particularly sharp, indicating the porosity of the precursor. The XRD diffraction peaks of the prepared NiCo-PBA match the standard peak shape of NiCo-PBA (JCPDS No. 89-3738). These peaks are marked as a cubic lattice structure with a space group of Fm-3m (the main peaks are located at 2θ of about 14.8°, 17.4°, 24.7°, 35.2°, 39.7°, 43.5°, 50.7°, 53.9° and 57.2°), indicating the successful preparation of NiCo-PBA.

[0032] (2) Preparation of the porous composite electrocatalyst

[0033] Put the precursor prepared in step (1) into a crucible, and directly calcine the precursor in a nitrogen atmosphere at 500 °C at a heating rate of 10 °C / min for 2 h to obtain a porous nickel-cobalt-nitrogen-carbon composite electrocatalyst (NiCo@NC-500).

[0034] The scanning electron microscope results are as Figure 1 shown. It can be seen from the picture that the electrocatalyst synthesized in the ionic liquid mixed system presents a porous structure formed by the accumulation of nanoparticles. The porous structure enables the electrocatalyst to provide a larger specific surface area and the contact area between the electrode and the electrolyte.

[0035] The transmission electron microscope results are as Figure 2 shown. It can be seen from the picture that the catalyst presents a porous structure and can still maintain a certain porous structure after calcination. The porous structure enables the electrocatalyst to provide a larger specific surface area and the contact area between the electrode and the electrolyte.

[0036] The X-ray diffraction analysis spectrum is as Figure 4As shown, it can be seen from the figure that all the diffraction peaks of NiCo@NC are located between the diffraction peaks of Ni (JCPDS No. 04-0850) and Co (JCPDS No. 15-0806). The three different peaks at 44.2°, 51.6° and 76.1° correspond to the (111), (200) and (220) crystal planes of the face-centered cubic NiCo alloy, indicating that NiCo@NC has been successfully prepared.

[0037] Its N2 adsorption-desorption curve is as Figure 5 shown. It can be analyzed from the figure that the specific surface area of NiCo@NC-500 is 68.4 m 2 / g.

[0038] Its pore size distribution curve is as Figure 6 shown. It can be seen from the figure that most of NiCo-PBA are mesopores, and its total pore volume is 0.226 cm 3 / g

[0039] Example 2

[0040] (1) Preparation of the precursor

[0041] According to the mass fraction, 0.35 parts of NiCl2·6H2O and 0.35 parts of Na3Co(CN)6 are respectively dissolved in 30 parts and 30 parts of [C4mim][BF4] / H2O / MgCl2 mixed solution; among them, the mixed system contains 70 wt% ionic liquid and 30 wt% water, and the concentration of MgCl2 is 0.15 mol / L; then, the solution containing NiCl2·6H2O is slowly dropped into the solution containing Na3Co(CN)6 with a syringe, and the reaction temperature is controlled at 25 °C. After the dropping is completed, the reaction solution is stirred at 25 °C for 24 h. After stopping stirring, the solution is allowed to stand for 48 h; then the mixed solution is centrifuged, and the precipitate is washed 4 times with water and ethanol, and then placed in a vacuum drying oven at 70 °C for 18 h to obtain the precursor NiCo-PBA.

[0042] Its X-ray diffraction analysis spectrum is as Figure 3 shown (corresponding to Figure 3 the precursor 2 therein). It can be seen that the peaks on the XRD spectrum are not particularly sharp, indicating the porosity of the precursor. The XRD diffraction peaks of the prepared NiCo-PBA match the standard peak shape of NiCo-PBA (JCPDS No. 89-3738). These peaks are marked as a cubic lattice structure with a space group of Fm-3m (the main peak is located at 2 θ °, about 14.8°, 17.4°, 24.7°, 35.2°, 39.7°, 43.5°, 50.7°, 53.9° and 57.2°), indicating that NiCo-PBA has been successfully prepared.

[0043] (2) Preparation of Porous Composite Electrocatalyst

[0044] Put the precursor prepared in step (1) into a crucible, and directly calcine the precursor in a nitrogen atmosphere at 600 °C at a heating rate of 5 °C / min for 4 h to obtain a porous nickel-cobalt-nitrogen-carbon composite electrocatalyst (NiCo@NC-600).

[0045] The X-ray diffraction analysis spectrum is as shown in Figure 4 From the figure, it can be seen that all the diffraction peaks of NiCo@NC are located between the diffraction peaks of Ni (JCPDS No. 04-0850) and Co (JCPDS No. 15-0806). The three different peaks at 44.2°, 51.6° and 76.1° correspond to the (111), (200) and (220) crystal planes of the face-centered cubic NiCo alloy, indicating that NiCo@NC has been successfully prepared.

[0046] The N2 adsorption-desorption curve is as shown in Figure 5 From the figure, it can be analyzed that the specific surface area of NiCo@NC-600 is 45.2 m 2 / g.

[0047] The pore size distribution curve is as shown in Figure 6 From the figure, it can be seen that most of NiCo@NC-600 are mesopores, and its total pore volume is 0.149 cm 3 / g.

[0048] Example 3

[0049] (1) Preparation of Precursor

[0050] According to the mass fraction, dissolve 0.4 parts of NiSO4·6H2O and 0.4 parts of K3Co(CN)6 in 40 parts and 20 parts of [C4mim][PF6] / H2O / CaCl2 mixed solution respectively; among them, the mixed system contains 80 wt% ionic liquid and 20 wt% water, and the concentration of CaCl2 is 0.2 mol / L; then, slowly drip the solution containing NiSO4·6H2O into the solution containing K3Co(CN)6, and control the reaction temperature at 20 °C. After the dripping is completed, the reaction solution is stirred at 20 °C for 24 h. After stopping stirring, the solution is allowed to stand for 72 h; then the mixed solution is centrifuged, and the precipitate is washed 5 times with water and ethanol, and then placed in a vacuum drying oven at 80 °C for 12 h to obtain the precursor NiCo-PBA.

[0051] (2) Preparation of Porous Composite Electrocatalyst

[0052] Put the precursor prepared in step (1) into a crucible, and directly calcine the precursor in a helium atmosphere at 700 °C at a heating rate of 3 °C / min for 6 h to obtain a porous nickel-cobalt-nitrogen-carbon composite electrocatalyst (NiCo@NC-700).

[0053] The X-ray diffraction analysis spectrum is as Figure 4 shown. It can be seen from the figure that all the diffraction peaks of NiCo@NC are located between the diffraction peaks of Ni (JCPDS No. 04-0850) and Co (JCPDS No. 15-0806). The three different peaks at 44.2°, 51.6°, and 76.1° correspond to the (111), (200), and (220) crystal planes of the face-centered cubic NiCo alloy, indicating that NiCo@NC has been successfully prepared.

[0054] The N2 adsorption-desorption curve is as Figure 5 shown. It can be analyzed from the figure that the specific surface area of NiCo@NC-700 is 32.7 m 2 / g.

[0055] The pore size distribution curve is as Figure 6 shown. It can be seen from the figure that most of NiCo@NC-700 are mesopores, and its total pore volume is 0.108 cm 3 / g

[0056] Comparative Example 1

[0057] (1) Preparation of the precursor

[0058] According to the mass parts, dissolve 0.4 parts of NiSO4·6H2O and 0.4 parts of K3Co(CN)6 in 60 parts of water; then, slowly drip the solution containing NiSO4·6H2O into the solution containing K3Co(CN)6 with a syringe, and control the reaction temperature at 20 °C. After the dropping is completed, stir the reaction solution at 20 °C for 24 h. After stopping stirring, let the solution stand for 72 h; then centrifuge the mixture, wash the precipitate with water and ethanol 5 times, and place it in a vacuum drying oven at 80 °C for 12 h to obtain the precursor NiCo-PBA-W.

[0059] (2) Preparation of the comparative sample

[0060] Put the precursor prepared in step (1) into a crucible, and directly calcine the precursor in a nitrogen atmosphere at 500 °C at a heating rate of 10 °C / min for 2 h to obtain a comparative sample (NiCo@NC-500-W).

[0061] Application of the porous composite electrocatalyst NiCo@NC in the electrolytic hydrogen evolution reaction

[0062] Experimental method: The catalytic performance was tested in a 0.5 M H2SO4 electrolyte using a three-electrode system. The working electrode was a glassy carbon electrode loaded with the catalyst (4 mg / cm 2 ), the reference electrode was Ag / AgCl (3 M KCl), and the counter electrode was a graphite rod. The electrocatalytic hydrogen evolution reaction (HER) activity was evaluated by linear sweep voltammetry (LSV, 5 mV / s) and Tafel slope analysis. The specific experimental data are as follows:

[0063] Table 1 Comparison of catalyst performance in each example

[0064]

[0065] The catalyst in Example 1 showed the best HER activity (η 10 = 156 mV), and the Tafel slope (72 mV / dec) indicated that the reaction followed the Volmer-Heyrovsky mechanism.

[0066] 2. Influence of raw material mass fraction on catalytic performance (single-factor experiment)

[0067] Using the catalyst obtained in Example 1, the amounts of nickel salt and cobalt hexacyanoate were adjusted (the ratios of Examples 1, 2, and 3). The results are as follows:

[0068] Table 2 Influence of different amounts of nickel salt and cobalt hexacyanoate on catalytic performance

[0069]

[0070] Conclusion: Increasing the mass fraction of Ni and Co salts will lead to an increase in the grain size of the precursor, densification of the pore structure, a decrease in the specific surface area, and a gradual decrease in catalytic performance. The catalyst in Experimental Group 1 showed the best HER activity (η 10 = 156 mV). Therefore, the ratio of Example 1 (0.3 parts) is the optimal choice.

[0071] 3. Comparative experiment with traditional aqueous solvent system

[0072] Table 3 Performance comparison of NiCo@NC in Example 1 and traditional aqueous solvent catalysts

[0073]

[0074] Note: *NiCo@NC-500-W is a comparative sample prepared by the traditional aqueous solvent, and NiCo@NC-500 is the catalyst obtained in Example 1.

[0075] The ionic liquid mixed system reduces the overpotential by 42%, improves the Tafel slope by 33.9%, and increases the specific surface area by 46.6%, confirming that the material synthesized by the present invention has a lower overpotential, faster reaction kinetics and better stability than the materials synthesized by traditional methods, improving the efficiency of hydrogen production by electrolyzing water.

Claims

1. A porous composite electrocatalyst, characterized in that, The preparation method comprises the following steps: 1) Preparation of the precursor: 0.3 - 0.4 parts of nickel salt and 0.3 - 0.4 parts of cobalt hexacyanide are respectively dissolved in 20 - 40 parts of a mixed solution composed of ionic liquid, water and inorganic salt. The nickel salt solution is dropped into the cobalt hexacyanide solution, followed by stirring reaction. After standing for 24 - 72 h, centrifugation, washing and vacuum drying are carried out to obtain the nickel-cobalt Prussian blue analogue NiCo-PBA precursor. 2) Preparation of the porous composite electrocatalyst: The precursor is calcined in an inert atmosphere to obtain the porous composite electrocatalyst NiCo@NC.

2. The porous composite electrocatalyst according to claim 1, wherein: In step 1), the nickel salt is one or a mixture of two or more of nickel chloride hexahydrate NiCl2·6H2O, nickel nitrate hexahydrate Ni(NO3)2·6H2O or nickel sulfate hexahydrate NiSO4·6H2O.

3. The porous composite electrocatalyst according to claim 1, characterized in that: In step 1), the cobalt hexacyanide is one or a mixture of two of potassium hexacyanocobaltate K3Co(CN)6 or sodium hexacyanocobaltate Na3Co(CN)6.

4. A porous composite electrocatalyst according to claim 1, characterized in that: In step 1), in the mixed solution, the ionic liquid accounts for 60 - 80 wt%, water accounts for 20 - 40 wt%, and the concentration of the inorganic salt is 0.05 - 0.2 mol / L.

5. The porous composite electrocatalyst according to claim 1, characterized in that: In step 1), the ionic liquid is 1-ethyl-3-methylimidazolium tetrafluoroborate [C n mim][BF4] (n = 2 to 8), 1-ethyl-3-methylimidazolium hexafluorophosphate [C n mim][PF6] (n = 2 to 8), or a mixture of one or more of them.

6. The porous composite electrocatalyst according to claim 1, characterized in that: In step 1), the inorganic salt is one or a mixture of two or more of magnesium chloride MgCl2, calcium chloride CaCl2 or zinc chloride ZnCl2.

7. A porous composite electrocatalyst according to claim 1, characterized in that: In step 1), the stirring reaction is carried out at 20 - 30 °C for 12 - 36 h.

8. The porous composite electrocatalyst according to claim 1, wherein: In step 2), the calcination is carried out by heating to 400 - 700 °C at a heating rate of 3 - 10 °C / min and calcining for 2 - 6 h.

9. The porous composite electrocatalyst according to claim 1, wherein: The inert atmosphere in step 2) is one or a mixture of two or more of nitrogen, argon or helium.

10. Application of the porous composite electrocatalyst according to any one of claims 1 - 9 in electrocatalytic water hydrogen evolution.

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