A cobalt phosphide water electrolysis catalyst and a method of making the same

Abstract

The application provides a cobalt phosphide water electrolysis catalyst and a preparation method thereof, and the preparation method comprises the following steps: (1) soaking foam nickel in a polyvinylpyrrolidone solution, and obtaining modified foam nickel after reaction; (2) mixing a cobalt nitrate hexahydrate solution and a 2-methylimidazole solution to obtain a mixed solution, adding the modified foam nickel into the mixed solution, and obtaining a metal organic framework ZIF-67@foam nickel material after reaction; (3) carrying out a separated gas phosphorization reaction on the metal organic framework ZIF-67@foam nickel material under a nitrogen atmosphere, and obtaining the cobalt phosphide water electrolysis catalyst. The cobalt phosphide catalyst prepared in the application has a high specific surface area and porosity, is beneficial to the exposure of active sites, and has excellent water electrolysis catalytic performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalysts, in particular to a cobalt phosphide water electrolysis catalyst and a preparation method thereof. BACKGROUND

[0002] The water electrolysis catalyst can accelerate the reaction kinetics, reduce the energy barrier of water decomposition, and save energy consumption. The water electrolysis catalyst includes a noble metal-based electrocatalyst and a non-noble transition metal-based electrocatalyst. The noble metal-based electrocatalyst has excellent water electrolysis catalytic performance, but it cannot be widely used in industrial water electrolysis hydrogen production due to its rare raw materials and high price. In recent years, non-noble transition metal phosphides, carbides, nitrides, oxides and hydroxides have shown excellent electrocatalytic performance.

[0003] The transition metal phosphide has a similar structure to hydrogenase. The negatively charged P atom in the catalyst can capture protons and act as a site for H2 dissociation. It is also an active site for the reduction of oxygen molecules to hydroxyl ions. However, the transition metal phosphide prepared by the prior art has irregular morphology, and the surface active site is less exposed, which cannot fully exert its catalytic performance. Therefore, based on the above problems, it is necessary to study a transition metal phosphide catalyst with good catalytic performance. SUMMARY

[0004] The present application provides a cobalt phosphide water electrolysis catalyst and a preparation method thereof. The cobalt phosphide catalyst prepared by the method has a high specific surface area and porosity, which is beneficial to the exposure of active sites and has excellent water electrolysis catalytic performance.

[0005] In a first aspect, the present application provides a preparation method of a cobalt phosphide water electrolysis catalyst, which comprises the following steps:

[0006] (1) soaking the foamed nickel in a polyvinylpyrrolidone solution to obtain modified foamed nickel after reaction;

[0007] (2) mixing a cobalt nitrate hexahydrate solution and a 2-methylimidazole solution to obtain a mixed solution, and adding the modified foamed nickel into the mixed solution to obtain a metal organic framework ZIF-67@foamed nickel material after reaction;

[0008] (3) carrying out a separation type gas phosphidation reaction on the metal organic framework ZIF-67@foamed nickel material under a nitrogen atmosphere to obtain the cobalt phosphide water electrolysis catalyst.

[0009] Preferably, in step (1), the solvent of the polyvinylpyrrolidone solution is hydrochloric acid; and the mass concentration of the polyvinylpyrrolidone solution is 1-30%.

[0010] Preferably, the relative molecular mass of the polyvinylpyrrolidone in the polyvinylpyrrolidone solution is 0.8-1.3 million; preferably, the relative molecular mass of the polyvinylpyrrolidone is 0.8-220 million.

[0011] Preferably, in step (1), the temperature of the reaction is 25-30℃, and the time is 25-35 min; the reaction is preferably carried out under ultrasonic conditions.

[0012] Preferably, in step (2), the solvent of the cobalt nitrate hexahydrate solution and the 2-methylimidazole solution is anhydrous methanol.

[0013] The molar ratio of the cobalt nitrate hexahydrate to the 2-methylimidazole is 1:(1-10).

[0014] Preferably, in step (2), the temperature of the reaction is 25-30℃, and the time is 25-35 min; the reaction is preferably carried out under ultrasonic conditions 20-40 kHz.

[0015] Preferably, in step (3), the phosphating agent used in the separation type gas phosphating reaction is sodium hypophosphite.

[0016] The temperature of the reaction is 300-500℃, and the time is 1.5-2.5 h; the heating rate is 8-12℃ / min.

[0017] Preferably, before step (3), a step of heating reaction of the metal-organic framework ZIF-67@foam nickel material in a molten salt medium under a nitrogen atmosphere is further included.

[0018] Preferably, the molten salt medium includes potassium chloride and lithium chloride, wherein the molar ratio of the potassium chloride to the lithium chloride is (1-10):(10-1).

[0019] Preferably, the temperature of the heating reaction is 500-800℃, and the time is 1.5-2.5 h; the heating rate is 2-10℃ / min.

[0020] In a second aspect, the present application provides a cobalt phosphide water electrolysis catalyst as described in any one of the above first aspect.

[0021] Compared with the prior art, the present application has at least the following beneficial effects:

[0022] (1) The polyvinylpyrrolidone is used to modify the foamed nickel first, then the modified foamed nickel is compounded with the metal organic framework, so that the metal organic framework ZIF-67 grows on the surface of the modified foamed nickel, and finally the phosphorized cobalt catalyst is prepared by phosphating treatment, the modified foamed nickel is beneficial to the activity expression of the catalyst, thereby being beneficial to the diffusion of the electrolyte and the electron transfer, and the catalytic performance of the prepared phosphorized cobalt catalyst is more excellent; meanwhile, the phosphorized cobalt catalyst in the application well maintains the polyhedral morphology of the metal organic framework template, has a high specific surface area and porosity, is beneficial to the exposure of the active sites of the phosphorized cobalt catalyst, and thus has excellent electrocatalytic hydrogen evolution and electrocatalytic oxygen evolution performance. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings described below are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0024] Figure 1 is the electron scanning electron microscope image of the metal organic framework ZIF-67@foamed nickel material provided in embodiment 1 of the present application;

[0025] Figure 2 is the electron scanning electron microscope image of the metal organic framework ZIF-67@foamed nickel material provided in embodiment 2 of the present application;

[0026] Figure 3 is the electron scanning electron microscope image of the metal organic framework ZIF-67@foamed nickel material provided in embodiment 3 of the present application;

[0027] Figure 4 is the electron scanning electron microscope image of the metal organic framework ZIF-67@foamed nickel material provided in embodiment 4 of the present application;

[0028] Figure 5 is the electron scanning electron microscope image of the metal organic framework ZIF-67@foamed nickel material after molten salt heat treatment provided in embodiment 7 of the present application;

[0029] Figure 6 is the electron scanning electron microscope image of the metal organic framework ZIF-67@foamed nickel material after heat treatment provided in embodiment 10 of the present application;

[0030] Figure 7 is the alternating current impedance diagram of the phosphorized cobalt electrolytic water catalyst provided in embodiments 1 to 4 of the present application;

[0031] Figure 8is a phosphorus cobalt electrolytic water catalyst provided by the present application embodiment 1 to 4 overpotential of 0.25V when the capacitance current density and scanning rate relationship diagram of the catalyst;

[0032] Figure 9 is a phosphorus cobalt electrolytic water catalyst 1mol / L of the catalyst in the KOH solution provided by the present application embodiment 1 to 4 and comparative example 2 to 3 oxygen evolution activity diagram of the catalyst;

[0033] Figure 10 is a phosphorus cobalt electrolytic water catalyst Tafel slope diagram provided by the present application embodiment 1 to 4 and comparative example 2 to 3;

[0034] Figure 11 is a phosphorus cobalt electrolytic water catalyst provided by the present application embodiment 7 to 9 hydrogen evolution activity diagram of the catalyst;

[0035] Figure 12 is a phosphorus cobalt electrolytic water catalyst provided by the present application embodiment 7 to 9 hydrogen evolution Tafel slope diagram of the catalyst;

[0036] Figure 13 is a phosphorus cobalt electrolytic water catalyst provided by the present application embodiment 7 to 9 oxygen evolution activity diagram of the catalyst;

[0037] Figure 14 is a phosphorus cobalt electrolytic water catalyst provided by the present application embodiment 7 to 9 oxygen evolution Tafel slope diagram of the catalyst. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0039] The transition metal phosphide catalyst prepared in the prior art has a large particle size and irregular morphology, so that the surface active site of the catalyst is less, and the catalytic performance of the prepared catalyst is poor. In view of this, the present application provides a preparation method of a phosphorus cobalt electrolytic water catalyst, which comprises the following steps:

[0040] (1) the foamed nickel is soaked in a polyvinylpyrrolidone solution, and modified foamed nickel is obtained after reaction;

[0041] (2) mixing a cobalt nitrate hexahydrate solution and a 2-methylimidazole solution to obtain a mixed solution, and adding the modified nickel foam into the mixed solution to obtain a metal organic framework ZIF-67@nickel foam material after reaction;

[0042] (3) performing a separated gas phosphorization reaction on the metal organic framework ZIF-67@nickel foam material under a nitrogen atmosphere to obtain the cobalt phosphide electrolytic water catalyst.

[0043] In the present application, the nickel foam is first soaked in a polyvinylpyrrolidone solution, which can modify the surface of the nickel foam, and then the modified nickel foam is soaked in a mixed solution containing a cobalt nitrate hexahydrate solution and a 2-methylimidazole solution, and the metal organic framework ZIF-67 grows on the surface of the nickel foam, thereby obtaining a metal organic framework ZIF-67@nickel foam material, and finally the metal organic framework ZIF-67@nickel foam material is subjected to phosphorization treatment, thereby preparing a cobalt phosphide electrolytic water catalyst. In the present application, by modifying the surface of the nickel foam, the metal organic framework ZIF-67 grown on the surface of the nickel foam has a regular morphology, which is a well-defined dodecahedron structure. The three-dimensional foam structure can expose more active sites of the catalyst, and the nickel foam also provides certain nickel active sites, thereby making the catalyst exhibit excellent catalytic activity. By controlling the relative molecular mass of the polyvinylpyrrolidone, the size of the metal organic framework ZIF-67 grown on the surface of the nickel foam can be controlled, so as to ensure that the prepared catalyst has a high specific surface area and porosity, thereby having high catalytic performance.

[0044] According to some preferred embodiments, in step (1), the solvent of the polyvinylpyrrolidone solution is hydrochloric acid; and the mass concentration of the polyvinylpyrrolidone solution is 1-30% (for example, it can be 1%, 5%, 10%, 15%, 20%, 25% or 30%).

[0045] In the polyvinylpyrrolidone solution, the relative molecular mass of the polyvinylpyrrolidone is 0.8-130 million (for example, it can be 0.8 million, 1 million, 5 million, 5.8 million, 8 million, 10 million, 15 million, 22 million, 40 million, 80 million, 100 million or 130 million); preferably, the relative molecular mass of the polyvinylpyrrolidone is 0.8-22 million (for example, it can be 0.8 million, 1 million, 5 million, 10 million, 15 million, 20 million or 22 million).

[0046] In the present application, the polyvinylpyrrolidone with the above relative molecular mass is used to modify the foamed nickel, the polyvinylpyrrolidone can be attached to the surface of the foamed nickel, by controlling the relative molecular mass of the polyvinylpyrrolidone attached to the surface of the foamed nickel, the size of the metal organic framework ZIF-67 grown on the surface of the foamed nickel can be controlled, so that the prepared cobalt phosphide catalyst has a larger electrochemical active area and excellent catalytic activity performance; the experiments of the present application prove that when the relative molecular mass of the polyvinylpyrrolidone used is within the above range, the electrocatalytic performance of the catalyst is more improved, if the relative molecular mass of the polyvinylpyrrolidone is higher than the above range, the corresponding viscosity is larger, thereby it is not conducive to the dispersion of ZIF-67 and active sites on the surface of the foamed nickel, and thus the catalytic performance of the catalyst is reduced; at the same time, it should be pointed out that since the small size nanomaterial is superior to the active expression of the catalyst, therefore in the present application, the relative molecular mass of the polyvinylpyrrolidone is preferably 0.8-220,000, which is more conducive to preparing the cobalt phosphide catalyst with good catalytic performance.

[0047] According to some preferred embodiments, in step (1), the temperature of the reaction is 25-30℃ (for example, it can be 25℃, 26℃, 27℃, 28℃, 29℃ or 30℃), and the time is 25-35min (for example, it can be 25min, 28min, 30min, 32min or 35min); the reaction is preferably carried out under ultrasonic conditions.

[0048] In the present application, when preparing the modified foamed nickel, a certain amount of polyvinylpyrrolidone can be first dissolved in 2mol / L hydrochloric acid to prepare a polyvinylpyrrolidone solution with a mass concentration of 1-30%, then the foamed nickel can be cut into a sheet with a size of 1cm×2cm and a thickness of 0.3-2mm, the cut foamed nickel is immersed in the polyvinylpyrrolidone solution, and then ultrasonic reaction is carried out at room temperature, so that the polyvinylpyrrolidone can be successfully attached to the surface of the foamed nickel, thereby modifying the foamed nickel; it should be pointed out that in the present application, the ratio of foamed nickel to polyvinylpyrrolidone has no specific requirements, as long as the foamed nickel can be completely immersed in the polyvinylpyrrolidone solution.

[0049] In the present application, after the foamed nickel is modified by the polyvinylpyrrolidone solution, the modified foamed nickel is taken out from the polyvinylpyrrolidone solution and washed and dried, deionized water can be used for repeated washing during washing, for example, 2-3 times, and then the foamed nickel is placed in a vacuum oven at 60℃ for drying, so that the modified foamed nickel material can be obtained.

[0050] According to some preferred embodiments, in step (2), the solvent of the cobalt nitrate hexahydrate solution and the 2-methylimidazole solution is anhydrous methanol.

[0051] The molar ratio of the cobalt nitrate hexahydrate and the 2-methylimidazole is 1:(1-10) (for example, it can be 1:1, 1:2, 1:4, 1:5, 1:6, 1:8 or 1:10).

[0052] According to some preferred embodiments, in step (2), the temperature of the reaction is 25-30℃ (for example, it can be 25℃, 27℃, 28℃, 29℃ or 30℃), and the time is 25-35 min (for example, it can be 25 min, 28 min, 30 min, 32 min or 35 min); the reaction is preferably carried out under ultrasonic conditions.

[0053] In the present application, when preparing the metal organic framework ZIF-67@foam nickel material, the cobalt nitrate hexahydrate and the 2-methylimidazole can be respectively dissolved in anhydrous methanol to obtain a cobalt nitrate hexahydrate solution with a concentration of 0.1 mol / L and a 2-methylimidazole solution with a concentration of 0.4 mol / L, respectively, then the 2-methylimidazole solution is slowly poured into the cobalt nitrate hexahydrate solution, a mixed solution is obtained after mixing, and the modified foam nickel is placed in the mixed solution for ultrasonic reaction, and after ultrasonic reaction, it is placed for 24 h, the foam nickel material after reaction is taken out from the solution and washed with methanol for 3-4 times, and finally it is placed in a vacuum oven at 60℃ for drying for 12 h, to obtain the metal organic framework ZIF-67@foam nickel material, which can also be referred to as ZIF-67 / NF material or ZIF-67@NF material.

[0054] According to some preferred embodiments, in step (3), the phosphating agent used in the separation type gas phosphating reaction is sodium hypophosphite; the temperature of the phosphating reaction is 300-500℃ (for example, it can be 300℃, 350℃, 400℃, 450℃ or 500℃), and the time is 1.5-2.5 h (for example, it can be 1.5 h, 1.8 h, 2 h or 2.5 h); the heating rate is 8-12℃ / min (for example, it can be 8℃ / min, 9℃ / min, 10℃ / min or 12℃ / min).

[0055] In the present application, after the metal organic framework ZIF-67@foam nickel material is prepared, the phosphating treatment is carried out on it by using sodium hypophosphite powder, at this time, the metal cobalt and metal nickel in the ZIF-67@NF material can be phosphatized by PH3 formed after the sodium hypophosphite is heated and decomposed, and then the phosphor cobalt catalyst is obtained, in the present application, the temperature of the phosphating reaction is too low or too high, which is not conducive to the full occurrence of the phosphating reaction, if the temperature of the phosphating reaction is too low, the NaH2PO2 thermal decomposition produces PH3 too slowly, if the temperature of the phosphating reaction is too high, PH3 is easy to lose. At the same time, it should be pointed out that, since sodium hypophosphite is easy to be oxidized, and the PH3 produced after its decomposition is a toxic gas, when the separation type phosphating reaction is carried out, the quartz boat containing sodium hypophosphite can be placed in the upstream of the tube furnace, and the ZIF-67@NF material is placed in the downstream of the tube furnace, first, inert gas is introduced into it, then it is heated to the target temperature, after the reaction, it is naturally cooled, and then washed with deionized water and anhydrous ethanol for 2-3 times, and finally dried in a vacuum oven at 60℃, to obtain the phosphor cobalt electrolytic water catalyst. In the present application, the copper sulfate solution can be used to absorb the part of PH3 gas produced by the pyrolysis of sodium hypophosphite which does not participate in the reaction.

[0056] According to some preferred embodiments, before step (3), it further includes the step of placing the metal organic framework ZIF-67@foam nickel material in the molten salt medium for heating reaction under a nitrogen atmosphere.

[0057] In the present application, before the phosphating reaction is carried out, the metal organic framework ZIF-67@foam nickel material is placed in the molten salt medium for heat treatment, the molten salt medium can penetrate into the inside of the metal organic framework ZIF-67, so as to further make the pore structure of its surface more abundant, thereby being conducive to the exposure of the active sites on the surface of the phosphor cobalt catalyst, so as to make it fully play the catalytic performance, and further enhance the catalytic performance of the phosphor cobalt catalyst.

[0058] According to some preferred embodiments, in step (3), the molten salt medium includes potassium chloride and lithium chloride, wherein the molar ratio of the potassium chloride to the lithium chloride is (1-10):(10-1) (for example, it can be 1:10, 0.5:2, 1:1, 1:2, 1:5, 2:3, 2:2, 3:2, 4:2, 4:5, 8:2, 9:1, 10:6 or 10:1), more preferably, the molar ratio of the potassium chloride to the lithium chloride is (0.5-2):5.

[0059] In the present application, the prepared metal organic framework ZIF-67@foam nickel material is first placed in a molten salt medium for heat treatment. Due to the templating effect of the molten salt medium, a special liquid environment can be provided during the molten salt heat treatment process, thereby penetrating into the ZIF-67. After washing, the molten salt on the surface of ZIF-67 is removed, so that the surface of ZIF-67 retains a rich pore structure, thereby increasing the specific surface area of the prepared catalyst, increasing the number of active sites exposed, and facilitating the diffusion of electrolyte on the surface of the catalyst and electron transfer, thereby making the cobalt phosphide catalyst have excellent hydrogen evolution and oxygen evolution performance. It should be noted that, in the present application, by controlling the molar ratio of the molten salt medium, the templating effect on cobalt phosphide can be further strengthened, thereby exposing more active sites.

[0060] According to some preferred embodiments, the temperature of the heating reaction is 500-800℃ (for example, it can be 500℃, 600℃, 700℃ or 800℃), and the time is 1.5-2.5h (for example, it can be 1.5h, 1.8h, 2h or 2.5h); in the present application, the molten salt heat treatment is preferably carried out within the above temperature range, which is more conducive to the metal organic framework ZIF-67@foam nickel material exposing more internal sites under the strong polarization of the molten salt medium. When the temperature is lower than the above range, the flowability of the molten salt is poor, it is difficult to enter the inside of the ZIF-67@foam nickel material, and it is difficult to form a rich hollow structure to expose more active sites. When the temperature is too high, the skeleton structure of the ZIF-67@foam nickel material will collapse.

[0061] The heating rate of the reaction is 2-10℃ / min (for example, it can be 2℃ / min, 5℃ / min, 8℃ / min or 10℃ / min), and the cooling rate is 3-5℃ / min (3℃ / min, 4℃ / min or 5℃ / min).

[0062] In the present application, when the metal organic framework ZIF-67@foam nickel material is subjected to molten salt heat treatment, a certain molar ratio of molten salt medium can be mixed and ground first, the metal organic framework ZIF-67@foam nickel material is placed in a quartz boat, then the ground molten salt medium is added to the quartz boat, and the quartz boat is placed in a tube furnace, and the temperature is raised at a certain rate, in the present application, the temperature is preferably raised and lowered in stages, which is more conducive to protecting the skeleton structure of the ZIF-67@foam nickel material, the temperature is raised at a rate of 6-10℃ / min when the temperature is lower than 500℃, and the temperature is raised at a rate of 2-5℃ / min when the temperature is higher than 500℃, and the temperature is kept constant after the temperature is raised to the target temperature; after the reaction is completed, the temperature is lowered at a rate of 3-5℃ / min when the temperature is higher than 500℃, and the temperature is naturally cooled when the temperature is lower than 500℃, then the product is placed in a vacuum drying oven at 60℃ for storage.

[0063] It should be noted that, in the present application, before the phosphating reaction and molten salt heat treatment, nitrogen can be introduced into the reactor to expel oxygen, and the nitrogen is introduced for 25-35min, which can avoid oxidation of the ZIF-67@foam nickel material.

[0064] The present application also provides a phosphorized cobalt water electrolysis catalyst prepared by the preparation method described in any one of the above.

[0065] In order to more clearly illustrate the technical solutions and advantages of the present application, the following describes in detail a phosphorized cobalt water electrolysis catalyst and a preparation method thereof through several embodiments.

[0066] Example 1:

[0067] (1) 40mL of 2mol / L hydrochloric acid is prepared into a polyvinylpyrrolidone solution with a mass concentration of 1% by adding polyvinylpyrrolidone with a relative molecular mass of 80,000, 1×2cm foam nickel is soaked in the polyvinylpyrrolidone solution, ultrasonic reaction is carried out at 25℃ for 30min, then the foam nickel is taken out of the polyvinylpyrrolidone solution and washed with deionized water for 3 times, and dried in a vacuum oven at 60℃ for 6h to obtain modified foam nickel;

[0068] (2) 5.8206 g of cobalt nitrate hexahydrate was dissolved in 200 mL of anhydrous methanol to obtain a cobalt nitrate hexahydrate solution, 6.5683 g of 2-methylimidazole was dissolved in 200 mL of anhydrous methanol to obtain a 2-methylimidazole solution, the 2-methylimidazole solution was slowly poured into the cobalt nitrate hexahydrate solution, after ultrasonic reaction at 25℃ for 30 min, standing for 24 h, a mixed solution was obtained, the modified nickel foam was taken out from the mixed solution, washed with methanol for 3 times, and dried in a vacuum oven at 60℃ for 12 h to obtain a metal organic framework ZIF-67@nickel foam material; wherein the molar ratio of cobalt nitrate hexahydrate to 2-methylimidazole is 1:4;

[0069] (3) A quartz boat containing 1 g of sodium hypophosphite powder was placed at the upstream of the tube furnace, and the metal organic framework ZIF-67@nickel foam material was placed at the downstream of the tube furnace, after nitrogen was introduced for 30 min, the tube furnace was heated to 300℃ at a heating rate of 10℃ / min, and reacted for 2 h, and then naturally cooled to room temperature 25℃, washed with deionized water and anhydrous ethanol for 3 times respectively, and dried in a vacuum oven at 60℃ for 12 h to obtain a cobalt phosphide electrolytic water catalyst, denoted as ZIF-67 / NF-1-300*1P.

[0070] Example 2:

[0071] Example 2 is basically the same as Example 1, except that in step (1), when preparing the modified nickel foam, the relative molecular mass of the polyvinylpyrrolidone is 580,000; denoted as ZIF-67 / NF-2-300*1P.

[0072] Example 3:

[0073] Example 3 is basically the same as Example 1, except that in step (1), when preparing the modified nickel foam, the relative molecular mass of the polyvinylpyrrolidone is 220,000, denoted as ZIF-67 / NF-3-300*1P.

[0074] Example 4:

[0075] Example 4 is basically the same as Example 1, except that in step (1), when preparing the modified nickel foam, the relative molecular mass of the polyvinylpyrrolidone is 1,300,000, denoted as ZIF-67 / NF-4-300*1P.

[0076] Figures 1 to 4The surface morphology images of the metal-organic framework ZIF-67@nickel foam prepared in Examples 1 to 4 are shown respectively. As can be seen from the figures, the ZIF-67 grown on nickel foam treated with polyvinylpyrrolidone of different relative molecular masses in Examples 1 to 4 are all dodecahedrons with sharp edges, and their sizes are distributed in the range of 500-800, 700-800, 700-1000 and 800-1200 nm respectively. It can be seen that the larger the relative molecular mass of polyvinylpyrrolidone used to treat nickel foam, the larger the size of ZIF-67 on its surface.

[0077] Depend on Figure 7 It can be seen that the charge transfer resistance of the cobalt phosphide catalyst surface in Examples 1 to 4 is 5.970Ω, 43.298Ω, 63.454Ω, and 100.095Ω, respectively. With the decrease in the relative molecular mass of polyvinylpyrrolidone, the charge transfer resistance of the cobalt phosphide catalyst surface decreases, and the hydrogen evolution performance improves. Within the non-Radial region of 0.2–0.3 V vs. RHE, the double-layer capacitance of the cobalt phosphide catalyst in Examples 1 to 4 is estimated using cyclic voltammetry curves. Figure 8 It can be seen that the double-layer capacitance values ​​in Examples 1 to 4 are 21.11 mF·cm. -2 3.94 mF·cm -2 3.14 mF·cm -2 and 2.88mF·cm -2 As the relative molecular mass of polyvinylpyrrolidone decreases, the double-layer capacitance of the cobalt phosphide catalyst increases, thus improving the hydrogen evolution performance. The cobalt phosphide catalysts prepared in Examples 1 to 4 exhibit good alkaline hydrogen evolution performance.

[0078] Depend on Figure 9 It can be seen that the cobalt phosphide catalyst in Examples 1 to 4 reaches 10 mA·cm⁻¹. -2 The overpotentials of the current densities were 384 mV, 393 mV, 386 mV and 401 mV, respectively. It can be seen that the cobalt phosphide catalysts prepared in Examples 1 to 4 of the present invention have good oxygen evolution activity.

[0079] Example 5:

[0080] Example 5 is basically the same as Example 1, except that in step (3), the sodium hypophosphite powder is 0.5g, denoted as ZIF-67 / NF-1-300*0.5P.

[0081] Hydrogen evolution performance: The cobalt phosphide catalyst prepared in Example 5 exhibits hydrogen evolution performance at a current density of 10 mA·cm⁻¹. -2 In Example 5, the overpotential was 146 mV and the current density was 100 mA·cm⁻¹. -2At that time, the overpotential was 440mV, and the Tafel slope was 130.1mV·dec. -1 Oxygen evolution performance: The cobalt phosphide catalyst prepared in Example 5 exhibits performance at a current density of 10 mA·cm⁻¹. -2 In Example 5, the overpotential was 398 mV and the current density was 100 mA·cm⁻¹. -2 At that time, the overpotential was 609 mV, and the Tafel slope was 63.3 mV·dec. -1 .

[0082] Example 6:

[0083] Example 6 is basically the same as Example 1, except that in step (3), when preparing the cobalt phosphide water electrolysis catalyst, a quartz boat containing 1g of sodium hypophosphite powder is placed upstream of the tube furnace, and the catalyst precursor is located downstream of the tube furnace. After nitrogen gas is introduced for 35min, the tube furnace is heated to 500℃ at a heating rate of 10℃ / min, and the reaction is kept at a constant temperature for 2h. After natural cooling to room temperature of 25℃, it is washed three times with deionized water and anhydrous ethanol, and dried in a vacuum oven at 60℃ for 12h to obtain the cobalt phosphide water electrolysis catalyst, which is denoted as ZIF-67 / NF-1-500*1P.

[0084] Hydrogen evolution performance: The cobalt phosphide catalyst prepared in Example 6 exhibits hydrogen evolution performance at a current density of 10 mA·cm⁻¹. -2 In Example 6, the overpotential was 270 mV and the current density was 100 mA·cm⁻¹. -2 At that time, the overpotential was 624 mV, and the Tafel slope was 188.9 mV·dec. -1 Oxygen evolution performance: The cobalt phosphide catalyst prepared in Example 6 exhibits performance at a current density of 10 mA·cm⁻¹. -2 In Example 6, the overpotential was 380mV and the current density was 100mA·cm. -2 At that time, the overpotential was 603 mV, and the Tafel slope was 62.0 mV·dec. -1 .

[0085] Example 7:

[0086] (1) Polyvinylpyrrolidone with a relative molecular mass of 0.8 million was added to 40 mL of 2 mol / L hydrochloric acid to prepare a polyvinylpyrrolidone solution with a mass concentration of 1%. A 1×2 cm piece of nickel foam was immersed in the polyvinylpyrrolidone solution and ultrasonically reacted at 25 °C for 30 min. The nickel foam was then removed from the polyvinylpyrrolidone solution and rinsed three times with deionized water. It was then dried in a vacuum oven at 60 °C for 6 h to obtain modified nickel foam.

[0087] (2) mixed solution was obtained, the modified foam nickel was added into the mixed solution, after ultrasonic reaction for 30 min at 25℃, the modified foam nickel was taken out from the mixed solution, washed with methanol for 3 times, dried in a vacuum oven at 60℃ for 12 h, to obtain a metal organic framework ZIF-67@foam nickel material; wherein the molar ratio of the cobalt nitrate hexahydrate and 2-methylimidazole was 1:4;

[0088] (3) 1.6191 g of potassium chloride and 1.3809 g of lithium chloride were mixed and ground to obtain a molten salt medium, the metal organic framework ZIF-67@foam nickel material was placed in a quartz boat, and the molten salt medium was added, the quartz boat was placed in the middle section of the tube furnace, after nitrogen was introduced for 30 min, the tube furnace was heated to 400℃ at a heating rate of 10℃ / min, and reacted for 2 h, then cooled to room temperature 25℃ at a rate of 5℃ / min, washed with deionized water and anhydrous ethanol for 3 times respectively, and dried in a vacuum oven at 60℃ for 12 h, to obtain a catalyst precursor;

[0089] (4) a quartz boat containing 1 g of sodium hypophosphite powder was placed upstream of the tube furnace, and the catalyst precursor was placed downstream of the tube furnace, after nitrogen was introduced for 30 min, the tube furnace was heated to 300℃ at a heating rate of 10℃ / min, and reacted for 2 h, then naturally cooled to room temperature 25℃, washed with deionized water and anhydrous ethanol for 3 times respectively, and dried in a vacuum oven at 60℃ for 12 h, to obtain a cobalt phosphide electrolytic water catalyst, denoted as ZIF-67 / NF-1-400s-300*1P.

[0090] Example 8:

[0091] Example 8 was basically the same as Example 7, except that in step (3), when preparing the catalyst precursor, the tube furnace was first heated to 500℃ at a heating rate of 10℃ / min, then heated to 600℃ at a heating rate of 2℃ / min, reacted for 2 h at 600℃, first cooled to 500℃ at a rate of 5℃ / min, then naturally cooled to room temperature 25℃, washed with deionized water and anhydrous ethanol for 3 times respectively, and dried in a vacuum oven at 60℃ for 12 h, to obtain a catalyst precursor, denoted as ZIF-67 / NF-1-600s-300*1P.

[0092] Example 9:

[0093] Example 9 is basically the same as Example 7, except that in step (3), when preparing the catalyst precursor, the tube furnace is first heated to 500°C at a heating rate of 8°C / min, and then heated to 800°C at a heating rate of 4°C / min. The reaction is kept at 800°C for 2 hours. The temperature is first lowered to 500°C at a rate of 5°C / min, and then naturally cooled to room temperature of 25°C. The tube furnace is washed three times with deionized water and anhydrous ethanol, and then dried in a vacuum oven at 60°C for 12 hours to obtain the catalyst precursor, which is denoted as ZIF-67 / NF-1-800s-300*1P.

[0094] Figures 11 to 14 The hydrogen evolution performance and oxygen evolution performance of the cobalt phosphide catalysts prepared in Examples 7 to 9 are shown in the graphs. Figures 11 to 12 As can be seen from this, at a current density of 10 mA·cm -2 At that time, the overpotentials in Examples 7 to 9 were 211, 205, and 181 mV, respectively, and 100 mA·cm⁻¹. -2 At the given current densities, the required overpotentials are 516, 492, and 466 mV, respectively, with Tafel slopes of 155.5, 142.3, and 132.8 mV·dec, respectively. -1 As the molten salt heat treatment temperature increases, the hydrogen evolution performance of the prepared catalyst gradually improves; Figures 13 to 14 It can be seen that at 10mA·cm -2 At the given current density, the overpotentials of the catalysts in Examples 7 to 9 were 437, 433, and 437 mV, respectively, with corresponding Tafel slopes of 70.8, 76.4, and 71.4 mV·dec. -1 As the molten salt heat treatment temperature increases, the oxygen evolution performance of the prepared catalyst gradually improves.

[0095] Example 10:

[0096] Example 10 is basically the same as Example 7, except that in step (3), the metal-organic framework ZIF-67@nickel foam material is placed in the middle section of a tube furnace, nitrogen is introduced for 30 min, the tube furnace is heated to 800°C at a heating rate of 10°C / min, and the reaction is kept at a constant temperature for 2 h. The temperature is then reduced to room temperature of 25°C at a rate of 5°C / min. The material is washed three times with deionized water and anhydrous ethanol, and dried in a vacuum oven at 60°C for 12 h to obtain the catalyst precursor, denoted as ZIF-67 / NF-1-800-300*1P.

[0097] Hydrogen evolution performance: The cobalt phosphide catalyst prepared in Example 10 exhibits hydrogen evolution performance at a current density of 10 mA·cm⁻¹. -2 At that time, the overpotential in Example 10 was 259mV and the current density was 100mA·cm. -2The overpotential is 570 mV and the Tafel slope value is 164.1 mV·dec -1 ; oxygen evolution performance: the overpotential of the cobalt phosphide catalyst prepared in Example 10 is 481 mV and the Tafel slope value is 74.4 mV·dec -2 at a current density of 10 mA·cm -1 .

[0098] Comparative Example 1:

[0099] (1) 5.8206 g of cobalt nitrate hexahydrate was dissolved in 200 mL of anhydrous methanol to obtain a cobalt nitrate hexahydrate solution, 6.5683 g of 2-methylimidazole was dissolved in 200 mL of anhydrous methanol to obtain a 2-methylimidazole solution, the 2-methylimidazole solution was slowly poured into the cobalt nitrate hexahydrate solution, and after ultrasonic reaction at 25℃ for 30 min, it was placed for 24 h, centrifuged at 6000 r / min for 5 min, washed with methanol for 3 times, and dried in a vacuum oven at 60℃ for 12 h to obtain metal organic framework ZIF-67; wherein the molar ratio of cobalt nitrate hexahydrate to 2-methylimidazole is 1:4;

[0100] (2) A quartz boat containing 1 g of sodium hypophosphite powder was placed upstream of the tube furnace, and the metal organic framework ZIF-67 was placed downstream of the tube furnace, nitrogen was introduced for 30 min, the tube furnace was heated to 300℃ at a heating rate of 10℃ / min, and reacted for 2 h, and then naturally cooled to room temperature 25℃, washed with deionized water and anhydrous ethanol for 3 times, and dried in a vacuum oven at 60℃ for 12 h to obtain a cobalt phosphide electrolytic water catalyst, denoted as ZIF-67-300*1P.

[0101] Hydrogen evolution performance: the overpotential of the cobalt phosphide catalyst prepared in Comparative Example 1 is 351 mV and the Tafel slope value is 203.9 mV·dec -2 at a current density of 10 mA·cm -1 . Comparative Example 2:

[0102] Comparative Example 2 is basically the same as Example 7, except that in step (2), the foam nickel used is foam nickel that has not been modified with polyvinylpyrrolidone, denoted as ZIF-67 / NF-300*1P.

[0103] Comparative Example 3:

[0104] A quartz boat containing 1g of sodium hypophosphite powder was placed upstream of a tube furnace, and a 1×2cm piece of nickel foam was placed downstream of the tube furnace. After purging with nitrogen for 30 minutes, the tube furnace was heated to 300℃ at a heating rate of 10℃ / min and reacted at a constant temperature for 2 hours. The mixture was then naturally cooled to room temperature of 25℃, rinsed three times with deionized water and anhydrous ethanol, and dried in a vacuum oven at 60℃ for 12 hours to obtain the water electrolysis catalyst, denoted as NF-300*1P.

[0105] Depend on Figure 9 It can be seen that the catalysts prepared in Comparative Examples 2 and 3 reach 10 mA·cm⁻¹. -2 The overpotentials of the current densities were 349 mV and 343 mV, respectively.

[0106] The electrochemical performance of the catalysts in Examples 1 to 10 and Comparative Examples 1 to 4 was tested, and the test results are shown in Table 1.

[0107] The specific testing methods are as follows: Electrochemical tests were all conducted using the Chenhua electrochemical workstation CHI660E at room temperature. To avoid the influence of oxygen in the electrolyte on the electrode performance test results, a 10 mL / min solution was used before testing. -1 Nitrogen gas was introduced into the electrolyte at a rate of 30 min. The catalytic performance of the catalyst for HER and OER was characterized using a standard three-electrode system; total water splitting was performed using a two-electrode system. In the three-electrode system, the reference electrode was Ag / AgCl(E) Ag / AgCl =0.223V vsNHE), with a Pt plate as the counter electrode. Tests were conducted in alkaline (1M KOH) and acidic (0.5M H2SO4) electrolyte solutions, respectively. The potential measured by the electrochemical workstation (vs Ag / AgCl) was converted to the electrode potential relative to the reversible hydrogen electrode (RHE) using the following equation.

[0108] E vs RHE =E apply -rE Ag / AgCl (vs NHE) + 0.0592 × pH

[0109] Among them, E vs RHE is the electrode potential relative to RHE after the conversion, E apply The potential value applied to the electrochemical workstation relative to Ag / AgCl, E Ag / AgCl (vs NHE) represents the electrode potential of the Ag / AgCl reference electrode relative to NHE, and pH represents the pH value of the electrolyte.

[0110] Table 1

[0111]

[0112]

[0113] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the same. Although the present application has been described in detail with reference to the foregoing examples, those of ordinary skill in the art will understand that they can still modify the technical solutions described in the foregoing examples, or make equivalent replacements for some of the technical features therein. Such modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a cobalt phosphide catalyst for electrolysis of water, characterized by, The preparation method comprises the following steps: (1) soaking the foamed nickel in a polyvinylpyrrolidone solution, and obtaining modified foamed nickel after reaction; the relative molecular mass of the polyvinylpyrrolidone in the polyvinylpyrrolidone solution is 0.8-1.3 million; (2) mixing a cobalt nitrate hexahydrate solution and a 2-methylimidazole solution to obtain a mixed solution, and adding the modified foamed nickel into the mixed solution, and obtaining a metal organic framework ZIF-67@foamed nickel material after reaction; (3) under a nitrogen atmosphere, performing a separated gas phosphating reaction on the metal organic framework ZIF-67@foamed nickel material to obtain the cobalt phosphide electrolytic water catalyst; before step (3), a step of heating the metal organic framework ZIF-67@foamed nickel material in a molten salt medium under a nitrogen atmosphere is further included; the molten salt medium comprises potassium chloride and lithium chloride, wherein the molar ratio of the potassium chloride to the lithium chloride is (1-10):(10-1); the heating reaction is performed at a temperature of 500-800 DEG C for 1.5-2.5 h.

2. The production method according to claim 1, characterized by, In step (1): The solvent of the polyvinylpyrrolidone solution is hydrochloric acid; the mass concentration of the polyvinylpyrrolidone solution is 1-30%; and the relative molecular mass of the polyvinylpyrrolidone is 0.8-220,000.

3. The preparation method according to claim 1, characterized in that, In step (1): The reaction is performed at a temperature of 25-30 DEG C for 25-35 min; and the reaction is performed under ultrasonic conditions of 20-40 kHz.

4. The method of claim 1, wherein, In step (2): The solvents of the cobalt nitrate hexahydrate solution and the 2-methylimidazole solution are both anhydrous methanol; The molar ratio of the cobalt nitrate hexahydrate to the 2-methylimidazole is 1:(1-10).

5. The preparation method according to claim 1, characterized in that, In step (2): The reaction is performed at a temperature of 25-30 DEG C for 25-35 min; and the reaction is performed under ultrasonic conditions.

6. The method of claim 1, wherein, In step (3): The phosphating agent used in the separated gas phosphating reaction is sodium hypophosphite; the phosphating reaction is performed at a temperature of 300-500 DEG C for 1.5-2.5 h, and the temperature rising rate is 8-12 DEG C / min.

7. The preparation method according to claim 1, characterized in that: The temperature rising rate of the heating reaction is 2-10 DEG C / min.

8. A cobalt phosphide water electrolysis catalyst characterized in that, The preparation method is prepared by the preparation method in any one of claims 1-7.

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