A kind of NiCo 2 O 4 Preparation method of catalyst, NiCo 2 O 4 Catalyst and its application

Abstract

The present invention discloses a preparation method of a NiCo2O4 catalyst, comprising the following steps: (1) dissolving nickel salt and cobalt salt to obtain a homogeneous solution; enabling ammonia volatilized from a first container filled with ammonia water to contact the surface of the homogeneous solution and undergo homogeneous precipitation on the surface of the homogeneous solution; (2) after the homogeneous precipitation reaction ends, performing solid-liquid separation to collect the solid-phase product, and obtaining a precursor through washing, drying, and grinding; (3) performing calcination treatment on the precursor obtained in step (2), thereby obtaining the NiCo2O4 catalyst. The present invention also provides a NiCo2O4 catalyst prepared by the above preparation method and its application. The preparation method of the present invention is based on the preparation of the NiCo2O4 catalyst through gas-liquid interface contact. The preparation process is based on the diffusion of ammonia gas from the gas phase to the liquid phase to cause homogeneous precipitation of nickel and cobalt ions, and the catalytic performance of the product after calcination is good.

Description

Technical Field

[0001] The present invention belongs to the field of catalytic materials, and particularly relates to a preparation method of an electrolytic water hydrogen production catalyst, an electrolytic water hydrogen production catalyst and an application thereof. Background Art

[0002] Energy and environmental problems are two major problems plaguing human society at present. Electrolysis of water is one of the most common and effective methods for hydrogen production. The decomposition of water consists of two half-reactions: HER (hydrogen evolution reaction) at the cathode and OER at the anode. Among them, OER is one of the key reactions in electrolysis of water, which is a four-electron transfer step and has slow kinetics. At present, noble metal Ir-based or Ru-based materials (such as IrO 2 and RuO 2 ) are considered to be the most efficient catalysts for the OER process. However, their low reserves, high prices and poor stability seriously hinder their large-scale applications. Transition metal oxides are inexpensive, have high reserves and good OER performance, and are expected to be good substitutes for noble metals. Among them, spinel-type transition metal oxides have been widely studied due to their advantages such as multiple oxidation-reduction states, good electrochemical stability, high reserves and low cost. The single spinel-type oxide Co 3 O 4 is one of the representatives, with an overpotential generally of 400 - 500 mV and a Tafel slope generally of 100 - 160 mV / dec, having good performance. However, its conductivity is poor, and the adsorption energy for oxygen evolution intermediates can be further optimized and improved, which makes its overpotential still high and the kinetics slow when used as an electrolytic water oxygen evolution catalyst. For NiO, although its raw materials are more inexpensive and easily available compared to Co 3 O 4 , there are few studies on using it for electrolysis of water, mainly because the overpotentials of both HER and OER are very high, greater than 500 mV, and the kinetics are extremely slow, resulting in serious energy loss when used for electrolysis of water.

[0003] NiCo 2 O 4 As a binary metal oxide, it combines the advantages of Co 3 O 4 and NiO, with an overpotential as low as 300 - 400 mV and a Tafel slope generally of 80 - 120 mV / dec. The reason may be that nickel replaces cobalt at the tetrahedral sites of Co 3 O 4 , thereby improving the charge distribution around cobalt, enhancing the conductivity of Co 3 O 4 , and optimizing the adsorption energy for oxygen evolution intermediates. The performance of NiCo 2 O 4 is better than that of Co 3 O4 and NiO are excellent, but it is difficult to synthesize homogeneous phases, and a single Co is easily precipitated during calcination 3 O 4 and NiO, which affects the release of OER performance. In addition, the electrolysis of water occurs on the surface of the catalyst, so it is necessary to increase the surface area of the catalyst by adjusting the morphology and dispersion state of the catalyst to improve its performance. However, in traditional methods, such as liquid-phase precipitation and hydrothermal methods, the reaction rate of the precursor is too fast, the product is easily agglomerated, the specific surface area is small, and it is difficult to synthesize homogeneous products, and the electrocatalytic performance is difficult to reflect. Therefore, there is an urgent need to develop a NiCo 2 O 4 synthesis method Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology, and provide a method for preparing a NiCo 2 O 4 catalyst based on gas-liquid interface contact, which is homogeneous, has excellent morphology and good catalytic performance, a NiCo 2 O 4 catalyst and its application. To solve the above technical problems, the technical solution proposed by the present invention is as follows

[0005] A method for preparing a NiCo 2 O 4 catalyst, comprising the following steps

[0006] (1) Dissolve nickel salt and cobalt salt to obtain a homogeneous solution; make the ammonia volatilized from the first container containing ammonia contact the surface of the homogeneous solution and undergo homogeneous precipitation on the surface of the homogeneous solution, forming a solid-phase film on the surface of the homogeneous solution and forming powder precipitation in the homogeneous solution

[0007] (2) After the homogeneous precipitation reaction ends, separate the solid and liquid to collect the solid-phase product, and obtain the precursor through washing, drying and grinding

[0008] (3) Calcinate the precursor obtained in step (2), and the NiCo 2 O 4 catalyst is obtained

[0009] In the present invention, the reaction is carried out based on the principle of self-diffusion of ammonia gas, homogeneous precipitation occurs in the nickel and cobalt mixed solution, a solid-phase film is formed on the surface, and a mixed powder precipitate of hydroxides is formed in the solution; after a period of time, when the color of the solution fades, the reaction ends; the reaction equation is as follows

[0010] Ni 2+ +2Co 2+ +6NH 3 ·H2 O = Ni(OH) 2 ↓ + 2Co(OH) 2 ↓ + 6NH 4 + 。

[0011] In the above preparation method, preferably, when solid-liquid separation is carried out to collect the solid-phase product, only the powder precipitate formed in the homogeneous solution is collected. In the present invention, ammonia diffuses on the surface of the solution to form a solid-phase thin film. The gas-phase surface (the side close to the solution surface) of the solid-phase thin film is relatively dense, and the liquid-phase surface (the side close to the bottom of the solution) is a relatively loose lamellar structure perpendicular to the gas-phase surface. The gas-phase surface can limit the rate of ammonia diffusion into the main body of the solution and play a regulating role. The lamellar structure of the liquid-phase surface can provide nucleation sites and a stable and orderly ammonia diffusion channel for the precipitation reaction in the solution, which is an important condition for the occurrence of the homogeneous precipitation reaction and the formation of products with good morphology. The powder precipitate obtained thus has a more excellent and homogeneous morphology. However, our further research shows that there are significant differences in the properties between the solid-phase thin film and the powder precipitate. The gas-phase surface of the solid-phase thin film has a closely packed structure, and the structure of the gas-phase surface accounts for a large proportion in the whole thin film, which results in a small specific surface area and few active sites, and is not conducive to the export of oxygen during the electrolysis of water. The powder precipitate is a porous flower-like microsphere structure composed of sheet structures, with many pores, a large specific surface area, many active sites, and is easy to export oxygen during the electrolysis of water. Therefore, in the present invention, only the powder precipitate is taken as the precursor material. It should be emphasized that although the solid-phase thin film may not ultimately be used as a precursor, it plays a very important role in the homogeneous formation of the powder precipitate. Controlling the formation progress of the solid-phase thin film is beneficial to the homogeneous formation of the powder precipitate.

[0012] In the above preparation method, preferably, the solid-liquid separation to collect the solid-phase product includes the following steps: after the homogeneous precipitation reaction is completed, deionized water is slowly injected along the inner wall of the second container containing the homogeneous solution. When the solid-phase thin film in the second container rises above the top of the second container, the injection of deionized water is stopped. After standing for the powder precipitate to settle, the second container is then placed in a third container, and deionized water is slowly injected into the third container until the solid-phase thin film on the surface of the second container floats away from the second container. Then the second container is taken out for solid-liquid separation, and the powder precipitate is obtained. Since the homogeneity and morphology of the solid-phase thin film are inferior to those of the powder precipitate, and the solid-phase thin film is also brittle and will quickly settle after fragmentation, the separation method is inappropriate and extremely likely to cause the mixing of the solid-phase thin film and the powder precipitate, affecting the performance of the powder precipitate. The present invention uses the slow water addition and floating method to remove it, which can greatly avoid the mixing of the solid-phase thin film and the powder precipitate.

[0013] In the above preparation method, preferably, the ammonia volatilized from the first container containing ammonia water contacts the surface of the homogeneous solution in the following manner: a conduit is led out from the first container, the end of the conduit is connected to a funnel, the funnel is inverted under the surface liquid of the homogeneous solution, and a valve is installed in the conduit. Compared with other ammonia gas diffusion methods, the device of the present invention can control the volatilization rate of ammonia gas and thus the reaction rate by adjusting the valve and temperature. Through the regulation of the reaction rate and process by the valve, it is easy to prepare products with a relatively uniform size distribution, regular and uniform morphology. In addition, the above device can also direct the introduction of ammonia gas, improve the utilization rate of ammonia gas, eliminate many uncontrollable factors in the ammonia gas diffusion process, avoid the waste of ammonia gas and reduce environmental pollution. More importantly, compared with simply and roughly placing the container containing ammonia water and the container containing the reaction solution directly in a closed container, the diffusion rate of ammonia gas into the reaction solution is neither stable nor certain, the formation rate of the solid-phase film is slow and uneven, which will affect the function of the solid-phase film and the phase type of the powder precipitate. The directional introduction of ammonia gas adopted in the present invention can stably and continuously transport ammonia gas into the nickel-cobalt mixed solution, which is conducive to the rapid formation of the gas-liquid interface and the liquid-liquid interface, and is beneficial to the function of the gas-liquid interface and the liquid-liquid interface, which is conducive to the formation of homogeneous precipitation and the obtaining of a homogeneous precipitation bimetallic precursor. Moreover, the above device can ensure the formation of a solid-phase film at the middle position of the homogeneous solution, and there is a large operating space around the solid-phase film, which is more convenient for separating the solid-phase film, and the operation of injecting water in the previous separation step can be omitted, and the use of the third container can be saved.

[0014] In the above preparation method, preferably, the nickel salt includes any one of sulfate, nitrate, hydrochloride or acetate; the anion of the cobalt salt is the same as that of the nickel salt; the concentration of nickel ions in the homogeneous solution is 0.01 - 0.10 mol / L, and the concentration of cobalt ions is twice that of nickel ions. To ensure the formation of a homogeneous single precipitate, the anions of the nickel salt and the cobalt salt are preferably the same. If the concentration of the above nickel and cobalt ions is too high, the reaction is too fast, which will affect the morphology and dispersibility of the product; if the concentration is too low, the yield is too low.

[0015] In the above preparation method, preferably, the initial concentration of the ammonia water is 2 - 7 mol / L, and the molar amount of ammonia gas in the ammonia water is controlled to be 30 - 60 times that of the nickel salt. The amount of the above ammonia water needs to ensure the complete reaction of nickel and cobalt ions, but its concentration needs to be controlled. If the concentration is too low, the reaction is too slow; if the concentration is too high, the product particles generated are too large, which will affect the morphology of the product.

[0016] In the above preparation method, preferably, the reaction temperature of the homogeneous precipitation is controlled at 25 - 40 °C, and the reaction time is 2 - 3 h. If the above temperature is too low, the ammonia gas diffuses slowly and the reaction is too slow; if the temperature is too high, the reaction is too fast, and the product particles generated are too large, which will affect the morphology of the product.

[0017] In the above preparation method, preferably, during the calcination treatment, the calcination temperature is controlled at 350-400 °C, the heating rate is 2-5 °C / min, the calcination time is 2-4 h, and the atmosphere is an air atmosphere. The control of the above calcination temperature and heating rate has a great influence on the product morphology and phase composition. It is difficult to obtain a pure phase at a low calcination temperature. Too high a temperature will cause particle fragmentation, making it difficult to inherit the morphology and consuming too much energy. If the heating rate is too small, the required time is too long. If the heating rate is too large, the precursor structure will be damaged. If the calcination time is too short, the reaction is incomplete. If the calcination time is too long, the reaction will no longer occur and the energy consumption is too high.

[0018] As a general technical concept, the present invention also provides a NiCo prepared by the above preparation method 2 O 4 catalyst, wherein the NiCo 2 O 4 catalyst has a flower-like microsphere structure with a particle size of 2-5 μm and a specific surface area of 200-400 m 2 / g.

[0019] As a general technical concept, the present invention also provides an application of the above NiCo 2 O 4 catalyst in hydrogen production by electrolysis of water.

[0020] In the prior art, liquid phase precipitation and hydrothermal methods are mostly used for double metal coprecipitation, and it is difficult to achieve homogeneous precipitation of double metals. The present invention first proposes a method for uniform coprecipitation of double metals. Specifically: The present invention is based on gas-liquid interface contact to prepare NiCo 2 O 4 catalyst. The preparation process is based on the diffusion of ammonia gas from the gas phase to the liquid phase to cause homogeneous precipitation of nickel and cobalt ions, controlling the source of the reaction products, and adjusting the concentrations of ammonia water and the nickel-cobalt mixed solution can achieve the control of the reaction rate and the yield of the precursor. The formed precursor has a flower-like microsphere structure with a size distribution in the range of 2-5 μm, a large specific surface area of 200-400 m 2 / g. By low-temperature calcination in air, the final homogeneous product NiCo 2 O 4 can be formed. During calcination, single Co 3 O 4 and NiO will not precipitate. The morphology of the product after calcination is inherited, which can provide more active sites and a relatively good electronic structure, with good catalytic performance. The flower-like microsphere structure is also beneficial to the penetration of the electrolyte and the evolution of oxygen, which can reduce the resistance of the OER process, making it have a smaller overpotential. In an alkaline electrolyte, the OER overpotential is 250-300 mV and the Tafel slope is 60-80 mV / dec.

[0021] Compared with the prior art, the advantages of the present invention are as follows:

[0022] 1. The preparation method of the present invention is based on the preparation of NiCo 2 O 4 catalyst through gas-liquid interface contact. The preparation process is based on the diffusion of ammonia gas from the gas phase to the liquid phase, causing homogeneous precipitation of nickel and cobalt ions. The final product NiCo 2 O 4 can be obtained by low-temperature calcination in air. After calcination, the morphology of the product is inherited, and it has good catalytic performance. The OER overpotential in alkaline electrolyte is 250 - 300 mV, and the Tafel slope is 60 - 80 mV / dec.

[0023] 2. The preparation method of the present invention has the advantages of simple synthesis method, rapid reaction, high yield, and can synthesize binary metal oxide catalysts with high specific surface area and high activity for electrolyzing water. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0025] Figure 1 It is a schematic diagram of the experimental device used in the preparation method of the present invention.

[0026] Figure 2 It is the SEM image of the precursor prepared in Example 1.

[0027] Figure 3 It is the SEM image of NiCo 2 O 4 prepared in Example 2.

[0028] Figure 4 It is the XRD pattern of NiCo 2 O 4 prepared in Example 3.

[0029] Figure 5 It is the LSV curve of NiCo 2 O 4 prepared in Example 4.

[0030] Figure 6 It is the Tafel slope graph of NiCo 2 O 4 prepared in Example 5. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] For the convenience of understanding the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings of the specification and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0032] Unless otherwise defined, all the technical terms used hereinafter have the same meanings as those commonly understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0033] Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment, etc. used in the present invention can be obtained through market purchase or can be prepared by existing methods.

[0034] Example 1:

[0035] A preparation method of a NiCo 2 O 4 catalyst, comprising the following steps:

[0036] Preparation of NiCo 2 O 4 : Take 0.53 g of NiSO 4 ·6H 2 O, 1.12 g of CoSO 4 ·7H 2 O and place them in a beaker, add 40 mL of deionized water and stir to dissolve to form a homogeneous solution. Take another 4.3 mL of concentrated ammonia water (14 mol / L) and transfer it to a conical flask, then add 25.7 mL of ionized water to it and stir to make it uniform. The conical flask and the beaker are connected by a conduit and a funnel. The conduit is inserted into the conical flask, the funnel is inverted below the liquid level in the beaker, and the end of the funnel is connected to the other end of the conduit (as Figure 1 shown). React based on the principle of ammonia self-diffusion. Stop the reaction when the solution in the beaker tends to be colorless. React at 25 °C for about 3 h. At this time, a solid-phase film is formed on the surface of the homogeneous solution, and powder precipitation is formed in the homogeneous solution. Collect the powder precipitation, and then centrifuge and wash the powder precipitation in the beaker with deionized water and ethanol three times respectively, and then dry it in a vacuum drying oven at 70 °C. Take out the dried sample and grind it (the SEM diagram of the ground product is as Figure 2 shown), and finally calcine it at a constant temperature of 350 °C (5 °C / min) in an air atmosphere for 2 h to obtain the required product. Through XRD characterization, the product has complete crystallization and corresponds to the PDF card 73-1702, which is a pure phase of NiCo 2 O 4 ; Through BET characterization, its specific surface area is 321 m 2 / g; Characterized by SEM, its morphology is a flower-like microsphere structure with a particle size of about 3.3 μm. Compared with the precursor, the morphology is preserved. In this example, a third container can be introduced to separate the solid-phase thin film from the powder precipitate.

[0037] Preparation of the working electrode: Disperse the prepared catalyst (5 mg) in 1 mL of deionized water and 40 μL of Nafion, and ultrasonicate for 1 h to form a uniform catalyst suspension (ink). Then take 10 μL of the ink and drop it onto a polished glassy carbon electrode, and dry it under natural environmental conditions.

[0038] Electrochemical OER performance test: The test uses a standard three-electrode test system, with Hg / HgO as the reference electrode, a platinum wire as the counter electrode, and a glassy carbon electrode (φ = 3 mm) coated with the prepared catalyst as the working electrode. The electrolyte is 1.0 mol / L KOH solution, and all data are obtained without iR compensation testing. The linear sweep voltammetry (LSV) rate is 5 mV / s. All potentials in this article are calibrated as the reversible hydrogen electrode potential (RHE) according to E RHE = E Hg / HgO + 0.098 V + 0.059 × pH. The stability of the catalyst was tested using amperometric i-t curve parameters.

[0039] Example 2:

[0040] A preparation method of a NiCo 2 O 4 catalyst, comprising the following steps:

[0041] Preparation of NiCo 2 O 4 : Take 1.06 g of NiSO 4 ·6H 2 O, 2.24 g of CoSO 4 ·7H 2O was placed in a beaker, and 40 mL of deionized water was added and stirred to dissolve it to form a homogeneous solution. Another 10.0 mL of concentrated ammonia water (14 mol / L) was transferred to a conical flask, and then 36.6 mL of ionized water was added thereto and stirred to make it uniform. The conical flask and the beaker were connected by a conduit and a funnel. The conduit was inserted into the conical flask, the funnel was inverted below the liquid level in the beaker, and the end of the funnel was connected to the other end of the conduit. The reaction was carried out based on the principle of ammonia self-diffusion. The reaction was stopped when the solution in the beaker tended to be colorless. The reaction was carried out at 27 °C for about 2.5 h. At this time, a solid-phase film was formed on the surface of the homogeneous solution, and powder precipitates were formed in the homogeneous solution. The powder precipitates were collected, and then the powder precipitates in the beaker were centrifugally washed with deionized water and ethanol three times each, and then dried in a vacuum drying oven at 70 °C. The dried sample was taken out and ground, and finally calcined at 400 °C (4 °C / min) in an air atmosphere for 3 h to obtain the required product. By XRD characterization, the product had a complete crystal structure, corresponding to the PDF card 73-1702, and was a pure phase of NiCo 2 O 4 ; By BET characterization, its specific surface area was 398 m 2 / g; By SEM characterization (as Figure 3 shown), its morphology was a flower-like microsphere structure, and the particle size was about 2.5 μm.

[0042] Other steps were the same as those in Example 1.

[0043] Example 3:

[0044] A preparation method of a NiCo 2 O 4 catalyst, comprising the following steps:

[0045] (1) Preparation of NiCo 2 O 4 : Take 0.09 g of NiCl 2 ·6H 2 O, 0.19 g of CoCl 2 ·6H 2O was placed in a beaker, and 40 mL of deionized water was added and stirred to dissolve it to form a homogeneous solution. Another 1.1 mL of concentrated ammonia water (14 mol / L) was transferred to a conical flask, and then 2.9 mL of deionized water was added thereto and stirred to make it uniform. The conical flask and the beaker were connected by a conduit and a funnel. The conduit was inserted into the conical flask, the funnel was inverted below the liquid level in the beaker, and the end of the funnel was connected to the other end of the conduit. The reaction was carried out based on the principle of ammonia self-diffusion. The reaction was stopped when the solution in the beaker tended to be colorless. The reaction was carried out at 30 °C for about 2.5 h. At this time, a solid-phase film was formed on the surface of the homogeneous solution, and a powder precipitate was formed in the homogeneous solution. The powder precipitate was collected, and then the powder precipitate in the beaker was centrifugally washed with deionized water and ethanol three times respectively, and then dried in a vacuum drying oven at 70 °C. The dried sample was taken out and ground, and finally calcined at 350 °C (3 °C / min) in an air atmosphere for 4 h to obtain the required product. After XRD characterization (as Figure 4 shown), the product had a complete crystal structure, corresponding to the PDF card 73-1702, and was a pure phase NiCo 2 O 4 ; After BET characterization, its specific surface area was 346 m 2 / g; After SEM characterization, its morphology was a flower-like microsphere structure, and the particle size was about 2.9 μm.

[0046] Other steps were the same as those in Example 1.

[0047] Example 4:

[0048] A preparation method of a NiCo 2 O 4 catalyst, comprising the following steps:

[0049] (1) Preparation of NiCo 2 O 4 : Take 0.57 g of NiCl 2 ·6H 2 O, 1.14 g of CoCl 2 ·6H 2O was placed in a beaker, and 40 mL of deionized water was added and stirred to dissolve it to form a homogeneous solution. Another 7.7 mL of concentrated ammonia water (14 mol / L) was transferred to a conical flask, and then 13.9 mL of ionized water was added thereto and stirred to make it uniform. The conical flask and the beaker were connected by a conduit and a funnel. The conduit was inserted into the conical flask, the funnel was inverted below the liquid level in the beaker, and the end of the funnel was connected to the other end of the conduit. The reaction was carried out based on the principle of ammonia self-diffusion. After the solution in the beaker tended to be colorless, the reaction was stopped. The reaction was carried out at 32 °C for about 3 h. At this time, a solid-phase film was formed on the surface of the homogeneous solution, and powder precipitation was formed in the homogeneous solution. The powder precipitation was collected, and then the powder precipitation in the beaker was centrifugally washed three times with deionized water and ethanol respectively, and then dried in a vacuum drying oven at 70 °C. The dried sample was taken out and ground, and finally calcined at 400 °C (2 °C / min) in an air atmosphere for 2 h to obtain the required product. After XRD characterization, the product had complete crystallization and corresponded to the PDF card 73-1702, which was a pure phase NiCo 2 O 4 ; After BET characterization, its specific surface area was 278 m 2 / g; After SEM characterization, its morphology was a flower-like microsphere structure with a particle size of about 3.1 μm.

[0050] Other steps were the same as those in Example 1.

[0051] Figure 5 is the NiCo prepared in this example 2 O 4 LSV curve. It can be seen from the figure that: when the current density was 10 mA / cm 2 , the corresponding overpotential was 289 mV, and when the current density was 100 mA·cm -2 , the corresponding overpotential was 378 mV.

[0052] Example 5:

[0053] A preparation method of a NiCo 2 O 4 catalyst, comprising the following steps:

[0054] (1) Preparation of NiCo 2 O 4 : Take 0.23 g of Ni(NO 3 ) 2 ·6H 2 O, 0.47 g of Co(NO 3 ) 2 ·6H 2O was placed in a beaker, and 40 mL of deionized water was added and stirred to dissolve it to form a homogeneous solution. Another 2.9 mL of concentrated ammonia water (14 mol / L) was transferred to a conical flask, and then 3.8 mL of ionized water was added thereto and stirred to make it uniform. The conical flask and the beaker were connected by a conduit and a funnel. The conduit was inserted into the conical flask, the funnel was inverted below the liquid surface in the beaker, and the end of the funnel was connected to the other end of the conduit. The reaction was carried out based on the principle of ammonia self-diffusion. The reaction was stopped when the solution in the beaker tended to be colorless. The reaction was carried out at 40 °C for about 2 h. At this time, a solid-phase film was formed on the surface of the homogeneous solution, and a powder precipitate was formed in the homogeneous solution. The powder precipitate was collected, and then the powder precipitate in the beaker was centrifugally washed three times with deionized water and ethanol respectively, and then dried in a vacuum drying oven at 70 °C. The dried sample was taken out and ground, and finally calcined at 400 °C (5 °C / min) in an air atmosphere for 4 h to obtain the required product. By XRD characterization, the product had a complete crystal structure, corresponding to the PDF card 73-1702, and was a pure phase NiCo 2 O 4 ; By BET characterization, its specific surface area was 333 m 2 / g; By SEM characterization, its morphology was a flower-like microsphere structure, and the particle size was about 4.3 μm.

[0055] Other steps were the same as those in Example 1.

[0056] Figure 6 This was the NiCo prepared in this example 2 O 4 Tafel slope diagram. It can be seen from the figure that the Tafel slope was 74 mV / dec.

[0057] Example 6:

[0058] A preparation method of a NiCo 2 O 4 catalyst, comprising the following steps:

[0059] (1) Preparation of NiCo 2 O 4 : Take 0.81 g of Ni(NO 3 ) 2 ·6H 2 O, 1.63 g of Co(NO 3 ) 2 ·6H 2O was placed in a beaker, and 40 mL of deionized water was added and stirred to dissolve it to form a homogeneous solution. Another 11.0 mL of concentrated ammonia water (14 mol / L) was transferred to a conical flask, and then 11.0 mL of ionized water was added thereto and stirred to make it uniform. The conical flask and the beaker were connected by a conduit and a funnel. The conduit was inserted into the conical flask, the funnel was inverted below the liquid surface in the beaker, and the end of the funnel was connected to the other end of the conduit. The reaction was carried out based on the principle of ammonia self-diffusion. The reaction was stopped when the solution in the beaker tended to be colorless. The reaction was carried out at 35 °C for about 2 h. At this time, a solid-phase film was formed on the surface of the homogeneous solution, and a powder precipitate was formed in the homogeneous solution. The powder precipitate was collected, and then the powder precipitate in the beaker was centrifugally washed three times with deionized water and ethanol respectively, and then dried in a vacuum drying oven at 70 °C. The dried sample was taken out and ground, and finally calcined at 350 °C (4 °C / min) in an air atmosphere for 3 h to obtain the required product. After XRD characterization, the product had a complete crystal structure, corresponding to the PDF card 73-1702, and was a pure phase NiCo 2 O 4 ; After BET characterization, its specific surface area was 333 m 2 / g; After SEM characterization, its morphology was a flower-like microsphere structure, and the particle size was about 2.9 μm.

[0060] Other steps were the same as those in Example 1.

[0061] Example 7:

[0062] A preparation method of a NiCo 2 O 4 catalyst, comprising the following steps:

[0063] (1) Preparation of NiCo 2 O 4 : Take 0.30 g of (CH 3 COO) 2 Ni·4H 2 O, 0.60 g of (CH 3 COO) 2 Co·4H 2O was placed in a beaker, and 40 mL of deionized water was added and stirred to dissolve it to form a homogeneous solution. Another 5.0 mL of concentrated ammonia water (14 mol / L) was transferred to a conical flask, and then 5.0 mL of ionized water was added thereto and stirred to make it uniform. The conical flask and the beaker were connected by a conduit and a funnel. The conduit was inserted into the conical flask, the funnel was inverted below the liquid level in the beaker, and the end of the funnel was connected to the other end of the conduit. The reaction was carried out based on the principle of ammonia self-diffusion. The reaction was stopped when the solution in the beaker tended to be colorless. The reaction was carried out at 37 °C for about 2 h. At this time, a solid-phase film was formed on the surface of the homogeneous solution, and a powder precipitate was formed in the homogeneous solution. The powder precipitate was collected, and then the powder precipitate in the beaker was centrifugally washed three times with deionized water and ethanol respectively, and then dried in a vacuum drying oven at 70 °C. The dried sample was taken out and ground, and finally calcined at 400 °C (4 °C / min) in an air atmosphere for 2 h to obtain the required product. After XRD characterization, the product had a complete crystal structure and corresponded to the PDF card 73-1702, which was a pure phase of NiCo 2 O 4 ; After BET characterization, its specific surface area was 364 m 2 / g; After SEM characterization, its morphology was a flower-like microsphere structure, and the particle size was about 3.5 μm.

[0064] Other steps were the same as those in Example 1.

[0065] Example 8:

[0066] A preparation method of a NiCo 2 O 4 catalyst, comprising the following steps:

[0067] (1) Preparation of NiCo 2 O 4 : Take 0.80 g of (CH 3 COO) 2 Ni·4H 2 O, 1.60 g of (CH 3 COO) 2 Co·4H 2O was placed in a beaker, and 40 mL of deionized water was added and stirred to dissolve it to form a homogeneous solution. Another 9.0 mL of concentrated ammonia water (14 mol / L) was transferred to a conical flask, and then 21.0 mL of ionized water was added thereto and stirred to make it uniform. The conical flask and the beaker were connected by a conduit and a funnel. The conduit was inserted into the conical flask, the funnel was inverted below the liquid surface in the beaker, and the end of the funnel was connected to the other end of the conduit. The reaction was carried out based on the principle of ammonia self-diffusion. The reaction was stopped after the solution in the beaker tended to be colorless. The reaction was carried out at 33 °C for about 3 h. At this time, a solid-phase thin film was formed on the surface of the homogeneous solution, and a powder precipitate was formed in the homogeneous solution. The powder precipitate was collected, and then the powder precipitate in the beaker was centrifugally washed three times with deionized water and ethanol respectively, and then dried in a vacuum drying oven at 70 °C. The dried sample was taken out and ground, and finally calcined at 350 °C (5 °C / min) in an air atmosphere for 3 h to obtain the required product. By XRD characterization, the product had complete crystallization and corresponded to the PDF card 73-1702, and was a pure phase of NiCo 2 O 4 ; By BET characterization, its specific surface area was 333 m 2 / g; By SEM characterization, its morphology was a flower-like microsphere structure, and the particle size was about 4.3 μm.

[0068] Other steps were the same as those in Example 1.

[0069] Example 9:

[0070] A preparation method of a NiCo 2 O 4 catalyst, comprising the following steps:

[0071] The reaction conditions were the same as those in Example 2. After the reaction ended, the solid-phase thin film and the powder precipitate were collected respectively, and then the solid-phase thin film and the powder precipitate in the beaker were centrifugally washed three times with deionized water and ethanol respectively, and then dried in a vacuum drying oven at 70 °C. The dried sample was taken out and ground, and finally calcined at 400 °C (4 °C / min) in an air atmosphere for 3 h to obtain the required product. By XRD characterization, both the solid-phase thin film and the powder had complete crystallization and corresponded to the PDF card 73-1702, and were a pure phase of NiCo 2 O 4 ; By BET characterization, the specific surface area of the solid-phase thin film was 123 m 2 / g, and the specific surface area of the powder precipitate was 398 m 2 / g; By SEM characterization, the morphology of the powder was a flower-like microsphere structure, the particle size was about 2.5 μm, the gas-phase surface of the thin film was a closely packed structure, and the liquid-phase surface was a lamellar structure growing perpendicular to the gas-phase surface.

[0072] The same test steps as those in Example 1 were adopted for the product obtained by calcining the solid-phase thin film, and the results are shown in Table 1 below.

[0073] Comparative Example 1:

[0074] A preparation method of NiCo 2 O 4 catalyst, comprising the following steps:

[0075] Take 1.45 g of Ni(NO 3 ) 2 ·6H 2 O, 2.91 g of Co(NO 3 ) 2 ·6H 2 O and 2.10 g of urea and dissolve them in 20 mL of deionized water in sequence to form a mixed solution. After stirring the mixed solution in a magnetic stirrer for 1 h, transfer it to a 50 mL stainless steel reaction kettle with a polytetrafluoroethylene lining. After sealing, react at 120 °C for 12 h. Subsequently, rinse the product with water and absolute ethanol several times. After separating the product, dry it in a vacuum drying oven at 60 °C for 12 h. Then, put the product into a muffle furnace again and heat it from room temperature to 350 °C at a heating rate of 2 °C / min and hold for 2 h to obtain NiCo 2 O 4 . Characterized by XRD, the product has a complete crystal structure, corresponding to the PDF card 73 - 1702, but there are impurity peaks of NiO; characterized by BET, its specific surface area is 178 m 2 / g; characterized by SEM, its morphology is a nanoneedle structure, the diameter of the nanoneedles is about 5 nm, and the length is about 14 μm.

[0076] The electrochemical test steps are the same as those in Example 1.

[0077] Comparative Example 2:

[0078] A preparation method of NiCo 2 O 4 catalyst, comprising the following steps:

[0079] (1) Preparation of NiCo 2 O 4 : Take 0.53 g of NiSO 4 ·6H 2 O, 1.12 g of CoSO 4 ·7H 2O was placed in a beaker, and 40 mL of deionized water was added and stirred to dissolve it to form a homogeneous solution. Another 8.6 mL of concentrated ammonia water (14 mol / L) was transferred to another beaker, and then 21.5 mL of deionized water was added thereto and stirred to make it uniform. The two beakers were placed in a closed container for reaction. The reaction was carried out based on the principle of ammonia self-diffusion. The reaction was stopped after the solution in the beaker containing the nickel-cobalt mixed solution tended to be colorless. The reaction was carried out at 25 °C for about 4 h. The precipitate in the beaker was collected, and then the precipitate in the beaker originally containing the nickel-cobalt mixed solution was centrifugally washed three times with deionized water and ethanol respectively, and then dried in a vacuum drying oven at 70 °C. The dried sample was taken out and ground, and finally calcined at 350 °C (5 °C / min) in an air atmosphere for 2 h to obtain the required product. After XRD characterization, the product had a complete crystal structure and corresponded to the PDF card 73-1702, but there were impurity peaks of NiO; after BET characterization, its specific surface area was 241 m 2 / g; after SEM characterization, its morphology was a flower-like microsphere structure with a particle size of about 5.3 μm.

[0080] The electrochemical test procedure was the same as that in Example 1.

[0081] The performance data of the NiCo prepared in Examples 1-9 and Comparative Examples 1 and 2 2 O 4 catalysts are shown in Table 1 below.

[0082] Table 1: Performance data of NiCo prepared in Examples 1-9 and Comparative Examples 1-2 2 O 4

[0083]

[0084] ​

Claims

1. A NiCo 2 O 4 catalyst preparation method, It is characterized in that it includes the following steps: (1) Dissolve nickel salt and cobalt salt to obtain a homogeneous solution; make the ammonia volatilized from the first container filled with ammonia water contact the surface of the homogeneous solution and carry out homogeneous precipitation on the surface of the homogeneous solution, forming a solid-phase thin film on the surface of the homogeneous solution and powder precipitate in the homogeneous solution; (2) After the homogeneous precipitation reaction ends, separate the solid from the liquid to collect the solid-phase product, and obtain the precursor through washing, drying and grinding; (3) Calcinate the precursor obtained in step (2) to obtain the NiCo 2 O 4 catalyst; When separating the solid from the liquid to collect the solid-phase product, only collect the powder precipitate formed in the homogeneous solution; Separating the solid from the liquid to collect the solid-phase product includes the following steps: after the homogeneous precipitation reaction ends, slowly inject deionized water along the inner wall of the second container containing the homogeneous solution, stop injecting deionized water when the solid-phase thin film in the second container is higher than the top of the second container, let it stand for the powder precipitate to settle, then place the second container into the third container, slowly inject deionized water into the third container until the solid-phase thin film on the surface of the second container floats away from the second container, then take out the second container and carry out solid-liquid separation to obtain the powder precipitate; Making the ammonia volatilized from the first container filled with ammonia water contact the surface of the homogeneous solution adopts the following method: lead out a conduit from the first container, connect the end of the conduit to a funnel, invert the funnel under the surface liquid of the homogeneous solution, and a valve is installed in the conduit.

2. The preparation method according to claim 1, it is characterized in that the nickel salt includes any one of sulfate, nitrate, hydrochloride or acetate; the anion of the cobalt salt is the same as that of the nickel salt; the concentration of nickel ions in the homogeneous solution is 0.01 - 0.10 mol / L, and the concentration of cobalt ions is twice that of nickel ions.

3. The preparation method according to claim 1, it is characterized in that the initial concentration of the ammonia water is 2 - 7 mol / L, and the molar amount of ammonia gas in the ammonia water is controlled to be 30 - 60 times that of the nickel salt.

4. The preparation method according to claim 1, it is characterized in that control the reaction temperature of the homogeneous precipitation to be 25 - 40 °C, and the reaction time is 2 - 3 h.

5. The preparation method according to claim 1, it is characterized in that when carrying out the calcination treatment, control the calcination temperature to be 350 - 400 °C, the heating rate to be 2 - 5 °C / min, the calcination time to be 2 - 4 h, and the atmosphere is air atmosphere.

6. A NiCo catalyst prepared by the preparation method according to any one of claims 1-5 2 O 4 catalyst It is characterized in that The NiCo 2 O 4 catalyst has a flower-like microsphere structure with particle sizes of 2-5 μm and a specific surface area of 200-400 m 2 / g.

7. Use of a NiCo 2 O 4 catalyst in hydrogen production by electrolysis of water.

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