CN116905039A - Double-function electrolytic water catalyst and preparation method and application thereof - Google Patents

Abstract

The invention provides a bifunctional electrolysis water catalyst and its preparation method and application. The method includes: 1) making a mixture including a nickel source, an iron source, CeO ₂ , an alkali source and water undergo a hydrothermal reaction to obtain NiFe-LDH/ CeO ₂ composite material; 2) Using foam metal as a carrier, the NiFe‑LDH/CeO ₂ composite material is loaded onto the foam metal using a binder and dispersant to obtain a NiFe‑LDH/CeO ₂ /foam metal catalyst; among which, nickel The molar ratio of source, iron source and CeO ₂ is (2‑4): 1: (0.5‑0.8); the mass ratio of NiFe‑LDH/CeO ₂ composite material, binder and dispersant is (5‑10) mg :(0.05-0.1)mL:(0.5-1.5)mL. The catalyst obtained by this method can be used as an OER and HER dual-functional electrolysis water catalyst, effectively reducing costs.

Description

A bifunctional water electrolysis catalyst and its preparation method and application

Technical field

The present invention relates to the field of electrochemistry, and specifically relates to a bifunctional electrolysis water catalyst and its preparation method and application.

Background technique

Currently, electrocatalytic water splitting technology (electrolysis of water) is considered one of the cleanest energy conversion technologies. This technology includes anode oxygen evolution reaction (OER) and cathode hydrogen evolution reaction (HER). The electrocatalysts used in these two reactions Mainly precious metals, with small reserves and high costs, hinder the development of electrolyzed water technology.

NiFe-LDH material is relatively low-cost and is one of the catalysts with excellent OER performance in alkaline media. The development and utilization of NiFe-LDH material is a current research hotspot. However, NiFe-LDH has poor performance when catalyzing HER, making it difficult for NiFe-LDH to be used as a dual-functional electrolysis water catalyst for OER and HER, which increases the complexity of the design and preparation of hydrogen energy equipment.

Based on this, developing a bifunctional water electrolysis catalyst that can be used for OER and HER to reduce the cost of electrolyzing water for hydrogen production is an urgent problem that needs to be solved.

Contents of the invention

The invention provides a method for preparing a bifunctional water electrolysis catalyst, which can prepare OER and HER bifunctional water electrolysis catalysts and reduce the cost of electrolyzing water to produce hydrogen.

The invention also provides a bifunctional water electrolysis catalyst, which is prepared by the above method. The bifunctional water electrolysis catalyst can be used as a catalyst for OER and HER at the same time, reducing the cost of raw materials and hydrogen energy equipment.

The present invention further provides a method for electrolyzing water to produce hydrogen. When the above-mentioned bifunctional water electrolysis catalyst is used as an OER and HER catalyst to perform an electrolysis water reaction, the catalytic activity and catalytic stability are excellent.

The invention provides a preparation method of a bifunctional water electrolysis catalyst, which includes:

1) Make a hydrothermal reaction occur in a mixture including a nickel source, an iron source, CeO ₂ , an alkali source, and water to obtain a NiFe-LDH/CeO ₂ composite material;

2) Using foam metal as a carrier, use a binder and a dispersant to load the NiFe-LDH/CeO ₂ composite material onto the foam metal to obtain a NiFe-LDH/CeO ₂ /foam metal catalyst;

Wherein, the molar ratio of the nickel source, iron source and CeO ₂ is (2-4): 1: (0.5-0.8); the mass volume of the NiFe-LDH/CeO ₂ composite material, binder and dispersant The ratio is (5-10)mg: (0.05-0.1)mL: (0.5-1.5)mL.

According to an embodiment of the present invention, the alkali source includes sodium hydroxide and sodium carbonate.

According to an embodiment of the present invention, the binder includes naphthol, and the dispersant includes absolute ethanol.

According to an embodiment of the present invention, step 1) includes dispersing the CeO ₂ in water to form a dispersion, and simultaneously adding dropwise an aqueous solution of an alkali source and a mixed aqueous solution of a nickel source and an iron source into the dispersion, and the dropwise addition is completed The hydrothermal reaction is then carried out to obtain the NiFe-LDH/CeO ₂ composite material;

Control the pH of the dispersion during the dropping process to be 9.5-10.5.

According to an embodiment of the present invention, the mass volume ratio of the NiFe-LDH/CeO ₂ composite material to the foam metal is (0.005-0.01) g: (2-3) cm ³ .

According to an embodiment of the present invention, the CeO ₂ includes cubic CeO ₂ .

According to an embodiment of the present invention, step 2) includes: loading the mixture of the binder, dispersant and NiFe-LDH/CeO ₂ composite material onto the foam metal through air flow, and then freeze-drying to obtain the NiFe-LDH/CeO ₂ /foam metal catalyst;

The flow rate of the air flow is 1-3m; the freeze-drying temperature is -20~-10°C, and the time is 3-6h.

According to an embodiment of the present invention, the temperature of the hydrothermal reaction is 120-150°C, and the time is 12-24 hours.

The invention also provides a bifunctional electrolysis water catalyst, which is prepared by any one of the aforementioned preparation methods. This dual-functional electrolysis water catalyst can serve as both an OER and HER catalyst, effectively reducing raw material costs and hydrogen energy equipment costs.

The present invention also provides a method for electrolyzing water to produce hydrogen. When the above-mentioned bifunctional water electrolysis catalyst is used as a catalyst for OER and HER, it has higher catalytic activity and stability.

In the preparation method of the present invention, CeO ₂ is embedded in situ on NiFe-LDH, and then the NiFe-LDH embedded with CeO ₂ is loaded on the foam metal through a binder and a dispersant. By controlling the nickel source, iron source, The molar ratio of CeO ₂ and the mass to volume ratio of NiFe-LDH/CeO ₂ , binder and dispersant enable the resulting NiFe-LDH/CeO ₂ /foam metal catalyst to serve as both an OER and HER catalyst, thus reducing electrolysis The cost of producing hydrogen from water, and the bifunctional water electrolysis catalyst prepared by this method also has high catalytic activity and catalytic stability, providing an effective design idea for the development of low-cost, high-activity bifunctional water electrolysis catalysts .

Description of the drawings

Figure 1a is an SEM image of cubic CeO ₂ prepared in Example 1;

Figure 1b1 is an SEM image of the NiFe-LDH/CeO ₂ composite material prepared in Example 1 at the 200nm scale;

Figure 1b2 is an SEM image of the NiFe-LDH/CeO ₂ composite material prepared in Example 1 at the 100nm scale;

Figure 1c1 is an SEM image of the NiFe-LDH/CeO ₂ composite material prepared in Example 8 at the 200nm scale;

Figure 1c2 is an SEM image at 100nm scale of the NiFe-LDH/CeO ₂ composite prepared in Example 8;

Figure 1d1 is an SEM image of the NiFe-LDH composite material prepared in Comparative Example 1 at the 200nm scale;

Figure 1d2 is an SEM image of the NiFe-LDH composite material prepared in Comparative Example 1 at the 100nm scale;

Figures 2a and 2b are TEM images at 100nm of the NiFe-LDH/CeO ₂ composite material prepared in Example 1;

Figure 2c is an HRTEM image of the NiFe-LDH/CeO ₂ composite material prepared in Example 1 at the 10nm scale;

Figure 2d is an HRTEM image of the NiFe-LDH/CeO ₂ composite material prepared in Example 1 at the 5nm scale;

Figure 3 is the XRD spectrum of the NiFe-LDH/CeO ₂ composite material prepared in Example 1 and the NiFe-LDH composite material prepared in Comparative Example 1.

Detailed ways

In order to enable those skilled in the art to better understand the solution of the present invention, the present invention will be described in further detail below. The specific embodiments listed below only describe the principles and features of the present invention, and the examples are only used to explain the present invention and do not limit the scope of the present invention. Based on the embodiments of the present invention, all other implementations obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

A first aspect of the invention provides a preparation method of a bifunctional water electrolysis catalyst, including:

1) Make a hydrothermal reaction occur in a mixture including a nickel source, an iron source, CeO ₂ , an alkali source, and water to obtain a NiFe-LDH/CeO ₂ composite material;

2) Using foam metal as a carrier, use a binder and dispersant to load the NiFe-LDH/CeO ₂ composite material onto the foam metal to obtain a NiFe-LDH/CeO ₂ /foam metal catalyst;

Among them, the molar ratio of nickel source, iron source and _CeO2 is (2-4):1: (0.5-0.8); the mass and volume ratio of NiFe-LDH/ _CeO2 composite material, binder and dispersant is (5 -10)mg: (0.05-0.1)mL: (0.5-1.5)mL.

The above-mentioned nickel source includes nickel nitrate hexahydrate, nickel sulfate hexahydrate, and nickel chloride, and the above-mentioned iron source includes nonahydrate ferric nitrate, ferric sulfate, and ferric chloride.

The above step 1) can embed CeO ₂ on NiFe-LDH (nickel iron binary hydrotalcite) in situ.

The above-mentioned foam metal includes nickel foam (NF), copper foam, and titanium foam. In consideration of preparation cost and corrosion resistance of the catalyst, nickel foam is preferred.

The above step 2) can load the NiFe-LDH/CeO ₂ composite material on the foam metal. Among them, Ni, Fe and CeO ₂ serve as active components.

The catalyst prepared by the above method can be used to catalyze OER and HER at the same time, without the need for complex design of hydrogen energy equipment and the use of expensive precious metal raw materials, effectively reducing the cost of hydrogen production through electrolysis of water. At the same time, the bifunctional water electrolysis catalyst prepared by this method also has excellent catalytic activity and catalytic stability.

According to the inventor's analysis, the reason why this catalyst can be used to catalyze OER and HER at the same time is that: Ni and Fe themselves have OER performance. After the introduction of CeO ₂ , on the one hand, CeO ₂ has oxygen vacancy defects, which is beneficial to the HER performance; on the other hand, The interface between _CeO2 and Ni and Fe components can also provide HER active sites.

Furthermore, the catalyst prepared by the above method also has excellent catalytic activity and catalytic stability because: on the one hand, the active components Ni, Fe, and CeO ₂ themselves are easy to aggregate, and CeO ₂ is grown in situ on NiFe-LDH. It can avoid its aggregation, fully exert the catalytic activity and improve the catalytic stability; at the same time, the in-situ growth of CeO ₂ on NiFe-LDH can also enhance the electron transfer and ion transport capabilities during the electrocatalytic process, and improve the electrolysis of water. During the process, Ce in CeO ₂ can be converted between trivalent and tetravalent, and store and release oxygen, which is beneficial to catalytic activity; on the other hand, foam metal as a carrier can greatly enhance the conductivity and conductivity of the material. Stability, and the catalyst has a mesoporous structure and a larger specific surface area, exposing more active sites, accelerating the contact between the active components and the electrolyte, and further improving the catalytic activity.

The inventor found that when the molar ratio of nickel source, iron source and _CeO2 is (2-4):1: (0.5-0.8), the electrolysis water catalyst has excellent catalytic performance. When this molar ratio is not satisfied, The catalytic activity and catalytic stability will be reduced, which may be caused by interactions between electrons.

Further, when the mass volume ratio of NiFe-LDH/CeO ₂ composite material, binder, and dispersant is controlled to (5-10) mg: (0.05-0.1) mL: (0.5-1.5) mL, NiFe can be -LDH/CeO ₂ composite material is uniformly and firmly loaded on the surface of foam metal, avoiding the problem of reduced catalytic activity or stability caused by uneven loading or falling off of Ni, Fe, and CeO ₂ in the catalyst.

It should be noted that after the hydrothermal reaction is completed, the obtained product needs to be alternately rinsed with water and absolute ethanol to remove impurities in the product such as carbonate impurities, nickel-iron oxides, etc. The invention does not limit the number of rinses, as long as It is enough to ensure that the impurities in the reaction product are eliminated. The washed product is dried to obtain NiFe-LDH/CeO ₂ composite material.

According to the inventor's research, when the alkali source includes sodium hydroxide (NaOH) and sodium carbonate ( _Na2CO3 ), _CeO2 can be more firmly embedded on NiFe-LDH, which is beneficial to improving the catalytic stability of the electrolysis water catalyst.

In a specific implementation process, the binder includes naphthol, and the dispersant includes absolute ethanol.

The combination of the above-mentioned binder and dispersant can enable the NiFe-LDH/CeO ₂ composite material to be evenly, quickly and firmly loaded on the foam metal, further improving the catalytic activity and catalytic stability of the water electrolysis catalyst.

In the present invention, step 1) includes dispersing CeO ₂ in water to form a dispersion, and simultaneously dropping an aqueous solution of an alkali source and a mixed aqueous solution of a nickel source and an iron source into the dispersion, and performing a hydrothermal reaction after the addition is completed to obtain NiFe-LDH/CeO ₂ composite material;

Control the pH of the dispersion during the dropping process to be 9.5-10.5.

The above process can uniformly disperse Ni, Fe, and _CeO2 , and then form a NiFe-LDH/ _CeO2 composite material with regular morphology through hydrothermal reaction.

When adding dropwise the aqueous solution of the alkali source, the mixed aqueous solution of the nickel source and the iron source, the pH of the dispersion needs to be controlled to 9.5-10.5 to ensure that Ni and Fe can evenly settle on CeO ₂ , thus facilitating the formation of a regular morphology NiFe-LDH/CeO ₂ composite material.

During specific implementation, the mass-to-volume ratio of NiFe-LDH/CeO ₂ composite material to metal foam is (0.005-0.01)g: (2-3)cm ³ . Under this mass-to-volume ratio, sufficient active components can be loaded on the metal foam to give full play to the synergistic effect of the metal foam and the active components on catalytic activity and catalytic stability.

In the present invention, CeO ₂ includes cubic CeO ₂ . The unique morphology of cubic CeO ₂ enables it to be firmly embedded between NiFe-LDH and not easy to fall off, which is beneficial to improving catalytic activity and catalytic stability. Compared with other forms of CeO ₂ , choosing cubic CeO ₂ has a better effect on improving catalytic performance.

During specific implementation, cubic CeO ₂ is prepared by the following method: after ultrasonic treatment of a mixed solution of an aqueous solution of cerium nitrate hexahydrate (Ce(NO ₃ ) ₃ ·6H ₂ O) and an aqueous sodium hydroxide solution for 20-30 min, it is placed at 150 Hydrothermal reaction at -180℃ for 24-30h, washing treatment with water and absolute ethanol alternately, drying, and then roasting at 600-650℃ for 120min to obtain cubic CeO ₂ ; among them, Ce(NO ₃ ) ₃ ·6H ₂ The molar ratio of O to sodium hydroxide is 1:120, the concentration of the aqueous solution of Ce(NO ₃ ) ₃ ·6H ₂ O is 0.01g/mL, and the concentration of the aqueous sodium hydroxide solution is 0.32g/mL.

The above step 2) includes: loading the mixture of binder, dispersant and NiFe-LDH/CeO ₂ composite material onto the foam metal through air flow, and then freeze-drying to obtain the NiFe-LDH/CeO ₂ /foam metal catalyst;

The flow rate of the air flow is 1-3m; the freeze-drying temperature is -20~10°C and the time is 3-6h.

Loading the NiFe-LDH/CeO ₂ composite material on the foam metal through air flow is beneficial to uniformly loading active components on the foam metal. During specific implementation, when the flow rate of the air flow is controlled to be 1-3m, the active components can be evenly loaded on the foam metal quickly.

The NiFe-LDH/CeO ₂ /foam metal catalyst prepared by the freeze-drying method can maintain the pore structure of the catalyst, the embedded structure of CeO ₂ and the NiFe-LDH structure to a great extent, which is beneficial to improving the catalytic activity and catalytic stability of the catalyst. During specific implementation, when the freeze-drying temperature is controlled to -20~-10°C and the freeze-drying time is 3-6 hours, a catalyst with better morphology can be obtained in a shorter time.

In the present invention, the temperature of the hydrothermal reaction is 120-150°C and the time is 12-24 hours.

A second aspect of the present invention provides a bifunctional water electrolysis catalyst prepared by any of the above methods. The bifunctional water electrolysis catalyst is relatively low-cost and can be used as an OER and HER catalyst at the same time.

A third aspect of the present invention provides a method for electrolyzing water to produce hydrogen, using the above-mentioned bifunctional water electrolysis catalyst as an OER and HER catalyst. During the specific implementation process, the present invention selects 1M KOH as the electrolyte. Of course, the inventor can also select other types of electrolytes, such as 1M NaOH, etc. When electrolyzing water through the above method, a current of 10mA/ ^cm2 can be obtained with only a battery voltage of 1.68V, and the current density can still be maintained as high as 96% after electrolysis at a current of 10mA/ ^cm2 for 100h.

Below, the present invention will be described in more detail through specific examples.

Example 1

1) Preparation of cubic _CeO2

The mixed solution of Ce(NO ₃ ) ₃ ·6H ₂ O aqueous solution and NaOH aqueous solution was ultrasonically treated for 30 min, then placed in a hydrothermal reaction at 180°C for 24 h, washed alternately with water and absolute ethanol, dried, and then dried at 600 Roast at ℃ for 120 minutes to obtain cubic CeO ₂ ;

Among them, the molar ratio of Ce(NO ₃ ) ₃ ·6H ₂ O and NaOH is 1:120, the concentration of the aqueous solution of Ce(NO ₃ ) ₃ ·6H ₂ O is 0.01g/mL, and the concentration of the aqueous solution of NaOH is 0.32g/mL. ;

2) Preparation of NiFe-LDH/CeO ₂ composite materials

Disperse 0.05g CeO ₂ in 10mL water to form a dispersion;

Dissolve 0.44g Ni(NO ₃ ) ₂ ·6H ₂ O and 0.20g Fe(NO ₃ ) ₃ ·9H ₂ O in 25ml water to form a mixed solution of nickel source and iron source;

Dissolve 0.50g NaOH and 1.3g Na ₂ CO ₃ in 25 ml water to form an aqueous solution of alkali source;

The aqueous solution of the alkali source, the nickel source and the mixed aqueous solution of the iron source are simultaneously added dropwise to the dispersion. The pH of the dispersion is controlled to be 10 during the dropwise addition. After the dropwise addition, a hydrothermal reaction is performed at 120°C for 12 hours, and then water is used , washed with absolute ethanol alternately and then dried to obtain NiFe-LDH/CeO ₂ composite material;

Among them, the molar ratio of nickel source, iron source and CeO ₂ is 3:1:0.6;

3) Preparation of NiFe-LDH/CeO ₂ /nickel foam (NF) catalyst

The NiFe-LDH/CeO ₂ composite material was mixed with naphthol solution and absolute ethanol, loaded onto 1×3×0.2cm ³ nickel foam at an air flow rate of 2m, and then freeze-dried at -15°C for 6h. Obtain NiFe-LDH/CeO ₂ /NF catalyst;

Among them, the mass and volume ratio of NiFe-LDH/CeO ₂ composite material, binder and dispersant is 5mg: 0.05mL: 1mL, and the mass and volume ratio of NiFe-LDH/CeO ₂ composite material and foam metal is 0.005g: 3cm ³ .

Example 2

The difference between this embodiment and Example 1 is that the alkali source is sodium hydroxide, and the other conditions are the same as Example 1.

Example 3

The difference between this embodiment and Example 1 is that the alkali source is sodium carbonate, and the other conditions are the same as Example 1.

Example 4

The difference between this embodiment and Example 1 is that the dispersant is water.

Example 5

The difference between this embodiment and Embodiment 1 is that the adhesive is conductive carbon glue.

Example 6

The difference between this Example 1 and Example 1 is that when the aqueous solution of the alkali source and the mixed aqueous solution of the nickel source and the iron source are added dropwise, the pH is controlled to be 12.

Example 7

The difference between this embodiment and Example 1 is that the mass-to-volume ratio of the NiFe-LDH/CeO ₂ composite material to the metal foam is 0.015g:3cm ³ .

Example 8

The difference between this embodiment and Embodiment 1 is that CeO ₂ is a nanorod.

Example 9

The difference between this embodiment and Example 1 is that in step 2), the aqueous solution of the alkali source, the mixed aqueous solution of the nickel source and the iron source are simultaneously added dropwise to the CeO ₂ dispersion, and the dispersion of the dispersion is controlled during the dropwise addition. The pH is 9.5. After the dropwise addition, hydrothermal reaction is carried out at 120°C for 24 hours, followed by alternate washing with water and absolute ethanol and drying to obtain the NiFe-LDH/CeO ₂ composite material;

Among them, the molar ratio of nickel source, iron source and CeO ₂ is 4:1:0.8;

In step 3), mix the NiFe-LDH/CeO ₂ composite with naphthol solution and absolute ethanol, load it onto 1×3×0.2cm ³ copper foam at an air flow rate of 3m, and then place it at -20°C. After freeze-drying for 3 hours, NiFe-LDH/CeO ₂ /foam copper catalyst was obtained;

Among them, the mass and volume ratio of NiFe-LDH/CeO ₂ composite material, binder and dispersant is 10mg: 0.1mL: 1.5mL, and the mass and volume ratio of NiFe-LDH/CeO ₂ composite material and foam metal is 0.01g: 3cm ³ .

Comparative example 1

The difference between this comparative example and Example 1 is that no CeO ₂ is added, a NiFe-LDH composite material is first prepared, and then a NiFe-LDH/NF catalyst is further prepared.

Comparative example 2

The difference between this comparative example and Example 1 is that no binder or dispersant is used. The foam metal is immersed in a mixture including a nickel source, an iron source, CeO ₂ , an alkali source, and water, and a hydrothermal reaction is performed together to obtain NiFe-LDH/CeO ₂ /NF catalyst was used.

Comparative example 3

The difference between this comparative example and Example 1 is that the NiFe-LDH/CeO ₂ composite material is not supported on the nickel foam, and the NiFe-LDH/CeO ₂ catalyst is directly obtained.

Comparative example 4

The difference between this comparative example and Example 1 is that the molar ratio of nickel source, iron source, and CeO ₂ is 6:1:1, and a NiFe-LDH/CeO ₂ /NF catalyst was obtained.

Comparative example 5

The difference between this comparative example and Example 1 is that the mass to volume ratio of the NiFe-LDH/CeO ₂ composite material, binder, and dispersant is 12 mg: 0.2 mL: 2 mL, and a NiFe-LDH/CeO ₂ /NF catalyst is obtained.

Test example 1

Characterize the microstructure of the cubic CeO ₂ prepared in Example 1 of the present invention, the NiFe-LDH/CeO ₂ composite material prepared in Example 1 and Example 8, and the NiFe-LDH composite material prepared in Comparative Example 1 by SEM (scanning electron microscope). Appearance. Figure 1a is an SEM image of CeO ₂ prepared in Example 1 of the present invention. Figures 1b1 and 1b2 show SEM images of the NiFe-LDH/CeO ₂ composite material obtained in Example 1 at the 200nm scale and 100nm scale. Figures 1c1 and 1b2 Figure 1c2 shows the SEM images of the NiFe-LDH/CeO ₂ composite material prepared in Example 8 at the 200nm scale and the 100nm scale. Figures 1d1 and 1d2 show the NiFe-LDH prepared in Comparative Example 1 at the 200nm scale and the 100nm scale. SEM image.

It can be seen from the figure that the present invention successfully prepared cubic CeO ₂ . Compared with Comparative Example 1, Example 1 of the present invention has cubic CeO ₂ uniformly grown on nickel-iron binary hydrotalcite nanosheets. Example 8 has uniform growth on nickel-iron binary hydrotalcite nanosheets. Rod-shaped CeO ₂ grows uniformly on the hydrotalcite nanosheets, which shows that the present invention successfully embeds CeO ₂ into the NiFe-LDH structure and achieves uniform embedding, which is beneficial to improving catalytic performance.

Test example 2

The micromorphology of the NiFe-LDH/CeO ₂ composite material prepared in Example 1 of the present invention was characterized by TEM (transmission electron microscope) and HRTEM (high-resolution transmission electron microscope). The results are shown in Figure 2. Figures 2a and 2b are TEM images at 100nm of the NiFe-LDH/CeO ₂ composite material prepared in Example 1. Figure 2c and Figure 2d are respectively 10nm and 5nm scale TEM images of the NiFe-LDH/CeO ₂ composite material prepared in Example 1. HRTEM image below.

According to Figure 2a and Figure 2b, in the NiFe-LDH/CeO ₂ composite material prepared in Example 1 of the present invention, CeO ₂ nanoparticles grow uniformly on the well-defined NiFe-LDH nanosheets and rarely aggregate, which shows that NiFe- LDH nanosheets can prevent _CeO2 nanoparticles from agglomerating. At the same time, Ni and Fe on NiFe-LDH nanosheets are also fixed and difficult to aggregate.

The lattice fringes in Figure 2c and Figure 2d are the (222) crystal face of CeO ₂ and the (220) crystal face of CeO ₂ respectively. The lattice spacing of the (222) crystal face is 0.156 nm, and the lattice spacing of the (220) crystal face is 0.156 nm. The lattice spacing is 0.191nm, which further demonstrates that _CeO2 is successfully embedded on NiFe-LDH nanosheets.

Test example 3

The crystallization conditions of the NiFe-LDH/CeO ₂ composite material prepared in Example 1 of the present invention and the NiFe-LDH composite material prepared in Comparative Example 1 were characterized by XRD (X-ray diffraction) patterns. The results are shown in Figure 3.

According to Figure 3, it can be seen that compared with Comparative Example 1, Example 1 of the present invention has a new diffraction peak that is highly consistent with the CeO ₂ standard diffraction peak (JCPDS78-0694), which once again shows that CeO ₂ is successfully introduced in the present invention.

Test example 4

The catalysts prepared in Examples 1-9 and Comparative Examples 1-5 of the present invention were used as OER and HER catalysts to electrolyze water for hydrogen production in 1.0 M KOH. The catalytic activity of the water electrolysis catalyst is expressed by testing the battery potential at 10mA/ ^cm2 ; the catalytic activity of the water electrolysis catalyst is tested by continuing to electrolyze water at 10mA/ ^cm2 and testing the current density of the battery after 100 hours compared to the initial current density retention rate. stability. The results are shown in Table 1.

Table 1 Catalytic activity and catalytic stability of catalysts

sample Battery potential (V) Current density retention rate (%) Example 1 1.68 96 Example 2 1.72 94 Example 3 1.75 90 Example 4 1.69 93 Example 5 1.77 86 Example 6 1.73 93 Example 7 1.70 90 Example 8 1.78 81 Example 9 1.75 89 Comparative example 1 / / Comparative example 2 1.85 77 Comparative example 3 1.93 64 Comparative example 4 1.83 90 Comparative example 5 1.82 91

According to Table 1, it can be seen that when the catalysts of Examples 1-9 of the present invention are used as bifunctional electrolysis water catalysts, the battery potential can be as low as 1.68V, the current density retention rate can be as high as 96%, and they have excellent catalytic activity and catalytic stability. sex.

The inventor found through experiments that Comparative Example 1 cannot be used as a HER and OER dual-functional water electrolysis catalyst, while the catalysts prepared in Examples 1-9 of the present invention can be used as HER and OER dual-functional water electrolysis catalysts. In addition, when the catalysts of Comparative Examples 2-5 are used as OER and HER dual-functional electrolysis water catalysts, they require higher battery potentials, and when foam metal is not introduced (Comparative Example 3) or foam metal is directly combined with nickel and iron sources, , when the cerium source is hydrothermally combined in situ (Comparative Example 2), the catalytic stability is poor.

Compared with Examples 2-8, the catalytic activity and stability of the catalyst prepared in Example 1 are higher, which shows that compared with selecting sodium hydroxide and sodium carbonate as alkali sources respectively (Example 2 and Example 3), Choosing both as alkali sources is more conducive to obtaining a catalyst with excellent performance; compared to choosing other types of dispersants or binders (Examples 4 and 5), naphthol and ethanol are selected as dispersants and binders at the same time. When the binder is used, the performance of the catalyst is even better; in addition, the cubic CeO ₂ is selected, and the mass volume ratio of the NiFe-LDH/CeO ₂ composite and the metal foam is controlled to (0.005-0.01)g: (2-3)cm ³ , and Controlling the pH of the aqueous solution for dripping alkali and the mixed aqueous solution of nickel and iron sources to 9.5-10.5 is beneficial to obtaining a catalyst with good catalytic activity and catalytic stability.

In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention are clearly and completely described above in conjunction with specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, not all of them. Example. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

Claims (10)

1. A method for preparing a bifunctional water electrolysis catalyst, which is characterized by comprising: 1) Make a hydrothermal reaction occur in a mixture including a nickel source, an iron source, CeO ₂ , an alkali source, and water to obtain a NiFe-LDH/CeO ₂ composite material; 2) Using foam metal as a carrier, use a binder and a dispersant to load the NiFe-LDH/CeO ₂ composite material onto the foam metal to obtain a NiFe-LDH/CeO ₂ /foam metal catalyst; Wherein, the molar ratio of the nickel source, iron source and CeO ₂ is (2-4): 1: (0.5-0.8); the mass volume of the NiFe-LDH/CeO ₂ composite material, binder and dispersant The ratio is (5-10)mg: (0.05-0.1)mL: (0.5-1.5)mL. 2. The preparation method according to claim 1, characterized in that the alkali source includes sodium hydroxide and sodium carbonate. 3. The preparation method according to claim 1 or 2, characterized in that the binder includes naphthol, and the dispersant includes absolute ethanol. 4. The preparation method according to any one of claims 1-3, characterized in that step 1) includes dispersing the _CeO in water to form a dispersion, and simultaneously dripping the alkali into the dispersion. The aqueous solution of the source, the mixed aqueous solution of the nickel source and the iron source, after the dropwise addition is completed, the hydrothermal reaction is performed to obtain the NiFe-LDH/CeO ₂ composite material; Control the pH of the dispersion during the dropping process to be 9.5-10.5. 5. The preparation method according to any one of claims 1-4, characterized in that the mass volume ratio of the NiFe-LDH/ _CeO composite material to the metal foam is (0.005-0.01) g: (2 -3)cm ³ . 6. The preparation method according to any one of claims 1 to 5, characterized in that the CeO ₂ includes cubic CeO ₂ . 7. The preparation method according to any one of claims 1-6, characterized in that step 2) includes: loading the mixture of the binder, dispersant and NiFe-LDH/ _CeO composite material by air flow onto the metal foam, and then freeze-dried to obtain the NiFe-LDH/CeO ₂ /metal foam catalyst; The flow rate of the air flow is 1-3m; the freeze-drying temperature is -20~-10°C, and the time is 3-6h. 8. The preparation method according to any one of claims 1 to 7, characterized in that the temperature of the hydrothermal reaction is 120-150°C and the time is 12-24 hours. 9. A bifunctional water electrolysis catalyst, characterized in that it is prepared by the preparation method described in any one of claims 1-8. 10. A method for electrolyzing water to produce hydrogen, characterized in that the electrolytic water catalyst according to claim 9 is used as a catalyst for OER and HER.