Difunctional electrocatalyst as well as preparation method and application thereof

Abstract

The invention discloses a bifunctional electrocatalyst and a preparation method and application thereof, and belongs to the technical field of electrocatalytic water decomposition, the preparation method comprises the following steps: adding pretreated foamed nickel into an aqueous solution containing a cerium source for hydrothermal reaction, and then sequentially cooling, washing and drying to obtain a NiCeOH precursor composite material; wherein the pH value of the mixed solution in the hydrothermal reaction process is 1-7; and carrying out heat treatment on the NiCeOH precursor composite material and sodium hypophosphite, and cooling to obtain the difunctional electrocatalyst. The release amount of the substrate nickel source is controlled by accurately adjusting the pH value of the solution, and a new technical thought is provided for catalyst synthesis. The characterization result shows that the catalyst has excellent charge transfer performance especially when the pH value is 2. Under the alkaline condition, the catalyst shows excellent bifunctional electrocatalytic activity and super-strong stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrocatalytic water splitting, and particularly relates to a bifunctional electrocatalyst and a preparation method and application thereof. BACKGROUND

[0002] Electrocatalytic water splitting is a key technology for realizing large-scale production of green hydrogen energy, and the core challenge lies in reducing the overpotential of anode OER and cathode HER to improve the overall energy conversion efficiency. At present, commercial catalysts mainly rely on noble metal materials (such as Pt / C for HER and IrO2 / RuO2 for OER), and the high cost and scarcity of which seriously restrict large-scale application.

[0003] In recent years, transition metal-based catalysts (such as Co, Ni and Fe-based compounds) have become a potential choice to replace noble metal catalysts due to their low cost, high abundance and controllable electronic structure. However, the existing transition metal catalysts still have the following problems:

[0004] 1. Limitation of single-function catalyst: Most catalysts only have high activity for hydrogen evolution reaction (HER) or oxygen evolution reaction (OER), and it is difficult to simultaneously catalyze both reactions in the same electrolysis system, resulting in complex electrolytic cell structure and increased cost.

[0005] 2. Insufficient stability: Under long-term high-potential working conditions, transition metal catalysts are prone to structural collapse or active site deactivation, affecting their industrial applicability.

[0006] 3. Low interface charge transport efficiency: In traditional catalysts, the interface between the active site and the conductive substrate is not in good contact, which leads to blocked electron transport and limits the catalytic kinetics. SUMMARY

[0007] In view of the above technical problems, the application provides a bifunctional electrocatalyst and a preparation method and application thereof.

[0008] To achieve the above purpose, the application provides the following technical scheme:

[0009] One of the technical schemes of the application is:

[0010] A preparation method of a bifunctional electrocatalyst, comprising the following steps:

[0011] The pretreated foamed nickel is added to a water solution containing a cerium source for hydrothermal reaction, and then cooling, washing and drying are sequentially performed to obtain a NiCeOH precursor composite material; wherein the pH value of the mixed solution in the hydrothermal reaction process is 1-7.

[0012] The NiCeOH precursor composite material and sodium hypophosphite are heat-treated and cooled to obtain a bifunctional electrocatalyst, namely Ni2(P4O 12 )-CeP5 composite material.

[0013] Beneficial effect: The present invention adjusts the pH value of the solution to 1-7 through hydrothermal reaction, and is used to precipitate an appropriate amount of nickel source from the nickel foam carrier, and then grows in situ with the added rare earth element Ce through hydrothermal reaction to obtain the NiCeOH precursor composite material, and then undergoes sodium hypophosphite phosphating treatment to obtain the target composite material Ni2(P4O 12 )-CeP5. That is, the present invention innovatively proposes to control the release amount of the base nickel source by precisely adjusting the pH value of the solution, providing a new technical idea for catalyst synthesis. And according to the characterization results of the present invention, especially when the pH is 2, the obtained composite material presents a unique nanoflower structure and has relatively excellent charge transfer performance. Under alkaline conditions, the catalyst exhibits excellent bifunctional electrocatalytic activity and super stability, and its hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performances are better than those of the precious metal benchmark catalysts Pt / C and RuO2 / C. The bifunctional water decomposition catalyst composed of the catalyst is superior to the precious metal water decomposition catalyst composed of Pt / C and RuO2 / C. In addition, it is confirmed by XPS, zeta potential, UPS and other characterization methods combined with built-in electric field theory analysis that the material has a fast charge transfer rate, which is closely related to its excellent catalytic performance.

[0014] In summary, the Ni2(P4O 12 The )-CeP5 composite material has performance comparable to that of precious metal catalysts, and its preparation process is simple and cost-effective, showing broad application prospects in the field of industrial water electrolysis for hydrogen production. Furthermore, the method of regulating the release of nickel source by controlling the solution pH has important guiding significance for the development of other transition metal-based catalysts.

[0015] In addition, the present invention uses nickel foam as a catalyst carrier in the preparation process. In the electrocatalytic water splitting process, the specific advantages are as follows:

[0016] 1.Excellent electrical conductivity

[0017] Nickel foam has extremely high electronic conductivity, significantly facilitating charge transfer during electrocatalytic reactions. In the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), its high conductivity effectively reduces interfacial resistance, ensuring rapid accumulation and transfer of reaction charges, thereby improving catalytic efficiency.

[0018] 2. High specific surface area and abundant active sites

[0019] The three-dimensional porous network structure of the nickel foam provides a large specific surface area, enabling sufficient exposure of catalyst active sites and enhancing the probability of contact between reactants (such as H2O, OH-, etc.) and catalytic sites. In addition, the nickel foam itself contains nickel elements, and the deposition of nickel ions (Ni 2 +) can be controlled by adjusting the pH value of the solution to combine with cerium ions (Ce 3+ ) in the solution, thereby generating a highly active catalyst in situ and further optimizing the catalytic performance.

[0020] 3. Optimized mass transfer and reaction kinetics

[0021] The open-pore structure of the nickel foam not only facilitates uniform loading of the catalyst, but also promotes rapid diffusion of reactants and products (such as O2, H2), reduces mass transfer limitations, and improves overall reaction rates. At the same time, uniform distribution of the catalyst helps maintain long-term stability and prevents aggregation or shedding of active components.

[0022] 4. Low cost and scalability

[0023] The nickel foam is inexpensive, easy to prepare, and has good mechanical strength, making it suitable for industrial production. The synergistic effect of the nickel foam with transition metal catalysts can significantly reduce the dependence on noble metals, making the present application more economical and practical.

[0024] Optionally, the pretreatment process is as follows: the nickel foam is ultrasonically washed in 0.5 mol / L sulfuric acid solution, deionized water, and ethanol for 15 minutes respectively, cleaned with deionized water, and naturally dried for standby use.

[0025] Optionally, the aqueous solution containing a cerium source is obtained by dissolving urea, ammonium fluoride, and cerium nitrate hexahydrate in deionized water.

[0026] Further, the amount ratio of urea, ammonium fluoride, cerium nitrate hexahydrate, and deionized water is 4.5 mmol:4.0 mmol:1.2 mmol:40 mL.

[0027] Optionally, the pH value of the mixed solution during the hydrothermal reaction is 2.

[0028] Optionally, the conditions for the hydrothermal reaction are as follows: incubation at 100-180℃ in an oven for 10 hours.

[0029] Further, the conditions for the hydrothermal reaction are as follows: incubation at 120℃ in an oven for 10 hours.

[0030] Optionally, the conditions during the drying process are as follows: drying in an oven at 60℃ for 3 hours.

[0031] Optionally, the conditions during the heat treatment process are as follows:

[0032] The NiCeOH precursor composite material is placed downstream of the tube furnace, and sodium hypophosphite is placed upstream of the tube furnace, and heated at a temperature increasing rate of 5℃·min -1 The temperature is increased to 350℃ at a rate of 5℃·min

[0033] The second technical solution of the present application is:

[0034] A bifunctional electrocatalyst prepared by the above preparation method.

[0035] Beneficial effects: The bifunctional catalyst Ni2(P4O 12 )-CeP5 composite material prepared by the present application can be widely used in alkaline electrolytic cells, and when it is used for full water decomposition, the stability reaches 260 hours at 100mA -2 cm-2, which provides key technical support for large-scale application of green hydrogen energy.

[0036] The third technical solution of the present application is:

[0037] Application of the above bifunctional electrocatalyst in full water decomposition.

[0038] Compared with the prior art, the bifunctional catalyst prepared by the preparation method of the present application has the following advantages and technical effects:

[0039] 1. High-efficiency bifunctional catalytic activity: simultaneously optimizing the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activity in the same catalyst system, significantly reducing the overpotential of full water decomposition, and improving the overall energy conversion efficiency.

[0040] 2. Compared with traditional single-function catalysts (such as Pt / C only suitable for HER, and IrO2 / RuO only suitable for OER), the present application avoids the complex structure of composite catalyst systems and simplifies the design of electrolytic cells.

[0041] 3. Excellent electrical conductivity and charge transport efficiency: using a high-conductivity carrier (such as a nickel foam), ensuring fast electron transport during the reaction, reducing interface resistance, and improving reaction kinetics. Compared with ordinary carbon-based carriers or non-conductive substrates, the present application effectively solves the problems of charge accumulation and transmission bottleneck.

[0042] 4. Abundant active sites and high specific surface area: The bifunctional catalyst with unique morphology is synthesized in the present application. Especially when the pH is 2, the novel bifunctional catalyst with nanoflower morphology is synthesized in the present application. The open porous structure promotes the rapid diffusion of reactants (H2O, OH-) and products (H2, O2), reduces the mass transfer resistance, increases the contact area of reactants while the active component is optimized, greatly increases the exposure of catalytic sites, and improves the contact efficiency of reactants. Compared with traditional powder catalysts, the present application avoids the problem of active site agglomeration, and significantly improves the utilization rate of the catalyst.

[0043] 5. Enhanced stability and durability

[0044] Through the synergistic effect of the carrier and the active component, the dissolution or structural collapse of the catalyst under high potential conditions is prevented, and the service life is prolonged. A simple preparation process (such as in-situ growth) is adopted, which is suitable for industrial scale-up production and has significant economic advantages.

[0045] 6. Low cost and scalable production: Based entirely on non-noble metal materials (such as Ni, Ce, etc.), and the nickel source comes from a nickel foam substrate, greatly reducing the cost of raw materials. Compared with pure transition metal catalysts (such as Ni / Ce-based oxides which are easily oxidized and deactivated), the present application significantly improves the corrosion resistance and mechanical stability through component regulation and interface optimization. For example, the hydrogen evolution reaction can continue to run for 320 hours under the condition of -10 mA·cm -2 , and the oxygen evolution reaction can continue to run for 500 hours under the condition of 50 and 100 mA·cm -2 , with certain stability. BRIEF DESCRIPTION OF DRAWINGS

[0046] The accompanying drawings, which form a part of the present application, are used to provide further understanding of the present application, and the schematic embodiments of the present application and their descriptions are used to explain the present application, and do not constitute an improper limitation on the present application. In the drawings:

[0047] Figure 1 X-ray powder diffraction pattern of the novel bifunctional electrocatalyst Ni2(P4O 12 )-CeP5 composite material prepared in Example 1;

[0048] Figure 2 X-ray powder diffraction pattern of the precursor NiCeOH composite material prepared in Comparative Example 1;

[0049] Figure 3 In Table a is the precursor NiCeOH composite material prepared in Example 1 (i.e. Comparative Example 1), and b is the scanning electron microscope image of the novel bifunctional electrocatalyst Ni2(P4O 12 )-CeP5 composite material prepared in Example 1;

[0050] Figure 4 The new bifunctional electrocatalyst Ni2(P4O 12 )-CeP5 composite material; where a is a transmission electron microscopy image, b is a high-resolution transmission electron microscopy image, c is a selected area electron diffraction (SAED) image, and d is a Ni2(P4O 12 )-Distribution diagram of each element of CeP5 composite material;

[0051] Figure 5 a is a novel bifunctional electrocatalyst Ni2(P4O 12 )-CeP5 composite material N2 adsorption / desorption isotherms, b is the pore size distribution and contact angle results;

[0052] Figure 6 a is a novel bifunctional electrocatalyst Ni2(P4O 12 )-CeP5 composite material, CeP5 composite material prepared in Comparative Example 2 and Ni2(P4O 12 ) Ultraviolet photoelectron spectroscopy (UPS) analysis of the composite material, b is the UV-visible spectrum analysis diagram;

[0053] Figure 7 a is a scanning electron microscope image of the electrocatalyst prepared in Comparative Example 3, and b is a scanning electron microscope image of the electrocatalyst prepared in Comparative Example 2;

[0054] Figure 8 a is a scanning electron microscope image of the electrocatalyst prepared in Comparative Example 6, b is a scanning electron microscope image of Comparative Example 7, c is a scanning electron microscope image of Comparative Example 8, and d is a scanning electron microscope image of the electrocatalyst prepared in Comparative Example 9;

[0055] Figure 9 a is a scanning electron microscope image of the electrocatalyst prepared in Comparative Example 10, b is a scanning electron microscope image of Comparative Example 11, c is a scanning electron microscope image of Comparative Example 12, d is a scanning electron microscope image of Comparative Example 13, e is a scanning electron microscope image of Comparative Example 14, and f is a scanning electron microscope image of the electrocatalyst prepared in Comparative Example 15;

[0056] Figure 10 Where ac is the new bifunctional electrocatalyst Ni2(P4O 12 )-CeP5 composite material, CeP5 composite material prepared in Comparative Example 2 and Ni2(P4O 12 ) X-ray photoelectron spectrum of the composite material, d is the cyclic voltammogram of HER, and e is the cyclic voltammogram of OER; wherein a is the 2p spectrum of Ni, b is the 3d spectrum of Ce, and c is the 2p spectrum of P;

[0057] Figure 11Electrochemical performance test results of the electrocatalysts prepared for Example 1, Comparative Examples 1-4 in 1.0 M KOH, wherein a is the electrocatalytic hydrogen evolution linear sweep curve; b is the Tafel slope plot; c is the performance comparison results plot; d is the double layer capacitance plot; e is the ECSA active surface area plot, f is the electrochemical impedance spectroscopy plot; g is the three electrode stability test results of the Ni2(P4O 12 )-CeP5 composite and the Tafel slope plot of the HER catalysts reported in the prior art;

[0058] Figure 12 Electrochemical performance test results of the electrocatalysts prepared for Example 1, Comparative Examples 1-3 and Comparative Example 5 in 1.0 M KOH for oxygen evolution, wherein a is the electrocatalytic oxygen evolution linear sweep curve; b is the Tafel slope plot; c is the performance comparison results plot; d is the double layer capacitance plot; e is the ECSA active surface area plot, f is the electrochemical impedance spectroscopy plot; g is the three electrode stability test results of the Ni2(P4O 12 )-CeP5 composite and the Tafel slope plot of the OER catalysts reported in the prior art;

[0059] Figure 13 Electrochemical performance (hydrogen evolution) test plots of the electrocatalysts prepared for Example 1 and Comparative Examples 6-9. Wherein a is the electrocatalytic hydrogen evolution linear sweep curve; b is the Tafel slope plot; c is the double layer capacitance plot; d is the electrochemical impedance spectroscopy plot;

[0060] Figure 14 Electrochemical performance (hydrogen evolution) test plots of the electrocatalysts prepared for Example 1 and Comparative Examples 10-15. Wherein a is the electrocatalytic hydrogen evolution linear sweep curve; b is the Tafel slope plot; c is the double layer capacitance plot; d is the electrochemical impedance spectroscopy plot;

[0061] Figure 15 Electrochemical performance (oxygen evolution) test plots of the electrocatalysts prepared for Example 1 and Comparative Examples 6-9. Wherein a is the electrocatalytic oxygen evolution linear sweep curve; b is the Tafel slope plot; c is the double layer capacitance plot; d is the electrochemical impedance spectroscopy plot;

[0062] Figure 16 Electrochemical performance (oxygen evolution) test plots of the electrocatalysts prepared for Example 1 and Comparative Examples 10-15. Wherein a is the electrocatalytic oxygen evolution linear sweep curve; b is the Tafel slope plot; c is the double layer capacitance plot; d is the electrochemical impedance spectroscopy plot;

[0063] Figure 17 Novel bifunctional electrocatalyst Ni2(P4O 12)-CeP5 composite full water splitting process and results. a is full water splitting schematic; b is two electrode test; c is two electrode performance comparison results; d is new bifunctional electrocatalyst Ni2(P4O 12 )-CeP5 composite two electrode system compared to full water splitting cell voltage of bifunctional catalysts reported in the prior art; e is new bifunctional electrocatalyst Ni2(P4O 12 )-CeP5 composite two electrode system full water splitting at 100 mA -2 Stability test results; f is new bifunctional electrocatalyst Ni2(P4O 12 )-CeP5 composite full water splitting under solar cell. g is full water splitting of new bifunctional electrocatalyst Ni2(P4O DETAILED DESCRIPTION

[0064] Various exemplary embodiments of the present application will now be described in detail, without intent to limit the application, which is only limited by the claims. But it is to be appreciated that certain features and / or subcombinations of these embodiments can constitute additional embodiments.

[0065] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. In addition, where particular ranges of values are given, understand that every intervening value, between the lower and upper limits of that range and any other stated or intervening value in that stated range, is encompassed. The upper and lower limits of these intervening values can independently be included or excluded in the range, and each intervening value is independently encompassed in the range. These smaller ranges are thus each individually intended to be encompassed within the application.

[0066] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, the preferred methods and materials are described. All patents, patent applications, publications, and descriptions mentioned herein are incorporated by reference to the extent allowed by law. In the case of conflict between the description herein and the incorporated material, the description herein shall control.

[0067] In the description of the application specific embodiments, numerous specific details are set forth in order to provide a thorough understanding of the application. However, those of ordinary skill in the art will recognize that the application can be practiced without the specific details given herein. In other instances, well-known methods, procedures and materials have not been described in detail so as not to unnecessarily obscure aspects of the application. Other embodiments of the application will be apparent to those of ordinary skill in the art from a review of the description of the application and practice of the application.

[0068] As used herein, the terms "comprise", "comprising", "include", "including", "have", "having" and the like are open-ended and do not exclude additional elements or steps.

[0069] The embodiment of the present application discloses a preparation method of a novel bifunctional electrocatalyst, comprising the following steps: adding foamed nickel into a water solution containing a Ce source, adjusting the pH of the solution by a hydrothermal method to obtain a nickel source, then growing a rare earth element Ce in situ to obtain a NiCeOH composite material, and then adding the NiCeOH composite material and sodium hypophosphite into a tube furnace to perform phosphating treatment to obtain a Ni2(P4O 12 )-CeP5 composite material, so that the novel bifunctional electrocatalyst is obtained.

[0070] In some optional embodiments, the specific steps of the hydrothermal method are as follows:

[0071] Urea (CO(NH2)2), ammonium fluoride (NH4F) and cerium nitrate tetrahydrate are added into water, and a uniform reaction solution is obtained by stirring and ultrasonic treatment; then nitric acid is added into the solution to adjust the pH of the solution, the foamed nickel carrier is added, and hydrothermal reaction is performed to obtain the NiCeOH composite material.

[0072] In some optional embodiments, the content of the cerium nitrate hexahydrate in 40 mL of water is 1.2 mmol.

[0073] As a comparison, the content of cerium in the cerium nitrate hexahydrate is also compared, and the content of the cerium nitrate hexahydrate in 40 mL of water is (0.6, 0.8, 1.0, 1.2 and 1.4 mmol) respectively. According to the linear scan curves of the electrocatalytic hydrogen evolution and oxygen evolution obtained, when the content of the cerium nitrate hexahydrate is 1.2 mmol, the electrocatalytic performance of the hydrogen evolution and oxygen evolution is optimal.

[0074] In some optional embodiments, the temperature of the hydrothermal reaction is 100-180 DEG C, and the time is 10 h.

[0075] As a comparison, the content of the cerium nitrate hexahydrate is controlled to be constant, and the pH value of the solution (pH = 1, 2, 3, 4, 5, 6, 7) is changed. According to the results, when the pH value of the solution is 2, the morphology is nanoflower. This structure not only has a high specific surface area, but also helps to increase the active surface area of the reactant, enhances the penetration of the electrolyte and the diffusion of oxygen, improves the catalytic performance, and has the optimal electrocatalytic performance.

[0076] In some optional embodiments, the pH value of the reaction solution is 2, and the time is 10 h.

[0077] In some optional embodiments, the phosphating treatment is as follows: under a nitrogen atmosphere, the NiCeOH composite material is placed downstream, sodium hypophosphite is placed upstream, the heating rate is 5 DEG C·min -1 -1, the temperature is heated to 350 DEG C at a heating rate of 5 DEG C·min 12 -1, the temperature is heated to 350 DEG C at a heating rate of 5 DEG C·min

[0078] In addition, the embodiment of the present application also provides a novel bifunctional electrocatalyst prepared according to the above method and application thereof in full water decomposition.

[0079] The test method and steps used in the following effect verification process of the present application are as follows:

[0080] Test method:

[0081] The electrocatalytic hydrogen evolution test was carried out on an electrochemical workstation (Bio-Logic VMP3, France) by adopting a three-electrode system. The Ni2(P4O 12 )-CeP5 oxygen evolution electrocatalyst prepared in Example 1 was used as the working electrode, a graphite plate was used as the counter electrode, a saturated calomel electrode was used as the reference electrode, 1.0M KOH solution was used as the electrolyte, the test temperature was 25℃, and the scanning speed was 5mV / s. The electrode potential was obtained by the saturated calomel electrode, and reversible hydrogen electrode (RHE) and impedance compensation correction were carried out. All the potentials in the present application were obtained according to the following Nernst equation:

[0082] E RHE = E SCE + 0.241 + 0.059pH - iR

[0083] wherein i is the test current (A), R is the solution impedance (Ω), E RHE is the reversible hydrogen electrode potential, and E SCE is the standard silver chloride electrode potential; the water electrolysis test was carried out on an electrochemical workstation (Bio-Logic VMP3, France) by adopting a two-electrode system.

[0084] The electrocatalytic oxygen evolution test was carried out on an electrochemical workstation (Bio-Logic VMP3, France) by adopting a three-electrode system. The Ni2(P4O 12 )-CeP5 oxygen evolution electrocatalyst prepared in Example 1 was used as the working electrode, a graphite plate was used as the counter electrode, a saturated calomel electrode was used as the reference electrode, 1.0M KOH solution was used as the electrolyte, the test temperature was 25℃, and the scanning speed was 5mV / s. The electrode potential was obtained by the saturated calomel electrode, and reversible hydrogen electrode (RHE) and impedance compensation correction were carried out. All the potentials in the present application were obtained according to the following Nernst equation:

[0085] E RHE = E SCE + 0.241 + 0.059pH - iR

[0086] Wherein i is the current (A) of the test, R is the solution impedance (Ω); the electrolytic water test takes a two-electrode system on an electrochemical workstation (Bio-Logic VMP3, France).

[0087] Full water decomposition test: take a two-electrode system on an electrochemical workstation (Bio-Logic VMP3, France), which is composed of an anode and a cathode. 1.0 mol / L potassium hydroxide solution is used as electrolyte, the test temperature is 25℃, the scanning speed is 2mV / s, and the scanning range is 0-2.5V. Among them, the oxygen evolution reaction is an anodic reaction, and the oxygen evolution reaction electrode is the Ni2(P4O 12 )-CeP5 electrocatalyst prepared in Example 1 or the RuO2 electrode material prepared in Comparative Example 5; the hydrogen evolution reaction is a cathodic reaction, and the hydrogen evolution reaction electrode is the Ni2(P4O 12 )-CeP5 prepared in Example 1 or the Pt / C electrode material prepared in Comparative Example 4.

[0088] The "room temperature" described in the present application refers to 20-30℃, unless otherwise specified.

[0089] The "parts" described in the present application refer to mass parts, unless otherwise specified.

[0090] The raw materials used in the present application are all purchased from the market.

[0091] The technical solutions of the present application are further illustrated by the following examples.

[0092] Example 1

[0093] A preparation method of a bifunctional electrocatalyst Ni2(P4O 12 )-CeP5 composite material, comprising the following steps:

[0094] (1) Pretreatment of foamed nickel: cut the commercial foamed nickel into 1.5×3cm 2 size, then ultrasonically wash in 0.5mol / L sulfuric acid solution, deionized water and ethanol respectively for 15 minutes, clean with deionized water and air dry for standby.

[0095] (2) Preparation of reaction solution: weigh 4.5mmol urea, 4.0mmol ammonium fluoride and 1.2mmol cerium nitrate hexahydrate into 40mL deionized water solution, stir for 30 minutes, and adjust the pH of the reaction solution to 2 with nitric acid.

[0096] (3) Hydrothermal reaction: the clean nickel foam treated in step (1) was placed in the uniform solution prepared in step (2) in a reaction kettle, and then was kept in an oven at 120°C for 10 hours. After the reaction, the product was naturally cooled to room temperature, washed with deionized water, and then dried in an oven at 60°C for 3 hours to obtain a NiCeOH precursor composite material.

[0097] (4) Thermal treatment reaction: the NiCeOH precursor composite material obtained in step (3) was placed downstream of a tube furnace, and sodium hypophosphite was placed upstream of the tube furnace. The temperature was raised to 350°C at a rate of 5°C / min under N2 atmosphere, and then was kept for 2 hours. After natural cooling to room temperature, the target catalyst Ni2(P4O -1 )-CeP5 composite material was obtained. 12

[0098] Comparative Example 1

[0099] A method for preparing a NiCeOH composite material, and the preparation steps are the same as (1)-(3) in Example 1.

[0100] Comparative Example 2

[0101] A method for preparing a CeP5 composite material electrocatalyst, which is the same as Example 1, except that nickel foam is not used as a nickel source.

[0102] The specific preparation process is as follows:

[0103] (1) Preparation of reaction solution: 4.5 mmol of urea, 4.0 mmol of ammonium fluoride and 1.2 mmol of cerium nitrate hexahydrate were weighed and added to 40 mL of deionized water solution, stirred for 30 minutes, and then the pH of the reaction solution was adjusted to 2 with nitric acid.

[0104] (2) Hydrothermal reaction: the uniform solution prepared in step (1) was placed in a reaction kettle, and then was kept in an oven at 120°C for 10 hours. After the reaction, the product was naturally cooled to room temperature, washed with deionized water, and then dried in an oven at 60°C for 3 hours. Then, the product was placed downstream of a tube furnace, and sodium hypophosphite was placed upstream of the tube furnace. The temperature was raised to 350°C at a rate of 5°C / min under N2 atmosphere, and then was kept for 2 hours. After natural cooling to room temperature, the powder CeP5 was obtained. -1

[0105] (3) 2 mg of the powder CeP5 was weighed and added to a mixed solution prepared by mixing 200 μL of deionized water, 200 μL of anhydrous ethanol and 10 μL of Nafion solution (purchased from Alfa-Aesar), and was ultrasonically dissolved for 30 minutes. Then, the CeP5 slurry after ultrasonic homogenization was dropped on a 1×1 cm 2 ​​CeP5 composite material electrocatalyst can be obtained by drying at room temperature.

[0106] Comparative Example 3

[0107] A method for preparing a Ni2(P4O 12 ) electrocatalyst, which is the same as Example 1, except that no cerium nitrate hexahydrate is added in step (3).

[0108] The specific preparation process is as follows:

[0109] (1) Pretreatment of foamed nickel: Commercial foamed nickel is cut into 1.5 x 3 cm 2 in size, then ultrasonically washed in 0.5 mol / L sulfuric acid solution, deionized water and ethanol respectively for 15 minutes, cleaned with deionized water and naturally air-dried for standby use.

[0110] (2) Preparation of reaction solution: 4.5 mmol of urea and 4.0 mmol of ammonium fluoride are weighed and added to 40 mL of deionized water solution, stirred for 30 minutes, and the reaction solution is adjusted to pH 2 with nitric acid.

[0111] (3) Hydrothermal reaction: The foamed nickel treated in step (1) is placed in the uniform solution prepared in step (2), placed in a reaction kettle, then heated in an oven at 120℃ for 10 hours, naturally cooled to room temperature after the reaction is completed, then washed with deionized water, then placed in a 60℃ oven for drying for 3h, to obtain a precursor composite material.

[0112] (4) Heat treatment reaction: The NiCeOH precursor composite material obtained in step (3) is placed downstream of a tube furnace, and sodium hypophosphite is placed upstream of the tube furnace, heated to 350℃ at a rate of 5℃·min -1 under N2 atmosphere, and naturally cooled to room temperature after being kept for 2h to obtain the target catalyst Ni2(P4O 12 ) composite material.

[0113] Comparative Example 4

[0114] The preparation process of Pt / C electrode material is as follows:

[0115] 2mg of Pt / C (commercially available) is weighed and added to a mixed solution prepared by mixing 200μL of deionized water, 200μL of anhydrous ethanol and 10μL of Nafion solution, ultrasonically dissolved for 30 minutes, then the Pt / C slurry after ultrasonic homogenization is dropped on a 1cm 2 foamed nickel, dried at room temperature for standby use.

[0116] Comparative Example 5

[0117] Preparation of RuO2 electrode material:

[0118] Weigh 2 mg of RuO2(commercially available) into a mixed solution made by mixing 200 μL of deionized water, 200 μL of absolute ethanol and 10 μL of Nafion solution, and ultrasonically dissolve for 30 minutes. Then, drop the ultrasonically homogenized RuO2slurry onto 1 cm 2 of foamed nickel and dry at room temperature for use.

[0119] Comparative Example 6

[0120] The same as Example 1, except that the amount of Ce(NO3)2.6H2O added in step (2) was 0.6 mmol, respectively.

[0121] Comparative Example 7

[0122] The same as Example 1, except that the amount of Ce(NO3)2.6H2O added in step (2) was 0.8 mmol, respectively.

[0123] Comparative Example 8

[0124] The same as Example 1, except that the amount of Ce(NO3)2.6H2O added in step (2) was 1.0 mmol, respectively.

[0125] Comparative Example 9

[0126] The same as Example 1, except that the amount of Ce(NO3)2.6H2O added in step (2) was 1.4 mmol, respectively.

[0127] Comparative Example 10

[0128] The same as Example 1, except that the pH of the reaction solution adjusted by nitric acid in step (2) was pH = 1.

[0129] Comparative Example 11

[0130] The same as Example 1, except that the pH of the reaction solution adjusted by nitric acid in step (2) was pH = 3.

[0131] Comparative Example 12

[0132] The same as Example 1, except that the pH of the reaction solution adjusted by nitric acid in step (2) was pH = 4.

[0133] Comparative Example 13

[0134] The same as Example 1, except that the pH of the reaction solution adjusted by nitric acid in step (2) was pH = 5.

[0135] Comparative Example 14

[0136] The same as Example 1, except that the pH of the reaction solution adjusted by nitric acid in step (2) was pH = 6.

[0137] Comparative Example 15

[0138] The same as Example 1, except that the pH of the reaction solution prepared by nitric acid in step (2) is 7.

[0139] Effect verification

[0140] 1. Characterization of structure, composition and morphology

[0141] Figure 1 The novel bifunctional electrocatalyst Ni2(P4O 12 )-CeP5 composite material X-ray powder diffraction pattern, by Figure 1 It can be seen that the Ni2(P4O 12 )-CeP5 composite material has CeP5 and Ni2(P4O 12 ) Typical characteristic peaks of X-ray powder diffraction.

[0142] Figure 2 This is the X-ray powder diffraction pattern of the precursor NiCeOH composite material prepared in Comparative Example 1. It can be seen that it corresponds to the standard cards of Ce(OH)3 and Ni2O2(OH) respectively.

[0143] Figure 3 a is the precursor NiCeOH composite material prepared in Example 1 (ie, Comparative Example 1), b is the novel bifunctional electrocatalyst Ni2(P4O 12 )-CeP5 composite material scanning electron microscope image. Figure 3 In a, it can be seen that the precursor NiCeOH composite material has a nanoflower morphology. Figure 3 As can be seen in Figure b, after phosphating with sodium hypophosphite at a high temperature of 350°C, its morphology remains unchanged and is still a nanoflower morphology, which shows that phosphating has no effect on its morphology.

[0144] Figure 4 The new bifunctional electrocatalyst Ni2(P4O 12 )-CeP5 composite material electron microscope image; where a is a transmission electron microscope image, Figure 4 The a further confirmed that Ni2(P4O 12 )-CeP5 nanoflower morphology; b is a high-resolution transmission electron microscopy image, from Figure 4 As can be seen in b, Ni2(P4O 12 )-CeP5 composites correspond to the lattice fringes of CeP5(431) and Ni2(P4O 12 ) (040)(310) crystal plane; c is the selected area electron diffraction (SAED) pattern, showing that Ni2(P4O 12)'s (040), (310) surface and CeP5's (431) surface have clear diffraction rings; d is Ni2(P4O 12 )-CeP5 composite material, it can be seen that Ni2(P4O 12 )-CeP5 composite materials have uniform distribution of various elements.

[0145] Figure 5 a is a novel bifunctional electrocatalyst Ni2(P4O 12 )-CeP5 composite material N2 adsorption / desorption isotherm, b is the pore size distribution diagram and contact angle result diagram. Figure 5 A new bifunctional electrocatalyst Ni2(P4O 12 )-CeP5 composite material shows a typical type III isotherm with mesoporous characteristics and obvious hysteresis loop. 12 )-CeP5 composite material BET surface area (28.285m 2 ·g -1 ), which helps expose more active sites, promotes electrolyte diffusion, and improves gas emission. Figure 5 The contact angle test of the catalyst in b can obtain a new bifunctional electrocatalyst Ni2(P4O 12 )-CeP5 composite material exhibits superhydrophilicity, because when a water droplet falls on the electrode surface, the water droplet immediately penetrates the electrode surface, reducing the static contact angle to zero. This superhydrophilicity promotes close contact between the electrolyte and the electrode and rapid diffusion of the electrolyte, enhances the transfer of mass and charge, and accelerates the reaction kinetics. The CeP5 composite material and Ni2(P4O 12 ) composites, the water contact angles were 45.9° and 37°, respectively.

[0146] Figure 6 a is a novel bifunctional electrocatalyst Ni2(P4O 12 )-CeP5 composite material, CeP5 composite material prepared in Comparative Example 2 and Ni2(P4O 12 ) Ultraviolet photoelectron spectroscopy (UPS) analysis of composite materials, b is the UV-visible spectrum analysis diagram. Figure 6 a and b can be analyzed to obtain Ni2(P4O 12 )-CeP5 composite material can spontaneously transfer electrons from CeP5 to Ni2(P4O 12 ) composite materials.

[0147] Figure 7 a is the scanning electron microscope image of the electrocatalyst prepared in comparative example 3, and b is the scanning electron microscope image of the electrocatalyst prepared in comparative example 2. It can be seen that the Ni2(P4O12 ) The morphology of the composite material is nano-needle-like and sticks together and grows on the nickel foam; the morphology of the CeP5 composite material prepared in comparative example 2 is cotton-like.

[0148] Figure 8 a is a scanning electron microscope image of the electrocatalyst prepared in Comparative Example 6, b is a scanning electron microscope image of Comparative Example 7, c is a scanning electron microscope image of Comparative Example 8, and d is a scanning electron microscope image of the electrocatalyst prepared in Comparative Example 9; Figure 8 Figure a is a scan of comparative example 6 with a cerium nitrate metal content of 0.6 mmol, from which it can be seen that it has a stacked flaky morphology. Figure b is a scan of comparative example 7 with a cerium nitrate metal content of 0.8 mmol, from which it can be seen that it has a nano-needle structure. Figure c is a scan of comparative example 8 with a cerium nitrate metal content of 1.0 mmol, from which it has a nano-needle morphology. Figure d is a scan of comparative example 9 with a cerium nitrate metal content of 1.4 mmol, from which it has a stone block structure. According to the above scanning electron microscope images, different cerium ion contents lead to different morphologies of the electrocatalysts finally prepared. The larger the surface area, the more active sites exposed on the surface, and the better the electrocatalytic performance. By comparison Figure 3 and Figure 8 It can be judged that when the cerium content in cerium nitrate hexahydrate is 1.2 mmol, its morphology is nanoflower-like, with more exposed active surface area, thereby enhancing the permeation of electrolyte and diffusion of oxygen, improving the catalytic performance, and the electrocatalytic performance is optimal.

[0149] Figure 9 Figures a and b show scanning electron micrographs of the electrocatalysts prepared in Comparative Example 10, Comparative Example 11, Comparative Example 12, Comparative Example 13, Comparative Example 14, and Comparative Example 15, respectively. These images show significant differences in the catalyst morphology as the pH value of the reaction solution increases. Comparing the electrocatalytic performance graphs at different pH values ​​of the reaction solution, the electrocatalyst exhibits optimal performance when the pH of the reaction solution is 2.

[0150] Figure 10 Where ac is the new bifunctional electrocatalyst Ni2(P4O 12 )-CeP5 composite material, CeP5 composite material prepared in Comparative Example 2 and Ni2(P4O 12 ) X-ray photoelectron spectrum of the composite material, d is the cyclic voltammogram of HER, e is the cyclic voltammogram of OER; where a is the 2p spectrum of Ni, b is the 3d spectrum of Ce, and c is the 2p spectrum of P. Figure 10 From a, we can see that Ni2(P4O 12 ) compared to the electrocatalyst Ni2(P4O 12 )-CeP5 Ni 2p moves to higher binding energy. Figure 10As can be seen from FIG. b, compared with the electrocatalyst CeP5, the new bifunctional electrocatalyst Ni2(P4O 12 )-CeP5 has a more complex electronic structure of Ce 3d, which also means that the electron transfer is stronger. Figure 10 As can be seen from FIG. c, compared with the electrocatalysts CeP5 and Ni2(P4O 12 ), the new bifunctional electrocatalyst Ni2(P4O 12 )-CeP5 has more electron transfer of P 2p, moving to a higher binding energy, which also means that the electron transfer is stronger. This indicates that Ce adjusts the electronic state of the Ni and P centers, resulting in strong electronic interaction between Ce and Ni, P. Figure 10 FIGS. d and e are cyclic voltammograms of HER and OER, respectively, from which it can be seen that the new bifunctional electrocatalyst Ni2(P4O 12 )-CeP5 has a lower potential in HER and OER, which further indicates that it has better performance in HER and OER.

[0151] 2. The electrochemical test results are as follows:

[0152] Figure 11 The hydrogen evolution electrochemical performance test results of the electrocatalysts prepared in Example 1 and Comparative Examples 1-4 in 1.0M KOH are shown in the schematic diagram, wherein a is the electrocatalytic hydrogen evolution linear sweep curve; b is the Tafel slope diagram; c is the performance comparison result diagram; d is the double-layer capacitance diagram; e is the ECSA active surface area diagram; f is the electrochemical impedance spectrum diagram; and g is the three-electrode stability test results of the Ni2(P4O 12 )-CeP5 composite and the Tafel slope diagram of the HER catalyst reported in the prior art (see Table 1 for details). From a-f in FIG. Figure 11 , it can be seen that the Ni2(P4O 12 )-CeP5 composite prepared in Example 1 has excellent electrochemical hydrogen evolution performance and fast charge transfer rate. From the three-electrode stability in g, Figure 11 , it can be seen that under the condition of-10mA·cm -2 , the overpotential almost does not increase after 320 hours of continuous operation, which further proves the superior stability thereof.

[0153] Table 1

[0154]

[0155] Figure 12The results of the electrochemical performance test of the composite material prepared for Example 1, Comparative Examples 1-3 and Comparative Example 5 in 1.0M KOH, wherein a is the electrocatalytic oxygen evolution linear scan curve; b is the Tafel slope diagram; c is the performance comparison result diagram; d is the electric double layer capacitance diagram; e is the summary of the ECSA active surface area diagram, f is the electrochemical impedance spectrum diagram; g is the three-electrode stability test results of the Ni2(P4O 12 )-CeP5 composite material and the Tafel slope diagram of the OER catalyst reported in the prior art (see Table 2 for details). From a-f in Figure 12 , it can be seen that the Ni2(P4O 12 )-CeP5 composite material prepared in Example 1 has excellent electrochemical oxygen evolution performance and fast charge transfer rate. From the three-electrode stability of g in Figure 12 , it can be seen that the overpotential almost does not increase under the conditions of 50 and 100mA·cm -2 for 500h, further proving its superior stability.

[0156] Table 2

[0157] Catalyst References Cr-Co x P]]> Adv. Funct. Mater., 33 (2023) 2214081. Ru, Ni-CoP Appl. Catal. B Environ. Energy, 298 (2021) 120488. [RuNi / ZrNiN x ]]> Adv. Mater., n / a 2501586. CoP / MoP@C, N J. Alloys Compd., 895 (2022) 162595. Fe(OH)3 / MoNiO x ]]> J. Electroanal. Chem., 935 (2023) 117311. Mo-CoMOF@NF Small, 21 (2025) 2407933. NiRu-OH / NF Chem. Commun., 60 (2024) 8220-8223. NiCo-LDHs / NiCoS NanoRes., 15 (2022) 4986-4995. Ni3S2 / VG@NiC Chem. Eng. J., 415 (2021) 129048. FeCoLDH / NF NanoRes., 15 (2022) 10021-10028. CoMoSx / NF Angew. Chem. Int. Ed., 59 (2020) 1659-1665. (Fe, Co)OOH / MI Adv. Mater., 34 (2022) 2200270. h / RuFeOOH@Ti3C2T x ]]> Small, 18 (2022) 2200173. <![CDATA[Co-FeOOH-O v / IF]]> Small, 19 (2023) 2301255.

[0158] Figure 13 The electrochemical performance (hydrogen evolution) test diagram of the electrocatalyst prepared for Example 1 and Comparative Examples 6-9. Wherein a is the electrocatalytic hydrogen evolution linear scan curve; b is the Tafel slope diagram; c is the electric double layer capacitance diagram; d is the electrochemical impedance spectrum diagram. According to the comparison, it can be concluded that when the content of cerium in cerous nitrate hexahydrate is 1.2mmol, the electrochemical performance is the best, the Tafel slope is the lowest, the electrochemical impedance is the smallest, and the double layer capacitance value is the largest.

[0159] Figure 14 The electrochemical performance (hydrogen evolution) test diagram of the electrocatalyst of Example 1 and Comparative Examples 10-15. Wherein a is the electrocatalytic hydrogen evolution linear scan curve; b is the Tafel slope diagram; c is the electric double layer capacitance diagram; d is the electrochemical impedance spectrum diagram. According to the comparison, it can be concluded that when the pH value of the reaction solution is 2, the electrochemical performance is the best, the Tafel slope is the lowest, the electrochemical impedance is the smallest, and the double layer capacitance value is the largest.

[0160] Figure 15 The electrochemical performance (oxygen evolution) test diagram of the electrocatalyst prepared for Example 1 and Comparative Examples 6-9. Wherein a is the electrocatalytic oxygen evolution linear scan curve; b is the Tafel slope diagram; c is the electric double layer capacitance diagram; d is the electrochemical impedance spectrum diagram. According to the comparison, it can be concluded that when the content of cerium in cerous nitrate hexahydrate is 1.2mmol, the electrochemical performance is the best, the Tafel slope is the lowest, the electrochemical impedance is the smallest, and the double layer capacitance value is the largest.

[0161] Figure 16 The electrochemical performance (oxygen evolution) test graphs of the electrocatalysts prepared in Example 1 and Comparative Examples 10-15 are shown. Figure a is the linear scan curve for electrocatalytic oxygen evolution; b is the Tafel slope; c is the double-layer capacitance; and d is the electrochemical impedance spectroscopy. Comparison shows that when the pH value of the reaction solution is 2, the electrochemical performance is optimal, with the lowest Tafel slope, the smallest electrochemical impedance, and the largest double-layer capacitance.

[0162] Figure 17 Novel bifunctional electrocatalyst Ni2(P4O 12 )-CeP5 composite material full water decomposition process and results, where a is the full water decomposition schematic diagram; b is the two-electrode test; c is the performance comparison result of the two electrodes; d is the new bifunctional electrocatalyst Ni2(P4O 12 )-CeP5 composed of two-electrode system and the bifunctional catalyst reported in the prior art (see Table 3 for details); e is a new bifunctional electrocatalyst Ni2(P4O 12 )-CeP5 composite material composed of two-electrode system for full water splitting at 100mA -2 Stability test results; f is a new bifunctional electrocatalyst Ni2(P4O 12 )-CeP5 composite material full water splitting application in solar cells. Figure 17 It can be seen from the figure that the novel bifunctional electrocatalyst Ni2(P4O 12 )-CeP5 composite material has excellent full water splitting performance, and is superior to the two electrodes composed of Pt / C and RuO2, and is also superior to most water splitting catalysts reported in the prior art. Figure 17 It can be seen from the figure that the new bifunctional electrocatalyst Ni2(P4O 12 The two-electrode system composed of )-CeP5 composite material was tested at 100 mA·cm -2 It can run stably for 260 hours under the same conditions, which also shows that the new bifunctional electrocatalyst Ni2(P4O 12 )-CeP5 composite material has good stability and durability.

[0163] Table 3

[0164] OER catalysts reported in prior art References Co-CeO2@CNF || Ni2Fe@CNF Materials, 13 (2020) 856. [CAT] g-C3N4 / CeO2 / Fe3O4 ChemCatChem., 10 (2018) 5587-5592. CoFe-P / NF J. Colloid Interface Sci., 622 (2022) 250-260. Fe2O3@CeO2 Energy Environ. Sci., 17 (2024) 5260-5272. Fe 0.14 Co 0.86 -P / CC]]> J. Colloid Interface Sci., 600 (2021) 811-819. <![CDATA[(Ni 0.33 Fe 0.67 )2P / NF]]> Adv. Funct. Mater., 27 (2017) 1702513. NiFeLDH@NiCoP / NF Adv. Funct. Mater., 28 (2018) 1706847. Ni-S-P-O J. Mater. Chem. A, 9 (2021) 7736-7749. CoSe2 / FeSe2 Mater. Chem. pHys., 275 (2022) 125201.

[0165] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing a bifunctional electrocatalyst, characterized in that: The following steps are involved: The pretreated nickel foam is added to an aqueous solution containing a cerium source for a hydrothermal reaction, followed by cooling, washing, and drying to obtain a NiCeOH precursor composite material; wherein the pH value of the mixed solution during the hydrothermal reaction is 1-7; The NiCeOH precursor composite material and sodium hypophosphite are heat-treated and cooled to obtain a bifunctional electrocatalyst, namely Ni2(P4O 12 )-CeP5 composite material.

2. The method for preparing a bifunctional electrocatalyst according to claim 1, characterized in that: The aqueous solution containing the cerium source is prepared by dissolving urea, ammonium fluoride and cerium nitrate hexahydrate in water.

3. The method for preparing a bifunctional electrocatalyst according to claim 2, characterized in that: The usage ratio of the urea, ammonium fluoride, cerium nitrate hexahydrate and water is 4.5 mmol: 4.0 mmol: 1.2 mmol: 40 mL.

4. The method for preparing a bifunctional electrocatalyst according to claim 1, characterized in that: The pH value of the mixed solution during the hydrothermal reaction is 2.

5. The method for preparing a bifunctional electrocatalyst according to claim 1, characterized in that: The hydrothermal reaction conditions are: hydrothermal reaction at 100-180° C. for 10 hours.

6. The method for preparing a bifunctional electrocatalyst according to claim 5, characterized in that: The hydrothermal reaction conditions are: hydrothermal reaction at 120° C. for 10 hours.

7. The method for preparing a bifunctional electrocatalyst according to claim 1, characterized in that: The conditions in the drying process are: drying at 60° C. for 3 h.

8. The method for preparing a bifunctional electrocatalyst according to claim 1, characterized in that: The steps in the heat treatment process are: The NiCeOH precursor composite material was placed downstream of the tube furnace, and sodium hypophosphite was placed upstream of the tube furnace. -1 Heat to 350℃ at a heating rate of 1000℃ and keep at this temperature for 2h.

9. A bifunctional electrocatalyst, characterized in that The invention is prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the bifunctional electrocatalyst according to claim 9 in overall water splitting.

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