Ce-doped graphene NiFe-LDH bifunctional catalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of catalysts, and provides a Ce-doped graphene NiFe-LDH bifunctional catalyst as well as a preparation method and application thereof. The preparation method of the bifunctional catalyst comprises the following steps: performing hydrothermal reaction on graphene oxide, a nickel source, an iron source and a cerium source in an aqueous solution containing a protective agent and a precipitator at 100-120 DEG C to obtain the Ce-doped graphene NiFe LDH bifunctional catalyst. According to the invention, NiFi-LDH is used as a framework, synergistic doping of Ce and transition metals (Ni, Fe) on graphene-loaded layered double hydroxides (LDH) is realized, and the graphene-loaded layered double hydroxides have substantially high porosity and can be printed on a gas diffusion electrode as a bifunctional catalyst layer to improve the electrochemical reaction efficiency. The preparation method provided by the invention has the characteristics of mild synthesis conditions, easily available raw materials, simple process and strong expandability, and is easy to realize industrial application. The catalyst provided by the invention has excellent OER and HER performances, and the activity and stability of the NiFe-LDH catalyst in alkaline water electrolysis are effectively improved.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and in particular to a Ce-doped graphene-NiFe-LDH bifunctional catalyst, its preparation method, and its application. Background Technology

[0002] With the increasing global demand for clean energy and the growing emphasis on environmental protection, water electrolysis, as a highly efficient hydrogen production technology, has attracted significant attention in the renewable energy sector. Compared to hydrogen produced from fossil fuels, which has low purity and high carbon content, water electrolysis yields hydrogen with high purity and fewer impurities, and is considered the most promising green hydrogen supply method for the future. Generally, two half-cell reactions occur during water electrolysis: the hydrogen evolution reaction (HER), where water is reduced to produce hydrogen; and the oxygen evolution reaction (OER), where water is oxidized to produce oxygen.

[0003] The high-purity hydrogen produced by water electrolysis has enormous application potential. However, even after a century of industrialization of water electrolysis hydrogen production technology, large-scale water electrolysis hydrogen production technology remains hampered by high costs (Prog. Energy Combust. Sci., 2010, 36(3):307-326). Catalysts play a crucial role in energy conversion, effectively reducing energy consumption and improving energy conversion efficiency. Currently, the most advanced electrocatalysts mainly rely on precious metals such as platinum (Pt), ruthenium (Ru), or iridium (Ir). However, these precious metal catalysts are constrained by high costs, limited reserves, and poor stability. Therefore, it is essential to explore non-precious metal electrocatalysts that are more abundant, more affordable, and more efficient. Such catalysts also hold great application potential. In addition, many non-precious metal catalysts have low intrinsic activity, making it difficult to meet the requirements of efficient water electrolysis hydrogen production. Catalysts such as some transition metal oxides and hydroxides exhibit low catalytic activity in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), requiring high overpotentials to achieve a certain current density. Furthermore, the structure of some catalysts is prone to collapse in strongly alkaline environments, all of which affect water electrolysis efficiency. To address these issues, this invention introduces the transition metal ion Ce. Ce doping can modulate the electronic structure of NiFe-LDH, introducing more defects and active sites on its surface, thereby providing more reactive centers for HER and OER, reducing the overpotential, and promoting the catalytic reaction. Simultaneously, Ce incorporation improves the crystal structure of NiFe-LDH, making it more stable and reducing the dissolution and loss of metal ions during alkaline water electrolysis, thus enhancing catalyst stability. The addition of graphene also provides a stable substrate for the catalyst, supporting the entire catalytic system, increasing electron flow, and further improving overall catalytic activity.

[0004] Graphene possesses excellent electronic conductivity, a large specific surface area, and good chemical stability, providing excellent support and electron transport channels for catalysts. NiFe layered double hydroxides (LDHs) have a unique layered structure, providing abundant active sites to promote reactant adsorption and reaction. Ce doping further optimizes the electronic structure and surface properties of the catalyst, enhancing its activity and stability. The introduction of Ce can modulate the redox performance of NiFe LDHs, improve the availability of surface charge, thereby increasing the Faraday efficiency, promoting oxygen adsorption and activation, and enhancing the overall catalytic performance of the bifunctional catalyst (Materials Today Physics, 2024, 101619).

[0005] In the field of carbon-based materials, 2D reduced graphene oxide (rGO) exhibits high photothermal conversion efficiency and excellent conductivity due to its carbon atoms in an sp2 honeycomb structure (Energy Storage, 78 (2024), Article 109950). Furthermore, rGO possesses a 2D planar structure similar to NiFe-LDH nanosheets, allowing for tight stacking with NiFe-LDH nanosheets in its bifunctional material. Studies have confirmed that rGO significantly improves charge transfer in NiFe-LDH during the OER (oxygen evolution reaction) process (Catal. BEnviron., 205 (2017), pp. 551-558). In addition, rGO's inherent good conductivity accelerates charge transfer on the catalyst surface and increases the electrochemical specific surface area; these factors combined significantly enhance the electrocatalytic activity of OER. Meanwhile, Ce-doped graphene-NiFe LDH bifunctional catalysts combine multiple advantages. Graphene possesses excellent electronic conductivity, a large specific surface area, and good chemical stability, providing excellent support and electron transport channels for catalysts. NiFe layered hydrogen hydroxide (LDH) has a unique layered structure, providing abundant active sites to promote reactant adsorption and reaction. Ce doping further optimizes the electronic structure and surface properties of the catalyst, enhancing its activity and stability. The introduction of Ce can modulate the redox performance of NiFe LDH, improve the availability of surface charge, thereby increasing the Faraday efficiency, promoting oxygen adsorption and activation, and improving the overall catalytic performance of the bifunctional catalyst (Materials Today Physics, 2024. 101619.). However, how to combine Ce doping with graphene support to prepare catalysts with excellent electrochemical hydrogen evolution reaction (HER) performance and oxygen evolution reaction (OER) bifunctional catalytic activity remains a technological gap. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a Ce-doped graphene-NiFe-LDH bifunctional catalyst, its preparation method, and its applications. In the Ce-doped graphene-NiFe-LDH bifunctional catalyst provided by this invention, NiFe-LDH serves as the framework, achieving synergistic doping of Ce and transition metals (Ni, Fe) on graphene-supported layered double hydroxides (LDH). This catalyst exhibits high porosity and can be printed as a bifunctional catalyst layer on a gas diffusion electrode to improve electrochemical reaction efficiency.

[0007] The first aspect of this invention provides a method for preparing a Ce-doped graphene NiFe-LDH bifunctional catalyst, comprising the following steps: subjecting graphene oxide, a nickel source, an iron source, and a cerium source to a hydrothermal reaction in an aqueous solution containing a protective agent and a precipitant at 100–120°C to obtain the Ce-doped graphene NiFe-LDH bifunctional catalyst.

[0008] In the technical solution of this invention, graphene oxide is produced by the Hummer method; the iron source is an iron salt selected from at least one of FeSO4·7H2O, FeCl3·6H2O, Fe(NO3)3·9H2O, and Fe(CH3COO)3; the nickel source is a nickel salt selected from at least one of NiSO4·6H2O, NiCl2·6H2O, Ni(NO3)2·6H2O, and Ni(CH3COO)2; and the cerium source is a cerium salt selected from at least one of Ce(SO4)3·6H2O, CeCl3·7H2O, and Ce(NO3)3·6H2O.

[0009] Furthermore, the mass ratio of graphene in graphene oxide to iron in the iron source is 1:7 to 1:10;

[0010] Furthermore, the mass ratio of nickel in the nickel source to iron in the iron source is 3:1 to 5:1;

[0011] Furthermore, the mass ratio of cerium in the cerium source to the mass ratio of iron in the iron source is 1:5 to 1:10.

[0012] In the technical solution of the present invention, the protective agent is selected from at least one of ammonium fluoride and ammonium acetate; the mass ratio of the protective agent to the iron in the iron source is 3:1 to 6:1.

[0013] In the technical solution of the present invention, the precipitant is selected from at least one of urea and ethylenediamine; the mass ratio of the precipitant to the iron in the iron source is 1:1 to 3:1.

[0014] In the technical solution of the present invention, a hydrothermal reaction is carried out in a reaction vessel; the hydrothermal reaction time is 6 to 12 hours, and the preparation method also includes a pretreatment of removing oxides from the surface of graphene by ultrasound; the posttreatment after the reaction includes filtration, washing and drying.

[0015] A second aspect of this invention provides a Ce-doped graphene-NiFe-LDH bifunctional catalyst, prepared according to the above-described method. Using graphene as a support, Ce-doped NiFe-LDH is loaded onto the graphene support to form the Ce-NiFe-LDH / graphene bifunctional catalyst, which has a petal-like structure. This layered stacking structure is more stable, and the layered stacking facilitates electron transfer and enhances the adsorption of metal ions, thereby improving the catalyst's conductivity and ultimately enhancing its electrocatalytic performance.

[0016] Furthermore, the inventors discovered that the Ce-doped graphene NiFe-LDH bifunctional catalyst exhibits bifunctional catalytic activity for hydrogen evolution (HER) and oxygen evolution (OER).

[0017] A third aspect of the present invention provides the application of Ce-doped graphene-NiFe-LDH bifunctional catalysts in the fabrication of electrodes, particularly in the fabrication of gas diffusion electrodes.

[0018] Furthermore, its use in the preparation of catalyst layers for gas diffusion electrodes.

[0019] In some specific embodiments, the Ce-doped graphene-NiFe-LDH bifunctional catalyst described above can be printed as a catalyst layer on a gas diffusion electrode.

[0020] Furthermore, when the Ce-doped graphene-NiFe-LDH bifunctional catalyst is used in the preparation of gas diffusion electrodes, the water electrolysis reaction is carried out under alkaline conditions, and the catalyst is printed on the gas diffusion electrode as both the cathode and anode catalyst layers for the water electrolysis reaction.

[0021] In the technical solution of the present invention, the sheet structure of the Ce-doped graphene NiFe-LDH bifunctional catalyst can increase the exposure of metal active sites, thereby increasing the porosity of the gas diffusion electrode catalyst layer and promoting charge transfer and H proton mass transfer within the catalyst layer.

[0022] Compared with existing technologies, the Ce-doped graphene-NiFe-LDH bifunctional catalyst of the present invention, its preparation method, and its application have the following beneficial effects:

[0023] 1) This invention provides a Ce-doped graphene-NiFe-LDH bifunctional catalyst. This catalyst is synthesized using a simple hydrothermal method, which eliminates the need for complex processing to obtain a clean surface electrocatalyst. It offers advantages such as environmental friendliness and reduced preparation costs. The preparation method employed features mild synthesis conditions, readily available raw materials, simple process, and strong scalability, making it easy to implement in industrial applications.

[0024] 2) The Ce-doped graphene NiFe-LDH bifunctional catalyst provided by this invention is applied to water electrolysis. The catalyst has excellent OER and HER performance, which effectively improves the activity and stability of NiFe-LDH catalyst in alkaline water electrolysis.

[0025] 3) This invention utilizes NiFi-LDH as a framework to achieve synergistic doping of Ce and transition metals (Ni, Fe) on graphene-supported layered double hydroxides (LDH). This Ce-(Ni,Fe)LDH / graphene bifunctional catalyst exhibits high porosity and excellent bifunctional catalytic activity for hydrogen evolution (HER) and oxygen evolution (OER), making it suitable for green energy storage and energy conversion applications such as water electrolysis. It can also be printed as a bifunctional catalyst layer on gas diffusion electrodes to improve electrochemical reaction efficiency. Attached Figure Description

[0026] Figure 1 The HER test results of NiFe LDH, Ce-NiFe LDH, and Ce-NiFe LDH / GO in 1M KOH are shown.

[0027] Figure 2 This is a Tafel fitting diagram of the HER performance of NiFe LDH, Ce-NiFe LDH, and Ce-NiFe LDH / GO in 1M KOH according to the present invention.

[0028] Figure 3 The overpotential analysis diagram shows the HER performance of NiFe LDH, Ce-NiFe LDH, and Ce-NiFe LDH / GO in 1M KOH according to the present invention.

[0029] Figure 4 The image shows the double-layer capacitance of the NiFe LDH, Ce-NiFe LDH, and Ce-NiFe LDH / GO in 1M KOH.

[0030] Figure 5 The EIS electrochemical impedance spectroscopy (EIS) plots show the HER performance of NiFe LDH, Ce-NiFe LDH, and Ce-NiFe LDH / GO in 1M KOH according to the present invention.

[0031] Figure 6 The OER test results of NiFe LDH, Ce-NiFe LDH, and Ce-NiFe LDH / GO in 1M KOH are shown.

[0032] Figure 7 This is a Tafel fitting diagram of the OER performance of NiFe LDH, Ce-NiFe LDH, and Ce-NiFe LDH / GO in 1M KOH according to the present invention.

[0033] Figure 8 The overpotential analysis diagram shows the OER performance of NiFe LDH, Ce-NiFe LDH, and Ce-NiFe LDH / GO in 1M KOH according to the present invention.

[0034] Figure 9 The image shows the double-layer capacitance of the OER performance of NiFe LDH, Ce-NiFe LDH, and Ce-NiFe LDH / GO in 1M KOH.

[0035] Figure 10 The image shows the EIS electrochemical impedance spectroscopy (EIS) plots of the OER performance of NiFe LDH, Ce-NiFe LDH, and Ce-NiFe LDH / GO in 1M KOH according to the present invention.

[0036] Figure 11 This is a structural diagram of the water electrolysis cell of the present invention.

[0037] Figure 12 The LSV curve shows the overall electrochemical efficiency of Ce-NiFe LDH / GO in a dual-electrode configuration in 1M KOH for the overall decomposition of water according to the present invention.

[0038] Figure 13 The CP curve shows the electrochemical efficiency of the Ce-NiFe LDH / GO in the overall water decomposition under a dual-electrode configuration in 1M KOH according to the present invention.

[0039] Figure 14 The images show the SEM morphology and energy dispersive spectroscopy (EDS) of the Ce-doped graphene-NiFe LDH bifunctional catalyst prepared in Example 1 of this invention. Figure 14 a to c are SEM scans of NiFe LDH, Ce-NiFe LDH, and Ce-NiFe LDH / GO, respectively; Figure 14 d to e are mapping diagrams of Ce-NiFe LDH / GO. Detailed Implementation

[0040] The following embodiments are merely some, not all, of the embodiments of the present invention. Therefore, the detailed descriptions of the embodiments provided below are not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0041] In this invention, unless otherwise specified, all equipment and raw materials are commercially available or commonly used in the industry. The methods described in the following embodiments are conventional methods in the art, unless otherwise specified.

[0042] The graphene oxides in the following examples were all pre-fabricated using the Hummer method.

[0043] Graphene oxide was prepared using the Hummer process, specifically as follows: 23 mL of concentrated sulfuric acid was added to a 500 mL beaker in an ice-water bath. Then, 1 g of flake graphite and 0.5 g of sodium nitrate were weighed using an electronic balance, mixed, and added to the beaker, stirring until homogeneous. 3 g of potassium permanganate was added to the reaction flask in portions, stirring thoroughly after each addition, controlling the reaction temperature to not exceed 20°C, and continuing stirring for approximately 2 hours. The reaction system was then heated to approximately 35°C and stirred for another 30 minutes. 46 mL of deionized water was slowly added to the beaker, stirring continuously until the solution turned brownish-yellow. 5 g of 30% hydrogen peroxide was added dropwise until the solution turned bright yellow. The solution was filtered while hot and washed with 5% HCl solution and deionized water until the filtrate was neutral. Finally, it was freeze-dried to obtain graphene oxide.

[0044] Example 1: Ce-doped graphene-NiFe-LDH bifunctional catalyst

[0045] Ce-doped graphene-NiFe-LDH bifunctional catalyst prepared by hydrothermal method

[0046] 10 mg of graphene oxide was dispersed in 40 ml of distilled water and sonicated for 10 min to obtain an aqueous graphene dispersion. 3 mmol Ni(NO3)2·6H2O, 1 mmol Fe(NO3)3·9H2O, 0.1 mmol CeCl3·7H2O, 4 mmol NH4F, and 1 mmol urea were added to the aqueous graphene dispersion. After sonication for 30 min, the solution was transferred to a 70 ml polytetrafluoroethylene-lined reactor and hydrothermally reacted at 120 °C for 6 hours.

[0047] The reaction product was filtered, washed, and dried to obtain a Ce-doped graphene-NiFe-LDH bifunctional catalyst.

[0048] This embodiment also synthesized a Ce-doped NiFe-LDH bifunctional catalyst without graphene. The preparation process is the same as above, except that the graphene in the preparation process is omitted.

[0049] This embodiment also synthesized a simple NiFe-LDH bifunctional catalyst, prepared in the same manner as above, for better comparison.

[0050] In this embodiment, the above-mentioned catalyst was also used to prepare an electrode, as follows:

[0051] 1. Pretreatment of nickel foam

[0052] Cut the nickel foam, which will serve as the electrode, into 1*1cm pieces. 2 The squares (areas exposed to the electrolyte solution) were then washed and sonicated in a 1:1 isopropanol:deionized water mixture. The nickel foam was then dried at 60°C for 1 hour.

[0053] 2. Preparation of Catalyst Ink

[0054] In preparing the catalyst ink, 10 mg of catalyst was mixed with 0.5 mL of deionized water, 0.5 mL of isopropanol and 0.22 mL of Nafion solution, and sonicated at room temperature for 30 min. The mixture was then coated onto nickel foam and dried to obtain the working electrode.

[0055] Electrodes were prepared using the NiFe-LDH and Ce-NiFe-LDH from Example 1, following the same procedure as above.

[0056] I. Characterization and Analysis of Catalysts

[0057] The morphology of the Ce-doped graphene-NiFe LDH bifunctional catalyst was characterized by scanning electron microscopy (SEM), and its electronic structure and composition were characterized by X-ray photoelectron spectroscopy (XPS). The structure of the Ce-doped graphene-NiFe LDH bifunctional catalyst was characterized by energy-dispersive X-ray spectroscopy (EDX). Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) analyses were performed using a CHI760 electrochemical workstation. Electrochemical tests were conducted in 1M KOH solution. The working electrode was a catalyst-modified nickel foam electrode, the counter electrode was a platinum wire, and the reference electrode was a Hg / HgO electrode.

[0058] II. Performance Testing:

[0059] LSV, EIS, and ECSA analyses were performed using a CHI 760 electrochemical workstation. The electrolyte was 1M KOH solution. The working electrode was a catalyst-modified nickel foam electrode, the counter electrode was a platinum sheet, and the reference electrode was a Hg / HgO electrode. The working electrode was modified with a pre-prepared slurry of nickel foam.

[0060] (1) Performance testing of the electrochemical hydrogen evolution reaction (HER)

[0061] During LSV testing, the voltage window was set to -0.8V to -2V, and the scan rate was 5mV / s. -1 The LSV curves compared the hydrogen evolution capabilities of three catalysts: NiFe-LDH, Ce-NiFe-LDH, and Ce-NiFe-LDH / GO. Figure 1 ), at 20mAcm -2 The overpotentials were 401 mV, 411 mV, and 410 mV, respectively. A commercially available Pt / C catalyst was also measured, with an overpotential of 530 mV. The HER performance of all three catalysts was superior to that of the commercial catalyst. Ce-NiFe-LDH / GO exhibited a relatively small overpotential at the same current density, second only to NiFe-LDH. Tafel curve fitting was further performed on the three catalysts. Figure 2 The values ​​are 269.73 mV dec. -1 331.8mV dec -1 and 264.17mV dec -1 Furthermore, the overpotentials of the three catalysts at different current densities were compared to obtain an overpotential comparison analysis diagram. Figure 3 The above results indicate that the catalyst doped with Ce and graphene oxide has significantly improved performance.

[0062] ECSA tests were performed on the three catalysts at 20 mV s. -1 40mV s -1 60mV s -1 80mV s -1 100mV s -1 120mV s -1 CV tests were performed at different scan rates, with the voltage window set to -0.5V to -0.6V, and the double-layer capacitance Cdl plot was plotted. Figure 4 The greater the slope, the larger its electrochemical surface area.

[0063] EIS testing was performed on the three catalysts. Figure 5 The results showed that Ce-NiFe LDH / GO had the lowest electrical impedance.

[0064] In summary, Ce-NiFe-LDH / GO exhibits the best HER performance.

[0065] (2) Oxygen Evolution Reaction (OER) Performance Test

[0066] During LSV testing, the voltage window was set to 0.2V–0.8V, and the scan rate was 5mV / s. -1The LSV curves compared the hydrogen evolution capabilities of three catalysts: NiFe LDH, Ce-NiFe LDH, and Ce-NiFe LDH / GO. Figure 6 ), at 10mA cm -2 The overpotentials were 249 mV, 265 mV, and 248 mV, respectively. A commercial RuO catalyst was also measured, with an overpotential of 320 mV. The OER performance of all three catalysts was superior to that of the commercial catalyst, while Ce-NiFe LDH / GO exhibited the lowest overpotential at the same current density. Tafel curve fitting was further performed on the three catalysts. Figure 7 The values ​​are 100.27 mV dec. -1 100.39mVdec -1 and 84.35mV dec -1 Furthermore, the overpotentials of the three catalysts at different current densities were compared to obtain an overpotential comparison analysis diagram. Figure 8 The above results indicate that the catalyst doped with Ce and graphene oxide has significantly improved performance.

[0067] ECSA tests were performed on the three catalysts at 20 mV s. -1 40mV s -1 60mV s -1 80mV s -1 100mV s -1 120mV s -1 CV tests were performed at different scan rates, with the voltage window set to 0.15V–0.25V, and the double-layer capacitance Cdl plot was drawn. Figure 9 The greater the slope, the larger the electrochemical surface area. The results show that the electrochemical surface areas of the three are approximately the same.

[0068] EIS testing was performed on the three catalysts. Figure 10 The results showed that Ce-NiFe LDH / GO had the lowest electrical impedance.

[0069] In summary, Ce-NiFe LDH / GO exhibits the best OER performance.

[0070] (3) Application of catalysts in total hydrolysis

[0071] Ce-NiFe LDH / GO was formulated into a catalyst ink and sprayed onto nickel foam, serving as both the cathode and anode for full hydrolysis testing. The electrolyzer structure is as follows: Figure 11As shown. Given the excellent bifunctional activity of Ce-NiFe LDH / GO, namely its bifunctional catalytic activity for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), we further tested the overall water splitting performance of Ce-NiFe LDH / GO as both anode and cathode using a 1.0M KOH dual-electrode system. Polarization curves ( Figure 12 The data shows that Ce-NiFeLDH / GO requires only a 1.852V battery voltage to drive a 10mAcm in alkaline media. -2 The current density. At 10 mA cm⁻¹ -2 Further time-potential measurement experiments were conducted at current densities, such as... Figure 13 As shown, the obtained potential stabilized within 24 hours without significant increase, highlighting the long-term stability of the system. After stability testing, 1.855V was required to reach 10 mAcm. -2 The current density remains almost constant, indicating good stability throughout the water electrolysis process.

[0072] (4) Figure 2 The images show the SEM morphology and mapping of the three catalysts prepared in Example 1 of this invention.

[0073] From the figure ( Figure 14 As can be seen from a to c), NiFe-LDH has sheet-like aggregated particles, Ce-NiFe-LDH has a hexagonal structure, and Ce-NiFe-LDH / GO has a petal-like structure. The layered stacking of this structure is more stable, and the layered stacking mode is conducive to electron transfer and enhances the adsorption of metal ions, which can improve the conductivity of the catalyst and thus improve its electrocatalytic performance.

[0074] Figure 14 Figures d to e show the mapping diagrams of the Ce-NiFe-LDH / GO catalyst, indicating that Ni, Fe, and Ce are uniformly distributed in the catalyst.

[0075] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing a Ce-doped graphene-NiFe-LDH bifunctional catalyst, characterized in that, The process includes the following steps: A hydrothermal reaction is carried out in an aqueous solution containing a protective agent and a precipitant at 100–120°C to obtain the Ce-doped graphene NiFe-LDH bifunctional catalyst.

2. The preparation method according to claim 1, characterized in that, The graphene oxide was produced using the Hummer process; The iron source is an iron salt, selected from at least one of FeSO4·7H2O, FeCl3·6H2O, Fe(NO3)3·9H2O, and Fe(CH3COO)3; The nickel source is a nickel salt, selected from at least one of NiSO4·6H2O, NiCl2·6H2O, Ni(NO3)2·6H2O, and Ni(CH3COO)2; The cerium source is a cerium salt selected from at least one of Ce(SO4)3·6H2O, CeCl3·7H2O, and Ce(NO3)3·6H2O.

3. The preparation method according to claim 1, characterized in that, The mass ratio of the graphene oxide to the iron in the iron source is 1:7 to 1:10; The mass ratio of nickel in the nickel source to iron in the iron source is 3:1 to 5:

1. The mass ratio of cerium in the cerium source to the mass ratio of iron in the iron source is 1:5 to 1:

10.

4. The preparation method according to claim 1, characterized in that, The protective agent is selected from at least one of ammonium fluoride and ammonium acetate; the mass ratio of the protective agent to the iron in the iron source is 3:1 to 6:

1.

5. The preparation method according to claim 1, characterized in that, The precipitant is selected from at least one of urea and ethylenediamine; the mass ratio of the precipitant to the iron in the iron source is 1:1 to 3:

1.

6. The preparation method according to claim 1, characterized in that, The hydrothermal reaction time is 6 to 12 hours, and the preparation method also includes a pretreatment to remove oxides from the graphene surface by ultrasound; the post-reaction process also includes filtration, washing and drying.

7. A Ce-doped graphene-NiFe-LDH bifunctional catalyst, prepared according to any one of claims 1 to 6, characterized in that, Using graphene as a support, the graphene support is loaded with Ce-doped NiFe-LDH to form the bifunctional catalyst, which has a petal-like structure. This structure is stable in layered stacking, and the layered stacking mode is conducive to electron transfer.

8. The Ce-doped graphene-NiFe-LDH bifunctional catalyst according to claim 7, characterized in that, The catalyst has dual-function catalytic activity for hydrogen evolution (HER) and oxygen evolution (OER).

9. The application of the Ce-doped graphene-NiFe-LDH bifunctional catalyst of claim 8 in the preparation of electrodes, characterized in that, In the preparation of a gas diffusion electrode, the catalyst is printed as a catalyst layer on the gas diffusion electrode for use in the water electrolysis reaction.

10. The application according to claim 9, characterized in that, The water electrolysis reaction is carried out under alkaline conditions, and the catalyst is printed on the gas diffusion electrode as both the cathode and anode catalyst layers for the water electrolysis reaction.

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