Expanded graphite-based catalyst, and preparation method and application thereof

Abstract

This invention provides an expanded graphite-based catalyst, its preparation method, and its application, relating to the field of electrocatalysis technology. The expanded graphite-based catalyst provided by this invention comprises an expanded graphite-based material (including expanded graphite and a binder) supported on the surface of a current collector, a nickel-iron layered double hydroxide deposited on the surface of the expanded graphite-based material, and Ni3S2 deposited on the surface of the nickel-iron layered double hydroxide. The expanded graphite-based catalyst provided by this invention exhibits excellent trifunctional (OER, UOR, and HER) catalytic activity and cycling stability. Example results show that the expanded graphite-based catalyst (under alkaline conditions) exhibits excellent trifunctional (OER, UOR, and HER) catalytic activity and cycling stability at 10 mA·cm⁻¹. ‑2 At the specified current density, the overpotential of OER was as low as 229.2 mV, the overpotential of UOR as low as 111.6 mV, and the overpotential of HER as low as 93.2 mV; for all three reactions, at 100 mA·cm⁻¹ ‑2 It can operate stably for more than 100 hours under high current density.

Description

Technical Field

[0001] This invention relates to the field of electrocatalysis technology, and in particular to an expanded graphite-based catalyst, its preparation method, and its application. Background Technology

[0002] Hydrogen energy, with its outstanding characteristics of high energy density and zero carbon emissions throughout the process, has become a green and clean energy source with great development potential. Electrocatalytic water splitting is an effective technical route for producing high-purity hydrogen, but its large-scale application is limited by the oxygen evolution reaction (OER) at the anolyte. This reaction involves complex four-electron transfer steps, and the breaking of OH bonds and the formation of OO bonds both require overcoming high energy barriers, resulting in a slow reaction kinetic rate, which has become a key bottleneck restricting the development of electrocatalytic water splitting technology.

[0003] Faced with this technological challenge, the resource utilization of urea in wastewater is gradually becoming a new direction for sustainable development that combines environmental value and energy significance. Approximately 80% of the nitrogen in municipal wastewater originates from urea in human urine. Direct discharge of this substance without treatment can easily lead to a series of ecological problems such as eutrophication and water acidification. It is noteworthy that urea is not merely a pollutant; it is not only a core raw material for the preparation of agricultural fertilizers and animal feed additives, but also possesses considerable energy development value: it contains 6.71% hydrogen by mass, has a solubility of up to 1079 g / L at 20°C, and an energy density of up to 16.9 MJ / L. Traditional urea removal processes generally suffer from low efficiency and have not fully exploited its hydrogen source potential. Therefore, technologies for producing hydrogen from urea in urine have become a research hotspot in the field of energy materials.

[0004] Nickel-based electrocatalytic materials, typically represented by nickel-iron layered double hydroxides (NiFe-LDH), exhibit outstanding catalytic activity in the oxygen evolution reaction (OER) and urea oxidation reaction (UOR), effectively meeting the catalytic requirements of these two reactions. However, these materials generally suffer from a critical weakness: extremely poor catalytic performance in the hydrogen evolution reaction (HER). Because they cannot simultaneously achieve efficient catalysis of OER, UOR, and HER, they fail to meet the practical requirements of multifunctional catalytic performance in a complete water electrolysis system, thus severely limiting the comprehensive promotion and practical application of this type of nickel-based material in the field of complete water electrolysis. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide an expanded graphite-based catalyst, its preparation method, and its applications. The expanded graphite-based catalyst provided by this invention can achieve highly efficient catalysis of three types of reactions: OER, UOR, and HER.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: The present invention provides an expanded graphite-based catalyst comprising an expanded graphite-based material supported on the surface of a current collector, a nickel-iron layered double hydroxide deposited on the surface of the expanded graphite-based material, and Ni3S2 deposited on the surface of the nickel-iron layered double hydroxide, wherein the expanded graphite-based material comprises expanded graphite and a binder.

[0007] Preferably, the current collector is nickel foam; the expanded graphite-based catalyst is nanospheres.

[0008] This invention provides a method for preparing the expanded graphite-based catalyst described above, comprising the following steps: Expanded graphite, binder and solvent are mixed to form a slurry, and the resulting slurry is desolventized and molded to obtain an expanded graphite-based material; The expanded graphite-based material is loaded onto the surface of the current collector as a working electrode, and a mixed solution of iron salt, nickel salt and urea is used as the electrolyte to perform the first electrodeposition, thereby depositing a nickel-iron layered double hydroxide on the surface of the expanded graphite-based material. Using expanded graphite-based material with deposited nickel-iron layered double hydroxides as the working electrode and a mixed solution of nickel salt and sulfur source as the electrolyte, a second electrodeposition is performed to deposit Ni3S2 on the surface of the nickel-iron layered double hydroxides, thereby obtaining the expanded graphite-based catalyst.

[0009] Preferably, the iron salt in the mixed solution of iron salt, nickel salt and urea includes ferric nitrate and the nickel salt includes nickel nitrate; the concentrations of iron salt, nickel salt and urea in the mixed solution of iron salt, nickel salt and urea are independently 0.1~0.2 mol / L.

[0010] Preferably, the nickel salt in the mixed solution of nickel salt and sulfur source includes nickel nitrate, and the sulfur source includes thiourea; the concentration of nickel salt in the mixed solution of nickel salt and sulfur source is 0.1~0.2 mol / L, and the concentration of sulfur source is 0.5~1.5 mol / L.

[0011] Preferably, the first and second electrodepositions are performed using a three-electrode system, with a saturated calomel electrode as the reference electrode and a platinum wire as the counter electrode.

[0012] Preferably, the potential for the first electrodeposition is -0.8 to -1.2V, and the deposition time is 600 to 1800s.

[0013] Preferably, the potential for the second electrodeposition is -0.6 to -1V, and the deposition time is 900 to 2100s.

[0014] This invention provides the application of the expanded graphite-based catalyst described in the above technical solutions or the expanded graphite-based catalyst prepared by the above technical solutions in the electrolysis of water.

[0015] Preferably, the water used for water electrolysis includes urea.

[0016] This invention provides an expanded graphite-based catalyst, comprising an expanded graphite-based material supported on a current collector surface, a nickel-iron layered double hydroxide (NiFe-LDH) deposited on the surface of the expanded graphite-based material, and Ni3S2 deposited on the surface of the nickel-iron layered double hydroxide. The expanded graphite-based material comprises expanded graphite (EG) and a binder. Compared with the prior art, this invention has the following advantages: This invention achieves a comprehensive improvement and breakthrough in catalytic performance through scientific component design and precise structural control. Specifically, on the one hand, by leveraging the excellent HER catalytic properties of Ni3S2, the performance defects of NiFe-LDH in the HER reaction are effectively compensated, successfully realizing highly efficient synergistic catalysis of OER, UOR, and HER reactions, completely solving the pain point of the single catalytic function of traditional single nickel-based materials. On the other hand, through the heterogeneous interface interaction formed between Ni3S2, NiFe-LDH, and expanded graphite (EG), and the electron transfer regulation effect at the interface, the catalytic synergistic effect among the components is further enhanced, and the electron transport path is significantly optimized. At the same time, by fully utilizing the unique advantages of expanded graphite (EG) as a support—high conductivity, large specific surface area, and the ability to promote the full exposure of catalytic active sites—interfacial charge transfer resistance is effectively reduced, significantly improving the overall catalytic efficiency and cycle stability of the catalyst. This invention successfully breaks through the application limitations of traditional single nickel-based electrocatalytic materials. The expanded graphite-based catalyst provided has excellent trifunctional (OER, UOR, and HER) catalytic activity and cycle stability, ultimately providing a more feasible and superior technical solution for the industrialization and practical application of the whole water electrolysis system.

[0017] In this embodiment of the invention, the expanded graphite-based catalyst provided by the present invention is used as the working electrode, the Hg / HgO electrode as the reference electrode, and the platinum sheet electrode as the counter electrode. In a 1.0 mol / L KOH electrolyte, at 5 mV·s... -1 Under the sweep rate test conditions, linear sweep voltammetry tests were performed for OER, UOR, and HER. The results show that the expanded graphite-based catalyst provided by this invention exhibits excellent OER, UOR, and HER activity and stability under alkaline conditions: 10 mA·cm⁻¹ -2 At the specified current density, the overpotential of OER was as low as 229.2 mV, the overpotential of UOR as low as 111.6 mV, and the overpotential of HER as low as 93.2 mV; for all three reactions, the electrode at 100 mA·cm⁻¹... -2 It can operate stably for more than 100 hours under high current density, demonstrating outstanding stability. Attached Figure Description

[0018] Figure 1 Scanning electron microscope image of the Ni3S2 / NiFe-LDH / EG catalyst prepared in Example 1; Figure 2 The OER linear sweep voltammetry curves of the Ni3S2 / NiFe-LDH / EG catalysts prepared in Examples 1-5 are shown. Figure 3 The UOR linear sweep voltammetry curves of the Ni3S2 / NiFe-LDH / EG catalysts prepared in Examples 1-5 are shown. Figure 4 The HER linear sweep voltammetry curves of the Ni3S2 / NiFe-LDH / EG catalysts prepared in Examples 1-5 are shown. Figure 5 The voltage-time chronopotential curves are for the Ni3S2 / NiFe-LDH / EG catalyst prepared in Example 1. Figure 5 In the middle, (a) corresponds to OER, (b) corresponds to UOR, and (c) corresponds to HER; Figure 6 The OER linear sweep voltammetry curves are for the catalysts prepared in Example 1 and Comparative Examples 1-4. Figure 7 The UOR linear sweep voltammetry curves are for the catalysts prepared in Example 1 and Comparative Examples 1-4. Figure 8 The HER linear sweep voltammetry curves are for the catalysts prepared in Example 1 and Comparative Examples 1-4. Figure 9 The UOR||HER and OER||HER total hydrolysis performance curves of the catalyst prepared in Example 1. Detailed Implementation

[0019] The present invention provides an expanded graphite-based catalyst comprising an expanded graphite-based material supported on the surface of a current collector, a nickel-iron layered double hydroxide (NiFe-LDH) deposited on the surface of the expanded graphite-based material, and Ni3S2 deposited on the surface of the nickel-iron layered double hydroxide, wherein the expanded graphite-based material comprises expanded graphite (EG) and a binder.

[0020] In this invention, the current collector is preferably nickel foam (NF). This invention does not have any special requirements for the nickel foam, and any nickel foam well known to those skilled in the art can be used.

[0021] This invention does not impose any special requirements on the expanded graphite, which can be prepared using commercially available products or methods well known to those skilled in the art. In the embodiments of this invention, the expanded graphite is prepared according to CN119503790 A. In this invention, the binder can be Nafion (a perfluorosulfonic acid polymer). This invention does not impose any special requirements on the amount of binder used, as long as it is sufficient to achieve bonding of the expanded graphite. In the embodiments of this invention, the mass ratio of expanded graphite to Nafion is 19:0.05.

[0022] This invention does not have any special requirements for the loading amount of the expanded graphite-based material on the surface of the current collector.

[0023] In this embodiment of the invention, nickel foam (current collector) and expanded graphite are used as composite supports (denoted as EG / NF composite supports). The EG / NF composite supports can provide a good loading and support basis for the active components, help the catalyst composite structure to fully expose the catalytic active sites, and significantly improve the interfacial charge migration efficiency, thereby helping to solve the performance and application problems of existing non-precious metal oxygen evolution catalysts.

[0024] In this invention, nickel-iron layered double hydroxide (NiFe-LDH) serves as the core component of OER / UOR, achieving excellent intrinsic activity through bimetallic electronic synergy and layered mass transfer advantages. Ni3S2 compensates for the shortcomings of HER performance and assists in improving OER / UOR activity, realizing synergistic catalysis of the three reactions (OER, UOR, and HER). Expanded graphite (EG) support has both high conductivity and large specific surface area characteristics, which can disperse active components and inhibit their exfoliation, effectively reducing interfacial charge transfer resistance and significantly improving the overall catalytic efficiency and cycle stability of the catalyst.

[0025] In this invention, the expanded graphite-based catalyst is preferably nanosphere-shaped, which is beneficial for fully exposing the active sites to enhance the trifunctional catalytic activity of OER, UOR and HER.

[0026] The expanded graphite-based catalyst provided by this invention, with its complementary components and three-phase synergy, possesses excellent trifunctional (OER, UOR, and HER) catalytic activity and long-term cycle stability, breaking through the application limitations of single nickel-based materials.

[0027] This invention provides a method for preparing the expanded graphite-based catalyst described above, comprising the following steps: Expanded graphite, binder and solvent are mixed to form a slurry, and the resulting slurry is desolventized and molded to obtain an expanded graphite-based material; The expanded graphite-based material is loaded onto the surface of the current collector as a working electrode, and a mixed solution of iron salt, nickel salt and urea is used as the electrolyte to perform the first electrodeposition, thereby depositing a nickel-iron layered double hydroxide on the surface of the expanded graphite-based material. Using expanded graphite-based material with deposited nickel-iron layered double hydroxides as the working electrode and a mixed solution of nickel salt and sulfur source as the electrolyte, a second electrodeposition is performed to deposit Ni3S2 on the surface of the nickel-iron layered double hydroxides, thereby obtaining the expanded graphite-based catalyst.

[0028] Unless otherwise specified, all raw materials involved in this invention are commercially available products well known in the art.

[0029] This invention involves mixing expanded graphite, binder, and solvent to form a slurry, then removing the solvent from the resulting slurry and molding it to obtain an expanded graphite-based material.

[0030] In this invention, the binder is preferably Nafion. In this embodiment, the Nafion is added in the form of a 5wt% Nafion solution, and the mass ratio of expanded graphite to Nafion solution is 19:1. The solvent is preferably ethanol. This invention does not have special requirements on the amount of solvent used, as long as it can form a slurry. The slurry preparation is preferably carried out under ultrasonic conditions. In this invention, the solvent removal method is preferably water bath heating and stirring. In this embodiment, the water bath heating and stirring temperature is 60°C. In this invention, after molding, it is also preferred to include cutting. In this embodiment, the molded material is cut into dimensions of 1cm × 1cm (approximately 1mg in mass). In this invention, the expanded graphite serves as the electrodeposition substrate.

[0031] After obtaining the expanded graphite-based material, the present invention loads the expanded graphite-based material onto the surface of the current collector as a working electrode (denoted as the first working electrode), and uses a mixed solution of iron salt, nickel salt and urea as the electrolyte to perform a first electrodeposition, thereby depositing a nickel-iron layered double hydroxide on the surface of the expanded graphite-based material.

[0032] In this embodiment of the invention, the method of loading the current collector surface is as follows: the expanded graphite-based material is pressed together with the current collector using a tablet press, and the pressing pressure is 10 MPa. Taking the current collector as nickel foam as an example, in this embodiment of the invention, the first working electrode is represented as an EG / NF composite electrode.

[0033] In this invention, the iron salt in the mixed solution of iron salt, nickel salt, and urea preferably includes ferric nitrate (e.g., Fe(NO3)3·9H2O), and the nickel salt preferably includes nickel nitrate (e.g., Ni(NO3)2·6H2O). The solvent for the mixed solution of iron salt, nickel salt, and urea is preferably a mixture of N,N-dimethylformamide (DMF) and water, with a volume ratio of DMF to water of 10:1, and the water is preferably deionized water. In this invention, the concentrations of iron salt, nickel salt, and urea in the mixed solution of iron salt, nickel salt, and urea are preferably independently 0.1~0.2 mol / L, and can be 0.15 mol / L. In an embodiment of this invention, the method for preparing the mixed solution of iron salt, nickel salt, and urea is as follows: a mixed solvent of DMF and water is prepared at a volume ratio of 10:1; iron salt, nickel salt, and urea are mixed and added to the mixed solvent; and the mixture is ultrasonically stirred to obtain the mixed solution of iron salt, nickel salt, and urea.

[0034] In this invention, the first electrodeposition is preferably performed using a three-electrode system, with the reference electrode preferably being a saturated calomel electrode (SCE) and the counter electrode preferably being a platinum wire. In this embodiment, a CHI760E electrochemical workstation is used to construct the three-electrode system. In this invention, the potential for the first electrodeposition is preferably -0.8 to -1.2 V, and can be -0.8, -0.9, -1, -1.1, or -1.2 V; the deposition time is preferably 600 to 1800 s, and can be 600, 900, 1000, 1200, 1500, or 1800 s; the first electrodeposition is preferably constant potential deposition.

[0035] After the first electrodeposition is completed, the obtained material is preferably rinsed and dried in sequence; the drying temperature is preferably 65°C, and the drying is preferably vacuum drying.

[0036] After depositing nickel-iron layered double hydroxides on the expanded graphite-based material, the present invention uses the expanded graphite-based material on which the nickel-iron layered double hydroxides are deposited as the working electrode (denoted as the second working electrode) and a mixed solution of nickel salt and sulfur source as the electrolyte to perform a second electrodeposition, thereby depositing Ni3S2 on the surface of the nickel-iron layered double hydroxides to obtain the expanded graphite-based catalyst.

[0037] In this embodiment of the invention, the second working electrode is represented as a NiFe-LDH / EG / NF composite electrode.

[0038] In this invention, the nickel salt in the mixed solution of nickel salt and sulfur source preferably includes nickel nitrate (such as Ni(NO3)2·6H2O), and the sulfur source preferably includes thiourea (SC(NH2)2). The solvent of the mixed solution of nickel salt and sulfur source is preferably a mixed solvent of DMF and water, wherein the volume ratio of DMF to water in the mixed solvent is preferably 10:1, and the water is preferably deionized water. In this invention, the concentration of nickel salt in the mixed solution of nickel salt and sulfur source is preferably 0.1~0.2 mol / L, which can be 0.15 mol / L, and the concentration of sulfur source is preferably 0.5~1.5 mol / L, which can be 1 mol / L. In an embodiment of this invention, the mixed solution of nickel salt and sulfur source is prepared by: preparing a mixed solvent of DMF and water at a volume ratio of 10:1, adding the nickel salt and sulfur source to the mixed solvent, and ultrasonically stirring to obtain the mixed solution of nickel salt and sulfur source.

[0039] In this invention, the second electrodeposition is preferably performed using a three-electrode system, with the reference electrode preferably being a saturated calomel electrode and the counter electrode preferably being a platinum wire. In this invention, the potential for the second electrodeposition is preferably -0.6 to -1V, and can be -0.6, -0.7, -0.8, -0.9, or -1V; the deposition time is preferably 900 to 2100 s, and can be 1000, 1200, 1500, 1800, 2000, or 2100 s; the second electrodeposition is preferably constant potential deposition.

[0040] After the second electrodeposition is completed, the obtained material is preferably rinsed and dried sequentially to obtain the expanded graphite-based catalyst. In this invention, the drying temperature is preferably 65°C, and the drying is preferably vacuum drying.

[0041] In this embodiment of the invention, the expanded graphite-based catalyst is represented as Ni3S2 / NiFe-LDH / EG.

[0042] The preparation method provided by this invention is simple to operate and can be widely applied to energy storage and conversion technologies involving water electrolysis and other oxygen evolution reactions, thus having high practical value.

[0043] This invention provides the application of the expanded graphite-based catalyst described in the above technical solutions or the expanded graphite-based catalyst prepared by the above technical solutions in the electrolysis of water.

[0044] In this invention, the water used for water electrolysis preferably includes urea, and the concentration of urea in the water is preferably 0.1~0.2 mol / L, and can be 0.15 mol / L. In this invention, the water electrolysis is preferably carried out under alkaline conditions.

[0045] The expanded graphite-based catalyst provided by this invention has excellent OER, UOR, HER activity and stability, successfully breaking through the application limitations of traditional single nickel-based electrocatalytic materials, and has broad market application prospects in the field of water electrolysis.

[0046] To further illustrate the present invention, the expanded graphite-based catalyst, its preparation method, and its application provided by the present invention are described in detail below with reference to examples, but these should not be construed as limiting the scope of protection of the present invention.

[0047] The expanded graphite in this example was prepared according to Example 2 of CN119503790 A: Example 1 An expanded graphite-based catalyst is prepared by the following steps: (1) Weigh expanded graphite (EG) and Nafion solution (5wt%) at a mass ratio of 19:1, mix with ethanol and ultrasonically prepare slurry, stir and remove alcohol in a 60℃ water bath, shape and cut and press onto the surface of nickel foam (NF) to obtain EG / NF composite electrode. (2) Add ferric nitrate nonahydrate (Fe(NO3)3·9H2O, 0.15M), nickel nitrate hexahydrate (Ni(NO3)2·6H2O, 0.15M) and urea (CO(NH2)2, 0.15M) to a mixed solvent of DMF and deionized water (the volume ratio of DMF to deionized water is 10:1) to obtain a mixed solution of iron salt, nickel salt and urea; (3) A three-electrode system was built using a CHI760E electrochemical workstation. The working electrode was the EG / NF composite electrode prepared in the previous stage, the reference electrode was a saturated calomel electrode (SCE), and the counter electrode was a platinum wire. The mixed solution of the iron salt, nickel salt and urea was used as the electrolyte. The electrode was deposited at a constant potential of -1V for 1200s. After rinsing the product, it was vacuum dried overnight to obtain the NiFe-LDH / EG / NF composite electrode. (4) Add nickel nitrate hexahydrate (Ni(NO3)2·6H2O, 0.15M) and thiourea (SC(NH2)2, 1.0M) to a mixed solvent of DMF and deionized water (the volume ratio of DMF to deionized water is 10:1) to obtain a mixed solution of nickel salt and sulfur source. (5) Using the mixed solution of the nickel salt and sulfur source as the electrolyte, and the NiFe-LDH / EG / NF composite electrode as the working electrode, a three-electrode system was used to deposit the catalyst at a constant potential of -0.9V for 1500s. After washing the product, it was vacuum dried overnight to obtain the expanded graphite-based catalyst, which is denoted as Ni3S2 / NiFe-LDH / EG catalyst (Ni3S2 / NiFe-LDH / EG-1200).

[0048] Figure 1The image shown is a scanning electron microscope (SEM) image of the Ni3S2 / NiFe-LDH / EG catalyst prepared in Example 1. Figure 1 It can be seen that the morphology of the prepared Ni3S2 / NiFe-LDH / EG catalyst is that of nanosphere aggregates.

[0049] Using the Ni3S2 / NiFe-LDH / EG catalyst prepared in Example 1 as the working electrode, the Hg / HgO electrode as the reference electrode, and the platinum sheet electrode as the counter electrode, an electrolysis was performed in 1.0 M KOH electrolyte at 5 mV·s⁻¹. -1 Under the scan rate test conditions, linear scan voltammetry tests were performed for OER, UOR, and HER. For the UOR linear scan voltammetry test, urea (0.33M) was added to the electrolyte. The test results are shown below. Figures 2-4 Among them, the potentials measured by OER, UOR and HER are converted according to formulas (1) to (3) respectively (in each formula, E(RHE) represents the electrode potential relative to the reversible hydrogen electrode, and η represents the overpotential): .

[0050] Figure 2 The OER linear sweep voltammetric curves showed that, in 1.0 M KOH electrolyte, 5 mV·s -1 Under the sweep rate test conditions, the Ni3S2 / NiFe-LDH / EG catalyst prepared in Example 1 only requires an overpotential of 229.2 mV to reach 10 mA·cm⁻¹. -2 The current density exhibits excellent electrocatalytic OER activity of the catalyst. Figure 3 The UOR linear sweep voltammetry curves show that the Ni3S2 / NiFe-LDH / EG catalyst prepared in Example 1 requires only 111.6 mV overpotential to reach 10 mA·cm⁻¹. -2 The current density exhibits excellent electrocatalytic UOR activity of the catalyst. Figure 4 The HER linear sweep voltammetry curves showed that the Ni3S2 / NiFe-LDH / EG catalyst prepared in Example 1 only required an overpotential of 93.2 mV to reach 10 mA·cm⁻¹. -2 The current density exhibits excellent electrocatalytic HER activity of the catalyst.

[0051] Figure 5 The voltage-time chronopotential curves are for the Ni3S2 / NiFe-LDH / EG catalyst prepared in Example 1. Figure 5 In the diagram, (a) corresponds to OER, (b) corresponds to UOR, and (c) corresponds to HER. Figure 5 It can be seen that the Ni3S2 / NiFe-LDH / EG catalyst prepared in Example 1 exhibits excellent long-term stability at 100 mA·cm⁻¹.-2 It can operate stably for more than 100 hours at a current density.

[0052] Example 2 An expanded graphite-based catalyst is prepared by the following steps: (1) Weigh expanded graphite (EG) and Nafion solution (5wt%) at a mass ratio of 19:1, mix with ethanol and ultrasonically prepare slurry, stir and remove alcohol in a 60℃ water bath, shape and cut and press onto the surface of nickel foam (NF) to obtain EG / NF composite electrode. (2) Add ferric nitrate nonahydrate (Fe(NO3)3·9H2O, 0.15M), nickel nitrate hexahydrate (Ni(NO3)2·6H2O, 0.15M) and urea (CO(NH2)2, 0.15M) to a mixed solvent of DMF and deionized water (the volume ratio of DMF to deionized water is 10:1) to obtain a mixed solution of iron salt, nickel salt and urea; (3) A three-electrode system was built using a CHI760E electrochemical workstation. The working electrode was the EG / NF composite electrode prepared in the previous stage, the reference electrode was a saturated calomel electrode (SCE), and the counter electrode was a platinum wire. The mixed solution of the iron salt, nickel salt and urea was used as the electrolyte. The electrode was deposited at a constant potential of -1V for 600s. After rinsing the product, it was vacuum dried overnight to obtain the NiFe-LDH / EG / NF composite electrode. (4) Add nickel nitrate hexahydrate (Ni(NO3)2·6H2O, 0.15M) and thiourea (SC(NH2)2, 1.0M) to a mixed solvent of DMF and deionized water (the volume ratio of DMF to deionized water is 10:1) to obtain a mixed solution of nickel salt and sulfur source. (5) Using the mixed solution of the nickel salt and sulfur source as the electrolyte, and the NiFe-LDH / EG / NF composite electrode as the working electrode, a three-electrode system was used to deposit the catalyst at a constant potential of -0.9V for 1500s. After washing the product, it was vacuum dried overnight to obtain the expanded graphite-based catalyst, which is denoted as Ni3S2 / NiFe-LDH / EG catalyst (Ni3S2 / NiFe-LDH / EG-600).

[0053] Using the Ni3S2 / NiFe-LDH / EG catalyst prepared in Example 2 as the working electrode, the Hg / HgO electrode as the reference electrode, and the platinum sheet electrode as the counter electrode, an electrolysis was performed in 1.0 M KOH electrolyte at 5 mV·s⁻¹. -1 Under the scan rate test conditions, linear scan voltammetry tests were performed for OER, UOR, and HER. For the UOR linear scan voltammetry test, urea (0.33M) was added to the electrolyte. The test results are shown below. Figures 2-4 (Data processing is the same as in Example 1).

[0054] Figure 2 , Figure 3 , Figure 4 The linear sweep voltammetry curves show that the Ni3S2 / NiFe-LDH / EG catalyst prepared in Example 2 exhibits good performance at 10 mA·cm⁻¹. -2 At a given current density, its OER, UOR, and HER overpotentials are 236mV, 133mV, and 152mV, respectively.

[0055] Example 3 An expanded graphite-based catalyst is prepared by the following steps: (1) Weigh expanded graphite (EG) and Nafion solution (5wt%) at a mass ratio of 19:1, mix with ethanol and ultrasonically prepare slurry, stir and remove alcohol in a 60℃ water bath, shape and cut and press onto the surface of nickel foam (NF) to obtain EG / NF composite electrode. (2) Add ferric nitrate nonahydrate (Fe(NO3)3·9H2O, 0.15M), nickel nitrate hexahydrate (Ni(NO3)2·6H2O, 0.15M) and urea (CO(NH2)2, 0.15M) to a mixed solvent of DMF and deionized water (the volume ratio of DMF to deionized water is 10:1) to obtain a mixed solution of iron salt, nickel salt and urea; (3) A three-electrode system was built using a CHI760E electrochemical workstation. The working electrode was the EG / NF composite electrode prepared in the previous stage, the reference electrode was a saturated calomel electrode (SCE), and the counter electrode was a platinum wire. The mixed solution of the iron salt, nickel salt and urea was used as the electrolyte. The electrode was deposited at a constant potential of -1V for 900s. After washing the product, it was vacuum dried overnight to obtain the NiFe-LDH / EG / NF composite electrode. (4) Add nickel nitrate hexahydrate (Ni(NO3)2·6H2O, 0.15M) and thiourea (SC(NH2)2, 1.0M) to a mixed solvent of DMF and deionized water (the volume ratio of DMF to deionized water is 10:1) to obtain a mixed solution of nickel salt and sulfur source. (5) Using the mixed solution of the nickel salt and sulfur source as the electrolyte, and the NiFe-LDH / EG / NF composite electrode as the working electrode, a three-electrode system was used to deposit the catalyst at a constant potential of -0.9V for 1500s. After washing the product, it was vacuum dried overnight to obtain the expanded graphite-based catalyst, which is denoted as Ni3S2 / NiFe-LDH / EG catalyst (Ni3S2 / NiFe-LDH / EG-900).

[0056] Using the Ni3S2 / NiFe-LDH / EG catalyst prepared in Example 3 as the working electrode, the Hg / HgO electrode as the reference electrode, and the platinum sheet electrode as the counter electrode, an electrolysis was performed in 1.0 M KOH electrolyte at 5 mV·s⁻¹. -1Under the scan rate test conditions, linear scan voltammetry tests were performed for OER, UOR, and HER. For the UOR linear scan voltammetry test, urea (0.33M) was added to the electrolyte. The test results are shown below. Figures 2-4 (Data processing is the same as in Example 1).

[0057] Figure 2 , Figure 3 , Figure 4 The linear sweep voltammetry curves show that the Ni3S2 / NiFe-LDH / EG catalyst prepared in Example 3 exhibits good performance at 10 mA·cm⁻¹. -2 At a current density of , its OER, UOR, and HER overpotentials are 230mV, 130mV, and 149mV, respectively.

[0058] Example 4 An expanded graphite-based catalyst is prepared by the following steps: (1) Weigh expanded graphite (EG) and Nafion solution (5wt%) at a mass ratio of 19:1, mix with ethanol and ultrasonically prepare slurry, stir and remove alcohol in a 60℃ water bath, shape and cut and press onto the surface of nickel foam (NF) to obtain EG / NF composite electrode. (2) Add ferric nitrate nonahydrate (Fe(NO3)3·9H2O, 0.15M), nickel nitrate hexahydrate (Ni(NO3)2·6H2O, 0.15M) and urea (CO(NH2)2, 0.15M) to a mixed solvent of DMF and deionized water (the volume ratio of DMF to deionized water is 10:1) to obtain a mixed solution of iron salt, nickel salt and urea; (3) A three-electrode system was built using a CHI760E electrochemical workstation. The working electrode was the EG / NF composite electrode prepared in the previous stage, the reference electrode was a saturated calomel electrode (SCE), and the counter electrode was a platinum wire. The mixed solution of the iron salt, nickel salt and urea was used as the electrolyte. The electrode was deposited at a constant potential of -1V for 1500s. After washing the product, it was vacuum dried overnight to obtain the NiFe-LDH / EG / NF composite electrode. (4) Add nickel nitrate hexahydrate (Ni(NO3)2·6H2O, 0.15M) and thiourea (SC(NH2)2, 1.0M) to a mixed solvent of DMF and deionized water (the volume ratio of DMF to deionized water is 10:1) to obtain a mixed solution of nickel salt and sulfur source. (5) Using the mixed solution of the nickel salt and sulfur source as the electrolyte, and the NiFe-LDH / EG / NF composite electrode as the working electrode, a three-electrode system was used to deposit the catalyst at a constant potential of -0.9V for 1500s. After washing the product, it was vacuum dried overnight to obtain the expanded graphite-based catalyst, which is denoted as Ni3S2 / NiFe-LDH / EG catalyst (Ni3S2 / NiFe-LDH / EG-1500).

[0059] Using the Ni3S2 / NiFe-LDH / EG catalyst prepared in Example 4 as the working electrode, the Hg / HgO electrode as the reference electrode, and the platinum sheet electrode as the counter electrode, an electrolysis was performed in 1.0 M KOH electrolyte at 5 mV·s⁻¹. -1 Under the scan rate test conditions, linear scan voltammetry tests were performed for OER, UOR, and HER. For the UOR linear scan voltammetry test, urea (0.33M) was added to the electrolyte. The test results are shown below. Figures 2-4 (Data processing is the same as in Example 1).

[0060] Figure 2 , Figure 3 , Figure 4 The linear sweep voltammetry curves show that the Ni3S2 / NiFe-LDH / EG catalyst prepared in Example 4 exhibits good performance at 10 mA·cm⁻¹. -2 At a current density of , its OER, UOR, and HER overpotentials are 237mV, 140mV, and 134mV, respectively.

[0061] Example 5 An expanded graphite-based catalyst is prepared by the following steps: (1) Weigh expanded graphite (EG) and Nafion solution (5wt%) at a mass ratio of 19:1, mix with ethanol and ultrasonically prepare slurry, stir and remove alcohol in a 60℃ water bath, shape and cut and press onto the surface of nickel foam (NF) to obtain EG / NF composite electrode. (2) Add ferric nitrate nonahydrate (Fe(NO3)3·9H2O, 0.15M), nickel nitrate hexahydrate (Ni(NO3)2·6H2O, 0.15M) and urea (CO(NH2)2, 0.15M) to a mixed solvent of DMF and deionized water (the volume ratio of DMF to deionized water is 10:1) to obtain a mixed solution of iron salt, nickel salt and urea; (3) A three-electrode system was built using a CHI760E electrochemical workstation. The working electrode was the EG / NF composite electrode prepared in the previous stage, the reference electrode was a saturated calomel electrode (SCE), and the counter electrode was a platinum wire. The mixed solution of the iron salt, nickel salt and urea was used as the electrolyte. The electrode was deposited at a constant potential of -1V for 1800s. After washing the product, it was vacuum dried overnight to obtain the NiFe-LDH / EG / NF composite electrode. (4) Add nickel nitrate hexahydrate (Ni(NO3)2·6H2O, 0.15M) and thiourea (SC(NH2)2, 1.0M) to a mixed solvent of DMF and deionized water (the volume ratio of DMF to deionized water is 10:1) to obtain a mixed solution of nickel salt and sulfur source. (5) Using the mixed solution of the nickel salt and sulfur source as the electrolyte, and the NiFe-LDH / EG / NF composite electrode as the working electrode, a three-electrode system was used to deposit the catalyst at a constant potential of -0.9V for 1500s. After washing the product, it was vacuum dried overnight to obtain the expanded graphite-based catalyst, which is denoted as Ni3S2 / NiFe-LDH / EG catalyst (Ni3S2 / NiFe-LDH / EG-1800).

[0062] Using the Ni3S2 / NiFe-LDH / EG catalyst prepared in Example 5 as the working electrode, the Hg / HgO electrode as the reference electrode, and the platinum sheet electrode as the counter electrode, an electrolysis was performed in 1.0 M KOH electrolyte at 5 mV·s. -1 Under the scan rate test conditions, linear scan voltammetry tests were performed for OER, UOR, and HER. For the UOR linear scan voltammetry test, urea (0.33M) was added to the electrolyte. The test results are shown below. Figures 2-4 (Data processing is the same as in Example 1).

[0063] Figure 2 , Figure 3 , Figure 4 The linear sweep voltammetry curves show that the Ni3S2 / NiFe-LDH / EG catalyst prepared in Example 5 exhibits good performance at 10 mA·cm⁻¹. -2 At a current density of , its OER, UOR, and HER overpotentials are 238mV, 143mV, and 147mV, respectively.

[0064] Figure 2 The OER linear sweep voltammetry curves of the Ni3S2 / NiFe-LDH / EG catalysts prepared in Examples 1-5 are shown below. Figure 2 It can be known that 10mA·cm -2 The overpotential ranking at different current densities is as follows: Ni3S2 / NiFe-LDH / EG-1200 < Ni3S2 / NiFe-LDH / EG-900 < Ni3S2 / NiFe-LDH / EG-600 < Ni3S2 / NiFe-LDH / EG-1500 < Ni3S2 / NiFe-LDH / EG-1800, with the catalyst of Example 1 (deposition for 1200 s) exhibiting the best OER activity.

[0065] Figure 3 The UOR linear sweep voltammetry curves of the Ni3S2 / NiFe-LDH / EG catalysts prepared in Examples 1-5 are shown below. Figure 3 It can be seen that in a 1.0M KOH + 0.33M urea solution, 10mA·cm -2The overpotential ranking at different current densities is as follows: Ni3S2 / NiFe-LDH / EG-1200 < Ni3S2 / NiFe-LDH / EG-900 < Ni3S2 / NiFe-LDH / EG-600 < Ni3S2 / NiFe-LDH / EG-1500 < Ni3S2 / NiFe-LDH / EG-1800. Example 1 exhibits the best UOR activity.

[0066] Figure 4 The above are HER linear sweep voltammetry curves of the Ni3S2 / NiFe-LDH / EG catalysts prepared in Examples 1-5. Figure 4 It can be known that 10mA·cm -2 The overpotential ranking at different current densities is as follows: Ni3S2 / NiFe-LDH / EG-1200 < Ni3S2 / NiFe-LDH / EG-1500 < Ni3S2 / NiFe-LDH / EG-1800 < Ni3S2 / NiFe-LDH / EG-900 < Ni3S2 / NiFe-LDH / EG-600. The catalyst in Example 1 exhibits the best HER activity.

[0067] Comparative Example 1 (1) Weigh expanded graphite (EG) and Nafion solution (5wt%) at a mass ratio of 19:1, mix with ethanol and ultrasonically prepare slurry, stir and remove alcohol in a 60℃ water bath, shape and cut and press onto the surface of nickel foam (NF) to obtain EG / NF composite electrode. (2) Add nickel nitrate hexahydrate (Ni(NO3)2·6H2O, 0.15M) and thiourea (SC(NH2)2, 1.0M) to a mixed solvent of DMF and deionized water (the volume ratio of DMF to deionized water is 10:1) to obtain a mixed solution of nickel salt and sulfur source. (3) A three-electrode system was built using a CHI760E electrochemical workstation. The working electrode was the EG / NF composite electrode prepared in the previous stage, the reference electrode was a saturated calomel electrode (SCE), and the counter electrode was a platinum wire. The mixed solution of the nickel salt and sulfur source was used as the electrolyte. The electrode was deposited at a constant potential of -0.9V for 1500s. After washing the product, it was vacuum dried overnight to obtain the Ni3S2 / EG / NF composite electrode. (4) Add ferric nitrate nonahydrate (Fe(NO3)3·9H2O, 0.15M), nickel nitrate hexahydrate (Ni(NO3)2·6H2O, 0.15M) and urea (CO(NH2)2, 0.15M) to a mixed solvent of DMF and deionized water (the volume ratio of DMF to deionized water is 10:1) to obtain a mixed solution of iron salt, nickel salt and urea; (5) Using a mixed solution of iron salt, nickel salt and urea as electrolyte, and a Ni3S2 / EG / NF composite electrode as working electrode, a three-electrode system was used to deposit at a constant potential of -1V for 1200s. After washing the product, it was vacuum dried overnight to obtain the catalyst (denoted as NiFe-LDH / Ni3S2 / EG).

[0068] The catalyst prepared in Comparative Example 1 was subjected to linear sweep voltammetry tests for OER, UOR, and HER, under the same test conditions as in the examples. The test results are shown below. Figures 6-8 (Data processing is the same as in Example 1).

[0069] Figure 6 , Figure 7 , Figure 8 The linear sweep voltammetric characteristics of OER, UOR, and HER indicate that the catalyst prepared in Comparative Example 1 exhibits good performance at 10 mA·cm⁻¹. -2 At the given current density, the overpotentials of OER, UOR, and HER are 239.3mV, 129.7mV, and 127.0mV, respectively.

[0070] Comparative Example 2 (1) Weigh expanded graphite (EG) and Nafion solution (5wt%) at a mass ratio of 19:1, mix with ethanol and ultrasonically prepare slurry, stir and remove alcohol in a 60℃ water bath, shape and cut and press onto the surface of nickel foam (NF) to obtain EG / NF composite electrode. (2) Add ferric nitrate nonahydrate (Fe(NO3)3·9H2O, 0.15M), nickel nitrate hexahydrate (Ni(NO3)2·6H2O, 0.15M) and urea (CO(NH2)2, 0.15M) to a mixed solvent of DMF and deionized water (the volume ratio of DMF to deionized water is 10:1) to obtain a mixed solution of iron salt, nickel salt and urea; (3) A three-electrode system was built using a CHI760E electrochemical workstation. The working electrode was the EG / NF composite electrode prepared in the previous stage, the reference electrode was a saturated calomel electrode (SCE), and the counter electrode was a platinum wire. The mixed solution of the iron salt, nickel salt and urea was used as the electrolyte. The product was deposited at a constant potential of -1V for 1200s. After washing, the product was vacuum dried overnight to obtain the catalyst (denoted as NiFe-LDH / EG).

[0071] The catalyst prepared in Comparative Example 2 was subjected to linear sweep voltammetry tests for OER, UOR, and HER, under the same test conditions as in the Example. The test results are shown below. Figures 6-8 (Data processing is the same as in Example 1).

[0072] Depend on Figure 6 The OER linear sweep voltammetric characteristic curve shows that 10 mA·cm⁻¹ can be achieved. -2At the specified current density, the NiFe-LDH / EG catalyst prepared in Comparative Example 2 requires an overpotential of 244.4 mV, while the Ni3S2 / NiFe-LDH / EG catalyst prepared in Example 1 requires only 229.2 mV, demonstrating significantly superior catalytic performance. Figure 7 The UOR linear sweep voltammetric characteristic curve shows that it reaches 10 mA·cm -2 The required overpotential for the NiFe-LDH / EG catalyst prepared in Comparative Example 2 is 130.6 mV, while the required overpotential for the Ni3S2 / NiFe-LDH / EG catalyst prepared in Example 1 is only 111.6 mV, indicating that the latter exhibits superior catalytic performance. Figure 8 The HER linear sweep voltammetry results show that the NiFe-LDH / EG catalyst prepared in Comparative Example 2 needs to output 10 mA·cm⁻¹. -2 The required current density is 206.5 mV overpotential, while the Ni3S2 / NiFe-LDH / EG catalyst prepared in Example 1 only requires 93.2 mV, and its catalytic effect is significantly better than that of Comparative Example 2.

[0073] Comparative Example 3 (1) Weigh expanded graphite (EG) and Nafion solution (5wt%) at a mass ratio of 19:1, mix with ethanol and ultrasonically prepare slurry, stir and remove alcohol in a 60℃ water bath, shape and cut and press onto the surface of nickel foam (NF) to obtain EG / NF composite electrode. (2) Add nickel nitrate hexahydrate (Ni(NO3)2·6H2O, 0.15M) and thiourea (SC(NH2)2, 1.0M) to a mixed solvent of DMF and deionized water (the volume ratio of DMF to deionized water is 10:1) to obtain a mixed solution of nickel salt and sulfur source. (3) A three-electrode system was built using a CHI760E electrochemical workstation. The working electrode was the EG / NF composite electrode prepared in the previous stage, the reference electrode was a saturated calomel electrode (SCE), and the counter electrode was a platinum wire. The mixed solution of the nickel salt and sulfur source was used as the electrolyte. The catalyst was deposited at a constant potential of -0.9V for 1500s. After washing the product, it was vacuum dried overnight to obtain the catalyst (denoted as Ni3S2 / EG).

[0074] The catalyst prepared in Comparative Example 3 was subjected to linear sweep voltammetry tests for OER, UOR, and HER, under the same test conditions as in the examples. The test results are shown below. Figures 6-8 (Data processing is the same as in Example 1).

[0075] Figure 6 , Figure 7 , Figure 8 The linear sweep voltammetric characteristics curves of OER, UOR, and HER show that the catalyst prepared in Comparative Example 3 exhibits good performance at 10 mA·cm⁻¹. -2At the given current density, the overpotentials of OER, UOR, and HER are 314.6 mV, 132.8 mV, and 148.2 mV, respectively.

[0076] Comparative Example 4 Expanded graphite (EG) and Nafion solution (5wt%) were weighed at a mass ratio of 19:1, mixed with ethanol and ultrasonically prepared into a slurry. The slurry was then removed by stirring in a 60°C water bath, shaped, cut, and pressed onto nickel foam (NF) to obtain the NF / EG catalyst.

[0077] The catalyst prepared in Comparative Example 4 was subjected to linear sweep voltammetry tests for OER, UOR, and HER, under the same test conditions as in the examples. The test results are shown below. Figures 6-8 (Data processing is the same as in Example 1).

[0078] Figure 6 , Figure 7 , Figure 8 The linear sweep voltammetric curves of OER, UOR, and HER show that the catalyst prepared in Comparative Example 4 exhibits good performance at 10 mA·cm⁻¹. -2 At the given current density, the overpotentials of OER, UOR, and HER are 331.6mV, 167.6mV, and 231.2mV, respectively.

[0079] Figure 6 The OER linear sweep voltammetry curves of the catalysts prepared in Example 1 and Comparative Examples 1-4 are shown below. Figure 6 It can be known that 10mA·cm -2 The overpotential order at different current densities is Ni3S2 / NiFe-LDH / EG < NiFe-LDH / Ni3S2 / EG < NiFe-LDH / EG < Ni3S2 / EG < NF / EG, with the Ni3S2 / NiFe-LDH / EG catalyst in Example 1 exhibiting the best OER activity.

[0080] Figure 7 The UOR linear sweep voltammetry curves are for the catalysts prepared in Example 1 and Comparative Examples 1-4. Figure 7 It can be known that 10mA·cm -2 The overpotential order at different current densities is Ni3S2 / NiFe-LDH / EG < NiFe-LDH / Ni3S2 / EG < NiFe-LDH / EG < Ni3S2 / EG < NF / EG, with the catalyst in Example 1 exhibiting the best UOR activity.

[0081] Figure 8 The above are HER linear sweep voltammetry curves of the catalysts prepared in Example 1 and Comparative Examples 1-4. Figure 8 It can be known that 10mA·cm -2The overpotential order at different current densities is Ni3S2 / NiFe-LDH / EG < NiFe-LDH / Ni3S2 / EG < Ni3S2 / EG < NiFe-LDH / EG < NF / EG, with the catalyst in Example 1 exhibiting the best HER activity.

[0082] Figure 9 The total water splitting curve of the catalyst prepared in Example 1 (a two-electrode system was built using a CHI760E electrochemical workstation, with both electrodes being the Ni3S2 / NiFe-LDH / EG catalyst material prepared in Example 1, and the electrolytes being 1M KOH + 0.33M urea and 1M KOH, respectively) shows that when urea is present in the system, the reaction requires only a lower operating voltage (10 mA·cm). -2 At a current density of 1.50V in the presence of urea, the operating voltage is 1.56V in the absence of urea.

[0083] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An expanded graphite-based catalyst, characterized in that, The material includes an expanded graphite-based material loaded on the surface of a current collector, a nickel-iron layered double hydroxide deposited on the surface of the expanded graphite-based material, and Ni3S2 deposited on the surface of the nickel-iron layered double hydroxide, wherein the expanded graphite-based material comprises expanded graphite and a binder.

2. The expanded graphite-based catalyst according to claim 1, characterized in that, The current collector is nickel foam; the expanded graphite-based catalyst is nanospheres.

3. The method for preparing the expanded graphite-based catalyst according to claim 1 or 2, characterized in that, Includes the following steps: Expanded graphite, binder and solvent are mixed to form a slurry, and the resulting slurry is desolventized and molded to obtain an expanded graphite-based material; The expanded graphite-based material is loaded onto the surface of the current collector as a working electrode, and a mixed solution of iron salt, nickel salt and urea is used as the electrolyte to perform the first electrodeposition, thereby depositing a nickel-iron layered double hydroxide on the surface of the expanded graphite-based material. Using expanded graphite-based material with deposited nickel-iron layered double hydroxides as the working electrode and a mixed solution of nickel salt and sulfur source as the electrolyte, a second electrodeposition is performed to deposit Ni3S2 on the surface of the nickel-iron layered double hydroxides, thereby obtaining the expanded graphite-based catalyst.

4. The preparation method according to claim 3, characterized in that, The iron salt in the mixed solution of iron salt, nickel salt and urea includes ferric nitrate and nickel salt includes nickel nitrate; the concentrations of iron salt, nickel salt and urea in the mixed solution of iron salt, nickel salt and urea are independently 0.1~0.2 mol / L.

5. The preparation method according to claim 3, characterized in that, The nickel salt in the mixed solution of nickel salt and sulfur source includes nickel nitrate, and the sulfur source includes thiourea; the concentration of nickel salt in the mixed solution of nickel salt and sulfur source is 0.1~0.2 mol / L, and the concentration of sulfur source is 0.5~1.5 mol / L.

6. The preparation method according to claim 3, characterized in that, The first and second electrodepositions were performed using a three-electrode system, with a saturated calomel electrode as the reference electrode and a platinum wire as the counter electrode.

7. The preparation method according to claim 3 or 6, characterized in that, The potential for the first electrodeposition is -0.8 to -1.2V, and the deposition time is 600 to 1800s.

8. The preparation method according to claim 3 or 6, characterized in that, The potential for the second electrodeposition is -0.6 to -1V, and the deposition time is 900 to 2100s.

9. The application of the expanded graphite-based catalyst according to claim 1 or 2 or the expanded graphite-based catalyst prepared by any one of claims 3 to 8 in the electrolysis of water.

10. The application according to claim 9, characterized in that, The water used in the electrolysis of water includes urea.

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