An ultra-hydrophilic molybdenum-doped iron-nickel sulfide foam nickel self-supporting electrode and a preparation method thereof

Abstract

This invention discloses a superhydrophilic molybdenum-doped iron-nickel sulfide foam nickel self-supporting electrode. Using foam nickel as the conductive substrate and self-supporting framework, an Fe7S8 / Ni3S2 catalytic layer is grown in situ on the surface of the foam nickel. In the catalytic layer, Fe7S8 and Ni3S2 form a tightly coupled heterogeneous interface, and Mo is distributed in a Mo-S coordinated dispersed state within the catalytic layer. The catalytic layer exhibits an open three-dimensional hierarchical structure and possesses superhydrophilicity, with a contact angle of 0° at 90 ms when a water droplet contacts it. The preparation method includes the following steps: 1. Preparation of the MIL-(NiFe)@NF precursor; 2. Preparation of Mo-Fe7S8 / Ni3S2@NF. In a 1M KOH electrolyte, when the current density is 10 mA cm⁻¹... ‑2 Under the specified conditions, when used as an electrode for hydrogen evolution reaction, the hydrogen evolution overpotential is 50-60 mV and the current retention rate is 95-98%; when used as an oxygen evolution catalyst material, the oxygen evolution overpotential is 200-210 mV and the current retention rate is 90-95%; when used as both a cathode and anode, the cell voltage is no higher than 1.46 V and the current decay rate is 3-5%.

Description

Technical Field

[0001] This invention relates to the fields of electrocatalytic water splitting materials and electrochemical energy technology, specifically to a superhydrophilic molybdenum-doped iron-nickel sulfide foam nickel self-supporting electrode and its preparation method. Background Technology

[0002] Electrolysis of water for hydrogen production offers advantages such as a wide range of raw material sources, high product purity, and environmental friendliness. However, catalysts based on precious metals suffer from high costs, limited resource reserves, and poor stability under long-term strong alkaline and high-current operating conditions. Among transition metal-based catalysis, nickel-based sulfides exhibit good alkaline hydrogen evolution activity and high conductivity, while iron-based sulfides offer advantages such as low cost, environmental friendliness, and tunable multiple valence states. However, single-phase nickel-based or iron-based sulfides suffer from limited active site types, mismatched adsorption / desorption of reaction intermediates, low interfacial charge transfer efficiency, and insufficient structural stability during long-term reactions.

[0003] To address the technical challenges of single-phase, i.e., single-component transition metal catalysts, multi-component synergy and interfacial electronic structure modulation can be employed to enhance the adsorption / desorption capacity of active sites for H*. For example, existing literature 1 (Modulating Interband Energy Separation of Boron-Doped Fe7S8 / FeS2 Electrocatalysts to Boost Alkaline Hydrogen Evolution Reaction, Advanced Functional Materials, 2022) theoretically calculated and prepared a Boron-doped Fe7S8 / FeS2 electrocatalyst. By utilizing Boron doping to adjust the energy level matching between the d orbitals of Fe atoms and the p orbitals of S atoms, i.e., adjusting the adsorption strength of Fe-S active sites for H*, it promotes the desorption of adsorbed hydrogen intermediates, thereby promoting charge transfer and reducing the dissociation energy barrier of water molecules, achieving a technical effect of an overpotential of 113 mV in alkaline HER. However, this technical solution cannot solve the dual-function synergy problem in oxygen evolution reaction and overall water splitting. At the same time, since this technical solution only solves the intrinsic electronic structure adjustment of the active phase, it cannot improve the bonding between the catalyst layer and the conductive framework and the overall conductive contact effect of the electrode. In other words, it cannot solve the problem of active site shielding and increased interfacial resistance caused by the use of binders in traditional powder or coated catalysts.

[0004] To avoid the problems of active site masking and increased interfacial resistance caused by binders in traditional powder materials, conductive substrates such as carbon cloth, nickel foam, and copper foam can be used as self-supporting electrodes, allowing the catalyst layer to grow in situ on the substrate surface, thereby improving electrode conductivity and active site utilization. For example, existing literature 2 (One-step electrodeposition synthesis of NiFePS on carbon cloth as self-supported electrodes for electrochemical overall water splitting [J]. Journal of Colloid and Interface Science, 2024.) describes the in-situ growth of NiFePS nanosheet catalysts on the surface of hydrophilic treated carbon cloth (CC) using a one-step electrodeposition method, achieving a conductivity of 10 mA·cm⁻¹ under 1.0 M KOH conditions. -2 The technology achieves an overpotential of 91 mV. The principle behind this is the strong interfacial coupling between the NiFePS nanosheets and the carbon cloth substrate, and the abundance of active sites and rapid charge transport capabilities within the ultrathin nanosheet structure. However, after prolonged operation in the electrolyte, this technology exhibits partial oxidation and reconstruction on the catalyst surface, resulting in a performance retention rate decrease to 85%.

[0005] To enhance the intrinsic activity and electrochemically active surface area of ​​transition metal sulfides, heterometallic doping can be used to modulate the local electronic structure, metal valence state distribution, and surface adsorption energy of the catalyst, thereby improving water dissociation, intermediate adsorption, and charge transfer kinetics. For example, existing literature 3 (Modulation of electronic structure of Ni3S2 via Fe and Mo co-doping to enhance the bifunctional electrocatalytic activities for HER and OER[J]. Journal of Colloid and Interface Science, 2024.) uses Keplerian polymolybdate as a precursor to construct an in-situ Fe-MoS2 / Ni3S2@NF co-doped Ni3S2 nanorod array on nickel foam via a hydrothermal method. This electrode operates at 10 mA cm⁻¹. -2The overpotentials for HER and OER were 74 mV and 80 mV, respectively. The basic principle of this technique is to adjust the local electronic structure of Ni3S2 through Fe / Mo co-doping, promote interfacial electron transfer, and increase active sites. However, this technique uses Ni3S2 as the main phase, i.e., it is still a single active phase, and cannot utilize the complementary effects of different metal centers in the HER / OER process.

[0006] To further improve the electron transport capacity, adsorption compatibility with reaction intermediates, and structural stability of the catalyst, a strongly coupled heterointerface can be constructed to achieve interfacial charge redistribution and synergistic activity of multiple active sites. For example, existing literature 4 (High activity and stability in Ni2P / (Co,Ni)OOH heterointerface with a multiple-hierarchy structure for alkaline hydrogen evolution reaction[J]. Nano Research, 2023.) uses a two-step method to construct a hierarchical Ni2P / (Co,Ni)OOH heterointerface material, achieving high activity and stability in alkaline HER at 100 mA cm⁻¹. -2 The overpotential is 169 mV, and the Tafel slope is 41 mVdec. -1 The technical effect is as follows: Strong charge transfer exists at the Ni2P / (Co,Ni)OOH heterostructure interface, which reduces the mismatch in the adsorption of active H species. Simultaneously, the Coulomb attraction generated at the interface helps enhance the stability of the two bonds. However, this type of heterostructure phase is not formed by in-situ transformation of the same precursor, meaning it cannot form a continuous contact interface or achieve a uniform spatial distribution of the metal components.

[0007] The above analysis reveals the following technical problems with the existing technology: 1. Multi-component structures suffer from uneven distribution of active components and insufficient contact at heterogeneous interfaces; 2. Self-supporting electrodes tend to focus on a single half-reaction and cannot simultaneously handle HER and OER. 3. Current doping control methods cannot simultaneously achieve the effects of multiphase interface synergy and enhanced structural stability; 4. Existing heterostructures often lack spatially confined pre-organization in the precursor stage, which makes it impossible to effectively control the generation of active phase and the construction of interfaces during subsequent phase transformation. Summary of the Invention

[0008] The purpose of this invention is to provide a superhydrophilic molybdenum-doped iron-nickel sulfide foam nickel self-supporting electrode and its preparation method.

[0009] The basic principle involved in this invention is, 1. By constructing a multi-metal sulfide heterostructure in situ on a conductive substrate, the aim is to simultaneously regulate the electronic structure, increase active sites, and improve structural stability. 2. Through the strong coupling effect of the heterogeneous interface, the redistribution of interface charge is promoted, and the transport of electrons between different active sites is accelerated; 3. By modulating the local electronic structure of the catalyst layer through Mo doping, the adsorption / desorption behavior of H* and oxygen-containing intermediates is optimized; 4. The open hierarchical structure formed by MOF precursor derivation can expose more active sites, improve electrolyte wetting efficiency and promote bubble release; Ultimately, the synergistic effect of structural, interfacial, and electronic effects improves the hydrogen evolution, oxygen evolution, and overall water splitting performance of the electrode.

[0010] The specific functions of each component are as follows: Nickel foam, as a conductive substrate and self-supporting framework, allows the catalyst layer to grow in situ on its surface, avoiding the problems of active site shielding, increased interfacial resistance and catalyst layer detachment caused by the use of binders in traditional powder catalysts, thereby improving electron transport efficiency and structural stability. MOF precursors can spatially confine and pre-organize the active components of Ni and Fe, which is beneficial to the uniform generation of Fe7S8 and Ni3S2 in the subsequent sulfurization reconstruction process, and realize the in-situ construction of Fe7S8 / Ni3S2 heterostructure interface, thereby enhancing the interfacial bonding and charge transfer capabilities. Mo doping, in synergy with the Fe7S8 / Ni3S2 heterostructure, can modulate the local electronic structure of the catalyst layer, improve the adsorption / desorption behavior of water molecules, hydrogen intermediates, and oxygen-containing intermediates at the active sites, reduce the energy barriers of HER and OER reactions, and enhance bifunctional catalytic activity.

[0011] To achieve the above objectives, the present invention adopts the following technical solution: A superhydrophilic molybdenum-doped iron-nickel sulfide foam nickel self-supporting electrode uses foam nickel as a conductive substrate and self-supporting framework. An Fe7S8 / Ni3S2 catalytic layer is grown in situ on the surface of the foam nickel. In the catalytic layer, Fe7S8 and Ni3S2 form a tightly coupled heterogeneous interface, and Mo is distributed in the catalytic layer in a Mo-S coordination state. The self-supporting electrode is superhydrophilic, with a contact angle of 0° when a water droplet contacts it for 90 ms. The Mo-Fe7S8 / Ni3S2 catalyst layer has an open three-dimensional hierarchical structure, which is formed by the interweaving of nanorods and nanoparticles; wherein the nanoparticles have a particle size of 10-20 nm, and Fe, Ni, Mo and S elements are uniformly distributed in the catalyst layer.

[0012] A method for preparing a superhydrophilic molybdenum-doped iron-nickel sulfide foam nickel self-supporting electrode includes the following steps: Step 1, Preparation of MIL-(NiFe)@NF precursor: First, nickel nitrate, ferrous chloride and terephthalic acid are dissolved in mixed solvent A and stirred to obtain nickel-iron reaction solution. Then, nickel foam NF is immersed in nickel-iron reaction solution to carry out the first hydrothermal reaction. After the reaction is completed, it is washed and dried to obtain MIL-(NiFe)@NF precursor. In step 1, the molar ratio of nickel nitrate, ferrous chloride, and terephthalic acid is 5:4:8; the mixed solvent A is obtained by mixing DMF and anhydrous ethanol in a volume ratio of 2:1. In step 1, the conditions for preparing the nickel-iron reaction solution by stirring are: stirring time of 0.5-1 h; In step 1, the conditions for the first hydrothermal reaction are: the temperature of the first hydrothermal reaction is 130-170℃, and the time of the first hydrothermal reaction is 3-8 h. Step 2, Preparation of Mo-Fe7S8 / Ni3S2@NF: Sodium molybdate, thioacetamide and urea are dissolved in mixed solvent B to obtain a molybdenum-containing reaction solution. Then, MIL-(NiFe)@NF is immersed in the molybdenum-containing reaction solution for a second hydrothermal reaction. After the reaction is completed, it is washed and dried to obtain the superhydrophilic molybdenum-doped iron-nickel sulfide foam nickel self-supporting electrode Mo-Fe7S8 / Ni3S2@NF. In step 2, the molar ratio of sodium molybdate, thioacetamide, and urea is 1:25:100; the mixed solvent B is obtained by mixing anhydrous ethanol and deionized water in a volume ratio of 3:2. In step 2, the conditions for preparing the molybdenum-containing reaction solution by stirring are that the solution stirring time is 0.5-1 h; In step 2, the conditions for the second hydrothermal reaction are: the temperature of the second hydrothermal reaction is 150-170℃, and the reaction time is 2-3 h.

[0013] When the superhydrophilic molybdenum-doped iron-nickel sulfide foam nickel self-supporting electrode is used as a hydrogen evolution reaction electrode in 1 MKOH electrolyte, at a current density of 10 mA cm⁻¹ -2 At that time, the hydrogen evolution overpotential is 50-60 mV, and the Tafel slope is 40-50 mVdec. -1 Under continuous operation for 24 hours, the current retention rate is 95-98%.

[0014] When superhydrophilic molybdenum-doped iron-nickel sulfide foam nickel self-supporting electrode is used as an oxygen evolution catalyst material, in a 1 M KOH electrolyte, at a current density of 10 mA cm⁻¹ -2At that time, the oxygen evolution overpotential was 200-210 mV, and the Tafel slope was 50-60 mV dec. -1 Under continuous operation for 24 hours, the current retention rate is 90-95%.

[0015] When a superhydrophilic molybdenum-doped iron-nickel sulfide foam nickel self-supporting electrode is used simultaneously as both cathode and anode, a symmetrical total water splitting device is constructed in a 1.0 M KOH electrolyte. At a current density of 10 mA·cm⁻¹, -2 At that time, the tank voltage is no higher than 1.46V; after 24 hours of continuous operation, the current decay rate is 3-5%.

[0016] The technical effects of this invention have been tested and confirmed to be: XRD analysis showed that MIL-(NiFe)@NF was successfully grown in situ on the surface of nickel foam. After sulfidation reconstruction, characteristic peaks of Fe7S8 and Ni3S2 appeared in Mo-Fe7S8 / Ni3S2@NF, and no obvious characteristic peaks of independent Mo-based crystal phases were observed, indicating that Mo may exist in a doped or highly dispersed form.

[0017] XPS testing revealed the presence of Mo-S bond characteristic peaks in Mo-Fe7S8 / Ni3S2@NF, indicating that Mo participates in the construction of a local metal-sulfur coordination environment rather than simply being physically attached to the electrode surface.

[0018] SEM, TEM, HRTEM and EDS tests show that Mo-Fe7S8 / Ni3S2@NF maintains an open three-dimensional structure, with the surface composed of interwoven nanorods and 10-20 nm nanoparticles; the (122) crystal plane of Ni3S2 and the (300) crystal plane of Fe7S8 are in direct adjacent contact, and Fe, Ni, Mo and S elements are uniformly distributed, indicating that the Fe7S8 / Ni3S2 hetero interface is constructed synchronously with Mo doping.

[0019] Dynamic water contact angle tests showed that the contact angles of NF, Fe7S8 / Ni3S2@NF, Ni3S2@NF, and Fe7S8@NF were 122.34°, 106.67°, 114.34°, and 117.72°, respectively, at 80-100 ms, while the contact angle of Mo-Fe7S8 / Ni3S2@NF dropped to 0°, exhibiting superhydrophilic properties.

[0020] Electrochemical tests show that in 1.0 M KOH, when the current density is 10 mA·cm⁻¹ -2 At that time, the HER overpotential of Mo-Fe7S8 / Ni3S2 was 50-60 mV, the OER overpotential was 200-210 mV, and the Tafel slopes of HER and OER were 40-50 mV·dec. -1 and 50-60 mV·dec-1 All of them are superior to NF and each comparative sample, indicating that they have high bifunctional electrocatalytic activity and fast reaction kinetics.

[0021] Stability tests show that when the current density is 10 mA·cm⁻¹ -2 When running continuously for 24 hours, the current retention rates of Mo-Fe7S8 / Ni3S2 in HER and OER were 95-98% and 90-95%, respectively, indicating that it has good alkaline hydrogen evolution and oxygen evolution stability.

[0022] Overall water splitting tests showed that when a symmetrical electrolytic cell was constructed using Mo-Fe7S8 / Ni3S2@NF as both cathode and anode, in a 1.0 M KOH solution, at a current density of 10 mA·cm⁻¹, the water splitting performance was satisfactory. -2 At this time, the cell voltage can be as low as 1.46 V, and the current decay rate is 3-5% after 24 hours of continuous operation, indicating that it can be used as a dual-function self-supporting electrode for alkaline whole water decomposition.

[0023] Theoretical calculations show that the ΔG values ​​for Ni3S2, Fe7S8, Fe7S8 / Ni3S2, and Mo-Fe7S8 / Ni3S2 are... H* The values ​​were 1.17 eV, 1.61 eV, 0.57 eV, and -0.27 eV, respectively. This indicates that the Fe7S8 / Ni3S2 heterointerface can improve the hydrogen adsorption behavior of single-phase sulfides, and Mo doping further increases ΔG. H* It approaches a thermally neutral adsorption state and modulates the metal-sulfur coordination and interfacial electronic structure, thereby improving the HER / OER reaction kinetics.

[0024] Compared with the prior art, the present invention has the following advantages: 1. This invention uses nickel foam as a conductive substrate and a self-supporting framework, enabling the catalyst layer to grow in situ on the substrate surface, thus avoiding the problems of active site shielding, increased interfacial resistance, and structural detachment caused by the use of binders in traditional powder catalysts. 2. This invention uses MIL-(NiFe)@NF as a precursor to achieve the organization and uniform distribution of Ni and Fe active components, which is beneficial to the synchronous generation of Fe7S8 and Ni3S2 and the in-situ construction of heterogeneous interfaces during the subsequent sulfurization reconstruction process. 3. This invention optimizes H* adsorption / desorption behavior and improves interfacial charge transfer efficiency and reaction kinetics by using the Fe7S8 / Ni3S2 heterostructure interface and Mo doping to synergistically regulate the local electronic structure. 4. The Mo-Fe7S8 / Ni3S2@NF obtained by this invention has a superhydrophilic surface, which can improve the electrolyte wetting efficiency and bubble desorption rate, thereby reducing the interfacial mass transfer resistance; 5. This invention forms an open three-dimensional catalytic layer interwoven with nanorods and nanoparticles through mild hydrothermal sulfidation reconstruction, which is beneficial for exposing more active sites and shortening the transport paths of electrons, ions, and reactants; 6. The Mo-Fe7S8 / Ni3S2@NF obtained in this invention is suitable for HER, OER and overall water splitting, and exhibits low overpotential, low cell voltage and good stability in 1.0 M KOH. Attached Figure Description

[0025] Figure 1 XRD of the precursor MIL-(NiFe)@NF; Figure 2 XRD patterns of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3; Figure 3 The XPS high-resolution spectrum of Mo 3d in Example 1; Figure 4 SEM images of the precursor MIL-(NiFe)@NF and Example 1; Figure 5 The TEM, HRTEM, and EDS images are from Example 1. Figure 6 The contact angles of Example 1, NF, Comparative Example 1, Comparative Example 2, and Comparative Example 3; Figure 7 The linear sweep voltammetry curves for Example 1, NF, Comparative Example 1, Comparative Example 2, and Comparative Example 3 are shown below. Figure 8 Tafel slope plots for Example 1, NF, Comparative Example 1, Comparative Example 2, and Comparative Example 3; Figure 9 This is a 24-hour cycle test diagram for Example 1; Figure 10 The diagram shows the overall water decomposition test performance of Example 1, NF, Comparative Example 1, Comparative Example 2 and Comparative Example 3, the schematic diagram of the hydrolysis mechanism of Example 1 and the actual application diagram. Figure 11 The graph shows the DFT theoretical calculation results for Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3. Detailed Implementation

[0026] The present invention will be further described in detail through embodiments and with reference to the accompanying drawings, but this is not intended to limit the scope of the invention.

[0027] Example 1 A method for preparing a superhydrophilic molybdenum-doped iron-nickel sulfide foam nickel self-supporting electrode includes the following steps: Step 1, Preparation of MIL-(NiFe)@NF precursor: First, under room temperature conditions, with a stirring time of 30 min, 1 mmol nickel nitrate, 0.8 mmol ferrous chloride and 1.6 mmol terephthalic acid were dissolved in mixed solvent A and stirred to obtain a nickel-iron reaction solution. Then, with a first hydrothermal reaction temperature of 150℃ and a first hydrothermal reaction time of 5 h, nickel foam NF was immersed in the nickel-iron reaction solution for the first hydrothermal reaction. After the reaction was completed, the solution was washed and dried to obtain the MIL-(NiFe)@NF precursor. The mixed solvent A is obtained by mixing DMF and anhydrous ethanol in a volume ratio of 2:1; To demonstrate the structural characteristics of MIL-(NiFe)@NF, XRD tests were performed. The test results are as follows: Figure 1 As shown, MIL-(NiFe)@NF exhibits both NF and MIL-53, i.e., the characteristic peak of MIL-(NiFe). The test results demonstrate the successful in-situ preparation of MIL-(NiFe) on the NF surface.

[0028] To verify the microstructure of MIL-(NiFe)@NF, SEM measurements were performed. The results are as follows: Figure 4 As shown, MIL-(NiFe)@NF is assembled from uniform and flat two-dimensional nanosheets, exhibiting an overall clustered flower-like morphology and a loose and open three-dimensional configuration.

[0029] Step 2, Preparation of Mo-Fe7S8 / Ni3S2@NF: Under room temperature conditions, with a stirring time of 30 min, 0.2 mmol sodium molybdate, 5 mmol thioacetamide and 20 mmol urea were dissolved in mixed solvent B to obtain a molybdenum-containing reaction solution. Then, with a second hydrothermal reaction temperature of 160℃ and a second hydrothermal reaction time of 3 h, MIL-(NiFe)@NF was immersed in the molybdenum-containing reaction solution for a second hydrothermal reaction. After the reaction was completed, the mixture was washed and dried to obtain the superhydrophilic molybdenum-doped iron-nickel sulfide foam nickel self-supporting electrode Mo-Fe7S8 / Ni3S2@NF. The mixed solvent B is obtained by mixing anhydrous ethanol and deionized water in a volume ratio of 3:2.

[0030] To verify the composition of Mo-Fe7S8 / Ni3S2@NF, XRD tests were performed. The test results are as follows: Figure 2 As shown, the characteristic peaks of the original MIL-(NiFe) in Mo-Fe7S8 / Ni3S2@NF disappear, and characteristic peaks of Fe7S8 and Ni3S2 appear, while no characteristic peaks related to Mo are present. The test results indicate that step 2 converts MIL-(NiFe) into Fe7S8 and Ni3S2, and the Mo element may exist in a doped or highly dispersed form.

[0031] Since Mo was not directly detected, an XPS test was performed on Mo. The test results are as follows. Figure 3 As shown, characteristic peaks of Mo-S bonds are present in Mo-Fe7S8 / Ni3S2@NF. The test results indicate that Mo participates in the construction of the local coordination environment.

[0032] To verify the microstructure of Mo-Fe7S8 / Ni3S2@NF, SEM measurements were performed. The test results are as follows: Figure 4 As shown, Mo-Fe7S8 / Ni3S2@NF maintains an open three-dimensional configuration overall, but it has a multi-level rough structure with surface-transformed nanorods and nanoparticles interwoven, and the nanoparticles have a particle size of 10-20 nm. To further verify the microstructure of Mo-Fe7S8 / Ni3S2@NF, TEM and HRTEM tests were performed. The test results are as follows: Figure 5 As shown, the (122) crystal plane of Ni3S2 and the (208) crystal plane of Fe7S8 are in direct adjacent contact, and the Fe, Ni, Mo and S elements are uniformly distributed. The test results show that Ni3S2 and Fe7S8 form a tightly coupled heterostructure interface, and the Mo doping is constructed simultaneously with the Fe7S8 / Ni3S2 heterostructure.

[0033] To demonstrate the wetting properties of Mo-Fe7S8 / Ni3S2@NF, dynamic water contact angle tests were conducted. Simultaneously, for comparison, dynamic water contact angle tests were performed on pure nickel foam NF.

[0034] The dynamic water contact angle test results of NF are as follows: Figure 6 After contacting the NF surface, the water droplet remained a distinct spherical droplet for 90 ms, with a contact angle of 122.34°. The test results of Mo-Fe7S8 / Ni3S2@NF are as follows: Figure 6 Water droplets spread rapidly upon contact with the Mo-Fe7S8 / Ni3S2@NF surface, and the contact angle drops to 0° after 90 ms. Test results show that Mo-Fe7S8 / Ni3S2@NF has superhydrophilic characteristics, which is beneficial for the rapid wetting of the catalyst layer by the electrolyte, improves the solid-liquid interface contact efficiency, and significantly increases the desorption rate of bubbles during the reaction.

[0035] To demonstrate the electrochemical performance of Mo-Fe7S8 / Ni3S2@NF, electrochemical tests were conducted. Simultaneously, for comparison, electrochemical tests were performed on NF. The test method was as follows: a three-electrode system was formed in 1.0 M KOH electrolyte, using the sample as the working electrode, a mercuric oxide electrode as the reference electrode, and graphite as the counter electrode, with a current density of 10 mA·cm⁻¹.-2 .

[0036] The linear sweep voltammetry curve test results of NF are as follows: Figure 7 As shown, the overpotential of NF in HER is 286 mV; and the overpotential in OER is 445 mV.

[0037] The linear sweep voltammetry results of Mo-Fe7S8 / Ni3S2@NF are as follows: Figure 7 As shown, the overpotential of Mo-Fe7S8 / Ni3S2@NF in HER is 51.78 mV; and the overpotential in OER is 202 mV.

[0038] The Tafel slope can be calculated using current polarization testing. The calculation results of NF are as follows Figure 8 As shown, in NF within HER, the Tafel slope is 121.51 mV·dec -1 In the OER, the Tafel slope is 115.33 mV·dec. -1 ; The calculation results of Mo-Fe7S8 / Ni3S2@NF are as follows: Figure 8 As shown, the Tafel slope of Mo-Fe7S8 / Ni3S2@NF in HER is 45.62 mV·dec -1 In the OER, the Tafel slope is 51.42 mV·dec. -1 ; Calculation results show that Mo-Fe7S8 / Ni3S2@NF has good reaction kinetics.

[0039] To demonstrate the stability of Mo-Fe7S8 / Ni3S2@NF, stability performance tests were conducted. The test results are as follows: Figure 9 As shown, the current density is 10 mA cm⁻¹ -2 Under a cycle time of 24 h, the current retention rate of Mo-Fe7S8 / Ni3S2@NF was 98.8% in HER and 95.2% in OER. The test results indicate that Mo-Fe7S8 / Ni3S2@NF exhibits good stability in hydrogen evolution and oxygen evolution tests.

[0040] To demonstrate the performance of Mo-Fe7S8 / Ni3S2@NF in overall water splitting, a symmetrical two-electrode system with Mo-Fe7S8 / Ni3S2@NF as both cathode and anode was tested in 1.0 M KOH. The test results are as follows: Figure 10 As shown, when the current density is 10 mA·cm -2With a cell voltage of 1.46 V and a continuous operating time of 24 h, the current decay rate was 2.3%. The test results indicate that Mo-Fe7S8 / Ni3S2@NF can be used as a bifunctional self-supporting electrode for alkaline bulk water splitting.

[0041] To demonstrate at the atomic scale the synergistic regulatory effect of Mo doping and the Fe7S8 / Ni3S2 heterointerface on the local electronic structure of the catalyst, the strength of metal-sulfur bonding, and the adsorption behavior of key reaction intermediates, theoretical calculations were performed. The calculation results are as follows: Figure 11 As shown, Hydrogen adsorption free energy ΔG at the Mo-Fe7S8 / Ni3S2 heterostructure H* The value is -0.27 eV. The calculation results show that ΔG H* Approaching a thermally neutral adsorption state, the heterostructure can balance the adsorption of hydrogen intermediates and the desorption of hydrogen. d-band center ε of Mo-Fe7S8 / Ni3S2 d The value is -2.48 eV. The calculation results show that the electronic state distribution of the surface metal active sites can be adjusted, thereby improving the interfacial reaction kinetics. The integral crystal orbital Hamiltonian population (ICOHP) of Fe-S is -1.0424. The calculation results show that the Ni-S bond has strong bonding and electronic coupling effects, which can improve the stability of electron transport in the catalytic reaction process. The integral crystal orbital Hamiltonian population (ICOHP) of Ni-S is -1.7824. The calculation results show that the Fe-S bond has a weak bonding effect. Its role is that Mo doping and heterostructure interface effects regulate the electronic environment around the Fe site, which is conducive to the formation of reaction intermediate adsorption active sites. Combining the d-band center and ICOH calculation results, it can be seen that Mo doping can synergistically induce local electronic structure reconstruction with the Fe7S8 / Ni3S2 heterostructure interface. Among them, the Ni-S structure provides strong electronic coupling and transport channels, and the Fe sites provide electronic tunability. That is, the synergistic electronic effect of "doping regulation + heterostructure interface coupling" ultimately improves the reaction kinetics performance.

[0042] To demonstrate the role of Mo in the technical solution, Comparative Example 1 is provided, which is a method for preparing a self-supporting nickel foam electrode of iron-nickel sulfide without adding Mo, i.e., containing only Fe7S8 / Ni3S2@NF.

[0043] Comparative Example 1 A method for preparing a nickel-iron sulfide foamed nickel self-supporting electrode is disclosed. The steps in the preparation method not specifically described are the same as those in Example 1, except that sodium molybdate is not added in step 2. The resulting nickel-iron sulfide foamed nickel self-supporting electrode is referred to as Fe7S8 / Ni3S2@NF.

[0044] To determine the phase composition of Fe7S8 / Ni3S2@NF, XRD analysis was performed. The results are as follows: Figure 1 As shown, Fe7S8 / Ni3S2@NF exhibits characteristic peaks for both Fe7S8 and Ni3S2, but lacks the characteristic peak for MIL-(NiFe). The test results indicate that MIL-(NiFe) can be converted to Fe7S8 and Ni3S2 without the addition of sodium molybdate, meaning that Mo does not affect the formation of the host phases Fe7S8 and Ni3S2.

[0045] To demonstrate the wetting properties of Fe7S8 / Ni3S2@NF, dynamic water contact angle tests were conducted. The test results are as follows: Figure 6 As shown, after contacting the Fe7S8 / Ni3S2@NF surface, the water droplet remained a distinctly spherical droplet with a contact angle of 106.67° for 90 ms. The test results indicate that Fe7S8 / Ni3S2 cannot acquire superhydrophilic characteristics without the addition of sodium molybdate. This is because doping with Mo can modulate the local coordination environment of the catalyst layer, forming polar metal-sulfur coordination sites and defect / unsaturated active sites on the material surface, thereby significantly enhancing the adsorption of water molecules and OH⁻ on the electrode surface.

[0046] To demonstrate the electrochemical performance of Fe7S8 / Ni3S2@NF, electrochemical performance tests were conducted. The results of the linear sweep voltammetry curves for Fe7S8 / Ni3S2@NF are shown below. Figure 7 As shown, the overpotential of Fe7S8 / Ni3S2@NF in HER is 139.94 mV; and the overpotential in OER is 293 mV.

[0047] The Tafel slope was calculated using current polarization testing. The calculation results for Fe7S8 / Ni3S2@NF are as follows: Figure 8 As shown, the Tafel slope of Fe7S8 / Ni3S2@NF in HER is 146.18 mV·dec -1 In the OER, the Tafel slope is 56.81 mV·dec. -1 Calculations show that the reaction kinetics of Fe7S8 / Ni3S2@NF are slow. This is because the lack of sodium molybdate prevents the modulation of the local electronic structure at the interface. Furthermore, the absence of superhydrophilicity results in poor wettability of the electrode surface, significantly reducing electrolyte wetting and bubble desorption efficiency, thus significantly decreasing the interfacial charge transfer rate, reactant transport rate, and product release rate.

[0048] To demonstrate the performance of Fe7S8 / Ni3S2@NF in overall water splitting, a symmetrical two-electrode system with Fe7S8 / Ni3S2@NF as both cathode and anode was tested in 1.0 M KOH. The test results are as follows: Figure 10 As shown, when the current density is 10 mA·cm -2 The cell voltage was 1.55 V. Compared with the Mo-Fe7S8 / Ni3S2@NF obtained in Example 1, it can be seen that adding sodium molybdate can reduce the cell voltage.

[0049] To illustrate the local electronic structure of the catalyst at the atomic scale in relation to the Mo-doped Fe7S8 / Ni3S2@NF heterostructure, theoretical calculations were performed. The calculation results are as follows: Figure 11 As shown, Hydrogen adsorption free energy ΔG at the Fe7S8 / Ni3S2 heterostructure H* The value is 0.57 eV. Calculation results show that the ΔG of Fe7S8 / Ni3S2 is... H* Deviating from the thermally neutral adsorption state; d-band center ε of Fe7S8 / Ni3S2 d The value is -2.49 eV, which is negligible compared to the Mo-Fe7S8 / Ni3S2 obtained in Example 1, meaning that Mo doping has no substantial impact on the bulk electronic structure of the Fe7S8 / Ni3S2 heterostructure interface.

[0050] To further demonstrate the role of Ni3S2 and Fe7S8 in the technical solution, Comparative Examples 2 and 3 are provided, which are methods for preparing sulfide foam nickel self-supporting electrodes containing only Ni3S2@NF and only Fe7S8@NF, respectively.

[0051] Comparative Example 2 A method for preparing a nickel sulfide foam nickel self-supporting electrode is disclosed. The steps in the preparation method not specifically described are the same as those in Example 1, except that: in step 1, ferrous chloride is not added, and in step 2, sodium molybdate is not added. The resulting nickel sulfide foam nickel self-supporting electrode is referred to as Ni3S2@NF.

[0052] To verify the phase composition of Ni3S2@NF, XRD analysis was performed. The test results are as follows: Figure 2 As shown, characteristic peaks of Ni3S2 are present in Ni3S2@NF. Test results indicate that MIL-(Ni) can be converted to Ni3S2 without the addition of ferrous chloride and sodium molybdate, meaning that Mo and Fe7S8 do not affect the formation of the host phase Ni3S2.

[0053] To demonstrate the wetting properties of Ni3S2@NF, dynamic water contact angle tests were conducted. The test results are as follows: Figure 6 As shown, after contacting the Ni3S2@NF surface, the water droplet still maintains a distinct spherical shape at 90 ms, with a contact angle of 114.34°.

[0054] Compared with NF and Fe7S8 / Ni3S2@NF obtained in Comparative Example 1, it can be seen that the antennae are all greater than 90°, that is, they are all hydrophobic and there is no substantial difference. Therefore, it can be further proved that the superhydrophilicity of Mo-Fe7S8 / Ni3S2@NF comes from the addition of Mo element. The reason is that Mo element and S element can form Mo-S to adjust the local coordination environment, thereby obtaining superhydrophilicity. Forming Ni3S2 alone or constructing only Fe7S8 / Ni3S2 heterostructure cannot affect the hydrophilicity.

[0055] To demonstrate the electrochemical performance of Ni3S2@NF, electrochemical performance tests were conducted. The results of the linear sweep voltammetry curves for Ni3S2@NF are shown below. Figure 7 As shown, the overpotential of Ni3S2@NF in the HER is 208.00 mV; the overpotential in the OER is [missing value].

[0056] The Tafel slope can be calculated through current polarization testing. The test results for Ni3S2@NF are as follows: Figure 8 As shown, the Tafel slope of Ni3S2@NF in HER is 120.92 mV·dec -1 In the OER, the Tafel slope is 127.69 mV·dec -1 .

[0057] The comparative analysis of electrochemical performance is summarized in Table 1 after Comparative Example 3.

[0058] To demonstrate the performance of Ni3S2@NF in overall water splitting, a symmetrical two-electrode system with Ni3S2@NF as both cathode and anode was tested in 1.0 M KOH. The test results are as follows: Figure 10 As shown, when the current density is 10 mA·cm -2 The slot voltage is 1.73 V.

[0059] The comparative analysis of the overall water decomposition performance test is summarized in Table 2 after Comparative Example 3.

[0060] To illustrate the local electronic structure of the catalyst at the atomic scale in relation to the Mo-doped Fe7S8 / Ni3S2@NF heterostructure, theoretical calculations were performed. The calculation results are as follows: Figure 11 As shown, the hydrogen adsorption free energy ΔG of Ni3S2 H* 1.17 eV, d-band center ε d It is −2.59 eV.

[0061] The comparative analysis of theoretical calculations is summarized in Table 3 after Comparative Example 3.

[0062] Comparative Example 3 A method for preparing an iron sulfide-containing nickel foam self-supporting electrode is disclosed. The steps in the preparation method not specifically described are the same as those in Example 1, except that: in step 1, nickel nitrate is not added, and in step 2, sodium molybdate is not added. The resulting iron sulfide-containing nickel foam self-supporting electrode is referred to as Fe7S8@NF.

[0063] To determine the phase composition of Fe7S8@NF, XRD analysis was performed. The results are as follows: Figure 2 As shown, characteristic peaks of Fe7S8 are present in Fe7S8@NF. The test results indicate that MIL-(Fe) can be converted to Fe7S8 without the addition of nickel nitrate and sodium molybdate, meaning that Mo and Ni3S2 do not affect the formation of the host phase Fe7S8.

[0064] To demonstrate the wetting properties of Fe7S8@NF, a dynamic water contact angle test was conducted. The test results are as follows: Figure 6 As shown, after contacting the Fe7S8@NF surface, the water droplet still maintains a distinct spherical shape at 90 ms, with a contact angle of 117.72°.

[0065] Compared with NF and Fe7S8 / Ni3S2@NF obtained in Comparative Example 1, it can be seen that the antennae are all greater than 90°, that is, they are all hydrophobic and there is no substantial difference. Therefore, the conclusion is the same as that obtained in Comparative Example 2, that is, the superhydrophilicity of Mo-Fe7S8 / Ni3S2@NF comes from the addition of Mo element.

[0066] To demonstrate the electrochemical performance of Fe7S8@NF, electrochemical performance tests were conducted. The results of the linear sweep voltammetry curves for Fe7S8@NF are shown below. Figure 7 As shown, the overpotential of Fe7S8@NF in the HER is 198.00 mV; and the overpotential in the OER is 325.00 mV.

[0067] The Tafel slope can be calculated through current polarization testing, and the test results are as follows: Figure 8 As shown, the Tafel slope of Fe7S8@NF in HER is 119.30 mV·dec -1 The Tafel slope in the OER is 91.77 mV·dec. -1 .

[0068] The comparative analysis of electrochemical performance is summarized in Table 1 after Comparative Example 3.

[0069] To demonstrate the performance of Fe7S8@NF in overall water splitting, a symmetrical two-electrode system with Fe7S8@NF as both cathode and anode was tested in 1.0 M KOH. The test results are as follows: Figure 10 As shown, when the current density is 10 mA·cm -2 The slot voltage is 1.69 V.

[0070] The comparative analysis of the overall water decomposition performance test is summarized in Table 2 after Comparative Example 3.

[0071] To illustrate the local electronic structure of the catalyst at the atomic scale in relation to the Mo-doped Fe7S8 / Ni3S2@NF heterostructure, theoretical calculations were performed. The calculation results are as follows: Figure 11 As shown, The hydrogen adsorption free energy ΔG of Fe7S8 H* The value is 1.61 eV. Calculation results show that the ΔG of Fe7S8 is... H* It deviates significantly from the thermally neutral adsorption state.

[0072] The comparative analysis of theoretical calculations is summarized in Table 3 after Comparative Example 3.

[0073] The comparative analysis of electrochemical performance is shown in Table 1. Comparing Ni3S2@NF and Fe7S8@NF with NF, it can be determined that the introduction of Ni3S2 and Fe7S8 alone can reduce the overpotential in HER, specifically by 198.00 mV and 208.00 mV respectively, with no substantial difference between the two.

[0074] If there is no synergistic effect between Ni3S2 and Fe7S8, the overpotential in the HER should be between 198.00 and 208.00 mV when both Ni3S2 and Fe7S8 are introduced simultaneously. However, according to the test results of Fe7S8 / Ni3S2@NF, the overpotential in the HER is significantly reduced to 139.94 mV when both Ni3S2 and Fe7S8 are introduced simultaneously. This phenomenon indicates that there is a synergistic effect between Ni3S2 and Fe7S8.

[0075] The reason is that Ni3S2 and Fe7S8 form a Fe7S8 / Ni3S2 heterojunction interface, which can redistribute the interfacial charge and generate a synergistic effect of multiple active sites, thereby improving the adsorption / desorption behavior of hydrogen intermediates, increasing the interfacial charge transfer efficiency and HER reaction kinetics.

[0076] Table 1 Summary of Electrochemical Performance

[0077] The comparative analysis of the overall water splitting performance test results is shown in Table 2. Comparing Ni3S2@NF and Fe7S8@NF with NF, it can be determined that the introduction of Ni3S2 and Fe7S8 alone can reduce the cell voltage required for overall water splitting. Specifically, the voltages are 1.73 V and 1.69 V, respectively, with no substantial difference between the two.

[0078] If there is no synergistic effect between Ni3S2 and Fe7S8, the cell voltage of the resulting electrode in overall water splitting should be between 1.69 and 1.73 V after simultaneously introducing Ni3S2 and Fe7S8. However, according to the test results of Fe7S8 / Ni3S2@NF, the overall water splitting cell voltage is significantly reduced to 1.55 V when Ni3S2 and Fe7S8 are introduced simultaneously. This phenomenon indicates that there is a significant synergistic effect between Ni3S2 and Fe7S8.

[0079] Table 2 Summary of Overall Water Decomposition Performance

[0080] The comparative analysis of theoretical calculations is shown in Table 3. Comparing Ni3S2 and Fe7S8, it can be determined that the introduction of either Ni3S2 or Fe7S8 alone significantly deviates from the thermally neutral adsorption state. Specifically, the hydrogen adsorption free energy ΔG... H* The values ​​are 1.17 eV and 1.61 eV, respectively; among which, the ΔG of Fe7S8 is... H* The higher value of Fe7S8 compared to Ni3S2 indicates that Fe7S8 alone has a weaker ability to regulate H* adsorption behavior, and neither of them can meet the requirement of near-0 eV hydrogen adsorption free energy for efficient HER.

[0081] If there is no interfacial synergy between Ni3S2 and Fe7S8, then after simultaneously introducing Ni3S2 and Fe7S8, the resulting Fe7S8 / Ni3S2 ΔG H* It should be between 1.17 and 1.61 eV. According to the calculation results for Fe7S8 / Ni3S2, the ΔG of the Fe7S8 / Ni3S2 heterostructure... H* The value decreased to 0.57 eV, which is significantly lower than that of the two single-phase sulfides, indicating that there is a heterointerface synergistic effect between Ni3S2 and Fe7S8.

[0082] Furthermore, after doping with Mo, ΔG H* Adjusting the value from 0.57 eV to -0.27 eV reduces the deviation from 0.57 eV to 0.27 eV, indicating that Mo doping can further optimize the adsorption / desorption behavior of hydrogen intermediates based on the Fe7S8 / Ni3S2 heterointerface.

[0083] Meanwhile, the d-band centers of Fe7S8 / Ni3S2 and Mo-Fe7S8 / Ni3S2 are -2.49 eV and -2.48 eV, respectively, with no substantial difference between them. This indicates that Mo doping did not significantly change the position of the main d-band center of the heterostructure. In other words, the role of Mo is to further improve the adsorption behavior of hydrogen intermediates through Mo-S local coordination and active site environment regulation.

[0084] In summary, theoretical calculations show that the Fe7S8 / Ni3S2 heterointerface can improve the hydrogen adsorption free energy of single-phase sulfides, and Mo doping can further optimize local active sites, thus jointly promoting the HER reaction kinetics.

[0085] Table 3 Summary of Theoretical Calculation Performance

[0086] Based on the test results and analysis of the above-mentioned Examples 1, 1, 2, and 3, the following conclusions can be drawn: Pure NF mainly serves as a conductive substrate and self-supporting framework, with limited intrinsic catalytic activity. The formation of Ni3S2 or Fe7S8 alone reduces both the HER and OER overpotentials, indicating that both can participate in water electrolysis as sulfide-active phases.

[0087] Further comparison of Comparative Example 1 with Comparative Examples 2 and 3 reveals that Fe7S8 / Ni3S2@NF exhibits a lower HER / OER overpotential and overall water splitting cell voltage, indicating that Fe7S8 and Ni3S2 do not simply coexist physically, but rather form a heterogeneous interface with synergistic effects. This heterogeneous interface can promote interfacial charge transfer, modulate the electronic environment around the Fe / Ni active sites, and improve the adsorption / desorption behavior of reaction intermediates.

[0088] With the further introduction of Mo, the Mo-Fe7S8 / Ni3S2@NF obtained in Example 1 exhibited the best HER, OER, and overall water splitting performance. XRD results showed that the introduction of Mo did not disrupt the Fe7S8 / Ni3S2 host phase; XPS results showed that Mo participated in the construction of the Mo-S local coordination environment; TEM / HRTEM results showed that Fe7S8 and Ni3S2 formed a tightly coupled heterogeneous interface, and Mo, Fe, Ni, and S elements were uniformly distributed.

[0089] Wetting performance tests showed that NF, Ni3S2@NF, Fe7S8@NF and Fe7S8 / Ni3S2@NF were all hydrophobic; while Mo-Fe7S8 / Ni3S2@NF showed a contact angle of 0° at 90 ms, exhibiting superhydrophilic characteristics. This indicates that the introduction of Mo can significantly improve the wettability of the catalyst layer surface, which is beneficial for rapid electrolyte wetting and desorption of reaction bubbles.

[0090] Based on XPS and theoretical calculations, it can be seen that Mo participates in the construction of the Mo-S local coordination environment and further modulates the electronic structure around the active site, thus affecting ΔG. H* The adsorption state is closer to that of a thermally neutral state, which is beneficial for improving the HER reaction kinetics. It should be noted that the change in the d-band center before and after Mo doping is small, indicating that the effect of Mo is mainly reflected in the regulation of the local coordination environment and the adsorption behavior of active sites, rather than significantly changing the position of the host band structure of the heterostructure.

[0091] In summary, the performance improvement of Mo-Fe7S8 / Ni3S2@NF obtained in Example 1 mainly stems from: Ni3S2 and Fe7S8 providing the basic sulfide active phase; the Fe7S8 / Ni3S2 heterostructure promoting interfacial charge transfer and intermediate adsorption regulation; Mo doping further optimizing the metal-sulfur local coordination environment, active site electronic structure, and surface wettability; the MOF-derived open hierarchical structure increasing the active area and mass transfer efficiency; and the nickel foam self-supporting structure enhancing the bonding force and electron transport capability between the catalytic layer and the conductive substrate. These factors collectively improve the overall catalytic performance of Mo-Fe7S8 / Ni3S2@NF in HER, OER, and overall water splitting.

[0092] The technical solution of the present invention has the following technical effects: 1. The MIL-(NiFe) precursor can pre-organize Ni and Fe elements, which is beneficial for the synchronous generation of Fe7S8 and Ni3S2 and the in-situ construction of heterogeneous interfaces. 2. The introduction of Mo can regulate the local coordination environment and interfacial electronic structure of metal-sulfur, thereby improving reaction kinetics; 3. The multi-level rough structure can increase the electrochemical active area and improve electrolyte wetting and bubble desorption behavior; 4. The self-supporting superhydrophilic electrode structure avoids the use of adhesives, reduces interfacial resistance, and improves structural stability. 5. The obtained Mo-Fe7S8 / Ni3S2@NF can be used simultaneously for HER, OER and overall water splitting, and has good application prospects for bifunctional water electrolysis.

Claims

1. A superhydrophilic molybdenum-doped iron-nickel sulfide foam nickel self-supporting electrode, characterized in that: Using nickel foam as a conductive substrate and a self-supporting framework, an Fe7S8 / Ni3S2 catalytic layer is grown in situ on the surface of the nickel foam. In the catalytic layer, Fe7S8 and Ni3S2 form a tightly coupled heterogeneous interface, and Mo is distributed in the catalytic layer in a Mo-S coordination state. The self-supporting electrode is superhydrophilic, with a contact angle of 0° when a water droplet contacts it for 90 ms.

2. The superhydrophilic molybdenum-doped iron-nickel sulfide foam nickel self-supporting electrode according to claim 1, characterized in that: The Mo-Fe7S8 / Ni3S2 catalyst layer has an open three-dimensional hierarchical structure, which is formed by the interweaving of nanorods and nanoparticles; wherein the nanoparticles have a particle size of 10-20 nm, and Fe, Ni, Mo and S elements are uniformly distributed in the catalyst layer.

3. A method for preparing a superhydrophilic molybdenum-doped iron-nickel sulfide foam nickel self-supporting electrode, characterized in that... Includes the following steps: Step 1, Preparation of MIL-(NiFe)@NF precursor: First, nickel nitrate, ferrous chloride and terephthalic acid are dissolved in mixed solvent A and stirred to obtain nickel-iron reaction solution. Then, nickel foam NF is immersed in nickel-iron reaction solution to carry out the first hydrothermal reaction. After the reaction is completed, it is washed and dried to obtain MIL-(NiFe)@NF precursor. Step 2, Preparation of Mo-Fe7S8 / Ni3S2@NF: Sodium molybdate, thioacetamide and urea are dissolved in mixed solvent B to obtain a molybdenum-containing reaction solution. Then, MIL-(NiFe)@NF is immersed in the molybdenum-containing reaction solution for a second hydrothermal reaction. After the reaction is completed, it is washed and dried to obtain the superhydrophilic molybdenum-doped iron-nickel sulfide foam nickel self-supporting electrode Mo-Fe7S8 / Ni3S2@NF.

4. The preparation method according to claim 3, characterized in that: In step 1, the molar ratio of nickel nitrate, ferrous chloride, and terephthalic acid is 5:4:8; the mixed solvent A is obtained by mixing DMF and anhydrous ethanol in a volume ratio of 2:

1. In step 2, the molar ratio of sodium molybdate, thioacetamide, and urea is 1:25:100; the mixed solvent B is obtained by mixing anhydrous ethanol and deionized water in a volume ratio of 3:

2.

5. The preparation method according to claim 3, characterized in that: In step 1, the conditions for preparing the nickel-iron reaction solution by stirring are: stirring time of 0.5-1 h; In step 1, the conditions for the first hydrothermal reaction are: the temperature of the first hydrothermal reaction is 130-170℃, and the time of the first hydrothermal reaction is 3-8 h.

6. The preparation method according to claim 3, characterized in that: In step 2, the conditions for preparing the molybdenum-containing reaction solution by stirring are that the solution stirring time is 0.5-1 h; In step 2, the conditions for the second hydrothermal reaction are: the temperature of the second hydrothermal reaction is 150-170℃, and the reaction time is 2-3 h.

7. The superhydrophilic molybdenum-doped iron-nickel sulfide foam nickel self-supporting electrode according to claim 1, characterized in that: When applied as a hydrogen evolution reaction electrode, the overpotential for hydrogen evolution is 50-60 mV at a current density of 10 mA cm -2 -1 in 1 M KOH electrolyte, the Tafel slope is 40-50 mV dec -1 -1, and the current retention is 95-98% under continuous operation for 24 h.

8. The superhydrophilic molybdenum-doped iron-nickel sulfide foam nickel self-supporting electrode according to claim 1, characterized in that: As an application of oxygen evolution catalyst material, in 1 M KOH electrolyte, when the current density is 10 mA cm -2 , the oxygen evolution overpotential is 200-210 mV, the Tafel slope is 50-60 mV dec -1 ; under the condition of continuous operation for 24 h, the current retention rate is 90-95%.

9. The superhydrophilic molybdenum-doped iron-nickel sulfide foam nickel self-supporting electrode according to claim 1, characterized in that: When used simultaneously as both cathode and anode, a symmetrical total water splitting device was constructed in a 1.0 M KOH electrolyte, with a current density of 10 mA·cm⁻¹. -2 At that time, the tank voltage is no higher than 1.46 V; after 24 hours of continuous operation, the current decay rate is 3-5%.

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